Enhanced ectodysplasin-A receptor (EDAR) signaling alters multiple fiber characteristics to produce the East Asian hair form.

Hair morphology differs dramatically between human populations: people of East Asian ancestry typically have a coarse hair texture, with individual fibers being straight, of large diameter, and cylindrical when compared to hair of European or African origin. Ectodysplasin-A receptor (EDAR) is a cell surface receptor of the tumor necrosis factor receptor (TNFR) family involved in the development of hair follicles, teeth, and sweat glands. Analyses of genome-wide polymorphism data from multiple human populations suggest that EDAR experienced strong positive selection in East Asians. It is likely that a nonsynonymous SNP in EDAR, rs3827760, was the direct target of selection as the derived p.Val370Ala variant is seen at high frequencies in populations of East Asian and Native American origin but is essentially absent from European and African populations. Here we demonstrate that the derived EDAR370A common in East Asia has a more potent signaling output than the ancestral EDAR370 V in vitro. We show that elevation of Edar activity in transgenic mice converts their hair phenotype to the typical East Asian morphology. The coat texture becomes coarse, with straightening and thickening of individual hairs and conversion of fiber cross-sectional profile to a circular form. These thick hair fibers are produced by enlarged hair follicles, which in turn develop from enlarged embryonic organ primordia. This work shows that the multiple differences in hair form between East Asian and other human populations can be explained by the simplest of genetic alterations.

The Edar subfamily in feather placode formation.

A subgroup of the TNF receptor family, composed of Edar, Troy and Xedar, are implicated in the development of ectodermal appendages, such as hair follicles, teeth and sweat glands. We have isolated chicken orthologues of these three receptors and analysed their roles in early feather development. Conservation of protein sequences between mammalian and avian proteins is variable, with avian Edar showing the greatest degree of sequence identity. cXedar differs from its mammalian orthologue in that it contains an intracellular death domain. All three receptors are expressed during early feather morphogenesis and dominant negative forms of each receptor impair the epithelial contribution to feather bud morphogenesis, while the dermal contribution appears unaffected. Hyperactivation of each receptor leads to more widespread assumption of placode fate, though in different regions of the skin. Receptor signaling converges on NF-kappaB, and inhibiting this transcription factor alters feather bud number and size in a stage-specific manner. Our findings illustrate the roles of these three receptors during avian skin morphogenesis and also suggest that activators of feather placode fate undergo mutual regulation to reach a decision on skin appendage location and size.