The hair cycle
Laura Alonso1 and Elaine Fuchs2,*
1 Department of Medicine, Division of Endocrinology, University of Pittsburgh, 200 Lothrop Street, Pittsburgh, PA 15261, USA
2 Howard Hughes Medical Institute, Laboratory of Mammalian Cell Biology and Development, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
* Author for correspondence (e-mail: [email protected] )
The hair coat, which keeps most mammals warm, dry and protectedfrom harmful elements, requires a constant supply of new hairsthroughout the lifetime of the animal. To produce new hairs,existing follicles undergo cycles of growth (anagen), regression(catagen) and rest (telogen). During each anagen phase, folliclesproduce an entire hair shaft from tip to root; during catagenand telogen, follicles reset and prepare their stem cells sothat they can receive the signal to start the next growth phaseand make the new hair shaft. The hair cycle represents a remarkablemodel for studies of the regulation of stem cell quiescenceand activation, as well as transit-amplifying cell proliferation,cell-fate choice, differentiation and apoptosis in a regenerativeadult epithelial tissue. Here we summarize the major eventsof the hair cycle, and touch on known regulators of the transitions.Detailed reviews of the hair cycle and its regulation can befound elsewhere (Lavker et al., 2003; Millar, 2002; Muller-Roveret al., 2001).
Source: Journal of Cell Science 119, 391-393 (2006)