Showing papers by "Daniel Choquet published in 2017"

Hippocampal LTP and contextual learning require surface diffusion of AMPA receptors

Abstract: Surface diffusion of AMPA receptors, from extra-synaptic to synaptic sites at the plasma membrane, is essential for full long-term potentiation in hippocampal neurons and for fear conditioning in living mice. Learning and memory are thought to rely on the long-term potentiation (LTP) of excitatory synaptic transmission, as a result of either an increase in presynaptic release of the neurotransmitter (glutamate) or recruitment of its postsynaptic receptor (AMPAR) in greater numbers. Now, using molecular techniques for immobilizing AMPARs, Daniel Choquet and colleagues demonstrate that surface diffusion of the receptor, from extra-synaptic to synaptic sites at the plasma membrane, is essential for full LTP in hippocampal neurons, and for fear conditioning in living mice. The results suggest new targets for the deliberate modulation of synaptic plasticity, learning and memory. Long-term potentiation (LTP) of excitatory synaptic transmission has long been considered a cellular correlate for learning and memory1,2. Early LTP (less than 1 h) had initially been explained either by presynaptic increases in glutamate release3,4,5 or by direct modification of postsynaptic AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor function6,7. Compelling models have more recently proposed that synaptic potentiation can occur by the recruitment of additional postsynaptic AMPA receptors (AMPARs)8, sourced either from an intracellular reserve pool by exocytosis or from nearby extra-synaptic receptors pre-existing on the neuronal surface9,10,11,12. However, the exact mechanism through which synapses can rapidly recruit new AMPARs during early LTP remains unknown. In particular, direct evidence for a pivotal role of AMPAR surface diffusion as a trafficking mechanism in synaptic plasticity is still lacking. Here, using AMPAR immobilization approaches, we show that interfering with AMPAR surface diffusion markedly impairs synaptic potentiation of Schaffer collaterals and commissural inputs to the CA1 area of the mouse hippocampus in cultured slices, acute slices and in vivo. Our data also identify distinct contributions of various AMPAR trafficking routes to the temporal profile of synaptic potentiation. In addition, AMPAR immobilization in vivo in the dorsal hippocampus inhibited fear conditioning, indicating that AMPAR diffusion is important for the early phase of contextual learning. Therefore, our results provide a direct demonstration that the recruitment of new receptors to synapses by surface diffusion is a critical mechanism for the expression of LTP and hippocampal learning. Since AMPAR surface diffusion is dictated by weak Brownian forces that are readily perturbed by protein–protein interactions, we anticipate that this fundamental trafficking mechanism will be a key target for modulating synaptic potentiation and learning.

Localization-based super-resolution imaging meets high-content screening.

Abstract: An automated system for data acquisition and analysis enables high-content screening localization microscopy and increases the throughput and information content of super-resolution microscopy methods such as dSTORM, DNA-PAINT and (spt)PALM.

Semisynthetic fluorescent pH sensors for imaging exocytosis and endocytosis.

Abstract: The GFP-based superecliptic pHluorin (SEP) enables detection of exocytosis and endocytosis, but its performance has not been duplicated in red fluorescent protein scaffolds. Here we describe "semisynthetic" pH-sensitive protein conjugates with organic fluorophores, carbofluorescein, and Virginia Orange that match the properties of SEP. Conjugation to genetically encoded self-labeling tags or antibodies allows visualization of both exocytosis and endocytosis, constituting new bright sensors for these key steps of synaptic transmission.

Pre-post synaptic alignment through neuroligin tunes synaptic transmission efficiency

Abstract: The nanoscale organization of neurotransmitter receptors relative to pre-synaptic release sites is a fundamental determinant of both amplitude and reliability of synaptic transmission. How modifications in the alignment between pre- and post-synaptic machineries affect synaptic current properties has only been addressed with computer modeling, and therefore remains hypothetical. Using dual-color single molecule based super-resolution microscopy, we found a strong spatial correlation between AMPA receptor (AMPAR) nanodomains and the post-synaptic adhesion protein neuroligin-1 (NLG1). Expression of a C-terminal truncated form of NLG1 disrupted this correlation without affecting the intrinsic organization of AMPAR nanodomains. Moreover, this NLG1 dominant-negative mutant significantly shifted the pre-synaptic release machinery from AMPAR synaptic clusters. Electrophysiology and computer modeling show that this physical shift is sufficient to induce a significant decrease in synaptic transmission. Thus, our results suggest the necessity for synapses to release glutamate in front of AMPAR nanodomains, to maintain a high efficiency of synaptic responses.

Semisynthetic pH-Sensitive Fluorophores For Imaging Exocytosis And Endocytosis

Abstract: The GFP-based superecliptic pHluorin (SEP) enables detection of exocytosis and endocytosis, but its performance has not been duplicated in red fluorescent protein scaffolds. Here we describe semisynthetic pH-sensitive protein conjugates that match the properties of SEP. Conjugation to genetically encoded self-labeling tags or antibodies allows visualization of both exocytosis and endocytosis, constituting new bright sensors for these key steps of synaptic transmission.