Llorente, B. | bioRxiv Science

bioRxiv2017

Mechanistic view and genetic control of DNA recombination during meiosis

Meiotic recombination is essential for fertility and allelic shuffling. Canonical recombination models fail to capture the observed complexity of meiotic recombinants. Here we revisit these models by analyzing meiotic heteroduplex DNA tracts genome-wide in combination with meiotic DNA double-strand break (DSB) locations. We provide unprecedented support to the synthesis-dependent strand annealing model and establish estimates of its associated template switching frequency and polymerase processivity. We show that resolution of double Holliday junctions (dHJs) is biased toward cleavage of the pair of strands containing newly synthesized DNA near the junctions. The suspected dHJ resolvase Mlh1-3 as well as Mlh1-2, Exo1 and Sgs1 promote asymmetric positioning of crossover intermediates relative to the initiating DSB and bidirectional conversions. Finally, we show that crossover-biased dHJ resolution depends on Mlh1-3, Exo1, Msh5 and to a lesser extent on Sgs1. These properties are likely conserved in eukaryotes containing the ZMM proteins, which includes mammals.

genetics↗

bioRxiv2017

Variation Of The Meiotic Recombination Landscape And Properties Over A Broad Evolutionary Distance In Yeasts

Meiotic recombination is a major factor of genome evolution, deeply characterized in only a few model species, notably the yeast Saccharomyces cerevisiae. Consequently, little is known about variations of its properties across species. In this respect, we explored the recombination landscape of Lachancea kluyveri, a protoploid yeast species that diverged from the Saccharomyces genus more than 100 million years ago and we found striking differences with S. cerevisiae. These variations include a lower recombination rate, a higher frequency of chromosomes segregating without any crossover and the absence of recombination on the chromosome arm containing the sex locus. In addition, although well conserved within the Saccharomyces clade, the S. cerevisiae recombination hotspots are not conserved over a broader evolutionary distance. Finally and strikingly, we found evidence of frequent reversion of meiotic commitment to mitotic growth allowing allele shuffling without meiosis completion. Identification of this major but underestimated evolutionary phenomenon illustrates the relevance of exploring non-model species.\n\nAuthor summaryMeiotic recombination promotes accurate chromosome segregation and genetic diversity. To date, the mechanisms and rules lying behind recombination were dissected using model organisms such as the budding yeast Saccharomyces cerevisiae. To assess the conservation and variation of this process over a broad evolutionary distance, we explored the meiotic recombination landscape in Lachancea kluyveri, a budding yeast species that diverged from S. cerevisiae more than 100 million years ago. The meiotic recombination map we generated revealed that the meiotic recombination landscape and properties significantly vary across distantly related yeast species, supporting that recombination hotspots conservation across yeast species is likely associated to the conservation of synteny. Finally, the frequent meiotic reversions we observed led us to re-evaluate their evolutionary importance.

genomics↗