Alterations in membrane sugars during epidermal differentiation: visualization with lectins and role of glycosidases

Differentiation in keratinizing epithelia involves the orderly transformation of basal germinal cells into an exterior cornified layer. We have employed rhodamine-conjugated lectins to visualize distinctive changes in the localization of keratinocyte membrane glycoconjugates during epidermal differentiation. The dermis, basement membrane, and epidermal cell membranes stained positively for mannose, alpha- and beta-galactose, N-acetyl-glucosamine, and sialic acid. In contrast, only the viable epidermis demonstrated N-acetyl-galactosamine, while alpha-L-fucose staining was limited to the upper stratum spinosum and stratum granulosum. Neuraminidase treatment extended the binding of certain lectins, e.g., peanut agglutinin, to regions of the skin that otherwise did not label. Whereas the granular cell membranes displayed the largest number of carbohydrates, these sugars could no longer be visualized after granular cells differentiated into the stratum corneum. Loss of lectin staining may be attributable to the presence of a family of sugar-specific glycosidases that we obtained from granular and cornified cell cytosol fractions. Finally, as further support for sugar deletion during cornification, we found that glycosphingolipids are hydrolyzed to ceramides coincident with both loss of lectin staining and the emergence of glycosidase activity. These results suggest: 1) that carbohydrates on keratinocyte cell membranes can be used as markers of epidermal differentiation, and 2) that removal of cell surface sugars during cornification may be due to the action of specific glycosidases in the outer epidermis.