A two-colour flowcytometric study of cell kinetics and differentiation of human keratinocytes in culture.

Double histochemical staining followed by flow cytometric analysis was performed to determine whether involucrin synthesis is associated with a particular phase of the cell cycle. In low-calcium medium (0.1 mM) monolayer cultures the expression of involucrin was confined to about 8% of the total cell populations. When the concentration of calcium was increased to 1.8 mM, the percentage increased and the distribution pattern of the cell cycle changed. The addition of retinoic acid at concentrations in the range 10(-8) M to 10(-6) M to a high-calcium medium induced a further increase. The greatest increase in involucrin expression (up to five-fold) occurred in both the G1/G0 and G2 + M phases, while S phase cells showed a two-fold increase. The results indicate that involucrin synthesis is induced by retinoic acid, which occurs at any stage of the cell cycle, even in the S phase.