Kit signaling is involved in hair follicle morphogenesis and regeneration in mice

Keratinocytes are the predominant cell type in the epidermis. The mammalian epidermis is maintained by a pool of self-renewing stem cells that reside primarily in the basal layer of the interfollicular epidermis and within specialized niches of the hair follicle (HF). In HFs, Kit-Kit ligand (Kitl) signaling is important for melanocyte development. Melanocyte stem cells expressing Kitl are maintained in niches composed of HF stem cells or keratinocyte stem cells. We observed that conditional Kitl overexpression prevents hair growth; however, the role of Kit-Kitl signaling in keratinocytes and HF in postnatal and adult skin remains unknown. Here, using genetically modified mice expressing the Kitl transgene under the control of a doxycycline-inducible promoter, we investigated the impact of Kit-Kitl signaling on HF morphogenesis and regenerative cycling in postnatal and adult skin. We observed a reversible but thorough delay in hair growth and regenerative cycling when Kitl induction was initiated at the onset of anagen in both postnatal and adult tissues. Conversely, HF structure or cycling was not affected by Kitl overexpression at catagen. These findings indicate that Kitl signaling in follicular keratinocytes is crucial for HF morphogenesis and regenerative cycling in postnatal and adult mice.