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

I-labeUed epidermal growth factor (I-EGF) and I-labeUed insulin-like growth factor-I (I-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 I-EGF was inhibited by increasing concentrations of EGF, but not by various other growth factors and hormones. Chemical cross-linking of I-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 ^I-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 IIGF-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.