Fig. 3. Effects on branchial pouch development of the RARß agonist BMS453. Embryos were hybridized with a Pax1 antisense probe after 12, 24 and 48 hours in culture. (A,B) external views. (C-F) Embryos cut sagittally into halves; the medial side of the right half is displayed. (G-L) Ventral views of flat mounts from isolated pharyngeal endoderm. B1-B3, branchial arches 1 to 3, respectively; B1-2, fused first and second branchial arches; H, heart; O, otocyst; P1-P3, pharyngeal pouches 1 to 3, respectively; P1-2, fused first and second pharyngeal pouches; S, somites. A-F and G-L are displayed at the same magnification.