Fig. 6. (A-K) Graft of SHH-producing cells between the caudal neural tube and the presomitic mesoderm of 10-15 ss chick embryos. (A) Immediately after the graft, clumps of cells are aligned to the left of the enlarged neural tube (between arrowheads). (B) Whole-mount Shh in situ hybridisation 1 day after the graft, at 25 ss (E3). The grafted cells are localised lateral to the neural tube (arrowheads). (C) A cross-section of the whole mount in B shows that the cells are still grouped (arrow) and that the neuroepithelium has expanded dorsoventrally on the side of the graft. (D,E) Serial cross-sections 3 days after the graft (E5) hybridised with Shh (D) and HNF3ß (E) probes. SHH-producing cells (arrow) are now dispersed and the Shh+, HNF3ß– lateral floor plate has widened. (F-K) Serial cross-sections 5 days after the graft (E7) show that the ventral and lateral neural tube is enlarged and perturbed on the side of the graft. Shh (F), HNF3ß (G), Netrin1 (H), Nkx2.2 (I), Sim1 (J) and CSox1 (K) expression patterns in the region facing the SHH-producing cells are characteristic of the lateral floor plate. RP, roof plate. Arrowheads, MFP limits; arrows, LFP lateral limit.

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