Synthesis and role of cell surface glycoproteins in preimplantation mouse development

Cell surface glycoproteins apparently influence cell interactions, morphogenesis and the course of cellular differentiation. We have therefore investigated the biosynthesis of glycoproteins in 8-cell mouse embryos by using 1.0 μg tunicamycin/ml, a specific inhibitor of glycosylation of N-glycosidically linked glycoproteins. The antibiotic had little effect on the incorporation of leucine into polypeptides, but the incorporation of glucosamine and mannose was inhibited by about 60% with a marked reduction in their incorporation into the majority of the glycopeptides as analysed on polyacrylamide gels. The binding of concanavalin A (conA) and peanut lectin to the embryonic cell surface was also markedly diminished by tunicamycin. However, the binding of peanut lectin to isolated blastomeres displayed a polar distribution with predominant binding to the outer apical surface in all cases, despite a marked reduction in microvilli. Hence tunicamycin has no substantial effect on the molecular distribution of at least some cell surface antigens. Analysis of iodinated cell surface components showed that two components of mol, wt <68 000 and >165 000 were inhibited by tunicamycin. Whereas embryos in the control group underwent compaction and blastulation, those in the experimental group remained uncompacted, although cleavage continued to about the 32-cell stage. However, some embryos initially underwent partial compaction but later decompacted in the presence of tunicamycin; numerous adherens and possibly a few gap junctions were also detected between blastomeres. We suggest that a number of cell surface antigens including N-glycosidically linked glycoproteins may be engaged sequentially during compaction.