The Clock Within: Molecular Clock in Epidermis Regulates Circadian Rhythms and Stem Cell Cycles

Janich et al. discovered that the molecular clock in the epidermis regulates both circadian rhythms and the cycles of dormancy and proliferation in mouse epidermal stem-cell populations. They identified two subpopulations of stem cells in the hair-follicle bulge with different clock machinery expressions, affecting dormancy and proliferation genes. Disruption of the Bmal1 gene reduced proliferative cells and increased dormant stem cells, while deleting Per1 and Per2 increased proliferation. This study emphasized the circadian clock's role in epidermal homeostasis and suggested that differentiating cells might use clock machinery to direct epigenetic marks. It also raised questions about the conservation of this mechanism in other adult stem cells, indicating potential future research directions.