Noggin is required for induction of the hair follicle growth phase in postnatal skin

During postnatal development, the hair follicle (HF) shows cyclic activity with periods of relative resting, active growth (anagen), and regression. W e demonstrate that similar to the HF induction in embryonic skin, initiatio n of a new hair growth phase in postnatal skin requires neutralization of t he inhibitory activity of bone morphogenetic protein 4 (BMP4) by the BMP an tagonist noggin. In the resting HF, BMP4 mRNA predominates over noggin in t he epithelium and mesenchyme, and the BMP receptor IA is prominently expres sed in the follicular germ. Anagen development is accompanied by down-regul ation of the BMP4 and increased noggin mRNA in the HF. Furthermore, adminis tration of noggin protein induces new hair growth phase in postnatal teloge n skin in vivo. In contrast, BMP4 induces selective arrest of anagen develo pment in the non-tylotrich (secondary) HF. As a hair growth inducer, noggin increases Shh mRNA in the HF whereas BMP4 down-regulates Shh. This suggest s that modulation of BMP4 signaling by noggin is essential for hair growth phase induction in postnatal skin and that the hair growth-inducing effect of noggin is mediated, at least in part, by Shh.