Identification Of The Association Between Meat Quality Gene Mutations And Fatty Acid Composition In Mongolia Sheep

As one of the main sheep breeds in China,Mongolia sheep is famous for their delicious,fresh and tender meat.However,the studies focusing on the function of meat quality-related gene in Mongolia sheep were little.Fatty acids affecting meat quality,nutritional value and flavor are an important factor for mutton sheep.Therefore,the identification of candidate genes and mutations related to intramuscular fat(IMF)deposition and fatty acid(FA)composition,and utilization of molecular markerassisted breeding to select sheep breeds with good meat quality and the better combination of fatty acid composition,are very important in mutton sheep industry.In this study,160 Sonid and 116 Ujimqin sheep were used for experiments.The FA components and IMF in longissimus dorsi muscle were detected.Real-time quantitative PCR was used to detect the expression levels of Fatty acid binding protein4 gene(FABP4),Fatty acid synthase(FASN),Calpastatin(CAST),Stearoyl Co A desaturase(SCD),Cell division cycle 10(CDC10)and Myosin binding protein C1(MYBPC1)genes,and then perform the correlation analysis between the expression levels and fatty acid composition and IMF content in Mongolia sheep.The mutations of FABP4,FASN and CAST genes of Mongolia sheep were identified by using genome resequencing and Sanger direct sequencing technologies.The genotypes of each mutation locus of 276 samples were detected by mass spectrometry genotyping,and then the genetic diversity of the mutant loci and their effects on fatty acid composition and IMF content of Mongolia sheep were analyzed.The results are as follows:(1)The 37 kinds of fatty acids,including 17 kinds of saturated fatty acids and 20 kinds of unsaturated fatty acids were detected in the longissimus dorsi muscle of Mongolia sheep.There were significant correlations among the part of FA,one kind FA and combinations of fatty acid types,and one kind of fatty acids and IMF.(2)FABP4,FASN,CAST,SCD,CDC10 and MYBPC1 genes were differently expressed in 11 tissues of Mongolia sheep(n = 3),and they were mainly expressed in subcutaneous fat and muscle tissue.(3)The expression levels of FABP4 and FASN genes were significantly positively correlated with UFA(Unsaturated fatty acid,P < 0.05),and the expression levels of CAST genes were significantly positively correlated with n6-PUFA(Polyunsaturated fatty acid,P < 0.05)in FA components.The expression levels of SCD gene were significantly negatively correlated with SCFA(Short chain fatty acid,P < 0.05)and MCSFA(Medium chain fatty acids,P < 0.05)in FA components(P < 0.05).The expression levels of MYBPC1 gene were significantly positively correlated with n6-PUFA(P < 0.01).The expression levels of CDC10 gene were significantly negatively correlated with MCFA and positively correlated with n6/n3-PUFA(P < 0.05).(4)There were 9 novel single nucleotide polymorphisms(SNPs)identified in FABP4 gene,and all SNPs showed low or moderate polymorphism.Association analyses showed that each of 9 SNPs had significant effects on part of fatty acid components in Mongolia sheep,and the g.62827699A>C SNP had significant effects on lauric acid(C12:0,P < 0.05),oleic acid(C18:1,P < 0.05)and total monounsaturated fatty acids(MUFA,P < 0.05).FABP4 gene haplotype combination H4H4 had significant effects on FA compositions of Mongolia sheep(P < 0.05).(5)Three SNPs of FASN gene were found,and each site presents moderate polymorphism.Association analyses showed that each of the 3 SNPs had significant effects on part of FA components in Mongolia sheep.The g.12316076A>C SNP had significant effects on C12:0(P < 0.05),total saturated fatty acids(SFA,P < 0.05),C18:1(P < 0.05)and total unsaturated fatty acids(UFA,P < 0.05).Haplotype H2H4 of FASN gene has significant influence on fatty acid composition of Mongolia sheep(P < 0.05).The g.12321670A>G,g.12316076A>C and g.12314825A>G mutations lead changes in secondary structure,free energy and stability of m RNA.(6)Twelve SNPs were found in CAST gene,all of which showed low or moderate polymorphism.Association analyses showed that each of the 12 SNPs had significant effects on part of FA composition of Mongolia sheep.The mutant loci g.102045276C>T,g.102070394C>T,and g.102015758T>C had significant effects on C12:0(P < 0.05),myristic acid(C14:0,P < 0.05),Oleic acid(P < 0.05)and total unsaturated fatty acids(P < 0.05).CAST gene haplotype H7H7 significantly affected PUFA/SFA(P < 0.05).The m RNA secondary structure,free energy and stability was changed by each of 12 mutations.The g.102035686G>C SNP led a missense mutation(Glu216Arg)which could affects both the secondary and tertiary structures of the CAST gene encoded protein.The g.62827699A>C SNP of FABP4 gene,the g.12316076A>C SNP of FASN gene and the g.102045276C>T SNP,g.102070394C>T SNP and g.102015758T>C SNP of CAST gene could be considered as a useful DNA molecular marker for Mongolia sheep breeding with better meat quality and fatty acid components.