Vésicule synaptique

Les vésicules synaptiques sont de petits compartiments des terminaux présynaptiques des neurones, stockant des neurotransmetteurs qui sont susceptibles d'être libérés dans l'espace intersynaptique à la suite de l'arrivée d'un potentiel d'action dépolarisant et l'augmentation des niveaux calciques intracellulaires. Le nombre ou la taille du pool de vésicules synaptiques est variable selon le type de neurones considérés (quelques dizaines pour les petites synapses telles que celles trouvées dans l'hippocampe). Ils sont libérés dans cet espace intersynaptique par exocytose ; lorsque les vésicules contenant les neurotransmetteurs fusionnent avec la membrane présynaptique. Les neurotransmetteurs (glutamate, GABA, acétylcholine...) ainsi libérés diffusent dans l'espace intersynaptique et vont se lier aux récepteurs postsynaptiques et modifier localement le potentiel électrique ou l'état métabolique du neurone postsynaptique. Les vésicules synaptiques sont ensuite retrouvées par endocytose

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A conditional GABAergic synaptic vesicle marker for Drosophila

Brian Donal McCabe

Background: Throughout the animal kingdom, GABA is the principal inhibitory neurotransmitter of the nervous system. It is essential for maintaining the homeostatic balance between excitation and inhibition required for the brain to operate normally. Identification of GABAergic neurons and their GABA release sites are thus essential for understanding how the brain regulates the excitability of neurons and the activity of neural circuits responsible for numerous aspects of brain function including information processing, locomotion, learning, memory, and synaptic plasticity, among others. New method: Since the structure and features of GABA synapses are critical to understanding their function within specific neural circuits of interest, here we developed and characterized a conditional marker of GABAergic synaptic vesicles for Drosophila, 9XV5-vGAT. Results: 9XV5-vGAT is validated for conditionality of expression, specificity for localization to synaptic vesicles, specificity for expression in GABAergic neurons, and functionality. Its utility for GABAergic neurotransmitter phenotyping and identification of GABA release sites was verified for ellipsoid body neurons of the central complex. In combination with previously reported conditional SV markers for acetylcholine and glutamate, 9XV5-vGAT was used to demonstrate fast neurotransmitter phenotyping of subesophageal ganglion neurons. Comparison with existing methods: This method is an alternative to single cell transcriptomics for neurotransmitter phenotyping and can be applied to any neurons of interest represented by a binary transcription system driver. Conclusion: A conditional GABAergic synaptic vesicle marker has been developed and validated for GABA neurotransmitter phenotyping and subcellular localization of GABAergic synaptic vesicles.

2022

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Proteolytic processing of the synaptic cell adhesion molecule neurexin-3beta and the neurobiological functions of the resulting cleavage products

Magda Maria Palczynska

Neurexins are key synaptic cell adhesion molecules involved in synapse specification and maturation. They couple synaptic activity and cell adhesion to regulate activity-dependent synapse development. Recently, neurexin processing by alpha- and gamma- secretases has been reported. In the present study, we characterized the sites at which Nrxn3beta is processed by alpha- and gamma- secretases, identified the enzymes responsible for the shedding, characterised the fragments resulting from the cleavage and investigated the potential functions of generated fragments. We show that Nrxn3beta is shed at two sites- one processed by ADAM17, the other by ADAM10. The shedding generates two soluble ectodomain (sNrxn3beta) fragments and two C-terminal fragments (CTFs). Each CTF is further processed by gamma-secretase to generate one intracellular domain (ICD) and multiple P3-like or Abeta-like fragments. We show that the production of the main sNrxn3beta generated by ADAM10 affects axonal bouton development and spinogenesis during adult newborn neuron development in vivo. Moreover, we demonstrate that sNrxn3beta affects the expression of genes associated with regulation of synaptic vesicle exocytosis (Rab3a), NMDA receptor subunit composition (Grin2c) and metalloprotease inhibition (TIMP-1). Furthermore, we report first evidence that the ICD generation might influence the levels of a protein responsible for the NMDA delivery to dendritic sites (KIF17). The investigation of properties of neurexin P3-like and Abeta-like fragments revealed a tendency of Abeta-like fragments to form oligomers and exert a toxic effect in primary cortical neurons. Our study shed light on the molecular pathways regulated by neurexin cleavage fragments and their possible implications in different pathologies.

EPFL2016

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Generation and Characterization of Anti-VGLUT Nanobodies Acting as Inhibitors of Transport

Andrea Volterra

The uptake of glutamate by synaptic vesicles is mediated by vesicular glutamate transporters (VGLUTs). The central role of these transporters in excitatory neurotransmission underpins their importance as pharmacological targets. Although several compounds inhibit VGLUTs, highly specific inhibitors were so far unavailable, thus limiting applications to in vitro experiments. Besides their potential in pharmacology, specific inhibitors would also be beneficial for the elucidation of transport mechanisms. To overcome this shortage, we generated nanobodies (Nbs) by immunization of a llama with purified rat VGLUT1 and subsequent selection of binders from a phage display library. All identified Nbs recognize cytosolic epitopes, and two of the binders greatly reduced the rate of uptake of glutamate by reconstituted liposomes and subcellular fractions enriched with synaptic vesicles. These Nbs can be expressed as functional green fluorescent protein fusion proteins in the cytosol of HEK cells for intracellular applications as immunocytochemical and biochemical agents. The selected binders thus provide valuable tools for cell biology and neuroscience.

Amer Chemical Soc2017

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Neurotransmetteur

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Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to

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thumb|537x537px|Schéma complet d’un neurone. Un neurone, ou une cellule nerveuse, est une cellule excitable constituant l'unité fonctionnelle de la base du système nerveux. Les neurones assurent la

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