Ultrastructural analysis of wild-type and RIM1α knockout active zones in a large cortical synapse

• Published in: Cell reports (Cambridge) 2022-09, Vol.40 (12), p.111382-111382, Article 111382
• Main Authors: Lichter, Katharina, Paul, Mila Marie, Pauli, Martin, Schoch, Susanne, Kollmannsberger, Philip, Stigloher, Christian, Heckmann, Manfred, Sirén, Anna-Leena
• Format: Article
• Language: English
• Subjects: active zone; acute brain slices; CA3; electron tomography; high-pressure freezing; hippocampal mossy fiber bouton; RIM1α; SV pool; synaptic ultrastructure, presynaptic
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2022.111382

Rab3A-interacting molecule (RIM) is crucial for fast Ca2+-triggered synaptic vesicle (SV) release in presynaptic active zones (AZs). We investigated hippocampal giant mossy fiber bouton (MFB) AZ architecture in 3D using electron tomography of rapid cryo-immobilized acute brain slices in RIM1α−/− and wild-type mice. In RIM1α−/−, AZs are larger with increased synaptic cleft widths and a 3-fold reduced number of tightly docked SVs (0–2 nm). The distance of tightly docked SVs to the AZ center is increased from 110 to 195 nm, and the width of their electron-dense material between outer SV membrane and AZ membrane is reduced. Furthermore, the SV pool in RIM1α−/− is more heterogeneous. Thus, RIM1α, besides its role in tight SV docking, is crucial for synaptic architecture and vesicle pool organization in MFBs. [Display omitted] •Near-to-native AZ ultrastructure in hippocampal MFBs is altered in absence of RIM1α•RIM1α deletion increases the AZ surface area and synaptic cleft width•RIM1α deletion influences number, structure, and position of tightly docked SVs•RIM1α deletion leads to a heterogeneous SV pool organization Applying electron tomography on high-pressure frozen acute brain slices, Lichter et al. investigate the 3D near-to-native ultrastructure of presynaptic active zones in hippocampal mossy fiber synapses in wild-type and RIM1α knockout mice. Besides its role in tight vesicle docking, RIM1α is crucial for synaptic architecture and vesicle pool organization.