Redundant requirements for rars in hindbrain patterning. Dorsal views of flat-mounted hindbrains at 15 hpf (12-somite), anterior to the left, labeled by two-color in situ hybridization for either hoxb5a/krox20 (A–E, K–N) or valentino/krox20 (F–J, O–R). Hindbrain rhombomeres are numbered (1–7), arrowheads indicate the location of the first somite. (A, F) Controls. (B–E) Embryos injected with MOs targeting raraa (B), rarab (C) rarga (D) or rargb (E) show reduced hoxb5a expression in posterior neural tube and mesoderm (blue), but no defects in krox20 expression in r3 or r5 (red). (G–J) Embryos injected with each of the four MOs alone show no defects in valentino (val) expression, or in the position of somite 1 (arrowheads). (K, L) Combined injection of raraa and rarab MOs (K; N = 22), or rarga and rargb MOs (L; N = 25) causes a reduction in hoxb5a expression. (M) Combined injection of the rarga MO with both raraa and rarab MOs (N = 25) causes severe reduction in hoxb5a expression in the neural tube, but mesodermal expression persists. These triple morphants retain the r5 stripe of krox20 expression unlike embryos treated with a pan-RAR antagonist, AGN 193109 (N). (O–Q) raraa/rarab double morphants (O; 35/38), rarga/rargb double morphants (P; N = 20), and raraa/rarab/rarga triple morphants (Q; N = 22) all show slight reductions in val expression, while its expression is almost completely eliminated by AGN treatments (R; N = 25).