Expression of myostatin gene in regenerating skeletal muscle of the rat and its localization

The expression of myostatin mRNA was examined in regenerating skeletal musc le of the rat. Skeletal muscle regeneration was induced by injecting bupiva caine or hypertonic saline solution into the femoral muscle, and the tissue s were collected 48 h after the treatment. In situ hybridization analysis r evealed that the cells positive for myostatin message were localized in the regenerating area of the bupivacaine-treated tissues, where a numerous num ber of mononucleated cells were present. The myostatin-positive mononucleat ed cells contained both myogenic and nonmyogenic cells, as revealed by immu nohistochemical staining for desmin and vimentin. Bupivacaine treatment to the testes resulted in no myostatin message expression in the testicular vi mentin positive cells, suggesting that the expression of myostatin message in vimentin-positive cells is a skeletal muscle specific phenomenon. Furthe rmore, crushed muscle extract prepared from regenerating skeletal muscle ha d induced myostatin mRNA expression in skeletal muscle-derived fibroblasts in a dose-dependent manner. These results indicated that myostatin is expre ssed during skeletal muscle regeneration both in myogenic and nonmyogenic c ells, and suggested that some factor(s) capable of inducing myostatin expre ssion in fibroblasts are present in regenerating skeletal muscle. (C) 2000 Academic Press.