Cyclin-Dependent Kinase 4 Levels Affect the Number of Hair Follicle Stem Cells in Mouse Epidermis

The study investigated the role of Cyclin-dependent kinase 4 (CDK4) in hair follicle stem cells and skin tumorigenesis using a mouse model. It was found that altering CDK4 levels affected the number of Keratinocyte Stem Cells (KSC) in the hair follicle. Specifically, overexpression of CDK4 led to a 4-fold decrease in KSCs, while CDK4 deletion resulted in a 4-fold increase. This change in KSC numbers was linked to the asymmetric cell division of KSCs, influencing the balance between stem cells and transit amplifying cells. The findings suggested that the number of progenitor cells might correlate with susceptibility to papilloma development, supporting the hypothesis that CDK4 expression levels play a critical role in skin tumorigenesis.