Interaction between the melanocortin 1 receptor (MC1R) and agouti signalling protein genes (ASIP), and their association with black and brown coat colour phenotypes in peruvian alpaca

The aim of this work was to assess the interaction between MC1R and ASIP genes in determining coat colour variation in black and brown Peruvian alpacas. Skin biopsies were collected from 25 black alpacas and 15 brown alpacas. Genomic DNA was isolated, amplified and sequenced. Black alpacas were dominant homozygous (E/E) or heterozygous (E/e) at MC1R locus while brown alpacas were heterozygous at the locus. All the black animals were heterozygous for the non-functional alleles at ASIP locus (a(H) - a(Delta 57) - a(ht) ). On the contrary, brown alpacas were dominant homozygous (A/A) or heterozygous (A/a(ht) ) at this locus. When the combined genotypes at MC1R and ASIP were considered together, alpacas with black coats had four possible genotype combinations namely a(H)/a(Delta 57) - E/E, a(H)/a(ht) - E/E, a(H)/a(Delta 57) - E/e and a(H)/a(ht) - E/e. The brown alpacas were found to have the A/a(ht) - E/e and the A/A - E/e genotype. Our results show that the two genes interact to sinergically modulate the amount of melanin synthetised in alpaca fibre. In black coat alpacas in fact, the expression of non-functional ASIP results in the failure of pheomelanin production while the functional MC1R allows the synthesis almost exclusively of eumelanin. On the other hand, the brown coat phenotype is produced when the animal possesses at least one functional copy of the gene at both ASIP and MC1R loci. In fact, MC1R binds both ASIP and alpha-MSH allowing a mixed melanogenesis characterised by the synthesis of eumelanin and pheomelanin granules in a similar ratio.