Protein secretion by the mouse blastocyst: differences in the polypeptide composition secreted into the blastocoel and medium.

To initiate studies on the protein microenvironment of the mouse blastocoel, we examined the electrophoretic profile of newly synthesized proteins secreted into the blastocoel, as well as those secreted into the medium. Although most polypeptides reveal no relative enrichment, some proteins (e.g., proteins of Mr = 155,000 and 33,000) are enriched in the blastocoel relative to those secreted apically into the medium. In addition, some proteins (e.g., proteins of Mr = 102,000 and 40,000) are enriched in the medium relative to the blastocoel. The relative amount of newly synthesized protein secreted into the blastocoel is about 2.5% of total protein synthesis. In addition, the trophectoderm and inner cell mass contribute to these proteins. Results of these studies suggest a potential function for these blastocoel-enriched proteins in inner cell mass development.