title: Absence of Neuroplastin-65 Affects Synaptogenesis in Mouse Inner Hair Cells and Causes Profound Hearing Loss.
abstract: The Neuroplastin gene encodes two synapse-enriched protein isoforms, Np55 and Np65, which are transmembrane glycoproteins that regulate several cellular processes, including the genesis, maintenance, and plasticity of synapses. We found that an absence of Np65 causes early-onset sensorineural hearing loss and prevented the normal synaptogenesis in inner hair cells (IHCs) in the newly identified mouse mutant pitch. In wild-type mice, Np65 is strongly upregulated in the cochlea from around postnatal day 12 (P12), which corresponds to the onset of hearing. Np65 was specifically localized at the presynaptic region of IHCs. We found that the colocalization of presynaptic IHC ribbons and postsynaptic afferent terminals is greatly reduced in pitch mutants. Moreover, IHC exocytosis is also reduced with mutant mice showing lower rates of vesicle release. Np65 appears to have a nonessential role in vision. We propose that Np65, by regulating IHC synaptogenesis, is critical for auditory function in mammals.
  
  
  CONCLUSIONS
  In the mammalian cochlea, the sensory inner hair cells (IHCs) encode auditory information. They do this by converting sound wave-induced mechanical motion of their hair bundles into an electrical current. This current generates a receptor potential that controls release of glutamate neurotransmitter from their ribbon synapses onto the auditory afferent fiber. We show that the synapse-enriched protein Np65, encoded by the Neuroplastin gene, is localized at the IHC presynaptic region. In mutant mice, absence of Np65 causes early-onset sensorineural hearing loss and prevents normal neurotransmitter release in IHCs and colocalization of presynaptic ribbons with postsynaptic afferents. We identified Neuroplastin as a novel deafness gene required for ribbon synapse formation and function, which is critical for sound perception in mammals.
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Leanne
authors.initials: L
authors.lastname: Carrott
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom, m.bowl@har.mrc.ac.uk s.brown@har.mrc.ac.uk.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bowl
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Carlos
authors.initials: C
authors.lastname: Aguilar
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Johnson
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Lauren
authors.initials: L
authors.lastname: Chessum
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Melissa
authors.initials: M
authors.lastname: West
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Susan
authors.initials: S
authors.lastname: Morse
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Joanne
authors.initials: J
authors.lastname: Dorning
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Smart
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Rachel
authors.initials: R
authors.lastname: Hardisty-Hughes
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Greg
authors.initials: G
authors.lastname: Ball
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Andrew
authors.initials: A
authors.lastname: Parker
authors.affiliation: Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, United Kingdom, and.
authors.forename: Alun R
authors.identifier: http://orcid.org/0000-0002-0662-1073
authors.initials: AR
authors.lastname: Barnard
authors.affiliation: Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, United Kingdom, and.
authors.forename: Robert E
authors.initials: RE
authors.lastname: MacLaren
authors.affiliation: Mary Lyon Centre, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom.
authors.forename: Sara
authors.initials: S
authors.lastname: Wells
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom.
authors.forename: Walter
authors.initials: W
authors.lastname: Marcotti
authors.affiliation: Mammalian Genetics Unit, Medical Research Council Harwell, Harwell Campus, Oxfordshire OX11 0RD, United Kingdom, m.bowl@har.mrc.ac.uk s.brown@har.mrc.ac.uk.
authors.forename: Steve D M
authors.initials: SD
authors.lastname: Brown
mesh_terms: D000818:Animals; D003638:Deafness / Q000503:physiopathology*; D005260:Female; D006199:Hair Cells, Auditory, Inner / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D055495:Neurogenesis; D013569:Synapses / Q000378:metabolism* / Q000473:pathology*
chemical_list: D008562:Membrane Glycoproteins; C577174:neuroplastin protein, mouse
keywords: exocytosis; hearing loss; inner hair cell; neuroplastin; ribbon synapse; synaptogenesis