Cell surface glycoproteins change during gastrulation in Pleurodeles waltlii

Identification of the cell surface glycoproteins is an essential requirement for elucidating the mechanisms that mediate intercellular adhesion and cell migration in gastrulating amphibian embryos. In our experiments the glycoproteins present at the surface of isolated cells at blastula and gastrula stages were labelled with 3H-labelled sodium borohydride. The procedure included the oxidation of either galactosyl and, or, N-acetylgalactosaminyl residues with galactose oxidase or sialic acid with sodium metaperiodate. The tritiated components were analysed by two-dimensional gel electrophoresis. On the surface of isolated embryonic cells, 23 glycoproteins have been identified. The most important observation was the labelling of 15 new glycoproteins during gastrulation. At the late blastula stage, eight glycoproteins containing galactosyl or N-acetyl-galactosaminyl residues are labelled, while 23 are labelled at the late gastrula stage. In other experiments, glycoproteins labelled by [3H]fucose or [3H]mannose or precipitated by concanavalin A(ConA)-, or wheat-germ agglutinin (WGA)-Sepharose were studied by two-dimensional gel electrophoresis in order to provide supplementary data on the synthesis and lectin-binding properties of major cell surface glycoproteins. It appears that approximately 100 different glycoproteins are revealed by these methods. Among them, 13 have been identified as major cell surface glycoproteins, 12 being labelled by [3H]mannose, four by [3H]fucose, 10 bearing an affinity for ConA and five for WGA. These 13 glycoproteins are synthesized throughout gastrulation without qualitative variation.