Candidate Genes for Color Phenotypes in the Dromedary Camel (Camelus dromedarius)

The color of skin and hair depends on the synthesis, relative amounts and distribution of eumelanin and pheomelanin. The process is regulated by a dozen of major and hundreds of modifier genes. Among the main regulators are the melanocortin 1 receptor (MC1R) and its antagonist, the agouti signaling protein (ASIP). Mutations in these genes have been associated with various color phenotypes in many species, though not yet in camels. Here we sequenced the coding regions of MC1R and ASIP in black, white and wild type dromedaries and identified a missense mutation in MC1R and a nonsense mutation in ASIP. TaqMan genotyping assays were designed for the two mutations and analyzed in a population of 145 dromedaries comprised of 26 black, 36 white and 83 wild type animals. All black dromedaries were homozygous for the wild-type MC1R and for the nonsense mutation in ASIP, suggesting the latter being causative for the black color. Heterozygosity or homozygosity for a missense mutation c.901C>T in MC1R was significantly (P <0.0001) associated with the white coat color suggesting a possible dominant negative effect. Notably, the same mutation is associated with white color also in Peruvian alpacas. As anticipated, the majority of beige/red/brown dromedaries were homozygous for the wild type MC1R, though additional mutations in this or other genes might modify the amount/intensity and distribution of pigment, and require further studies. The findings contribute to coat color genomics in camelids and lay a foundation for the development of molecular tests.