Abstract
Hearing relies on faithful synaptic transmission at the ribbon synapse of cochlear inner hair cells (IHCs)1,2,3. At present, the function of presynaptic ribbons at these synapses is still largely unknown1,4. Here we show that anchoring of IHC ribbons is impaired in mouse mutants for the presynaptic scaffolding protein Bassoon. The lack of active-zone-anchored synaptic ribbons reduced the presynaptic readily releasable vesicle pool, and impaired synchronous auditory signalling as revealed by recordings of exocytic IHC capacitance changes and sound-evoked activation of spiral ganglion neurons. Both exocytosis of the hair cell releasable vesicle pool and the number of synchronously activated spiral ganglion neurons co-varied with the number of anchored ribbons during development. Interestingly, ribbon-deficient IHCs were still capable of sustained exocytosis with normal Ca2+-dependence. Endocytic membrane retrieval was intact, but an accumulation of tubular and cisternal membrane profiles was observed in ribbon-deficient IHCs. We conclude that ribbon-dependent synchronous release of multiple vesicles at the hair cell afferent synapse is essential for normal hearing.
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Acknowledgements
We would like to thank A. Brandt and A. Schoenle for providing custom analysis software; S. Anderson and S. Lacas-Gervais for help in setting up auditory physiology and immunohistochemistry in the InnerEarLab, respectively; and J. H. Brandstaetter, F. Wolf and S. W. Hell for discussions and suggestions; members of the InnerEarLab for counting of spots and discussion; E. Neher, T. Sakaba, L. Lagnado, C. Kubisch, M. C. Liberman and E. Livesey for comments on the manuscript; F. Kirchhoff and M. Lenoir for help with confocal and electron microscopy, respectively; and M. Köppler, F. Tribillac and C. Cazevieille for technical assistance. We would like to thank M. Eybalin for initial collaboration. This work was supported by grants from the Deutsche Forschungsgemeinschaft to T.M. and to E.D.G., by a Tandem-Project of the Max Planck Society (to E. Neher and T.M.), a Human Frontiers in Science Program grant to T.M., a grant from the Fonds der Chemischen Industrie to E.D.G, and a grant from Acouphènes-Languedoc-Roussillon to J.-L. Puel.
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Supplementary information
Supplementary Figure S1
This file contains images that support the morphological results of this study. (DOC 518 kb)
Supplementary Figure S2
This file presents recordings of sound-evoked cochlear potentials and otoacoustic emissions. (DOC 370 kb)
Supplementary Figure S3
This file details the hair cell physiology of the mice used in the study. (DOC 803 kb)
Supplementary Table S1
This details the quantification of our light and electron microscopy of WT and mutant synapses and relates morphological findings to physiology. (DOC 54 kb)
Supplementary Movie S1a
This movie displays an animated 3D-reconstruction of a WT organ of Corti to illustrate the quantitative confocal synapse analysis. We counted 68 GluR spots (red) and 64 ribbon-containing synapses (juxtaposed red GluR and green RIBEYE spots) in 6 IHCs (green nuclei). (MPG 561 kb)
Supplementary Movie S1b
This movie displays an animated 3D-reconstruction of a mutant organ of Corti, where we counted 53 GluR spots and 12 ribbon-containing synapses in 7 IHCs. (MPG 561 kb)
Supplementary Methods
This file describes additional methods used in this study, including the 4Pi microscopy and model of size distribution. (DOC 23 kb)
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Khimich, D., Nouvian, R., Pujol, R. et al. Hair cell synaptic ribbons are essential for synchronous auditory signalling. Nature 434, 889–894 (2005). https://doi.org/10.1038/nature03418
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DOI: https://doi.org/10.1038/nature03418