1019 - DECONVOLUTION OF HEMATOPOIETIC COMMITMENT DECISIONS BY GENOME-WIDE ANALYSIS OF PROGRESSIVE DNA METHYLATION CHANGES

Abstract

Advances in single cell transcriptome analyses have resulted in the derivation of new models to describe the hierarchical organization of the mammalian hematopoietic system. While such an approach appears to be effective at discerning the trajectory of differentiation from hematopoietic stem cells (HSCs) to a given mature lineage, it remains a challenge to identify definitive points where specific lineage fates become restricted. 5-MeC is a stable epigenetic modification, whose remodeling is integral to the process of enforcing lineage-restricted gene expression programs. We have previously observed that the remodeling of the DNA methylome appears to be both progressive and irreversible during the process of hematopoietic differentiation, suggesting that this modification could be used to unambiguously identify molecular marks of lineage commitment. To pursue this concept, we generated a genome-wide DNA methylation map of murine hematopoiesis. This map, comprised of a total of 147,232 differentially methylated regions (DMRs), encompasses 26 different FACS-purified populations. Analysis of these DMRs revealed progressive lineage-specific DNA methylation dynamics that would be indicative of a molecular mechanism of cell fate restriction. Lineage-specific DMRs could already be identified within the early hematopoietic stem and multipotent progenitor compartments, supporting the concept that lineage restriction occurs early during differentiation. In contrast with previous studies, integration of our methylome data with single cell gene expression data encompassing the entire hematopoietic component of the bone marrow, revealed an unprecedented degree of correlation between the transcriptional program and DNA methylation levels. Both inflammatory challenge and ageing resulted in remodeling of the HSC DNA methylome in vivo, in a manner that was not predominantly associated with priming towards any particular differentiated cell fate. Rather the reprogrammed methylome may represent an epigenetic memory of gene expression programs resulting from extrinsic stimuli.