Expression and structures of human placental hormone genes as a function of placental development.

Abstract

One important function of the human placenta is the synthesis of peptide hormones during pregnancy (Boime et al., 1978). -The major ones elaborated by the trophoblast are human chorionic gonadotropin (hCG) and human placental lactogen (hPL). Their time course of appearance in maternal serum during pregnancy is quite different; hCG peaks in the first trimester, while hPL reaches maximal levels near term. The factors controlling their synthesis appear not to be the same. Thus, the human placenta represents a convenient and unique tissue for studying expression of human hormonal genes during development. Placental lactogen is a single nonglycosylated polypeptide chain which shares greater than 90% homology with human growth hormone. Chorionic gonadotropin consists of two nonidentical glycosylated subunits (alpha and beta) linked noncovalently. The amino acid sequence of hCGa is virtually identical to that of the a-subunits contained in human pituitary gonadotropins, and in thyrotropin (Bahl, 1977). The $3-subunit confers the unique biologic action on each hormone, although there is also significant homology between the $3-subunits (Bahl, 1977). The 13-subunit of hCG$3 contains an extra 30 amino acid peptide at the carboxyl end of the molecule, which is not found in the other $3-subunits (Morgan et al., 1975). The amounts of aand 13-subunits secreted