Fig. 4. Proposed cellular kinetics in the early anagen hair follicle. (A) In anagen I, the activation of hair germ cells (red) may be the initial event of anagen induction by a follicular-papilla-derived signal (yellow arrow). (B) In anagen II, the activity of the hair germ (yellow arrow) induces proliferation of putative stem cells of the bulge region (black arrows). (C) In anagen IIIa, the active downward growth of bulge-derived cells (black arrows) results in the formation of the outer root sheath and provides the penetration of the hair follicle into the deep dermis. (D) In anagen IIIb, the upward proliferation of hair germ cells (white arrows) results in formation of the ascending compartment of the anagen hair follicle (hair shaft and inner root sheath).
