Tmc Reliance Is Biased by the Hair Cell Subtype and Position Within the Ear

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.

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Structure and Development of Vestibular Hair Cells in the Larval Bullfrog

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348947908800323 ◽

1979 ◽

Vol 88 (3) ◽

pp. 427-437 ◽

Cited By ~ 23

Author(s):

Cheuk W. Li ◽

Edwin R. Lewis

Keyword(s):

Hair Cell ◽

Hair Cells ◽

High Frequency ◽

Low Frequency ◽

Type A ◽

Cell Types ◽

Sensory Organs ◽

Sensory Epithelia ◽

Sensory Structures ◽

Vestibular Organs

Structure and development of hair cells in vestibular sensory organs of the larval bullfrog were examined with scanning electron microscopy. The larval vestibular sensory epithelia resembled those of the adult frog. Based on morphology of the ciliary tufts, seven hair cell types were identified. One of them, the type A hair cell, appears to be the morphogenetic precursor of other hair cell types. The size of the stereocilia of type A hair cells is comparable to the surrounding microvilli. The distribution of immature type A hair cells suggests that the periphery of the sensory epithelia is the principal growth zone and the site of formation of new hair cells. However, a far greater number of type A hair cells were found in high frequency sensitive sensory organs (sacculus, amphibian and basilar papillae) than low frequency sensitive vestibular sensory structures (canal cristae, utriculus and lagena). This phenomenon may suggest that the time period required for the maturation of type A hair cells to their ultimate hair cell types in the low frequency sensitive vestibular organs is shorter than in the high frequency sensory structures. It is also possible that the low frequency sensitive vestibular organs may have completed their morphogenetic development in the early larval stages, while morphogenesis of hair cells in the high frequency sensory structures continues throughout the lifetime of a bullfrog.

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alms1 mutant zebrafish do not show hair cell phenotypes seen in other cilia mutants

10.1101/2020.11.13.381954 ◽

2020 ◽

Author(s):

Lauren Parkinson ◽

Tamara M. Stawicki

Keyword(s):

Hearing Loss ◽

Hair Cell ◽

Hair Cells ◽

Intraflagellar Transport ◽

Cell Loss ◽

Cell Types ◽

Mutant Mice ◽

Alström Syndrome ◽

Metabolic Defects ◽

Alstrom Syndrome

ABSTRACTMultiple cilia-associated genes have been shown to affect hair cells in zebrafish (Danio rerio), including the human deafness gene dcdc2, the radial spoke gene rsph9, and multiple intraflagellar transport (IFT) and transition zone genes. Recently a zebrafish alms1 mutant was generated. The ALMS1 gene is the gene mutated in the ciliopathy Alström Syndrome a disease that causes hearing loss among other symptoms. The hearing loss seen in Alström Syndrome may be due in part to hair cell defects as Alms1 mutant mice show stereocilia polarity defects and a loss of hair cells. Hair cell loss is also seen in postmortem analysis of Alström patients. The zebrafish alms1 mutant has metabolic defects similar to those seen in Alström syndrome and Alms1 mutant mice. We wished to investigate if it also had hair cell defects. We, however, failed to find any hair cell related phenotypes in alms1 mutant zebrafish. They had normal lateral line hair cell numbers as both larvae and adults and normal kinocilia formation. They also showed grossly normal swimming behavior, response to vibrational stimuli, and FM1-43 loading. Mutants also showed a normal degree of sensitivity to both short-term neomycin and long-term gentamicin treatment. These results indicate that cilia-associated genes differentially affect different hair cell types.

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The development of cooperative channels explains the maturation of hair cell’s mechanotransduction

10.1101/654764 ◽

2019 ◽

Author(s):

Francesco Gianoli ◽

Thomas Risler ◽

Andrei S. Kozlov

Keyword(s):

Ion Channels ◽

Hair Cell ◽

Inner Ear ◽

Hair Cells ◽

Hair Bundle ◽

Mechanical Stimuli ◽

Biophysical Properties ◽

Tip Link ◽

Fast Adaptation ◽

Kinetics Of

ABSTRACTHearing relies on the conversion of mechanical stimuli into electrical signals. In vertebrates, this process of mechano-electrical transduction (MET) is performed by specialized receptors of the inner ear, the hair cells. Each hair cell is crowned by a hair bundle, a cluster of microvilli that pivot in response to sound vibrations, causing the opening and closing of mechanosensitive ion channels. Mechanical forces are projected onto the channels by molecular springs called tip links. Each tip link is thought to connect to a small number of MET channels that gate cooperatively and operate as a single transduction unit. Pushing the hair bundle in the excitatory direction opens the channels, after which they rapidly reclose in a process called fast adaptation. It has been experimentally observed that the hair cell’s biophysical properties mature gradually during postnatal development: the maximal transduction current increases, sensitivity sharpens, transduction occurs at smaller hair-bundle displacements, and adaptation becomes faster. Similar observations have been reported during tip-link regeneration after acoustic damage. Moreover, when measured at intermediate developmental stages, the kinetics of fast adaptation varies in a given cell depending on the magnitude of the imposed displacement. The mechanisms underlying these seemingly disparate observations have so far remained elusive. Here, we show that these phenomena can all be explained by the progressive addition of MET channels of constant properties, which populate the hair bundle first as isolated entities, then progressively as clusters of more sensitive, cooperative MET channels. As the proposed mechanism relies on the difference in biophysical properties between isolated and clustered channels, this work highlights the importance of cooperative interactions between mechanosensitive ion channels for hearing.SIGNIFICANCEHair cells are the sensory receptors of the inner ear that convert mechanical stimuli into electrical signals transmitted to the brain. Sensitivity to mechanical stimuli and the kinetics of mechanotransduction currents change during hair-cell development. The same trend, albeit on a shorter timescale, is also observed during hair-cell recovery from acoustic trauma. Furthermore, the current kinetics in a given hair cell depends on the stimulus magnitude, and the degree of that dependence varies with development. These phenomena have so far remained unexplained. Here, we show that they can all be reproduced using a single unifying mechanism: the progressive formation of channel pairs, in which individual channels interact through the lipid bilayer and gate cooperatively.

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Cnidarian hair cell development illuminates an ancient role for the class IV POU transcription factor in defining mechanoreceptor identity

eLife ◽

10.7554/elife.74336 ◽

2021 ◽

Vol 10 ◽

Author(s):

Ethan Ozment ◽

Arianna N Tamvacakis ◽

Jianhong Zhou ◽

Pablo Yamild Rosiles-Loeza ◽

Esteban Elías Escobar-Hernandez ◽

...

Keyword(s):

Transcription Factor ◽

Hair Cell ◽

Hair Cells ◽

Cell Types ◽

Sister Group ◽

Cell Development ◽

Developmental Genetics ◽

Sea Anemones ◽

Recognition Elements ◽

Class Iv

Although specialized mechanosensory cells are found across animal phylogeny, early evolutionary histories of mechanoreceptor development remain enigmatic. Cnidaria (e.g. sea anemones and jellyfishes) is the sister group to well-studied Bilateria (e.g. flies and vertebrates), and has two mechanosensory cell types - a lineage-specific sensory-effector known as the cnidocyte, and a classical mechanosensory neuron referred to as the hair cell. While developmental genetics of cnidocytes is increasingly understood, genes essential for cnidarian hair cell development are unknown. Here we show that the class IV POU homeodomain transcription factor (POU-IV) - an indispensable regulator of mechanosensory cell differentiation in Bilateria and cnidocyte differentiation in Cnidaria - controls hair cell development in the sea anemone cnidarian Nematostella vectensis. N. vectensis POU-IV is postmitotically expressed in tentacular hair cells, and is necessary for development of the apical mechanosensory apparatus, but not of neurites, in hair cells. Moreover, it binds to deeply conserved DNA recognition elements, and turns on a unique set of effector genes - including the transmembrane-receptor-encoding gene polycystin 1 - specifically in hair cells. Our results suggest that POU-IV directs differentiation of cnidarian hair cells and cnidocytes via distinct gene regulatory mechanisms, and support an evolutionarily ancient role for POU-IV in defining the mature state of mechanosensory neurons.

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Vestibular Type I and Type II Hair Cells. 1: Morphometric Identification in the Pigeon and Gerbil

Journal of Vestibular Research ◽

10.3233/ves-1997-7503 ◽

1997 ◽

Vol 7 (5) ◽

pp. 393-406

Author(s):

Anthony J. Ricci ◽

Katherine J. Rennie ◽

Stephen L. Cochran ◽

Golda A. Kevetter ◽

Manning J. Correia

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Cell Types ◽

Type I ◽

Type Ii ◽

Body Width ◽

Fixed Tissue ◽

Neck Width ◽

I Cells ◽

Plate Width

Classically, type I and type II vestibular hair cells have been defined by their afferent innervation patterns. Little quantitative information exists on the intrinsic morphometric differences between hair cell types. Data presented here define a quantitative method for distinguishing hair cell types based on the morphometric properties of the hair cell’s neck region. The method is based initially on fixed histological sections, where hair cell types were identified by innervation pattern, type I cells having an afferent calyx. Cells were viewed using light microscopy, images were digitized, and measurements were made of the cell body width, the cuticular plate width, and the neck width. A plot of the ratio of the neck width to cuticular plate width (NPR) versus the ratio of the neck width to the body width (NBR) established four quadrants based on the best separation of type I and type II hair cells. The combination of the two variables made the accuracy of predicting either type I or type II hair cells greater than 90%. Statistical cluster analysis confirmed the quadrant separation. Similar analysis was performed on dissociated hair cells from semicircular canal, utricle, and lagena, giving results statistically similar to those of the fixed tissue. Additional comparisons were made between fixed tissue and isolated hair cells as well as across species (pigeon and gerbil) and between end organs (semicircular canal, utricle, and lagena). In each case, the same morphometric boundaries could be used to establish four quadrants, where quadrant 1 was predominantly type I cells and quadrant 3 was almost exclusively type II hair cells. The quadrant separations were confirmed statistically by cluster analysis. These data demonstrate that there are intrinsic morphometric differences between type I and type II hair cells and that these differences can be maintained when the hair cells are dissociated from their respective epithelia.

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Beyond generalized hair cells: Molecular cues for hair cell types

Hearing Research ◽

10.1016/j.heares.2012.11.008 ◽

2013 ◽

Vol 297 ◽

pp. 30-41 ◽

Cited By ~ 33

Author(s):

Israt Jahan ◽

Ning Pan ◽

Jennifer Kersigo ◽

Bernd Fritzsch

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Cell Types

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The effects of Tmc1 Beethoven mutation on mechanotransducer channel function in cochlear hair cells

The Journal of General Physiology ◽

10.1085/jgp.201511458 ◽

2015 ◽

Vol 146 (3) ◽

pp. 233-243 ◽

Cited By ~ 24

Author(s):

Maryline Beurg ◽

Adam C. Goldring ◽

Robert Fettiplace

Keyword(s):

Hair Cell ◽

Hair Cells ◽

Outer Hair Cells ◽

Wild Type ◽

Cochlear Hair Cells ◽

Transmembrane Channel ◽

Adaptive Shift ◽

Electrical Transducer ◽

Protein Isoform ◽

The Relationship

Sound stimuli are converted into electrical signals via gating of mechano-electrical transducer (MT) channels in the hair cell stereociliary bundle. The molecular composition of the MT channel is still not fully established, although transmembrane channel–like protein isoform 1 (TMC1) may be one component. We found that in outer hair cells of Beethoven mice containing a M412K point mutation in TMC1, MT channels had a similar unitary conductance to that of wild-type channels but a reduced selectivity for Ca2+. The Ca2+-dependent adaptation that adjusts the operating range of the channel was also impaired in Beethoven mutants, with reduced shifts in the relationship between MT current and hair bundle displacement for adapting steps or after lowering extracellular Ca2+; these effects may be attributed to the channel’s reduced Ca2+ permeability. Moreover, the density of stereociliary CaATPase pumps for Ca2+ extrusion was decreased in the mutant. The results suggest that a major component of channel adaptation is regulated by changes in intracellular Ca2+. Consistent with this idea, the adaptive shift in the current–displacement relationship when hair bundles were bathed in endolymph-like Ca2+ saline was usually abolished by raising the intracellular Ca2+ concentration.

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The Mechanosensory Transduction Machinery in Inner Ear Hair Cells

Annual Review of Biophysics ◽

10.1146/annurev-biophys-062420-081842 ◽

2020 ◽

Vol 50 (1) ◽

Author(s):

Wang Zheng ◽

Jeffrey R. Holt

Keyword(s):

Hair Cell ◽

Inner Ear ◽

Hair Cells ◽

Annual Review ◽

Publication Date ◽

Fusion Partner ◽

Mechanical Stimuli ◽

Physical Stimulation ◽

Mechanosensory Transduction ◽

Protocadherin 15

Sound-induced mechanical stimuli are detected by elaborate mechanosensory transduction (MT) machinery in highly specialized hair cells of the inner ear. Genetic studies of inherited deafness in the past decades have uncovered several molecular constituents of the MT complex, and intense debate has surrounded the molecular identity of the pore-forming subunits. How the MT components function in concert in response to physical stimulation is not fully understood. In this review, we summarize and discuss multiple lines of evidence supporting the hypothesis that transmembrane channel-like 1 is a long-sought MT channel subunit. We also review specific roles of other components of the MT complex, including protocadherin 15, cadherin 23, lipoma HMGIC fusion partner-like 5, transmembrane inner ear, calcium and integrin-binding family member 2, and ankyrins. Based on these recent advances, we propose a unifying theory of hair cell MT that may reconcile most of the functional discoveries obtained to date. Finally, we discuss key questions that need to be addressed for a comprehensive understanding of hair cell MT at molecular and atomic levels. Expected final online publication date for the Annual Review of Biophysics, Volume 50 is May 6, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

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Putative pore-forming subunits of the mechano-electrical transduction channel, Tmc1/2b, require Tmie to localize to the site of mechanotransduction in zebrafish sensory hair cells

10.1101/393330 ◽

2018 ◽

Cited By ~ 1

Author(s):

Itallia V. Pacentine ◽

Teresa Nicolson

Keyword(s):

Hair Cell ◽

Inner Ear ◽

Hair Cells ◽

Transmembrane Domain ◽

Cell Activity ◽

Sensory Hair ◽

Transmembrane Channel ◽

Extracellular Region ◽

Normal Site ◽

Sensory Hair Cells

AbstractMutations in transmembrane inner ear (TMIE) cause deafness in humans; previous studies suggest involvement in the mechano-electrical transduction (MET) complex in sensory hair cells, but TMIE’s precise role is unclear. In tmie zebrafish mutants, we observed that GFP-tagged Tmc1 and Tmc2b, which are putative subunits of the MET channel, fail to target to the hair bundle. In contrast, overexpression of Tmie strongly enhances the targeting of Tmc2b-GFP to stereocilia. To identify the motifs of Tmie underlying the regulation of the Tmcs, we systematically deleted or replaced peptide segments. We then assessed localization and functional rescue of each mutated/chimeric form of Tmie in tmie mutants. We determined that the first putative helix was dispensable and identified a novel critical region of Tmie, the extracellular region and transmembrane domain, which mediates both mechanosensitivity and Tmc2b-GFP expression in bundles. Collectively, our results suggest that Tmie’s role in sensory hair cells is to target and stabilize Tmc subunits to the site of MET.Author summaryHair cells mediate hearing and balance through the activity of a pore-forming channel in the cell membrane. The transmembrane inner ear (TMIE) protein is an essential component of the protein complex that gates this so-called mechanotransduction channel. While it is known that loss of TMIE results in deafness, the function of TMIE within the complex is unclear. Using zebrafish as a deafness model, Pacentine and Nicolson demonstrate that Tmie is required for the localization of other essential complex members, the transmembrane channel-like (Tmc) proteins, Tmc1/2b. They then evaluate twelve unique versions of Tmie, each containing mutations to different domains of Tmie. This analysis reveals that some mutations in Tmie cause dysfunctional gating of the channel as demonstrated through reduced hair cell activity, and that these same dysfunctional versions also display reduced Tmc expression at the normal site of the channel. These findings link hair cell activity with the levels of Tmc in the bundle, reinforcing the currently-debated notion that the Tmcs are the pore-forming subunits of the mechanotransduction channel. The authors conclude that Tmie, through distinct regions, is involved in both trafficking and stabilizing the Tmcs at the site of mechanotransduction.

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Cnidarian hair cell development illuminates an ancient role for the class IV POU transcription factor in defining mechanoreceptor identity

10.1101/2021.10.12.464036 ◽

2021 ◽

Author(s):

Ethan Ozment ◽

Arianna N. Tamvacakis ◽

Jianhong Zhou ◽

Pablo Yamild Rosiles-Loeza ◽

Esteban Elías Escobar-Hernandez ◽

...

Keyword(s):

Transcription Factor ◽

Hair Cell ◽

Hair Cells ◽

Cell Types ◽

Sister Group ◽

Cell Development ◽

Developmental Genetics ◽

Sea Anemones ◽

Recognition Elements ◽

Class Iv

Although specialized mechanosensory cells are found across animal phylogeny, early evolutionary histories of mechanoreceptor development remain enigmatic. Cnidaria (e.g. sea anemones and jellyfishes) is the sister group to well-studied Bilateria (e.g. flies and vertebrates), and has two mechanosensory cell types – a lineage-specific sensory-effector known as the cnidocyte, and a classical mechanosensory neuron referred to as the hair cell. While developmental genetics of cnidocytes is increasingly understood, genes essential for hair cell development are unknown. Here we show that the class IV POU homeodomain transcription factor (POU-IV) – an indispensable regulator of mechanosensory cell differentiation in Bilateria and cnidocyte differentiation in Cnidaria – controls hair cell development in the sea anemone cnidarian Nematostella vectensis. N. vectensis POU-IV is postmitotically expressed in tentacular hair cells, and is necessary for development of the apical mechanosensory apparatus, but not of neurites, in hair cells. Moreover, it binds to deeply conserved DNA recognition elements, and turns on a unique set of effector genes – including the transmembrane-receptor-encoding gene polycystin 1 – specifically in hair cells. Our results suggest that POU-IV directs differentiation of cnidarian hair cells and cnidocytes via distinct gene regulatory mechanisms, and support an evolutionarily ancient role for POU-IV in defining the mature state of mechanosensory neurons.

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