Histochemical and autoradiographic study of the cultured rat visceral yolk sac

The proliferation and differentiation potentiality of the rat visceral yolk sac was investigated both in organ culture and after grafting in vivo. Using alkaline phosphatase as a marker for germ cells, it was shown that these cells are absent in the 12-day-old visceral yolk sac examined before and after organ culture. Therefore, the only cells that proliferate and differentiate must be of endodermal and/or mesodermal origin. By labelling the cells with [3H]thymidine both the endodermal and mesodermal cells were found to proliferate. After 10 days in organ culture or implantation in vivo differentiated tissues (e.g. squamous epidermis, endodermal cysts and giant trophoblast cells) were regularly detected. Several of these differentiated cells contained the radiolabel indicating that they derived from the initial proliferating endodermal and/or mesodermal cells.