The expression of myostatin mRNA was examined in regenerating skeletal muscle of the rat. Skeletal muscle regeneration was induced by injecting bupivacaine or hypertonic saline solution into the femoral muscle, and the tissues were collected 48 h after the treatment. In situ hybridization analysis revealed that the cells positive for myostatin message were localized in the regenerating area of the bupivacaine-treated tissues, where a numerous number of mononucleated cells were present. The myostatin-positive mononucleated cells contained both myogenic and nonmyogenic cells, as revealed by immunohistochemical staining for desmin and vimentin. Bupivacaine treatment to the testes resulted in no myostatin message expression in the testicular vimentin-positive cells, suggesting that the expression of myostatin message in vimentin-positive cells is a skeletal muscle-specific phenomenon. Furthermore, crushed muscle extract prepared from regenerating skeletal muscle had induced myostatin mRNA expression in skeletal muscle-derived fibroblasts in a dose-dependent manner. These results indicated that myostatin is expressed during skeletal muscle regeneration both in myogenic and nonmyogenic cells, and suggested that some factor(s) capable of inducing myostatin expression in fibroblasts are present in regenerating skeletal muscle.
Copyright 2000 Academic Press.