Association of Six1 and Six4 gene expression with meat tenderness in Tan sheep
Sine oculis-related homeobox 1 (Six1) and 4 (Six4) transcription factors are expressed in developing and adult muscle. These Six homeoproteins are required to activate the fast-type muscle program in the mouse primary myotome. Whether Six1 and Six4 genes have a role in meat tenderness in Tan sheep has not yet been established. To study the characteristics and mechanisms of meat tenderness in Tan sheep, we sampled the musculus triceps muscle, the longest neck muscles, abdominal muscles, gluteus and biceps femoris muscle and measured Warner-Bratzler shear force and texture profile analysis using a texture analyzer (TMS-Pro), and mRNA expression of Six1 and Six4by real-time PCR, and we performed a correlation analysis. The Warner-Bratzler shear force was significantly different among the five different muscles, but there was no difference in this measure between the triceps and biceps femoris muscles. Hardness, gumminess and chewiness were significantly different among the different muscles. Six1 and Six4 mRNA expression was significantly higher in the longest neck muscles than in the other muscles. There was a significant negative correlation between Six1 mRNA expression and the texture parameters gumminess and chewiness, and a significant positive correlation between Six4 mRNA expression and gumminess and chewiness. Based on these results, we suggest that Six1 and Six4 not only regulate muscle fiber typing, but also meat tenderness in Tan sheep. They could thus be candidate genes for selecting for meat tenderness.