Reference gene selection and myosin heavy chain (MyHC) isoform expression in muscle tissues of domestic yak (Bos grunniens)

Domestic yak (Bos grunniens) is the most crucial livestock in the Qinghai-Tibetan Plateau, providing meat and other necessities for local people. The skeletal muscle of adult livestock is composed of muscle fibers, and fiber composition in muscle has influence on meat qualities, such as tenderness, pH, and color. Real-time quantitative polymerase chain reaction (RT-qPCR) is a powerful tool to evaluate the gene expression of muscle fiber, but the normalization of the data depends on the stability of expressed reference genes. Unfortunately, there is no consensus for an ideal reference gene for data normalization in muscle tissues of yak. In this study, we aimed to assess the stability of 14 commonly used candidate reference genes by using five algorithms (GeNorm, NormFinder, BestKeeper, Delat Ct and Refinder). Our results suggested UXT and PRL13A were the most stable reference genes, while the most commonly used reference gene, GAPDH, was most variably expressed across different muscle tissues. We also found that the extensor digitorum lateralis (EDL), trapezius pars thoracica (TPT), and psoas major (PM) muscle had the higher content of type I muscle fibers and the lowest content of type IIB muscle fibers, while gluteobiceps (GB) muscle had the highest content of type IIB muscle fibers. Our study provides the suitable reference genes for accurate analysis of yak muscle fiber composition.