Polymorphisms Of The DFAT1 Gene And Its Association With Milk Quality Traits In Yak

Diacylglycerol acyltransferase 1（DGAT1）,as an important candidate gene for milk fat traits,plays a key role in triglycerides synthesis.In this study,we evaluated the tissue expression of Gannan yak DGAT1 mRNA by Quantitavie real-time PCR（qPCR）.The mutaions in CDS and 3’-untranslated region（UTR）,intron5-exon7,exon8 and intron15-exon17 in yak DGAT1 were also detected using DNA pool sequencing and PCR-SSCP,respectively.The DGAT1 structure and function were predicted and the association between polimorplisms in part regions of yak DGAT1 and milk quality trais were analyzed.The results showed:（1）The relative expression of DGAT1 gene was significantly different in varited tissues of Gannan yaks.The higher expression level of DGAT1 were found in mammary gland,longissimus dorsi,heart and subcutaneous fat,moderate in kidney,small intestine,large intestine,but low in spleen.（2）The yak DGAT1,putatively belongs to the hydrophilic protein that locats on the cell membrane with eight transmembrane helical regions,was mainly composed of aliphatic amino acids.The secondary structure of yak DGAT1 was Mix model withα-helix and random coil mainly.The protein was presumed to be a cell membrane enzyme that exerts biological functions mainly in the cell membrane.（3）The Yak DGAT1 gene had rich polymorphism.Five SNPs in the CDS region were identified when it aligned with the bovine suquences.Thec.*197T>C,c.562+32_c.562+33insCCCCGC,c.1336C>T and c.1249-23C>T were detected in 3’-UTR,intron5-exon7 and intron15-exon17 regions,respectively.The c.1336C>T leads to the conversion of the p.Arg447Cys.This three regions of DGAT1 gene of four yak groups showed moderately polymorphic（0.25<PIC<0.5）.The c.691-c.692 AA>GC（K232A）was also detected in exon8 of Gannan yak and Tianzhu white yak.Linkage relationship and closed to linkage equilibrium were found in 3’-UTR,intron5-exon7 and intron15-exon17 regions of yak DGAT1,and total of 12 haplotypes were constructed among those three regions in Gannan yak.（4）The variations in detected regions had significant effects on some milk quality traits of Gannan yak.The allele A₁ in 3’-UTR region had a decreasing trend in individual milk fat rate and total solid percentage,the allele A₄ and allele C₄ in intron15-exon17 had an increasing trend in individual milk quality traits（except lactose rate）and milk fat percentage,while allele B₄ had a significant negative effect on individual milk fat rate and total solid percentage.The variation in intron5-exon7 was not significantly correlated with the milk quality traits.（5）The haplotypes A₁-A₂-A₄ and B₁-A₂-C₄ of DGAT1 had a significant positive effect on milk protein rate,non-fat solids percentage and milk fat rate in Gannan yak.The haplotype A₁-A₂-B₄ had a significant negative effect on milk fat rate and total solid percentage.So selecting haplotypes A₁-A₂-A₄ and B₁-A₂-C₄ or eliminating haplotypes A₁-A₂-B₄ would significantly improve milk quality traits in yak offspring populations.