Fig. 6. Effect of retinoic acid and FGF2 treatments expression of Hoxb genes. All embryos are presented in the dorsal view and were hybridized with riboprobes shown on the left of each horizontal panel. Embryos treated with retinoic acid are at stage 15-17. Untreated control embryos are at stage 15 for Hoxb1 and Hoxb3 and stage 11-13 for Hoxb5 to Hoxb8. FGF2-treated embryos are at stage 11-13. Asterisks mark the level of the otic vesicle. Arrowheads indicate the anterior limit of expression of genes in the neural tube. In retinoic acid-treated embryos, an anterior shift in the expression is seen for Hoxb1, Hoxb3 and Hoxb5. FGF2 treatment causes anterior shifts in the expression of Hoxb6, Hoxb7 and Hoxb8.