Study On Associations Between C-fos And MyoG Genes And Muscle Fibre Traits In Pigs

With the development of chinese ecomomy and improvement of people's life,more emphasis wasplayed on the meat quality. Meat quality was determined mainly by muscle fibre histological traits, andthere was significant correlation between muscle fibre traits and meat quality. Muscle fibre werecontroled mainly by genes. Seeking for major genes or molecular marker influencing muscle fibre traitsand putting marker-assisted selection in practice were main methods to improve meat quality because itwas very difficult to measure muscle fibre traits in vivo.Large White and Beijing Black pigs (up to 90 kg) were used to study muscle fibre traits. Serialmuscle sections (10μm ) were obtained on a cryostat and stained by the method of H-E andSDH.Differences of traits between breeds and associations between traits were analyzed. SNPs ofmyogenin (MyoG) and c-fos genes influencing development of muscle fibre were analyzed byPCR-SSCP technique. Gene and genotype frequencies were calculated for the polymorphic loci inMyoG gene and c-fos gene. And variance analysis was completed for distribution of genotypesfrequency between different breeds. Effects of genotypes in different locus on muscle fibre traits wereestimated. The results indicated that:(1) The means of backfat thickness, muscle fibre density,percentage of red muscle fibre and middlemuscle fibre were higher in Beijing Black pigs than that of in Large White pigs 99.16 %, 26.90 %, 22.41% and 18.24%, respectively; And the means of eye muscle area, muscle fibre diameter, muscle fibrearea and percentage of white muscle fibre were higher in Large White pigs than that of in Beijing Blackpigs 24.16%, 10.85%, 10.75% and 4.78%, respectively.(2) Muscle fibre diameter was significantly positive correlation to muscle fibre area, percentage ofwhite muscle fibre and eye muscle area; Muscle fibre density was significantly positive correlation topercentage of red and middle muscle fibre and backfat thickness.(3) MyoG gene (all of the exons) and c-fos gene (all of the exons) were amplified to identify thenucleotide diversity. Polymorphisms were detected in the loci of MyoG exonl-1, c-fos exon4-1, c-fosexon4-2. The analysis results of polymorphisms were MyoG exon 1 A→G (2512 ), c-fosexon4-1 G→A(2650 ), c-fos exon4-2 A→G ( 2 910). The results showed that the alteration of a single base in the lociof MyoG exonl-1 and c-fos exon4-1 are all silent mutation, no substitution of amino acid happened afterhomologous analysis of protein coded by different homozygote genotypes. The alteration of a singlebase in these exons were caused by the swinging of genetic coden.And the alteration of a single base inthe locus of c-fos exon4-2 was missense mutation (Asn→Ser).(4) Some differences of gene frequency between different breeds in MyoG exonl-1 and c-fosexon4-1, exon4-2 were discovered. No significant difference for the distribution of genotype frequencywere discovered in the locus ofMyoG exonl-1 (P＞0.05), and existing significant differences for thedistribution ofgenotype frequency in the loci ofc-fos exon4-1 and exon4-2 (P＜0.01) between differentbreeds. (5) The least square means of containing different slaughter weights, sexes, breeds and genotypesfor muscle fibre traits were estimated with the fixed model. All of traits were influenced significantly byslaughter weights and breeds (P＜0.01); Genotypes of c-fos exon4-2 had significant effects on the traitsbesides of backfat thickness and percentage of mediated muscle fibre at level of P＜0.01. And sexes hadno significant influence on all of the traits (P＞0.05).(6) The analysis of association between the polymorphisms of MyoG exonl-1 , c-fos exon4-1and muscle fibre traits showed that muscle fibre area and diameter would be minished and muscle fibredensity would be increased while increasing the frequency of allele A in the locus of MyoG exonl-1,and muscle fibre density and percentage of red muscle fibre would be increased while increasing thefrequency of allele B in the locus of c-fosexon4-1; Allele B had increased muscle fibre area, and allele Ahad increased muscle fibre density in the locus of c-fos exon4-2.All analyses can be concluded that: The locus of MyoG exonl-1, c-fos exon4-1 and exon4-2 wereconsidered as molecular marker for selecting muscle fibre traits because associations between theirpolymorphism and muscle fibre traits had been observed.