Membrane Traffic at Synapses
Team Leader : David Perrais
The team (July 2020)
From left to right (without masks): Julie, Lou, Etienne,
David, Silvia, Vincent, May, Zehra, Mathias
Vesicular trafficking is one of the most salient features of synaptic physiology. In the tiny (less than 1 µm wide) chemical synapses, presynaptic vesicles concentrate and release neurotransmitter molecules which bind to post-synaptic receptors. The exocytosis and recycling of synaptic vesicles is a very prominent and essential feature of neuronal physiology that is highly controlled in time and space. Moreover, post-synaptic membrane trafficking, although not as prominent quantitatively, is pivotal for the maintenance of signal transduction complexes supporting synaptic transmission and plasticity. Most of our knowledge about synapse physiology comes from studying glutamatergic synapses which represent the majority of synapses in the brain. Nevertheless, other types of synapses, such as neuromodulatory dopaminergic synapses, could have a very different molecular composition and operate in a different way. However, because they represent a small minority of synapses formed from a very small number of neurons, their analysis has been difficult through classical cellular and molecular methods.
Our goal in the team is to use the most advanced fluorescence imaging techniques together with refined purification of synaptic elements (synaptosomes) to address the mechanisms regulating synapse function through membrane trafficking events in normal brain physiology or in the course of disease. To achieve this goal, we use, on top of the standard techniques of the modern neuroscience lab (molecular biology, biochemistry, imaging, electrophysiology), two unique expertise developed by the two PIs: first, with David Perrais, we develop methods to detect individual exocytosis and endocytosis events with pH sensitive fluorophores and perform quantitative imaging. Second, with Etienne Herzog, we purify synaptosomes from adult animals with fluorescence activated synaptosome sorting (FASS), which enables powerful proteomics, transcriptomics and functional approaches.
Altogether, we aim at identifying new pathways in specific synapses and test their relevance for synaptic nanostructure and function in the normal and diseased brain.
Post-synaptic exocytosis and synaptic plasticity - Cell Reports Sept 2021
Synapses, the basic building blocks of neural networks, are both very stable and capable of rapid and long-lasting modifications, a phenomenon known as synaptic plasticity. The modification of a synapse often involves the addition of synaptic receptors (long-term potentiation or LTP) or the removal of part of the synaptic receptors (long-term depression or LTD). This rapid plasticity is possible because synaptic receptors are not immobile in the synapse but travel to intracellular compartments called recycling endosomes (RE). The regulation of RE trafficking has thus become an important topic of study for understanding the mechanisms of synaptic plasticity.
Picture of all contributors of this study. David Perrais and May Bakr stand in front of "The paint pipette", taken by May, which was awarded the best IINS picture prize in 2020.
In this study, we searched for the molecules involved in these phenomena, in particular the proteins responsible for exocytosis called SNAREs. The VAMP2 protein, target of the tetanus toxin (released by the bacterium responsible for tetanus and one of the most deadly in humans), was known to block LTP. However, to our surprise, it only marginally affected RE exocytosis. We therefore searched for other SNARE proteins and found VAMP4 to be responsible for the majority of RE exocytosis, whereas VAMP2 is involved in only a small fraction of exocytosis, but plays a major role in the exocytosis of REs containing AMPA-type postsynaptic receptors (see Figure). Furthermore, VAMP4 deletion also alters the trafficking of AMPA receptors that are in greater quantity at the surface of neurons, increasing synaptic transmission and limiting its plasticity by occlusion.
This work shows the great diversity of membrane trafficking mechanisms in the dendrites of neurons that allows receptors to be delivered when and where they are needed to regulate individual synapses. It was the result of a long-term work, over more than eight years, of many students, engineers and researchers of the IINS.
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« Alumni & Guests »
Anne-Sophie Hafner (Guest, 2017-2018)
Magalie Martineau (post-doc, 2015-2019 - Now Research and Development specialist at EIF Innovation, Paris, France)
Léa Claverie (PhD student, 2015-2019 - Now Project Manager at Euroquality, Bordeaux, France)
Florencia Angelo (Lab Manager, 2015-2020)
Thi Nhu Ngoc Van (post-doc, 2014-2016 - Now Project Manager at Sys2dia, Montpellier, France)
Julia Krapivkina (PhD student, 2012-2016 - Now Project Manager at Assystem, Paris, France)
Xiao Min Zhang (PhD Student, 2012-2016 - Now Assistant Prof at Sun Yat Sen University - China)
Morgane Rosendale (PhD student and post-doc, 2011-2016 - Now post-doctoral fellow at Institute for Molecular Sciences, Bordeaux)
Damien Jullié (PhD student, 2008-2012 - Now Research Specialist at UCSF Weill Institute for Neurosciences, San Francisco, USA)