Generation of the Mouse Line Targeting Outer Bulge Hair Follicle Cells.

Outer bulge (OB) hair follicle stem cells (HFSCs) play a crucial role in maintaining hair follicle structural stability and regulating the hair follicle cycle. Previous studies demonstrated that keratin 24 () exhibits spatiotemporally restricted expression in OB HFSCs. Here, we report the generation of the mouse line. When crossed with or reporter lines, offspring exhibited specific labeling () or ablation () of cells. In mice, phase-specific tamoxifen (TAM) administration demonstrated spatiotemporal fidelity of Cre activity to endogenous expression patterns. Lineage tracing revealed that tdTomato-labeled cells differentiated into the outer root sheath (ORS) during the anagen phase and persisted when hair follicles reentered telogen. Ablation of cells via diphtheria toxin (DT) administration significantly delayed anagen initiation. Mice under continuous depletion of HFSCs experienced substantial mortality after ionizing irradiation. Notably, ionizing radiation triggered a marked expansion of tdTomato-labeled cells, accompanied by maintained hair follicle homeostasis. Taken together, this study established a mouse line targeting OB HFSCs, which are essential for hair follicle development and damage repair.