Is upward basal cell movement independent of mitosis in the normal epidermis?

An analysis has been made of the possible mechanisms by which cells leave the basal layer distally during cell replacement in the steady state mammalian epidermis. Etoh's concept (1975) of cells actively migrating from the basal layer is challenged. Computer experiments suggest that if basal cell migration is an active process, the rate of cell migration consistent with the kinetics of the process being examined would yield a depopulation value far higher than the one observed experimentally. We found by contrast that rates of migration comparable to those found experimentally after mitosis inhibition by irradiation were obtained in our computer simulation experiments if it was assumed that distal basal cell migration is a passive event resulting from cells being extruded from the basal layer. We believe that there is not at present sufficient data to support the concept of active cell migration from the basal layer. The evidence favours the concept that in normal steady state epidermal populations, cells are passively removed from the basal layer as a result of forces generated, directly or indirectly, by dividing cells.