Mc1r, Agouti signaling protein (ASIP) and CBD103 are involved in brindle coat colour of Boxer and Great Dane dogs

In most mammals, variations in skin and hair colour (brown/black eumelanin and the red/yellow phaeomelanin) are mainly achieved by the interaction between two genes: Agouti signaling protein (ASIP) and melanocortin 1 receptor (Mc1r) encoding a ligand-receptor system that controls the eumelanin/pheomelanin switching. In domestic dogs, pigment type-switching is also controlled by an unexpected allele (CBD103) of K locus encoding a secreted protein (β-defensin) previously studied for its role in immunity. Interaction studies reveal that Mc1r is epistatic to variation at Agouti and K loci. In this work, we examined Mc1r, ASIP and CBD103 as candidate genes for brindle or fawn Boxer and Great Dane animals. The brindle phenotype in domestic dogs consists of an irregular pattern of red-yellow stripes alternating with black-brown. We found that all brindle dogs are heterozygous for ΔG23 mutation previously reported by Barsh’s team. In addition, we report for the fi rst time two interesting insertions in Agouti promoter region. The innovation of this work is the discovery of new alternative transcripts of Agouti that could be involved in brindle coat colour pattern in dogs. The interaction between CBD103 mutation and Agouti insertions promoting the different transcripts is discussed. This can be a starting point in better understanding their involvement in pigment switching leading to the brindle pattern formation.