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. Author manuscript; available in PMC: 2018 Dec 1.
Published in final edited form as: Stem Cells. 2017 Sep 23;35(12):2323–2330. doi: 10.1002/stem.2696

Figure 1. Specification of hair follicle stem cells and the establishment of quiescent cellular state during embryonic skin development.

Figure 1

A. In newly formed hair germs, HF-SCs are specified as Sox9-expressing progenitors. At this stage, all Sox9-expressing cells are highly proliferative. B. When hair follicles continue to grow, some HF-SCs exit cell cycle and adapt the quiescent cellular state. Whereas the precise mechanism remains to be determined, the establishment of quiescence is generally correlated with increased expression of several negative regulators of the PI(3)K pathway. C. In fully developed hair follicles, HF-SCs are mostly quiescent and only occasionally activated to fuel hair growth or repair wound.