Immunofluorescent localization of a monoclonally defined carbohydrate cell surface antigen (IIC3) during mouse...

A monoclonal antibody (anti-IIC3), raised against F9 embryonal carcinoma cells, detects an antigen which is first expressed at the compacted morula stage and segregates with the trophectoderm of the mouse blastocyst. We have further examined the expression of this antigen during embryonic development. Immunofluorescence experiments on sectioned embryos demonstrate that IIC3 expression is associated with the differentiation of extra-embryonic cell types. It is expressed at the cell surface of the trophectoderm of the attaching blastocyst and differentially by the two derivatives of this layer. The primary and secondary trophoblastic giant cells label intracellularly, whereas the cells of the ectoplacental cone and labyrinth placenta label at the cell surface. IIC3 is also expressed by the primitive endoderm of the blastocyst and subsequently by the visceral endoderm. The parietal endoderm does not express IIC3. Partial characterization of the IIC3 antigen with sugar hapten inhibition and glycosidase digestion experiments, suggests that the antigen is a lactosaminoglycan-like molecule, with galactose and N-acetylgalactosamine residues representing part of the antigenic determinant. Neuraminidase and fucosidase treatment exposed additional anti-IIC3-antigenic sites on the extra-embryonic ectoderm and chorion. A possible role for IIC3 in normal embryonic-uterine interactions is discussed.