Fig. 2

Posterior rhombomere markers require progressively higher levels of RA signaling. Embryos are stained in blue for hoxb1b at 10 hpf (bud stage) (A–D), vhnf1 at 10.3–10.6 hpf (1–2 s) (E–H), at 18–19 hpf (18–20 s), hoxb1a (I–L), val (M–P) and hoxd4a (Q–T) and efnb2a at 11.6 hpf (5 s) (U–X). Other markers in red are pax2a, to label the MHB (A–H) and inner ear (I–T), and krox-20 (E–X), which labels r3 and r5 (Oxtoby and Jowett, 1993). Dorsal views show anterior to the left. Pharmacological treatment or genotype is shown at the top of each column. Control embryos treated with DMSO show wild-type expression patterns (A, E, I, M, Q, U). raldh2 mutant embryos show subtle reduction in expression of hoxb1b (B, 7/7 embryos), vhnf1 (F, 9/11 embryos), hoxd4a (R, 9/9 embryos) and efnb2a (V, 14/14 embryos show reduced expression in r7) and slight expansion of hoxb1a in r4 (J, 9/9 embryos), krox-20 in r3 and r5 (J, N, R, 17/17 embryos) and val in r5/r6 (N, 8/8 embryos). 1 μM DEAB-treated embryos show more severe reduction in expression of hoxb1b (C, 18/18 embryos), vhnf1 (G, 18/18 embryos), krox-20 in r5 (K, O, S, 38/47 embryos), val in r5/r6 (O, 18/23) and hoxd4a (S, 24/24 embryos), greater expansion of domains of krox-20 in r3 (K, O, S, 47/47 embryos) and hoxb1a in r4 (K, 21/21 embryos) and loss of efnb2a in r7 (W, 17/17 embryos). 1 μM DEAB-treated embryos can also show expansion of r5 and reduced r6 (not shown, 9/47 embryos). 5 μM DEAB-treated embryos show even more severe reduction of hoxb1b expression (D, 15/15 embryos), loss of expression of vhnf1 (H, 15/15 embryos), krox-20 in r5 (L, P, T, 31/41 embryos), val in r5–r6 (P, 20/28 embryos) and efnb2a in r7 (X, 17/17 embryos), and even greater expansion of domains of krox-20 in r3 (L, P, T, 41/41 embryos) and hoxb1a in r4 (L, 12/12 embryos). The val-expressing cells in r4 are the Mauthner neurons (Moens et al., 1998). The arrows in U–X point to efnb2a expression in developing somites (Durbin et al., 1998), posterior to the r7 efnb2a domain in control (U) and raldh2 mutant (V) embryos. r3, rhombomere 3 krox-20 expression. Scale bars: 50 μm.