Characterization of Vestibular Dysfunction in the Mouse Model for Usher Syndrome 1F

Department of Otolaryngology-Head and Neck Surgery, University Hospitals of Cleveland, Case Western Reserve University, Cleveland, OH 44106, USA.
Journal of the Association for Research in Otolaryngology (Impact Factor: 2.6). 07/2005; 6(2):106-18. DOI: 10.1007/s10162-004-5032-3
Source: PubMed


The deaf-circling Ames waltzer (av) mouse harbors a mutation in the protocadherin 15 (Pcdh15) gene and is a model for inner ear defects associated with Usher syndrome type 1F. Earlier studies showed altered cochlear hair cell morphology in young av mice. In contrast, no structural abnormality consistent with significant vestibular dysfunction in young av mice was observed. Light and scanning electron microscopic studies showed that vestibular hair cells from presumptive null alleles Pcdh15
and Pcdh15
are morphologically similar to vestibular sensory cells from control littermates, suggesting that the observed phenotype in these alleles might be a result of a central, rather than peripheral, defect. In the present study, a combination of physiologic and anatomic methods was used to more thoroughly investigate the source of vestibular dysfunction in Ames waltzer mice. Analysis of vestibular evoked potentials and angular vestibulo-ocular reflexes revealed a lack of physiologic response to linear and angular acceleratory stimuli in Pcdh15 mutant mice. Optokinetic reflex function was diminished but still present in the mutant animals, suggesting that the defect is primarily peripheral in nature. These findings indicate that the mutation in Pcdh15 results in either a functional abnormality in the vestibular receptor organs or that the defects are limited to the vestibular nerve. AM1-43 dye uptake has been shown to correlate with normal transduction function in hair cells. Dye uptake was found to be dramatically reduced in Pcdh15 mutants compared to control littermates, suggesting that the mutation affects hair cell function, although structural abnormalities consistent with significant vestibular dysfunction are not apparent by light and scanning electron microscopy in the vestibular neuroepithelia of young animals.

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Available from: Karen S Pawlowski
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    • "Documenting the salient features of cochlear pathology in different alleles of av will help us understand (a) the function of Pcdh15 in hair cell development and (b) the cause of inner ear disorders in USH1F and DFNB23 patients. Reports on av mutants in the literature show that mutation in Pcdh15 affects hair bundle morphogenesis and polarity (Hampton et al., 2003; Pawlowski et al., 2006; Raphael et al., 2001; Washington et al., 2005) and mechanotransduction (Alagramam et al., 2005). More recently, a detailed study on the localization and function of Pcdh15 in hair cells by Senften et al. (2006) strongly supports the role of Pcdh15 in bundle morphogenesis and polarity. "
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    ABSTRACT: We have characterized a new allele of the protocadherin 15 gene (designatedPcdh15(av-6J)) that arose as a spontaneous, recessive mutation in the C57BL/6J inbred strain at Jackson Laboratory. Analysis revealed an inframe deletion in Pcdh15, which is predicted to result in partial deletion of cadherin domain (domain 9) in Pcdh15. Morphologic study revealed normal to moderately defective cochlear hair cell stereocilia in Pcdh15(av-6J) mutants at postnatal day 2 (P2). Stereocilia abnormalities were consistently present at P5 and P10. Degenerative changes including loss of inner and outer hair cells were seen at P20, with severe sensory cell loss in all cochlear turns occurring by P40. The hair cell phenotype observed in the 6J allele between P0 and P20 is the least severe phenotype yet observed in Pcdh15 alleles. However, young Pcdh15(av-6J) mice are unresponsive to auditory stimulation and show circling behavior indicative of vestibular dysfunction. Since these animals show severe functional deficits but have relatively mild stereocilia defects at a young age they may provide an appropriate model to test for a direct role of Pcdh15 in mechanotransduction.
    Full-text · Article · Oct 2006 · Hearing Research
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    • "The otoconia in these mutants degenerate in a similar time course as the loss of the epithelium, though fragments of the gelatinous membrane can still be present (Johnsson et al., 1980; Takumida et al., 1997a,b; Yamane et al., 1984). Young Ames waltzer mice have no obvious defects in vestibular structure (Alagramam et al., 2005), suggesting degeneration, as opposed to altered development, as the cause of otoconial loss. New-mutant mice have age-dependent demineralization of saccular otoconia (Kitamura et al., 1991b) that accompanies the complete degeneration of saccular hair cells. "
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    ABSTRACT: Human vestibular dysfunction is an increasing clinical problem. Degeneration or displacement of otoconia is a significant etiology of age-related balance disorders and Benign Positional Vertigo (BPV). In addition, commonly used antibiotics, such as aminoglycoside antibiotics, can lead to disruption of otoconial structure and function. Despite such clinical significance, relatively little information has been compiled about the development and maintenance of otoconia in humans. Recent studies in model organisms and other mammalian organ systems have revealed some of the proteins and processes required for the normal biomineralization of otoconia and otoliths in the inner ear of vertebrates. Orchestration of extracellular biomineralization requires bringing together ionic and proteinaceous components in time and space. Coordination of these events requires the normal formation of the otocyst and sensory maculae, specific secretion and localization of extracellular matrix proteins, as well as tight regulation of the endolymph ionic environment. Disruption of any of these processes can lead to the formation of abnormally shaped, or ectopic, otoconia, or otoconial agenesis. We propose that normal generation of otoconia requires a complex temporal and spatial control of developmental and biochemical events. In this review, we suggest a new hypothetical model for normal otoconial and otolith formation based on matrix vesicle mineralization in bone which we believe to be supported by information from existing mutants, morphants, and biochemical studies.
    Full-text · Article · Jun 2006 · Brain Research
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    ABSTRACT: Mice with a targeted disruption of the gene encoding the stilbene-insensitive electroneutral sodium bicarbonate cotransporter (NBC3; slc4a7) exhibit cochlear and retinal degeneration. To establish the progressive nature of sensory cells loss in slc4a7-/- deficient mice, we studied the morphology of cochleas of slc4a7-/- and slc4a7+/+ mice from postnatal day two (P2) to ninety (P90). Cell death was evaluated in slc4a7-/- cochleas using the TUNEL technique and caspase-3 immunoreactivity. The time course of NBC3 expression in the cochlea was assessed by immunohistochemistry using an antibody against NBC3. Between P2 and P8, slc4a7-/- mice cochlea exhibit normal morphology. There was a normal complement of inner and outer hair cells from the hook to the apical region. At P15, slc4a7-/- mice cochlea inner and outer hair cells were still present at the hook region, and vacuoles were seen underneath Hensen's cells. At P21, inner and outer hair cells were degenerated in this region. Between P30 and P90, there was a pronounced loss of hair cells and spiral ganglia neurons. Morphological analysis of the spiral ligament showed a progressive loss of type II and IV fibrocytes beginning at day 21. Transmission electron microscopy observations at P30 and P90 revealed that type II and IV fibrocytes showed shrinkage and vacuolization. In addition, hair cells were deteriorated with evidence of shrinkage and picnotic nuclei. TUNEL staining showed apoptotic cells at P8 in the organ of Corti at the basal region of the cochlea. At P15, caspase-3 immunoreactivity was present in supporting cells of the organ of Corti. NBC3 mild immunoreactivity was detected in the organ of Corti at P11. There was an increase in the expression of NBC3 in the spiral ligament between P17 and P19. From P21 to P90, NBC3 expression was confined to the spiral ligament and inner and outer sulcus cells. The vestibular sensory epithelia from slc4a7-/- mice were normal from P2 to P90. Damage of the sensory epithelia at the high frequency zone of the cochlea suggests that NBC3 may play an important physiological role in this region.
    No preview · Article · Dec 2005 · Developmental Brain Research
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