Swine PPAR-γ2 expression upregulated in skeletal muscle of transgenic mice via the swine Myozenin-1 gene promoter.

Myozenin-1 (Myoz1) gene-encoded calsarcin-2 protein was expressed exclusively in fast-twitch muscles. Peroxisome proliferator-activated receptor γ2 (PPAR-γ2) is a key regulator of adipocyte differentiation, fatty acid uptake and storage in mammals. In this study, transgenic (TG) mice were generated by injecting linearized DNA that contained mouse creatine kinase M-type enhancer, Myoz1 core promoter, swine PPAR-γ2 (sPPAR-γ2) and SV40 polyadenylation sequences into pronuclei of fertilized FVB/NJ mouse embryos using microinjection technology. Then, the TG mice were used to identify whether swine Myoz1 (sMyoz1) promoter could upregulate sPPAR-γ2 expression in skeletal muscle in a TG mouse model. The results showed that the sMyoz1 promoter indeed upregulated sPPAR-γ2 expression on both the RNA and protein levels. The target genes of PPAR-γ in fat formation pathways, such as fatty acid-binding protein 4 (FABP4) and lipoprotein lipase (LPL), were also overexpressed on the RNA level. Meanwhile, the level of skeletal muscle triacylglycerol in TG mice was increased (P < 0.05), and the result of Oil Red-O staining in the skeletal muscle sections also showed that the number of lipid droplets was significantly increased in TG mice compared to wild-type mice, which might improve the intramuscular fat (IMF) content. For pork, the quality was mostly influenced by the IMF; the identification of swine muscle-specific promoter, sMyoz1, could further serve to develop transgenic pigs with higher intramuscular fat contents and improve pork quality.