Heterochromatin suppresses gross chromosomal rearrangements at centromeres by repressing Tfs1/TFIIS-dependent transcription

Akiko K Okita,Dayalini Weerasekara,Jie Su,Tatsuro S Takahashi,Faria Zafar,Hiroshi Kimura,Yota Murakami,Hisao Masukata,Takuro Nakagawa,Takuya Kajitani

doi:10.1038/s42003-018-0251-z

Abstract

Heterochromatin, characterized by histone H3 lysine 9 (H3K9) methylation, assembles on repetitive regions including centromeres. Although centromeric heterochromatin is important for correct segregation of chromosomes, its exact role in maintaining centromere integrity remains elusive. Here, we found in fission yeast that heterochromatin suppresses gross chromosomal rearrangements (GCRs) at centromeres. Mutations in Clr4/Suv39 methyltransferase increased the formation of isochromosomes, whose breakpoints were located in centromere repeats. H3K9A and H3K9R mutations also increased GCRs, suggesting that Clr4 suppresses centromeric GCRs via H3K9 methylation. HP1 homologs Swi6 and Chp2 and the RNAi component Chp1 were the chromodomain proteins essential for full suppression of GCRs. Remarkably, mutations in RNA polymerase II (RNAPII) or Tfs1/TFIIS, the transcription factor that facilitates restart of RNAPII after backtracking, specifically bypassed the requirement of Clr4 for suppressing GCRs. These results demonstrate that heterochromatin suppresses GCRs by repressing Tfs1-dependent transcription of centromere repeats.

Highlights

Heterochromatin, characterized by histone H3 lysine 9 (H3K9) methylation, assembles on repetitive regions including centromeres
Clr4Δ increased gross chromosomal rearrangements (GCRs) rate even in the absence of mat2P-mat3M (Fig. 1c, blue dots) and rec[12] (Fig. 1c, orange dots). These results show that Clr[4] suppresses spontaneous GCRs in mitotic cells
Most of the GCR products formed in cid14Δ ago1Δ cells were isochromosomes whose breakpoints were located in centromere repeats

Summary

Introduction

Heterochromatin, characterized by histone H3 lysine 9 (H3K9) methylation, assembles on repetitive regions including centromeres. We found in fission yeast that heterochromatin suppresses gross chromosomal rearrangements (GCRs) at centromeres. The presence of repetitive elements is a threat to genome stability Recombination events such as crossover and break-induced replication (BIR) between repetitive elements give rise to gross chromosomal rearrangements (GCRs), which cause cell death and genetic diseases including cancer[2,3]. Heterochromatin is marked by histone H3 lysine 9 (H3K9) methylation that is catalyzed by specific methyltransferases such as fission yeast Clr[4] and mammalian Suv[397]. A clr[4] deletion increases RNA polymerase II (RNAPII) localization and derepresses transcription at centromere repeats[8], demonstrating that H3K9 methylation causes transcriptional silencing. The RNA-induced transcriptional silencing (RITS) complex, which consists of small

Methods

Results

Conclusion