Vesicle reuse revisited
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520
Neurons communicate at the synapse by releasing neurotransmitter from synaptic vesicles. After exocytosis, synaptic vesicle membrane and protein are locally recycled for reuse in the presynaptic terminal. The mechanisms involved in the recycling of synaptic vesicle material have yet to be fully resolved (reviewed in ref. 1). The traditional model of vesicle recycling posits that vesicles merge with the plasma membrane and then are later retrieved in perisynaptic regions by endocytosis (2–4). A second model, often referred to as “kiss-and-run” (5), suggests that neurotransmitter is released through a fusion pore that allows the vesicle to release neurotransmitter while retaining its protein and/or lipid (6). By refilling with neurotransmitter, vesicles formed in this manner could potentially become rapidly available for reuse. Evidence for rapid reuse of synaptic vesicles has been found in rat hippocampal neurons (7, 8), yet the contribution of this mechanism to pool recycling remains debated. The work by Li et al. (9) in a recent issue of PNAS introduced new tools and new data to this debate.
thy-1 SynaptopHluorin Mice: A New Tool for Visualizing Synaptic Transmission
Li et al. (9) develop a new tool for neurobiologists to exploit in their study of synaptic transmission. The authors make use of synaptopHluorin (10), a synaptic vesicle protein (synaptobrevin) that has been concatenated with a pH-sensitive GFP on its luminal side. pHluorin exhibits minimal fluorescence under acidic conditions and because secretory vesicles maintain an acidic interior, exocytosis of vesicles carrying synaptopHluorin is indicated by an abrupt brightening in fluorescence, and the retrieval of vesicle constituents is indicated by a dimming in the emission signal as newly formed organelles acidify (11). This technique for visualizing exocytosis, first developed by Miesenbock and colleagues (10), has been used by neurobiologists to study properties of …
