Go-expression of cytokeratins and vimentin by highly invasive trophoblast in the white-winged vampire bat, Diaemus youngi, and the black mastiff bat,Molossus ater, with observations on intermediate filament proteins in the decidua and intraplacental trophoblast

Histological and immunocytochemical studies of gravid reproductive tracts o btained from the white-winged vampire bat (Diaemus youngi) and the black ma stiff bat (Molossus ater) have established that both species develop unusua lly invasive trophoblast. This is released by the developing discoidal haem ochorial placenta, expresses both cytokeratins and vimentin, and invades th e myometrium and adjacent tissues (including the ovaries) via interstitial migration within the walls of maternal blood vessels. Hence, this trophobla st is noteworthy for the extent to which it undergoes an epithelial-mesench ymal transformation. In Molossus, it originates from the cytotrophoblastic shell running along the base of the placenta, is mononuclear, and preferent ially invades maternal arterial vessels serving the discoidal placenta. Thi s trophoblast may have a role in dilatation of these vessels when the disco idal placenta becomes functional. In Diaemus, the highly invasive trophobla st appears to originate instead from a layer of syncytiotrophoblast on the periphery of the placenta, is multinucleated, and vigorously invades both a rterial and venous vessels. During late pregnancy, it becomes extensively b ranched and sends attenuated processes around many of the myometrial smooth muscle fibres. In view of its distribution, this trophoblast could have im portant influences upon myometrial contractility and the function of blood vessels serving the gravid tract. Other aspects of intermediate filament ex pression in the uteri and placentae of these bats are also noteworthy. Many of the decidual giant cells in Molossus co-express cytokeratins and viment in, while the syncytiotrophoblast lining the placental labyrinth in Diaemus late in pregnancy expresses little cytokeratin.