Responses to mutant Hras by homeostatic skin and following injury. (A) Hras G12V induces different responses from HFSCs and epidermal SCs. Top: Schematic showing different phases of normal hair cycling. Middle: After Hras G12V induction, HFSCs (pink) become hyperactivated and the lower follicle undergoes massive hypertrophy and downgrowth but eventually undergoes normal cyclical regression. Bottom: In contrast, Hras G12V-induced epidermal SCs in the basal layer undergo tumorigenesis to become SCCs. (B) Response of mutant HFSCs to wounding depends on the wound site. Top: In this hypothetical scheme, skin wounding prompts a normal response whereby mutant HFSCs (red), like normal HFSCs, migrate into the wound site to promote healing. Rarely, this phenomenon can lead to tumorigenesis. Bottom: In contrast, wounding of the HF bulb region does not initiate any response from mutant HFSCs.