Coordinate expression of X and Y haptens during murine embryogenesis.

The X hapten (Gal beta 1----4[Fuc alpha 1----3]GlcNAc) may play an important role in the adhesion of blastomeres during compaction. Therefore, we have investigated more thoroughly developmental changes in the fucosylation of lactoseries carbohydrate chains and the enzymatic basis of these fucosylation changes using well-characterized monoclonal antibodies. The Y hapten (Fuc alpha 1----2Gal beta 1----4[Fuc alpha 1----3]GlcNAc) and polymeric X haptens were detected by fluorescence-activated flow cytometry on murine embryonal carcinoma cells. In paraffin sections of postimplantation mouse embryos, the Y hapten was detected in the embryonic ectoderm and visceral endoderm on Days 5.5-7.5; this pattern of antigen expression is identical to that previously reported for the X hapten (SSEA-1). Thus, the Gal:alpha 1----2 (H) and GlcNAc:alpha 1----3 (X) fucosyltransferases appear to be co-regulated during embryogenesis. Reciprocal changes in X and Y hapten expression were observed, however, during preimplantation development. Unlike the X hapten, the Y hapten is expressed maximally on 16-cell morulae and 32- to 64-cell blastocysts. Eight-cell embryos cultured to the blastocyst stage in vitro did not acquire the Y hapten, however, suggesting a role for the uterine environment in carbohydrate antigen expression. Homogenates of F9 embryonal carcinoma cells were found to possess a potent GlcNAc:alpha 1----3 fucosyltransferase activity, as well as a weaker Gal:alpha 1----2 fucosyltransferase activity, using paragloboside as a substrate. The results suggest that embryonic cell surface carbohydrate phenotypes represent a balance in the competition between glycosyltransferases for available substrates. Rapid changes in carbohydrate expression during development may reflect intermediate states of cellular commitment and determination that are critical for lineage formation and morphogenesis.