This image shows interaction between the tau protein and protein phosphatase 1 (PP1) in a cultured rat hippocampal neuron. The neuron is stained for β-III tubulin (green) and the red puncta represent co-localization of individual tau and PP1 molecules as determined by proximity ligation assay. The functional interaction between these molecules has implications for axonal transport dysregulation in Alzheimer's disease and other tauopathies. For more information, see the article by Combs et al. (pages 9431–9451). Cover image: Benjamin Combs.