Neurotrophin-3 involvement in the regulation of hair follicle morphogenesis.

Hair follicle epithelium and nervous system share a common ectodermal origin, and some neurotrophins can modulate keratinocyte proliferation and apoptosis. It is therefore reasonable to ask whether growth factors that control neural development are also involved in the regulation of hair follicle morphogenesis. Focusing on neurotrophin-3 (NT-3) and its high-affinity-receptor [tyrosine kinase C (TrkC)], we show that hair placode keratinocytes express TrkC mRNA and immunoreactivity early during murine hair follicle morphogenesis. In later stages of hair follicle development, TrkC mRNA, TrkC-, and NT-3-immunoreactivity are seen in keratinocytes of the proximal hair bulb as well as in dermal papilla fibroblasts. Compared with the corresponding wild-type animals, early stages of hair follicle morphogenesis are significantly accelerated in newborn NT-3 overexpressing mice, whereas these are retarded in newborn heterozygous NT-3 knockout (+/-) mice. These observations suggest that NT-3 is an important growth modulator during morphogenesis and remodeling of neuroectodermal-mesenchymal interaction systems like the hair follicle.