Polyembryoma of ovary producing alpha-fetoprotein and HCG: immunoperoxidase and electron microscopic study

Polyembryoma of ovary producing alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) was studied by indirect immunoperoxidase method for AFP and HCG, and electron microscopy. Clinically, this patient showed pseudoprecocious puberty caused by elevated HCG which is synthesized by trophoblastic cells in polyembryoma. She is put under VAC (vincristine, actinomycin-D, cyclophosphamide) chemotherapy after operation and shows no signs of recurrence including reelevation of serum AFP at five months after operation. Embryoid bodies which we studied correspond to normal embryo at 15- or 16-day stage. Immunoperoxidase study showed that AFP is synthesized by yolk sac cells of the embryoid bodies and HCG is synthesized by syncytiotrophoblastic cells. The finding about AFP synthesis suggests that normal embryo at 15- or 16-day stage may begin AFP synthesis. Electron microscopic study showed that each part of the embryoid bodies had some characteristic structures. Most striking features found in the cytodifferentiation of the embryoid bodies were noticed in some special differentiation of plasma membrane and existence of surface coat. Desmosomes were found in endodermal cells and yolk sac cells. Ectodermal cells were attached to each other by zonulae occludentes and adherentes. Microvilli were found in ectodermal cells and yolk sac cells. Two different kinds of surface coat were found in mesodermal cells and lining cells of yolk sac cavity: thin-layered deposit of electron-dense material covering the plasma membrane facing intercellular space of mesodermal cells and endodermal cells, and thick-layered deposit of electron-dense material which covered the plasma membrane facing yolk sac cavity of endodermal cells and yolk sac cells. Presence of similar characteristic material in RER of yolk sac cells led us to speculate that thick deposit was synthesized by yolk sac cells and secreted into yolk sac cavity. Combined with immunoperoxidase study by light microscopy, we assume that this thick-layered deposit has some close relation to AFP.