Biology subjects

Toulme, E.

Publications and source records attributed to Toulme, E..

3 recordsLinked to original sources

bioRxiv2021

Engineering paralog-specific PSD-95 synthetic binders as potent and minimally invasive imaging probes

Despite the constant advances in fluorescence imaging techniques, monitoring endogenous proteins still constitutes a major challenge in particular when considering dynamics studies or super-resolution imaging. We have recently evolved specific protein-based binders for PSD-95, the main postsynaptic scaffold proteins at excitatory synapses. Since the synthetic binders recognize epitopes not directly involved in the target protein activity, we consider them here as tools to develop endogenous PSD-95 imaging probes. After confirming their lack of impact on PSD-95 function, we validated their use as intrabody fluorescent probes. We further engineered the probes and demonstrated their usefulness in different super-resolution imaging modalities (STED, PALM and DNA-PAINT) in both live and fixed neurons. Finally, we exploited the binders to enrich at the synapse genetically encoded calcium reporters. Overall, we demonstrate that these evolved binders constitute a robust and efficient platform to selectively target and monitor endogenous PSD-95 using various fluorescence imaging techniques.

neuroscience↗

bioRxiv2021

Targeted sensors for glutamatergic neurotransmission

Optical report of neurotransmitter release allows visualization of excitatory synaptic transmission. Sensitive genetically-encoded glutamate reporters operating with a range of affinities and emission wavelengths are available. However, without targeting to synapses, the specificity of the fluorescent signal is uncertain, compared to sensors directed at vesicles or other synaptic markers. We fused the state-of-the-art reporter iGluSnFR to glutamate receptor auxiliary proteins in order to target it to postsynaptic sites. Chimeras of Stargazin and gamma-8 that we named SnFR-{gamma}2 and SnFR-{gamma}8, retained function and reported spontaneous glutamate release in hippocampal cells, with apparently diffraction-limited spatial precision. In autaptic neurons on micro island cultures, evoked release could be quantitatively detected at tens of synapses in a field of view whilst evoked currents were recorded simultaneously. These experiments revealed a specific postsynaptic deficit from Stargazin overexpression, resulting in synapses with normal release but without postsynaptic responses. This defect was reverted by delaying overexpression. By working at different calcium concentrations, we determined that SnFR-{gamma}2 is a linear reporter of the global quantal parameters and short term synaptic plasticity, whereas iGluSnFR is not. On average, half of iGluSnFR regions of interest showing evoked fluorescence changes had intense rundown, whereas less than 5% of SnFR-{gamma}2 ROIs did. We provide an open-source analysis suite for extracting quantal parameters including release probability from fluorescence time series of individual and grouped synaptic responses. Taken together, postsynaptic targeting improves several properties of iGluSnFR and further demonstrates the importance of subcellular targeting for optogenetic actuators and reporters.

neuroscience↗

bioRxiv2020

Functional architecture of the synaptic transducers at a central glutamatergic synapse

Neuronal synapses transduce information via the consecutive action of three transducers: voltage-gated Ca2+-channels, fusion-competent synaptic vesicles, and postsynaptic receptors. Their physical distance is thought to influence the speed and efficiency of neurotransmission. However, technical limitations have hampered resolving their nanoscale arrangement. Here, we developed a new method for live-labeling proteins for electron microscopy (EM), revealing that release-competent vesicles preferentially align with Ca2+-channels and postsynaptic AMPA receptors within 20-30 nm and thereby forming a transsynaptic tripartite nanocomplex. Using functional EM, we show that single action potentials cause vesicles within the nanocomplex to fuse with a 50% probability. The loss of the presynaptic scaffold disrupts the formation of the tripartite transducers. Strikingly, the forced transsynaptic alignment of the Ca2+-channel subunit 2{delta}1 and AMPA receptors suffice to restore neurotransmission in a scaffold lacking synapse. Our results demonstrate a synaptic transducer nanocomplex that actively contributes to the organization of central synapses.

neuroscience↗