The Study On Variation Of Sheep EPAS1 Gene And Its Genetic Effects

In this study,the nine populations,including Plateau-type Tibetan sheep,Oura-type Tibetan sheep,Valley-type Tibetan sheep,Ujumqin sheep,Sunite sheep,Tan sheep,Guangling big-tail sheep,Small-tail Han sheep and Hu sheep,living in different geographic locations were selected as experimental materials.Variations of sheep EPAS1 gene were screened by mixed samples sequencing technology and these variations were genotyped via directly PCR-product sequencing.Association analysis between allele frequencies of these loci and altitude was conducted by multiple comparisons.Orthologs of this gene were applied in phylogenetic relationship analysis and potential positively selected sites were calculated among species.Furthermore,Selection signals were detected within sheep populations based on Fst-outlier test and variations were mapped on predicted protein structure,furthering understand the functional impact.This research could provide theoretical reference for understanding hypoxia adaptation of sheep and genetic resources conservation.The main results are as follow:1.31 SNP and 1 Indel were detected by the mixed samples sequencing in the nine sheep populations,10 of which were genic variations and g.31546G>A?g.32826T>C?g.32946G>A?g.35117T>C were nonsynonymous substitution.The correlation analysis between allele frequencies and altitude found that there were 10 SNP significantly correlated with altitude and g.225G>A?g.256C>T?g.21324G>A?g.32918A>G?g.33007T>C?g.33683T>C?g.37143T>C were significantly different between high and low altitude sheep populations.2.The inter-species evolution analysis showed that EPAS1 gene has undergone strong positive selection and three positively selected sites(498S?538S?553P)were identified based on Na?ve Empirical Bayes test.The intra-species evolution analysis of 32 loci among all sheep populations demonstrated that g.31546G>A?g.31895G>A?g.35117T>C were under positive selection.g.31546G>A was a nonsynonymous substitution encoding valine to methionine amino acid shift in exon 12 while g.35117T>C encoded an amino acid shift(phenylalanine to leucine)in exon 15.g.225G>A?g.31895G>A?g.33220C>T?g.35117T>C were identified among six Mongolian sheep populations and former three were located in inter-genic region.In summary,g.35117T>C was detected in all sheep populations categories.3.The association study showed that there are two loci correlating significantly with first parity litter size of Hu sheep.The individuals with AA genotype in loci g.32946G>A have more litter size than GA genotype and TC and CC genotype of g.33048C>T have higher first parity litter size than TT genotype.Furthermore,two loci were significantly associated with average litter size of Hu sheep.TT individuals in g.37143T>C have more average litter size than CC genotype while individuals with GG of g.41040G>A has higher litter size records than AA genotype.In conclusion,EPAS1 gene was inferred under positive selection among species after local duplication,which allowed it to accumulate nonsynonymous substitutions and boost its protein stability.EPAS1 gene is also undergoing adaptive positive selection,and the loci under positive selection are increasing allele frequencies to response hypoxic environment.