Evolution of fast skeletal myosin heavy chain genes of fish

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In the present study, to elucidate the evolutionary relationship of fast skeletal myosin heavy chain genes (MYHs), MYHs of teleosts and tetrapods were compared with those of agnathan lampreys, one of the most primitive jawless fish. As a result, lampreys contained at least three fast skeletal MYHs which were clustered in ahead-to-tail manner on a single genomic region. Moreover, there was an apparent synteny in the corresponding MYH cluster regions between lamprey and tetrapod, implying that fast skeletal MYH clustering was a very early event in vertebrate evolution. Although zebrafish MYH promoters showed apparent activity to direct reporter gene expression in myogenic cells derived from mouse, those of lamprey had no activity. These results suggest thatthe common ancestor of vertebrate fast skeletal MYHs had been diverged into those of agnathan fish, teleosts and tetrapods. Tetrapods are assumed to have subsequently developed a transcriptional network system different from that of agnathan fish.