My oh my(osin): Insights into how auditory hair cells count, measure, and shape

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.

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Sensory Transduction and Adaptation in Inner and Outer Hair Cells of the Mouse Auditory System

Journal of Neurophysiology ◽

10.1152/jn.00914.2007 ◽

2007 ◽

Vol 98 (6) ◽

pp. 3360-3369 ◽

Cited By ~ 40

Author(s):

Eric A. Stauffer ◽

Jeffrey R. Holt

Keyword(s):

Hair Cells ◽

Slow Component ◽

Outer Hair Cells ◽

Fast Component ◽

Sensory Transduction ◽

Hair Bundle ◽

Sensory Cells ◽

Auditory Hair Cells ◽

Inner Hair Cells ◽

The Difference

Auditory function in the mammalian inner ear is optimized by collaboration of two classes of sensory cells known as inner and outer hair cells. Outer hair cells amplify and tune sound stimuli that are transduced and transmitted by inner hair cells. Although they subserve distinct functions, they share a number of common properties. Here we compare the properties of mechanotransduction and adaptation recorded from inner and outer hair cells of the postnatal mouse cochlea. Rapid outer hair bundle deflections of about 0.5 micron evoked average maximal transduction currents of about 325 pA, whereas inner hair bundle deflections of about 0.9 micron were required to evoke average maximal currents of about 310 pA. The similar amplitude was surprising given the difference in the number of stereocilia, 81 for outer hair cells and 48 for inner hair cells, but may be reconciled by the difference in single-channel conductance. Step deflections of inner and outer hair bundles evoked adaptation that had two components: a fast component that consisted of about 60% of the response occurred over the first few milliseconds and a slow component that consisted of about 40% of the response followed over the subsequent 20–50 ms. The rate of the slow component in both inner and outer hair cells was similar to the rate of slow adaptation in vestibular hair cells. The rate of the fast component was similar to that of auditory hair cells in other organisms and several properties were consistent with a model that proposes calcium-dependent release of tension allows transduction channel closure.

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Class III myosins shape the auditory hair bundles by limiting microvilli and stereocilia growth

The Journal of Cell Biology ◽

10.1083/jcb.201509017 ◽

2016 ◽

Vol 212 (2) ◽

pp. 231-244 ◽

Cited By ~ 29

Author(s):

Andrea Lelli ◽

Vincent Michel ◽

Jacques Boutet de Monvel ◽

Matteo Cortese ◽

Montserrat Bosch-Grau ◽

...

Keyword(s):

Hair Cells ◽

Late Onset ◽

Critical Role ◽

Normal Hearing ◽

Hair Bundle ◽

Class Iii ◽

Auditory Hair Cells ◽

Mechanoelectrical Transduction ◽

Hair Bundles ◽

Myosin Iiia

The precise architecture of hair bundles, the arrays of mechanosensitive microvilli-like stereocilia crowning the auditory hair cells, is essential to hearing. Myosin IIIa, defective in the late-onset deafness form DFNB30, has been proposed to transport espin-1 to the tips of stereocilia, thereby promoting their elongation. We show that Myo3a−/−Myo3b−/− mice lacking myosin IIIa and myosin IIIb are profoundly deaf, whereas Myo3a-cKO Myo3b−/− mice lacking myosin IIIb and losing myosin IIIa postnatally have normal hearing. Myo3a−/−Myo3b−/− cochlear hair bundles display robust mechanoelectrical transduction currents with normal kinetics but show severe embryonic abnormalities whose features rapidly change. These include abnormally tall and numerous microvilli or stereocilia, ungraded stereocilia bundles, and bundle rounding and closure. Surprisingly, espin-1 is properly targeted to Myo3a−/−Myo3b−/− stereocilia tips. Our results uncover the critical role that class III myosins play redundantly in hair-bundle morphogenesis; they unexpectedly limit the elongation of stereocilia and of subsequently regressing microvilli, thus contributing to the early hair bundle shaping.

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Auditory Hair Cells and Sensory Transduction

Oxford Research Encyclopedia of Neuroscience ◽

10.1093/acrefore/9780190264086.013.85 ◽

2017 ◽

Author(s):

Jeffrey R. Holt ◽

Gwenaëlle S.G. Géléoc

Keyword(s):

Hair Cells ◽

Water Movement ◽

Semicircular Canals ◽

Linear Acceleration ◽

Sensory Transduction ◽

Hair Bundle ◽

Apical Surface ◽

Mechanical Stimuli ◽

Auditory Hair Cells ◽

Aquatic Vertebrates

The organs of the vertebrate inner ear respond to a variety of mechanical stimuli: semicircular canals are sensitive to angular velocity, the saccule and utricle respond to linear acceleration (including gravity), and the cochlea is sensitive to airborne vibration, or sound. The ontogenically related lateral line organs, spaced along the sides of aquatic vertebrates, sense water movement. All these organs have a common receptor cell type, which is called the hair cell, for the bundle of enlarged microvilli protruding from its apical surface. In different organs, specialized accessory structures serve to collect, filter, and then deliver these physical stimuli to the hair bundles. The proximal stimulus for all hair cells is deflection of the mechanosensitive hair bundle. Hair cells convert mechanical information contained within the temporal pattern of hair bundle deflections into electrical signals, which they transmit to the brain for interpretation.

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Cytoskeletal functions in sensory receptors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155955 ◽

1989 ◽

Vol 47 ◽

pp. 796-797

Author(s):

Beth Burnside

Keyword(s):

Hair Cells ◽

Outer Segment ◽

Olfactory Receptors ◽

Sensory Cells ◽

Basal Bodies ◽

Sensory Receptors ◽

Structural Requirements ◽

Auditory Hair Cells ◽

Receptor Proteins ◽

Taste Cells

Since the shapes of sensory receptors are so exquisitely specialized for mediating their unique functions, the cytoskeletons of sensory cells are deployed for morphogenetic and motile objectives in particularly interesting ways. Receptors erect cytoskeletal scaffolding to support two basic sorts of surface elaborations: 1) those designed to achieve the most effective presentation of specialized membrane laden with receptor proteins (photoreceptors, olfactory receptors, taste cells, and chemoreceptors), and 2) those designed to respond directly to mechanical perturbations in the cell's environment (auditory hair cells, mechanoreceptors). Each of these receptor types has specific structural requirements.Sensory receptors have built their surface elaborations upon either microtubule- or actin-based scaffoldings. Microtubule-based scaffoldings have evolved from motile cilia, and the axoneme has been modified to various ends. All ciliary-derived receptors so far described, except (curiously) those from the worm Caenorhabdites elegans, are associated with basal bodies which nucleate the assembly of surface specializations. The mechanisms for elaborating the myriad membrane specializations associated with ciliary receptors are not yet understood. Recently it has been shown that in vertebrate photoreceptors, actin is not required for the addition of membrane to the outer segment, but it is required for the proper assembly of new disks .

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