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Special Senses
Published in Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard, Toxicologic Pathology, 2018
Kenneth A. Schafer, Oliver C. Turner, Richard A. Altschuler
Scar formation in the cochlea is a response of the supporting cells to the loss of traumatized sensory hair cells (Bohne 1976; Raphael and Altschuler 1991, 1992). Supporting cells swell and fill in the spaces of Nuel, so that they are now touching the lateral wall of the outer hair cell. Loss of the spaces of Nuel is the earliest sign of scar formation (type 1 scar). The upper portions of the neighboring supporting cells then push into the upper area where the outer hair cells reside below the cuticular plate and then envelop it. The apices of the supporting cells form junctional complexes and maintain the barrier between the endolymph of the scala media and the perilymph of the scala tympani, thus maintaining the endocochlear potential and cochlear function. When the type 1 scar is viewed from above with a fluorescent filamentous actin label (phalloidin), the convergence of the supporting cells in the space formerly occupied by the outer hair cell forms a characteristic actin-labeled bridge. This aids in identification of hair cell loss when doing quantitative assessments for a cytocochleogram. The type 1 scar will remain in this phase when there is only moderate outer hair cell loss, but it progresses to other phases when many hair cells are lost in the same region, and particularly if inner hair cells are also lost.
Anatomy
Published in Stanley A. Gelfand, Hearing, 2017
The inner and outer hair cells were shown in relation to the cross-section of the organ of Corti in Figure 2.17. A closer look at these cells is provided in Figure 2.23. The hair cells are so-named because of the presence of cilia on their upper surfaces. Notice in Figure 2.23 that the upper surface of each hair cell contains a thickening called the cuticular plate which is topped by three rows of stereocilia, as well as a noncuticular area that contains the basal body of a rudimentary kinocilium.
Anatomy of the Cochlea and Vestibular System: Relating Ultrastructure to Function
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
The parallel actin filaments in the stereocilia (Figure 47.5e,f) are closely packed and are cross-linked by a number of different proteins such as espin, fimbrin, fascin and plastin 1, the last being the second most abundant protein in stereocilia after actin.2,8–13 The high density of actin filaments and the extensive cross-linking between them imposes rigidity on the shaft of the stereocilium, which tapers significantly at its proximal end (Figure 47.5a,g) where it is embedded into the cuticular plate (Figure 47.5a,c,d), a rigid platform formed of a meshwork of actin filaments and other proteins in the apical cytoplasm of the hair cell (Figure 47.5a,c,d).14–17 As a result, when pushed at its tip, the stereocilium pivots at the taper like a stiff rod. The fundamental nature of this stereociliary rigidity for all hair cells is evidenced by the hearing impairment and vestibular disorders that result from mutations in genes that encode for such actin-cross-linker proteins. Mice with such mutations are often recognized by erratic and/or circling behaviours, for example the ‘jerker’ mouse strain, which has a mutation in the gene for the cross-linking protein espin, and in which stereocilia are thinner than normal.10–13 Loss of plastin 1 results in progressive hearing loss and balance dysfunction and progressive thinning of stereocilia.9,12 Actin filaments descend from the stereocilium into the cuticular plate as a rootlet, which is cross-linked into the actin meshwork (Figure 47.5h).15 The rootlet is formed of densely packed actin filaments (Figure 47.5e). The actin bundling protein TRIOBP plays a key role in the formation and maintenance of the rootlet.18 In addition to actin, the cuticular plate contains spectrin,19 another actin cross-linking protein that has elastic, deformation-resisting properties, and tropomyosin,16,17 a protein that binds around actin and stiffens it. Around its lateral margin, the cuticular plate is linked to the lateral plasma membrane at the level of the intercellular junction15,16 with which, on the supporting cell side, actin and other cytoskeletal proteins are also associated (Figures 47.6b,c,d and 47.7e,h). This may provide a means of support for the cuticular plate so that the stereocilia themselves are supported on a rigid platform, enhancing their ability to respond to small displacement forces.
The applications of targeted delivery for gene therapies in hearing loss
Published in Journal of Drug Targeting, 2023
Melissa Jones, Bozica Kovacevic, Corina Mihaela Ionescu, Susbin Raj Wagle, Christina Quintas, Elaine Y. M. Wong, Momir Mikov, Armin Mooranian, Hani Al-Salami
Myosin motor protein, Myo6 has been suggested as a therapeutic target, with mutations in Myo6 linked to a range of pathologies [87]. Myo6 is reported as unique to the inner and outer hair cells in the organ of Corti, mainly located at their cuticular plate [80]. However, transcriptomic analysis by Liu et al. determined that transcripts of many proteins thought to be specific to hair cells were also found in supporting cells. Transcript analysis showed that supporting Deiters cells were also detected to express Myo6 at comparable levels to both outer and inner hair cells. Alternative myosin proteins which are also believed to be unique for hair cells, Myo7a and Myo15 were also found by this transcriptome study to have expression in supporting cells, with Myo7a in both Deiters cells and pillar cells, and Myo15 in pillar cells [86].
Human cochlear microanatomy – an electron microscopy and super-resolution structured illumination study and review
Published in Hearing, Balance and Communication, 2020
Wei Liu, Rudolf Glueckert, Annelies Schrott-Fischer, Helge Rask-Andersen
Contractile mechanisms along microtubule bundles seem to be of importance for active vibratory responses during hearing, in animals as well as in humans. Inner and OHCs stereocilia and cuticular plates contain contractile elements such as actin together with an intricate cross-linking molecular machinery whose organization is still poorly understood [9]. Actin filaments and microtubules can crosslink in OHCs [10,11]. Contractile proteins were described in supporting cells in guinea pigs by Flock et al. [12] and were noted to be giving stability to the cells. They contain non-muscle β- and γ actin isoforms and α-actinin [13,14] whereas the cuticular plate contains actin, α-actinin, myosin, tropomyosin, spectrin, profilin and fodrin [10,15]. Non-muscle actin subunits are present in human Deiters cells, IPCs and OPCs and contain a remarkable three-dimensional (3D) interacting skeletal system of actin strands and microtubules anchored to the plasma cell membranes (Figure 3). Opposing pillars appear to be coupled with functional elements to relay basilar membrane (BM) vibrations to the reticular lamina (RL) and sensory hair cells that have no direct contact with the BM (Figure 4). In humans, TEM shows a dense meshwork associated with cell junctional complexes at the plasma membrane referred to as surfoskelosomes [13]. These are located in the pillar heads and foot (basal bodies) that contain organized actin and are closely associated with microtubules [16]. Deiters’ cells also express organized actin in basal bodies. Border and phalangeal cells around the IHCs do not express cytoplasmic actin possibly since they are positioned on a rigid fundament operative as principal sensory receptors.