Sequence characterization of the melanocortin 1 receptor (MC1R) gene in sheep with different coat colours and identification of the putative e allele at the ovine Extension locus

摘要

Sequence of the melanocortin 1 receptor (MC1R) gene (the Extension locus) was obtained from a panel of 73 animals belonging to 9 Italian sheep breeds or populations (Appenninica, Bergamasca, Comisana, Cornigliese-like, Delle Langhe, Massese, Merinizzata Italiana, Sarda and Valle del Belice) with different coat colours. Evaluation of the identified polymorphisms on this phenotype was reported with in silico predictions and comparative approaches within and across breeds and across species. Five novel single nucleotide polymorphisms (SNPs), organized in three haplotypes, were detected. Another haplotype, including the two missense mutations already described for the E-D allele, was identified in few Massese sheep. One SNP (c.199C>T) caused a predicted amino acid substitution (p.R67C) in a highly conserved position of the first intracellular loop of the MC1R protein. The same substitution causes recessive pheomelanism in other species. We propose that the p.67C allele represents the recessive e allele at the ovine Extension series that was, so far, not completely recognized in sheep by classical genetic studies. This polymorphism was analysed in a total of 388 sheep of the 9 investigated breeds. The p.67C allele was identified only in the Valle del Belice breed (allele frequency of 21.3% in 176 analysed animals of this breed) in which the presence of epistatic white-determining loci might mask, at least in part, its effects. Confirming the effect of this novel allele on coat colour will lead to new perspectives on the composition of specialized coloured sheep lines.