ABSTRACT
The mammalian hair cycle is a fascinating example of tissue development and remodeling that occurs throughout life. Because the hair follicle undergoes a dynamic series of changes in which epithelial cell loss due to terminal differentiation is balanced by new cell formation, this “steady-state” condition, by definition, is under the control of stem cells. The bulge location of follicular stem cells was quite unexpected, since the germinative matrix of the bulb had been traditionally considered the site of follicular stem cells. A bulb location for follicular stem cells is, however, inconsistent with several known properties of the hair follicle. The lack of evidence for slow-cycling cells in sebaceous or meibomian glands, combined with the proximity of the sebaceous gland to the bulge region, raises the possibility that the follicular stem cells may be the source of basal sebocytes. Mouse mutations potentially valuable for studying hair cycle and follicular stem cells are tabulated.
