Effects of myostatin gene knockout on porcine extraocular muscles.

Myostatin (MSTN), a negative regulator of skeletal muscle mass, is not well known in extraocular muscles (EOMs). EOMs are specialized skeletal muscles. Hence, in this study, the effect of MSTN on the superior rectus (SR) and superior oblique (SO) of 2-month-old MSTN knockout (MSTN ^-/- ) and wild-type (WT) pigs of the same genotype was investigated. SR ( P  < 0.01) and SO ( P  < 0.001) fiber cross-sectional areas of MSTN ^-/- pigs were significantly larger than those of WT pigs. Compared with WT pigs, MSTN ^-/- SO displayed a decrease in type I fibers (WT: 27.24%, MSTN ^-/- : 10.32%, P  < 0.001). Type IIb fibers were higher in MSTN ^-/- pigs than in WT pigs (WT: 30.38%, MSTN ^-/- : 62.24%, P  < 0.001). The trend in SR was the same as that in SO, although the trend in SO was greater than that in SR. The expression of myogenic differentiation factor (MyoD) and myogenic (MyoG) showed a significant increase in MSTN ^-/- SO (about 2.5-fold and 2-fold, respectively at the gene expression level, about 1.5-fold at the protein level) compared with WT pigs. MSTN plays an important role in the development of EOMs and regulates the muscle fiber type by modulating the gene expression of MyoD and MyoG in pigs.