Genome-wide Maps of Histone Modifications Unwind In Vivo Chromatin States of the Hair Follicle Lineage

SummaryUsing mouse skin, where bountiful reservoirs of synchronized hair follicle stem cells (HF-SCs) fuel cycles of regeneration, we explore how adult SCs remodel chromatin in response to activating cues. By profiling global mRNA and chromatin changes in quiescent and activated HF-SCs and their committed, transit-amplifying (TA) progeny, we show that polycomb-group (PcG)-mediated H3K27-trimethylation features prominently in HF-lineage progression by mechanisms distinct from embryonic-SCs. In HF-SCs, PcG represses nonskin lineages and HF differentiation. In TA progeny, nonskin regulators remain PcG-repressed, HF-SC regulators acquire H3K27me3-marks, and HF-lineage regulators lose them. Interestingly, genes poised in embryonic stem cells, active in HF-SCs, and PcG-repressed in TA progeny encode not only key transcription factors, but also signaling regulators. We document their importance in balancing HF-SC quiescence, underscoring the power of chromatin mapping in dissecting SC behavior. Our findings explain how HF-SCs cycle through quiescent and activated states without losing stemness and define roles for PcG-mediated repression in governing a fate switch irreversibly.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (369 K)Download as PowerPoint slideHighlights► Hair follicle lineage progression is governed by PcG-regulation distinct from ESCs ► PcG-regulation adds an irreversible clamp to the SC→committed progeny switch ► Chromatin mapping reveals how HF-SCs induce self-renewal without differentiating ► Chromatin mapping is a powerful tool to identify new regulators of SC behavior