Ultrastructure of cultured rat placental cells

Rat placental cells (RPCs) derived from explants of gestation day 12 chorioallantoic placental primordia were propagated as ascites RPCs and as in vitro cultured RPCs. Although the morphological characteristics of ascites RPCs and in vitro cultured RPCs differed markedly by light microscopy, evaluation by electron microscopy revealed that all RPCs were epithelioid. Morphological differences at the light microscope level were attributable to environmental conditions. When RPCs were compared with placental cells in situ, RPC characteristics most closely resembled those of layer-one trophoblast cells (germinal cytotrophoblast) present in the labyrinthine region of the placenta. RPCs, which appear to be a relatively homogeneous population of trophoblast cells, may be valuable tools for evaluating the relationships between maternal and fetal cells during pregnancy and for studying the growth and differentiation of extraembryonic cells.