Abstract
cDNA clones encoding the myogenic regulatory factors, myogenin, MyoD and myf‐5 were cloned by reverse‐transcription polymerase chain reaction from larvae and embryos of the common carp. MEF2 cDNAs were also identified from an adult carp cDNA library. During the period of somite formation for carp, myf‐5 was the first factor to be expressed followed by MEF2C and MyoD, then myogenin and MEF2A, and finally skeletal myosin heavy chain and α‐actin. This study also examined, by Northern blot analysis, the accumulated mRNA levels of myosin heavy chain (MyHC) isoforms in carp fast skeletal muscle during water temperature acclimation from 20 to 30°C in relation to those of MyoD family and MEF2 family members. There was a dramatic decrease in the transcripts of the MyHC isoform predominantly expressed in cold‐acclimated carp and a significant increase in the transcripts of the MyHC isoform predominantly expressed in warm‐acclimated carp. Over the same acclimation period, the transcription levels of myogenin, MEF2A and MEF2C changed significantly, whereas MyoD transcripts were rather constant. The possible roles of MRFs and related transcription factors in muscle differentiation of fish are discussed.