Fig. 6. Expression of Cyp1B1 in the pharyngeal arch region and its role in the patterning of the epibranchial placodes. (Aa-Ac) Cyp1B1 is expressed in the endoderm of the pharyngeal pouch (PP) and grooves (Aa,Ab, blue arrows). Longitudinal section through the region shown (Ac, white line) shows highly localised expression to the endoderm of PP2 (white arrows in Ab). (Ba-Bc) At a similar stage, Raldh2 is not expressed in the region of the pharyngeal pouches (Ba, black arrow). Cyp26C1, known to attenuate RA-signalling, is also expressed in the endoderm of PP1-3 (Bb,Bc, white arrows). (C) Electroporation strategy used to overexpress Cyp1B1 in the ectoderm adjacent to the endoderm of the PPs. (Da-Dc) Phox2a expression in the epibranchial placodes of the non-electroporated side of an embryo (Da, black arrows). Ectopic expression of Cyp1B1 represses the expression of Phox2a (Db, white arrows). The observed effects are coincident with ectopic sites of GFP expression (Dc, white arrows).