Fig. 2. cyp26b1 is expressed in condensing chondrocytes and perichondrium. Stainings of wild-type zebrafish at the stages indicated in the upper right corners and with the in situ RNA probes or antibodies indicated in the lower right corners. fli1a-positive neural crest cells in D were visualized by anti-GFP immunostaining of a Tg(fli1a:EGFP)y1 transgenic embryo (Isogai et al., 2003). (A,B,D,E,H,I) Lateral views; (C,L-Q) dorsal views; (F,J) longitudinal sections; (G,K) transverse sections. (A-D) cyp26b1 is expressed close to, but not within, postmigratory cranial neural crest (CNC) cells. Arrows in A,B point to dlx2a-positive, cyp26b1-negative cells that according to lineage-tracing data are likely to give rise to the ethmoid plate (e). Arrows in C,D point to two cyp26b1 domains close to the pharyngeal arch-forming CNC. (E-H) cyp26b1 is expressed in chondrogenic mesenchymal condensations. (F,G,H) Magnifications of regions indicated in E. In F,G, pharyngeal endoderm is counterstained with zn5 antibody; in H, neural crest derivatives are stained for sox9a transcripts; double-positive domains in pharyngeal arch (pa) condensations are marked. (I-K) cyp26b1 is expressed in perichondrial cells around the pharyngeal arches (J), the ethmoid plate (K), and along the entire length of the ceratohyal (ch) and the ceratobranchials (cb) (I; inset shows magnification of one cb). (L-Q) By contrast, osx (L), opn (M) and col10a1 (N) are restricted to perichondrial cells around the ossifying, Alizarin Red (alR)-positive region of the ceratohyal (O). In col10a1-positive cells, cyp26b1 levels are lower than in the adjacent col10a1-negative perichondrium (P,Q; arrows point to cells double positive for cyp26b1 and col10a1). spt, subpallial telencephalon; vt, ventral thalamus.