Progress on hair follicle stem cells

Hair follicle stem cells are not only crucial for hair follicle morphogenesis and cycling but also serve as the source of epidermis and sebaceous gland. Cells in bulge area of hair follicle outer root sheath possess a number of characteristics for stem cells, including slow cycling, multipotential differentiation and self renewal ability. Therefore bulge area has been defined as the location of hair follicle stem cells. Proliferation and differentiation of hair follicle stem cells are induced by their surrounding microenvironment among them the most important in adult hair follicle cycling was dermal papillar cells. Investigators have proposed many hypotheses to explain the rise of stem cells in hair follicle morphogenesis and hair cycling, including bulge activation hypothesis and stem cell migration hypothesis. The difference and common ground of these two hypotheses are compard. Several signal pathways, such as Wnt, BMP and Shh signal transduction pathways, are involved in the molecular events happened during hair follicle morphogenesis and cycling. β catenin and LEF1/TCF were important for the conversion of stem cells to matrix cells and in triggering hair follicle keratin gene expression.