Fig. 1

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.