CHARACTERIZATION AND DISTRIBUTION OF EPIDERMAL GROWTH-FACTOR RECEPTORS IN THE SKIN AND WOOL FOLLICLES OF THE SHEEP FETUS DURING DEVELOPMENT

We have determined the binding affinity and capacity and relative dist ribution of epidermal growth factor (EGF) receptors in the skin of the Merino sheep fetus before and during the development of the wool foll icle population. Autoradiography of tissue sections incubated with [I- 125]EGF revealed that label was confined predominantly to the epidermi s and dermoepidermal junction before follicle formation, at 30 and 55 d of gestation. During follicle initiation (Days 60 to 65), receptor a ctivity was distributed over the epidermis, including the epidermal ag gregations of primordia at the dermoepidermal junction. However, recep tor concentrations, as revealed by grain counts of autoradiographs, we re reduced in these regions when compared with 55-d skin. The receptor distribution over the epidermis and its derivatives did not alter dur ing subsequent follicle development, although the intensity of labelin g increased as the follicles matured. Specific receptor binding was no t observed above background levels in the dermis and dermal papillae d uring all stages of follicle development. At follicle maturation, EGF receptors were widely distributed over the cells of the epidermis and the epidermal derivatives of the cutaneous appendages but were particu larly localized in the sebaceous glands and outer root sheath (see als o Wynn et al. 1989). EGF immunoreactive material has also been found a t these sites (du Cros et al. 1999), suggesting an autocrine role for EGF in the regulation of cell function. It is likely that the differen tiation-promoting activities of EGF may predominate over those of grow th, because the receptor-bearing cells were not members of rapidly pro liferating populations.