Schematic representation of rat Hr structural and functional domains (reproduced from Thompson ; Hsieh et al. ) (A), and natural mutants of Hr that cause hair loss in mice and humans (B). The positions of the three repression domains (RD1, RD2, RD3), and JmjC domain are indicated yellow and red, respectively. Nuclear localization signal (NLS), and zinc-finger domain are boxed in black [7, 31]. Interacting domains 1 and 2 (ID1 and ID2) mediating the interaction between Hr and the retinoic acid receptor-related orphan receptor-alpha (RORα)  or with the thyroid hormone receptor (TR)  are boxed in green and blue, respectively. Specific cetacean, toothed whale, baleen whale, and Delphinoidea mutations are highlighted in red, blue, pink, and green, respectively [34–41].