Polymorphisms of the Ovine Leptin Gene and its Association with Growth and Carcass Traits in Three Iranian Sheep Breeds

Leptin (LEP), the expression product of the obese gene produced primarily in the adipose tissue, is related to feed intake, growth and lipid metabolism. The aim of this study was to study the possible association between polymorphism of the LEP gene with growth and carcass traits among three Iranian sheep breeds of the Shal, Zandi and Zel varieties. A total of 180 purebred animals of the Shal, Zandi and Zel, breeds were chosen for this study. Three flocks, each comprising of 60 ewes of three breeds, were derived from Aboureyhan sheep populations. The Shal (n=18), Zandi (n=24) and Zel (n=17) lambs were screened for polymorphism of the LEP gene. Following genomic DNA extraction from whole blood samples, polymerase chain reaction (PCR) was carried out in order to amplify a 260 bp fragment of the target gene. Polymorphisms were detected using the single strand conformational polymorphism (SSCP) technique. Two genotypes of AA and AG with frequencies of 0.53 and 0.47 in the Shal 0.70 and 0.30 in the Zandi and 0.65, 0.35 in the Zel breed were observed, respectively. The frequencies of alleles A and G were 0.74, 0.26 in the Shal breed, 0.85, 0.15 in the Zandi breed and 0.82, 0.18 in the Zel breed, respectively. Chi-Square test (c2) confirmed the Hardy-Weinberg equilibrium for the LEP loci. Average heterozygosity (30%) of the LEP locus for the three breeds was slightly low. Comparison of the sequence of the target gene available in the GeneBank with the results of the present study showed two single nucleotide polymorphisms (SNP) A®G and T®C transitions at 113 and 165 bp positions, respectively. In the Shal breed, the A113G SNP associated with an increase in cold carcass weight (p< 0.01), fat-tail percent (p< 0.05) and total body fat weight (p< 0.05). In the Zel breed, the A113G SNP was associated with an increase in fat-tail percent (p< 0.05) and reduction in slaughter weight (p< 0.05), cold carcass weight (p< 0.01) and lean meat weight (p< 0.01). Therefore, a significant association between SNP within the LEP gene and certain carcass traits in the Shal and Zel breeds is proposed. In the Zandi breed the A113G SNP was not associated with carcass traits but showed a reduction in weaning weight (P< 0.05).