A comparison of developmental changes in surface charge in mouse blastocysts and uterine epithelium using DEAE beads and dextran sulfate in vitro.

The ability of 3.5-day mouse blastocysts and vesicles prepared from maternal uterine epithelium to adhere to surfaces by charge interactions was compared by observing their adhesion to DEAE-Sephadex beads in the presence of increasing concentrations of dextran sulfate. The adhesion frequency for both the blastocysts and epithelium declined in a manner suggesting that predominantly ionic sites were being titrated, but differences between the two tissues in characteristics of the titration curve and susceptibility to neuraminidase digestion indicated that nonionic interactions were relatively more important for blastocysts. Because the threshold concentration of dextran sulfate required to initiate displacement of uterine epithelium from the DEAE beads was at least 4X that required to initiate the displacement of blastocysts, we argue that the uterine epithelium had at least 4X more interactive charged groups on its surface than the blastocysts. These differences were even more pronounced 4.5 days after mating, a time when attachment to the uterine epithelium is normally first seen in vivo. Blastocysts isolated at this time showed a marked increase in resistance to polyanion competition, but the epithelium showed a nearly 50% decline in surface negative charge that was not compensated by nonionic mechanisms. These observations support the conclusion that the initial adhesion of blastocysts in vivo is accompanied by a reduction in negativity of the uterine epithelial surface and by the formation of new trophoblast cell surfaces that adhere by nonelectrostatic interactions.