Molecular Study of the Extension Locus in Association with Coat Colour Variation of Iranian Indigenous Sheep Breeds

Abstract

A tremendous variety is observed in coat colouration of the Iranian indigenous sheep, whereas a few molecular based studies have been carried out to identify the responsible genes in this geographical area. Function and distribution of melanin, categorized as phaeomelanin and eumelanin determine the coat colour in vertebrates, which are primarily regulated by interactions of the two main loci, agouti and extension, currently termed as Agouti Signalling Protein and Melanocortin 1 Receptor, respectively. In current study, the upstream region and a part of the coding sequence of the MC1R gene were assessed in three Iranian sheep breeds, Zandi, Baluchi and Zel, through molecular methods and in silico predictions. PCR-SSCP results of the 5' UTR flanking region showed a clear banding pattern in which the E^ab was most frequent (67 per cent), observed in the individuals with light coloured phenotypes like white Baluchi and light grey and cream Zandi sheep, while the two homozygous patterns, E^aa and E^bb were rare in the populations. Direct sequencing the fragments revealed that the pattern is consistent with the–206G>A polymorphic site in the upstream region and four putative transcription binding sites close to this site were defined and characterized. The 12A>G and 51G>A transitions were also detected and verified as silent mutations in the 5' end of the coding region of the MC1R gene, with synonymous effect on amino acid sequence. Semi quantitative RT-PCR of various phenotypes resulted in acquisition of the highest expression in the dark grey phenotype of the Zel sheep.