Study On Polymorphisms Of MC4R And ME1 Genes And Associations With Backfat Thickness In Pigs

Fat deposition is an important economic trait in pigs which is associated with the quality of the pork and its economic values. MC4R (Melanocortin- 4 receptor ) and ME1 (malic enzyme 1 ) gene are candidate genes which are likely to be associated with fat deposition. MC4R is a member of the superfamily of G protein coupled receptors, which affects body weight, energy homeostasis and food intake in human and mouse. The ME1 gene plays a key role in the endogenous fat acid biosynthesis, it catalyses the oxidative decarboxylation of L-malate to produce pyruvate and CO2 with the concomitant reduction of NADP+ to NADPH. NADPH produced in this way are used in fat acid biosynthesis and many other metabolic processes. In this study, the polymorphisms of MC4R and ME1 gene and their relationship with backfat thickness were performed to find the molecular markers for fat deposition, thereby to provide a new method for pig breeding.The Asp298Asn polymorphism of MC4R gene in Laiwu, Yorkshire×Laiwu and commercial crossbred pig populations was investigated using PCR-RFLP method, and the relationship of this mutation with backfat thickness was analyzed. The present study also cloned the 5'regulatory region of porcine ME1 gene, screened its polymorphisms and analyzed their associations with backfat thickness in commercial crossbred pigs.1. With regard to the results of MC4R, it indicated that only genotype 11 exists in 33 individuals of Laiwu pigs, and three genotypes of 11, 12 and 22 were detected in Yorkshire×Laiwu and commercial crossbred populations. The distributions of allele and genotype frequencies in Yorkshire×Laiwu and commercial crossbred populations were similar with the frequency of allele 1 being higher than that of allele 2. In commercial crossbred pigs, the mean backfat thickness of individuals with genotype 22 was significant higher than thoses individuals with genotypes 12 (P < 0.01) and 11 (P < 0.05). This study provided evidence that the Asp298Asn polymorphism of MC4R gene is associated with backfat thickness in commercial crossbred pigs with western pigs as parental lines, and therefore, can be used as a DNA marker for pig breeding in such kind of populations.2. A fragment of ~1.2 kb of the 5'regulatory region of porcine ME1 gene was cloned. The polymorphisms of three mutation sites involved -486,-283 and -1068 of ME1 gene were investigated using PCR-RFLP and PCR-SSCP methods. At -486 site, the distribution of polymorphism in six pig populations including wild boar, Laiwu, Duroc,Yokshire, Yorkshire×Laiwu and commercial crossbred populations were examined. The results indicated that only BB and AB genotype exist and allele B was dominant in all detected populations. All of the six populations were at Hardy-Weinberg equilibrium with respect to this mutation site(P>0.05). No polymorphism was detected at -283 site. At -1068 site, three genotypes were found in Duroc, Yorkshire and commercial crossbred populations except wild boar and Laiwu pigs, in which only AB and BB were detected. The distributions of allele and genotype frequencies in five pig populations were significantly different: with the highest frequence of BB genotype being in Laiwu and the lowest in wild boar pig population.3. Association analysis indicated that there were no significant difference in the mean backfat thickness of commercial crossbred individuals with different genotype at -486 site of ME1(P=0.1402>0.05). But the mean backfat thickness of individuals with genotype BB was lower than thoses individuals with genotypes AB, so allele B has a trend to decrease backfat thickness. At -1068 site, there were significant difference in the mean backfat thickness of commercial crossbred individuals of different genotype(P=0.025 <0.05). Allele A had an effect on decreasing backfat thickness.The present study will provide some data for further elucidating the genes underling fat deposition and for improving the quality of pork.