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Xu Z, Oshima K, Heller S. PIST regulates the intracellular trafficking and plasma membrane expression of cadherin 23. BMC Cell Biol 2010; 11:80. [PMID: 20958966 PMCID: PMC2967513 DOI: 10.1186/1471-2121-11-80] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2010] [Accepted: 10/19/2010] [Indexed: 02/02/2023] Open
Abstract
Background The atypical cadherin protein cadherin 23 (CDH23) is crucial for proper function of retinal photoreceptors and inner ear hair cells. As we obtain more and more information about the specific roles of cadherin 23 in photoreceptors and hair cells, the regulatory mechanisms responsible for the transport of this protein to the plasma membrane are largely unknown. Results PIST, a Golgi-associated, PDZ domain-containing protein, interacted with cadherin 23 via the PDZ domain of PIST and the C-terminal PDZ domain-binding interface (PBI) of cadherin 23. By binding to cadherin 23, PIST retained cadherin 23 in the trans-Golgi network of cultured cells. The retention was released when either of the two known cadherin 23-binding proteins MAGI-1 and harmonin was co-expressed. Similar to MAGI-1 and harmonin, PIST was detected in mouse inner ear sensory hair cells. Conclusions PIST binds cadherin 23 via its PDZ domain and retains cadherin 23 in trans-Golgi network. MAGI-1 and harmonin can compete with PIST for binding cadherin 23 and release cadherin 23 from PIST's retention. Our finding suggests that PIST, MAGI-1 and harmonin collaborate in intracellular trafficking of cadherin 23 and regulate the plasma membrane expression of cadherin 23.
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Affiliation(s)
- Zhigang Xu
- Department of Otolaryngology--Head & Neck Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA.
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Abstract
The 6-billion human population provides a vast reservoir of mutations, which, in addition to the opportunity of detecting very subtle defects, including specific cognitive dysfunctions as well as late appearing disorders, offers a unique background in which to investigate the roles of cell-cell adhesion proteins. Here we focus on inherited human disorders involving members of the cadherin superfamily. Most of the advances concern monogenic disorders. Yet, with the development of single nucleotide polymorphism (SNP) association studies, cadherin genes are emerging as susceptibility genes in multifactorial disorders. Various skin and heart disorders revealed the critical role played by desmosomal cadherins in epidermis, hairs, and myocardium, which experience high mechanical stress. Of particular interest in that respect is the study of Usher syndrome type 1 (USH1), a hereditary syndromic form of deafness. Studies of USH1 brought to light the crucial role of transient fibrous links formed by cadherin 23 and protocadherin 15 in the cohesion of the developing hair bundle, the mechanoreceptive structure of the auditory sensory cells, as well as the involvement of these cadherins in the formation of the tip-link, a key component of the mechano-electrical transduction machinery. Finally, in line with the well-established role of cadherins in synaptic formation, maintenance, strength, and plasticity, a growing number of cadherin family members, especially protocadherins, have been found to be involved in neuropsychiatric disorders.
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Affiliation(s)
- Aziz El-Amraoui
- Institut Pasteur, Unité de Génétique et Physiologie de l'Audition, 25 Rue du Dr Roux, 75015 Paris, France.
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Development and regeneration of sensory transduction in auditory hair cells requires functional interaction between cadherin-23 and protocadherin-15. J Neurosci 2010; 30:11259-69. [PMID: 20739546 DOI: 10.1523/jneurosci.1949-10.2010] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Tip links are extracellular filaments that connect pairs of hair cell stereocilia and convey tension to mechanosensitive channels. Recent evidence suggests that tip links are formed by calcium-dependent interactions between the N-terminal domains of cadherin-23 (CDH23) and protocadherin-15 (PCDH15). Mutations in either CDH23 or PCDH15 cause deafness in mice and humans, indicating the molecules are required for normal inner ear function. However, there is little physiological evidence to support a direct role for CDH23 and PCDH15 in hair cell mechanotransduction. To investigate the contributions of CDH23 and PCDH15 to mechanotransduction and tip-link formation, we examined outer hair cells of mouse cochleas during development and after chemical disruption of tip links. We found that tip links and mechanotransduction with all the qualitative properties of mature transduction recovered within 24 h after disruption. To probe tip-link formation, we measured transduction currents after extracellular application of recombinant CDH23 and PCDH15 fragments, which included putative interaction domains (EC1). Both fragments inhibited development and regeneration of transduction but did not disrupt transduction in mature cells. PCDH15 fragments that carried a mutation in EC1 that causes deafness in humans did not inhibit transduction development or regeneration. Immunolocalization revealed wild-type fragments bound near the tips of hair cell stereocilia. Scanning electron micrographs revealed that hair bundles exposed to fragments had a reduced number of linkages aligned along the morphological axis of sensitivity of the bundle. Together, the data provide direct evidence implicating CDH23 and PCDH15 proteins in the formation of tip links during development and regeneration of mechanotransduction.
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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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Bahloul A, Michel V, Hardelin JP, Nouaille S, Hoos S, Houdusse A, England P, Petit C. Cadherin-23, myosin VIIa and harmonin, encoded by Usher syndrome type I genes, form a ternary complex and interact with membrane phospholipids. Hum Mol Genet 2010; 19:3557-65. [PMID: 20639393 PMCID: PMC2928128 DOI: 10.1093/hmg/ddq271] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Cadherin-23 is a component of early transient lateral links of the auditory sensory cells' hair bundle, the mechanoreceptive structure to sound. This protein also makes up the upper part of the tip links that control gating of the mechanoelectrical transduction channels. We addressed the issue of the molecular complex that anchors these links to the hair bundle F-actin core. By using surface plasmon resonance assays, we show that the cytoplasmic regions of the two cadherin-23 isoforms that do or do not contain the exon68-encoded peptide directly interact with harmonin, a submembrane PDZ (post-synaptic density, disc large, zonula occludens) domain-containing protein, with unusually high affinity. This interaction involves the harmonin Nter-PDZ1 supramodule, but not the C-terminal PDZ-binding motif of cadherin-23. We establish that cadherin-23 directly binds to the tail of myosin VIIa. Moreover, cadherin-23, harmonin and myosin VIIa can form a ternary complex, which suggests that myosin VIIa applies tension forces on hair bundle links. We also show that the cadherin-23 cytoplasmic region, harmonin and myosin VIIa interact with phospholipids on synthetic liposomes. Harmonin and the cytoplasmic region of cadherin-23, both independently and as a binary complex, can bind specifically to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), which may account for the role of this phospholipid in the adaptation of mechanoelectrical transduction in the hair bundle. The distributions of cadherin-23, harmonin, myosin VIIa and PI(4,5)P2 in the growing and mature auditory hair bundles as well as the abnormal locations of harmonin and myosin VIIa in cadherin-23 null mutant mice strongly support the functional relevance of these interactions.
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Affiliation(s)
- Amel Bahloul
- Département de Neuroscience, Institut Pasteur, Paris, France
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56
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Targeting of the hair cell proteins cadherin 23, harmonin, myosin XVa, espin, and prestin in an epithelial cell model. J Neurosci 2010; 30:7187-201. [PMID: 20505086 DOI: 10.1523/jneurosci.0852-10.2010] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We have developed an advantageous epithelial cell transfection model for examining the targeting, interactions, and mutations of hair cell proteins. When expressed in LLC-PK1-CL4 epithelial cells (CL4 cells), the outer hair cell protein prestin showed faithful domain-specific targeting to the basolateral plasma membrane. We examined the consequences of mutations affecting prestin activity and assigned a targeting role to the cytoplasmic tail. The stereociliary link protein cadherin 23 (Cdh23) was targeted to the plasma membrane of CL4 cell microvilli, the topological equivalent of stereocilia. In cells coexpressing the Cdh23 cytoplasmic binding protein harmonin, a large fraction of harmonin became colocalized with Cdh23 in microvilli. Using this assay and in vitro protein binding assays, we formulated an alternative model for Cdh23-harmonin binding, in which the primary interaction is between the harmonin N-domain and a 35-residue internal peptide in the Cdh23 cytoplasmic tail. Contrary to a previous model, we found no role for the Cdh23 C-terminal PDZ (PSD-95/Dlg/ZO-1)-binding motif and observed that Cdh23 bound similar levels of harmonin with or without the exon 68 peptide. We also examined two proteins involved in stereocilium elongation. The stereociliary actin-bundling protein espin was targeted to CL4 cell microvilli and caused microvillar elongation, whereas espin with the c.2469delGTCA or c.1988delAGAG human deafness mutation showed defects in microvillar targeting and elongation. The unconventional myosin motor myosin XVa accumulated at the tips of espin-elongated microvilli, by analogy to its location in stereocilia, whereas myosin XVa with the c.4351G>A or c.4669A>G human deafness mutation did not, revealing functional deficits in motor activity.
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Johnson KR, Yu H, Ding D, Jiang H, Gagnon LH, Salvi RJ. Separate and combined effects of Sod1 and Cdh23 mutations on age-related hearing loss and cochlear pathology in C57BL/6J mice. Hear Res 2010; 268:85-92. [PMID: 20470874 DOI: 10.1016/j.heares.2010.05.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 04/16/2010] [Accepted: 05/04/2010] [Indexed: 10/19/2022]
Abstract
Both the ahl allele of Cdh23 and the null mutation of Sod1 have been shown to contribute to age-related hearing loss (AHL) in mice, but mixed strain backgrounds have confounded analyses of their individual and combined effects. To test for the effects of Sod1 deficiency independently from those of Cdh23(ahl), we produced mice with four digenic genotypes: Sod1(+/+)Cdh23(ahl)(/ahl), Sod1(+/+)Cdh23(+/+), Sod1(-/-)Cdh23(ahl)(/ahl), and Sod1(-/-)Cdh23(+/+), all on a uniform C57BL(/)6J strain background. We assessed hearing loss by ABR threshold measurements and evaluated cochlear pathologies in age-matched mice of each digenic combination. ABR analysis showed that Sod1(+/+)Cdh23(+/+) mice retain normal hearing up to 15 months of age and that hearing loss of Sod1(+/+)Cdh23(ahl)(/ahl) mice is more age and frequency dependent than that of Sod1(-/-)Cdh23(+/+) mice. ABR results also showed that mice with both gene mutations (Sod1(-/-)Cdh23(ahl)(/ahl)) exhibit the earliest onset and most severe hearing loss, greater than predicted for strictly additive effects. Histological analysis of cochleas showed that hair cell lesions are most severe in Sod1(-)(/-)Cdh23(ahl)(/ahl) mice followed closely by Sod1(+)(/+)Cdh23(ahl)(/ahl) mice and much smaller in Sod1(-)(/-)Cdh23(+)(/+) and Sod1(+)(/+)Cdh23(+)(/+) mice. Despite extensive damage to cochlear hair cells, vestibular hair cells appeared remarkably normal in all strains. Although both Sod1(-/-) and Cdh23(ahl)(/ahl) genotypes had strong effects on hearing loss, the Cdh23(ahl/ahl) genotype was primarily responsible for the increase in hair cell loss, suggesting that the two mutations have different underlying mechanisms of pathology.
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Etournay R, Lepelletier L, Boutet de Monvel J, Michel V, Cayet N, Leibovici M, Weil D, Foucher I, Hardelin JP, Petit C. Cochlear outer hair cells undergo an apical circumference remodeling constrained by the hair bundle shape. Development 2010; 137:1373-83. [PMID: 20332152 DOI: 10.1242/dev.045138] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Epithelial cells acquire diverse shapes relating to their different functions. This is particularly relevant for the cochlear outer hair cells (OHCs), whose apical and basolateral shapes accommodate the functioning of these cells as mechano-electrical and electromechanical transducers, respectively. We uncovered a circumferential shape transition of the apical junctional complex (AJC) of OHCs, which occurs during the early postnatal period in the mouse, prior to hearing onset. Geometric analysis of the OHC apical circumference using immunostaining of the AJC protein ZO1 and Fourier-interpolated contour detection characterizes this transition as a switch from a rounded-hexagon to a non-convex circumference delineating two lateral lobes at the neural side of the cell, with a negative curvature in between. This shape tightly correlates with the 'V'-configuration of the OHC hair bundle, the apical mechanosensitive organelle that converts sound-evoked vibrations into variations in cell membrane potential. The OHC apical circumference remodeling failed or was incomplete in all the mouse mutants affected in hair bundle morphogenesis that we tested. During the normal shape transition, myosin VIIa and myosin II (A and B isoforms) displayed polarized redistributions into and out of the developing lobes, respectively, while Shroom2 and F-actin transiently accumulated in the lobes. Defects in these redistributions were observed in the mutants, paralleling their apical circumference abnormalities. Our results point to a pivotal role for actomyosin cytoskeleton tensions in the reshaping of the OHC apical circumference. We propose that this remodeling contributes to optimize the mechanical coupling between the basal and apical poles of mature OHCs.
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Affiliation(s)
- Raphaël Etournay
- Unité de Génétique et Physiologie de l'Audition, INSERM UMRS587-Université Paris VI, Institut Pasteur, 25 rue du Dr Roux, Paris Cedex 15, France
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59
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Zallocchi M, Sisson JH, Cosgrove D. Biochemical characterization of native Usher protein complexes from a vesicular subfraction of tracheal epithelial cells. Biochemistry 2010; 49:1236-47. [PMID: 20058854 DOI: 10.1021/bi9020617] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Usher syndrome is the major cause of deaf/blindness in the world. It is a genetic heterogeneous disorder, with nine genes already identified as causative for the disease. We noted expression of all known Usher proteins in bovine tracheal epithelial cells and exploited this system for large-scale biochemical analysis of Usher protein complexes. The dissected epithelia were homogenized in nondetergent buffer and sedimented on sucrose gradients. At least two complexes were evident after the first gradient: one formed by specific isoforms of CDH23, PCDH15, and VLGR-1 and a different one at the top of the gradient that included all of the Usher proteins and rab5, a transport vesicle marker. TEM analysis of these top fractions found them enriched in 100-200 nm vesicles, confirming a vesicular association of the Usher complex(es). Immunoisolation of these vesicles confirmed some of the associations already predicted and identified novel interactions. When the vesicles are lysed in the presence of phenylbutyrate, most of the Usher proteins cosediment into the gradient at a sedimentation coefficient of approximately 50 S, correlating with a predicted molecular mass of 2 x 10(6) Da. Although it is still unclear whether there is only one complex or several independent complexes that are trafficked within distinct vesicular pools, this work shows for the first time that native Usher protein complexes occur in vivo. This complex(es) is present primarily in transport vesicles at the apical pole of tracheal epithelial cells, predicting that Usher proteins may be directionally transported as complexes in hair cells and photoreceptors.
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Affiliation(s)
- Marisa Zallocchi
- Usher Syndrome Center, Boys Town National Research Hospital, 555 North 30th Street, Omaha, Nebraska 68131, USA
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60
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Abstract
Usher syndrome (USH) comprises a group of autosomal recessively inherited disorders characterized by a dual sensory impairment of the audiovestibular and visual systems. Three major clinical subtypes (USH type I, USH type II and USH type III) are distinguished on the basis of the severity of the hearing loss, the presence or absence of vestibular dysfunction and the age of onset of retinitis pigmentosa (RP). Since the cloning of the first USH gene (MYO7A) in 1995, there have been remarkable advances in elucidating the genetic basis for this disorder, as evidence for 11 distinct loci have been obtained and genes for 9 of them have been identified. The USH genes encode proteins of different classes and families, including motor proteins, scaffold proteins, cell adhesion molecules and transmembrane receptor proteins. Extensive information has emerged from mouse models and molecular studies regarding pathogenesis of this disorder and the wide phenotypic variation in both audiovestibular and/or visual function. A unifying hypothesis is that the USH proteins are integrated into a protein network that regulates hair bundle morphogenesis in the inner ear. This review addresses genetics and pathological mechanisms of USH. Understanding the molecular basis of phenotypic variation and pathogenesis of USH is important toward discovery of new molecular targets for diagnosis, prevention and treatment of this debilitating disorder.
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Affiliation(s)
- Denise Yan
- Department of Otolaryngology, Miller School of Medicine, University of Miami, Miami, FL 33136, USA
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61
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Zaghloul NA, Katsanis N. Functional modules, mutational load and human genetic disease. Trends Genet 2010; 26:168-76. [PMID: 20226561 DOI: 10.1016/j.tig.2010.01.006] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Revised: 01/14/2010] [Accepted: 01/22/2010] [Indexed: 11/17/2022]
Abstract
The ability to generate a massive amount of sequencing and genotyping data is transforming the study of human genetic disorders. Driven by such innovation, it is likely that whole exome and whole-genome resequencing will replace regionally focused approaches for gene discovery and clinical testing in the next few years. However, this opportunity brings a significant interpretative challenge to assigning function and phenotypic variance to common and rare alleles. Understanding the effect of individual mutations in the context of the remaining genomic variation represents a major challenge to our interpretation of disease. Here, we discuss the challenges of assigning mutation functionality and, drawing from the examples of ciliopathies as well as cohesinopathies and channelopathies, discuss possibilities for the functional modularization of the human genome. Functional modularization in addition to the development of physiologically relevant assays to test allele functionality will accelerate our understanding of disease architecture and enable the use of genome-wide sequence data for disease diagnosis and phenotypic prediction in individuals.
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Affiliation(s)
- Norann A Zaghloul
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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62
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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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63
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Mutation analysis in the long isoform of USH2A in American patients with Usher Syndrome type II. J Hum Genet 2009; 54:732-8. [PMID: 19881469 DOI: 10.1038/jhg.2009.107] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Usher syndrome type II (USH2) is an autosomal recessive disorder characterized by moderate to severe hearing impairment and progressive visual loss due to retinitis pigmentosa (RP). To identify novel mutations and determine the frequency of USH2A mutations as a cause of USH2, we have carried out mutation screening of all 72 coding exons and exon-intron splice sites of the USH2A gene. A total of 20 USH2 American probands of European descent were analyzed using single strand conformational polymorphism (SSCP) and direct sequencing methods. Ten different USH2A mutations were identified in 55% of the probands, five of which were novel mutations. The detected mutations include three missense, three frameshifts and four nonsense mutations, with c.2299delG/p.E767fs mutation, accounting for 38.9% of the pathological alleles. Two cases were homozygotes, two cases were compound heterozygotes and one case had complex allele with three variants. In seven probands, only one USH2A mutation was detected and no pathological mutation was found in the remaining eight individuals. Altogether, our data support the fact that c.2299delG/p.E767fs is indeed the most common USH2A mutation found in USH2 patients of European Caucasian background. Thus, if screening for mutations in USH2A is considered, it is reasonable to screen for the c.2299delG mutation first.
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May-Simera HL, Ross A, Rix S, Forge A, Beales PL, Jagger DJ. Patterns of expression of Bardet-Biedl syndrome proteins in the mammalian cochlea suggest noncentrosomal functions. J Comp Neurol 2009; 514:174-88. [PMID: 19396898 DOI: 10.1002/cne.22001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Bardet-Biedl syndrome is a heterogeneous disorder causing a spectrum of symptoms, including visual impairment, kidney disease, and hearing impairment. Evidence suggests that BBS gene mutations cause defective ciliogenesis and/or cilium dysfunction. Cochlear development is affected by BBS gene deletion, and adult Bbs6(-/-) and Bbs4(-/-) mice are hearing impaired. This study addresses BBS protein expression in the rodent cochlea, to gain a better understanding of its function in vivo. As predicted by in vitro studies, Bbs6 immunofluorescence was localized to the basal bodies of supporting cells and sensory hair cells prior to the onset of hearing. In adult tissue, Bbs6 expression persisted in afferent neurons, including within the dendrites that innervate hair cells, implicating Bbs6 in a sensory neuronal function. Bbs2, which interacts with Bbs6, was also localized to hair cell basal bodies and stereociliary bundles. Additionally, Bbs2 was expressed in supporting cells at their intercellular boundaries, in a spatiotemporal pattern mirroring the development of the microtubule network. Bbs4 localized to cilia and developing cytoplasmic microtubule arrays. Pcm-1, a microtubular protein that interacts with Bbs4 in vitro, showed a comparable expression. Depolymerization of microtubules in slice preparations of the living cochlea resulted in Bbs4 and Pcm-1 mislocalization. Pcm-1 was also mislocalized in Bbs4(-/-) mice. This suggests that Bbs4/Pcm-1 interactions may be important in microtubule-dependent cytoplasmic trafficking in vivo. In summary, our findings indicate that BBS proteins adopt a range of cellular distributions in vivo, not restricted to the centrosome or cilium, and so broaden the possible underlying pathomechanisms of the disease.
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Affiliation(s)
- Helen L May-Simera
- Institute of Child Health, University College London, London WC1N1EH, United Kingdom
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Grillet N, Xiong W, Reynolds A, Kazmierczak P, Sato T, Lillo C, Dumont RA, Hintermann E, Sczaniecka A, Schwander M, Williams D, Kachar B, Gillespie PG, Müller U. Harmonin mutations cause mechanotransduction defects in cochlear hair cells. Neuron 2009; 62:375-87. [PMID: 19447093 DOI: 10.1016/j.neuron.2009.04.006] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Revised: 03/06/2009] [Accepted: 04/06/2009] [Indexed: 10/20/2022]
Abstract
In hair cells, mechanotransduction channels are gated by tip links, the extracellular filaments that consist of cadherin 23 (CDH23) and protocadherin 15 (PCDH15) and connect the stereocilia of each hair cell. However, which molecules mediate cadherin function at tip links is not known. Here we show that the PDZ-domain protein harmonin is a component of the upper tip-link density (UTLD), where CDH23 inserts into the stereociliary membrane. Harmonin domains that mediate interactions with CDH23 and F-actin control harmonin localization in stereocilia and are necessary for normal hearing. In mice expressing a mutant harmonin protein that prevents UTLD formation, the sensitivity of hair bundles to mechanical stimulation is reduced. We conclude that harmonin is a UTLD component and contributes to establishing the sensitivity of mechanotransduction channels to displacement.
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Affiliation(s)
- Nicolas Grillet
- Department of Cell Biology, Institute for Childhood and Neglected Disease, The Scripps Research Institute, La Jolla, CA 92037, USA
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Sengupta S, George M, Miller KK, Naik K, Chou J, Cheatham MA, Dallos P, Naramura M, Band H, Zheng J. EHD4 and CDH23 are interacting partners in cochlear hair cells. J Biol Chem 2009; 284:20121-9. [PMID: 19487694 DOI: 10.1074/jbc.m109.025668] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cadherin 23 (CDH23), a transmembrane protein localized near the tips of hair cell stereocilia in the mammalian inner ear, is important for delivering mechanical signals to the mechano-electric transducer channels. To identify CDH23-interacting proteins, a membrane-based yeast two-hybrid screen of an outer hair cell (OHC) cDNA library was performed. EHD4, a member of the C-terminal EH domain containing a protein family involved in endocytic recycling, was identified as a potential interactor. To confirm the interaction, we first demonstrated the EHD4 mRNA expression in hair cells using in situ hybridization. Next, we showed that EHD4 co-localizes and co-immunoprecipitates with CDH23 in mammalian cells. Interestingly, the co-immunoprecipitation was found to be calcium-sensitive. To investigate the role of EHD4 in hearing, compound action potentials were measured in EHD4 knock-out (KO) mice. Although EHD4 KO mice have normal hearing sensitivity, analysis of mouse cochlear lysates revealed a 2-fold increase in EHD1, but no increase in EHD2 or EHD3, in EHD4 KO cochleae compared with wild type, suggesting that a compensatory increase in EHD1 levels may account for the absence of a hearing defect in EHD4 KO mice. Taken together, these data indicate that EHD4 is a novel CDH23-interacting protein that could regulate CDH23 trafficking/localization in a calcium-sensitive manner.
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Affiliation(s)
- Soma Sengupta
- Department of Communication Sciences and Disorders, Hugh Knowles Center, Northwestern University, Evanston, Illinois 60208, USA
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Linking genes underlying deafness to hair-bundle development and function. Nat Neurosci 2009; 12:703-10. [PMID: 19471269 PMCID: PMC3332156 DOI: 10.1038/nn.2330] [Citation(s) in RCA: 127] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Accepted: 04/07/2009] [Indexed: 11/25/2022]
Abstract
The identification of genes underlying monogenic, early-onset forms of deafness in humans has provided unprecedented insight into the molecular mechanisms of hearing in the peripheral auditory system. The molecules involved in the development and function of the cochlea eluded characterization until recently due to the paucity of the principle cell types present in cochlear hair cells, yet a genetic approach has circumvented this problem and succeeded in identifying proteins and deciphering some of the molecular complexes that operate in these cells . In combination with mouse models, the genetic approach is now revealing some of the principles underlying the development and physiology of the cochlea. The review centers on this facet of the genetics of hearing. Focusing on the hair bundle, the mechanosensory device of the sensory hair cell, we highlight recent advances in understanding the way in which the hair bundle is formed, how it operates as a mechanotransducer and how it processes sound. In particular, we discuss how this work highlights the roles played by various hair-bundle link types.
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Lelli A, Asai Y, Forge A, Holt JR, Géléoc GSG. Tonotopic gradient in the developmental acquisition of sensory transduction in outer hair cells of the mouse cochlea. J Neurophysiol 2009; 101:2961-73. [PMID: 19339464 DOI: 10.1152/jn.00136.2009] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inner ear hair cells are exquisite mechanosensors that transduce nanometer scale deflections of their sensory hair bundles into electrical signals. Several essential elements must be precisely assembled during development to confer the unique structure and function of the mechanotransduction apparatus. Here we investigated the functional development of the transduction complex in outer hair cells along the length of mouse cochlea acutely excised between embryonic day 17 (E17) and postnatal day 8 (P8). We charted development of the stereociliary bundle using scanning electron microscopy; FM1-43 uptake, which permeates hair cell transduction channels, mechanotransduction currents evoked by rapid hair bundle deflections, and mRNA expression of possible components of the transduction complex. We demonstrated that uptake of FM1-43 first occurred in the basal portion of the cochlea at P0 and progressed toward the apex over the subsequent week. Electrophysiological recordings obtained from 234 outer hair cells between E17 and P8 from four cochlear regions revealed a correlation between the pattern of FM1-43 uptake and the acquisition of mechanotransduction. We found a spatiotemporal gradient in the properties of transduction including onset, amplitude, operating range, time course, and extent of adaptation. We used quantitative RT-PCR to examine relative mRNA expression of several hair cell myosins and candidate tip-link molecules. We found spatiotemporal expression patterns for mRNA that encodes cadherin 23, protocadherin 15, myosins 3a, 7a, 15a, and PMCA2 that preceded the acquisition of transduction. The spatiotemporal expression patterns of myosin 1c and PMCA2 mRNA were correlated with developmental changes in several properties of mechanotransduction.
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Affiliation(s)
- Andrea Lelli
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, Virginia 22908-1392, USA
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69
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Abstract
PURPOSE OF REVIEW The present review addresses the mechanisms, genetics and pathogenesis of Usher syndrome. RECENT FINDINGS Recent molecular findings have provided more information regarding the pathogenesis of this disorder and the wide phenotypic variation in both audiovestibular and/or visual systems. Evidence has begun to emerge supporting a theory of a protein interactome involving the Usher proteins in both the inner ear and the retina. This interactome appears to be important for hair cell development in the ear but its role in the retina remains unclear. SUMMARY Understanding clinical disease progression and molecular pathways is important in the progress towards developing gene therapy to prevent blindness due to Usher syndrome as well as delivering prognostic information to affected individuals.
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70
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A mouse model for nonsyndromic deafness (DFNB12) links hearing loss to defects in tip links of mechanosensory hair cells. Proc Natl Acad Sci U S A 2009; 106:5252-7. [PMID: 19270079 DOI: 10.1073/pnas.0900691106] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Deafness is the most common form of sensory impairment in humans and is frequently caused by single gene mutations. Interestingly, different mutations in a gene can cause syndromic and nonsyndromic forms of deafness, as well as progressive and age-related hearing loss. We provide here an explanation for the phenotypic variability associated with mutations in the cadherin 23 gene (CDH23). CDH23 null alleles cause deaf-blindness (Usher syndrome type 1D; USH1D), whereas missense mutations cause nonsyndromic deafness (DFNB12). In a forward genetic screen, we have identified salsa mice, which suffer from hearing loss due to a Cdh23 missense mutation modeling DFNB12. In contrast to waltzer mice, which carry a CDH23 null allele mimicking USH1D, hair cell development is unaffected in salsa mice. Instead, tip links, which are thought to gate mechanotransduction channels in hair cells, are progressively lost. Our findings suggest that DFNB12 belongs to a new class of disorder that is caused by defects in tip links. We propose that mutations in other genes that cause USH1 and nonsyndromic deafness may also have distinct effects on hair cell development and function.
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71
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MAGI-1, a candidate stereociliary scaffolding protein, associates with the tip-link component cadherin 23. J Neurosci 2008; 28:11269-76. [PMID: 18971469 DOI: 10.1523/jneurosci.3833-08.2008] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Inner ear hair-cell mechanoelectrical transduction is mediated by a largely unidentified multiprotein complex associated with the stereociliary tips of hair bundles. One identified component of tip links, which are the extracellular filamentous connectors implicated in gating the mechanoelectrical transduction channels, is the transmembrane protein cadherin 23 (Cdh23), more specifically, the hair- cell-specific Cdh23(+68) splice variant. Using the intracellular domain of Cdh23(+68) as bait, we identified in a cochlear cDNA library MAGI-1, a MAGUK (membrane-associated guanylate kinase) protein. MAGI-1 binds via its PDZ4 domain to a C-terminal PDZ-binding site on Cdh23. MAGI-1 immunoreactivity was detectable throughout neonatal stereocilia in a distribution similar to that of Cdh23. As development proceeded, MAGI-1 occurred in a punctate staining pattern on stereocilia, which was maintained into adulthood. Previous reports suggest that Cdh23 interacts via an internal PDZ-binding site with the PDZ1 domain of the stereociliary protein harmonin, and potentially via a weaker binding of its C terminus with harmonin's PDZ2 domain. We propose that MAGI-1 has the ability to replace harmonin's PDZ2 binding at Cdh23's C terminus. Moreover, the strong interaction between PDZ1 of harmonin and Cdh23 is interrupted by a 35 aa insertion in the hair-cell-specific Cdh23(+68) splice variant, which puts forward MAGI-1 as an attractive candidate for an intracellular scaffolding partner of this tip-link protein. Our results consequently support a role of MAGI-1 in the tip-link complex, where it could provide a sturdy connection with the cytoskeleton and with other components of the mechanoelectrical transduction complex.
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72
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Chaudhry AM, Marsh-Rollo SE, Aksenov V, Rollo CD, Szechtman H. Modifier Selection by Transgenes: The Case of Growth Hormone Transgenesis and Hyperactive Circling Mice. Evol Biol 2008. [DOI: 10.1007/s11692-008-9036-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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73
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Human hereditary hearing impairment: mouse models can help to solve the puzzle. Hum Genet 2008; 124:325-48. [DOI: 10.1007/s00439-008-0556-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2008] [Accepted: 08/29/2008] [Indexed: 12/31/2022]
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74
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Müller U. Cadherins and mechanotransduction by hair cells. Curr Opin Cell Biol 2008; 20:557-66. [PMID: 18619539 DOI: 10.1016/j.ceb.2008.06.004] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2008] [Revised: 06/12/2008] [Accepted: 06/13/2008] [Indexed: 10/21/2022]
Abstract
Mechanotransduction, the conversion of a mechanical stimulus into an electrical signal is crucial for our ability to hear and to maintain balance. Recent findings indicate that two members of the cadherin superfamily are components of the mechanotransduction machinery in sensory hair cells of the vertebrate inner ear. These studies show that cadherin 23 (CDH23) and protocadherin 15 (PCDH15) form several of the extracellular filaments that connect the stereocilia and kinocilium of a hair cell into a bundle. One of these filaments is the tip link that has been proposed to gate the mechanotransduction channel in hair cells. The extracellular domains of CDH23 and PCDH15 differ in their structure from classical cadherins and their cytoplasmic domains bind to distinct effectors, suggesting that evolutionary pressures have shaped the two cadherins for their function in mechanotransduction.
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Affiliation(s)
- Ulrich Müller
- Department of Cell Biology, Institute for Childhood and Neglected Disease, The Scripps Research Institute, La Jolla, CA 92037, USA.
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75
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Cadherin 23-like polypeptide in hair bundle mechanoreceptors of sea anemones. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2008; 194:811-20. [PMID: 18654787 DOI: 10.1007/s00359-008-0352-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2008] [Revised: 06/19/2008] [Accepted: 07/03/2008] [Indexed: 10/21/2022]
Abstract
We investigated hair bundle mechanoreceptors in sea anemones for a homolog of cadherin 23. A candidate sequence was identified from the database for Nematostella vectensis that has a shared lineage with vertebrate cadherin 23s. This cadherin 23-like protein comprises 6,074 residues. It is an integral protein that features three transmembrane alpha-helices and a large extracellular loop with 44 contiguous, cadherin (CAD) domains. In the second half of the polypeptide, the CAD domains occur in a quadruple repeat pattern. Members of the same repeat group (i.e., CAD 18, 22, 26, and so on) share nearly identical amino acid sequences. An affinity-purified antibody was generated to a peptide from the C-terminus of the cadherin 23-like polypeptide. The peptide is expected to lie on the exoplasmic side of the plasma membrane. In LM, the immunolabel produced punctate fluorescence in hair bundles. In TEM, immunogold particles were observed medially and distally on stereocilia of hair bundles. Dilute solutions of the antibody disrupted vibration sensitivity in anemones. We conclude that the cadherin 23-like polypeptide likely contributes to the mechanotransduction apparatus of hair bundle mechanoreceptors of anemones.
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76
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Lefèvre G, Michel V, Weil D, Lepelletier L, Bizard E, Wolfrum U, Hardelin JP, Petit C. A core cochlear phenotype in USH1 mouse mutants implicates fibrous links of the hair bundle in its cohesion, orientation and differential growth. Development 2008; 135:1427-37. [PMID: 18339676 DOI: 10.1242/dev.012922] [Citation(s) in RCA: 164] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The planar polarity and staircase-like pattern of the hair bundle are essential to the mechanoelectrical transduction function of inner ear sensory cells. Mutations in genes encoding myosin VIIa, harmonin, cadherin 23, protocadherin 15 or sans cause Usher syndrome type I (USH1, characterized by congenital deafness, vestibular dysfunction and retinitis pigmentosa leading to blindness) in humans and hair bundle disorganization in mice. Whether the USH1 proteins are involved in common hair bundle morphogenetic processes is unknown. Here, we show that mouse models for the five USH1 genetic forms share hair bundle morphological defects. Hair bundle fragmentation and misorientation (25-52 degrees mean kinociliary deviation, depending on the mutant) were detected as early as embryonic day 17. Abnormal differential elongation of stereocilia rows occurred in the first postnatal days. In the emerging hair bundles, myosin VIIa, the actin-binding submembrane protein harmonin-b, and the interstereocilia-kinocilium lateral link components cadherin 23 and protocadherin 15, all concentrated at stereocilia tips, in accordance with their known in vitro interactions. Soon after birth, harmonin-b switched from the tip of the stereocilia to the upper end of the tip link, which also comprises cadherin 23 and protocadherin 15. This positional change did not occur in mice deficient for cadherin 23 or protocadherin 15. We suggest that tension forces applied to the early lateral links and to the tip link, both of which can be anchored to actin filaments via harmonin-b, play a key role in hair bundle cohesion and proper orientation for the former, and in stereociliary elongation for the latter.
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Affiliation(s)
- Gaelle Lefèvre
- Unité de Génétique des Déficits Sensoriels, UMRS587 INSERM-Université Paris VI, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris cedex 15, France
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77
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Abstract
Primary cilia are essential components of diverse cellular processes. Many of the requirements can be linked to the apparent signaling function of primary cilia. Recent studies have also uncovered a role for primary cilia in planar cell polarity (PCP) signaling. PCP refers to the coordinated orientation of cells along an axis parallel to the plane of the cell sheet. In vertebrates, the inner ear sensory organs display distinctive forms of PCP. One of the inner ear PCP characteristics is the coordinated positioning of a primary cilium eccentrically in every sensory hair cell within each organ. The inner ear, therefore, provides an opportunity to explore the cellular role of primary cilia in PCP signaling. In this chapter, we will introduce the PCP of the inner ear sensory organs, describe the conserved mechanism underlying the establishment of the planar polarity axis in invertebrates and vertebrates, and highlight a unique requirement for primary cilia in PCP regulation in vertebrates. Additionally, we will discuss a potentially ubiquitous role for cilia in cellular polarization in general.
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78
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Li A, Xue J, Peterson EH. Architecture of the mouse utricle: macular organization and hair bundle heights. J Neurophysiol 2007; 99:718-33. [PMID: 18046005 DOI: 10.1152/jn.00831.2007] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hair bundles are critical to mechanotransduction by vestibular hair cells, but quantitative data are lacking on vestibular bundles in mice or other mammals. Here we quantify bundle heights and their variation with macular locus and hair cell type in adult mouse utricular macula. We also determined that macular organization differs from previous reports. The utricle has approximately 3,600 hair cells, half on each side of the line of polarity reversal (LPR). A band of low hair cell density corresponds to a band of calretinin-positive calyces, i.e., the striola. The relation between the LPR and the striola differs from previous reports in two ways. First, the LPR lies lateral to the striola instead of bisecting it. Second, the LPR follows the striolar trajectory anteriorly, but posteriorly it veers from the edge of the striola to reach the posterior margin of the macula. Consequently, more utricular bundles are oriented mediolaterally than previously supposed. Three hair cell classes are distinguished in calretinin-stained material: type II hair cells, type ID hair cells contacting calretinin-negative (dimorphic) afferents, and type IC hair cells contacting calretinin-positive (calyceal) afferents. They differ significantly on most bundle measures. Type II bundles have short stereocilia. Type IC bundles have kinocilia and stereocilia of similar heights, i.e., KS ratios (ratio of kinocilium to stereocilia heights) approximately 1, unlike other receptor classes. In contrast to these class-specific differences, bundles show little regional variation except that KS ratios are lowest in the striola. These low KS ratios suggest that bundle stiffness is greater in the striola than in the extrastriola.
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Affiliation(s)
- A Li
- Department of Biological Sciences and Neuroscience Program, Ohio University, Athens, OH 45701, USA
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79
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Wagatsuma M, Kitoh R, Suzuki H, Fukuoka H, Takumi Y, Usami S. Distribution and frequencies of CDH23 mutations in Japanese patients with non-syndromic hearing loss. Clin Genet 2007; 72:339-44. [PMID: 17850630 DOI: 10.1111/j.1399-0004.2007.00833.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mutations in the CDH23 gene are known to be responsible for both Usher syndrome type ID (USH1D) and non-syndromic hearing loss (DFNB12), and the molecular confirmation of the CDH23 gene has become important in the diagnosis of these conditions. The present study was performed to find whether the CDH23 mutations are also responsible for non-syndromic hearing loss in patients in the Japanese population. A total of 51 sequence variants were found in 64 Japanese probands with non-syndromic sensorineural hearing impairment from autosomal recessive families. Among them, at least four missense mutations in six patients from five families were confirmed to be responsible for deafness by segregation study. All mutations detected were missense mutations, corroborating the previous reports regarding DFNB12. The present data confirmed that CDH23 mutations are frequently found and significantly responsible in Japanese. Interestingly, the CDH23 mutation spectrum in Japanese is very different from that found in Caucasians. This Japanese spectrum may be representative of those in Eastern Asian populations and its elucidation is expected to facilitate the molecular diagnosis of DFNB12 and USH1D.
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Affiliation(s)
- M Wagatsuma
- Department of Otorhinolaryngology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto 390-8621, Japan
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80
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Kazmierczak P, Sakaguchi H, Tokita J, Wilson-Kubalek EM, Milligan RA, Müller U, Kachar B. Cadherin 23 and protocadherin 15 interact to form tip-link filaments in sensory hair cells. Nature 2007; 449:87-91. [PMID: 17805295 DOI: 10.1038/nature06091] [Citation(s) in RCA: 503] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2007] [Accepted: 07/10/2007] [Indexed: 11/09/2022]
Abstract
Hair cells of the inner ear are mechanosensors that transduce mechanical forces arising from sound waves and head movement into electrochemical signals to provide our sense of hearing and balance. Each hair cell contains at the apical surface a bundle of stereocilia. Mechanoelectrical transduction takes place close to the tips of stereocilia in proximity to extracellular tip-link filaments that connect the stereocilia and are thought to gate the mechanoelectrical transduction channel. Recent reports on the composition, properties and function of tip links are conflicting. Here we demonstrate that two cadherins that are linked to inherited forms of deafness in humans interact to form tip links. Immunohistochemical studies using rodent hair cells show that cadherin 23 (CDH23) and protocadherin 15 (PCDH15) localize to the upper and lower part of tip links, respectively. The amino termini of the two cadherins co-localize on tip-link filaments. Biochemical experiments show that CDH23 homodimers interact in trans with PCDH15 homodimers to form a filament with structural similarity to tip links. Ions that affect tip-link integrity and a mutation in PCDH15 that causes a recessive form of deafness disrupt interactions between CDH23 and PCDH15. Our studies define the molecular composition of tip links and provide a conceptual base for exploring the mechanisms of sensory impairment associated with mutations in CDH23 and PCDH15.
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Affiliation(s)
- Piotr Kazmierczak
- The Scripps Research, Institute Department of Cell Biology, La Jolla, California 92037, USA
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81
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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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82
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Longo-Guess CM, Gagnon LH, Fritzsch B, Johnson KR. Targeted knockout and lacZ reporter expression of the mouse Tmhs deafness gene and characterization of the hscy-2J mutation. Mamm Genome 2007; 18:646-56. [PMID: 17876667 PMCID: PMC2613174 DOI: 10.1007/s00335-007-9049-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2007] [Accepted: 06/14/2007] [Indexed: 01/03/2023]
Abstract
The Tmhs gene codes for a tetraspan transmembrane protein that is expressed in hair cell stereocilia. We previously showed that a spontaneous missense mutation of Tmhs underlies deafness and vestibular dysfunction in the hurry-scurry (hscy) mouse. Subsequently, mutations in the human TMHS gene were shown to be responsible for DFNB67, an autosomal recessive nonsyndromic deafness locus. Here we describe a genetically engineered null mutation of the mouse Tmhs gene (Tmhs ( tm1Kjn )) and show that its phenotype is identical to that of the hscy missense mutation, confirming the deleterious nature of the hscy cysteine-to-phenylalanine substitution. In the targeted null allele, the Tmhs promoter drives expression of a lacZ reporter gene. Visualization of beta-galactosidase activity in Tmhs ( tm1Kjn ) heterozygous mice indicates that Tmhs is highly expressed in the cochlear and vestibular hair cells of the inner ear. Expression is first detectable at E15.5, peaks around P0, decreases slightly at P6, and is absent by P15, a duration that supports the involvement of Tmhs in stereocilia development. Tmhs reporter gene expression also was detected in several cranial and cervical sensory ganglia, but not in the vestibular or spiral ganglia. We also describe a new nontargeted mutation of the Tmhs gene, hscy-2J, that causes abnormal splicing from a cryptic splice site within exon 2 and is predicted to produce a functionally null protein lacking 51 amino acids of the wild-type sequence.
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83
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Michalski N, Michel V, Bahloul A, Lefèvre G, Barral J, Yagi H, Chardenoux S, Weil D, Martin P, Hardelin JP, Sato M, Petit C. Molecular characterization of the ankle-link complex in cochlear hair cells and its role in the hair bundle functioning. J Neurosci 2007; 27:6478-88. [PMID: 17567809 PMCID: PMC6672440 DOI: 10.1523/jneurosci.0342-07.2007] [Citation(s) in RCA: 160] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Several lines of evidence indicate that very large G-protein-coupled receptor 1 (Vlgr1) makes up the ankle links that connect the stereocilia of hair cells at their base. Here, we show that the transmembrane protein usherin, the putative transmembrane protein vezatin, and the PDZ (postsynaptic density-95/Discs large/zona occludens-1) domain-containing submembrane protein whirlin are colocalized with Vlgr1 at the stereocilia base in developing cochlear hair cells and are absent in Vlgr1-/- mice that lack the ankle links. Direct in vitro interactions between these four proteins further support their involvement in a molecular complex associated with the ankle links and scaffolded by whirlin. In addition, the delocalization of these proteins in myosin VIIa defective mutant mice as well as the myosin VIIa tail direct interactions with vezatin, whirlin, and, we show, Vlgr1 and usherin, suggest that myosin VIIa conveys proteins of the ankle-link complex to the stereocilia. Adenylyl cyclase 6, which was found at the base of stereocilia, was both overexpressed and mislocated in Vlgr1-/- mice. In postnatal day 7 Vlgr1-/- mice, mechanoelectrical transduction currents evoked by displacements of the hair bundle toward the tallest stereocilia (i.e., in the excitatory direction) were reduced in outer but not inner hair cells. In both cell types, stimulation of the hair bundle in the opposite direction paradoxically resulted in significant transduction currents. The absence of ankle-link-mediated cohesive forces within hair bundles lacking Vlgr1 may account for the electrophysiological results. However, because some long cadherin-23 isoforms could no longer be detected in Vlgr1-/- mice shortly after birth, the loss of some apical links could be involved too. The premature disappearance of these cadherin isoforms in the Vlgr1-/- mutant argues in favor of a signaling function of the ankle links in hair bundle differentiation.
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MESH Headings
- Adenylyl Cyclases/metabolism
- Animals
- Animals, Newborn
- Carrier Proteins/metabolism
- Chelating Agents/pharmacology
- Cilia/physiology
- Cochlea/cytology
- Egtazic Acid/analogs & derivatives
- Egtazic Acid/pharmacology
- Embryo, Mammalian
- Extracellular Matrix Proteins/metabolism
- Gene Expression Regulation, Developmental/physiology
- Hair Cells, Auditory/metabolism
- Hair Cells, Auditory/ultrastructure
- Mechanotransduction, Cellular/genetics
- Mechanotransduction, Cellular/physiology
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Membrane Potentials/radiation effects
- Membrane Proteins/metabolism
- Mice
- Mice, Knockout
- Microscopy, Electron, Scanning/methods
- Organ Culture Techniques
- Patch-Clamp Techniques
- Receptors, G-Protein-Coupled/deficiency
- Subtilisin/pharmacology
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Affiliation(s)
- Nicolas Michalski
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Vincent Michel
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Amel Bahloul
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Gaëlle Lefèvre
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Jérémie Barral
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 168, Institut Curie, 75248 Paris cedex 05, France
| | - Hideshi Yagi
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Research and Education Program for Life Science, University of Fukui, Eiheiji, Fukui 910-1193, Japan, and
| | - Sébastien Chardenoux
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Dominique Weil
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Pascal Martin
- Centre National de la Recherche Scientifique Unité Mixte de Recherche 168, Institut Curie, 75248 Paris cedex 05, France
| | - Jean-Pierre Hardelin
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
| | - Makoto Sato
- Division of Cell Biology and Neuroscience, Department of Morphological and Physiological Sciences, Research and Education Program for Life Science, University of Fukui, Eiheiji, Fukui 910-1193, Japan, and
| | - Christine Petit
- Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche en Santé 587, Collège de France, Institut Pasteur, 75724 Paris cedex 15, France
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84
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Halbleib JM, Nelson WJ. Cadherins in development: cell adhesion, sorting, and tissue morphogenesis. Genes Dev 2007; 20:3199-214. [PMID: 17158740 DOI: 10.1101/gad.1486806] [Citation(s) in RCA: 734] [Impact Index Per Article: 43.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Tissue morphogenesis during development is dependent on activities of the cadherin family of cell-cell adhesion proteins that includes classical cadherins, protocadherins, and atypical cadherins (Fat, Dachsous, and Flamingo). The extracellular domain of cadherins contains characteristic repeats that regulate homophilic and heterophilic interactions during adhesion and cell sorting. Although cadherins may have originated to facilitate mechanical cell-cell adhesion, they have evolved to function in many other aspects of morphogenesis. These additional roles rely on cadherin interactions with a wide range of binding partners that modify their expression and adhesion activity by local regulation of the actin cytoskeleton and diverse signaling pathways. Here we examine how different members of the cadherin family act in different developmental contexts, and discuss the mechanisms involved.
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Affiliation(s)
- Jennifer M Halbleib
- Department of Biological Sciences, Stanford University, Stanford, California 94305, USA
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85
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Fung S, Wang F, Chase M, Godt D, Hartenstein V. Expression profile of the cadherin family in the developingDrosophila brain. J Comp Neurol 2007; 506:469-88. [DOI: 10.1002/cne.21539] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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86
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Yonezawa S, Yoshizaki N, Kageyama T, Takahashi T, Sano M, Tokita Y, Masaki S, Inaguma Y, Hanai A, Sakurai N, Yoshiki A, Kusakabe M, Moriyama A, Nakayama A. Fates of Cdh23/CDH23 with mutations affecting the cytoplasmic region. Hum Mutat 2006; 27:88-97. [PMID: 16281288 DOI: 10.1002/humu.20266] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BUS/Idr mice carrying a mutant waltzer allele (vbus) are characterized by splayed hair bundles in inner ear sensory cells, providing a mouse homolog of USH1D/DFNB12. RT-PCR-based screening for the presence of mutations in mouse Cdh23, the gene responsible for the waltzer phenotype, has identified a G>A mutation in the donor splice site of intron 67 (Cdh23:c.9633+1G>A: GenBank AF308939.1), indicating that two altered Cdh23 molecules having intron-derived COOH-terminal structures could be generated in BUS mouse tissues. Immunochemical analyses with anti-Cdh23 antibodies showed, however, no clear Cdh23-related proteins in vbus/vbus tissues, while the antibodies immunoreacted with approximately 350 kDa proteins in control mice. Immunofluorescent experiments revealed considerable weakening of Cdh23 signals in sensory hair cell stereocilia and Reissner's membrane in the vbus/vbus inner ear, and transmission electron microscopy demonstrated abundant autophagosome/autolysosome vesicles, suggesting aberrant Cdh23:c.9633+1G>A-derived protein-induced acceleration of lysosomal bulk degradation of proteins. In transfection experiments, signal sequence-preceded FLAG-tagged transmembrane plus cytoplasmic regions (TMCy) of tissue-specific Cdh23(+/-68) isoforms were localized to filamentous actin-rich protrusions and the plasma membrane of cultured cells, whereas FLAG-TMCy:c.9633+1G>A proteins were highly insoluble and retained in the cytoplasm. In contrast, FLAG-tagged TMCy:p.Arg3175His and human TMCy:c.9625_9626insC forms were both localized to the plasma membrane in cultured cells, allowing prediction that USH1D-associated CDH23:p.Arg3175His and CDH23:c.9625_9626insC proteins could be transported to the plasma membrane in vivo. The present results thus suggest different fates of CDH23/Cdh23 with mutations affecting the cytoplasmic region.
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Affiliation(s)
- Satoshi Yonezawa
- Institute for Developmental Research, Aichi Human Service Center, Kasugai, Japan.
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87
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Riazuddin S, Ahmed ZM, Fanning AS, Lagziel A, Kitajiri SI, Ramzan K, Khan SN, Chattaraj P, Friedman PL, Anderson JM, Belyantseva IA, Forge A, Riazuddin S, Friedman TB. Tricellulin is a tight-junction protein necessary for hearing. Am J Hum Genet 2006; 79:1040-51. [PMID: 17186462 PMCID: PMC1698716 DOI: 10.1086/510022] [Citation(s) in RCA: 205] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2006] [Accepted: 10/04/2006] [Indexed: 12/13/2022] Open
Abstract
The inner ear has fluid-filled compartments of different ionic compositions, including the endolymphatic and perilymphatic spaces of the organ of Corti; the separation from one another by epithelial barriers is required for normal hearing. TRIC encodes tricellulin, a recently discovered tight-junction (TJ) protein that contributes to the structure and function of tricellular contacts of neighboring cells in many epithelial tissues. We show that, in humans, four different recessive mutations of TRIC cause nonsyndromic deafness (DFNB49), a surprisingly limited phenotype, given the widespread tissue distribution of tricellulin in epithelial cells. In the inner ear, tricellulin is concentrated at the tricellular TJs in cochlear and vestibular epithelia, including the structurally complex and extensive junctions between supporting and hair cells. We also demonstrate that there are multiple alternatively spliced isoforms of TRIC in various tissues and that mutations of TRIC associated with hearing loss remove all or most of a conserved region in the cytosolic domain that binds to the cytosolic scaffolding protein ZO-1. A wild-type isoform of tricellulin, which lacks this conserved region, is unaffected by the mutant alleles and is hypothesized to be sufficient for structural and functional integrity of epithelial barriers outside the inner ear.
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Affiliation(s)
- Saima Riazuddin
- Section on Human Genetics, Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, MD 20850, USA
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88
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Kremer H, van Wijk E, Märker T, Wolfrum U, Roepman R. Usher syndrome: molecular links of pathogenesis, proteins and pathways. Hum Mol Genet 2006; 15 Spec No 2:R262-70. [PMID: 16987892 DOI: 10.1093/hmg/ddl205] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Usher syndrome is the most common form of deaf-blindness. The syndrome is both clinically and genetically heterogeneous, and to date, eight causative genes have been identified. The proteins encoded by these genes are part of a dynamic protein complex that is present in hair cells of the inner ear and in photoreceptor cells of the retina. The localization of the Usher proteins and the phenotype in animal models indicate that the Usher protein complex is essential in the morphogenesis of the stereocilia bundle in hair cells and in the calycal processes of photoreceptor cells. In addition, the Usher proteins are important in the synaptic processes of both cell types. The association of other proteins with the complex indicates functional links to a number of basic cell-biological processes. Prominently present is the connection to the dynamics of the actin cytoskeleton, involved in cellular morphology, cell polarity and cell-cell interactions. The Usher protein complex can also be linked to the cadherins/catenins in the adherens junction-associated protein complexes, suggesting a role in cell polarity and tissue organization. A third link can be established to the integrin transmembrane signaling network. The Usher interactome, as outlined in this review, participates in pathways common in inner ear and retina that are disrupted in the Usher syndrome.
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Affiliation(s)
- Hannie Kremer
- Department of Otorhinolaryngology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
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89
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Phillips KR, Tong S, Goodyear R, Richardson GP, Cyr JL. Stereociliary myosin-1c receptors are sensitive to calcium chelation and absent from cadherin 23 mutant mice. J Neurosci 2006; 26:10777-88. [PMID: 17050716 PMCID: PMC6674754 DOI: 10.1523/jneurosci.1847-06.2006] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The identities of some of the constituents of the hair-cell transduction apparatus have been elucidated only recently. The molecular motor myosin-1c (Myo1c) functions in adaptation of the hair-cell response to sustained mechanical stimuli and is therefore an integral part of the transduction complex. Recent data indicate that Myo1c interacts in vitro with two other molecules proposed to be important for transduction: cadherin 23 (Cdh23), a candidate for the stereociliary tip link, and phosphatidylinositol 4,5-bisphosphate (PIP2), which is abundant in the membranes of hair-cell stereocilia. It is not known, however, whether these interactions occur in hair cells. Using an in situ binding assay on saccular hair cells, we demonstrated previously that Myo1c interacts with molecules at stereociliary tips, the site of transduction, through sequences contained within its calmodulin (CaM)-binding neck domain, which can bind up to four CaM molecules. In the current study, we identify the second CaM-binding IQ domain as a region of Myo1c that mediates CaM-sensitive binding to stereociliary tips and to PIP2 immobilized on a solid support. Binding of Myo1c to stereociliary tips of cochlear and vestibular hair cells is disrupted by treatments that break tip links. In addition, Myo1c does not bind to stereocilia from mice whose hair cells lack Cdh23 protein despite the presence of PIP2 in the stereociliary membranes. Collectively, our data suggest that Myo1c and Cdh23 interact at the tips of hair-cell stereocilia and that this interaction is modulated by CaM.
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Affiliation(s)
- Kelli R. Phillips
- Sensory Neuroscience Research Center and
- Departments of Biochemistry and Molecular Pharmacology and
| | - Song Tong
- Sensory Neuroscience Research Center and
- Otolaryngology, West Virginia University School of Medicine, Morgantown, West Virginia 26506-9303, and
| | - Richard Goodyear
- School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
| | - Guy P. Richardson
- School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, United Kingdom
| | - Janet L. Cyr
- Sensory Neuroscience Research Center and
- Departments of Biochemistry and Molecular Pharmacology and
- Otolaryngology, West Virginia University School of Medicine, Morgantown, West Virginia 26506-9303, and
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90
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Ahmed ZM, Goodyear R, Riazuddin S, Lagziel A, Legan PK, Behra M, Burgess SM, Lilley KS, Wilcox ER, Riazuddin S, Griffith AJ, Frolenkov GI, Belyantseva IA, Richardson GP, Friedman TB. The tip-link antigen, a protein associated with the transduction complex of sensory hair cells, is protocadherin-15. J Neurosci 2006; 26:7022-34. [PMID: 16807332 PMCID: PMC6673907 DOI: 10.1523/jneurosci.1163-06.2006] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Sound and acceleration are detected by hair bundles, mechanosensory structures located at the apical pole of hair cells in the inner ear. The different elements of the hair bundle, the stereocilia and a kinocilium, are interconnected by a variety of link types. One of these links, the tip link, connects the top of a shorter stereocilium with the lateral membrane of an adjacent taller stereocilium and may gate the mechanotransducer channel of the hair cell. Mass spectrometric and Western blot analyses identify the tip-link antigen, a hitherto unidentified antigen specifically associated with the tip and kinocilial links of sensory hair bundles in the inner ear and the ciliary calyx of photoreceptors in the eye, as an avian ortholog of human protocadherin-15, a product of the gene for the deaf/blindness Usher syndrome type 1F/DFNB23 locus. Multiple protocadherin-15 transcripts are shown to be expressed in the mouse inner ear, and these define four major isoform classes, two with entirely novel, previously unidentified cytoplasmic domains. Antibodies to the three cytoplasmic domain-containing isoform classes reveal that each has a different spatiotemporal expression pattern in the developing and mature inner ear. Two isoforms are distributed in a manner compatible for association with the tip-link complex. An isoform located at the tips of stereocilia is sensitive to calcium chelation and proteolysis with subtilisin and reappears at the tips of stereocilia as transduction recovers after the removal of calcium chelators. Protocadherin-15 is therefore associated with the tip-link complex and may be an integral component of this structure and/or required for its formation.
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91
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Gao M, Sotomayor M, Villa E, Lee EH, Schulten K. Molecular mechanisms of cellular mechanics. Phys Chem Chem Phys 2006; 8:3692-706. [PMID: 16896432 DOI: 10.1039/b606019f] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Mechanical forces play an essential role in cellular processes as input, output, and signals. Various protein complexes in the cell are designed to handle, transform and use such forces. For instance, proteins of muscle and the extracellular matrix can withstand considerable stretching forces, hearing-related and mechanosensory proteins can transform weak mechanical stimuli into electrical signals, and regulatory proteins are suited to forcing DNA into loops to control gene expression. Here we review the structure-function relationship of four protein complexes with well defined and representative mechanical functions. The first example is titin, a protein that confers passive elasticity on muscle. The second system is the elastic extracellular matrix protein, fibronectin, and its cellular receptor integrin. The third protein system is the transduction apparatus in hearing and other mechanical senses, likely containing cadherin and ankyrin repeats. The last system is the lac repressor protein, which regulates gene expression by looping DNA. This review focuses on atomic level descriptions of the physical mechanisms underlying the various mechanical functions of the stated proteins.
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Affiliation(s)
- Mu Gao
- Beckman Institute, Department of Physics, Center for Biophysics and Computational Biology, College of Medicine, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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92
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Mburu P, Kikkawa Y, Townsend S, Romero R, Yonekawa H, Brown SDM. Whirlin complexes with p55 at the stereocilia tip during hair cell development. Proc Natl Acad Sci U S A 2006; 103:10973-8. [PMID: 16829577 PMCID: PMC1544159 DOI: 10.1073/pnas.0600923103] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Hearing in mammals depends upon the proper development of actin-filled stereocilia at the hair cell surface in the inner ear. Whirlin, a PDZ domain-containing protein, is expressed at stereocilia tips and, by virtue of mutations in the whirlin gene, is known to play a key role in stereocilia development. We show that whirlin interacts with the membrane-associated guanylate kinase (MAGUK) protein, erythrocyte protein p55 (p55). p55 is expressed in outer hair cells in long stereocilia that make up the stereocilia bundle as well as surrounding shorter stereocilia structures. p55 interacts with protein 4.1R in erythrocytes, and we find that 4.1R is also expressed in stereocilia structures with an identical pattern to p55. Mutations in the whirlin gene (whirler) and in the myosin XVa gene (shaker2) affect stereocilia development and lead to early ablation of p55 and 4.1R labeling of stereocilia. The related MAGUK protein Ca2+-calmodulin serine kinase (CASK) is also expressed in stereocilia in both outer and inner hair cells, where it is confined to the stereocilia bundle. CASK interacts with protein 4.1N in neuronal tissue, and we find that 4.1N is expressed in stereocilia with an identical pattern to CASK. Unlike p55, CASK labeling shows little diminution of labeling in the whirler mutant and is unaffected in the shaker2 mutant. Similarly, expression of 4.1N in stereocilia is unaltered in whirler and shaker2 mutants. p55 and protein 4.1R form complexes critical for actin cytoskeletal assembly in erythrocytes, and the interaction of whirlin with p55 indicates it plays a similar role in hair cell stereocilia.
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Affiliation(s)
- Philomena Mburu
- *Medical Research Council Mammalian Genetics Unit, Harwell OX11 ORD, United Kingdom; and
| | - Yoshiaki Kikkawa
- Department of Animal Science, Tokyo Metropolitan Institute of Medical Science, 3-18-22, Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan
| | - Stuart Townsend
- *Medical Research Council Mammalian Genetics Unit, Harwell OX11 ORD, United Kingdom; and
| | - Rosario Romero
- *Medical Research Council Mammalian Genetics Unit, Harwell OX11 ORD, United Kingdom; and
| | - Hiromichi Yonekawa
- Department of Animal Science, Tokyo Metropolitan Institute of Medical Science, 3-18-22, Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan
| | - Steve D. M. Brown
- *Medical Research Council Mammalian Genetics Unit, Harwell OX11 ORD, United Kingdom; and
- To whom correspondence should be addressed. E-mail:
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93
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McHugh RK, Friedman RA. Genetics of hearing loss: Allelism and modifier genes produce a phenotypic continuum. ACTA ACUST UNITED AC 2006; 288:370-81. [PMID: 16550584 DOI: 10.1002/ar.a.20297] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recent genetic and genomic studies have greatly advanced our knowledge of the structure and function of genes involved in hearing loss. We are starting to recognize, however, that many of these genes do not appear to follow traditional Mendelian expression patterns and are subject to the effects of allelism and modifier genes. This review presents two genes illustrative of this concept that have varied expression pattern such that they may produce either syndromic or nonsyndromic hearing loss. One of these genes, cadherin 23, produces a spectrum of phenotypic traits, including presbycusis, nonsyndromic prelingual hearing loss (DFNB12), and syndromic hearing loss as part of Usher syndrome (Usher 1D). Missense mutations in CDH23 have been associated with presbycusis and DFNB12, whereas null alleles cause the majority of Usher 1D. Modifier gene products that interact with cadherin 23 also affect the phenotypic spectrum. Similarly, allelsim in the gene encoding wolframin (WFS1) causes either a nonsyndromic dominant low-frequency hearing loss (DFNA6/14/38) or Wolfram syndrome. Missense mutations within a defined region are associated with DFNA6/14/38, while more severe mutations spanning WFS1 are found in Wolfram syndrome patients. The phenotypic spectrum of Wolfram syndrome is also hypothesized to be influenced by modifier genes products. These studies provide increasing evidence for the importance of modifier genes in elucidating the functional pathways of primary hearing loss genes. Characterizing modifier genes may result in better treatment options for patients with hearing loss and define new diagnostic and therapeutic targets.
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Affiliation(s)
- Richard K McHugh
- Section on Hereditary Disorders of the Ear, House Ear Institute, Los Angeles, California 90057, USA
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94
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Ricci AJ, Kachar B, Gale J, Van Netten SM. Mechano-electrical transduction: new insights into old ideas. J Membr Biol 2006; 209:71-88. [PMID: 16773495 PMCID: PMC1839004 DOI: 10.1007/s00232-005-0834-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Indexed: 11/26/2022]
Abstract
The gating-spring theory of hair cell mechanotransduction channel activation was first postulated over twenty years ago. The basic tenets of this hypothesis have been reaffirmed in hair cells from both auditory and vestibular systems and across species. In fact, the basic findings have been reproduced in every hair cell type tested. A great deal of information regarding the structural, mechanical, molecular and biophysical properties of the sensory hair bundle and the mechanotransducer channel has accumulated over the past twenty years. The goal of this review is to investigate new data, using the gating spring hypothesis as the framework for discussion. Mechanisms of channel gating are presented in reference to the need for a molecular gating spring or for tethering to the intra- or extracellular compartments. Dynamics of the sensory hair bundle and the presence of motor proteins are discussed in reference to passive contributions of the hair bundle to gating compliance. And finally, the molecular identity of the channel is discussed in reference to known intrinsic properties of the native transducer channel.
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Affiliation(s)
- A J Ricci
- Neuroscience Center, Louisiana State University, New Orleans, LA 70112, USA.
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95
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Senften M, Schwander M, Kazmierczak P, Lillo C, Shin JB, Hasson T, Géléoc GSG, Gillespie PG, Williams D, Holt JR, Müller U. Physical and functional interaction between protocadherin 15 and myosin VIIa in mechanosensory hair cells. J Neurosci 2006; 26:2060-71. [PMID: 16481439 PMCID: PMC2712835 DOI: 10.1523/jneurosci.4251-05.2006] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Hair cells of the mammalian inner ear are the mechanoreceptors that convert sound-induced vibrations into electrical signals. The molecular mechanisms that regulate the development and function of the mechanically sensitive organelle of hair cells, the hair bundle, are poorly defined. We link here two gene products that have been associated with deafness and hair bundle defects, protocadherin 15 (PCDH15) and myosin VIIa (MYO7A), into a common pathway. We show that PCDH15 binds to MYO7A and that both proteins are expressed in an overlapping pattern in hair bundles. PCDH15 localization is perturbed in MYO7A-deficient mice, whereas MYO7A localization is perturbed in PCDH15-deficient mice. Like MYO7A, PCDH15 is critical for the development of hair bundles in cochlear and vestibular hair cells, controlling hair bundle morphogenesis and polarity. Cochlear and vestibular hair cells from PCDH15-deficient mice also show defects in mechanotransduction. Together, our findings suggest that PCDH15 and MYO7A cooperate to regulate the development and function of the mechanically sensitive hair bundle.
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96
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Abstract
Cochlear hair cells respond with phenomenal speed and sensitivity to sound vibrations that cause submicron deflections of their hair bundle. Outer hair cells are not only detectors, but also generate force to augment auditory sensitivity and frequency selectivity. Two mechanisms of force production have been proposed: contractions of the cell body or active motion of the hair bundle. Here, we describe recently identified proteins involved in the sensory and motor functions of auditory hair cells and present evidence for each force generator. Both motor mechanisms are probably needed to provide the high sensitivity and frequency discrimination of the mammalian cochlea.
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Affiliation(s)
- Robert Fettiplace
- Department of Physiology, University of Wisconsin Medical School, 185 Medical Sciences Building, 1300 University Avenue, Madison, Wisconsin 53706, USA.
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97
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Reiners J, Nagel-Wolfrum K, Jürgens K, Märker T, Wolfrum U. Molecular basis of human Usher syndrome: deciphering the meshes of the Usher protein network provides insights into the pathomechanisms of the Usher disease. Exp Eye Res 2006; 83:97-119. [PMID: 16545802 DOI: 10.1016/j.exer.2005.11.010] [Citation(s) in RCA: 197] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2005] [Revised: 11/15/2005] [Accepted: 11/21/2005] [Indexed: 11/17/2022]
Abstract
Usher syndrome (USH) is the most frequent cause of combined deaf-blindness in man. It is clinically and genetically heterogeneous and at least 12 chromosomal loci are assigned to three clinical USH types, namely USH1A-G, USH2A-C, USH3A (Davenport, S.L.H., Omenn, G.S., 1977. The heterogeneity of Usher syndrome. Vth Int. Conf. Birth Defects, Montreal; Petit, C., 2001. Usher syndrome: from genetics to pathogenesis. Annu. Rev. Genomics Hum. Genet. 2, 271-297). Mutations in USH type 1 genes cause the most severe form of USH. In USH1 patients, congenital deafness is combined with a pre-pubertal onset of retinitis pigmentosa (RP) and severe vestibular dysfunctions. Those with USH2 have moderate to severe congenital hearing loss, non-vestibular dysfunction and a later onset of RP. USH3 is characterized by variable RP and vestibular dysfunction combined with progressive hearing loss. The gene products of eight identified USH genes belong to different protein classes and families. There are five known USH1 molecules: the molecular motor myosin VIIa (USH1B); the two cell-cell adhesion cadherin proteins, cadherin 23 (USH1D) and protocadherin 15, (USH1F) and the scaffold proteins, harmonin (USH1C) and SANS (USH1G). In addition, two USH2 genes and one USH3A gene have been identified. The two USH2 genes code for the transmembrane protein USH2A, also termed USH2A ("usherin") and the G-protein-coupled 7-transmembrane receptor VLGR1b (USH2C), respectively, whereas the USH3A gene encodes clarin-1, a member of the clarin family which exhibits 4-transmembrane domains. Molecular analysis of USH1 protein function revealed that all five USH1 proteins are integrated into a protein network via binding to PDZ domains in the USH1C protein harmonin. Furthermore, this scaffold function of harmonin is supported by the USH1G protein SANS. Recently, we have shown that the USH2 proteins USH2A and VLGR1b as well as the candidate for USH2B, the sodium bicarbonate co-transporter NBC3, are also integrated into this USH protein network. In the inner ear, these interactions are essential for the differentiation of hair cell stereocilia but may also participate in the mechano-electrical signal transduction and the synaptic function of maturated hair cells. In the retina, the co-expression of all USH1 and USH2 proteins at the synapse of photoreceptor cells indicates that they are organized in an USH protein network there. The identification of the USH protein network indicates a common pathophysiological pathway in USH. Dysfunction or absence of any of the molecules in the mutual "interactome" related to the USH disease may lead to disruption of the network causing senso-neuronal degeneration in the inner ear and the retina, the clinical symptoms of USH.
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Affiliation(s)
- Jan Reiners
- Institute of Zoology, Department of Cell and Matrix Biology, Johannes Gutenberg University of Mainz, Müllerweg 6, D-55099 Mainz, Germany
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98
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Jones SM, Johnson KR, Yu H, Erway LC, Alagramam KN, Pollak N, Jones TA. A quantitative survey of gravity receptor function in mutant mouse strains. J Assoc Res Otolaryngol 2006; 6:297-310. [PMID: 16235133 PMCID: PMC2504620 DOI: 10.1007/s10162-005-0009-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Accepted: 06/20/2005] [Indexed: 02/04/2023] Open
Abstract
The purpose of this research was to identify vestibular deficits in mice using linear vestibular evoked potentials (VsEPs). VsEP thresholds, peak latencies, and peak amplitudes from 24 strains with known genetic mutations and 6 inbred background strains were analyzed and descriptive statistics generated for each strain. Response parameters from mutant homozygotes were compared with heterozygote and/or background controls and all strain averages were contrasted to normative ranges. Homozygotes of the following recessive mutations had absent VsEPs at the ages tested: Espn(je), Atp2b2dfw-2J, Spnb4qv-lnd2J, Spnb4qv-3J, Myo7ash1, Tmie(sr), Myo6sv, jc, Pcdh15av-J, Pcdh15av-2J, Pcdh15av-3J, Cdh23v-2J, Sans(js), hr, Kcne1pkr and Pou3f4del. These results suggest profound gravity receptor deficits for these homozygotes, which is consistent with the structural deficits that have been documented for many of these strains. Homozygotes of Catna2cdf, Grid2ho4J, Wnt1sw, qk, and Mbpshi strains and heterozygotes of Grid2lc had measurable VsEPs but one or more response parameters differed from the respective control group (heterozygote or background strain) or were outside normal ranges. For example, qk and Mbpshi homozygotes showed significantly prolonged latencies consistent with the abnormal myelin that has been described for these strains. Prolonged latencies may suggest deficits in neural conduction; elevated thresholds suggest reduced sensitivity, and reduced amplitudes may be suggestive for reduced neural synchrony. One mutation, Otx1jv, had all VsEP response parameters within normal limits--an expected finding because the abnormality in Otxljv is presumably restricted to the lateral semicircular canal. Interestingly, some heterozygote groups also showed abnormalities in one or more VsEP response parameters, suggesting that vestibular dysfunction, although less severe, may be present in some heterozygous animals.
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Affiliation(s)
- Sherri M Jones
- Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC 27858, USA.
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99
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Schlichting K, Wilsch-Bräuninger M, Demontis F, Dahmann C. Cadherin Cad99C is required for normal microvilli morphology in Drosophila follicle cells. J Cell Sci 2006; 119:1184-95. [PMID: 16507588 DOI: 10.1242/jcs.02831] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Microvilli are actin-filled membranous extensions common to epithelial cells. Several proteins have been identified that localize to microvilli. However, most of these proteins are dispensable for the normal morphogenesis of microvilli. Here, we show by immunoelectron microscopy that the non-classical cadherin Cad99C localizes to microvilli of Drosophila ovarian follicle cells. Loss of Cad99C function leads to disorganized and abnormal follicle cell microvilli. Conversely, overexpression of Cad99C in follicle cells results in large bundles of microvilli. Furthermore, altered microvilli morphology correlates with defects in the assembly of the vitelline membrane, an extracellular layer secreted by follicle cells that is part of the eggshell. Finally, we provide evidence that Cad99C is the homolog of vertebrate protocadherin 15. Mutations in the gene encoding protocadherin 15 lead to the disorganization of stereocilia, which are microvilli-derived extensions of cochlear hair cells, and deafness (Usher syndrome type 1F). Our data suggest an essential role for Cad99C in microvilli morphogenesis that is important for follicle cell function. Furthermore, these results indicate that insects and vertebrates use related cadherins to organize microvilli-like cellular extensions.
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Affiliation(s)
- Karin Schlichting
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
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100
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Affiliation(s)
- Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Rockville, MD, USA
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