Rab-interacting molecule (RIM)-binding protein 2 (BP2) is a multidomain protein of the presynaptic active zone (AZ). By binding to RIM, bassoon (Bsn), and voltage-gated Ca2+ channels (CaV), it is considered to be a central organizer of the topography of CaV and release sites of synaptic vesicles (SVs) at the AZ. Here, we used RIM-BP2 knock-out (KO) mice and their wild-type (WT) littermates of either sex to investigate the role of RIM-BP2 at the endbulb of Held synapse of auditory nerve fibers (ANFs) with bushy cells (BCs) of the cochlear nucleus, a fast relay of the auditory pathway with high release probability. Disruption of RIM-BP2 lowered release probability altering short-term plasticity and reduced evoked EPSCs. Analysis of SV pool dynamics during high-frequency train stimulation indicated a reduction of SVs with high release probability but an overall normal size of the readily releasable SV pool (RRP). The Ca2+-dependent fast component of SV replenishment after RRP depletion was slowed. Ultrastructural analysis by superresolution light and electron microscopy revealed an impaired topography of presynaptic CaV and a reduction of docked and membrane-proximal SVs at the AZ. We conclude that RIM-BP2 organizes the topography of CaV, and promotes SV tethering and docking. This way RIM-BP2 is critical for establishing a high initial release probability as required to reliably signal sound onset information that we found to be degraded in BCs of RIM-BP2-deficient mice in vivo. SIGNIFICANCE STATEMENT: Rab-interacting molecule (RIM)-binding proteins (BPs) are key organizers of the active zone (AZ). Using a multidisciplinary approach to the calyceal endbulb of Held synapse that transmits auditory information at rates of up to hundreds of Hertz with submillisecond precision we demonstrate a requirement for RIM-BP2 for normal auditory signaling. Endbulb synapses lacking RIM-BP2 show a reduced release probability despite normal whole-terminal Ca2+ influx and abundance of the key priming protein Munc13-1, a reduced rate of SV replenishment, as well as an altered topography of voltage-gated (CaV)2.1 Ca2+ channels, and fewer docked and membrane proximal synaptic vesicles (SVs). This hampers transmission of sound onset information likely affecting downstream neural computations such as of sound localization.
Journal of Neuroscience
This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the Collaborative Sensory Research Center 1286 [to C.W. (A4) and T.M. (B5)] and under Germany’s Excellence Strategy Grant EXC 2067/1-390729940. We thank S. Gerke, A.J. Goldak, and C. Senger-Freitag for expert technical assistance; G. Hoch for developing image analysis routines; and S. Chepurwar and N. Strenzke for technical support and discussion regarding in vivo experiments. We also thank Dr. Christian Rosenmund, Dr. Katharina Grauel, and Dr. Stephan Sigrist for providing RIM-BP2 KO mice and Dr. Masahiko Watanabe for providing the anti-neurexin-antibody, and Dr. Toshihisa Ohtsuka for the anti-ELKS-antibody. J. Neef for help with the STED imaging and image analysis; E. Neher and S. Rizzoli for discussion and comments on the manuscript; K. Eguchi for help with the statistical analysis; and C. H. Huang and J. Neef for constant support and scientific discussion.
Butola T, Alvanos T, Hintze A, et al. RIM-binding protein 2 organizes Ca21 channel topography and regulates release probability and vesicle replenishment at a fast central synapse. Journal of Neuroscience. 2021;41(37):7742-7767. doi:10.1523/JNEUROSCI.0586-21.2021
Butola, T., Alvanos, T., Hintze, A., Koppensteiner, P., Kleindienst, D., Shigemoto, R., … Moser, T. (2021). RIM-binding protein 2 organizes Ca21 channel topography and regulates release probability and vesicle replenishment at a fast central synapse. Journal of Neuroscience. Society for Neuroscience. https://doi.org/10.1523/JNEUROSCI.0586-21.2021
Butola, Tanvi, Theocharis Alvanos, Anika Hintze, Peter Koppensteiner, David Kleindienst, Ryuichi Shigemoto, Carolin Wichmann, and Tobias Moser. “RIM-Binding Protein 2 Organizes Ca21 Channel Topography and Regulates Release Probability and Vesicle Replenishment at a Fast Central Synapse.” Journal of Neuroscience. Society for Neuroscience, 2021. https://doi.org/10.1523/JNEUROSCI.0586-21.2021.
T. Butola et al., “RIM-binding protein 2 organizes Ca21 channel topography and regulates release probability and vesicle replenishment at a fast central synapse,” Journal of Neuroscience, vol. 41, no. 37. Society for Neuroscience, pp. 7742–7767, 2021.
Butola T, Alvanos T, Hintze A, Koppensteiner P, Kleindienst D, Shigemoto R, Wichmann C, Moser T. 2021. RIM-binding protein 2 organizes Ca21 channel topography and regulates release probability and vesicle replenishment at a fast central synapse. Journal of Neuroscience. 41(37), 7742–7767.
Butola, Tanvi, et al. “RIM-Binding Protein 2 Organizes Ca21 Channel Topography and Regulates Release Probability and Vesicle Replenishment at a Fast Central Synapse.” Journal of Neuroscience, vol. 41, no. 37, Society for Neuroscience, 2021, pp. 7742–67, doi:10.1523/JNEUROSCI.0586-21.2021.
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