Muscle Development and Muscular Dystrophy in Chicken

Abstract

In developing skeletal muscle, both contractile and regulatory proteins are synthesized and assembled into myofibrillar structures, while in dystrophic muscles, they are gradually disassembled and the muscle contractile activity is substantially decreased. For the understanding of the myofibrillar disorganization, variation of myofibrillar proteins in the dystrophic muscle should be clarified. In this study, alteration of C-protein and troponin T (TNT) during muscle development and progression of muscular dystrophy was examined with chicken as a model animal. At embryonic stages, cardiac-type C-protein (Cc) was detected first and transiently in skeletal muscles. At neonatal ages, slow- (Cs) and fast type (Cf) C-proteins were coexpressed in the pectoralis muscle (PM) of both normal and dystrophic chicken, but Cs disappeared, leaving continued expression of only Cf as muscle development progressed up to 2 weeks posthatch. In the dystrophic chicken PM, however, myofiber containing Cs reappeared and increased in number with the progression of muscular dystrophy. C-Proteins were further examined by 2D-PAGE. Two variants of slow C-protein (Cs3 and Cs4) were detected in adult muscle tissues. C-Proteins in the neonatal PM were Cf and Cs3, but in dystrophic PM, both Cs3 and Cs4 were detected in addition to Cf. These results indicate that C-protein varies during development and also in the process of degeneration of chicken skeletal muscles, and in addition the dystrophic muscle differs from the neonatal muscle with regards to C-protein isoform expression. Troponin T also exhibited remarkable isoform change during muscle development. The neonatal and dystrophic PMs differed in TNT isoform pattern although they shared several common TNT isoforms. The author conclude that the dystrophic muscle resembles the neonatal muscle, but does not recapture simply the nature of the latter muscle, but shifts toward a somewhat different direction.