Biology subjects

Reissner, C.

Publications and source records attributed to Reissner, C..

3 recordsLinked to original sources

bioRxiv2025

Optical recordings of synaptic vesicle fusion reveal diffusional dispersion

The primary unit of exocytosis, the synaptic vesicle, is replete with proteins which enable vesicle fusion. For maintaining synaptic transmission the vesicle proteins have to be rapidly cleared from the active zone. The immediate fate of the cargo post-fusion and the precise mechanism of its resorting into a readily retrievable pool (RRetP) for endocytosis remains unclear. To address this, we developed a purely presynaptic preparation, the xenapse, presynaptic boutons formed en face directly onto a glass coverslip enabling optical single vesicle recording by total internal reflection microscopy (TIRFM). Electron microscopy showed xenapses contain a few hundred synaptic vesicles (SVs), of which [~]40 SVs are primed (readily releasable pool, RRP), as revealed by single vesicle recordings using the pH-sensitive fluorescent protein pHluorin. Single fusion events synchronous with action potentials could be localized with [~]20 nm precision and rapid post-fusion diffusional dispersion of vesicular proteins observed with diffusion constants in the order of 0.1 {micro}m2/s. Unroofing of xenapses revealed numerous Clathrin-coated structures, enriched for vesicle cargo and numerically equivalent to about twice the measured RRP size. In this way SV proteins are rapidly cleared from the release site into this RRetP of pre-assembled pits to allow for rapid re-docking and re-priming at vacated release sites in synapses tuned for high-fidelity fast signaling.

neuroscience↗

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↗

bioRxiv2023

Regulation of hippocampal mossy fiber-CA3 synapse function by a Bcl11b/C1ql2/Nrxn3(25b+) pathway

The transcription factor Bcl11b has been linked to neurodevelopmental and neuropsychiatric disorders associated with synaptic dysfunction. Bcl11b is highly expressed in dentate gyrus granule neurons and is required for the structural and functional integrity of mossy fiber-CA3 synapses. The underlying molecular mechanisms, however, remained unclear. We show that the synaptic organizer molecule C1ql2 is a direct functional target of Bcl11b that regulates synaptic vesicle recruitment and long-term potentiation at mossy fiber-CA3 synapses in vivo and in vitro. Furthermore, we demonstrate C1ql2 to exert its functions through direct interaction with a specific splice variant of neurexin-3, Nrxn3(25b+). Interruption of C1ql2-Nrxn3(25b+) interaction by expression of a non-binding C1ql2 mutant or by deletion of Nrxn3 in the dentate gyrus granule neurons recapitulates major parts of the Bcl11b as well as C1ql2 mutant phenotype. Together, this study identifies a novel C1ql2-Nrxn3(25b+)-dependent signaling pathway through which Bcl11b controls mossy fiber-CA3 synapse function. Thus, our findings contribute to the mechanistic understanding of neurodevelopmental disorders accompanied by synaptic dysfunction.

neuroscience↗