Fig. 8. Model of avian floor-plate development from E1.5 to E7 at the thoracic level. Hensen’s node is schematically represented at 5 ss (E1.5) when it becomes inserted into the neural plate which expresses the gene Sox1 (Sox1+). One day later (E2.5) at the same level, Hensen’s node has split into floor plate and notochord. The node-derived floor plate (ND FP, in red), like the node itself, expresses HNF3ß and Shh. ND FP and perhaps also the notochord, induce adjacent neural plate cells (arrows) to express HNF3ß and Shh, thus forming at E3.5 a lateral floor plate (LFP, in blue), which retains Shh expression while loosing HNF3ß expression (E7). LFP expresses continuously neural genes (Sox1, Nkx2.2 and Sim1) that are never expressed in the node-derived medial floor plate (MFP). Netrin1 is expressed both in MFP and LFP cells.

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