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Figure 7 | BMC Developmental Biology

Figure 7

From: Regulation of Hoxb4 induction after neurulation by somite signal and neural competence

Figure 7

BMP4-dependent Hoxb4 up-regulation requires RA at the level of somites 1–5. (A-C, E-G) Flat-mounted neural tube from embryos treated with DMSO (A-C) or BMS493 (E-G) from 4 to 5 somite stages. Embryos were cultured either in the control medium (A, E), in the conditioned medium of BMP4-transfected cells (BMP4-CM; B, F) or in the presence of recombinant BMP4 (rBMP4; C, G) until they reached the 10 to 12 somite stages. In the absence of BMS493 (A-C), additional BMP4 causes ventral expansion of Hoxb4 expression (B, C, n = 12 for each) compared to control (A). In the presence of BMS493 (E-G), Hoxb4 is not up-regulated at the level of somites 1 to 6 regardless of additional BMP4 (F, G, n = 16 for each), except that a slight up-regulation is observed at the ventral neural tube by rBMP4 (G, double arrow). At more posterior levels, ventral expansion is induced by additional BMP4 (arrows in F, G). Arrowheads indicate rhombomere 6/7 boundary (r6/7). Brackets indicate the level of somites 1 to 6. Scale bar; 100 μm. (D, H) Whole mount chick embryos cultured ex ovo with DMSO (D) or BMS493 (H) from the 2 to 4 somite stages and incubated until the 22 somite stage. Hoxb4 expression is specifically blocked in the neural tube at the level of somites 1 to 6 (bracket) (n = 4). Scale bar; 200 μm. (I-K) Neural tube explants at the level of somites 1 to 5, without flanking somites, cultured in the presence of RA or recombinant BMP4 (rBMP4) for 24 hours and analyzed for Hoxb4 expression. While RA sufficiently up-regulates Hoxb4 (J), rBMP4 does not do so (K) (n = 3 for each). Scale bar; 200 μm. (L-N) Transverse sections of embryos cultured ex ovo in the control medium (L), with RA (M) or with recombinant BMP4 (N). Sections are at the level of somite 3 to 4. Control embryos show Hoxb4 expression localized to the dorsal side (n = 5/5). Exogenous RA causes a stronger and broader expression in the dorsal half of the neural tube, but the expression domain does not expand to ventral regions (M, arrow) (n = 6/7. 1/7 showed a expansion close to the floor plate). Recombinant BMP4 causes an expansion of Hoxb4 expression to the ventral side of the neural tube (double arrow) (n = 4/6. 2/6 showed only a weak expansion to the floor plate). Scale bar; 100 μm.

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