Shown is a zebrafish larva head with GCAMP expression (recolored as a purple–yellow gradient), and a spinal backfill of dextran red to highlight neurons (recolored as cyan). Enlarged and overlaid on the larva head is a cranial blood vessel containing exosomes expressing CD63-phluorin (recolored as green). Zebrafish larvae with a mutation in VPS4A–a gene associated with neurodevelopmental defects in humans–have less active midbrain motor command neurons (top center, cyan), and a reduced number of exosomes (green in the overlaid blood vessel). See Anna Shipman et al. for more information on VPS4A mutant zebrafish larvae, which may provide insight into VPS4A mutations in humans. The images were taken on separate microscopes and were modified using ImageJ/FIJI and Adobe Photoshop. Cover image: Anna Shipman and Teresa Nicolson.