Isolation and characterization of myostatin complementary deoxyribonucleicacid clones from two commercially important fish: Oreochromis mossambicus and Morone chrysops

In mammals. skeletal muscle mass is negatively regulated by a muscle-derive d growth/differentiating factor named myostatin (MSTN) that belongs to the transforming growth factor-beta superfamily. Although putative MSTN homolog s have been identified from several vertebrates, nonmammalian orthologs rem ained poorly defined. Thus, we isolated and characterized MSTN complementar y DNA clones from the skeletal muscle of the tilapia Oreochromis mossambicu s and the white bass Morone chrysops. The nucleic and amino acid sequences from both fish species are highly homologous to the previously identified m ammalian and avian orthologs, and both possess conserved cysteine residues and putative RXXR proteolytic processing sites that are common to all trans forming growth factor-beta family members. Western blotting of conditioned medium from human embryonal kidney (HEK293) cells overexpressing a His-tagg ed tilapia MSTN indicates that the secreted fish protein is processed in a manner similar to mouse MSTN. However, in contrast to mice, MSTN expression in tilapia is not limited to skeletal muscle as it occurs in many tissues. Furthermore, the timing of MSTN expression in developing tilapia larvae co incides with myogenesis. These results suggest that the biological actions of MSTN in the tilapia and possibly in other fishes may not be limited to m yocyte growth repression, but may additionally influence different cell typ es and organ systems.