Study On The Relationship Between Polymorphism Of DGAT1, DGAT2 Gene And Some Economic Traits In Cattles

The RACE technology was used to clone bovine DGAT2 gene 3′-cDNA, and DGAT2 gene intron 3,5,6 and 7 were cloned by PCR. PCR－SSCP and PCR-RFLP technologies were applied to detect the polymorphisms of DGAT1 gene exon 8 and DGAT2 gene in three dairy cattles (Sanhe cattle, Chinese Holstein and Chinese Simmental), three Chiense breeds(Luxi cattle, Jinnan cattle and Qinchuan cattle) and four cross-breeding populations (Limousin×local cattle, Simmental ×local cattle, Charolais×local cattle, Angus× local cattle). The associations between these polymorphisms and some cattle economic traits were analyzed using the SSPS general linear model (GLM). Results were obtained as follows:1 Cloning of bovine DGAT2 gene 1) A 933bp sequence of bovine DGAT2 gene mRNA 3′-end was cloned, the similarity is 91%,89% and 90% respectively between the cloned sequence and human ( from 363 bp to 1218bp), mouse( from 557 bp to 1488bp) and rat DGAT2 gene mRNA(from 556bp to 1367bp ).2) The PCR products of primer PI3,PI5,PI6 and PI7 were 483bp,721bp,1 008bp and 2 132bp respectively. Aligning the PCR products with the cloned DGAT2 gene mRNA 3′-end showed that intron 3,5,6 and 7 of bovine DGAT2 gene are 365bp,568bp,802bp and 1945bp in length.There are no or low sequence similarities between this four introns and those of human DGAT2 gene.The SSCP polymorphisms of DGAT1 gene exon 8 in cattles and their effect on some cattle economic traits1) Two SSCP alleles(named allele K and allele A) of DGAT1 gene exon 8 were detected, sequencing result show: a substitution of GC to AA at 10433-10434 site results in the SSCP polymorphisms. The frequencies of allele K were 0.75,0.39,0.38,0.32,0.09,0.15 and 0.11 respectively in the seven cattles from Dachang county,Hebei province, and are 0.17,0.33,0.04 in the three dairy cattles.This locus is at Hardy-Weinberg equilibration (p>0.05)in Chiese Simmental cattle and Jinnan cattle.2) The analysis results showed: no significant association between genotypes and backfat depth , marbling score ,intestine fat weigt in beef cattles(p>0.05).But there was coeffect between age and genotypes on backfat depth,at age of 25,30,36 and 42 months ,the value of backfat depth in KK genotypes are higher than that in AA genotypes (p<0.05),and the KK and KA genotypes had higher backfat depth than AA genotypes.3) Significant effect of genotypes on the aliving weight ,hot carcass weight and dressing percentage(p<0.05),the value of individuals with genotypes AA and KK are higher. The average milk fat percantage was affected by polymorphisms at the DGAT1 exon 8 in Sanhe cattles and Chinese Simmental cattles(p<0.05),KK and KA had 0.8% and 0.41% higher value than AA genotypes in Sanhe cattles ,and only KK and AA genotypes had differences in milk fat(p=0.012)in Chinese Holstein,the former had 0.27% higher value.The polymorphisms at DGAT2 gene and their effects on some traits in cattles1)No PCR-SSCPs at DGAT2 gene exon5,6and 7,and no EcoRI, HindIII, HaeIII, MspI, TaqI,PuvII,BamHI,HhaI,PstI,Hsp21 and HpaII polymorphic cleavage sites at intron 5 were detected.No polymorphic EcoRI, HindIII, HaeIII and PstI polymorphic sites at intron 6,and no polymorphic EcoRI, HindIII ,HaeII, Msp, TaqI,BamHI,HhaI and HpaII sites at intron 7 were found in experimental cattles.There is a PuvII PCR-RFLP site at intron 7,but only one homozygote and the heterozygosity were detected ,and distributing frequency of the heterozygosity is very low.2) A G to T transversion at 655bp of PI6 PCR product digested by MspI was detected .Only in Luxi cattles, the frequency of aelle A is higher than that of aelle B .This locus is not at Hardy-Weinberg equilibration (p<0.05 or p<0.01)in Luxi ,Jinnan and Sanhe cattles.The dressing percentage of the individuals with genotype AA was much higher(p<0.01). The individuals with genotype AA in Sanhe cattles had higher average milk fat percentage and dry product percentage(p=0.005 and p=0.047)。3) The C toT transversion at 413bp of PI6 PCR product was detected .The distr...