Revelation of Replicative Capability of Hair Follicle Germinative Epidermal Cells after Repeated Plucking: Implications for Stem Cells and Hair Growth Cycle Control

The aim of this study was to evaluate the validity of bulge hypothesis on the limited proliferative potential of epidermal cells located at the basal end of hair follicle. Fibers of rat vibrissa follicles were plucked once or repeatedly and then pattern of cell replication and sequence of regenerative events was examined by measuring length of growing fiber, histology of regenerating follicle and immunohistochemistry (BrdU uptake of epidermal cells). Data provided here demonstrated that after single or multiple depletions, a new epidermal matrix originated merely from the residual germinative epidermal cells of the follicle base and cells from the bulge region had no role in formation of this structure. The matrix is the source of a new fiber which grows at a equivalent rate to its native counterparts from unplucked follicles. The total length of hair produced from the plucked follicles was much longer when compared to the fiber produced in normal follicles. Based on our results, replicative potential of epidermal cells located at the follicle base is not limited to a single cycle. We therefore consider it unlikely as cessation of growth phase of follicle is due to restricted proliferative potential of these cells.