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Journal of Molecular Evolution

, Volume 44 , Issue 3 , pp 289 –298 | Cite as

Evolution of Chordate Actin Genes: Evidence from Genomic Organization and Amino Acid Sequences

  • Takehiro  Kusakabe
  • Isato  Araki
  • Noriyuki  Satoh
  • William R.  Jeffery

Abstract.

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.

Key words: Actin — Ascidians — Vertebrates — Multigene family — Muscle actin — Cytoplasmic actin — Chordates — Introns 

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Copyright information

© Springer-Verlag New York Inc. 1997

Authors and Affiliations

  • Takehiro  Kusakabe
    • 1
  • Isato  Araki
    • 3
  • Noriyuki  Satoh
    • 3
  • William R.  Jeffery
    • 2
  1. 1.Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 060, JapanJP
  2. 2.Bodega Marine Laboratory, University of California, P.O. Box 247, Bodega Bay, CA 94923, USAUS
  3. 3.Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-01, JapanJP

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