“Of Mice and Men” the Cell Cycle in Human Epidermis in Vivo

This article deals with and compares cell cycle information obtained in mouse and in human epidermis in vivo. In order to compare data in mouse and in man, DNA labeling and mitotic index experiments were performed to obtain cell cycle information in normal human epidermis in vivo. Experiments were also performed on genetically inbred and outbred strains of mice—to provide a clue to the differences observed between mouse and man. The article makes the following points:1. In contrast to mouse epidermis, there are no consistent diurnal fluctuations in and there is no cell kinetic relationship between mitotic and DNA-labeling indices in normal human epidermis in vivo. The variability from individual to individual in human subjects and the lack of cell cycle-related circadian fluctuations, preclude the use of statistical analysis and the use of conventional cell kinetic principles in understanding epidermal cell proliferation in man and may preclude the use of circadian rhythmicity for therapy scheduling.2. The consistent and intelligible cell cycle information obtained in laboratory mice (as compared to man) is not due to the genetically inbred condition of mice.3. This report introduces the use of ambient temperature as a potential nontoxic cell cycle tool for manipulating epidermal cell proliferation in the therapy of human proliferative skin diseases