| Both Banna miniature pig (BNMP) and Tibetan minature pig (TBMP) are rare genetic resources in China. The miniature pigs have been used as the experimental animal models in the human disease research and the xenotransplantation because they showed similar anatomy, physiology, nutrition and metabolism with humans. Until now, the dwarfism mechanisms for the miniature pigs have become a hot spot in our area. Insulin-like growth factors (IGFs) system, including IGF-1, IGF-2, IGF-1R and IGF-2R, plays crucial roles in the control of embryonic and postnatal development in vertebrate species, and also it is the key mediator for the growth hormone (GH).In our research, we analyzed the SNPs and the tissue expression patterns of IGF-1, IGF-2, IGF-1R and IGF-2R genes in the BNMP and TBMP compared with "Junmu" white Pig and Large white pig. Our results will reveal the relationship between growths related genes and the dwarfism from the genomic and gene expression level so that we would obtain the key genes and SNPs for the dwarfism.The SNPs for the exons of IGF-1, IGF-2, IGF-1R and IGF-2R were screened by PCR-SSCP. The results showed that three mutations were found in exons of IGF-1 (G201A in exon 3, A440G and T455C in exon 4) and IGF-2 (A36T and G109A in exon 3, C53T in exon 8), separately. No SNP was found in exons of IGF-1R. A G384A mutation was found in exon 48 of IGF-2R. The above 7 mutations are all silent mutations, which means no substitution of amino acid was found. Among which, six genotypes were detected in IGF-1 exon 4 and IGF-2 exon 3, separately, resulting in a high Polymorphism (PIC 0.30-0.60) which means their polymorphisms were biased significantly.The IGF-1, IGF-2, IGF-1R and IGF-2R expression patterns were analyzed with semi-quantitative PCR in the heart, liver, kidney and muscle tissues of the four pig breeds. The results showed that they were expressed everywhere in the four pig breeds. In the miniature pigs, the IGFs family expressed in the liver>the kidney>the muscle. In the large pigs, IGF-1 and IGF-2 gene expressed highest in the liver, then the muscle; IGF-1R and IGF-2R expressed highest in the kidney, lowest in the muscle. The above results showed that different expression patterns of IGFs were found in the miniature and large pigs which reveals that IGFs may be a potential gene for the drawfismThe expressions of IGF-1 and IGF-2 genes in muscle tissues of the four pig breeds were further tested with Real-Time PCR. The results showed that the highest expression level of IGF-1 was found in the muscles of Large white pig, and the lowest in BNMP (P<0.05); The highest level of IGF-2 was in "Junmu" white Pig, and the lowest in TBMP (P<0.05). No significant difference was found in the miniature pigs, or the large pigs (P>0.05).The analysis of expression variance showed that the expressions of IGFs genes may have relationships with the growth of the muscle.From the above all, IGFs and genes of receptors of IGFs would possibly be a gene family related with dwarfism. The relationship between IGFs and the quantitative character of meat performance needs further research. Our research laid a foundation of the research of the dwarfism mechanism of the miniature pig, and laid a certain molecular theoretical foundation of the exploitation of a comprehensive resource specific to the growth and mechanisms of development of pigs. |
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