The presynaptic ribbon maintains vesicle populations at the hair cell afferent fiber synapse
- Stanford University, United States
- National Institute of Deafness and Communicative Disorders, United States
- University of the Saarland, Germany
- Washington University at St. Louis, United States
Abstract
The ribbon is the structural hallmark of cochlear inner hair cell (IHC) afferent synapses, yet its role in information transfer to spiral ganglion neurons (SGNs) remains unclear. We investigated the ribbon's contribution to IHC synapse formation and function using KO mice lacking RIBEYE. Despite loss of the entire ribbon structure, synapses retained their spatiotemporal development and KO mice had a mild hearing deficit. IHCs of KO had fewer synaptic vesicles and reduced exocytosis in response to brief depolarization; high stimulus level rescued exocytosis in KO. SGNs exhibited a lack of sustained excitatory postsynaptic currents (EPSCs). We observed larger postsynaptic glutamate receptor plaques, potentially in compensation for the reduced EPSC rate in KO. Surprisingly, large amplitude EPSCs were maintained in KO, while a small population of low amplitude slower EPSCs was increased in number. The ribbon facilitates signal transduction at physiological stimulus levels by retaining a larger residency pool of synaptic vesicles.
Article and author information
Author details
Funding
National Institutes of Health (DC009913)
- Anthony J Ricci
Action on Hearing Loss
- Mark A Rutherford
National Institutes of Health (DC014712)
- Mark A Rutherford
National Institutes of Health (DC013721)
- Mamiko Niwa
National Institutes of Health (P30 44992)
- Anthony J Ricci
National Institutes of Health (Z01-DC000002)
- Willy Sun
- Bechara Kachar
National Institutes of Health (ZIC DC000081)
- Willy Sun
- Bechara Kachar
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved institutional animal care and use committee (IACUC) protocol 14345 of Stanford University. The protocol was approved by the Committee on the Ethics of Animal Experiments of the University of Minnesota. All auditory measurements were performed under Ketamine (100mg/kg) and Xylazine,(10mg/kg) and every effort was made to minimize suffering.
Copyright
This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
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The presynaptic ribbon maintains vesicle populations at the hair cell afferent fiber synapse
eLife 7:e30241.
https://doi.org/10.7554/eLife.30241
Further reading
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- Neuroscience
By influencing calcium homeostasis, local protein synthesis and the endoplasmic reticulum, a small protein called Rab10 emerges as a crucial cytoplasmic regulator of neuropeptide secretion.
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- Neuroscience
Dense core vesicles (DCVs) transport and release various neuropeptides and neurotrophins that control diverse brain functions, but the DCV secretory pathway remains poorly understood. Here, we tested a prediction emerging from invertebrate studies about the crucial role of the intracellular trafficking GTPase Rab10, by assessing DCV exocytosis at single-cell resolution upon acute Rab10 depletion in mature mouse hippocampal neurons, to circumvent potential confounding effects of Rab10’s established role in neurite outgrowth. We observed a significant inhibition of DCV exocytosis in Rab10-depleted neurons, whereas synaptic vesicle exocytosis was unaffected. However, rather than a direct involvement in DCV trafficking, this effect was attributed to two ER-dependent processes, ER-regulated intracellular Ca2+ dynamics, and protein synthesis. Gene Ontology analysis of differentially expressed proteins upon Rab10 depletion identified substantial alterations in synaptic and ER/ribosomal proteins, including the Ca2+ pump SERCA2. In addition, ER morphology and dynamics were altered, ER Ca2+ levels were depleted, and Ca2+ homeostasis was impaired in Rab10-depleted neurons. However, Ca2+ entry using a Ca2+ ionophore still triggered less DCV exocytosis. Instead, leucine supplementation, which enhances protein synthesis, largely rescued DCV exocytosis deficiency. We conclude that Rab10 is required for neuropeptide release by maintaining Ca2+ dynamics and regulating protein synthesis. Furthermore, DCV exocytosis appeared more dependent on (acute) protein synthesis than synaptic vesicle exocytosis.
