The hair follicle—a stem cell zoo

Recent studies on stem cells in the adult hair follicle (HF) have uncovered a veritable menagerie of exceptionally diverse and dynamic keratinocytes with stem cell properties located in distinct regions of the HF. Although endowed with specific functions during normal hair follicle maintenance, the majority of these cells can act as multipotent stem cells in stress situations, such as physical injury, which argues for an unanticipated degree of plasticity of these cells. This review provides an overview of the different epithelial stem cell populations, identified in the mouse HF, and their relationships with one another, and envisions possible cellular mechanisms underlying normal HF maintenance and skin regeneration.