Munc13-3 Is Required for the Developmental Localization of Ca2+ Channels to Active Zones and the Nanopositioning of Cav2.1 Near Release Sensors

Publication date: 20 February 2018
Source:Cell Reports, Volume 22, Issue 8
Author(s): Valentin Kusch, Grit Bornschein, Desiree Loreth, Julia Bank, Johannes Jordan, David Baur, Masahiko Watanabe, Akos Kulik, Manfred Heckmann, Jens Eilers, Hartmut Schmidt
Spatial relationships between Cav channels and release sensors at active zones (AZs) are a major determinant of synaptic fidelity. They are regulated developmentally, but the underlying molecular mechanisms are largely unclear. Here, we show that Munc13-3 regulates the density of Cav2.1 and Cav2.2 channels, alters the localization of Cav2.1, and is required for the development of tight, nanodomain coupling at parallel-fiber AZs. We combined EGTA application and Ca²⁺-channel pharmacology in electrophysiological and two-photon Ca²⁺ imaging experiments with quantitative freeze-fracture immunoelectron microscopy and mathematical modeling. We found that a normally occurring developmental shift from release being dominated by Ca²⁺ influx through Cav2.1 and Cav2.2 channels with domain overlap and loose coupling (microdomains) to a nanodomain Cav2.1 to sensor coupling is impaired in Munc13-3-deficient synapses. Thus, at AZs lacking Munc13-3, release remained triggered by Cav2.1 and Cav2.2 microdomains, suggesting a critical role of Munc13-3 in the formation of release sites with calcium channel nanodomains.

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Teaser

Central synapses shift from microdomain to nanodomain coupling between Ca²⁺ channels and release sensors during development. Kusch et al. show that Munc13-3 is a critical regulator of this process. Munc13-3 differentially regulates density and localization of Cav2.1 and Cav2.2 channels and establishes nanodomain coupling between Cav2.1 channels and release sensors.


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