Modified Protein Expression in the Tectorial Membrane of the Cochlea Reveals Roles for the Striated Sheet Matrix

Jones, Gareth P.; Elliott, Stephen J.; Russell, Ian J.; Lukashkin, Andrei N.

doi:10.1016/j.bpj.2014.11.1854

Cited by 13 publications

(32 citation statements)

References 49 publications

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“…Measurements on isolated TMs (Jones et al 2015) suggest that the striated-sheet matrix can enhance energy dissipation and suppress SOAEs in normal animals. Although this is a possible explanation for the increased incidence of SOAEs in Ceacam16 KO mice, Otoa KO mice retain striated-sheet matrix within the main body of the TM but are, nonetheless, excellent emitters.…”

Section: Discussionmentioning

confidence: 99%

Increased Spontaneous Otoacoustic Emissions in Mice with a Detached Tectorial Membrane

Cheatham¹,

Ahmad²,

Zhou³

et al. 2015

JARO

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Mutations in genes encoding tectorial membrane (TM) proteins are a significant cause of human hereditary hearing loss , and several mouse models have been developed to study the functional significance of this accessory structure in the mammalian cochlea. In this study, we use otoacoustic emissions (OAE), signals obtained from the ear canal that provide a measure of cochlear function, to characterize a mouse in which the TM is detached from the spiral limbus due to an absence of otoancorin (Otoa, Lukashkin et al. 2012). Our results demonstrate that spontaneous emissions (SOAE), sounds produced in the cochlea without stimulation, increase dramatically in mice with detached TMs even though their hearing sensitivity is reduced. This behavior is unusual because wild-type (WT) controls are rarely spontaneous emitters. SOAEs in mice lacking Otoa predominate around 7 kHz, which is much lower than in either WT animals when they generate SOAEs or in mutant mice in which the TM protein Ceacam16 is absent (Cheatham et al. 2014). Although both mutants lack Hensen's stripe, loss of this TM feature is only observed in regions coding frequencies greater than~15 kHz in WT mice so its loss cannot explain the low-frequency, de novo SOAEs observed in mice lacking Otoa. The fact that~80 % of mice lacking Otoa produce SOAEs even when they generate smaller distortion product OAEs suggests that the active process is still functioning in these mutants but the system(s) involved have become less stable due to alterations in TM structure.

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Section: Discussionmentioning

confidence: 99%

Increased Spontaneous Otoacoustic Emissions in Mice with a Detached Tectorial Membrane

Cheatham¹,

Ahmad²,

Zhou³

et al. 2015

JARO

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“…In a similar manner, deletion of β-tectorin also produced a reduction in acoustic sensitivity, but this reduction was accompanied by an enhanced sharpness of mechanical tuning (262). This surprising result has been ascribed to a reduced longitudinal coupling of the tectorial membrane that caused the tuned vibrations to be narrower and less distributed (95) (132) (196). CEACAM-16 is a third glycoprotein in the tectorial membrane, and it is thought to interact with both α-tectorin and β-tectorin.…”

Section: Frequency Tuningmentioning

confidence: 99%

Hair Cell Transduction, Tuning, and Synaptic Transmission in the Mammalian Cochlea

Fettiplace

2017

Comprehensive Physiology

284

273

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Sound pressure fluctuations striking the ear are conveyed to the cochlea, where they vibrate the basilar membrane on which sit hair cells, the mechanoreceptors of the inner ear. Recordings of hair cell electrical responses have shown that they transduce sound via sub-micrometer deflections of their hair bundles, which are arrays of interconnected stereocilia containing the mechanoelectrical transducer (MET) channels. MET channels are activated by tension in extracellular tip links bridging adjacent stereocilia, and they can respond within microseconds to nanometer displacements of the bundle, facilitated by multiple processes of Ca2+-dependent adaptation. Studies of mouse mutants have produced much detail about the molecular organization of the stereocilia, the tip links and their attachment sites, and the MET channels localized to the lower ends of each tip link. The mammalian cochlea contains two categories of hair cells. Inner hair cells relay acoustic information via multiple ribbon synapses that transmit rapidly without rundown. Outer hair cells are important for amplifying sound-evoked vibrations. The amplification mechanism primarily involves contractions of the outer hair cells, which are driven by changes in membrane potential and mediated by prestin, a motor protein in the outer hair cell lateral membrane. Different sound frequencies are separated along the cochlea, with each hair cell being tuned to a narrow frequency range; amplification sharpens the frequency resolution and augments sensitivity 100-fold around the cell’s characteristic frequency. Genetic mutations and environmental factors such as acoustic overstimulation cause hearing loss through irreversible damage to the hair cells or degeneration of inner hair cell synapses.

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“…Based on its strategic position above the organ of Corti, conventional cochlear models (25-29) have implicated local mechanical properties (i.e., mass, stiffness) of the TM in stimulating the sensory hair bundles of hair cells and in cochlear tuning. Recent dynamic measurements of the TM, in vitro (17,(30)(31)(32)(33) and in vivo (34), suggest that the TM supports longitudinal coupling, with large spatial extents across a broad range of frequencies. This longitudinal coupling manifests in the form of propagating traveling waves that are thought to contribute to hearing mechanisms (17,21,30,(35)(36)(37)(38)(39)(40).…”

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confidence: 99%

Longitudinal spread of mechanical excitation through tectorial membrane traveling waves

Sellon

Farrahi

Ghaffari

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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The mammalian inner ear separates sounds by their frequency content, and this separation underlies important properties of human hearing, including our ability to understand speech in noisy environments. Studies of genetic disorders of hearing have demonstrated a link between frequency selectivity and wave properties of the tectorial membrane (TM). To understand these wave properties better, we developed chemical manipulations that systematically and reversibly alter TM stiffness and viscosity. Using microfabricated shear probes, we show that (i) reducing pH reduces TM stiffness with little change in TM viscosity and (ii) adding PEG increases TM viscosity with little change in TM stiffness. By applying these manipulations in measurements of TM waves, we show that TM wave speed is determined primarily by stiffness at low frequencies and by viscosity at high frequencies. Both TM viscosity and stiffness affect the longitudinal spread of mechanical excitation through the TM over a broad range of frequencies. Increasing TM viscosity or decreasing stiffness reduces longitudinal spread of mechanical excitation, thereby coupling a smaller range of best frequencies and sharpening tuning. In contrast, increasing viscous loss or decreasing stiffness would tend to broaden tuning in resonance-based TM models. Thus, TM wave and resonance mechanisms are fundamentally different in the way they control frequency selectivity.cochlear mechanics | traveling waves | resonance | tectorial membrane | viscoelastic materials T he sharp frequency selectivity of auditory nerve fiber responses to sound is a hallmark of mammalian cochlear function. This remarkable signal processing originates in the mechanical stage of the cochlear signal processing chain (1-7), as evidenced by measured motions and mechanical properties of the basilar membrane (BM) (2-9) and tectorial membrane (TM) (10-24). Although the hydromechanical mechanisms underlying BM motions have been characterized based on experimental and theoretical studies, the mechanisms underlying TM motions remain unclear.The TM is an acellular matrix that overlies the hair bundles of sensory receptor cells. Based on its strategic position above the organ of Corti, conventional cochlear models (25-29) have implicated local mechanical properties (i.e., mass, stiffness) of the TM in stimulating the sensory hair bundles of hair cells and in cochlear tuning. Recent dynamic measurements of the TM, in vitro (17,(30)(31)(32)(33) and in vivo (34), suggest that the TM supports longitudinal coupling, with large spatial extents across a broad range of frequencies. This longitudinal coupling manifests in the form of propagating traveling waves that are thought to contribute to hearing mechanisms (17,21,30,(35)(36)(37)(38)(39)(40). Genetic modification studies provide further support that the spatial extent of TM waves may play a significant role in cochlear tuning (30,32). Although these measurements, models, and genetic modification studies have confirmed the importance of TM mechanical properties in ...

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Modified Protein Expression in the Tectorial Membrane of the Cochlea Reveals Roles for the Striated Sheet Matrix

Cited by 13 publications

References 49 publications

Increased Spontaneous Otoacoustic Emissions in Mice with a Detached Tectorial Membrane

Increased Spontaneous Otoacoustic Emissions in Mice with a Detached Tectorial Membrane

Hair Cell Transduction, Tuning, and Synaptic Transmission in the Mammalian Cochlea

Longitudinal spread of mechanical excitation through tectorial membrane traveling waves

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