In a previous study on neonatal rat skin (Green MR, Basketter DA, Couchman JR, Rees DA: Dev Biol 100:506-512, 1983) a close positive correlation was found between epidermal growth factor (EGF) receptor tissue distribution and areas of potential epithelial cell proliferation. We now report on the binding distribution of [125I]EGF, representing the tissue localization of available EGF receptors, during embryonic rat skin development including hair follicle formation and the adult hair growth cycle. At 16 days embryonic development a relatively low receptor density is seen over all the epidermal cell layers but by 17 days, with the onset of very rapid epidermal proliferation, labeling increases and becomes restricted to the basal epidermal cells. Between 17 and 20 days embryonic development, available receptors for EGF are consistently absent from epidermal basal cells overlaying the dermal condensates marking the first stage of hair follicle development. This restricted and temporary loss of EGF receptors above these specialized mesenchymal condensates implies a role for the EGF receptor and possibly EGF or an EGF-like ligand in stimulating the epithelial downgrowth required for hair follicle development. In the anagen hair bulb, receptors for EGF are detected over the outer root sheath and the epithelial cell layers at the base of the follicle and show a correlation with the areas of epithelial proliferation in the hair bulb. During the catagen and telogen phases of the hair cycle, receptors are observed in high numbers on all the undifferentiated or dedifferentiating cells of the degenerating epithelial strand and secondary hair germ. Dermal cells are, in general, less heavily labeled than the basal epithelial cells of skin except for the developing striated muscle (panniculus carnosus) in embryonic skin which is more heavily labeled. The data are discussed in terms of a possible role for the EGF receptor and associated EGF or EGF-like ligands in specific areas of epithelial tissue morphogenesis during embryonic skin maturation, hair follicle development, and hair cycling.
Keywords: Animals; Autoradiography; Cell Differentiation; Epidermal Growth Factor; Epithelium; Hair; Morphogenesis; Rats; Rats, Inbred Strains; Receptor, Epidermal Growth Factor; Receptors, Cell Surface; Skin