Categories: Pigmentation phene

Possible human homologues (MIM numbers): 266300 (trait) , 155555 (gene)

Cross-species summary: The extension locus encodes the melanocyte-stimulating hormone receptor (MSHR; now known as MC1R). This receptor controls the level of tyrosinase within melanocytes. Tyrosinase is the limiting enzyme involved in synthesis of melanins: high levels of tyrosinase result in the production of eumelanin (dark colour, e.g. brown or black), while low levels result in the production of phaeomelanin (light colour, e.g. red or yellow). When melanocyte-stimulating hormone (MSH) binds to its receptor, the level of tyrosinase is increased, leading to production of eumelanin. The wild-type allele at the extension locus corresponds to a functional MSHR, and hence to dark pigmentation in the presence of MSH. As explained by Schneider et al. (PLoS Genet 10(2): e1004892; 2015), "The most common causes of melanism (black coat) mutations are gain-of-function alterations in MC1R, or loss-of function alterations in ASIP, which encodes Agouti signaling protein, a paracrine signaling molecule that inhibits MC1R signaling". Mutations in MC1R have been associated with white colouring in several species.

Species in which this phene is found:
lorises (Lorisidae)
coyote (Canis latrans)
dog (Canis lupus familiaris)
red fox (Vulpes vulpes)
American black bear (Ursus americanus)
domestic cat (Felis catus)
jaguar (Panthera onca)
ass (donkey) (Equus asinus)
horse (Equus caballus)
Przewalski's horse (Equus przewalskii)
pig (Sus scrofa)
Arabian camel (Camelus dromedarius)
reindeer (Rangifer tarandus)
taurine cattle (Bos taurus)
indicine cattle (zebu) (Bos indicus)
goat (Capra hircus)
sheep (Ovis aries)
rabbit (Oryctolagus cuniculus)
Mongolian gerbil (Meriones unguiculatus)
domestic guinea pig (Cavia porcellus)
domestic yak (Bos grunniens)
fallow deer (Dama dama)
alpaca (Vicugna pacos)
gray squirrel (Sciurus carolinensis)
raccoon dog (Nyctereutes procyonoides)
antarctic fur seal (Arctocephalus gazella)
woolly mammoth (Mammuthus primigenius)
rock pocket mouse (Chaetodipus intermedius)
oldfield mouse (Peromyscus polionotus)
lesser earless lizard (Holbrookia maculata)
Geoffroy's cat (Leopardus geoffroyi)
jaguarundi (Herpailurus yaguarondi)
Colocolo (Leopardus colocolo)
little striped whiptail (Aspidoscelis inornata)
water buffalo (Bubalus bubalis)
Arctic fox (Vulpes lagopus)