Spo11: Difference between revisions

In the budding yeast ''SacharomycesSaccharomyces cerevisiae'', the meiotic defects in recombination and chromosome disjunction of ''spo11'' mutants are alleviated by X-irradiation.<ref name="pmid8514137">{{cite journal | vauthors = Thorne LW, Byers B | title = Stage-specific effects of X-irradiation on yeast meiosis | journal = Genetics | volume = 134 | issue = 1 | pages = 29–42 |year date = May 1993 | doi = 10.1093/genetics/134.1.29 | pmid = 8514137 | pmc = 1205431 |doi= |url=}}</ref> This finding indicates that X-ray induced DNA damages can initiate crossover recombination leading to proper disjunction independently of SPO11.

In the worm ''Caenorhabditis elegans'', a homolog of ''spo11'' is ordinarily employed in the initiation of meiotic recombination. However, radiation induced-breaks can also initiate recombination in mutants deleted for this ''spo11'' homolog.<ref name="pmid9708740">{{cite journal | vauthors = Dernburg AF, McDonald K, Moulder G, Barstead R, Dresser M, Villeneuve AM | title = Meiotic recombination in C. elegans initiates by a conserved mechanism and is dispensable for homologous chromosome synapsis | journal = Cell | volume = 94 | issue = 3 | pages = 387–98 |year date = August 1998 | pmid = 9708740 | doi = 10.1016/s0092-8674(00)81481-6 |url s2cid = 10198891 | doi-access = free }}</ref>

[[Deamination]] of cytosine resulting in the dU:dG mismatch is one of the most common single-base-altering lesions in non-replicating DNA. ''Spo11'' mutants of the fission yeast ''Schizosaccharomyces pombe'' and ''C. elegans'' undergo meiotic crossover recombination and proper chromosome segregation when dU:dG lesions are produced in their DNA.<ref name=Pauklin>{{cite journal | vauthors = Pauklin S, Burkert JS, Martin J, Osman F, Weller S, Boulton SJ, Whitby MC, Petersen-Mahrt SK | display-authors = 6 | title = Alternative induction of meiotic recombination from single-base lesions of DNA deaminases | journal = Genetics | volume = 182 | issue = 1 | pages = 41–54 |year date = May 2009 | pmid = 19237686 | pmc = 2674839 | doi = 10.1534/genetics.109.101683 |url=}}</ref> This crossover recombination does not involve the formation of large numbers of double-strand breaks, but does require uracil DNA-glycosylase, an enzyme that removes uracil from the DNA phosphodiester backbone and initiates base excision repair. Thus, it was proposed that base excision repair of DNA damage such as a uracil base, an [[AP site|abasic site]], or a single-strand nick is sufficient to initiate meiotic crossover recombination in ''S. pombe'' and ''C. elegans''.<ref name=Pauklin />

In ''S. pombe'', a mutant defective in the ''spo11'' homolog ''Rec12'' is deficient in meiotic recombination. However recombination can be restored to near normal levels by a deletion in ''rad2'', a gene that encodes an endonuclease involved in [[Okazaki fragments|Okazaki fragment]] processing (Farah et al., 2005). Both crossover and non-crossover recombination were increased but double-strand breaks were undetectable. On the basis of the biochemical properties of the rad2 deletion, it was proposed that meiotic recombination can be initiated by DNA lesions other than double-strand breaks, such as nicks and gaps which accumulate during premeiotic DNA replication when Okasaki fragment processing is deficient.<ref name="pmid16118186">{{cite journal | vauthors = Farah JA, Cromie G, Davis L, Steiner WW, Smith GR | title = Activation of an alternative, rec12 (spo11)-independent pathway of fission yeast meiotic recombination in the absence of a DNA flap endonuclease | journal = Genetics | volume = 171 | issue = 4 | pages = 1499–511 |year date = December 2005 | pmid = 16118186 | pmc = 1456079 | doi = 10.1534/genetics.105.046821 |url=}}</ref>

== Absence of ''Spo11'' in some sexual species ==

The most recent common ancestor of the social [[amoeba]] genera ''[[Dictyostelium]]'', ''[[Polysphondylium]]'' and ''[[Acytostelium]]'', appears to have lacked the ''Spo11'' gene.<ref name=Bloomfield>{{cite journal | vauthors = Bloomfield G | title = Atypical ploidy cycles, Spo11, and the evolution of meiosis | journal =Semin. Seminars in Cell Dev.& Biol.Developmental Biology | volume = 54 |issue= |pages = 158–64 |year date = June 2016 | pmid = 26811992 | doi = 10.1016/j.semcdb.2016.01.026 | url = https://zenodo.org/record/889469 }}</ref><ref name="pmid18663385">{{cite journal | vauthors = Malik SB, Pightling AW, Stefaniak LM, Schurko AM, Logsdon JM | title = An expanded inventory of conserved meiotic genes provides evidence for sex in Trichomonas vaginalis | journal =PLoS PLOS ONE | volume = 3 | issue = 8 | pages = e2879 |year date = August 2007 | pmid = 18663385 | pmc = 2488364 | doi = 10.1371/journal.pone.0002879 |url doi-access = free }}</ref> Such an ancestor likely lived several hundred million years ago.<ref name="pmid24040233">{{cite journal | vauthors = Fiz-Palacios O, Romeralo M, Ahmadzadeh A, Weststrand S, Ahlberg PE, Baldauf S | title = Did terrestrial diversification of amoebas (amoebozoa) occur in synchrony with land plants? | journal =PLoS PLOS ONE | volume = 8 | issue = 9 | pages = e74374 | year = 2013 | pmid = 24040233 | pmc = 3770592 | doi = 10.1371/journal.pone.0074374 |url bibcode = 2013PLoSO...874374F | doi-access = free }}</ref> ''[[Dictyostelium discoideum]]'' and ''[[Polysphondylium pallidum]]'' are both capable of [[meiosis|meiotic]] [[sexual reproduction]] (see ''[[Dictyostelium discoideum#Sexual reproduction|''D. discoideum'' sexual reproduction]]'' and ''[[Polysphondylium pallidum#Sexual reproduction|''P. pallidum'' sexual reproduction]]''). Bloomfield<ref name=Bloomfield /> speculated that dormant cells in the soil might be exposed to many kinds of stress, such as desiccation or radiation, that could induce spontaneous [[DNA damage (naturally occurring)|DNA damage]]. Such damage would make the induction of double-strand breaks by Spo11 redundant for the initiation of [[genetic recombination|recombination]] during meiosis, and thus explain its absence in this group.

== References ==