Jak/Stat signaling mediates proliferation in the apc mutant hypothalamus. (A) Proliferating cells are increased and neurogenesis is decreased in the apc mutant hypothalamus. Lateral confocal projections are shown with the neuronal marker HuC/D in green and the proliferation marker PCNA in red. Anterior is to the left and the hypothalamus is indicated by the dotted lines. (B) Both stat3 mRNA expression and pStat3 levels are increased in the apc mutant hypothalamus at 36 hpf. In situ hybridization for stat3 mRNA (top) and immunohistochemistry for pStat3 (bottom) are shown in transverse cryosections. (C) BrdU incorporation in the hypothalamus is increased in apc mutants, and restored to wild-type levels by AG-490 treatment. Embryos were labeled with BrdU for 1 hour and fixed for analysis at 36 hpf. Confocal projections from the ventral brain surface through the 36 hpf hypothalamus are shown. BrdU immunohistochemistry is red, TO-PRO-3 nuclear stain is in blue. (D) The BrdU labeling index is significantly increased in the apc mutant hypothalamus compared to wild-type siblings, and restored to wild-type levels by AG-490 treatment. Error bars = s.d., p < 0.05 by student's t-test.