title: Myosin VIIa and sans localization at stereocilia upper tip-link density implicates these Usher syndrome proteins in mechanotransduction.
abstract: In the most accepted model for hair cell mechanotransduction, a cluster of myosin motors located at the stereocilia upper tip-link density (UTLD) keeps the tip-link under tension at rest. Both myosin VIIa (MYO7A) and myosin 1c have been implicated in mechanotransduction based on functional studies. However, localization studies are conflicting, leaving open the question of which myosin localizes at the UTLD and generates the tip-link resting tension. Using immunofluorescence, we now show that MYO7A and sans, a MYO7A-interacting protein, cluster at the UTLD. Analysis of the immunofluorescence intensity indicates that eight or more MYO7A molecules are present at each UTLD, consistent with a direct role for MYO7A in maintaining tip-link tension. MYO7A and sans localization at the UTLD is confirmed by transfection of hair cells with GFP-tagged constructs for these proteins. Cotransfection studies in a heterologous system show that MYO7A, sans, and the UTLD protein harmonin-b form a tripartite complex and that each protein is capable of interacting with one another independently. We propose that MYO7A, sans, and harmonin-b form the core components of the UTLD molecular complex. In this complex, MYO7A is likely the motor element that pulls on CDH23 to exert tension on the tip-link.
authors.affiliation: Laboratory of Cell Structure and Dynamics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: M'hamed
authors.initials: M
authors.lastname: Grati
authors.forename: Bechara
authors.initials: B
authors.lastname: Kachar
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins; D002522:Chlorocebus aethiops; D002923:Cilia / Q000378:metabolism* / Q000648:ultrastructure; D003598:Cytoskeletal Proteins; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006168:Guinea Pigs; D018069:Hair Cells, Vestibular / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D051379:Mice; D008817:Mice, Mutant Strains; D008855:Microscopy, Electron, Scanning; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D000081412:Myosin VIIa; D009218:Myosins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009925:Organ of Corti / Q000378:metabolism / Q000648:ultrastructure; D054730:Protein Interaction Domains and Motifs; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D052245:Usher Syndromes / Q000503:physiopathology
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C000631455:MYO7A protein, human; D046912:Multiprotein Complexes; C000631456:Myo7a protein, mouse; C000631457:Myo7a protein, rat; D000081412:Myosin VIIa; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; C477451:Sans protein, mouse; C492262:Ush1c protein, mouse; D049452:Green Fluorescent Proteins; D009218:Myosins