A genomewide survey of developmentally relevant genes in Ciona intestinalis
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Cell junctions and the extracellular matrix (ECM) are crucial components in intercellular communication. These systems are thought to have become highly diversified during the course of vertebrate evolution. In the present study, we have examined whether the ancestral chordate already had such vertebrate systems for intercellular communication, for which we have searched the genome of the ascidian Ciona intestinalis. From this molecular perspective, the Ciona genome contains genes that encode protein components of tight junctions, hemidesmosomes and connexin-based gap junctions, as well as of adherens junctions and focal adhesions, but it does not have those for desmosomes. The latter omission is curious, and the ascidian type-I cadherins may represent an ancestral form of the vertebrate type-I cadherins and desmosomal cadherins, while Ci-Plakin may represent an ancestral protein of the vertebrate desmoplakins and plectins. If this is the case, then ascidians may have retained ancestral desmosome-like structures, as suggested by previous electron-microscopic observations. In addition, ECM genes that have been regarded as vertebrate-specific were also found in the Ciona genome. These results suggest that the last common ancestor shared by ascidians and vertebrates, the ancestor of the entire chordate clade, had essentially the same systems of cell junctions as those in extant vertebrates. However, the number of such genes for each family in the Ciona genome is far smaller than that in vertebrate genomes. In vertebrates these ancestral cell junctions appear to have evolved into more diverse, and possibly more complex, forms, compared with those in their urochordate siblings.
KeywordsBasal chordates Ciona intestinalis Genomewide survey Genes Cell junctions
This research was supported by Grants-in-Aid for Scientific Research from MEXT, Japan to Y. Satou (13044001) and N.S. (12202001), by a CREST project of Japan Science and Technology Corporation (N.S., E.S., and S.W.) and by support from NSERC, Ottawa (to I.A.M.). Y. Sasakura was a Postdoctoral Fellow of JSPS with research grant no. 14000967. We thank Kazuko Hirayama, Chikako Imaizumi, Asako Fujimoto, and Hisayoshi Ishikawa for their technical support.
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