Immunoprecipitation of intracisternal A-particle-associated antigens from preimplantation mouse embryos.

Murine intracisternal A-particles (IAP) are endogenous retrovirus particles expressed in large numbers in certain neoplastic tissues and during early stages of normal preimplantation mouse (outbred ICR) embryogenesis. IAP-associated antigens synthesized by preimplantation mouse embryos were precipitated by a rabbit (New Zealand White) antibody prepared against IAP from murine myeloma 104E. Characterization of the embryo immunoprecipitates with the use of one- and two- dimensional polyacrylamide gel electrophoresis revealed that a group of five proteins was synthesized by two- to eight-cell stages, but only three of these (molecular weight of 67,000, 69,000, and 73,000) correlated with the morphologic expression of IAP in embryos. ONly the proteins with molecular weights of 75,000 and 77,000 were detected in morulae and blastocysts, when embryos were IAP-negative. This is the first biochemical identification of endogenous retrovirus-associated antigens in preimplantation mouse embryos.