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

Novel cell types and developmental lineages revealed by single-cell RNA-seq analysis of the mouse crista ampullaris

This study provides transcriptomic characterization of the cells of the crista ampullaris, sensory structures at the base of the semicircular canals that are critical for vestibular function. We performed single-cell RNA-seq on ampullae microdissected from E16, E18, P3, and P7 mice. Cluster analysis identified the hair cells, support cells and glia of the crista as well as dark cells and other nonsensory epithelial cells of the ampulla, mesenchymal cells, vascular cells, macrophages, and melanocytes. Cluster-specific expression of genes predicted their spatially restricted domains of gene expression in the crista and ampulla. Analysis of cellular proportions across developmental time showed dynamics in cellular composition. The new cell types revealed by single-cell RNA-seq could be important for understanding crista function and the markers identified in this study will enable the examination of their dynamics during development and disease.

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.

The fine structure of the developing otolithic organs of the rat

The fine structure of the otolithic organs in fetal and neonatal rats were studied by light and transmission electron microscopy. The otoconia were found at the 16.5 gestational day while the otolithic membrane appeared much later. Types II and I hair cells were first observed at the 16.5 and 18.5 gestational days, respectively. Secretory granules in the supporting cells seemed to release an organic material which was destined to be incorporated into the organic matrix of the otoconia and/or the otolithic membrane. Protrusions of apical cytoplasm, cytoplasmic globules and dilated rough endoplasmic reticulum (rER) were observed in epithelial cells of both sensory and non-sensory regions, in particular, in the transitional cells. By contrast, otoconia were mainly located above the neuroepithelial area. The functional roles of protrusions and cytoplasmic globules in the genesis of otoconia remain to be clarified. In addition, the pathway for transport of calcium remains obscure.

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.

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.

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.

Carbohydrates of the guinea pig vestibular supporting cells

Ultrastructural localization of glycoconjugates with special reference to the synthesizing process was studied in the guinea pig vestibular supporting cells using the tannic acid and ruthenium red staining technique. The extracellular glycoconjugate (glycocalyx) was well stained by the ruthenium red which may be synthesized by GERL complex. The supporting cell has a numerous number of granules which also contain tannic acid positive glycoconjugate. These granules were closely related to the Golgi complex as well as the apical cell surface. It may be indicated that the glycoconjugate of the supporting cells is glycosylated at the Golgi complex, stored in the granules, transported, secreted, and form otoconial membrane and the cupula.

Functional aspects of carbohydrate complex of the statoconial membrane of the guinea pig utricular macula

A functional aspect of the carbohydrate complex of the statoconial membrane of the guinea pig utricular macula was observed by the use of the lectins as well as the ruthenium red staining techniques. The ruthenium red staining technique visualized the whole structure of the statoconial membrane as well as the contact zone between the sensory epithelium and the statoconial membrane. The statoconial membrane is composed of the otoconial layer, gelatinous layer, and subcupular meshwork. The otoconial layer was interconnected with sensory epithelium by the gelatinous layer and subcupular meshwork which formed honeycomb structure and housed the sensory hair bundle. This may allow the free movement of the sensory hair bundle. The gelatinous layer and the subcupular meshwork contain N-acetylglucosamine, mannose, and galactose which form acidic mucopolysaccharide and glycoprotein. It has been indicated that these carbohydrate complex may play an important role for the mechanical coupling not only between the statoconial membrane and the sensory epithelium but also between the sensory hair bundle and the statoconial membrane.