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Fig. 1 AL,O: Expression of radar in the pharyngeal arch cartilages. (A-D,O lateral; E-L ventral). The expression of radar, sox9a, sox9b, and gdf5 in ventral arches is evident by in situ hybridization at 77 hours postfertilization (hpf). B,C,F,G,J,K: sox9a (B,F,J) is detected in cartilage while sox9b (C,G,K) is localized to the epithelial sheath surrounding cartilages (K). D,H,L: gdf5 is expressed in the jaw joint (white arrow, H) and medially in posterior arches, and at the basihyal (black arrows; Chiang et al.,[2001]; Yan et al.,[2005]). radar expression is detected in the jaw and along the ventral midline (E and arrows in I). M,N: Transverse sections detecting radar and gdf5 transcript. Both are expressed in the jaw joint (paired ventral staining in M and N) while only gdf5 is expressed dorsally in the pharynx (N). O: High resolution whole-mount imaging shows radar is detectable between posterior arch pharyngeal cartilages (arrow; lateral view; left = anterior). P: Sagittal section shows that radar is expressed surrounding medial hypobranchial cartilages. Q-S: Sagittal sections showing sox9a, sox9b, and gdf5 transcripts. gdf5 and radar are coexpressed near the midline around ceratohyals and hypobranchials though radar extends more ventrally below hypobranchials. bh, basihyal; ch, ceratohyal; hb1, hypobranchial 1; hb2, hypobranchial 2; hb3, hypobranchial 3; ep, ethmoid plate; e, eye; m, mouth opening.