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Nanomachinery Organizing Release at Neuronal and Ribbon Synapses

1,2,3,* and 1,2,3,4,5,*
1
Molecular Architecture of Synapses Group, Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37075 Göttingen, Germany
2
Center for Biostructural Imaging of Neurodegeneration, University Medical Center Göttingen, 37075 Göttingen, Germany
3
Collaborative Research Center 889 “Cellular Mechanisms of Sensory Processing”, 37099 Göttingen, Germany
4
Collaborative Research Center 1286 “Quantitative Synaptology”, 37099 Göttingen, Germany
5
Auditory Neuroscience Group, Max Planck Institute for Experimental Medicine, 37075 Göttingen, Germany
*
Authors to whom correspondence should be addressed.
Int. J. Mol. Sci. 2019, 20(9), 2147; https://doi.org/10.3390/ijms20092147
Received: 8 April 2019 / Revised: 26 April 2019 / Accepted: 26 April 2019 / Published: 30 April 2019
(This article belongs to the Special Issue Neurotransmitter Secretion and Release)
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Abstract

A critical aim in neuroscience is to obtain a comprehensive view of how regulated neurotransmission is achieved. Our current understanding of synapses relies mainly on data from electrophysiological recordings, imaging, and molecular biology. Based on these methodologies, proteins involved in a synaptic vesicle (SV) formation, mobility, and fusion at the active zone (AZ) membrane have been identified. In the last decade, electron tomography (ET) combined with a rapid freezing immobilization of neuronal samples opened a window for understanding the structural machinery with the highest spatial resolution in situ. ET provides significant insights into the molecular architecture of the AZ and the organelles within the presynaptic nerve terminal. The specialized sensory ribbon synapses exhibit a distinct architecture from neuronal synapses due to the presence of the electron-dense synaptic ribbon. However, both synapse types share the filamentous structures, also commonly termed as tethers that are proposed to contribute to different steps of SV recruitment and exocytosis. In this review, we discuss the emerging views on the role of filamentous structures in SV exocytosis gained from ultrastructural studies of excitatory, mainly central neuronal compared to ribbon-type synapses with a focus on inner hair cell (IHC) ribbon synapses. Moreover, we will speculate on the molecular entities that may be involved in filament formation and hence play a crucial role in the SV cycle. View Full-Text
Keywords: exocytosis; membrane fusion; synaptic vesicles; synaptic vesicle tethering; synaptic vesicle pools; active zone; release machinery; ribbon synapses; electron microscopy; electron tomography exocytosis; membrane fusion; synaptic vesicles; synaptic vesicle tethering; synaptic vesicle pools; active zone; release machinery; ribbon synapses; electron microscopy; electron tomography
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Chakrabarti, R.; Wichmann, C. Nanomachinery Organizing Release at Neuronal and Ribbon Synapses. Int. J. Mol. Sci. 2019, 20, 2147.

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