title: Harmonin-b, an actin-binding scaffold protein, is involved in the adaptation of mechanoelectrical transduction by sensory hair cells.
abstract: We assessed the involvement of harmonin-b, a submembranous protein containing PDZ domains, in the mechanoelectrical transduction machinery of inner ear hair cells. Harmonin-b is located in the region of the upper insertion point of the tip link that joins adjacent stereocilia from different rows and that is believed to gate transducer channel(s) located in the region of the tip link's lower insertion point. In Ush1c (dfcr-2J/dfcr-2J) mutant mice defective for harmonin-b, step deflections of the hair bundle evoked transduction currents with altered speed and extent of adaptation. In utricular hair cells, hair bundle morphology and maximal transduction currents were similar to those observed in wild-type mice, but adaptation was faster and more complete. Cochlear outer hair cells displayed reduced maximal transduction currents, which may be the consequence of moderate structural anomalies of their hair bundles. Their adaptation was slower and displayed a variable extent. The latter was positively correlated with the magnitude of the maximal transduction current, but the cells that showed the largest currents could be either hyperadaptive or hypoadaptive. To interpret our observations, we used a theoretical description of mechanoelectrical transduction based on the gating spring theory and a motor model of adaptation. Simulations could account for the characteristics of transduction currents in wild-type and mutant hair cells, both vestibular and cochlear. They led us to conclude that harmonin-b operates as an intracellular link that limits adaptation and engages adaptation motors, a dual role consistent with the scaffolding property of the protein and its binding to both actin filaments and the tip link component cadherin-23.
authors.affiliation: Institut Pasteur, Unité de Génétique et Physiologie de l'Audition, Paris 75015, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Michalski
authors.forename: Vincent
authors.initials: V
authors.lastname: Michel
authors.forename: Elisa
authors.initials: E
authors.lastname: Caberlotto
authors.forename: Gaelle M
authors.initials: GM
authors.lastname: Lefèvre
authors.forename: Alexander F J
authors.initials: AF
authors.lastname: van Aken
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Tinevez
authors.forename: Emilie
authors.initials: E
authors.lastname: Bizard
authors.forename: Christophe
authors.initials: C
authors.lastname: Houbron
authors.forename: Dominique
authors.initials: D
authors.lastname: Weil
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Hardelin
authors.forename: Guy P
authors.initials: GP
authors.lastname: Richardson
authors.forename: Corné J
authors.initials: CJ
authors.lastname: Kros
authors.forename: Pascal
authors.initials: P
authors.lastname: Martin
authors.forename: Christine
authors.initials: C
authors.lastname: Petit
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000222:Adaptation, Physiological; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D005455:Fluorescent Antibody Technique; D006199:Hair Cells, Auditory, Inner / Q000378:metabolism*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D051379:Mice; D008817:Mice, Mutant Strains; D008855:Microscopy, Electron, Scanning; D018408:Patch-Clamp Techniques
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C492262:Ush1c protein, mouse