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Fig. 7 Mutation in arnt1, but not arnt2, prevents AHR2-dependent TCDD toxicity. (A-F) Wild-type or mutant larvae were exposed to (A-C) 0.1% DMSO or (D-F) 2,3,7,8-tetrachlorodibenzodioxin (TCDD) from 1-3 dpf and imaged at 3 dpf. (A,D) Wild-type larvae exposed to TCDD lack an S-shaped cardiac loop and exhibit cardiac edema, unlike vehicle-treated wild-type siblings. (B,E) arnt1 mutant larvae (arnt1bcm2/bcm2) treated with vehicle and TCDD show normal heart looping and do not have cardiac edema. (C,F) arnt2 mutant larvae (arnt2bcm3/bcm3) treated with vehicle show expected heart looping similar to wild-type siblings, but arnt2 homozygous mutant larvae treated with TCDD lack an S-shaped cardiac loop similar to wild type and exhibit cardiac edema similar to TCDD-treated wild-type larvae. Arrows indicate location of the heart. Larvae were genotyped after imaging and representative images are shown. TCDD-treated wild-type siblings of arnt1 mutant larvae, n=9 larvae across three clutches; TCDD treated arnt1 mutant larvae, n=21 larvae across three clutches. TCDD treated wild-type siblings of arnt2 larvae, n=19 larvae across three clutches; TCDD treated arnt2 mutant larvae, n=22 larvae across four clutches. All larvae are oriented with anterior towards the left and dorsal towards the top. Scale bar: 100 μm.