Contractile protein content reflects myosin heavy chain isoform gene expression

¹ Department of Animal Sciences, Purdue University, W. Lafayette, IN 47907

^* To whom correspondence should be addressed. E-mail: dgerrard{at}purdue.edu.

	Abstract

Muscle fiber types are classified on contractile speed and type of metabolism. Fast contracting fibers contain mainly glycolytic-based metabolism, whereas slow contracting fibers contain a more oxidative type of energy metabolism. The relationship between genes controlling these functional characteristics and the relative protein abundance in porcine muscle is unknown. The objective of this study was to determine expression of adult myosin heavy chain (MyHC) genes and their corresponding protein content in various porcine muscles. Moreover, changes in expression of 2 genes involved in energy metabolism (glycogen synthase, GS; citrate synthase, CS) were determined on muscles varying in MyHC. Using real time PCR, relative transcript abundance was determined for the adult MyHC isoforms (type I, IIA, IIX, IIB), GS, and CS in the masseter (MAS), diaphragm (DIA), longissimus dorsi (LD), cutaneous trunci (CT), and red (RST) and white (WST) semitendinosus muscles of 7 pigs. Each muscle was subjected to SDS-PAGE analyses for determining the relative abundance of each MyHC. Relative transcript abundance of type IIB MyHC was greatest (P < 0.05) in LD, WST, and CT, whereas type I MyHC expression was greatest (P < 0.05) in MAS, DIA, and RST. Glycogen synthase gene expression was least in the MAS (P < 0.01) but exhibited a similar pattern to MyHC IIB expression across muscles. Citrate synthase transcript abundance, however, varied (P < 0.05) independently of MyHC gene expression. Type I and IIB MyHC expression was correlated with tissue protein content (R² = 0.76 and 0.78, respectively), while type IIA and X MyHC expressions did not correlate with SDS-PAGE-determined protein content. These data show differences in MyHC gene expression across various porcine muscles and suggest that the expression of these genes are reflective of the type of myosin contained within the muscle. Moreover, these data show expression of energy-specific genes differ greatly across porcine muscles with vastly different functions.

Key Words: myosin heavy chain , porcine, skeletal muscle

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