REQUIREMENT OF INNER CELL MASS FOR EFFICIENT CHORIONIC-GONADOTROPIN SECRETION BY BLASTOCYSTS OF COMMON MARMOSETS (CALLITHRIX-JACCHUS)

The role of the inner cell mass in the induction of chorionic gonadotr ophin synthesis and secretion by the trophoblast of the peri-implantat ion primate blastocyst was studied in common marmoset monkeys. An in v itro system for the culture of blastocysts commencing with blastocysts collected 8 days after conception was developed. Chorionic gonadotrop hin measured in the spent culture fluid was first detected in most bla stocysts after 3 or 4 days (day 11 or 12) of culture at a time equival ent to implantation in vitro. Initial secretion of chorionic gonadotro phin coincided with development of parietal endoderm and histological appearance of syncytiotrophoblast in the polar trophoblast. Little cho rionic gonadotrophin was secreted by blastocysts with a poorly develop ed, or absent, inner cell mass. Mural trophoblast removed from blastoc ysts after 2 days of culture (day 10) grew in vitro as a unilaminar ve sicle but failed to secrete significant amounts of chorionic gonadotro phin. However, mural trophoblast from older blastocysts (days 13 and 1 4) after chorionic gonadotrophin secretion had commenced continued to secrete chorionic gonadotrophin, with trophoblast from day 14 blastocy sts secreting significantly more than that from day 13. It was conclud ed from these studies that while mural trophoblast from marmoset blast ocysts will proliferate in vitro in the absence of an inner cell mass, efficient induction of chorionic gonadotrophin secretion requires the presence of the inner cell mass or its derivatives. Once chorionic go nadotrophin secretion has commenced, secretion will continue in the ab sence of the inner cell mass.