If we are lucky, our hair, like the rest of our skin, constantly renews itself throughout our life. The epidermal stem cells that are central to hair renewal reside in a region of the hair follicle called the bulge. Now, though,Nijhof and coworkers identify a potential new reservoir of mouse epidermal progenitor cells just above the bulge. These cells are characterised by the expression of MTS24, a cell-surface marker for thymic epithelial progenitor cells (see ). The researchers show that although MTS24+ cells do not express the bulge-specific stem-cell markers CD34 or keratin 15, they can form colonies in vitro. Furthermore, their overall gene expression profile resembles that of bulge stem cells. Given these results, the researchers propose that MTS24+ keratinocytes are committed progenitor cells that are derived from the bulge stem cells. Further characterisation of these cells, they suggest, might reveal ways to modify keratinocyte progenitor cell behaviour during hair loss, wound healing and cancer.
