The development of hair follicles and nail

Abstract

The hair follicle and nail unit develop and regenerate through epithelial-mesenchymal interactions. Here, we review some of the key signals and molecular interactions that regulate mammalian hair follicle and nail formation during embryonic development and how these interactions are reutilized to promote their regeneration during adult homeostasis and in response to skin wounding. Finally, we highlight the role of some of these signals in mediating human hair follicle and nail conditions.

Fig. 1.. Morphological changes of HF during hair cycle and development.

(a) Repetitive hair cycle is achieved by coordinated regulation of a variety of cell cypes in HF such as EpSCs, McSCs, DP cells, and dermal sheath cells. (b) Reciprocal communications between epidermal and dermal cells lead to HF development. HF EpSCs, hair follicle epithelial stem cells; TACs, transit-amplifying cells; McSCs, melanocyte stem cells; MCs, melanocytes; SG, sebacious gland; sHG, secondary hair germ; DP, dermal papilla; HS, hair shaft; IRS, inner root sheath; ORS, outer root sheath; DC, dermal condensates.

Fig. 2.. Spatio-tempral regulation of Wnt and SHH pathways during DC/DP fomration in embryonic skin (a) and skin wounds (b).

It remains to be determined whether Wnt and SHH pathways cooperate with each other to develop neogenic HFs in skin wounds as those pathways do during HF development. DC, dermal condensates DP; dermal papilla.

Fig. 3.. Anatomy of mouse digit tip.

Various signaling pathways such as Wnt and BMP regulate nail development.