Active zone scaffolds differentially accumulate Unc13 isoforms to tune Ca2+ channel–vesicle coupling

MA Böhme, C Beis, S Reddy-Alla, E Reynolds… - Nature …, 2016 - nature.com
MA Böhme, C Beis, S Reddy-Alla, E Reynolds, MM Mampell, AT Grasskamp, J Lützkendorf…
Nature neuroscience, 2016nature.com
Brain function relies on fast and precisely timed synaptic vesicle (SV) release at active zones
(AZs). Efficacy of SV release depends on distance from SV to Ca2+ channel, but molecular
mechanisms controlling this are unknown. Here we found that distances can be defined by
targeting two unc-13 (Unc13) isoforms to presynaptic AZ subdomains. Super-resolution and
intravital imaging of developing Drosophila melanogaster glutamatergic synapses revealed
that the Unc13B isoform was recruited to nascent AZs by the scaffolding proteins Syd-1 and …
Abstract
Brain function relies on fast and precisely timed synaptic vesicle (SV) release at active zones (AZs). Efficacy of SV release depends on distance from SV to Ca2+ channel, but molecular mechanisms controlling this are unknown. Here we found that distances can be defined by targeting two unc-13 (Unc13) isoforms to presynaptic AZ subdomains. Super-resolution and intravital imaging of developing Drosophila melanogaster glutamatergic synapses revealed that the Unc13B isoform was recruited to nascent AZs by the scaffolding proteins Syd-1 and Liprin-α, and Unc13A was positioned by Bruchpilot and Rim-binding protein complexes at maturing AZs. Unc13B localized 120 nm away from Ca2+ channels, whereas Unc13A localized only 70 nm away and was responsible for docking SVs at this distance. Unc13Anull mutants suffered from inefficient, delayed and EGTA-supersensitive release. Mathematical modeling suggested that synapses normally operate via two independent release pathways differentially positioned by either isoform. We identified isoform-specific Unc13-AZ scaffold interactions regulating SV-Ca2+-channel topology whose developmental tightening optimizes synaptic transmission.
nature.com