Figure 1. Wound-induced hair follicle neogenesis. In mice, skin wounds create an embryonic-like state in the surrounding cells that allows for the generation of new skin and hair follicles. The wounded dermis causes the recruitment of gd T cells to the site of injury [a]. The T cells produce fibroblast growth factor 9 (Fgf9; Gaf) [b], which binds to keratinocyte growth factor receptor (Kgfr; Fgfr2; Cd332) and fibroblast growth factor receptor 3 (Fgfr3; Cd333) [c]. This leads to the activation of Fgfr2 and Fgfr3 and production and activation of wingless-type MMTV integration site family member 2a (Wnt2; Wnt2a) [d]. The protein stimulates the production of Fgf9 by some fibroblasts to initiate a feedback loop to generate more activated Wnt2a [e]. Wnt2a then activates a signaling pathway that causes fibroblast proliferation [f] and dermis cell-fate determination to promote development of new hair follicles [g].