Figure 4.

A. Schematic illustration of hair cycling in a population of hair follicles. B. A two-dimensional CA model can predict regenerative patterns in a large population of hair SCs. Skin pigmentation patterns result from color changes of many HFs when they collectively cycle through four phases: P (blue)→A (yellow)→R (red)→C (green). Distinct hypothetical activator/inhibitor signaling profiles can be assigned to all four phases. C. Cellular Automata model for the observed hair wave. Wiggly white lines indicate the spreading of the hair wave from hairs in propagating anagen to hairs in competent telogen, whereas hairs in autonomous anagen or propagating anagen cannot initiate the hair cycle in hair follicles that are in refractory telogen. D. Hair follicles may regenerate in response to intrinsic signals which drive each individual follicle or to extrinsic signals which can couple the activation of the hair cycle in neighboring follicles. By modulating the strength of intrinsic stem cell activation (Y axis) and the probability of coupled activation (X axis), different animals or different physiological conditions in the same animal can significantly alter the global dynamics of hair regeneration. As a result, versatile hair growth patterns in rabbits, mice, normal and alopecic human scalps can be explained within the same patterning framework based simply on how hair stem cell activities are “managed”. Panels B, C and D are from Plikus et al., 2011.