Change in cell-surface glycoproteins of mouse embryos before implantation

The early biochemical ontogeny of the mammalian cell surface has been examined in mouse embryos. After in vitro incubation of embryos in D-[(3)H]- or D-[(14)C]glucosamine, the cell-surface glycopeptides were removed by trypsinization, digested with Pronase, and fractionated by gel filtration on Sephadex G-50; radioactivity was determined in the fractions by scintillation counting. Cochromatography of digests from the surfaces of embryos of two age groups yielded markedly different elution patterns. The labeled surface material from embryos in or near the blastocyst stage, when the outermost cells are differentiating into trophoblast, was substantially enriched, as compared with material from cleavage-stage embryos, in relatively more rapidly eluted components of presumed higher molecular weight. A similar change has previously been reported by others in cultured mammalian cell lines after viral transformation, in comparison with corresponding untransformed cells. This similarity between blastocysts and transformed cells suggests that the early biochemical differentiation of the surface, as the embryo passes into the blastocyst stage, may be responsible for the stage-specific capacity of the outermost cells to attach to the uterine wall in response to an implantation-initiating stimulus and to become invasive.