Ultrastructural localization of binding sites for the lectins RCA I, WGA, and LTA in the preimplantation mouse embryo

In biological tissues, specific carbohydrate moieties of the oligosaccharide chains of glycoproteins can be localized by lectin binding. Such carbohydrate moieties are among the factors that mediate cell-cell or cell-matrix interactions during pre- and postimplantation embryonic development. Binding sites for the lectins RCA I, WGA, and LTA were localized in preimplantation mouse embryos at the ultrastructural level with the help of postembedding lectin gold cytochemistry. WGA and RCA I binding sites, but no CTA binding sites, were present in the zona pellucida. WGA and RCA I binding sites were found at cell surfaces of morulae and in cells of the inner cell mass of blastocysts, suggesting that N-acetylglucosamine-, terminal beta-galactosyl-, and N-acetylgalactosamine-rich glycoproteins might be involved in cell-cell and cell-matrix interactions. WGA binding sites were found predominantly in electron lucid vesicles of the blastomeres, whereas RCA I was detected in electron dense vesicles of the compacted morula and later in the polar trophoblast cells. This allows early identification of blastomere cells that later differentiate into the polar trophoblast.