Localization of trophoblast-defined surface antigens during early mouse embryogenesis.

The binding pattern of a rabbit antiserum raised against mouse-ectoplacental-cone trophoblast on component cell populations in the pre-implantation and early post-implantation mouse embryo has been examined at the electron-microscope level using an immunoperoxidase-labelling technique. Binding was not detectable on the 1-cell stage, appeared at low levels at the 8-cell stage and was heavy on the trophectoderm and its trophoblast giant cell and extra-embryonic ectoderm descendants in the post-implantation embryo. In contrast, immunosurgically isolated 3 1/2-day inner cell masses (ICM) showed only slight labelling, whilst ICM derivatives in the 7 1/2-day embryo were unlabelled. The results indicate that the antiserum may be identifying a trophoblast-specific surface determinant(s), which appears with the differentiation of the trohectoderm and is maintained on some of the cell populations derived from this tissue at least until the early post-implantation stages.