Localization and characterization of EGF/TGF-alpha receptors on peri-implantation trophoblast in sheep.

Receptors for epidermal growth factor (EGF) have been identified on the ovine trophoblast as early as day 15 of gestation. A radioligand assay with 125I-labelled EGF was used to detect high and low affinity binding sites on the trophoblastic and placental membranes. The binding of 125I-labelled EGF was inhibited by increasing concentrations of unlabelled EGF. Competition studies with other peptide hormones including transforming growth factor alpha (TGF-alpha), insulin-like growth factor-I (IGF-I) and ovine placental lactogen confirmed the specificity of EGF/TGF-alpha for its receptor. Cross-linking experiments using disuccinimidyl suberate (DSS) revealed a radiolabelled band of relative molecular mass 170 kDa. Immunohistochemical localization of the receptors demonstrated their distribution on the epithelial layer cells. The presence of receptors for EGF/TGF-alpha suggests that these factors could be involved in the regulation of embryonic development and fetal growth.