Mapping Epigenomic Type-Specific Differences Occurring During Hematopoiesis

Formation of the blood from self-renewing hematopoietic stem cells to terminal lineages necessarily involves epigenomic modifications of the genome to control regulator and signature gene expression. By analysing the global expression profiles of hematopoietic stem cells (HSCs), in vivo differentiated CD4+ T cells and CD19+ B cells as well as in vitro differentiated erythrocyte precursor cells, we identified hundreds of transcripts showing type-specific expression in these cell types. To understand the epigenomic changes related to tissue-specific expression during HSC differentiation, we examined the genome-wide distribution of H3K4me1, H3K4me3, H3K27me1, H3K27me3, histone variant H2A.Z, chromatin remodeler BRG1, and RNA Polymerase II in the same four cell types, as well as embryonic stem cells. Analysis of these datasets revealed that numerous key differentiation genes are primed for expression by Brg1 and Pol II binding, as well as bivalent modifications in the HSCs prior to their expression in downstream differentiated cell types. Much of this bivalency in HSC is retained from embryonic stem cells. After differentiation, these modified regions resolve to active chromatin modification configuration in the specific lineage, while in parallel differentiated lineages the bivalent modification remains; Pol II and Brg1 are lost in closer lineages but bivalency resolves to silent monovalency in more distant lineages. Correlation of tissue-specific gene expression with the epigenomic changes predicts tens of thousands of potential common enhancers and tissue-specific enhancers, which may critically contribute to the expression patterns. We provide a valuable dataset for further understanding the regulatory mechanisms of differentiation and function of blood lineages. This SuperSeries is composed of the SubSeries listed below. Overall design: Refer to individual Series.