References of "Toonen, Ruud F"
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See detailPresynaptic inhibition upon CB1 or mGlu2/3 receptor activation requires ERK/MAPK phosphorylation of Munc18-1.
Schmitz, Sabine UL; King, Cillian; Kortleven, Christian et al

in The EMBO journal (2016)

Presynaptic cannabinoid (CB1R) and metabotropic glutamate receptors (mGluR2/3) regulate synaptic strength by inhibiting secretion. Here, we reveal a presynaptic inhibitory pathway activated by ... [more ▼]

Presynaptic cannabinoid (CB1R) and metabotropic glutamate receptors (mGluR2/3) regulate synaptic strength by inhibiting secretion. Here, we reveal a presynaptic inhibitory pathway activated by extracellular signal-regulated kinase (ERK) that mediatesCB1R- andmGluR2/3-induced secretion inhibition. This pathway is triggered by a variety of events, from foot shock-induced stress to intense neuronal activity, and induces phosphorylation of the presynaptic protein Munc18-1. Mimicking constitutive phosphorylation of Munc18-1 results in a drastic decrease in synaptic transmission.ERK-mediated phosphorylation of Munc18-1 ultimately leads to degradation by the ubiquitin-proteasome system. Conversely, preventingERK-dependent Munc18-1 phosphorylation increases synaptic strength.CB1R- andmGluR2/3-induced synaptic inhibition and depolarization-induced suppression of excitation (DSE) are reduced uponERK/MEKpathway inhibition and further reduced whenERK-dependent Munc18-1 phosphorylation is blocked. Thus,ERK-dependent Munc18-1 phosphorylation provides a major negative feedback loop to control synaptic strength upon activation of presynaptic receptors and during intense neuronal activity. [less ▲]

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See detailLiprin-alpha2 promotes the presynaptic recruitment and turnover of RIM1/CASK to facilitate synaptic transmission.
Spangler, Samantha A.; Schmitz, Sabine UL; Kevenaar, Josta T. et al

in The Journal of cell biology (2013), 201(6), 915-28

The presynaptic active zone mediates synaptic vesicle exocytosis, and modulation of its molecular composition is important for many types of synaptic plasticity. Here, we identify synaptic scaffold ... [more ▼]

The presynaptic active zone mediates synaptic vesicle exocytosis, and modulation of its molecular composition is important for many types of synaptic plasticity. Here, we identify synaptic scaffold protein liprin-alpha2 as a key organizer in this process. We show that liprin-alpha2 levels were regulated by synaptic activity and the ubiquitin-proteasome system. Furthermore, liprin-alpha2 organized presynaptic ultrastructure and controlled synaptic output by regulating synaptic vesicle pool size. The presence of liprin-alpha2 at presynaptic sites did not depend on other active zone scaffolding proteins but was critical for recruitment of several components of the release machinery, including RIM1 and CASK. Fluorescence recovery after photobleaching showed that depletion of liprin-alpha2 resulted in reduced turnover of RIM1 and CASK at presynaptic terminals, suggesting that liprin-alpha2 promotes dynamic scaffolding for molecular complexes that facilitate synaptic vesicle release. Therefore, liprin-alpha2 plays an important role in maintaining active zone dynamics to modulate synaptic efficacy in response to changes in network activity. [less ▲]

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See detailMunc13 controls the location and efficiency of dense-core vesicle release in neurons.
van de Bospoort, Rhea; Farina, Margherita; Schmitz, Sabine UL et al

in The Journal of cell biology (2012), 199(6), 883-91

Neuronal dense-core vesicles (DCVs) contain diverse cargo crucial for brain development and function, but the mechanisms that control their release are largely unknown. We quantified activity-dependent ... [more ▼]

Neuronal dense-core vesicles (DCVs) contain diverse cargo crucial for brain development and function, but the mechanisms that control their release are largely unknown. We quantified activity-dependent DCV release in hippocampal neurons at single vesicle resolution. DCVs fused preferentially at synaptic terminals. DCVs also fused at extrasynaptic sites but only after prolonged stimulation. In munc13-1/2-null mutant neurons, synaptic DCV release was reduced but not abolished, and synaptic preference was lost. The remaining fusion required prolonged stimulation, similar to extrasynaptic fusion in wild-type neurons. Conversely, Munc13-1 overexpression (M13OE) promoted extrasynaptic DCV release, also without prolonged stimulation. Thus, Munc13-1/2 facilitate DCV fusion but, unlike for synaptic vesicles, are not essential for DCV release, and M13OE is sufficient to produce efficient DCV release extrasynaptically. [less ▲]

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See detailAutomated analysis of neuronal morphology, synapse number and synaptic recruitment.
Schmitz, Sabine UL; Hjorth, J. J. Johannes; Joemai, Raoul M. S. et al

in Journal of neuroscience methods (2011), 195(2), 185-93

The shape, structure and connectivity of nerve cells are important aspects of neuronal function. Genetic and epigenetic factors that alter neuronal morphology or synaptic localization of pre- and post ... [more ▼]

The shape, structure and connectivity of nerve cells are important aspects of neuronal function. Genetic and epigenetic factors that alter neuronal morphology or synaptic localization of pre- and post-synaptic proteins contribute significantly to neuronal output and may underlie clinical states. To assess the impact of individual genes and disease-causing mutations on neuronal morphology, reliable methods are needed. Unfortunately, manual analysis of immuno-fluorescence images of neurons to quantify neuronal shape and synapse number, size and distribution is labor-intensive, time-consuming and subject to human bias and error. We have developed an automated image analysis routine using steerable filters and deconvolutions to automatically analyze dendrite and synapse characteristics in immuno-fluorescence images. Our approach reports dendrite morphology, synapse size and number but also synaptic vesicle density and synaptic accumulation of proteins as a function of distance from the soma as consistent as expert observers while reducing analysis time considerably. In addition, the routine can be used to detect and quantify a wide range of neuronal organelles and is capable of batch analysis of a large number of images enabling high-throughput analysis. [less ▲]

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