INVESTIGATING THE FUNCTION OF PERICENTROMERIC HETEROCHROMATIN IN SCHIZOSACCHAROMYCES POMBE

Abstract

In Schizosaccharomyces pombe (fission yeast), heterochromatin is a compact chromatin structure that surrounds the centromere and is involved in gene silencing. It plays a crucial role in ensuring proper chromosome segregation during mitosis, with cells lacking pericentromeric heterochromatic regions exhibiting lagging chromosomes during anaphase and sensitivity to the microtubule inhibitor thiabendazole (TBZ). Improper chromosome segregation can lead to cell death, aneuploidy, and genetic diseases, characteristics observed in cancer cells. Despite the absence of significant heterochromatin proteins, S. pombe cells can grow without apparent defects, raising questions about the significance of heterochromatin. In this study, S. pombe cells without heterochromatin that have evolved for about 360 generations display recoveries in chromosome lagging and reduced TBZ sensitivity. Genetic crosses between evolved cells and parental cells without heterochromatin indicate that suppressor mutations antagonize the TBZ sensitivity in the absence of heterochromatin. Whole genome sequencing combined with genetic confirmation identified a point mutation in an outer kinetochore protein Ndc80 and a frameshift mutation in the kinesin 8 family motor protein, Klp5. Although the ndc80 mutant partially suppresses the TBZ sensitivity of loss of heterochromatin, deletion of Klp5 almost completely alleviates the phenotype in cells without heterochromatin and in cells without RNAi machinery, as well as recovering the growth defect caused by RNAi mutants. My results support a novel function of pericentromeric heterochromatin in stabilizing microtubule dynamics during mitotic division.