DEVELOPMENT Adult hair follicles sustain repeated cycles of hair loss and regrowth. Stem cells reside within a small niche, called the bulge, located in the upper part of the hair follicle. These stem cells are responsible for driving this cycle of growth and can repopulate follicles and surrounding epidermis damaged by wounding. However, the first hair follicles in mice arise from the developing epidermis, not from preexisting bulge stem cells, and these first-time hair follicles do not exhibit the conspicuous bulge that only becomes apparent some weeks after birth. Nowak et al. have analyzed the origins of the hair follicle stem cell niche in developing mice. The stem cells of the bulge are in fact established much earlier than previously suspected and begin to form in the embryo. These cells, which are characterized by expression of the transcription factor Sox9, not only contribute to the formation of the initial hair follicle, but also give rise to the adult bulge stem cells that are responsible for the maintenance of the hair follicle itself. Ablation of Sox9 left the embryos without bulge cells, and the mice never grew any hair and did not have any sebaceous glands. Moreover, the skin did not repair epidermal wounds well when Sox9 was missing. These results implicate Sox9 in establishment of the hair follicle stem cell population and show that early stem cells can contribute to skin morphogenesis before assuming their role as adult stem cells. — PJH Cell Stem Cell 3 , 33 (2008).