DNA sequence differences are determinants of meiotic recombination outcome

Abstract

Meiotic recombination is essential for producing healthy gametes, and also generates genetic diversity. DNA double-strand break (DSB) formation is the initiating step of meiotic recombination, producing, among other outcomes, crossovers between homologous chromosomes (homologs), which provide physical links to guide accurate chromosome segregation. The parameters influencing DSB position and repair are thus crucial determinants of reproductive success and genetic diversity. Using Schizosaccharomyces pombe, we show that the distance between sequence polymorphisms across homologs has a strong impact on meiotic recombination rate. The closer the sequence polymorphisms are to each other across the homologs the fewer recombination events were observed. In the immediate vicinity of DSBs, sequence polymorphisms affect the frequency of intragenic recombination events (gene conversions). Additionally, and unexpectedly, the crossover rate of flanking markers tens of kilobases away from the sequence polymorphisms was affected by their relative position to each other amongst the progeny having undergone intragenic recombination. A major regulator of this distance-dependent effect is the MutSα-MutLα complex consisting of Msh2, Msh6, Mlh1, and Pms1. Additionally, the DNA helicases Rqh1 and Fml1 shape recombination frequency, although the effects seen here are largely independent of the relative position of the sequence polymorphisms.

Intragenic meiotic recombination in Schizosaccharomyces pombe is sensitive to environmental temperature changes

“…Our meiotic recombination assay (Osman et al 2003;Lorenz et al 2014;Brown et al 2019) consists of intragenic markers (point mutations in the ade6 gene) and the intergenic markers ura4 + -aim2 and his3 + -aim, which are introduced to flank the ade6 gene (Fig. 2).…”

“…We tested five different combinations of ade6 heteroalleles: two large intragenic intervals containing an M26-type hotspot allele (ade6-3083 × ade6-469, 1320 bp and ade6-M216 × ade6-3049, 1168 bp), one large intragenic interval containing non-hotspot alleles only (ade6-M375 × ade6-469, 1335 bp) and two small intragenic intervals containing an M26-type hotspot allele (ade6-M216 × ade6-3083, 85 bp and ade6-3049 × ade6-469, 254 bp) ( Fig. 2b) (Lorenz et al 2010(Lorenz et al , 2012Brown et al 2019). The ade6-M26 hotspot and its variants, ade6-3049, ade6-3083 and ade6-3074, are a well-studied type of meiotic recombination hotspot (Steiner and Smith 2005;Wahls and Davidson 2012).…”

Gene conversion: a non-Mendelian process integral to meiotic recombination

“…Notably, S. cerevisiae msh2∆ mutants have been exploited to improve our understanding of meiotic recombination mechanisms in an engineered polymorphic region harbouring a hotspot (Ahuja et al 2021 ) and on a genome-wide scale (Martini et al 2011 ; Marsolier-Kergoat et al 2018 ; Cooper et al 2021 ). This approach uncovered molecular details of non-Mendelian events during meiotic recombination at an unprecedented resolution (see below), but this also has its limitations because deletion of mutS α (and mutL α) genes does also affect overall gene conversion and crossover frequency (Martini et al 2011 ; Brown et al 2019 ; Ahuja et al 2021 ; Cooper et al 2021 ).…”

“…Genetic factors which direct or influence the formation and repair of DSBs will affect the frequency of both non-Mendelian and Mendelian segregation events, because these genetic outcomes are determined by the amount and type of meiotic recombination occurring at any given locus. Even the mismatch repair factors MutSα (Msh2-Msh6), Mutsβ (Msh2-Msh3), and MutLα (Mlh1-Pms1), which deal with mismatches in hDNA to produce gene conversions, and modulate the number of non-Mendelian segregation events at polymorphic sites by antirecombination, do also influence overall crossover frequency (Martini et al 2011 ; Brown et al 2019 ; Ahuja et al 2021 ; Cooper et al 2021 ). Having said this, the frequency of gene conversion and crossover outcomes can be differentially affected by experimental conditions and certain mutant backgrounds (Rockmill et al 2013 ; Brown et al 2020 ).…”

Catalase T-Deficient Fission Yeast Meiocytes Show Resistance to Ionizing Radiation

“…To check whether the deletion of the antioxidant defense gene ctt1 or the Fe 2+ /Mn 2+ -transporter gene pcl1 contribute to the fidelity of meiosis under standard laboratory conditions, we measured spore viability and recombination frequencies in wild type and the two deletion mutants. We employed a genetic recombination assay that allows us to determine gene conversion and crossover frequencies alongside crossover rate associated with gene conversion events [35,43]. As part of these experiments spore viability was measured, as well.…”