title: Subunit determination of the conductance of hair-cell mechanotransducer channels.
abstract: Cochlear hair cells convert sound stimuli into electrical signals by gating of mechanically sensitive ion channels in their stereociliary (hair) bundle. The molecular identity of this ion channel is still unclear, but its properties are modulated by accessory proteins. Two such proteins are transmembrane channel-like protein isoform 1 (TMC1) and tetraspan membrane protein of hair cell stereocilia (TMHS, also known as lipoma HMGIC fusion partner-like 5, LHFPL5), both thought to be integral components of the mechanotransduction machinery. Here we show that, in mice harboring an Lhfpl5 null mutation, the unitary conductance of outer hair cell mechanotransducer (MT) channels was reduced relative to wild type, and the tonotopic gradient in conductance, where channels from the cochlear base are nearly twice as conducting as those at the apex, was almost absent. The macroscopic MT current in these mutants was attenuated and the tonotopic gradient in amplitude was also lost, although the current was not completely extinguished. The consequences of Lhfpl5 mutation mirror those due to Tmc1 mutation, suggesting a part of the MT-channel conferring a large and tonotopically variable conductance is similarly disrupted in the absence of Lhfpl5 or Tmc1. Immunolabelling demonstrated TMC1 throughout the stereociliary bundles in wild type but not in Lhfpl5 mutants, implying the channel effect of Lhfpl5 mutations stems from down-regulation of TMC1. Both LHFPL5 and TMC1 were shown to interact with protocadherin-15, a component of the tip link, which applies force to the MT channel. We propose that titration of the TMC1 content of the MT channel sets the gradient in unitary conductance along the cochlea.
authors.affiliation: Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706; and.
authors.forename: Maryline
authors.initials: M
authors.lastname: Beurg
authors.affiliation: Department of Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Wei
authors.initials: W
authors.lastname: Xiong
authors.affiliation: Department of Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhao
authors.affiliation: Department of Molecular and Cellular Neuroscience, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Müller
authors.affiliation: Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706; and fettiplace@wisc.edu.
authors.forename: Robert
authors.initials: R
authors.lastname: Fettiplace
mesh_terms: D000818:Animals; D005260:Female; D006198:Hair Cells, Auditory / Q000502:physiology*; D008297:Male; D040542:Mechanotransduction, Cellular; D051379:Mice; D018345:Mice, Knockout
keywords: LHFPL5; TMC1; cochlea; hair cell; mechanotransducer channels