LAUSR

Synaptic vesicles cluster by partitioning into phase-separated condensates Clusters of synaptic vesicles (SVs) are distinctive features of axon terminals in neurons. SVs contain neurotransmitters that are released upon electrical activity. The discovery of SVs as defined packages of neurotransmitters provided the molecular basis for the quantized theory of synaptic transmission in discrete units of information (1, 2). It has remained enigmatic what holds these vesicles together in clusters. On page 604 of this issue, Milovanovic et al. (3) show that synapsin 1, a protein that is essential for SV cluster formation, condenses into liquid droplets in vitro. Lipid vesicles and other SV cluster components specifically partition into these condensates, suggesting that SV cluster formation occurs through protein phase separation.