Cerebellum structure in Plexin-B2-deficient mice. Sagittal sections from adult Plexin-B2−/− mice. A, B, Sections immunostained for CaBP and parvalbumin and counterstained with Hoechst. A, Parvalbumin-labeled molecular layer interneurons are localized in the islands of ectopic CaBP-expressing Purkinje cells (arrows), dispersed among Hoechst-labeled granule cells. B, Higher magnification of a Purkinje cell island. Parvalbumin-positive interneurons are intermingled in Purkinje cell dendrites (arrowheads), and some typical basket cell “pinceaux” (arrow) are observed at the base of Purkinje cell bodies at the interface with granule cells. C, D, Section immunostained for CaBP (C) and vGlut2 (D) and counterstained with Hoechst. Ectopic CaBP-positive Purkinje cells (arrows in C) are contacted by vGlut2-labeled climbing fibers (arrows in D), whereas vGlut2-labeled mossy fiber rosettes (arrowheads in D) are found on granule cells. E, F, Section stained for PLAP histochemistry and immunostained for CaBP and counterstained with Hoechst. In F, PLAP staining was converted to red color using Photoshop. E, PLAP expression is concentrated in the molecular layer (ML, parallel fibers) and in the islands of ectopic Purkinje cells (arrows in E, F). Scale bars: A, 240 μm; B–D, 60 μm; E, F, 130 μm.