Temperature-dependent expression patterns of grass carp fast skeletal myosin heavy chain genes.

Three types of myosin heavy chain cDNA clone named 10 degrees C, intermediate and 30 degrees C types were isolated from fast skeletal muscles of thermally acclimated grass carp Ctenopharyngodon idellus. Three clones encompassing parts of 3'-translated and entire 3'-untranslated regions showed high heterogeneities in their nucleotide sequences in the 3'-untranslated region. The comparison in the deduced amino acid sequence of the 10 degrees C-type clone with those of the intermediate- and 30 degrees C-type clones showed 88% and 89% identities, respectively. By contrast, the deduced amino acid sequence of the intermediate-type clone shared much higher identity of 97% with its 30 degrees C-type counterpart. Northern blot analysis demonstrated that the 10 degrees C- and 30 degrees C-type clones were predominantly expressed in grass carp acclimated to 10 and 30 degrees C, respectively. The intermediate type was expressed both in grass carp acclimated to 20 and 30 degrees C. Furthermore, expression patterns of the three myosin heavy chain genes were altered in accompaniment with seasonal temperature fluctuation. In autumn and winter grass carp expressed the 10 degrees C-type gene almost exclusively, whereas it was completely replaced by the intermediate- and 30 degrees C-type genes in spring and summer. These results suggest that tetraploid grass carp also undergo an adaptation to fluctuating environmental temperatures by selectively expressing fast skeletal myosin heavy chain isoforms as do diploid common carp previously reported.