Two myostatin genes are differentially expressed in myotomal muscles of the trout (Oncorhynchus mykiss)

Myostatin (GDF8) has been shown to be a major genetic determinant of skelet al muscle growth in mammals. In this study, we report the cloning of two tr out cDNAs that encode two distinct myostatin-related proteins. The presence in this fish species of two myostatin genes (Tmyostatin 1 and Tmyostatin 2 ) probably results from the recent tetraploidisation of the salmonid genome . A comparative reverse-transcriptase-linked polymerase chain reaction assa y revealed that Tmyostatin 1 mRNA was present ubiquitously in trout tissues , while Tmyostatin 2 mRNA expression was restricted to muscle and brain. In developing muscle, Tmyostatin I expression was observed in eyed-stage embr yos well before hatching, whereas Tmyostatin 2 was expressed only in free-s wimming larvae. In myotomal muscle from adult animals, Tmyostatin I mRNA ac cumulation was similar in both slow- and fast-twitch fibres, and its concen tration did not change during the muscle wasting associated with sexual mat uration. In contrast, Tmyostatin 2 mRNA accumulated predominantly in slow-t witch fibres, and its concentration decreased dramatically in wasting muscl es from maturing animals. This work shows that two distinct myostatin genes are present in the trout genome. Furthermore, it indicates that these two trout myostatin genes (I) exhibit a distinct expression pattern in muscle a nd non-muscle tissues and (ii) are not upregulated during the muscle wastin g that accompanies sexual maturation.