Study On The Polymorphism, MRNA Expression Of Leptin And Its Receptor Genes And Their Association With Traits In Sheep

The leptin gene (Lep) is one of the earliest discovered genes related to obesity. Mediated by its receptor (LEPR), leptin plays important regulatory roles in fat metabolism. With two sheep breeds of distinct tail types (Guangling Large Tailed and Small Tailed Han Sheep) as experimental animals, we studied the polymorphism, mRNA expression of Lep and LEPR genes at DNA and RNA levels.PCR-SSCP technique was used to study the polymorphism of5’ UTR and promoter sequence in Lep and LEPR genes in96animals from the two sheep breeds. The effects of genotypes and haplotypes of Lep and LEPR genes on tail and slaughter traits in the two breeds were analysed to reveal probable relationship between the polymorphism and economic traits. The results showed that genetic variations existed in Lep and LEPR genes, with three genotypes (AA, BB and AB) for each fragment amplified by16pairs of primers. Ten single nucleotide polymorphisms (SNPs) in Lep gene and nine SNPs in LEPR gene were detected. Association study showed that genotypes at loci amplified by P6, P7and P10primers in Lep gene had significant effects on absolute tail fat weight (P<0.05), and the absolute tail fat weight of animals with haplotype4(AGTG) were significantly higher than those with other haplotypes. In LEPR gene, the polymorphism at locus amplified by P15primer had a significant effect on tail length (P<0.05), and tail length of animals with BB genotype significantly higher than those with AA and BB genotypes. The relative tail fat weight of-animals with haplotype5(TGTA) and haplotype7(TAAA) were significantly higher than those with other haplotypes. So we inferred that Lep and LEPR had influences on sheep tail and fat deposition. These results provided theoretical basis for maker-assisted selection of meat quality traits in sheep and references for genetic improvement of the same traits in other livestock species.Real-time PCR technique was used to study the ontogenetic mRNA expression of Lep and LEPR genes in the two breeds. Associations between mRNA abundances and tail and slaughter traits were analysed by Pearson’s correlation. The main purpose is to discuss the probable relationship between the mRNA expression and fat metabolism. Adipose tissues from seven parts of the body, i.e. great and small omenta, tail, subcutaneous, mesenteric, perirenal and retroperitoneal, were collected from96animals (48for each breed with equal sex ratios) from2to12months of age at the interval of two months to study the mRNA expression. The results showed that both Lep and LEPR expressed spatiotemporally in the two breeds. As the main effects, sex and breed did basically not influenced the expression of Lep and LEPR, but the breed by age interaction affected the expression of the two genes to different extents. Although the two genes had a synergistic effect on the regulation of fat deposition and energy metabolism, their expressions were inversely regulated. Association analysis between mRNA expression and traits showed that different degrees of correlations existed for different adipose tissues. Close relations were found between mRNA expressions in tail fat for the two genes and tail and slaughter traits in the two breeds. These results provided the important scientific bases for further research on the genetic mechanism of fat metabolism in sheep.