Deleterious role of centromeric crossovers in chromosomal segregation during meiosis

Abstract

Crossover formation (CO) during meiotic recombination is one of the important processes that provides right amount of tension for the homologous chromosomes to properly segregate in the first meiotic division (MI). CO formation is necessary in meiosis, yet regions near centromere (pericentric regions) have mechanisms to repress them. Earlier studies have shown that COs that are too close to the centromere, leads to meiotic chromosome mis-segregation, which may further result in aneuploid gametes and eventually aneuploid or dead zygote. Although the harmful effects of COs near the centromeres are well known, the different kinds of mis-segregations that it gives rise to and the mechanisms behind them have still not been well discussed. Here, we have used live cell imaging in mutants proficient in centromeric recombination to understand how pericentric crossovers can lead to defects in chromosomal segregation during meiosis in fission yeast, Schizosaccharomyces pombe. Live cell imaging provides a more effective approach than using viability assays to address the basis of chromosomal mis-segregation resulting from pericentric crossovers. An assay was designed to determine centromeric crossover (C-CO) frequency and classify the different segregation patterns in the mutants into meiosis I or meiosis II mis-segregation events. Lastly, a strategy has been planned to further look into the mechanism behind such mis-segregations.