Expression of intermediate filament proteins in the mature inner ear of the rat and guinea pig

Epithelial-mesenchymal transition, and collective and individual cell migration regulate epithelial changes in the amikacin-damaged organ of Corti

Characterizing the microenvironment of a damaged organ of Corti and identifying the basic mechanisms involved in subsequent epithelial reorganization are critical for improving the outcome of clinical therapies. In this context, we studied the expression of a variety of cell markers related to cell shape, cell adhesion and cell plasticity in the rat organ of Corti poisoned with amikacin. Our results indicate that, after severe outer hair cell losses, the cytoarchitectural reorganization of the organ of Corti implicates epithelial-mesenchymal transition mechanisms and involves both collective and individual cell migratory processes. The results also suggest that both root cells and infiltrated fibroblasts participate in the homeostasis of the damaged epithelium, and that the flat epithelium that may emerge offers biological opportunities for late regenerative therapies.

Impact of morphometry, myelinization and synaptic current strength on spike conduction in human and cat spiral ganglion neurons

BACKGROUND

Our knowledge about the neural code in the auditory nerve is based to a large extent on experiments on cats. Several anatomical differences between auditory neurons in human and cat are expected to lead to functional differences in speed and safety of spike conduction.

METHODOLOGY/PRINCIPAL FINDINGS

Confocal microscopy was used to systematically evaluate peripheral and central process diameters, commonness of myelination and morphology of spiral ganglion neurons (SGNs) along the cochlea of three human and three cats. Based on these morphometric data, model analysis reveales that spike conduction in SGNs is characterized by four phases: a postsynaptic delay, constant velocity in the peripheral process, a presomatic delay and constant velocity in the central process. The majority of SGNs are type I, connecting the inner hair cells with the brainstem. In contrast to those of humans, type I neurons of the cat are entirely myelinated. Biophysical model evaluation showed delayed and weak spikes in the human soma region as a consequence of a lack of myelin. The simulated spike conduction times are in accordance with normal interwave latencies from auditory brainstem response recordings from man and cat. Simulated 400 pA postsynaptic currents from inner hair cell ribbon synapses were 15 times above threshold. They enforced quick and synchronous spiking. Both of these properties were not present in type II cells as they receive fewer and much weaker (∼26 pA) synaptic stimuli.

CONCLUSIONS/SIGNIFICANCE

Wasting synaptic energy boosts spike initiation, which guarantees the rapid transmission of temporal fine structure of auditory signals. However, a lack of myelin in the soma regions of human type I neurons causes a large delay in spike conduction in comparison with cat neurons. The absent myelin, in combination with a longer peripheral process, causes quantitative differences of temporal parameters in the electrically stimulated human cochlea compared to the cat cochlea.

Evidence for a partial epithelial-mesenchymal transition in postnatal stages of rat auditory organ morphogenesis

The epithelial-mesenchymal transition (EMT) plays a crucial role in the differentiation of many tissues and organs. So far, an EMT was not detected in the development of the auditory organ. To determine whether an EMT may play a role in the morphogenesis of the auditory organ, we studied the spatial localization of several EMT markers, the cell-cell adhesion molecules and intermediate filament cytoskeletal proteins, in epithelium of the dorsal cochlea during development of the rat Corti organ from E18 (18th embryonic day) until P25 (25th postnatal day). We examined by confocal microscopy immunolabelings on cryosections of whole cochleae with antibodies anti-cytokeratins as well as with antibodies anti-vimentin, anti-E-cadherin and anti-β-catenin. Our results showed a partial loss of E-cadherin and β-catenin and a temporary appearance of vimentin in pillar cells and Deiters between P8 and P10. These observations suggest that a partial EMT might be involved in the remodelling of the Corti organ during the postnatal stages of development in rat.

The spiral ganglion: connecting the peripheral and central auditory systems

In mammals, the initial bridge between the physical world of sound and perception of that sound is established by neurons of the spiral ganglion. The cell bodies of these neurons give rise to peripheral processes that contact acoustic receptors in the organ of Corti, and the central processes collect together to form the auditory nerve that projects into the brain. In order to better understand hearing at this initial stage, we need to know the following about spiral ganglion neurons: (1) their cell biology including cytoplasmic, cytoskeletal, and membrane properties, (2) their peripheral and central connections including synaptic structure; (3) the nature of their neural signaling; and (4) their capacity for plasticity and rehabilitation. In this report, we will update the progress on these topics and indicate important issues still awaiting resolution.

Neurofilament localization and phosphorylation in the developing inner ear of the rat

Detailed understanding of neurofilament protein distribution in the inner ear can shed light on regulatory mechanisms involved in neuronal development of this tissue. We assessed the spatio-temporal changes in the distribution of neurofilaments in the developing rat inner ear between embryonic day 12 and 30 days after birth, using antibodies against phosphorylated as well as non-phosphorylated light (NFL), medium (NFM) and heavy (NFH) neurofilament subunits. Our results show that during development, the onset of neurofilament expression in the rat inner ear is on embryonic day 12, earlier than previously shown. We demonstrate that neurofilament subunits of different molecular weight emerge in a developmental stage-dependent order. In addition, we determined that neurofilaments of the vestibular nerve mature earlier than neurofilaments of the cochlear nerve. Cochlear neurofilament maturation progresses in a gradient from base to apex, and from inner to outer hair cells. The sequential pattern of neurofilament expression we describe may help understand the consequences of certain mutations, and contribute to develop therapeutic strategies.

Mutations of ESRRB encoding estrogen-related receptor beta cause autosomal-recessive nonsyndromic hearing impairment DFNB35

In a large consanguineous family of Turkish origin, genome-wide homozygosity mapping revealed a locus for recessive nonsyndromic hearing impairment on chromosome 14q24.3-q34.12. Fine mapping with microsatellite markers defined the critical linkage interval to a 18.7 cM region flanked by markers D14S53 and D14S1015. This region partially overlapped with the DFNB35 locus. Mutation analysis of ESRRB, a candidate gene in the overlapping region, revealed a homozygous 7 bp duplication in exon 8 in all affected individuals. This duplication results in a frame shift and premature stop codon. Sequence analysis of the ESRRB gene in the affected individuals of the original DFNB35 family and in three other DFNB35-linked consanguineous families from Pakistan revealed four missense mutations. ESRRB encodes the estrogen-related receptor beta protein, and one of the substitutions (p.A110V) is located in the DNA-binding domain of ESRRB, whereas the other three are substitutions (p.L320P, p.V342L, and p.L347P) located within the ligand-binding domain. Molecular modeling of this nuclear receptor showed that the missense mutations are likely to affect the structure and stability of these domains. RNA in situ hybridization in mice revealed that Esrrb is expressed during inner-ear development, whereas immunohistochemical analysis showed that ESRRB is present postnatally in the cochlea. Our data indicate that ESRRB is essential for inner-ear development and function. To our knowledge, this is the first report of pathogenic mutations of an estrogen-related receptor gene.

The human fetal cochlea can be a source for auditory progenitors/stem cells isolation

The development of new stem cell-based technologies is creating new hopes in regenerative medicine. Hearing-impaired individuals should benefit greatly from the development of a cell-based regenerative strategy to treat deafness. An important achievement would be to develop a human-based system that could bring the advances made in animal models closer to clinical application. In this work, we have explored the suitability of the developing fetal cochlea to be used as a source for the extraction of auditory progenitor/stem cells. We have established cultures that express critical markers such as NESTIN, SOX2, GATA3 and PAX2. These cultures can be expanded in vitro for several months and differentiating markers such as ATOH1/HATH1 and POU4F3/BRN3C can be induced by manipulating the culture conditions using specific growth factors such as bFGF, EGF and retinoic acid.

Nestin expression in the developing rat cochlea sensory epithelia

An intermediate filament (IF), nestin, is used as an immature cell marker because nestin occurs in neural progenitors during early development. Recent cell culture studies have indicated that proliferating otic progenitor cells express nestin in vitro. However, localization of nestin in the developing inner ear has not yet been clarified. In this study, the ontogenetical expression of nestin epitopes in the rat cochlea was examined immunohistochemically. Sensory epithelial cells in the rat Corti organ (e.g. hair cells and support cells) transiently demonstrated immunoreactivity for nestin during the late embryonic period. After birth, nestin expression in the sensory epithelia disappeared gradually. The findings of this study indicate that the expression of nestin epitopes in the developing cochlea is linked with the plasticities of sensory epithelial cells, such as proliferation or differentiation.

Glial fibrillary acidic protein expression and promoter activity in the inner ear of developing and adult mice

The intermediate filament glial fibrillary acidic protein (GFAP) is a classic marker for several types of glial cells, including astrocytes and nonmyelinating Schwann cells. The pattern of expression of GFAP in the postnatal murine inner ear, from postnatal day 3 (P3) to P38, was studied by anti-GFAP immunostaining in wild-type mice as well as in two lines of transgenic mice expressing either beta-galactosidase (LacZ) or green fluorescent protein (GFP) under the control of the GFAP promoter. Analysis of protein and promoter activity shows that several classes of supporting cells in the sensory epithelia, as well as Schwann cells and satellite cells express GFAP. Early after birth, all cochlear supporting cells express GFAP, in a gradient decreasing in intensity from base to apex. After P15, GFAP expression in the organ of Corti is mostly restricted to supporting cells of the inner hair cell area (i.e., inner border and inner phalangeal cells) and outer hair cell area (i.e., Deiters' cells). A small population of limbic cells also showed expression in a base-to-apex gradient. In the vestibular organs, high expression was detected in supporting cells in extrastriolar regions of the utricular macula and in the canal ampullae, with weaker staining in the saccular macula. These results suggest that supporting cells of the inner ear have important similarities to glial cells and may play roles similar to those of astrocytes or Schwann cells in supporting the normal development and maintenance of neurons and sensory cells of the inner ear.

The molecular architecture of the inner ear

The inner ear is structurally complex. A molecular description of its architecture is now emerging from the use of contemporary methods of cell and molecular biology, and from studies of ontogenetic development. With the application of clinical and molecular genetics, it has now become possible to identify genes associated with inherited, non-syndromic deafness and balance dysfunction in humans and in mice. This work is providing new insights into how the tissues of the inner ear are built to perform their tasks, and into the pathogenesis of a range of inner ear disorders.

Immunohistochemistry and microwave decalcification of human temporal bones

Processing of human temporal bones is a long, expensive process and the resulting celloidin sections are difficult to use for immunohistochemistry. We tested the ability of immunohistochemical assays to work in human temporal bones that were decalcified using a microwave oven. Tissue was trimmed to an approximate cube (1.5-2 cm/side) containing only the cochlea and immersed in fresh EDTA with paraformaldehyde every 6 h. This sized block required 190-400 h to decalcify. The decalcified tissue was embedded in paraffin and sectioned. Sections were immunoassayed with anti-cytochrome c oxidase, anti-neurofilament or anti-peripherin. All three antibodies labeled the appropriate structures. This procedure may stimulate advancement in the understanding of human inner ear pathology.

Keratin filament deployment and cytoskeletal networking in a sensory epithelium that vibrates during hearing

The intricate and spatially precise ways in which keratin intermediate filaments are deployed in certain cochlear epithelial cells, called supporting cells, suggests that these filaments make a micromechanically important contribution to the functional design of the guinea pig organ of Corti. Filament arrays that include keratins 8, 18, and 19 are confined mainly to regions close to the ends of large transcellular microtubule bundles in supporting cells. These cells and their microtubule bundles link sensory hair cells to a specialized basement membrane that vibrates during hearing. The keratin filament arrays apparently help anchor the ends of the microtubule bundles to cell surfaces. Filaments are concentrated at the apices and bases of most cells that contact hair cells. Substantial arrays of adherens junctions link the apices of these cells. Hence, keratin filaments may contribute to a cytoskeletal network that distributes mechanical forces from cell to cell and that coordinates the displacement of neighboring hair cells. However, high concentrations of keratin filaments have not been detected at the apices of one of the supporting cell types, which apparently has a mechanical role that is different from that of the others. Transmission electron microscopy has revealed previously undescribed filament networks at all the locations where the binding of antibodies to keratins is most marked. There is evidence that intercellular linkage of the keratin networks via their association with actin-containing meshworks and adherens junctions is more extensive than linkage provided by desmosomes.

Application of a platinum replica method to the study of the cytoskeleton of isolated hair cells, supporting cells and whole mounts of the organ of Corti

We adapted a method of platinum replica to study the cytoskeleton of isolated cells of the guinea pig organ of Corti. This technique combined high image resolution with the ability to visualize the three-dimensional organization of the cytoskeleton of a whole cell. The procedure includes: isolation of hair cells and supporting cells using collagenase digestion, attachment of the cells to a coverslip, detergent extraction, chemical fixation, critical point drying, platinum/carbon coating, and transmission electron microscopy analysis. By using the method of platinum replica, we confirmed the existence of structural domains in the cortical lattice of outer hair cells. Based on the analysis of the partly destroyed cortical lattice, we propose that circumferential filaments are underlined with a thin flexible network. In addition, we established that the base of each stereocilium had a cone-like expansion of actin filaments and was surrounded by a thin bundle of filaments. We also produced replicas of the protrusion of the cuticular plate into the cytoplasm (infracuticular network) and the reticular lamina cytoskeleton. Our data indicated that the platinum replica method is useful for studying structural interactions among different cytoskeletal elements in the reticular lamina, as well as the cortex of outer hair cells and the cytoskeleton of supporting cells.

The early postnatal development of F-actin patterns in the organ of Corti of the gerbil (Meriones unguiculatus) and the horseshoe bat (Rhinolophus rouxi)

The arrangements of F-actin in hair cells and non-sensory cells were studied in paraformaldehyde-fixed cochleae of horseshoe bats and gerbils in several postnatal stages and in the adult. Phallotoxin-labeled midmodiolar cryostat sections of the organ of Corti were analyzed with confocal fluorescence microscopy. In both species, the arrangement of F-actin in the adult organ of Corti was essentially similar to that described in other mammals; however, both species showed their own species-typical specializations in staining of the Deiters cells. In the gerbil, a distinct baso-apical gradient in morphology and staining properties was found in the upper compartment of the Deiters cells. In the bat, F-actin label within the Deiters cups was most pronounced in the basal cochlear turn and less abundant in the apical turns. During the first postnatal week, the sensory epithelium of the gerbil lacked the tunnel of Corti and the spaces of Nuel. Only the reticular lamina and the surface of the greater epithelial ridge were intensely labeled for F-actin. At 9 days after birth (DAB), when the tunnel of Corti and the inner spiral sulcus were formed, the footplates of Deiters and pillar cells and the apices of pillar cells began to show intense F-actin label. At 12 DAB, corresponding to onset of hearing, F-actin staining was found throughout the supporting cell bodies, but was less intense than in the adult. The specialized upper compartment of the Deiters cells differentiated around 15-20 DAB. In the neonate bat, gross-morphology of the organ of Corti was almost adult-like, but only the reticular lamina and the head- and footplates of pillar cells showed intense F-actin staining. The F-actin cytoskeleton of the Deiters cells bodies was poorly developed. At the onset of hearing (between 3rd and 5th DAB), supporting cells showed only a slight increase of F-actin mainly at mechanically important cell regions, namely the Deiters cups, the contact zone of pillar headplates and the footplates of supporting cells. The most intense increase of F-actin occurred between onset of hearing and 16 DAB. At 16 DAB, the F-actin distribution within the supporting cells was similar to the adult. In both species, there were no clear baso-apical gradients in development of F-actin patterns. It is proposed that F-actin insertion in supporting cells after the onset of hearing contributes to maturation of cochlear function.

Cytoskeletal and calcium-binding proteins in the mammalian organ of Corti: cell type-specific proteins displaying longitudinal and radial gradients

Whole mounts and tissue sections of the organ of Corti from two representative mammalian species, the Mongolian gerbil (Meriones unguiculatus) and the guinea pig (Cavea porcellus) were probed with antibodies to cytoskeletal and calcium-binding proteins (actin, tubulin, including post-translational modifications, spectrin, fimbrin, calmodulin, parvalbumin, calbindin, S-100 and calretinin). All of the proteins tested were expressed in both species. New findings include the following. Actin is present in large accumulations in cell bodies of the Deiters cells under the outer hair cells (OHC), as well as in the filament networks previously described. These accumulations are more prominent in the apical turns. Tubulin is present in sensory cells in the tyrosinated (more dynamic) form, while tubulin in the supporting cells is post-translationally modified, indicating greater stability. Fimbrin, present in the stereocilia of both IHCs and OHCs, is similar to the isoform of fimbrin found in the epithelial cells of the intestine (fimbrin-I), which implies that actin bundling by fimbrin is reduced in the presence of increased calcium. Parvalbumin appears to be an IHC-specific calcium-binding protein in the gerbil as well as in the guinea pig; labeling displays a longitudinal gradient, with hair cells at the apex staining intensely and hair cells at the base staining weakly. Calbindin displays a similar longitudinal gradient, with staining intense in the IHCs and OHCs at the apex and weak to absent in the base. In the middle turns of the guinea pig cochlea, OHCs in the first row near the pillar cells lose immunoreactivity to calbindin before those in the second and third rows. Calmodulin is found throughout the whole cochlea in the IHCs and OHCs in the stereocilia, cuticular plate, and cell body. Calretinin is present in IHCs and Deiters cells in both species, as well as the tectal cell (modified Hensen cell) in the gerbil. S-100 is a supporting cell-specific calcium-binding protein which has not been localized in the sensory cells of these two species. The supporting cells containing S-100 include the inner border, inner phalangeal, pillar, Deiters, tectal (in gerbil) and Hensen cells, where labeling displays a longitudinal gradient decreasing in intensity towards the apex (opposite to what has been seen with labeling for other proteins in the cochlea).

Post-translational modifications of tubulin suggest that dynamic microtubules are present in sensory cells and stable microtubules are present in supporting cells of the mammalian cochlea

Post-translational modifications to tubulin in the sensory and supporting cells of the cochlea were studied using antibodies specific to the tyrosinated, detyrosinated, acetylated and polyglutamylated isoforms. In the sensory cells, microtubules which label intensely with antibodies to tyrosinated tubulin are found in networks within the cytoplasm. Microtubules which label with antibodies to detyrosinated tubulin and polyglutamylated tubulin, but not acetylated tubulin, form a small component of the microtubules found in the cytoplasm only in the region below the cuticular plate. Microtubules in the supporting cells (inner and outer pillar cells and Deiters cells) are arranged in bundles and contain little tyrosinated tubulin. They are composed instead of predominantly post-translationally modified isoforms which include detyrosinated, acetylated and polyglutamylated tubulin. The findings suggest that microtubules in the sensory cells form dynamic structures, since microtubules that undergo cyclic polymerization and depolymerization predominantly contain tubulin that has not yet had its carboxy-terminal tyrosine residue removed. The presence of microtubules in the supporting cells in which the tubulin has been polymerized into microtubules long enough to be post-translationally modified, provides evidence that these microtubules are stable, long-lived and could contribute to the structural support of the sensory organ of Corti.

Formation of two microtubule-nucleating sites which perform differently during centrosomal reorganization in a mouse cochlear epithelial cell

This report provides evidence for the formation of a cell surface-associated centrosome with two spatially discrete microtubule-nucleating sites that perform differently; the minus ends of microtubules remain anchored to one site but escape from the other. Centrosomal reorganization in the cells in question, outer pillar cells of the organ of Corti, indicates that its pericentriolar material becomes intimately associated with the plasma membrane at the two nucleating sites. Two large microtubules bundles assemble in each cell. A beam which includes about 1,300 microtubules spans most of the cell apex. It is positioned at right angles to a pillar with about 4,500 microtubules which is oriented parallel to the cell's longitudinal axis. The beam's microtubules elongate from, and remain attached to, a centrosomal region with two centrioles which acts as a microtubule-nucleating site. However, the elongating microtubules do not radiate from the immediate vicinity of the centrioles. During beam assembly, the minus ends of the microtubules are concentrated together close to the plasma membrane (less than 0.2 micron away in many cases) at a site which is located to one side of the cell apex. High concentrations of the pillar's microtubules elongating from one particular site have not been detected. Analyses of pillar assembly indicate that the following sequence of events occurs. Pillar microtubules elongate from an apical cell surface-associated nucleating site, which becomes more distantly separated from the centriolar locality as cell morphogenesis progresses. Microtubules do not accumulate at this apical nucleating site because they escape from it. They migrate down to lower levels in the cell where the mature bundle is finally situated and their plus ends are captured at the cell base.

Three microtubule-organizing centres collaborate in a mouse cochlear epithelial cell during supracellularly coordinated control of microtubule positioning

Large cell surface-associated microtubule bundles that include about 3,000 microtubules assemble in certain epithelial cells called inner pillar cells in the mouse organ of Corti. Microtubule-organizing centres (MTOCs) at both ends and near the middle of each cell act in concert during control of microtubule positioning. In addition, the three cell surface-associated microtubule-organizing centres are involved in coordinating the connection of bundle microtubules to cytoskeletal components in neighbouring cells and to a basement membrane. The precisely defined locations of the three MTOCs specify the cell surface regions where microtubule ends will finally be anchored. The MTOCs are modified as anchorage proceeds. Substantial fibrous meshworks assemble at the surface sites occupied by the MTOCs and link microtubule ends to cell junctions. This procedure also connects the microtubule bundle to cytoskeletal arrays in neighbouring cells at two of the MTOC sites, and to the basilar membrane (a substantial basement membrane) in the case of the third site. A fourth meshwork that is not positioned at a major MTOC site is involved in connecting one side of the microtubule bundle to the cytoskeletons of two other cell neighbours. The term surfoskelosome is suggested for such concentrations of specialized cytoskeletal materials and junctions at cell surface anchorages for cytoskeletal arrays. The large microtubule bundle in each cell is composed of two closely aligned microtubule arrays. Bundle assembly begins with nucleation of microtubules by a centrosomal MTOC that is attached to the apical cell surface. These microtubules elongate downwards and the plus ends of many of them are apparently captured by a basal MTOC that is attached to the plasma membrane at the bottom of the cell. In the lower portion of the cell, the microtubule bundle also includes a basal array of microtubules but these elongate in the opposite direction. This investigation provides evidence that they extend upwards from the basal MTOC to be captured by a medial MTOC which is attached to the plasma membrane and situated near the mid-level of the cell. However, there are substantial indications that the basal array's microtubules are also nucleated by the apically situated centrosomal MTOC, but escape from it, and are translocated downwards for capture of their plus ends by the basal MTOC. If this is the case, then these microtubules continue to elongate after translocation and extend back up to the medial MTOC, which captures their minus ends.

Neurofilament proteins form an annular superstructure in guinea-pig type I vestibular hair cells

Neurofilaments, the neuron-specific intermediate filaments, are composed of three immunochemically distinct subunits: NF-L, NF-M and NF-H that can be either phosphorylated or unphosphorylated. In mammals, the distribution of these subunits has been described in vestibular ganglion neurons, but there are no reports on the presence of neurofilaments in vestibular hair cells. We investigated, by immunocytochemistry, neurofilaments in vestibular hair cells from rat and guinea-pig using antibodies against the three subunits and to dephosphorylated NF-H (clone SMI 32, recognizes also NF-M on immunoblots), on Vibratome sections of the vestibular end-organs and on isolated hair cells. Various immunostaining protocols were used, as appropriate for the method of observation: laser scanning confocal microscopy (immunofluorescence) and transmission electron microscopy (immunoperoxidase, pre-embedding technique). In rat and guinea-pig cristae and utricles, neurofilament immunoreactivity was observed in axons inside and below the sensory epithelia. In guinea-pig, in addition to this staining, intensely immunoreactive annular structures were found in the basal regions of hair cells. These rings were detected with anti-NF-L, -NF-M and -dephosphorylated NF-H/M antibodies, but not with anti-phosphorylation-independent NF-H. Ring-containing hair cells were present in all regions of the sensory epithelia but were more abundant in the peripheral areas. All levels of observation (Vibratome and thin sections, and isolated hair cells) showed that only the guinea-pig type I hair cells contained a neurofilament ring. High-resolution observations showed that the ring was located below the nucleus, often close to smooth endoplasmic reticulum and the cell membrane.

F-actin, tubulin and spectrin in the organ of Corti: comparative distribution in different cell types and mammalian species

Laser scanning confocal microscopy was used to determine the distribution of actin, spectrin and tubulin in whole mounts of the organ of Corti of guinea pig, monkey, rat and chinchilla. Actin, spectrin and tubulin were localized in all cell types in the auditory epithelium. No specialized cytoskeletal organization of tubulin was detected in the cytoplasmic domain of hair cells. The only specialized organization of actin and spectrin in the cytoplasmic domain was the infra-cuticular network, found exclusively in apical guinea pig outer hair cells. In contrast, the lateral wall of inner and outer hair cells contained a homogeneous distribution of label specific for actin and spectrin. The label intensity was similar in the base and the apex of the cochlea. These results indicate that the distribution of spectrin and actin in the auditory epithelium is similar to that in other epithelial cells, suggesting that actin and spectrin participate in the formation of cellular shape and possibly in docking molecules to the membrane.

Reorganization of the centrosome and associated microtubules during the morphogenesis of a mouse cochlear epithelial cell

Reorganization of centrosomal microtubule-organizing centres and the minus ends of microtubules occurs as the centrosomal ends of large microtubule bundles are repositioned and anchored to cell junctions in certain epithelial cells called inner pillar cells in the mouse organ of Corti. The microtubule bundle that assembles in each cell consists of two distinct microtubule arrays that run closely alongside each other. Both arrays are attached to the cell surface at their upper and lower ends. One of the arrays spans the entire length of a cell but the other is confined to its lower portion. Initially, about 3,000 microtubules elongate downwards from an apically situated centrosome in each cell. Subsequently, the minus ends of these microtubules, and the centrosome and its two centrioles, migrate for about 12 microns to the tip of a laterally directed projection. Then, a meshwork of dense material accumulates to link microtubule minus ends and the centrosome to cell junctions at the tip of the projection. Pericentriolar satellite bodies, which form after the initial burst of microtubule nucleation, may represent a condensed and inactive concentration of microtubule-nucleating elements. Surprisingly, as a cell matures, about 2,000 microtubules are eliminated from the centrosomal end of the microtubule bundle. However, about 2,000 microtubules are added to the basal portion of each bundle at levels that are remote with respect to the location of the centrosome. Possibly, these microtubules have escaped from the centrosome. If this is the case, then both the plus and minus ends of most of the errant microtubules are captured by sites at the cell surface where the ends are finally anchored. Alternatively, each cell possesses at least one other major microtubule-nucleating site (which does not possess centrioles) in addition to its centrosome.

Cytoskeletal polypeptides: cell-type specific markers useful in investigative otorhinolaryngology

In the last decade, it has been established that eukaryotic cells possess a cytoskeleton, i.e. an integrated cytoplasmic network of microfilaments (MFs), microtubules (MTs) and intermediate filaments (IFs). Moreover, certain cell membrane specializations as well as the inner lamina of the nuclear membrane also participate in the cytoskeletal structure. Although this definition of the cytoskeleton is up to date it is obvious that the future course of cell biology will be reflected in a revised definition. While the bulk of structural polypeptides involved were characterized at regular intervals, surprisingly, the function of the cytoskeleton remained largely speculative and is still less precisely defined. The most widely postulated function concerns mechanical support and integration of diverse cellular activities and thus refers to cellular architecture. Briefly, the mechanical function is thought to involve cell movement, adhesive interaction with the extracellular matrix and neighbouring cells, as well as the stabilization of cell shape. The integrative function refers to intracellular movement, i.e. transport and positioning to the appropriate locations of organelles, intracellular particles, RNA and proteins. It has been established from numerous investigations that (certain) cytoskeletal polypeptides provide significant information about the cellular origin and differentiation state. This consideration constitutes the most prominent reflection underlying this review. Furthermore, this appreciation encourages additional efforts to explore these markers in normal and pathological conditions. The first purpose of this review is briefly to summarize our present comprehension of the molecular components of the cytoskeleton, restricted to the filamentous trinity for practical reasons. The second and main aim is to survey the field with respect to otorhinolaryngology-related issues. To the author's knowledge, this has not been dealt with in the past. In bridging this gap in the literature, I hope to provoke additional interest in one of the fastest moving areas of cell biology. A comprehensive review covering the whole cytoskeleton has been covered by Preston et al. (The Cytoskeleton and Cell Motility. Blackie, Glasgow and London, 1990, pp. 7-69, 188-191). Additional information on the participating substructures is provided in the text, inclusive of last year's reviews.

Cytokeratin expression in normal and (pre)malignant head and neck epithelia: an overview

Intermediate filament proteins (IFPs) are important markers of tissue differentiation and have been receiving increasing interest, in particular, through their applicability in the characterization of malignant tumors. Cytokeratins (Cks) are a family of IFPs that are typically specific for epithelial cells. They are expressed in certain combinations depending on the type of epithelium and the degree of differentiation. This review presents a critical analysis of the available data on Ck expression in normal and (pre) neoplastic epithelia of the head and neck region. Special attention is paid to technical and cell biologic pitfalls, which can lead to false-negative or false-positive data. It appears that only a limited fraction of the reported data contributes substantially to our knowledge of IFP expression in head and neck cancer because of the use of ill-defined, often formalin-fixed and paraffin-embedded, tissue specimens, and the application of limited panels of monoclonal antibodies. It is concluded that the use of immunocytohistochemistry is promising for the differential diagnosis of head and neck tumors and contributes to our knowledge on their biologic behavior. However, documentations of more complete Ck expression patterns of normal and (pre)malignant epithelium are required, together with their correlation to clinical parameters.

Immunocytochemical localization of intermediate filaments in the guinea pig vestibular periphery with special reference to their alteration after ototoxic drug administration

The present study examined the immunocytochemical localization of various intermediate filaments (IFs), 68 kDa, 160 kDa and 200 kDa neurofilament protein (NFP), cytokeratin (CK) 1, 8, 10 and 19, vimentin, and glial fibrillary acidic protein (GFAP) in the vestibular end-organs and ganglia of normal and streptomycin-treated guinea pigs. In normal animals, 68 kDa, 160 kDa and 200 kDa NFP were found in afferent nerve fibers and nerve terminals (probably nerve chalices). Fine nerve fibers (probably efferent and/or sympathetic nerve fibers) were also immunoreactive to NFP. In the vestibular ganglia, 68 kDa and 160 kDa NFP were predominantly distributed in larger cells, whereas 200 kDa NFP was also found in some small ganglion cells. Cytokeratin 8 and 19 were located in supporting cells, transitional cells, dark cells of vestibular end-organs, and the epithelial cell lining of the membranous labyrinth. Vimentin was observed in the hair cells distributed in the central region of the end organs, supporting cells, most connective tissue cells, and Schwann cells of the vestibular ganglion. Although GFAP-like immunoreactivity was evident in glial cells of the proximal vestibular nerve, no immunoreactivity was detected in the distal portion of the vestibular nerve, vestibular ganglion, or vestibular end-organs. These highly distinct staining patterns of IFs indicated that they may play different roles in the different cell types, and that they may serve as a specific marker for each cell type. In streptomycin-treated guinea pigs, immunoreactivities for NFP and vimentin (found in the hair cells) decreased after treatment, whereas immunoreactivities for the other IFs were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein gene product 9.5 in the developing cochlea of the rat: cellular distribution and relation to the cochlear cytoskeleton

Protein gene product 9.5 was immunolocalized in the adult and early postnatal (P2-P15) rat cochlea, and its distribution compared with a 200 kDa highly phosphorylated neurofilament subunit (neurofilament 200) and alpha-tubulin. In the adult, Protein gene product 9.5 was expressed exclusively in cochlear nerve fibres and ganglion cells, a small percentage of these (Type II ganglion cells and olivocochlear bundle fibres) being intensely positive for both protein gene product and neurofilament 200. In postnatal development, pillar and Deiters' cells were at first (P2-P15) strongly positive for protein gene product 9.5, and hair cells moderately so. At P2, all nerve fibres and ganglion cells showed co-expression of protein gene product 9.5 and neurofilament 200, but at later stages, the subset of intensely co-labelled neurons appeared, nerve fibres at P7 onwards and ganglion cells from P12. There was no overt correlation between the onset of protein gene product 9.5 and alpha-tubulin expression in any cochlear component. Protein gene product 9.5 expression in ganglion cells was at first (P2 and P7) mainly nuclear, and later also cytoplasmic. It is concluded that there is a clear correlation of high levels of protein gene product 9.5 and neurofilament protein expression, and that protein gene product 9.5 is expressed in some non-neuronal cells of the cochlea during its early development, persisting until after hearing has commenced.

Characterization of marginal and Claudius' cells growing from cochlear explants in vitro

Tissue specimens of stria vascularis together with spiral ligament were transferred from the guinea pig cochlea to tissue culture dishes. To characterize and identify cells growing out from the explants, indirect immunofluorescence microscopy was used. The expression of the intermediate-sized filaments vimentin and cytokeratin 18 in cells on the surface of tissue specimens and in cells growing out from the explants after different cultivation periods were compared. Basically, three types of cells grew from the explants during several days: marginal cells, Claudius' cells and fibroblast-like cells. In primary cultures of explants, growth of marginal cells was observed in 25% of the dishes. Their proliferative activity, estimated by the use of the BrdUrd-DNA antibody, started in the stria vascularis and continued across the attachment of Reissner's membrane down to the bottom of the cell culture dish. The newly-formed marginal cells expressed cytokeratin 18 in the same way that original marginal cells on the tissue specimen do. If the newly-formed marginal cells were in contact with fibroblast-like cells or were forming groups (domes) on the bottom, they expressed vimentin. In 3% of the dishes growth of Claudius' cells was observed. Proliferative activity of these cells was found at the point where the basilar membrane was attached to the spiral ligament. New Claudius' cells spread at the opposite side of an explant when compared with the location of new marginal cells. Original as well as newly-formed Claudius' cells contained cytokeratin 18. Fibroblast-like cells were commonly present in cultures and contained only vimentin.

Developmentally-regulated coexpression of vimentin and cytokeratins in the rat inner ear

In the present study the expression of vimentin-type intermediate filament proteins and cytokeratins was studied immunohistochemically in the rat inner ear from 12 days postconception up to 40 days after birth. With the use of a broad spectrum monoclonal antibody, cytokeratin expression was found to be present in the whole epithelial lining except for the sensory cells, throughout all the developmental stages examined. Vimentin was detected in the mesenchymal cells, the mesenchyme-derived tissues and the intermediate cells of the stria vascularis, confirming their origin from melanocyte precursor cells. In addition, the coexpression of vimentin and cytokeratins in the epithelial lining of the membranous inner ear was found to be developmentally regulated. During the final stages of differentiation, vimentin expression disappeared from the majority of the cell types. In the mature cochlea the coexpression of vimentin and cytokeratins was still found in the supporting cells of the organ of Corti, in the cells of Claudius and in external sulcus cells. As far as we could conclude from this study, the sensory cells showed only vimentin expression but not cytokeratin expression. A possible relationship between vimentin expression in adult epithelial cells of the inner ear and a specialised function of these cells is discussed.