Diverse epigenetic strategies interact to control epidermal differentiation [Illumina bead array]

It is becoming clear that interconnected functional gene networks, rather than single genes in isolation, govern stem cell self-renewal and differentiation. To identify potential epigenetic networks that impact on human epidermal stem cells we performed siRNA based genetic screens for 332 chromatin modifiers. We developed a Bayesian mixture model to predict putative functional interactions between those epigenetic modifiers that regulated differentiation. This allowed us to discover a network of genetic interactions involving EZH2, UHRF1 (both known to regulate epidermal self-renewal), ING5 (a MORF complex component), BPTF and SMARCA5 (NURF complex components). Genome-wide localisation and global mRNA expression analysis revealed that these factors impact two distinct but functionally related gene sets, including integrin extracellular matrix receptors that mediate anchorage of epidermal stem cells to their niche. Using a competitive epidermal reconstitution assay we confirmed that ING5, BPTF, SMARCA5, EZH2 and UHRF1 control differentiation under physiological conditions. Thus, regulation of distinct gene expression programs through the interplay between diverse epigenetic strategies protects epidermal stem cells from differentiation.

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