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/* Signaling Pathway and linkages */
=== Signaling Pathway and linkages ===
'''Molecular mediators of hair follicle embryogenesis:''' * Identification of the molecular pathways controlling differentiation and proliferation in mammalian hair follicles provides the crucial link to understanding the regulation of normal hair growth, the basis of hereditary hair loss diseases, and the origin of follicle-based tumors.* Homeobox (hox), hedgehog (hh), patched (ptc), wingless (wg}/wnt, disheveled (dsh), engrailed (en), Notch 1 and armadillo/B-catenin genes are all critical for hair follicle.*
* Wnt pathway: Maintains hair-inducing activity of the dermal papilla.
* Hedgehog pathway
* STAT pathway
* TGF beta/BMP Pathway: Bone morphogenetic protein (BMP) signaling have been implicated in the regulation of both proliferation and differentiation in the hair follicle. BMP2 is expressed in the embryonic ectoderm, but then localizes to the early hair follicle placode and underlying mesenchyme. BMP4 is expressed in the early dermal condensate. Research results show that BMPs are a key component of the signaling network controlling hair development and are required to induce the genetic program regulating hair shaft differentiation in the anagen hair follicle.
* FGF Pathway
* MAPK Pathway
* Testosterone Pathway
* NOTCH Pathway: Notch-1 is expressed in ectodermal-derived cells of the follicle, in the inner cells of the embryonic placode and the follicle bulb, and in the suprabasal cells of the mature outer root sheath. Delta-1, one of the three ligands is only expressed during embryonic follicle development and is exclusive to the mesenchymal cells of the pre-papilla located beneath the follicle placode, and appears to promote and accelerate placode formation, while suppressing placode formation in surrounding cells. Other ligands, Serrate 1 and Serrate 2, are expressed in matrix cells destined to form the inner root sheath and hair shaft.
* Sonic hedgehog (SHH) pathway: Sonic hedgehog (SHH) signaling plays a critical role in hair follicle development, but how it controls these processes remains unclear. Skin from mice lacking SHH have extremely effete hair follicles with poorly developed dermal papillae, suggesting that SHH controls follicular proliferation, and follicle size.
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