Ultrastructural analysis of wildtype and RIM1α knock-out active zones in a large cortical synapse

Abstract

SummaryRab3A-interacting molecule (RIM) is crucial for fast Ca2+-triggered synaptic vesicle (SV) release in presynaptic active zones (AZ). While loss of RIM1α impairs long-term plasticity at hippocampal giant mossy fiber boutons (MFB), it remains unclear how AZ ultrastructure is altered. We investigated 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 heights and with a three-fold reduced number of tightly docked SVs (0-2nm). 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, beside its role in tight SV docking, is crucial for synaptic architecture and vesicle pool organization in MFBs.

Visualizing Presynaptic Active Zones and Synaptic Vesicles

“…Electron microscopy of AZs continues to provide critical insights, as for example was recently shown for structural transitions during synaptic vesicle (SV) priming ( Grushin et al, 2022 ; Lichter et al, 2022 ). Evaluating the dimensions of electron dense material below docked SVs can provide information how the chaperone Munc13, synaptotagmin, SNARE complexes, and complexins are assembled ( Rothman et al, 2017 ; Zhou et al, 2017 ).…”