Dominant and recessive deafness caused by mutations of a novel gene, TMC1, required for cochlear hair-cell function

Positional cloning of hereditary deafness genes is a direct approach to identify molecules and mechanisms underlying auditory function. Here we report a locus for dominant deafness, DFNA36, which maps to human chromosome 9q13-21 in a region overlapping the DFNB7/B11 locus for recessive deafness. We identified eight mutations in a new gene, transmembrane cochlear-expressed gene 1 (TMC1), in a DFNA36 family and eleven DFNB7/B11 families. We detected a 1.6-kb genomic deletion encompassing exon 14 of Tmc1 in the recessive deafness (dn) mouse mutant, which lacks auditory responses and has hair-cell degeneration. TMC1 and TMC2 on chromosome 20p13 are members of a gene family predicted to encode transmembrane proteins. Tmc1 mRNA is expressed in hair cells of the postnatal mouse cochlea and vestibular end organs and is required for normal function of cochlear hair cells.     

Mutations in the gene encoding pejvakin, a newly identified protein of the afferent auditory pathway, cause DFNB59 auditory neuropathy

Auditory neuropathy is a particular type of hearing impairment in which neural transmission of the auditory signal is impaired, while cochlear outer hair cells remain functional. Here we report on DFNB59, a newly identified gene on chromosome 2q31.1-q31.3 mutated in four families segregating autosomal recessive auditory neuropathy. DFNB59 encodes pejvakin, a 352-residue protein. Pejvakin is a paralog of DFNA5, a protein of unknown function also involved in deafness. By immunohistofluorescence, pejvakin is detected in the cell bodies of neurons of the afferent auditory pathway. Furthermore, Dfnb59 knock-in mice, homozygous for the R183W variant identified in one DFNB59 family, show abnormal auditory brainstem responses indicative of neuronal dysfunction along the auditory pathway. Unlike previously described sensorineural deafness genes, all of which underlie cochlear cell pathologies, DFNB59 is the first human gene implicated in nonsyndromic deafness due to a neuronal defect.     

Targeted disruption of otog results in deafness and severe imbalance

Genes specifically expressed in the inner ear are candidates to underlie hereditary nonsyndromic deafness. The gene Otog has been isolated from a mouse subtractive cDNA cochlear library. It encodes otogelin, an N-glycosylated protein that is present in the acellular membranes covering the six sensory epithelial patches of the inner ear: in the cochlea (the auditory sensory organ), the tectorial membrane (TM) over the organ of Corti; and in the vestibule (the balance sensory organ), the otoconial membranes over the utricular and saccular maculae as well as the cupulae over the cristae ampullares of the three semi-circular canals. These membranes are involved in the mechanotransduction process. Their movement, which is induced by sound in the cochlea or acceleration in the vestibule, results in the deflection of the stereocilia bundle at the apex of the sensory hair cells, which in turn opens the mechanotransduction channels located at the tip of the stereo-cilia. We sought to elucidate the role of otogelin in the auditory and vestibular functions by generating mice with a targeted disruption of Otog. In Otog-/- mice, both the vestibular and the auditory functions were impaired. Histological analysis of these mutants demonstrated that in the vestibule, otogelin is required for the anchoring of the otoconial membranes and cupulae to the neuroepithelia. In the cochlea, ultrastructural analysis of the TM indicated that otogelin is involved in the organization of its fibrillar network. Otogelin is likely to have a role in the resistance of this membrane to sound stimulation. These results support OTOG as a possible candidate gene for a human nonsyndromic form of deafness.     

Normal hearing in Splotch (Sp/+), the mouse homologue of Waardenburg syndrome type 1.

Splotch is considered a model of Waardenburg syndrome type I (WSI) because the abnormalities are caused by mutations in homologous genes, Pax-3 in mice and PAX3 (HuP2) in humans. We examined inner ear structure and function in Splotch mutants (Sp/+) and found no sign of auditory defects, in contrast to the deafness in many WSI individuals. The difference in expression of the genes in the two species may be due to different parts of the gene being mutated, or may result from variations in modifying influences as yet undefined.     

Beethoven, a mouse model for dominant, progressive hearing loss DFNA36

Despite recent progress in identifying genes underlying deafness, there are still relatively few mouse models of specific forms of human deafness. Here we describe the phenotype of the Beethoven (Bth) mouse mutant and a missense mutation in Tmc1 (transmembrane cochlear-expressed gene 1). Progressive hearing loss (DFNA36) and profound congenital deafness (DFNB7/B11) are caused by dominant and recessive mutations of the human ortholog, TMC1 (ref. 1), for which Bth and deafness (dn) are mouse models, respectively.     

A nuclear-mitochondrial DNA interaction affecting hearing impairment in mice

The pathophysiologic pathways and clinical expression of mitochondrial DNA (mtDNA) mutations are not well understood. This is mainly the result of the heteroplasmic nature of most pathogenic mtDNA mutations and of the absence of clinically relevant animal models with mtDNA mutations. mtDNA mutations predisposing to hearing impairment in humans are generally homoplasmic, yet some individuals with these mutations have severe hearing loss, whereas their maternal relatives with the identical mtDNA mutation have normal hearing. Epidemiologic, biochemical and genetic data indicate that nuclear genes are often the main determinants of these differences in phenotype. To identify a mouse model for maternally inherited hearing loss, we screened reciprocal backcrosses of three inbred mouse strains, A/J, NOD/LtJ and SKH2/J, with age-related hearing loss (AHL). In the (A/J x CAST/Ei) x A/J backcross, mtDNA derived from the A/J strain exerted a significant detrimental effect on hearing when compared with mtDNA from the CAST/Ei strain. This effect was not seen in the (NOD/LtJ x CAST/Ei) x NOD/LtJ and (SKH2/J x CAST/Ei) x SKH2/J backcrosses. Genotyping revealed that this effect was seen only in mice homozygous for the A/J allele at the Ahl locus on mouse chromosome 10. Sequencing of the mitochondrial genome in the three inbred strains revealed a single nucleotide insertion in the tRNA-Arg gene (mt-Tr) as the probable mediator of the mitochondrial effect. This is the first mouse model with a naturally occurring mtDNA mutation affecting a clinical phenotype, and it provides an experimental model to dissect the pathophysiologic processes connecting mtDNA mutations to hearing loss.     

Mutations in Cdh23, encoding a new type of cadherin, cause stereocilia disorganization in waltzer, the mouse model for Usher syndrome type 1D

Mouse chromosome 10 harbors several loci associated with hearing loss, including waltzer (v), modifier-of deaf waddler (mdfw) and Age-related hearing loss (Ahl). The human region that is orthologous to the mouse 'waltzer' region is located at 10q21-q22 and contains the human deafness loci DFNB12 and USH1D). Numerous mutations at the waltzer locus have been documented causing erratic circling and hearing loss. Here we report the identification of a new gene mutated in v. The 10.5-kb Cdh23 cDNA encodes a very large, single-pass transmembrane protein, that we have called otocadherin. It has an extracellular domain that contains 27 repeats; these show significant homology to the cadherin ectodomain. In v(6J), a GT transversion creates a premature stop codon. In v(Alb), a CT exchange generates an ectopic donor splice site, effecting deletion of 119 nucleotides of exonic sequence. In v(2J), a GA transition abolishes the donor splice site, leading to aberrant splice forms. All three alleles are predicted to cause loss of function. We demonstrate Cdh23 expression in the neurosensory epithelium and show that during early hair-cell differentiation, stereocilia organization is disrupted in v(2J) homozygotes. Our data indicate that otocadherin is a critical component of hair bundle formation. Mutations in human CDH23 cause Usher syndrome type 1D and thus, establish waltzer as the mouse model for USH1D.     

Urocortin-deficient mice show hearing impairment and increased anxiety-like behavior

Urocortin is a member of the corticotropin-releasing hormone peptide family and is found in many discrete brain regions. The distinct expression pattern of urocortin suggests that it influences such behaviors as feeding, anxiety and auditory processing. To better define the physiological roles of urocortin, we have generated mice carrying a null mutation of the urocortin gene. Urocortin-deficient mice have normal basal feeding behavior and stress responses, but show heightened anxiety-like behaviors in the elevated plus maze and open-field tests. In addition, hearing is impaired in the mutant mice at the level of the inner ear, suggesting that urocortin is involved in the normal development of cochlear sensory-cell function. These results provide the first example of a function for any peptidergic system in hearing.     

Mutations in COL11A2 cause non-syndromic hearing loss (DFNA13)

We report that mutation of COL11A2 causes deafness previously mapped to the DFNA13 locus on chromosome 6p. We found two families (one American and one Dutch) with autosomal dominant, non-syndromic hearing loss to have mutations in COL11A2 that are predicted to affect the triple-helix domain of the collagen protein. In both families, deafness is non-progressive and predominantly affects middle frequencies. Mice with a targeted disruption of Col11a2 also were shown to have hearing loss. Electron microscopy of the tectorial membrane of these mice revealed loss of organization of the collagen fibrils. Our findings revealed a unique ultrastructural malformation of inner-ear architecture associated with non-syndromic hearing loss, and suggest that tectorial membrane abnormalities may be one aetiology of sensorineural hearing loss primarily affecting the mid-frequencies.     

Disruption of Bardet-Biedl syndrome ciliary proteins perturbs planar cell polarity in vertebrates

The evolutionarily conserved planar cell polarity (PCP) pathway (or noncanonical Wnt pathway) drives several important cellular processes, including epithelial cell polarization, cell migration and mitotic spindle orientation. In vertebrates, PCP genes have a vital role in polarized convergent extension movements during gastrulation and neurulation. Here we show that mice with mutations in genes involved in Bardet-Biedl syndrome (BBS), a disorder associated with ciliary dysfunction, share phenotypes with PCP mutants including open eyelids, neural tube defects and disrupted cochlear stereociliary bundles. Furthermore, we identify genetic interactions between BBS genes and a PCP gene in both mouse (Ltap, also called Vangl2) and zebrafish (vangl2). In zebrafish, the augmented phenotype results from enhanced defective convergent extension movements. We also show that Vangl2 localizes to the basal body and axoneme of ciliated cells, a pattern reminiscent of that of the BBS proteins. These data suggest that cilia are intrinsically involved in PCP processes.     

Mutation of CDH23, encoding a new member of the cadherin gene family, causes Usher syndrome type 1D

Usher syndrome type I (USH1) is an autosomal recessive disorder characterized by congenital sensorineural hearing loss, vestibular dysfunction and visual impairment due to early onset retinitis pigmentosa (RP). So far, six loci (USH1A-USH1F) have been mapped, but only two USH1 genes have been identified: MYO7A for USH1B and the gene encoding harmonin for USH1C. We identified a Cuban pedigree linked to the locus for Usher syndrome type 1D (MIM 601067) within the q2 region of chromosome 10). Affected individuals present with congenital deafness and a highly variable degree of retinal degeneration. Using a positional candidate approach, we identified a new member of the cadherin gene superfamily, CDH23. It encodes a protein of 3,354 amino acids with a single transmembrane domain and 27 cadherin repeats. In the Cuban family, we detected two different mutations: a severe course of the retinal disease was observed in individuals homozygous for what is probably a truncating splice-site mutation (c.4488G-->C), whereas mild RP is present in individuals carrying the homozygous missense mutation R1746Q. A variable expression of the retinal phenotype was seen in patients with a combination of both mutations. In addition, we identified two mutations, Delta M1281 and IVS51+5G-->A, in a German USH1 patient. Our data show that different mutations in CDH23 result in USH1D with a variable retinal phenotype. In an accompanying paper, it is shown that mutations in the mouse ortholog cause disorganization of inner ear stereocilia and deafness in the waltzer mouse.     

Cardiac defects and renal failure in mice with targeted mutations in Pkd2

PKD2, mutations in which cause autosomal dominant polycystic kidney disease (ADPKD), encodes an integral membrane glycoprotein with similarity to calcium channel subunits. We induced two mutations in the mouse homologue Pkd2 (ref.4): an unstable allele (WS25; hereafter denoted Pkd2WS25) that can undergo homologous-recombination-based somatic rearrangement to form a null allele; and a true null mutation (WS183; hereafter denoted Pkd2-). We examined these mutations to understand the function of polycystin-2, the protein product of Pkd2, and to provide evidence that kidney and liver cyst formation associated with Pkd2 deficiency occurs by a two-hit mechanism. Pkd2-/- mice die in utero between embryonic day (E) 13.5 and parturition. They have structural defects in cardiac septation and cyst formation in maturing nephrons and pancreatic ducts. Pancreatic ductal cysts also occur in adult Pkd2WS25/- mice, suggesting that this clinical manifestation of ADPKD also occurs by a two-hit mechanism. As in human ADPKD, formation of kidney cysts in adult Pkd2WS25/- mice is associated with renal failure and early death (median survival, 65 weeks versus 94 weeks for controls). Adult Pkd2+/- mice have intermediate survival in the absence of cystic disease or renal failure, providing the first indication of a deleterious effect of haploinsufficiency at Pkd2on long-term survival. Our studies advance our understanding of the function of polycystin-2 in development and our mouse models recapitulate the complex human ADPKD phenotype.     

The gene mutated in bare patches and striated mice encodes a novel 3beta-hydroxysteroid dehydrogenase.

X-linked dominant disorders that are exclusively lethal prenatally in hemizygous males have been described in human and mouse. None of the genes responsible has been isolated in either species. The bare patches (Bpa) and striated (Str) mouse mutations were originally identified in female offspring of X-irradiated males. Subsequently, additional independent alleles were described. We have previously mapped these X-linked dominant, male-lethal mutations to an overlapping region of 600 kb that is homologous to human Xq28 (ref. 4) and identified several candidate genes in this interval. Here we report mutations in one of these genes, Nsdhl, encoding an NAD(P)H steroid dehydrogenase-like protein, in two independent Bpa and three independent Str alleles. Quantitative analysis of sterols from tissues of affected Bpa mice support a role for Nsdhl in cholesterol biosynthesis. Our results demonstrate that Bpa and Str are allelic mutations and identify the first mammalian locus associated with an X-linked dominant, male-lethal phenotype. They also expand the spectrum of phenotypes associated with abnormalities of cholesterol metabolism.     

Positional identification of TNFSF4, encoding OX40 ligand, as a gene that influences atherosclerosis susceptibility

Ath1 is a quantitative trait locus on mouse chromosome 1 that renders C57BL/6 mice susceptible and C3H/He mice resistant to diet-induced atherosclerosis. The quantitative trait locus region encompasses 11 known genes, including Tnfsf4 (also called Ox40l or Cd134l), which encodes OX40 ligand. Here we report that mice with targeted mutations of Tnfsf4 had significantly (P 相似文献   

Association of cadherin 23 with polygenic inheritance and genetic modification of sensorineural hearing loss

Age-related hearing loss (AHL) in common inbred mouse strains is a genetically complex quantitative trait. We found a synonymous single-nucleotide polymorphism in exon 7 of Cdh23 that shows significant association with AHL and the deafness modifier mdfw (modifer of deafwaddler). The hypomorphic Cdh23(753A) allele causes in-frame skipping of exon 7. Altered adhesion or reduced stability of CDH23 may confer susceptibility to AHL. Homozygosity at Cdh23(753A) or in combination with heterogeneous secondary factors is a primary determinant of AHL in mice.     

Mitochondrial point mutations do not limit the natural lifespan of mice

Whether mitochondrial mutations cause mammalian aging, or are merely correlated with it, is an area of intense debate. Here, we use a new, highly sensitive assay to redefine the relationship between mitochondrial mutations and age. We measured the in vivo rate of change of the mitochondrial genome at a single-base pair level in mice, and we demonstrate that the mutation frequency in mouse mitochondria is more than ten times lower than previously reported. Although we observed an 11-fold increase in mitochondrial point mutations with age, we report that a mitochondrial mutator mouse was able to sustain a 500-fold higher mutation burden than normal mice, without any obvious features of rapidly accelerated aging. Thus, our results strongly indicate that mitochondrial mutations do not limit the lifespan of wild-type mice.     

Hermansky-Pudlak syndrome is caused by mutations in HPS4, the human homolog of the mouse light-ear gene

Hermansky-Pudlak syndrome (HPS) is a disorder of organelle biogenesis in which oculocutaneous albinism, bleeding and pulmonary fibrosis result from defects of melanosomes, platelet dense granules and lysosomes. HPS is common in Puerto Rico, where it is caused by mutations in the genes HPS1 and, less often, HPS3 (ref. 8). In contrast, only half of non-Puerto Rican individuals with HPS have mutations in HPS1 (ref. 9), and very few in HPS3 (ref. 10). In the mouse, more than 15 loci manifest mutant phenotypes similar to human HPS, including pale ear (ep), the mouse homolog of HPS1 (refs 13,14). Mouse ep has a phenotype identical to another mutant, light ear (le), which suggests that the human homolog of le is a possible human HPS locus. We have identified and found mutations of the human le homolog, HPS4, in a number of non-Puerto Rican individuals with HPS, establishing HPS4 as an important HPS locus in humans. In addition to their identical phenotypes, le and ep mutant mice have identical abnormalities of melanosomes, and in transfected melanoma cells the HPS4 and HPS1 proteins partially co-localize in vesicles of the cell body. In addition, the HPS1 protein is absent in tissues of le mutant mice. These results suggest that the HPS4 and HPS1 proteins may function in the same pathway of organelle biogenesis.