The hair follicle epithelium forms a tube-like structure that is continuous with the epidermis, but how the lumen of this structure is created during morphogenesis and regeneration remains unclear. Now, Sunny Wong and colleagues identify a novel population of cells that initiates hair follicle lumen formation in mice (). The researchers first provide a detailed characterisation of the infundibulum, the region encompassing the hair follicle mouth, and identify a population of keratin 79 (K79)-positive epithelial cells within this region. Using lineage tracing, they show that these cells are specified early during hair follicle development and migrate outwards from the hair germ into the epidermis prior to lumen formation. This migratory event is also observed during regeneration of the hair follicle; K79-positive cells are specified in the secondary hair germ and migrate out, eventually forming a continuous layer with pre-existing K79-positive cells. These findings identify both a novel mode of epithelial tube morphogenesis and a unique population of cells that migrate throughout the life cycle of the hair follicle.
