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First published online 15 December 2008
doi: 10.1242/dev.026419

This Article Figures Only Full Text Full Text (PDF) Supplementary Material All Versions of this Article: dev.026419v1 dev.026419v2 136/2/285    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Development Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Imai, K. S. Articles by Satou, Y. Search for Related Content PubMed PubMed Citation Articles by Imai, K. S. Articles by Satou, Y. Social Bookmarking                         What's this?

Gene regulatory networks underlying the compartmentalization of the Ciona central nervous system

¹ Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.
² Department of Molecular and Cellular Biology, Division of Genetics and Development, University of California, Berkeley, CA 94720, USA.

^* Author for correspondence (e-mail: yutaka{at}ascidian.zool.kyoto-u.ac.jp)

Accepted 7 November 2008

The tripartite organization of the central nervous system (CNS) may be an ancient character of the bilaterians. However, the elaboration of the more complex vertebrate brain depends on the midbrain-hindbrain boundary (MHB) organizer, which is absent in invertebrates such as Drosophila. The Fgf8 signaling molecule expressed in the MHB organizer plays a key role in delineating separate mesencephalon and metencephalon compartments in the vertebrate CNS. Here, we present evidence that an Fgf8 ortholog establishes sequential patterns of regulatory gene expression in the developing posterior sensory vesicle, and the interleaved `neck' region located between the sensory vesicle and visceral ganglion of the simple chordate Ciona intestinalis. The detailed characterization of gene networks in the developing CNS led to new insights into the mechanisms by which Fgf8/17/18 patterns the chordate brain. The precise positioning of this Fgf signaling activity depends on an unusual AND/OR network motif that regulates Snail, which encodes a threshold repressor of Fgf8 expression. Nodal is sufficient to activate low levels of the Snail repressor within the neural plate, while the combination of Nodal and Neurogenin produces high levels of Snail in neighboring domains of the CNS. The loss of Fgf8 patterning activity results in the transformation of hindbrain structures into an expanded mesencephalon in both ascidians and vertebrates, suggesting that the primitive MHB-like activity predates the vertebrate CNS.

Key words: Ciona intestinalis, Gene regulatory network, Fgf8

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