Progression of Inner Ear Pathology in Ames Waltzer Mice and the Role of Protocadherin 15 in Hair Cell Development

Department of Otolaryngology-Head and Neck Surgery, University of Texas Southwestern Medical Center, Dallas, TX 75390-9035, USA.
Journal of the Association for Research in Otolaryngology (Impact Factor: 2.6). 07/2006; 7(2):83-94. DOI: 10.1007/s10162-005-0024-5
Source: PubMed


The Ames waltzer (av) mouse mutant exhibits auditory and vestibular abnormalities resulting from mutation of protocadherin 15 (Pcdh15). Ames waltzer has been identified as an animal model for inner ear pathology associated with Usher syndrome type 1F. Studies correlating anatomical phenotype with severity of genetic defect in various av alleles are providing better understanding of the role played by Pcdh15 in inner ear development and of sensorineural abnormalities associated with alterations in Pcdh15 protein structure as a result of gene mutation. In this work we present new findings on inner ear pathology in four alleles of av mice with differing mutations of Pcdh15 as well as varying alterations in inner ear morphology. Two alleles with in-frame deletion mutations (Pcdh15
and Pcdh15
) and two presumptive functional null alleles (Pcdh15
and Pcdh15
) were studied. Light and electron microscopic observations demonstrated that the severity of cochlear and vestibular pathology in these animals correlates positively with the extent of mutation in Pcdh15 from embryonic day 18 (E18) up to 12 months. Electron microscopic analysis of immature ears indicated early abnormalities in the arrangement of stereocilia and the inner and outer hair cell cuticular plates, stereocilia rootlets, and the actin meshwork within the cuticular plate. In severe cases, displacement of the kinocilium and alterations in the shape of the cuticular plate was also observed. Mice harboring in-frame deletion mutations showed less disorganization of stereocilia and cuticular plates in the organ of Corti than the presumptive functional null alleles at P0–P10. A slower progression of pathology was also seen via light microscopy in older animals with in-frame deletions, compared to the presumptive functional null mutations. In summary, our results demonstrate that mutation in Pcdh15 affects the initial formation of stereocilia bundles with associated changes in the actin meshwork within the cuticular plate; these effects are more pronounced in the presumed null mutation compared to mutations that only affect the extracellular domain. The positive correlation of severity of effects with extent of mutation can be seen well into adulthood.

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Available from: Karen S Pawlowski
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    • "Several proteins have been shown to localize in the cuticular plate, including alpha-actinin, spectrin, fimbrin, protocadherin 15, myosin 6, and myosin 7a [40], [41], [42], [43], [44], [45], [46], [47], [48], [49]. Mutations in protocadherin 15, myosin 6, or myosin 7a genes can cause disorganization of cuticular plate or result in stereocila fusion [50], [51], [52], [53]. But the mechanism about how the development and maintenance of this actin-rich organelle is regulated remains to be elucidated. "
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    ABSTRACT: Mammalian FCHSD1 and FCHSD2 are homologous proteins containing an amino-terminal F-BAR domain and two SH3 domains near their carboxyl-termini. We report here that FCHSD1 and FCHSD2 are expressed in mouse cochlear sensory hair cells. FCHSD1 mainly localizes to the cuticular plate, whereas FCHSD2 mainly localizes along the stereocilia in a punctuate pattern. Nervous Wreck (Nwk), the Drosophila ortholog of FCHSD1 and FCHSD2, has been shown to bind Wsp and play an important role in F-actin assembly. We show that, like its Drosophila counterpart, FCHSD2 interacts with WASP and N-WASP, the mammalian orthologs of Drosophila Wsp, and stimulates F-actin assembly in vitro. In contrast, FCHSD1 doesn't bind WASP or N-WASP, and can't stimulate F-actin assembly when tested in vitro. We found, however, that FCHSD1 binds via its F-BAR domain to the SH3 domain of Sorting Nexin 9 (SNX9), a well characterized BAR protein that has been shown to promote WASP-Arp2/3-dependent F-actin polymerization. FCHSD1 greatly enhances SNX9's WASP-Arp2/3-dependent F-actin polymerization activity. In hair cells, SNX9 was detected in the cuticular plate, where it colocalizes with FCHSD1. Our results suggest that FCHSD1 and FCHSD2 could modulate F-actin assembly or maintenance in hair cell stereocilia and cuticular plate.
    Full-text · Article · Feb 2013 · PLoS ONE
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    • "In cases where the insult is severe or a prolonged period of time has passed since the insult, the supporting cells may degenerate as well and form or are replaced by a flat layer of polymorphic cuboidal cells, which we refer to as the " flat epithelium " (Fig. 1C) (Kim et al., 2007). The flat epithelium can be observed frequently as the outcome of severe hearing loss caused by various etiologies including hereditary deafness (Pawlowski et al., 2006), aminoglycoside insult in guinea pigs (Izumikawa et al., 2008; Shibata et al., 2010), and in humans with prolonged history of deafness (Nadol et al., 2006). This highly degenerated condition of sensory epithelium that remains in the deaf ears will likely be the substrate to first receive any of the future therapies. "
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    ABSTRACT: Following the onset of sensorineural hearing loss, degeneration of mechanosensitive hair cells and spiral ganglion cells (SGCs) in humans and animals occurs to variable degrees, with a trend for greater neural degeneration with greater duration of deafness. Emergence of the cochlear implant prosthesis has provided much needed aid to many hearing impaired patients and has become a well-recognized therapy worldwide. However, ongoing peripheral nerve fiber regression and subsequent degeneration of SGC bodies can reduce the neural targets of cochlear implant stimulation and diminish its function. There is increasing interest in bio-engineering approaches that aim to enhance cochlear implant efficacy by preventing SGC body degeneration and/or regenerating peripheral nerve fibers into the deaf sensory epithelium. We review the advancements in maintaining and regenerating nerves in damaged animal cochleae, with an emphasis on the therapeutic capacity of neurotrophic factors delivered to the inner ear after an insult. Additionally, we summarize the histological process of neuronal degeneration in the inner ear and describe different animal models that have been employed to study this mechanism. Research on enhancing the biological infrastructure of the deafened cochlea in order to improve cochlear implant efficacy is of immediate clinical importance.
    Full-text · Article · May 2011 · Hearing research
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    • "A similar breeding scheme was used to obtain mice heterozygous (+/av3J) or homozygous (av3J/av3J) for the av3J allele of Pcdh15, and mice that were heterozygous (+/v2J) or homozygous (v2J/v2J) for the v2J allele of Cdh23. Offspring from the av3J and av6J lines were genotyped as described previously by Pawlowski et al and Zheng et al respectively [21], [49]. Offspring from the v2J line were genotyped using a scheme that takes advantage of the point mutation that results in the loss of HpyCH4 III restriction site in the target sequence. "
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    ABSTRACT: Immunocytochemical studies have shown that protocadherin-15 (PCDH15) and cadherin-23 (CDH23) are associated with tip links, structures thought to gate the mechanotransducer channels of hair cells in the sensory epithelia of the inner ear. The present report describes functional and structural analyses of hair cells from Pcdh15(av3J) (av3J), Pcdh15(av6J) (av6J) and Cdh23(v2J) (v2J) mice. The av3J and v2J mice carry point mutations that are predicted to introduce premature stop codons in the transcripts for Pcdh15 and Cdh23, respectively, and av6J mice have an in-frame deletion predicted to remove most of the 9th cadherin ectodomain from PCDH15. Severe disruption of hair-bundle morphology is observed throughout the early-postnatal cochlea in av3J/av3J and v2J/v2J mice. In contrast, only mild-to-moderate bundle disruption is evident in the av6J/av6J mice. Hair cells from av3J/av3J mice are unaffected by aminoglycosides and fail to load with [(3)H]-gentamicin or FM1-43, compounds that permeate the hair cell's mechanotransducer channels. In contrast, hair cells from av6J/av6J mice load with both FM1-43 and [(3)H]-gentamicin, and are aminoglycoside sensitive. Transducer currents can be recorded from hair cells of all three mutants but are reduced in amplitude in all mutants and have abnormal directional sensitivity in the av3J/av3J and v2J/v2J mutants. Scanning electron microscopy of early postnatal cochlear hair cells reveals tip-link like links in av6J/av6J mice, substantially reduced numbers of links in the av3J/av3J mice and virtually none in the v2J/v2J mice. Analysis of mature vestibular hair bundles reveals an absence of tip links in the av3J/av3J and v2J/v2J mice and a reduction in av6J/av6J mice. These results therefore provide genetic evidence consistent with PCDH15 and CDH23 being part of the tip-link complex and necessary for normal mechanotransduction.
    Full-text · Article · Apr 2011 · PLoS ONE
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