Induction of the zebrafish ventral brain and floorplate requires cyclops/nodal signalling.
Sampath, Karuna; Rubinstein, Amy L.; Cheng, Abby M. S.; Liang, Jennifer O.; Fekany, Kimberly; Solnica-Krezel, Lilianna; Korzh, Vladimir; Halpern, Marnie E.; Wright, Christopher V. E.
[Letter] Nature. 395(6698):185-189, September 10, 1998.

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Zebrafish cyclops (cyc) mutations cause deficiencies in the dorsal mesendoderm [1,2] and ventral neural tube [3,4], leading to neural defects and cyclopia [5,6].Here we report that cyc encodes a transforming growth factor-beta (TGF-beta)-related intercellular signalling molecule that is similar to mouse nodal [7]. cyc is expressed in dorsal mesendoderm at gastrulation and in the prechordal plate until early somitogenesis. Expression reappears transiently in the left lateral-plate mesoderm, and in an unprecedented asymmetric pattern in the left forebrain. Injection of cyc RNA non-autonomously restores sonic hedgehog-expressing cells of the ventral brain and floorplate that are absent in cyc mutants, whereas inducing activities are abolished by cycm294, a mutation of a conserved cysteine in the mature ligand. Our results indicate that cyc provides an essential non-cell-autonomous signal at gastrulation, leading to induction of the floorplate and ventral brain.

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