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First published online 24 September 2003
doi: 10.1242/dev.00756
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Régionalisation Nerveuse CNRS/ENS UMR 8542, Département de Biologie Ecole normale supérieure, 46 rue d'Ulm, 75005 Paris, France
* Author for correspondence (e-mail: wassef{at}wotan.ens.fr)
Accepted 15 July 2003
During vertebrate development, an organizing signaling center, the isthmic organizer, forms at the boundary between the midbrain and hindbrain. This organizer locally controls growth and patterning along the anteroposterior axis of the neural tube. On the basis of transplantation and ablation experiments in avian embryos, we show here that, in the caudal midbrain, a restricted dorsal domain of the isthmic organizer, that we call the isthmic node, is both necessary and sufficient for the formation and positioning of the roof plate, a signaling structure that marks the dorsal midline of the neural tube and that is involved in its dorsoventral patterning. This is unexpected because in other regions of the neural tube, the roof plate has been shown to form at the site of neural fold fusion, which is under the influence of epidermal ectoderm derived signals. In addition, the isthmic node contributes cells to both the midbrain and hindbrain roof plates, which are separated by a boundary that limits cell movements. We also provide evidence that mid/hindbrain roof plate formation involves homeogenetic mechanisms. Our observations indicate that the isthmic organizer orchestrates patterning along the anteroposterior and the dorsoventral axis.
Key words: Mid/hindbrain junction, Isthmic organizer, Mid/hindbrain organizer, Roof plate, Homeogenetic mechanisms, Hensen's node, Dorsoventral patterning, Chick, Quail
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