Dedifferentiation maintains melanocyte stem cells in a dynamic niche.

For unknow reasons, the melanocyte stem cell (McSC) system fails earlier than other adult stem cell populations, which leads to hair greying in most humans and mice. Current dogma states that McSCs are reserved in an undifferentiated state in the hair follicle niche, physically segregated from differentiated progeny that migrate away following cues of regenerative stimuli. Here we show that most McSCs toggle between transit-amplifying and stem cell states for both self-renewal and generation of mature progeny, a mechanism fundamentally distinct from those of other self-renewing systems.