An SNN retrocopy insertion upstream of GPR22 is associated with dark red coat color in Poodles

Abstract

Pigment production and distribution is controlled through multiple genes, resulting in a wide range of coat color phenotypes in dogs. Dogs that produce only the pheomelanin pigment vary in intensity from white to deep red. The Poodle breed has a wide range of officially recognized coat colors, including the pheomelanin-based white, cream, apricot, and red coat colors, which are not fully explained by the previously identified genetic variants involved in pigment intensity. Here, a genome-wide association study for pheomelanin intensity was performed in Poodles which identified an association on canine chromosome 18. Whole-genome sequencing data revealed an SNN retrocopy insertion (SNNL1) in apricot and red Poodles within the associated region on chromosome 18. While equal numbers of melanocytes were observed in all Poodle skin hair bulbs, higher melanin content was observed in the darker Poodles. Several genes involved in melanogenesis were also identified as highly overexpressed in red Poodle skin. The most differentially expressed gene however was GPR22, which was highly expressed in red Poodle skin while unexpressed in white Poodle skin (log2 fold change in expression 6.1, P < 0.001). GPR22 is an orphan G-protein-coupled receptor normally expressed exclusively in the brain and heart. The SNNL1 retrocopy inserted 2.8 kb upstream of GPR22 and is likely disrupting regulation of the gene, resulting in atypical expression in the skin. Thus, we identify the SNNL1 insertion as a candidate variant for the CFA18 pheomelanin intensity locus in red Poodles.

Keywords: GWAS; canine; coat color; dog; inherited; pheomelanin; retrogene.