Epidermal homeostasis: a balancing act of stem cells in the skin

Abstract

The skin barrier is essential to protect animals from the external environment. The proper establishment of the skin barrier during embryogenesis and its maintenance during adult homeostasis is crucial for survival. Different modes of asymmetric stem cell (SC) division contribute to the development and the homeostasis of the skin barrier. Different populations of SCs reside in the skin epidermis and contribute to the homeostasis of the different epidermal compartments, such as the interfollicular epidermis, hair follicles and sebaceous glands. Slow-cycling hair follicle SCs form early during skin embryogenesis and are responsible for formation of the sebaceous glands, completion of hair follicle morphogenesis and efficient wound repair of epidermis. In the adult, hair follicle SCs are required for wound repair and for the normal cyclic bouts of hair growth that occur throughout life. The molecular mechanisms that govern embryonic development of the epidermis are reused during postnatal life to regulate harmoniously the balance between SC activation and differentiation, ensuring the homeostasis of the different compartments of the skin epidermis.