The agouti gene in black and brown alpaca

The agouti gene encodes agouti signalling protein (ASIP) which regulates pheomelanin and eumelanin synthesis in mammals. To investigate the role of agouti in coat color variation of alpaca, we characterised the agouti gene on 27 black and 12 brown alpaca. The exon-4 hosts three loss-of-function recessive mutations: g.3836C>T, g.3896G>A and g.3866_3923del57, involved in eumelanin synthesis. The deletion at the position p.C109-Rdel19 eliminates the two beta sheets and the R-F-F- motif from the agouti functional domain, which are essential against alfa-MSH. Therefore, the deleted allele appears to lose function. The other ANPs observed at the amino acid position 98 and 118 change the conserved R to C and the R-F-Fmotif into H-F-F-. The R-F-F- motif is important for functioning at MCRs; the disruption of this motif may result in a non functional agouti protein since the alteration of residues in and around R-F-F- causes a decrease in agouti protein inhibition of alfa-MSH binding to MCRs during signal transduction. The three mutations are randomly distributed among the black alpaca. In our sample, we observed two genotypes : g.3836C>T/g.3896G>A (10 animals) and g.3836C>T/g.3866_3923del57 (17 animals). Among the brown alpaca, 2 are homozygous for the wild allele, 12 are heterozygous for g.3896G>A mutation, carriers for black phenotype.