Intramuscular fat (IMF) content in pork is an important element of consumer preference and is positively correlated with meat quality, including tenderness and juiciness. With advances in RNA sequencing technologies, transcriptome-related differences can be associated with specific traits in animals. The objective of this study was to investigate differentially expressed genes (DEGs) closely related to IMF content in porcine longissimus muscle using RNA sequencing. A total of 107 Berkshire pigs were used for IMF content measurements, and significant differences between extremely high (H, n = 3) and low (L, n = 3) IMF content groups were found (P < 0.0001). From multi-dimensional scaling analyses, it was observed that the relationships between H and L groups were similar to each other. Here, we identified a total of 134 genes that were differentially expressed between the groups (false discovery rate <0.05; fold change ≥2). Functional analyses with DEGs revealed that lipid metabolism (SCD and FASN) was one of the significant biological processes related to IMF content determination. In addition, we found that DEGs related to muscle regeneration (MYOG and VEGFA) and extracellular matrix (COL1A1, COL1A2, COL5A1, COL14A1 and COL15A1) were changed among individuals with extreme IMF contents. These results will aid in understanding the regulation of IMF content in pigs.

The purpose of this study was to determine the structure of the porcine PPARGC1A 5' upstream region, and to find suitable molecular markers for improved meat quality and good lean meat production. Ten DNA polymorphisms, including 7 SNPs, 2 microsatellites, and 1 insertion or deletion were newly found in the 5' upstream region of PPARGC1A. Three SNPs that had restriction enzyme site were evaluated for associations with muscle fiber characteristics and production traits. Two hundred fifty-two pigs (Yorkshire and Landrace) were used in this analysis. The c.-2894G>A genotypes was significantly associated with muscle fiber characteristics, including the number of fiber type I and IIb composition (P < 0.05), mean cross-sectional area of fibers (P < 0.01), and fiber number per unit area (P < 0.05). The animals with the GG genotype had a higher percentage of type I fibers and a lower percentage of type IIb fibers with better meat quality [higher pH value (P < 0.05) and lower drip loss (P < 0.05)] and lean meat production [larger loin eye area (P < 0.05)]. Moreover, the mRNA expression levels of PPARGC1A among genotypes were significantly different with the highest level of GG genotype. The c.-2885G>T and c.-1402A>T sites showed similar results that had significant effects on the mean cross-sectional area (CSA; P < 0.05), fiber number per unit area (P < 0.05) and loin eye area (P < 0.01). Therefore, we suggest that the c.-2894G>A polymorphism in the 5' upstream region of the porcine PPARGC1A gene can be used as a meaningful molecular marker for simultaneous improvement of lean meat production and quality traits.

The peroxisome proliferator-activated receptor-gamma coactivator-1A (encoded by PPARGC1A) is involved in the formation of type I fibres. Therefore, the PPARGC1A gene can be considered as a functional candidate gene for muscle fibre type composition and meat quality in pigs. The aim of this study was to investigate the associations of the p.C430S polymorphic site in exon 8 of the PPARGC1A gene with muscle fibre characteristics and meat quality traits. The polymorphism was genotyped by PCR-RFLP using AluI restriction enzyme on a total of 152 Yorkshire pigs. Statistical analyses revealed that the p.C430S genotypes significantly affected number (P < 0.05) and area (P < 0.01) of type I muscle fibre, and were significantly associated with muscle pH (P < 0.001) and lightness(P < 0.01). On the basis of these results, we suggest that the p.C430S polymorphism can induce variation of type I fibre formation in porcine longissimus dorsi muscle and that it can be used as a meaningful molecular marker for better meat quality.