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Fig. 2 Teeth do not form in case of defective pouch 6 contact with ectoderm. (A–F) vgo−/− mutant zebrafish at 5 dpf. (Middle) show midline with (arrow) or without (arrowhead) developing tooth germs; (Left and Right) show corresponding contact of pouch 6 with ectoderm and ensuing gill slit formation (Right) or absence thereof (Left), respectively. (G–I) Edema (thin arrow) causing extremely perturbed pouch formation in a vgo−/− mutant zebrafish at 96 hpf (G), tooth absence (H, arrowheads), and corresponding lack of contact of pouch 6 with ectoderm (I, arrowhead). (J–L) Extreme unilateral edema (J, thin arrow) in a 7 dpf laf−/− mutant zebrafish preventing pouch 6 contact with ectoderm, and corresponding tooth absence on that side (K, arrowhead), while pouch 6 at the contralateral side has opened into a gill slit (L) and a tooth is present (K and L, arrow). (M–O) Unilateral edema in a 96 hpf Tg(krt4:gfp) zebrafish preventing pouch 6 contact with ectoderm, and corresponding tooth absence on that side (M, arrowhead), while pouch 6 at the contralateral side has opened into a gill slit (O) and a tooth is present (N, arrow). Cartoons show the transverse sections from which the different details are taken (boxed areas). Dark gray: cartilage; medium gray: endoderm; light gray: other tissues. Abbreviations: asterisks: pharyngeal lumen; b: brain; ed: edema; nt: notochord; ov: otic vesicle; P6: pouch 6. (Scale bars, 50 µm.)