Active Zone Scaffold Protein Ratios Tune Functional Diversity across Brain Synapses

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• High-throughput electron microscopy is mapping neural circuits, but synaptic function varies.
• Synaptic vesicle release efficacy, timing, and frequency depend on calcium channel proximity to release machinery.
• Voltage-gated calcium channels (VGCCs) and synaptic vesicle release are organized at the nanometer scale.

Purpose of the Study:

• To investigate how scaffold proteins influence the positioning of release factors relative to VGCCs.
• To determine the impact of this organization on synaptic vesicle release and short-term plasticity.
• To explore the concept of "nanoscopic molecular fingerprints" for synapse identification.

Main Methods:

• Combined light super-resolution microscopy with in vivo electrophysiology.
• Investigated scaffold proteins Bruchpilot (BRP) and Syd-1 in the Drosophila olfactory system.
• Analyzed the clustering of Unc13 release factor isoforms (Unc13A and Unc13B) relative to VGCCs.

Main Results:

• BRP/Unc13A clusters were found close to VGCCs, while Syd-1/Unc13B clusters were further away.
• The ratio of BRP/Unc13A to Syd-1/Unc13B varied significantly between different synapse types.
• This differential clustering resulted in distinct synapse-specific forms of short-term plasticity.

Conclusions:

• Variations in scaffold protein/(M)Unc13 modules tune synapse-specific release features.
• Tightly versus loosely coupled modules create distinct synaptic temporal characteristics.
• "Nanoscopic molecular fingerprints" can identify synapses with specific temporal properties.