Receptors for epidermal growth factor and insulin-like growth factor-I on preimplantation trophoderm of the pig

¹²⁵I-labelled epidermal growth factor (¹²⁵I-EGF) and ¹²⁵I-labelled insulin-like growth factor-I (¹²⁵I-IGF-I) bound to trophoderm cells from pig blastocysts obtained on days 15-19 of pregnancy. Specific binding was detected on freshly isolated cell suspensions and on cells cultured for several days. The binding of ¹²⁵I-EGF was inhibited by increasing concentrations of EGF, but not by various other growth factors and hormones. Chemical cross-linking of ¹²⁵I-EGF to its receptors using disuccinimidyl suberate (DSS) revealed a radiolabelled band of relative molecular mass 160 000, similar to that identified as the EGF receptor in other cell types. The binding of ¹²⁵I-IGF-I was inhibited by both IGF-I and insulin, indicating that the receptors were either type I IGF receptors or insulin receptors. Cross-linking of ¹²⁵I-IGF-I to serum-free supernatants from trophoderm cultures showed that the cells secreted an IGF-binding protein, giving a complex of relative molecular mass about 45 000. The presence of receptors for EGF and IGF/insulin suggests that these factors could be involved in regulating the growth and development of the early blastocyst.