Biology subjects

Thoumine, o.

Publications and source records attributed to Thoumine, o..

3 recordsLinked to original sources

bioRxiv2025

A nanobody-gold conjugate for the detection of GFP-tagged synaptic proteins by dual light-electron microscopy

To meet the constantly improving spatial resolution offered by advanced microscopy techniques to study sub-cellular structures in biology, there is a need for small, monovalent probes that label proteins of interest with high specificity and minimal distance to the target, and are compatible with various imaging modalities. In this direction, we designed a strategy to generate minimal-size probes composed of a controlled 1:1 conjugate between a small domain binder and a 1.4 nm-gold nanoparticle with direct access to fluorescent labelling for dual light-electron microscopy. Our approach was applied to the widely used single-domain antibody against GFP (GBP). The modified GBP-gold conjugate retained normal binding to purified GFP in vitro, specifically labelled COS-7 cells and neurons expressing GFP-tagged synaptic membrane proteins, and penetrated readily into tight cell-cell contacts including neuronal synapses. The optional fluorescence labelling with a second ALFA nanobody allowed dSTORM imaging, while the silver-enhanced nanogold particle detected in TEM was used to characterize the number and nanoscale organization of individual proteins in the synaptic cleft. We counted a small number of endogenous neurexins in the pre-synapse and a larger number of AMPA receptors in the post-synapse, often aligned in nanodomains. This GBP-gold probe thus emerges as a potent tool to label an ever-increasing repertoire of GFP-tagged proteins in numerous biological organisms and models.

bioengineering↗

bioRxiv2024

Dissecting the binding mechanisms of synaptic membrane adhesion complexes using a micropattern based cellular model

The formation of adhesive cell-cell contacts is based on the intrinsic binding properties between specific transmembrane ligand-receptor pairs. In neurons, synaptic adhesion molecules provide a physical linkage between pre- and post-synaptic compartments, but the strength and the dynamic of these complexes in their actual membrane environments remain essentially unknown. To access such information, we developed a versatile assay to measure the affinity and binding kinetics of synaptic ligand-receptor interactions, based on the immobilization of Fc-tagged ligands on micropatterned substrates combined with live imaging of fluorescently-tagged counter receptors in heterologous cells. We applied this strategy to study the heterophilic complex formed between neurexin-1{beta} (Nrx1{beta}) and neuroligin-1 (Nlg1), compared to the homophilic SynCAM1 complex. First, the control of ligand density combined to the measurement of steady-state receptor enrichment at micropatterns demonstrates the high specificity of the matching molecular interactions and allows for the quantification of the two-dimensional affinity of the interaction in a membrane environment. Second, long-term FRAP experiments performed on the two molecular complexes and fitted with analytical models, demonstrate a diffusion-limited regime for SynCAM1 and a reaction-limited regime for Nlg1. This analysis provides a very long bond lifetime of the Nrx1{beta}-Nlg1 complex, which by comparison with a monomeric mutant of Nlg1, can be attributed to the constitutive dimerization of Nlg1. Finally, we used the stable Nrx1{beta}-Nlg1 complex as a pseudo-synaptic platform to analyze the rapid binding kinetics between the scaffolding protein PSD-95 and the intracellular domain of Nlg1, dissecting the contribution of the different PDZ domains through the use of specific PSD-95 point mutants.

neuroscience↗

bioRxiv2021

MDGAs are fast-diffusing molecules that delay excitatory synapse development by altering neuroligin behavior

MDGAs are molecules that can bind neuroligins in cis and interfere with trans-synaptic neurexin-neuroligin interactions, thereby impairing synapse development. However, the sub-cellular localization and dynamics of MDGAs, as well as their specific mode of action in neurons are still unclear. Here, using both surface immunostaining of endogenous MDGAs and single molecule tracking of recombinant MDGAs in dissociated hippocampal neurons, we show that MDGA1 and MDGA2 molecules are homogeneously distributed and exhibit fast membrane diffusion, with a small reduction in mobility across neuronal maturation in culture Using shRNAs and CRISPR/Cas9 strategies to knock-down/out MDGA1 or MDGA2, we demonstrate an increase in the density of excitatory synapses accompanied by enhanced membrane immobilization and an increase in the phosphotyrosine level of neuroligins associated with excitatory post-synaptic differentiation. Finally, we show that decreasing MDGA expression level reduces the mobility of AMPA receptors and increases the frequency of AMPA receptor mediated mEPSCs. Overall, our results support a mechanism by which interactions between MDGAs and neuroligin-1 delays the assembly of functional excitatory synapses containing AMPA receptors.

neuroscience↗