Fig. 8. Lateral disc transformations during anagen-catagen transition. (A) During anagen, bulge-derived cells that have high proliferative potential migrate downward (blue arrow) and form the lateral disc, which resides on the periphery of the hair bulb and is inactive. Hair matrix cells (red) actively proliferate. (B) In early catagen, owing to the diminution of the hair matrix, the lateral disc cells come into direct contact with follicular papilla (FP) cells. (C) In late catagen, lateral disc cells travel upward along with the FP and gradually transform into the hair germ (change of blue color into red). (D) In the telogen hair follicle (HF), hair germ cells and bulge cells reside as two separate and functionally discrete structures. Owing to FP-dependent ‘education’ during previous catagen, hair germ cells acquire selective sensitivity to FP-derived signaling and the commitment to produce the ascending HF layers.