Alström Syndrome protein ALMS1 localizes to basal bodies of cochlear hair cells and regulates cilium-dependent planar cell polarity.

Alström Syndrome is a life-threatening disease characterized primarily by numerous metabolic abnormalities, retinal degeneration, cardiomyopathy, kidney and liver disease, and sensorineural hearing loss. The cellular localization of the affected protein, ALMS1, has suggested roles in ciliary function and/or ciliogenesis. We have investigated the role of ALMS1 in the cochlea and the pathogenesis of hearing loss in Alström Syndrome.

A comparative study of gland cells implicated in the nerve dependence of salamander limb regeneration.

Limb regeneration in salamanders proceeds by formation of the blastema, a mound of proliferating mesenchymal cells surrounded by a wound epithelium. Regeneration by the blastema depends on the presence of regenerating nerves and in earlier work it was shown that axons upregulate the expression of newt anterior gradient (nAG) protein first in Schwann cells of the nerve sheath and second in dermal glands underlying the wound epidermis. The expression of nAG protein after plasmid electroporation was shown to rescue a denervated newt blastema and allow regeneration to the digit stage.

The Membrane Properties of Cochlear Root Cells are Consistent with Roles in Potassium Recirculation and Spatial Buffering.

Auditory transduction, amplification, and hair cell survival depend on the regulation of extracellular [K(+)] in the cochlea. K(+) is removed from the vicinity of sensory hair cells by epithelial cells, and may be distributed through the epithelial cell syncytium, reminiscent of "spatial buffering" in glia. Hypothetically, K(+) is then transferred from the epithelial syncytium into the connective tissue syncytium within the cochlear lateral wall, enabling recirculation of K(+) back into endolymph.

Rapid hair cell loss: a mouse model for cochlear lesions.

In comparison to other mammals, mice have proved extremely resistant to aminoglycoside-induced hair cell ablation in vivo. In this paper we examine the pattern and extent of cochlear lesions rapidly induced with a combination of a single dose of aminoglycoside (kanamycin) followed by a loop diuretic (bumetanide). With this protocol, the vestibular system was unaffected, but in the cochlea, there was extensive loss of outer hair cells (OHC) that commenced in the basal coil and progressed apically so that, by 48 h, OHC loss was almost complete.

Gap junctions in the inner ear: comparison of distribution patterns in different vertebrates and assessement of connexin composition in mammals.

The distribution and size of gap junctions (GJ) in the sensory epithelia of the inner ear have been examined in a reptile (gecko), birds (chicken and owl), and mammals (mouse, guinea pig, gerbil, and bat), and the connexin composition of GJs in the mammalian inner ear has been assessed. Freeze fracture revealed a common pattern of GJ distribution in auditory and vestibular sensory epithelia in the different vertebrate classes. In all these tissues, GJs are numerous, often occupying more than 25% of the plasma membrane area of supporting cells and sometimes composed of more than 100,000 channels.

Hair cell recovery in the vestibular sensory epithelia of mature guinea pigs.

The progression of recovery of the vestibular sensory epithelia of guinea pigs after gentamicin-induced hair cell injury was assessed quantitatively and qualitatively. Evaluations were made of the number of cells bearing hair bundles by using scanning electron microscopy (SEM) and of identifiable hair cells in thin sections. Both assessment procedures showed that an initial loss of hair cells in utricular maculae is followed by significant recovery in the number of hair cells present.

Postnatal maturation of the organ of Corti in gerbils: morphology and physiological responses.

The organ of Corti, the sensory epithelium of hearing in mammals, matures postnatally in the gerbil. Quantitative analyses of the postnatal development of the organ of Corti, including supporting cells and the basilar membrane, were carried out. The morphological study confirmed that maturation of the sensory cells proceeds with a base-to-apex gradient, with the outer hair cells appearing to mature before the inner hair cells.

Postnatal development of membrane specialisations of gerbil outer hair cells.

Using a combination of freeze-fracture and thin sections, this study examines the maturation of the membrane specialisations of the gerbil outer hair cells (OHC) between 2 and 16 days after birth (DAB). The apical membrane, the junctional region around the neck of the cell, and the lateral and basal membranes are described. The results suggest a sequential development of the different components of the lateral wall.

Two modes of hair cell loss from the vestibular sensory epithelia of the guinea pig inner ear.

In the vestibular and auditory neurosensory epithelia of poikilothermic vertebrates and of birds, damaged sensory "hair" cells are often deleted by extrusion from the apical surface. In contrast, in the adult mammalian auditory epithelium (the organ of Corti), the bodies of damaged hair cells degenerate within the epithelium. To determine whether this apparent difference is species related or is associated with the differing structural organisation of the epithelia, hair cell deletion in the mammalian vestibular end-organs was examined.

Ultrastructural evidence for hair cell regeneration in the mammalian inner ear.

It has long been thought that hair cell loss from the inner ears of mammals is irreversible. This report presents scanning electron micrographs and thin sections of the utricles from the inner ears of guinea pigs that show that, after hair cell loss caused by treatment with the aminoglycoside gentamicin, hair cells reappeared. Four weeks after the end of treatment, a large number of cells with immature hair bundles in multiple stages of development could be identified in the utricle.

Structural variability of the sub-surface cisternae in intact, isolated outer hair cells shown by fluorescent labelling of intracellular membranes and freeze-fracture.

The intracellular membrane systems in intact, isolated outer hair cells were visualised using the fluorescent membrane probe 3,3'-dihexyloxacarbocyanine iodide (DiOC6) and by freeze-fracture, and f-actin distribution was examined with rhodamine-phalloidin. DiOC6 stained the sub-surface cisternal membranes in the lateral wall and revealed a membrane system running in the centre of the cell from the nucleus to the sub-cuticular region. In optical sections of the lateral wall of fluorescently labelled cells, obtained by scanning laser confocal microscopy, the sub-surface membrane appeared as a fenestrated sheet or a fine network of tubules.

Scanning electron microscopy of the mammalian organ of Corti: assessment of preparative procedures.

Different fixation, drying and coating procedures have been applied in preparation of the organ of Corti for scanning electron microscopy (SEM), and structural features of the apical surface of the tissue in unfixed, freeze-fractured preparations used in assessing their effects on morphology. Fixation with glutaraldehyde alone or osmium tetroxide alone causes artefacts that are substantially avoided when tissue is doubly fixed in glutaraldehyde followed by osmium. Significant improvements in preservation are also obtained when tissue is additionally processed through thiocarbohydrazide-osmium (TOTO) processing.