Expression of Frizzled genes in developing and postnatal hair follicles.

Embryonic hair follicle development and postnatal hair growth rely on intercellular communication within the epithelium and between epithelial and mesenchymal cells. Several members of the WNT family of paracrine intercellular signaling molecules are expressed in specific subsets of cells in developing and mature mouse hair follicles, suggesting them as candidates for some of the intercellular signals that operate in these organs. As WNT ligands activate several different signaling pathways, they may play multiple and complex roles in developing and postnatal skin. To begin to investigate these functions, we have used in situ hybridization to identify cells that express Frizzled (Fz) WNT receptor genes, and so are potentially receptive to WNT ligands. We find that several Fz genes are specifically expressed at sites of known activity of the WNT/beta-catenin signaling pathway, allowing us to identify candidate receptors for canonical WNT ligands important in appendage development. The expression of additional Fz genes is specifically elevated at locations and developmental stages other than those that display WNT/beta-catenin pathway activity, suggesting that signaling through alternate WNT pathways may contribute to the development and function of skin and hair.