Involvement of tyrosinase-related protein 1 gene in the light brown plumage phenotype of Falco cherrug

Coat pigmentation in birds and other vertebrates depends on the balance of two types of melanins: brown-grey-black eumelanin and yellow-red pheomelanin.1 Although it is known that more than 150 genes impact pigmentation, there are a few key genes in the melanogenic pathway: MC1R (melanocortin 1 receptor), ASIP (agouti signaling protein), MITF (microphthalmia-associated transcription factor), MLPH (melanophilin), TYRP1 (tyrosinase-related protein 1), SLC45A2 (solute carrier family 45 member 2) and TYR (tyrosinase).1-3 Previous studies have reported a correlation between genetic variations in the sex-linked TYRP1 gene and variation of plumage colour in Japanese quail, domestic pigeon and duck, but no data are available for falcons.4-6 Here, we investigated the involvement of polymorphisms of the TYRP1 gene in the brown plumage phenotype of Falco cherrug. Forty-two F. cherrug bred in captivity from a two-generation pedigree were evaluated to test the inheritance of a colour trait, i.e. wild-type and a lighter mutant (Fig. 1). The F1 generation consisted of 12 females, nine of which were light brown, and 18 males (Table S1). The sex-linked inheritance of the phenotype and the light brown plumage observed in the offspring of carrier males and wild-type females indicates a sex-linked inheritance of these mutations and the involvement of a Z-chromosome gene as previously described for other bird species (Fig. S1).7,8 The sequences of the TYRP1 exons were obtained from one wild-type and one mutant female by Sanger sequencing (Table S2). Exon 1 of the TYRP1 amplicon was then sequenced in all animals. Sequences were deposited in GenBank (Accession numbers KX181731 and KX181733). Two mutations - c.79C>T and c.79_80insT - were found in exon 1 of all light brown females. Translation predicts a frameshift change and a premature stop codon at position 81 of the deduced protein sequence, which in the wild-type form contains 536 amino acids. The cited-above mutation in the TYRP1 gene was found in all nine brown females of the F1 generation. Moreover, in three F0 and six F1 wild-type males double peaks downstream of the polymorphic site revealed that these animals were heterozygous for the mutations. Previous genetic studies on coat colour of mammalian and avian species also reported a key role of TYRP1 gene in coat or plumage color via the production of the dark eumelanin.