Stratification and terminal differentiation of cultured epidermal cells

Abstract

As keratinocytes move from the basal to the outer layers of a stratified squamous epithelium, they enlarge and terminally differentiate. Hence, the stage of terminal differentiation is correlated with both cell size and position. To determine whether position is an important signal in differentiation, we have now grown human keratinocytes in conditions that prevented stratification but not cell enlargement. Involucrin, a marker of terminal differentiation, was synthesized in such a monolayer, but only by large cells. We conclude that the onset of involucrin synthesis, while normally restricted to cells in a non-basal position, does not depend on this position for an essential signal; however, a signal associated with increased cell size is not ruled out. When monolayer cultures were induced to stratify, the large involucrin-containing cells preferentially adopted a suprabasal position, indicating that terminal differentiation is associated with a decrease in substrate adhesiveness. Suprabasal cell position is therefore a consequence rather than a cause of terminal differentiation.