mRNA Expression of the Arnt2 dimerization partner, Sim1, is reduced in the hypothalamus and ventral thalamus of arnt2-/- larvae at 72 hpf. ISH of sim1 in a cross section of the brain taken through the ventral thalamus and hypothalamus of a representative WT larva and arnt2-/- larva at 72 hpf shows reduced expression in the arnt2-/- mutant (compare right top and right bottom). In the left panel, black arrows indicate the plane at which the cross section (shown in the right panel) was taken. Eyes of the representative WT larva and arnt2-/- larva were removed after euthanasia (left top and left bottom) so that the pattern of sim1 staining in the whole-mount brain could be seen in lateral view. vt, ventral thalamus; h, hypothalamus.