The author would like to thank Matthew Kelley, Tiziana Cogliati, Jessica Gumerson, Uwe Wolfrum, Rivka Levron, Viola Kretschmer and Zoe Mann and for their critical evaluation of the manuscript. This work was funded by the Sofja Kovalevskaya Award (Humbodlt Foundation) and the Johannes-Gutenberg University, Mainz, Germany.

<ol><li>Waters, A. M., Beales, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ciliopathies%3A+an+expanding+disease+spectrum%5BTitle%5D)+AND+%22Pediatr+Nephrol%22%5BJournal%5D)">Ciliopathies: an expanding disease spectrum.</a> Pediatr Nephrol. 26, 1039-1056 (2011).</li>
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<li>Copley, C. O., Duncan, J. S., Liu, C., Cheng, H., Deans, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Postnatal+refinement+of+auditory+hair+cell+planar+polarity+deficits+occurs+in+the+absence+of+Vangl2%5BTitle%5D)+AND+%22The+Journal+of+neuroscience+%3A+the+official+journal+of+the+Society+for+Neuroscience%22%5BJournal%5D)">Postnatal refinement of auditory hair cell planar polarity deficits occurs in the absence of Vangl2.</a> The Journal of neuroscience : the official journal of the Society for Neuroscience. 33, 14001-14016 (2013).</li>
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</ol>

The author declares no competing financial interests.

When preparing cochlear tissue for analysis, there are a few key points to bear in mind. Firstly, differences in genetic background can modify the cochlear phenotype, making it necessary to analyze and compare only littermate controls. Secondly, complete removal of the tectorial membrane is required to obtain the best images with immunohistochemistry and is essential for SEM. The tectorial membrane is an opaque structure and can obscure the cells of the sensory epithelium directly beneath it, making imaging more challeng...

Primary cilia are long microtubule-based appendages that extend from the surface of most mammalian cells. Primary cilia are often confused with motile cilia, of which there are always multiple per cell, and whose purpose is to move fluid across membrane surfaces. Primary cilia, in contrast, adopt sensory roles and are consequently also referred to as sensory cilia. Once long forgotten, this organelle has recently been &#39;rediscovered&#39; as a result of its association with a multitude of human genetic diseases1. Ideally positioned as a signaling organelle, the primary cilium has been shown to regulate numerous signaling pathways, many of which are important not only in tissue homeostasis and disease, but also during development2.
One of the first signaling pathways shown to be associated with cilia dysfunction was the non-canonical Wnt signaling pathway, known also as the planar cell polarity (PCP) pathway3. This signaling cascade initially identified in Drosophila, is critical for embryogenesis; in particular for convergence and extension processes and for the correct orientation of cells in the plane of epithelia4. The sequential signaling of a core set of regulatory proteins translates directional cues which ultimately lead to cytoskeletal rearrangements and result in the coordinated polarization of epithelial cells in a plane5. The process of convergence and extension is absolutely required for the cochlear duct to elongate and for correct cellular patterning6. As this is regulated via activation of the PCP pathway, one of the most striking phenotypes of cochlea PCP mutants is a shortened cochlear duct with disorganized sensory epithelia7. Similarly, mouse mutants, which lack cilia, also exhibit such a convergence and extension phenotype8,9, though precisely how this is regulated remains to be elucidated.
Because convergence and extension processes are critical for the outgrowth of the cochlear duct, and cellular patterning of the sensory epithelia within the cochlear duct, the developing cochlea is an ideal organ in which to examine PCP signaling during vertebrate development. The organ of Corti, the term given to the specialized sensory epithelium that lines the cochlear duct, is comprised of non-sensory supporting cells and mechanosensory hair cells which must be uniformly oriented for the cochlea to function10. The mechanosensory hair cells are so called because of the stereociliary bundles that extend from the cuticular plate (apical surface) of each sensory hair cell11. These act as primary transducers of mechanosensation and despite their nomenclature as stereocilia, are actually comprised of modified actin filament-based microvilli. Within each chevron-shaped hair bundle, three rows of stereocilia are organized in a highly ordered and regular pattern in a stair case-like manner. Real microtubule-based cilia, termed kinocilia, are required for the development and orientation of the stereociliary bundles12. Upon each hair cell, one single kinocilium is physically attached to the stereocilia bundle, located centrally adjacent to the tallest row of stereocilia. The precise function of the kinocilium is unclear, and one hypothesis is that the kinocilium &#39;pulls&#39; the stereocilia into shape as they mature from microvilli12. In vertebrates, kinocilia in the cochlea are only present transiently and retract from the hair cells in mice prior to the onset of hearing11,13,14.
Complete loss of cilia in the developing cochlea results in severely shortened cochlear ducts, mis-formed and mis-oriented stereociliary bundles, as well as mis-positioned basal bodies8,9. A functional cilium is not just comprised of the ciliary axoneme. Many proteins associated with cilia function occur in complexes localized to cilia-related subdomains such as the basal body, transition zone, or ciliary axoneme15. The basal body, derived from the mother centriole of the centrosome, is also a microtubule-organizing center for microtubules extending away from the cilium into the cell body and can regulate intracellular trafficking as well as ciliary trafficking. The ciliary transition zone is another region where ciliary function is regulated in terms of organizing import and export of ciliary compounds16.
Multiple studies have identified a connection between cilia and non-canonical Wnt (PCP signaling), though the precise mechanism is unclear17. Redundancy of ciliary and PCP genes and the sensitivity of cell polarity to generalized cellular abnormalities, make it difficult to directly link a mutation to PCP-specific deficits. One of the read outs of PCP signaling is the positioning of the basal body and primary cilium, therefore segregating the primary from the secondary defects is challenging. Some studies in zebrafish and mouse mutants have suggested no connection between cilia and Wnt signaling18-20. Discrepancies in the data may reflect species, tissue, or temporal-dependent differences in ciliary contributions towards Wnt signaling. Furthermore, normal Wnt responsiveness might be retained if basal bodies remain functional. A deeper insight into the role of ciliary proteins in cellular signaling pathways and other biological phenomena is crucial for our understanding of cellular and developmental biology, as well as for the development of targeted treatment strategies.

<table><tbody><tr><td>Tools/Equipment</td><td></td><td></td><td></td></tr><tr><td>Silicone elastomere - Sylgard 184</td><td>Sigma-Aldrich</td><td>761028-5EA</td><td>See Note 2</td></tr><tr><td>Micro dissecting scissors-straight blade</td><td>Various</td><td></td><td></td></tr><tr><td>Fine forceps (no. 5 and 55) and blunt forceps</td><td>Various</td><td></td><td></td></tr><tr><td>Dissecting microscope.</td><td>Various</td><td></td><td></td></tr><tr><td>Uncoated glass microscope slides</td><td>Various</td><td></td><td></td></tr><tr><td>Microscope cover slips (22 mm &amp;times; 40 mm &amp;times; 0.15 mm)</td><td>Various</td><td></td><td></td></tr><tr><td>Transfer pipettes</td><td>Various</td><td></td><td></td></tr><tr><td>Minutien pins</td><td>&amp;nbsp;Fine Science Tools</td><td>26002-10</td><td></td></tr><tr><td>SEM sample holder</td><td>tousimis</td><td>8762</td><td></td></tr><tr><td>Scanning electron microscopy studs</td><td>TED PELLA</td><td>16111</td><td></td></tr><tr><td>PELCO Tabs: Carbon adhesive</td><td>TED PELLA</td><td>16084-3</td><td></td></tr><tr><td>Fluorescent Microscope</td><td>Various</td><td></td><td></td></tr><tr><td>Critical Point Dryer</td><td>Various</td><td></td><td></td></tr><tr><td>Scanning Electron Microscope</td><td>Various</td><td></td><td></td></tr><tr><td>Glass microscope slides</td><td>Various</td><td></td><td></td></tr><tr><td>Glass coverslips</td><td>Various</td><td></td><td></td></tr><tr><td>Kimwipe Tissue&amp;nbsp;</td><td>Various</td><td></td><td></td></tr><tr><td>Fine Paint Brush</td><td></td><td></td><td></td></tr><tr><td>Reagents</td><td></td><td></td><td></td></tr><tr><td>1&amp;times; Phosphate buffered saline (PBS)</td><td>Gibco/Life Technologies</td><td>10010023</td><td></td></tr><tr><td>Paraformaldehyde&amp;nbsp; (PFA) (EM Grade Required for EM)</td><td>Various</td><td></td><td>Prepare a 4% solution in 1&amp;times; PBS made fresh each time. EM Grade Required for EM.</td></tr><tr><td>2.5% Glutaraldehyde Grade1</td><td>Sigma-Aldrich</td><td>G5882</td><td></td></tr><tr><td>Tris-HCl (pH 7.5)</td><td>Various</td><td></td><td></td></tr><tr><td>NaCl</td><td>Various</td><td></td><td></td></tr><tr><td>CaCl 2</td><td>Various</td><td></td><td></td></tr><tr><td>Triton X-100</td><td>Various</td><td></td><td></td></tr><tr><td>Normal Goat Serum</td><td>Various</td><td></td><td></td></tr><tr><td>AffiniPure Fab Fragment Donkey Anti-Mouse IgG (H+L)</td><td>Jackson ImmunoResearch</td><td>715-007-003</td><td></td></tr><tr><td>Fluoromount-G Mounting media</td><td>SouthernBiotech</td><td>0100-01</td><td></td></tr><tr><td>10&amp;times; Hanks&amp;rsquo; Balanced Salt Solution (HBSS)</td><td>Gibco/Life Technologies</td><td>14065</td><td></td></tr><tr><td>Hepes</td><td>Gibco/Life Technologies</td><td>15630-080</td><td></td></tr><tr><td>Osmium tetroxide (OsO4 )</td><td>Sigma-Aldrich/Fluka Analytical</td><td>75632</td><td></td></tr><tr><td>Tannic acid</td><td>Sigma-Aldrich</td><td>403040</td><td></td></tr><tr><td>Ethanol 200 proof</td><td>Various</td><td></td><td></td></tr><tr><td>Antibodies</td><td></td><td></td><td></td></tr><tr><td>anti Arl13b</td><td>Protein Tech</td><td>17711-1-AP</td><td>Suggested concentration 1:1,000</td></tr><tr><td>anti acetylated tubulin (611-B1)</td><td>Sigma-Aldrich</td><td>T6793</td><td>Suggested concentration 1:800</td></tr><tr><td>anti gamma tubulin (GTU-88)</td><td>Sigma-Aldrich</td><td>T6557</td><td>Suggested concentration 1:200</td></tr><tr><td>anti Zo_1&amp;nbsp;</td><td>Invitrogen</td><td>40-2300</td><td>Suggested concentration 1:500</td></tr><tr><td>Myosin VI</td><td>Proteus Biosciences</td><td>25-6791</td><td>Suggested concentration 1:1000</td></tr><tr><td>Myosin VIIa</td><td>Proteus Biosciences</td><td>25-6790</td><td>Suggested concentration 1:1,000</td></tr><tr><td>anti Vangl2</td><td>Merk Millipore</td><td>ABN373</td><td>Suggested concentration 1:250</td></tr><tr><td>anti G&amp;alpha;i3</td><td>Sigma-Aldrich</td><td>G4040</td><td>Suggested concentration 1:250</td></tr><tr><td>Alexa Fluor&amp;reg; 488 Phalloidin</td><td>Invitrogen/Life Technologies</td><td>A12379</td><td>Suggested concentration 1:300 - 1,000</td></tr><tr><td>Alexa Fluor&amp;reg; 568 Phalloidin</td><td>Invitrogen/Life Technologies</td><td>A12380</td><td>Suggested concentration 1:300 - 1,000</td></tr></tbody></table>

evaluation of planar-cell-polarity phenotypes in ciliopathy mouse mutant cochlea

In recent years, primary cilia have emerged as key regulators in development and disease by influencing numerous signaling pathways. One of the earliest signaling pathways shown to be associated with ciliary function was the non-canonical Wnt signaling pathway, also referred to as planar cell polarity (PCP) signaling. One of the best places in which to study the effects of planar cell polarity (PCP) signaling during vertebrate development is the mammalian cochlea. PCP signaling disruption in the mouse cochlea disrupts cochlear outgrowth, cellular patterning and hair cell orientation, all of which are affected by cilia dysfunction. The goal of this protocol is to describe the analysis of PCP signaling in the developing mammalian cochlea via phenotypic analysis, immunohistochemistry and scanning electron microscopy. Defects in convergence and extension are manifested as a shortening of the cochlear duct and/or changes in cellular patterning, which can be quantified following dissection from developing mouse mutants. Changes in stereociliary bundle orientation and kinocilia length or positioning can be observed and quantitated using either immunofluorescence or scanning electron microscopy (SEM). A deeper insight into the role of ciliary proteins in cellular signaling pathways and other biological phenomena is crucial for our understanding of cellular and developmental biology, as well as for the development of targeted treatment strategies.

Cochlea Dissection and Tissue Preparation
After removal of the brain, post mid-line sagittal dissection of a P0 mouse head, the bony labyrinth, seen from behind, can be visualized (Figure 1A, white arrow) and removed. Figure 1B shows the isolated bony labyrinths with the cochlear hair facing upwards, ventral, (left) and from behind, dorsal (right). The white arrow points to the ...

Watch this Scientific Journal Video about Evaluation of Planar-Cell-Polarity Phenotypes in Ciliopathy Mouse Mutant Cochlea at JoVE.com

Evaluation of Planar-Cell-Polarity Phenotypes in Ciliopathy Mouse Mutant Cochlea

Primary cilia influence various signaling pathways. The mammalian cochlea is ideal for examining planar cell polarity (PCP) signaling. Cilia dysfunction affects cochlear outgrowth, cellular patterning and hair cell orientation, readouts of PCP. Our goal is to analyze PCP signaling in mouse cochlea via phenotypic analysis, immunohistochemistry and scanning electron microscopy.

In recent years, primary cilia have emerged as key regulators in development and disease by influencing numerous signaling pathways. One of the earliest ...

evaluation-planar-cell-polarity-phenotypes-ciliopathy-mouse-mutant

Research

JoVE Journal

Medicine

10.4K Views.  Johannes Gutenberg-Universität Mainz. Primary cilia influence various signaling pathways. The mammalian cochlea is ideal for examining planar cell polarity (PCP) signaling. Cilia dysfunction affects cochlear outgrowth, cellular patterning and hair cell orientation, readouts of PCP. Our goal is to analyze PCP signaling in mouse cochlea via phenotypic analysis, immunohistochemistry and scanning electron microscopy.

Video: Evaluation of Planar-Cell-Polarity Phenotypes in Ciliopathy Mouse Mutant Cochlea

Culture of Embryonic Mouse Cochlear Explants and Gene Transfer by Electroporation

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair cells are aligned in one row of inner hair cells and three rows of outer hair cells that extend along the basal to apical axis of the cochlea. The explant culture technique described here provides an efficient method to isolate and maintain cochlear explants from the embryonic mouse inner ear. Also, the morphology and molecular characteristics of sensory hair cells and nonsensory supporting cells within the cochlear explant cultures resemble those observed in vivo and can be studied within its intrinsic cellular environment. The cochlear explants can serve as important experimental tools for the identification and characterization of molecular and genetic pathways that are involved in cellular specification and patterning. Although transgenic mouse models provide an effective approach for gene expression studies, a considerable number of mouse mutants die during embryonic development thereby hindering the analysis and interpretation of developmental phenotypes. The organ of Corti from mutant mice that die before birth can be cultured so that their in vitro development and responses to different factors can be analyzed. Additionally, we describe a technique for electroporating embryonic cochlear explants ex vivo which can be used to downregulate or overexpress specific gene(s) and analyze their potential endogenous function and test whether specific gene product is necessary or sufficient in a given context to influence mammalian cochlear development1-8.

We present a method that describes isolation and culture of cochlear explants from embryonic mouse inner ear. We also demonstrate a method for gene transfer into cochlear explants via square-wave electroporation. The in vitro explant culture coupled with gene transfer technique enables researchers to study the effects of altering gene expression during development.

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair ...

Developmental Biology

Isolating LacZ-expressing Cells from Mouse Inner Ear Tissues using Flow Cytometry

Isolation of specific cell types allows one to analyze rare cell populations such as stem/progenitor cells. Such an approach to studying inner ear tissues presents a unique challenge because of the paucity of cells of interest and few transgenic reporter mouse models. Here, we describe a protocol using fluorescence-conjugated probes to selectively label LacZ-positive cells from the neonatal cochleae.
The most common underlying pathology of sensorineural hearing loss is the irreversible damage and loss of cochlear sensory hair cells, which are required to transduce sound waves to neural impulses. Recent evidence suggests that the murine auditory and vestibular organs harbor stem/progenitor cells that may have regenerative potential1,2. These findings warrant further investigation, including identifying specific cell types with stem/progenitor cell characteristics. The Wnt signaling pathway has been demonstrated to play a critical role in maintaining stem/progenitor cell populations in several organ systems3-7. We have recently identified Wnt-responsive Axin2-expressing cells in the neonatal cochlea, but their function is largely unknown8.
To better understand the behavior of these Wnt-responsive cells in vitro, we have developed a method of isolating Axin2-expressing cells from cochleae of Axin2-LacZ reporter mice9. Using flow cytometry to isolate Axin2-LacZ positive cells from the neonatal cochleae, we could in turn execute a variety of experiments on live cells to interrogate their behavior as stem/progenitor cells. Here, we describe in detail the steps for the microdissection of neonatal cochlea, dissociation of these tissues, labeling of the LacZ-positive cells using a fluorogenic substrate, and cell sorting. Techniques for dissociating cochleae into single cells and isolating cochlear cells via flow cytometry have been described2,10-12. We have made modifications to these techniques to establish a novel protocol to isolate LacZ-expressing cells from the neonatal cochlea.

Flow cytometry is a powerful tool allowing for the isolation and study of specific cell populations. This protocol describes steps for isolating LacZ-expressing cells from cochlear tissues from neonatal transgenic mice. Dissociated cochlear cells were labeled using fluorescent-conjugated substrates of &#946;-galactosidase prior to separation via flow cytometry.

Isolation of specific cell types allows one to analyze rare cell populations such as stem/progenitor cells. Such an approach to studying inner ear tissues ...

Neuroscience

Three-dimensional Organotypic Cultures of Vestibular and Auditory Sensory Organs

The sensory organs of the inner ear are challenging to study in mammals due to their inaccessibility to experimental manipulation and optical observation. Moreover, although existing culture techniques allow biochemical perturbations, these methods do not provide a means to study the effects of mechanical force and tissue stiffness during development of the inner ear sensory organs. Here we describe a method for three-dimensional organotypic culture of the intact murine utricle and cochlea that overcomes these limitations. The technique for adjustment of a three-dimensional matrix stiffness described here permits manipulation of the elastic force opposing tissue growth. This method can therefore be used to study the role of mechanical forces during inner ear development. Additionally, the cultures permit virus-mediated gene delivery, which can be used for gain- and loss-of-function experiments. This culture method preserves innate hair cells and supporting cells and serves as a potentially superior alternative to the traditional two-dimensional culture of vestibular and auditory sensory organs.

Three-dimensional organotypic cultures of the murine utricle and cochlea in optically clear collagen I gels preserve innate tissue morphology, allow for mechanical stimulation through adjustment of matrix stiffness, and permit virus-mediated gene delivery.

The sensory organs of the inner ear are challenging to study in mammals due to their inaccessibility to experimental manipulation and optical observation. ...

Whole Mount Dissection and Immunofluorescence of the Adult Mouse Cochlea

The organ of Corti, housed in the cochlea of the inner ear, contains mechanosensory hair cells and surrounding supporting cells which are organized in a spiral shape and have a tonotopic gradient for sound detection. The mouse cochlea is approximately 6 mm long and often divided into three turns (apex, middle, and base) for analysis. To investigate cell loss, cell division, or mosaic gene expression, the whole mount or surface preparation of the cochlea is useful. This dissection method allows visualization of all cells within the organ of Corti when combined with immunostaining and confocal microscopy to image cells at different planes in the z-axis. Multiple optical cross-sections can also be obtained from these z-stack images. In addition, the whole mount dissection method can be used for scanning electron microscopy, although a different fixation method is needed. Here, we present a method to isolate the organ of Corti as three intact cochlear turns (apex, middle, and base). This method can be used for mice ranging from one week of age through adulthood and differs from the technique used for neonatal samples where calcification of the cochlea is incomplete. A slightly modified version can be used for dissection of the rat cochlea. We also demonstrate a procedure for immunostaining with fluorescently tagged antibodies.

We present a method to isolate the adult organ of Corti as three intact cochlear turns (apex, middle, and base). We also demonstrate a procedure for immunostaining with fluorescently tagged antibodies. Together these techniques allow the study of hair cells, supporting cells, and other cell types found in the cochlea.

The organ of Corti, housed in the cochlea of the inner ear, contains mechanosensory hair cells and surrounding supporting cells which are organized in a ...

Cryosectioning and Immunostaining Mouse Inner Ear Tissue: From Embryonic to Adult Stages

This protocol details general histology methods for preparing inner ear samples from embryonic, neonatal, and adult mice. The purpose of this protocol is to provide a straightforward and standardized method for inner ear tissue processing for researchers, possibly new to the field, interested in working with the mouse cochlea. Included here are protocols for dissection, fixation, embedding, cryosectioning, and immunostaining. Section immunostaining is one of the best methods for examining individual cells within the context of the entire cochlea.
Key steps include dissecting the inner ear away from the skull, fixing the tissue using 4% paraformaldehyde, embedding with Optimal Cutting Temperature compound, cryosectioning, and immunostaining with antibodies targeting specific proteins expressed by the cochlea.
Included in our methods are special considerations made for the cochlea given its 
shape and structure.&#160;Reasonably good focus and dissection skills are needed, as tissue damage can affect the quality of immunostaining and consistency among samples. However, with the procedures we outline, most users can be trained in a few weeks to make beautiful preparations. Overall, this protocol offers a valuable way to promote research to understand auditory development, function, and disease in mouse models.

This protocol, intended for novice users of mouse inner ear tissue, comprehensively details steps for processing mouse inner ears at different developmental stages for section immunostaining.

This protocol details general histology methods for preparing inner ear samples from embryonic, neonatal, and adult mice. The purpose of this protocol is ...

Morphological and Functional Evaluation of Ribbon Synapses at Specific Frequency Regions of the Mouse Cochlea

Cochlear inner hair cells (IHCs) transmit acoustic signals to spiral ganglion neurons (SGNs) through ribbon synapses. Several experimental studies have indicated that hair cell synapses may be the initial targets in sensorineural hearing loss (SNHL). Such studies have proposed the concept of cochlear &#34;synaptopathy&#34;, which refers to alterations in ribbon synapse number, structure, or function that result in abnormal synaptic transmission between IHCs and SGNs. While cochlear synaptopathy is irreversible, it does not affect the hearing threshold. In noise-induced experimental models, restricted damage to IHC synapses in select frequency regions is employed to identify the environmental factors that specifically cause synaptopathy, as well as the physiological consequences of disturbing this inner ear circuit. Here, we present a protocol for analyzing cochlear synaptic morphology and function at a specific frequency region in adult mice. In this protocol, cochlear localization of specific frequency regions is performed using place-frequency maps in conjunction with cochleogram data, following which the morphological characteristics of ribbon synapses are evaluated via synaptic immunostaining. The functional status of ribbon synapses is then determined based on the amplitudes of auditory brainstem response (ABR) wave I. The present report demonstrates that this approach can be used to deepen our understanding of the pathogenesis and mechanisms of synaptic dysfunction in the cochlea, which may aid in the development of novel therapeutic interventions.

This manuscript describes an experimental protocol for evaluating the morphological characteristics and functional status of ribbon synapses in normal mice. The present model is also suitable for noise-induced and age-related cochlear synaptopathy-restricted models. The correlative results of previous mouse studies are also discussed.

Cochlear inner hair cells (IHCs) transmit acoustic signals to spiral ganglion neurons (SGNs) through ribbon synapses. Several experimental studies have ...

Cochlear Surface Preparation in the Adult Mouse

Auditory processing in the cochlea depends on the integrity of the mechanosensory hair cells. Over a lifetime, hearing loss can be acquired from numerous etiologies such as exposure to excessive noise, the use of ototoxic medications, bacterial or viral ear infections, head injuries, and the aging process. Loss of sensory hair cells is a common pathological feature of the varieties of acquired hearing loss. Additionally, the inner hair cell synapse can be damaged by mild insults. Therefore, surface preparations of cochlear epithelia, in combination with immunolabeling techniques and confocal imagery, are a very useful tool for the investigation of cochlear pathologies, including losses of ribbon synapses and sensory hair cells, changes in protein levels in hair cells and supporting cells, hair cell regeneration, and determination of report gene expression (i.e., GFP) for verification of successful transduction and identification of transduced cell types. The cochlea, a bony spiral-shaped structure in the inner ear, holds the auditory sensory end organ, the organ of Corti (OC). Sensory hair cells and surrounding supporting cells in the OC are contained in the cochlear duct and rest on the basilar membrane, organized in a tonotopic fashion with high-frequency detection occurring in the base and low-frequency in the apex. With the availability of molecular and genetic information and the ability to manipulate genes by knockout and knock-in techniques, mice have been widely used in biological research, including in hearing science. However, the adult mouse cochlea is miniscule, and the cochlear epithelium is encapsulated in a bony labyrinth, making microdissection difficult. Although dissection techniques have been developed and used in many laboratories, this modified microdissection method using cell and tissue adhesive is easier and more convenient. It can be used in all types of adult mouse cochleae following decalcification.

This article presents a modified cochlear surface preparation method that requires decalcification and use of a cell and tissue adhesive to adhere the pieces of cochlear epithelia to 10 mm round cover slips for immunohistochemistry in adult mouse cochleae.

Auditory processing in the cochlea depends on the integrity of the mechanosensory hair cells. Over a lifetime, hearing loss can be acquired from numerous ...

Whole Neonatal Cochlear Explants as an In vitro Model

Untreated hearing loss imposes significant costs on the global healthcare system and impairs individuals' quality of life. Sensorineural hearing loss is characterized by the cumulative and irreversible loss of sensory hair cells and auditory nerves in the cochlea. Entire and vital cochlear explants are one of the fundamental tools in hearing research to detect hair cell loss and to characterize the molecular mechanisms of the inner ear cells. Many years ago, a protocol for neonatal cochlear isolation was developed, and although it has been modified over time, it still holds potential for improvement. 
This paper presents an optimized protocol for isolating and culturing whole neonatal cochlear explants in multi-well culture chambers that enables the study of hair cells and spiral ganglion neuron cells along the entire length of the cochlea. The protocol was tested using cochlear explants from mice and rats. Healthy cochlear explants were obtained to study the interaction between hair cells, spiral ganglion neuron cells, and the surrounding supporting cells. 
One of the main advantages of this method is that it simplifies the organ culture steps without compromising the quality of the explants. All three turns of the organ of Corti are attached to the bottom of the chamber, which facilitates in vitro experiments and the comprehensive analysis of the explants. We provide some examples of cochlear images from different experiments with live and fixed explants, demonstrating that the explants retain their structure despite exposure to ototoxic drugs. This optimized protocol can be widely used for the integrative analysis of the mammalian cochlea.

Whole Neonatal Cochlear Explants as an In vitro Model

The current protocol updates previous protocols and incorporates relatively straightforward approaches for culturing high-quality cochlear explants. This provides reliable data acquisition and high-resolution imaging in live and fixed cells. This protocol supports the ongoing trend of studying inner ear cells.

Untreated hearing loss imposes significant costs on the global healthcare system and impairs individuals' quality of life. Sensorineural hearing loss is ...

Dissection of the Auditory Bulla in Postnatal Mice: Isolation of the Middle Ear Bones and Histological Analysis

In most mammals, auditory ossicles in the middle ear, including the malleus, incus and stapes, are the smallest bones. In mice, a bony structure called the auditory bulla houses the ossicles, whereas the auditory capsule encloses the inner ear, namely the cochlea and semicircular canals. Murine ossicles are essential for hearing and thus of great interest to researchers in the field of otolaryngology, but their metabolism, development, and evolution are highly relevant to other fields. Altered bone metabolism can affect hearing function in adult mice, and various gene-deficient mice show changes in morphogenesis of auditory ossicles in utero. Although murine auditory ossicles are tiny, their manipulation is feasible if one understands their anatomical orientation and 3D structure. Here, we describe how to dissect the auditory bulla and capsule of postnatal mice and then isolate individual ossicles by removing part of the bulla. We also discuss how to embed the bulla and capsule in different orientations to generate paraffin or frozen sections suitable for preparation of longitudinal, horizontal, or frontal sections of the malleus. Finally, we enumerate anatomical differences between mouse and human auditory ossicles. These methods would be useful in analyzing pathological, developmental and evolutionary aspects of auditory ossicles and the middle ear in mice.

We present a protocol to isolate the auditory bulla, capsule, and ossicles from postnatal mice for whole mount and histological analysis.

In most mammals, auditory ossicles in the middle ear, including the malleus, incus and stapes, are the smallest bones. In mice, a bony structure called ...

Biology

Dissection of the Endolymphatic Sac from Mice

The study of mutant mouse models of human hearing and balance disorders has unraveled many structural and functional changes which may contribute to the human phenotypes. Although important progress has been done in the understanding of the development and function of the neurosensory epithelia of the cochlea and vestibula, limited knowledge is available regarding the development, cellular composition, molecular pathways and functional characteristics of the endolymphatic sac. This is, in large part, due to the difficulty of visualizing and microdissecting this tissue, which is an epithelium comprised of only one cell layer. The study presented here describes an approach to access and microdissect the endolymphatic sac from the wild-type mouse inner ear at different ages. The result of a similar dissection is shown in a pendrin-deficient mouse model of enlargement of the vestibular aqueduct. A transgenic mouse with a fluorescent endolymphatic sac is presented. This reporter mouse can be used to readily visualize the endolymphatic sac with limited dissection and determine its size. It can also be used as an educational tool to teach how to dissect the endolymphatic sac. These dissection procedures should facilitate further characterization of this understudied part of the inner ear.

This study describes how to dissect the endolymphatic sac from the inner ear of the mouse at different ages. The result of a similar dissection is shown in an Slc26a4-null mouse model of enlargement of the endolymphatic sac. A transgenic mouse with a fluorescent reporter expressed in the endolymphatic sac is presented as a model to readily visualize the endolymphatic sac, and educational tool.

The study of mutant mouse models of human hearing and balance disorders has unraveled many structural and functional changes which may contribute to the ...

Evaluation of Planar-Cell-Polarity Phenotypes in Ciliopathy Mouse Mutant Cochlea

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