eve1 expression in 4V¹, the first tooth to develop in the zebrafish. A: 48 hours postfertilization (hpf), activation of the transcription of eve1 in tooth 4V¹. Top: In situ hybridisation (ISH) with probe to eve1 (ISH eve1), whole-mount, lateral view. Bottom: Interpretative drawing. The first bilateral eve1-expressing cells cluster (approximately 20 µm in diameter) is located in the ventral part of the pharynx, just posterior and dorsal to the fifth branchial arch (arrow). Pharyngeal arches are numbered (I to V). B-E: Transverse sections through the pharyngeal region, at the level of the Vth branchial arch. Left panels: ISH eve1; middle panels: camera lucida drawing of the mirror image of the section; right panels: control, nonhybridised specimen. B,C: At 48 hpf. Placode stage of tooth 4V1 (initiation/early morphogenesis) (arrows). D,E: At 72 hpf. Early differentiation stage (differentiation of the inner dental epithelium cells) of tooth 4V1 (arrows). On controls, tooth 4V¹ appears as a placode at 48 hpf (C, arrow). By 56-72 hpf, the ameloblasts of tooth 4V¹ differentiate (E, arrow). The arrowheads point to the regions in which teeth 3V¹ and 5V¹ start to form (out of focus). e, epidermis; nc, notochord; oc, otic capsule; phe, pharyngeal epithelium; y, yolk. Scale bars = 100 μm in A, 50 μm in B-E.

eve1 expression in differentiating ameloblasts of first generation (3V¹ and 5V¹) and replacement (4V², 3V² and 5V²) teeth. A-E: At 80 hours postfertilization (hpf). A: Transcription of eve1 in teeth 3V¹ and 5V¹. Top: ISH eve1, whole-mount, lateral view. Bottom: Interpretative drawing. While the transcription has ceased in tooth 4V¹, two new bilateral eve1-expressing cell clusters appear that correspond to the forming teeth 3V¹ and 5V¹ (arrows). B-E: Transverse sections through the pharyngeal region at the level of the Vth branchial arch. Left panels: In situ hybridization (ISH) eve1; middle panels: camera lucida drawing of the mirror image of the section; right panels: control, nonhybridised specimen. Early differentiation stage of teeth 3V1 (B, C), 5V1 (D,E). The arrows point to tooth 4V¹, in which dental matrix has accumulated. C,E: the arrowheads indicate the location of teeth 3V¹ and 5V¹, respectively. F,G: At 120 hpf. Early differentiation stage of replacement tooth 4V². Left panel: ISH eve1; right panel: control, nonhybridised specimen. In G, the black arrows point to teeth 3V¹, the white arrowheads to teeth 5V1, and the white arrows to tooth 4V². H,I: At 168 hpf. Early differentiation stage of replacement teeth 3V² and 5V², respectively. Left panels: ISH eve1; right panels: camera lucida drawings of the mirror image of the section. pf, pectoral fin; other abbreviations as in Figure 1A. Scale bars = 100 μm in A, 50 μm in B-I.