Intersectin and endophilin condensates prime synaptic vesicles for release site replenishment

Area of Science:

• Neuroscience
• Cell Biology
• Synaptic Plasticity

Background:

• Synaptic vesicle fusion is crucial for neurotransmission.
• Replenishment of release sites by nearby vesicles is essential for sustained synaptic function.
• The precise mechanisms and localization of these replacement vesicles remain incompletely understood.

Purpose of the Study:

• To investigate the molecular mechanisms governing the localization and availability of replacement synaptic vesicles.
• To identify proteins involved in clustering vesicles near active zones for rapid replenishment.
• To understand the role of intersectin-1 and endophilin A1 in synaptic vesicle dynamics.

Main Methods:

• Utilized mouse hippocampal excitatory synapses for experiments.
• Investigated the role of intersectin-1 and endophilin A1 in vesicle clustering.
• Analyzed vesicle proximity to the plasma membrane using electron microscopy.
• Examined synaptic depression phenotypes in the absence or mutation of key proteins.

Main Results:

• Intersectin-1 forms dynamic molecular condensates with endophilin A1, clustering replacement vesicles near active zones.
• Absence of intersectin-1 leads to reduced vesicle clustering and impaired replenishment, causing synaptic depression.
• Mutations disrupting intersectin-1 and endophilin A1 interaction yield similar synaptic deficits.
• Endophilin A1 is required for mobilizing the replacement vesicle pool sequestered by intersectin-1.

Conclusions:

• Identified a novel 'replacement zone' in synapses where vesicles are actively stored for release site replenishment.
• Intersectin-1 and endophilin A1 play critical roles in maintaining this replacement pool through condensate formation and vesicle mobilization.
• Disruption of this mechanism leads to synaptic depression, highlighting its importance for sustained neurotransmission.