Highly condensed chromatins are formed adjacent to subtelomeric and decondensed silent chromatin in fission yeast.

Atsushi Matsuda,Yasushi Hiraoka,Chie Mori,Hiroshi Kimura,Haruhiko Asakawa,Yuji Chikashige,Tokuko Haraguchi,Da-Qiao Ding,Chizuru Ohtsuki

doi:10.1038/ncomms8753

Abstract

It is generally believed that silent chromatin is condensed and transcriptionally active chromatin is decondensed. However, little is known about the relationship between the condensation levels and gene expression. Here we report the condensation levels of interphase chromatin in the fission yeast Schizosaccharomyces pombe examined by super-resolution fluorescence microscopy. Unexpectedly, silent chromatin is less condensed than the euchromatin. Furthermore, the telomeric silent regions are flanked by highly condensed chromatin bodies, or ‘knobs'. Knob regions span ∼50 kb of sequence devoid of methylated histones. Knob condensation is independent of HP1 homologue Swi6 and other gene silencing factors. Disruption of methylation at lysine 36 of histone H3 (H3K36) eliminates knob formation and gene repression at the subtelomeric and adjacent knob regions. Thus, epigenetic marks at H3K36 play crucial roles in the formation of a unique chromatin structure and in gene regulation at those regions in S. pombe.

Highlights

It is generally believed that silent chromatin is condensed and transcriptionally active chromatin is decondensed
Using super-resolution microscopy, we are able to examine the spatial organization of the genome within the small nucleus of S. pombe
We found that the silent chromatin was highly decondensed; its transcription was repressed in that region

Summary

Introduction

It is generally believed that silent chromatin is condensed and transcriptionally active chromatin is decondensed. Epigenetic marks at H3K36 play crucial roles in the formation of a unique chromatin structure and in gene regulation at those regions in S. pombe. Despite having accumulated knowledge of chromatin domains at the biochemical level, we know little about the structural organization of chromatin in three-dimensional space. S. pombe contains many heterochromatin factors that are conserved in higher eukaryotes, and its nucleosome contains no histone H1 and no known histone H3 variants except for the CENP-A homologue (Cnp[1]). This makes it one of the simplest model organisms to understand the molecular basis of heterochromatin formation. Few structural studies have been done of chromatin in S. pombe due to its small nucleus (B2 mm in diameter)

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Results

Conclusion