Parrington, John-Redesigning Life - How Genome Editing Will Transform The World-Oxford University Press (2016)
Parrington, John-Redesigning Life - How Genome Editing Will Transform The World-Oxford University Press (2016)
Parrington, John-Redesigning Life - How Genome Editing Will Transform The World-Oxford University Press (2016)
3
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ACKN OW LEDG EM EN T S
I would like to thank a number of people who have helped bring this, my
second book, to fruition. I owe a particular debt to Latha Menon, my
editor at Oxford University Press, who always expertly balances her critical
comments with great encouragement about the work at hand. I would also
like to thank Jenny Nugee of the OUP editorial team, for her help on a multi-
tude of practical matters, and Elizabeth Stone at Bourchier Limited for her
meticulous copy-editing of the book. I gained some extremely valuable in-
sights and suggestions for changes to the text from Margarida Ruas, as well
as some very helpful comments from three anonymous reviewers who read
my original proposal and one who read a late draft of the book. Margarida
Ruas also produced a superb set of line drawings. I also owe many thanks to
Anthony Morgan for producing the author photo for the book cover. For
their expert assistance with marketing and publicity, and answers to my
many questions on this front, I would like to thank Phil Henderson and Kate
Farquhar-Thomson of OUP. I owe thanks also to friends and colleagues
who have indulged my many speculations about the new technologies de-
scribed in the book, as well as providing helpful feedback and suggestions.
My final set of thanks is to my family, for providing such a warm and lovely
home environment that meant so much to me during the long hours spent
on researching and writing. Finally, there is a debt that is hard to express
adequately in words, and that is to my mother. As well as her encourage-
ment at every stage of my life, through both ups and downs, she also com-
municated her great love of books and reading, her ability to look for the
positive in every situation, and a questioning and enquiring attitude to life.
It is to her memory that I dedicate this book.
CON TEN T S
List of Platesix
List of Figuresxi
Glossary 291
Endnotes 293
Index of names337
Index of subjects343
LI ST OF P LATE S
ix
LI ST OF FIG U R E S
xi
List of Figur es
xii
1 Brainbow identifies neurons by colour.
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R EDESIGNING LIFE
like Mozart, or have Einstein’s scientific genius? And if life forms in the
future become truly synthetic, does that mean that one day we’ll have syn-
thetic people too?
But there are other, more troubling future scenarios that can be imagined
if genetic modification were to become as easy as cutting and pasting a
Word file. For what is to stop such technology being used to engineer new
lethal types of viruses, or synthetic life forms escaping and taking over the
world? And how could we ensure that new types of genetically modified
(GM) food—whether animal or plant—were safe to eat? Could such plants
pose a risk to the environment? And what about the welfare of the modified
animals? This is also potentially an issue if scientists develop new types of
mutant animals to model human disease. Will this lead to pain and suf-
fering in a wider range of species, including our biological cousins—mon-
keys and other primates? And if researchers developed GM primates to
study how the human brain works, could this lead to a Planet of the Apes-type
scenario? For that matter, could the technology be used as a tool to recreate
long-extinct organisms such as woolly mammoths or fearsome dinosaurs
like Tyrannosaurus rex?
The prospect of being able to modify life in such a routine manner may
either excite or horrify, depending on your viewpoint. Yet although these
imagined future scenarios sound like science fiction rather than fact, it’s
time we discussed the new technologies that are transforming our ability to
manipulate life. For while the scenarios above are fictional, thanks to the
new technologies—particularly one called ‘genome editing’2 but also a new
branch of science called ‘synthetic biology’—many soon may not be.3
Of course, you could be forgiven for thinking genome manipulation is
nothing new. After all, isn’t that the scientific basis for all those debates
about GM crops, gene therapy, or designer babies? And indeed, we’ve had
the technology to cut and paste gene sequences in a test tube since the
1970s,4 while in the 1980s it became possible to modify the genome of an
organism as complex as a mouse.5 But the difference between genome edit-
ing and past forms of genetic engineering is a bit like comparing letterpress
printing with the first word processor, or modern motor cars with horse-
2
Introduction: The Gene R e volu tion
A Scientific Revolution
Perhaps most astonishing is the speed at which the new genetic engineering
is taking place.7 Despite genome editing being a recent development, it’s
been taken up and applied in various different ways at a pace that has sur-
prised many scientists. And it is for this reason that Science magazine named
CRISPR/CAS9 its ‘Breakthrough of the Year’ in 2015, instead of the Pluto
flyby or the discovery of a new human ancestor.8 ‘We all kind of marvel at
how fast this took off as a technology,’ said Doudna. ‘There’s just a really
tremendous feeling of excitement for the potential of CRISPR.’9 One way
the technology is having a major impact in biomedical science is through a
new-found ability to modify genomes from species ranging from simple
bacteria through to mammals—not only mice, but large animals like pigs
and monkeys. At the same time, the capacity of genome editing to geneti-
cally modify animals and plants important for agriculture looks set to have
a huge impact on food production.
Yet amidst the excitement, the new technology is also creating controversy,
precisely because of its greatly enhanced accuracy and power compared to
past genetic engineering approaches. That isn’t only due to the potential
impact in already controversial areas like GM crops and animal models of
disease, but because genome editing is equally applicable to human cells. In
November 2015, the technology was used to treat a baby with an aggressive
form of child leukaemia, producing what doctors called a ‘near miracle’
recovery.10 More controversially, genome editing has been used to modify
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R EDESIGNING LIFE
the genome of human embryos for the first time in history. And although
there was no intention of implanting the embryos into a woman, this has
led some scientists to call for a ban on such research, saying that it’s ‘dan-
gerous and ethically unacceptable’.11
The range of potential applications of genome editing are such that
Dustin Rubinstein, who’s applying this technology at the University of
Wisconsin-Madison, believes ‘it’s really going to just empower us to have
more creativity . . . to get into the sandbox and have more control over what
you build. You’re only limited by your imagination.’6 Yet, as Jennifer Doudna
recently pointed out, ‘Great things can be done with the power of technol-
ogy—and there are things you would not want done. Most of the public
does not appreciate what is coming.’12 Surely, given the scale of the scientific
revolution now underway, this is a deficit that needs correcting if the wider
public are to influence the way genome editing is employed. But taking part
in such a debate requires a proper understanding of the underlying science
and what distinguishes the new technology from previous approaches to
modifying life. Such was the stimulus for writing this book.
There are other major developments taking place in biotechnology too.
For instance, take the new field of optogenetics.13 This employs laser beams
to stimulate—or inhibit—nerve cells in the brain of a mouse, allowing sci-
entists to better understand how this organ works, but also to control
behaviour. This approach is revolutionizing neuroscience by making it pos
sible to uncover how particular nerve cells contribute to complex brain
functions like learning, memory, pain, and pleasure. ‘Optogenetics is not
just a flash in the pan,’ believes neuroscientist Robert Gereau of Washington
University in Saint Louis. ‘It allows us to do experiments that were not
doable before. This is a true game changer like few other techniques in sci-
ence.’14 In addition, scientists are identifying other ways to manipulate nerve
cell activity with electromagnetism and ultrasound. What’s more, this tech-
nology has recently been used to manipulate other cell types, such as those
of the heart or the pancreatic cells that secrete insulin.
Or consider the latest in stem cell technology. The development of stem
cells with ‘pluripotent’ potential—the ability to give rise to any cell type in
4
Introduction: The Gene R e volu tion
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R EDESIGNING LIFE
changes being introduced into a new human life, such as those that alter
looks, skills, or personality? Optogenetics is revealing new information
about how the brain works but could it one day be used as a form of mind
control? And while synthetic biology might lead to the production of novel
life forms with a variety of practical uses, how can we be sure these new life
forms will not overrun the planet and cause harm?
Such are the themes of the book. But it’s now time to step back a little
and, in the first chapter, consider whether, for all the novelty of genome ed-
iting and other technologies for transforming life, the human capacity for
modifying life might not be quite so new after all.
6
1
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R EDESIGNING LIFE
altering their genes. And while this was done without knowledge of the
material basis of inheritance, recent advances in genome analysis mean we
can now pinpoint in precise molecular detail the genetic changes that oc-
curred during the agricultural revolution that transformed human society
12,000 years ago.22 Such changes resulted from humans selecting certain
wild variants over others and, in the process, creating rice or wheat from
wild grasses or the domestic pig from a wild boar. Yet although the agricul-
tural revolution was the main driver for such changes, it’s not the first
example of humans transforming the genome of a species. For that, we
must look even further back, to a time when all humans lived as small
groups of hunter gatherers. It was then that we adopted one particular wild
species which not only transformed our hunting capacity but also evolved
into a faithful companion—a status it has maintained to this day. By now
you’ve probably guessed that I’m talking about the dog.
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R EDESIGNING LIFE
contact because of the latter’s fondness for consuming the refuse that a set-
tlement’s occupants would throw out,30 including the human faeces that
accumulated on the edge of primitive settlements.31 Based on this unsa-
voury starting point, the wolves that were more docile and least afraid of
humans would thereby be most likely to consume such refuse: eventually
this would lead to interactions with humans and the tame wolves being ac-
cepted into the life of the settlement.
For either theory to work, our human ancestors would have had to recog-
nize some value in keeping such a canine companion, and here the hunting
skills of wolves may have been a key factor. Subsequently, through natural
selection, the human settlements that hunted using tame wolves would have
been more likely to survive because of their greater efficiency at bringing
home meat. In line with this possibility, even today some tribes in Nicaragua
depend on dogs to detect prey, while traditional moose hunters in Arctic
regions bring home 56 per cent more prey when accompanied by dogs.30
As well as ensuring that a bond developed between humans and their
tame wolves, this joint activity between the two species may have helped
select wolves most suited to this role, and possibly also humans that could
work best with their wolf helpers. For instance, Pat Shipman of Pennsylvania
State University believes working with wolves could have led to the evolu-
tion of a distinctive human characteristic—our eyes with their white sclera,
coloured iris, and black pupil—which contrast with those of other primates
that have a dark sclera. Since wolves’ eyes also have a white sclera, Shipman
thinks this feature evolved in humans to aid communication with our new
canine companions. It is much easier to work out what humans/animals are
gazing at if they have a white sclera. Shipman argues that this change prob-
ably aided communication between humans themselves, since ‘it provides
a very useful form of non-verbal communication and would have been of im-
mense help to early hunters. They would have been able to communicate
silently but very effectively.’32
Shipman believes the new-found alliance between humans and wolves
was so important that it may have been a key factor in the disappearance of
the Neanderthals, who became extinct between 30,000 and 40,000 years
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ago. Explanations for this extinction range from the effects of climate change,
genocide by modern humans, or a battle for scarce resources between
Neanderthals and humans—which our species eventually won thanks to
our superior skills. Shipman favours the last scenario but with a twist,
namely that tame wolves gave us the edge in this competition. ‘Early wolf-
dogs would have tracked and harassed animals like elk and bison and would
have hounded them until they tired,’ she said. ‘Then humans would have
killed them with spears or bows and arrows. This meant the dogs did not
need to approach these large cornered animals to finish them off—often
the most dangerous part of a hunt—while humans didn’t have to expend
energy in tracking and wearing down prey.’32 While speculations like these
are thought-provoking, they are difficult to confirm in the absence of a ma-
chine to replay prehistory. Yet what genome analysis is revealing with much
higher certainty are the precise molecular changes that occurred as wolves
evolved into dogs.
This analysis suggests that dogs are a product of a process called neoteny,
which also seems to have been central to human evolution. Through neot-
eny, an evolving species retains juvenile features into adulthood. So human
adults have many physical features—a flatter and broader face, hairless
body, large head-to-body ratio—in common with young, but not older,
apes.33 This slowing of development was crucial in human evolution, allow-
ing a greater capacity for learning. And recent studies indicate that, through
genetic changes that promote neoteny, adult dogs have also retained an
inclination to learn into adulthood that is absent in wolves. This helped
them gain important skills to aid their human masters, like tracking and
fetching prey, as well as a love of learning and performing tricks that may
have enhanced their attractiveness as pets. Importantly, while dogs often
compete over objects when playing with other dogs, they are usually more
cooperative when the play partner is a human.34 This may have helped the
dog–owner relationship develop.
Another important characteristic in dogs is their capacity to eat a varied
diet. Genetic analysis by Kerstin Lindblad-Toh of Uppsala University,
Sweden, has revealed that dogs differ from wolves in several genes that aid
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R EDESIGNING LIFE
A Feline Interloper
While dogs may be humankind’s oldest friend, cats are the other main rivals
for our affections, so much so that they are now the world’s most popular
pet, outnumbering dogs by around three to one.37 This popularity is undoubt
edly helped by the fact that cats are far more self-reliant than dogs—so they
require virtually no training; they can groom themselves; and they may be
left alone without pining for their owner, but nevertheless (usually) greet us
affectionately when we return home.
Some behavioural differences between cats and dogs have a basis in the
biology of the two species, namely wild cats and wolves, from which these
pets evolved. However, they also reflect the distinct ways in which these spe-
cies entered our lives and their subsequent evolution. For while humans
have cohabited with dogs for at least 30,000 years, genome analysis indi-
cates that cats only joined our households 10,000–12,000 years ago. And
here there’s a clear link with the period during the agricultural revolution
when humans first began to grow enough cereal plants to accumulate a sur-
plus, and thereby a need to store grain.38
The accumulation of grain in this way made it possible, for the first time,
for humans to begin living together in large groups, and led to the birth of
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Natur al Bor n Mu tants
cities. But grain stores also attracted rats and mice. And wild cats that preyed
on these rodents must have made a sufficient difference to the ability of
people in the new cities to keep their grain safe for them to be welcomed
into these places of human habitation. The Natufians, who inhabited the
Levant region of the Middle East and are widely regarded to have invented
agriculture, seem to have been the first people to attract the wild Arabian
cat into their lives in this way.37 Subsequently, cats in ancient Egypt became
so important they were worshipped as gods.39
While the initial relationship of cats to people in these first cities was prob-
ably like today’s urban foxes, which are adapted to a human environment
while retaining an essential wildness, the usefulness and subsequent evolu-
tion of wild cats led to them being assimilated into human households. And
recent analysis of domesticated cat genomes in comparison to those of wild
cats has provided some fascinating insights into this evolution. Such analysis
has revealed that domestic cats differ in genes that control aggressive behav-
iour, formation of memories, and the ability to learn from both fear- and
reward-based stimuli.40 According to ‘anthrozoologist’ John Bradshaw of
Bristol University, such genetic changes ‘give domestic kittens the ability to
become sociable with people—but if they don’t encounter humans until
they’re over 10 weeks old, they can remain as “wild” as any wildcat’.41 In add-
ition, like dogs, our feline companions tolerate a more varied diet than just
meat, making it easier for them to fit into a domestic lifestyle by eating table
scraps. So cats have a longer intestine than their wild cousins and enhanced
activity of genes that aid digestion of fatty plant matter.40
In other respects though, cats are more similar to wild cats than dogs are
to wolves, or as Bradshaw puts it, modern cats have ‘three paws firmly
planted in the wild’.42 This may be due to their more recent evolution, but
probably also reflects the fact that, while the first cats showed their useful-
ness to city-dwelling people because of their rodent-catching skills, there
was probably no human selection for these skills analogous to the way dogs
were selected for specific characteristics that were useful during a hunt.
Maybe this explains why cats can be affectionate or aloof, serene or savage,
since they are that much closer to wild cats than dogs are to wolves.
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R EDESIGNING LIFE
While cats protected our grain stores in ancient times, that grain had to
come from plants, and a key feature of the agricultural revolution was the
cultivation of wild plant species in a fixed location for the first time. Humans
are not the only organisms that cultivate other species—certain ants, bee-
tles, and termites ‘farm’ fungus43—but we are the only ones that do so on
such a widespread scale and with so many different farmed varieties.
Importantly, like our technologies in general, farming is constantly evolv-
ing. Thus, from the moment humans began to cultivate wild plants we also
began to select for specific characteristics in these plants, and so the evolu-
tion of the different domesticated species began.
Now, through genome analysis, we’re beginning to understand the
molecular basis of the evolution of staple crops like rice, maize, and wheat.44
In fact, all such cereal crops are varieties of grass, and at the genetic level
they’re much more similar than might appear from their superficial differ-
ences. Human selection led to the development of these distinct types of
plants with very different attributes as foodstuffs. In some cases, different
populations have also made selections based on distinct properties of the
same plant: so in some parts of the world people traditionally eat long-grain
rice, while others prefer short-grain, sticky varieties.44
In some cases, the characteristics for which a particular plant is bred have
changed over time. So lettuce was originally grown in ancient Egypt for its
seeds, which were used to produce oil, and the original plant formed no
head of leaves; only subsequently was there selection for plants with large
leaves.45 Meanwhile, cabbage, which is part of the mustard family, was ori-
ginally so toxic it was eaten in small quantities for medicinal properties. It
was only through selective breeding that it evolved into the non-toxic plant
we can eat today with impunity.46 Such changes in what are viewed as
important attributes even in the same plant pose a challenge for genomic
studies of crop plants. Quite contradictory tendencies may have been se-
lected at different points in a plant’s history, and this complicates the genetic
analysis.44
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R EDESIGNING LIFE
16
Natur al Bor n Mu tants
Another reason for keeping domestic animals is for primarily aesthetic pur-
poses. I say primarily because a prize-winning dog or cat can clearly be a
pet as well as a show object. In fact, pedigree breeding is a relatively recent
phenomenon; so the large number of dog breeds we now take for granted
date back less than two hundred years, to the Victorian era.54 The Industrial
Revolution, which fuelled the rise of modern capitalism, also, for the first
time, generated a significant middle class with both the time and money to
indulge themselves.55 And one form that such indulgence took was breeding
specific types of dogs and cats, but also pigeons, and even mice, and pre-
senting these at shows. Driven purely by aesthetic notions, in only a short
period of time such competitive breeding created the 400 types of dogs
with their fantastic range of size, shape, and looks, from the tiny Chihuahua
to the huge Great Dane.54
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R EDESIGNING LIFE
The study of pedigree breeds has played an important role in the bio-
logical sciences, for instance stimulating Charles Darwin’s theory of evolu-
tion by natural selection.56 His voyage around the world in the HMS Beagle is
rightly credited with helping him formulate this theory, since it exposed
him to many natural varieties of animals and plants.57 Yet an equally import-
ant stimulus was Darwin’s observations of the many pigeon breeds being
created in Britain by ‘pigeon fanciers’, for these showed how rapidly size,
shape, and form could be influenced by artificial selection. A particular
object of selection for such fanciers was the crest—feathers on the neck and
head that grow upwards rather than downwards, as in wild pigeons.58
Michael Shapiro of the University of Utah, who studies the genetics of crest
formation, has described the different types. ‘Some are small and pointed,’
he said. ‘Others look like a shell behind the head; some people think they
look like mullets. They can be as extreme as an Elizabethan collar.’58
Darwin’s study of pigeons, which started in March 1855, was to be strictly a
way of collecting facts about the variation in a domestic species: there was
to be ‘no amusement’.59 However, by November of that year he wrote to his
friend the geologist Charles Lyell, who was planning a visit: ‘I will show you
my pigeons! Which are the greatest treat, in my opinion, which can be of-
fered to a human being.’59 Darwin had been caught up in a craze so popular
in mid-nineteenth-century Britain that it crossed the class divide, counting
miners, weavers, and Queen Victoria herself amongst its many enthusiasts.
Whitwell Elwin, who reviewed Darwin’s unpublished manuscript detail-
ing his ideas about evolution, dismissed the work as a whole, calling it ‘a
wild & foolish piece of imagination . . . for an outline it is too much & for a
thorough discussion of the question it is not near enough’.56 However, he
liked the section about pigeons, and recommended that Darwin scrap the
main manuscript and write a short book about pigeons instead. ‘Everybody
is interested in pigeons,’ he wrote, and a book like this would ‘be reviewed
in every journal in the kingdom and soon be on every table.’56 Luckily
Darwin and his publisher ignored this advice, and we ended up with The
Origin of Species, not The Little Book of Pigeons. None the less, Darwin’s obser-
vations of artificial selection and how it produced the many different pigeon
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breeds was a key step in the evolution of his theory. It led to a recognition
that selection could also arise in nature, with competition for scarce re-
sources resulting in the variants in the population which thrive in such cir-
cumstances being more likely to survive and produce offspring, which
would inherit their traits.60
Recently, studies of pedigree breeds have become important in a different
way, by providing new insights into the genetic basis of human disease.
Since pet dogs and cats share our homes and our food (though less so now
in societies in which people buy specialized pet foods), their environment is
also more similar to ours than other mammalian species. Most importantly,
the huge number of dog and cat varieties are not just different in size, shape,
and behaviour, but also have different susceptibility to specific diseases.61
And now, by analysing the genomes of these different breeds, it’s becoming
possible to pinpoint the molecular basis of such differences, with import-
ance not only for veterinary, but also human, medicine.
So narcolepsy—the brain disorder that causes a person to suddenly fall
asleep at inappropriate times and which can be potentially fatal if, say,
driving—is particularly common in Dobermann Pinschers. Genome ana-
lysis of this breed identified a link between this condition and a gene that
regulates the brain’s uptake of a neurotransmitter called hypocretin.61
Subsequent analysis of brain fluid from human narcoleptics showed they
lacked this chemical. Studies of how hypocretin can block sleep may iden-
tify ways to prevent narcolepsy, or conversely lead to treatments for insom-
nia. Meanwhile, a study led by Leslie Lyons of the University of Missouri
found that an important cause of kidney failure in old age—polycystic
kidney disease—is associated with mutations in the same gene in both
people and cats.62 And since some cat breeds are susceptible to type 2 dia-
betes, asthma, and other conditions found in humans, the search is now on
for the feline genes associated with these conditions.
The study of naturally occurring mutations in different pedigree breeds
is also leading to the identification of genes involved in body morphology.
Dwarfism is a defining feature of dog breeds like Dachshunds, Pekingese,
and Basset Hounds. In all such breeds, this is due to a change in the gene
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R EDESIGNING LIFE
coding for fibroblast growth factor, which, as its name suggests, is involved
in growth.54 Changes in another gene, coding for bone morphogenesis pro-
tein (BMP), are responsible for the differently shaped skulls of sheepdogs,
with their long snouts, compared to flat-faced bulldogs.63 Understanding
how BMP performs this role could lead to new insights into the molecular
basis of human disorders of the skull and face.
Studies of the behavioural quirks of pets may even lead to new insights
into human psychiatric disorders.64 Dobermann Pinschers are particularly
prone to a condition that causes them to chase their tails for hours on end,
or suck on a toy or one of their paws so compulsively that it interferes with
their sleeping or eating. Such canine compulsive disorder is thought to have
similarities with obsessive-compulsive disorder (OCD) in humans. And
Border Collies sometimes overreact to loud noises in a manner similar to
people with anxiety disorders. But while behavioural quirks are often par-
ticular to specific breeds, in other cases a dog will display a behaviour that is
unusual for its pedigree. A new project called Darwin’s Dogs, run by scien-
tists at the University of Massachusetts, is now trying to identify genetic links
to such behavioural characteristics.64 Miranda Workman of Buffalo, New
York, is one pet owner who has enrolled her dogs in the scheme, because
she wants to know why her Dutch Shepherd Athena has a jovial side not
usually found in this guard dog breed, and why Sherlock, her Jack Russell, is
more shy and sensitive than most terriers. ‘I have some dogs that don’t
necessarily fit the stereotype,’ she said. ‘Is it their environment that’s dif-
ferent or are they different? It will be fun to find out why they are that way.’64
Although the study of naturally occurring mutations in dogs and cats for
biomedical purposes may be novel, as applied to other species in an experi-
mental setting it’s far from a new idea. Indeed, genetics has been intimately
bound up with the investigation of mutants from its origins in the late nine-
teenth century. In the popular consciousness the word mutant tends to
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DNA polymerase
Free
nucleotide
units
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R EDESIGNING LIFE
e xposure to normal sunlight causes the skin of such people to blister, and
they are prone to skin cancer. Another DNA repair defect, Cockayne syn-
drome, leads to premature ageing,68 while defects in the breast cancer 1 and
2 (BRCA1 and BRCA2) genes, both involved in DNA repair, causes a strong
tendency to develop breast and ovarian cancer. This latter defect made the
headlines when actress Angelina Jolie made public her decision to have a
double mastectomy and removal of her ovaries after her mother and aunt,
with whom she shared the BRCA1 gene defect, died prematurely from ovar-
ian and breast cancer, respectively.69 That defects in the same cellular pro-
cess can have such varied effects reflects the fact that different types of DNA
repair are more important in some parts of the body than others.
Mutations can cause cancer because any change in DNA that results in
abnormalities in the proteins regulating cell growth and division may lead
to tumour growth. In fact multiple changes in the genome of a cell are gen-
erally required for this to happen, which is why our likelihood of succumb-
ing to cancer increases with age, reflecting the gradual accumulation of
mutations in our bodies over time.70 However, if a mutation occurs in the
sperm or egg DNA, a susceptibility to a particular type of cancer can be in-
herited. This was the case with Angelina Jolie, whose inherited BCRA1 gene
defect meant that, before her mastectomy, her risk of getting breast cancer
before the age of 70 was 65 to 87 per cent compared to a 12.5 per cent risk in
most women.71 In fact, each one of us is likely to be carrying numerous
harmful mutations in our genomes. These can result in other serious dis-
eases besides cancer, such as cystic fibrosis.72 That such mutations don’t
generally result in disease is because we have every gene in duplicate, and
it’s sufficient in most cases for a person to have only a single functional gene
for this not to cause a problem.
While many people are aware of the link between mutations and disease,
there is much less recognition of the fact that, without mutations, we human
beings, or indeed any of the other species on the planet, would not exist. To
understand why, we need to return to Darwin’s theory of natural selection.
Darwin recognized that evolutionary change took place because some vari-
ants in a population are more suited to survive in a particular environment,
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Natur al Bor n Mu tants
and therefore to reproduce, than others.73 And we now know that muta-
tions in DNA underlie such differences between individuals, some of which
enhance survival. This ensures the spread of such mutations through a
population and ultimately the evolution of a species.
A Model of Life
Darwin never identified the material basis of inheritance. That was left to
the monk Gregor Mendel, who, in the 1860s, studying the inheritance of
pea plants, first proposed that inherited characteristics are passed down as
discrete ‘factors’, which we now call genes.74 Mendel showed that the inher-
itance of pea characteristics, like purple or white flowers, or short or long
stems, followed precise mathematical patterns, which he divided into two
types: dominant, in which a single defective gene can cause the character-
istic, being passed down from an affected individual to half their offspring;
and recessive, in which two defective genes are required, so that two unaf-
fected carriers of the characteristic have a one in four chance of having an
affected offspring (see Figure 2). Mendel’s work complemented Darwin’s
ideas by providing a material basis for species variation and its transmission
across generations. But Darwin died not knowing of Mendel’s findings,
which were also overlooked by other scientists. It was only when Mendel’s
findings were rediscovered in 1900 that Darwinism and Mendelism were
united into a single theory of evolution and inheritance.73
A a
Self pollination A
AA Aa 3 : 1
Dominant trait Recessive trait
Aa (Purple colour) (White colour)
a
Aa aa
23
R EDESIGNING LIFE
The realization that genes are made out of DNA had to wait almost an-
other half century, when Oswald Avery at the Rockefeller University in New
York showed in 1944 that DNA was the molecule of inheritance,75 while
Watson and Crick identified DNA’s double helix structure at Cambridge
University in 1953.76 Not only did this latter discovery reveal how the mol-
ecule replicated, subsequent studies showed how it acted as a code for the
assembly of proteins. However, long before these discoveries, in the 1900s,
Thomas Hunt Morgan, of Columbia University in New York, had recog-
nized that mutant organisms offered a way to study the material basis of
genes, since the pattern of inheritance of their abnormal characteristics
could be studied, and the genes associated with the mutation identified.
Initially working with mice, Morgan quickly switched his studies to fruit
flies (Drosophila melanogaster), because he realized that, with their rapid re
production time and large numbers of offspring, there was far more chance
of spotting rare mutants that did arise.77 And through patient identification
and characterization of such mutants, Morgan’s team confirmed Mendel’s
findings in an animal species. They also identified new patterns of inherit-
ance, such as a mutation that caused white eyes instead of the normal red
ones, but typically only in males. The discovery that some characteristics
are sex-linked led to the realization that the associated genes must be lo-
cated on the X chromosome. This explained why human disorders like hae-
mophilia generally only affect males: haemophilia is a recessive disorder
and females with two X chromosomes are therefore usually protected, since
it is unlikely that both copies are abnormal.78
Despite these promising initial findings with naturally occurring muta-
tions, fruit fly genetics really only took off when Hermann Muller, a former
member of Morgan’s team, discovered a way to greatly boost the mutation
rate in this species.79 Muller might have only been 5´2˝ in height, but he was
a larger-than-life character who inspired and outraged in equal measure.
For Muller was as passionate about socialism as he was about science, and
he seemed to believe that a Bolshevik should be, well, bolshie—a stance that
would get him into trouble throughout his life. In Morgan’s group, Muller
made some important contributions, such as showing that mutations in
24
Natur al Bor n Mu tants
one gene could alter the expression of another gene, implying that genes
interact. However, Muller didn’t feel his ideas were given sufficient credit in
Morgan’s publications, and he moved to set up his own lab at the University
of Texas. Here he showed that irradiating fruit flies with X-rays dramatically
increased the number of mutants in subsequent offspring. ‘In a few months
Muller found more mutant genes than the total from all the Drosophila labs
up to that time,’ said James Crow, who was a graduate student at Texas and
later became a professor at the University of Wisconsin-Madison.80 The dis-
covery was made in the mid-1920s, 30 years after the discovery of X-rays by
William Röntgen.81
Unfortunately, Muller’s socialist views led to trouble with the authorities.
He helped publish a Communist newspaper at his university, and the FBI
tracked his activities. In 1932, Muller moved to Russia, expecting to find
himself amongst kindred spirits, only to discover that the country was in
the grip of Stalin’s clampdown on both personal and academic freedom. By
the time he left in 1937, many of Muller’s students and colleagues had ‘disap-
peared’ or been shipped to Siberia, and he was lucky not to meet a similar
fate, as traditional genetics was increasingly seen as a ‘bourgeois deviation’
in the new totalitarian state.
Despite these troubles, Muller’s greatest triumph was still to come. In
1945, he was awarded the Nobel Prize. The award not only recognized the
importance of Muller’s findings for basic science, but also reflected increas-
ing awareness of the dangerous effects of radiation on human genes.79 This
was shown in practice by the tragically early death of Marie Curie, who,
with her husband Pierre, had isolated the naturally radioactive elements
polonium and radium.82 Describing these studies, Marie wrote how ‘one of
our joys was to go into our workroom at night; we then perceived on all
sides the feebly luminous silhouettes of the bottles or capsules containing
our products. . . . The glowing tubes looked like faint, fairy lights.’83 Marie
paid a terrible price for her lack of awareness of the health risks associated
with radiation. She succumbed to aplastic anaemia, a cancer of the blood
brought on by massive exposure to radiation during her work, which would
result in her death in 1934.82 The devastating effects of radiation on human
25
R EDESIGNING LIFE
Fancy Mice
While fruit fly studies have furthered our understanding of many basic bio-
logical processes, ultimately scientists need to study a mammalian ‘model’
of human health and disease, given that we are mammals ourselves. And
the species that has been the favoured choice in this respect is the mouse. In
26
Natur al Bor n Mu tants
addition to its rapid reproductive cycle and small size, the establishment of
the mouse as a model organism was helped by the existence of naturally
occurring mutant mice thanks to the nineteenth-century interest of breed
ing ‘fancy’ mice with differently coloured coats and other characteristics as
a hobby.88 Mendel himself first began studying inheritance of coat colour in
mice, breeding these in his living quarters.89 However, the local religious
leader, Bishop Schaffgotsch, was outraged that a monk who had taken the
vow of chastity was encouraging—and watching—rodent sex, and ordered
Mendel to ‘stop the work with the smelly creatures’.90 In response, Mendel
turned to cultivating peas instead, remarking that it was lucky that the bishop
‘did not understand that plants also had sex!’89 So it was that pea plants, not
mice, became the first model organism of genetics.
When geneticists did begin studying mice in the early twentieth century,
they were greatly helped by the activities of a woman called Abbie Lathrop.91
She initially trained as a teacher but gave up this vocation because of chronic
ill health. This didn’t, however, prevent her beginning a new career, breeding
fancy mice. These turned out to be of great interest not only to mice ‘fan-
ciers’, but also to geneticists. The business was such a success that at one
point Lathrop had more than 11,000 mice.91 The animals were fed oats and
crackers; Lathrop got through one and a half tons of oats and 12 barrels of
crackers each month. She also paid local children seven cents an hour to
clean the cages.92 But, most importantly, Lathrop kept careful records of the
different mouse breeds, and these would later prove vital for scientists inter-
ested in determining the inheritance pattern of interesting mouse charac-
teristics.
At one point Lathrop noticed that some mouse breeds were particularly
prone to developing lesions on their skin.91 She sent samples to several sci-
entists asking for advice about their origin, and one of these, Leo Loeb at
Pennsylvania University, diagnosed the lesions as malignant. Lathrop and
Loeb’s joint interest in the genetic basis of this cancer susceptibility subse-
quently developed into a valuable collaboration. Amongst the important
findings the pair made was the discovery that removing the ovaries from
mice susceptible to mammary gland tumours reduced the incidence of
27
R EDESIGNING LIFE
such tumours. This finding had eventual relevance for treatment of breast
cancer in humans, as one way of treating this cancer is to block the effects
of the hormone oestrogen, which is secreted by the ovaries and inhibited by
the anti-cancer drug tamoxifen, also known as Nolvadex®. Such was the
importance of Lathrop’s mice that, when she died in 1918, many were used
to populate a new mouse breeding and research institute founded by
Clarence Little at Bar Harbor, Maine,93 despite him once patronizingly
describing Lathrop as a ‘talented pet-shop owner’.90 The institute, now
known as the Jackson Laboratory, continues to be the world’s largest sup-
plier of inbred mouse breeds to this day.
Enhancing Abnormality
28
Natur al Bor n Mu tants
London has tracked down many of the genes involved by identifying mutant
mice that fail to respond to a sound stimulus, or have problems in balance,
which can be linked to deafness. Steel likens the quest to identify genes
associated with each defect to solving a puzzle. ‘You have no idea of what
the mechanism might be before you start studying the genetics,’ she said.
‘So, it’s a bit like putting a jigsaw together, or unwrapping a parcel, as you
find out what’s going on inside.’97 According to her, ‘characterising these
mutants taught us many lessons. First, many of the genes that we found had
never been linked to deafness before. That told us that there are many dif-
ferent genes that can cause deafness. Second, there are a wide variety of
mechanisms that can cause hearing impairment.’97 The studies showed that
genetic defects can cause deafness at birth, but also create susceptibility to
hearing loss in later years. Characterization of the genes associated with
deafness may lead to greater understanding of the molecular mechanisms
those genes regulate, and hopefully to new drugs for treating both congeni-
tal and progressive hearing loss.95
Although the study of mouse mutants is proving of great value for bio-
medical research it does raise important issues about animal welfare, since
defects in a particular gene could potentially result in an abnormality that
causes pain or distress. In fact, surprisingly, many mouse mutations have
quite subtle effects on the body, perhaps because the developing embryo
compensates for loss of a particular gene by enhancing or repressing the
activity of other genes.98 But this is not always the case. A naturally occur-
ring deaf mutant, the whirler mouse, is so-named because of its rapid circ-
ling and head-tossing motions. This odd behaviour is due to a defect in a
gene involved in forming hair-like projections in the cochlea, a component
of the inner ear.99 Because these projections play important roles in hearing
and balance, study of this mutant has led to important insights into both
these processes.
Another naturally occurring mouse mutant eats excessively, becomes
severely obese, and develops diabetes, because of a defect in a gene coding
for the hormone leptin, which regulates appetite by signalling to the brain
that the animal is full.100 Study of this mutant may reveal new ways to
29
R EDESIGNING LIFE
30
2
Supersize My Mouse
31
R EDESIGNING LIFE
to Saturday, 28 February 1953, when Jim Watson and Francis Crick first
determined the double helix structure of DNA. At their celebratory drinks
at the Eagle pub in Cambridge, Crick’s boast that he and Watson had dis-
covered the ‘secret of life’105 may have bemused anyone else listening, but
wasn’t so far wrong in terms of the impact of the discovery on our under-
standing of the natural world.
The discovery initiated the age of molecular biology by providing a uni-
fying principle to genetics that had been lacking: the recognition that life
can be viewed as a linear code. The genetic blueprint, DNA, can be seen as a
long string of four different letters—defined by the chemical names aden-
ine, cytosine, guanine, and thymine, generally abbreviated to A, C, G, and T.
Importantly, the order of these four letters is not random, but occurs in a
precise sequence of triplets, each coding for a particular amino acid, the units
from which proteins are composed.106 So a linear code based on the four
DNA letters is ‘transcribed’ first into ribonucleic acid (RNA)—DNA’s chem-
ical cousin—and then ‘translated’ into proteins, themselves linear molecules,
but composed of 20 different units—the amino acids (see Figure 3).
DNA
G G G G C T G
A T C C T G A G A C A T
C T C C A C A
T A A C A T G T G T
Transcription
mRNA
A U G C C A C U C A U
U A G C A C G
Translation
Protein
(Amino acid chain)
32
Supersize My Mouse
Unlike DNA, with its unvarying double helix, each type of protein folds
into a unique 3D shape based on its specific sequence of amino acids. It’s
because of these differences in shape and size that proteins can perform so
many different roles in the cell, acting as cellular building blocks, motors,
and transporters, as well as carrying out many other functions. The genetic
code—the connection between the sequence of letters in the DNA and that
of the amino acids in proteins (see Figure 3)—was cracked by the mid-
1960s.107 But knowing how the code worked didn’t immediately translate
into an ability to manipulate it. That only became possible with the discov-
ery of natural processes in bacteria that provided key tools for genetic
engineering.
Engineering Life
The first of these processes allows bacteria to defend themselves from infec-
tion. Since we generally think of bacteria being the infective agents, it may
seem strange that these microorganisms suffer infection themselves. Yet
just as humans can be infected by viruses, so bacteria have their own vir-
uses to deal with—so-called bacteriophages.108 And just as our own immune
system wards off infectious agents, so bacteria have their own miniature
form of immunity. This process was discovered by Werner Arber of the
University of Geneva, in the 1960s, but Hamilton Smith of Johns Hopkins
University in Baltimore, Maryland, worked out its specific details in 1970.109
He showed that bacteria produce catalytic proteins—enzymes—that rec-
ognize a specific DNA sequence in the genome of an invading virus and
chop the DNA at that point. The target sequences are small, typically four to
six letters, and each bacterial species produces its own set of one or more
unique cutting enzymes.
So Escherichia coli, more commonly known as E. coli—the bacterium that
lives inside a human gut but also exists in more dangerous forms—pro-
duces an enzyme named EcoRI that cuts within the sequence GAATTC.
Since this sequence occurs many times within any typical long stretch of
33
R EDESIGNING LIFE
DNA, this poses the question of why the enzyme doesn’t cut the bacteri-
um’s own genome into pieces. What prevents this happening is that, just as
our immune system can distinguish invading microorganisms from our
own cells and tissues, E. coli has also evolved a mechanism to protect its
genome. This involves the recognition site GAATTC being chemically
modified with a methyl (–CH3) group in the bacterial DNA, which prevents
the site being cut in the genome. Because of this, the cutting proteins have
become known as ‘restriction enzymes’, since their action is restricted to
targeting only foreign DNA.110
Many different bacterial species produce their own unique restriction
enzyme with a distinct cutting site. So, armed with a variety of such en-
zymes, it’s possible to cut anywhere in a DNA sequence. The first use of
such enzymes was demonstrated by Daniel Nathans, also at Johns Hopkins,
who employed HindII and HindIII, restriction enzymes Hamilton Smith
had purified from the Haemophilus influenza bacterium, to cut the SV40
monkey virus into 11 pieces, thereby creating the first ‘restriction map’.111
Long before it became possible to identify a piece of DNA by its sequence,
this method made it possible to do so by the precise number and size of
fragments it could be cut into, like a kind of molecular fingerprint. For
these discoveries, Arber, Smith, and Nathans were awarded a Nobel Prize in
1978.109
When told he’d been awarded the greatest prize in science, Hamilton
Smith’s response was initially one of shock. ‘Are you kidding?’ he said when
a reporter told him about the award. ‘I just didn't imagine it would be taken
in that light.’112 This feeling was shared by his family. When Smith’s mother
heard the news on her car radio, puzzled, she turned to her husband and
said, ‘I didn't know there was another Hamilton Smith at Hopkins.’112 The
fact was that, before the award, Smith was viewed at Johns Hopkins only as
a fairly obscure researcher, known more for his moth-eaten sweaters, shirts
worn bare at the elbows, and thick glasses through which he squinted as if
he’d just emerged from a cave, than for any sense of impending fame.112 His
studies of restriction enzymes were seen as highly esoteric, if they were rec-
ognized at all. However, Smith’s discovery was about to make him famous
34
Supersize My Mouse
35
R EDESIGNING LIFE
Restriction
enzyme Gene of
interest
DNA
Foreign DNA ligase
Bacterial DNA
plasmid, with a restriction enzyme, use DNA ligase to attach the two to-
gether, then introduce the resulting gene construct into a bacterium (see
Figure 4). Cohen achieved this by using a ‘heat shock’ to get the bacterium to
take up the DNA. Since uptake of the gene construct into the bacterium is
highly inefficient, this rare event must be selected for. Such selection makes
use of the antibiotic resistance genes that plasmids typically contain. If the
experiment is carried out in a solution containing the antibiotic, only those
cells containing the plasmid DNA survive.
Birth of Biotechnology
36
Supersize My Mouse
37
R EDESIGNING LIFE
such risks and devise ways to reduce them, to be held at the Asilomar Con
ference Center in Pacific Grove, California, in February 1975.118 The meeting
was to discuss the possibility that, while ‘the new technology opened extra-
ordinary avenues for genetics and could ultimately lead to exceptional
opportunities in medicine, agriculture and industry . . . unfettered pursuit of
these goals might have unforeseen and damaging consequences for human
health and Earth’s ecosystems’.118 In line with such concerns, in the run-up
to the meeting a voluntary moratorium was proposed, and despite the
commercial potential of the new technology, this was universally observed
not only in academia but also in the biotechnology industry. One effect of
publicizing the potential risks of recombinant technology was that, in the
build-up to the meeting, the media ‘had a field day conjuring up fantastical
“what if” scenarios’.118 Some scientists feared this would turn the public
against recombinant DNA technology. However, the fact that at the meeting
itself there were not only scientists but also lawyers, journalists, and gov-
ernment officials provided an opportunity for members of the public to
be informed ‘about the deliberations, as well as the bickering, accusations,
wavering views and ultimately the consensus’ of how to maximize the
potential and minimize the risks of biotechnology.118
The Asilomar meeting decided that recombinant DNA technology could
continue, but only following strict guidelines that regulated the safe dis-
posal of GM bacteria. It also introduced genetic safeguards that limited the
bacteria’s ability to survive in the wild, should any accidentally escape.
Importantly, according to Berg, the meeting introduced the principle that
‘the best way to respond to concerns created by emerging knowledge or
early-stage technologies is for scientists from publicly funded institutions
to find common cause with the wider public about the best way to regu-
late—as early as possible’. Berg was particularly concerned that ‘once scien-
tists from corporations begin to dominate the research enterprise, it will
simply be too late’.118 So, although the biotechnology industry had devel-
oped from academic science, already some of the priorities and interests of
the two spheres were diverging, in ways that remain relevant today.
38
Supersize My Mouse
A Giant Mouse
So much for introducing a gene into a bacterium. But what about manipu-
lating the genome of a complex, multicellular organism? Such a GM or-
ganism—a mouse—was created in 1974 by Rudolf Jaenisch, now at the
Whitehead Institute and the Massachusetts Institute of Technology in
Boston.119 At this time he was working as a postdoctoral researcher in
Arnold Levine’s laboratory at Princeton University. Jaenisch had joined
Levine’s group because the lab was pursuing an exciting new area of re-
search—the role of certain viruses in causing cancer. Jaenisch’s project was
to study the mechanism of replication of the SV40 virus mentioned in the
section ‘Engineering Life’. However, only two months after his arrival,
Levine told Jaenisch that ‘he was going on sabbatical to Europe and that I
should run the lab’.119 What might have overwhelmed a lesser individual
became an important step in Jaenisch’s career development, for while con-
tinuing his main project into SV40 replication with Levine’s graduate students,
the absence of his supervisor meant he began exploring areas of research
that he might not have otherwise.
In particular, Jaenisch became fascinated by a puzzling fact related to the
cancer-causing ability of SV40. When injected into mice, the virus only
caused formation of tumours in tissues such as bone, muscle, cartilage, and
fat, but not others like the liver. Jaenisch reasoned that this selectivity must
arise either because SV40 could not infect liver cells, or because these cells
were turning off replication of the virus after infection.119 To test which scen-
ario was correct, Jaenisch decided to see if he could infect an early mouse
embryo with the virus. Since at this stage of life all cells are pluripotent,
meaning they can give rise to any cell type, this should allow him to intro-
duce the virus into all tissues of the body. The only problem was the fact
that no one had ever tried such an experiment. Undeterred, Jaenisch sought
help from Beatrice Mintz of the Fox Chase Cancer Centre in Philadelphia, an
expert on isolating and culturing mouse embryos. With her help, Jaenisch
injected mouse embryos with SV40, then implanted them into females.
39
R EDESIGNING LIFE
40
Supersize My Mouse
A
Metal-regulatory Heavy metal
transcription factor Transcription “ON”
RNA
polym
erase
B
Metallothionein
Egg implanted Normal diet
promoter Growth hormone
in female mouse
gene
Recombinant
plasmid Diet containg
Recombinant plasmid cadmium
injected into fertilized
mouse egg Progeny carrying
growth hormone gene
regulated by heavy metals
the first time man was able to experimentally modify the genetic code that
will make the next individual.’122
Such transgenic mice have been useful to biomedical research in numer-
ous ways. For instance, they have been used to study why genes are turned
on in some cell types in the body but off in others. Investigating this issue
could help us understand the molecular mechanisms underlying the devel-
opment of the different bodily tissues, and why sometimes such mechan-
isms go wrong, leading to a developmental abnormality or cancer. Many
different regulatory elements are present in the promoter of any given gene.
By fusing each separately to a ‘reporter’ gene, and then creating transgenic
mice expressing such gene constructs, it’s possible to uncover the specific
contribution of each regulatory element.123 The first such reporter gene was
a bacterial gene called β-galactosidase. The presence of the protein product
of this gene can be detected by a chemical reaction that produces a blue
colour, thereby labelling the cells in which the gene is normally turned on.
41
R EDESIGNING LIFE
But an even more direct way of visualizing gene promoter activity uses
genes coding for fluorescent proteins that, when fused to regulatory elem-
ents, signal their presence by the fluorescence they emit in a particular cell
type or tissue. By such means scientists can track the expression of a gene
product during a bodily process.
This approach has proved very important for studying the progression of
disease in mice models. Osteoarthritis is a painful joint disease that affects
millions of people around the world.124 This disorder is generally first de-
tected when painful symptoms occur, but by then the disease has already
progressed to a late stage. So there is a lot of interest in understanding the
mechanisms underlying the initial stages of osteoarthritis in order to im-
prove its diagnosis and treatment. Recently, researchers at Tufts University
and Harvard University Medical Schools used a fluorescent reporter ap-
proach to monitor the activity of a gene involved in loss of cartilage in the
joint—the key characteristic of osteoarthritis—in mice in which the condi-
tion had been triggered by injury. ‘The fluorescent probe made it easy to see
the activities that lead to cartilage breakdown in the initial and moderate
stages of osteoarthritis, which is needed for early detection and adequate
monitoring of the disease,’ said Shadi Esfahani, one of the researchers.124
The team believe their approach could be used to study the effectiveness of
new osteoarthritis drugs, leading to improved treatments.
Crop Controversy
Transgenic technology has also been used to create GM plants both for re-
search and agriculture. This technology has been employed to produce
plants that are resistant to viruses, other infectious agents, and even to in-
sects; to create forms that are more resistant to weedkiller so that the latter
can be used more effectively to destroy neighbouring weeds; and to change
the appearance, flavour, and nutrient composition of the modified plant.125
There is now widespread production of such crops, with a recent report
claiming that ‘around one 10th of the world’s planted crops are GM.’126 There
42
Supersize My Mouse
has also been substantial opposition to GM crops, for instance from the Soil
Association, an organization committed to ‘organic’ methods of farming,
on three main grounds.127 First, concerns have been raised about the impact
of such crops on the environment, for instance if a herbicide resistance gene
were to be transmitted to weeds. Second, some have claimed that GM crops
will not help ordinary farmers, but rather allow giant agribusiness compa-
nies to further increase their grip on the farming industry. Finally, there are
claims that GM crops pose risks to human health.
Assessing the scientific basis of such claims has not been helped by the
highly polarized way in which the debate has developed. Science journalist
Natasha Gilbert claimed in an article in Nature in 2013 that, ‘in the pitched
debate over genetically modified (GM) foods and crops, it can be hard to see
where scientific evidence ends and dogma and speculation begin’.128 To try
to get a clearer picture about the impact of GM crops, Gilbert looked at
three key issues: whether the spread of herbicide resistance genes in the
USA had helped create superweeds; whether the introduction of GM insect-
resistant cotton in India had dramatically increased suicide rates amongst
small farmers; and whether transgenes in GM crops imported into Mexico
from the USA had contaminated local maize strains.128
Gilbert claims that, in only one of these cases, is there an unambiguous
answer: namely that the suicide rate amongst Indian farmers does not seem
to have been directly affected by the introduction of modified cotton. So a
study by Ian Plewis of the University of Manchester in 2012 found that the
suicide rate in areas of India that now grow GM cotton did not change sig-
nificantly following the introduction of such cotton to India in 2002.129 In
contrast, Gilbert did find evidence of an increase in resistant weeds in fields
planted with GM herbicide-resistant crops. But this may reflect overreliance
on one specific herbicide rather than any actual transfer of transgenes, as
the same phenomenon has also been seen in fields planted with standard
crops. Finally, Gilbert found evidence both for and against the possibility
that transgenes from GM plants can spread to non-modified crops.128
One aspect of GM crops that has caused particular controversy is so-
called ‘terminator’ technology. A plan to develop this technology, which
43
R EDESIGNING LIFE
creates transgenic plants that produce sterile seeds, thereby forcing farmers
to buy new seed for each planting, was announced by the multinational
Monsanto in 1998.130 The proposal generated huge opposition, on the
grounds that it would force farmers in the developing world to purchase
expensive seed each year from Monsanto, rather than saving new seed to
sow the following season as was their normal practice. In fact, many con-
ventional hybrid crops—the result of breeding two different plant var-
ieties131—also produce sterile seeds. And, according to Paul Moyes of the
European Association for Bioindustries, ‘plant breeders and farmers have
preferred hybrid seeds for more than 30 years because they were more pro-
ductive. This means they have to buy their seeds again every year because
hybrid seeds can only be used once.’130 Nevertheless, the fact that termina-
tor technology seemed to represent a deliberate attempt to impose such
sterility was seized upon by anti-GM activists. So, for example, Andrew
Simms of Christian Aid, the development charity, said, ‘Terminator tech-
nology was the lynchpin of a strategy to protect corporate royalties in de-
veloping countries.’130 And indeed, opposition was such that, in 1999,
Monsanto’s chairman Robert Shapiro was forced to promise not to com-
mercialize the technology.
Turning to the third controversial aspect of GM crops, the question of
how safe they are for human consumption, there are two potential areas of
concern.132 One is that genetic modification of crops may cause harmful
chemical changes in the resulting food product. The second concern is
linked to the way GM crops are produced. Because integration of transgenes
into the genome is so inefficient, antibiotic resistance is used to select for the
rare cases in which integration occurs, a gene that confers such resistance
being included in the gene construct. However, this additional gene could,
in theory, be transferred to bacteria in soil or the human gut, where it might
then create antibiotic resistance in a pathogenic bacterium.
In fact, there is little evidence to indicate toxicity of GM foods, despite
widespread media coverage of a study by Árpád Pusztai of the Rowett
Research Institute in Aberdeen in 1999.133 The study appeared to show that
rats fed GM potatoes suffered damage to their vital organs and immune
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45
R EDESIGNING LIFE
Findings like this have led Mark Lynas, an environmental campaigner and
one of the founders of the anti-GM crop movement, to recently publicly
apologize for opposing the planting of GM crops in Britain. ‘The first gen-
eration of GM crops were suspect, I believed then, but the case for contin-
ued opposition to new generations—which provide life-saving vitamins for
starving people—is no longer justifiable,’ he said.135
What this discussion of the benefits and risks of GM crops does highlight
is that such issues are not purely scientific ones. Instead, they are intimately
connected with the development of GM crops in a free market system, with
all that implies in terms of the interests of public versus private ownership,
and the priorities of profit compared to those of a sustainable agriculture
that benefits the maximum number of people.126 These are issues to which
we will return in Chapter 6 when assessing more recent approaches to gen-
etic modification of plants and animals that are already promising to have a
major impact on agriculture.
Genes as Therapy
46
Supersize My Mouse
Nn Nn Nn nn
NN Nn Nn nn Nn nn Nn nn
Normal Carrier Carrier Affected Affected Normal Affected Normal
operation of this organ, leading to lung dysfunction and infection. But this
has also made cystic fibrosis a potential target for gene therapy, since lung
cells are relatively accessible via the respiratory tract.137 Diseases affecting
the blood cells are also targets for gene therapy, since the stem cells that pro-
duce such cells are located in the bone marrow. By extracting a sample of
bone marrow, introducing a functional copy of the gene that’s defective into
the stem cells within, and then replacing the treated bone marrow, it should
be possible to treat the disorder.138
Unfortunately, gene therapy using standard transgenic technology has
been far from a success story. A key challenge is getting a gene construct
into an affected tissue. Attempts to do this include wrapping the gene con-
struct in a detergent shell, to help it cross the cell’s fatty membrane.137
However, this is an inefficient process. An alternative strategy uses a virus
to carry the gene construct into the cell.139 This is a potentially attractive
route because viruses have evolved to cross cellular boundaries and, in
some cases, even integrate their genetic material into the genome of a host
cell. This latter property is a particular feature of retroviruses, of which
human immunodeficiency virus (HIV) is the most famous member.140
A safe, adapted form of HIV was used in a clinical trial carried out in Paris
in the late 1990s to treat a disorder called severe combined immunodeficiency
(SCID). In this disorder, a gene defect in white blood cells leaves sufferers
without a functioning immune system and thereby extremely vulnerable to
47
R EDESIGNING LIFE
Recombinant retrovirus
carrying correct form of gene
Bone marrow cells
with defective gene
infection. The treatment of bone marrow from such individuals with a retro-
virus carrying a normal copy of the defective gene cured the disorder (see
Figure 7).141 However, some treated patients subsequently developed leukae-
mia. An investigation showed that while the retrovirus had successfully car-
ried the normal gene into the genomes of sufferers’ cells, in some cases it also
disrupted the action of genes that control cell growth and division, causing
cancer. A more recent trial led by Patrick Aubourg at the French National
Institute of Health and Medical Research in Paris, has been successful in
curing SCID without causing leukaemia in the process. ‘The new generation
of [viral] vectors is much safer, although the risk is not zero,’ said Aubourg.142
For a dominant genetic disorder like Huntington’s disease, the problem is
not the loss of a gene, but rather the fact that the mutant gene product dis-
rupts normal cellular function. In this case, every generation is affected,
with the chance of an affected person passing on the condition to their
48
Supersize My Mouse
c hildren being one in two (see Figure 6). In Huntington’s, what begins as odd,
jerky movements of the limbs rapidly progresses into psychosis and full-
scale dementia.143 The condition has not been considered suitable for gene
therapy because treatment would involve precisely replacing the mutant
gene with the normal version, something not possible with standard trans-
genic approaches. But at the end of the 1980s, a more precise way to modify
genes was identified, and it came from a surprising starting point—cancers
called teratomas that can occur in various locations in the body, but are par-
ticularly common in tumours of the testicles and ovaries.144
Teratomas have a startling property first identified by Leroy Stevens at
the Jackson Laboratory, Maine, in 1953. Newly arrived at this mouse breeding
institute, Stevens noticed that one mouse breed had a tendency to develop
abnormally enlarged testicles. ‘We killed it, and looked at the testes, and
they had strange things inside,’ said Don Varnum, a technician working
with Stevens.145 This was somewhat of an understatement given that the
tumour, for this is what it was, comprised a grotesque mishmash of dif-
ferent tissues, including bone, hair, and teeth. It was as if the tumour cells
could form any cell type in the body. And the discovery of teratomas in
humans showed that this wasn’t just a peculiarity of mice. Teratomas were
also discovered in ovaries and in other parts of the body, like the brain.144
Trying to understand the phenomenon would occupy Stevens for the rest
of his career. In 1970 he made a major step forward when he discovered that
cells from an early mouse embryo, transplanted into the testicles of adult
mice, also generated teratomas. Based on this observation, Stevens pro-
posed that teratomas might provide a clue as to how the unspecialized cells
of the embryo could develop into all the specialized cell types that make up
the body—so-called ‘pluripotency’.145
Pluripotent Potential
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R EDESIGNING LIFE
the mid-1970s, Evans began studying teratoma cells in culture and found
little difference between them and cells extracted from a normal embryo.146
Were the tumour cells simply unspecialized cells that only became malig-
nant in the wrong environment? In line with this, while cells isolated from
normal embryos turned malignant when injected into an adult mouse, tera-
toma cells injected into an early mouse embryo became part of the normal
tissues of the resulting mouse. This suggested that embryonic cells might be
used to generate a whole mouse. And indeed, by taking embryonic cells
from one mouse breed and injecting these into the embryo of another,
Evans showed that the resulting offspring were ‘chimaeras’—products of
more than one original embryo and named after those mythical beasts like
the Sphinx with the head of one animal and the body of another.146
This chimaeric quality was shown graphically by taking embryonic cells
from a black mouse and injecting these into the embryo of a white one. This
produced mice with patches of black amongst mainly white fur, and genetic
analysis showed that other tissues of these animals were a similar patch-
work, suggesting the embryonic cells could develop into any cell type. This
capacity included an ability to develop into the cells that form the next gen-
eration—sperm and eggs—since breeding male and female chimaeras led
to some offspring that were totally black, that is, totally derived from the
embryonic cells.146 Reflecting their pluripotent properties, the embryonic
cells were named embryonic stem (ES) cells.
The discovery of ES cells immediately suggested a new route for making
transgenic mice. Rather than injecting a gene construct into a fertilized egg
and hoping it would integrate into the latter’s genome, an ES cell could be
genetically modified and used to create a transgenic mouse. Nonetheless,
the same limitations would apply to such a mouse as with the standard
route—unless a way were found to modify a gene in the ES cell more pre-
cisely than was possible with standard methods. In the end, such precision
was achieved using a process that occurs naturally in cells, called ‘homolo-
gous recombination’.147 This occurs when two pieces of DNA that contain
sequences which are identical, or very similar, come into contact. Such
proximity triggers a cellular mechanism in which the two sequences are
50
Supersize My Mouse
51
R EDESIGNING LIFE
52
Supersize My Mouse
Homologous
DNA template
Repaired DNA
53
R EDESIGNING LIFE
Targeting vector
Targeted Random
Homology arms for
gene insertion integration
homologous recombination
Modified genome carries a neoR gene Modified genome carries a neoR and a
inserted in the target gene tk gene inserted in a random location
but no tk gene (neoR tk–) (neoR tk+)
Add neomycin and
gancyclovir to cells
Fig. 10. Strategy for selecting correct gene targeting events in ES cells
War I, while Capecchi’s father, a fighter pilot, perished in World War II. His
American mother became an anti-fascist activist in Mussolini’s Italy during
that war, but was caught in 1941 by the Gestapo and sent to Dachau concen-
tration camp. Capecchi was only 4 years old, and his mother’s provision for
someone to look after her son if she was arrested fell through. So for the
next four years Capecchi fended for himself, ‘sometimes living in the streets,
sometimes joining gangs of other homeless children, sometimes living in
orphanages’.158 Miraculously, his mother survived Dachau, and in 1946,
after a year’s search, she finally traced her son to a hospital in Reggio Emilia,
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Supersize My Mouse
where he was surviving on a cup of coffee and a crust of bread each day in a
ward for abandoned children.158
The half-starved Capecchi left for the USA with his mother, and after grow
ing up on a Quaker commune, he eventually made it to the Massachusetts
Institute of Technology, and then Harvard University. There he worked with
Jim Watson, co-discoverer of the DNA double helix structure, but there
were still plenty of obstacles in his way, for his first grant application to de-
velop gene targeting, submitted to the US NIH, was rejected as being ‘not
worthy of pursuit’.158 Luckily, Capecchi decided to carry on regardless, and
when he applied for an NIH grant a second time, his application was greeted
enthusiastically, and with an added note: ‘We are glad that you didn’t follow
our advice.’158
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R EDESIGNING LIFE
Target
Cre gene gene
Cell-type
specific
promoter
Cre protein
Target
gene
Progeny mice with target gene removed only in cells expressing Cre
56
Supersize My Mouse
the protein to carry oxygen and giving the red blood cells of sufferers an
odd, sickle shape.162 My colleagues and I recently identified an infertile man
whose sperm’s inability to activate his partner’s eggs to develop into em-
bryos is caused by a single amino acid change in the phospholipase C zeta
(PLCζ) protein, which appears to play a central role in the egg activation
process.163
To address these cases, gene targeting can also be used to create mice
with such a subtle change.159 This ‘knockin’ approach may also be used to
attach a fluorescent tag to a protein to allow its movements to be tracked
during particular cellular processes. This can provide clues about a pro-
tein’s function, and, if a protein only found in a particular cell type is tagged,
this also makes it possible to fluorescently ‘label’ such a cell type and thereby
identify it in a living animal so its properties can be studied. This can be par-
ticularly important in the brain, where it can be difficult to distinguish dif-
ferent cell types on morphological grounds. In fact, the use of fluorescent
tags, and indeed of light itself, in combination with knockout and trans-
genic technology, has gone way beyond simply identifying the location of a
protein in a living cell or of that cell in the body. It’s now becoming possible
to use light to trigger functional activity in a cell. This is transforming our
understanding of how the brain works, but also other organs in the body, in
some very exciting ways. So let’s now look at what light has to offer as a tool
to manipulate life.
57
3
W here would life be, without light? The centrality of the Sun’s rays to
our existence has been recognized since the dawn of humanity,
with light featuring strongly in accounts of life’s creation in various reli-
gious texts. In the Bible, God commands ‘Let there be light!’, while worship
of the Sun was central to religions like those of the ancient Egyptians, the
Aztecs, and the Celts.164 This ancient acknowledgement of light’s import-
ance reflects the fact that the world’s ecosystem is ultimately powered by
solar rays. Plants use photosynthesis to turn the Sun’s energy into organic
molecules, which animals like ourselves either consume directly by eating
plants, or indirectly by feeding on other animals. Solar rays also provide the
warmth that allows cellular activities to take place at a reasonable rate, and
allow us to see what’s around us. So important is light to life that organisms
from simple microbes to our own species have evolved cellular and bodily
mechanisms to detect the day–night cycle.165 This body clock tells us when
it’s time to go to bed, and also regulates our metabolism. It’s the reason why
we suffer jet lag, and why many shift workers are prone to ill health, with
recent studies suggesting this may be due to disturbances in the normal pat-
tern of gene activity.166
Organisms have also developed ways to directly sense the Sun’s rays,
from light-sensitive pores on the surface membranes of single-celled algae,
to sensors on the skin of worms that regulate their movement, or the exquis-
ite structure of the human eye that allows us to see with such colour and
precision.167 Some organisms even generate light. Fireflies, with their glowing
patterns—signals to attract mates—can make the forests they inhabit look
like something from a fairy tale.168 Other phosphorescent land organisms
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Light as a Life Tool
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60
Light as a Life Tool
with the egg.179 What’s more, our analysis of sperm from an infertile man in
which the PLCζ protein is mutated showed that the mutant protein is incor-
rectly localized, preventing it from performing its normal role.180
While such studies use a light microscope, if an antibody is tagged with a
heavy metal like gold it’s possible, with an electron microscope, to pinpoint
the location of proteins in subcellular structures. In 2013 Gregory Frolenkov
and colleagues at the University of Kentucky used this approach to uncover
the precise interaction between two proteins called protocadherin-related
15 (PCDH15) and cadherin-related 23 (CDH23), in the hair cells of the inner
ear, thereby defining their role in the hearing process.181 According to
Frolenkov, the study ‘reveals the details of a process that is likely to be vital
for the development, maintenance, and restoration of normal hearing’.182
And since the genes coding for the PCDH15 and CDH23 proteins can be mu-
tated in a type of deafness called Usher syndrome, this information could
help devise new treatments for this particular type of hearing disorder.181
A Living Palette
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R EDESIGNING LIFE
in Nagasaki, and at the age of 16 he was lucky to survive the atomic bomb
that devastated the city in 1945, being only seven and a half miles from the
centre of the blast.183 This demonstration of the lethal application of atomic
physics didn’t destroy his growing passion for science and, studying chem-
istry at Nagoya University, Shimomura became fascinated by ‘sea fireflies’.
These organisms, actually tiny crustaceans that emit a blue light, are par-
ticularly abundant in the sea off Kone and Ikuchi islands, near Hiroshima.
In 1956, as a graduate student, Shimomura decided to try and isolate lucif-
erin, the luminescent substance in these organisms, despite the fact that US
researchers had been trying in vain to do so for over twenty years. For ten
months Shimomura also had no success, until one night he ‘accidentally’
added a strong acid to a sea firefly extract.184 Next morning he saw that the
acid treatment had caused the luciferin to form pure crystals. ‘That success
offered hope for my future, which had looked grey ever since the end of
World War II,’ he later recalled. ‘I was so excited and happy that I wasn’t able
to sleep at night.’185
Later, having moved to the USA, Shimomura became a researcher at the
Woods Hole Marine Biological Laboratory near Cape Cod, where he began
studying phosphorescent jellyfish. Shimomura found that their vivid colour
is the product of two proteins—aequorin, which generates blue light when
it comes into contact with calcium ions,186 and green fluorescent protein
(GFP), which only becomes phosphorescent when in close proximity with
light from aequorin. Because aequorin emits light following contact with
calcium, scientists recognized that it could be used to detect changes in the
concentration of this ion in the cell. Such calcium ‘signals’ convey informa-
tion coming from the outside of the cell to effector proteins. These effector
proteins carry out important tasks in the body, for instance as regulators of
heart contraction, secretion of insulin by the pancreas, and release of neuro-
transmitters in the brain.187
Lionel Jaffe and colleagues, also at Woods Hole, used aequorin to show
that calcium signals play a key role during activation of the egg by the sperm
during fertilization. By injecting the protein into fish eggs and then adding
fish sperm under a microscope, Jaffe’s team showed that, as the sperm fuses
62
Light as a Life Tool
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R EDESIGNING LIFE
We can learn much from studies of cells in culture, but there are limits to
how much they can reflect the complexity of many bodily processes. A par-
ticularly powerful use of protein labelling combines this technique with
transgenic technology to create a whole animal that expresses a labelled
protein in its cells. One study investigated the inheritance of subcellular
structures called mitochondria, which produce most of the energy in our
bodies. Mitochondria have another distinctive feature. They contain their
own DNA genome, distinct from that in the cell nucleus. This reflects the
fact that these subcellular structures were originally free-living bacteria that
became incorporated into our single-celled ancestors about 1.5 billion years
ago, in a relationship that became mutually beneficial: the mitochondria
providing energy and the host cell a sheltering environment.193
How vital mitochondria are to multicellular life is shown by the effects of
cyanide, which blocks energy production by these tiny powerhouses, caus-
ing almost instant death.194 Some people have mutations in their mitochon-
drial genome, leading to a reduction in the capacity of these subcellular
structures to produce energy.195 This particularly affects processes requir-
ing lots of energy, like vision, muscle contraction, and conduction of im-
pulses in the brain. These gene defects tend to be associated with muscle
weakness, neurological problems, and in one type of disorder, blindness
that occurs in middle age. The particular symptoms vary depending upon
which gene is affected and its specific role in the energy-making process.
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Light as a Life Tool
But what all these disorders have in common is their inheritance through
the mother.195
This inheritance pattern reflects the fact that a human embryo only in-
herits mitochondria from the egg, not from the sperm. Why this is so, was
for a long time not very clear. For although the egg is substantially bigger
than a sperm, and consequently contributes more mitochondria, the sperm
also contains these structures; indeed, mitochondria supply the energy that
powers the sperm’s rapidly beating tail.196 Moreover, studies of the fertiliza-
tion process have shown that the whole sperm is engulfed by the egg fol-
lowing the fusion of these two cells.197 So why isn’t any sperm mitochondrial
DNA passed on to the next generation?
To find out, in 2001 Hiromichi Yonekawa and colleagues at Tokyo
Metropolitan Institute of Medical Science created male transgenic mice in
which a protein only found in mitochondria was labelled with GFP.198 Since
this colours the mitochondrion with fluorescence, it allowed Yonekawa’s
team to track the movement of the mitochondria in sperm from such mice
as they fertilize the egg. Sperm mitochondria are concentrated in a region
called the midpiece that lies midway between the sperm head and tail,
making it easier to track their movements under a fluorescence microscope.
The researchers found that when the sperm unites with an egg, the fluores-
cent mitochondria are engulfed into the egg with the rest of the sperm body,
where they remain visible. But then the fluorescence suddenly disappears.198
Further investigation revealed that the egg has a mechanism for identifying
the male mitochondria and destroying them, although why it does this re-
mains unclear.199
Other studies that have used this technology to study the reproductive
process may have very important implications for medicine, and indeed
society, in the future. For such studies have challenged a long-accepted
dogma, namely that women are born with a finite supply of eggs that’s de-
pleted throughout life and exhausted at the menopause. Instead, it now
seems possible that women may retain a hidden capacity to produce fertile
eggs after the normal child-bearing age. This suggestion, first proposed by
Jonathan Tilly of Massachusetts General Hospital in Boston in 2004, is
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R EDESIGNING LIFE
based on the idea that stem cells exist in the ovaries of both young and old
mammals, with the potential to develop into fertile eggs. In 2009 Ji Wu and
colleagues at Jiao Tong University, Shanghai, isolated and cultured such
putative stem cells, and infected them with a virus expressing GFP. When
Wu’s team injected the cells into the ovaries of sterilized female mice, the
mice gave birth to green fluorescent offspring, suggesting that the stem cells
gave rise to these offspring.200 Subsequently, in 2012, Tilly and colleagues
identified similar stem cells in human ovaries. And after expressing GFP in
these cells with a virus, they showed that these stem cells could generate
green fluorescent eggs in human ovary tissue transplanted into a mouse
(see Figure 12).201
Not everyone is convinced of the existence of stem cells that can produce
eggs in the ovaries of either mice or humans. Some critics believe the first
study’s findings resulted from the sterilization procedure not being totally
effective, and the virus transferring its GFP fluorescence to normal eggs still
remaining in the host ovary.200 Something similar could account for the
apparent generation of green fluorescent eggs from the human ovary stem
cells. And at least four other research groups have failed to reproduce Tilly’s
or Wu’s findings. ‘We immediately repeated the experiment . . . My lab never
got the cells,’ said Kui Liu, of the University of Gothenburg in Sweden.202
Yet a previous high-profile critic of Tilly, Evelyn Telfer, who studies egg
Mouse transplanted
Stem cells with human
Ovarian
follicles ovarian tssue
GFP-positive
eggs in
ovarian follicles
Fig. 12. Ovaries contain stem cells that can produce eggs
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Light as a Life Tool
67
R EDESIGNING LIFE
68
Light as a Life Tool
69
R EDESIGNING LIFE
Dendrites
Cell body
Myelin sheath
Axon
Direction of impulse
Light-Induced Thoughts
Fluorescently labelling cells in the brain to measure both their electrical prop-
erties and anatomical relationships is one way in which light has been har-
nessed for biomedical research. An even more remarkable technology uses
light to activate cells in the living brain. Optogenetics, as this new technology
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Light as a Life Tool
71
R EDESIGNING LIFE
Axon segment
At rest Outside
Inside
Action potential
Na+
K+ Action potential
Na+
K+
K+ Action potential
Na+
K+
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Light as a Life Tool
Na+
Channelrhodopsin
(ChR) allows sodium
ions to pass through the
plasma membrane in
reponse to blue light A blue light pulse initiates
an action potential in the
neuron containing the
channelrhodopsin gene
that they could now respond to light.218 Few people thought this ap-
proach would ever work in mammals, but, undeterred, Karl Deisseroth
of Stanford University decided to see if he could develop this technology
in rodents.
A practising psychiatrist as well as a neuroscientist, Deisseroth is con-
cerned that psychiatry’s ability to treat the most intractable disorders—
severe depression, schizophrenia, autism—is limited by a lack of under-
standing of how the brain works. ‘A cardiologist can explain a damaged
heart muscle to a patient,’ he said. ‘With depression, you cannot say what it
really is. People can give drugs of different kinds, put electrodes in and
stimulate different parts of the brain and see changed behavior—but there
is no tissue-level understanding. That problem has framed everything. How
do we build the tools to keep the tissue intact but let us see and control
what’s going on?’219 Deisseroth decided that using transgenic technology to
express opsins in rodents could provide a revolutionary way to explore the
functional role of different neurons in the mammalian brain.
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A key initial question was whether the microbial proteins would func-
tion as well in rodent neurons as they did in those of the fruit fly. To test this,
Deisseroth’s research team—at that time just himself and two graduate stu-
dents, Feng Zhang and Ed Boyden—expressed a microbial opsin in rat neu-
rons in culture using a viral carrier. When light was shone on to the cells,
this triggered an action potential.219 So, could a similar effect be obtained in
the living rodent brain? In fact it took several years for Deisseroth and his
team to achieve this aim because it meant not only using transgenic ap-
proaches to modify specific cell types in the rodent brain to become respon-
sive to light, but also finding ways to deliver light deep into the brain. This
latter goal was achieved using an ultra-thin fibre-optic wire attached to a
laser light source, surgically implanted into the brain. A combination of
these approaches allowed Deisseroth’s team to make a dramatic demon-
stration of the power of optogenetics. By stimulating neurons in the motor
cortex—the region of the brain that controls movement—they showed that
light could be used to make a mouse run in circles, like a remote-controlled
toy. ‘That’s really the moment we knew that it could drive very, very robust
behavior,’ said Zhang.219 But what fully convinced the neuroscience com-
munity of the power of optogenetics as a tool to study key mechanisms of
brain function and dysfunction were a series of studies published in 2009.
First, another of Deisseroth’s graduate students, Viviana Gradinaru, pub-
lished a study with him in Science describing the use of optogenetics to
define the precise neuron connections in Parkinson’s disease.219 Shortly
afterwards, another study involving Zhang and Deisseroth was published
in the same journal that examined the cellular basis of pleasure and reward.
Such feelings are particularly associated with the neurotransmitter dopa-
mine. By activating dopamine-producing neurons with light, the research-
ers could drive reinforced behaviour in the absence of any other cue or
reward.219 This study provided important information about the nerve im-
pulses that may underlie addiction or conditions like depression, in which a
person is unable to be pleased or excited by events around them. In add-
ition, two other studies published in Nature by Deisseroth and his colleagues
used optogenetics to identify neurons that regulate brain activities, which
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Light as a Life Tool
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R EDESIGNING LIFE
muscles, presumably so we don’t act out the dreams flashing through our
mind. ‘People used to think that this region of the medulla was only in-
volved in the paralysis of skeletal muscles during REM sleep,’ said Dan.
‘What we showed is that these neurons triggered all aspects of REM sleep,
including muscle paralysis and the typical cortical activation that makes the
brain look more awake than in non-REM sleep.’221 Dan believes that al-
though other regions of the brain have been implicated in the sleep–wake
cycle, ‘because of the strong induction of REM sleep . . . this might be a crit-
ical node of a relatively small network that makes the decision whether you
go into dream sleep or not’.221 Given that many psychiatric disorders are
associated with abnormalities in REM sleep, the researchers hope that such
studies might provide insights into the basis of these disorders and possibly
future treatments for insomnia.
Making a Memory
Optogenetics has also been used to explore how memories are encoded in
the brain. Memory has been a topic of scientific interest ever since Aristotle
wrote On Memory and Reminiscence in 350 bc.222 He compared memories to
impressions made in a wax tablet, a writing device in use at the time.223 In
the eighteenth century, the English philosopher David Hartley first pro-
posed that memories were encoded in the activity of the brain. It was only
in 1904, however, that the German biologist Richard Semon linked memor-
ies to changes in specific groups of brain neurons which he called ‘en-
grams’.223 An important insight into the potential physical basis of memory
was made by Tim Bliss and Terje Lømo at the University of Oslo in the late
1960s. They discovered that repeatedly electrically stimulating a neuron
in a region of the brain called the hippocampus boosted the cell’s ability to
talk to a neighbouring neuron.224 This communication between neurons
occurs across tiny gaps called synapses, and Bliss and Lømo realized that
such strengthening of synaptic connections—which they called long-term
potentiation (LTP)—could be the physical basis of memory. Studies carried
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Light as a Life Tool
out subsequently have shown that synapses are strengthened when rodents
run around an enclosure, and that blocking LTP with drugs, or knocking
out genes that regulate LTP, can impair memory in mice.225 Other studies
have shown that another process called long-term depression (LTD) has the
opposite effect.
Yet despite these pieces of indirect evidence in support of the link be-
tween LTP, LTD, and memory, direct evidence for such a link has remained
elusive, with Robert Malenka commenting recently that ‘proof of causal-
ity—that LTP is actually used for the encoding of a memory in a manner
that is absolutely required—has been extremely difficult, if not impossible,
to generate’.225 But optogenetics has now supplied what looks like such evi-
dence, in a study led by Roberto Malinow at the University of California,
San Diego. He and his colleagues created a virus that expressed microbial
opsin and injected this into specific neurons in the brain of a rat. In classical
‘conditioning’ studies of memory formation, rats can be trained to fear a
specific sound by following the sound with an electric shock. After such
conditioning the sound alone will make the rats freeze in fear.225
By using light to stimulate neurons connecting a brain region involved
in processing sound with one that handles fear, and then giving the rats
a shock, Malinow’s team created the same kind of fearful memory without
the rats ever hearing the sound. This demonstrated, according to Malinow,
that ‘we can make a memory of something that the animal never experi-
enced before’.225 And an examination of the synapses of the neurons in-
volved showed that the rats had undergone molecular changes that are a
hallmark of LTP. What’s more, when light was used to induce LTD, the rats
no longer cowered after the simulated sound stimulus was triggered in
their brains. Subsequent use of light to induce LTP was sufficient to reim-
plant the fear. ‘We were playing with memory like a yo-yo,’ said Malinow.225
The Nobel laureate Eric Kandel, a pioneer of the study of the cellular basis
of memory, believes the findings show ‘more directly than the indirect
evidence that existed before that LTP has a role in memory storage and it
can be wiped out by LTD . . . This is the best evidence so far available,
period.’225
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R EDESIGNING LIFE
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Light as a Life Tool
consecutive days had an effect that persisted even in the absence of light
stimulation. ‘We were able to cure the animals’ depression,’ said Tonegawa.227
One important finding of the study was that an alternative strategy that in-
volved exposure to females for five days did not cure the depressive state. ‘I
think that’s one of the most intriguing aspects of the study,’ said Amit Etkin,
a Stanford neuroscientist. ‘There’s something special about the encoding of
a positive memory that differs from simply being rewarded.’227
But it’s not only in the study of brain functions that optogenetics is
showing its potential. According to Karl Deisseroth, ‘if you had to pick the
next logical tissue for work on optogenetics, the heart is a great one’.228 This
is because heart cells are also activated by electrical impulses. And indeed
Philipp Sasse and colleagues at the University of Bonn have engineered
mouse ES cells to respond to light, and then induced them to turn into heart
cells.228 Shining light on to a patch of cells in a culture dish made the cells
beat in unison. In contrast, when the researchers shone light on already
beating cells, those cells began beating out of synchrony with the others, in
what Sasse calls ‘a cardiac arrest in a petri dish’.228 And by using the modi-
fied stem cells to make transgenic mice, Sasse and his team showed that
shining light on to the hearts of such mice in different places also made
these beat out of step, mimicking the arrhythmias that can trigger fatal
heart attacks in humans.228
These studies look to be just the start of an expansion in the range of
application of optogenetics. There are now moves to stimulate skeletal
muscles with light, since they are naturally activated by nervous impulses,
with the idea that this might be used to study certain forms of paralysis and
ultimately identify ways to overcome them. The technique may be applied to
other excitable cells, like those of the immune system and insulin-secreting
pancreatic cells, to better understand their properties, as well as conditions
such as auto-immune disorders and diabetes.228
Optogenetics has also now been extended beyond the initiation of elec-
trical impulses. Some chemicals in the brain do not stimulate pumps or
channels but instead activate receptors in the cell surface that regulate
important enzymes. By genetically fusing such receptors with opsins, it has
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been possible to activate such enzymes, and thereby the cellular processes
that they regulate.229 Meanwhile, there have been important new develop-
ments in the fibre-optic technologies that deliver light to the deepest reaches
of the brain and other parts of the body. Ed Boyden is working on ‘multi-
wave’ arrays that emit light at multiple points, allowing larger areas of the
brain to be targeted.230 What’s more, use of different types of opsins that
respond to infra-red light, which has a long wavelength and can penetrate
deep into living tissue, now make it possible to control brain activity inside
a genetically engineered mouse from a device outside its skull, without the
need for implanted optic fibres.231
Other scientists are working to eliminate the need for external stimula-
tion by light, by creating types of opsins that provide their own illumin-
ation. So Jack Tung, Robert Gross, and colleagues at Emory University,
Georgia, and Georgia Tech, have taken the enzyme luciferase, which pro-
duces a bioluminescent product when exposed to luciferin—the chemical
first isolated by Osamu Shimomura in 1956—and fused it to an inhibitory
opsin.232 They then expressed this gene construct in the brain of a rat and
showed that when luciferin was injected into the brain, this disabled the
brain’s ability to respond to an amphetamine drug. The researchers are now
using this approach to study ways to halt or prevent seizures—a character-
istic feature of epilepsy—in rodents. ‘We think that this approach may be
particularly useful for modelling treatments for generalized seizures and
seizures that involve multiple areas of the brain,’ said Tung. ‘We’re also
working on making luminopsins responsive to seizure activity: turning on
the light only when it is needed.’232
Other research has shown that light itself may eventually be dispensed
with as a stimulus to regulate neurons. So Sreekanth Chalasani and col-
leagues at the Salk Institute in California have developed a technique they
call ‘sonogenetics’ that uses ultrasound to control the behaviour of neu-
rons.233 Admittedly, the demonstration was carried out in nematode worms,
not mammals. Chalasani and his colleagues identified a cell surface protein
pore called transient receptor potential cation channel C4 (TRPC4), that is
naturally sensitive to sound waves. By introducing this protein into worm
80
Light as a Life Tool
neurons the researchers could control their behaviour using ultrasound. ‘As
soon as the ultrasound hits the worm, the neuron turns on,’ said Chalasani.
‘And when the neuron becomes active, it is telling the rest of the neural cir-
cuit, “Hey, I've become active.” When that information passes along, the
animal then turns, goes back, and goes off in a different direction.’233 It re-
mains to be seen whether this approach can be applied to mice, but it seems
highly likely. And since ultrasound waves can penetrate the skull, it’s possible
that this approach could be used to study GM rodents in a non-invasive
fashion.
Given the powerful ways in which optogenetics has been used in mice
and other model animals, would it be possible to use this technology in
people? For instance, could a light-emitting device on the skull, use of lumi-
nopsins, or even ultrasound, be used to treat a human patient with a brain
disorder like epilepsy or Parkinson’s disease, or perhaps someone with a
psychiatric or mood disorder? Of course, for this to be possible there would
need to be some way of precisely genetically modifying the brain cells of
such an individual. As we saw in Chapter 2, until now such precision has
only been possible in mice, and more recently rats, and then only indirectly
by first modifying ES cells, and then using these to create a whole animal
knockout or knockin. But all that has begun to change. It’s now time to ex-
plore in detail the revolution taking place in biology, called genome editing.
81
4
82
The Gene Scissors
statement, a study was published showing that this approach had been used
to genetically modify human embryos for the first time in history.236
Why genome editing has created such a stir is best understood by com-
paring it to the genetic engineering approaches considered in Chapter 2.
There, we looked at two main approaches to gene modification. One in-
volves the random insertion of a gene construct into the genome of a host
cell. The advantage of this approach is that it can be applied to practically
any cell. But its usefulness for biomedicine and agriculture has been limited
by its inefficiency and also the fact that it involves essentially dumping a
piece of DNA randomly into the genome. Also, it only provides the possi-
bility of adding a foreign gene to a genome, not of modifying one already
there.
The second approach, using ES cells, has a much greater level of preci-
sion. As we saw, it can be used to totally eliminate a gene’s action in a mouse
or introduce more subtle modifications, like a mutation to model disease or
a fluorescent tag to label a gene’s protein product. The limitation here lies
not in the flexibility of the approach but rather in the gene targeting, which
is a complicated procedure that must first be carried out on ES cells. Only
subsequently can these be used to create a GM rodent. This use of ES cells is
also associated with a more fundamental problem. It has not been possible
to isolate, and thereby genetically modify, ES cells from other mammalian
species besides mice, and more recently, rats and humans.237 Cells with
many properties similar to mouse ES cells have been isolated from other
mammalian species like pigs and sheep.238 But despite the superficial simi-
larity, for some reason these cells lack the pluripotency required for making
GM versions of these other species.239
In contrast to such limitations of traditional genetic engineering ap-
proaches, the power of genome editing lies in four key features.240 First, the
technique can be applied to practically any cell type from any plant or
animal species, ranging from bacteria to humans. Second, it can precisely
target any region in a genome, thereby completely knocking out the func-
tion of a gene, or subtly modifying it, by introducing a mutation or fluores-
cent tag. Third, the efficiency of gene targeting is extremely high, so no
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R EDESIGNING LIFE
84
The Gene Scissors
Molecular Scissors
The discovery that a break in the DNA double helix inside a living cell can
lead to precise modifications of that part of the genome was first made in
the late 1990s by Maria Jasin and colleagues at the Memorial Sloan Kettering
Cancer Center, New York. Jasin’s main interest was in understanding how
such breaks play a role in tumour formation. She was studying the BRCA2
gene, which, as we noted in Chapter 1, plays an important role in DNA
repair. Its absence greatly increases the risk of breast and ovarian cancer,
since DNA breaks are much less likely to be repaired.246 An interesting side
aspect of this study was the discovery that, in a normal cell, the repair pro-
cess can proceed in two ways: either by connecting the two broken ends
together, but in such a clumsy manner that this adds or deletes DNA se-
quence; or in a much more accurate fashion by homologous recombination
that restores the correct sequence (see Figure 16).247
This showed that if a way were found to accurately create a break in the
genome at a specific place, the cell’s own repair machinery would then
create a mismatch join that could result in a knockout of the gene, or if a
suitable complementary piece of DNA was available, a substitution that
would create a knockin modification. The only problem was that, at this
time, no obvious way of creating a sequence-specific DNA break was
known.
In fact another decade would pass before such a tool became avail-
able. This arose from a discovery made by Srinivasan Chandrasegaran and
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R EDESIGNING LIFE
Insertions or deletions
Homologous
Inaccurately repaired DNA template DNA
86
The Gene Scissors
87
R EDESIGNING LIFE
Fok
Fok
l
l
ACACACCTTCAGCATGTTGGTGGGAC ACACACCTTCAGCATGTTGGTGGGAC
TGTGTGGAAGTCGTACAACCACCCTG TGTGTGGAAGTCGTACAACCACCCTG
l
Fok
l
Fok
Specific DNA binding by Specific DNA binding by
zinc finger domains TALEN modules
ACACACCTTCAGC ATGTTGGTGGGAC
TGTGTGGAAGTCG TACAACCACCCTG
Double strand break
thrombosis can lead to heart attacks and stroke in people, this zebrafish
mutant could help scientists to understand the molecular basis of throm-
bosis. It may also be used to test drugs that can inhibit excessive clotting.
More recently, the cutting part of FokI has been fused to the DNA recog-
nition part of a different protein family, called transcription activator-like
effectors, or TALEs. These proteins are secreted by bacteria that infect
plants; they activate expression of particular genes in the plant cell and
thereby make it easier for the pathogen to establish itself in its host. Once
fused to FokI, these are referred to as TALE nucleases, or TALENs (see
Figure 17).253 Importantly, there are far more TALEs than zinc finger pro-
teins, making it possible to target a much larger variety of regions in the
genome with TALENs than with ZFNs. And as such, these new tools have
been used to successfully modify genomes from species as diverse as yeast,
fruit flies, zebrafish, pigs, and cress, as well as human cells in culture.253
88
The Gene Scissors
Despite the power of ZFNs and TALENs, they remain a relatively cumber-
some tool. The fact that these proteins must each be created anew to gen-
erate a novel cutting specificity has limited the ease with which they can be
produced and employed in biomedicine. Because of this, after the develop-
ment of these cutting tools, the search continued for better ones. In the end,
a major breakthrough on this front came with the discovery that a sequence-
specific cutting enzyme existed in bacteria that was different from ZFNs
and TALENs in one key respect: the recognition device that guides this cut-
ting enzyme to a specific sequence in the DNA genome is the chemical
cousin of DNA, namely RNA.
A CRISPR Cut
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R EDESIGNING LIFE
species.255 It was Jansen and his colleagues who christened the sequences
CRISPR. They also found that these sequences were generally found next to
CRISPR associated (CAS) genes that coded for proteins with a similar struc-
ture to enzymes which interacted with DNA. The researchers concluded
that this association suggested a ‘functional relationship’ existed between
the CAS genes and CRISPR sequences; however, the role of this relationship
remained unclear.255
Then, three years later, in 2005, several research groups independently
made an intriguing discovery. They noticed that the CRISPR spacers looked
a lot like the DNA of bacteriophages—the viruses that infect bacteria which
we came across in Chapter 2. Crucially, when Eugene Koonin, an evolution-
ary biologist at the National Center for Biotechnology Information in
Bethesda, Maryland, heard about this discovery, ‘the whole thing clicked’.256
Koonin suggested that bacteria use CAS enzymes to grab fragments of
DNA from viruses. They then insert the viral DNA fragments between their
own CRISPR sequences. Later, if a virus of the same type comes along, the
bacteria use CRISPR to recognize the invader, creating what science jour-
nalist Carl Zimmer has called a ‘molecular most-wanted gallery’.256 In other
words, just as our own immune system remembers past infections and re-
sponds rapidly if they reappear, which is why we’re generally only infected
once by viruses like chicken pox, so bacteria possess an analogous system.
Far from being useless pieces of junk DNA, it was now looking as if CRISPR
sequences played a key role in bacterial immunity. And this discovery was
to have an immediate practical application in an unexpected area.
In particular, Rodolphe Barrangou, a microbiologist working for Danisco,
recognized that the CRISPR sequences might provide an important defence
for the bacteria that converted milk into yogurt at his company, for some-
times entire cultures would be lost to outbreaks of bacteriophage.256 To
test Koonin’s hypothesis, Barrangou and his colleagues infected the milk-
fermenting bacterium Streptococcus thermophilus with bacteriophage. The
viruses killed most of the bacteria, but some survived. Analysis of the resist-
ant bacteria confirmed that they had inserted DNA fragments from the
bacteriophage into their spacers. When the researchers deleted the new
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The Gene Scissors
spacers, the bacteria lost their resistance. This discovery led many manufac-
turers to select for customized CRISPR sequences in their cultures so the
bacteria could withstand virus outbreaks. ‘If you’ve eaten yogurt or cheese,
chances are you’ve eaten CRISPR-ized cells,’ said Barrangou.256
So much for the functional role of the CRISPR sequences, but what re-
mained unclear was the underlying mechanism of this defence system. In
the end, the big breakthrough on this front was made by Jennifer Doudna,
of the University of California, Berkeley, and Emmanuelle Charpentier, a
French scientist working at Umeå University, Sweden. Doudna was brought
up in Hilo, a region of Hawaii with dramatic waterfalls, fertile rainforests,
and blooming tropical gardens.257 It sounds like an ideal place in which to
grow up, but with her blonde hair and blue eyes Doudna felt out of place
amongst the other children, who were mainly of Polynesian and Asian des-
cent. ‘I think to them I looked like a freak,’ she recently recalled. ‘And I felt
like a freak.’257 This feeling of isolation contributed to a kind of bookishness
that led to an interest in science from a young age. Doudna found her calling
at school after hearing a female scientist discuss her cancer research studies.
‘I was just dumbstruck,’ she said. ‘I wanted to be her.’257
Spells as a graduate student working for Jack Szostak at Harvard
University, and then postdoctoral research with Thomas Cech at the
University of Colorado, provided Doudna with impeccable mentorship, for
both men went on to receive Nobel Prizes for their work. Doudna was al-
ready recognized as an expert in the structures of different RNAs—increas-
ingly seen as a key player in the cell alongside DNA—when she was asked
by the Berkeley environmental researcher Jillian Banfield for help with
sequencing the genome of a bacterium isolated from an abandoned
Californian mine. Doudna recalls, ‘I remember thinking this is probably the
most obscure thing I ever worked on.’258 The analysis revealed CRISPR se-
quences, and, while analysing them, Doudna became fascinated by this bac-
terial defence system and determined to understand its molecular basis. In
particular, given her interest in RNA, Doudna was intrigued to discover that
this molecule appeared to play an important role as an intermediary in the
CRISPR system, although how it did so remained unclear.
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R EDESIGNING LIFE
92
The Gene Scissors
UGA
C G
G C
CAS9 G C
U A
G C
AA UUUUC G
G A G
A T U
U A G
C G A
G C A
Guide RNA A A A
G UG A
A U A
U A A
U A G
U A U
U A U
C
GGGGCCACUAGGGACAGGAUG UAAGGCUAGUCCGUUAUCAA
CCCCGGTGATCCCTGTCCTAACC
GGGGCCACTAGGGACAGGATTGG
CCCCGGTGATCCCTGTC CTAACC
GGGGCCACTAGGGACAG GATTGG
that varies. Since the guide RNA can be generated in a few days for a small
sum, CRISPR can be performed in a fraction of the time and cost of the
other technologies. Indeed, James Haber of Brandeis University recently es-
timated that ZFNs, which typically cost US$5,000 or more to order, are
150 times more expensive than the combined cost of CAS9 and a guide RNA,
which comes to about $30. ‘That effectively democratized the technology
so that everyone is using it,’ said Haber. ‘It’s a huge revolution.’263 So what
form is this revolution taking?
The most straightforward way of using genome editing is to create a
knockout cell or organism. When a cutting enzyme cuts DNA at a specific
sequence, the cell responds by seeking to repair the break. But when this
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R EDESIGNING LIFE
Life in a Dish
One key system used in biomedical research is human cells grown in culture.
Such cells may be obtained from biopsies or organs donated to research by
people when they die. However, such ‘primary’ cells have an inbuilt limited
lifespan, so that, if allowed to divide in a culture dish, after 40 to 60 cell divi-
sions (the figure varies depending on cell type), the cells eventually stop div-
iding. This is called the ‘Hayflick limit’ after Leonard Hayflick, the man who
discovered it in 1962, and it is thought to be connected to the natural ageing
process.264 Cancer cells have no such limit to their capacity to divide, having
gained immortality through mutations that overcome the natural barriers
to unlimited division that normal cells possess. The first and most famous
of such ‘immortalized cell lines’ is the HeLa cell.265
This was isolated from the highly malignant ovarian tumour of Henrietta
Lacks, a poor black woman, in 1941, without her knowledge or consent. Lacks
soon succumbed to the cancer, but HeLa cells continue to multiply in the
incubators of laboratories across the world, having been used to develop the
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The Gene Scissors
polio vaccine, aided research into cancer and AIDS, and used to assess
the effect of toxins and radiation on human cells.265 Subsequently, many
other immortalized human cell lines were isolated from tumours, while
infection of normal human cells with tumorigenic viruses can immortalize
such cells.266 Some immortalized cell lines retain characteristics of the cell
types from which they originated in the body. This means that they can be
used to study the specific properties of such cell types in a culture dish. For
instance, some immortalized cell lines isolated from the pancreas will se-
crete insulin in response to a glucose stimulus, just like normal pancreatic
beta cells.267
As we saw in Chapter 2, the discovery of ways to precisely modify the gen-
omes of mouse ES cells, and then the use of these to create a GM mouse,
revolutionized biomedicine by making it possible to dissect gene function in
a living mammal. Ironically, humans are the only other species besides mice
and rats in which it has been possible to isolate ES cells.268 Clearly though,
there are ethical reasons why it would be impossible to use such cells to
create, first, living human chimaeras and then breed these to produce GM
humans. So the question was whether genome editing could be applied to
immortalized human cell lines, or indeed primary cells generated from
biopsies, in order to study the roles of specific genes in cellular processes.
In fact, even prior to the development of genome-editing technology,
there has been a way to modify the expression of genes in human cells using
an approach called ‘RNA interference’.269 This is a natural process found in
cells of species ranging from petunias to people, whereby certain types of
RNA act to suppress gene expression. As we saw in Chapter 2, the DNA se-
quence of letters in a gene acts as a linear code that’s translated into another
linear code, the unique string of amino acids that makes up each protein.
However, this isn’t a direct translation; rather it requires an intermediary—
messenger RNA—essentially a copy of the protein-coding sequence of each
gene. In RNA interference, small regulatory RNAs either trigger destruction
of the messenger RNA or block its translation into protein. The process is
regulated by proteins that exist naturally in cells—one called DICER gener-
ates the small regulatory RNAs, also known as siRNAs; while a protein
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R EDESIGNING LIFE
DICER
RISC incorporates
complementary mRNA
RISC
mRNA degradation
mRNA No protein
synthesis
siRNA duplex
Translation block
RISC incorporates
partially complementary mRNA
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The Gene Scissors
blocks expression of a gene. Second, the approach can only be used to in-
hibit gene expression, not introduce subtle alterations like the knockin ap-
proach discussed. Because of this, when CRISPR genome editing was first
developed, an obvious question was whether it could be used to make
knockouts or knockins of genes in cultured human cells. And the person
who showed that this was indeed the case was a scientist we have already
come across—Feng Zhang.
As we saw in Chapter 3, as a PhD student Zhang worked with Karl
Deisseroth, who would later say of Zhang that his ‘skills were absolutely
essential to the creation of optogenetics’.272 However, making his mark in
one hot new area of biotechnology was clearly not enough for Zhang, who
has been called the ‘Midas of Methods’ because of his pioneering role in dif-
ferent areas of biotechnology.272 As a postdoctoral researcher working with
Paola Arlotta at Harvard University, he devised a way to use TALEs not
to cut, but to activate genes artificially. Arlotta has subsequently praised
Zhang’s capacity for highly inventive problem solving. ‘He has an ability to
see the simplicity of things,’ she said. ‘That’s a gift that not everybody has.’272
Subsequently, having set up his own group at the Broad Institute, itself part
of the Massachusetts Institute of Technology, Zhang heard about CRISPR
from a speaker at a scientific advisory board meeting. ‘I was bored,’ he said,
‘so as the researcher spoke, I just Googled it.’273 Then he went to Miami for
a conference, but while there he spent his time reading papers on CRISPR
and filling his notebook with ideas about how to use it to modify the human
genome. ‘That was an extremely exciting weekend,’ he remarked.273 Back in
Boston, Zhang quickly set about seeing whether the technology could be
adapted to edit human cells in culture. In early 2013 he published his find-
ings, showing he could knock out not just one gene, but several simultan-
eously, in such cells. In fact, he was not the only scientist to pursue this goal;
in the same issue of Science in which Zhang’s paper was published, George
Church reported that he had also edited human cells with CRISPR/CAS9.273
The ability to knock out genes in a human cell line is proving important in
uncovering the functions of those genes. The Human Genome Project showed
that there are just over 22,000 genes in our genome, but our understanding
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of their functions is still very incomplete. And the molecular basis of many
important cellular processes is far from clear. So there is much work still
to be done to connect particular genes with specific processes. One way to
do this is to knock out genes individually and assess the effect on a particu-
lar process. But it could take many years to screen a whole genome by this
route. A more powerful approach is to carry out a so-called ‘genome-wide
screen’.274 In such a screen, cells are cultured in thousands of individual ‘wells’
arrayed in a grid. Into each well a CRISPR/CAS9 construct is introduced that
inhibits the expression of a specific gene. Given there are over 22,000 genes
in the human genome, an equivalent number of wells need to be screened.
Then all these wells are subjected to a test of the cellular process of interest.
Such a screen, by a group led by Feng Zhang, identified genes involved in
the developing resistance of human melanoma cells, growing in a culture,
to the drug vemurafenib, also known as Zelboraf®, which is used to treat
skin cancer.275 Since such drug resistance is a major reason why some can-
cers start regrowing following initial successful treatment, this could pro-
vide important information that allows clinicians to devise ways to combat
such resistance. Another study led by Zhang and Philip Sharp, also at the
Massachusetts Institute of Technology, used genome editing to screen for
genes involved in tumour formation in a mouse model. According to Sharp,
it’s important to study cancer in a living animal because ‘tumour evolution
is an extremely complex set of processes, or hallmarks, controlled by net-
works of genes’.276
The study’s aim was to identify genes involved in metastasis, the process
in which malignant cells escape their tissue of origin and travel around the
body in the blood, spreading cancer where they go. First, genome editing
was used to knock out genes in cultured mouse lung cells across the whole
genome (see Figure 20). These cells were then injected into live mice, and in
some cases this created metastatic tumours. By isolating these tumours and
sequencing their genomes, it was possible to identify the genes knocked out
and establish a role for these genes in metastasis. Zhang believes the study
‘represents a first step toward using CAS9 to identify important genes in
cancer and other complex diseases’.276
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The Gene Scissors
Cell line
expressing
CAS9
Remote-Controlled Genes
In these studies, genome editing was used to knock out genes. However, the
same approach can also be used to introduce more subtle knockin changes,
such as single amino acid modifications like those found in human dis-
eases, or the addition of a fluorescent tag. We saw in Chapter 2 how such
subtle genetic modifications can be introduced into the genome of a mouse
using ES cells as an intermediary. However, with genome editing, it’s pos
sible to create a knockin mouse in a single step simply by including a seg-
ment of DNA similar to the region of the gene to be modified.277 Compared
to the complicated construct required for the ES cell method, such a DNA
fragment can be made in hours on a DNA synthesizer. As such, the CRISPR/
CAS9 approach is making it feasible to rapidly generate mouse knockouts
and knockins to study the functional role of specific genes in a whole
animal model. So while standard knockout and knockin mice generated via
ES cells typically take 18 months and cost up to $20,000, according to
Douglas Mortlock, a transgenic mouse expert at Vanderbilt University,
‘now we can basically squirt this stuff into mouse embryos and three weeks
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R EDESIGNING LIFE
later mice are born that have the mutation . . . at a cost of $3,000 or less. It’s
stunning.’278
A particularly interesting aspect of genome editing though is that its
range of potential uses goes way beyond creating standard knockout, and
knockin, cells or whole animals. So, especially for CRISPR/CAS9, the ability
to direct the enzyme CAS9 to a particular sequence in the genome has
opened up possibilities beyond just disabling a gene or modifying the prop-
erties of its protein product. Instead, the capacity to position CAS9 in this
sequence-specific manner can also be used to switch genes on or off in a
controlled fashion. In this case, instead of acting like a pair of scissors,
CRISPR/CAS9 works more like a dimmer switch. To understand how, it’s
worth looking in more detail at how genes are expressed.
Genes in organisms as diverse as bacteria and humans are regulated by
gene regulatory proteins known as transcription factors.279 These proteins
bind to regulatory DNA sequences adjacent to the gene (the so-called gene
promoter) and thereby affect the activity of the RNA polymerase that pro-
duces the messenger RNA that acts as the intermediary between a gene and
its protein product (see Figure 21A). Given that each gene is controlled by a
large number of regulatory sequences, which can activate but also inhibit
the polymerase, this allows an exquisite level of control depending on
which transcription factors happen to be in any particular cell type.
The gene constructs used to create a standard transgenic mouse generally
include a regulatory DNA sequence adjacent to the gene that binds a power-
ful activating transcription factor, thereby ensuring the gene is always
turned on. Alternatively, a transgenic mouse may be engineered so that the
regulatory region binds the transcription factor only when the mouse is in-
jected with a specific chemical, allowing reversible control of gene expres-
sion in the animal.280 A limitation of this approach is that the transgene is a
foreign gene inserted randomly in the genome. But genome editing makes it
possible to reversibly control the expression of a cell’s own genes. A guide
RNA directs a version of CAS9 engineered not to cut DNA, but instead to
attract a specific transcription factor to a site in the genome (see Figure 21B).
While one version of this approach uses a transcription factor that can be
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The Gene Scissors
A
Transcription Factors Transcription “ON”
RNA
Transcription
polymerase
initiation site
Promoter
B
Catalytically
inactive
Guide CAS9 Trancriptional
RNA activator protein Transcription
RNA “ON”
polymerase
Promoter
induced to bind by a chemical injected into the mouse, there may be other
potential ways to turn gene expression on or off. One would be a cross be-
tween the optogenetic approach we looked at in Chapter 3 and CRISPR/CAS9.
Moritoshi Sato’s team at the University of Tokyo recently demonstrated
how light can be used to regulate CRISPR/CAS9 genome editing. For Sato,
one limitation of conventional CRISPR/CAS9 technology was that ‘the exist-
ing CAS9 does not allow us to modify the genome of a small subset of cells in
tissue, such as neurons in the brain . . . we have been interested in the develop-
ment of a powerful tool that enables spatial and temporal control of genome
editing’.281 To achieve this, Sato and his colleagues split CAS9 into two inac-
tive halves, each tagged with light-sensitive tags. When the two halves are
expressed in a cell with a guide RNA they are unable to edit their target gene;
however, when blue light is shone upon the cell, the two halves unite to form
an active enzyme, which cuts the DNA (see Figure 22). The study impressed
Paul Knoepfler, a biologist at the University of California, Davis, who said that
‘this is an effective new system for extremely precise control of gene editing
via light’.281 And although it has only been tested in cultured cells, given the
speed of development of genome editing it’s surely only a matter of time
before such an approach is developed in a mouse model. In such a model it
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Blue light
Genomic DNA
Dark
CAS9 is activated
light sensitive
tags
Split CAS9
DNA double strand break
fragments
Guide
RNA
Edited DNA
102
The Gene Scissors
it seems possible that we’ll soon see a situation in which a gene engineered
to respond to a regulatory protein is directly activated by a magnetic field.
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R EDESIGNING LIFE
this second parting of the ways was a clash about patents, with Feng Zhang
filing an application that claimed he had been first to develop the genome-
editing technology.287 Yet doesn’t the timescale of discovery we outlined in
the section ‘A CRISPR Cut’ show it was Doudna and Charpentier who not
only first discovered the basic mechanism of CRISPR/CAS9 but also recog-
nized its potential as a genome-editing tool? Certainly that was the opinion
of the committee who, in November 2014, awarded the two scientists each
a Breakthrough Prize. These prizes, worth $3 million, twice the value of a
Nobel Prize, were set up by Yuri Milner, a Russian entrepreneur who left a
PhD in physics to make $1 billion through investments in internet compa
nies, Mark Zuckerberg of Facebook fame, Sergey Brin, who co-founded
Google, and Jack Ma, the Chinese internet magnate.288
However, Zhang seems intent on challenging the idea that his contribu-
tion to the genome-editing discovery was a secondary one. Backing this
position, Robert Desimone, who heads the McGovern Institute for Brain
Research, where Feng has an appointment, recently challenged The Economist’s
account of how CRISPR/CAS9 was invented. In a letter to the magazine he
wrote that Doudna and Charpentier’s paper studied ‘a purified protein in a
test tube: it involved no cells, no genomes and no editing. Rather, the paper
simply highlighted the potential that genome editing might be possible.’289
And the Broad Institute, part of the Massachusetts Institute of Technol
ogy, where Zhang also has an appointment, released a statement saying the
institute ‘was not the first to file a patent request related to CRISPR. How
ever, [it] was the first to file a patent that described an actual invention—
experimental data regarding a successful method for mammalian genome
editing.’290 Meanwhile, in January 2016, Eric Lander, the head of the Broad
Institute, came under fire for a review article he wrote for Cell, entitled ‘The
Heroes of CRISPR’. Although the article was supposed to be an objective
history of genome editing, some critics argued that it skewed the history
of CRISPR to favour Feng Zhang’s contribution, with Berkeley professor
Michael Eisen calling it ‘science propaganda at its most repellent’ and ‘a
deliberate effort to undermine Doudna and Charpentier’s patent claims
and prizeworthiness’.291
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The Gene Scissors
The controversy surrounding the dispute may be one factor behind the
failure to award a Nobel Prize for the CRISPR/CAS9 discovery in October
2015. Doudna and Charpentier were tipped to win the prize for chemistry
by Thomson Reuters but instead it went to Tomas Lindahl, Paul Modrich,
and Aziz Sancar, for their studies of DNA repair.292 In fact, it would be very
unusual for a Nobel Prize to be awarded for a discovery as recent as the
CRISPR/CAS9 one, but it’s possible that the Nobel Committee would also
prefer to see a clearer resolution of each individual’s role in the discovery.290
And, demonstrating that some senior geneticists have concerns about the
current patent battle, Nobel laureate John Sulston, who played a key role
in the Human Genome Project, has drawn attention to the dangers of pat-
enting as fundamental a technology as genome editing. ‘This is not just a
philosophical point of view,’ he said. ‘It’s actually the case that monopolistic
control of this kind would be bad for science, bad for consumers and bad for
business, because it removes the element of competition.’293
In fact, the very speed with which CRISPR/CAS9 genome-editing tech-
nology is evolving may itself be a factor that could scupper attempts to
monopolize ownership of the technology. Thus, a recent report concluded
that, ‘given the pace of innovation in gene editing, today’s legal fights could
end up serving little purpose. Improved versions of CRISPR/CAS9 have al-
ready been invented, and entirely new methods are likely.’294 And, indeed,
recent studies of natural CRISPR systems are revealing a vast menagerie of
different types. Tapping that diversity could lead to more effective genome
editing, or open the way to applications no one has thought of yet. ‘You can
imagine that many labs—including our own—are busily looking at other
variants and how they work,’ said Doudna. ‘So stay tuned.’295
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modify the genome of a human embryo for the first time in history (see
Plate 2). The news first appeared in the form of a rumour. On 12 March
2015, a comment piece appeared in Nature by Edward Lanphier, president of
Sangamo BioSciences and chairman of the Alliance for Regenerative
Medicine, and four co-authors, all experts in genome editing. This called on
scientists not to use CRISPR/CAS9 to modify human embryos, even for re-
search.296 It transpired that Lanphier and his co-authors had heard that un-
specified scientists had already used this approach to create GM human em-
bryos and were seeking to publish their findings. Normally, when a paper is
submitted to an academic journal, it is sent to scientific experts who send
back comments and a recommendation about whether to publish the
study.297 In this ‘peer review’ process, the reviewers remain anonymous to
the researchers submitting the paper, while they themselves should not
reveal to colleagues or friends that they are reviewing a particular study. In
this case though, the reviewers clearly felt it was in the public interest to
raise the alarm.
The call for a ‘voluntary moratorium’ on attempts to use genome editing
to modify human embryos had clear similarities with the situation in the
run-up to the Asilomar conference in 1975. At that time, as we saw in
Chapter 2, fears about the safety of the new recombinant DNA technology
led to a halt of any further development of the technology until potential
risks had been discussed and safety guidelines agreed. Yet while some scien-
tists agreed with Lanphier’s call for a moratorium, others were less con-
vinced. Lanphier himself said: ‘We are humans, not transgenic rats. We
believe there is a fundamental ethical issue in crossing the boundary to
modifying the human germ line.’298 However, George Church was more
qualified in his thoughts about the new development, saying that there
should be a moratorium on embryo editing, but only ‘until safety issues are
cleared up and there is general consensus that it is OK’.298
On 22 April 2015, the study that had been the main object of the rumours
was published in a relatively obscure journal called Protein & Cell—having re-
portedly been rejected by reviewers for both Nature and Science on ‘ethical
grounds’—and it was finally possible to examine what had been achieved in
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The Gene Scissors
detail.299 The study was led by Junjiu Huang, of Sun Yat-Sen University in
China, and the report revealed that Huang and his team had used CRISPR/
CAS9 to correct a gene defect that underlies the disease β-thalassaemia, a
potentially fatal blood disorder.299 The defect is in the β-globin gene, which
codes for one of the components of the haemoglobin protein that carries
oxygen around the blood.
In an attempt to counter potential ethical objections, Huang and his team
used embryos created by the accidental union of two sperm with a single
egg; such embryos were obtained from a local in vitro fertilization (IVF)
clinic, which would normally have discarded them.300 These embryos can
undergo the first stages of development but will never result in a live birth.
The study showed that CRISPR/CAS9 could correct the gene defect, but
with low efficiency and accuracy. So only a fraction of the treated embryos
were successfully modified, and there were also a number of ‘off-target’ ef-
fects upon other genes in the genome. ‘If you want to do it in normal em-
bryos, you need to be close to 100%,’ said Huang. ‘That’s why we stopped.
We still think it’s too immature.’300 However, George Church is less con-
vinced, pointing out that the Chinese researchers did not use the most up-
to-date CRISPR/CAS9 methods and that many of the problems of efficiency
and accuracy could have been avoided if they had.298
Following the publication of the paper, scientists remained deeply div
ided about the wisdom of seeking to apply genome editing to a human
embryo. For Edward Lanphier, the result ‘underlines what we said before:
we need to pause this research and make sure we have a broad based discus-
sion about which direction we’re going here’.299 However, George Daley, a
stem-cell biologist at Harvard University, supports editing of human em-
bryos for research purposes. He believes that employing genome editing to
modify the genomes of human embryos grown in culture could be used to
study the role of certain genes in early development. ‘Some questions about
early human development can only be addressed by studying human em-
bryos,’ he said.298
Meanwhile, philosophers of ethics have been equally divided on this
issue. John Harris, a bioethicist at Manchester University, said that although
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108
5
T he use of other species to model human health and disease has been
central to biomedical science since its inception. As early as the seven-
teenth century William Harvey was using dogs to demonstrate the circula-
tion of the blood. Nowadays, the details of such vivisection seem barbaric,
with the animals being cut open while they writhed in agony on the operat-
ing table, with no anaesthetics or painkillers to alleviate their distress.303
And currently in Britain, all experiments on live animals, whether involving
surgery or a GM mouse that will spend its whole life being monitored in a
cage and may never undergo any invasive procedures, must be carried out
under the strict regulations of a Home Office licence.304 Anaesthetics or
painkillers must also be used wherever possible to alleviate distress in the
animal, although there will be experiments in which the whole point of
the exercise is to study the pain response. Similar regulations apply to re-
search on animals in the USA, Japan, Australia, China, and other coun-
tries.305 Despite such guidelines, it’s not surprising that, since most people
are sensitive to the suffering of other creatures, animal experimentation
remains controversial.
Yet if we really want to understand how the human body works, and
what happens when things go wrong in disease, then animal experimenta-
tion will continue to be central to biomedical research.306 Opponents of
such experimentation often point to alternatives like biochemical analysis
carried out in a test tube, study of cells in culture, or modelling of bodily
processes on a computer. In fact, such approaches form a normal part of
biomedical research; so, for instance, my colleagues and I carried out more
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than half of our recent studies into the molecular basis of calcium signals on
cells in culture.307 But when researching the biology of the heart, the liver, or
the brain, it’s impossible to get a picture of the true complexity of these organs
from such studies. That’s because the structure of organs, and the way dif-
ferent cell types interact within that structure, have so far proved impos-
sible to mimic accurately in culture.306 This is particularly the case with the
brain, with its billions of cells, themselves existing as hundreds of different
cell types, connected by trillions of nerve connections; although, as we’ll
explore in Chapter 8, ways in which it may be studied could be starting to
change with new advances in human stem-cell research. Another reason
why cultured cells cannot mimic the complexity of many processes occur-
ring in a living animal is that organs communicate with each other and the
rest of the body via hormones, growth factors, and other chemicals.
Of course, animal experiments do not necessarily have to involve mam-
mals. So much of our knowledge of the mechanisms by which genes are
turned on or off originally came from studies of bacteria,308 while the genes
regulating the cell cycle—the process by which cells reproduce and divide—
were originally identified in yeast.309 We saw in Chapter 1 how studies of
fruit flies laid the foundation for modern genetics, and how, more recently,
this organism has furthered our understanding of embryo development,
particularly that of the nervous system and brain. The lowly nematode
worm has also been of great importance in this respect. Studies of the
nematode identified the phenomenon of controlled cell death, the process
whereby cells commit suicide, which is important in precise modelling of
the embryo during development and the prevention of cancer during adult-
hood.310 And, as we saw in Chapter 3, the zebrafish has also been an import-
ant organism for studying embryogenesis.311
The reason we can gain valuable insights from these different organisms
is that all life evolved from the same original genetic stock, and also because
evolution has an innate conservatism. It tends to adapt what is already there,
rather than totally fashioning things anew, with the consequence that there
is a remarkable degree of similarity between many processes occurring in
such organisms and those in the human body.312
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The reasons for studying such non-mammalian lifeforms are both eth-
ical and scientific. Ethically, it’s seen as more acceptable to carry out experi-
ments on ‘lower’ organisms because, having a less developed nervous
system, they are judged less likely to feel pain or distress. To some extent
this is a subjective judgement. In Britain it was only in the mid-1980s that it
became necessary to have a licence to study zebrafish or frogs, perhaps
because studies on warm-blooded furry animals like mice excite more in-
terest than ones on cold-blooded, slimy ones. Yet frogs and fish are still
complex organisms, and there’s increasing recognition that they also need
to be treated in ways that minimize any pain or distress they may suffer. Studies
of invertebrate species, apart from the octopus, still require no licence.313
Invertebrate species also have features that make them valuable for re-
search purposes.314 With their short lifespans and large numbers of off-
spring, fruit flies and worms have been particularly suitable for genetics,
because it’s possible to dose them with radiation or mutagenic chemicals,
and then screen resulting offspring for mutant forms.315 For studies of
embryogenesis, the fact that fly and worm embryos develop outside the
mother makes them much more amenable for study than the mammal in
its mother’s womb. The zebrafish embryo also develops outside its mother’s
body, yet being a vertebrate it shares many specific features of development
with mammals. That zebrafish embryos are transparent is important be-
cause it allows sophisticated imaging approaches to be used to study what’s
going on at the molecular level inside the cells of a living embryo.316
Genome editing looks set to have a big impact on the study of these non-
mammalian organisms because of the sheer speed at which genes can be
targeted using this technology. In June 2015, Shawn Burgess at the US NIH
showed that CRISPR/CAS9 genome editing can be used to knock out genes
in the zebrafish on a mass scale. ‘What we have done is to establish an entire
pipeline for knocking out many genes and testing their function quickly in
a vertebrate model,’ he said.317 Burgess’s team successfully mutated 82
genes, about 50 of which are similar to human genes linked to deafness.
Such mutants can now be screened to assess exactly how such genes are
involved in hearing. But Burgess has even bigger ambitions. ‘We’ve shown
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that with relatively moderate resources, you can analyse hundreds of genes,’
he said. ‘On the scale of big science, you could target every gene in the
genome with what would be a relatively modest scientific investment.’318
Mice as Models
Undoubtedly though, a principal way that genome editing will affect bio-
medical research is through its capacity to precisely modify the genomes of
different mammals. Despite the importance of research in worms, flies, and
fish, major differences exist between mammals and other multicellular
organisms. Such differences include not just the development of the mam-
malian embryo inside the womb, but also the particular challenges posed
by maintaining a constant body temperature in a warm-blooded animal. In
addition, in mammals there has been a trend in some species towards larger
brains and a greater role for learning compared to instinct, with this feature
being particularly pronounced in the primate group of which our own
human species is a member.319
We saw in Chapter 2 how the discovery of ways to create knockout and
knockin mice using ES cells was a key development in biomedical science.
Yet the mouse is far from being the best mammalian model for many as-
pects of human health and disease.320 This is partly due to its much smaller
size compared to people, and also because of the shortness of the mouse
lifespan. But mice also differ from humans in the biology of some cell types
and tissues that limit the usefulness of this species as a model. Take, for in-
stance, the heart. Understanding the molecular and cellular basis of cardiac
function, and why hearts fail, is a pressing matter given the increasing num-
bers of people succumbing to cardiovascular disease.
A study by Emanuele Di Angelantonio and colleagues at Cambridge Uni
versity published in July 2015 found that a combination of heart disease and
diabetes can shorten a person’s life dramatically. ‘An individual in their 60s
who has both conditions has an average reduction in life expectancy of about
15 years,’ he said.321 This is particularly a problem given the recent dramatic
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Another important use for GM mice is to develop and test new therapies.
For while basic scientific research aims to uncover how molecules, cells, tis-
sues, and organs combine to make a living, functioning human being, the
ultimate goal of biomedical research is to devise new ways to treat disease.
A central aspect of modern medicine is its arsenal of drugs—generally
small molecular weight chemicals that can either be ingested or injected
and which have a beneficial effect upon the body. Because drugs may be inef-
fective, or have nasty, even fatal, side effects, testing new drugs on animals
prior to their use in human clinical trials is a vital part of drug develop-
ment.328 Such testing allows the clinical usefulness of a drug to be assessed,
but also its potential for adverse side effects. Testing can be carried out on
an unmodified animal if the aim is purely to assess the potential toxic effects
of a drug. But given that the point of drugs is to treat disease, drug testing in
animals should also test the capacity of a drug to relieve the symptoms, or
even better remove the underlying cause, of an illness. In this respect too,
knockout and knockin mice models of disease have been important.329
But there are also some limitations to the usefulness of the mouse as a
model for understanding human heart function and disease.330 One major
difference is the speed at which the hearts of the two species beat. A typical
mouse pulse is 600 beats a minute, whereas our own is around a tenth of
that speed. This reflects significant molecular differences between the mouse
and human heart. The protein responsible for the heart’s contractile force is
different, as are the cellular pumps and channels that produce the chemical
signals that regulate heart contraction.330 And because of these differences,
trying to model human heart disease in a mouse by knocking out or subtly
altering specific genes may result in misleading information about the
importance of such genetic factors for humans.
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that pigs are important models for surgery, since similar procedures can be
used as in human surgery.333 It also means the various devices developed for
sophisticated imaging of the human body are directly applicable to the pig,
which can help in the comparison of pathologies in the two species.
Pigs may also become important as a source of heart transplants. This
might seem odd, given that another human heart would seem to be the
most obvious choice for such a transplant. Here though, we face a number
of problems. The first is that human donors are in short supply because of
the lack of people volunteering to donate an organ after their death, the dif-
ficulty of getting consent from grieving relatives, and a reduction in most
countries of the rate of fatal road accidents (the most reliable source of
healthy organs).334 ‘It’s a cruel situation currently, that someone who needs
a heart transplant has to pin their chance for a healthy life on the untimely
death of another person,’ said David Dunn, an expert on transplantation at
the State University of New York in Oswego.335 Even if an organ is available,
it’s highly likely to be rejected by the recipient’s immune system. Each of us
has proteins called major histocompatibility complexes (MHCs) on the sur-
face of the cells that make up our major organs. These tell our immune sys-
tems that these organs are part of us, and subtle differences in MHCs in a trans-
planted heart will cause the immune system to generally attack it as a foreign
body.336 This can lead to severe blood clots and failure of the new organ.
With thousands of different MHC variants, the chance of finding a donor
with the same profile as the person requiring a transplant is slim indeed.
Because of this, and the shortage of donors, there is much interest in trans-
planting pig hearts into people whose own heart has failed, so-called ‘xeno-
transplantation’.336 Transplanting a normal pig heart would also lead to
rejection because of the mismatch between the MHC proteins. But, unlike
human donor hearts, there is a potential solution: to genetically modify the
pigs so that the MHC proteins on their hearts are no longer recognized as
foreign by the human immune system. And the same would apply to other
organs too, so such pigs could be the source of a new liver, kidney, pancreas,
or lungs.336
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Although Venter and Church both believe they’ll soon be able to deliver
modified pigs whose organs will not be rejected by a human recipient, a big
challenge will be confirming that such organs are safe to transplant. It will
not only be necessary to show that the pig organ won’t be rejected by the
recipient’s body, but also that the organ is compatible with the rest of the
human body in a more general sense. Although a pig organ may function
perfectly well as an isolated entity in a human being, recent studies indicate
that interactions between organs also play a key role in bodily function.
Such studies show that the heart has other functions besides its vital role in
pumping the blood around the body; for instance, it also produces hor-
mones that send signals to other organs.342 It will be important, therefore, to
confirm that a transplanted pig heart can also fulfil these other functions.
Another concern is the possibility of pathogens like bacteria or viruses
being transferred from the donor heart to the recipient human. Careful
breeding in sterile conditions can eliminate most problematic microorgan-
isms from the bodies of donor pigs. However, there is one class of viruses
that poses a problem in this respect—retroviruses. As we saw in Chapter 2,
these viruses, of which HIV is the most famous member, can integrate their
genetic material into the genomes of the cells they infect. This is one reason
why a person infected with HIV can go for years without showing any
symptoms. And pigs, through exposure to such viruses in the past, also
contain retroviral DNA in their genomes, called porcine endogenous retro-
viruses, or PERVs, to use their rather unfortunate acronym.
One concern is that such retroviruses might become activated in a human
host’s body and cause a serious disease in that individual.343 An even more
serious concern is that such a transplanted virus could jump to other human
individuals and cause an epidemic. Since HIV seems to have first arisen in
humans by jumping species from chimpanzees,344 the potential conse-
quences of the spread of a virus from pigs to humans needs to be taken very
seriously. One particular concern is that viruses that jump species can have
far more serious effects in their new host than in the previous one. The pre-
cursor of HIV has few adverse effects in chimpanzees. Jonathan Allan, a vir-
ologist at the Southwestern Foundation for Biomedical Research in San
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Antonio, USA, remarked on this: ‘African primates all carry their own little
viruses. In some species, the viruses have been there for thousands of years.
And the natural host never gets sick.’345 However, in a species that has not
evolved to tolerate a particular virus the consequences can be devastating,
as seen with HIV in humans.
Until recently, there seemed little that could be done about the presence
of PERVs in potential donor pigs. ‘They were part of these animals’ gen-
omes,’ said Jay Fishman, associate director of the transplant centre at
Massachusetts General Hospital.335 Instead, those in favour of transplanting
pig organs into humans pointed to studies like one in which pig hearts
transplanted into baboons failed to show any activation of pig retroviruses
once inside the baboon’s body.346 None the less, the potential risks of allow-
ing such viruses into a human body have always been one of the objections
levelled against xenotransplantation. So, according to George Church, bil-
lions of dollars were invested in xenotransplantation research in the mid- to
late 1990s, but funding fizzled out because of the inability to find a way to
remove the viral sequences.347 Yet in October 2015, Church and his team
used CRISPR/CAS9 to delete all the PERVs in the genomes of pig kidney
cells in culture.348 ‘Fast-forward 15 years later, we got rid of them in 14 days
with CRISPR and a lot less money,’ said Church.347
Church’s team first analysed the genomic DNA of the pig cells. This re-
vealed 62 PERVs located at different sites in the genome; however, these
were practically identical in sequence, reflecting their origin from a single
ancestor that invaded the pig genome millions of years ago. The researchers
then used a form of CRISPR/CAS9 that didn’t just cut the viral DNA but
deleted it from the genome. Amazingly, in some cells this treatment elimin-
ated all 62 copies of the virus from the pig genome. And those edited cells
showed up to a thousandfold reduction in their ability to infect human
kidney cells with PERVs in a culture dish.348 In addition, Church claimed at a
US National Academy of Sciences meeting on genome editing that he and
his colleagues have successfully created pig embryos with inactivated PERV
sequences—the next step towards raising cloned pigs with retrovirus-free
organs.348 Because of this, and the plans to alter pig MHCs, David Dunn
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The potential usefulness of pigs for modelling human health and disease,
and as a source of replacement organs, is due to the great similarities in
basic physiology between the two species. But one human organ that’s
peculiar in both size and complexity compared to other mammalian spe-
cies is the brain. Human beings are unique in possessing a self-conscious
awareness, a language capacity that allows us to communicate with other
humans as well as think, talk, and write conceptually, and an ability to de-
velop and use new tools and technologies in each new generation.349 Such
characteristics must ultimately be based on the distinctive biology of the
human brain, although obviously the shape of the mouth, throat, and hand
are also vital in allowing us to articulate thoughts vocally and use tools.350
This poses the question of how to model the human brain, both in terms of
its normal function but also degenerative diseases like Parkinson’s and
Alzheimer’s and personality disorders like schizophrenia, depression, and
bipolar disorder.
The problem that such disorders pose for society is shown by recent fig-
ures from the US National Alliance on Mental Illness, which indicate that
about one in four adults in the USA experiences a diagnosable mental dis-
order in a given year.351 Figures from the UK Mental Health Foundation
reveal a similar situation in Britain.352 Of course, one might wonder what
type of ‘illness’ affects such a large proportion of the population, and some
experts criticize what they see as the increasing overmedicalization of indi-
viduals whose actions lie within the spectrum of normal human behaviour.
Peter Kinderman, head of Liverpool University’s Institute of Psychology,
remarked: ‘Many people who are shy, bereaved, eccentric, or have uncon-
ventional romantic lives will suddenly find themselves labeled as mentally
ill. It’s not humane, it’s not scientific, and it won’t help decide what help a
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in the brains of those with mental disorders. ‘I felt that we really needed to
go back to the lab and concentrate more on fundamental knowledge of
brain mechanisms and genetics,’ he said.356 And a chance to pursue such a
goal arose when he was asked to direct the McGovern Institute in 2004.
Under Desimone, the institute has recruited top researchers working in
the most cutting-edge aspects of neuroscience. Feng Zhang, who, as we saw
in Chapters 3 and 4, helped pioneer both optogenetics and CRISPR/CAS9
genome editing, joined the McGovern Institute in 2011. Zhang is also critical
of the current lack of precision that underlies our understanding of the biol-
ogy of mental disorders and the drugs used to treat them. ‘Traditionally
when we think about developing drugs to treat brain diseases, it’s all about
this hypothesis that there’s some kind of chemical imbalance,’ he said. ‘All
the cells in the brain live in this milieu of chemicals, and if there’s an imbal-
ance in the composition of the chemicals, then the brain has problems. But
that’s a very gross and inaccurate way of thinking about how the brain func-
tions.’356 Instead Zhang believes the focus should be on understanding the
‘abnormal signalling between different cells in specific neural circuits . . .
probably underlying many of the neurological or psychiatric diseases that
we know today’356—features highlighted by the optogenetic studies being
carried out by himself and others.
Optogenetics is only one of the technologies being developed at the
McGovern Institute. Another approach is the use of genome editing to
assess the functional relevance of genomic regions shown to be associated
with mental disorders in humans. On the completion of the Human
Genome Project in 2003, some influential figures predicted that we would
soon identify the genes associated with such disorders. Consequently,
Daniel Koshland, editor of Science, declared that the basis for ‘illnesses such
as manic depression, Alzheimer’s, schizophrenia and heart disease’ would
all be unravelled, with new drug treatments for these conditions sure to
follow.357 Unfortunately, the reality has proved rather more complex.
The main strategy in trying to identify genes associated with human dis-
orders has been so-called ‘genome-wide association studies’ (GWAS).358
These studies typically analyse the genomes of a large number of individuals
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with a disorder and compare them with people lacking the disorder. And
studies of schizophrenic individuals have indeed identified links with a
number of genomic regions. But far from identifying a few clear links, these
studies have found associations with over a hundred different regions.359
And each of these regions of the genome individually appear to have only a
minor impact. What’s more, the same complexity is emerging from genetic
studies of other mental disorders such as bipolar disorder, depression, and
autism.360 Currently there is a debate about whether this indicates that gen-
etic predisposition to such disorders requires changes in a large number of
different genomic regions, or whether rare differences have a much more
significant impact, but only in a few individuals.361 Either way, this still
leaves the question of how to assess the functional importance of these gen-
etic differences.
Up till now, the main way to do this has employed ES cells to create
knockout or knockin mice with defects in genes associated with human
mental disorders. This makes it possible to explore the underlying biology
of such disorders, as well as test drugs that may be used to treat them. Here
genome editing can play a vital role by dramatically reducing the time and
cost required to produce such mice. Guoping Feng, a scientist at the McGovern
Institute, is pioneering this ‘high-throughput’ approach. ‘We have models
of obsessive-compulsive disorder and autism,’ he said. ‘By studying these
mice we want to learn what’s wrong with their brains.’362 In one such model,
mice show obsessive self-grooming, and Feng has shown that this behav-
iour ceases when the missing gene is reintroduced, even in adulthood. ‘The
brain is amazingly plastic,’ said Feng. ‘At least in a mouse, we have shown
that the damage can often be repaired.’362 So far he has only created mice
with differences in single genes, but human mental disorders appear to
involve many contributing genetic differences. And here the capacity of
CRISPR/CAS9 for editing multiple genes simultaneously will be very
important.
Such a focus on mice does, however, raise the question of whether we can
gain a meaningful idea of the role of specific genes or neurons in human
mental disorder purely from studying rodent models. One concern is that
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many potential drugs for brain disorders have been tested successfully in
mice, only to prove ineffective in subsequent human trials. Thus, according
to Robert Desimone, ‘a lot of the treatments that are tried out in mice seem
very promising, and then they go into clinical trials and don’t go anywhere.
You hear the expression all the time that this is a great time to have
Alzheimer’s disease if you’re a mouse. You could say the same thing about
autism or any number of disorders.’356
Modify My Monkey
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Prefrontal cortex
likely to be increased interest in using such primates to study the brain, not-
withstanding the potential controversy this may generate in terms of eth-
ical issues.
That genome editing can be employed in primates was demonstrated in
January 2014 by Weizhi Ji and colleagues at the Yunnan Key Laboratory of
Primate Biomedical Research in China. They used CRISPR/CAS9 to knock
out the genes peroxisome proliferator-activated receptor gamma (PPARγ)
and recombination activating gene 1 (RAG1) in cynomolgus macaque mon-
keys.366 Ji and his team targeted the genes in fertilized macaque eggs, then
implanted these into surrogate mothers. Two resulting offspring, named
Ningning and Mingming, had knockouts in the genes. PPARγ regulates
metabolism and RAG1 is involved in immunity, and the researchers are now
investigating what effect loss of these genes has upon these bodily func-
tions. Ji’s team subsequently targeted dystrophin—the gene defective in
people with Duchenne muscular dystrophy (DMD)—in rhesus macaque
monkeys, and found that this caused severe muscle degeneration similar to
that observed in humans with this condition.367 The macaque may therefore
be a useful model for studying such diseases that affect humans.
But the main interest in GM primates is for studying brain disorders.
With this in mind, scientists at the McGovern Institute are now in the pro-
cess of using CRISPR/CAS9 to create GM macaques, as well as marmo-
sets—a smaller primate species with a faster breeding cycle.362 Because both
species are very social with highly structured communication patterns, they
should offer a valuable new route for assessing the role of genes involved in
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social interaction. The aim is first to try to breed primates with a condition
similar to autism, and then to move on to schizophrenia and other dis-
orders. Such primate models will be important for understanding not only
the basic biology of mental disorders, but also for testing new drugs. Robert
Desimone hopes that ‘the primate models will give us better testing and
treatment platforms’.356
Such is the potential of gene editing in primates, but the application of
the technology in this manner is creating controversy. Troy Seidle, of
Humane Society International, believes there should be an outright ban on
the genetic manipulation of primates: ‘You can’t genetically manipulate a
highly sentient non-human primate without compromising its welfare,
perhaps significantly. GM primates will be just as intelligent, just as sensi-
tive to physical and psychological suffering as their non-GM counterparts,
and our moral responsibility toward them is no less.’368 Such opposition
may have an impact in countries that would otherwise be well placed to
develop the use of GM primates in brain research. In the USA, commercial
airlines have already ceased all primate shipments by air within the country,
making it difficult for researchers to transport animals.369 Many airlines in
Europe have taken similar steps, although Air France still provides a service.
And a recent report showed that a compromise European Union initiative,
which was supposed to balance the welfare of primates while allowing
some research on this animal group, is already in danger of unravelling be-
cause of political lobbying by animal rights activists.369
Consequently, future development and study of GM primates may well
shift to countries where there are fewer ethical concerns about such re-
search. As we mentioned earlier in this section, the first successful use of
genome editing to create such modified primates was in China. And China
not only has more relaxed attitudes to primate research but is also invest-
ing significant funds in this area. The dynamics of the situation are illus-
trated by the changing fortunes of the Yunnan Key Laboratory of Primate
Biomedical Research in Kunming, the institute in which Weizhi Ji and his
colleagues announced the birth of the first genome-edited primates. Ji re-
calls that when he first began his career at the Kunming Institute of Zoology
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in 1982, ‘we did not have enough funding for research. We just did very
simple work, such as studying how to improve primate nutrition.’370
The subsequent expansion of the Chinese economy has led to a growth
in the country’s scientific ambitions, and major funds are being invested in
transforming the primate research institute at Kunming. It now boasts 75
covered homes for primates, housing more than 4,000 animals, which
spend their time swinging on hanging ladders and scampering up and
down wire mesh walls, while 60 trained animal keepers look after them full
time.370 The institute also has extensive facilities for creating genome-edit-
ing constructs, microinjection systems for injecting these into fertilized
monkey eggs, incubators for culturing the resulting embryos, and facilities
for implanting these into surrogate mothers. So, despite the ambitions of
well-established US centres of science like the McGovern Institute to de-
velop GM primates for studies of brain function, big future breakthroughs
in this area may well be at Chinese institutes like the one at Kunming.
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Feeding Humanity
While it’s important to recognize the problems associated with the indus-
trialization and globalization of agriculture, it would be equally mistaken
to underestimate its success in feeding the world’s growing population—
albeit with huge continuing inequalities in food distribution. But can these
methods continue to feed the planet in the future? The ability of food pro-
duction to keep pace with a world population that rose from 3 to 7 billion
between 1960 and 2011 was primarily due to the remarkable increase in crop
yields with only a slight expansion in land cultivated that occurred in this
period, thanks to the ‘Green Revolution’.383 Spearheaded by Iowa-born
plant geneticist Norman Borlaug, the Green Revolution introduced more
productive varieties of wheat, corn, and rice into many parts of the world,
combined with greater use of fertilizer and irrigation. The resulting increase
in crop yields fed people directly, as well as the livestock that provide meat.
But the success story of the Green Revolution shouldn’t blind us to the
problems that still exist, with an estimated 795 million people—one in nine
people on the planet—lacking sufficient food to lead a healthy active life.384
And many problems lie ahead. Since at least the turn of the millennium,
increases in wheat, rice, and other cereal crop yields have begun showing
signs of slowing.385, 386 This isn’t only worrying because such a rise is neces-
sary to keep pace with a growing world population, predicted to reach at
least 9 billion by 2050, but also because recent evidence suggests that the
fall in yield is linked to global warming.
A study by David Lobell, an environmental scientist at Stanford Univer
sity, and Wolfram Schlenker, an economist at Columbia University, found
that, from 1980 to 2008, climate change depressed yields of wheat and corn;
yields still rose during that time but overall production was 2 to 3 per cent
less than it would have been in the absence of global warming.385 This
finding suggests that climate change, widely scientifically accepted as being
the result of human activity, has not only already adversely affected food
production, but that this negative impact will intensify as the planet heats
up.386 A particularly worrying aspect of the findings is that agriculture
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and then only for a limited range of products, particularly those not des-
tined for direct human consumption. Moreover, the continuing political
controversy over GM crops means that, for some parts of the world, devel-
opment has been at a virtual standstill. So in Europe, since the first GM crop
was produced in 1994—a tomato whose ripening was delayed, giving it a
longer shelf life—the European Union has granted just two licences to cul-
tivate GM crops: one for plants engineered to resist corn borers and another
for a starchy potato used to make paper.387
The limitations of previous GM crops are far from just political though.
As we saw in Chapter 2, one problem with standard transgenic technology
is that it involves randomly inserting a foreign gene into the genome of the
host cell. Not only does this mean the technology is incapable of making the
sort of subtle alterations such as those in a knockout or knockin mouse, but
it also means the inserted gene may disrupt some other gene in the host
genome, leading to unwanted, and possibly adverse, consequences. At the
same time, this is a very inefficient process, so usually an antibiotic resist-
ance gene is included in the transgene construct in order that plant cells that
have taken up this construct can be selected.388 And, as we also saw in
Chapter 2, this has led to fears about such resistance being transferred to
harmful bacteria.
In contrast, genome editing of plant cells, as with other types of cells, can be
used both to delete specific genes or introduce more subtle changes, like the
substitution of one type of amino acid for another, similar to what happens
in a disease like sickle cell anaemia in humans.389 A sign of how important
genome editing is seen to be by agribusiness was shown by the announce-
ment in October 2015 that DuPont had signed an agreement with Jennifer
Doudna’s company Caribou Biosciences to develop CRISPR/CAS9 as a key
new technology for crop production.390 Indeed, DuPont says it’s already
using this technology to make drought-resistant corn and wheat that is
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plants are seldom tasty, nutritious, and easy to harvest,’ said Palmgren.399
The process of perfecting the hybrid plant is time-consuming and difficult
to control. With genome editing, there’s no need to go through extensive
crossing to induce the characteristic, which makes the whole process a lot
faster.
Palmgren has even suggested that ‘all crops would benefit from rewild-
ing’.399 This would not only protect them against pests and disease, but also
allow them to draw nutrients from the soil more efficiently. However, not
everyone agrees with this conclusion. ‘I find their whole premise to be
rather flawed,’ said Clay Sneller, a plant breeder and geneticist at Ohio State
University in Columbus. ‘They appear to think that during breeding we
have accumulated negative mutations, and if we got rid of those mutations
then the crop would be better. They reviewed no evidence that this occurs
on a wide scale in genes that truly matter.’399 Such concerns show that there
will be many divergences of opinion about the best way to employ genome
editing in agriculture. However, the precision of the new technology means
that different strategies can now be put to a practical test.
Improving a plant’s resistance to disease or its capacity for growth is only
one way in which genome editing is likely to have an impact on crops. The
other important impact will be on the food produced from such crops. For
instance, in April 2015 a potato plant was engineered so that it doesn’t
accumulate sweet sugars at typical cold storage temperatures.400 This modi-
fication will let it last longer and, when fried, it won’t produce as much
acrylamide, a suspected carcinogen that can accumulate in some fried food.
The modified potato was created by Daniel Voytas in collaboration with a
biotechnology company called Cellectis Plant Sciences. The genome editing
disabled a gene that turns sucrose into glucose and fructose and took only
about a year to achieve. ‘If you did it via breeding it would take five to 10
years,’ said Voytas.400 Luc Mathis, CEO of Cellectis, claims that developing
the potato cost a tenth of that needed to create a standard transgenic plant
and bring it to market.
A particularly beneficial development for human health could be the use
of genome editing to create crops that don’t trigger dangerous food allergies.
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that genome edited plants may have unintended adverse effects on the
environment and human health.
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many parts of the USA in recent winters, due to the partial breakdown of
the polar vortex that typically confines cold weather to the Arctic region,
allowing cold-air breakouts to the south. While such temperature swings
can cause chaos to cities and their transport networks, undoubtedly the
most serious impact will be on the plant and animal species that provide
food for the Earth’s 7 billion humans. As we saw in the section ‘Feeding
Humanity’, global warming is already having a worrying effect on the yields
of staple crops like wheat and corn. The central highlands of Mexico, for
example, experienced their driest and wettest years on record back to back
in 2011 and 2012, according to Matthew Reynolds, a physiologist at the
International Maize and Wheat Improvement Center in El Batán. Such vari-
ation is ‘worrisome and very bad for agriculture,’ he said. ‘If you have a rela-
tively stable climate, you can breed crops with genetic characteristics that
follow a certain profile of temperatures and rainfall. As soon as you get into
a state of flux, it’s much more difficult to know what traits to target.’385
It’s here that genome editing may aid the development of crops able to
withstand the extremes of temperature, drought, wind, and snow predicted
to be coming our way.410 To deal with such extreme changes, scientists may
need to do more than tinker with existing crop plants; a major transform-
ation of plants’ basic biology may be required. Daniel Voytas, working with
researchers at the Rice Research Institute in Los Baños, in the Philippines,
aims to rewrite the physiology of rice, by focusing on the process of photo-
synthesis.385 This is the cellular mechanism, common to all plants, that traps
energy from the Sun and uses it to convert carbon dioxide and water into
glucose, as a preliminary to producing the other complex molecules of life.
Photosynthesis can occur both as the C3 form, found in rice and wheat and
other grain-producing plants, or the more complex C4 form, used by plants
like corn and sugarcane.411 The two types are distinguished by the initial
molecule formed, with either a 3-carbon or 4-carbon sugar being produced.
An important difference between the two processes is that C4 photosyn-
thesis is far more efficient at high temperatures and dryness, so if a way
were found to create C4 versions of rice and wheat, their yields could be in-
creased in regions becoming hotter and drier due to climate change.405
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If genome editing has the potential to vastly expand the possible range of
GM plants that can be grown, the technology may have an even bigger impact
on farm animals, which, as we saw in Chapter 2, have been little affected by
standard transgenic techniques. Political opposition has also played a role
here, similar to the situation with GM crops. GM pigs created by standard
genetic engineering approaches in the mid-1990s at first looked like they
might have a chance of commercial success, only to meet opposition be-
cause of their artificial origins. The pigs were produced by Cecil Forsberg
and his team at the University of Guelph, Canada, using standard transgenic
methods to engineer them to express an enzyme, phytase, normally gener-
ated by the gut bacteria of cows and other ruminant animals.412 Phytase breaks
down phosphorus-containing phytate in plants, but normally pigs do not
have such bacteria and require a phosphate supplement in their feed. The
gene construct used to create the GM pigs contained the gene coding for
phytase linked to a tissue-specific mouse gene promoter, which meant the
bacterial enzyme was only produced and secreted by the pig salivary glands.
Forsberg named the GM pig variety he had created the ‘enviropig’, because
it produced manure with lower levels of phosphorus, notorious for leaching
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into groundwater beneath pig farms and fuelling algal blooms in local
streams and lakes.412 He also claimed that the pigs would be more econom-
ical, since they would not require the extra cost of adding mineral phos-
phorus or commercially produced phytase to their feed to ensure that they
obtained the nutritional phosphorus they require. But attempts to obtain
approval to develop the pigs commercially foundered after opposition from
anti-GM activists. They argued that, because of their low-phosphorus
manure, if the enviropigs were approved for human consumption, ‘agricul-
ture [would have] an excuse to put them in even more concentrated facil-
ities’, as Alison Van Eenennaam of the University of California, Davis, who
studies the commercial application of GM technologies, put it.412 Such
opposition meant that, in 2011, the Ontario Pork Producers Marketing
Board, funder of the project, withdrew its support. Unable to find another
industry backer, the researchers decided they had no alternative but to ter-
minate the project. ‘These pigs were healthy pigs that did perform as they
were designed to perform. They just didn’t meet the social requirement,’
said Forsberg.412
Another transgenic animal project that produced a potentially important
commercial product, but then stalled subsequently, is a super-sized salmon.
This fish, named the AquAdvantage salmon by its creators Garth Fletcher
and his colleagues at Memorial University of Newfoundland, was produced
in 1989. They introduced a gene construct combining a growth hormone
gene from Chinook salmon and a highly active regulatory DNA element
from the eel-like ocean pout into fertilized Atlantic salmon eggs.412 The
resulting GM salmon grow to market size in half the time required for a con-
ventional farmed variety, while consuming 25 per cent less food overall. In
order for the fish to be approved for sale, the researchers had to demonstrate
that the salmon’s meat had the same composition as a normal fish. And to
prevent escape and interbreeding with wild fish, the GM salmon are all
sterile females and their watery enclosures at Prince Edward Island have
physical barriers between them and the sea. In recognition of these safe-
guards, a 2010 environmental impact assessment found that breeding the
AquAdvantage salmon shouldn’t harm wild fish. In November 2015, after
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years of delays, the FDA finally approved the salmon for sale.413 Yet, due to a
vigorous campaign of opposition, 65 supermarkets, along with seven sea-
food companies and restaurants, have already signed a pledge not to carry
it. ‘We don’t want Prince Edward Island to be known around the world as
the home of the Frankenfish,’ said Leo Broderick, a retired schoolteacher on
the island who travelled to an FDA meeting in Maryland to campaign
against the salmon’s approval.414
As we have seen, a major difference between genome editing and pre-
vious transgenic approaches is the capacity of genome editing to introduce
precise changes to one or more genes in a way that doesn’t cause other
changes to the genome. It is also cheap, highly efficient, and can be applied
to practically any animal species. So could these features allow the new
technology to have a major impact on the development of livestock for the
industry in a way that previous approaches have not?
One way that genome editing is being applied to livestock can be illustrated
by a recent study in which scientists used this technology to produce
Brazilian Nelore cattle with increased muscle mass. This study, led by Scott
Fahrenkrug of the University of Minnesota, in collaboration with the Roslin
Institute in Edinburgh and Texas A&M University, introduced a mutation
found in Belgian Blue cattle—hulking animals that provide unusually large
amounts of prized, lean cuts of beef—into rangy Nelore cattle which are
heat-tolerant.415 The mutation, which inhibits production of a muscle-
supressing protein, myostatin, increases muscle mass. The introduction of
this mutation into the Nelore cattle has created animals that provide prime
meat cuts but can be kept in hot countries like Brazil, unlike Belgian Blues.
And such is the interest from the livestock industry that British-based com-
pany Genus, the world’s largest breeder of pigs and cattle, has funded some
of the study’s research. Jonathan Lightner is the head of research and devel-
opment (R&D) at Genus. ‘We haven’t realized the opportunity for genetic
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Selective breeding
across many centuries
Wild ancestor of
modern cattle
Hornless mutation
introduced
Holstein dairy cattle into dairy cattle Genome-edited
have horns dairy cattle
with no horns
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Lightner believes that, because of its potential for eliminating such animal
suffering, the project could be viewed much more positively by the public
than previous GM experiments. ‘There may be an opportunity for a dif-
ferent public acceptance dialogue and different regulations,’ he said. ‘This
isn’t a glowing fish. It’s a cow that doesn’t have to have its horns cut off.’415
As for dairy farmers, they are interested, but also cautious about the
potential of genome editing. Tom Lawlor, head of R&D for the Holstein
Association USA, thinks that the technology ‘is very cool’.415 But he also
believes many milk producers are afraid of genetic engineering. ‘The tech-
nology definitely looks promising and seems to work, but we would enter
into it slowly as opposed to rapidly for fear the consumer would get the
wrong idea,’ he said. ‘We get scared to death, because our product is milk,
and it’s wholesome.’415 Lawlor also points to other scientific initiatives that
provide an alternative route to a hornless dairy cow, such as the 1000 Bull
Genomes Project. This has decoded the genomes of 234 dairy bulls, includ-
ing Swiss Fleckviehs, Holsteins, and Jerseys, and means that breeders can
now accurately size up an animal’s genetic profile at birth. As a conse-
quence, a few naturally occurring hornless bulls of these breeds are
approaching top-ranked status, and such genetic selection may be seen as a
less controversial strategy than direct genetic engineering.415
Another potentially important use for genome editing is in developing
animals that are resistant to disease. One such disease is African swine fever,
caused by a highly contagious pig virus, and characterized by high fever,
loss of appetite, haemorrhages in the skin and internal organs, and death in
two to ten days on average.416 The disease remained restricted to Africa
until 1957, when it was reported in Lisbon. Subsequently, the disease became
established in the Iberian Peninsula, and sporadic outbreaks occurred in
France, Belgium, and other European countries during the 1980s. Both
Spain and Portugal eradicated the disease by the mid-1990s only through a
mass slaughter policy. But from 2012 to 2015, outbreaks were reported in
Lithuania, Ukraine, Poland, and Latvia, and the disease remains a serious
threat to domestic pigs across Europe.416 In contrast to the severe reactions
of domestic pigs to the virus, wild warthogs are far less affected. This is
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in the feed going into the animal to produce meat protein.’418 There is a par-
ticular current relevance to Speight’s research, as Queensland farmers are
increasingly turning to supplementary feeds to keep their remaining stock
alive due to the impact of a severe drought in this region in recent years.419
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152
7
I n the developed world it’s easy to take for granted the wonders of modern
medicine. Vaccines and antibiotics, anaesthetics and painkillers, laser and
keyhole surgery, drugs to treat diabetes or heart disease, whole body imag-
ing devices—the list could go on. In fact, the situation is very different in far
too many parts of the world, with a staggering third of the Earth’s popula-
tion still lacking access to even the most basic health provision.422 For sev-
eral billion people, this lack of health care is compounded by inadequate
food and access to clean water and sanitation facilities. Little wonder that
malaria, tuberculosis, cholera—and even simple malnutrition—remain
major causes of death in much of the developing world. The additional ter-
rible burden of HIV is heavily concentrated in Sub-Saharan Africa and is
now the world’s biggest infectious killer.423 This is the reason why, even as
life expectancy rises globally, it remains stubbornly low in the developing
world. So while US average life expectancy is 79, in Zambia it’s 55.424
Even in the developed world, gross inequalities in health still exist. Half a
century after Martin Luther King Jr said that ‘of all forms of inequality, i njustice
in health care is the most shocking and inhumane’,425 millions in the
USA lack access to proper health care because they can’t afford medical
insurance. And ethnic minorities are particularly vulnerable, with a World
Health Organization (WHO) report showing that infants born to African-
American women are 1.5 to 3 times more likely to die than other infants in
the USA.426 Even in Britain, with its publicly funded National Health
Service (NHS), there is still a substantial link between income and health.
A recent study by the UK Institute of Health Equity found that the average
gap in life expectancy across Britain between the best- and worst-off is
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seven years, but in London this difference rises to 17, and in Glasgow there
is a 28-year difference in life expectancy between rich and poor.427
Such statistics show that the amazing technological advances in medi-
cine over the past century mean little without an equal focus on the social
inequalities that can cause ill health. Nevertheless, it would be equally
wrong to belittle the importance of developing new medical technologies.
For all the progress, there is still much that remains backward about modern
medicine. So, despite important advances in our understanding of the
molecular basis of cancer, the main treatment for this disease remains crude
surgery, or chemical or radiation therapies that have serious, sometimes
life-threatening effects in normal cells and tissues.428 As for degenerative
disorders of the brain like Alzheimer’s and other forms of dementia, which
affect one in six people over 80, despite recent advances in our understand-
ing of such disorders, they remain essentially untreatable.429
And, as we saw in Chapter 3, although there are now a large variety of
drugs for treating personality disorders like schizophrenia, bipolar dis-
order, or depression, these remain blunt tools that, as many psychiatrists
acknowledge, treat some of the symptoms but not the underlying causes of
these disorders. Finally, there are concerns about how long we can rely on
one of the most powerful tools of modern medicine—antibiotics—with
Sally Davies, Britain’s chief medical officer, recently warning that antibiotic-
resistant bacteria represent a ‘ticking time bomb’ that threatens to take us
back to nineteenth-century standards of health care.430
What is the likely impact of our new-found skills in genome editing on this
situation? This technology has led to great excitement because of its potential
to advance biomedical research, as we saw in Chapter 5. So genome editing
not only makes it possible to study gene function in human cells in culture
but has greatly accelerated the development of knockout and knockin mice,
and also made it possible to develop models of human health and disease in
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The prospect of being able to correct ‘defective’ genes has been a dream in
medicine ever since the link between genetics and human disease was first
identified. Yet, as we saw in Chapter 2, gene therapy via standard transgenic
approaches has been far from a success story—even for well-characterized
single-gene disorders—because of two main obstacles.436 One is the difficulty
in getting gene constructs into tissues and across the membranes of cells in
the body. Viruses can effectively transport gene constructs into cells, but their
use also carries risks. The second obstacle has been the lack of a technology
to precisely engineer the genomes of treated cells. Instead, traditional gene
therapy has meant introducing a foreign DNA construct randomly into the
genome of the host cell. Not only can this disrupt the host genome and cause
damage, such as activating an oncogene (which can lead to cancer), but it’s
also only useful for treating recessive disorders in which a gene product is
absent, as in cystic fibrosis, not for treating dominant ones like Huntington’s
where a defective gene product disrupts normal cell function.
Since genome editing is so new, particularly the CRISPR/CAS9 version
that’s rapidly becoming the dominant approach, its full potential as a thera-
peutic strategy in humans is still only at the first stages of assessment, yet
already there are highly promising signs. Demonstrations of the technolo-
gy’s therapeutic potential have so far mainly involved mouse models of dis-
ease, although, encouragingly, there are now ongoing clinical trials and an
apparent recent success in treating childhood leukaemia that we’ll look at in
the section ‘New Cancer Cures’. Two main approaches are being pursued.
First, genome editing is being used to modify cells outside the body.
Although this is much easier to achieve in a controlled fashion, it does limit
this approach to only a few cell types, such as those in the bone marrow;
consequently, this restricts the types of diseases that can be treated to those
affecting the blood or immune system. Second, genome editing is being
employed to target cells located within the body. Although this opens up
the possibility of using the technology to modify practically any type of
genetic disease, technically this second approach is a lot more challenging.
The first animal study to demonstrate the clinical potential of genome
editing was carried out by Jinsong Li’s team at the Shanghai Institute for
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said Anderson. ‘We think it’s an important proof of principle that this tech-
nology can be applied to animals to cure disease. The fundamental advan-
tage is that you are repairing the defect, you are actually correcting the DNA
itself.’439 However, he also acknowledged that the efficiency and safety of the
approach would need to be significantly improved before the technology
could be tested in humans.
Huntington’s disease is a well-known single-gene disorder of the brain.440
This dominant disorder affects a relatively large number of individuals—12
in every 100,000 people in Britain. The condition typically starts with
twitching and mood swings, but rapidly progresses to full-scale dementia
and death, generally in middle age. Because sufferers generally already have
children before they begin to show symptoms, the disease is passed down
through the generations. The identification of the genetic defect under-
lying Huntington’s disease in 1993—a decade before the completion of the
Human Genome Project—was a triumph of modern genetics.441 Sufferers
of the disorder were found to have a defect in a gene named huntingtin. This
gene has a repetitive DNA sequence, CAG, at its start that is repeated around
17 times in normal individuals. Each CAG codes for the amino acid glutam-
ine, so a typical individual will have 17 glutamine amino acid units at the
start of the huntingtin protein. However, faulty DNA replication can cause
the CAG repeats to expand, and if a person inherits 36 or more, they will
succumb to Huntington’s disorder. The reason is that the extra glutamines
cause the huntingtin protein to form aggregates within cells, making those
cells—particularly neurons—dysfunctional.
The identification of the huntingtin gene defect was greeted with hope
that this would quickly lead to a cure for this disorder. Unfortunately, all it
has meant is that people at risk can now have a genetic test that reveals how
many CAG repeats are present in their huntingtin gene. This is obviously
welcome news if it shows an individual is free of risk, and can also help
those considering having children. However, since a positive result is effect-
ively a death sentence, it’s not surprising that most people at risk choose not
to take the test. In 2010, journalist Charlotte Raven who took the test and
found she was positive described how she initially ‘thought taking the test
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would be like finding out the weather before you go on holiday’.442 Instead,
it was more like finding that ‘there was a bomb on the plane when you were
already airborne. I felt impotent and envious of the uninformed majority.
I wished I didn’t know.’442
Now though, there has been a glimmer of renewed hope for those with
the disorder, following a study by Nicole Déglon and colleagues at the
University of Lausanne in October 2015. The researchers infected two
groups of healthy adult mice with a virus expressing the mutant huntingtin
gene. One of the groups was also injected with a virus expressing CAS9
enzyme and a guide RNA targeting the huntingtin gene. Déglon believes
that what her team found is ‘remarkably encouraging’.443 After only three
weeks, the two groups of mice showed a striking contrast. While those only
treated with the mutant huntingtin showed large amounts of protein aggre-
gation in their brain cells, those with the mutant protein and the CRISPR/
CAS9 treatment had almost none—the genome editing had prevented
expression of almost 90 per cent of the mutant huntingtin. ‘Having reached
about 90% [blockage of production], this changes the story [of Huntington’s
therapy] completely,’ said Déglon. ‘It opens new treatment strategies that
are based in DNA, and so would have a permanent benefit for the rest of
someone’s life.’443
In fact, there are many issues that need addressing before this approach is
considered both effective and safe as a way to target Huntington’s disease in
humans. In Déglon’s study the guide RNAs targeted both normal and
mutant huntingtin. ‘If there is no specificity for mutant huntingtin, that’s a
concern,’ said Abdellatif Benraiss, a neuroscientist at the University of
Rochester in New York. ‘This is not a treatment for 4 weeks or 4 months,
this is going to be permanent.’443 For although huntingtin’s normal role re-
mains unclear, it is thought to be involved in important functions like trans-
porting substances in cells. ‘As bad as too much huntingtin is, we still need
one copy [of its gene] so it can do its job in our bodies,’ said Benraiss.443
Another issue is that the mutant protein was expressed artificially in the
mice. However, Déglon’s team are designing guide RNAs that distinguish
the normal and mutant huntingtin gene and only target the latter. And they
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were able to kill human Burkitt lymphoma cells by deleting myeloid cell
leukaemia 1 (MCL1), a gene that has been shown to keep cancer cells alive’.449
Although this was a ‘pre-clinical’ study involving only human cells grown
in culture, Aubrey, who’s also a haematologist at the Royal Melbourne
Hospital, believes that, ‘as a clinician, it is very exciting to see the prospect
of new technology that could in the future provide new treatment options
for cancer patients’.449 Another researcher on the study, Marco Herold, is
equally optimistic about the potential of genome editing for cancer therapy
as well as research into the molecular basis of tumour formation, saying
that, ‘in addition to its very exciting potential for disease treatment, we have
shown that it has the potential to identify novel mutations in cancer-causing
genes and genes that “suppress” cancer development, which will help us to
identify how they initiate or accelerate the development of cancer’.449
Most exciting of all was the news in November 2015 about an apparently
successful use of genome editing to treat leukaemia in a British baby. The
story had all the elements of a film script—a dying baby, desperate parents,
and a team of doctors with a highly experimental new treatment.450 Yet this
was real life, and the parents, Lisa Foley and Ashleigh Richards, only al-
lowed the new therapy to be used to treat their daughter Layla’s cancer after
all else had failed. Layla was born a healthy 7lb 10oz in June 2014, but three
months later she developed a fast heartbeat, went off her milk, and cried
more than usual.451 At first the problem was thought to be nothing more
than a stomach bug, but blood tests revealed she had infant acute lympho-
blastic leukaemia; indeed, Layla’s doctors described it as one of the most
aggressive forms of this cancer they’d ever seen. Layla was immediately
given chemotherapy and a bone marrow transplant to replace her can-
cerous blood cells. Yet despite several rounds of the treatment, the leukae-
mia returned. At that point the doctors told Layla’s parents there was
nothing more they could offer, apart from palliative care to ease the baby’s
suffering before she succumbed to the cancer. But Ashleigh and Lisa begged
the doctors not to give up. ‘We didn’t want to accept palliative care and give
up on our daughter, so we asked the doctors to try anything for our daughter,
even if it hadn’t been tried before,’ said Lisa.451
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The plea was enough to make the doctors at Great Ormond Street
Children’s Hospital in London, where Layla was being treated, reconsider
their options. And they decided to try a genome-editing approach, despite
the fact that it had only been tested on mice. ‘The treatment was highly
experimental and we had to get special permissions, but she appeared
ideally suited for this type of approach,’ said Waseem Qasim of University
College London’s Institute of Child Health, a consultant immunologist at
the hospital who led the treatment.451 This involved taking T-cells—a cen-
tral component of the immune system—from a donor, and using TALENs
to engineer the cells in order to prevent them from attacking the baby’s own
cells and becoming resistant to the chemotherapy drugs, and also to give
them the capacity to attack the leukaemic cells. Renier Brentjens of the
Memorial Sloan Kettering Cancer Center in New York explained why this
latter modification was important. ‘Your own T-cells won’t recognize your
tumor cells,’ he said. ‘They think the tumor cell is, in fact, a normal cell. You
need to re-educate these T-cells.’450 At first nothing seemed to be happening,
but after two weeks a rash appeared, showing the engineered cells were
having an effect. Two months later, Layla was completely clear of the cancer,
which allowed the doctors to give her a second bone marrow transplant to
replace her entire blood and immune system. After three months she was
well enough to go home.
Waseem Qasim believes the approach could have much wider applica-
tion for other types of childhood leukaemia. ‘We have only used this treat-
ment on one very strong little girl, and we have to be cautious about claiming
this will be a suitable treatment option for all children,’ he said. ‘But this is a
landmark in the use of new gene engineering technology and the effects for
this child have been staggering.’451 Other experts have cautiously welcomed
the news. ‘This is a very exciting first effort and the authors imply that they
are taking this to wider trial,’ said Stephan Grupp of the University of
Pennsylvania. ‘More patients treated will give us a better idea of what the
true impact these genetically engineered T cells will have on leukaemia.’450
What does seem likely is that this is probably only the first of many such
interventions.
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If genome editing has such potential for treating cancer, what about other
common human disorders, like diabetes, heart disease, stroke, or mental
conditions like schizophrenia, bipolar disorder, or depression? The main
difficulty is that, in spite of initial hopes following completion of the Human
Genome Project that we would soon identify clear genetic differences
underlying such conditions, the reality has proved to be rather more com-
plex, as we saw in Chapter 5.452 To reiterate, there is currently a major debate
about whether such disorders are due to many common genetic differences,
each with a small effect, or a few rare ones with large effects in specific indi-
viduals. However, a 2015 review of the genetic basis of mental disorder con-
cluded that, ‘in bipolar disorder and schizophrenia, increasing evidence
supports the role of rare, disease-causing mutations in brain-expressed
genes’.453 Working out the role of these mutations is complicated by the fact
that, unlike Mendelian disorders, which tend to be due to mutations that
affect the amino acid sequence of a gene’s protein product, most mutations
associated with common disorders are located in the regulatory elements
that control the gene’s expression.454
This may explain why mental disorders like schizophrenia don’t appear
to follow a Mendelian pattern of inheritance, because the effects of muta-
tions in regulatory elements (of which there are often many for each gene,
all playing a contributing role to its expression) are likely to have much
more subtle effects on a gene than those that change its protein-coding
sequence.454 Such a mutation may mean that an individual is more suscep-
tible to schizophrenia, but only if certain environmental triggers are also
present. For instance, one recent study found that possession of a mutation
that affects expression of protein kinase B alpha (PKB), a gene involved in
several important processes in the brain, increases a person’s risk of schizo-
phrenia, but only if the individual also takes cannabis as a teenager.455
Findings like these help to explain previous observations of a link between
this disorder and cannabis use, but also why most young people who take
this drug do not succumb to schizophrenia.456
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The success of anti-HIV drugs means that infection with the virus no
longer constitutes a death sentence. People diagnosed sufficiently early and
who take a cocktail of such drugs can now expect to live long and fruitful
lives.462 The continuing large number of deaths from AIDS worldwide,
which totalled 1.5 million in 2013,459 is mainly due to lack of access to these
drugs, and general poverty and lack of proper health care in the developing
countries in which most such deaths occur. Yet, despite the success of cur-
rent anti-HIV drugs, the search continues for more effective treatments for
a number of reasons. One is that although they keep HIV in check, and
thereby prevent its destructive effects on the immune system, such drugs do
not eradicate the virus from the body.461 In part this is because retroviruses
such as HIV integrate their genomes into those of the host cells they infect,
as we saw in Chapter 2. If an infected person stops drug treatment, the inte-
grated virus can become reactivated, which means that, currently, people
with HIV need to continue taking the drug cocktail for the rest of their lives,
which is both expensive from a health provision point of view, but also cre-
ates the risk of development of drug resistance and toxic side effects.463
Genome editing offers new possibilities for the treatment of HIV infec-
tion in a number of important ways. One is to make an infected person
resistant to the virus by genetically modifying the cells of the immune
system that HIV normally infects. This strategy seeks to mimic a genetic
difference found naturally in certain rare human individuals who are resist-
ant to HIV. Such individuals have been identified by the fact that although
they have repeatedly come into contact with the virus, for instance as pros-
titutes or drug abusers who have shared needles, they have nevertheless re-
mained free of HIV infection.464 And studies have shown that a key way in
which such natural immunity occurs in these individuals is through loss of
function of the C-C chemokine receptor 5 (CCR5) gene, which normally acts
as a cooperative partner, or co-receptor, to the cluster of differentiation 4
(CD4) receptor that exists on white blood cells.
HIV normally uses the CCR5 and CD4 proteins as a molecular gateway to
gain entry into the immune system’s T-cells (see Figure 25). In the rare indi-
viduals who don’t produce a functional CCR5 protein, the virus can’t do this
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Receptor
HIV
(CD4)
Co-receptor
(CCR5)
CD4
HIV cannot infect cells
that lack CCR5
as in the case
of resistant people
and fails to infect their T-cells or compromise their immune system, which
then promptly eliminates the virus. Remarkably, clinicians in Berlin showed
that bone marrow from someone with natural resistance to HIV, if trans-
planted into an infected person, can cure them of the disease. Or at least this
appears to be the case for one individual, Timothy Ray Brown, a man in-
fected with HIV and treated this way in 2008, who has reportedly been free
of the virus ever since.465 Brown was lucky in that the MHC proteins on his
tissues, whose role in transplant rejection we noted in Chapter 5, matched
those of the donor. Unfortunately, this isn’t the case for most HIV sufferers,
but a study carried out in November 2014 suggested that deleting CCR5
from an infected person’s T-cells could eliminate HIV and cure them of
AIDS.465
The study, led by Chad Cowan and Derrick Rossi at Harvard University,
used CRISPR/CAS9 genome editing to knock out CCR5 in human bone
marrow cells grown in culture. The cells were then treated with a chemical
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cocktail that induced them to turn into T-cells. ‘We showed that you can
knock out CCR5 very efficaciously . . . that the cells are still functional, and
we did very, very deep sequencing analysis to show that there were no un-
wanted mutations, so it appears to be safe,’ said Cowan.465 This suggests that
it may be possible to take an infected person’s bone marrow cells, use
genome editing to knock out CCR5, and then introduce the modified cells
back into the patient, where hopefully they will eradicate HIV from the
body. The next step is to test this strategy in an animal model. ‘There are
excellent mouse models you can give a human immune system and then
infect with HIV,’ said Cowan. ‘We can give our cells to the mice and see if
they’re protected from HIV.’465
In fact, genome editing of CCR5 using ZFNs is already being employed in
human patients. In March 2014, Sangamo BioSciences, a company based in
Richmond, California, published results from a clinical trial that used this
approach to treat cells from 12 people infected with the virus.466 After tar-
geting CCR5 in patients’ T-cells, the treated cells were introduced back into
the patients. The results were positive—at the time of the announcement,
half the participants were able to stop taking their anti-retroviral drugs—
and Sangamo reported that it has treated over 70 patients using this
approach.466
Targeting CCR5 is one way in which genome editing may be used to treat
HIV; an alternative is to disable the virus itself. A number of studies have
shown that CRISPR/CAS9 can be used to excise the integrated viral DNA
from the genomes of infected cells. For instance, in July 2014, Kamel Khalili
and his team at Temple University in Philadelphia showed that they could
use this approach to completely remove the HIV genome from several
human cell lines, including one derived from T-cells of the immune system.
‘We were extremely happy with the outcome,’ said Khalili. ‘It was a little bit
mind-boggling how this system really can identify a single copy of the virus
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in the HCV RNA genome, but, instead of cutting the RNA, it creates a road-
block that prevents the viral genome from being replicated by its RNA-
dependent RNA polymerase. Weiss, Grakoui, and their colleagues found
that after introducing the modified CAS9 and its guide RNA into human
liver cells in culture, the cells became resistant to infection by HCV.471 The
researchers believe this approach might eventually be used to treat chronic
HCV infection. And given that other non-retroviral RNA viruses like ’flu or
Ebola also have an RNA genome, this strategy may have much wider applic-
ability. Currently, one clinical approach being developed to combat Ebola
involves the use of RNA interference or RNAi, the technology mentioned in
Chapter 4. But according to Weiss, viruses can develop mechanisms to
thwart RNAi. ‘Since Cas9 [sic] is a bacterial protein and eukaryotic viruses
have likely not encountered it, they would not have ways to evade Cas9,’ he
said. ‘Thus, Cas9 could be effective in inhibiting viruses when the RNAi
system cannot.’472
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that confers resistance in one bacterium can spread rapidly through a bac-
terial population if such resistance allows survival. Even if the mutation
only occurs in one in a million cells, the fact that bacteria can reproduce
themselves in less than half an hour makes the spread of resistance a real
problem. In addition, bacteria can swap antibiotic resistance genes through
a process named horizontal gene transfer. Most dangerous of all, bacteria
can develop resistance to multiple antibiotics.473
Another negative feature of antibiotics is that, since they affect all bac-
teria, they can adversely affect those that live in our guts and other parts of
our body. This would not be a problem if such bacteria were just useless
parasites, but this is far from the case. An increasing number of studies
show that many bacteria in our bodies have a beneficial role. A study by
Andrés Moya of the University of Valencia on the effects of antibiotic treat-
ment in human patients found that their ‘gut bacteria present a lower cap-
acity to produce proteins, as well as deficiencies in key activities, during and
after the treatment’.474 Specifically, the study suggested that, after the treat-
ment, the bacteria showed less capacity to absorb iron, digest certain foods,
and produce essential molecules for the patient. Findings like these imply
that excessive antibiotic use can lead to health problems, such as those
associated with digestion.
Genome editing offers a way to target harmful bacteria without affecting
the beneficial ones that help keep us healthy. With its precision, the tech-
nique can be used to target one bacterial species while leaving others un-
harmed. A challenge here, as with targeting of human cells, is to get the
genome-editing tools into their bacterial target. Here, viruses may provide a
solution. We saw in Chapter 2 how, just as viruses can infect our cells and
cause disease, so bacteria have their own viral problem to deal with, namely
viruses called bacteriophage, or phage for short. Indeed, the CRISPR/CAS9
process evolved precisely to combat infection by such viruses. And just as
disabled retroviruses have been used to introduce gene constructs into
human cells, so there is now the possibility of engineering phage to carry
gene-editing tools into a target bacterium (see Plate 3). Chase Beisel and col-
leagues at North Carolina State University showed that this approach could
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50% chance of passing mutant gene Mutant gene pool does not increase
in the population of mosquitoes
Mutant/ Wild-type
gene drive Gene-drive inheritance
cut repair
CRISPR/Cas9
100% chance of passing mutant gene Mutant gene pool increases exponentially
via mutation chain reaction in the population of mosquitoes
falciparum. And tests showed that the modified mosquitoes passed on the
gene to 99.5 per cent of their offspring. James believes the ‘technology could
have a major role in sustaining malaria control and elimination as part of
the eradication agenda’.478
A type of gene drive called a ‘crash drive’ can even dramatically reduce
numbers of a malarial mosquito species. In December 2015, Andrea Crisanti
and Tony Nolan at Imperial College London reported their development of
mosquitoes with gene drives that disrupt three genes for female fertility,
each of which acts at a different stage of egg formation.479 Since the female
mosquitoes are infertile only when a copy is inherited from both parents,
the gene drives would have to be spread throughout a population before
having an effect. ‘The field has been trying to tackle malaria for more than
100 years,’ said Crisanti. ‘If successful, this technology has the potential to
substantially reduce the transmission of malaria.’479
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But not everyone is happy about the pace of this type of research. A letter,
published in August 2015 in Science by teams in Britain, the USA, Australia,
and Japan, stated that while gene drives might save lives and bring other
benefits, the accidental release of modified organisms ‘could have unpre-
dictable ecological consequences’.478 Another fear is that a gene altered in
mosquitoes to dramatically reduce their population numbers might some
how be transferred into another insect species. What if it jumped, say, into
honey bees, whose populations in the wild are already declining? If this
happened, farmers might have a hard time pollinating their crops and the
world could face food shortages. For this reason, Kevin Esvelt of Harvard
University, who is also researching gene drives to eradicate malaria, has
called for a wider debate involving scientists, policymakers, and the public
about the pros and cons of the strategy. ‘There is no societal precedent
whatsoever for a widely accessible and inexpensive technology capable of
altering the shared environment,’ he said.480
A Question of Delivery
Such are the possibilities of genome editing for directly treating both the
genetic basis of disease and that caused by various infectious agents. Yet
some major obstacles remain. One is that the efficiency and accuracy of the
technology still needs to be improved considerably before it can be applied
routinely to living human beings. However, such is the speed of develop-
ment of the technology that it’s quite likely that such problems will eventu-
ally be ironed out. A more fundamental obstacle is getting the genome-ed-
iting tools into the cells of the tissues or organs to be treated.481 This has
been a major challenge for previous attempts at gene therapy. A central
problem is that cells are enclosed by a protective membrane that acts as a
barrier to large molecules like proteins, or nucleic acids like DNA and RNA.
An additional obstacle is delivering genome-editing tools to the tissue of
interest without their being degraded in the process by the body’s natural
defence mechanisms.
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In fact, there is another way to modify the genome of the next generation
besides genetic engineering of the fertilized egg or embryo, and that is to
target the sperm or egg, or alternatively the stem cells that give rise to these
in the testicles or ovary. Showing that it’s possible to use genome editing to
target the latter, Kent Hamra and colleagues at the University of Texas
Southwestern cultured rat testicular stem cells and then used CRISPR/
CAS9 to knock out certain selected genes in them.489 The GM stem cells
were then reintroduced into the testicles of rats, whose own stem cells had
been destroyed by chemotherapy. After allowing the transplanted stem
cells to produce sperm in the host testicles, the rats were then mated with
females. What Hamra and his colleagues found was that the resultant off-
spring had been genetically modified in a single step.
Such findings are likely to be of future importance for biomedical science
for a number of reasons. One is that although Hamra’s team followed quite
a complicated route to modify testicular stem cells—which involved isola-
tion and culture of such cells and transplantation into a host testicle—their
findings suggest that it might be possible to carry out genome editing on
the stem cells of the intact testicles. If so, this could greatly simplify not only
production of GM versions of rodents but also of other mammalian spe-
cies; such treated animals could simply be mated to females to produce GM
offspring.
Such an approach in human beings might be used to treat certain types
of male infertility, particularly those in which a genetic defect prevents the
testicular stem cells giving rise to sperm.490 Currently this type of infertility
is untreatable, for although IVF can be used to treat patients whose sperm
are immobile or cannot bind or fuse with the egg, it cannot be employed if
no sperm are produced at all. Of course, any use of genome editing in this
manner would be controversial, since, while curing infertility, it would also
result in the modification of the genome not only in that individual but in
future generations. Nevertheless, a case might be made that, if such an ap-
proach could be carried out effectively and safely, it should be considered as
a way to allow infertile couples to conceive.
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8
Regenerating Life
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The other human tissue that most lends itself to transplantation is the
bone marrow. This tissue produces our blood cells—both the red cells that
carry oxygen around the body and remove waste carbon dioxide, and the
white cells that constitute our immune system. The first person to recog-
nize the potential of bone marrow transplantation to treat leukaemia and
other blood cancers was E. Donnall Thomas of the Fred Hutchinson Cancer
Research Center in Seattle.495 In the 1960s, Thomas and his team began
developing ways to use radiation and chemotherapy to destroy a cancer pa-
tient’s diseased bone marrow and then replace it with new marrow from a
healthy donor. Owing to this technique, some leukaemias that were once a
death sentence now have cure rates of up to 90 per cent. Bone marrow
transplantation has also been used to successfully treat non-malignant
blood disorders, such as sickle cell anaemia, when an appropriate donor
can be found.496 In recognition of his achievements, Thomas was awarded a
Nobel Prize in 1990.
We now recognize that the capacity of skin to regrow when grafted to
another part of the body, or transplanted bone marrow to regenerate a whole
new blood system, is due to a special type of cell—the stem cell.497 These
cells are distinguished from normal cells by their ability to divide indefin-
itely and capacity to give rise to more specialized cell types. Stem cells are a
reflection of the fact that we all start life as a single cell—the fertilized egg.
By the process of embryo development, this single cell will eventually develop
into a human being composed of almost 4 trillion cells. These cells can be
distinguished by their specific properties, there being over 200 cell types in
a human being.498 Cell types are distinguished by shape, size, and functional
properties, but ultimately this reflects the fact that, while all have the same
genome, the extent to which different genes are turned on or off varies.
In the very early embryo, all cells can give rise to any cell in the body—
so-called ‘pluripotency’.499 We know this because, as we saw in Chapter 2,
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isolation of such cells from an early mouse embryo provides us with ES cells
which, when injected into another mouse embryo, can give rise to any cell
type in the body, including the eggs and sperm. Following Martin Evans’
discovery of such ES cells, which allowed the production of knockout and
knockin mice, there was a concerted effort to identify ES cells in other
mammalian species. As we saw, this effort has been unsuccessful, except
recently in another rodent species, rats. Yet, as we also noted, there is one
other mammalian species in which ES cells have been isolated besides these
two rodent ones, and that is our own.
James Thomson and colleagues at the University of Wisconsin first achieved
this feat in 1998, using ‘spare’ early embryos donated by IVF patients.500
Thomson’s team generated five immortalized ES cell lines from these em-
bryos; subsequent work by other researchers has isolated hundreds more. For
obvious ethical reasons, it’s impossible to carry out the ultimate test of human
ES cell pluripotency—to inject them into an early human embryo, implant
this into a woman, and see whether the ES cells give rise to all the different
human cell types in a resulting chimaera human being. However, human ES
cells have all the expected properties of such cells. For instance, they form
the teratomas mentioned in Chapter 2 if injected into a mouse, which is also
a key property of mouse ES cells. Most importantly for therapeutic pur-
poses, human ES cells can give rise to different specialized human cell types
in culture, if exposed to chemical agents that induce this change. The reason
is that this process mimics events that take place in the embryo.
During normal embryo development, stem cells give rise to more spe-
cialized cell types through a process called differentiation.501 This process,
which produces all the different human cell types and the tissues and organs
that contain them, is triggered by growth factors, hormones, and other
chemical messengers that bind to receptors on the surface of the stem cell.
When these receptors are activated, they send signals to the cell nucleus.
These signals activate regulatory factors that switch some genes on or
others off, in a specific pattern. As a result, proteins specific to a particular
cell type are produced. That is why one cell becomes a beating heart cell,
while another becomes a neuron that relays electrical impulses in the brain.
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‘We do have some successes we are very excited about,’ said Anderson. ‘The
bottom line is we have reason to believe it is possible to use Doug’s cells in
our devices and cure diabetes in animals.’508 An alternative strategy would
be to genetically modify surface proteins on the beta cells so they are no
longer recognized by the immune system. And here genome editing could
be important, by making it possible to precisely alter the characteristics of
ES cells or differentiated cells derived from them.
While the pluripotent properties of human ES cells have led to great
excitement about their therapeutic potential, development and use of these
cells has its problems. For a start, there are ethical concerns about the der-
ivation of these cells from human embryos. For people who believe an early
human embryo has the same rights as a human child or adult, use of such
cells is tantamount to murder. Such a viewpoint had a significant impact on
public funding for ES cell research in the USA under President George
Bush.509 During this period, all federal funding for such research was with-
drawn, and only private funds and initiatives like the California Institute
for Regenerative Medicine allowed cutting-edge ES cell work to proceed.
In Germany, use of embryos for research is restricted by the 1991 Embryo
Protection Act, which makes the derivation of ES cell lines a criminal
offence.510
Ethical concerns are not the only obstacle faced by scientists seeking to
develop ES cells for therapeutic purposes. In Chapter 5, I mentioned how
the transplantation of tissues or organs from one human to another usually
leads to rejection of the transplanted tissue or organ because of differences
in the MHC proteins between the two individuals. The mismatch is detected
by the immune system, which then attacks the transplanted tissue or organ
as foreign. Because of this, people requiring a new liver, heart, or kidney
must be precisely matched with a donor who happens to share a similar
MHC profile. MHC mismatch is also a problem for those seeking to use cells
derived from ES cells therapeutically.511 Since they are originally derived
from human embryos of a particular genetic make-up, ES cells also have a
specific MHC profile, so again a precise match is needed.
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One solution to this problem came from the discovery that it was possible
to clone mammals. In 1996, the birth of Dolly the sheep, the first mammal
cloned from a differentiated adult cell, shattered the dogma that once a cell
becomes differentiated it no longer has the potential to give rise to other
cell types. Keith Campbell, Ian Wilmut, and their colleagues at the Roslin
Institute took an udder cell from a sheep, removed its nucleus, and trans-
planted the nucleus into a sheep egg whose own nucleus had been removed.
They showed that when a differentiated cell genome is exposed to the envir-
onment of the egg cytoplasm it can be ‘reprogrammed’ to develop into a
whole new organism.512 In fact, Dolly the sheep was not the first demonstra-
tion of cloning. In the 1960s, John Gurdon at Oxford University produced
cloned frogs from differentiated frog cell nuclei in exactly this manner.513
However, failure to reproduce this finding in mice led to the idea that this
was a peculiarity of amphibians. So Dolly’s birth came as a revelation and
also acted as a major stimulus to exploring the phenomenon of cloning and
pluripotency in greater detail.
The birth of Dolly, and subsequent success in cloning other mammalian
species including mice, raised the question of whether it would be possible
to clone a human being. Since cloning is an inefficient procedure, with
many cloned embryos failing to develop and those that do having various
defects, on safety grounds alone it would be highly inadvisable to try to
clone a person, never mind the many ethical issues. However, a cloned
human embryo could be a valuable source of ES cells, and ultimately of tis-
sues used for therapeutic purposes.514 So someone requiring a replacement
tissue or organ could supply a differentiated cell, say a skin cell, whose nu-
cleus would be removed and implanted into a human egg to create a cloned
embryo. This could then be used to create ES cells, and ultimately tissues or
organs for transplantation. And since these would be genetically identical
to the person requiring the transplant, they would not be rejected. Cloned
ES cells could also be important for investigating the molecular basis of
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paper cannot be some error from a simple mistake, but can only be seen as
ad eliberate fabrication to make it look like 11 stem-cell lines using results
from just two’.517 In 2009, Hwang was ‘convicted of fabricating data, misus-
ing research funds, and trading illegally in human eggs’ and received a two-
year suspended prison term, although he never went to jail. Looking back at
the incident in 2014, Hwang said: ‘I created an illusion and made it look as if
it were real. I was drunk in the bubble I created.’517
The exposure of Hwang’s fabrication of data led some people to wonder
whether it would ever be possible to clone human embryos to provide a
source of ES cells, and a lack of positive results in this direction seemed in
line with such a conclusion. But in May 2013, Shoukhrat Mitalipov and col-
leagues at the Oregon Health and Science University produced cloned
human ES cells from foetal skin cells and cells taken from an 8-month-old
baby with a rare metabolic disorder called Leigh syndrome.519 Mitalipov’s
team succeeded where others had failed by pre-testing a variety of different
procedures in studies of cloning in monkeys. The researchers also carried
out tests to prove that their cloned ES cells could form various cell types,
including heart cells that were able to contract spontaneously.
Mitalipov’s success still left open the question of whether ES cells could
be cloned from an adult human being. This was demonstrated in April 2014
by Young Gie Chung and Dong Ryul Lee and colleagues at the CHA
University in Seoul, and independently by Dieter Egli and his team at the
New York Stem Cell Foundation Research Institute. In the first study, the
cloned ES cells were generated using nuclei from two healthy men, aged 35
and 75, while, in the second, they were cloned from a 32-year-old woman
with type 1 diabetes.520 In this second case the researchers also succeeded in
differentiating these ES cells into insulin-producing cells.
Ironically, the news that it had finally proved possible to create human ES
cells from embryos cloned from adult humans generated far less excitement
than the original claim made by WooSuk Hwang a decade earlier. The
reason was that, in the intervening decade, alternative routes had emerged
for the generation of pluripotent cells. One such route, mentioned in
Chapter 7, was identified by scientists studying the stem cells in testicles that
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normally give rise to sperm. These studies showed that, with the right com-
bination of growth factors and hormones, such cells could differentiate into
many different cell types. A study led by Martin Dym of Georgetown
University Medical Center in Washington DC in 2009 showed that human
testicular stem cells could be induced to differentiate into cell types like
those of the pancreas, heart, or brain. ‘Given these advances, and with fur-
ther validation, it is possible that in the not-too-distant-future, men could
be cured of disease with a biopsy of their own testes,’ said Dym.521 This dis-
covery suggested that the stem cells that give rise to the eggs and sperm
were not as different from ES cells as had been supposed. In fact, other find-
ings were already challenging the unique status of ES cells in an even more
dramatic fashion.
Reprogramming Revolution
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Different types of
differentiated cells
types. This discovery led to Yamanaka being awarded a Nobel Prize with
John Gurdon in 2012.523 Yamanaka expressed the inducing genes using
retroviral constructs. This poses safety issues for the use of iPS cells for
therapeutic purposes, since, as we saw in Chapter 2, expression of genes
using such a viral route can lead to cancer. However, it has since proved pos-
sible to create iPS cells by introducing the transcription factors as proteins
that can enter the cell thanks to special tags which allow them to gain entry
across the cell’s surface membrane.524
Indeed, for a brief period after the publication of two papers in Nature in
January 2014, it seemed that generating iPS cells might be almost trivial.525
The studies, by Haruko Obokata of the RIKEN Centre for Developmental
Biology in Kobe, Japan, brought the 30-year-old researcher to international
prominence. For what Obokata claimed to have discovered was that mouse
skin cells only needed to be exposed to a weak citric acid solution for half an
hour, or alternatively simply squeezed, and, amazingly, after this treatment
they were transformed into iPS cells. Or rather STAP cells, for Obokata
coined her own acronym, standing for ‘stimulus-triggered acquisition of
pluripotency’, to describe her creation.525 The discovery seemed to have
wider relevance than simply providing an easier way of generating iPS cells,
because, as Obokata pointed out, the STAP mechanism might shed light on
the way cells gather wear and tear during our lifetimes. ‘By studying the
mechanism we might be able to learn more about how the age of cells is also
locked in,’ she said.525 Commentating on the study, Dusko Ilic, a stem-cell
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period, neither Obokata herself, nor any other researcher, has reproduced
her findings.
The scandal surrounding STAP cells should not detract from the very
real existence of bona fide iPS cells, for these have now been reproducibly
generated in thousands of laboratories across the world. And compared to
ES cells, iPS cells have many potential advantages. One is that there are far
fewer ethical concerns about them, because they are not derived from a
human embryo. And since these cells can be generated from differentiated
cells from any human individual, this means it should be possible to gen-
erate tissues or organs from iPS cells from an individual and use them to
treat the same individual. In addition, the relative ease with which it’s pos-
sible to generate iPS cells, compared to the complicated cloning and ES cell
derivation procedures, is one factor underlying the current excitement
about these cells and their research and therapeutic potential. This also dis-
tinguishes them from testicular stem cells, which can only be obtained via a
testicular biopsy, which carries its own risks and is obviously only possible
in men. Both ES cells and iPS cells can give rise to therapeutically important
cell types. We’ve seen in the section ‘A Very Gifted Cell’ how Doug Melton
and his colleagues have identified a way to generate many pancreatic beta
cells from human ES cells. Melton also found that he could produce such
beta cells from human iPS cells.527
Will it ever be possible to grow whole organs in culture using either ES or
iPS cells? One potential problem is that an organ is a complicated structure,
often consisting of multiple cell types and blood vessels assembled in a pre-
cise fashion. But some exciting progress has recently been made. In July
2013, Takanori Takebe and colleagues at Yokohama City University created
‘mini-livers’ from iPS cells.528 Takebe’s team used iPS cells to make three cell
types that normally combine to form the developing liver in a human
embryo—hepatic endoderm cells, mesenchymal stem cells, and endothe-
lial cells. When mixed together, the three cell types not only divided in cul-
ture but also organized themselves into 3D liver ‘buds’, complete with blood
vessels. Transplanted into a mouse whose immune system had been engin-
eered not to reject human tissues, the human liver buds matured, the human
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blood vessels connected to the mouse host’s blood vessels, and the liver
buds began performing many functions of the mature organ, like metabol-
izing sugars and drugs. When the mouse’s own liver was disabled, the
human liver buds kept the animal alive for two months. The researchers
claimed ‘this is the first report demonstrating the generation of a functional
human organ from pluripotent stem cells’.528 Malcolm Allison, a stem-cell
expert at Queen Mary University of London, believes the study’s findings
offer ‘the distinct possibility of being able to create mini-livers from the
skin cells of a patient dying of liver failure, and when transplanted would
not be subjected to immune rejection as happens with conventional liver
transplants today’.529
Self-Organizing Organs
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intestine, which is why people with this disorder also have problems with
digestion. Clevers’ team take rectal biopsies from people with cystic fibro-
sis, use the cells to create personalized gut organoids, and then apply a
potential drug. If the treatment opens the ion channels, then water can flow
inwards and the gut organoids swell up. ‘It’s a black-and-white assay,’ said
Clevers, and one that is much quicker, cheaper, and safer as a first resort
than trying drugs in people.530 This approach has already been used to
assess the effectiveness of a drug called ivacaftor, also known as Kalydeco®
and five other cystic-fibrosis drugs in about a hundred patients; at least two
are now taking Kalydeco® as a result.
Clevers and his colleagues are also using organoid culture to test therap-
ies for treating cancer. They have grown gut organoids from cells extracted
from colorectal tumours and, with David Tuveson, a cancer researcher at
Cold Spring Harbor Laboratory in New York, they have also generated pan-
creas organoids using biopsies taken from people with pancreatic cancer.
In both cases, the organoids are now being used to identify drugs that work
best on particular tumours. ‘What patients are looking for is a logical ap-
proach to their cancer,’ said Tuveson. ‘I’m very excited about what we’re
learning.’530
Undoubtedly the biggest challenge for those seeking to grow organs in
culture is the brain. As we mentioned in Chapter 3, the human brain is the
most complex structure in our bodies, indeed in the known universe (alien
brains may be more complex!). It may be asking a lot to grow a whole
human brain in culture. Still, Jürgen Knoblich and his colleagues at the
Institute of Molecular Biotechnology in Vienna have recently had some suc-
cess in growing formations of cells that mimic some of the brain’s regions.
Knoblich’s team created iPS cells from human skin and cultured these with
growth factors and other chemicals identified as being important for brain
development. The iPS cells first differentiated into neuroectoderm, the layer
of cells that eventually gives rise to the embryo’s nervous system. This was
then suspended in a gel scaffold to help it develop into 3D structures.
Remarkably, in less than a month, the stem cells developed into tiny orga-
noids corresponding to most of the regions of the brain. ‘If you zoom out
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and look at the whole, it’s not a brain,’ said Knoblich. ‘But our cultures con-
tain individual brain regions that have a functional relationship with one
another.’531 Besides parts of cortex, which normally forms the outer layer of
the brain, the structures also contained regions of forebrain, which makes
neurons that connect to the cortex, and the choroid plexus, which gener-
ates the spinal fluid (see Plate 4).
Such organoids are useful for studying human brain disorders. People
with a condition called microcephaly are born with a head that is much
smaller than normal. Most children with microcephaly also have a small
brain and intellectual disability. Knoblich and his colleagues created iPS
cells from an individual with this condition and used them to create brain
organoids.531 During the initial stages of brain development, stem cells go
through a phase in which they divide to make more stem cells, increasing
their numbers. After a certain period, some of these cells switch to produ-
cing neurons. Knoblich’s team found that the period of stem-cell multipli-
cation was reduced in the case of the microcephalic iPS cells. This suggests
that one cause of microcephaly is that there aren’t enough stem cells avail-
able to turn into neurons, leading to a smaller brain. The researchers also
found that the reduced number of neurons in the microcephalic brain
structures was associated with lack of a protein called centrosomin, which
is known to play an important role as a regulator of neuronal growth.532
When Knoblich’s team added this protein to the microcephalic organoids,
the number of neurons increased.531 So one way to treat this condition
might be to enhance expression of this protein in the brain.
In October 2015, Rene Anand of Ohio State University announced at a
conference that he had made a major breakthrough in the creation of brain
organoids by growing structures from human iPS cells that included 98 per
cent of the cells that exist in the brain of a 5-week human foetus. Amazingly,
the mini-brains contained a spinal cord and even a retina. Anand claimed
his team’s work is different from previous studies, because ‘our organoids
have most of the brain parts’.533 This is important, he added, because ‘if you
want to study Parkinson’s, you need the midbrain. The best I can tell from
all published research on organoids is they don’t have the midbrain. We
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have midbrains and we are already moving toward trying to study them.’533
Anand believes the development of the organoids may be pushed even fur-
ther. ‘If we let it go to 16 or 20 weeks that might complete it, filling in that 1%
of missing genes,’ he said.533
Reactions by other scientists to Anand’s claims have been mixed. Zameel
Cader, a neurologist at the John Radcliffe Hospital in Oxford, said that al-
though the work sounds very exciting, ‘when someone makes such an extra
ordinary claim as this, you have to be cautious until they are willing to reveal
their data’.534 However, Rudolph Tanzi, an Alzheimer’s research pioneer at
Harvard University, said ‘I think it took all of us by surprise. The results
were absolutely astounding . . . it’s an incredible achievement.’533 Creating a
foetal brain that includes so many different types of brain cells amounts to
a ‘quantum leap forward’, he added.533 Anand has said that using this approach
to learn more about Alzheimer’s is a ‘high priority’ for his team. This would
involve taking skin cells from Alzheimer sufferers from which to create iPS
cells, allowing these to differentiate into brain organoids, and then investi-
gating whether differences can be detected with the normal brain in the
development of the organoids in a 3D matrix. These differences might cast
light on the molecular and cellular mechanisms that underlie Alzheimer’s.
One strategy being pursued in such studies is to focus on individuals
with a particularly severe form of Alzheimer’s, which shows early onset,
affecting people in their 30s and 40s. It is hoped that the behaviour of brain
organoids created from such individuals may show more obvious differ-
ences in their growth and development. More generally, the strategy of
focusing on a specific subset of people with a common brain disorder is al-
ready leading to some interesting insights. Flora Vaccarino and colleagues
at Yale University selected autistic patients with enlarged heads, a condition
that affects about a fifth of people with the disorder.535 The researchers then
created brain organoids from these patients and also from the patients’ fa-
thers, who did not have autism. Vaccarino’s team found that genes involved
with directing the proliferation of cells were overexpressed in the autistic
organoids. What’s more, according to Vaccarino, the analysis revealed that
‘the cells of the patients divide faster than the fathers’’.535
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Developing new approaches for getting ES or iPS cells to develop into com-
plex 3D structures is one important aspect of stem-cell technology. An
equally crucial one is the ability to control the differentiation pathway. At
the heart of such control is an understanding of the genetic pathways under-
lying the development of specific cell types, tissues, and organs in the normal
developing embryo. Just as important is having the ability to manipulate
such pathways in a culture dish. And it’s here that a combination of genome
editing and stem-cell technology is proving particularly fertile. In particu-
lar, the flexibility and efficiency of approaches like CRISPR/CAS9 are taking
the genetic manipulation of ES and iPS cells, and the differentiated cells de-
rived from them, to a previously undreamt of level of sophistication.
As I mentioned in Chapter 2, the development of knockout and knockin
mice was made possible by the use of homologous recombination to target
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specific genes in mouse ES cells. However, not only is this approach ineffi-
cient, requiring drug selection to identify the one-in-a-million event in
which it takes place, but for some reason it has never worked well with
human ES cells. In contrast, CRISPR/CAS9 is highly efficient in such cells.
Even more important, an adapted version of this method, developed by Su-
Chun Zhang of the University of Wisconsin, can now be applied at any stage
of differentiation.536 To do this, Zhang’s team developed a version of CRISPR/
CAS9 in which the CAS9 enzyme can only be activated by stimulation with
a specific chemical. This means that human ES cells can be engineered so
that a specific gene is primed to be edited, but this will only happen when the
cells, or their differentiated cell progeny, are treated with the chemical.
With this approach, Zhang’s team can now ‘take out the gene at any given
time, in any type of cell’.536 This is important because shutting a gene off too
soon can kill the stem cell or inhibit its development. And, according to
Zhang, ‘you may want to delete it after the cells have differentiated into
heart, brain or liver cells . . . That precision is one reason I see so much
promise in this technology.’ Zhang now wants to apply his new approach to
the study of brain development. ‘You can very quickly pin down exactly
what [a] gene does, at the stem cell stage, neural stem cell stage or at the dif-
ferentiated neuron stage,’ he said.536
To demonstrate this precision, Zhang’s team engineered human ES cells
so that they could knock out orthodenticle homeobox 2 (OTX2), a gene
known to be involved in formation of the midbrain, at any stage of the dif-
ferentiation of human ES cells into different types of brain structures. During
brain development, the midbrain develops before the forebrain, the site of
higher mental functions. By delaying the knock out of the gene, Zhang and
his colleagues were able to show that the gene is also essential for the forma-
tion of the forebrain. ‘If you knock it out, you simply don’t have the cerebral
cortical cells, and they are essential to what it takes to be human,’ said
Zhang. ‘This is a really definitive way to show what genes are doing.’536
While the combination of stem technology and genome editing prom-
ises to have a major impact on biomedical research, it also has important
implications for the development of new therapies. In particular, genome
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editing provides a new level of genetic precision that looks set to transform
the way stem cells are used to create replacement cells, tissues, and organs.
And the ease with which it’s now possible to generate iPS cells from par-
ticular individuals and use genome editing to alter them, means that this
specific combination may be a powerful new type of disease treatment.
Take for instance a study by Linzhao Cheng and colleagues at Johns
Hopkins University, which demonstrated how CRISPR/CAS9 could be used
to treat the recessive single-gene disorder sickle cell anaemia.537 We’ve come
across the molecular basis of this disorder in previous chapters: it results
from a single amino acid change in the β-globin protein. That alteration
makes the haemoglobin molecules form rope-like cables that cause the red
blood cells that contain them to bend into rigid, sickle shapes. The sickle
cells lodge in narrow capillaries, cutting off local blood supplies and caus-
ing great pain in the affected body parts, especially the hands, feet, and
intestines. The depletion of the red blood cells also causes the overwhelming
fatigue of anaemia. Eventually, this disorder can prove fatal.537
Cheng’s team took blood cells from people suffering from sickle cell
anaemia and induced them to change into iPS cells. They then used CRISPR/
CAS9 to correct the mutation in the β-globin gene that causes the disorder.
Finally, the researchers coaxed the corrected iPS cells to differentiate into
mature red blood cells that did not have the abnormal sickle shape. To
become medically useful, the technique of growing blood cells from stem
cells will need to be much more efficient and scaled up significantly. The
lab-grown stem cells would also need to be tested for safety. But Cheng be-
lieves that ‘this study shows it may be possible in the not-too-distant future
to provide patients with sickle cell disease with an exciting new treatment
option’.538 Cheng’s approach may also be useful for treating other disorders
of the blood.
In Chapter 7 we saw how a virus was used to deliver genome-editing tools
that partially reversed the muscle defects in a mouse model of Duchenne
muscular dystrophy, or DMD, raising the possibility that this approach
might be used to treat boys with this disorder. But a strategy involving
both genome editing and iPS cells might also offer a route to treat DMD in
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guide RNA could create a tool that worked in human lungs as well. ‘It
seemed incredibly scary that you might have students who were working
with such a thing,’ said Doudna.542 In fact, Andrea Ventura of the Memorial
Sloan Kettering Cancer Center in New York, whose postdoc carried out the
work, believes his lab carefully considered the safety implications: the guide
RNAs were designed to target genome regions unique to mice and the virus
was disabled so it could not replicate. However, he agreed that it’s import-
ant to anticipate even remote risks. ‘The guides are not designed to cut the
human genome, but you never know,’ he said. ‘It’s not very likely, but it still
needs to be considered.’542
Similarly, some scientists are urging caution about the need to consider
potential adverse effects of the new technology when used as a therapeutic
strategy. In particular, concerns have been raised about the need to make
sure this technology does not introduce unwanted changes elsewhere in
the genome that have consequences for health. ‘These enzymes will cut in
places other than the places you have designed them to cut, and that has
lots of implications,’ said James Haber, a molecular biologist at Brandeis
University. ‘If you’re going to replace somebody’s sickle-cell gene in a stem
cell, you’re going to be asked, “Well, what other damage might you have
done at other sites in the genome?” ’542 In fact, much work is being done to
eliminate such unwanted ‘off-target’ effects. However, Haber believes the
technology will have to be very precise indeed, since low-frequency events
could potentially be dangerous if they accelerate a cell’s growth and lead to
cancer.
Ironically, the very ease with which CRISPR/CAS9 can be employed
poses challenges in ensuring it’s used responsibly. So Katrine Bosley, CEO
of Editas, a company in Cambridge, Massachusetts, pursuing CRISPR/
CAS9-mediated gene therapy, and a veteran of commercializing new tech-
nologies, said that while the problem in the past has been convincing others
that an approach will work, ‘with CRISPR it’s almost the opposite. There’s
so much excitement and support, but we have to be realistic about what it
takes to get there.’542 And, given the controversy about the use of genome
editing to modify the human germline, that means there are many technical,
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9
Life as a Machine
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region now, you’re more likely to bump into tourists drawn to the alien-
looking landscapes or come to learn about the history of the mines than
actual miners. But these days there’s another type of visitor to the Rio Tinto
too: biologists fascinated by its unusual life forms.545 For this region is also
known for its extremophiles, the name given to microorganisms that live in
the most inhospitable conditions on Earth. Such is the interest in these mi-
croorganisms that the US National Aeronautics and Space Administration
(NASA) has set up a project named the Mars Astrobiology Research and
Technology Experiment, on the basis that, if life exists on Mars, it may have
common features with the life forms that thrive in this region’s iron-rich
soil which has similarities to that on the red planet. Justifying the interest,
Carol Stoker, leader of the project, argues that ‘the Rio Tinto area is an
important analogue to searching for life in liquid water, deep beneath the
subsurface of Mars’.545
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80 ˚C
72
˚ C
˚C
60
94
40 Primers bind to
complementary strands
20
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together. Then the sample is cooled to around 50–60°C, which allows two
‘primers’—short DNA sequences that match those at the start and end of
the region to be amplified—to bind to their complementary sequences in
the two separated strands of the DNA template. Next the temperature is
raised to 72°C, which allows DNA polymerase, the enzyme that replicates
DNA, to synthesize a new strand between the two primers. Finally, the tem-
perature is raised to 94°C and the process begins again. Typically, a PCR
reaction will undergo around 30 such cycles, all in the same plastic tube, on
a device called a thermal cycler that rapidly varies its temperature. However,
an equally crucial aspect of PCR is that the DNA polymerase used is not the
usual variety taken from an E. coli bacterium, since this becomes rapidly
inactive above 37°C, the normal temperature for such bacteria that live in
environments like the human gut. Instead, the polymerase comes from a
heat-resistant bacterial species called Thermus aquaticus that lives in boiling
hot springs at Yellowstone Park.555
PCR involves one very specific use of a protein from a thermophilic bac-
terium, but do extremophiles also have a more general practical importance?
Certainly Peter Golyshin of Bangor University, who studies such life forms,
believes so. ‘Chemical synthesis is often conducted in harsh conditions
with high temperatures, high pressures and high solvent concentrations,’
he said. ‘The anticipation is that enzyme catalysts produced by microbes
that live in hostile environments could be used in these industrial pro-
cesses.’556 Unfortunately, many extremophile microorganisms have proved
difficult to culture in the laboratory using tried and tested microbiology
techniques. This may be because standard culture media—a nutrient-rich
jelly on which bacteria are grown in a lab—does not contain all the other
microbes that live in their natural environment. It seems that extremophile
bacteria rely partly on the metabolic by-products of other microbial species
that thrive in their shared habitat.
According to Golyshin, one way around this problem is ‘instead of trying
to grow the microbes in the usual way we can just harvest their DNA, ex-
press their genes in surrogate hosts such as yeast or E. coli, and apply sub-
strates to see if they actively convert it or not’.556 The greatest diversity of
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One pioneer of this approach is Craig Venter, who led one of the teams that
first sequenced the human genome. Since then, Venter has headed several
biotechnology projects, like the development of genome-edited pigs for
xenotransplantation mentioned in Chapter 5. But one of his primary inter-
ests is synthetic biology. And, in 2010, Venter announced that he and his
colleagues had created the world’s first synthetic life form, following a pro-
ject that cost $40 million and engaged 20 scientists working for more than
a decade.559 Certainly it was an extraordinary feat, for Venter’s team took the
complete genome sequence of an existing bacterium—Mycoplasma my-
coides—and resynthesized it from scratch using lab chemicals. They then
inserted this genome into a bacterial cell whose own genome had been
excised. The researchers finally showed that the artificial genome could
propagate itself and the cell through subsequent generations. As a twist, the
researchers included extra sequences that served as ‘watermarks’, proving
authorship of the new life form.
Opinions vary as to the novelty of the creation. Julian Savulescu, a bio-
ethicist at Oxford University, believes that: ‘Venter is creaking open the most
profound door in humanity’s history, potentially peeking into its destiny . . . He
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is going towards the role of a god: creating artificial life that could never
have existed naturally.’559 Others have been more critical, pointing out that,
to have truly created synthetic life, Venter’s team would need to do more
than just copy an existing natural genome, and instead it would also be
necessary to synthesize the bacterial cell’s wall, membrane, and cytoplas-
mic contents.560
While the criticism that there is more to a bacterium than its genome is a
valid one, it’s important to recognize that Venter and colleagues’ long-term
goal was always about more than artificially synthesizing an existing bac-
terial genome and showing it could be propagated across generations in an-
other bacterium’s vacant shell. This was just supposed to be the first stage in
a plan to strip life down to its bare essentials, so that entirely novel genomic
elements could be added on. Or, as Venter himself put it, ‘once we have a
minimal chassis, we can add anything else to it’.561 Such a minimal genome
needs to be identified before it can be constructed—and in August 2015 a
team led by Bernhard Palsson at the University of California, San Diego, did
precisely that.562
Palsson’s team took various bacterial species with different genomes and
modelled their growth in a wide variety of environments, with different
nutrient requirements. According to the researchers, this ‘forces the cell to
use a wide array of its biochemical pathways. By defining . . . those genes ex-
pressed across all simulation conditions, we select those that are used
regardless of nutrient availability.’562 The end result was a set of genes, reac-
tions, and processes universally required by bacteria. This minimal definition
will be key to creating useful synthetic bacteria in the future, according to
Laurence Yang, a researcher involved in the study, because ‘by defining the
vital set of genes and functions that need to always be present in a cell to
sustain life, we can begin to realize new ways to engineer a cell to optimize
production of a desired product without sacrificing the cell’s health’.562 Of
course, a key question now is identifying which novel elements should be
added to Venter’s ‘minimal chassis’ to provide useful new functions.
It’s not only bacteria that have potential uses for industry and medicine.
Human cells differ from bacteria in that our genomes are contained within
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Biohackers in Hackney
While many people may lack the knowledge or confidence to suggest pos-
sible novel uses for synthetic biology, that may be starting to change if a small
but growing movement of ‘biohackers’ get their way. Although ‘hacker’
now often has negative connotations, signifying someone who sabotages,
or steals information from, the computer of an individual or organization,
the word’s original meaning is someone who tinkers with technology to
make or repurpose things. And biohackers play with biotechnology in their
spare time with the aim of making new life forms as part of a new do-it-
yourself biology (DIYbio) movement.568 Cathal Garvey, a biohacker based in
Dublin, believes that ‘Biohacking, or DIYbio, has got to be one of the most
exciting subcultures active today.’569 The members of this movement pay a
small monthly fee to cover the costs of rent, reagents, and equipment to
maintain a shared lab, which provides affordable access to anyone inter-
ested in biotechnology.568
In 2010 there were only a handful of biohacker groups around the world
but this had grown to over 70 by 2016, with groups in the USA, Europe,
Canada, Australia, South America, and Asia.568 One London biohacker
group is based in a laboratory called Biohackspace, located, appropriately,
in Hackney.570 In March 2015 the UK Health and Safety Executive, or HSE,
registered Biohackspace as ‘GM Centre 3266’—the first laboratory in Britain
that allows anyone to have a go at genetic engineering. Biohackspace has
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about 20 regular members from diverse backgrounds, but few have scien-
tific training.570 Projects at Biohackspace range from generating genetically
modified bacteria to create new forms of art, to modifying brewer’s yeast to
make new ‘craft beers’.
Another biohacker group, BioCurious, is based in Sunnyvale, California.
Like other biohackers, its members are enthused by the possibilities offered
by CRISPR/CAS9 technology, partly for its precision but also because it’s so
quick, cheap, and easy to use, making it ideal for amateur biotechnologists.
One BioCurious member, Johan Sosa, an IT consultant, is already using the
genome-editing technology. ‘Currently we’re creating the guide RNA that
we’re going to use to edit a yeast genome,’ he said.570 One use of the technol-
ogy will be in the ‘Real Vegan Cheese’ project, whose aim is to modify bak-
er’s yeast so that it produces milk proteins.
Although run by amateurs, biohacker groups often seek advice from
professional biologists. For instance, Darren Nesbeth, a synthetic biologist
at University College London, has advised the members of Biohackspace
about health and safety issues. ‘They’ve got a licence now from the HSE to
do genetic modification, which requires they have a safety panel of individ-
uals,’ he said. ‘There’s a framework and guidance there equivalent to what
happens at a university.’570 Despite such safeguards, it’s perhaps not sur-
prising that the biohacker movement has caught the attention of the secur-
ity services. The FBI and US Department of Defense have already been in
touch with the BioCurious group and sent agents to visit their lab. ‘At the
beginning they were coming through quite frequently—at least once a
month, formally,’ said Maria Chavez, director of community for the group.
‘Informally, I’m not sure how many times they may have dropped in.’570
The response from professional scientists has been mixed. David Relman,
a professor of infectious diseases and co-director of Stanford University’s
Center for International Security and Cooperation, said that ‘I do not think
that we want an unregulated, non-overseen community of freelance practi-
tioners of [CRISPR/CAS9] technology.’571 In contrast, Darren Nesbeth be-
lieves that the biohacker movement could help alter the perception that
genetic engineering can only be done by academics in universities. ‘I see it
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218
Life as a M achine
But this could soon be about to change, thanks to attempts to redesign life
in a number of different ways. ‘To make proteins with more than 20 amino
acids—possibly as many as 30 or 40—requires thinking outside of the box
of the standard genetic code,’ said molecular biologist Patrick O’Donoghue
from Western University, Ontario, Canada.574 One such way of thinking
outside the box being pioneered by teams led by George Church at Harvard
University and Farren Isaacs at Yale University involves modifying the
genetic code in such a way that it can be used to produce additional amino
acids.
To achieve this feat, the researchers have manipulated one of the genetic
code’s elements, the so-called ‘stop codon’. In Chapter 2 we mentioned the
fact that which amino acid gets added next in a growing protein chain
is specified by three-letter DNA sequences, called codons (see Figure 29).
However, as well as codons that specify the different amino acids, the
Second letter
U C A G
UUU Phe UCU UAU Tyr UGU Cys U
UUC (F) UCC Ser UAC (Y) UGC (C) C
U
UUA Leu UCA (S) UAA UGA STOP A
STOP
UUG (L) UCG UAG UGG Trp(W) G
CUU CCU CAU His CGU U
CUC Leu CCC Pro CAC (H) CGC C
C Arg
CUA (L) CCA (P) CAA Gin CGA (R) A
Third letter
First letter
G
GUC Val GCC Ala GAC (D) GGC Gly C
GUA (V) GCA (A) GAA Glu GGA (G) A
GUG GCG GAG (E) GGG G
Initiation codon
Chain terminator codon (STOP)
Amino acids shown as three-letter and single-letter abbreviations
Fig. 29. The three-letter genetic code and the corresponding amino acids
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While such studies tamper with the existing genetic code via its codon
usage, an even more radical approach seeks to transform the DNA code
itself. To do this, some scientists have sought to create a menagerie of exotic
letters beyond A, T, C, and G, which can partner up and be copied in similar
ways.577 One such pair is referred to as X-Y, although its true chemical name
is more complex. And this extra X-Y pair has now been used to create ex-
panded versions of nucleic acids called XNAs, the X standing for ‘xeno’. The
development of such XNAs was pioneered by Steven Benner, a biological
chemist at the Foundation for Applied Molecular Evolution in Gainesville,
Florida. Benner first became interested in this issue as a graduate student in
the 1970s. At that time chemists were starting to try to build molecules that
could carry out the same functions as natural enzymes or antibodies with
different chemical structures. But, according to Benner, DNA was largely
ignored. ‘Chemists were looking at every other class of molecule from a
design perspective except the one at the centre of biology,’ he said.577 Even
tually, Benner’s interest led to the development of the first XNAs.
A major challenge has been developing a replicating system that can
reproduce such XNAs.577 While XNA, like DNA and RNA, can be synthe-
sized chemically, this is still a relatively inefficient, error-prone, and costly
process. In a living cell, DNA and RNA are replicated by enzymes called
polymerases, from nucleotides—the units out of which RNA and DNA are
made. Such polymerases do not normally synthesize nucleic acids from
anything other than the A, C, G, and T varieties used to make DNA, or the U
that replaces T in RNA. There is a good reason for this, which is that such
enzymes have evolved to precisely recognize these specific nucleotides and
no others, in order to maximize the accuracy of the nucleic acid copying
process. However, through trial and error, Benner and his colleagues identi-
fied XNAs that could be replicated in a test tube by a DNA polymerase.577
While this work was done outside the cell, Floyd Romesberg and col-
leagues at Synthorx, a biotechnology company linked to the Scripps
Research Institute in San Diego, recently showed that XNA containing the
X-Y addition can be successfully replicated in bacteria over many gener-
ations.578 So aside from curiosity, what is the point of making an organism
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Natural
DNA mRNA Amino acids
T A A
A T U
C G
G
G C
C
G C G
T A U
G C G
A T
A 20 amino acids
T A A from which proteins can be built
4 nucleotides 64 codons
2 base pairs
Expanded
DNA mRNA Amino acids
X Y Y
A T U
C G G
G C C
G C G
T A U
G C G
A T A 172 amino acids
Y X X from which proteins can be built
Fig. 30. Expanding the genetic code with the X-Y base pair
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So artificial amino acids could be added that give proteins unusual proper-
ties, such as the ability to bind to metals—resulting in novel adhesives. Or
enzymes could be developed that are activated only in the presence of other
molecules—which could be useful for drugs. Recoding could also aid bio-
medical research: novel amino acids, such as those carrying a fluorescent
tag, could be inserted and used to track cellular processes.576
The potential usefulness of this approach also goes beyond simply
making an expanded repertoire of proteins. Scientists, like Philipp Holliger
at the MRC Laboratory of Molecular Biology in Cambridge, are interested in
how another form of XNAs—this time with a different chemical backbone
to the one found in normal DNA—might be an important tool in biomedi-
cine.582 Importantly, Holliger and his colleagues recently reported that some
XNAs can form 3D structures and catalyse chemical reactions in the same
way as protein enzymes. Such XNAzymes, as they’ve been named, are able to
cut RNAs. As regulatory RNAs are increasingly known to play important roles
in human health and disease, altering their properties using XNAzymes
might have important therapeutic potential. One advantage of XNAs,
according to Holliger, is that they ‘are chemically extremely robust and, be-
cause they do not occur in nature, they are not recognised by the body’s
natural degrading enzymes. This might make them an attractive candidate
for long-lasting treatments that can disrupt disease-related RNAs.’582
As well as acting as catalysts, there’s also a hope that XNAs might have an
important role to play in the development of nanotechnology, which seeks
to create microscopic devices and structures that could have numerous
applications.582 The creation of such devices from DNA makes use of the
fact that this molecule can be coaxed into a variety of different shapes by
harnessing the same forces that normally hold the double helix together—
the attraction between the letters A and T, or G and C. By matching up the
letters on a long strand of DNA with those on smaller strands of this mol-
ecule, Paul Rothemund of Caltech first showed, in 2006, that the larger
strand could be stapled in place to create 3D shapes that Rothemund called
‘DNA origami’.583 This technology has already led to some useful practical
applications, such as the creation of a DNA origami ruler, which can be
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Bacteria with genomes that have been engineered to contain XNAs or which
have been dramatically modified might have important uses as organisms
in their own right, not just as sources of modified proteins or nucleic acids.
One important application could be the creation of bacteria resistant to
bacteriophages—the viruses that infect bacteria. By recoding the genes of
bacteria used in the industrial production of enzymes, hormones, and food
products, researchers could block infection by such viruses, saving tons of
material that goes to waste from viral contamination.
The reason that changing the genetic code can lead to such resistance
is that viruses replicate by using the host’s own replication machinery
and the raw molecules—the nucleotides and amino acids—that power this.
However, in a bacterium whose genome has been reconfigured so that
the amber stop codon no longer signals the end of a protein, viral genes
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not to whole organisms but to cells in culture. Animal cells cultured in huge
bioreactors play increasingly important roles in industry. For instance,
Chinese hamster ovary (CHO) cells are used by biotech company Genzyme
to produce the drugs imiglucerase, also known as Cerezyme® and agalsi-
dase beta, known as Fabrazyme®, for treatment of the rare genetic disorders
Gaucher disease and Fabry disease, respectively. Recently, the company lost
more than $100 million in sales of these drugs after a viral infection im-
peded the cells’ growth and they had to be completely replaced.581 Thus, the
production of modified CHO cells with an altered genetic code that pre-
vents replication of viruses in such cells could have important implications
for industry.
While the production of cells with modified genomes for cell culture may
be an immediate goal, scientists are also talking about the possibility of
creating whole animals or plants with radically altered genetic codes. The
commercial potential of crops and livestock with a built-in resistance to
infection by any type of virus could make such organisms very attractive to
farmers. And although more ambitious than engineering a bacterium,
genome editing makes such a goal more feasible. Certainly, George Church
believes virus-resistant plants and animals could eventually be created. ‘It’s
more of a challenge but it’s not out of reach,’ he said.581 Indeed, Church be-
lieves that a similar approach might even be used to create virus-resistant
humans.581 If this were the case, then one day we might have the possibility
of creating people with a natural built-in immunity to every virus, ranging
from the common cold and flu, through to lethal viruses such as HIV or
Ebola. Although such a scenario may be scientifically feasible, whether
most people would see it as a welcome development remains to be seen.
And on this note, it’s now time to examine, in the final chapter, exactly how
society should seek to deal with the amazing new technologies described so
far, and what measures we should be discussing to maximize their potential
for human benefit while minimizing the possibility of them being used to
cause harm, either accidentally or deliberately, to our own species and all
the other life forms with which we co-exist on planet Earth.
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I n this book, we have encountered many mutant life forms, whether nat-
urally occurring or produced by treatment with radiation or chemical
mutagens. But this concluding chapter begins with a fictional mutant—
Spiderman—the comic-book superhero. Spiderman was born when a
geeky teenager, Peter Parker, was bitten by a radioactive spider, which
turned him into a mutant superhuman gifted with ‘the agility and propor-
tionate strength of an arachnid’.585 Spiderman’s story aptly illustrates the
fantastical qualities sometimes ascribed to mutants, as well as reflecting the
fears and preoccupations of the Cold War era in which he arose. But a quote
from this superhero seems particularly relevant to this book: that ‘with
great power comes great responsibility’.586
For there seems no doubt that the new technologies described within
these pages—genome editing, optogenetics, stem-cell technology, syn-
thetic biology—provide humanity with unprecedented powers to manipu-
late the natural world, but also pose crucial questions about how such
powers will be used in a responsible fashion. And such is the importance of
this issue that the discussion about how to employ such technologies surely
cannot be left only to scientists but needs active public involvement. At the
same time, the debate is only likely to progress if based on facts and real
possibilities, not fears and misconceptions based on a misunderstanding of
the science underlying these technologies. With this in mind, I’d like to im-
agine some possible future scenarios, as one way of assessing the potential,
and risks, of these new ways to redesign life. Undoubtedly the most difficult
aspect is trying to predict how current discoveries might impact on the future.
For not only do science and technology evolve rapidly, but how society handles
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In the first vision, imagined by Kim Stanley Robinson in his Mars trilogy,
the quest by future colonizers of the red planet for a fair and equal society
requires a bitter revolutionary struggle with echoes of the American War
of Independence.587 Meanwhile, back on Earth, civilization has been rent
apart by the disastrous effects of global warming. So it is rebel scientists
on Mars who develop a form of genome editing that makes it possible to
repair the effects of ageing and thereby grant human beings a greatly ex-
panded lifespan.588 The ability to live to an extreme age is mainly pre-
sented as a liberating new feature of human existence, but Robinson also
explores more negative aspects, such as memory loss, mental instability,
and existential boredom. Further on in the trilogy, manipulation of the
human genome allows people to breathe the thin Martian atmosphere,
which is itself transformed by various means, and as people begin to col-
onize other planets and moons in the solar system besides Mars, they are
artificially adapted to low light levels in these outer reaches. While there is
plenty of social strife in this vision of the future, as well as disagreements
about the extent to which humans should seek to transform the environ-
ments of other planets to make them habitable, genetic engineering is
mainly portrayed in a positive light.
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How likely are either of these future scenarios? Beginning with more posi-
tive possibilities first, to what extent is genome editing really likely to initi-
ate a revolution in medicine? By providing more sophisticated animal
models of human disease, genome editing could help identify new molecu-
lar targets for disease treatment and thereby new drugs. Yet a key question,
if we are ever to see medical advances of the type envisaged by Kim Stanley
Robinson, is how feasible it will be to use genome editing for direct gene
therapy in human beings. Genome editing is likely to have the biggest initial
impact on genetic disorders of the blood, by making it possible to remove
bone marrow, correct a genetic defect in the stem cells that generate the
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various blood cell types, and then replace the treated tissue. But how feas-
ible will it be to treat genetic defects in other parts of the body?
A major challenge will be finding effective ways to get genome-editing
tools into cells within tissues and organs in situ in the body. Viruses are par-
ticularly powerful delivery vehicles since they have evolved highly sophisti-
cated ways of gaining access to the cell but they also carry risks, as we saw
in Chapter 2, when we looked at the use of retroviruses to treat severe com-
bined immune disease (SCID). This treatment was effective, but the inser-
tion of the retrovirus’s genetic material into the host cell genome led to the
activation of an oncogene, and subsequent leukaemia, in some patients in
initial clinical trials. Modified retroviruses have now been developed with
much less chance of disrupting the host cell genome in dangerous ways.591
In addition, there is now a move to develop other types of viruses as deliv-
ery vehicles—like the adenovirus, the agent responsible for the common
cold.592 Unlike retroviruses, this virus does not generally integrate its gen-
etic material into the host genome. While seen as a negative characteristic
for standard transgenic approaches, this is now viewed as an attractive
safety feature, since the adenovirus can deliver genome-editing tools and
exit the cell without causing collateral damage.
Another strategy would be to modify the genome-editing tools them-
selves so they can gain entry to a cell. For instance, the genome-editing
enzyme CAS9 could be tagged with a ‘cell-penetrating peptide’.593 These are
sequences of amino acids found in proteins that have evolved to naturally
cross cell membranes, also known as ‘Trojan horse’ peptides because of
their ability to subvert normal cellular boundaries, just as the Greeks en-
tered Troy in clandestine fashion. The transactivator of transcription (TAT)
peptide of HIV is particularly adept at crossing such membranes thanks to
its particular chemical properties that allow it to penetrate this normally
impervious barrier.593
In October 2011 Gerard Wong and colleagues at the University of
California in Los Angeles showed that TAT interacts with the cell’s ‘cyto-
skeleton’ and specific receptors on the surface of the cell to facilitate its pas-
sage across the cell membrane. ‘Prior to this, people didn’t really know how
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it all worked, but we found that the HIV TAT peptide is really kind of like a
Swiss Army Knife molecule, in that it can interact very strongly with mem-
branes, as well as with the cytoskeletons of cells,’ said Wong.594 By using
such information to improve TAT’s penetrative capacity, and attaching it to
CAS9, the latter may be adapted so that it can penetrate cells in the body as
part of a therapeutic strategy. It may also be possible to introduce CRISPR
guide RNAs into the cell using this approach.
If delivery of genome-editing tools becomes straightforward, this could
mean that single-gene disorders like cystic fibrosis and muscular dystrophy
could finally be treated by directly introducing genome-editing tools into
the lungs and muscles respectively, or ensuring that they reach their specific
destination via the blood through molecular tags that target these organs.
Disorders of the brain like Huntington’s disease might also be treated in this
way, although here an additional obstacle is the ‘blood–brain barrier’, which
protects this vital and sensitive organ from infectious agents. But certain
types of adenovirus can cross this barrier, and these may be commandeered
to direct genome-editing tools to different brain regions.595 In fact, we are al-
ready beginning to see some exciting progress on these fronts, albeit in the
treatment of mouse models of muscular dystrophy and Huntington’s, as we
saw in Chapter 7. And, given that recent studies suggest there are thousands
of single-gene disorders that, while rare in any particular individual, cumu-
latively affect millions of people,596 such strategies may, in the future, have a
huge impact in reducing pain and suffering in the human population.
What about the prospects for treatment of more common diseases like
cancer, diabetes, or mental disorders like schizophrenia? Here a complicat-
ing factor is identifying which genetic differences underlie such conditions
and therefore which might be corrected by gene therapy. For, as we saw in
Chapter 7, the more we learn about the genetics of such disorders, the more
complex the situation appears. Take, for instance, cancer. We’ve already
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Showing the pace of research in this area, Karl Deisseroth has formed a
company to pursue optogenetics trials in human patients.613 The company,
named Circuit Therapeutics, plans to initially focus on the treatment of
chronic pain. Neurons affected by chronic pain are located in and outside
the spinal cord, making them a more accessible target than the brain. ‘In
animal models it works incredibly well,’ said Scott Delp, a neuroscientist at
Stanford, who works closely with Deisseroth.613 Meanwhile, another com-
pany, RetroSense Therapeutics, which is based in Michigan, is soon to begin
human trials of optogenetics to treat a genetic condition that causes blind-
ness, which will involve stimulating neurons in the retina to bypass the
defect.613 In both these cases, the accessibility of the spinal cord and eye
make these logical starting points for therapy, but the fact that Circuit
Therapeutics is also planning to develop treatments for Parkinson’s and
other neurological disorders of the brain suggests that clinical trials in these
areas may not be far behind.613
Would such technological solutions to psychiatric disorders risk detract-
ing from other ways of tackling such disorders that focus on the social causes
of mental illness? This is particularly important given a study that showed a
strong link between economic crisis and stress, anxiety, and depression. The
study, by researchers from Roehampton University in London and the chil-
dren’s charity Elizabeth Finn Care, found that the incidence of depression
jumped between four- and fivefold during the economic crisis of 2009.614
Commenting on the findings in 2010, Steve Field, chairman of the Royal
College of General Practitioners, said: ‘GPs across the country have been
seeing a definite increase in the last year in the number of patients coming to
see them with mental health and physical issues. These appeared to be related
to either losing their job or fearing their job and livelihood are threatened.’614
So even if optogenetics could one day be used to treat depressive people
by triggering ‘happy’ memories, one concern is that, without also tackling
the social factors that trigger depression, we might end up with a situation
similar to Aldous Huxley’s Brave New World. In Huxley’s novel the govern-
ment provides its populace with the drug soma, which subdues all ‘malice
and bad tempers’, thus avoiding any need to discover and potentially tackle
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A different strategy for tackling human disease would involve the replace-
ment of diseased, damaged, or aged tissues with replacement organs. As we
saw in Chapter 5, one source of such replacements might be pig organs
modified by genome editing so they are not rejected by the human host.616
A further alternative, though, would be to use human tissues and organs
developed using stem-cell technology. And the remarkable self-organizing
ability of stem cells in 3D cultures mentioned in Chapter 8 means this is not
such a far-fetched idea as it would once have seemed.617 Clearly, much more
needs to be done if the organoids created so far can be developed into real
replacement organs. None the less, particularly with the precision that can
now be achieved in the manipulation of gene expression in living cells via
genome editing, it’s not implausible to imagine a future in which a person’s
own cells are reprogrammed into pluripotent stem cells and used to gen-
erate replacement organs.617
It is one thing to imagine replacing a heart, pancreas, or liver, but the
brain of someone can’t simply be replaced. For, as Tufts University philoso-
pher Daniel Dennett once put it, a brain transplant would be the one type of
transplant surgery where it would be better ‘to be the donor not the recipi-
ent’.618 However, in a number of different areas of brain study there have
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Ovary
ES cells Artificial PGCs
ES cells
Testicle
are converted into
artificial PGCs
Fig. 31. Use of artificial primordial germ cells to make eggs and sperm
for making human babies (see Figure 31). This could be great news for infer-
tile individuals who fail to produce sperm or eggs in the normal manner, for
instance due to an early menopause, accident or injury, or exposure to
chemicals like the ones used for cancer chemotherapy. And indeed, al-
though the study by Saitou’s team was only in mice, soon after reporting
their findings the lab began getting emails from infertile couples desperate
to have a baby.626
There are still many technical challenges before this approach can even
be considered for clinical application. In their mice studies, Saitou’s team
found that their artificial PGCs only produced offspring at a third of the
rate for normal IVF. In addition, Yi Zhang, who studies epigenetic mechan-
isms at Harvard University, found that PGCs produced using Saitou’s
method do not erase their epigenetic programming as well as naturally
occurring ones. ‘We have to be aware that these are PGC-like cells and not
PGCs,’ he said.626 The difference raises questions about potential health
risks for babies created using this approach, because such epigenetic differ-
ences might lead to adverse effects in later life. In addition, both iPS and ES
cells frequently collect chromosomal abnormalities, genetic mutations,
and epigenetic irregularities during culture. According to Harry Moore, a
stem-cell biologist at the University of Sheffield, ‘there could be potentially
far-reaching, multi-generational consequences if something went wrong
in a subtle way’.626
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Let’s assume, though, that a way were found to ensure that eggs and
sperm produced in this manner were safe to use as a treatment for infertil-
ity. What ethical issues might this raise? One might assume that many
people would be happy about such an approach being used to help infertile
couples. But what if it allowed women to have children at any point in their
lives, for instance when they were well past the normal reproductive age?
Would this be seen as liberating or an irresponsible extension of a woman’s
reproductive age? And if the latter, is that double standards given that actor
Anthony Quinn conceived a child naturally at the age of 81?628 Let’s also
consider a further possibility. Currently, gay and lesbian couples can only
have children that are biologically related to one of them. However, con-
ceivably, with this approach, an egg could be produced from a skin cell of
one gay man and fertilized with the sperm of his partner, then implanted
into a surrogate mother.629 And a skin cell from a lesbian might be used to
make sperm to inseminate her female partner.
In fact, it may be difficult or even impossible to generate eggs from male
cells containing an X and Y chromosome, or sperm from female cells with
two X chromosomes, because of the role of the Y chromosome in generat-
ing the males of our species.629 It’s possible, though, that genome editing
might be used to genetically engineer PGCs to get around such problems.
And if this were the case, while some people might welcome same-sex cou-
ples being able to reproduce together, would others see this as a step too far
away from the ‘natural’ order of things? Finally, let’s suppose that an indi-
vidual decided they’d like to have both sperm and eggs created from their
skin cells. Imagine then that a woman had sperm generated in this way and
used them to inseminate herself, or a man pursued this goal using a surro-
gate mother. This would allow such a person to have a child with them-
selves.629 Now while many people might be happy with a same-sex couple
procreating using this approach, I imagine far more would have a problem
with this final scenario, not only because of the many ethical issues raised
by what’s been termed ‘the ultimate incest’,629 but also since such an ex-
treme form of inbreeding would be very inadvisable from a health point of
view. Yet it’s important to consider this final scenario, as well as the others,
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The use of stem-cell technology to generate artificial eggs and sperm raises
exciting future prospects for the treatment of infertility, if also some highly
controversial issues, but it seems likely that it will be some time before
anyone considers this a safe approach for the treatment of this disorder. The
question of whether genome editing of human embryos might be used for
clinical purposes requires more immediate consideration. For, as we saw in
Chapter 4, the news that scientists in China have used the CRISPR/CAS9
approach to correct a gene defect in a human embryo—albeit one that
could never have developed into a person—shows how rapidly research is
progressing in this direction. And the news has generated a storm of con-
troversy. However, the argument by some researchers that there should be
a ban on such research has been far from universally taken up by scientists.
For instance, Katherine Littler, senior policy adviser at the Wellcome Trust,
a leading funder of biomedical research in Britain, recently said: ‘We think
it’s important to look at the issues in relation to human cells, and particu-
larly the germ line, in clinical applications . . . Let’s have some well thought-
through debates. A moratorium is the wrong starting point.’630 And Debra
Mathews, of the Berman Institute of Bioethics at Johns Hopkins University,
believes that: ‘while there is controversy and deep moral disagreement
about human germline genetic modification, what is needed is not to stop
all discussion, debate and research’.631
Such a debate will involve discussing how genome editing might be used
in research into the mechanisms underlying human embryo development.
‘Much of our knowledge of early development comes from studies of mouse
embryos, yet it is becoming clear that gene activity and even some cell types
are very different in human embryos,’ said Robin Lovell-Badge of the Francis
Crick Institute in London. ‘Genome editing techniques could be used to ask
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how cell types are specified in the early embryo and the nature and import-
ance of the genes involved.’631 Yet other scientists fear such research may
prepare the ground for future use of human embryo genome editing for
therapeutic purposes. It has to be said that the arguments for wanting to
modify human embryos for such purposes have not been entirely convin-
cing, since it’s already possible to analyse human embryos that may have a
genetic disorder and distinguish ones that lack the genetic defect underlying
the disorder.632
This involves taking a single cell from an IVF embryo when it’s only a ball
of cells and carrying out DNA analysis on the cell. If an embryo is identified
as not possessing the defect, then it can be implanted into the mother. This
approach is now used to select embryos without defects in the CFTR gene
which causes cystic fibrosis; the huntingtin gene that leads to Huntington’s
disease, an early-onset dementia;632 and the BRCA genes, associated with
susceptibility to breast and ovarian cancer.633 And despite the method des-
troying the specific cell that is analysed, the embryo can compensate for this
loss so that resulting human individuals appear normal. For this reason,
Edward Lanphier, who, as we saw in Chapter 4, is opposed to human
embryo genome editing, believes that there are no convincing arguments to
justify the technology as a form of germline therapy. ‘You can do it,’ he said.
‘But there really isn’t a medical reason.’634 Yet advocates of genome editing
in human embryos for therapeutic purposes point to a growing number of
disorders associated with defects in numerous genes.634 It would be very dif-
ficult to select embryos with non-defective versions of multiple genes but
feasible to correct them with genome editing. But the genome-editing
method carries its own problems, because the more genes that need to be
targeted, the greater the chance of incomplete targeting and ‘off-target’ ef-
fects that could cause unwanted changes in other parts of the genome.
Even if germline genome editing in humans was made legal, it’s unlikely
that any IVF clinicians would risk carrying out such editing of a human
embryo for clinical purposes unless they could be absolutely sure this
wouldn’t result in incomplete targeting or other adverse effects. However,
as we discussed in Chapter 7, one possible area where a case might be made
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Roots of Intelligence
Concern about safety is only one of the issues that trouble people opposed
to germline genome editing. So, according to Edward Lanphier: ‘People say,
well, we don’t want children born with this, or born with that—but it’s a com
pletely false argument and a slippery slope toward much more unaccept
able uses.’634 A major worry is that using such an approach for therapeutic
purposes would lead ultimately to ‘designer babies’—human individuals
engineered at birth to have beautiful looks, high intelligence, or exceptional
ability at sport or music. Such fears run deep among scientists. So Eric
Lander recently warned that: ‘It has been only about a decade since we first
read the human genome. We should exercise great caution before we begin
to rewrite it.’637 And at an international conference that took place in
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Such negative findings do not bode well for anyone seeking to use genome
editing to produce the next Einstein. As for creating an artistic genius like
Mozart, a study led by Kári Stefánsson, central executive officer at deCODE,
a biotech company in Reykjavik, Iceland, points to some potential prob-
lems. The study found that genetic factors associated with an increased risk
of bipolar disorder and schizophrenia are found more often in writers,
painters, and musicians. ‘I think these results support the old concept of the
mad genius,’ said Stefánsson. ‘Creativity is a quality that has given us Mozart,
Bach, van Gogh. It’s a quality that is very important for our society. But it
comes at a risk to the individual, and 1% of the population pays the price for
it.’643 In fact, David Cutler, a geneticist at Emory University in Atlanta, be-
lieves the study’s identification of the genetic factors that raise the risk of
mental problems explain only about 0.25 per cent of the variation in artistic
ability among individuals. ‘If the distance between me, the least artistic
person you are going to meet, and an actual artist is one mile, these variants
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18-year-old newcomer to the club, ‘Ronaldo was a natural talent,’ but also
that ‘he crammed in thousands and thousands of hours of graft to turn him-
self into the perfect player.’651
If anyone has a claim to be an even better footballer than Ronaldo it’s
Lionel Messi. Yet Messi was born with a physical defect that should have cut
short any hope of a footballing career—a growth hormone abnormality
that would have resulted in him becoming no taller than 4´ 7˝ in adulthood
if left untreated.652 But while growing up in Argentina Messi found ways to
compensate for his small stature: unable to ‘muscle’ his way through a
team’s defence, he learned to glide through it, and in the process became a
dribbling maestro. When Barcelona’s sporting director Carles Rexach
spotted his potential, and the club provided him with growth hormone
treatment that allowed him to reach 5´6˝, the result was a multiple winner
of the Ballon d’Or—the trophy awarded annually to the world’s best foot-
baller.652 Now Messi is clearly gifted with great endurance and speed, which
may be rooted in specific genetic qualities. But the fact that what should
have been a handicap on the route to sporting success turned out to be a
crucial feature along such a route shows the complexities of individual his-
tory. What’s more, it’s hard to imagine any parent choosing genome editing
to endow their child with a growth hormone defect so that after a child-
hood spent battling to overcome this handicap, they might emerge as a
world-class football player.
It’s not just in sport that genius may require both nature and nurture. For
instance, who would have predicted that a youth judged a failure by his
teachers and who said ‘school failed me, and I failed the school’ would
become one of the greatest scientists of all time? Yet such was the experi-
ence of Albert Einstein.653 The young Charles Darwin was accused by his
father of caring ‘for nothing but shooting, dogs and rat-catching’, and of
being ‘a disgrace to yourself and all your family’.654 In fact, with hindsight,
we can recognize qualities shown even at an early age by these two scien-
tists that would later contribute to their great discoveries. So, as a youth,
Darwin’s interest in cataloguing the wildlife he caught bordered on obses-
sion. Later in his life, he played backgammon each evening with his wife, the
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The complexity of the link between biology and life experience, plus the
potential risks of off-target effects, should hopefully persuade anyone
thinking of trying to create a designer baby that this would not be a good
idea. But IVF practice also does not exist in a social vacuum. In Britain all
work on human embryos, whether for research or clinical purposes, re-
quires a licence from the Human Fertilisation and Embryology Authority,
or HFEA.658 In November 2015, the first HFEA application to carry out
genome editing on human embryos was made by Kathy Niakan of the
Francis Crick Institute in London. She stressed that her aim was not to cor-
rect a gene defect linked to disease, but rather to better understand molecu-
lar processes underlying normal human embryo development. So Niakan
will use CRISPR/CAS9 to knock out or otherwise manipulate different
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genes to see what effect this has on embryogenesis. ‘The knowledge we ac-
quire will be very important for understanding how a healthy human
embryo develops, and this will inform our understanding of the causes of
miscarriage,’ she said. ‘It is not a slippery slope [towards designer babies]
because the UK has very tight regulation in this area.’659 And Robin Lovell-
Badge, head of stem-cell biology at the institute, agreed: ‘There is clearly lots
of interesting and important research you can do with these techniques
which has nothing to do with clinical applications.’659
In contrast to the situation in Britain, in the USA public funds for re-
search on human embryos have been harder to obtain. We saw in Chapter 8
how no federal government funds were available for research on human
ES cells when George Bush was US president. This ban was relaxed under
the presidency of Barack Obama.660 However, demonstrating the generally
more conservative stance of the US government on human embryo re-
search, recently the NIH stated that it will not fund any genome-editing re-
search on human embryos.661 Justifying the ban, the NIH director Francis
Collins said that genome editing of embryos is ‘viewed almost universally as
a line that should not be crossed’.661 Yet a curious situation exists in the USA
whereby, although public funding for human embryo work has waxed and
waned, private funds none the less sustain this research at a high level.661
And ironically, because in the USA there is no organization like the
HFEA that regulates human embryo research, there are effectively no legal
limits on this type of research, or even on its clinical application, as long as
private money funds it. This raises the question of whether a body like the
HFEA that allows valuable research on human embryos to proceed, but ex-
cludes attempts to pursue such research in an unethical fashion or apply it
clinically, may be something other countries, including the USA, should
consider.
It would be a brave—or foolhardy—scientist who would attempt to use
genome editing on human embryos for therapeutic purposes at present,
given the possibility of things going wrong. There is likely to be far less pres-
sure, though, on using the technology for the manipulation of other species.
And, as we observed in Chapters 5 and 6, such manipulation will probably
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A Question of Safety
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much more of a threat do such weapons represent now that it’s possible to
manipulate the genomes of life forms, including harmful bacteria, with an
unprecedented level of precision?
In fact, biological weapons are not as new as might be imagined. The an-
cient Hittites sent plague victims into the camps of their enemies and
Herodotus, a Greek historian writing in the 5th century bc, described arch-
ers firing arrows tipped with manure to contaminate the wounds of their
victims.663 In 1763, as the British fought the French and their Native American
allies for possession of what’s now Canada, Sir Jeffrey Amherst, the British
commander-in-chief in North America, wrote to Colonel Henry Bouquet:
‘Could it not be contrived to send smallpox among these disaffected tribes
of Indians’ ?664 The colonel replied: ‘I will try to inoculate the [Native
American tribe] with some blankets that may fall in their hands, and take
care not to get the disease myself.’664 Smallpox decimated the Native
Americans, who had never been exposed to the disease and had no immu-
nity. During World War II, British and American scientists investigated the
possibility of using smallpox as a biological weapon; however, because of
the availability of a vaccine, it was not felt likely to be very effective.664 But in
1989, Vladimir Pasechnik, a Soviet scientist who defected to Britain, claimed
that the Soviet pharmaceutical company Biopreparat was a front for a mas-
sive bio-weapons programme, and another defector, Ken Alibek, said that a
goal of the programme was to create deadlier forms of smallpox against
which current vaccines would be useless.664
Yet for all the fears about biological weapons, and the willingness of indi-
viduals and governments to develop and even employ them, overall they
haven’t been a particularly effective weapon in history. For, although use of
such agents may tap into human fears about contamination by other life
forms that reach deep into our evolutionary past, shooting someone or
blowing them up is generally still far more effective than trying to infect
them with a biological agent. And we already have many vaccines and drugs
to combat known pathogens. But could this situation change if genome
editing made it possible to create new, super-lethal forms of known bacter-
ial or viral species, or even invent brand new pathogens?
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suicide in 2008 before he could be brought to trial.671 This case shows the
danger of uncritically believing war propaganda. But it also raises questions
about work being carried out in secret military laboratories in the name of
defence, and whether this shouldn’t also be subject to the sort of guidelines
established at Asilomar. The case further poses questions about the need
for transparency in work involving GM organisms, no matter what the
sector. This is surely important if we are to prevent potentially lethal agents
falling into the wrong hands, as well as to safeguard against the potential
misuse of such agents by governments. And such precautions may become
increasingly important as the genome-editing revolution progresses.
Moving away from engineered viruses and bacteria, how worried should
we be about the possibility of genome editing being used to create new—
and potentially dangerous—larger organisms? In Oryx and Crake, perhaps
the most dangerous aspect of the world that Jimmy must now inhabit is the
presence of numerous bizarre animals. Particularly sinister are the pigoons.
In the previous society, the ‘goal of the pigoon project was to grow an
assortment of foolproof human tissue organs in a transgenic knockout pig
host—organs that would transplant smoothly and avoid rejection, but
would also be able to fend off attacks by opportunistic microbes and vir-
uses’.672 However, the feral pigoons now roaming the ruins of civilization
seem to have acquired a measure of human-like intelligence, so now it is
they who hunt Jimmy. Other creations, like the snats—a cross between
snakes and rats—and glowing green rabbits, fit the general theme of a soci-
ety in which genetic engineering had become an anarchic pursuit in which
anything went. In one of Jimmy’s flashbacks, we learn that, in the biotech
companies, ‘there’d been a lot of fooling around . . . create-an-animal was so
much fun, said the guys doing it; it made you feel like God’.673
Back in the real world, it’s worth asking just how far genome editing
could go in modifying animals used for medical research, or indeed as a
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and social implications more closely.675 ‘We are not near the island of Dr.
Moreau, but science moves fast,’ NIH ethicist David Resnik said during the
November meeting. ‘The specter of an intelligent mouse stuck in a labora-
tory somewhere screaming “I want to get out” would be very troubling to
people.’675
Another area of research that holds great potential promise for the future
but also raises many ethical issues is the use of genome editing to manipu-
late the primate genome. Currently only a small proportion of medical re-
search is carried out on primates. In Britain in 2013, rodents were used in 82
per cent of studies but primates only in 0.05 per cent.676 Yet the placards
held by animal rights protestors often have photos of monkeys on them
because these are more likely to strike a chord with the public than pictures
of rats and mice. For reasons of cost alone it’s likely that primate studies will
always represent a tiny proportion of total research. However, our new-
found ability to precisely modify the genomes of primates may lead to
greater use of this animal group. For, as we saw in Chapter 5, despite wide-
spread use of rodents to model human brain function and disorders, there
are fundamental differences between human and rodent brains, not just in
size but also in structure, that mean there are limitations to what we can
learn from such studies.677
For instance, how much can we really learn from rodent studies about
complex human disorders like autism, schizophrenia, or bipolar disorder,
which have a strong social and language basis? Those who carry out such
studies point to the fact that while they may not reproduce the complexity
of these human disorders, they can identify cellular mechanisms that reveal
important insights into the underlying basis of these psychiatric condi-
tions. However, to model these disorders in a more sophisticated fashion
there seems no doubt that we could learn a lot from exploring the role of
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A Question of Language
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only giant companies, in a way that has not been possible with previous
forms of genetic engineering. This is important, because one criticism of
current agriculture and food production methods has been the recognition
of the need for sustainability and the value of locally sourced produce. Local
sourcing is seen as important because it minimizes unnecessary use of
fuel for transport, and is also part of a general increased recognition of the
fact that different communities have different resources, skills, and require-
ments.692
Far from locally sourced foods being merely a fad in countries like Britain
and the USA, there has been a revival of interest in indigenous vegetables in
the developing world. A recent report described how, at a popular restaur-
ant in Nairobi, ‘the waiting staff run back and forth from the kitchen, bring-
ing out steaming plates of deep-green African nightshade, vibrant amaranth
stew and the sautéed leaves of cowpeas’.693 This is in contrast to several
years ago, when European vegetables like kale were the main greens on the
menu. According to leading African nutritionists, such indigenous veget-
ables are not just tasty but also often richer in protein, vitamins, iron, and
other nutrients than non-native crops, and they are better able to endure
droughts and pests. As Mary Abukutsa-Onyango, a horticultural researcher
at Jomo Kenyatta University in Juja, Kenya, remarked, ‘in Africa, malnutri-
tion is such a problem. We want to see indigenous vegetables play a role.’693
Scientists like Abukutsa-Onyango in Africa, as well as those in other
parts of the developing world, are interested in studying indigenous veget-
ables to further tap their health benefits and improve them through select-
ive breeding. An obvious question is whether genome editing could be used
to refine such plants, as an alternative to a focus on cash crops that make
profits for big companies but do little to help feed ordinary people in far too
many developing countries. Meanwhile, the potential genetic value of these
crops hasn’t escaped the notice of researchers in the developed world.
Calestous Juma, director of the Science, Technology, and Globalization
Project at Harvard University, believes that as well as being amenable to
improvement by genome editing, such native crops may have valuable ‘traits
that may be useful for other crops’,693 if introduced by genome editing. But
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if such moves are to help ordinary people in the developing world, the latter
need to be properly involved in decisions about the development and use of
indigenous crops, and not merely treated as accessories by big companies
keen to identify attractive genetic characteristics, but who leave nothing for
local people in return.
Editing as Aesthetics
From food to frivolity. Genome editing could be used for purely aesthetic
purposes. For instance, how about using it to create designer pets? In
October 2015, researchers at the Beijing Genomics Institute announced that
they had created micro-pigs by TALEN genome editing and would be selling
them as pets.694 The micro-pigs were created from a small breed of pig
known as Bama, by disabling one of its copies of the gene coding for growth
hormone receptor. The animals weigh around 15 kilograms when mature,
or about the same as a medium-sized dog, as compared to 100 kilograms
for a normal adult pig. Each micro-pig is being offered for 10,000 yuan—
about £1,000. The animals are being developed to raise cash to fund stem-
cell experiments and other research that take place at the institute. ‘We plan
to take orders now and see what the scale of the demand is,’ said the insti-
tute’s director, Yong Li.694 Customers will also be able to select their pet pig’s
colour and coat pattern.
The project has horrified animal welfare groups. ‘The idea is completely
unacceptable,’ said Penny Hawkins, head of the British Royal Society for the
Prevention of Cruelty to Animals (RSPCA)’s research animals department.
‘In the past, pets have been bred by selecting animals, generation by gener-
ation, to produce a desired trait. Inducing a massive change in one go risks
creating animals that suffer all sorts of horrific impairments.’694 Some sci-
entists have also expressed caution about the project. ‘It’s questionable
whether we should impact the life, health and well-being of other animal
species on this planet light-heartedly,’ said Jens Boch of the Martin Luther
University of Halle-Wittenberg in Germany, one of the original pioneers of
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Engineering a Winner
So much for using cloning to resurrect a dead pet. But what about using
new genetic technologies to create an animal that can generate lots of
money by enhancing its sporting performance, like a genome-edited race-
horse? Horse racing is the second most popular spectator sport in Britain,
with over 6 million race-goers each year; it employs about 90,000 people
and generates £3.7 billion a year for the economy.698 Breeding racehorses is
big business. Take Frankel—the greatest and most successful thoroughbred
in modern racing history. Not only is Frankel himself valued at more than
£100 million, but for a mare to have a quick roll in the hay with him in the
hope of producing a similar winner costs £125,000. As with human athletes,
both nature and nurture help to create a great racehorse, with the training
regime being highly important. Yet the role of genetics is demonstrated
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by the fact that almost all the world’s half a million thoroughbreds derive
from only 28 ancestors born in the 18th and 19th centuries. And up to 95
per cent can be traced to just one stallion—the Darley Arabian, born in
1700.698
Surprisingly, it’s still rare for genetic analysis to be used to identify great
potential winning racehorses; instead breeding decisions are usually made
by studying pedigree—the records of bloodlines and race results going back
generations. There’s a problem though in relying on pedigree alone as a
guide to quality, for an ancestor five generations back only contributes 3 per
cent of an animal’s DNA. The Green Monkey is an example of the dangers
of relying on bloodlines. In 2006 this colt with an impeccable pedigree sold
for $16 million. Yet it ran just four times and failed to win once. To try to
improve matters, British scientist Stephen Harrison set up Canterbury-
based company Thoroughbred Genetics Limited in 2000. This company
was the first to offer DNA screening for racehorse performance. Using such
methods to identify the best combination of stallion and mare, Harrison’s
biggest success is Sacred Choice, with nine wins from 37 starts. Yet judged
by traditional criteria, its mother, Sacred Habit, didn’t seem up to much.
‘Sacred Habit was sold because it was a rusty animal,’ said Harrison. ‘And
yet it bred this multiple group-one winner.’698
Until recently, the type of genetic analysis available only provided a
low-resolution estimate of a horse’s sporting potential. However, the com-
plete sequencing of the horse genome in 2009 has made it possible to begin
pinpointing specific genetic differences that identify a great racehorse. In
2010, Emmeline Hill of University College Dublin discovered that variations
in the myostatin gene, which codes for a protein that regulates muscle
development and muscle fibre type, determines the type of race that most
suits an animal and whether or not it will be an early developer. Her com-
pany, Equinome, offers three tests to owners and trainers, including one
based on this single ‘speed’ gene. ‘It was the first time that anyone had iden-
tified a single gene to an athletic trait in a thoroughbred,’ said Donal Ryan,
managing director of Equinome. ‘It’s quite astonishing that a single gene
has such significance, but it does.’698
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Yet despite the value of such tests for identifying the best breeding part-
ners, creating a great winner still remains a lottery, for the reason men-
tioned in Chapter 2—the mixing and matching of the paternal and mater-
nal genomes that occurs during egg and sperm formation often leads to
unpredictable results in offspring. Simon Marsh, a top horse breeder, re-
mains sceptical about some claims being made about the value of genetic
analysis in selecting the best breeding matches: ‘You can predict, if you are
on the front row of the grid in a Formula One race that you are probably
going to win the grand prix,’ he said. ‘But if you have the greatest stallion in
the world and the best mare in the world, there’s no reason why their pro-
geny won’t be beaten by something that cost just 10% of the price.’698
Such pessimism might be misplaced if we introduce another factor into
the equation—the technologies described in this book. One obvious
strategy would be to clone a great racer. Currently, the Jockey Club bans the
use of cloned horses, although an indication of changing views on this
matter was the decision in 2012 of the International Federation for Equestrian
Sports to allow cloned horses to compete in future Olympic Games.699 In
the USA, the governing body of quarter horse racing—sprinting contests
over short distances between small animals—lost a legal challenge to their
ruling against clones, setting a legal precedent that may also affect thor-
oughbred racing.699 But cloning is still a relatively inefficient process and
can lead to problems of ill health in some offspring. It also can’t be applied
to dead horses, unless they have been cryopreserved.
In contrast, as further insights emerge about the contribution of specific
genetic differences to racehorse biology, genome editing might in the future
be used to fine-tune a horse’s performance, or even recreate the genetic dif-
ferences that made a deceased horse a winner. For instance, DNA might be
taken from the corpse of a famous horse and used as a guide to genome
editing. One of the most famous horses in British racing history is Red Rum,
who won the Grand National steeplechase race three times. This sporting
legend died in 1995, and is buried at the finishing line at the Aintree ground
in Liverpool where the race takes place, with his head facing the winning
post.700 So maybe a DNA sample could be obtained from Red Rum’s remains,
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and his genome sequenced and used as a guide to genome editing another
great winner. But would this be considered sacrilegious to the memory of
this sporting legend or acceptable practice in the pursuit of creating an-
other winner? And what would an ability to genetically stack the odds in a
horse’s favour do to the nature of the sport?
Manufacturing Mammoths
If watching horses run around a track is not your cup of tea, you may be
interested in much larger animals—like woolly mammoths. Some labora-
tories are intent in trying to resurrect this icon of the Ice Age using the latest
technologies. In particular, as well as raising funds through cloning dead
pets, Woo-Suk Hwang’s Sooam Biotech company is pursuing this goal. The
company recently cloned the endangered coyote, and plans to use this tech-
nology to repopulate endangered species such as Ethiopian wolves, the
American red wolf, and the Lycaon or African wild dog.697 However, it’s
Sooam’s particular focus on the woolly mammoth that has excited most
commentators’ attention.
Recently, scientists from the company established a collaboration with
researchers at Russia’s North-Eastern Federal University in Yakutsk, the cap-
ital of the Sakha Republic in Siberia, to clone this long-extinct mammal.697
With no live mammoths, success will depend on finding a well-preserved
dead mammoth in the frozen tundra, extracting one of its cells, and implant-
ing the cell’s nucleus into an elephant egg from which the nucleus has been
removed. Finally, the resulting cloned embryo will be implanted into a
female elephant. To pursue this goal, Sooam scientists travel every
summer to Siberia, deeper and deeper into the Arctic Circle, looking for a
mammoth sample suitable for use in cloning. ‘The point is to find some-
thing that’s better than anything we’ve found before,’ said Sooam re-
searcher Insung Hwang. ‘That’s why we go on expeditions every year. That’s
why we try to improve our techniques of preserving the tissues during
transportation—we even built a lab in Yakutsk to really shorten that time of
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a starling, or even a golden eagle, wouldn’t have the same effect on your
pulse rate as a Tyrannosaurus rex, birds, including the domestic chicken, are
closer genetically to dinosaurs than previously imagined. The idea that
birds evolved from dinosaurs has been around since 1860, when German
scientists discovered the fossil of a creature they named Archaeopteryx, after
the ancient Greek words: archaīos, meaning ‘ancient’, and ptéryx, meaning
‘wing’.706 Archaeopteryx had wings and feathers, yet looked remarkably like
a dinosaur. But it was particularly comparisons of the genomes of birds
and reptiles that confirmed that our feathered friends are genetically quite
close to their dinosaur ancestors. And now some scientists want to create a
dinosaur-like organism by modifying a bird genome. One such scientist is
Jack Horner of Montana State University.707 As a child he had two dreams:
one was to be a palaeontologist, the other was to have a pet dinosaur. His
first dream came true when he was only 8, for Horner found a dinosaur
bone near his home in Montana. Since then he’s unearthed many more
dinosaur remains—including foetuses within eggs. One of Horner’s major
discoveries was that some dinosaurs built nests, lived in colonies, and cared
for their young.707
But it’s the second part of Horner’s dream that’s proving to be the most
controversial. Since birds are the evolutionary descendants of dinosaurs,
Horner believes they have dormant DNA that, if activated, could allow
them to develop some of the traits dinosaurs had, such as teeth, three-
fingered hands, and tails. ‘For me, creating a dinosaur is the biggest project
we have,’ said Horner. ‘It’s like the moon project. We know we can do it—it
just takes time and money. And we will get it done. We will make a dino-
chicken-like animal pretty soon.’707
Demonstrating that such ideas are not totally off the wall, recently scien-
tists engineered a chicken embryo so that its beak became a dinosaur-like
snout and palate, similar to that of small feathered dinosaurs like Velociraptor.
The study was led by Bhart-Anjan Bhullar of Yale University in New Haven
and Arkhat Abzhanov of Harvard University, who said they did not set out
to create a ‘dino-chicken’.708 Rather, they were interested in understanding
the molecular processes that led to the development of the beak, a key
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aspect of bird anatomy. It is also the part of the avian skeleton that has
‘diversified most extensively and most radically,’ said Bhullar.708 Yet despite
this diversity—ranging from flamingos to pelicans—very little is known
about ‘what the heck a beak actually is,’ he added. ‘I wanted to know what
the beak was skeletally, functionally and when this major transformation
occurred from a normal vertebrate snout to the very unique structures used
in birds.’708
To study this question, the researchers trawled through the genomes of
organisms ranging from mice, emus, alligators, lizards, and turtles. They
found that birds have a unique cluster of genes related to facial develop-
ment, which the non-beaked creatures lack. When they silenced these
genes, the beak structure reverted to its ancestral state. So too did the pal-
atal bone in the roof of the mouth. For now Bhullar has no plans, or ethical
approval, to hatch the snouted chickens. But he believes they would have
been able to survive ‘just fine’. ‘These weren’t drastic modifications,’ said
Bhullar. ‘They are far less weird than many breeds of chicken developed
by chicken hobbyists and breeders.’708
What other genetic changes would be required to make a chicken more
dinosaur-like? Jack Horner believes that, besides the beak change, other
modifications are required to make a ‘chickenosaurus’. So scientists would
have to give it teeth and a long tail, and revert its wings back into arms and
hands. Horner likens this to breeding a wolf into a Chihuahua, except on an
accelerated timescale.707 Yet not everyone thinks the task will be so straight-
forward. Bhart-Anjan Bhullar believes that if dinosaur-like features were to
be restored, it’s still possible that they wouldn’t function correctly: ‘You
could perhaps give a chicken fingers, but if the fingers don’t have the right
muscles on them, or if the nervous system and the brain are not properly
wired to deal with a hand that has separate digits, then you may have to do
a considerable amount of additional engineering.’709
Of course, there are other reasons why many people would have con-
cerns about scientists trying to recreate extinct dinosaur species, not least if
they’ve watched any of the Jurassic Park films, where things generally end up
going badly wrong. Such fears don’t seem to deter Horner though. Indeed,
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he thinks that genome editing might be used not only to resurrect extinct
animals but even create mythical creatures. ‘As absurd and wild as it sounds,
I honestly believe that even before we make a dino-chicken, we could make
a unicorn,’ he said. ‘Wouldn’t it be fun to have a unicorn? I mean, just think
of the possibilities of making mythical creatures—mixing and matching
different characteristics!’709 All of which gives a flavour of some of the eth-
ical conundrums that genome-editing technology may throw up in the
future. But the greatest dilemmas are likely to relate to the use of biotech-
nology to transform the human species or create human-like organisms.
In the section ‘Talent Born or Made?’, we discussed why the use of genome
editing to generate ‘designer babies’ with desirable characteristics like great
intelligence or musical or sporting ability may be far from a trivial matter, if
it is possible at all. None the less, it’s also important to consider how a
greater awareness of the role of genetics in forming a human individual as
well as also the technologies discussed in this book—genome editing, but
also optogenetics, stem-cell technology, and synthetic biology—might
transform humanity in the future. For instance, what if it really does prove
feasible to create genome-edited pigs whose hearts, pancreases, lungs, and
livers can be transplanted into people requiring these organs? Or what
about pig–human chimaeras as a source of actual human organs? Will this
mean that human lives will be greatly extended, because any failure of a
person’s vital organs will be fixed by another transplant, acquired for little
more than the price of buying some pork steaks at the butchers? And if such
a strategy becomes commonplace in medicine, will this alter our perception
of what it means to be human, or will acquiring spare organs in this manner
simply be seen as equivalent to having a hearing aid or heart pacemaker?
Of course, there is still the question of what happens when the most dis-
tinctive human organ of all fails—a person’s brain. For even if human life-
spans could be greatly extended with a succession of genetically engineered
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heart, liver, kidney, or lung transplants, this might be of little use without
the means to rejuvenate the brain. We’re all increasingly familiar with the
spectacle of degenerative diseases like Alzheimer’s robbing elderly people
of their mental faculties and much of their individuality. So it seems likely
that such problems would only increase as people’s lifespans are extended,
unless we find ways to better understand and treat such forms of dementia.
Here, a solution will rely on scientists gaining a clearer idea about the molecu-
lar and cellular changes that underlie dementia and thereby identifying new
drug targets. But there’s also the possibility that creation of human brain
structures from ES cells or personalized iPS cells could one day be used
to treat degenerative disorders like Alzheimer’s and Parkinson’s, and even
those that affect personality, like depression, schizophrenia or bipolar dis-
order.
Apart from the safety aspects of introducing artificially generated neu-
rons into the brain—we’d need to be sure such cells wouldn’t form tu-
mours—there is also the question of whether such infusions might alter
personality. But then, in the future, might stem-cell technology even be
used to engineer people with a permanently upbeat mood? And if not
through stem-cell technology, could a similar outcome be achieved using
optogenetics or other technologies that manipulate neuronal activity, or
even the expression of genes, using magnetic fields or radio signals? For this
to be possible, individuals’ brains would need to be genetically engineered
to respond in the correct fashion, but, with future advances in genome edit-
ing, it’s not inconceivable that this could become routine. If it did, this raises
a more worrying possibility, which is that such a technology might be used
to brainwash people into accepting a repressive political system or to erase
certain memories and plant false ones. There would need to be safeguards
against their misuse.
The replacement or rejuvenation of human organs is one way in which
an individual human life could be radically altered in the future. But could
genome editing also one day allow human beings to acquire completely
novel characteristics, borrowed from the rest of the animal kingdom? For
instance, could a human gain the ability to detect sensitive odours like a
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dog, the night vision of a cat, or even a capacity to remain underwater for
long periods of time like a dolphin? A potential problem is that such prop-
erties have evolved over millions of years in tandem with the other changes
that combine to give such organisms their unique characteristics. So it’s by
no means clear that such characteristics could be engineered into a person
in a functional manner, without having detrimental effects on the rest of
the human body.
There is another possibility: electronic gadgetry might allow a human to
acquire such characteristics. Such a strategy could well involve a combin-
ation of electronic devices and tissue implants, perhaps derived from per-
sonalized iPS cells. Either way, does this mean that, in the future, humanity
might undergo a diversification into individuals with quite different charac-
teristics, depending on which animal quality attracted them? And might
people of the future decide to transform their unborn children in this
fashion, by engineering IVF embryos, in an even more radical take on de-
signer babies?
The possible fusion of electronics and bioengineering leads us to another
possibility—that a human brain grown in culture might be linked to sen-
sory inputs that would allow it to detect and possibly learn. Such a brain
might then be allowed to become the controlling device within a computer
or robot. While such a scenario may sound like the plot for a bad horror
movie, recent advances in the culture of human brains from iPS cells of the
sort described in Chapter 8 mean that this possibility can no longer be dis-
regarded as pure fantasy. Of course, there would be many ethical issues in-
volved in treating a human brain in this fashion, but let’s imagine that such
an experiment went ahead. What would be the nature of the interaction of
such a brain with the outside world? Would it see itself as human? And how
would it feel about being contained inside a machine in this manner?
Taking our thought experiment a step further, given recent advances in
the creation of 3D structures representing diverse human tissues and organs,
is it possible that one day different organs could be combined to make an
artificial human being? This is the main premise of the classic 1980s science-
fiction film Blade Runner. In this future dystopia, stem-cell technology is used
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It’s time to bring this book to a close. Let’s return to society as it stands in
the first part of the 21st century and assess the relationship of the biotech-
nologies discussed in these pages to that society. At the start of this book, I
made a point of locating the development of new genetic technologies as
part of two unique human characteristics: our ability to make and use tools;
and our self-conscious awareness, which allows us to plan how to employ
such tools. It is these attributes that have allowed humankind to manipulate
the world around us—both living and non-living—in such remarkable
fashion. And as a consequence, our species has been able to grow to 7 bil-
lion in number and also to progress, in less than 50,000 years, from living
in caves to sending people into space and robots to explore the surface
of Mars.
Yet despite such amazing progress, how much are we in control of our
destiny and how sustainable is our society? For, currently, a number of
major challenges face humanity and it remains to be seen how well we will
stand up to the test. Undoubtedly, the biggest problem of our time is global
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warming. It is difficult nowadays to find any serious scientist who does not
believe that phenomena caused by human activities—primarily rising CO2
emissions but also other greenhouse gases—are causing a rapid warming of
the planet. And numerous studies now point to the dire future consequences
of such warming. The NASA glaciologist Eric Rignot of the University of
California, Irvine, recently concluded that ‘a large sector of the western
Antarctic ice sheet has gone into a state of irreversible retreat . . . This retreat
will have major consequences for sea level rise worldwide.’711 If both the
western and eastern ice sheets—which cover an area the size of the USA
and Mexico combined—were to melt completely, this would raise global
sea levels by an astounding 60 metres or 196 feet.712
What remains unclear is how rapidly the process will occur. But even a
rise of 7 metres, which some scientists are now predicting by the end of the
century, would flood London, New York, and many other major cities.713
An even more worrying long-term prediction has been made by another
NASA scientist, James Hansen, of Columbia University, who has been called
the ‘father of climate change awareness’.714 He believes that once it reaches a
certain point, global warming may enter a ‘runaway’ phase, leading eventu-
ally to conditions like that on the planet Venus.715 Given that Venus has a
surface temperature of 482°C, this would clearly mean the end not just of
human civilization on Earth but probably all other life. However, long
before we reach that point, human populations, and the animals and plants
we rely on for food, will have to face the effects of rising global temperat-
ures and sea levels.716 Yet, despite the seriousness of the threat, a succession
of conferences involving world leaders have failed even to reduce the rise in
CO2 emissions, never mind reverse them.717 So Hansen’s verdict on the cli-
mate conference that took place in Paris in December 2015 was that it was a
‘fraud’, with ‘no action, just promises’.714
Genome editing might offer humanity a way of engineering crops and
livestock so that they can cope with an increasingly stressful climate. The
technology might also be used to create livestock that contribute less to
global methane emissions. Methane is a powerful greenhouse gas, being 25
times as efficient as trapping the Sun’s heat as CO2.718 And a surprising 26
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per cent of all methane emissions in the USA come from the burps and farts
of cows and other ruminants that produce the gas as a by-product of their
digestive process. Yet individual animals can vary considerably in the
amount of methane they produce, and a new European Union-funded pro-
ject named RuminOmics aims to use cutting-edge technologies, including
genome editing, to try and produce a milk-producing breed that produces
less methane.719 Such a breed could be attractive to farmers because a herd
that emits less methane is likely to be more productive. According to
Lorenzo Morelli, director of the faculty of agriculture at the Catholic
University of Sacred Heart in Piacenza, Italy, and a partner in the project,
‘The methane is lost energy that could go into producing milk. So if we can
find the right genetic mix, we can find cattle that are less polluting, more
productive, and more profitable for the famer.’719
At the same time, genome editing could provide us with ways to keep
ahead of microorganisms that are rapidly becoming resistant to current
antibiotics. But it seems astonishing that our society is capable of generat-
ing such amazing new technologies as genome editing, optogenetics, and
organoids created from stem cells, yet lacks the political will to stop global
warming, which, if unchecked, will ultimately threaten humanity itself.
Because of this, it’s worth asking some searching questions—and such
questions are increasingly being asked in some very interesting places.
Bill Gates, co-founder of Microsoft and the world’s richest man, recently
pledged $2 billion to counter climate change, while encouraging other
wealthy individuals to do the same.720 Not so unexpected you might say,
given that Gates has a long history of philanthropy, particularly in terms of
funding new technologies to help people in the developing world, who will
be worst hit by global warming. More surprising was Gates’ rejection of
claims typically made by free market advocates that the only way to reduce
climate change is to leave it to private enterprise.
According to Gates, the problem with such a strategy is that ‘there’s no
fortune to be made. Even if you have a new energy source that costs the
same as today’s and emits no CO2, it will be uncertain compared with what’s
tried-and-true and already operating at unbelievable scale and has gotten
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288
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sidered in this book is that such technologies might lead to better treat-
ments for mental disorders. Currently, the drugs available to treat such dis-
orders leave much to be desired. Indeed, Simon Schulz, director of the
Centre of Neurotechnology at Imperial College London, believes there is a
fundamental problem with the present strategy, ‘because it is becoming
exponentially more difficult to find new compounds that can deal with the
disease in question but which don’t affect other things’.725 Instead, Schulz
points to technologies like optogenetics, which might be applied in humans
after genome editing of cells in the brain. ‘This method doesn’t need to be
used with light,’ he said. ‘You could put a similar sensitivity in the neuron to
make it drug-activated instead. I see that—in particular—as being a really
powerful approach in the future.’725 In fact, such a strategy may have great
potential for medicine, but also for misuse. ‘We’ll have the technology at
some point to place invasive implants into people’s heads to give them new
senses,’ said Schulz. ‘I’d imagine the military would like to be able to do that.
We might consider it unethical for them to do certain things. But on the
other hand, if you had someone who is tetraplegic and has to have these
implants then you have a strong ethical case to give them control of their
body to be able to live an independent life. And why would you stop with
normal body functionality? Why would you stop?’725
Now I’d be very surprised if there weren’t many people who would want
to stop not just at this point, but considerably sooner, when it comes to the
prospect of genetically engineering human brain cells. But Schulz makes a
valid argument when he asks us to consider whether what’s considered
acceptable in a few decades’ time might not be very different from today.
For, as he says, ‘Look at privacy as a social concept. Think about how our
great grandparents would have dealt with the level of exposure we now
have online. It’s something they would never have considered. What’s
acceptable now and what will be acceptable in 2035 may be quite different.
Are we developing technology for the ethics as they are now or the ethics of
2035?’725 Clearly, though, in any democratic society, if perspectives are to
change, this needs to be on the basis of maximum open public discussion.
And while the prospects offered by genome editing or stem-cell technology
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for medicine are very exciting, evidently there needs to be much thought
about the safety and ethics of treating human patients with such radically
different forms of therapy, and also about the welfare of the animals em-
ployed to model disease using the new technologies.
As for the question of whether genome editing should ever be used to
modify the human germline, there are many different viewpoints, as we’ve
seen at various points in this book, with some violently opposed and others
who argue that, in some circumstances, it might be justified as a treatment
for disease. As we’ve also seen, some people even believe that, if proved to
be safe, then it might be quite valid to use genome editing of the human
germline to ‘enhance’ the species. At the moment it would be hard to find
anyone proposing to make practical use of the technology in this way. Yet
who knows what the situation might be in five or ten years’ time, if genome
editing becomes increasingly fail-safe and our ability to interpret the genome
itself more refined. At the same time, will genetic modification of our near-
est primate relatives begin to blur the boundaries between what is human
and what is not? These are as much social questions as scientific ones, and
as they concern us all, they should be the subject of a far-reaching, scientif-
ically informed public debate. Hopefully, this book will prove to be a useful
starting point.
290
G LOSSARY
291
Glossary
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336
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338
INDE X of names
339
INDE X of names
340
INDE X of names
341
INDE X of names
342
I N DE X OF SUBJEC T S
343
INDE X of subjects
344
INDE X of subjects
345
INDE X of subjects
346
INDE X of subjects
347
INDE X of subjects
‘junk’ food 113, 132, 268, 288 Manchester United football club 252
Jurassic Park (film) 278, 280 Mars (planet) 206, 230, 284
Mars Astrobiology Research and
keratin proteins 16 Technology Experiment 206
King Solomon’s mines 205 Mars trilogy (books) 230
knockin mutants 54, 57, 70, 81, 84–5, 87, 94, measles 17
97, 99–100, 112–14, 117, 123–4, 128, 135, Medical Research Council (UK) 225, 235
154, 183, 199 Mendelian pattern of inheritance 155, 164
knockout mutants 54, 55–6, 56, 57, 81, menopause 65, 67, 244
84–5, 87, 93, 96–7, 99–100, 102, 112–14, messenger RNA (mRNA) 32, 95, 96,
117, 123–5, 135, 154, 183, 199, 260 100, 220, 223
metabolism 53, 58, 115, 125
Lancelot Encore (cloned dog) 272 metallothionein gene 40, 41
language 120, 127–9, 222, 241, 262, 264–5 metastasis of tumours 98, 99
Lego® 215 methane 207, 285–6
Leigh syndrome 189 microcephaly 197
leptin hormone 29 microelectrodes in neuroscience 68
lesbians 245 Microphagia (book) 59
lettuce 14, 136 micro-pigs 271–2
leukaemia 3, 48, 156, 162–3, 176, 182, 232, 234 military 260, 284, 289
life expectancy 108, 112, 153–4 Mingming (knockout monkey) 125
light microscope 60–1 mitochondria 64–5, 237
liver 5, 39, 110, 115–17, 157, 170–1, 181, 186, moas (extinct bird species) 278
193–4, 200, 235, 240, 281–2 Momoko (cloned dog) 273
livestock 45, 130–1, 133, 146, 149–51, 228, monkeys 2–3, 34, 84, 124–5, 127, 129, 189, 262–5
268–9, 272, 285, 287–8 Monsanto company 44, 134
local sourcing of food ingredients 270 moon project 279
long-term depression (LTD) 77 mosquitoes 173–4, 174, 175, 288
long-term potentiation (LTP) 76–8 Mount Olympus 181
luciferin 62, 80 Mowgli (fictional character) 9
luminopsins 81 multinational companies 44, 132, 231, 288
lungs 46–7, 98, 99, 116–17, 160, 194–5, mutants 1–2, 20–1, 24–5, 27–30, 48–9, 61,
202–3, 233, 235, 258, 281–2 88, 99, 111, 157, 159–60, 174, 229
Lycaon (African wild dog) 276 mutation chain reaction (MCR) 173, 174
lysosomes 96 mutations 9, 15–16, 19–24, 28–30, 51, 53, 64,
83, 94, 100, 139, 141, 146–7, 147, 151, 157,
macaque monkeys 125, 125 160–2, 164–6, 169, 171–4, 174, 177,
magnetic stimulation 102–3, 238, 282 201–2, 207, 226, 234–5, 243–4, 267
major histocompatibility complex (MHC) Mycoplasma mycoides bacterium 211, 214
genes 116–17, 119, 168, 186 myelin sheath (of neuron) 70
malaria 153, 173–5, 288 myeloid cell leukaemia 1 (MCL1) gene 162
mammals 3, 26, 66, 73, 75, 80, 83–4, 95, 104, myeloproliferative neoplasms (MPN)
110–12, 114, 120, 124, 152, 128–9, 155, 179, Research Foundation 176
183, 187, 276 myostatin gene 146, 151, 274
348
INDE X of subjects
349
INDE X of subjects
pluripotency 4–5, 39, 49–50, 83, 180, 182–3, Red Rum (racehorse) 275
186–7, 189–91, 191, 192, 194, 240, 242–3 regulatory elements in genes 41–2, 89, 164
polycystic kidney disease 19 regulatory RNAs 95, 224
polymerase chain reaction (PCR) 207–8, replicants (Blade Runner) 284
208, 209 reporter genes 41–2, 68
porcine endogenous retroviruses repressive political systems 282
(PERVs) 118–19 restriction enzymes 34–6, 84, 86
pore proteins 55, 58, 63, 71, 80, 96, 102 retinoblastoma (RB1) gene 235
potato blight 136–7, 269 RetroSense Therapeutics company 239
potatoes 12, 44–5, 84, 135–7, 139, 141, 266, 269 retroviruses 47, 48, 118–19, 165, 167, 170,
powdery mildew disease of wheat 138 172, 232
prefrontal cortex of brain 124, 125 reverse transcriptase 166, 170
primary cells 94–5 rhodopsin gene 69, 71
primates 2, 10, 112, 119, 124–7, 129, 155, ribosomes 171
262–5, 290 rice 8, 12, 14–15, 45, 84, 133, 136, 141, 143–4
primers (in PCR) 208, 209 Rio Tinto mining region in Spain 205–6
primordial germ cells (PGCs) 242–4, 244, 255 RNA interference 95–6, 96, 103, 140, 171
profit motive 5, 46, 142, 268–9, 286–7 RNA interference silencing complex
progesterone 87 (RISC) 96, 96
prokaryotes 213 RNA polymerase 41, 100, 101, 171
Prometheus (mythical character) 31, 181 RNA-dependent RNA polymerase 170
promoter of gene 40–2, 56, 100, 101, 144, robots 284
166, 215 Royal College of General Practitioners
protease of HIV 166 (UK) 239
protein kinase B alpha (PKB) gene 164 Royal Society (UK) 45, 59
protocadherin-related 15 (PCDH15) gene 61 Royal Society for the Prevention of Cruelty
psychiatric disorders 20, 76, 239, 263, 265 to Animals (RSPCA, UK) charity 271–2
pump proteins 71 RuminOmics project 286
350
INDE X of subjects
351
INDE X of subjects
352
ANCESTORS IN OUR GENOME
The New Science of Human Evolution
-
Eugene E. Harris
“Simply indispensable for any reader wishing to learn about the latest
research on human origins” Library Journal
“In the ‘Age of Genomics,’ this book is an absolute must-have for anyone
interested in human evolution. In the most accessible manner, Eugene E.
Harris enlightens how and why genomes represent such powerful evidence
to understand our past.”
Jean-Jacques Hublin,
Max Planck Institute for Evolutionary Anthropology
-
Dawn Field and Neil Davies
-
John Parrington
-
John Archibald