Active zone scaffolds differentially accumulate Unc13 isoforms to tune Ca(2+) channel-vesicle coupling

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Brain function depends on rapid and timed synaptic vesicle (SV) release at active zones (AZs).
• The distance between SVs and Ca(2+) channels influences release efficacy, but the molecular mechanisms are unclear.

Purpose of the Study:

• To investigate the molecular mechanisms controlling SV-Ca(2+) channel distance at presynaptic active zones.
• To understand the roles of unc-13 (Unc13) isoforms in synaptic transmission and AZ organization.

Main Methods:

• Super-resolution microscopy
• Intravital imaging in developing Drosophila melanogaster glutamatergic synapses
• Mathematical modeling of synaptic release pathways

Main Results:

• Two Unc13 isoforms, Unc13A and Unc13B, are recruited to distinct AZ subdomains by specific scaffolding protein complexes.
• Unc13B localizes further from Ca(2+) channels (120 nm), while Unc13A localizes closer (70 nm) and is crucial for SV docking.
• Unc13A deficiency leads to inefficient, delayed, and EGTA-supersensitive SV release.

Conclusions:

• Isoform-specific interactions between Unc13 proteins and AZ scaffolds regulate SV-Ca(2+) channel topology.
• Developmental refinement of these interactions optimizes synaptic transmission through distinct release pathways.