Dbl2 Regulates Rad51 and DNA Joint Molecule Metabolism to Ensure Proper Meiotic Chromosome Segregation.

Silvia Polakova,Alexander Schleiffer,Juraj Gregan,Zsigmond Benko,Ivana Misova,Randy W Hyppa,Gerald R Smith,Lucia Molnarova

doi:10.1371/journal.pgen.1006102

Abstract

To identify new proteins required for faithful meiotic chromosome segregation, we screened a Schizosaccharomyces pombe deletion mutant library and found that deletion of the dbl2 gene led to missegregation of chromosomes during meiosis. Analyses of both live and fixed cells showed that dbl2Δ mutant cells frequently failed to segregate homologous chromosomes to opposite poles during meiosis I. Removing Rec12 (Spo11 homolog) to eliminate meiotic DNA double-strand breaks (DSBs) suppressed the segregation defect in dbl2Δ cells, indicating that Dbl2 acts after the initiation of meiotic recombination. Analyses of DSBs and Holliday junctions revealed no significant defect in their formation or processing in dbl2Δ mutant cells, although some Rec12-dependent DNA joint molecules persisted late in meiosis. Failure to segregate chromosomes in the absence of Dbl2 correlated with persistent Rad51 foci, and deletion of rad51 or genes encoding Rad51 mediators also suppressed the segregation defect of dbl2Δ. Formation of foci of Fbh1, an F-box helicase that efficiently dismantles Rad51-DNA filaments, was impaired in dbl2Δ cells. Our results suggest that Dbl2 is a novel regulator of Fbh1 and thereby Rad51-dependent DSB repair required for proper meiotic chromosome segregation and viable sex cell formation. The wide conservation of these proteins suggests that our results apply to many species.

Highlights

During meiosis, haploid gametes are produced from diploid precursor cells
To identify novel regulators of meiosis, we screened a library of fission yeast deletion mutants and found that deletion of the dbl2 gene led to missegregation of PLOS Genetics | DOI:10.1371/journal.pgen
We show that Dbl2 is required for proper segregation of chromosomes during meiosis by regulating Rad51 function and joint molecules (JMs) metabolism, apparently by promoting formation of the helicase Fbh1 foci at the sites of double-strand breaks (DSBs) repair to dissociate a minor class of JMs

Summary

Introduction

Haploid gametes are produced from diploid precursor cells. The reduction of chromosome number is achieved by a single round of DNA replication followed by two rounds of chromosome segregation, termed meiosis I and meiosis II. The formation of crossovers, as a result of meiotic recombination, and the attachment of sister kinetochores to microtubules emanating from the same spindle pole (mono-orientation) ensure that homologous centromeres are pulled in opposite directions on meiosis I spindles [2,3]. Crossovers and cohesion between sister chromatids distal to crossovers are responsible for holding homologs together until the onset of anaphase I, when a protease called separase cleaves cohesin along chromosome arms [4,5,6]. This allows segregation of recombined homologs to opposite poles of the meiosis I spindle. Deprotection of centromeric cohesin and a second round of separase activation allow cleavage of the centromeric cohesin at the onset of anaphase II, which is followed by segregation of sister centromeres in meiosis II [10]

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