Fig. 1. Distribution of Pn-1-expressing cells and the PN-1 protein during cerebellar development. PN-1 expression was monitored by beta-galactosidase detection in the developing postnatal cerebellum of PN-1 knock-in mice (A-F) and the distribution of the PN-1 protein was determined using specific antibodies (G-M). Following beta-galactosidase detection, sagittal sections were counterstained with neutral red (A-D) or anti-calbindin (E,F) to identify Purkinje cells and Bergmann glia. At early stages [P0 (A,B) and P2 (C,D)] beta-galactosidase activity is detected in Purkinje cells and in some CGNPs (arrowheads). By P8 (E,F), the overall expression is reduced and the labelling of the EGL has vanished. Beta-galactosidase activity remains in Purkinje cells and in the surrounding Bergmann glia cell bodies (F, arrowheads). At P0 (G,H), P2 (I,J) and P8 (K,M), the PN-1 protein is detected in the PCL. High levels of PN-1 protein are observed in the Bergmann glial cells (H,J,L, black arrowheads) and diffuse staining is observed in Purkinje cell bodies and dendrites (H,J,M, red arrowheads). Some PN-1 protein is also detected in postmitotic CGNPs (M, green arrowheads). The PN-1-protein distribution is graded along the anteroposterior axis. Initially (P0), it is rather prominent in the dorsal anterior lobes (G, arrow), and it then (P2) extends to the dorsal anterior and ventral posterior lobes (I, arrows). Later (P8), PN-1 protein is present in the dorsal anterior lobes (K, arrows) and in the deep fissures of the central lobes (K, asterisks). EGL, external granular layer; IGL, internal granular layer; PCL, Purkinje cell layer. Scale bars: 200 µm in A for A,C and in G for G,I; 50 µm in B for B,D,F; 250 µm in E; 30 µm in H for H,J; 350 µm in K; 60 µm in L for L,M.