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High resolution chromatin dynamics during a yeast stress response

ABSTRACT: Covalent histone modifications are highly conserved and play multiple roles in eukaryotic transcription regulation. Because of extensive crosstalk between transcriptional processes and histone modifications, steady state observations are insufficient to fully disentangle histone modification networks. As transient perturbation of feedback mechanisms can reveal network structure, we mapped 26 histone modifications genome-wide over a time course following dramatic transcriptional reprogramming – response to diamide stress in yeast. Interestingly, while we observed limited combinatorial complexity in steady-state histone modification patterns, consistent with previous studies, the combinatorial complexity of histone modification space increased modestly during the stress response, resulting from roughly 3% of nucleosomes transiently populating rare histone modification states. We show that most of these short-lived histone mark combinations result from differences in histone modification dynamics that transiently uncouple highly correlated marks, with slow histone methylation changes often lagging the more rapid changes in acetylation. Together, our results provide the first detailed view of an epigenome in transition.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE61888 | GEO | 2014/11/29

SECONDARY ACCESSION(S): PRJNA262623

REPOSITORIES: GEO

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Project description:Packaging of eukaryotic genomes into chromatin has wide-ranging effects on gene transcription. Curiously, it is commonly observed that deletion of a global chromatin regulator affects expression of only a limited subset of genes bound to or modified by the regulator in question. However, in many single-gene studies it has become clear that chromatin regulators often do not affect steady-state transcription, but instead are required for normal transcriptional reprogramming by environmental cues. We therefore have systematically investigated the effects of 83 histone mutants, and 119 deletion mutants, on induction/repression dynamics of 200 transcripts in response to diamide stress in yeast. Importantly, we find that chromatin regulators play far more pronounced roles during gene induction/repression than they do in steady-state expression. Furthermore, by jointly analyzing the substrates (histone mutants) and enzymes (chromatin modifier deletions) we identify specific interactions between histone modifications and their regulators. Combining these functional results with genome-wide mapping of several histone marks in the same time course, we systematically investigated the correspondence between histone modification occurrence and function. We follow up on one pathway, finding that Set1-dependent H3K4 methylation primarily acts as a gene repressor during diamide stress, specifically at genes involved in ribosome biosynthesis. Set1-dependent repression of ribosomal genes occurs via distinct pathways for ribosomal protein genes and ribosomal biogenesis genes, which can be separated based on genetic requirements for repression and based on chromatin changes during gene repression. Together, our dynamic studies provide a rich resource for investigating chromatin regulation, and show that the M-bM-^@M-^\activatingM-bM-^@M-^] mark H3K4me3 functions largely as a repressor in yeast. We set to track how histone modifications change during transcriptional reprogramming. We perfomed a time course experiment following treatment of mid-log growing yeast (BY4741) with diamide. Samples were collected at t=0,4,8,15,30,60 and fixed by crosslinking. We extracted mononucleosomes by MNase digestion and then applied ChIP for selected histone modifications. The IPed material was hybridized to genomic tiling arrays against the input material.

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High resolution chromatin dynamics during a yeast stress response

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