The mouse Ames waltzer hearing-loss mutant is caused by mutation of Pcdh15, a novel protocadherin gene.

The neuroepithelia of the inner ear contain hair cells that function as mechanoreceptors to transduce sound and motion signals. Mutations affecting these neuroepithelia cause deafness and vestibular dysfuction in humans. Ames waltzer (av) is a recessive mutation found in mice that causes deafness and a balance disorder associated with the degeneration of inner ear neuroepithelia. Here we report that the gene that harbours the av mutation encodes a novel protocadherin. Cochlear hair cells in the av mutants show abnormal stereocilia by 10 days after birth (P10). This is the first evidence for the requirement of a protocadherin for normal function of the mammalian inner ear.

A new spontaneous mutation in the mouse protocadherin 15 gene.

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.

A new mouse insertional mutation that causes sensorineural deafness and vestibular defects.

This article describes a new recessive insertional mutation in the transgenic line TgN2742Rpw that causes deafness and circling behavior in mice. Histologic analysis revealed virtually complete loss of the cochlear neuroepithelium (the organ of Corti) in adult mutant mice. In association with the neuroepithelial changes, there is a dramatic reduction of the cochlear nerve supply. Adult mutants also show morphological defects of the vestibular apparatus, including degeneration of the saccular neuroepithelium and occasional malformation of utricular otoconia. Audiometric evaluations demonstrated that the mice displaying the circling phenotype are completely deaf. Molecular analysis of this mutant line revealed that the transgenic insertion occurred without creating a large deletion of the host DNA sequences. The mutant locus was mapped to a region on mouse chromosome 10, where other spontaneous, recessive mutations causing deafness in mice have been mapped.

Neuroepithelial defects of the inner ear in a new allele of the mouse mutation Ames waltzer.

This report presents new findings regarding a recessive insertional mutation in the transgenic line TgN2742Rpw that causes deafness and circling behavior in mice homozygous for the mutation. The mutant locus was mapped to a region on mouse chromosome 10 close to three spontaneous recessive mutations causing deafness: Ames waltzer (av), Waltzer (v), and Jackson circler (jc). Complementation testing revealed that the TgN2742Rpw mutation is allelic with av. Histological and auditory brainstem response (ABR) evaluation of animals that have the new allele balanced with the av(J) allele (called compound heterozygotes, TgN2742Rpw/av(J)) supports our genetic analysis. ABR evaluation shows complete absence of auditory response throughout the life span of TgN2742Rpw/av(J) compound heterozygotes. Scanning electron microscopy revealed abnormalities of inner and outer hair cell stereocilia in the cochleae of TgN2742Rpw mutants at 10 days after birth (DAB). The organ of Corti subsequently undergoes degeneration, leading to nearly complete loss of the cochlear neuroepithelium in older mutants by about 50 DAB. The vestibular neuroepithelia remain morphologically normal until at least 30 DAB. However, by 50 days, degenerative changes are evident in the saccular macula, which progresses to total loss of the saccular neuroepithelium in older animals. The new allele of av reported here will be designated av(TgN2742Rpw).

Mutations in the novel protocadherin PCDH15 cause Usher syndrome type 1F.

We have determined the molecular basis for Usher syndrome type 1F (USH1F) in two families segregating for this type of syndromic deafness. By fluorescence in situ hybridization, we placed the human homolog of the mouse protocadherin Pcdh15 in the linkage interval defined by the USH1F locus. We determined the genomic structure of this novel protocadherin, and found a single-base deletion in exon 10 in one USH1F family and a nonsense mutation in exon 2 in the second. Consistent with the phenotypes observed in these families, we demonstrated expression of PCDH15 in the retina and cochlea by RT-PCR and immunohistochemistry. This report shows that protocadherins are essential for maintenance of normal retinal and cochlear function.