Figure 4

Requirement for planar signaling in the up-regulation of Hoxb4. (A) Neural tube from somite level 1–5 was dissected from 5 somite stage embryos with adjacent somites and a foil barrier was placed in the neural tube at the level between somites 2 and 3 (arrow). Following a 24-hour culture, no up-regulation of Hoxb4 was seen anterior to the barrier (n = 7/10. 3/10 showed weak expression anterior to the barrier). (B) Ex ovo cultured chick embryo inserted with a foil barrier placed across the whole tissues at the level posterior to the 2^nd somite, at the 2 somite stage. Following a 24-hour culture, Hoxb4 expression in the anterior side of the barrier is inhibited (arrowheads in B'). Other cases of this experiment together with controls are shown in Additional File 1. (C) Neural tube from somite level 1–5 was dissected from 5 somite stage embryos. Somites 1 and 2 were removed while somites 3–5 were kept. Hoxb4 expression is absent in the anterior neural tube (bracket) (n = 5/6. 1/6 showed weak expression in the neural tube level 1 and 2). (D, E) Neural tube at somite level 1 and 2 was dissected either without (D) or with (E) somites and fused with a somite level 5 neural tube that included flanking somites. Bracket marks the somite level 1–2 region, whereas arrow marks the somite level 2/5 border. Following a 24-hour culture, (D) shows weak expression in the somite level 2 region but not in the somite level 1 region (n = 8/10. 2/10 showed no expression). (E) shows expression in both the level 1 and 2 regions (n = 5/5). Scale bars; 500 μm (B), 200 μm (B', E).