Melanocyte Stem Cells: A Melanocyte Reservoir in Hair Follicles for Hair and Skin Pigmentation

The document reviews the role of melanocyte stem cells (MelSCs) in hair and skin pigmentation, their identification, characteristics, and importance in hair pigmentation, greying, and skin repigmentation. MelSCs are found in hair follicles and are crucial for pigmentation, forming a 'hair pigmentary unit' with hair follicle stem cells. They are slow-cycling, undifferentiated cells that can self-renew and supply differentiated melanocytes. The review discusses the development of melanocytes, their role in melanin production, and the cyclic regeneration of hair follicles. It also covers the distinction between human 'amelanotic melanocytes' and mouse MelSCs, and the existence of a melanocyte reservoir in hair follicles. The document concludes that MelSCs are essential for understanding hair pigmentation, greying, and potential treatments for pigmentary disorders, highlighting the importance of the microenvironment for MelSC maintenance. It also notes that TGF-ß and Notch signaling are critical for MelSC maintenance, while genotoxic stress can lead to premature greying by causing MelSC depletion. Understanding MelSCs may provide insights into tissue aging, cancer development, and new treatments for hair greying by focusing on preventing MelSC depletion and promoting their renewal.