Differentiation potentiality of rat visceral yolk sac in organ culture.

Visceral yolk sacs removed at day 12 of pregnancy in the rat were kept in organ culture for as long as 28 days. During this in vitro culture, proliferation of the endoderm and the mesoderm as well as of poorly differentiated cells was observed. The latter displayed neither the characteristics of endodermal nor mesodermal cells and their presence was frequently associated with the development of giant trophoblast cells. The hypothesis is proposed that these trophoblast cells originate from these poorly differentiated cells that acquire in vivo and in vitro the potentiality to differentiate.