Polyoma virus-induced hemangiomas in grafts of visceral yolk sac and of embryos

The development of hemangiomas in grafts of visceral yolk sac and embryos after in vitro infection with polyoma virus is described. These hemangiomas were shown to be positive for the polyoma tumor-specific transplantation antigen(s) and to develop as well in recipient virgin as in pregnant rats. In grafts of fetal skin or gut infected with polyoma virus neoplastic transformation was never observed.

Rat yolk-sac antigen-2 defined by monoclonal antibodies

The distribution of the rat yolk-sac antigen-2 (Rat YSA-2) as defined by a monoclonal antibody raised against rat yolk-sac carcinoma cells is described. The antigen is present on rat yolk-sac carcinoma, on parietal yolk-sac endoderm and on the epithelium of fetal and adult gut and of the adult proximal kidney tubules. It is not present on a variety of rat tumors other than yolk-sac carcinomas and not detectable on pre-implantation and post-implantation embryos. Rat YSA-2 differs from YSA-I, other stage-specific embryonic antigens, basement membrane antigens, intestinal and tubular antigens.

A rat yolk-sac antigen defined by monoclonal antibodies

The distribution of a rat yolk-sac antigen (Rat YSA-I) as defined by a monoclonal antibody raised against rat yolk-sac carcinoma cells is described. The antigen is present on rat yolk-sac carcinomas, on visceral yolk-sac endoderm and on embryonal endoderm of 9-day-old embryos. It is not present on a variety of rat tumors other than yolk-sac carcinomas and not detectable on pre-implantation embryos, inner cell mass and fetal endoderm. Rat YSA-I differs from alpha-fetoprotein and Forssman antigen and is species-specific. In adult rats the only cells displaying this antigen are the spermatozoa and certain cells of the spermatogenic lineage.

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.