Life and death fate decisions allow cells to avoid massive apoptotic death in response to genotoxic stress. While the regulatory mechanisms and signaling pathways controlling DNA repair and apoptosis are well characterized, the precise molecular strategies that determine the ultimate choice of DNA repair and survival or apoptotic cell death remain incompletely understood. Here, we report that a protein tyrosine phosphatase, Eya, is involved in promoting efficient DNA repair rather than apoptosis in response to genotoxic stress in specific tissue/cell types by executing a damage-signal dependent dephosphorylation of an H2AX C-terminal tyrosine phosphate (Y142). This post-translational modification determines the relative recruitment of either DNA repair or pro-apoptotic factors to the tail of γH2AX and allows it to function as an active determinant of repair/survival versus apoptotic responses to DNA damage, revealing an additional phosphorylation-dependent mechanism that modulates survival/apoptotic decisions during mammalian organogenesis.

Hair follicle stem cells (HFSCs) and their transit amplifying cell (TAC) progeny sense BMPs at defined stages of the hair cycle to control their proliferation and differentiation. Here, we exploit the distinct spatial and temporal localizations of these cells to selectively ablate BMP signaling in each compartment and examine its functional role. We find that BMP signaling is required for HFSC quiescence and to promote TAC differentiation along different lineages as the hair cycle progresses. We also combine in vivo genome-wide chromatin immunoprecipitation and deep-sequencing, transcriptional profiling, and loss-of-function genetics to define BMP-regulated genes. We show that some pSMAD1/5 targets, like Gata3, function specifically in TAC lineage-progression. Others, like Id1 and Id3, function in both HFSCs and TACs, but in distinct ways. Our study therefore illustrates the complex differential roles that a key signaling pathway can play in regulation of closely-related stem/progenitor cells within the context of their overall niche.

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