Fig. 1

The impact of circadian rhythms on various types of stem cells. In the hippocampus, the clock genes control the neurogenesis of neural stem cells. Circadian rhythms also regulate the proliferation and differentiation of hair follicle stem cells and melanocyte stem cells in the skin. In the digestive tract, the cell cycling of intestinal stem cells is under the control of the light and dark cycles. The proliferation, differentiation, and mobilization of HSCs also depend on the circadian clock. Circadian clock also contributes to the regulation of PSCs, although their response to circadian rhythms depends on their differentiation status. When undifferentiated, PSCs show less rhythmicity in clock gene expression; however, they activate rhythmic expression of several clock gene upon differentiation. The circadian clock in cancer stem cells is often dysfunctional or functions in favor of tumorigenesis. In general, circadian clock genes regulate the signaling pathways, cell cycle, differentiation and fate of embryonic and adult stem cells