Coat colours in the Massese sheep breed are associated with mutations in the agouti signalling protein (ASIP) and melanocortin 1 receptor (MC1R) genes

Abstract

Massese is an Italian dairy sheep breed characterized by animals with black skin and horns and black or apparent grey hairs. Owing to the presence of these two coat colour types, this breed can be considered an interesting model to evaluate the effects of coat colour gene polymorphisms on this phenotypic trait. Two main loci have been already shown to affect coat colour in sheep: Agouti and Extension coding for the agouti signalling protein (ASIP) and melanocortin 1 receptor (MC1R) genes, respectively. The Agouti locus is affected by a large duplication including the ASIP gene that may determine the Agouti white and tan allele (A Wt ). Other disrupting or partially inactivating mutations have been identified in exon 2 (a deletion of 5 bp, D 5 ; and a deletion of 9 bp, D 9 ) and in exon 4 (g.5172T.A, p.C126S) of the ASIP gene. Three missense mutations in the sheep MC1R gene cause the dominant black E D allele (p.M73K and p.D121N) and the putative recessive e allele (p.R67C). Here, we analysed these ASIP and MC1R mutations in 161 Massese sheep collected from four flocks. The presence of one duplicated copy allele including the ASIP gene was associated with grey coat colour (P 5 9.4E-30). Almost all animals with a duplicated copy allele (37 out of 41) showed uniform apparent grey hair and almost all animals without a duplicated allele (117 out of 120) were completely black. Different forms of duplicated alleles were identified in Massese sheep including, in almost all cases, copies with exon 2 disrupting or partially inactivating mutations making these alleles different from the A Wt allele. A few exceptions were observed in the association between ASIP polymorphisms and coat colour: three grey sheep did not carry any duplicated copy allele and four black animals carried a duplicated copy allele. Of the latter four sheep, two carried the E D allele of the MC1R gene that may be the cause of their black coat colour. The coat colour of all other black animals may be determined by non-functional ASIP alleles (non-agouti alleles, A a ) and in a few cases by the E D Extension allele. At least three frequent ASIP haplotypes ([D 5 :g.5172T], [N:g.5172A] and [D 5 :g.5172A]) were detected (organized into six different diplotypes). In conclusion, the results indicated that coat colours in the Massese sheep breed are mainly derived by combining ASIP and MC1R mutations.

Genetic background of coat colour in sheep

“…Surprisingly, Peñagaricano et al (2012) did not identify a significant difference in the expression of ASIP for black or white skin samples. The results contrast with those of Norris and Whan (2008) and Fontanesi et al (2011), who indicated the duplication of the functional ASIP region as a cause of the white phenotype. The other conclusion of the research is that ovine MC1R was not expressed in spotted skin samples.…”

A genome-wide scan study identifies a single nucleotide substitution in ASIP associated with white versus non-white coat-colour variation in sheep (Ovis aries)

“…Mutations in ASIP have also been shown to be responsible for the wild-/self-type coat pattern polymorphism in Soay sheep (Gratten et al, 2010). Also, the duplicated copy allele (s) in ASIP gene was found to be associated with grey coat colour (Fontanesi et al, 2011), which could explain the observation that coat-colour variation from grey to black/white spotted (non-white coat colour) was marginally explained by SNPs in and close to the ASIP gene. In addition, recessive genetic variants at the ASIP were found to be associated with reduced lifetime fitness in a wild population of Soay sheep (Gratten et al, 2012).…”

“…The highest-ranked SNP (s66432.1; F ST ¼ 0.731), which showed a single and strong selection signal, was located at the position 67.95 Mb within the ASIP gene. In sheep, the duplicated ASIP allele (s) was (were) found to account for the white and black sheep (for example, Norris and Whan, 2008;Fontanesi et al, 2011), and ASIP displayed strong evidence for positive selection in a quite recent study across a worldwide collection of breeds (Kijas et al, 2012). A total of four genomic regions containing X9 consecutive significant average values o0.05 were identified to be under positive selection using the five-SNP sliding-window analysis (Table 2), whereas no region was observed with balancing selection.…”

Duplication of chicken defensin7 gene generated by gene conversion and homologous recombination

“…In recent years, advances in high-throughput genome scan technologies, particularly DNA hybridization on array platforms and next-generation sequencing methods, have allowed the identification of a large number of structural variants in multiple species. Although not as comprehensive as those for human, CNV maps have been produced in cattle (2,3), horse (4), sheep (5,6), pig (7), goat (8), duck (9), and chicken (10,11).…”