A polymorphism in the porcine miR-208b is associated with microRNA biogenesis and expressions of SOX-6 and MYH7 with effects on muscle fibre characteristics and meat quality

MicroRNAs (miRNAs) encoded by the myosin heavy chain (MHC) genes are muscle-specific miRNAs (myomiRs) and regulate the expression of MHC isoforms in skeletal muscle. These miRNAs have been implicated in muscle fibre types and their characteristics by affecting the heterogeneity of myosin. In pigs, miR-208b and miR-499 are embedded in introns of MYH7 and MYH7b respectively. Here, we identified a novel single nucleotide polymorphism (SNP) in intron 30 of MYH7 by which porcine miR-208b is encoded. Based on the association study using a total of 487 pigs including Berkshire (n=164), Landrace (n=121) and Yorkshire (n=202), the miR-208b SNP (g.17104G>A) had significant effects on the proportions of types I and IIb fibre numbers (P<0.010) among muscle fibre characteristics and on drip loss (P=0.012) in meat quality traits. Moreover, the SNP affected the processing of primary miR-208b into precursor miR-208b with a marginal trend towards significance (P=0.053), thereby leading to significant changes in the levels of mature miR-208b (P=0.009). These SNP-dependent changes in mature miR-208b levels were negatively correlated with the expression levels of its target gene, SOX-6 (P=0.038), and positively associated with the expression levels of its host gene, MYH7 (P=0.046). Taken together, our data suggest that the porcine miR-208b SNP differentially represses the expression of SOX-6 by regulating miRNA biogenesis, thereby affecting the expression of MYH7 and the traits of muscle fibre characteristics and meat quality.