Zebrafish satb2 expression marks the prechondrogenic mesenchyme. A–J: Transverse (A–C,F–J) and parasagittal (D,E) sections are shown. Wild-type zebrafish embyos at 38 hours postfertilization (hpf; A–E) and 48 hpf (F–J) were sectioned following whole-mount in situ hybridization using the zebrafish antisense satb2 riboprobe. A–C: Progressive sections along the anterior–posterior axis of the embryo at 38 hpf showed satb2 expression in the brain and the mesenchymal precursors of the ethmoid plate and trabeculae while the ectoderm was satb2-negative. D,E: Parasagittal sections showed abundant satb2 expression in the mesenchyme of the maxillary condensations and pharyngeal arches 1–5 (1–5) that surrounded a core of satb2-negative mesoderm. F–J: Progressive sections along the anterior–posterior axis of the embryo at 48 hpf showed satb2 expression in the brain and eyes. G,H: satb2 expression was subsequently detected in the prechondrogenic mesenchyme of the ethmoid plate and trabeculae but not in the overlying ectoderm. I,J: Further posteriorly, the prechondrogenic mesenchyme of all seven pharyngeal arches was satb2 positive as well as scapulocoracoid of the pectoral fin. br, brain; ep, ethmoid plate; tr, trabeculae; e, ectoderm; mx, maxillary condensations; 1–5, pharyngeal arches 1–5; m, mesoderm; co, scapulocoracoid; oc, oral cavity; pf, pectoral fin.
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