Nodal regulates neural tube formation in the Ciona intestinalis embryo
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Overexpression of a lefty orthologue, Ci-lefty, caused a failure of neural tube closure in the protochordate ascidian Ciona intestinalis. The body bent dorsally, and anterior–posterior elongation was inhibited. A similar phenotype was observed in embryos treated with SB431542, an inhibitor of Nodal receptors, suggesting that Ci-Lefty antagonized Nodal signaling as reported in other deuterostome species. Overexpression of Ci-nodal also resulted in a similar phenotype, suggesting that a correct quantity and/or a spatial restriction of Nodal signaling are important for the neural tube to form. In addition to known Ci-Nodal target genes, orthologues of Zic (Ci-ZicL) and cdx (Ci-cdx) were activated by Ci-Nodal. Expression of a dominant negative Ci-cdx caused defects in neural tube formation similar to those obtained on treatment with SB431542 or overexpression of Ci-lefty. A regulatory cascade composed of Ci-Nodal, Ci-ZicL, and Ci-Cdx may play an important role in neural tube formation in the Ciona embryo.
KeywordsAscidian Neural tube formation Lefty Nodal Cdx ZicL
We thank Nori Satoh and Kazuko Hirayama at Kyoto University and Zenji Imoto at the Usa Marine Biological Institute of Kochi University for providing animals. We thank Hidetoshi Saiga at Tokyo Metropolitan University for kindly providing the plasmid containing EnR. We are also grateful to You Katsuyama for valuable advice. This work was supported by MEXT Japan. K. M. was supported by the Sasakawa Scientific Research Grant from The Japan Science Society.
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