The constant renewal of skin and hair suggests there must be a population of stem cells capable of generating these pigment-producing cells, but so far such cells have not been found. In 25 April Nature, Emi Nishimura and colleagues from Kyoto University, Japan show that melanocyte stem cells exist, and are strongly influenced by their highly specific environment (their niche) (Nature 2002, 416:854-860).

Nishimura et al. used Dct-lacZ transgenic mice and observed stem cells of the melanocyte lineage in the lower permanent portion of mouse hair follicles. These cells were present present throughout the hair cycle. In addition, induction of repigmentation process in K14-steel factor transgenic mice showed that a portion of amplifying stem-cell progeny could migrate from the niche and retain sufficient self-renewing capability to repopulate vacant niches. "The re-pigmentation process we observed strongly suggests that human melanoblasts in the outer root sheath are the...

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