The adaptive response of MyoD family proteins in overloaded, regenerating and denervated rat muscles

Using Western blot analysis, we investigated whether the amount of myogenic regulatory factors differs in slow-type and fast-type muscles. In addition , we examined the adaptive response of myogenic regulatory factor protein i n the overloaded rat muscles by the ablation of synergists, in the regenera ting muscles following bupivacaine injection and in the denervated muscle. The amount of myogenin protein in the slow-type muscle was markedly greater . In contrast, the proteins MyoD and Myf-5 were selectively accumulated in the fast-type muscles. A gradual down-regulation of MyoD and Myf-5 proteins was detected in the denervated fast-type muscles, but not in the myogenin protein content. A rapid down-regulation of myogenic regulatory factor prot ein was observed both of the mechanically overloaded and in the regeneratin g muscles. These results indicate that the fast-type-specific gene expressi on in muscle is modulated by MyoD and Myf-5 proteins and suggest that myoge nin protein plays an important role in the reconstruction of damaged neurom uscular connections. (C) 1999 Elsevier Science B.V. All rights reserved.