Ttc21b Is Required in Bergmann Glia for Proper Granule Cell Radial Migration

Proper cerebellar development is dependent on tightly regulated proliferation, migration, and differentiation events. Disruptions in any of these leads to a range of cerebellar phenotypes from ataxia to childhood tumors. Animal models have shown that proper regulation of ( ) signaling is crucial for normal cerebellar architecture, and increased signaling leads to cerebellar tumor formation. Primary cilia are known to be required for the proper regulation of multiple developmental signaling pathways, including . ( ) is required for proper primary cilia form and function, and is primarily thought to restrict signaling. Here we investigated a role for in cerebellar development. Surprisingly, ablation in Bergmann glia resulted in the accumulation of ectopic granule cells in the lower/posterior lobes of the cerebellum and a reduction in signaling. ablation in just Purkinje cells resulted in a similar phenotype seen in fewer cells, but across the entire extent of the cerebellum. These results suggest that expression is required for Bergmann glia structure and signaling in the developing cerebellum, and in some contexts, augments rather than attenuates signaling.