Fig. 6. BMS453-induced branchial arch defects and ectopic activation of the RARß2 promoter are prevented by the panRAR-selective antagonist BMS493. Embryos carrying the Rarb2-lacZ transgene in a wild-type genetic background were cultured for 48 hours. B1-B3, branchial arches 1 to 3, respectively; B1-2, fused first and second branchial arches; O, otocyst; R7, rhombomere 7; R3/R4, boundary between rhombomeres 3 and 4. Arrowheads indicate the first branchial cleft.