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Fig. 6 Expression of zebrafish satb2 is conserved compared with other vertebrates. A: A duplex reverse transcriptase-polymerase chain reaction (RT-PCR) designed to simultaneously amplify β-actin (555 bp) and satb2 (306 bp) indicated that satb2 was expressed from 24 to 96 hours postfertilization (hpf). The negative control (-ve) in which the cDNA is replaced with sterile water did not produce an amplicon. B–I: satb2 expression was analyzed using the satb2 antisense riboprobe. Images B, C, E, F, and I are lateral images with anterior facing left. Image D is a higher magnification, dorsolateral view of the pharyngeal arches in C. Image G is a frontal view of the embryonic face, and image H is a dorsal view of the embryo shown in F and G. B: satb2 expression was first detected at 32 hpf in the most anterior–ventral aspect of the first pharyngeal arch/mandible. C,D: By 36 hpf, satb2 expression was detected in the ventral mesenchyme of pharyngeal arches 1–5 and maxillary condensations. D: Expression in the pharyngeal arches clearly marked the mesenchyme surrounding a core of satb2-negative mesoderm. E,F: This expression pattern persisted but became more intense such that by 40 hpf satb2 expression was observed in all the pharyngeal arches, forebrain, scapulocoracoid of the pectoral fin and, by 48 hpf, the eye. G: Frontal views of 48 hpf larvae showed satb2 expression marking the trabeculae and ethmoid plate of the anterior neurocranium. H: Expression in the arches appeared to mark areas that form the cartilage elements of the pharyngeal skeleton. I: The expression pattern of satb2 continued until 60 hpf and thereafter declined. mx, maxillary condensations; 1–7, pharyngeal arches 1–7; m, mesoderm; br, forebrain; co, scapulocoracoid; tr, trabeculae; ep, ethmoid plate.