Fig. 4. The epidermal regulatory network. BMP signaling activates target genes directly, including Xvent2 and Msx1 (which activate the epidermal pathway and suppress neural fates when ectopically overexpressed). Xvent2 and Msx1 regulate the more-restricted pro-epidermal genes Xap2, Dlx3 and Xgrhl1, which can directly regulate epidermal structural genes such as the cytokeratin gene Xk81.1a, but which do not have neural-inhibiting functions.