RESUMEN
In the lateral line system, water motion is detected by neuromast organs, fundamental units that are arrayed on a fish's surface. Each neuromast contains hair cells, specialized mechanoreceptors that convert mechanical stimuli, in the form of water movement, into electrical signals. The orientation of hair cells' mechanosensitive structures ensures that the opening of mechanically gated channels is maximal when deflected in a single direction. In each neuromast organ, hair cells have two opposing orientations, enabling bi-directional detection of water movement. Interestingly, Tmc2b and Tmc2a proteins, which constitute the mechanotransduction channels in neuromasts, distribute asymmetrically so that Tmc2a is expressed in hair cells of only one orientation. Here, using both in vivo recording of extracellular potentials and calcium imaging of neuromasts, we demonstrate that hair cells of one orientation have larger mechanosensitive responses. The associated afferent neuron processes that innervate neuromast hair cells faithfully preserve this functional difference. Moreover, Emx2, a transcription factor required for the formation of hair cells with opposing orientations, is necessary to establish this functional asymmetry within neuromasts. Remarkably, loss of Tmc2a does not impact hair cell orientation but abolishes the functional asymmetry as measured by recording extracellular potentials and calcium imaging. Overall, our work indicates that oppositely oriented hair cells within a neuromast employ different proteins to alter mechanotransduction to sense the direction of water motion.
Asunto(s)
Sistema de la Línea Lateral , Pez Cebra , Animales , Pez Cebra/fisiología , Sistema de la Línea Lateral/fisiología , Mecanotransducción Celular/fisiología , Calcio , Agua , CabelloRESUMEN
Hearing impairment (HI) is a common disorder of sensorineural function with a highly heterogeneous genetic background. Although substantial progress has been made in the understanding of the genetic etiology of hereditary HI, many genes implicated in HI remain undiscovered. Via exome and Sanger sequencing of DNA samples obtained from consanguineous Pakistani families that segregate profound prelingual sensorineural HI, we identified rare homozygous missense variants in four genes (ADAMTS1, MPDZ, MVD, and SEZ6) that are likely the underlying cause of HI. Linkage analysis provided statistical evidence that these variants are associated with autosomal recessive nonsyndromic HI. In silico analysis of the mutant proteins encoded by these genes predicted structural, conformational or interaction changes. RNAseq data analysis revealed expression of these genes in the sensory epithelium of the mouse inner ear during embryonic, postnatal, and adult stages. Immunohistochemistry of the mouse cochlear tissue, further confirmed the expression of ADAMTS1, SEZ6, and MPDZ in the neurosensory hair cells of the organ of Corti, while MVD expression was more prominent in the spiral ganglion cells. Overall, supported by in silico mutant protein analysis, animal models, linkage analysis, and spatiotemporal expression profiling in the mouse inner ear, we propose four new candidate genes for HI and expand our understanding of the etiology of HI.
Asunto(s)
Proteína ADAMTS1/genética , Carboxiliasas/genética , Pérdida Auditiva Sensorineural/genética , Proteínas de la Membrana/genética , Proteína ADAMTS1/química , Proteína ADAMTS1/metabolismo , Animales , Carboxiliasas/química , Carboxiliasas/metabolismo , Femenino , Genes Recesivos , Células Ciliadas Auditivas/metabolismo , Pérdida Auditiva Sensorineural/patología , Humanos , Masculino , Proteínas de la Membrana/química , Proteínas de la Membrana/metabolismo , Ratones , Mutación , Linaje , Dominios ProteicosRESUMEN
Cytokinetic membrane abscission is a spatially and temporally regulated process that requires ESCRT (endosomal sorting complexes required for transport)dependent control of membrane remodeling at the midbody, a subcellular organelle that defines the cleavage site. Alteration of ESCRT function can lead to cataract, but the underlying mechanism and its relation to cytokinesis are unclear. We found a lens-specific cytokinetic process that required PI3K-C2α (phosphatidylinositol-4-phosphate 3-kinase catalytic subunit type 2α), its lipid product PI(3,4)P2 (phosphatidylinositol 3,4-bisphosphate), and the PI(3,4)P2binding ESCRT-II subunit VPS36 (vacuolar protein-sorting-associated protein 36). Loss of each of these components led to impaired cytokinesis, triggering premature senescence in the lens of fish, mice, and humans. Thus, an evolutionarily conserved pathway underlies the cell typespecific control of cytokinesis that helps to prevent early onset cataract by protecting from senescence.
Asunto(s)
Catarata/patología , Senescencia Celular , Citocinesis , Complejos de Clasificación Endosomal Requeridos para el Transporte/metabolismo , Cristalino/citología , Fosfatidilinositol 3-Quinasas/metabolismo , Fosfatidilinositoles/metabolismo , Envejecimiento Prematuro , Animales , Evolución Biológica , Proteínas de Unión al Calcio/metabolismo , Catarata/metabolismo , Proteínas de Ciclo Celular/metabolismo , Línea Celular , Humanos , Cristalino/crecimiento & desarrollo , Cristalino/metabolismo , Ratones , Mutación , Fosfatidilinositol 3-Quinasas/genética , Fosfatidilinositol 4,5-Difosfato/metabolismo , Tubulina (Proteína)/metabolismo , Pez Cebra , Proteínas de Pez Cebra/genética , Proteínas de Pez Cebra/metabolismoRESUMEN
To enable hearing, the sensory hair cell contains specialized subcellular structures at its apical region, including the actin-rich cuticular plate and circumferential band. ACF7 (actin crosslinking family protein 7), encoded by the gene Macf1 (microtubule and actin crosslinking factor 1), is a large cytoskeletal crosslinking protein that interacts with microtubules and filamentous actin to shape cells. ACF7 localizes to the cuticular plate and the circumferential band in the hair cells of vertebrates. The compelling expression pattern of ACF7 in hair cells, combined with conserved roles of this protein in the cytoskeleton of various cell types in invertebrates and vertebrates, led to the hypothesis that ACF7 performs a key function in the subcellular architecture of hair cells. To test the hypothesis, we conditionally target Macf1 in the inner ears of mice. Surprisingly, our data show that in young, but mature, conditional knockout mice cochlear hair cell survival, planar cell polarity, organization of the hair cells within the organ of Corti, and capacity to hear are not significantly impacted. Overall, these results fail to support the hypothesis that ACF7 is an essential hair cell protein in young mice, and the purpose of ACF7 expression in the hair cell remains to be understood.
Asunto(s)
COVID-19 , SARS-CoV-2 , Prueba de COVID-19 , Pruebas Diagnósticas de Rutina , Hospitales , HumanosRESUMEN
Fish use the highly stereotyped lateral line system to swim against a current. New research reveals that the order of the lateral line system is less important than brain response asymmetries for achieving this navigational feat.
Asunto(s)
Ondas Encefálicas , Sistema de la Línea Lateral , Animales , Peces , Natación , AguaRESUMEN
Viral testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), particularly early in the COVID-19 pandemic, was limited by supply of reagents. We pooled nasopharyngeal samples from patients at low risk of SARS-CoV-2 infection in groups of 3 for testing. Three weeks of testing using this strategy resulted in 530 patient tests in 179 cartridges; 4 positive test groups required the use of 11 additional cartridges with an overall positive rate of 0.8% in a low-risk population. This strategy resulted in the use of 340 fewer cartridges than if each test were performed on one patient sample. Pooled testing of low-risk populations allows for continued testing even when supplies are relatively scarce.
Asunto(s)
Betacoronavirus/genética , Infecciones por Coronavirus/diagnóstico , ADN Viral/análisis , Pruebas Genéticas/métodos , Pacientes Internos , Pandemias , Neumonía Viral/diagnóstico , COVID-19 , Infecciones por Coronavirus/epidemiología , Infecciones por Coronavirus/virología , Humanos , Neumonía Viral/epidemiología , Neumonía Viral/virología , SARS-CoV-2RESUMEN
Rates of posttraumatic stress are elevated in individuals who have experienced childhood and/or cumulative trauma, and trauma appraisals have been suggested as a possible mediator of this effect. This study tested the proposed mediating role of trauma appraisals between both childhood and cumulative trauma, and two markers of trauma-related distress; posttraumatic stress and depression. Mediation models were developed and tested with data collected from a sample of trauma-exposed, treatment receiving adults (N = 106). Trauma appraisals fully mediated relationships between childhood trauma and PTSD/depression. Appraisals also mediated the relationships between cumulative trauma and depression. When appraisal subscales were simultaneously entered, alienation appraisals were the only significant mediator of these relationships. The study found support for the proposed mediating role of trauma appraisals between different forms of trauma and trauma related distress. Alienation appraisals were particularly emphasised.
RESUMEN
Perception of sound is initiated by mechanically gated ion channels at the tips of stereocilia. Mature mammalian auditory hair cells require transmembrane channel-like 1 (TMC1) for mechanotransduction, and mutations of the cognate genetic sequences result in dominant or recessive heritable deafness forms in humans and mice. In contrast, zebrafish lateral line hair cells, which detect water motion, require Tmc2a and Tmc2b. Here, we use standard and multiplex genome editing in conjunction with functional and behavioral assays to determine the reliance of zebrafish hearing and vestibular organs on Tmc proteins. Surprisingly, our approach using multiple mutant alleles demonstrates that hearing in zebrafish is not dependent on Tmc1, nor is it fully dependent on Tmc2a and Tmc2b. Hearing however is absent in triple-mutant zebrafish that lack Tmc1, Tmc2a and Tmc2b. These outcomes reveal a striking resemblance of Tmc protein reliance in the vestibular sensory epithelia of mammals to the maculae of zebrafish. Moreover, our findings disclose a logic of Tmc use where hearing depends on a complement of Tmc proteins beyond those employed to sense water motion.
Asunto(s)
Pérdida Auditiva Sensorineural/genética , Audición/genética , Proteínas de la Membrana/genética , Proteínas de Pez Cebra/genética , Animales , Sordera/genética , Sordera/patología , Células Ciliadas Auditivas/metabolismo , Células Ciliadas Auditivas/patología , Células Ciliadas Auditivas Internas/metabolismo , Células Ciliadas Auditivas Internas/patología , Pérdida Auditiva Sensorineural/patología , Humanos , Mecanotransducción Celular/genética , Ratones , Mutación/genética , Estereocilios/genética , Estereocilios/patología , Pez Cebra/genéticaRESUMEN
Hair cells are heterogenous, enabling varied roles in sensory systems. An emerging hypothesis is that the transmembrane channel-like (Tmc) proteins of the hair cell's mechanotransduction apparatus vary within and between organs to permit encoding of different mechanical stimuli. Five anatomical variables that may coincide with different Tmc use by a hair cell within the ear are the containing organ, cell morphology, cell position within an organ, axis of best sensitivity for the cell, and the hair bundle's orientation within this axis. Here, we test this hypothesis in the organs of the zebrafish ear using a suite of genetic mutations. Transgenesis and quantitative measurements demonstrate two morphologically distinct hair cell types in the central thickness of a vestibular organ, the lateral crista: short and tall. In contrast to what has been observed, we find that tall hair cells that lack Tmc1 generally have substantial reductions in mechanosensitivity. In short hair cells that lack Tmc2 isoforms, mechanotransduction is largely abated. However, hair cell Tmc dependencies are not absolute, and an exceptional class of short hair cell that depends on Tmc1 is present, termed a short hair cell erratic. To further test anatomical variables that may influence Tmc use, we map Tmc1 function in the saccule of mutant larvae that depend just on this Tmc protein to hear. We demonstrate that hair cells that use Tmc1 are found in the posterior region of the saccule, within a single axis of best sensitivity, and hair bundles with opposite orientations retain function. Overall, we determine that Tmc reliance in the ear is dependent on the organ, subtype of hair cell, position within the ear, and axis of best sensitivity.
RESUMEN
The pathogenic variant c.144T>G (p.N48K) in the clarin1 gene (CLRN1) results in progressive loss of vision and hearing in Usher syndrome IIIA (USH3A) patients. CLRN1 is predicted to be an essential protein in hair bundles, the mechanosensory structure of hair cells critical for hearing and balance. When expressed in animal models, CLRN1 localizes to the hair bundle, whereas glycosylation-deficient CLRN1N48K aggregates in the endoplasmic reticulum, with only a fraction reaching the bundle. We hypothesized that the small amount of CLRN1N48K that reaches the hair bundle does so via an unconventional secretory pathway and that activation of this pathway could be therapeutic. Using genetic and pharmacological approaches, we find that clarin1 knockout (clrn1KO/KO ) zebrafish that express the CLRN1c.144T>G pathogenic variant display progressive hair cell dysfunction, and that CLRN1N48K is trafficked to the hair bundle via the GRASP55 cargo-dependent unconventional secretory pathway (GCUSP). On expression of GRASP55 mRNA, or on exposure to the drug artemisinin (which activates GCUSP), the localization of CLRN1N48K to the hair bundles was enhanced. Artemisinin treatment also effectively restored hair cell mechanotransduction and attenuated progressive hair cell dysfunction in clrn1KO/KO larvae that express CLRN1c.144T>G , highlighting the potential of artemisinin to prevent sensory loss in CLRN1c.144T>G patients.
Asunto(s)
Células Ciliadas Auditivas/fisiología , Mecanotransducción Celular/genética , Proteínas de la Membrana , Vías Secretoras/genética , Animales , Animales Modificados Genéticamente , Artemisininas/farmacología , Células Ciliadas Auditivas/efectos de los fármacos , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Proteínas de la Membrana/fisiología , Pez CebraRESUMEN
KEY POINTS: The synaptic ribbon is an organelle that coordinates rapid and sustained vesicle release to enable hearing and balance. Ribeye a and b proteins are major constituents of the synaptic ribbon in hair cells. In this study, we use optically clear transgenic zebrafish to examine the potential dynamics of ribeye proteins in vivo. We demonstrate that ribeye proteins are inherently dynamic but are stabilized at the ribbons of hair cells in the ear and the lateral line system. ABSTRACT: Ribeye protein is a major constituent of the synaptic ribbon, an organelle that coordinates rapid and sustained vesicle release to enable hearing and balance. The ribbon is considered to be a stable structure. However, under certain physiological conditions such as acoustic overexposure that results in temporary noise-induced hearing loss or perturbations of ion channels, ribbons may change shape or vanish altogether, suggesting greater plasticity than previously appreciated. The dynamic properties of ribeye proteins are unknown. Here we use transgenesis and imaging to explore the behaviours of ribeye proteins within the ribbon and also their intrinsic properties outside the context of the ribbon synapse in a control cell type, the skin cell. By fluorescence recovery after photobleaching (FRAP) on transgenic zebrafish larvae, we test whether ribeye proteins are dynamic in vivo in real time. In the skin, a cell type devoid of synaptic contacts, Ribeye a-mCherry exchanges with ribbon-like structures on a time scale of minutes (t1/2 = 3.2 min). In contrast, Ribeye a of the ear and lateral line and Ribeye b of the lateral line each exchange at ribbons of hair cells an order of magnitude slower (t1/2 of 125.6 min, 107.0 min and 95.3 min, respectively) than Ribeye a of the skin. These basal exchange rates suggest that long-term ribbon presence may require ribeye renewal. Our studies demonstrate that ribeye proteins are inherently dynamic but are stabilized at the ribbons of sensory cells in vivo.
Asunto(s)
Animales Modificados Genéticamente/fisiología , Proteínas del Ojo/química , Células Ciliadas Auditivas/fisiología , Proteínas del Tejido Nervioso/química , Sinapsis/fisiología , Proteínas de Pez Cebra/química , Pez Cebra/fisiología , Animales , Proteínas del Ojo/genética , Proteínas del Ojo/metabolismo , Células Ciliadas Auditivas/citología , Mecanotransducción Celular , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Estabilidad Proteica , Proteínas de Pez Cebra/genética , Proteínas de Pez Cebra/metabolismoRESUMEN
Detection of water motion by the lateral line relies on mechanotransduction complexes at stereocilia tips. This sensory system is comprised of neuromasts, patches of hair cells with stereociliary bundles arranged with morphological mirror symmetry that are mechanically responsive to two opposing directions. Here, we find that transmembrane channel-like 2b (Tmc2b) is differentially required for mechanotransduction in the zebrafish lateral line. Despite similarities in neuromast hair cell morphology, three classes of these cells can be distinguished by their Tmc2b reliance. We map mechanosensitivity along the lateral line using imaging and electrophysiology to determine that a hair cell's Tmc2b dependence is governed by neuromast topological position and hair bundle orientation. Overall, water flow is detected by molecular machinery that can vary between hair cells of different neuromasts. Moreover, hair cells within the same neuromast can break morphologic symmetry of the sensory organ at the stereocilia tips.
Asunto(s)
Sistema de la Línea Lateral/metabolismo , Mecanorreceptores/metabolismo , Mecanotransducción Celular/genética , Proteínas de la Membrana/metabolismo , Movimiento (Física) , Agua , Proteínas de Pez Cebra/metabolismo , Animales , Sistema de la Línea Lateral/fisiología , Mecanorreceptores/fisiología , Mecanotransducción Celular/fisiología , Proteínas de la Membrana/genética , Proteínas de la Membrana/fisiología , Pez Cebra , Proteínas de Pez Cebra/genética , Proteínas de Pez Cebra/fisiologíaRESUMEN
Cisplatin and other related platinum antineoplastic drugs are commonly used in the treatment of a variety of cancers in both adults and children but are often associated with severe side effects, including hearing loss. Cisplatin's ototoxic effects are multifaceted, culminating in irreversible damage to the mechanosensory hair cells in the inner ear. Platinum drugs act on cancerous cells by forming nuclear DNA adducts, which may initiate signaling leading to cell cycle arrest or apoptosis. Moreover, it was reported that cisplatin may induce mitochondrial DNA damage in non-cancerous cells. Therefore, protecting mitochondria may alleviate cisplatin-induced insult to non-proliferating cells. Thus, it is important to identify agents that shield the mitochondria from cisplatin-induced insult without compromising the anti-tumor actions of the platinum-based drugs. In this study we tested the protective properties of mitochondrial division inhibitor, mdivi-1, a derivative of quinazolinone and a regulator of mitochondrial fission. Interestingly, it has been reported that mdivi-1 increases the apoptosis of cells that are resistant to cisplatin. The ability of mdivi-1 to protect hair cells against cisplatin-induced toxicity was evaluated in a fish model. Wild-type (Tübingen strain), cdh23 mutant, and transgenic pvalb3b::GFP zebrafish stably expressing GFP in the hair cells were used in this study. Larvae at 5-6 days post fertilization were placed in varying concentrations of cisplatin (50-200 µM) and/or mdivi-1 (1-10 µM) for 16 h. To evaluate hair cell's viability the number of hair bundles per neuromast were counted. To assess hair cell function, we used the FM1-43 uptake assay and recordings of neuromast microphonic potentials. The results showed that mdivi-1 protected hair cells of lateral line neuromasts when they were challenged by 50 µM of cisplatin: viability of hair cells increased almost twice from 19% ± 1.8% to 36% ± 2.0% (p < 0.001). No protection was observed when higher concentrations of cisplatin were used. In addition, our data were in accord with previously reported results that functional mechanotransduction strongly potentiates cisplatin-induced hair cell toxicity. Together, our results suggest that mitochondrial protection may prevent cisplatin-induced damage to hair cells.
RESUMEN
The organ of Corti has evolved a panoply of cells with extraordinary morphological specializations to harness, direct, and transduce mechanical energy into electrical signals. Among the cells with prominent apical specializations are hair cells and nearby supporting cells. At the apical surface of each hair cell is a mechanosensitive hair bundle of filamentous actin (F-actin)-based stereocilia, which insert rootlets into the F-actin meshwork of the underlying cuticular plate, a rigid organelle considered to hold the stereocilia in place. Little is known about the protein composition and development of the cuticular plate or the apicolateral specializations of organ of Corti supporting cells. We show that supervillin, an F-actin cross-linking protein, localizes to cuticular plates in hair cells of the mouse cochlea and vestibule and zebrafish sensory epithelia. Moreover, supervillin localizes near the apicolateral margins within the head plates of Deiters' cells and outer pillar cells, and proximal to the apicolateral margins of inner phalangeal cells, adjacent to the junctions with neighboring hair cells. Overall, supervillin localization suggests this protein may shape the surface structure of the organ of Corti.
Asunto(s)
Células Ciliadas Auditivas/metabolismo , Proteínas de la Membrana/metabolismo , Proteínas de Microfilamentos/metabolismo , Órgano Espiral/metabolismo , Estereocilios/metabolismo , Vestíbulo del Laberinto/metabolismo , Citoesqueleto de Actina/metabolismo , Animales , Ratones , Pez CebraRESUMEN
The mechanisms underlying mechanosensory hair bundle formation in auditory sensory cells are largely mysterious. In this issue, Lelli et al. (2016. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201509017) reveal that a pair of molecular motors, myosin IIIa and myosin IIIb, is involved in the hair bundle's morphology and hearing.
Asunto(s)
Células Ciliadas Auditivas/fisiología , Microvellosidades/fisiología , Cadenas Pesadas de Miosina/fisiología , Miosina Tipo III/fisiología , Estereocilios/fisiología , Animales , HumanosRESUMEN
Permanency of mechanosensory stereocilia may be the consequence of low protein turnover or rapid protein renewal. Here, we devise a system, using optical techniques in live zebrafish, to distinguish between these mechanisms. We demonstrate that the stereocilium's abundant actin cross-linker fascin 2b exchanges, without bias or a phosphointermediate, orders of magnitude faster (t1/2 of 76.3 s) than any other known hair bundle protein. To establish the logic of fascin 2b's exchange, we examine whether filamentous actin is dynamic and detect substantial ß-actin exchange within the stereocilium's paracrystal (t1/2 of 4.08 hr). We propose that fascin 2b's behavior may enable cross-linking at fast timescales of stereocilia vibration while noninstructively facilitating the slower process of actin exchange. Furthermore, tip protein myosin XVa fully exchanges in hours (t1/2 of 11.6 hr), indicating that delivery of myosin-associated cargo occurs in mature stereocilia. These findings suggest that stereocilia permanency is underpinned by vibrant protein exchange.
Asunto(s)
Citoesqueleto/metabolismo , Estereocilios/metabolismo , Animales , Citoesqueleto/ultraestructura , Proteínas del Ojo/metabolismo , Células Ciliadas Auditivas/metabolismo , Células Ciliadas Auditivas/ultraestructura , Proteínas de Microfilamentos/metabolismo , Miosinas/metabolismo , Transporte de Proteínas , Estereocilios/ultraestructura , Pez Cebra , Proteínas de Pez Cebra/metabolismoRESUMEN
Usher syndrome type III (USH3) is characterized by progressive loss of hearing and vision, and varying degrees of vestibular dysfunction. It is caused by mutations that affect the human clarin-1 protein (hCLRN1), a member of the tetraspanin protein family. The missense mutation CLRN1(N48K), which affects a conserved N-glycosylation site in hCLRN1, is a common causative USH3 mutation among Ashkenazi Jews. The affected individuals hear at birth but lose that function over time. Here, we developed an animal model system using zebrafish transgenesis and gene targeting to provide an explanation for this phenotype. Immunolabeling demonstrated that Clrn1 localized to the hair cell bundles (hair bundles). The clrn1 mutants generated by zinc finger nucleases displayed aberrant hair bundle morphology with diminished function. Two transgenic zebrafish that express either hCLRN1 or hCLRN1(N48K) in hair cells were produced to examine the subcellular localization patterns of wild-type and mutant human proteins. hCLRN1 localized to the hair bundles similarly to zebrafish Clrn1; in contrast, hCLRN1(N48K) largely mislocalized to the cell body with a small amount reaching the hair bundle. We propose that this small amount of hCLRN1(N48K) in the hair bundle provides clarin-1-mediated function during the early stages of life; however, the presence of hCLRN1(N48K) in the hair bundle diminishes over time because of intracellular degradation of the mutant protein, leading to progressive loss of hair bundle integrity and hair cell function. These findings and genetic tools provide an understanding and path forward to identify therapies to mitigate hearing loss linked to the CLRN1 mutation. SIGNIFICANCE STATEMENT: Mutations in the clarin-1 gene affect eye and ear function in humans. Individuals with the CLRN1(N48K) mutation are born able to hear but lose that function over time. Here, we develop an animal model system using zebrafish transgenesis and gene targeting to provide an explanation for this phenotype. This approach illuminates the role of clarin-1 and the molecular mechanism linked to the CLRN1(N48K) mutation in sensory hair cells of the inner ear. Additionally, the investigation provided an in vivo model to guide future drug discovery to rescue the hCLRN1(N48K) in hair cells.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica/genética , Células Ciliadas Auditivas/patología , Proteínas de la Membrana/metabolismo , Síndromes de Usher/patología , Proteínas de Pez Cebra/metabolismo , Animales , Animales Modificados Genéticamente , Vías Auditivas/metabolismo , Vías Auditivas/patología , Tipificación del Cuerpo/efectos de los fármacos , Tipificación del Cuerpo/genética , Cadherinas/genética , Modelos Animales de Enfermedad , Endodesoxirribonucleasas/farmacología , Femenino , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Genotipo , Pérdida Auditiva/genética , Humanos , Larva , Masculino , Proteínas de la Membrana/genética , Mutación/genética , Equilibrio Postural/genética , Análisis de Secuencia de Proteína , Sinapsis/metabolismo , Sinapsis/patología , Síndromes de Usher/complicaciones , Síndromes de Usher/genética , Trastornos de la Visión/etiología , Pez Cebra , Proteínas de Pez Cebra/genéticaRESUMEN
The mechanosensitive hair cells of the inner ear are crucial to hearing and vestibular function. Each hair cell detects the mechanical stimuli associated with sound or head movement with a hair bundle at the apical surface of the cell, consisting of a precise array of actin-based stereocilia. Each stereocilium inserts as a rootlet into a dense filamentous actin mesh known as the cuticular plate. Disruption of the parallel actin bundles forming the stereocilia results in hearing impairments and balance defects. The cuticular plate is thought to be involved in holding the stereocilia in place. However, the precise role of the cuticular plate in hair bundle development, maintenance, and hearing remains unknown. Ultrastructural studies have revealed a complex cytoskeletal architecture, but a lack of knowledge of proteins that inhabit the cuticular plate and a dearth of mutations that perturb relevant proteins have hindered our understanding of the functions of the cuticular plate. Here, we discuss what is known about the structure and development of this unique and poorly-understood actin-rich organelle.
Asunto(s)
Citoesqueleto de Actina/metabolismo , Células Ciliadas Auditivas/fisiología , Células Ciliadas Vestibulares/fisiología , Orgánulos/fisiología , Animales , HumanosRESUMEN
The precise morphology of the mechanosensitive hair bundle requires seamless integration of actin and microtubule networks. Here, we identify Acf7a (actin crosslinking family protein 7a) as a protein positioned to bridge these distinct cytoskeletal networks in hair cells. By imaging Acf7a-Citrine fusion protein in zebrafish and immunolabeling of vestibular and cochlear mouse hair cells, we show that Acf7a and ACF7 circumscribe, underlie, and are interwoven into the cuticular plate (CP), and they also encircle the basal body of the kinocilium. In cochlear hair cells, ACF7 localization is graded, with the highest concentration near each fonticulus--an area free of F-actin in the region of the CP that contains the basal body. During hair-cell development and regeneration, Acf7a precedes formation of the hair bundle and CP. Finally, electron tomography demonstrates that the ends of microtubules insert into the CP and are decorated with filamentous linkers connecting microtubules to the CP. These observations are consistent with ACF7 being a linker protein, which may shape the cytoskeleton of the hair cell early during hair-bundle genesis.