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 oligosacc haride chains of glycoproteins can be localized by lectin binding. Suc h carbohydrate moieties are among the factors that mediate cell-cell o r cell-matrix interactions during pre- and postimplantation embryonic development. Binding sites for the lectins RCA I, WGA, and LTA were lo calized 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 pe llucida. WGA and RCA I binding sites were found at cell surfaces of mo rulae and in cells of the inner cell mass of blastocysts, suggesting t hat N-acetylglucosamine-, terminal beta-galactosyl-, and N-acetylgalac tosamine-rich glycoproteins might be involved in cell-cell and cell-ma trix interactions. WGA binding sites were found predominantly in elect ron lucid vesicles of the blastomeres, whereas RCA I was detected in e lectron dense vesicles of the compacted morula and later in the polar trophoblast cells. This allows early identification of blastomere cell s that later differentiate into the polar trophoblast.