Meiosis

We have discovered that single-stranded DNA containing short guanine-rich motifs will self-associate at physiological salt concentrations to make four-stranded structures in which the strands run in parallel fashion. We believe these complexes are held together by guanines bonded to each other by Hoogsteen pairing. Such guanine-rich sequences occur in immunoglobulin switch regions, in gene promoters, and in chromosomal telomeres. We speculate that this self-recognition of guanine-rich motifs of DNA serves to bring together, and to zipper up in register, the four homologous chromatids during meiosis.

In this review, the pathways involving small RNAs are provided followed by a new and updated network that illustrates their interplay with diverse cellular mechanisms in Caenorhabditis elegans. The RNA silencing pathways are now recognized as key factors that connect together the many variations in biological processes, including transcriptional gene regulation, post-transcriptional gene silencing, translational gene silencing, apoptosis, meiosis, and antiviral defense. The utilization of small RNAs represents a specific, energy conserving, and fast mechanism of gene regulation via a core system known as RNA interference.

The objective of this study was to determine the influence of powdered coconut water (ACP-318®) diluted in high glucose (11.0 mm) TCM199 in the achievement of nuclear in vitro maturation (IVM) of canine oocytes. Cumulus oocyte complexes (COCs) (n = 632) were randomly allocated into three experimental groups named as group 1 (control group), group 2 (5% powdered coconut water) and group 3 (10% powdered coconut water). The percentage of meiotic resumption (MR) (GVBD to MII) was 39.1% (81/207), 50.2% (108/215) and 46.6% (98/210) for groups 1, 2 and 3 respectively (p < 0.05). There were no differences in MR rates among groups 2 and 3. The medium with ACP-318® slightly enhanced the nuclear maturation of canine oocytes when a comparison was established with rates of maturation exhibited by oocytes in the experimental group 1 without ACP-318® (p < 0.05). The results suggest that oocytes’ nuclear morphology integrity and meiosis achievement were positively influenced when exposed to high glucose TCM199 supplemented with 5% powdered coconut water. Further investigation must be performed for a better understanding of powdered coconut water influence in cellular events during IVM of dog oocytes.

In budding yeasts, the histone deacetylase Rpd3 resides in two different complexes called Rpd3L (large) and Rpd3S (small) that exert opposing effects on the transcription of meiosis-specific genes. By introducing mutations that disrupt the integrity and function of either Rpd3L or Rpd3S, we show here that Rpd3 function is determined by its association with either of these complexes. Specifically, the catalytic activity of Rpd3S activates the transcription of the two major positive regulators of meiosis, IME1 and IME2, under all growth conditions and activates the transcription of NDT80 only during vegetative growth. In contrast, the effects of Rpd3L depends on nutrients; it represses or activates transcription in the presence or absence of a nitrogen source, respectively. Further, we show that transcriptional activation does not correlate with histone H4 deacetylation, suggesting an effect on a nonhistone protein. Comparison of rpd3-null and catalytic-site point mutants revealed an ...

Preferential chromosome association at metaphase I has been analyzed and compared in autotetraploid cells obtained by colchicine treatment of hybrid diploid rye plants with different degrees of chromosomal divergence between homologs. The tendency to identical over homologous, but not identical, pairing preferences detected when homologous partners are contributed by less related parental lines indicates that chromosome differentiation may play an important role on preferential pairing behavior of polyploids. However, associations between more similar (identical) partners are not always favored, thus suggesting that additional factors must be considered. Other hypotheses for explaining pairing preferences in competitive situations are discussed. No clear relationship has been found between multivalent frequencies at metaphase I and chromosome differentiation between homologs or preferential pairing behavior. Therefore evolutionary divergences among related genomes should be carefull...

An idea is a thought that generates in the mind. It is a notion that exist in the mind as a representation or formulation. Usually thought is generated by one observation or the other in the environment, and this observation is always termed “issue” challenges or what you will. As long as there are issues of concern in the environment there will be ideas notions and formulations conceived and postulated into concept. In science this type of concept is termed an invention or innovation. Such innovation may remain without a brand name or not, such a case is a brand name now termed Quantum Biology.
The idea of quantum Biology is old as molecular Biology’s idea because one completes the other. Quantum is a term that may seem alien to Biology because it is more much applied in physics and Chemistry, forgetting that Biology is a member of this family of science. This particular observation had been made decades ago by some other versatile scientist who have advocated for it literally and numerically. The wise say: no army can stop an idea whose time has come” probably this is the time of quantum Biology.

The organisation of chromatin is non-random and shows a broad diversity across cell types, developmental stages, and cell cycle stages. During G0 and G1 phase of interphase, chromatin displays a bivalent status. The condensed chromatin (heterochromatin) at the nuclear periphery is mostly associated with low levels of gene expression, while the loosened chromatin (euchromatin) towards the interior of the nucleus is associated with higher gene expression. This quiescent picture of interphase radically changes when the cell cycle progresses toward cell division. Firstly, during S phase, DNA is replicated, and chromatin progressively condenses. This is followed by the G2 phase that shows a compact heterochromatin recruited towards the centre of the nucleus. At the beginning of mitosis, the chromosomes condense with a significant topological change in their organisation and are segregated during the next stages of the cell division. Meiotic chromosomes are also highly condensed as mitotic chromosomes but show a particular functional structure, which prepares germ cells to exchange DNA sequences between their homologous chromosomes to generate diversity. To summarise, chromatin experiences dramatic organisational changes during mitosis and meiosis. These changes in chromatin organisation during the lifetime of a cell show that chromatin is not a static entity but highly dynamic in nature.

For a variety of reasons, conventional light and electron microscopy have not been able to fully capture the finer details of chromatin organisation and dynamics. For a long time, description of the interphase nucleus was limited to delineate the euchromatin-heterochromatin dichotomy or describe some specific nuclear elements such as the nucleolus. Advancements in molecular biology during the last thirty years have brought an immense amount of information about how chromatin is organised and genes are regulated. As a classical example, the globin gene has been shown to display a highly constrained shape forced by chromatin looping that brings the regulatory regions to the promoter of the gene. Nowadays, genomic studies can acquire an immense amount of information regarding chromatin organisation and gene regulation, leaving one with the expectation that structure of individual genes could potentially be described visually if sufficient specificity and resolution were reached. With the advent of various super-resolution methods, in particular, single molecule localisation microscopy (SMLM) based methods and recently developed strategies for labelling DNA, it is now possible to study chromatin organisation and underlying gene regulatory mechanisms at the nanoscale.

During my PhD, I have analysed a broad range of nuclear phenotypes using SMLM. My analyses contribute to the description of a periodic and dynamic structure of chromatin. Moreover, I have described several elementary chromatin structures that I call chromatin domains, both in interphase and meiosis, that are potentially associated with a local function such as gene activation or silencing.

Firstly with colleagues, I established an experimental setup to study chromatin organisation with single molecule localisation microscopy. I investigated how UV-induced photo-conversion of conventional DNA dyes allows increasing sufficiently the labelling density such that it is possible to study various organisational aspects of chromatin in basal interphase. An adequate imaging protocol has been established to bring DNA minor groove binding dyes such as Hoechst 33258, Hoechst 33342 and DAPI (4’,6-diamidino-2-phenylindole) into an efficient blinking state necessary to record single molecule locations with high precision. This method was applied to several cell types to investigate the chromatin organisation during different stages of the cell cycle at the highest resolution currently achievable with light microscopy.

The results show that the method can capture several hierarchical levels of chromatin organisation. In reverse hierarchical order, I could describe previously known chromatin territories of 1000 nm, subchromosomal domains of 500 nm, chromatin domains of 100 to 400 nm (and further sub-categories of active or repressed domains) and chromatin fibres below 100 nm, mostly between 30 to 60 nm. Individual nucleosomal domains are also described, which tend to cluster in batches of 10-15 nucleosomes, a number close to one found in genomic studies upstream to promoter regions. Next, with colleagues, I studied the dynamics of chromatin using stress as a model system. It was found that short-term oxygen and nutrient deprivation provokes chromatin to shrink to a hollow, condensed ring and rod-like configuration, which reverses back to the initial structure when the stress conditions cease. The condensed network of rods and rings interspersed with large, chromatin-sparse nuclear voids were 40-700 nm in dimension, capturing another level of chromatin organisation not described before.

Finally, I explored the unique properties of chromatin during meiosis, which has escaped analysis at the single-molecule level until now. Single molecule analysis revealed unexpected highly recognisable periodic patterns of chromatin. Firstly, I observed that meiotic chromatin show unique clusters of 250 nm diameter along the synaptonemal complex, extended laterally by chromatin fibres forming loops. These clusters show a remarkable periodicity of 500 nm, a pattern possible to spot because of the highly deterministic nature of pachytene chromosomes and the resolution of the experimental setup. Furthermore, guided by genomic data, I selected histone modifications associated with different chromatin states to dissect the morphology of meiotic chromosomes. I could examine the morphology of these chromosomes into three spatially distinct nanoscale sub-compartments. Histone mark H3K4me3 associated with active chromatin was found in a lateral position, potentially located at the places of de novo double-strand breaks. Repressive histone mark H3K27me3 was shown to display a surprising medial symmetrical and periodic pattern, putatively associated with recombination. Finally, centromeric histone mark H3K9me3 locates at one of meiotic chromosome ends and is potentially associated with repression of repeated regions and pairing of homologous chromosomes at early stages. I summarise these findings in a comprehensive final model.

Overall, I have used new information brought by super-resolution technologies to show the dynamics of chromatin in various processes and novel orders of chromatin compaction, which were not reported previously. Among these new levels of chromatin compaction are the interphase hierarchical chromatin domains, the stress pattern of cells upon oxygen and nutrients deprivation and the novel epigenetic domains found at pachytene stage of meiosis. These architectures show that the organisation of chromatin is more complex than thought before, dynamic in nature and shows a high order of periodicity. Further investigation is, therefore, necessary to understand how chromatin transits from a ’beads-on-string’ model to the intermediary chromatin domains and finally to the commonly observed X-shaped chromosomes.

Compared to the diversity of other floral organs, the steps in anther ontogeny, final cell types, and overall organ shape are remarkably conserved among Angiosperms. Defects in pre-meiotic anthers that alter cellular composition or function typically result in male-sterility. Given the ease of identifying male-sterile mutants, dozens of genes with key roles in early anther development have been identified and cloned in model species, ordered by time of action and spatiotemporal expression, and used to propose explanatory models for critical steps in cell fate specification. Despite rapid progress, fundamental issues in anther development remain unresolved, and it is unclear if insights from one species can be applied to others. Here we construct a comparison of Arabidopsis, rice, and maize immature anthers to pinpoint distinctions in developmental pace. We analyze the mechanisms by which archesporial (pre-meiotic) cells are specified distinct from the soma, discuss what constitutes ...

F(1) backcrosses involving the DDK and C57BL/6 inbred mouse strains show transmission ratio distortion at loci on two different chromosomes, 11 and X. Transmission ratio distortion on chromosome X is restricted to female offspring while that on chromosome 11 is present in offspring of both sexes. In this article we investigate whether the inheritance of alleles at loci on one chromosome is independent of inheritance of alleles on the other. A strong nonrandom association between the inheritance of alleles at loci on both chromosomes is found among male offspring, while independent assortment occurs among female offspring. We also provide evidence that the mechanism by which this phenomenon occurs involves preferential cosegregation of nonparental chromatids of both chromosomes at the second meiotic division, after the ova has been fertilized by a C57BL/6 sperm bearing a Y chromosome. These observations confirm the influence of the sperm in the segregation of chromatids during female...

One of the most prospective directions of study of C.G. Jung’s synchronicity phenomenon
is reviewed considering the latest achievements of modern science. The attention is
focused mainly on the quantum entanglement and related phenomena – quantum
coherence and quantum superposition. It is shown that the quantum non-locality capable
of solving the Einstein-Podolsky-Rosen paradox represents one of the most adequate
physical mechanisms in terms of conformity with the Jung’s synchronicity hypothesis. An
attempt is made on psychophysiological substantiation of synchronicity within the context
of molecular biology. An original concept is proposed, stating that biological molecules
involved in cell division during mitosis and meiosis, particularly DNA may be considered
material carriers of consciousness. This assumption may be formulated on the basis of
phenomenology of Jung’s analytical psychology

Although a number of genes that play key roles during the meiotic process have been characterized in great detail, the whole process of meiosis is still not completely unraveled. To gain insight into the bigger picture, large-scale approaches like RNA-seq and microarray can help to elucidate the transcriptome landscape during plant meiosis, discover co-regulated genes, enriched processes, and highly expressed known and unknown genes which might be important for meiosis. These high-throughput studies are gaining more and more popularity, but their beginnings in plant systems reach back as far as the 1960&#39;s. Frequently, whole anthers or post-meiotic pollen were investigated, while less data is available on isolated cells during meiosis, and only few studies addressed the transcriptome of female meiosis. For this review, we compiled meiotic transcriptome studies covering different plant species, and summarized and compared their key findings. Besides pointing to consistent as well ...

Missegregation of chromosomes in meiosis, or nondisjunction, occurs relatively frequently in humans, and results in pregnancy loss. There is a correlation with advancing maternal age, but the cause of the dramatic increase of aneuploidy, and specifically trisomy (the presence of three copies of a chromosome rather then two), seen with age remains unknown. There is evidence to suggest that chronological age is less important than biological age for trisomy risk, and that regardless of their chronological age, some women are at a greater risk of having a trisomic pregnancy after having already experienced one. Several features of chromosomes are associated with aging, such as a decrease in telomere length, an increase in replication asynchrony at loci including centromeres, and an increase in somatic cell aneuploidy with increasing age. For some chromosomes (15 and 21) an association has also been observed between maternal age, reduced recombination along the chromosome, and risk for nondisjunction. In this project, I have investigated whether or not some women are predisposed to having a trisomic pregnancy. That is, can we predict who will have recurrent trisomy? After analyzing telomere length for an association, no significant decrease in length was seen for women experiencing recurrent trisomy when compared to control women. There was a trend, however, towards longer telomeres in women with a "good" reproductive history (children after 37 years of age) compared to women with a "poor" reproductive history (trisomy and/or recurrent trisomy). As well, although there was no significant increase in replication asynchrony in mothers of trisomy as a group, the younger mothers (<35 years old) of trisomies had increased replication asynchrony when compared to controls of the same age. The relationship between recombination and nondisjunction has been well established and my studies of chromosome 15 confirmed that decreased recombination is associated with meiosis I errors and increased recombination is associated with meiosis II errors. A family with an apparent inherited predisposition to missegregation of chromosome 21 seemed the ideal family in which to study possible genetic mechanisms of nondisjunction. Although nothing conclusive could be determined to be causing their segregation problems, a cryptic rearrangement involving the centromere of chromosome 21 is the most likely explanation. Finally, telomere length was not found to be shortened in children conceived through intracytoplasmic sperm injection (ICSI).

MUS81 is conserved among plants, animals, and fungi and is known to be involved in mitotic DNA damage repair and meiotic recombination. Here we present a functional characterization of the Arabidopsis thaliana homolog AtMUS81, which has a role in both mitotic and meiotic cells. The AtMUS81 transcript is produced in all tissues, but is elevated greater than 9-fold in the anthers and its levels are increased in response to gamma radiation and methyl methanesulfonate treatment. An Atmus81 transfer-DNA insertion mutant shows increased sensitivity to a wide range of DNA-damaging agents, confirming its role in mitotically proliferating cells. To examine its role in meiosis, we employed a pollen tetrad-based visual assay. Data from genetic intervals on Chromosomes 1 and 3 show that Atmus81 mutants have a moderate decrease in meiotic recombination. Importantly, measurements of recombination in a pair of adjacent intervals on Chromosome 5 demonstrate that the remaining crossovers in Atmus81 are interference sensitive, and that interference levels in the Atmus81 mutant are significantly greater than those in wild type. These data are consistent with the hypothesis that AtMUS81 is involved in a secondary subset of meiotic crossovers that are interference insensitive.

Maize anther ontogeny is complex, with the expression of more than 30 000 genes over 4 days of cell proliferation, cell fate acquisition and the start of meiosis. Although many male-sterile mutants disrupt these key steps, few have been investigated in detail. The terminal phenotypes of Zea mays (maize) male sterile 8 (ms8) are small anthers exhibiting meiotic failure. Here, we document much earlier defects: ms8 epidermal cells are normal in number but fail to elongate, and there are fewer, larger tapetal cells that retain, rather than secrete, their contents. ms8 meiocytes separate early, have extra space between them, occupied by excess callose, and the meiotic dyads abort. Thousands of transcriptome changes occur in ms8, including ectopic activation of genes not expressed in fertile siblings, failure to express some genes, differential expression compared with fertile siblings and about 40% of the differentially expressed transcripts appear precociously. There is a high correlation between mRNA accumulation assessed by microarray hybridization and quantitative real-time reverse transcriptase polymerase chain reaction. Sixty-three differentially expressed proteins were identified after two-dimensional gel electrophoresis followed by liquid chromatography tandem mass spectroscopy, including those involved in metabolism, plasmodesmatal remodeling and cell division. The majority of these were not identified by differential RNA expression, demonstrating the importance of proteomics in defining developmental mutants.

Male fertility in flowering plants depends on proper cellular differentiation in anthers. Meiosis and tapetum development are particularly important processes in pollen production. In this study, we showed that the tomato male sterile (ms10 (35) ) mutant of cultivated tomato (Solanum lycopersicum) exhibited dysfunctional meiosis and an abnormal tapetum during anther development, resulting in no pollen production. We demonstrated that Ms10 (35) encodes a basic helix-loop-helix transcription factor that is specifically expressed in meiocyte and tapetal tissue from pre-meiotic to tetrad stages. Transgenic expression of the Ms10 (35) gene from its native promoter complemented the male sterility of the ms10 (35) mutant. In addition, RNA-sequencing-based transcriptome analysis revealed that Ms10 (35) regulates 246 genes involved in anther development processes such as meiosis, tapetum development, cell-wall degradation, pollen wall formation, transport, and lipid metabolism. Our results i...

This research paper aims to explore some common examples of Seventeenth and Eighteenth century British satire as presented in John Wilmot’s poem “A Satire Against Reason and Mankind” (1679) and Jonathan Swift’s book Gulliver’s Travels (1726/1735) and essay “A Modest Proposal” (1729). It is well known that the political, religious and scientific turmoil of the time had a great impact on the production of this derisive literary genre as there was a general sense of disillusionment with humanity as a species. Yet, contrary to the popular use of satire, two other notable figures, William Shakespeare and John Donne, have used satire for more joyous subject matters. William Shakespeare’s “Sonnet 130” (1609) and “Sonnet 131” (1609) and John Donne’s “The Sun Rising” (1633) all employ satire as a tool of praise instead.

The meiotic developmental pathway in yeast enables both differentiation of vegetative cells into haploid spores that ensure long-term survival, and recombination of the parental DNA to create genetic diversity. Despite the importance of proper metabolic regulation for the supply of building blocks and energy, little is known about the reprogramming of central metabolic pathways in meiotically differentiating cells during passage through successive developmental stages. Metabolic regulation during meiotic differentiation in budding yeast was analysed by integrating information on genome-wide transcriptional activity, 26 enzymatic activities in the central metabolism, the dynamics of 67 metabolites, and a metabolic flux analysis at mid-stage meiosis. Analyses of mutants arresting sporulation at defined stages demonstrated that metabolic reprogramming is tightly controlled by the progression through the developmental pathway. The correlation between transcript levels and enzymatic acti...

MEZ1 (MEiosis-associated Zinc-finger protein 1) was first isolated as an anther-specific cDNA from Petunia hybrida. In the present study, we report its functional characterization, including its spatial and temporal expression profiles and phenotypes in MEZ1-silenced plants. MEZ1 transcripts were specifically localized in pollen mother cells during early stages of anther development, and were later distributed in vegetative tissues in anthers. Silencing of MEZ1 by cosuppression resulted in several anomalies during male meiosis that included inability of chromosomes to condense, loss of meiotic synchrony, and premature and apparently uncontrolled cytokinetic events. Consequently, by the end of meiosis 8–10 cells, instead of the normal 4, with varying DNA contents were formed in the MEZ1-silenced meiocytes. Most of these aborted prematurely, and those that matured had a distinctive morphology. MEZ1-silenced plants were female sterile when pollinated with wild-type pollen but they infrequently produced a few seeds upon self-pollination. Resulting T1 plants had increased ploidy levels and exhibited severe anomalies during male meiosis, rendering them completely sterile. We discuss possible role of MEZ1 in the proper progression of plant meiosis.