Evolution of fast skeletal myosin heavy chain genes of fish

为了阐明快速骨骼肌球蛋白重链基因（MYH）的进化关系，将硬骨鱼和四足动物的MYH与最原始的无颌鱼类之一无颌七鳃鳗的MYH进行了比较。结果表明，七鳃鳗至少含有三个快速骨架MYH，它们以首尾相连的方式聚集在一个基因组区域上。此外，在七鳃鳗和四足动物之间的MYH簇区域中存在明显的同线性，这意味着快速骨骼MYH簇是脊椎动物进化中非常早期的事件。虽然斑马鱼MYH启动子显示出明显的活性，直接报告基因在肌细胞来源于小鼠的表达，七鳃鳗没有活性。这些结果表明，脊椎动物快骨骼MYH的共同祖先已分化为无颌鱼类、硬骨鱼和四足动物的共同祖先。四足动物被认为是随后开发了一个转录网络系统不同的无颌鱼。

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.