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thumb|300px|Neurone A (transmetteur) vers neurone B (récepteur)1. Mitochondrie 2. vésicule synaptique avec neurotransmetteurs 3. Autorécepteur 4. Synapse libérant des neurotransmetteurs (sérotonine) 5. Récepteurs postsynaptiques activés par des neurotransmetteurs (induction d'un potentiel postsynaptique ) 6. Canaux calcium 7. Exocytose de vésicules 8. Neurotransmetteur recapturé L'exocytose (du grec -exo "hors de" et de -kutos "cavité, cellule") est le mécanisme par lequel la cellule libère de grandes biomolécules à travers sa membrane. L’exocytose a lieu quand des vésicules de transport ou de sécrétion fusionnent avec la membrane plasmique et que leur contenu sort dans le milieu extracellulaire. Exemple : expulsion des neuromédiateurs des vésicules synaptiques vers le milieu extracellulaire. C'est un mécanisme par lequel une cellule libère du matériel, contenu dans des compartiments membranaires intracellulaires, qu'elle a synthétisé. Les rôles

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En biologie cellulaire, une vésicule cytoplasmique est un organite relativement petit, séparé du cytosol par au moins une bicouche lipidique (similaire à la membrane cytoplasmique). Elle fait partie

Les neurotransmetteurs, ou neuromédiateurs, sont des composés chimiques libérés par les neurones (et parfois par les cellules gliales) agissant sur d'autres neurones, appelés neurones postsynaptiques,

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

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Control of Exocytosis by Synaptotagmins and Otoferlin in Auditory Hair Cells

Ralf Schneggenburger

In pre-hearing mice, vesicle exocytosis at cochlear inner hair cell (IHC) ribbon synapses is triggered by spontaneous Ca2+ spikes. At the onset of hearing, IHC exocytosis is then exclusively driven by graded potentials, and is characterized by higher Ca2+ efficiency and improved synchronization of vesicular release. The molecular players involved in this transition are still unknown. Here we addressed the involvement of synaptotagmins and otoferlin as putative Ca2+ sensors in IHC exocytosis during postnatal maturation of the cochlea. Using cell capacitance measurements, we showed that Ca2+-evoked exocytosis in mouse IHCs switches from an otoferlin-independent to an otoferlin-dependent mechanism at postnatal day 4. During this early exocytotic period, several synaptotagmins (Syts), including Syt1, Syt2 and Syt7, were detected in IHCs. The exocytotic response as well as the release of the readily releasable vesicle pool (RRP) was, however, unchanged in newborn mutant mice lacking Syt1, Syt2 or Syt7 (Syt1(-/-), Syt2(-/-) and Syt7(-/-) mice). We only found a defect in RRP recovery in Syt1(-/-) mice which was apparent as a strongly reduced response to repetitive stimulations. In post-hearing Syt2(-/-) and Syt7(-/-) mutant mice, IHC synaptic exocytosis was unaffected. The transient expression of Syt1 and Syt2, which were no longer detected in IHCs after the onset of hearing, indicates that these two most common Ca2+-sensors in CNS synapses are not involved in mature IHCs. We suggest that otoferlin underlies highly efficient Ca2+-dependent membrane-membrane fusion, a process likely essential to increase the probability and synchrony of vesicle fusion events at the mature IHC ribbon synapse.

Society for Neuroscience2010

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Reticulon 1-C/neuroendocrine-specific protein-C interacts with SNARE proteins

Liliane Glauser, Harald Hirling, Karina Kulangara, Juan-Carlos Sarria, Pascal Steiner

Reticulons are proteins of neuroendocrine cells localized primarily to the endoplasmic reticulum membrane. Despite their implication in cellular processes like apoptosis or axonal regeneration, their intracellular molecular function is still largely unknown. Here, we show that reticulon 1-C can be detected in a protein complex of 150-200 kDa, and that a number of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, i.e. syntaxin 1, syntaxin 7, syntaxin 13 and VAMP2, can be co-immunoprecipitated with reticulon 1-C. Moreover, it localizes to a nocodazole-sensitive, but calreticulin-negative domain of the endoplasmic reticulum. Finally, overexpression in PC12 cells of a reticulon 1-C fragment which binds to SNAREs, significantly enhances human growth hormone secretion. These results suggest that reticulons are involved in vesicle trafficking events, including regulated exocytosis.

2004

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Functional interactions between anthrax toxin receptors and the WNT signalling protein LRP6

Julie Deuquet Ariosa, Laurence Gouzi Abrami, Béatrice Kunz, Françoise Gisou van der Goot Grunberg

To exert its activity, anthrax toxin must be endocytosed and its enzymatic toxic subunits delivered to the cytoplasm. It has been proposed that, in addition to the anthrax toxin receptors (ATRs), lipoprotein-receptor-related protein 6 (LRP6), known for its role in Wnt signalling, is also required for toxin endocytosis. These findings have however been challenged. We show that LRP6 can indeed form a complex with ATRs, and that this interaction plays a role both in Wnt signalling and in anthrax toxin endocytosis. We found that ATRs control the levels of LRP6 in cells, and thus the Wnt signalling capacity. RNAi against ATRs indeed led to a drastic decrease in LRP6 levels and a subsequent drop in Wnt signalling. Conversely, LRP6 plays a role in anthrax toxin endocytosis, but is not essential. We indeed found that toxin binding triggered tyrosine phosphorylation of LRP6, induced its redistribution into detergent-resistant domains, and its subsequent endocytosis. RNAis against LRP6 strongly delayed toxin endocytosis. As the physiological role of ATRs is probably to interact with the extracellular matrix, our findings raise the interesting possibility that, through the ATR-LRP6 interaction, adhesion to the extracellular matrix could locally control Wnt signalling.

2008

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