Fig. 3. Effect of FGF treatment on Hoxb4 and Hoxb9 expression in the neural tube. Dorsal views of stage 14-15 embryos hybridized with Hoxb4 (A-C) or Hoxb9 (D-F). Untreated embryos (A,D), embryos treated overnight with FGF2 in culture (B,E), embryos electroporated with an e-FGF-expressing construct unilaterally in the left side of the neural tube (C,F). In both cases, Hoxb9 is upregulated by exogenous FGF (E,F) while Hoxb4 shows no change (B,C). In E, note that the anterior limit of the Hoxb9 expression reaches the level just posterior to the otic vesicle. Black arrowheads in F show the extended domain of Hoxb9 on the left and the control limit on the right in the neural tube.