Requirement of Heterochromatin for Cohesion at Centromeres

TLDR

Centromeres are heterochromatic, yet the role of this silent chromatin in maintaining sister chromatid cohesion during mitosis remains unclear. The study demonstrates that heterochromatin, via Swi6, is essential for recruiting Rad21 cohesin to centromeres, thereby distinguishing centromere from arm cohesion and ensuring accurate chromosome segregation.

Abstract

Centromeres are heterochromatic in many organisms, but the mitotic function of this silent chromatin remains unknown. During cell division, newly replicated sister chromatids must cohere until anaphase when Scc1/Rad21-mediated cohesion is destroyed. In metazoans, chromosome arm cohesins dissociate during prophase, leaving centromeres as the only linkage before anaphase. It is not known what distinguishes centromere cohesion from arm cohesion. Fission yeast Swi6 (a Heterochromatin protein 1 counterpart) is a component of silent heterochromatin. Here we show that this heterochromatin is specifically required for cohesion between sister centromeres. Swi6 is required for association of Rad21-cohesin with centromeres but not along chromosome arms and, thus, acts to distinguish centromere from arm cohesion. Therefore, one function of centromeric heterochromatin is to attract cohesin, thereby ensuring sister centromere cohesion and proper chromosome segregation.