Morphological assessment of placentomal trophoblastic epithelium in the placenta of West African Dwarf goats: a light and electron microscopic study

Abstract

Gravid uteri harvested from 11 pregnant West African Dwarf goats at different stages of gestation were used to study the morphology of goat placentomal trophoblastic epithelium. The trophoblastic epithelium was composed of two trophoblast cell types; the mononucleate trophoblast cells and the binucleate trophoblast cells. Mononucleate trophoblast cells were tall columnar cells that rested on the basal lamina and extended to the foetomaternal interface, where their microvillar processes interdigitated with similar processes of the uterine epithelial cells to form the foetomaternal contact zone. Mononucleate trophoblast cells lining the arcade zones of placentomes contained erythrocytes in their cytoplasm. These cells are morphologically modified for acquisition of nutrients from the maternal compartment. Binucleate trophoblast cells showed two nuclei per cell and numerous characteristic membrane-bound granules in their cytoplasm. In addition, the binucleate cells resided in an intraepithelial position, showed evidence of capacity to migrate within the trophoblastic epithelium and fused with uterine epithelial cells at the foetomaternal interface. It would appear that the roles of the binucleate cells include formation of foetomaternal-derived hybrid cells in the placentomes and translocation of foetally synthesized substances across the placental barrier into maternal tissues via their migration and fusion with uterine epithelial cells. Furthermore this study demonstrated morphological modifications of the placentomal trophoblastic epithelium including extension of foetal blood capillaries into an intraepithelial position within the trophectoderm, such that they are situated close to the foetomaternal contact zone. This may enhance haemotrophic exchange of nutrients and metabolites between maternal and foetal blood circulations by reducing the diffusion distance between foetal and maternal blood capillaries.