Experimental Sey mouse chimeras reveal the developmental deficiencies of Pax6-null granule cells in the postnatal cerebellum

► Pax6-null cells can contribute to the postnatal cerebellum. ► The Pax6-null chimeric cerebellum is smaller and underdeveloped. ► Pax6 is required for early foliation of the cerebellum. ► The Pax6-null mutation has a primary effect in the cerebellar granule cell. ► Cerebellar granule cells require Pax6 for normal differentiation and radial migration in the postnatal cerebellum.