Cover legend: Primary motor neurons in culture stained with a neurofilament antibody to visualize their highly polarized morphology. Nuclei are stained with DAPI (blue). The spinal muscular disease protein SMN facilitates the subcellular localization and trafficking of RNA-binding proteins and mRNAs along the long axonal processes. For more information, see the article by Fallini et al. in this issue (pages 3914–3925).