Unexpected roles of a shugoshin protein at subtelomeres

Junko Kanoh

doi:10.1266/ggs.17-00016

Abstract

A chromosome is composed of structurally and functionally distinct domains. Telomeres, which are located at the ends of linear chromosomes, play crucial roles in genome stability. Although substantial knowledge of telomeres has been accumulated, the regulation and function of subtelomeres, which are the domains adjacent to telomeres, remain largely unknown. In this review, I describe recent discoveries about the multiple roles of a shugoshin family protein, Sgo2, which is localized at centromeres in mitosis and contributes to precise chromosome segregation, in defining chromatin structure and functions of the subtelomeres in fission yeast. Sgo2 becomes enriched at the subtelomeres, particularly during G2 phase, and is essential for the formation of a highly condensed subtelomeric chromatin body called the knob. Furthermore, Sgo2 maintains the expression levels of subtelomeric genes and the timing of DNA replication at subtelomeric late origins.

Highlights

The telomere, a specialized chromatin structure at the ends of chromosomes, plays important roles in genome integrity, and the adjacent chromosomal region, the subtelomere, has recently become a focus of attention in the medical field
These results indicate that the association of Sgo2 with subtelomeres forms a new type of repressive chromatin domain that is distinct from H3K9me-Swi6-mediated heterochromatin
On the other hand, during interphase, Sgo2 is recruited to the subtelomeres and plays important roles in the formation of knobs, in the repression of gene transcription, and in the repression of replication to ensure proper gene expression and replication timing at the subtelomeres

Summary

Junko Kanoh*

A chromosome is composed of structurally and functionally distinct domains. Telomeres, which are located at the ends of linear chromosomes, play crucial roles in genome stability. Substantial knowledge of telomeres has been accumulated, the regulation and function of subtelomeres, which are the domains adjacent to telomeres, remain largely unknown. I describe recent discoveries about the multiple roles of a shugoshin family protein, Sgo, which is localized at centromeres in mitosis and contributes to precise chromosome segregation, in defining chromatin structure and functions of the subtelomeres in fission yeast. Sgo becomes enriched at the subtelomeres, during G2 phase, and is essential for the formation of a highly condensed subtelomeric chromatin body called the knob. Sgo maintains the expression levels of subtelomeric genes and the timing of DNA replication at subtelomeric late origins

INTRODUCTION

Subtelomeric homologous region

Spreading of heterochromatin

Conclusion and future prospects