This image shows a postnatal day 1 mouse cerebellum. Granule cell precursors and Purkinje cells layers are labelled with Pax6 (green) and Calbindin (red), respectively. Proliferation of cerebellar granule cell precursors is regulated by Rab23 through multidimensional actions on the Hedgehog signalling pathway: Rab23 represses the basal level of Shh signaling while facilitating activation of primary cilium-dependent extrinsic Sonic Hedgehog signaling. For more information, see the article by Hor et al. (pages 6850–6863) in this issue. Cover image: Catherine H. H. Hor.