Expression changes of transcripts for fast skeletal myosin heavy chain isoforms in relation to those of MyoD and MEF2 families during warm temperature acclimation of carp

Common carp (Cyprinus carpio L.) were acclimated to 30 degrees C from 20 de grees C over 24 h and maintained at that temperature for 35 days. Changes i n the expression of mRNA transcripts for fast myosin heavy chain (MyHC) iso forms, E12 of the E protein, and myogenic regulatory factors belonging to t he MyoD (MyoD, myogenin, myf-5) and myocyte enhancer factor-2 (MEF2A, MEF2C ) gene families were investigated in the fast myotomal muscle using norther n blot analysis. Myofibrillar Mg2+-ATPase activity gradually declined over 21 days and was significantly different from the starting level after only 3-5 days. Over the same time period there was a dramatic decrease in the mR NA transcripts of the MyHC isoform predominantly expressed in cold-acclimat ed carp (10 degrees C-type MyHC) and a significant increase in the transcri pts of the MyHC isoform predominantly expressed in warm-acclimated carp (30 degrees C-type MyHC). The levels of myogenin mRNA transcripts almost doubl ed over 3-7 days before declining to 30% of the starting levels for the rem ainder of the experiment. While the levels of E12 mRNA gradually decreased, MEF2A and MEF2C mRNA transcripts showed a significant decrease over 24 h a nd then stabilized at the lower levels. In contrast, the levels of MyoD mRN A were not affected by temperature acclimation. The possible role of myogen ic regulatory factors in the expression of temperature-specific isoforms of MyHC in common carp is briefly discussed.