| Description |
Every presynapse builds a core 'active zone' structure, where ion channels cluster and synaptic vesicles release their neurotransmitters. The core active-zone scaffold proteins SYD-2 (also known as liprin-α) and ELKS-1 undergo phase separation during an early stage of synapse development, and later mature into a solid structure. A developmental liquid phase of scaffold molecules is essential for the assembly of the synaptic active zone, before maturation into a stable final structure. Small unilamellar vesicle (SUV)-coated RIM/RIM-BP condensates are encapsulated by synapsin/SUV condensates, forming two distinct SUV pools reminiscent of the reserve and tethered SV pools that exist in presynaptic boutons. The SUV-coated RIM/RIM-BP condensates can further cluster Ca2+ channels anchored on membranes. RIMs and RIM-BPs are plausible organizers of active zones, and the formation of RIM and RIM-BP condensates may cluster VGCCs into nano- or microdomains and position the clustered Ca2+ channels with Ca2+ sensors on docked vesicles for efficient and precise synaptic transmissions. |