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

Abstract 12sI-labelled epidermal growth factor (125I-EGF) and 125I-labelled insulin-like growth factor-I (12SI-IGF-I) bound to trophodenn 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 12SI-EGF was inhibited by increasing concentrations of EGF, but not by various other growth factors and hormones. Chemical cross-linking of 12SI-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 l2iI-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 f25I-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.