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Section MOLECULAR NEUROSCIENCE
Post-Translational Control of Vesicular Release by NO
Julie-Myrtille Bourgognon* and Joern Steinert
MRC Toxicology Unit, UK. * Presenting e-mail: [email protected]
Nitric oxide (NO) signalling is implicated in several neurodegenerative diseases through induction of high NO release. However, its exact contribution to degeneration remains elusive due to the complexity of downstream nitrergic targets. High levels of NO can induce post-translational modifications which are associated with neuronal degeneration 1,2. NO reacts with superoxide anions to form cytotoxic peroxynitrite which in turn leads to 3-Nitrotyrosination with largely detrimental changes in protein function. Additionally, NO signalling alters protein function through S-nitrosylation To date, little is known as to what extent these post-translational modifications contribute to or exacerbate neuronal dysfunction. We use glutamatergic synapses as a model system to identify novel nitrergic signalling pathways to correlate protein modifications with functional changes.
The Drosophila neuromuscular junction was used to characterise nitrergic effects employing electrophysiological methods. Two-electrode-voltage-clamp (TEVC) analyses were carried out in HL-3 solution using sharp electrodes (20-30MQ). Data denote mean±SEM (n-number) with *p<0.05 indicating statistical significance (t-test, ANOVA). Evoked excitatory junctional currents (eEJC) amplitudes and quantal content (QC) were strongly reduced following NO exposure for >40min (eEJC: Ctrl: 119±7nA (22) vs NO: 62±8nA* (14); QC: Ctrl: 189±12 vs NO: 104±12*) suggesting a reduction in presynaptic release. Cumulative postsynaptic current analysis (500ms 50Hz train) further showed a reduced number of release-ready vesicles following NO exposure (Ctrl: 276±21 (22) vs NO: 108±19* (14)). Fluctuation analysis estimating the number of available release sites further confirmed a strong reduction under NO conditions. The above NO effects were detected following inhibition of the soluble guanylyl cyclase (sGC) and absent in the presence of N-ethylmaleimide which prevents the formation of S-nitrosothiols suggesting that NO modulates release via post-translational modifications. This interpretation is also supported by the findings that nitric oxide synthase (NOS) KO NMJs showed a strongly enhanced synaptic release and larger available vesicle pools. Importantly, enhancing presynaptic S-Nitrosoglutathione reductase (GSNOR) or glutamate-cysteine ligase (GCLC) enzyme activities, by overexpression (OE), prevented the above nitrergic effects. Both pathways favour denitrosylation by reducing S-nitro-sothiols and elevating cellular glutathione, respectively.
Together, our data suggest that NO can modify synaptic signalling possibly via inducing post-translational protein modifications. This data interpretation is supported by the notion that sGC inhibition is ineffective but modulation of neuronal nitrosylation pathways impacts on synaptic physiology implying presynaptic actions of NO in a sGC-in-dependent manner. The data extends our understanding of NO signalling, potentially leading to the identification of putative targets disease.
Acknowledgements
This study was funded by the MRC (JS) and The Henry Smith Charity (JB). References
1. Steinert, J. R., Chernova, T. & Forsythe, I. D. The Neuroscientist 16, 435-52, (2010).
2. Nakamura, T. et al. Neurobiology of disease, (2015).
Dynamic Control of Neural Progenitor Fates in the Developing Neocortex
Debra Silver*
Duke University School of Medicine, USA. * Presenting e-mail: [email protected]
Our laboratory studies neurogenesis, the process whereby neural progenitors generate neurons of the cerebral cortex during embryonic development. Our long-term objective is to help broaden our fundamental understanding of how the brain is built, how stem cells behave, and the etiology of neurodevelopmental diseases. The lab employs genetic,
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Section MOLECULAR NEUROSCIENCE
genomic, and cell biological tools including mouse genetics and live imaging. One major research direction focuses on post-transcriptional RNA regulation in neural progenitor behavior and function. A second research focus is aimed at understanding how human-specific enhancers contribute to unique features of human brain development, including progenitor proliferation. This seminar will discuss new discoveries from our lab including how mitosis impacts progenitor cell fate specification in the developing brain, and layers of dynamic RNA regulation in neural progenitors.
Becoming a New Neuron in the Cerebral Cortex
Denis Jabaudon*
Dpt. of Basic Neuroscience, University of Geneva, Switeerland. * Presenting e-mail: [email protected]
During neocortical development, excitatory neurons are born in the ventricular zone and migrate to the cortex, where they form the circuits that underlie mammalian skilled processing abilities. While the genetic programs that specify distinct subtypes of neurons within the neocortex are increasingly understood, how neuronal identity is dynamically acquired upon progenitor division is largely unknown. Identifying these primordial transcriptional processes is critical to understand how progenitor behavior is coupled to neuronal fate, and to provide mechanical insights into postmitotic neuron plasticity. Here, we will discuss recent findings from our laboratory on the mitotic and early-postmitotic biology of progenitors and their daughter cells, and how they inform neuronal specification and circuit assembly in the developing neocortex.
Dynamic Control of Neural Stem Cells
Ryoichiro Kageyama*
Institute for Virus Research; WPI-iCeMS, Kyoto University, Kyoto 606-8507, Japan. * Presenting e-mail: [email protected]
During brain development, neural stem cells gradually change their competency, giving rise to various types of neurons first and glial cells later. It is thus very important to maintain neural stem cells until the final stage of development to generate a full diversity of cell types. The basic helix-loop-helix (bHLH) factor Hesl plays an important role in maintenance of neural stem cells by repressing proneural gene expression. We found that the Hes1 expression oscillates by negative feedback, and that this oscillation is important for proliferation of neural stem cells, as sustained Hes1 expression inhibits proliferation of these cells. Hes1 oscillation drives the cyclic expression of proneural factors such as Asd1/Mash1. During neuronal differentiation, Hes1 expression disappears and proneural factor expression becomes sustained. By contrast, during astrocyte differentiation, Hes1 expression becomes dominant while proneural factor expression disappears. These results suggest that the multipotency is a state controlled by multiple oscillating fate-determination factors such as Hes1 and Asd1/Mash1, and that one of them becomes dominant during fate choice. We further showed by optogenetic approach that sustained expression of Asd1/Mash1 promotes neuronal differentiation, whereas oscillatory expression of Ascl1/Mash1 activates proliferation of neural stem cells, suggesting that the expression dynamics is important for the function of fate-determination factors. We also found that the Notch ligand Delta-like1 (Dll1), a downstream of Ascl1/ Mashl and Hesl, is expressed in an oscillatory manner, and that this oscillation is important for Hesl oscillation and proliferation of neural stem cells. These results indicate that the oscillatory expression of these factors in neural stem cells is essential for neural development.
Evolution of Cortical Development
A. Goffinet*
Université catholique de Louvain, Belgium. * Presenting e-mail: [email protected]
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