GSE27148
A comparative epigenomics approach reveals REST as a mediator of Polycomb reprogramming during neuronal differentiation
Transcription factors (TFs) in concert with chromatin pathways stably reset transcriptional programs during differentiation. Yet we know little how local sites of chromatin reprogramming are specified and how the estimated 3000 TF encoded in mammalian genomes contribute to chromatin dynamics. To identify candidate TFs we developed an integrated computational approach (Epi-MARA) that models chromatin dynamics in terms of predicted transcription factor binding sites and show that it correctly predicts key TFs involved in epigenome reorganization.  When applied to a time course of genome-wide H3 lysine 27 trimethylation (H3K27me3), a chromatin mark set by the Polycomb system, during neuronal differentiation of murine stem cells Epi-MARA predicted that the repressive transcription factor REST contributes to a gain of H3K27me3 at a subset of promoters during the transition from the stem to the progenitor state. To test this prediction we identified, genome-wide, the actual binding sites of REST and H3K27me3 during the differentiation in cells that are either wildtype or in which REST had been deleted. REST indeed localizes to a subset of sites that gain H3K27me3 in progenitors. Importantly, absence of REST in trans leads to a loss of H3K27me3 predominantly in the neuronal progenitor state and specifically at those regions where REST was bound. This function further requires REST binding sites in cis as their mutation leads to substantial loss of H3K27me3.   Taken together we provide a novel approach to identify epigenome and TF crosstalk during cellular reprogramming and prove experimentally the prediction that REST acts as an important recruiter of Polycomb repression during early steps of neurogenesis. Overall design: Dataset comprises of 15 ChIP-seq samples using chromatin from embryonic stem (ES) and neuronal progentor (NP) of wildtype and RESTko cells, which was immunoprecipitated, using antibodies against REST, H3K27me3, or Suz12