Seasonal changes in atrophy-associated proteins of the sonic muscle in the big-snout croaker, Johnius macrorhynus (Pisces, Sciaenidae), identified by using a proteomic approach.

In most sciaenids, males possess sonic muscles and produce sound through the contraction of these muscles and amplification of the swim bladder. The sonic muscles in some fishes exhibit seasonal changes in size. For example, they are hypertrophic in the spawning season, and atrophic in the non-spawning months. The protein profiles of the sonic muscle, red muscle, and white muscle in the Johnius macrorhynus were shown by two-dimensional electrophoresis (2-DE) and were compared to reveal differential protein expressions. About 80 up-regulated protein spots in the sonic muscle, and 30 spots related to six contractile proteins (fast muscle myosin heavy chain, skeletal alpha actin, alpha actin cardiac, tropomyosin, myosin light chain 2, and myosin light chain 3), four energy metabolic enzymes (enolase, acyl-CoA synthetase, creatine kinase, and cytochrome P450 monooxygenase), and two miscellaneous proteins (DEAD box protein and cyclin H) were identified. Seasonal hypertrophy and atrophy of the sonic muscles related to the reproductive cycle were verified in male big-snout croaker. The contents of some proteins were significantly different in the muscles under these conditions. The levels of cytochrome P450 monooxygenase, fast muscle myosin heavy chain, DEAD box proteins, isocitrate dehydrogenase, and creatine kinase were up-regulated in the hypertrophic muscle, but the levels of alpha actin cardiac, myosin light 2, and myosin light 3 were lower than in the atrophic muscle. Potential reasons for these differences in protein expression related to physiological adaptation are discussed.