GSE116477
ChIPseq on H3K27ac, H3K27me3 and H2AK119Ub on TXY cell line
During development, changes in gene transcription are accompanied by changes in chromatin modification but the order and causality of events often remain unclear. Here we address this question using X-chromosome inactivation (XCI), which entails chromosome-wide gene silencing and heterochromatin formation. We initiate XCI in female, mouse embryonic stem cells by inducing Xist expression and monitor subsequent changes in transcription and chromatin modification by allele-specific TTseq and ChIPseq respectively. An unprecedented temporal resolution has enabled us to define early alterations in chromatin that are induced upon Xist RNA coating. Xist-induced repression begins with histone deacetylation, which involves the histone deacetylase HDAC3 and occurs before efficient loss of H3K4me3 and H3K4me1 modifications. Polycomb-associated repressive histone marks accumulate rapidly, starting with PRC1-associated H2AK119Ub and followed by PRC2-associated H3K27me3. However, polycomb accumulates initially at large premarked domains, some of which correspond to Xist entry sites, and then spreads into genes. We also show that spreading can only ensue when transcriptional silencing has occurred. These results establish a detailed epigenomic time course for XCI and reveal a hierarchy of events with chromatin playing an important role in transcriptional silencing of the X chromosome. Overall design: Native ChIPseq on H3K27me3 and H2AK119Ub on TXY:Xist and TXY:XistdeltaA  cell line, after 2 days of differentiation, with or without DOX, in replicates.