Correlation between changes in cell adhesion and the ratio of N- to O-linked glycopeptides during chick embryo...

After treatment with trypsin, chick embryo fibroblasts exhibited an age-related difference in their capacity to readhere to the substratum, since 8-day-cells readhered more rapidly than 16-day-cells. Treatment with tunicamycin altered embryo cell readhesion to the substratum in varying degrees, depending on the duration of drug treatment and of readhesion assay. The effect of tunicamycin was not toxic and was totally reversible with time after its removal. These results indicated that embryo cell readhesion involved trypsin-sensitive cell surface glycoproteins. During embryo development, the glycosylation of cell surface glycoproteins altered markedly. The ratio of N-linked to O-linked glycan chains dropped from 80/20 in 8-day-cells to 55/45 in 16-day-cells, indicating that the relative labelling of O-linked glycan chains increased during embryo development. This result was confirmed by alkaline treatment of radiolabelled glycan chains, and by the fact that tunicamycin treatment reduced 14C-glucosamine incorporation by greater than or equal to 80% in 8-day-cells but only 60% in 16-day-cells. Marked changes were observed during embryo development in the structure of the N-linked glycan chains; concanavalin A-Sepharose chromatography showed that these changes concerned the glycopeptides containing complex type carbohydrate chains. The ratio of tri- plus tetra-antennary chains to bi-antennary chains increased about 2.5-fold between the 8th and 16th day of development. A correlation was noted between embryo cell readhesion to the substratum and N-glycosylation of cell surface glycoproteins. The N-linked glycoconjugates played a crucial part in cell readhesion. The possible role of O-linked structures in such readhesion is discussed.