Munc13-3 Is Required for the Developmental Localization of Ca2+ Channels to Active Zones and the Nanopositioning of Cav2.1 Near Release Sensors
Valentin Kusch,
Grit Bornschein,
Desiree Loreth,
Julia Bank,
Johannes Jordan,
David Baur,
Masahiko Watanabe,
Akos Kulik,
Manfred Heckmann,
Jens Eilers,
Hartmut Schmidt
Affiliations
Valentin Kusch
Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
Grit Bornschein
Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
Desiree Loreth
Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
Julia Bank
Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
Johannes Jordan
Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
David Baur
Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
Masahiko Watanabe
Department of Anatomy, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan
Akos Kulik
Institute of Physiology II, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany
Manfred Heckmann
Department of Physiology, Neurophysiology, Medical Faculty, University of Würzburg, Röntgenring 9, 97070 Würzburg, Germany
Jens Eilers
Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany
Hartmut Schmidt
Carl-Ludwig-Institute for Physiology, Medical Faculty, University of Leipzig, Liebigstrasse 27, 04103 Leipzig, Germany; Corresponding author
Summary: 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.
