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Young M, Lewis AH, Grandl J. Physics of mechanotransduction by Piezo ion channels. J Gen Physiol 2022; 154:213231. [PMID: 35593732 PMCID: PMC9127981 DOI: 10.1085/jgp.202113044] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 03/28/2022] [Accepted: 04/29/2022] [Indexed: 12/26/2022] Open
Abstract
Piezo ion channels are sensors of mechanical forces and mediate a wide range of physiological mechanotransduction processes. More than a decade of intense research has elucidated much of the structural and mechanistic principles underlying Piezo gating and its roles in physiology, although wide gaps of knowledge continue to exist. Here, we review the forces and energies involved in mechanical activation of Piezo ion channels and their functional modulation by other chemical and physical stimuli including lipids, voltage, and temperature. We compare the three predominant mechanisms likely to explain Piezo activation—the force-from-lipids mechanism, the tether model, and the membrane footprint theory. Additional sections shine light on how Piezo ion channels may affect each other through spatial clustering and functional cooperativity, and how substantial functional heterogeneity of Piezo ion channels arises as a byproduct of the precise physical environment each channel experiences. Finally, our review concludes by pointing out major research questions and technological limitations that future research can address.
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Affiliation(s)
- Michael Young
- Department of Neurobiology, Duke University Medical Center, Durham, NC
| | - Amanda H Lewis
- Department of Neurobiology, Duke University Medical Center, Durham, NC
| | - Jörg Grandl
- Department of Neurobiology, Duke University Medical Center, Durham, NC
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2
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Unbalanced bidirectional radial stiffness gradients within the organ of Corti promoted by TRIOBP. Proc Natl Acad Sci U S A 2022; 119:e2115190119. [PMID: 35737845 PMCID: PMC9245700 DOI: 10.1073/pnas.2115190119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Current understanding of cochlear mechanics assumes that stiffness of the cochlear partition varies only longitudinally along the cochlea. This work examines the stiffness of inner ear epithelium in individual cell types at the nanoscale level. We revealed unrecognized radial stiffness gradients of different magnitudes and opposite orientations within the epithelium. Remarkably, the observed bidirectional stiffness gradients are unbalanced between supporting and sensory cells. Deficiencies in deafness-associated Trio and F-actin binding protein (TRIOBP) caused diverse cytoskeletal ultrastructural remodeling in supporting and sensory cells and significantly diminishes the bidirectional radial stiffness gradients. These results demonstrate the complexity of the mechanical properties within the sensory epithelium and point to a hitherto unrecognized role of these gradients in sensitivity and frequency selectivity of hearing. Hearing depends on intricate morphologies and mechanical properties of diverse inner ear cell types. The individual contributions of various inner ear cell types into mechanical properties of the organ of Corti and the mechanisms of their integration are yet largely unknown. Using sub-100-nm spatial resolution atomic force microscopy (AFM), we mapped the Young’s modulus (stiffness) of the apical surface of the different cells of the freshly dissected P5–P6 cochlear epithelium from wild-type and mice lacking either Trio and F-actin binding protein (TRIOBP) isoforms 4 and 5 or isoform 5 only. Variants of TRIOBP are associated with deafness in human and in Triobp mutant mouse models. Remarkably, nanoscale AFM mapping revealed unrecognized bidirectional radial stiffness gradients of different magnitudes and opposite orientations between rows of wild-type supporting cells and sensory hair cells. Moreover, the observed bidirectional radial stiffness gradients are unbalanced, with sensory cells being stiffer overall compared to neighboring supporting cells. Deafness-associated TRIOBP deficiencies significantly disrupted the magnitude and orientation of these bidirectional radial stiffness gradients. In addition, serial sectioning with focused ion beam and backscatter scanning electron microscopy shows that a TRIOBP deficiency results in ultrastructural changes of supporting cell apical phalangeal microfilaments and bundled cortical F-actin of hair cell cuticular plates, correlating with messenger RNA and protein expression levels and AFM stiffness measurements that exposed a softening of the apical surface of the sensory epithelium in mutant mice. Altogether, this additional complexity in the mechanical properties of the sensory epithelium is hypothesized to be an essential contributor to frequency selectivity and sensitivity of mammalian hearing.
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Differentiation of embryonic stem cells into a putative hair cell-progenitor cells via co-culture with HEI-OC1 cells. Sci Rep 2021; 11:13893. [PMID: 34230535 PMCID: PMC8260610 DOI: 10.1038/s41598-021-93049-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 06/17/2021] [Indexed: 12/14/2022] Open
Abstract
Several studies have shown how different cell lines can influence the differentiation of stem cells through co-culture systems. The House Ear Institute-Organ of Corti 1 (HEI-OC1) is considered an important cell line for in vitro auditory research. However, it is unknown if HEI-OC1 cells can promote the differentiation of embryonic stem cells (ESCs). In this study, we investigated whether co-culture of ESCs with HEI-OC1 cells promotes differentiation. To this end, we developed a co-culture system of mouse ESCs with HEI-OC1 cells. Dissociated or embryonic bodies (EBs) of ESCs were introduced to a conditioned and inactivated confluent layer of HEI-OC1 cells for 14 days. The dissociated ESCs coalesced into an EB-like form that was smaller than the co-cultured EBs. Contact co-culture generated cells expressing several otic progenitor markers as well as hair cell specific markers. ESCs and EBs were also cultured in non-contact setup but using conditioned medium from HEI-OC1 cells, indicating that soluble factors alone could have a similar effect. The ESCs did not form into aggregates but were still Myo7a-positive, while the EBs degenerated. However, in the fully differentiated EBs, evidence to prove mature differentiation of inner ear hair cell was still rudimentary. Nevertheless, these results suggest that cellular interactions between ESCs and HEI-OC1 cells may both stimulate ESC differentiation.
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Optimized Tuning of Auditory Inner Hair Cells to Encode Complex Sound through Synergistic Activity of Six Independent K + Current Entities. Cell Rep 2021; 32:107869. [PMID: 32640234 DOI: 10.1016/j.celrep.2020.107869] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 04/08/2020] [Accepted: 06/16/2020] [Indexed: 02/06/2023] Open
Abstract
Auditory inner hair cells (IHCs) convert sound vibrations into receptor potentials that drive synaptic transmission. For the precise encoding of sound qualities, receptor potentials are shaped by K+ conductances tuning the properties of the IHC membrane. Using patch-clamp and computational modeling, we unravel this membrane specialization showing that IHCs express an exclusive repertoire of six voltage-dependent K+ conductances mediated by Kv1.8, Kv7.4, Kv11.1, Kv12.1, and BKCa channels. All channels are active at rest but are triggered differentially during sound stimulation. This enables non-saturating tuning over a far larger potential range than in IHCs expressing fewer current entities. Each conductance contributes to optimizing responses, but the combined activity of all channels synergistically improves phase locking and the dynamic range of intensities that IHCs can encode. Conversely, hypothetical simpler IHCs appear limited to encode only certain aspects (frequency or intensity). The exclusive channel repertoire of IHCs thus constitutes an evolutionary adaptation to encode complex sound through multifaceted receptor potentials.
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The Development of Cooperative Channels Explains the Maturation of Hair Cell's Mechanotransduction. Biophys J 2019; 117:1536-1548. [PMID: 31585704 PMCID: PMC6817549 DOI: 10.1016/j.bpj.2019.08.042] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 08/20/2019] [Accepted: 08/28/2019] [Indexed: 11/29/2022] Open
Abstract
Hearing relies on the conversion of mechanical stimuli into electrical signals. In vertebrates, this process of mechanoelectrical transduction (MET) is performed by specialized receptors of the inner ear, the hair cells. Each hair cell is crowned by a hair bundle, a cluster of microvilli that pivot in response to sound vibrations, causing the opening and closing of mechanosensitive ion channels. Mechanical forces are projected onto the channels by molecular springs called tip links. Each tip link is thought to connect to a small number of MET channels that gate cooperatively and operate as a single transduction unit. Pushing the hair bundle in the excitatory direction opens the channels, after which they rapidly reclose in a process called fast adaptation. It has been experimentally observed that the hair cell’s biophysical properties mature gradually during postnatal development: the maximal transduction current increases, sensitivity sharpens, transduction occurs at smaller hair-bundle displacements, and adaptation becomes faster. Similar observations have been reported during tip-link regeneration after acoustic damage. Moreover, when measured at intermediate developmental stages, the kinetics of fast adaptation varies in a given cell, depending on the magnitude of the imposed displacement. The mechanisms underlying these seemingly disparate observations have so far remained elusive. Here, we show that these phenomena can all be explained by the progressive addition of MET channels of constant properties, which populate the hair bundle first as isolated entities and then progressively as clusters of more sensitive, cooperative MET channels. As the proposed mechanism relies on the difference in biophysical properties between isolated and clustered channels, this work highlights the importance of cooperative interactions between mechanosensitive ion channels for hearing.
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Cartagena-Rivera AX, Le Gal S, Richards K, Verpy E, Chadwick RS. Cochlear outer hair cell horizontal top connectors mediate mature stereocilia bundle mechanics. SCIENCE ADVANCES 2019; 5:eaat9934. [PMID: 30801007 PMCID: PMC6382404 DOI: 10.1126/sciadv.aat9934] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Accepted: 01/10/2019] [Indexed: 05/23/2023]
Abstract
Outer hair cell (OHC) stereocilia bundle deflection opens mechanoelectrical transduction channels at the tips of the stereocilia from the middle and short rows, while bundle cohesion is maintained owing to the presence of horizontal top connectors. Here, we used a quantitative noncontact atomic force microscopy method to investigate stereocilia bundle stiffness and damping, when stimulated at acoustic frequencies and nanometer distances from the bundle. Stereocilia bundle mechanics were determined in stereocilin-deficient mice lacking top connectors and with detached tectorial membrane (Strc -/-/Tecta -/- double knockout) and heterozygous littermate controls (Strc +/-/Tecta -/-). A substantial decrease in bundle stiffness and damping by ~60 and ~74% on postnatal days P13 to P15 was observed when top connectors were absent. Additionally, we followed bundle mechanics during OHC top connectors development between P9 and P15 and quantified the observed increase in OHC bundle stiffness and damping in Strc +/-/Tecta -/- mice while no significant change was detected in Strc -/-/Tecta -/- animals.
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Affiliation(s)
- Alexander X. Cartagena-Rivera
- Section on Auditory Mechanics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
| | - Sébastien Le Gal
- Unité de Génétique et Physiologie de l’Audition, Institut Pasteur, 75015 Paris, France
- UMRS 1120, Institut National de la Santé et de la Recherche Médicale (INSERM), 75015 Paris, France
- Sorbonne Universités, Université Pierre et Marie Curie Paris 06, Complexité du Vivant, 75005 Paris, France
| | - Kerianne Richards
- Genomics and Computational Biology Core, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
| | - Elisabeth Verpy
- Unité de Génétique et Physiologie de l’Audition, Institut Pasteur, 75015 Paris, France
- UMRS 1120, Institut National de la Santé et de la Recherche Médicale (INSERM), 75015 Paris, France
- Sorbonne Universités, Université Pierre et Marie Curie Paris 06, Complexité du Vivant, 75005 Paris, France
| | - Richard S. Chadwick
- Section on Auditory Mechanics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892, USA
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Dionne G, Qiu X, Rapp M, Liang X, Zhao B, Peng G, Katsamba PS, Ahlsen G, Rubinstein R, Potter CS, Carragher B, Honig B, Müller U, Shapiro L. Mechanotransduction by PCDH15 Relies on a Novel cis-Dimeric Architecture. Neuron 2018; 99:480-492.e5. [PMID: 30057206 PMCID: PMC6168201 DOI: 10.1016/j.neuron.2018.07.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Revised: 06/06/2018] [Accepted: 06/29/2018] [Indexed: 10/28/2022]
Abstract
The tip link, a filament formed by protocadherin 15 (PCDH15) and cadherin 23, conveys mechanical force from sound waves and head movement to open hair-cell mechanotransduction channels. Tip-link cadherins are thought to have acquired structural features critical for their role in mechanotransduction. Here, we biophysically and structurally characterize the unusual cis-homodimeric architecture of PCDH15. We show that PCDH15 molecules form double-helical assemblies through cis-dimerization interfaces in the extracellular cadherin EC2-EC3 domain region and in a unique membrane-proximal domain. Electron microscopy studies visualize the cis-dimeric PCDH15 assembly and reveal the PCDH15 extracellular domain as a parallel double helix with cis cross-bridges at the two locations we defined. The helical configuration suggests the potential for elasticity through helix winding and unwinding. Functional studies in hair cells show that mutations that perturb PCDH15 dimerization contacts affect mechanotransduction. Together, these data reveal the cis-dimeric architecture of PCDH15 and show that dimerization is critical for sensing mechanical stimuli.
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Affiliation(s)
- Gilman Dionne
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Xufeng Qiu
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Micah Rapp
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
| | - Xiaoping Liang
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Bo Zhao
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Guihong Peng
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Phinikoula S Katsamba
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA
| | - Goran Ahlsen
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA
| | - Rotem Rubinstein
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA
| | - Clinton S Potter
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
| | - Bridget Carragher
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; National Resource for Automated Molecular Microscopy, Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY 10027, USA
| | - Barry Honig
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA.
| | - Ulrich Müller
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - Lawrence Shapiro
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA.
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8
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Vanniya S P, Srisailapathy CRS, Kunka Mohanram R. The tip link protein Cadherin-23: From Hearing Loss to Cancer. Pharmacol Res 2018; 130:25-35. [PMID: 29421162 DOI: 10.1016/j.phrs.2018.01.026] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2017] [Revised: 01/24/2018] [Accepted: 01/26/2018] [Indexed: 11/26/2022]
Abstract
Cadherin-23 is an atypical member of the cadherin superfamily, with a distinctly long extracellular domain. It has been known to be a part of the tip links of the inner ear mechanosensory hair cells. Several studies have been carried out to understand the role of Cadherin-23 in the hearing mechanism and defects in the CDH23 have been associated with hearing impairment resulting from defective or absence of tip links. Recent studies have highlighted the role of Cadherin-23 in several pathological conditions, including cancer, suggesting the presence of several unknown functions. Initially, it was proposed that Cadherin-23 represents a yet unspecified subtype of Cadherins; however, no other proteins with similar characteristics have been identified, till date. It has a unique cytoplasmic domain that does not bear a β-catenin binding region, but has been demonstrated to mediate cell-cell adhesions. Several protein interacting partners have been identified for Cadherin-23 and the roles of their interactions in various cellular mechanisms are yet to be explored. This review summarizes the characteristics of Cadherin-23 and its roles in several pathologies including cancer.
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Affiliation(s)
- Paridhy Vanniya S
- Department of Genetics, Dr. ALM PG Institute of Basic Medical Science, University of Madras, Taramani campus, Chennai, Tamilnadu, India
| | - C R Srikumari Srisailapathy
- Department of Genetics, Dr. ALM PG Institute of Basic Medical Science, University of Madras, Taramani campus, Chennai, Tamilnadu, India
| | - Ramkumar Kunka Mohanram
- SRM Research Institute, SRM Institute of Science and Technology, Kattankulathur, Tamilnadu, India.
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9
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Lipid bilayer mediates ion-channel cooperativity in a model of hair-cell mechanotransduction. Proc Natl Acad Sci U S A 2017; 114:E11010-E11019. [PMID: 29217640 DOI: 10.1073/pnas.1713135114] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mechanoelectrical transduction in the inner ear is a biophysical process underlying the senses of hearing and balance. The key players involved in this process are mechanosensitive ion channels. They are located in the stereocilia of hair cells and opened by the tension in specialized molecular springs, the tip links, connecting adjacent stereocilia. When channels open, the tip links relax, reducing the hair-bundle stiffness. This gating compliance makes hair cells especially sensitive to small stimuli. The classical explanation for the gating compliance is that the conformational rearrangement of a single channel directly shortens the tip link. However, to reconcile theoretical models based on this mechanism with experimental data, an unrealistically large structural change of the channel is required. Experimental evidence indicates that each tip link is a dimeric molecule, associated on average with two channels at its lower end. It also indicates that the lipid bilayer modulates channel gating, although it is not clear how. Here, we design and analyze a model of mechanotransduction where each tip link attaches to two channels, mobile within the membrane. Their states and positions are coupled by membrane-mediated elastic forces arising from the interaction between the channels' hydrophobic cores and that of the lipid bilayer. This coupling induces cooperative opening and closing of the channels. The model reproduces the main properties of hair-cell mechanotransduction using only realistic parameters constrained by experimental evidence. This work provides an insight into the fundamental role that membrane-mediated ion-channel cooperativity can play in sensory physiology.
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10
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Abdel-Hafez AMM, Elgayar SAM, Husain OA, Thabet HSA. Effect of nicotine on the structure of cochlea of guinea pigs. Anat Cell Biol 2014; 47:162-70. [PMID: 25276475 PMCID: PMC4178191 DOI: 10.5115/acb.2014.47.3.162] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 09/11/2014] [Accepted: 09/15/2014] [Indexed: 11/30/2022] Open
Abstract
Smoking has been positively associated with hearing loss in human. However, its effect on the cochlea has not been previously evaluated. Aim of work is to investigate the effect of nicotine, which is the primary pharmacological component of tobacco, on the structure of the cochlea of adult male guinea pigs. Fifteen male guinea pigs were classified into two groups: group I (control) and group II (nicotine treated group). Group II was further subdivided into two subgroups; IIA and IIB according to the dose of nicotine (3 mg/kg and 6 mg/kg, respectively). The cochlea was harvested and processed for light microscopy, transmission electron microscopy and scanning electron microscopy. Nicotine administration induced damage of outer hair cells which were distorted in shape with vacuolated cytoplasm and heterochromatic nuclei. Topography revealed damage of the stereocilia which included disorganization, bent and limp or complete loss and expansion of the surrounding supporting cells. These changes were more pronounced in the basal turn of the cochlea and mainly involved the outer hair cells. High dose induced more damage and resulted in protrusion of the apical poles of hair cells (blebing), particularly the outer two rows. Nicotine is proved to be harmful to the cells of the cochlea, particularly the outer hair cells of the basal turn. High doses induce blebing of hair cells.
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Affiliation(s)
| | - Sanaa A M Elgayar
- Department of Histology, Faculty of Medicine, Assiut University, Assiut, Egypt
| | - Ola A Husain
- Department of Histology, Faculty of Medicine, Assiut University, Assiut, Egypt
| | - Huda S A Thabet
- Department of Histology, Faculty of Medicine, Assiut University, Assiut, Egypt
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11
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Iwadate Y, Okimura C, Sato K, Nakashima Y, Tsujioka M, Minami K. Myosin-II-mediated directional migration of Dictyostelium cells in response to cyclic stretching of substratum. Biophys J 2013; 104:748-58. [PMID: 23442953 DOI: 10.1016/j.bpj.2013.01.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 01/03/2013] [Accepted: 01/07/2013] [Indexed: 11/29/2022] Open
Abstract
Living cells are constantly subjected to various mechanical stimulations, such as shear flow, osmotic pressure, and hardness of substratum. They must sense the mechanical aspects of their environment and respond appropriately for proper cell function. Cells adhering to substrata must receive and respond to mechanical stimuli from the substrata to decide their shape and/or migrating direction. In response to cyclic stretching of the elastic substratum, intracellular stress fibers in fibroblasts and endothelial, osteosarcoma, and smooth muscle cells are rearranged perpendicular to the stretching direction, and the shape of those cells becomes extended in this new direction. In the case of migrating Dictyostelium cells, cyclic stretching regulates the direction of migration, and not the shape, of the cell. The cells migrate in a direction perpendicular to that of the stretching. However, the molecular mechanisms that induce the directional migration remain unknown. Here, using a microstretching device, we recorded green fluorescent protein (GFP)-myosin-II dynamics in Dictyostelium cells on an elastic substratum under cyclic stretching. Repeated stretching induced myosin II localization equally on both stretching sides in the cells. Although myosin-II-null cells migrated randomly, myosin-II-null cells expressing a variant of myosin II that cannot hydrolyze ATP migrated perpendicular to the stretching. These results indicate that Dictyostelium cells accumulate myosin II at the portion of the cell where a large strain is received and migrate in a direction other than that of the portion where myosin II accumulated. This polarity generation for migration does not require the contraction of actomyosin.
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Affiliation(s)
- Yoshiaki Iwadate
- Department of Functional Molecular Biology, Graduate School of Medicine, Yamaguchi University, Yamaguchi, Japan.
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12
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A molecular level prototype for mechanoelectrical transducer in mammalian hair cells. J Comput Neurosci 2013; 35:231-41. [PMID: 23625048 DOI: 10.1007/s10827-013-0450-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Revised: 02/14/2013] [Accepted: 02/27/2013] [Indexed: 01/20/2023]
Abstract
The mechanoelectrical transducer (MET) is a crucial component of mammalian auditory system. The gating mechanism of the MET channel remains a puzzling issue, though there are many speculations, due to the lack of essential molecular building blocks. To understand the working principle of mammalian MET, we propose a molecular level prototype which constitutes a charged blocker, a realistic ion channel and its surrounding membrane. To validate the proposed prototype, we make use of a well-established ion channel theory, the Poisson-Nernst-Planck equations, for three-dimensional (3D) numerical simulations. A wide variety of model parameters, including bulk ion concentration, applied external voltage, blocker charge and blocker displacement, are explored to understand the basic function of the proposed MET prototype. We show that our prototype prediction of channel open probability in response to blocker relative displacement is in remarkable accordance with experimental observation of rat cochlea outer hair cells. Our results appear to suggest that tip links which connect hair bundles gate MET channels.
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13
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Selvakumar D, Drescher MJ, Drescher DG. Cyclic nucleotide-gated channel α-3 (CNGA3) interacts with stereocilia tip-link cadherin 23 + exon 68 or alternatively with myosin VIIa, two proteins required for hair cell mechanotransduction. J Biol Chem 2013; 288:7215-29. [PMID: 23329832 DOI: 10.1074/jbc.m112.443226] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previously, we obtained evidence for a photoreceptor/olfactory type of CNGA3 transcript in a purified teleost vestibular hair cell preparation with immunolocalization of CNGA3 protein to stereocilia of teleost vestibular and mammalian cochlear hair cells. The carboxyl terminus of highly Ca(2+)-permeable CNGA3 expressed in the mammalian organ of Corti and saccular hair cells was found to interact with an intracellular domain of microfibril interface-located protein 1 (EMILIN 1), a member of the elastin superfamily, also immunolocalizd to hair cell stereocilia (Selvakumar, D., Drescher, M. J., Dowdall, J. R., Khan, K. M., Hatfield, J. S., Ramakrishnan, N. A., and Drescher, D. G. (2012) Biochem. J. 443, 463-476). Here, we provide evidence for organ of Corti proteins, of Ca(2+)-dependent binding of the amino terminus of CNGA3 specifically to the carboxyl terminus of stereocilia tip-link protein CDH23 +68 (cadherin 23 with expressed exon 68) by yeast two-hybrid mating and co-transformation protocols, pulldown assays, and surface plasmon resonance analysis. Myosin VIIa, required for adaptation of hair cell mechanotransduction (MET) channel(s), competed with CDH23 +68, with direct Ca(2+)-dependent binding to the amino terminus of CNGA3. Based upon the premise that hair cell stereocilia tip-link proteins are closely coupled with MET, these results are consistent with the possibility that CNGA3 participates in hair-cell MET. Together with the demonstration of protein-protein interaction between HCN1 and tip-link protein protocadherin 15 CD3 (Ramakrishnan, N. A., Drescher, M. J., Barretto, R. L., Beisel, K. W., Hatfield, J. S., and Drescher, D. G. (2009) J. Biol. Chem. 284, 3227-3238; Ramakrishnan, N. A., Drescher, M. J., Khan, K. M., Hatfield, J. S., and Drescher, D. G. (2012) J. Biol. Chem. 287, 37628-37646), a protein-protein interaction for CNGA3 and a second tip-link protein, CDH23 +68, further suggests possible association of two different channels with a single stereocilia tip link.
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Affiliation(s)
- Dakshnamurthy Selvakumar
- Laboratory of Bio-otology, Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
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14
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CNGA3 is expressed in inner ear hair cells and binds to an intracellular C-terminus domain of EMILIN1. Biochem J 2012; 443:463-76. [PMID: 22248097 DOI: 10.1042/bj20111255] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The molecular characteristics of CNG (cyclic nucleotide-gated) channels in auditory/vestibular hair cells are largely unknown, unlike those of CNG mediating sensory transduction in vision and olfaction. In the present study we report the full-length sequence for three CNGA3 variants in a hair cell preparation from the trout saccule with high identity to CNGA3 in olfactory receptor neurons/cone photoreceptors. A custom antibody targeting the N-terminal sequence immunolocalized CNGA3 to the stereocilia and subcuticular plate region of saccular hair cells. The cytoplasmic C-terminus of CNGA3 was found by yeast two-hybrid analysis to bind the C-terminus of EMILIN1 (elastin microfibril interface-located protein 1) in both the vestibular hair cell model and rat organ of Corti. Specific binding between CNGA3 and EMILIN1 was confirmed with surface plasmon resonance analysis, predicting dependence on Ca2+ with Kd=1.6×10-6 M for trout hair cell proteins and Kd=2.7×10-7 M for organ of Corti proteins at 68 μM Ca2+. Pull-down assays indicated that the binding to organ of Corti CNGA3 was attributable to the EMILIN1 intracellular sequence that follows a predicted transmembrane domain in the C-terminus. Saccular hair cells also express the transcript for PDE6C (phosphodiesterase 6C), which in cone photoreceptors regulates the degradation of cGMP used to gate CNGA3 in phototransduction. Taken together, the evidence supports the existence in saccular hair cells of a molecular pathway linking CNGA3, its binding partner EMILIN1 (and β1 integrin) and cGMP-specific PDE6C, which is potentially replicated in cochlear outer hair cells, given stereociliary immunolocalizations of CNGA3, EMILIN1 and PDE6C.
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Pan B, Waguespack J, Schnee ME, LeBlanc C, Ricci AJ. Permeation properties of the hair cell mechanotransducer channel provide insight into its molecular structure. J Neurophysiol 2012; 107:2408-20. [PMID: 22323630 DOI: 10.1152/jn.01178.2011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Mechanoelectric transducer (MET) channels, located near stereocilia tips, are opened by deflecting the hair bundle of sensory hair cells. Defects in this process result in deafness. Despite this critical function, the molecular identity of MET channels remains a mystery. Inherent channel properties, particularly those associated with permeation, provide the backbone for the molecular identification of ion channels. Here, a novel channel rectification mechanism is identified, resulting in a reduced pore size at positive potentials. The apparent difference in pore dimensions results from Ca(2+) binding within the pore, occluding permeation. Driving force for permeation at hyperpolarized potentials is increased because Ca(2+) can more easily be removed from binding within the pore due to the presence of an electronegative external vestibule that dehydrates and concentrates permeating ions. Alterations in Ca(2+) binding may underlie tonotopic and Ca(2+)-dependent variations in channel conductance. This Ca(2+)-dependent rectification provides targets for identifying the molecular components of the MET channel.
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Affiliation(s)
- B Pan
- Department of Otolaryngology, Stanford University, 300 Pasteur Dr., Stanford, CA 94305, USA
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16
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Takemoto K, Mizutani T, Tamura K, Takeda K, Haga H, Kawabata K. The Number of Cyclic Stretch Regulates Cellular Elasticity in C2C12 Myoblasts. Cell 2012. [DOI: 10.4236/cellbio.2012.11001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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17
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Alharazneh A, Luk L, Huth M, Monfared A, Steyger PS, Cheng AG, Ricci AJ. Functional hair cell mechanotransducer channels are required for aminoglycoside ototoxicity. PLoS One 2011; 6:e22347. [PMID: 21818312 PMCID: PMC3144223 DOI: 10.1371/journal.pone.0022347] [Citation(s) in RCA: 184] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Accepted: 06/19/2011] [Indexed: 12/02/2022] Open
Abstract
Aminoglycosides (AG) are commonly prescribed antibiotics with potent bactericidal activities. One main side effect is permanent sensorineural hearing loss, induced by selective inner ear sensory hair cell death. Much work has focused on AG's initiating cell death processes, however, fewer studies exist defining mechanisms of AG uptake by hair cells. The current study investigated two proposed mechanisms of AG transport in mammalian hair cells: mechanotransducer (MET) channels and endocytosis. To study these two mechanisms, rat cochlear explants were cultured as whole organs in gentamicin-containing media. Two-photon imaging of Texas Red conjugated gentamicin (GTTR) uptake into live hair cells was rapid and selective. Hypocalcemia, which increases the open probability of MET channels, increased AG entry into hair cells. Three blockers of MET channels (curare, quinine, and amiloride) significantly reduced GTTR uptake, whereas the endocytosis inhibitor concanavalin A did not. Dynosore quenched the fluorescence of GTTR and could not be tested. Pharmacologic blockade of MET channels with curare or quinine, but not concanavalin A or dynosore, prevented hair cell loss when challenged with gentamicin for up to 96 hours. Taken together, data indicate that the patency of MET channels mediated AG entry into hair cells and its toxicity. Results suggest that limiting permeation of AGs through MET channel or preventing their entry into endolymph are potential therapeutic targets for preventing hair cell death and hearing loss.
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Affiliation(s)
- Abdelrahman Alharazneh
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California, United States of America
- Department of Special Surgery, Mu'tah University, Alkarak, Jordan
| | - Lauren Luk
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Markus Huth
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Ashkan Monfared
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California, United States of America
| | - Peter S. Steyger
- Department of Otolaryngology-Head and Neck Surgery, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Alan G. Cheng
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California, United States of America
- * E-mail: (AGC); (AJR)
| | - Anthony J. Ricci
- Department of Otolaryngology-Head and Neck Surgery, Stanford University, Stanford, California, United States of America
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California, United States of America
- * E-mail: (AGC); (AJR)
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Myosin VIIa and sans localization at stereocilia upper tip-link density implicates these Usher syndrome proteins in mechanotransduction. Proc Natl Acad Sci U S A 2011; 108:11476-81. [PMID: 21709241 DOI: 10.1073/pnas.1104161108] [Citation(s) in RCA: 147] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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.
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Cyclic stretch of the substratum using a shape-memory alloy induces directional migration in Dictyostelium cells. Biotechniques 2010; 47:757-67. [PMID: 19852761 DOI: 10.2144/000113217] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Living cells are constantly subjected to various mechanical stimulations. They must sense the mechanical aspects of their environment and respond appropriately for proper cell function. In general, cells adhere to substrata. Thus, the cells must receive and respond to mechanical stimuli mainly from the substrata. For example, migrating cells can create their own polarity and migrate in a certain direction even in the absence of any attractive substance. In order to generate such polarity, cells must sense mechanical stimuli from the substrata and transduce these stimuli into intracellular signals. To investigate the relationship between signals derived from mechanical stimuli and related cell functions, one of the most commonly used techniques is the application of mechanical stimuli via stretching of elastic substrata. Here, we developed a new stretching device using a shape-memory alloy (SMA). An SMA has three advantages as an actuator of stretching devices: (i) the cost of the SMA required for the device is inexpensive, approximately 30 USD, (ii) the size of an SMA is very small (0.62 mm in diameter and 22 mm in length), and (iii) an SMA does not generate any vibrating noise, which can negatively affect cells. In response to the cyclic stretching by the new stretching device, Dictyostelium discoideum cells migrated perpendicular to the stretching direction and the migrating speed increased significantly. To our knowledge, this is the first report indicating that migrating cells can create their own polarity by the mechanical stimuli from the substrata.
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Abstract
Mammals have an astonishing ability to sense and discriminate sounds of different frequencies and intensities. Fundamental for this process are mechanosensory hair cells in the inner ear that convert sound-induced vibrations into electrical signals. The study of genes that are linked to deafness has provided insights into the cell biological mechanisms that control hair cell development and their function as mechanosensors.
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Affiliation(s)
- Martin Schwander
- Department of Cell Biology, Dorris Neuroscience Center, The Scripps Research Institute, La Jolla, CA 92037, USA
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21
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Sakaguchi H, Tokita J, Müller U, Kachar B. Tip links in hair cells: molecular composition and role in hearing loss. Curr Opin Otolaryngol Head Neck Surg 2009; 17:388-93. [PMID: 19633555 DOI: 10.1097/moo.0b013e3283303472] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW Tip links are thought to be an essential element of the mechanoelectrical transduction (MET) apparatus in sensory hair cells of the inner ear. The molecules that form tip links have recently been identified, and the analysis of their properties has not only changed our view of MET but also suggests that tip-link defects can cause hearing loss. RECENT FINDINGS Structural, histological and biochemical studies show that the extracellular domains of two deafness-associated cadherins, cadherin 23 (CDH23) and protocadherin 15 (PCDH15), interact in trans to form the upper and lower part of each tip link, respectively. High-speed Ca imaging suggests that MET channels are localized exclusively at the lower end of each tip link. Biochemical and genetic studies provide evidence that defects in tip links cause hearing impairment in humans. SUMMARY The identification of the proteins that form tip links have shed new light on the molecular basis of MET and the mechanisms causing hereditary deafness, noise-induced hearing loss and presbycusis.
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Affiliation(s)
- Hirofumi Sakaguchi
- Department of Otolaryngology-Head and Neck Surgery, Kyoto Prefectural University of Medicine, Kyoto, Japan
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22
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Zheng J, Anderson CT, Miller KK, Cheatham M, Dallos P. Identifying components of the hair-cell interactome involved in cochlear amplification. BMC Genomics 2009; 10:127. [PMID: 19320974 PMCID: PMC2669096 DOI: 10.1186/1471-2164-10-127] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Accepted: 03/25/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Although outer hair cells (OHCs) play a key role in cochlear amplification, it is not fully understood how they amplify sound signals by more than 100 fold. Two competing or possibly complementary mechanisms, stereocilia-based and somatic electromotility-based amplification, have been considered. Lacking knowledge about the exceptionally rich protein networks in the OHC plasma membrane, as well as related protein-protein interactions, limits our understanding of cochlear function. Therefore, we focused on finding protein partners for two important membrane proteins: Cadherin 23 (cdh23) and prestin. Cdh23 is one of the tip-link proteins involved in transducer function, a key component of mechanoelectrical transduction and stereocilia-based amplification. Prestin is a basolateral membrane protein responsible for OHC somatic electromotility. RESULTS Using the membrane-based yeast two-hybrid system to screen a newly built cDNA library made predominantly from OHCs, we identified two completely different groups of potential protein partners using prestin and cdh23 as bait. These include both membrane bound and cytoplasmic proteins with 12 being de novo gene products with unknown function(s). In addition, some of these genes are closely associated with deafness loci, implying a potentially important role in hearing. The most abundant prey for prestin (38%) is composed of a group of proteins involved in electron transport, which may play a role in OHC survival. The most abundant group of cdh23 prey (55%) contains calcium-binding domains. Since calcium performs an important role in hair cell mechanoelectrical transduction and amplification, understanding the interactions between cdh23 and calcium-binding proteins should increase our knowledge of hair cell function at the molecular level. CONCLUSION The results of this study shed light on some protein networks in cochlear hair cells. Not only was a group of de novo genes closely associated with known deafness loci identified, but the data also indicate that the hair cell tip link interacts directly with calcium binding proteins. The OHC motor protein, prestin, also appears to be associated with electron transport proteins. These unanticipated results open potentially fruitful lines of investigation into the molecular basis of cochlear amplification.
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Affiliation(s)
- Jing Zheng
- Department of Communication Sciences and Disorders, The Hugh Knowles Center, Northwestern University, Evanston, IL 60208, USA.
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Myosin IIIa boosts elongation of stereocilia by transporting espin 1 to the plus ends of actin filaments. Nat Cell Biol 2009; 11:443-50. [PMID: 19287378 PMCID: PMC2750890 DOI: 10.1038/ncb1851] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Accepted: 01/19/2009] [Indexed: 11/22/2022]
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Coffin AB, Reinhart KE, Owens KN, Raible DW, Rubel EW. Extracellular divalent cations modulate aminoglycoside-induced hair cell death in the zebrafish lateral line. Hear Res 2009; 253:42-51. [PMID: 19285547 DOI: 10.1016/j.heares.2009.03.004] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Revised: 02/11/2009] [Accepted: 03/04/2009] [Indexed: 10/21/2022]
Abstract
Aminoglycoside antibiotics cause death of sensory hair cells. Research over the past decade has identified several key players in the intracellular cascade. However, the role of the extracellular environment in aminoglycoside ototoxicity has received comparatively little attention. The present study uses the zebrafish lateral line to demonstrate that extracellular calcium and magnesium ions modulate hair cell death from neomycin and gentamicin in vivo, with high levels of either divalent cation providing significant protection. Imaging experiments with fluorescently-tagged gentamicin show that drug uptake is reduced under high calcium conditions. Treating fish with the hair cell transduction blocker amiloride also reduces aminoglycoside uptake, preventing the toxicity, and experiments with variable calcium and amiloride concentrations suggest complementary effects between the two protectants. Elevated magnesium, in contrast, does not appear to significantly attenuate drug uptake, suggesting that the two divalent cations may protect hair cells from aminoglycoside damage through different mechanisms. These results provide additional evidence for calcium- and transduction-dependent aminoglycoside uptake. Divalent cations provided differential protection from neomycin and gentamicin, with high cation concentrations almost completely protecting hair cells from neomycin and acute gentamicin toxicity, but offering reduced protection from continuous (6 h) gentamicin exposure. These experiments lend further support to the hypothesis that aminoglycoside toxicity occurs via multiple pathways in a both a drug and time course-specific manner.
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Affiliation(s)
- Allison B Coffin
- Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology - Head and Neck Surgery, University of Washington, Box 357923, Seattle, WA 98195, USA
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Chiquet M, Gelman L, Lutz R, Maier S. From mechanotransduction to extracellular matrix gene expression in fibroblasts. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2009; 1793:911-20. [PMID: 19339214 DOI: 10.1016/j.bbamcr.2009.01.012] [Citation(s) in RCA: 257] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 01/12/2009] [Accepted: 01/22/2009] [Indexed: 12/22/2022]
Abstract
Tissue mechanics provide an important context for tissue growth, maintenance and function. On the level of organs, external mechanical forces largely influence the control of tissue homeostasis by endo- and paracrine factors. On the cellular level, it is well known that most normal cell types depend on physical interactions with their extracellular matrix in order to respond efficiently to growth factors. Fibroblasts and other adherent cells sense changes in physical parameters in their extracellular matrix environment, transduce mechanical into chemical information, and integrate these signals with growth factor derived stimuli to achieve specific changes in gene expression. For connective tissue cells, production of the extracellular matrix is a prominent response to changes in mechanical load. We will review the evidence that integrin-containing cell-matrix adhesion contacts are essential for force transmission from the extracellular matrix to the cytoskeleton, and describe novel experiments indicating that mechanotransduction in fibroblasts depends on focal adhesion adaptor proteins that might function as molecular springs. We will stress the importance of the contractile actin cytoskeleton in balancing external with internal forces, and describe new results linking force-controlled actin dynamics directly to the expression of specific genes, among them the extracellular matrix protein tenascin-C. As assembly lines for diverse signaling pathways, matrix adhesion contacts are now recognized as the major sites of crosstalk between mechanical and chemical stimuli, with important consequences for cell growth and differentiation.
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Affiliation(s)
- Matthias Chiquet
- Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, Maulbeerstrasse 66, CH-4058, Basel, Switzerland.
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26
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How hair cells hear: the molecular basis of hair-cell mechanotransduction. Curr Opin Otolaryngol Head Neck Surg 2009; 16:445-51. [PMID: 18797287 DOI: 10.1097/moo.0b013e32830f4ac8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE OF REVIEW This review aims to summarize our current knowledge regarding mechanotransduction by hair cells and to highlight unresolved questions. RECENT FINDINGS Despite over a quarter of a century of electrophysiological data describing hair-cell mechanotransduction, the molecular basis of this process is just now being revealed. Recent work has begun to identify candidate transduction complex molecules, and current work is aimed at confirming these hypotheses and identifying other proteins important for hair-cell function. SUMMARY Our senses of hearing and balance rely on the exquisite sensitivity of the hair cell and its transduction complex. Understanding the molecular basis for hair-cell mechanotransduction may provide us with the foundation for understanding the causes of, and perhaps the treatments for, auditory and vestibular deficits resulting from hair-cell dysfunction.
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Primary processes in sensory cells: current advances. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2008; 195:1-19. [PMID: 19011871 DOI: 10.1007/s00359-008-0389-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2008] [Revised: 10/25/2008] [Accepted: 10/25/2008] [Indexed: 12/20/2022]
Abstract
In the course of evolution, the strong and unremitting selective pressure on sensory performance has driven the acuity of sensory organs to its physical limits. As a consequence, the study of primary sensory processes illustrates impressively how far a physiological function can be improved if the survival of a species depends on it. Sensory cells that detect single-photons, single molecules, mechanical motions on a nanometer scale, or incredibly small fluctuations of electromagnetic fields have fascinated physiologists for a long time. It is a great challenge to understand the primary sensory processes on a molecular level. This review points out some important recent developments in the search for primary processes in sensory cells that mediate touch perception, hearing, vision, taste, olfaction, as well as the analysis of light polarization and the orientation in the Earth's magnetic field. The data are screened for common transduction strategies and common transduction molecules, an aspect that may be helpful for researchers in the field.
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Ramakrishnan NA, Drescher MJ, Barretto RL, Beisel KW, Hatfield JS, Drescher DG. Calcium-dependent binding of HCN1 channel protein to hair cell stereociliary tip link protein protocadherin 15 CD3. J Biol Chem 2008; 284:3227-3238. [PMID: 19008224 DOI: 10.1074/jbc.m806177200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cytoplasmic amino terminus of HCN1, the primary full-length HCN isoform expressed in trout saccular hair cells, was found by yeast two-hybrid protocols to bind the cytoplasmic carboxyl-terminal domain of a protocadherin 15a-like protein. HCN1 was immunolocalized to discrete sites on saccular hair cell stereocilia, consistent with gradated distribution expected for tip link sites of protocadherin 15a. HCN1 message was also detected in cDNA libraries of rat cochlear inner and outer hair cells, and HCN1 protein was immunolocalized to cochlear hair cell stereocilia. As predicted by the trout hair cell model, the amino terminus of rat organ of Corti HCN1 was found by yeast two-hybrid analysis to bind the carboxyl terminus of protocadherin 15 CD3, a tip link protein implicated in mechanosensory transduction. Specific binding between HCN1 and protocadherin 15 CD3 was confirmed with pull-down assays and surface plasmon resonance analysis, both predicting dependence on Ca(2+). In the presence of calcium chelators, binding between HCN1 and protocadherin 15 CD3 was characterized by a K(D) = 2.39 x 10(-7) m. Ca(2+) at 26.5-68.0 microm promoted binding, with K(D) = 5.26 x 10(-8) m (at 61 microm Ca(2+)). Binding by deletion mutants of protocadherin 15 CD3 pointed to amino acids 158-179 (GenBank accession number XP_238200), with homology to the comparable region in trout hair cell protocadherin 15a-like protein, as necessary for binding to HCN1. Amino terminus binding of HCN1 to HCN1, hypothesized to underlie HCN1 channel formation, was also found to be Ca(2+)-dependent, although the binding was skewed toward a lower effective maximum [Ca(2+)] than for the HCN1 interaction with protocadherin 15 CD3. Competition may therefore exist in vivo between the two binding sites for HCN1, with binding of HCN1 to protocadherin 15 CD3 favored between 26.5 and 68 microm Ca(2+). Taken together, the evidence supports a role for HCN1 in mechanosensory transduction of inner ear hair cells.
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Affiliation(s)
- Neeliyath A Ramakrishnan
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Marian J Drescher
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201.
| | - Roberto L Barretto
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Kirk W Beisel
- Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - James S Hatfield
- Electron Microscopy Laboratory, Veterans Affairs Medical Center, Detroit, Michigan 48201
| | - Dennis G Drescher
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201; Departments of Biochemistry and Molecular Biology, Wayne State University School of Medicine, Detroit, Michigan 48201
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van Aken AFJ, Atiba-Davies M, Marcotti W, Goodyear RJ, Bryant JE, Richardson GP, Noben-Trauth K, Kros CJ. TRPML3 mutations cause impaired mechano-electrical transduction and depolarization by an inward-rectifier cation current in auditory hair cells of varitint-waddler mice. J Physiol 2008; 586:5403-18. [PMID: 18801844 PMCID: PMC2655368 DOI: 10.1113/jphysiol.2008.156992] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
TRPML3 (mucolipin-3) belongs to one of the transient-receptor-potential (TRP) ion channel families. Mutations in the Trpml3 gene cause disorganization of the stereociliary hair bundle, structural aberrations in outer and inner hair cells and stria vascularis defects, leading to deafness in the varitint-waddler (Va) mouse. Here we refined the stereociliary localization of TRPML3 and investigated cochlear hair cell function in varitint-waddler (Va(J)) mice carrying the TRPML3<I362T/A419P> mutations. Using a TRPML3-specific antibody we detected a approximately 68 kDa protein with near-equal expression levels in cochlea and vestibule of wild-type and Va(J) mutants. At postnatal days 3 and 5, we observed abundant localization of TRPML3 at the base of stereocilia near the position of the ankle links. This stereociliary localization domain was absent in Va(J) heterozygotes and homozygotes. Electrophysiological recordings revealed reduced mechano-electrical transducer currents in hair cells from Va(J)/+ and Va(J)/Va(J) mice. Furthermore, FM1-43 uptake and [(3)H]gentamicin accumulation were decreased in hair cells in cultured organs of Corti from Va(J)/+ and Va(J)/Va(J) mice. We propose that TRPML3 plays a critical role at the ankle-link region during hair-bundle growth and that an adverse effect of mutant TRPML3 on bundle development and mechano-electrical transduction is the main cause of hearing loss in Va(J)/+ mutant mice. Outer hair cells of Va(J)/Va(J) mice additionally had depolarized resting potentials due to an inwardly rectifying leak conductance formed by the mutant channels, leading over time to hair-cell degeneration and contributing to their deafness. Our findings argue against TRPML3 being a component of the hair-cell transducer channel.
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Dynamic length regulation of sensory stereocilia. Semin Cell Dev Biol 2008; 19:502-10. [PMID: 18692583 DOI: 10.1016/j.semcdb.2008.07.006] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2008] [Accepted: 07/15/2008] [Indexed: 01/02/2023]
Abstract
Stereocilia, the mechanosensory organelles of hair cells, are a distinctive class of actin-based cellular protrusions with an unparalleled ability to regulate their lengths over time. Studies on actin turnover in stereocilia, as well as the identification of several deafness-related proteins essential for proper stereocilia structure and function, provide new insights into the mechanisms and molecules involved in stereocilia length regulation and long-term maintenance. Comparisons of ongoing investigations on stereocilia with studies on other actin protrusions offer new opportunities to further understand common principles for length regulation, the diversity of its mechanisms, and how the specific needs of each cell are met.
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Chiquet M, Tunç-Civelek V, Sarasa-Renedo A. Gene regulation by mechanotransduction in fibroblasts. Appl Physiol Nutr Metab 2008; 32:967-73. [PMID: 18059623 DOI: 10.1139/h07-053] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Mechanical forces are important for connective tissue homeostasis. How do fibroblasts sense mechanical stress and how do they translate this information into an adaptive remodeling of the extracellular matrix (ECM)? Tenascin-C is rapidly induced in vivo by loading muscles and in vitro by stretching fibroblasts. Regulation of tenascin-C expression by mechanical signals occurs at the transcriptional level. Integrin receptors physically link the ECM to the cytoskeleton and act as force transducers: intracellular signals are triggered when integrins engage with ECM, and later when forces are applied. We found that cyclic strain does not induce tenascin-C messenger ribonucleic acid (mRNA) in fibroblasts lacking the beta1-integrin chain. An important link in integrin-dependent mechanotransduction is the small guanosine 5'-triphosphatase. RhoA and its target kinase, ROCK. In fibroblasts, cyclic strain activates RhoA and thereby induces ROCK-dependent actin assembly. Interestingly, tenascin-C mRNA induction by cyclic strain was suppressed by relaxing the cytoskeleton with a ROCK inhibitor or by actin depolymerization. Conversely, chemical activators of RhoA enhanced the effect of strain both on actin dynamics and on tenascin-C expression. Thus, RhoA/ROCK-controlled actin dynamics are required for the induction of specific ECM genes by mechanical stress. These findings have implications for the understanding of regeneration and for tissue engineering.
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Affiliation(s)
- Matthias Chiquet
- ITI Research Institute for Dental and Skeletal Biology, University of Bern, Murtenstrasse 35, CH-3010 Bern, Switzerland.
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Ugawa S, Ishida Y, Ueda T, Yu Y, Shimada S. Hypotonic stimuli enhance proton-gated currents of acid-sensing ion channel-1b. Biochem Biophys Res Commun 2007; 367:530-4. [PMID: 18158916 DOI: 10.1016/j.bbrc.2007.12.096] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Accepted: 12/12/2007] [Indexed: 11/19/2022]
Abstract
Acid-sensing ion channels (ASICs) are strong candidates for mammalian mechanoreceptors. We investigated whether mouse acid-sensing ion channel-1b (ASIC1b) is sensitive to mechanical stimuli using oocyte electrophysiology, because ASIC1b is located in the mechanosensory stereocilia of cochlear hair cells. Hypotonic stimuli that induced membrane stretch of oocytes evoked no significant current in ASIC1b-expressing oocytes at pH 7.5. However, acid (pH 4.0 or 5.0)-evoked currents in the oocytes were substantially enhanced by the hypotonicity, showing mechanosensitivity of ASIC1b and possible mechanogating of the channel in the presence of other components. Interestingly, the ASIC1b channel was permeable to K(+) (a principal charge carrier for cochlear sensory transduction) and the affinity of the channel for amiloride (IC(50) (inhibition constant)=approximately 48.3 microM) was quite similar to that described for the mouse hair cell mechanotransducer current. Taken together, these data raise the possibility that ASIC1b participates in cochlear mechanoelectrical transduction.
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Affiliation(s)
- Shinya Ugawa
- Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan
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Abstract
Mechanical stimuli generated by head movements and changes in sound pressure are detected by hair cells with amazing speed and sensitivity. The mechanosensitive organelle, the hair bundle, is a highly elaborated structure of actin-based stereocilia arranged in precise rows of increasing height. Extracellular linkages contribute to its cohesion and convey forces to mechanically gated channels. Channel opening is nearly instantaneous and is followed by a process of sensory adaptation that keeps the channels poised in their most sensitive range. This process is served by motors, scaffolds, and homeostatic mechanisms. The molecular constituents of this process are rapidly being elucidated, especially by the discovery of deafness genes and antibody targets.
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Affiliation(s)
- Melissa A Vollrath
- Howard Hughes Medical Institute and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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Picciani R, Desai K, Guduric-Fuchs J, Cogliati T, Morton CC, Bhattacharya SK. Cochlin in the eye: functional implications. Prog Retin Eye Res 2007; 26:453-69. [PMID: 17662637 PMCID: PMC2064858 DOI: 10.1016/j.preteyeres.2007.06.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Aqueous humor is actively produced in the ciliary epithelium of the anterior chamber and has important functions for the eye. Under normal physiological conditions, the inflow and outflow of the aqueous humor are tightly regulated, but in the pathologic state this balance is lost. Aqueous outflow involves structures of the anterior chamber and experiences most resistance at the level of the trabecular meshwork (TM) that acts as a filter. The modulation of the TM structure regulates the filter and its mechanism remains poorly understood. Proteomic analyses have identified cochlin, a protein of poorly understood function, in the glaucomatous TM but not in healthy control TM from human cadaver eyes. The presence of cochlin has subsequently been confirmed by Western and immunohistochemical analyses. Functionally, cochlin undergoes multimerization induced by shear stress and other changes in the microenvironment. Cochlin along with mucopolysaccharide deposits has been found in the TM of glaucoma patients and in the inner ear of subjects affected by the hearing disorder DNFA9, a late-onset, progressive disease that also involves alterations in fluid shear regimes. In vitro, cochlin induces aggregation of primary TM cells suggesting a role in cell adhesion, possibly in mechanosensation, and in modulation of the TM filter.
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Affiliation(s)
- Renata Picciani
- Bascom Palmer Eye Institute, University of Miami, Miami, Florida, 33136
| | - Kavita Desai
- Bascom Palmer Eye Institute, University of Miami, Miami, Florida, 33136
| | - Jasenka Guduric-Fuchs
- Centre for Vision Sciences, Queen's University School of Biomedical Sciences, BELFAST BT12 6BA, UK
| | - Tiziana Cogliati
- Centre for Vision Sciences, Queen's University School of Biomedical Sciences, BELFAST BT12 6BA, UK
| | - Cynthia C. Morton
- Harvard Medical School, Brigham and Women's Hospital New Research Building, Room 160D, 77 Avenue Louis Pasteur, Boston, MA 02115
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Ren T, Gillespie PG. A mechanism for active hearing. Curr Opin Neurobiol 2007; 17:498-503. [PMID: 17707636 PMCID: PMC2259439 DOI: 10.1016/j.conb.2007.07.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Accepted: 07/19/2007] [Indexed: 11/25/2022]
Abstract
The remarkable sensitivity, frequency selectivity, and nonlinearity of the cochlea have been attributed to the putative 'cochlear amplifier', which consumes metabolic energy to amplify the cochlear mechanical response to sounds. Recent studies have demonstrated that outer hair cells actively generate force using somatic electromotility and active hair-bundle motion. However, the expected power gain of the cochlear amplifier has not been demonstrated experimentally, and the measured location of cochlear nonlinearity is inconsistent with the predicted location of the cochlear amplifier. We instead propose a 'cochlear transformer' mechanism to interpret cochlear performance.
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Affiliation(s)
- Tianying Ren
- Oregon Hearing Research Center, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, NRC 04, Portland, OR 97239-3098, USA.
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Mechanical signatures of transducer gating in the Drosophila ear. Curr Biol 2007; 17:1000-6. [PMID: 17524645 DOI: 10.1016/j.cub.2007.05.004] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Revised: 05/03/2007] [Accepted: 05/04/2007] [Indexed: 11/23/2022]
Abstract
Hearing relies on dedicated mechanotransducer channels that convert sound-induced vibrations into electrical signals [1]. Linking this transduction to identified proteins has proven difficult because of the scarcity of native auditory transducers and their tight functional integration into ears [2-4]. We describe an in vivo paradigm for the noninvasive study of auditory transduction. By investigating displacement responses of the Drosophila sound receiver, we identify mechanical signatures that are consistent with a direct mechanotransducer gating in the fly's ear. These signatures include a nonlinear compliance that correlates with electrical nerve responses, shifts with adaptation, and conforms to the gating-spring model of vertebrate auditory transduction. Analyzing this gating compliance in terms of the gating-spring model reveals striking parallels between the transducer mechanisms for hearing in vertebrates and flies. Our findings provide first insights into the mechanical workings of invertebrate mechanotransducer channels and set the stage for using Drosophila to specifically search for, and probe the roles of, auditory transducer components.
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Schneider ME, Dosé AC, Salles FT, Chang W, Erickson FL, Burnside B, Kachar B. A new compartment at stereocilia tips defined by spatial and temporal patterns of myosin IIIa expression. J Neurosci 2006; 26:10243-52. [PMID: 17021180 PMCID: PMC6674622 DOI: 10.1523/jneurosci.2812-06.2006] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Class III myosins are motor proteins that contain an N-terminal kinase domain and a C-terminal actin-binding domain. We show that myosin IIIa, which has been implicated in nonsyndromic progressive hearing loss, is localized at stereocilia tips. Myosin IIIa progressively accumulates during stereocilia maturation in a thimble-like pattern around the stereocilia tip, distinct from the cap-like localization of myosin XVa and the shaft localization of myosin Ic. Overexpression of deletion mutants for functional domains of green fluorescent protein (GFP)-myosin IIIa shows that the motor domain, but not the actin-binding tail domain, is required for stereocilia tip localization. Deletion of the kinase domain produces stereocilia elongation and bulging of the stereocilia tips. The thimble-like localization and the influence myosin IIIa has on stereocilia shape reveal a previously unrecognized molecular compartment at the distal end of stereocilia, the site of actin polymerization as well as operation of the mechanoelectrical transduction apparatus.
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Affiliation(s)
- Mark E. Schneider
- Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892
| | - Andréa C. Dosé
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, and
| | - Felipe T. Salles
- Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892
| | - Weise Chang
- Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892
| | - Floyd L. Erickson
- Department of Biological Sciences, Salisbury University, Salisbury, Maryland 21801
| | - Beth Burnside
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, and
| | - Bechara Kachar
- Section on Structural Cell Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892
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