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

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.

Histone H2A insufficiency causes chromosomal segregation defects due to anaphase chromosome bridge formation at rDNA repeats in fission yeast

“…The characteristic phenotype of the reunion of divided nuclei during meiosis I as observed in ∆hta2 cells has also been reported in the ∆dbl2 mutant 15 . However, unlike that in the ∆hta2 mutant, rDNA repeats were not involved in the ∆dbl2 mutant as observed by Nuc1-GFP (Supplementary Fig.…”

ZGRF1 variants implicated in a sensory reflex epilepsy

“…In-silico analysis of ZGRF1 has suggested three major domains in the protein: DUF2439, zf-GRF and helicase. DUF2439 has been implicated in meiotic chromosome segregation, crossover recombination and telomere maintenance in yeast (Polakova et al, 2016;Silva et al, 2016). There are at least six other zinc finger GRF-type proteins involved in aspects of DNA damage response, transcription or RNA regulatory activities.…”

“…Orthologs of this domain are found in Schizosaccharomyces pombe, Saccharomyces cerevisiae and Arabidopsis thaliana (Polakova et al, 2016). This domain has been implicated in meiotic chromosome segregation, crossover recombination and telomere maintenance (Polakova et al, 2016;Silva et al, 2016). A centrally placed second domain zf-GRF (zinc finger-GRF type) is a presumed zinc-binding domain of 45 amino acids named after three conserved residues within the domain.…”

Modulation of meiotic homologous recombination by DNA helicases

“…As mentioned above, Dbl2, a factor reported to recruit Fml1 to DSBs in vegetative cells (Yu et al ., ) apparently has a role in promoting Fbh1 focus formation during meiosis. A dbl2 Δ mutant displays very similar meiotic phenotypes to an fbh1 Δ mutant, including severe chromosome segregation defects and an accumulation of Rad51 foci (Polakova et al ., ). A physical interaction between Fbh1 and Dbl2 could not be demonstrated, but clearly Dbl2 has a role in controlling Rad51 deposition on chromatin by promoting Fbh1 action (Polakova et al ., ).…”

“…Indeed, deleting a Rad51/Dmc1 mediator or over‐expressing Fml1 reduces gene conversion‐associated crossover frequency and partially rescues the low spore viability of a mus81 Δ mutant (Hyppa and Smith, ; Lorenz et al ., , ). Whether Dbl2 contributes to Fml1–Mhf1–Mhf2 function is currently unclear, because Dbl2 is important for localization of the UvrD‐type DNA helicase Fbh1 (Polakova et al ., ), and since the associated phenotype is upstream of Fml1's roles, it masks a potential genetic interaction between Dbl2 and Fml1–Mhf1–Mhf2 (see below).…”