Cells within the bulge region of mouse hair follicle transiently proliferate during early anagen: heterogeneity and functional differences of various hair cycles

In the 1994 study, researchers found that cells within the bulge region of mouse hair follicles, which are normally slow-cycling, undergo transient proliferation during the early anagen phase of the hair cycle. This was observed in SENCAR mice aged 20-23 and 75-80 days, during the second and third hair cycles, using tritiated thymidine-labeling and colchicine-arrest techniques. The study also demonstrated that the first hair cycle is distinct from later cycles and that the second telogen phase's long duration suggests the need for an additional factor beyond dermal papilla proximity to initiate a new anagen phase. The findings support the hypothesis that bulge cells are follicular stem cells and that their activation is crucial for hair cycle regulation, but also indicate that other factors are involved in initiating the hair growth cycle.