Studies On Polymorphisms Of Olfactory Receptor (OR) And Taste Receptor (T1Rs) Genes Of Sheep

Mammals have sensitive sense of smell and taste. They can choose their preferences of food according to the smell and taste in the process of feeding. They look for and detect food far away through the smell in air depend on their olfaction, and choose food through the different tastes and textures inside the cavity. The smell and taste of mammals are determined by the smell receptors and taste receptors gene, which are very large gene families in mammalian genome. Researchs show that the animal’s senses of smell and taste are not only related to the number of receptor gene and pseudogene rate, but also closely linked with the receptor gene polymorphism. Ujimqin sheep and Hu sheep, which are two different kinds of China Mongolian sheep, were selected in this study to research the gene exon of OR gene(OR4A4, OR4C46, OR4D1) and T1 Rs gene(TAS1R1, TAS1R2, TAS1R3). Amplification and sequence analysis of Genetic variation were performed in the gene exon to reveal the exon polymorphism and genetic diversity of the six genes. The genetic diversity of the tow kinds of sheep and the impact on the m RNA and protein secondary structure result from the six genes were also found in this research. The results of this study are as follows:1. DNA pools and direct sequencing was performed to study genetic variation of the six genes of the two Chinese sheep strains of Mongolian. As a result, 26 mutant sites were found among the three OR genes. And there were 8 SNPs in OR4A47, 7 SNPs in OR4C46 and 11 SNPs in OR4D1, which reminded us of the high genetic polymorphism of the three genes between Ujimqin sheep and Hu sheep. 9 SNPs were found among the three T1 Rs genes. And there were 2 SNPs in TAS1R1, 5 SNPs in TAS1R2 and 1 SNP in TAS1R3. The same number SNPs of the six genes were detected in the two sheep breeds.2. MALDI- TOF MS was performed to analysis the genotype of the 20 SNP loci in 172 individuals of the two sheep breeds. And the population genetics analysis showed that the 20 SNPs loci in Ujimqin sheep have higher polymorphism than Hu sheep.3. Chi-square test of independence showed that the genotype of six SNPs in the three OR genes had significant differences between the tow sheep populations. Among the six SNPs, the snp4 was in OR4A47 gene, the snp6, snp7 and snp8 were in OR4C46 gene and the snp9, snp11 were in OR4D1 gene. Linkage disequilibrium analysis was taken to found that there was complete linkage between the three SNPs of OR4C46 and the tow SNPs of OR4D1. The genotype of five SNPs in T1 Rs genes had significant differences between the tow sheep populations, which include the snp13 of TAS1R1 gene, the snp15, snp17 and snp18 of TAS1R2 gene, and the snp20 of TAS1R3 gene.4. Bioinformatics software was taken to predict the influence of SNP on the secondary structure of m RNA and protein. The result showed that, in the three OR genes, the snp11 locus was synonymous mutations, leading to the change of m RNA secondary structure. And snp4, snp6, snp7, snp8 and snp9 were missense mutation, leading to the change of protein secondary structure. In TIRs genes, snp13, snp17 and snp20 were synonymous mutations, in which snp13 and snp20 resulted in the change of m RNA secondary structure and minimum free energy. And snp15 and snp18 were missense mutation, leading to the change of protein secondary structure of TAS1R2.In a word, there were significant differences of SNPs in the OR4A47, OR4C46, OR4D1, TAS1R1, TAS1R2 and TAS1R3 genes of the two sheep breeds. And some SNPs leaded to the change of the secondary structure of m RNA and protein, which further resulted in the change of the ability that receptor proteins combined with the molecular of smell and taste.