Inhibition of desmosome formation with tunicamycin and with lectin in corneal cell aggregates

Desmosome formation in chick corneal epithelium can be used as a tool to study cell interaction. In the present work, the possible role of carbohydrates in initiating junction formation is investigated. When corneal cells of 15-day chicks are dispersed, then aggregated in rotating medium, desmosomes form on a regular schedule and can be quantitated as desmosomes per micrometer of cell membrane cross section. Tunicamycin, at 0.05 μg/ml has little effect on incorporation of leucine into TCA-precipitable cell fractions, but lowers mannose incorporation, and inhibits desmosome formation. The inhibition is counteracted by the presence of leupeptin, a protease inhibitor. This finding can be interpreted as favoring a role of stabilization, rather than recognition for the carbohydrate moiety. Cytochalasin B inhibits cell surface turnover in isolated cells and enhances desmosome formation. Enhancement occurs even in the presence of tunicamycin. Ferritin-conjugated succinyl-Con A will label surfaces of freshly dispersed cells and when cells are aggregated in its presence, the label is internalized in cytoplasmic vacuoles and desmosomes do not form. To test further the possibility that a lectin binding component of the surface may be a specific recognition factor, cells were aggregated in the presence of a number of sugars. None inhibited junction formation. Thus, evidence favors a stabilizing role for carbohydrates, acting at some point in the process of junction formation and leaves open the possibility that a “recognition” function may also be involved.