Studies On Molecular Genetic Polymorphisms Of The IGF-I Gene And MyoG Gene In Pigs

The growth rate of porcine muscle is directly related to the economic benefits of pig production, and skeletal muscle growth is an important part of muscle growth in pig. Meat production capacity is related to muscle fiber numbers and growth. Myogenin belongs to the MyoD gene family and fulfills a key function in muscle differentiation by controlling the onset of myoblast fusion and the establishment of myofibers. Insulin-like growth factor I (IGF-I) is an important regulation factor for the functioning of growth hormon. IGF-I stimulates differentiation through a myogenin pathway and functions in the regulation of muscle growth, it also stimulates terminal myogenic differentiation by induction of myogenin gene expression. Insulin –like growth factor I and myogenin are related to the growth rate of porcine skeletal muscle . IGF-I gene (exon3 and exon4) and MyoG gene (5'-regulation region and all exons) were amplified to identify the nucleotide diversity. IGF-I exon3, IGF-I exon4, MyoG exon3, MyoG5'-1 and MyoG5'-3 appeared polymorphic. The results of polymorphisms are IGF-I exon3 c→t, IGF-I exon4 c→t, MyoG exon3 t→c, MyoG5'-1 c→a(-473), c→a(-456), MyoG5'-3 a→t (-44).The five polymorphic loci were not reported in the document. The potential elements and protein factors binding to the 5'-region of myogenin gene were predicted and different regulatory elements between polymorphisms of two loci (-473 and -44) were discovered. On these two sites, the changes of regulation elements were possibly made by the base changes. The alteration of a single base in exons (IGF-I exon3, IGF-I exon4 and MyoG exon3) are all silent mutation, no substitution of amino acid happened. The alteration of a single base in these exons were caused by the swinging of genetic coden. Gene and genotype frequencies were calculated for the polymorphic loci in IGF-I gene and MyoG gene. Some differences of gene frequency between different breeds in IGF-I exon3, IGF-I exon4 and MyoG exon3 were discovered. No significant differences for the distribution of gene frequency were discovered between breeds on MyoG5'-1 and MyoG5'-3 loci. The least square means of different IGF-I and MyoG genotype for growth traits were estimated with the fixed model. Backfat thickness and body weight at six months were influenced by the loci of IGF-I exon3 and 5'-1 in MyoG (P<0.05) respectively; Breed had significant effects on birth weight, weaning weight, body weight at six months at level of P<0.01 and on backfat thickness at level of P<0.05. The results suggested that insulin-like growth factor I (IGF-I) gene and myogenin (MyoG) gene are potential genetic markers in the study on porcine muscle growth and could be used as markers in marker assisted selection to improve the efficiency and accuracy of selection.