T-Ag inhibits implantation by EC cell derived embryoid bodies.

When introduced into EC cells of a blastocyst, polyomavirus (Py) T-Ag results in mice mosaic for T-Ag but otherwise essentially normal. It had been reported that SV40 T-Ag does not inhibit differentiation of F9 EC cells, but did inhibit endogenous retrovirus (ERV) production. We therefore sought to determine if Py T-Ag had any affect on EC derived embryoid body implantation onto mouse placenta. F9 EC cells were selected for T-Ag maintenance. Like the SV40 transformed cells, we show that these Py T-Ag selected EC cells no longer express IAP transcripts following differentiation into embryoid bodies. Normal and Py T-Ag selected F9 cells were differentiated into embryoid bodies then implanted into pseudopregnant mice. We observe, that normal F9 derived embryoid bodies underwent the initial stages of implantation whereas the Py T-Ag selected embryoid bodied did not implant. The implications of this observation with respect to trophectoderm and ERV function are discussed. We examine the idea that ERVs may be a required element for normal embryo implantation.