scholarly journals Actin filaments, stereocilia, and hair cells of the bird cochlea. V. How the staircase pattern of stereociliary lengths is generated

1988 ◽  
Vol 106 (2) ◽  
pp. 355-365 ◽  
Author(s):  
LG Tilney ◽  
MS Tilney ◽  
DA Cotanche
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Actin Filaments ◽  
Developmental Time ◽  
Final Phase ◽  
Set Up

The stereocilia on each hair cell are arranged into rows of ascending height, resulting in what we refer to as a "staircase-like" profile. At the proximal end of the cochlea the length of the tallest row of stereocilia in the staircase is 1.5 micron, with the shortest row only 0.3 micron. As one proceeds towards the distal end of the cochlea the length of the stereocilia progressively increases so that at the extreme distal end the length of the tallest row of the staircase is 5.5 micron and the shortest row is 2 micron. During development hair cells form their staircases in four phases of growth separated from each other by developmental time. First, stereocilia sprout from the apical surfaces of the hair cells (8-10-d embryos). Second (10-12-d embryos), what will be the longest row of the staircase begins to elongate. As the embryo gets older successive rows of stereocilia initiate elongation. Thus the staircase is set up by the sequential initiation of elongation of stereociliary rows located at increased distances from the row that began elongation. Third (12-17-d embryos), all the stereocilia in the newly formed staircase elongate until those located on the first step of the staircase have reached the prescribed length. In the final phase (17-d embryos to hatchlings) there is a progressive cessation of elongation beginning with the shortest step and followed by taller and taller rows with the tallest step stopping last. Thus, to obtain a pattern of stereocilia in rows of increasing height what transpires are progressive go signals followed by a period when all the stereocilia grow and ending with progressive stop signals. We discuss how such a sequence could be controlled.

scholarly journals Actin filaments, stereocilia, and hair cells of the bird cochlea. I. Length, number, width, and distribution of stereocilia of each hair cell are related to the position of the hair cell on the cochlea.

1983 ◽  
Vol 96 (3) ◽  
pp. 807-821 ◽  
Author(s):  
L G Tilney ◽  
J C Saunders
Keyword(s):  
Hair Cell ◽  
Surface Area ◽  
Hair Cells ◽  
Actin Filaments ◽  
Hexagonal Lattice ◽  
Frequency Discrimination ◽  
Sensory Epithelium ◽  
Scanning Microscopy ◽  
Apical Surface ◽  
Length Width

Located on the sensory epithelium of the sickle-shaped cochlea of a 7- to 10-d-old chick are approximately 5,000 hair cells. When the apical surface of these cell is examined by scanning microscopy, we find that the length, number, width, and distribution of the stereocilia on each hair cell are predetermined. Thus, a hair cell located at the distal end of the cochlea has 50 stereocilia, the longest of which are 5.5 microns in length and 0.12 microns in width, while those at the proximal end number 300 and are maximally 1.5 microns in length and 0.2 micron in width. In fact, if we travel along the cochlea from its distal to proximal end, we see that the stereocilia on successive hair cells gradually increase in number and width, yet decrease in length. Also, if we look transversely across the cochlea where adjacent hair cells have the same length and number of stereocilia (they are the same distance from the distal end of the cochlea), we find that the stereocilia of successive hair cells become thinner and that the apical surface area of the hair cell proper, not including the stereocilia, decreases from a maximum of 80 microns2 to 15 microns2. Thus, if we are told the length of the longest stereocilium on a hair cell and the width of that stereocilium, we can pinpoint the position of that hair cell on the cochlea in two axes. Likewise, if we are told the number of stereocilia and the apical surface of a hair cell, we can pinpoint the location of that cell in two axes. The distribution of the stereocilia on the apical surface of the cell is also precisely determined. More specifically, the stereocilia are hexagonally packed and this hexagonal lattice is precisely positioned relative to the kinocilium. Because of the precision with which individual hair cells regulate the length, width, number, and distribution of their cell extensions, we have a magnificent object with which to ask questions about how actin filaments that are present within the cell are regulated. Equally interesting is that the gradient in stereociliary length, number, width, and distribution may play an important role in frequency discrimination in the cochlea. This conclusion is amplified by the information presented in the accompanying paper (Tilney, L.G., E.H. Egelman, D.J. DeRosier, and J.C. Saunders, 1983, J. Cell Biol., 96:822-834) on the packing of actin filaments in this stereocilia.

scholarly journals The actin filament content of hair cells of the bird cochlea is nearly constant even though the length, width, and number of stereocilia vary depending on the hair cell location.

1988 ◽  
Vol 107 (6) ◽  
pp. 2563-2574 ◽  
Author(s):  
L G Tilney ◽  
M S Tilney
Keyword(s):  
Hair Cell ◽  
Actin Filament ◽  
Cross Sections ◽  
Hair Cells ◽  
Actin Filaments ◽  
Membrane Surface ◽  
Scanning Electron Micrographs ◽  
Length Width ◽  
Filament Content ◽  
Filament Bundle

By direct counts off scanning electron micrographs, we determined the number of stereocilia per hair cell of the chicken cochlea as a function of the position of the hair cell on the cochlea. Micrographs of thin cross sections of stereociliary bundles located at known positions on the cochlea were enlarged and the total number of actin filaments per stereocilium was counted and recorded. By comparing the counts of filament number with measurements of actin filament bundle width of the same stereocilium, we were able to relate actin filament bundle width to filament number with an error margin (r2) of 16%. Combining this data with data already published or in the process of publication from our laboratory on the length and width of stereocilia, we were able to calculate the total length of actin filaments present in stereociliary bundles of hair cells located at a variety of positions on the cochlea. We found that stereociliary bundles of hair cells contain 80,000-98,000 micron of actin filament, i.e., the concentration of actin is constant in all hair cells with a range of values that is less than our error in measurement and/or biological variation, the greatest variation being in relating the diameters of the stereocilia to filament number. We also calculated the membrane surface needed to cover the stereocilia of hair cells located throughout the cochlea. The values (172-192 micron 2) are also constant. The implications of our observation that the total amount of actin is constant even though the length, width, and number of stereocilia per hair cell vary are discussed.

scholarly journals The stable actin core of mechanosensory stereocilia features continuous turnover of actin cross-linkers

2018 ◽  
Vol 29 (15) ◽  
pp. 1856-1865 ◽  
Author(s):  
Pallabi Roy ◽  
Benjamin J. Perrin
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Head Movement ◽  
Actin Filaments ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Cross Linking ◽  
Sensory Hair Cells ◽  
Actin Turnover ◽  
Cross Linker

Stereocilia are mechanosensitive protrusions on the surfaces of sensory hair cells in the inner ear that detect sound, gravity, and head movement. Their cores are composed of parallel actin filaments that are cross-linked and stabilized by several actin-binding proteins, including fascin-2, plastin-1, espin, and XIRP2. The actin filaments are the most stable known, with actin turnover primarily occurring at the stereocilia tips. While stereocilia actin dynamics has been well studied, little is known about the behavior of the actin cross-linking proteins, which are the most abundant type of protein in stereocilia after actin and are critical for stereocilia morphogenesis and maintenance. Here, we developed a novel transgenic mouse to monitor EGFP-fascin-2 incorporation . In contrast to actin, EGFP-fascin-2 readily enters the stereocilia core. We also compared the effect of EGFP-fascin-2 expression on developing and mature stereocilia. When it was induced during hair cell development, we observed increases in both stereocilia length and width. Interestingly, stereocilia size was not affected when EGFP-fascin-2 was induced in adult stereocilia. Regardless of the time of induction, EGFP-fascin-2 displaced both espin and plastin-1 from stereocilia. Altering the actin cross-linker composition, even as the actin filaments exhibit little to no turnover, provides a mechanism for ongoing remodeling and repair important for stereocilia homeostasis.

scholarly journals Heterodimeric capping protein is required for stereocilia length and width regulation

2017 ◽  
Vol 216 (11) ◽  
pp. 3861-3881 ◽  
Author(s):  
Matthew R. Avenarius ◽  
Jocelyn F. Krey ◽  
Rachel A. Dumont ◽  
Clive P. Morgan ◽  
Connor B. Benson ◽  
...  
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Actin Filaments ◽  
Actin Polymerization ◽  
Vestibular Function ◽  
In Utero ◽  
In Utero Electroporation ◽  
Interacting Protein ◽  
Capping Protein ◽  
Dimension Control

Control of the dimensions of actin-rich processes like filopodia, lamellipodia, microvilli, and stereocilia requires the coordinated activity of many proteins. Each of these actin structures relies on heterodimeric capping protein (CAPZ), which blocks actin polymerization at barbed ends. Because dimension control of the inner ear’s stereocilia is particularly precise, we studied the CAPZB subunit in hair cells. CAPZB, present at ∼100 copies per stereocilium, concentrated at stereocilia tips as hair cell development progressed, similar to the CAPZB-interacting protein TWF2. We deleted Capzb specifically in hair cells using Atoh1-Cre, which eliminated auditory and vestibular function. Capzb-null stereocilia initially developed normally but later shortened and disappeared; surprisingly, stereocilia width decreased concomitantly with length. CAPZB2 expressed by in utero electroporation prevented normal elongation of vestibular stereocilia and irregularly widened them. Together, these results suggest that capping protein participates in stereocilia widening by preventing newly elongating actin filaments from depolymerizing.

The Organization of Actin Filaments in the Stereocilia of the Bird Cochlea

1980 ◽  
Vol 38 ◽  
pp. 554-555
Author(s):  
E.J. Battles ◽  
D. DeRosier ◽  
J.C. Saunders ◽  
L.G. Tilney
Keyword(s):  
Hair Cell ◽  
Diffraction Pattern ◽  
Sea Urchin ◽  
Actin Filaments ◽  
Optical Diffraction ◽  
Dense Material ◽  
Apical Surface ◽  
Structural Rigidity ◽  
High Degree ◽  
Degree Of Order

Extending from the apical surface of each hair cell of the chick cochlea are from 75 to 200 microvilli or stereocllia and one true cllium, the kinocilium. The stereocllia are arranged in rows of progressively increasing length (Fig. 1). Within each tapering sterocilium is a bundle of actin filaments with over 900 filaments near the tip yet only approximately 25 at the base where filaments are enmeshed in a dense material (Fig. 1); from here some of the filaments enter the apical surface of the cell (cuticular plate) as a rootlet. Examination of longitudinal sections of the stereocilia (Fig. 2) show that the filaments are aligned parallel to each other and show considerable order. Examination of an optical diffraction pattern of this bundle (Fig. 4) reveal that the actin filaments are packed such that the crossover points of adjacent actin filaments are inregister. A prominent reflection at 125Å−1 demonstrates that the filaments are cjossbridged by a macromolecular bridge situated at an average of 125Å−1 intervals (Fig. 4) in transverse sections the filaments appear hexagonally packed although there are regions where the filaments are less ordered (Fig. 3). In images processed in the computer to remove, noise and enhance detail periodic nature of the bridge can be clearly seen (see arrows Fig. 5). This image resembles that of an actin paracrystal formed from sea urchin extract composed of bundles of actin filaments crossbridged by a second protein. Thus the actin filaments in the bird stereocilia by being cross-bridged and packed with a high degree of order and produces a structure with considerable structural rigidity. Embryos were studied at various stages in development in an attempt to determine how the stereocilia form and how does the actin packing develops. These stages will be discussed.

scholarly journals Neuroplastin expression is essential for hearing and hair cell PMCA expression

2021 ◽  
Author(s):  
Xiao Lin ◽  
Michael G. K. Brunk ◽  
Pingan Yuanxiang ◽  
Andrew W. Curran ◽  
Enqi Zhang ◽  
...  
Keyword(s):  
Hair Cell ◽  
White Noise ◽  
Hair Cells ◽  
Normal Development ◽  
Single Photon ◽  
Photon Emission ◽  
Auditory Brainstem ◽  
Outer Hair Cells ◽  
Emission Computed Tomography ◽  
Cell Degeneration

AbstractHearing deficits impact on the communication with the external world and severely compromise perception of the surrounding. Deafness can be caused by particular mutations in the neuroplastin (Nptn) gene, which encodes a transmembrane recognition molecule of the immunoglobulin (Ig) superfamily and plasma membrane Calcium ATPase (PMCA) accessory subunit. This study investigates whether the complete absence of neuroplastin or the loss of neuroplastin in the adult after normal development lead to hearing impairment in mice analyzed by behavioral, electrophysiological, and in vivo imaging measurements. Auditory brainstem recordings from adult neuroplastin-deficient mice (Nptn−/−) show that these mice are deaf. With age, hair cells and spiral ganglion cells degenerate in Nptn−/− mice. Adult Nptn−/− mice fail to behaviorally respond to white noise and show reduced baseline blood flow in the auditory cortex (AC) as revealed by single-photon emission computed tomography (SPECT). In adult Nptn−/− mice, tone-evoked cortical activity was not detectable within the primary auditory field (A1) of the AC, although we observed non-persistent tone-like evoked activities in electrophysiological recordings of some young Nptn−/− mice. Conditional ablation of neuroplastin in Nptnlox/loxEmx1Cre mice reveals that behavioral responses to simple tones or white noise do not require neuroplastin expression by central glutamatergic neurons. Loss of neuroplastin from hair cells in adult NptnΔlox/loxPrCreERT mice after normal development is correlated with increased hearing thresholds and only high prepulse intensities result in effective prepulse inhibition (PPI) of the startle response. Furthermore, we show that neuroplastin is required for the expression of PMCA 2 in outer hair cells. This suggests that altered Ca2+ homeostasis underlies the observed hearing impairments and leads to hair cell degeneration. Our results underline the importance of neuroplastin for the development and the maintenance of the auditory system.

scholarly journals Inner hair cell stereocilia are embedded in the tectorial membrane

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Pierre Hakizimana ◽  
Anders Fridberger
Keyword(s):  
Electron Microscopy ◽  
Hair Cell ◽  
Mechanical Stimulation ◽  
Hair Cells ◽  
Viscous Drag ◽  
Tectorial Membrane ◽  
Inner Hair Cell ◽  
Inner Hair Cells ◽  
Inward Currents

AbstractMammalian hearing depends on sound-evoked displacements of the stereocilia of inner hair cells (IHCs), which cause the endogenous mechanoelectrical transducer channels to conduct inward currents of cations including Ca2+. Due to their presumed lack of contacts with the overlaying tectorial membrane (TM), the putative stimulation mechanism for these stereocilia is by means of the viscous drag of the surrounding endolymph. However, despite numerous efforts to characterize the TM by electron microscopy and other techniques, the exact IHC stereocilia-TM relationship remains elusive. Here we show that Ca2+-rich filamentous structures, that we call Ca2+ ducts, connect the TM to the IHC stereocilia to enable mechanical stimulation by the TM while also ensuring the stereocilia access to TM Ca2+. Our results call for a reassessment of the stimulation mechanism for the IHC stereocilia and the TM role in hearing.

scholarly journals Preliminary biochemical characterization of the stereocilia and cuticular plate of hair cells of the chick cochlea.

1989 ◽  
Vol 109 (4) ◽  
pp. 1711-1723 ◽  
Author(s):  
M S Tilney ◽  
L G Tilney ◽  
R E Stephens ◽  
C Merte ◽  
D Drenckhahn ◽  
...  
Keyword(s):  
Hair Cells ◽  
Actin Filaments ◽  
Biochemical Characterization ◽  
Cell Types ◽  
Sensory Epithelium ◽  
Tectorial Membrane ◽  
Uncharacterized Protein ◽  
Proteolytic Fragment ◽  
Cuticular Plate ◽  
Filament Bundles

The sensory epithelium of the chick cochlea contains only two cell types, hair cells and supporting cells. We developed methods to rapidly dissect out the sensory epithelium and to prepare a detergent-extracted cytoskeleton. High salt treatment of the cytoskeleton leaves a "hair border", containing actin filament bundles of the stereocilia still attached to the cuticular plate. On SDS-PAGE stained with silver the intact epithelium is seen to contain a large number of bands, the most prominent of which are calbindin and actin. Detergent extraction solubilizes most of the proteins including calbindin. On immunoblots antibodies prepared against fimbrin from chicken intestinal epithelial cells cross react with the 57- and 65-kD bands present in the sensory epithelium and the cytoskeleton. It is probable that the 57-kD is a proteolytic fragment of the 65-kD protein. Preparations of stereocilia attached to the overlying tectorial membrane contain the 57- and 65-kD bands. A 400-kD band is present in the cuticular plate. By immunofluorescence, fimbrin is detected in stereocilia but not in the hair borders after salt extraction. The prominent 125 A transverse stripping pattern characteristic of the actin cross-bridges in a bundle is also absent in hair borders suggesting fimbrin as the component that gives rise to the transverse stripes. Because the actin filaments in the stereocilia of hair borders still remain as compact bundles, albeit very disordered, there must be an additional uncharacterized protein besides fimbrin that cross-links the actin filaments together.

scholarly journals Responses of hair cells to statocyst rotation.

1975 ◽  
Vol 66 (4) ◽  
pp. 507-530 ◽  
Author(s):  
D L Alkon
Keyword(s):  
Hair Cell ◽  
Centrifugal Force ◽  
Hair Cells ◽  
New Technique ◽  
Force Vector ◽  
Generator Potential ◽  
Recording Apparatus ◽  
Intracellular Potentials ◽  
A New Technique

A new technique is described for stimulating hair cells of the Hermissenda statocyst. The preparation and recording apparatus can be rotated at up to 78 rpm while recording intracellular potentials. Hair cells in front of the centrifugal force vector depolarize in response to rotation. Hair cells in back of the centrifugal force vector hypoerpolarize in response to rotation. Mechanisms by which the hair cell generator potential might arise are examined.

Hes1 is a negative regulator of inner ear hair cell differentiation

Development ◽  
2000 ◽  
Vol 127 (21) ◽  
pp. 4551-4560 ◽  
Author(s):  
J.L. Zheng ◽  
J. Shou ◽  
F. Guillemot ◽  
R. Kageyama ◽  
W.Q. Gao
Keyword(s):  
Cell Differentiation ◽  
Hair Cell ◽  
Inner Ear ◽  
Cell Fate ◽  
Hair Cells ◽  
Outer Hair Cells ◽  
Negative Regulator ◽  
Pcr Analysis ◽  
Loss Of Function ◽  
Hair Cell Differentiation

Hair cell fate determination in the inner ear has been shown to be controlled by specific genes. Recent loss-of-function and gain-of-function experiments have demonstrated that Math1, a mouse homolog of the Drosophila gene atonal, is essential for the production of hair cells. To identify genes that may interact with Math1 and inhibit hair cell differentiation, we have focused on Hes1, a mammalian hairy and enhancer of split homolog, which is a negative regulator of neurogenesis. We report here that targeted deletion of Hes1 leads to formation of supernumerary hair cells in the cochlea and utricle of the inner ear. RT-PCR analysis shows that Hes1 is expressed in inner ear during hair cell differentiation and its expression is maintained in adulthood. In situ hybridization with late embryonic inner ear tissue reveals that Hes1 is expressed in supporting cells, but not hair cells, of the vestibular sensory epithelium. In the cochlea, Hes1 is selectively expressed in the greater epithelial ridge and lesser epithelial ridge regions which are adjacent to inner and outer hair cells. Co-transfection experiments in postnatal rat explant cultures show that overexpression of Hes1 prevents hair cell differentiation induced by Math1. Therefore Hes1 can negatively regulate hair cell differentiation by antagonizing Math1. These results suggest that a balance between Math1 and negative regulators such as Hes1 is crucial for the production of an appropriate number of inner ear hair cells.

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