Fiber-type distribution and expression of myosin heavy chain isoforms in newborn heterozygous myostatin-knockout pigs.

OBJECTIVES: To explore the effects of heterozygous myostatin-knockout (MSNT+/- ) on muscle characteristics, specifically fiber-type distribution and expression of myosin heavy chain isoforms in pigs.

RESULTS: The fiber cross-sectional area of the semitendinosus and semimembranosus muscles were much larger in MSTN+/- pigs at birth than in wild-type (WT) pigs. MSTN+/- pigs had a higher proportion of fast-type fibers and lower succinate dehydrogenase activity in muscles than WT pigs. The myosin heavy chain IIB mRNA level in both two muscles was ~ threefold higher in MSTN+/- pigs compared with WT pigs.

CONCLUSION: MSTN+/- pigs exhibit a disproportionate increase in muscle mass and can have a higher body weight due to fiber hypertrophy, a change in the fiber-type distribution, and alteration of myosin heavy chain isoforms levels, leading to more fast glycolytic fibers.