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Dissecting the nanoscale organization and dynamics of glutamate receptors at excitatory synapses

le 14 mars 2019
11h30

Séminaire de Harold Mac Gillavry (Universiteit Utrecht, Pays-Bas)

Neuronal synapses are composed of a large diversity of molecular complexes that are precisely organized to sustain efficient and fast synaptic transmission. At excitatory synapses, ionotropic glutamate receptors (iGluRs) carry the majority of fast synaptic transmission, while metabotropic glutamate receptors (mGluRs) modulate synaptic efficacy on a much slower time scale. Intriguingly, this functional distinction seems
reflected in their subsynaptic distribution. Ionotropic AMPA- and NMDA-type glutamate receptors accumulate in the core of the postsynaptic density (PSD) that directly appose the presynaptic release machinery. In contrast, mGluRs are mainly enriched in the perisynaptic domain. This distribution is predicted to have important functional consequences for synaptic transmission, yet we know little about the mechanisms that underlie this organization. This is mainly because the resolution of conventional light microscopy techniques is not sufficient to resolve substructure or motion within individual synapses. to overcome this, we use super-resolution imaging to directly investigate the subsynaptic distribution and mobility of glutamate receptors. Furthermore, to label and visualize endogenously expressed proteins in neurons we successfully adapted CRISPR/Cas9 mediated knock-in strategies. Combined, these approaches allow us to measure the mobility of endogenous synaptic proteins with live-cell imaging, and to dissect the subsynaptic distribution of synaptic proteins. Using two-color STED microscopy we found that the majority of synapses indeed displays a segregated distribution of iGluRs and mGluRs. While AMPAR subunits accumulate in distinct subsynaptic nanodomains, mGluRs are largely excluded from the PSD. Furthermore, using single-molecule tracking we found that AMPARs dynamically explore the dendrite, but become immobilized in subsynaptic nanodomains. In contrast, mGluR single-molecule trajectories rarely entered the synapse, but remained rather confined in nanodomains in the perisynaptic domain adjacent to the PSD. We currently investigate the mechanisms that underlie this explicit segregation to understand how glutamate receptors are dynamically positioned at synapses to control synaptic transmission and plasticity.

Harold Mac Gillavry est invité par Eric Denarier.

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Amphi Serge Kampf
Mise à jour le 25 février 2019

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