Christian G Specht

Christian G Specht
French Institute of Health and Medical Research | Inserm · Diseases and Hormones of the Nervous System (DHNS)

PhD

About

91
Publications
10,457
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3,449
Citations
Citations since 2016
40 Research Items
1694 Citations
2016201720182019202020212022050100150200250300
2016201720182019202020212022050100150200250300
2016201720182019202020212022050100150200250300
2016201720182019202020212022050100150200250300
Introduction
My research explores the regulation of molecular interactions in axons and at synapses using quantitative and dynamic single molecule imaging strategies.

Publications

Publications (91)
Preprint
Single-molecule localization microscopy (SMLM) applications are often hampered by the fixed frame rate at which data acquisition is performed. Here, we present an alternative new approach of acquiring and processing SMLM data based on an event-based (or neuromorphic vision) sensor. This type of sensor reacts to light intensity changes rather than i...
Article
Full-text available
Sylite, eine kurze, dimerisierte Fluoreszenzsonde auf Peptidbasis, bindet Gephyrin, ein charakteristisches Protein der inhibitorischen Synapse. Wie Christian G. Specht, Hans M. Maric et al. in ihrem Forschungsartikel (DOI: 10.1002/ange.202202078) berichten, macht Sylite inhibitorische Synapsen sowohl in Neuronenkulturen als auch in Hirngewebe sicht...
Article
Sylite, a short, dimerized peptide‐based fluorescent probe, binds gephyrin, a hallmark protein of the inhibitory synapse. As reported by Christian G. Specht, Hans M. Maric et al. in their Research Article (DOI: 10.1002/anie.202202078), Sylite visualizes inhibitory synapses both in neuron cultures and brain tissue and can be flexibly applied for wid...
Preprint
Full-text available
Numerous models have been developed to account for the complex properties of the random walks of biomolecules. However, when analysing experimental data, conditions are rarely met to ensure model identification. The dynamics may simultaneously be influenced by spatial and temporal heterogeneities of the environment, out-of-equilibrium fluxes and co...
Article
Visualization of inhibitory synapses requires protocols tailored to different sample types and imaging techniques, and usually relies on genetic manipulation or the use of antibodies that underperform in tissue immunofluorescence. Starting from an endogenous ligand of gephyrin, a universal marker of the inhibitory synapse, we developed a short pept...
Article
Full-text available
Visualization of inhibitory synapses requires protocols tailored to different sample types and imaging techniques, and usually relies on genetic manipulation or the use of antibodies that underperform in tissue immunofluorescence. Starting from an endogenous ligand of gephyrin, a universal marker of the inhibitory synapse, we developed a short pept...
Article
Full-text available
Precise quantitative information about the molecular architecture of synapses is essential to understanding the functional specificity and downstream signaling processes at specific populations of synapses. Glycine receptors (GlyRs) are the primary fast inhibitory neurotransmitter receptors in the spinal cord and brainstem. These inhibitory glycine...
Article
Full-text available
The function of synapses depends on spatially and temporally controlled molecular interactions between synaptic components that can be described in terms of copy numbers, binding affinities, and diffusion properties. To understand the functional role of a given synaptic protein, it is therefore crucial to quantitatively characterise its biophysical...
Preprint
Full-text available
Precise quantitative information about the molecular architecture of synapses is essential to understanding the functional specificity and downstream signaling processes at specific populations of synapses. Glycine receptors (GlyRs) are the primary fast inhibitory neurotransmitter receptors in the spinal cord and brain stem. These inhibitory glycin...
Article
Full-text available
Super-resolution imaging has revealed that key synaptic proteins are dynamically organized within sub-synaptic domains (SSDs). To examine how different inhibitory receptors are regulated, we carried out dual-color direct stochastic optical reconstruction microscopy (dSTORM) of GlyRs and GABAARs at mixed inhibitory synapses in spinal cord neurons. W...
Preprint
Full-text available
We introduce Sylites - small and versatile fluorogenic affinity probes for high-contrast visualization of inhibitory synapses. Having stoichiometric labeling and exceptional selectivity for neuronal gephyrin, a hallmark protein of the inhibitory post-synapse, Sylites enable superior synapse staining compared with antibodies. Combined with super-res...
Article
Full-text available
Signaling at nerve cell synapses is a key determinant of proper brain function, and synaptic defects - or synaptopathies - are at the basis of many neurological and psychiatric disorders. Collybistin (CB), a brain-specific guanine nucleotide exchange factor (GEF), is essential for the formation of γ-aminobutyric acidergic (GABAergic) postsynapses i...
Article
Full-text available
Postsynaptic scaffold proteins immobilise neurotransmitter receptors in the synaptic membrane opposite to presynaptic vesicle release sites, thus ensuring efficient synaptic transmission. At inhibitory synapses in the spinal cord, the main scaffold protein gephyrin assembles in dense molecule clusters that provide binding sites for glycine receptor...
Preprint
Full-text available
Postsynaptic scaffold proteins immobilise neurotransmitter receptors in the synaptic membrane opposite to presynaptic vesicle release sites, thus ensuring efficient synaptic transmission. At inhibitory synapses in the spinal cord, the main scaffold protein gephyrin assembles in dense molecule clusters that provide binding sites for glycine receptor...
Data
Postsynaptic scaffold proteins immobilise neurotransmitter receptors in the synaptic membrane opposite to presynaptic vesicle release sites, thus ensuring efficient synaptic transmission. At inhibitory synapses in the spinal cord, the main scaffold protein gephyrin assembles in dense molecule clusters that provide binding sites for glycine receptor...
Data
Postsynaptic scaffold proteins immobilise neurotransmitter receptors in the synaptic membrane opposite to presynaptic vesicle release sites, thus ensuring efficient synaptic transmission. At inhibitory synapses in the spinal cord, the main scaffold protein gephyrin assembles in dense molecule clusters that provide binding sites for glycine receptor...
Preprint
Full-text available
Super-resolution imaging of synapses has revealed that key synaptic proteins are dynamically organized within sub-synaptic domains (SSDs). At mixed inhibitory synapses in spinal cord neurons, both GlyRs and GABA A Rs reside at the same post-synaptic density (PSD). To examine how the different inhibitory receptors are organized and regulated, we car...
Chapter
The application of single-molecule localization microscopy (SMLM) to the study of synaptic proteins has shown that the postsynaptic density (PSD) is organized heterogeneously in subsynaptic domains (SSDs) that are thought to play important roles in neurotransmission and synaptic plasticity. However, the dense packing of neurotransmitter receptors a...
Article
We introduce junctured-DNA (J-DNA) forceps as a generic platform for real-time observation, at the single-molecule level, of biomolecular interactions. The tool is based on a modular double-strand DNA construct to which proteins of interest can be attached using various tagging strategies. When combined with magnetic tweezers, J-DNA allows us to si...
Article
Full-text available
GABAA and glycine receptors are thought to compete for gephyrin binding sites at mixed inhibitory synapses. Changes in the occupancy of one receptor type are therefore expected to have opposite effects on the clustering of the other receptors. This does not explain, however, whether different receptors can be regulated independently from one anothe...
Article
Full-text available
The application of super-resolution optical microscopy to investigating synaptic structures has revealed a highly heterogeneous and variable intra-synaptic organization. Dense subsynaptic protein assemblies named subsynaptic domains or SSDs have been proposed as structural units that regulate the efficacy of neuronal transmission. However, an in-de...
Article
Full-text available
The efficacy of synaptic transmission is determined by the number of neurotransmitter receptors at synapses. Their recruitment depends upon the availability of postsynaptic scaffolding molecules that interact with specific binding sequences of the receptor. At inhibitory synapses, gephyrin is the major scaffold protein that mediates the accumulatio...
Article
Full-text available
Accumulation of glycine receptors at synapses requires the interaction between the beta subunit of the receptor and the scaffold protein gephyrin. Here, we questioned whether different alpha subunits could modulate the receptors’ diffusion and propensity to cluster at spinal cord synapses. Using quantitative photoactivated localisation microscopy w...
Article
Full-text available
The ability to count molecules is essential to elucidating cellular mechanisms, as these often depend on the absolute numbers and concentrations of molecules within specific compartments. Such is the case at chemical synapses, where the transmission of information from presynaptic to postsynaptic terminals requires complex interactions between smal...
Article
Full-text available
This paper presents Yellow Fluorescence-Activating and absorption-Shifting Tag (Y-FAST), a small monomeric protein tag, half as large as the green fluorescent protein, enabling fluorescent labeling of proteins in a reversible and specific manner through the reversible binding and activation of a cell-permeant and nontoxic fluorogenic ligand (a so-c...
Article
Full-text available
The dynamic exchange of neurotransmitter receptors at synapses relies on their lateral diffusion in the plasma membrane. At synapses located on dendritic spines this process is limited by the geometry of the spine neck that restricts the passage of membrane proteins. Biochemical compartmentalisation of the spine is believed to underlie the input-sp...
Data
Figure A. Distribution of lentivirus expressed dendra-SP. Figure B. SP distribution within the spine neck. Figure C. Overlapping localisation of mGluR5 and SP in dendritic spines. Figure D. Role of neck width and SP for membrane protein diffusion in the spine neck. Figure E. Organisation of the actin cytoskeleton in SP+ and SP- spines. Table A. Flu...
Article
Full-text available
Significance We developed a small protein tag enabling fluorescent labeling of proteins in living cells and in multicellular organisms through the specific binding and activation of a cell-permeant and nontoxic fluorogenic ligand. This tag, called Yellow Fluorescence-Activating and absorption-Shifting Tag (Y-FAST), was engineered by directed evolut...
Article
The scaffold protein gephyrin plays a critical regulatory role in the transmission of nerve signals in inhibitory synapses.. Its interactions with receptors of inhibitory neurotransmitters, such as glycine or GABA, are postulated to be a key molecular mechanism of synaptic formation and plasticity. Previous studies have shown that glycine receptors...
Article
Synapses, although seemingly stable, undergo constant rearrangements and exhibit a high level of dynamic movement as revealed by molecular imaging. This apparent biological paradox has emerged as a key element enabling synaptic plasticity. The development of super-resolution imaging combined with theoretical modelling has advanced our understanding...
Article
Development of the nervous system requires extensive axonal and dendritic growth during which neurons massively increase their surface area. Here we report that the endoplasmic reticulum (ER)-resident SNARE Sec22b has a conserved non-fusogenic function in plasma membrane expansion. Sec22b is closely apposed to the plasma membrane SNARE syntaxin1. S...
Article
There are many differences between what can be extracted from biomolecules motion using small numbers of long trajectories (Qdots, Nanoparticles, fluorophores) or large numbers of short, dense trajectories (PALM, uPaint, Storm). Long time recordings allow various estimators to converge towards mostly accurate values, but don't allow access to the s...
Article
Protein mobility is conventionally analyzed in terms of an effective diffusion. Yet, this description often fails to properly distinguish and evaluate the physical parameters (such as the membrane friction) and the biochemical interactions governing the motion. Here, we present a method combining high-density single-molecule imaging and statistical...
Chapter
Nanoscopic imaging techniques provide a powerful set of tools for static and dynamic fluorescence microscopy below the diffraction limit of light. Among these super-resolution techniques, photoactivated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM) are based on the detection of single fluorophores, whose si...
Article
Full-text available
The strength of synaptic transmission is controlled by the number and activity of neurotransmitter receptors. However, little is known about absolute numbers and densities of receptor and scaffold proteins and the stoichiometry of molecular interactions at synapses. Here, we conducted three-dimensional and quantitative nanoscopic imaging based on s...
Article
The movement of proteins in the cell membrane is governed by the local friction and their interactions with molecular partners. Yet, most experimental descriptions fail to unequivocally distinguish these effects; instead, they combine the diffusive and energetic contributions into an effective diffusion coefficient or anomalous exponent. Here, we s...
Article
Little is known about the origin, supply pattern and production technology of Byzantine glass mosaic tesserae. In this study, we have analysed forty-eight glass tesserae from Sagalassos (Asia Minor) of different colours and from two archaeological contexts that were stratigraphically dated to the sixth century CE. The main aim was to identify the r...
Article
Single-molecule tracking (SMT) experiments have shown that post-synaptic receptors (e.g. AMPA, NMDA, Glycine or GABA receptors) can be described as being in a dynamic equilibrium between free extrasynaptic diffusion and confined motion at synapses where they are transiently stabilized by molecular scaffolds. Although these experiments have been use...
Article
Full-text available
Localization of single molecules in microscopy images is a key step in quantitative single particle data analysis. Among them, single molecule based super-resolution optical microscopy techniques require high localization accuracy as well as computation of large data sets in the order of 10(5) single molecule detections to reconstruct a single imag...
Article
The structure of the centrosome was resolved by EM many years ago to reveal a pair of centrioles embedded in a dense network of proteins. More recently, the molecular composition of the centrosome was catalogued by mass spectroscopy and many novel components were identified. Determining precisely where a novel component localizes to within the cent...
Article
Full-text available
Glycine receptors (GlyRs) can dynamically exchange between synaptic and extrasynaptic locations through lateral diffusion within the plasma membrane. Their accumulation at inhibitory synapses depends on the interaction of the β-subunit of the GlyR with the synaptic scaffold protein gephyrin. An alteration of receptor-gephyrin binding could thus shi...
Article
SAP97 is a multidomain scaffold protein implicated in the forward trafficking and synaptic localization of NMDA- and AMPA-type glutamate receptors. Alternative splicing of SAP97 transcripts gives rise to palmitoylated αSAP97 and L27-domain containing βSAP97 isoforms that differentially regulate the subsynaptic localization of GluR1 subunits of AMPA...
Data
Sample images of dendritic protrusions, showing the morphological variety of spines described in [42], as seen by PALM imaging (A). In panel (B), neck length and width of dendritic spines show no correlation with the spine head diameter (for quantification see Fig. 2E). (TIF)
Data
Simultaneous PALM imaging and QD tracking. ABP-tdEosFP (top) and QD signals (bottom) were simultaneously imaged in a hippocampal neuron at DIV 27. The detected ABP-tdEosFP fluorophores were used to reconstruct the actin cytoskeleton of the dendritic spine (cumulative movie, middle panel); the QD trajectory (bottom) served to outline the shape of th...
Data
Pointillist representation of live PALM imaging of a dendritic segment of an immature hippocampal neuron (DIV 9) at time 0 (black points), 12 min (blue) and 25 min (red) under continuous illumination and recording. The 405 nm laser power was continuously adjusted to yield a constant number of single molecule events. The chosen time-window for image...
Data
Live PALM imaging of a dendritic segment of a mature hippocampal neuron (DIV 27) under baseline conditions. The total length of the movie is 12.5 minutes. Each PALM frame was reconstructed from 2000 image frames of 25 ms, hence the temporal resolution is 50 s. The movie is rendered with a temporal sliding window of a step of 2.5 s. The width of the...
Data
Live PALM imaging of a large dendritic segment of a mature hippocampal neuron (DIV 28), treated with 10 µM AMPA, as indicated in the movie. Movie rendered with a sliding window of 2000 frames of 25 ms ( = 50 s) and a step of 2.5 s. Field of view, 35 µm×16 µm. (AVI)
Data
Movie of an individual spine during 10 µM AMPA treatment (detail from Movie S3, see also Fig. 6). Field of view, 8 µm×5 µm. (AVI)
Article
Full-text available
The actin cytoskeleton of dendritic spines plays a key role in morphological aspects of synaptic plasticity. The detailed analysis of the spine structure and dynamics in live neurons, however, has been hampered by the diffraction-limited resolution of conventional fluorescence microscopy. The advent of nanoscopic imaging techniques thus holds great...
Article
Full-text available
https://www.the-scientist.com/?articles.view/articleNo/29252/title/Opinion--Mutations-of-citations/
Article
The transmission of signals across synapses requires the precise interaction of a large number of different synaptic proteins such as neurotransmitter receptors, adhesion, scaffold, signaling and cytoskeletal proteins. In small central excitatory synapses, this molecular machinery is contained in specialized cellular compartments called dendritic s...
Article
Full-text available
The NMDA receptor (NMDAR) subunit GluN1 is an obligatory component of NMDARs without a known functional homolog and is expressed in almost every neuronal cell type. The NMDAR system is a coincidence detector with critical roles in spatial learning and synaptic plasticity. Its coincidence detection property is crucial for the induction of hippocampa...
Article
Full-text available
Synaptic plasticity is dependent on the differential sorting, delivery and retention of neurotransmitter receptors, but the mechanisms underlying these processes are poorly understood. We found that differential sorting of glutamate receptor subtypes began in the endoplasmic reticulum of rat hippocampal neurons. As AMPA receptors (AMPARs) were traf...