Treating the arl13b mutants with lithium mitigates the morphological defects in the cerebellum. A–D Representative images of embryos treated with 50 mmol/L LiCl at 30–37 hpf, fixed at 3 dpf, and immunostained with anti-tubulin antibody to reveal cerebellar morphology. Treatment of wild-type embryos with Li+ does not affect the cerebellar morphology (A, B) (arrows). The morphological defects of the cerebellum in arl13b mutants treated with Li+ are partially rescued (C, D) (arrow). A–D, Scale bar 100 μm. E Statistics revealing that the proportion of arl13b mutant embryos with cerebellar defects is dramatically decreased by LiCl treatment. F–I’’ Representative images of Tg(neurod1:EGFP) transgenic embryos used to label granule cells. Treating wild-type transgenic embryos with Li+ causes no defect (F–G’’) (dashed ovals). Treating arl13b morphant transgenic embryos restores the dorsomedial cluster of granule cells (H–I’’) (dashed ovals). F–I’’, Scale bar 100 μm. J The proportion of arl13b morphant embryos with cerebellar defects in the dorsomedial clusters is dramatically reduced by LiCl treatment.