Kusakabe T, Araki I, Satoh N, Jeffery W R
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
J Mol Evol. 1997 Mar;44(3):289-98. doi: 10.1007/pl00006146.
The origin and evolutionary relationship of actin isoforms was investigated in chordates by isolating and characterizing two new ascidian cytoplasmic and muscle actin genes. The exon-intron organization and sequences of these genes were compared with those of other invertebrate and vertebrate actin genes. The gene HrCA1 encodes a cytoplasmic (nonmuscle)-type actin, whereas the MocuMA2 gene encodes an adult muscle-type actin. Our analysis of these genes showed that intron positions are conserved among the deuterostome actin genes. This suggests that actin gene families evolved from a single actin gene in the ancestral deuterostome. Sequence comparisons and molecular phylogenetic analyses also suggested a close relationship between the ascidian and vertebrate actin isoforms. It was also found that there are two distinct lineages of muscle actin isoforms in ascidians: the larval muscle and adult body-wall isoforms. The four muscle isoforms in vertebrates show a closer relationship to each other than to the ascidian muscle isoforms. Similarly, the two cytoplasmic isoforms in vertebrates show a closer relationship to each other than to the ascidian and echinoderm cytoplasmic isoforms. In contrast, the two types of ascidian muscle actin diverge from each other. The close relationship between the ascidian larval muscle actin and the vertebrate muscle isoforms was supported by both neighbor-joining and maximum parsimony analyses. These results suggest that the chordate ancestor had at least two muscle actin isoforms and that the vertebrate actin isoforms evolved after the separation of the vertebrates and urochordates.
通过分离和鉴定两个新的海鞘细胞质和肌肉肌动蛋白基因，研究了脊索动物中肌动蛋白亚型的起源和进化关系。将这些基因的外显子-内含子组织和序列与其他无脊椎动物和脊椎动物的肌动蛋白基因进行了比较。基因HrCA1编码一种细胞质（非肌肉）型肌动蛋白，而MocuMA2基因编码一种成体肌肉型肌动蛋白。我们对这些基因的分析表明，在后口动物肌动蛋白基因中内含子位置是保守的。这表明肌动蛋白基因家族是从祖先后口动物中的单个肌动蛋白基因进化而来的。序列比较和分子系统发育分析也表明海鞘和脊椎动物肌动蛋白亚型之间存在密切关系。还发现海鞘中有两种不同的肌肉肌动蛋白亚型谱系：幼虫肌肉和成体体壁亚型。脊椎动物中的四种肌肉亚型彼此之间的关系比与海鞘肌肉亚型的关系更密切。同样，脊椎动物中的两种细胞质亚型彼此之间的关系比与海鞘和棘皮动物细胞质亚型的关系更密切。相比之下，海鞘的两种肌肉肌动蛋白彼此不同。邻接法和最大简约法分析都支持海鞘幼虫肌肉肌动蛋白与脊椎动物肌肉亚型之间的密切关系。这些结果表明，脊索动物祖先至少有两种肌肉肌动蛋白亚型，并表明脊椎动物肌动蛋白亚型是在脊椎动物和尾索动物分离之后进化而来的。
