Hair is normally maintained through a process that depends on the regeneration of tiny hair follicles. For humans and mice that have mutations in the Hairless gene, hair growth starts out normally, but once a strand is shed it cannot grow back. But just how Hairless controls the follicle regeneration process was unclear. Catherine C. Thompson of the Kennedy Krieger Research Institute and her colleagues determined that the Hairless protein is normally expressed in progenitor cells that are key for the rest and regrowth phases of follicles. When the team provided the protein to these types of cells in mice genetically modified to lack hair (see image, top), the animals eventually grew a coat of thick fur (see image, bottom).
In a paper published online this week by the Proceedings of the National Academy of Sciences, the scientists report that it is the Hairless protein's interaction with a second protein, known as Wise, that is responsible for the furry flurry. In the absence of the Hairless protein, Wise accumulates in the follicles and prevents the hair cycle from entering the regrowth phase. In that case, the hair follicle stays in its rest stage indefinitely. The Hairless protein won't be bottled anytime soon, however. The authors caution that hair follicle regeneration is a complex process, which likely hinges on other signaling pathways in addition to that of the Hairless gene.