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Mitochondrial calcium uniporter is essential for hearing and hair cell preservation in congenic FVB/NJ mice. Sci Rep 2021; 11:9660. [PMID: 33958614 PMCID: PMC8102556 DOI: 10.1038/s41598-021-88841-0] [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: 12/08/2020] [Accepted: 04/13/2021] [Indexed: 12/12/2022] Open
Abstract
Mitochondrial Ca2+ regulates a wide range of cell processes, including morphogenesis, metabolism, excitotoxicity, and survival. In cochlear hair cells, the activation of mechano-electrical transduction and voltage-gated Ca2+ channels result in a large influx of Ca2+. The intracellular rise in Ca2+ is partly balanced by the mitochondria which rapidly uptakes Ca2+ via a highly selective channel comprised of the main pore-forming subunit, the mitochondrial Ca2+ uniporter (MCU), and associated regulatory proteins. MCU thus contributes to Ca2+ buffering, ensuring cytosolic homeostasis, and is posited to have a critical role in hair cell function and hearing. To test this hypothesis, Ca2+ homeostasis in hair cells and cochlear function were investigated in FVB/NJ mice carrying the knockout allele of Mcu (Mcu+/− or Mcu−/−). The Mcu knockout allele, which originated in C57BL/6 strain cosegregated along with Cdh23ahl allele to the FVB/NJ strain, due to the close proximity of these genes. Neither Mcu+/− nor Mcu−/− genotypes affected cochlear development, morphology, or Ca2+ homeostasis of auditory hair cells in the first two postnatal weeks. However, Mcu−/− mice displayed high-frequency hearing impairment as early as 3 weeks postnatal, which then progressed to profound hearing loss at all frequencies in about 6 months. In Mcu+/− mice, significantly elevated ABR thresholds were observed at 6 months and 9 months of age only at 32 kHz frequency. In three-month-old Mcu−/− mice, up to 18% of the outer hair cells and occasionally some inner hair cells were missing in the mid-cochlear region. In conclusion, mitochondrial Ca2+ uniporter is not required for the development of cochlea in mice, but is essential for hearing and hair cell preservation in congenic FVB/NJ mice.
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Myosin-XVa Controls Both Staircase Architecture and Diameter Gradation of Stereocilia Rows in the Auditory Hair Cell Bundles. J Assoc Res Otolaryngol 2020; 21:121-135. [PMID: 32152769 DOI: 10.1007/s10162-020-00745-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 02/04/2020] [Indexed: 02/08/2023] Open
Abstract
Mammalian hair cells develop their mechanosensory bundles through consecutive phases of stereocilia elongation, thickening, and retraction of supernumerary stereocilia. Many molecules involved in stereocilia elongation have been identified, including myosin-XVa. Significantly less is known about molecular mechanisms of stereocilia thickening and retraction. Here, we used scanning electron microscopy (SEM) to quantify postnatal changes in number and diameters of the auditory hair cell stereocilia in shaker-2 mice (Myo15sh2) that lack both "long" and "short" isoforms of myosin-XVa, and in mice lacking only the "long" myosin-XVa isoform (Myo15∆N). Previously, we observed large mechanotransduction current in young postnatal inner (IHC) and outer (OHC) hair cells of both these strains. Stereocilia counts showed nearly identical developmental retraction of supernumerary stereocilia in control heterozygous, Myo15sh2/sh2, and Myo15∆N/∆N mice, suggesting that this retraction is largely unaffected by myosin-XVa deficiency. However, myosin-XVa deficiency does affect stereocilia diameters. In control, the first (tallest) and second row stereocilia grow in diameter simultaneously. However, the third row stereocilia in IHCs grow only until postnatal day 1-2 and then become thinner. In OHCs, they also grow slower than taller stereocilia, forming a stereocilia diameter gradation within a hair bundle. The sh2 mutation disrupts this gradation and makes all stereocilia nearly identical in thickness in both IHCs and OHCs, with only subtle residual diameter differences. All Myo15sh2/sh2 stereocilia grow postnatally including the third row, which is not a part of normal development. Serial sections with focused ion beam (FIB)-SEM confirmed that diameter changes of Myo15sh2/sh2 IHC and OHC stereocilia resulted from corresponding changes of their actin cores. In contrast to Myo15sh2/sh2, Myo15∆N/∆N hair cells develop prominent stereocilia diameter gradation. Thus, besides building the staircase, the short isoform of myosin-XVa is essential for controlling the diameter of the third row stereocilia and formation of the stereocilia diameter gradation in a hair bundle.
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Friedman TB, Belyantseva IA, Frolenkov GI. Myosins and Hearing. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1239:317-330. [DOI: 10.1007/978-3-030-38062-5_13] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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Akbariazar E, Vahabi A, Abdi Rad I. Report of a Novel Splicing Mutation in the MYO15A Gene in a Patient With Sensorineural Hearing Loss and Spectrum of the MYO15A Mutations. CLINICAL MEDICINE INSIGHTS-CASE REPORTS 2019; 12:1179547619871907. [PMID: 31579092 PMCID: PMC6757496 DOI: 10.1177/1179547619871907] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 07/30/2019] [Indexed: 12/29/2022]
Abstract
Introduction Autosomal recessive non-syndromic hearing loss (ARNSHL) is a genetically heterogeneous sensorineural disorder with an approximate incidence of 1.4:1000 in neonates. Mutations in more than 60 genes including the MYO15A gene has been reported in patients affected with ARNSHL. In the present study, we report a novel MYO15A mutation identified by clinical exome sequencing and confirmed by Sanger sequencing in a consanguineous Iranian family with ARNSHL. Case presentation A 22-year-old woman with congenital non-syndromic sensorineural hearing loss referred to our medical genetic center. Her parents were consanguineous with F = 1/16 (first cousin), and clinical examination of the patient exclude dysmorphic features. Sanger sequencing of GJB2 and GJB6 genes, which are the most common causes of ARNSHL, was negative. Then she underwent clinical exome sequencing. Outcome We found a novel homozygote variant (c.9611_9612+8delTGGTGAGCAT) in the MYO15A gene which creates a shift in the reading frame starting at codon 3204. This variant was confirmed by Sanger sequencing in the patient and also in her parents who were heterozygous. Discussion The present results suggest that the homozygous MYO15A (c.9611_9612+8delTGGTGAGCAT) variant is a pathogenic mutation and to the best of our knowledge, this mutation has not been reported in any database.
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Affiliation(s)
- Elinaz Akbariazar
- Department of Genetics, Urmia University of Medical Sciences, Urmia, Iran
| | - Ali Vahabi
- Department of Genetics, Urmia University of Medical Sciences, Urmia, Iran
| | - Isa Abdi Rad
- Department of Genetics, Urmia University of Medical Sciences, Urmia, Iran.,Cellular and Molecular Research Center, Urmia University of Medical Sciences, Urmia, Iran
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Transcriptomic analysis of mouse cochleae suffering from gentamicin damage reveals the signalling pathways involved in hair cell regeneration. Sci Rep 2019; 9:10494. [PMID: 31324869 PMCID: PMC6642124 DOI: 10.1038/s41598-019-47051-5] [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: 01/02/2019] [Accepted: 07/05/2019] [Indexed: 01/13/2023] Open
Abstract
There is a strong capacity for hair cell regeneration after damage in the inner ear of non-mammals. However, mammalian hair cells are substantially unable to regenerate. To obtain insights into the mechanism of this difference, we analyzed the transcriptomic changes in the mouse cochleae suffered from gentamicin damage and compared them with those in the chick cochleae suffered from the same damage. The results indicated that 2,230 genes had significantly differential expression between the gentamicin- and saline-treated mouse cochleae. Some of the differentially expressed genes were grouped into 265 signaling pathways, including the Notch, Wnt (Wingless and INT-1), Bmp (bone morphogenetic protein), FGF (fibroblast growth factor) and Shh (sonic hedgehog) pathways. Using pharmacological inhibitors or agonists of these pathways, the effects of these pathways on hair cell regeneration were further studied. The results indicated that Bmp alone and its coregulation with the Notch or Wnt signaling pathways increased the numbers of generated cells from transdifferentiation or proliferation in the mouse cochlea after damage, in addition to the reported coregulation of Notch and Wnt. Thus, this work indicates a new signaling pathway (Bmp) and its synergetic coregulation in mammalian hair cell regeneration, providing potential therapeutic targets to increase mammalian hair cell regeneration.
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Bai H, Wang X, Gao X, Bing J, Wang W, Zhang X, Xi C, Jiang L, Zhang X, Han Z, Zeng S, Xu J. Study of the Mechanisms by Which Aminoglycoside Damage Is Prevented in Chick Embryonic Hair Cells. J Assoc Res Otolaryngol 2018; 20:21-35. [PMID: 30341698 DOI: 10.1007/s10162-018-00700-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Accepted: 09/21/2018] [Indexed: 11/27/2022] Open
Abstract
A major side effect of aminoglycoside antibiotics is mammalian hair cell death. It is thus intriguing that embryonic chick hair cells treated with aminoglycosides at embryonic day (E) 12 are insensitive to ototoxicity. To exclude some unknown factors in vivo that might be involved in preventing aminoglycoside damage to embryonic hair cells, we first cultured chick embryonic basilar papilla (BP) with an aminoglycoside antibiotic in vitro. The results indicated that the hair cells were almost intact at E12 and E14 and were only moderately damaged in most parts of the BP at E16 and E18. Generally, hair cells residing in the approximate and abneural regions were more susceptible to streptomycin damage. After incubation with gentamicin-conjugated Texas Red (GTTR), which is typically used to trace the entry route of aminoglycosides, GTTR fluorescence was not remarkable in hair cells at E12, was weak at E14, but was relatively strong in the proximal part of BP at E18. This result indicates that the amounts of GTTR that entered the hair cells are related to the degrees of aminoglycoside damage. The study further showed that the fluorescence intensity of GTTR decreased to a low level at E14 to E18 after disruption of mechanotransduction machinery, suggesting that the aminoglycoside entry into hair cells was mainly through mechanotransduction channels. In addition, most of the entered GTTR was not found to be colocalized with mitochondria even at E18. This finding provides another reason to explain why embryonic chick hair cells are insensitive to aminoglycoside damage.
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Affiliation(s)
- Huanju Bai
- Beijing Key Laboratory of Gene Resource and Molecular Development, Beijing Normal University, Beijing, 100875, China
| | - Xi Wang
- Department of Otorhinolaryngology, The General Hospital of the PLA Rocket Force, Beijing, 100088, China
| | - Xue Gao
- Department of Otorhinolaryngology, The General Hospital of the PLA Rocket Force, Beijing, 100088, China
| | - Jie Bing
- Beijing Key Laboratory of Gene Resource and Molecular Development, Beijing Normal University, Beijing, 100875, China
| | - Weiqian Wang
- Department of Otorhinolaryngology, The General Hospital of the PLA Rocket Force, Beijing, 100088, China
| | - Xuebo Zhang
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, College of Life Sciences, Hainan Normal University, Haikou, 571158, China
| | - Chao Xi
- Beijing Key Laboratory of Gene Resource and Molecular Development, Beijing Normal University, Beijing, 100875, China
| | - Lingling Jiang
- Beijing Key Laboratory of Gene Resource and Molecular Development, Beijing Normal University, Beijing, 100875, China
| | - Xinwen Zhang
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, College of Life Sciences, Hainan Normal University, Haikou, 571158, China
| | - Zhongming Han
- Department of Otorhinolaryngology, The General Hospital of the PLA Rocket Force, Beijing, 100088, China
| | - Shaoju Zeng
- Beijing Key Laboratory of Gene Resource and Molecular Development, Beijing Normal University, Beijing, 100875, China.
| | - Jincao Xu
- Department of Otorhinolaryngology, The General Hospital of the PLA Rocket Force, Beijing, 100088, China.
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Rehman AU, Bird JE, Faridi R, Shahzad M, Shah S, Lee K, Khan SN, Imtiaz A, Ahmed ZM, Riazuddin S, Santos-Cortez RLP, Ahmad W, Leal SM, Riazuddin S, Friedman TB. Mutational Spectrum of MYO15A and the Molecular Mechanisms of DFNB3 Human Deafness. Hum Mutat 2016; 37:991-1003. [PMID: 27375115 DOI: 10.1002/humu.23042] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 06/26/2016] [Indexed: 12/17/2022]
Abstract
Deafness in humans is a common neurosensory disorder and is genetically heterogeneous. Across diverse ethnic groups, mutations of MYO15A at the DFNB3 locus appear to be the third or fourth most common cause of autosomal-recessive, nonsyndromic deafness. In 49 of the 67 exons of MYO15A, there are currently 192 recessive mutations identified, including 14 novel mutations reported here. These mutations are distributed uniformly across MYO15A with one enigmatic exception; the alternatively spliced giant exon 2, encoding 1,233 residues, has 17 truncating mutations but no convincing deafness-causing missense mutations. MYO15A encodes three distinct isoform classes, one of which is 395 kDa (3,530 residues), the largest member of the myosin superfamily of molecular motors. Studies of Myo15 mouse models that recapitulate DFNB3 revealed two different pathogenic mechanisms of hearing loss. In the inner ear, myosin 15 is necessary both for the development and the long-term maintenance of stereocilia, mechanosensory sound-transducing organelles that extend from the apical surface of hair cells. The goal of this Mutation Update is to provide a comprehensive review of mutations and functions of MYO15A.
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Affiliation(s)
- Atteeq U Rehman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Jonathan E Bird
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Rabia Faridi
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892.,Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 54550, Pakistan
| | - Mohsin Shahzad
- Department of Otorhinolaryngology Head & Neck Surgery, School of Medicine, University of Maryland, Baltimore, Maryland, 21201
| | - Sujay Shah
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Kwanghyuk Lee
- Center for Statistical Genetics, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Shaheen N Khan
- Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 54550, Pakistan
| | - Ayesha Imtiaz
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Zubair M Ahmed
- Department of Otorhinolaryngology Head & Neck Surgery, School of Medicine, University of Maryland, Baltimore, Maryland, 21201
| | - Saima Riazuddin
- Department of Otorhinolaryngology Head & Neck Surgery, School of Medicine, University of Maryland, Baltimore, Maryland, 21201
| | - Regie Lyn P Santos-Cortez
- Center for Statistical Genetics, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Wasim Ahmad
- Department of Biochemistry, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad, 45320, Pakistan
| | - Suzanne M Leal
- Center for Statistical Genetics, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Sheikh Riazuddin
- Allama Iqbal Medical Research Centre, Jinnah Hospital Complex, University of Health Sciences, Lahore, 54550, Pakistan
| | - Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892.
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Alternative Splice Forms Influence Functions of Whirlin in Mechanosensory Hair Cell Stereocilia. Cell Rep 2016; 15:935-943. [PMID: 27117407 PMCID: PMC4859837 DOI: 10.1016/j.celrep.2016.03.081] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Revised: 02/18/2016] [Accepted: 03/22/2016] [Indexed: 11/23/2022] Open
Abstract
WHRN (DFNB31) mutations cause diverse hearing disorders: profound deafness (DFNB31) or variable hearing loss in Usher syndrome type II. The known role of WHRN in stereocilia elongation does not explain these different pathophysiologies. Using spontaneous and targeted Whrn mutants, we show that the major long (WHRN-L) and short (WHRN-S) isoforms of WHRN have distinct localizations within stereocilia and also across hair cell types. Lack of both isoforms causes abnormally short stereocilia and profound deafness and vestibular dysfunction. WHRN-S expression, however, is sufficient to maintain stereocilia bundle morphology and function in a subset of hair cells, resulting in some auditory response and no overt vestibular dysfunction. WHRN-S interacts with EPS8, and both are required at stereocilia tips for normal length regulation. WHRN-L localizes midway along the shorter stereocilia, at the level of inter-stereociliary links. We propose that differential isoform expression underlies the variable auditory and vestibular phenotypes associated with WHRN mutations. Major WHRN isoforms WHRN-S and WHRN-L have distinct localizations within stereocilia Lack of WHRN-S and WHRN-L causes short stereocilia bundles and profound deafness In absence of WHRN-L, WHRN-S can preserve stereocilia length in certain hair cells Differential isoform expression underlies distinct phenotypes of known Whrn mutations
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9
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Abstract
Hair cells are designed to sense mechanical stimuli of sound using their apical stereocilia hair bundles. Mechanical deflection of this hair bundle is converted into an electrical signal through gating of mechano-electric transduction channels. Stiff probe stimulation of hair bundles is an invaluable tool for studying the transduction channel and its associated processes because of the speed and ability to precisely control hair bundle position. Proper construction of these devices is critical to their ultimate performance as is appropriate placement of the probe onto the hair bundle. Here we describe the construction and use of a glass probe coupled to a piezo-electric actuator for stimulating hair bundles, including the basic technique for positioning of the stimulating probe onto the hair bundle. These piezo-electric stimulators can be adapted to other mechanically sensitive systems.
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Affiliation(s)
- Anthony W Peng
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, 300 Pasteur Drive, Edwards Bldg., Stanford, CA, 94025, USA
- Department of Physiology and Biophysics, University of Colorado Anschutz Medical Campus, 12800 E 19th Ave Rm7127, Aurora, CO, 80045, USA
| | - Anthony J Ricci
- Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, 300 Pasteur Drive, Edwards Bldg., Stanford, CA, 94025, USA.
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, 94025, USA.
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Zou J, Mathur PD, Zheng T, Wang Y, Almishaal A, Park AH, Yang J. Individual USH2 proteins make distinct contributions to the ankle link complex during development of the mouse cochlear stereociliary bundle. Hum Mol Genet 2015; 24:6944-57. [PMID: 26401052 DOI: 10.1093/hmg/ddv398] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Accepted: 09/21/2015] [Indexed: 11/14/2022] Open
Abstract
Usher syndrome (USH) is the leading cause of inherited deaf-blindness, with type 2 (USH2) being the most common clinical form. Studies suggest that proteins encoded by USH2 causative genes assemble into the ankle link complex (ALC) at the hair cell stereociliary bundle; however, little is known about the in vivo assembly and function of this complex. Using various USH2 mutant mice, we showed by immunofluorescence that USH2 proteins play different roles in cochlear ALC assembly, with G protein-coupled receptor 98 being the most important protein. Complex assembly likely occurs at the stereociliary bundle but not along the protein transport route in the cell body. Stereociliary morphological defects in USH2 mutant mice suggest roles for the ALC in regulating inner hair cell stereociliary growth and differentiation as well as outer hair cell stereociliary rigidity and organization during development. These roles are unique from the bundle cohesion role of Usher syndrome type 1 protein complexes. Loss of individual USH2 gene expressions leads to variable morphological and functional consequences, correlating with the severity of ALC disruption. This finding suggests a potential genotype-phenotype correlation in USH2 patients. In summary, this study provides novel insights into the molecular mechanism underlying cochlear stereociliary bundle development and hearing loss pathogenesis of various USH2 subtypes. Our thorough phenotypical characterization of USH2 mouse models is essential for future use of these animal models in therapeutic development.
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Affiliation(s)
- Junhuang Zou
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA
| | - Pranav D Mathur
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA, Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT 84132, USA
| | - Tihua Zheng
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA
| | - Yong Wang
- Division of Otolaryngology, Department of Surgery, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132, USA and
| | - Ali Almishaal
- Department of Communication Sciences and Disorders, University of Utah, 390 South 1530 East, Salt Lake City, UT 84112, USA
| | - Albert H Park
- Division of Otolaryngology, Department of Surgery, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132, USA and
| | - Jun Yang
- Department of Ophthalmology and Visual Sciences, Moran Eye Center, University of Utah, 65 Mario Capecchi Drive, Salt Lake City, UT 84132, USA, Department of Neurobiology and Anatomy, University of Utah, 20 North 1900 East, Salt Lake City, UT 84132, USA, Division of Otolaryngology, Department of Surgery, University of Utah, 30 North 1900 East, Salt Lake City, UT 84132, USA and
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11
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Lu X, Sipe CW. Developmental regulation of planar cell polarity and hair-bundle morphogenesis in auditory hair cells: lessons from human and mouse genetics. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2015; 5:85-101. [PMID: 26265594 DOI: 10.1002/wdev.202] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Revised: 06/12/2015] [Accepted: 06/29/2015] [Indexed: 12/11/2022]
Abstract
Hearing loss is the most common and costly sensory defect in humans and genetic causes underlie a significant proportion of affected individuals. In mammals, sound is detected by hair cells (HCs) housed in the cochlea of the inner ear, whose function depends on a highly specialized mechanotransduction organelle, the hair bundle. Understanding the factors that regulate the development and functional maturation of the hair bundle is crucial for understanding the pathophysiology of human deafness. Genetic analysis of deafness genes in animal models, together with complementary forward genetic screens and conditional knock-out mutations in essential genes, have provided great insights into the molecular machinery underpinning hair-bundle development and function. In this review, we highlight recent advances in our understanding of hair-bundle morphogenesis, with an emphasis on the molecular pathways governing hair-bundle polarity and orientation. We next discuss the proteins and structural elements important for hair-cell mechanotransduction as well as hair-bundle cohesion and maintenance. In addition, developmental signals thought to regulate tonotopic features of HCs are introduced. Finally, novel approaches that complement classic genetics for studying the molecular etiology of human deafness are presented. WIREs Dev Biol 2016, 5:85-101. doi: 10.1002/wdev.202 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Xiaowei Lu
- Department of Cell Biology, University of Virginia, Charlottesville, VA, USA
| | - Conor W Sipe
- Department of Biology, University of Virginia, Charlottesville, VA, USA
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12
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Mathur P, Yang J. Usher syndrome: Hearing loss, retinal degeneration and associated abnormalities. Biochim Biophys Acta Mol Basis Dis 2014; 1852:406-20. [PMID: 25481835 DOI: 10.1016/j.bbadis.2014.11.020] [Citation(s) in RCA: 222] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 11/25/2014] [Accepted: 11/26/2014] [Indexed: 02/06/2023]
Abstract
Usher syndrome (USH), clinically and genetically heterogeneous, is the leading genetic cause of combined hearing and vision loss. USH is classified into three types, based on the hearing and vestibular symptoms observed in patients. Sixteen loci have been reported to be involved in the occurrence of USH and atypical USH. Among them, twelve have been identified as causative genes and one as a modifier gene. Studies on the proteins encoded by these USH genes suggest that USH proteins interact among one another and function in multiprotein complexes in vivo. Although their exact functions remain enigmatic in the retina, USH proteins are required for the development, maintenance and function of hair bundles, which are the primary mechanosensitive structure of inner ear hair cells. Despite the unavailability of a cure, progress has been made to develop effective treatments for this disease. In this review, we focus on the most recent discoveries in the field with an emphasis on USH genes, protein complexes and functions in various tissues as well as progress toward therapeutic development for USH.
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Affiliation(s)
- Pranav Mathur
- Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, UT 84132, USA; Department of Neurobiology and Anatomy, University of Utah, Salt Lake City, UT 84132, USA
| | - Jun Yang
- Department of Ophthalmology and Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, UT 84132, USA; Department of Neurobiology and Anatomy, University of Utah, Salt Lake City, UT 84132, USA; Department of Otolaryngology Head and Neck Surgery, University of Utah, Salt Lake City, UT 84132, USA.
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13
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Abstract
Usher syndrome (USH) is a neurosensory disorder affecting both hearing and vision in humans. Linkage studies of families of USH patients, studies in animals, and characterization of purified proteins have provided insight into the molecular mechanisms of hearing. To date, 11 USH proteins have been identified, and evidence suggests that all of them are crucial for the function of the mechanosensory cells of the inner ear, the hair cells. Most USH proteins are localized to the stereocilia of the hair cells, where mechano-electrical transduction (MET) of sound-induced vibrations occurs. Therefore, elucidation of the functions of USH proteins in the stereocilia is a prerequisite to understanding the exact mechanisms of MET.
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Affiliation(s)
- Zubair M Ahmed
- Division of Pediatric Ophthalmology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Ohio
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Indzhykulian AA, Stepanyan R, Nelina A, Spinelli KJ, Ahmed ZM, Belyantseva IA, Friedman TB, Barr-Gillespie PG, Frolenkov GI. Molecular remodeling of tip links underlies mechanosensory regeneration in auditory hair cells. PLoS Biol 2013; 11:e1001583. [PMID: 23776407 PMCID: PMC3679001 DOI: 10.1371/journal.pbio.1001583] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 05/02/2013] [Indexed: 11/18/2022] Open
Abstract
Sound detection by inner ear hair cells requires tip links that interconnect mechanosensory stereocilia and convey force to yet unidentified transduction channels. Current models postulate a static composition of the tip link, with protocadherin 15 (PCDH15) at the lower and cadherin 23 (CDH23) at the upper end of the link. In terminally differentiated mammalian auditory hair cells, tip links are subjected to sound-induced forces throughout an organism's life. Although hair cells can regenerate disrupted tip links and restore hearing, the molecular details of this process are unknown. We developed a novel implementation of backscatter electron scanning microscopy to visualize simultaneously immuno-gold particles and stereocilia links, both of only a few nanometers in diameter. We show that functional, mechanotransduction-mediating tip links have at least two molecular compositions, containing either PCDH15/CDH23 or PCDH15/PCDH15. During regeneration, shorter tip links containing nearly equal amounts of PCDH15 at both ends appear first. Whole-cell patch-clamp recordings demonstrate that these transient PCDH15/PCDH15 links mediate mechanotransduction currents of normal amplitude but abnormal Ca(2+)-dependent decay (adaptation). The mature PCDH15/CDH23 tip link composition is re-established later, concomitant with complete recovery of adaptation. Thus, our findings provide a molecular mechanism for regeneration and maintenance of mechanosensory function in postmitotic auditory hair cells and could help identify elusive components of the mechanotransduction machinery.
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Affiliation(s)
- Artur A. Indzhykulian
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Ruben Stepanyan
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Anastasiia Nelina
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
| | - Kateri J. Spinelli
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Zubair M. Ahmed
- Division of Pediatric Ophthalmology, Cincinnati Children's Research Foundation, Cincinnati, Ohio, United States of America
| | - Inna A. Belyantseva
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland, United States of America
| | - Thomas B. Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, Maryland, United States of America
| | - Peter G. Barr-Gillespie
- Oregon Hearing Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Gregory I. Frolenkov
- Department of Physiology, University of Kentucky, Lexington, Kentucky, United States of America
- * E-mail:
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15
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Kazmierczak P, Müller U. Sensing sound: molecules that orchestrate mechanotransduction by hair cells. Trends Neurosci 2011; 35:220-9. [PMID: 22177415 DOI: 10.1016/j.tins.2011.10.007] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2011] [Revised: 10/25/2011] [Accepted: 10/27/2011] [Indexed: 01/19/2023]
Abstract
Animals use acoustic signals to communicate and to obtain information about their environment. The processing of acoustic signals is initiated at auditory sense organs, where mechanosensory hair cells convert sound-induced vibrations into electrical signals. Although the biophysical principles underlying the mechanotransduction process in hair cells have been characterized in much detail over the past 30 years, the molecular building-blocks of the mechanotransduction machinery have proved to be difficult to determine. We review here recent studies that have both identified some of these molecules and established the mechanisms by which they regulate the activity of the still-elusive mechanotransduction channel.
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Affiliation(s)
- Piotr Kazmierczak
- Dorris Neuroscience Center, Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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16
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Abstract
Morphogenesis of sensory hair cells, in particular their mechanotransduction organelle, the stereociliary bundle, requires highly organized remodeling of the actin cytoskeleton. The roles of Rho family small GTPases during this process remain unknown. Here we show that deletion of Rac1 in the otic epithelium resulted in severe defects in cochlear epithelial morphogenesis. The mutant cochlea was severely shortened with a reduced number of auditory hair cells and cellular organization of the auditory sensory epithelium was abnormal. Rac1 mutant hair cells also displayed defects in planar cell polarity and morphogenesis of the stereociliary bundle, including bundle fragmentation or deformation, and mispositioning or absence of the kinocilium. We further demonstrate that a Rac-PAK (p21-activated kinase) signaling pathway mediates kinocilium-stereocilia interactions and is required for cohesion of the stereociliary bundle. Together, these results reveal a critical function of Rac1 in morphogenesis of the auditory sensory epithelium and stereociliary bundle.
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17
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Furness DN, Hackney CM, Evans MG. Localisation of the mechanotransducer channels in mammalian cochlear hair cells provides clues to their gating. J Physiol 2009; 588:765-72. [PMID: 20026619 DOI: 10.1113/jphysiol.2009.179614] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Our sense of hearing and balance relies on the very rapid gating of mechanotransducer channels known to be located close to the tops of the hair cell stereocilia within the stereociliary bundle. The molecular identity of the channels is unknown but functional aspects such as permeation, block and sensitivity to bundle displacement are well known. The channel has high calcium permeability and this feature has been used in conjunction with fast confocal calcium imaging to unambiguously localise the channels at the top of the two shorter rows of stereocilia in mammalian cochlear hair cells. The data suggest that they are completely absent from the tallest row. It is thought that the structures connecting stereocilia in adjacent rows, the tip links, are either directly responsible for the channel's mechanical gating, or are closely associated with the gating process. The channels must therefore be associated with the bottom part of the tip links and not the top. This feature has important implications for both the channel's gating mechanism and its regulatory adaptation mechanism. The tip link remains an attractive candidate for mechanical coupling between the bundle and the channel or an accessory protein. The localisation of the mechanotransducer channels to the lower end of the tip link represents an important milestone in the journey towards eventual identification of the channel and its gating mechanism.
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Affiliation(s)
- David N Furness
- Keele University, School of Life Sciences, Neuroscience Group, Institute for Science and Technology in Medicine, Keele ST5 5BG, UK
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18
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Shearer AE, Hildebrand MS, Webster JA, Kahrizi K, Meyer NC, Jalalvand K, Arzhanginy S, Kimberling WJ, Stephan D, Bahlo M, Smith RJH, Najmabadi H. Mutations in the first MyTH4 domain of MYO15A are a common cause of DFNB3 hearing loss. Laryngoscope 2009; 119:727-33. [PMID: 19274735 DOI: 10.1002/lary.20116] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
OBJECTIVES To use clinical and genetic analyses to determine the mutation causing autosomal recessive nonsyndromic hearing loss (ARNSHL) segregating in two consanguineous Iranian families. STUDY DESIGN Family study. METHODS Members of each family received otologic and audiometric examination for the type and extent of hearing loss. Linkage mapping using Affymetrix 50K GeneChips and short tandem repeat (STRP) analysis localized the hearing loss in both families to the DFNB3 locus. Direct sequencing of the MYO15A gene was completed on affected members of both families. RESULTS Family L-3165 segregated a novel homozygous missense mutation (c.6371G>A) that results in a p.R2124Q amino acid substitution in the myosin XVa protein, while family L-896 segregated a novel homozygous missense (c.6555C>T) mutation resulting in a p.P2073S amino acid change. CONCLUSIONS These are the first MYO15A mutations reported to cause DFNB3 sensorineural hearing loss in the Iranian population. Like other mutations located in the myosin tail homology 4 (MyTH4) domain, the p.R2124Q and p.P2073S mutations are predicted to disrupt the function of the myosin XVa protein, which is integral to the mechanosensory activity of hair cells in the inner ear.
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Affiliation(s)
- A Eliot Shearer
- Department of Otolaryngology-Head and Neck Surgery, University of Iowa, Iowa City, Iowa 52242, USA
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19
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Fast adaptation and Ca2+ sensitivity of the mechanotransducer require myosin-XVa in inner but not outer cochlear hair cells. J Neurosci 2009; 29:4023-34. [PMID: 19339598 DOI: 10.1523/jneurosci.4566-08.2009] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In inner ear hair cells, activation of mechanotransduction channels is followed by extremely rapid deactivation that depends on the influx of Ca(2+) through these channels. Although the molecular mechanisms of this "fast" adaptation are largely unknown, the predominant models assume Ca(2+) sensitivity as an intrinsic property of yet unidentified mechanotransduction channels. Here, we examined mechanotransduction in the hair cells of young postnatal shaker 2 mice (Myo15(sh2/sh2)). These mice have no functional myosin-XVa, which is critical for normal growth of mechanosensory stereocilia of hair cells. Although stereocilia of both inner and outer hair cells of Myo15(sh2/sh2) mice lack myosin-XVa and are abnormally short, these cells have dramatically different hair bundle morphology. Myo15(sh2/sh2) outer hair cells retain a staircase arrangement of the abnormally short stereocilia and prominent tip links. Myo15(sh2/sh2) inner hair cells do not have obliquely oriented tip links, and their mechanosensitivity is mediated exclusively by "top-to-top" links between equally short stereocilia. In both inner and outer hair cells of Myo15(sh2/sh2) mice, we found mechanotransduction responses with a normal "wild-type" amplitude and speed of activation. Surprisingly, only outer hair cells exhibit fast adaptation and sensitivity to extracellular Ca(2+). In Myo15(sh2/sh2) inner hair cells, fast adaptation is disrupted and the transduction current is insensitive to extracellular Ca(2+). We conclude that the Ca(2+) sensitivity of the mechanotransduction channels and the fast adaptation require a structural environment that is dependent on myosin-XVa and is disrupted in Myo15(sh2/sh2) inner hair cells, but not in Myo15(sh2/sh2) outer hair cells.
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20
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Breneman KD, Brownell WE, Rabbitt RD. Hair cell bundles: flexoelectric motors of the inner ear. PLoS One 2009; 4:e5201. [PMID: 19384413 PMCID: PMC2668172 DOI: 10.1371/journal.pone.0005201] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Accepted: 03/16/2009] [Indexed: 11/18/2022] Open
Abstract
Microvilli (stereocilia) projecting from the apex of hair cells in the inner ear are actively motile structures that feed energy into the vibration of the inner ear and enhance sensitivity to sound. The biophysical mechanism underlying the hair bundle motor is unknown. In this study, we examined a membrane flexoelectric origin for active movements in stereocilia and conclude that it is likely to be an important contributor to mechanical power output by hair bundles. We formulated a realistic biophysical model of stereocilia incorporating stereocilia dimensions, the known flexoelectric coefficient of lipid membranes, mechanical compliance, and fluid drag. Electrical power enters the stereocilia through displacement sensitive ion channels and, due to the small diameter of stereocilia, is converted to useful mechanical power output by flexoelectricity. This motor augments molecular motors associated with the mechanosensitive apparatus itself that have been described previously. The model reveals stereocilia to be highly efficient and fast flexoelectric motors that capture the energy in the extracellular electro-chemical potential of the inner ear to generate mechanical power output. The power analysis provides an explanation for the correlation between stereocilia height and the tonotopic organization of hearing organs. Further, results suggest that flexoelectricity may be essential to the exquisite sensitivity and frequency selectivity of non-mammalian hearing organs at high auditory frequencies, and may contribute to the “cochlear amplifier” in mammals.
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Affiliation(s)
- Kathryn D. Breneman
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America
| | - William E. Brownell
- Department of Otolaryngology - H&NS, Baylor College of Medicine, Houston, Texas, United States of America
| | - Richard D. Rabbitt
- Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States of America
- Marine Biological Laboratory, Woods Hole, Massachusetts, United States of America
- * E-mail:
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21
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P2X antagonists inhibit styryl dye entry into hair cells. Neuroscience 2009; 161:1144-53. [PMID: 19272432 DOI: 10.1016/j.neuroscience.2009.02.076] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2008] [Revised: 02/22/2009] [Accepted: 02/24/2009] [Indexed: 11/22/2022]
Abstract
The styryl pyridinium dyes, FM1-43 and AM1-43, are fluorescent molecules that can permeate the mechanotransduction channels of hair cells, the sensory receptors of the inner ear. When these dyes are applied to hair cells, they enter the cytoplasm rapidly, resulting in a readily detectable intracellular fluorescence that is often used as a molecular indication of mechanotransduction channel activity. However, such dyes can also permeate the ATP receptor, P2X(2). Therefore, we explored the contribution of P2X receptors to the loading of hair cells with AM1-43. The chick inner ear was found to express P2X receptors and to release ATP, similar to the inner ear of mammals, allowing for the endogenous stimulation of P2X receptors. The involvement of these receptors was evaluated pharmacologically, by exposing the sensory epithelium of the chick inner ear to 5 microM AM1-43 under different experimental conditions and measuring the fluorescence in hair cells after fixation of the tissue. Pre-exposure of the tissue to 5 mM EGTA for 15 min, which should eliminate most of the gating "tip links" of the mechanotransduction channels, deceased fluorescence by only 44%. In contrast, P2X receptor antagonists (pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid [PPADS], suramin, 2',3'-O-(2,4,6-trinitrophenyl) ATP [TNP-ATP], and d-tubocurarine) had greater effects on dye loading. PPADS, suramin, and TNP-ATP all decreased intracellular AM1-43 fluorescence in hair cells by at least 69% when applied at a concentration of 100 microM. The difference between d-tubocurarine-treated and control fluorescence was statistically insignificant when d-tubocurarine was applied at a concentration that blocks the mechanotransduction channel (200 microM). At a concentration that also blocks P2X(2) receptors (2 mM), d-tubocurarine decreased dye loading by 72%. From these experiments, it appears that AM1-43 can enter hair cells through endogenously activated P2X receptors. Thus, the contribution of P2X receptors to dye entry should be considered when using styryl pyridinium dyes to detect hair cell mechanotransduction channel activity, especially in the absence of explicit mechanical stimulation of stereocilia.
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22
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Novak P, Li C, Shevchuk AI, Stepanyan R, Caldwell M, Hughes S, Smart TG, Gorelik J, Ostanin VP, Lab MJ, Moss GWJ, Frolenkov GI, Klenerman D, Korchev YE. Nanoscale live-cell imaging using hopping probe ion conductance microscopy. Nat Methods 2009; 6:279-81. [PMID: 19252505 DOI: 10.1038/nmeth.1306] [Citation(s) in RCA: 335] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Accepted: 01/22/2009] [Indexed: 02/05/2023]
Abstract
We describe hopping mode scanning ion conductance microscopy that allows noncontact imaging of the complex three-dimensional surfaces of live cells with resolution better than 20 nm. We tested the effectiveness of this technique by imaging networks of cultured rat hippocampal neurons and mechanosensory stereocilia of mouse cochlear hair cells. The technique allowed examination of nanoscale phenomena on the surface of live cells under physiological conditions.
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23
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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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24
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Stepwise morphological and functional maturation of mechanotransduction in rat outer hair cells. J Neurosci 2008; 27:13890-902. [PMID: 18077701 DOI: 10.1523/jneurosci.2159-07.2007] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Inner ear mechanosensory hair cells convert mechanical vibrations into electrical signals via the coordinated interaction of multiple proteins precisely positioned within the sensory hair bundle. Present work identifies the time course for the acquisition and maturation of mechanoelectric transduction (MET) in rat cochlea outer hair cells maintained in organotypic cultures. A spatiotemporal developmental progression was observed morphologically and functionally with basal cochlea maturation preceding apical cochlea by 2-3 d in all measured properties. The fraction of mechanosensitive cells increased rapidly, with a midpoint at postnatal day 0 for basal cells, and correlated with myosin IIIa immunoreactivity. MET current magnitude increased over several days. Adaptation lagged the onset of transduction by a day and matured more slowly, overlapping but preceding the rise in myosin Ic immunoreactivity. Less than approximately 25% of myosin Ic expression was required for the mature adaptation response, suggesting multiple roles for this protein in hair bundle function. Directional sensitivity, lacking in immature responses, developed rapidly and correlated with the pruning of radial links and an increase in tenting of stereociliary tips. Morphological and electrophysiological data support a hypothesis in which key elements arrive independently at the site of MET, with a mature response occurring as membrane tension increases, likely by the increased tensioning of the tip link with the onset of adaptation. Organotypic cultures developed normal, tonotopically specific, MET response properties, suggesting that maturation was not influenced significantly by external factors such as innervation, endolymph, normal mechanical stimulation, or an intact organ of Corti.
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25
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Nishikawa S. Styryl Pyridinium Dyes FM1-43 and AM1-43 for Visualization of Sensory Nerve Fibers and Cells in Dental and Craniofacial Tissues of Small Experimental Animals. J Oral Biosci 2008. [DOI: 10.1016/s1349-0079(08)80026-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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26
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Mosaic complementation demonstrates a regulatory role for myosin VIIa in actin dynamics of stereocilia. Mol Cell Biol 2007; 28:1702-12. [PMID: 18160714 PMCID: PMC2258769 DOI: 10.1128/mcb.01282-07] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have developed a bacterial artificial chromosome transgenesis approach that allowed the expression of myosin VIIa from the mouse X chromosome. We demonstrated the complementation of the Myo7a null mutant phenotype producing a fine mosaic of two types of sensory hair cells within inner ear epithelia of hemizygous transgenic females due to X inactivation. Direct comparisons between neighboring auditory hair cells that were different only with respect to myosin VIIa expression revealed that mutant stereocilia are significantly longer than those of their complemented counterparts. Myosin VIIa-deficient hair cells showed an abnormally persistent tip localization of whirlin, a protein directly linked to elongation of stereocilia, in stereocilia. Furthermore, myosin VIIa localized at the tips of all abnormally short stereocilia of mice deficient for either myosin XVa or whirlin. Our results strongly suggest that myosin VIIa regulates the establishment of a setpoint for stereocilium heights, and this novel role may influence their normal staircase-like arrangement within a bundle.
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27
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Nal N, Ahmed ZM, Erkal E, Alper OM, Lüleci G, Dinç O, Waryah AM, Ain Q, Tasneem S, Husnain T, Chattaraj P, Riazuddin S, Boger E, Ghosh M, Kabra M, Riazuddin S, Morell RJ, Friedman TB. Mutational spectrum of MYO15A: the large N-terminal extension of myosin XVA is required for hearing. Hum Mutat 2007; 28:1014-9. [PMID: 17546645 DOI: 10.1002/humu.20556] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Human MYO15A is located on chromosome 17p11.2, has 66 exons and encodes unconventional myosin XVA. Recessive mutations of MYO15A are associated with profound, nonsyndromic hearing loss DFNB3 in humans, and deafness and circling behavior in shaker 2 mice. In the inner ear, this motor protein is necessary for the development of hair cell stereocilia, which are actin-filled projections on the apical surface and the site of mechanotransduction of sound. The longest isoform of myosin XVA has 3,530 amino acid residues. Two isoform classes of MYO15A are distinguished by the presence or absence of 1,203 residues preceding the motor domain encoded by alternatively-spliced exon 2. It is not known whether this large N-terminal extension of myosin XVA is functionally necessary for hearing. We ascertained approximately 600 consanguineous families segregating hereditary hearing loss as a recessive trait and found evidence of linkage of markers at the DFNB3 locus to hearing loss in 38 of these families ascertained in Pakistan (n=30), India (n=6), and Turkey (n=2). In this study, we describe 16 novel recessive mutations of MYO15A associated with severe to profound hearing loss segregating in 20 of these DFNB3-linked families. Importantly, two homozygous mutant alleles-c.3313G>T (p.E1105X) and c.3334delG (p.G1112fsX1124) of MYO15A-located in exon 2 are associated with severe to profound hearing loss segregating in two families. These data demonstrate that isoform 1, containing the large N-terminal extension, is also necessary for normal hearing.
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Affiliation(s)
- Nevra Nal
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville 20850, Maryland, USA
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28
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Mogensen MM, Rzadzinska A, Steel KP. The deaf mouse mutant whirler suggests a role for whirlin in actin filament dynamics and stereocilia development. ACTA ACUST UNITED AC 2007; 64:496-508. [PMID: 17326148 PMCID: PMC2682331 DOI: 10.1002/cm.20199] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Stereocilia, finger-like projections forming the hair bundle on the apical surface of sensory hair cells in the cochlea, are responsible for mechanosensation and ultimately the perception of sound. The actin cytoskeleton of the stereocilia contains hundreds of tightly cross-linked parallel actin filaments in a paracrystalline array and it is vital for their function. Although several genes have been identified and associated with stereocilia development, the molecular mechanisms responsible for stereocilia growth, maintenance and organisation of the hair bundle have not been fully resolved. Here we provide further characterisation of the stereocilia of the whirler mouse mutant. We found that a lack of whirlin protein in whirler mutants results in short stereocilia with larger diameters without a corresponding increase in the number of actin filaments in inner hair cells. However, a decrease in the actin filament packing density was evident in the whirler mutant. The electron-density at the tip of each stereocilium was markedly patchy and irregular in the whirler mutants compared with a uniform band in controls. The outer hair cell stereocilia of the whirler homozygote also showed an increase in diameter and variable heights within bundles. The number of outer hair cell stereocilia was significantly reduced and the centre-to-centre spacing between the stereocilia was greater than in the wildtype. Our findings suggest that whirlin plays an important role in actin filament packing and dynamics during postnatal stereocilium elongation.
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MESH Headings
- Actin Cytoskeleton/genetics
- Actin Cytoskeleton/metabolism
- Animals
- Cilia/metabolism
- Cilia/ultrastructure
- Cochlea/metabolism
- Cochlea/ultrastructure
- Deafness/genetics
- Deafness/metabolism
- Ear, Inner/metabolism
- Ear, Inner/ultrastructure
- Hair Cells, Auditory, Inner/metabolism
- Hair Cells, Auditory, Inner/ultrastructure
- Hair Cells, Auditory, Outer/metabolism
- Hair Cells, Auditory, Outer/ultrastructure
- Homozygote
- Intercellular Signaling Peptides and Proteins
- Membrane Proteins/genetics
- Membrane Proteins/physiology
- Mice
- Mice, Mutant Strains
- Microscopy, Electron, Scanning
- Mutation
- Proteins/genetics
- Proteins/metabolism
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Affiliation(s)
- Mette M Mogensen
- School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
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29
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Lezirovitz K, Pardono E, de Mello Auricchio MTB, de Carvalho E Silva FL, Lopes JJ, Abreu-Silva RS, Romanos J, Batissoco AC, Mingroni-Netto RC. Unexpected genetic heterogeneity in a large consanguineous Brazilian pedigree presenting deafness. Eur J Hum Genet 2007; 16:89-96. [PMID: 17851452 DOI: 10.1038/sj.ejhg.5201917] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Nonsyndromic autosomal recessive deafness accounts for 80% of hereditary deafness. To date, 52 loci responsible for autosomal recessive deafness have been mapped and 24 genes identified. Here, we report a large inbred Brazilian pedigree with 26 subjects affected by prelingual deafness. Given the extensive consanguinity found in this pedigree, the most probable pattern of inheritance is autosomal recessive. However, our linkage and mutational analysis revealed, instead of an expected homozygous mutation in a single gene, two different mutant alleles and a possible third undetected mutant allele in the MYO15A gene (DFNB3 locus), as well as evidence for other causes for deafness in the same pedigree. Among the 26 affected subjects, 15 were homozygous for the novel c.10573delA mutation in the MYO15A gene, 5 were compound heterozygous for the mutation c.10573delA and the novel deletion c.9957_9960delTGAC and one inherited only a single c.10573delA mutant allele, while the other one could not be identified. Given the extensive consanguinity of the pedigree, there might be at least one more deafness locus segregating to explain the condition in some of the subjects whose deafness is not clearly associated with MYO15A mutations, although overlooked environmental causes could not be ruled out. Our findings illustrate a high level of etiological heterogeneity for deafness in the family and highlight some of the pitfalls of genetic analysis of large genes in extended pedigrees, when homozygosity for a single mutant allele is expected.
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Affiliation(s)
- Karina Lezirovitz
- Centro de Estudos do Genoma Humano, Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil.
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30
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Grant L, Fuchs PA. Auditory transduction in the mouse. Pflugers Arch 2007; 454:793-804. [PMID: 17534654 DOI: 10.1007/s00424-007-0253-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2006] [Revised: 03/08/2007] [Accepted: 03/12/2007] [Indexed: 11/26/2022]
Abstract
The sensory hair cells of the mammalian cochlea transduce acoustic stimuli into auditory nerve activity. The biomechanical and molecular details of hair cell mechanotransduction are being acquired at an ever-finer level of resolution. In this review, we discuss how selected mouse mutants and transgenic models have contributed to, and will continue to shape, our understanding of the molecular basis of hair cell mechanotransduction. Functional and structural discoveries made originally in hair cells of nonmammalian vertebrates have been further pursued in the mouse inner ear, where transgenic manipulation can be applied to test molecular mechanisms. Additional insights have been obtained from mice bearing mutations in genes underlying deafness in humans. Taken together, these studies emphasize the elegance of mechanotransduction, enlarge the team of molecular players, and begin to reveal the remarkable adaptations that provide the sensitivity and temporal resolution required for mammalian hearing.
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Affiliation(s)
- Lisa Grant
- Otolaryngology, Head and Neck Surgery, The Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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