Neurons efficiently detect, integrate and transmit information through specialization of their plasma membrane into sub-domains such as the active zone or the post-synaptic membrane, with specific properties and morphology. The efficiency and accuracy of neurotransmission strongly depends on two apparently antagonist properties of synaptic membrane: the stability of its organization and its ability to adapt to plasticity events.
In addition, the structural stability of synapses has to be reconciled with the notion that cell membranes are fluid. Membrane molecules are compelled to move within the membrane surface due to thermal Brownian agitation, which favors the homogeneous distribution of the molecules. As a result, neurons spend energy to stop or reduce these movements, and maintain molecules in certain locations via mechanisms that decrease this fluidity.
These last ten years, we have approached these conceptual paradoxes by developing new technological and analytical tools that allows the monitoring of the behavior of synaptic components at the molecular level and change of the scale of analysis. More precisely, we have pioneered the development of quantum dot-based single particle tracking and analysis. This approach has enabled us in collaboration with Maxime Dahan to monitor the behavior of neurotransmitter receptors at the single molecule level and this was considered as a “major breakthrough” by Science magazine.
Studies of the diffusive properties of single synaptic molecules and in particular neurotransmitter receptors have reshaped our understanding of molecular trafficking in neurons and thereby unravel new regulatory mechanisms of synaptic neurotransmission. We demonstrated rapid exchanges between synaptic and extra-synaptic receptors and we showed that transient stabilization of receptors at synapses occurs by interaction with partners, such as scaffold proteins. Thus, the regulations of receptor-scaffold and scaffold–scaffold interactions are a central tenet for the maintenance and plasticity-related changes of receptor numbers at synapses.
With Christian Specht, our aim is to determine key aspects of the relationship between the synapse microstructure, molecular dynamics, and molecular interactions. More precisely we want to establish the link between diffusion dynamic and receptor trapping at synapses in relation with molecular interactions. This will posit the mechanisms responsible for receptor accumulation at synapses, and its regulations. We now want: 1) to establish how phosphorylation-dependent affinities within the postsynaptic assembly impact the diffusion dynamics and number of receptors at synapses; and 2) to link this regulation with excitation/inhibition equilibrium. To achieve these aims we are now implementing novel super-resolution imaging methods (PALM, STORM, STED microscopy, adaptive optics), single molecule tracking (3D-PALM, PALM-SPT) and specific analytical approaches using tools developed by physicists combined with electro-physiology.
In parallel, we are exploring other aspects of synapse functions:
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Dahan M, Triller A. Quantitative nanoscopy of inhibitory synapses: counting gephyrin molecules and receptor binding sites. Neuron. (2013) 79(2):308-21.
Pascual O, Ben Achour S, Rostaing P, Triller A, Bessis A. Microglia activation triggers astrocyte-mediated modulation of excitatory neurotransmission. Proc Natl Acad Sci U S A. (2012) 109(4):E197-205.
Specht CG, Grünewald N, Pascual O, Rostgaard N, Schwarz G, Triller A. Regulation of glycine receptor diffusion properties and gephyrin interactions by protein kinase C. EMBO J. (2011) 30(18):3842-53.
Ribrault C, Sekimoto K, Triller A. From the stochasticity of molecular processes to the variability of synaptic transmission. Nat Rev Neurosci. (2011) 12(7):375-87
Charrier C, Machado P, Tweedie-Cullen RY, Rutishauser D, Mansuy IM, Triller A. A crosstalk between β1 and β3 integrins controls glycine receptor and gephyrin trafficking at synapses. Nat Neurosci. (2010) 13(11):1388-95.
Bernard D, Prasanth KV, Tripathi V, Colasse S, Nakamura T, Xuan Z, Zhang MQ, Sedel F, Jourdren L, Coulpier F, Triller A, Spector DL, Bessis A. A long nuclear-retained non-coding RNA regulates synaptogenesis by modulating gene expression. EMBO J. (2010) 29(18):3082-93.
Renner M, Lacor PN, Velasco PT, Xu J, Contractor A, Klein WL, Triller A. Deleterious effects of amyloid beta oligomers acting as an extracellular scaffold for mGluR5. Neuron. (2010) 66(5):739-54.
Bannai H, Lévi S, Schweizer C, Inoue T, Launey T, Racine , Sibarita JB, Mikoshiba K and A Triller., Activity-dependent tuning of inhibitory neurotransmission based on GABAAR diffusion dynamics. Neuron (2009) 62:670-82.