Fig. 2

Expression pattern of mbx. Whole-mount in situ hybridization with probes shown at bottom right of each panel. Stages are indicated at bottom left, with % referring to epiboly, S to somite, and hpf to hours postfertilization. Approximate times after fertilization are 90% epiboly (9 hpf), bud (10 hpf), 1S (10.3 hpf), 3S (11 hpf), 5S (11.6 hpf), and 10S (14 hpf). Lateral view, anterior is left (F, I, K); anterior view, dorsal is up (A–E,N–Y); dorsal view, anterior is left (G, H, J, L, M). The expression of mbx is not detected by midgastrulation, but arises in the anterior neural ectoderm at late gastrula (A). At bud stage (B–D), mbx is expressed in a ring with a midline gap (B, arrowhead), and partly overlaps the ,em>six3 expression domain (C, overlap marked by dashed line). There is a gap between the fgf8 (D; asterisk) and mbx expression domains, while anterior mbx expression partly overlaps with dlx3 (N–P). During somitogenesis (N, Q, T, W), the posterior mbx domain fuses at the midline and increases in intensity, while the anterior domain elongates and then fades. Before fading, the anterior mbx domain overlaps with the eye field marked by mab21l2 (Q–S). The posterior stripe corresponds to the prospective tectum; this stripe (E; black arrowheads) is included in the otx2 expression domain (E; red arrowheads), overlaps with the posterior mab21l2 domain (Q–V), and is located just anterior of pax2.1 (W–Y). By 26 hpf, mbx is predominantly expressed in the tectum, with weak staining detected in some hindbrain and spinal neurons; mbx is excluded from the midbrain–hindbrain boundary (MHB) (F, G; arrowhead). (H–M) Expression pattern of mbx during hatching period; mbx is expressed in diencephalon (H: asterisk), tectum, otic vesicle, and rhombomeres at 48 and 72 hpf, while the retina is stained at 72 hpf, but not at 48 hpf (L, M).