Molecular studies on cells of the trophectodermal lineage of the postimplantation mouse embryo

Embryonic ectoderm (EmE), extraembryonic ectoderm (EE), ectoplacental cone diploid cells (EPC) and secondary giant cells (GC) were isolated from 7 1/2-day mouse embryos and their polypeptide synthetic profile assessed by fluorography of 2D polyacrylamide gels. Fifty polypeptides showed different distributions amongst the tissues, permitting characterization of each tissue by an array of polypeptide markers typical for the tissue at that developmental stage. The three tissues on the presumptive trophectoderm lineage did not show identical synthetic patterns. However, culture of EE cells in vitro resulted in conversion of their polypeptide synthetic profile to that of EPC after 2 days and of GC after 6 days, whilst culture of EPC cells converted their polypeptide synthetic profile to that of GC after only 4 days. These changes in polypeptide synthesis correlated well with the ploidy levels of the tissues at different times in culture.