Analysis On The Relationship Between SLA-DQA Gene Polymorphism And Piglets Diarrhea In Three Breeds

The swine major histocompatibility complex is the most abundant polymorphicgene cluster, which plays an important role in the animal's immune system, studieshave demonstrated that the MHC is associated with disease resistance andsusceptibility of various animals. Single-strand conformational polymorphism(PCR-SSCP) and sequencing were used in this study to analyse the geneticpolymorphism and its relationship with piglet diarrhea at four exons of the SLA-DQAgenes in three pig breeds in order to gain the molecular genetic informations andexplicit the swine genetic characteristics of the SLA-DQA gene, so as to inprove thedisease resistance of swine from the genetic nature, and analyze the possibility of theDQA gene as candidate gene in disease resistance. The results as follows:The results showed that exon2, exon3and exon4of SLA-DQA gene from threepig populations were detected polymorphism by PCR-SSCP, but there were nopolymorphism in exon1. Five alleles and eight genotypes (AB, BB, BD, BE, BC, CC,CD, DD) were detected from exon2, genotypes CC was only detected in Landracewith frequency of0.04, CD and DD were only detected in Duroc with frequency of0.01. Allele B is the dominant gene and allele D is the disadvantages gene in the threegroups. By sequencing, the new mutation4133bpC→A and3994bpT→A wasfound in allele C and E, respectively.Eight alleles and fourteen genotypes were detected in exon3fragment. Eightalleles which formed thirteen genotypes in Large white, alleles D and H were notdetected in Duroc and Landrace. Genotypes EE, DD and DH were not detected inLandrace, and BC, AB, CC, DD, DH were not detected in Duroc, allele B is thedominant gene in three groups. By sequencing and homology analysis that fourteenmutations were found in exon3, included six conversion of T→C, two conversion ofC→T and one conversion of A→C, two transversion of A→G and three transversionof G→A. Alleles B, E and F were deleted in the region of4727～4729bp. Thepolymorphisms would change as amino acid changed, and this mutations was missense mutations.Gained four alleles and six genotypes(AA, AB, CC, CD, BB, BC)in exon4,which detected in Duroc, but AA, AB, CC genotypes were only detected in Largewhite, BC was not detected in Landrace. AA was the dominant genotype and allele Awas the dominant allele in three groups. By sequencing, there were found three SNPs(5126bpA→G,5158bpA→T,5233bpG→A), respectively, those mutations aresynonymous mutations.The analysis results of the genetic polymorphisms showed that heterozygosity(He) of Duroc and Large white were0.62and0.79in exon2of DQA gene respectively.Which larger than Landrace, the polymorphism information content of three pigs were0.25<PIC <0.5, indicates moderate polymorphism. In exon3locus, heterozygosity(He) of Large white, Landrace and Duroc are0.54,0.46and0.35, PIC>0.5indicatedHighly polymorphism in three pigs. In exon4locus, heterozygosity (He) of Largewhite, Landrace and Duroc were0.37,0.50and0.68. respectively. The polymorphisminformation content of Duroc was highly polymorphism (PIC>0.5), Large white andLandrace are moderate polymorphism (0.25<PIC<0.5), this polymorphic locus inthree breeds was deviated from Hardy-Weinberg equilibrium by χ2test (P <0.05).The present results indicated that genotype had significant influence on pigletsdiarrhea (P <0.05), but the breed and gender showed no significant influence (P>0.05). The piglet diarrhea score of individual genotypes showed that CD wassignificantly higher than that of AB, BB, BC and BE (P <0.05) in exon2,BB, BC, BE,GF, DD and DH was significantly higher than that of BF, AB, CF, EF and CC (P <0.05) in exon3,CD was significantly higher than that of AA, BB, AB and CC (P <0.05) in exon4.