Fig. 5. Analyses of hindbrain development of bcox morphants. The expression patterns of krx20 (A,B) efna4 (C,D) and val (E,F) reveal no obvious alterations in the identity of rhombomeres 1 to 5 in bcox morphants when compared with controls (14 hpf/24 hpf, dorsal views). Whole-mount in situ hybridization for combinations of krx20 and myod (G,H, 14 hpf, dorsal view), as well as fgf8 and val (I,J, 20 hpf, lateral view) reveal no alterations in the distance between r5 and the first somite or between the midbrain hindbrain border and r5 (the bar and the curve give the distances found in wild-type embryos, respectively). (K,L, 22 hpf, lateral view) hoxb4a expression is reduced in bcox morphants (L) when compared with controls (L). (M,N, 22 hpf, lateral view) Treatment with 10^–9 M RA restores hoxb4a expression in bcox morphants (N). (O,P, 24 hpf, lateral view; Q,R, 31 hpf, dorsal view) In bcox morphants (P,R), ap2 expression is reduced along the whole rostrocaudal expression domain in hindbrain and spinal cord, and is absent at the level of the otic vesicle. (S, dorsal, T, lateral) Citral treatment of wild-type embryos provoked similar changes in ap2 expression as found in bcox morphants. ov, otic vesicle; r, rhombomeres; teg, tegmentum.