The time course of cerebellar foliation and lamination during early postnatal cerebellar development is delayed in Plxnb2 conditional knockout. (A) Pax6 immunostaining labels both pre- and postmitotic CGNs in the developing cerebellum, and Calbindin (CaBP) labels Purkinje cells. In controls, many cerebellar fissures have formed at P0, and deepen further at P2 and P4, whereas the cerebellum of En1Cre;Plxnb2fl/fl mutant displays a very shallow primary fissure (prf) at P0 and aberrant fissure development over time. Furthermore, ectopic Purkinje cell islets (arrowheads) are observed in Plxnb2 mutant internal granule layer. (B) 3D-Light sheet microscope imaging of TO-PRO-3 stained and iDISCO+ cleared (see Materials and methods) P4 cerebellum illustrating the foliation delay in Plxnb2 conditional KO. Right panels are optical sections (coronal or horizontal) through 3D-reconstructed images. Plxnb2 mutants develop aberrant shallow fissures and additional folia in different orientations. Abbreviations: pfr: primary fissure, ppf: prepyramidal fissure, sf: secondary fissure, pcn: precentral fissure, pcuf: preculminate fissure, pfl: posterolateral fissure. Scale bars: overview panels (A, B): 500 μm, magnifications in (A): 100 μm.