LOCALIZATION AND CHARACTERIZATION OF EGF TGF-ALPHA RECEPTORS ON PERIIMPLANTATION TROPHOBLAST IN SHEEP/

Receptors for epidermal growth factor (EGF) have been identified on th e ovine trophoblast as early as day 15 of gestation. A radioligand ass ay with I-125-labelled EGF was used to detect high and low affinity bi nding sites on the trophoblastic and placental membranes. The binding of I-125-labelled EGF was inhibited by increasing concentrations of un labelled EGF. Competition studies with other peptide hormones includin g transforming growth factor alpha (TGF-alpha), insulin-like growth fa ctor-I (IGF-I) and ovine placental lactogen confirmed the specificity of EGF/TGF-alpha for its receptor. Cross-linking experiments using dis uccinimidyl suberate (DSS) revealed a radiolabelled band of relative m olecular mass 170 kDa. Immunohistochemical localization of the recepto rs demonstrated their distribution on the epithelial layer cells. The presence of receptors for EGF/TGF-alpha suggests that these factors co uld be involved in the regulation of embryonic development and fetal g rowth.