Biology subjects

Maestroni, L.

Publications and source records attributed to Maestroni, L..

3 recordsLinked to original sources

bioRxiv2022

Remarkably high rate of meiotic recombination in the fission yeast Schizosaccharomyces pombe

In most eukaryotes, the number of meiotic crossovers (COs) is limited to 1-3 per chromosome, which are prevented from occurring close to one another by CO interference. The fission yeast Schizosaccharomyces pombe, an exception to this general rule, lacks CO interference and seems to have the highest CO number per chromosome. However, global CO frequency was indirectly estimated in this species, raising doubts about this exceptional recombination level. Here, we used an innovative strategy to directly determine COs genome-wide in S. pombe. We confirm the absence of crossover interference and reveal the presence of co-variation in CO number across chromosomes within tetrads, suggesting that a limiting pro-CO factor varies stochastically between meiocytes. CO number per chromosome varies linearly with chromosome size, with the three chromosomes having, on average, 15.9, 12.5, and 7.0 COs, respectively. This is significantly lower than previous estimates but reinforces S. pombes exceptional status as the eukaryote with the highest CO number per chromosome described to date and among the species with the highest rate of COs per unit of DNA.

genetics↗

bioRxiv2022

Condensin positioning at telomeres by Taz1 promotes telomere disjunction in anaphase

The localization of condensin along chromosomes is crucial for their accurate segregation in anaphase. Condensin is enriched at telomeres but how and for what purpose had remained elusive. Here we show that fission yeast condensin accumulates at telomere repeats through the balancing acts of Taz1, a core component of the shelterin complex that ensures telomeric functions, and Mit1, a nucleosome-remodeler associated with shelterin. We further show that condensin takes part in sister-telomere separation in anaphase, and that this event can be uncoupled from the prior separation of chromosome arms, implying a telomere-specific separation mechanism. Consistent with a cis-acting process, increasing or decreasing condensin occupancy specifically at telomeres modifies accordingly the efficiency of their separation in anaphase. Genetic evidence suggests that condensin promotes sister-telomere separation by counteracting cohesin. Thus, our results reveal a shelterin-based mechanism that enriches condensin at telomeres to drive in cis their separation during mitosis.

cell biology↗

bioRxiv2022

Comprehensive analysis of cis- and trans-acting factors affecting Break-Induced Replication

Break-induced replication (BIR) is a highly mutagenic eukaryotic homologous DNA recombination pathway that repairs one-ended DNA double strand breaks such as broken DNA replication forks and eroded telomeres. While searching for cis-acting factors regulating BIR efficiency, we found that BIR efficiency is the highest close to chromosome ends. The variations of BIR efficiency as a function of the length of DNA to replicate can be described as a combination of two decreasing exponential functions, a property in line with repeated cycles of strand invasion, elongation and dissociation that characterize BIR. Interestingly, the apparent processivity of BIR depends on the length of DNA already synthesized. BIR is more susceptible to disruption during the synthesis of the first [~]35-40 kb of DNA than later, notably when the template chromatid is being transcribed or heterochromatic. Finally, we show that the Srs2 helicase promotes BIR from both telomere proximal and telomere distal regions in diploid cells but only from telomere proximal sites in haploid cells. Altogether, we bring new light on the factors impacting a last resort DNA repair pathway.

genetics↗