Carbohydrates detected by lectins in the vestibular organ

The role of SLC26A4 in bony labyrinth development and otoconial mineralization in mouse models

Inner ear malformations are predominantly attributed to developmental arrest during the embryonic stage of membranous labyrinth development. Due to the inherent difficulty in clinically assessing the status of the membranous labyrinth, these malformations are diagnosed with radiographic imaging, based on the morphological characteristics of the bony labyrinth. While extensive research has elucidated the intricacies of membranous labyrinth development in mouse models, comprehensive investigations into the developmental trajectory of the bony labyrinth, especially about its calcification process, have been notably lacking. One of the most prominent types of inner ear malformations is known as incomplete partition (IP), characterized by nearly normal external cochlear appearance but pronounced irregularities in the morphology of the modiolus and inter-scalar septa. IP type II (IP-II), also known as Mondini dysplasia, is generally accompanied by an enlargement of the vestibular aqueduct and is primarily attributed to mutations in the SLC26A4 gene. In the case of IP-II, the modiolus and inter-scalar septa of the cochlear apex are underdeveloped or missing, resulting in the manifestation of a cystic structure on radiographic imaging. In this overview, we not only explore the normal development of the bony labyrinth in mice but also present our observations on otolith mineralization. Furthermore, we investigated the specifics of bony labyrinth and otolith mineralization in Slc26a4-deficient mice, which served as an animal model for IP-II. We ensured that these findings promise to provide valuable insights for the establishment of therapeutic interventions, optimal timing, targeted sites, and preventive measures when considering the management of this condition.

BODIPY-Conjugated Xyloside Primes Fluorescent Glycosaminoglycans in the Inner Ear of Opsanus tau

We report on a new xyloside conjugated to BODIPY, BX and its utility to prime fluorescent glycosaminoglycans (BX-GAGs) within the inner ear in vivo. When BX is administered directly into the endolymphatic space of the oyster toadfish (Opsanus tau) inner ear, fluorescent BX-GAGs are primed and become visible in the sensory epithelia of the semicircular canals, utricle, and saccule. Confocal and 2-photon microscopy of vestibular organs fixed 4 h following BX treatment, reveal BX-GAGs constituting glycocalyces that envelop hair cell kinocilium, nerve fibers, and capillaries. In the presence of GAG-specific enzymes, the BX-GAG signals are diminished, suggesting that chondroitin sulfates are the primary GAGs primed by BX. Results are consistent with similar click-xylosides in CHO cell lines, where the xyloside enters the Golgi and preferentially initiates chondroitin sulfate B production. Introduction of BX produces a temporary block of hair cell mechanoelectrical transduction (MET) currents in the crista, reduction in background discharge rate of afferent neurons, and a reduction in sensitivity to physiological stimulation. A six-degree-of-freedom pharmacokinetic mathematical model has been applied to interpret the time course and spatial distribution of BX and BX-GAGs. Results demonstrate a new optical approach to study GAG biology in the inner ear, for tracking synthesis and localization in real time.

Molecular organization and fine structure of the human tectorial membrane: is it replenished?

Auditory sensitivity and frequency resolution depend on the physical properties of the basilar membrane in combination with outer hair cell-based amplification in the cochlea. The physiological role of the tectorial membrane (TM) in hair cell transduction has been controversial for decades. New insights into the TM structure and function have been gained from studies of targeted gene disruption. Several missense mutations in genes regulating the human TM structure have been described with phenotypic expressions. Here, we portray the remarkable gradient structure and molecular organization of the human TM. Ultrastructural analysis and confocal immunohistochemistry were performed in freshly fixed human cochleae obtained during surgery. Based on these findings and recent literature, we discuss the role of human TMs in hair cell activation. Moreover, the outcome proposes that the α-tectorin-positive amorphous layer of the human TM is replenished and partly undergoes regeneration during life.

Morphological and biochemical analyses of otoliths of the ice-fish Chionodraco hamatus confirm a common origin with red-blooded species

The morphology and composition of the three otoliths of the Antarctic ice-fish Chionodraco hamatus were studied by scanning electron microscopy and X-ray diffraction. The composition of the sagitta, lapillus and asteriscus protein matrices was also analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, western blots and confocal laser scanning microscopy to reveal the presence of and to localize the calcium-binding proteins calmodulin, calbindin and S-100. Morphological results indicated that the otoliths in this ice-fish were similar to those of Trematomus bernacchii, a red-blooded Antarctic species [B. Avallone et al. (2003) J. Submicrosc. Cytol. Pathol. 35, 69-76], but rather different from those of other teleosts. These two Antarctic species possessed a completely vateritic asteriscus, whereas their sagitta and lapillus were made mostly of aragonite. Parallel analysis of protein patterns in C. hamatus and T. bernacchii revealed that the sagitta significantly differed from the lapillus and asteriscus in both species. The sagitta did not contain the S-100 protein and showed calmodulin and calbindin located in discontinuous or incremental zones, respectively. These results demonstrate that the otoliths of C. hamatus and T. bernacchii share more resemblances than differences and support the idea of a common origin of these species.

Localization of calbindin D-28K in the otoconia of lizard Podarcis sicula

The membranous labyrinth of lizard Podarcis sicula contains calcite and aragonite crystals. Saccule, utricle and lagena contain calcite crystals while aragonite crystals are present only in the saccule where they are very abundant. We have recently demonstrated the presence of calbindin D-28K in the organic matrix of lizard P. sicula otoconia. In order to define its localization, since calbindin modulates cellular Ca2+ level, otoconia from utricle and lagena were collected separately from those from saccule and then otoconial proteins were extracted. Immunoblot assay on proteins extracted from the otoconia and confocal laser scanning microscope analyses of otoconia using monoclonal anti-calbindin D-28K antibodies indicated that calbindin D-28K is a protein typical of aragonite crystals.

Calbindin D28K is a component of the organic matrix of lizard Podarcis sicula otoconia

The factors controlling otoconia growth are not well known but it seems that the type of proteins contained in the otoconia regulates the initiation and/or the subsequent rates of crystal growth determining the morphology and the size of the final crystal. In order to clarify the mechanism of otoconia formation and their turnover, major proteins contained in the otoconia from the maculae of the saccule, utricle and lagena of inner ear of lizard Podarcis sicula were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Coomassie staining of SDS-PAGE resulted in a major broad band of 15 kDa and four other bands of 21, 28, 45 and 97 kDa. The proteins of 15, 21, 28 and 45 kDa were separated by high-pressure liquid chromatography on a C-4-reverse-phase column and the incubation of blots with monoclonal anti-Calbindin D28K antibodies indicated that the band of 28 kDa was Calbindin D28K, a calcium-binding protein.

Structural basis for mechanical transduction in the frog vestibular sensory apparatus: III. The organization of the otoconial mass

The saccule and the utricle of the vestibular system detect linear acceleration and gravity. Sensory transduction in these organs depends on myriads of calcium carbonate crystals of high specific gravity, called otoconia, embedded in a filament matrix that overlies the sensory epithelium. The coexistence of hard crystals and slender filaments in this complex extracellular matrix makes it difficult to analyze by conventional electron microscopy. We have now examined this structure in the bullfrog saccule using the quick-freeze, deep-etch replica technique. The otoconia in their typical aragonite polymorph shape exhibit smooth surfaces and are embedded in a loose matrix made of two types of filaments. The regular surface of the otoconia forms a natural smooth background against which we could observe with unprecedented detail the network organization and substructure of the filaments. One type of filament is 8 nm in diameter, while the other, which has a characteristic beaded appearance, is 15 nm in diameter. Both types of filaments either make lateral connections with or end directly on the surface of the otoconia. A consistent observation was the presence of short filaments that directly cross-link adjacent otoconia. Very few otoconia were fractured in an orientation that would allow the study of their internal architecture. These otoconia presented a typical conchoidal cleavage of aragonite. Although crystallites were not clearly apparent, thin lamellar microstructures appeared oriented both perpendicularly and longitudinally to the major otoconial axis. This structural study establishes a framework for the identification of the molecular components present in this unique extracellular matrix and may also help elucidate their role in mechanical transduction.

The papilla neglecta of turtles: a detector of head rotations with unique sensory coding properties

The turtle papilla neglecta (PN) is a small organ lying in the ventrolateral utricular wall between the posterior crista (PC) and the utriculosaccular foramen. Innervated by a branch of the posterior ampullary nerve, the organ is covered by a cupula extending only a small distance into the endolymphatic space. Although most rotation-sensitive units in the posterior division of the eighth nerve have sensory coding properties expected of PC fibers, a few have unique properties. Intra-axonal labeling studies show that the former are PC units and the latter are PN units. PC units are maximally responsive to head rotations in the posterior canal plane and are sensitive to a combination of angular velocity and angular acceleration. PN units respond maximally to pitch rotations and are sensitive to a combination of angular acceleration and angular jerk. A maximal response to pitches can be related to the location of the PN, which allows it to sample endolymph flow from both vertical semicircular canals. Differences in response dynamics may reflect macromechanics. Because the cupula of each vertical canal occludes the endolymphatic space, its displacement should be proportional to endolymph displacement. In contrast, the PN cupula is probably coupled to endolymph flow by viscous forces, in which case its displacement should be proportional to endolymph velocity. In many vertebrates, the PN is similar to that seen in turtles in its location and in the size and shape of its cupula, which suggests that its function in these other species is also similar.

Inner ear content of glycosaminoglycans as shown by monoclonal antibodies

Inner ear cells are known to contain combinations of proteins and sugar, which histochemically have been identified to be proteoglycans. To visualize these components in the macula utriculi, crista ampullaris and in the cochlea four different monoclonal antibodies against hyaluronan (HA), keratan sulphate (KS), chondroitin-6-sulphate (C-6-S) and chondroitin-4-sulphate (C-4-S) were used. The results indicate that KS is predominantly present in the lining of the vestibular hair cells, in the otoconial layer and in nerve tissue. C-4-S is present in the sensory hairs as well as in the subepithelial layer but also in the tectorial and basilar membranes of the cochlea. HA is generally present in the surface area of vestibular hair cells, to some extent in the cochlear hair cells and in the stria vascularis. C-6-S is only present to a lesser degree in the inner ear.

Time-dependent alterations of 3-fucosyl-N-acetyl-lactosamine (CD15) expression in the endolymphatic sac of adult guinea pigs after glycerol administration

The present study examined the effect of glycerol administration on 3-fucosyl-N-acetyl-lactosamine (CD15) epitope expression in the endolymphatic sac (ES) of the guinea pig's inner ear. Adult guinea pigs were injected intravenously with glycerol (2 g/kg body wt.). CD15 expression was studied at 80 min up to 5 h after treatment. In untreated animals single cells and cell groups in the ES expressing CD15 epitope intra- and intercellularly were identified by immunohistochemistry to be mainly in the epithelial layer of the rugosal and distal part of the sac. Glycerol administration modulated the expression of CD15 epitope. In the epithelial layer, expression decreased and was nearly depleted after 3 h. After 4 h of glycerol administration, CD15 expression reappeared and reached the comparable level of controls. The numbers of CD15-positive cells in the lumen of the ES increased steadily and arrived at their the highest levels in 2-h specimens. The localization of CD15-epitope expression and its modulation after glycerol administration within the ES implies that this molecule may play a role in re-establishing the sac's normal function. In addition, we speculate that CD15 may be associated with processes of an immune response in the inner ear.

Carbohydrate distribution in the living utricular macula of the guinea pig detected by lectins

Carbohydrate distribution in the fresh utricular macula of the guinea pig was analysed using lectins such as Concanavalin A (ConA), Dolichos biflorus agglutinin (DBA), peanut agglutinin (PNA), soybean agglutinin (SBA), Ulex europeus agglutinin (UEA-1) and wheat germ agglutinin (WGA) by means of confocal laser scanning microscopy. The ciliary bundle was strongly reactive to ConA, PNA, SBA and WGA but not to DBA and UEA-I, showing that the ciliary bundle has abundant D-galactose (GaI), N-acetyl-D-glucosamine (GlcNAc), D-mannose (Man) and sialic acid(s) (Sia) but not detectable amounts of L-fucose (Fuc) and terminal N-acetyl-D-galactosamine (GalNAc). Similar patterns of lectin bindings with moderate-to-weak intensities were observed on the non-cilial apical surface, on the surface of the otoconia and in the gelatinous layer of the otoconial membrane. On the contrary, the globular substance, a precursor of the otoconia, was scarcely reactive to any lectin examined, implying that it lacks glycoconjugates on its surface. Previous histochemical studies reported that the otoconial membrane possesses a much higher affinity for lectins that does the sensory epithelium (including the cilia) in the vestibular organ. This discrepancy suggests that factors in the preparation process may affect the otoconial membrane or the surface coat of the cilia to change their lectin affinity. Meanwhile, sialidase treatment augmented the affinity of the ciliary bundle for DBA and PNA, indicating that sialylated GalNAc and Gal are present on the vestibular ciliary bundle.

Glycolipidic component of the epithelial cell coat of the endolymphatic sac

The endolymphatic sac (ES) is thought to synthesize and secrete glycoconjugates such as sulfated glycoproteins into the endolymphatic lumen. Ganglioside Gm1 is a specialized glycolipid containing one sialic acid molecule, which is generally found in the outer leaflet of the cell membrane. This glycolipid, which is known to be a specific receptor for cholera toxin (CT), acts as a membrane transducer and is involved in the modulation of cell metabolism, growth and regeneration. In the present study we identified Gm1 by studying the distribution of the FITC-labeled CT-subunit B in the ES epithelium of adult guinea pigs. Our findings indicate the presence of this ganglioside in the ES, with a predominant localization in the basolateral aspect of the epithelial cell layer. No detectable differences between ES cell types could be identified, whilst the ES distal and intermediate portions showed more reactivity than the proximal portion. This study, which represents the first description of a lipidic glycoconjugate component in the ES, provides evidence in support of the role of the ES in the turnover and regulation of inner ear fluids.

Localization of osteopontin in the otoconial organs of adult rats

Although it is known that mammalian otoconia consist of calcium bicarbonate and organic materials, none of the protein components have been identified in mammals at the molecular level, and the mechanisms of morphogenesis and calcification of the otoconia is still unclear. In the present study, we demonstrated the presence of osteopontin (OPN) in rat otoconia by using immunohistochemistry, and detected OPN mRNA in the sensory hair cells by a non-radioisotopic in situ hybridization technique. These results indicate that OPN is one of the protein components in rat otoconia and suggest that sensory hair cells are involved in the production of otoconia.

Histochemical detection of glycogen and glycoconjugates in the inner ear with modified concanavalin A-horseradish peroxidase procedures

Inner ears from neonatal and adult Mongolian gerbils were examined to determine developmental changes in the content of glycogen and glycoconjugates as shown by histochemical application of the jack bean lectin, concanavalin A (con A). Sections of fixed paraffin-embedded inner ears were stained using the con A-horseradish peroxidase sequence in conjunction with prior treatments including periodate oxidation with or without subsequent reduction and diastase digestion. In adult inner ear, brief periodate oxidation followed by reduction and con A-horseradish peroxidase staining demonstrated abundant glycogen in Deiters' cells and in fibrocytes of the spiral ligament and submacular plaque. This procedure also detected diastase-resistant glycoprotein, probably containing N-linked complex-type saccharides, in the basal and marginal regions of the tectorial membrane and in the otolithic membrane. During morphogenesis and maturation, various cochlear cells showed changes in their glycogen content possibly related to stage-specific energy requirements. Cellular glycogen storage reached adult levels by postnatal day 14. The tectorial membrane gradually acquired con A reactivity during the first postnatal week. Thus, application of modified con A staining procedures has provided further knowledge for comparison with data from previous biochemical and histochemical studies of carbohydrate-rich components in the inner ear.

Immunocytochemical analysis of a novel carbohydrate differentiation antigen (CDA-3C2) associated with olfactory and otic systems during embryogenesis in the rat

Carbohydrate differentiation antigens are known to display specific patterns of expression during mammalian development and are thought to participate in significant morphogenetic events. In the present study, two monoclonal antibodies that react with a novel carbohydrate differentiation antigen (CDA-3C2) were used to analyze, by light microscopy, the spatiotemporal distribution of this unique high molecular weight antigen during embryogenesis in the rat. Correlative analysis of the development of peripheral neural structures, in which CDA-3C2 was expressed, was carried out with an anti-neurofilament antibody. Enzymatic digestion, combined with Western blots, reveal that the CDA-3C2 epitope is a carbohydrate which is carried on a high molecular weight glycoprotein with a mass of greater than 1 million Daltons. Characteristic of carbohydrate antigens, immunoreactivity was found in several distinct cellular patterns: only along the apical border of cells, along lateral and basal membranes of cells, and extracellular-like staining in the mesenchyme. During neurulation, CDA-3C2 showed differential staining in the ectoderm, distinguishing lateral from neural regions. Following closure of the neural tube, there was a striking specificity of expression of CDA-3C2 in the periphery, found almost exclusively in olfactory and otic epithelial structures. While CDA-3C2 is found in placode-derived tissues that subserve sensory transduction, it appears to be primarily associated with the supportive cells (and their secretions) in both otic and olfactory regions and less so with the sensory cells. The data suggest that a unique carbohydrate antigen on a large macromolecule may play a role in neurulation and/or morphogenesis of the placode-derived otic and olfactory structures.

Immunoelectron microscopic analysis of a novel carbohydrate differentiation antigen (CDA-3C2) in the developing rat olfactory and otic systems

A carbohydrate differentiation antigen (CDA-3C2) exhibits a highly specific and restricted pattern of expression during rat embryogenesis. In the periphery of the embryo, this antigen is associated transiently with the lateral ectoderm but is retained only in the olfactory and otic epithelium throughout morphogenesis. At the light microscopic level, CDA-3C2 immunoreactivity appears mostly along cell periphery and in the extracellular matrix. The aim of the present study was to determine the specific cellular and subcellular distribution of CDA-3C2 in vivo in order to identify potential sites of cellular and tissue function of the antigen during embryogenesis. There was a strikingly similar subcellular distribution of CDA-3C2 in the developing otic and olfactory systems, found mostly along cell membranes, microvillar projections and acellular secretions of the epithelium. Mature sensory components of the epithelia were not immunoreactive, whereas supportive cells and their secreted structures were densely stained. The highly coincident nature of CDA-3C2 in both sensory epithelia suggests that this carbohydrate epitope, and possibly its carrier macromolecule, participate in a morphogenetic function common to these two sensory epithelia.

Histochemical localization of a beta-galactoside-binding lectin and its binding-sites in developing and adult rat cochlea

The presence of an endogenous rat beta-galactoside-specific lectin (S-Lac) and its specific binding ligands was analyzed, using a rabbit anti-human brain lectin of 14 kDa antibody (anti-HBL-14) and a probe consisting of a biotinylated derivative of the human lectin (HBL-biot) in adult and in developing rat cochleas. At PD1, some epithelial cells of the outer spiral sulcus (OSS) were specifically recognized by the anti-HBL-14 antibody. Then, anti-HBL-14 immunoreactivity progressively appeared in all OSS epithelial cells, and, from PD9 on, it also appeared in inner spiral sulcus (ISS) epithelial cells. Finally, young adult rats exhibited a well defined anti-HBL-14 immunoreactivity in epithelial cells of the inner and outer spiral sulcus. Using the biotinylated probe, from PD3 on, tectorial membrane (TM) and the sensory cells apical surfaces were labelled. The glycoconjugate expression within the developing organ of Corti seems to be highly complex. Lectin was detected in developing and adult epithelial cells surrounding the organ of Corti. In contrast, other glycoconjugates related to B and H human blood group antigens, were transiently present on sensory cells of the organ of Corti. Present findings can be correlated with significant events in development of the cochlea, mainly with cell-cell recognition or cellular adhesion.

Glycoconjugates in the vestibular organs as revealed by the silver methenamine method

The glycoconjugates in the vestibular organs of the guinea pig were studied after staining by the silver methenamine method and by the periodic acid-Schiff (PAS) reaction. The organic matrix of otoconia, otolithic membranes and cupulae were stained to the same degree by the PAS reaction. In contrast, the mineralizing and non-mineralizing matrices were clearly distinguished by the silver methenamine method. The otoconia were surrounded by an intensely stained organic matrix, while the otolithic membranes and cupulae were moderately stained. This histochemical difference suggests that the positively stained organic matrix of otoconia is not identical to the otolithic membranes and cupulae in terms of its biochemical composition. The strongly stained material may play an important role in turnover of calcium in otoconia. The contact areas between type I hair cell and nerve calyx were contained silver methenamine-positive material which is probably involved in adhesion of these cell membranes.

Regional differences in lectin binding patterns of vestibular hair cells

Surface glycoconjugates of hair cells and supporting cells in the vestibular endorgans of the bullfrog were identified using biotinylated lectins with different carbohydrate specificities. Lectin binding in hair cells was consistent with the presence of glucose and mannose (CON A), galactose (RCA-I), N-acetylglucosamine (WGA), N-acetylgalactosamine (VVA), but not fucose (UEA-I) residues. Hair cells in the bullfrog sacculus, unlike those in the utriculus and semicircular canals, did not strain for N-acetylglucosamine (WGA) or N-acetylgalactosamine (VVA). By contrast, WGA and, to a lesser extent, VVA, differentially stained utricular and semicircular canal hair cells, labeling hair cells located in peripheral, but not central, regions. In mammals, WGA uniformly labeled Type I hair cells while labeling, as in the bullfrog, Type II hair cells only in peripheral regions. These regional variations were retained after enzymatic digestion. We conclude that vestibular hair cells differ in their surface glycoconjugates and that differences in lectin binding patterns can be used to identify hair cell types and to infer the epithelial origin of isolated vestibular hair cells.

Glucuronic acid-containing glycosaminoglycans occur in otoconia: cytochemical evidence by hyaluronidase-gold labeling

Localization of glucuronic acid-containing glycosaminoglycans in the gerbil utricle was examined, using a hyaluronidase-gold labeling technique with special emphasis on the otoconia. Otoconia and the gelatinous layer of the otoconial membrane were strongly labeled by hyaluronidase-gold. The secretory granules in supporting cells were also strongly labeled, suggesting that the organic matrix of otoconia is secreted from the supporting cells. Otoconia seem to lose labeling while they degenerated. The degenerating otoconia were observed to be absorbed into dark cells. Glucuronic acid-containing glycosaminoglycans occur in otoconia. These glycosaminoglycans may play a crucial role in the formation and degeneration of otoconia.

Quantitative carbohydrate analyses of the tectorial and otoconial membranes of the guinea pig

Carbohydrate composition of the tectorial membrane (TM) and the otoconial membrane (OM) of the guinea pig was analyzed after hydrolysis, using high-performance anion-exchange chromatography and pulsed amperometric detection. Both of the tissues were highly glycosylated; the carbohydrate content being 24-42% of protein. GlcN, Gal, Glc and Man were found to be the major component sugars of TM, whereas little GalN was found. Fuc and NANA were also present, but NGNA was not detectable. After digestion with thermolysin for solubilization, OM was separated into two fractions: insoluble mineral particles of the otoconia (OM-ppt) and a soluble fraction from the gelatinous layer (OM-sup). These two fractions showed distinct carbohydrate composition from each other. Further analyses using glycosidases revealed that TM contained asialyl and monosialyl but little di-, tri- and tetrasialyl N-glycosides, and OM-sup did not seem to be susceptible to endo-beta-galactosidase, which is known to cleave some N-acetyl-polylactosamine and keratan sulfate. Based on these analyses, it can be suggested that most of the carbohydrates in TM are likely to be asialyl and monosialyl N-glycosides. N-Glycosides may be predominant in the otoconia as well, and a polymer structure consisting of GlcN(Ac) and Gal other than N-acetyl-polylactosamine may exist in the gelatinous layer of OM. O-Glycosylation of the usual type appeared to be minor in all the fractions.

Histochemical analysis of glycoconjugates in gelatinous membranes of the gerbil's inner ear

The gelatinous membranes of the gerbil inner ear were analyzed histochemically for glycoconjugates with a battery of twenty horseradish peroxidase-conjugated lectins. Glycoconjugates with mannose (Man) and/or glucose (Glc), galactose (Gal), fucose (Fuc), N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc) and N-acetylneuraminic acid (NeuAc) were detected in the tectorial and otolithic membranes and cupula. Differences in lectin reactivity were observed between tectorial and vestibular membranes and also among zones and between the medial and lateral regions of the middle zone of the tectorial membrane. The distribution of staining differed markedly for several lectins that bind specifically to GalNAc or to GlcNAc but vary in affinity for oligosaccharides containing these sugars in different sequences or linkages. The findings suggest presence of the terminal disaccharides GalNAc alpha 1,3Gal in tectorial membrane and Gal beta 1,3GalNAc in vestibular membranes. Lectin binding profiles provided evidence that the limbal zone's fibrous and attachment layers contain mainly O-glycosidically linked oligosaccharides whereas the middle zone's medial fibrous layer contains both O- and N-linked chains. The remaining regions of the tectorial membrane contain mainly N-linked oligosaccharides with bisected biantennary type chains predominating. Additionally, the marginal band and the middle zone's basal layer contain abundant N-linked oligosaccharides with a triantennary structure.

Glycoconjugates in the human fetal endolymphatic sac as detected by lectins

The distribution of glycoconjugates in the 11 to 16 weeks old human fetal endolymphatic sac (ES) was analyzed using six biotinylated lectins; Wheat germ agglutinin (WGA), Abrus precatorius agglutinin (APA), Ulex europaeus agglutinin I (UEA-I), Ricinus communis agglutinin 120 (RCA120), Helix pomatia agglutinin (HPA), Concanavalin A (ConA). In the 11 week old human fetus, fluorescent reactions with WGA, APA, RCA120 and ConA were detected in the ES. There was almost no reaction with HPA and UEA-I. In the 14 week old human fetus, however fluorescent reactions with HPA and UEA-I appeared. This result suggests that the presence of glycoconjugates changes during the maturation process of the ES. Glycoconjugates detected with HPA were related to the epithelial cell elements of the ES epithelium. The reaction with UEA-I suggests that the stainable substance present in the ES lumen may be secreted locally by the ES itself.

Carbohydrates associated with the cell coat surrounding cells of the rainbow trout saccular macula as revealed by lectin probes

The luminal surface of the saccular macula in the rainbow trout is covered with a glycoconjugate-rich cell coat. The aim of this study was to identify specific carbohydrate moieties present in this coat, using biotinylated lectins as probes. Saccular tissues were fixed in Karnovsky's fixative for 2 h at 1-2 degrees C, followed by incubation with biotinylated lectins for 12-16 h at 25 degrees C. Lectin binding was visualized by performing avidin-biotin-peroxidase reactions. As controls, specimens were reacted with solutions of lectins preincubated with their specific inhibitory sugars. Staining was observed that was consistent with the presence of glucose, galactose, fucose, mannose, N-acetylglucosamine, N-acetylneuraminic acid, and N-acetylgalactosamine in the cell coat. The variability in the intensity of staining associated with the lectin-carbohydrate complexes suggests quantitative differences among the various carbohydrate moieties detected. The presence of these carbohydrates in the cell coat of the trout saccular macula also suggests biochemical similarities between cell coats in teleost and mammalian inner ear structures.

Glycoconjugates in the otolithic organ of the developing chick embryo

The presence of glycoconjugates in the otolithic organ of developing chick embryos was investigated histochemically using lectins. On the 6-day-old chick embryo, intense labelling with lectins was observed in the sensory epithelium, on the surface of the epithelium and on the immature otoconia. The otoconia were intensely labelled with lectins at every stage of the chick embryos, while the labelling with lectins in the sensory epithelium became weaker with the maturing of the otoconia. In TEM observation, the secretory granules of the supporting cells of the sensory epithelium were labelled with lectin. The reaction of lectin was more intense in the electronic dense zone of the otoconium than in the electronic lucent zone at every stage of the chick embryos. These findings indicate that the precursors of the otoconia are secreted by the supporting cells of the sensory epithelium and that glycoconjugates play an important role in otoconial formation.

Carbohydrates in the guinea pig stria vascularis demonstrated with lectin-gold techniques

Soybean agglutinin (SBA), Helix pomatia agglutinin (HPA), Ricinus communis agglutinin-II (RCA-II), Limax flavus agglutinin (LFA) and wheat germ agglutinin (WGA) were employed to determine the localization of specific carbohydrates on thin sections of lowicryl K4M embedded guinea pig striae vasculares using the lectin-gold and glycoprotein-gold techniques. SBA, HPA and RCA-II gold labeling was observed in many of the cytoplasmic vesicles, endosomes and apical tubules located in the supranuclear region as well as on the microvilli and micropinocytotic invaginations of the luminal plasma membrane of the marginal cells. LFA labeling was found on the basal plasma membrane of the marginal cells as well as in the basement membrane of the perivascular spaces. WGA binding sites were detected along the plasma membrane of all types of cells constituting the stria vascularis. Our present results revealed that the membranes of internalization and many of the cytoplasmic vesicles, endosomes and apical tubules in the supranuclear region of the marginal cells are associated together and it is suggested that these structures may be related to the regulation of endolymph.

Proteins of the gelatinous layer of the trout saccular otolithic membrane

Although the otolithic membrane is thought to play an important role in the stimulation of vestibular hair cells, little is known about its chemical composition. We analyzed proteins of the gelatinous layer of this structure from the trout saccule, a probable organ of hearing in fish, by SDS-polyacrylamide gel electrophoresis. A relatively small number of major proteins were detected in homogenates of the 'membrane' layer, with apparent molecular weights ranging from 35 to greater than 300 kDa. Six bands, with molecular weights of 35, 43, 65, 94, 100, and 160 kDa, were particularly prominent. Periodic acid-Schiff (PAS) staining indicated that the 43, 94, 100, and 160 kDa bands were glycoproteins. Lectin binding on nitrocellulose blots confirmed the PAS results, and further suggested that the 35 and 65 kDa bands may be glycoproteins. Incubation of blots with human anti-collagen type II antibodies suggested that the 94 kDa band was a component of collagen type II or a related protein.

[Mechanisms of development of the dome in the semicircular canals of birds. II. Cellular reorganization]

A light microscopic study of the epithelia of the crista ampullaris of the semicircular canals of the embryonic chicken indicates that the epithelial cells undergo irregular degenerative changes, with continual mitotic replacement of surface cells. The cupula develops over the surface epithelia through vesicular secretions containing acidophils fibrillar material mixed with globular formations derived from fragmentation of the surface epithelial cells. Electron microscopic studies demonstrate the mode of secretion of rounded or oval supraepithelial bodies from surface epithelium, contributing to the development of the cupula ampullaris. These observations provide evidence of cytoplasmic contributions of surface epithelial cells of the crista ampullaris contributing to the development and continued reorganization of the cupula ampullaris during embryonic development.

[Mechanisms of development of the dome in the semicircular canals of birds. I. Cellular secretion]

A study of the crista ampullaris of the vestibular apparatus was carried out in chicken embryos. The study group included embryos between stages 24 and 39 of Hamburger-Hamilton. This study elucidates the relationship of the cupula with respect to the epithelium of the crista ampullaris. With electron microscopic examination, the rough endoplasmic reticulum of the crista epithelial sustentacular cells at developmental stage of 31 H-H, demonstrated dilatations containing secretory material. Vesicles, with adhering ribosomes appear to be formed from these dilatations. At later stages of development, the vesicular material took on the characteristics of the fibrillary material composing the cupula. In some cells, secretory vesicles are seen near the apical border of these cells, where they apparently secrete vesicular contents into the endolymphatic space, contributing to the formation of the cupula.

Effect of gentamicin on the carbohydrates of the vestibular end organs: an investigation by the use of FITC-lectins

The effect of gentamicin on the glycoconjugates in the vestibular end organs is demonstrated using FITC-lectins. Five milligrams of gentamicin dissolved in 0.1 ml. saline was injected in a single dose into the middle ear of adult guinea pigs. Seven days after the injection, the fluorescent reactivity of Wheat germ agglutinin (WGA), Abrus precatorius agglutinin (APA), Concanavaline A (Con A), and Latyrus odoratus agglutinin (LOA) was decreased in the apical epithelial cell surface as well as in the gelatinous layer of the otolithic membrane of the maculae. In the cupula of the crista ampullaris, the reactivity for WGA and Con A was reduced. The otoconia, however, showed no detectable changes. This indicates that gentamicin may induce an altered carbohydrate metabolism resulting in a decrease of N-acetyl-glucosamine, mannose, galactose and glucose in the glycocalyx lining the epithelial cells as well as in the gelatinous layer of the otolithic membrane or cupula in the vestibular end organs.

Lectin detection of carbohydrates in the endolymphatic sac

The carbohydrate contents of the guinea pig endolymphatic sac were investigated by the use of lectins. The lumen of the endolymphatic sac was filled with stainable precipitate containing N-acetyl glucosamine, mannose, glucose, galactose and fucose. N-Acetyl galactosamine was also detected but in minute amounts. This composition corresponded to other areas in the inner ear, such as the cupula, the otolithic membrane and the tectorial membrane. The function of these carbohydrates may play an important role in preventing the lumen of the endolymphatic sac from collapsing as well as in regulating transepithelial fluid transport.

Carbohydrate content of the endolymphatic sac. A histochemical and lectin-labelling study in the Mongolian gerbil

A secretory activity has recently been attributed to the endolymphatic sac (ES), as a possible way to contribute to the fluid balance of the entire endolymphatic compartment. Previous histochemical studies have indicated the existence of carbohydrate complexes in the secretory product, both neutral and acidic in nature. A thorough analysis of these compounds in the gerbilline ES was carried out using both transmission electron microscopic (TEM) histochemistry, using dialyzed iron and periodic acid--chromic--silver staining techniques, as well as immunoflourescence with fluorescein-labelled lectins (FITC-lectins). N-acetylglucosamine was found to be one of the major carbohydrate components both of the epithelial layer of the ES and of the luminal precipitate. Proofs for a local secretory activity and its intracellular pathway are presented, suggesting to be involved in the regulation of pressure and volume of inner ear fluids.

Histochemical studies of the vestibular nerve system in the developing chick embryo. Glycoconjugates in the vestibular end organs

Glycoconjugates of the vestibular end organs in the developing chick embryos were well defined and localized using lectins-HRP (WGA, PNA, UEA-1) and HID-AB stains. In spite of the fact that no differentiation of the otic vesicle was seen on the 4-day-old chick embryos, the luminal surface of the otic vesicle was labeled with lectins. The cupula and otoconia were labeled most intensely with lectins on the 6-day-old chick embryos. The reactivity of lectins with the cupula and otoconia was as follows: WGA greater than UEA-1 greater than PNA. As the vestibular end organs had become mature, the epithelial cells of the semicircular duct, utricle and saccule were labeled with lectins. These findings suggest that glycoconjugates play an important role in the development and formation of the vestibular end organs.

Wheat germ agglutinin and Helix pomatia agglutinin lectin binding on cochlear hair cells

The fluorescein labelled lectins FITC-WGA and FITC-HPA were used to identify specific carbohydrates in cochlear hair cells. Wheat germ agglutinin (WGA) bound with the cell coat of both inner and outer hair cells (IHC and OHC) suggesting the presence of either N-acetyl-D-glucosamine or sialic acid. In contrast, glycoconjugates with terminal N-acetyl-D-galactosamine residues that bind with Helix pomatia agglutinin (HPA), were demonstrated inside the plasma membrane of outer hair cells. WGA and HPA lectin binding implies the presence of anionic glycoconjugates that furnish added negative charge on the membranes to which they are fixed. The presence of sialic acid or N-acetyl-D-glucosamine on the extracellular surface of cochlear hair cell plasma membrane is consistent with the normal distribution of these glycoconjugates in the cell coat. The presence of the membrane associated oligosaccharide N-acetyl-D-galactosamine within the outer hair cell is inconsistent with the distribution of glycoproteins in internal membrane systems of other cell types.

Appearance and distribution of neuron-specific enolase and calbindin (CaBP 28 kDa) in the developing human inner ear

The onset and development of neuron-specific enolase (NSE) and calbindin immunoreactivities were studied in the inner ear of human fetuses aged from 6-7 to 14 weeks of gestation. NSE occurred very early in ganglion neurons. Its appearance in vestibular sensory cells at 8 weeks coincided with the formation of the first afferent synapses, and showed an apex/base gradient in the cristae. Calbindin was found in vestibular ganglion neurons at 6-7 weeks and in the cochlear ganglion neurons at 8-9 weeks. Vestibular sensory cells and the whole ventral wall of the cochlear duct were stained from 8-9 weeks. At 14 weeks, calbindin staining occurred only in the sensory cells of the cochlear neuroepithelium. Non-neuronal secretory structures, i.e. Kölliker's organ and some cells of the transitional zone of the utricle, were also reactive. Staining appeared in Kölliker's organ with a base to apex gradient and disappeared from it with an internal to external gradient. Calbindin appeared in vestibular sensory cells later than NSE staining, synapse formation and sensory hair bundle differentiation. By contrast in the cochlea, calbindin staining appeared in the neuroepithelium before sensory cell differentiation, but remained only in the hair cells after they had differentiated and been contacted by the afferent fibers.

Calbindin (CaBP 28 kDa) appearance and distribution during development of the mouse inner ear

Previous reports of the distribution of calbindin, a 28 kDa vitamin D-induced calcium-binding protein, in the mammalian peripheral vestibular system postulated that this protein was involved in the calcium-dependent mechanisms occurring in the hair cells and ganglion cells. In this study, we examined the possibility of a relationship between the presence of calbindin and neurotransmission by comparing calbindin appearance in the inner ear to the sequence of synaptogenesis. Calbindin distribution was studied by immunocytochemistry, in the developing mouse inner ear from gestational day 12 to postnatal day 40. During the early development, calbindin was localized in non-neuronal structures: Kolliker's organ, spiral limbus and crista supporting cells; and in cochlear and vestibular ganglion neurons and sensory cells. At later stages and in the adult, no reactivity was observed in the non-neuronal cell populations and only certain sensory and nerve cells remained stained: inner hair cells, outer hair cells, vestibular hair cells of the apex of the cristae and of the striola in the maculae, all Corti's ganglion neurons and some vestibular ganglion neurons. The sequence of appearance of calbindin immunoreactivity in the sensory and nerve cells was not completely parallel to the maturation sequence of the inner ear, especially synaptogenesis. The dual distribution of calbindin during development and its expression in specific sensory and nerve cells opens new perspectives on its role in the inner ear.

Cupulogenesis and glycoconjugates in the labyrinthine ampulla as revealed by WGA-gold labeling

We studied the distribution of wheat germ agglutinin (WGA)-bindable glycoconjugates in the vestibular ampulla of mongolian gerbils. WGA was conjugated with gold particles and applied to Lowicryl K4M sections of the ampulla. WGA-binding sites were found on the cupula and some of the secretory granules and Golgi apparatuses in the supporting cells of the sensory epithelia. The granules were seen to secrete into the endolymphatic space through reticular membrane. It is likely, therefore, that glycoconjugates are glycosylated at the Golgi apparatus in the supporting cells, stored in the granules, and secreted through the reticular membrane into the endolymphatic space to be used as a component of the cupula. The cell membranes of various cells, connective tissue filaments in the perilymphatic space and the cytoplasm of melanocytes were also labeled with WGA-gold.

A newly identified surface coat on cochlear hair cells

Routine electron microscope methods do not well preserve or stain the surface coat or glycocalyx on cochlear hair cells. In other tissues, enhanced preservation and staining of these glycoconjugates was obtained following fixation with glutaraldehyde containing a cationic dye (e.g., Alcian blue and ruthenium red). When cochleas were fixed with glutaraldehyde containing Alcian blue, the endolymphatic surface of hair cells, but not the supporting cells, displayed an extensive (approximately 90 nm thick) surface coat. Alcian blue positive material was also observed in the tectorial and basilar membranes and in a portion of the spiral ligament. In addition, acellular bands of Alcian blue positive material were observed between the tectorial membrane and the reticular lamina or inner sulcus cells. Although the function of these cochlear glycoconjugates is not yet known, it is proposed that they serve to attach the tectorial membrane to the organ of Corti, and they are involved in stereocilia fusion following sound exposure and ototoxic drug administration.

Ultrastructural morphology and protein content of the internal organic material of rat otoconia

Otoconia taken from the maculae of the saccule and utricle of the rat inner ear were investigated using transmission electron microscopy (TEM). Their ultrastructure was compared using various decalcification techniques. Similar preparations were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to assess their protein constituents. TEM results show loss of organic material during prolonged decalcification. This is not seen in samples decalcified overnight. The SDS-PAGE results show that rat otoconia contain a major broad band of 90-100 kDa, a major thin band of 56 kDa, and three other bands of 33, 45, and 50 kDa. The band of 56 kDa may be associated with the surface of the otoconia.