Figure 1.

(A) Construction of an HN-CNH chimeric embryo by grafting a quail Hensen’s node into a 6ss chicken embryo; thereafter, the floor plate and the notochord are made up of quail cells from thoracic level to the tail (see B). (B) One day after the graft, the chimeric neural tube and the quail notochord are microsurgically excised posteriorly to the last formed somites down to the cordoneural hinge. The neural tube–notochord complex is submitted to enzymatic dissociation and the neural tube alone is back-grafted in another chicken embryo of the same stage and deprived of its own neural tube/notochord complex at the same level (C). Note that quail cells (red) are absent in the posterior part of the back-grafted neural tube.