Molecular cloning of a cDNA sequence encoding a trophectoderm-specific marker during mouse blastocyst formation.

A cDNA clone has been isolated from a trophoblastoma cDNA library. The mRNA complementary to this sequence directs the in vitro synthesis of proteins. The two-dimensional electrophoretic pattern of migration of these proteins is superposable to that of the trophoblastoma intermediate filament proteins recognized by monoclonal antibody (mAb) TROMA-1. This mAb had previously been shown to label trophectoderm cells but not inner cell mass cells. With a sensitive binding assay (ultrasensitive enzymatic radioimmunoassay), these in vitro synthesized proteins were recognized by mAb TROMA-1. The proteins are immunoprecipitated by an antiserum directed against trophoblastoma intermediate filament proteins and by a serum directed against a major cytoskeletal protein found in murine extraembryonic endodermal cell lines (Endo-A) [Oshima R. G. (1981) J. Biol. Chem. 256, 8124-8133]. The cDNA sequence detects specific mRNA(s) migrating with 18S ribosomal RNA in trophoblastoma but not in embryonal carcinoma cells.