CLONING OF A TROUT FAST SKELETAL MYOSIN HEAVY-CHAIN EXPRESSED BOTH INEMBRYO AND ADULT MUSCLES AND IN MYOTUBES NEOFORMED IN-VITRO

In fish, little is known about the isoforms of myosin heavy chain in d eveloping muscle. Two cDNA libraries from whole skeletal muscle of emb ryo (eyed stage) (A) and from white muscle of 300 g body a eight immat ure trout (B) were constructed. Three cDNA clones were isolated and ch aracterised as encoding for a fast skeletal myosin heavy chain. Two cD NA clones A1 (1534 bp) and B6 (2203 bp) a which were extracted from th e two different libraries had the same nucleotide sequence including t he 3' untranslated region. The third cDNA B8 (1606 by) shared 98% iden tify with the others. The latter could possibly be an allelic isoform of the B6. Northern blot analysis revealed that the last skeletal MyoH C transcripts were expressed throughout development from myotube appea rance to the white muscle present at older stages (adult). These resul ts suggest that this myosin heavy chain is present throughout muscle d evelopment in fish and are consistent with the hyperplastic growth of fish muscle. The amino acid sequence of the trout myosin heavy chain d iverged from its mammalian and avian counterpart with respect to a hig her level of glycine which could be related to an environmental adapta tion by increasing thermal instability of the molecule.