Expression levels of myoglobin in muscle and non-muscle tissues of rainbow trout Oncorhynchus mykiss, a hypoxia intolerant species

Myoglobin (Mb) is one of the most intensively studied intracellular respiratory muscle proteins. Since the discovery of the fascinating fact that Mb is not confined only to oxidative muscle tissues but also is co-localized in different non-muscle tissues of cyprinids, hypoxia tolerant cyprinids have been established as the model teleost. Mb both at mRNA and protein levels have been reported in this study for the first time from a number of muscle and non-muscle tissues of rainbow trout Oncorhynchus mykiss, a hypoxia intolerant species. Mb transcript levels were high in the heart and slow skeletal muscle, and were comparatively high in the gonad and gill among the non-muscle tissues. Western-blotting by using anti-rainbow trout Mb peptide rabbit antibody detected Mb protein in the muscles and several non-muscle tissues. By both RNA in situ hybridization and immunofluorescence, Mb was localized in the cardiomyocytes and oxidative muscle fibers. On the other hand, Mb both at mRNA and protein levels was restricted to the lamellar epithelial cells of the gill, epithelial layers of hepato-biliary duct, neurons and endothelial cells of brain, ooplasm of gonad, kidney tubules, endothelial cells, and epithelial layer of intestine. Neuroglobin isoform 1 and 2 mRNAs along with Mb mRNA were localized in the granular layer of cerebellum. Considering the previous data reported for cyprinids, the expression sites of Mb in the muscle and non-muscle tissues of teleost could be universal, where Mb concerted with the other globins might play meaningful physiological roles.