Figure 9.

Unc5c transgene expression in Atoh1-expressing neurons rescues the axonal guidance of the hook bundle and pontine migration but not the cuneocerebellar tract in Unc5c^−/− mice. A–H, DiI crystals were placed into the cerebellum of E16.5 (A, B, C, D) and P0 (E, F, G, H) wild-type (A, E), TgAtoh1-Unc5c (B, F), Unc5c^−/− (C, G), and TgAtoh1-Unc5c;Unc5c^−/− (D, H) mice. Hindbrains were sectioned coronally to visualize cerebellar tracts and counterstained with Hoechst dye. Note that transgenic expression of Unc5c rescues the cerebellar midline crossing of the hook bundle (hb), but not the axonal projections of the IO neurons in TgAtoh1-Unc5c;Unc5c^−/− neonatal mice (D). Retrograde labeling of the ECN was not observed in TgAtoh1-Unc5c;Unc5c^−/− neonatal mice (H). Note that the presumptive inferior vestibular tract (IVN) is similarly labeled in all of the mice. I–L, Pontine neuron migration was assessed by X-Gal staining of hindbrains from E16.5 embryos of each genotype that are also heterozygous for the Atoh1^lacZ/+ reporter gene. Arrowheads indicate ectopic formation of PN in mutant (K). Transgenic expression of Unc5c rescues ectopic formation of PN (L). M–P, Axon migration of pontine neurons was visualized by unilateral DiI insertion. DiI was inserted in the normally positioned pontine nucleus in Unc5c^−/− brains (O). Arrows indicate normal projections of pontine neurons while arrowheads indicate rostrally and caudally projecting axons in the Unc5c^−/− hindbrain. Cb, Cerebellum.