Fig. 7. fgf24 expression during later embryonic and larval development. In all panels, anterior is towards the left unless specified, and fgf24 expression is visualized in purple. (A-D) 12 hpf (six-somite stage), dorsal views. (A) fgf24 is expressed in the nasal placode (asterisk), otic placode (arrow), lateral mesoderm (arrowhead) and tail bud mesenchyme surrounding Kupffer's vesicle. Expression of fgf24 in the otic placode was confirmed by co-labeling embryos with either krx20 (red), which labels rhombomere 3 (r3) and r5 (B) or pax2.1 (red), which labels the otic placode and the mid-hindbrain boundary (C). (D) fgf24 expression in lateral mesoderm (arrowhead) is in cells that lie adjacent and medial to those expressing pax2.1 (red). (E,F) 18 hpf. (E) fgf24 is expressed in nasal ectoderm and in a discrete domain of the retina (arrow, dorsal view). (F) Lateral view of fgf24-expressing cells in the posterior gut (arrow), in tail bud mesenchyme and in the caudal fin primordium (arrowhead). (G) 20 hpf, dorsal view. fgf24expression in early pectoral fin bud mesenchyme (arrow). (H-J) 24 hpf. (H) fgf24 expression persists in the posterior gut (arrow) and caudal fin primordium (arrowhead), but is no longer detected in the tail bud (lateral view, yolk extension removed). (I) fgf24 is expressed in the pharyngeal endoderm (arrowheads) and in the pectoral fin bud mesenchyme (arrow), and in a posterior domain of the otic epithelium (not in focus). Inset in I shows sagittal section through the otic vesicle (outlined), showing more clearly the expression of fgf24 in the posterior otic epithelium (arrow) and pharyngeal endoderm (arrowheads). (J) Transverse section (dorsal upwards) showing fgf24 expression in fin bud mesenchyme (arrow) and gut (arrowhead). (K-O) 52 hpf. (K) At this stage, fgf24 is no longer expressed in pectoral fin mesenchyme, but instead is strongly expressed in the apical ectodermal ridge. (L) Lateral view of head showing fgf24 expression in the first and second pharyngeal pouches (pp1, ppl2), and the posterior ectodermal margin (pem, arrow) of the second pharyngeal arch. A ventral view (M) shows fgf24 expression in all pharyngeal pouches (pp1 and pp2-6, small arrows), and the olfactory bulb. Additionally, fgf24 is expressed in tooth germs, which develop on only the most posterior (seventh) pharyngeal arch. (N) A close-up ventral view shows fgf24 expression in bilateral domains (arrowheads) adjacent to the lateral edges of the mouth. (O) fgf24 is expressed in the olfactory organ and the olfactory bulb (dorsal view, anterior is upwards). dis, distal; e, eye; kv, Kupffer's vesicle; mhb, mid-hindbrain boundary; mo, mouth; nec, nasal ectoderm; nc, notochord; nt, neural tube; ob, olfactory bulb; olf, olfactory organ; op, otic placode; ov, otic vesicle; pem, posterior ectodermal margin; psm, presomitic mesoderm; pro, proximal; ret, retina; tb, tail bud; tg, tooth germ; ye, yolk extension. Scale bars: 100 µm in A,G; 50 µm in B-F,H-O.

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