[Melanocyte stem cells in adults].

Melanocyte stem cells have been recently localized in mice, in the outer root sheath of the lower permanent portion of the hair follicle. Specific depletion of melanocyte stem cell population is responsible for natural hair greying in aging mice and humans. Melanocyte stem cells also seem to drive the growth of malignant melanomas. A few mutations, either spontaneous or genetically engineered, accelerate the natural process of hair greying with age. These mutations allowed the identification of genes and signalling pathways controlling emergence, maintenance and/or differentiation of melanocyte stem cells. This review summarizes recent studies on the melanocyte stem cells and defines a few major unanswered questions in the field.