Cyclin-Dependent Kinase 4 Expression Alters the Number of Keratinocyte Stem Cells in the Mouse Hair Follicle

The study investigated the role of cyclin-dependent kinase 4 (CDK4) in the regulation of bulge stem cells (BuSCs) in mouse hair follicles. The researchers found that CDK4 is highly expressed in BuSCs during the resting phase of the hair follicle cycle. Using gain- and loss-of-function models, they discovered that the removal of CDK4 delayed hair follicle development at early postnatal stages. Additionally, transgenic expression of CDK4 in the bulge region of hair follicles reduced the number of BuSCs, while genetic removal of CDK4 increased the number of BuSCs. This suggests that CDK4 plays a crucial role in regulating BuSC activation/proliferation and is necessary to maintain the balance between self-renewal and proliferation of BuSCs.