Recent progress in hair follicle stem cell markers and their regulatory roles

Table 1 Expression profile in postnatal hair cycle and related functions of some hair follicle stem cell markers

	Expression location in telogen	Expression location in anagen	Related functions	Ref.
CD34	Outer layer of bulge and HG (but not found in human HF)	Most peripheral layer of the ORS	Sustain the stemness of HFSCs	[14-22]
CD200	Bulge and HG	Relatively uniform throughout the whole HF, except for the Mx, DP and HS	Sustain the stemness of HFSCs	[20,22-26]
K15	Epidermal basal layer and HF bulge in neonatal mice; still strong in bulge in mature mice skin	ORS, the bulge is the strongest area	Not found	[22,27,28]
K19	Bulge	Mainly the U-ORS and the pb-ORS of HFs, stronger within the pb-ORS versus the bulge	Not found	[27,29-31]
Lgr5	Bulge, stronger in HG	The lower portion of the ORS, not overlapped with CD34	In the telogen-to-anagen transition	[32-38]
Lhx2	Bulge and HG	Through the ORS	Epidermal differentiation, HFSC quiescence, hair anchoring	[31,39-41]
Sox9	Bulge and HG	ORS, stronger in the sub-bulge region	Maintainess and differentiation of HFSCs	[12,31,42,43]
Runx1	Bulge, stronger in HG	The infundibulum, bulge, ORS, Mx and cortex	Regulating anagen initiation and HFSC proliferation	[12,42,44-50]
Axin2	Outer bulge cells	ORS	Maintainess of hair-forming ability	[51-60]
Nfatc1	Bulge	Bulge, overlapped with CD34 and Lhx2	Maintainess of HFSC quiescence	[46,61-65]
Foxp1	Bulge	Bulge, ORS, Mx	Maintainess of HFSC quiescence	[66-70]
Foxc1	Bulge, isthmus, sebaceous glands	Bulge, K6+ inner bulge layer, isthmus, IRS and sebaceous glands	Maintainess of the old bulge	[16,40,71-73]
Msi2	Basal layer of bulge and HG	Basal and suprabasal bulge, ORS and IRS	In the telogen-to-anagen transition	[74-77]

CD34: Leukocyte differentiation antigen 34; CD200: Leukocyte differentiation antigen 200; K15: Keratin 15; K19: Keratin 19; Lgr5: Leucine-rich repeat-containing G protein-coupled receptor 5; Lhx2: Lim-homeodomain transcription factor 2; Sox9: Sex-determining region Y-Box 9; Runx1: Runx family transcription factor 1; Axin2: Axin-related protein 2; Nfatc1: Nuclear factor of activated T cells c1; Foxp1: Forkhead Box P1; Foxc1: Forkhead Box C1; Msi2: Musashi 2; Mx: Matrix; HFSC: Hair follicle stem cell; HS: Hair shaft; HG: Hair germ; DP: Dermal papilla; ORS: Outer root sheath; IRS: Inner root sheath; pb-ORS: Proximal bulb outer root sheath; U-ORS: Upper outer root sheath.