Difference Of Muscle Fiber Histological Characteristics Between Large White And Tongcheng Pigs And Genetic Effects Of SH2B1, TMEM18, IDH3B Genes

Pork is the main source of animal protein in China. In late years, in order to increase the amount of lean meats available, pig breeders began to import breeding pigs from other countries in large quantities. But the locals discovered that pigs from foreign countries, though leaner, did not have as good of a flavor as the pigs that came from the areas that typically had fattier pigs. This research compared and analyzed the difference of muscle fiber histological characteristics and backfat thickness between Large White and Tongcheng pigs. Taking the molecular approach, this research found and verified new polymorphic loci related to backfat thickness. Furthermore,I compared these polymorphic loci among the Large White and Tongcheng pigs. My results are as listed below:(1) By means of the paraffin slice technique, found that the Large White Pig’s longissimus muscle and biceps femoris histological characteristics, and by using Tongcheng pig histological characteristics found from the same paraffin slice technique used in our lab, found that the Large White pig’s muscle fiber was thicker than that of Tongcheng pigs, but the unit area muscle fiber count was less. When the Large White pigs and Tongcheng pigs reached 100kg in weight, the longissimus muscle’s average area was 3347.24μm2 and1356μm2, and the biceps femoris was at 3545.62μm2 and 1429μm2. When the Large White and Tongcheng pigs reached 100kg in weight, the muscle fiber average density in the longissimus muscle was 216.07 fibers/mm2 and 369.85 fibers/mm2, and in the biceps femoris, it was 191.85 fibers/mm2 and 349.56 fibers/mm2.(2) I chose the newly reported genes related to human obesity SH2B1 and TMEM18 as candidate genes. I checked the corresponding pig’s SH2B1 and TMEM18 complete gene sequence. After scanning the exon sequence’s polymorphic loci, found the SH2B1’s 9th exon’s 237th base had a SNP(G/C), and furthermore brought about amino acid changes (alanine-proline), called G237C; on the SH2B1 gene’s 9th exon’s 274th and 275th loci there are two continuous polymorphic loci (T274C)(G275A). Among them, the T274C brought about amino acid changes (alanine-leucine). On the TMEM18’s first exon’s 91th base (5’UTR region), found a polymorphic loci T91G. Furthermore, among the Large White pigs verified the IDH3B gene promoter region 304bp indel variation, finding that the Large White pig population had this mutation.(3) Among the Large White pigs, when the aforementioned SNP loci carried out a association analysis with the back fat thickness properties, the results showed the SH2B1 gene’s T274C loci did not have a striking association with the Large White pig’s backfat thickness. The G237C loci showed a strong association with the Large White pig’s days to 100kg in weight (P=0.0123), with the lumbrosacral junction back fat thickness showing a striking association (P=0.0004). The TMEM18 gene T91G polymorphic loci exhibited a strong association with days to 100kg (P<0.0001), with the lumbrosacral junction’s back fat thickness also exhibiting a considerable association (P=0.0159). I did a association analysis with the IDH3B gene promoter region’s indel variation and the Large White pig’s back fat thickness shap and properties and found that these variations with should back fat thickness exhibited a strong association (P=0.0063). At the last rib’s back fat thickness and the three-point-average back fat thickness on average showed a strong association (P=0.0249,P=0.0143).(4) By using the PCR-RFLP method among the different kinds of Chinese local pigs, I detected the SH2B1 gene G237C base mutation loci, found that this SNP loci’s genotype frequency among different varieties had striking discrepancies, furthermore the G allele (corresponding to alanine) was the dominant allele, and the G allele among the Large White pigs was a superiority gene. This corresponding average back fat thickness among the Large White pigs was higher than the average of the C allele’s corresponding back fat thickness. Detected among the local pigs was the TMEM18 gene’s T91G base mutation loci, furthermore the T allele was the dominane gene, the T allele among the Large White pigs was the superiority allele. This corresponding back fat thickness average among Large White pigs was greater than the G allele’s corresponding back fat thickness average. Verified among the different Chinese local pigs was the IDH3B indel variation, and I found this variation’s genotype frequency among the different breeds was noteworthy, furthermore the deletion form allele was the dominant allele.