The DFNA15 deafness mutation affects POU4F3 protein stability, localization, and transcriptional activity

The transcription factor Pou4f3 is essential for the survival of postnatal and adult mouse cochlear hair cells and normal hearing

Introduction

Hair cells (HCs) of the cochlea are responsible for sound transduction and hearing perception in mammals. Genetic mutations in the transcription factor Pou4f3 cause non-syndromic autosomal dominant hearing loss in humans (DFNA15) which varies in the age of onset depending on the individual mutation. Mouse models with germline deletion or mutations in Pou4f3 have previously demonstrated its critical role in the maturation and survival of cochlear HCs during embryonic development. However, the role of Pou4f3 in auditory function and in the survival or maintenance of cochlear HCs after birth and during adulthood has not been studied.

Methods

Therefore, using the inducible CreER-loxP system, we deleted Pou4f3 from mouse cochlear HCs at different postnatal ages, relevant to specific stages of HC maturation and hearing function.

Results and discussion

Elevated auditory brainstem response thresholds and significant HC loss were detected in mice with Pou4f3 deletion compared to their control littermates, regardless of the age when Pou4f3 was deleted. However, HC loss occurred more rapidly when Pou4f3 was deleted from immature HCs. Additionally, HC loss caused by Pou4f3 deletion did not affect the number of cochlear supporting cells, but caused a delayed loss of spiral ganglion neurons at 4 months after the deletion. In conclusion, Pou4f3 is necessary for the survival of cochlear HCs and normal hearing at all postnatal ages regardless of their maturation state. Our data also suggest that Pou4f3 indirectly regulates the survival of spiral ganglion neurons.

An essential signaling cascade for avian auditory hair cell regeneration

Hearing loss is a chronic disease affecting millions of people worldwide, yet no restorative treatment options are available. Although non-mammalian species can regenerate their auditory sensory hair cells, mammals cannot. Birds retain facultative stem cells known as supporting cells that engage in proliferative regeneration when surrounding hair cells die. Here, we investigated gene expression changes in chicken supporting cells during auditory hair cell death. This identified a pathway involving the receptor F2RL1, HBEGF, EGFR, and ERK signaling. We propose a cascade starting with the proteolytic activation of F2RL1, followed by matrix-metalloprotease-mediated HBEGF shedding, and culminating in EGFR-mediated ERK signaling. Each component of this cascade is essential for supporting cell S-phase entry in vivo and is integral for hair cell regeneration. Furthermore, STAT3-phosphorylation converges with this signaling toward upregulation of transcription factors ATF3, FOSL2, and CREM. Our findings could provide a basis for designing treatments for hearing and balance disorders.

Ramifications of POU4F3 variants associated with autosomal dominant hearing loss in various molecular aspects

POU4F3, a member of the POU family of transcription factors, commonly causes autosomal dominant deafness. Exome sequencing was used to identify four novel variants in POU4F3 (NM_002700.2), including c.564dupA: p.Ala189SerfsTer26, c.743T > C:p.Leu248Pro, c.879C > A:p.Phe293Leu, and c.952G > A:p.Val318Met, and diverse aspects of the molecular consequences of their protein expression, stability, subcellular localization, and transcriptional activity were investigated. The expression of three mutant proteins, encoded by missense variants, was reduced compared to the wild-type protein, demonstrating that the mutants were unstable and vulnerable to degradation. Additionally, all the mutant proteins had distinct subcellular localization patterns. A mutant protein carrying p.Ala189SerfsTer26, in which both mono- and bi-partite nuclear localization signals were disrupted, showed abnormal subcellular localization. Resultantly, all the mutant proteins significantly reduced the transcriptional activity required to regulate the downstream target gene expression. Furthermore, we identified the altered expression of 14 downstream target genes associated with inner ear development using patient-derived lymphoblastoid cell lines. There was a significant correlation of the expression profile between patient-derived cells and the cochlear hair cells, which provided a breakthrough for cases where the collection of human cochlear samples for transcriptome studies was unfeasible. This study expanded the genotypic spectrum of POU4F3 in DFNA15, and further refined the molecular mechanisms underlying POU4F3-associated DFNA15.

Autosomal Dominant Non-Syndromic Hearing Loss (DFNA): A Comprehensive Narrative Review

Autosomal dominant non-syndromic hearing loss (HL) typically occurs when only one dominant allele within the disease gene is sufficient to express the phenotype. Therefore, most patients diagnosed with autosomal dominant non-syndromic HL have a hearing-impaired parent, although de novo mutations should be considered in all cases of negative family history. To date, more than 50 genes and 80 loci have been identified for autosomal dominant non-syndromic HL. DFNA22 (MYO6 gene), DFNA8/12 (TECTA gene), DFNA20/26 (ACTG1 gene), DFNA6/14/38 (WFS1 gene), DFNA15 (POU4F3 gene), DFNA2A (KCNQ4 gene), and DFNA10 (EYA4 gene) are some of the most common forms of autosomal dominant non-syndromic HL. The characteristics of autosomal dominant non-syndromic HL are heterogenous. However, in most cases, HL tends to be bilateral, post-lingual in onset (childhood to early adulthood), high-frequency (sloping audiometric configuration), progressive, and variable in severity (mild to profound degree). DFNA1 (DIAPH1 gene) and DFNA6/14/38 (WFS1 gene) are the most common forms of autosomal dominant non-syndromic HL affecting low frequencies, while DFNA16 (unknown gene) is characterized by fluctuating HL. A long audiological follow-up is of paramount importance to identify hearing threshold deteriorations early and ensure prompt treatment with hearing aids or cochlear implants.

Genetic Load of Alternations of Transcription Factor Genes in Non-Syndromic Deafness and the Associated Clinical Phenotypes: Experience from Two Tertiary Referral Centers

Sensorineural hearing loss is one of the most common inherited sensory disorders. Functional classifications of deafness genes have shed light on genotype- and mechanism-based pharmacological approaches and on gene therapy strategies. In this study, we characterized the clinical phenotypes and genotypes of non-syndromic deafness caused by transcription factor (TF) gene variants, one of the functional classifications of genetic hearing loss. Of 1280 probands whose genomic DNA was subjected to molecular genetic testing, TF genes were responsible for hearing loss in 2.6%. Thirty-three pathogenic variants, including nine novel variants, accounting for non-syndromic deafness were clustered in only four TF genes (POU3F4, POU4F3, LMX1A, and EYA4), which is indicative of a narrow molecular etiologic spectrum of TF genes, and the functional redundancy of many other TF genes, in the context of non-syndromic deafness. The audiological and radiological characteristics associated with the four TF genes differed significantly, with a wide phenotypic spectrum. The results of this study reveal the genetic load of TF gene alterations among a cohort with non-syndromic hearing loss. Additionally, we have further refined the clinical profiles associated with TF gene variants as a basis for a personalized, genetically tailored approach to audiological rehabilitation.

A Missense POU4F3 Variant Associated with Autosomal Dominant Midfrequency Hearing Loss Alters Subnuclear Localization and Transcriptional Capabilities

Background

The pathogenic variant, POU class 4 transcription factor 3 (POU4F3), is reported to cause autosomal dominant nonsyndromic hearing loss (ADNSHL). Previously, we have examined a four-generation midfrequency sensorineural hearing loss (MFSNHL) family (no. 6126) and established POU4F3 c.602T>C (p.Leu201Pro) as a potential disease-causing variant.

Objectives

We explored the structural and functional alterations that the c.602T>C (p.Leu201Pro) variant enforces on the POU4F3 protein.

Methods

We utilized wild-type (WT) and mutant (MUT) POU4F3 c.602T>C plasmid incorporation into HeLa cells to assess functional changes, by immunofluorescence and luciferase assays. To predict protein structural alterations in the MUT versus WT POU4F3, we also generated 3D structures to compare both types of POU4F3 proteins.

Results

The WT POU4F3 is ubiquitously present in the nucleus, whereas the MUT form of POU4F3 exhibits a more restricted nuclear presence. This finding is different from other publications, which report a cytoplasmic localization of the MUT POU4F3. We also demonstrated that, as opposed to WT POU4F3, the MUT POU4F3 had 40% reduced luciferase activity.

Conclusions

The reduced nuclear presence, combined with reduced transcriptional activity, suggests that the POU4F3 c.602T>C variant alters cellular activity and may contribute to the pathogenicity of POU4F3-related hearing loss. It, also, provides more evidence of the pathophysiological characteristics of MFSNHL.

Aldh inhibitor restores auditory function in a mouse model of human deafness

Genetic hearing loss is a common health problem with no effective therapy currently available. DFNA15, caused by mutations of the transcription factor POU4F3, is one of the most common forms of autosomal dominant non-syndromic deafness. In this study, we established a novel mouse model of the human DFNA15 deafness, with a Pou4f3 gene mutation (Pou4f3Δ) identical to that found in a familial case of DFNA15. The Pou4f3(Δ/+) mice suffered progressive deafness in a similar manner to the DFNA15 patients. Hair cells in the Pou4f3(Δ/+) cochlea displayed significant stereociliary and mitochondrial pathologies, with apparent loss of outer hair cells. Progression of hearing and outer hair cell loss of the Pou4f3(Δ/+) mice was significantly modified by other genetic and environmental factors. Using Pou4f3(-/+) heterozygous knockout mice, we also showed that DFNA15 is likely caused by haploinsufficiency of the Pou4f3 gene. Importantly, inhibition of retinoic acid signaling by the aldehyde dehydrogenase (Aldh) and retinoic acid receptor inhibitors promoted Pou4f3 expression in the cochlear tissue and suppressed the progression of hearing loss in the mutant mice. These data demonstrate Pou4f3 haploinsufficiency as the main underlying cause of human DFNA15 deafness and highlight the therapeutic potential of Aldh inhibitors for treatment of progressive hearing loss.

More than 50% of deafness cases are due to genetic defects with no treatment available. DFNA15, caused by mutations of the transcription factor POU4F3, is one of the most common types of autosomal dominant non-syndromic deafness. Here, we established a novel mouse model with the exact Pou4f3 mutation identified in human patients. The mutant mouse display similar auditory pathophysiology as human patients and exhibit multiple hair cell abnormalities. The onset and severity of hearing loss in the mouse model is highly modifiable to environmental factors, such as aging, noise exposure or genetic backgrounds. Using a new knockout mouse model, we found Pou4f3 haploinsufficiency as the underlying mechanism of human DFNA15. Importantly, we identified Aldh inhibitor as a potent small molecule for upregulation of Pou4f3 and treatment of hearing loss in the mutant mouse. The identification of Aldh inhibitor for treatment of DFNA15 deafness represents a major advance in the unmet medical need for this common form of progressive hearing loss.

Otoprotective Effect of 2,3,4',5-Tetrahydroxystilbene-2-O-β-d-Glucoside on Gentamicin-Induced Apoptosis in Mouse Cochlear UB/OC-2 Cells

Excessive levels of reactive oxygen species (ROS) lead to mitochondrial damage and apoptotic cell death in gentamicin-induced ototoxicity. 2,3,4',5-Tetrahydroxystilbene-2-O-β-d-glucoside (THSG), a bioactive constituent, isolated from Polygonum multiflorum Thunb., exhibits numerous biological benefits in treating aging-related diseases by suppressing oxidative damage. However, its protective effect on gentamicin-induced ototoxicity remains unexplored. Therefore, here, we aimed to investigate the otoprotective effect of THSG on gentamicin-induced apoptosis in mouse cochlear UB/OC-2 cells. We evaluated the effect of gentamicin and THSG on the ROS level, superoxide dismutase (SOD) activity, mitochondrial membrane potential, nuclear condensation, and lactate dehydrogenase (LDH) release, and the expression of apoptosis-related proteins was assessed to understand the molecular mechanisms underlying its preventive effects. The findings demonstrated that gentamicin increased ROS generation, LDH release, and promoted apoptotic cell death in UB/OC-2 cells. However, THSG treatment reversed these effects by suppressing ROS production and downregulating the mitochondrial-dependent apoptotic pathway. Additionally, it increased the SOD activity, decreased the expression of apoptosis-related proteins, alleviated the levels of the apoptotic cells, and impaired cytotoxicity. To the best of our knowledge, this is the first study to demonstrate that THSG could be a potential therapeutic option to attenuate gentamicin-induced ototoxicity.

Four Novel Variants in POU4F3 Cause Autosomal Dominant Nonsyndromic Hearing Loss

Hereditary hearing loss is one of the most common sensory disabilities worldwide. Mutation of POU domain class 4 transcription factor 3 (POU4F3) is considered the pathogenic cause of autosomal dominant nonsyndromic hearing loss (ADNSHL), designated as autosomal dominant nonsyndromic deafness 15. In this study, four novel variants in POU4F3, c.696G>T (p.Glu232Asp), c.325C>T (p.His109Tyr), c.635T>C (p.Leu212Pro), and c.183delG (p.Ala62Argfs∗22), were identified in four different Chinese families with ADNSHL by targeted next-generation sequencing and Sanger sequencing. Based on the American College of Medical Genetics and Genomics guidelines, c.183delG (p.Ala62Argfs∗22) is classified as a pathogenic variant, c.696G>T (p.Glu232Asp) and c.635T>C (p.Leu212Pro) are classified as likely pathogenic variants, and c.325C>T (p.His109Tyr) is classified as a variant of uncertain significance. Based on previous reports and the results of this study, we speculated that POU4F3 pathogenic variants are significant contributors to ADNSHL in the East Asian population. Therefore, screening of POU4F3 should be a routine examination for the diagnosis of hereditary hearing loss.

Identification of two novel mutations in POU4F3 gene associated with autosomal dominant hearing loss in Chinese families

Autosomal dominant non‐syndromic hearing loss is genetically heterogeneous with 47 genes identified to date, including POU4F3. In this study, by using a next‐generation sequencing panel targeting 127 deafness genes, we identified a pathogenic frameshift mutation c.704_705del and a missense mutation c.593G>A in two three‐generation Chinese families with late‐onset progressive ADNSHL, respectively. The novel mutations of POU4F3 co‐segregated with the deafness phenotype in these two families. c.704_705del caused a frameshift p.T235fs and c.593G>A caused an amino acid substitution of p.R198H. Both mutations led to an abnormal and incomplete protein structure. POU4F3 with either of the two mutations was transiently transfected into HEI‐OC1 and HEK 293 cell lines and immunofluorescence assay was performed to investigate the subcellular localization of mutated protein. The results indicated that both c.704_705del (p.T235fs) and c.593G>A (p.R198H) could impair the nuclear localization function of POU4F3. The p.R198H POU4F3 protein was detected as a weak band of the correct molecular weight, indicating that the stability of p.R198H POU4F3 differed from that of the wild‐type protein. While, the p.T235fs POU4F3 protein was expressed with a smaller molecular weight, implying this mutation result in a frameshift and premature termination of the POU4F3 protein. In summary, we report two novel mutations of POU4F3 associated with progressive ADNSHL and explored their effects on POU4F3 nuclear localization. These findings expanded the mutation spectrum of POU4F3 and provided new knowledge for the pathogenesis of POU4F3 in hearing loss.

RNA-seq analysis of potential lncRNAs for age-related hearing loss in a mouse model

Age-related hearing loss (AHL) is an important health problem in the elderly population. Its molecular mechanisms have not been fully elucidated. In this study, we analyzed the differential expression of lncRNAs and mRNAs in the cochleae of six-week-old and one-year-old C57BL/6J mice through RNA-seq analysis. We found 738 and 2033 differentially expressed lncRNAs and mRNAs, respectively, in these two groups (corrected P < 0.05). We focused on the intersection of known genes associated with hearing loss and differentially expressed mRNAs in RNA-seq. There are 34 mRNAs in this intersection, which include all 29 mRNAs enriched in the sensory perception of sound (GO: 0007605). We selected 11 lncRNAs that are predicted to regulate the 34 mRNAs to validate their expression levels in animal and cellular models of AHL by qRT-PCR. Among these lncRNAs, four were significantly different in both animal and cellular models of AHL, and the lncRNA NONMMUT010961.2 was the most markedly different. Knocking down lncRNA NONMMUT010961.2, we found the expression of oxidative stress and apoptosis-related gene Ar and hearing loss-related gene Hgf is significantly reduced in HEI-OC1 cells. Our results suggest that lncRNAs NONMMUT010961.2 may be associated with AHL and may thus lead to a new treatment for AHL.

Pou4f3 gene mutation promotes autophagy and apoptosis of cochlear hair cells in cisplatin-induced deafness mice

Pou4f3 plays an important role in the development of hair cells in the inner ear sensory epithelia. Autophagy is related to the auditory damage. However, the role and mechanism of Pou4f3 on drug-induced ototoxicity are incompletely understood. Hence, this study aimed to explore the effects of Pou4f3 on the apoptosis of cochlear hair cells (CHCs) and to explore whether autophagy was involved in this process. The cisplatin was used to produce a loss of CHCs to create a murine model of deafness. The AAV vectors were delivered into the scala media through the lateral wall. Compared with the control mice, the cisplatin-treated mice exhibited significantly enhanced apoptosis and autophagy in the cochleae, accompanied by a notably decreased Pou4f3 levels. Both mutation and knockdown of Pou4f3 promoted the apoptosis- and autophagy-related protein levels, and enhanced the cisplatin-induced levels of apoptosis- and autophagy-related proteins. Furthermore, the autophagy activator rapamycin promoted the apoptosis and autophagy in the cochlea. In addition, the autophagy inhibitor 3-MA overturned the promoting effect of Pou4f3 knockdown on the apoptosis and autophagy. Collectively, in cisplatin-induced deafness mice, the Pou4f3 gene mutation facilitated apoptosis of cochlear hair cells, at least partially, through inducing autophagy.

Computational analysis based on audioprofiles: A new possibility for patient stratification in office-based otology

Genetic contribution to progressive hearing loss in adults is underestimated. Established machine learning-based software could offer a rapid supportive tool to stratify patients with progressive hearing loss. A retrospective longitudinal analysis of 141 adult patients presenting with hearing loss was performed. Hearing threshold was measured at least twice 18 months or more apart. Based on the baseline audiogram, hearing thresholds and age were uploaded to AudioGene v4® (Center for Bioinformatics and Computational Biology at The University of Iowa City, IA, USA) to predict the underlying genetic cause of hearing loss and the likely progression of hearing loss. The progression of hearing loss was validated by comparison with the most recent audiogram data of the patients. The most frequently predicted loci were DFNA2B, DFNA9 and DFNA2A. The frequency of loci/genes predicted by AudioGene remains consistent when using the initial or the final audiogram of the patients. In conclusion, machine learning-based software analysis of clinical data might be a useful tool to identify patients at risk for having autosomal dominant hearing loss. With this approach, patients with suspected progressive hearing loss could be subjected to close audiological followup, genetic testing and improved patient counselling.

OHC-TRECK: A Novel System Using a Mouse Model for Investigation of the Molecular Mechanisms Associated with Outer Hair Cell Death in the Inner Ear

Outer hair cells (OHCs) are responsible for the amplification of sound, and the death of these cells leads to hearing loss. Although the mechanisms for sound amplification and OHC death have been well investigated, the effects on the cochlea after OHC death are poorly understood. To study the consequences of OHC death, we established an OHC knockout system using a novel mouse model, Prestin-hDTR, which uses the prestin promoter to express the human diphtheria toxin (DT) receptor gene (hDTR). Administration of DT to adult Prestin-hDTR mice results in the depletion of almost all OHCs without significant damage to other cochlear and vestibular cells, suggesting that this system is an effective tool for the analysis of how other cells in the cochlea and vestibula are affected after OHC death. To evaluate the changes in the cochlea after OHC death, we performed differential gene expression analysis between the untreated and DT-treated groups of wild-type and Prestin-hDTR mice. This analysis revealed that genes associated with inflammatory/immune responses were significantly upregulated. Moreover, we found that several genes linked to hearing loss were strongly downregulated by OHC death. Together, these results suggest that this OHC knockout system is a useful tool to identify biomarkers associated with OHC death.

Hereditary hearing loss; about the known and the unknown

Hereditary hearing loss is both clinically and genetically very heterogeneous. Despite the large number of genes that have been associated with the condition, many cases remain unexplained. Novel gene associations with hearing loss are to be expected but also are defects of regulatory regions of the genome which are currently not routinely addressed in molecular genetic testing and research. Inheritance patterns other than monogenic might be more common than assumed in isolated cases and diagnoses might have been missed because of misinterpretation of identified DNA variants. This review summarizes current insights in the genetics of hearing loss, the next steps that are being taken in research, and their challenges. Furthermore, genotype-phenotype correlations and modifying factors are discussed as these are instrumental in counselling hearing impaired individuals and/or their family members.

Diagnosis, Intervention, and Prevention of Genetic Hearing Loss

It is estimated that at least 50% of congenital or childhood hearing loss is attributable to genetic causes. In non-syndromic hearing loss, which accounts for 70% of genetic hearing loss, approximately 80% of cases are autosomal recessive, 15% autosomal dominant, and 1-2% mitochondrial or X-linked. In addition, 30% of genetic hearing loss is syndromic. The genetic causes of hearing loss are highly heterogeneous. So far, more than 140 deafness-related genes have been discovered. Studies on those genes tremendously increased our understanding of the inner ear functions at the molecular level. It also offers important information for the patients and allows personalized and accurate genetic counseling. In many cases, genetic diagnosis of hearing loss can help to avoid unnecessary and costly clinical testing, offer prognostic information, and guide future medical management. On the other hand, a variety of gene therapeutic approaches have been developed aiming to relieve or converse the hearing loss due to genetic causes. Prevention of genetic hearing loss is feasible through prepregnancy and prenatal genetic diagnosis and counseling.

A novel missense variant in the nuclear localization signal of POU4F3 causes autosomal dominant non-syndromic hearing loss

Autosomal dominant non-syndromic hearing loss (ADNSHL) is genetically heterogeneous with more than 35 genes identified to date. Using a massively parallel sequencing panel targeting 159 deafness genes, we identified a novel missense variant of POU4F3 (c.982A>G, p.Lys328Glu) which co-segregated with the deafness phenotype in a three-generation Taiwanese family with ADNSHL. This variant could be classified as a "pathogenic variant" according to the American College of Medical Genetics and Genomics guidelines. We then performed subcellular localization experiments and confirmed that p.Lys328Glu compromised transportation of POU4F3 from the cytoplasm to the nucleus. POU3F4 p.Lys328Glu was located within a bipartite nuclear localization signal (NLS), and was the first missense variant in bipartite NLS of POU4F3 validated in functional studies. These findings expanded the mutation spectrum of POU4F3 and provided insight into the pathogenesis associated with aberrant POU4F3 localization.

POU4F3 mutation screening in Japanese hearing loss patients: Massively parallel DNA sequencing-based analysis identified novel variants associated with autosomal dominant hearing loss

A variant in a transcription factor gene, POU4F3, is responsible for autosomal dominant nonsyndromic hereditary hearing loss, DFNA15. To date, 14 variants, including a whole deletion of POU4F3, have been reported to cause HL in various ethnic groups. In the present study, genetic screening for POU4F3 variants was carried out for a large series of Japanese hearing loss (HL) patients to clarify the prevalence and clinical characteristics of DFNA15 in the Japanese population. Massively parallel DNA sequencing of 68 target candidate genes was utilized in 2,549 unrelated Japanese HL patients (probands) to identify genomic variations responsible for HL. The detailed clinical features in patients with POU4F3 variants were collected from medical charts and analyzed. Novel 12 POU4F3 likely pathogenic variants (six missense variants, three frameshift variants, and three nonsense variants) were successfully identified in 15 probands (2.5%) among 602 families exhibiting autosomal dominant HL, whereas no variants were detected in the other 1,947 probands with autosomal recessive or inheritance pattern unknown HL. To obtain the audiovestibular configuration of the patients harboring POU4F3 variants, we collected audiograms and vestibular symptoms of the probands and their affected family members. Audiovestibular phenotypes in a total of 24 individuals from the 15 families possessing variants were characterized by progressive HL, with a large variation in the onset age and severity with or without vestibular symptoms observed. Pure-tone audiograms indicated the most prevalent configuration as mid-frequency HL type followed by high-frequency HL type, with asymmetry observed in approximately 20% of affected individuals. Analysis of the relationship between age and pure-tone average suggested that individuals with truncating variants showed earlier onset and slower progression of HL than did those with non-truncating variants. The present study showed that variants in POU4F3 were a common cause of autosomal dominant HL.

A Novel Nonsense Mutation of POU4F3 Gene Causes Autosomal Dominant Hearing Loss

POU4F3 gene encodes a transcription factor which plays an essential role in the maturation and maintenance of hair cells in cochlea and vestibular system. Several mutations of POU4F3 have been reported to cause autosomal dominant nonsyndromic hearing loss in recent years. In this study, we describe a pathogenic nonsense mutation located in POU4F3 in a four-generation Chinese family. Target region capture sequencing was performed to search for the candidate mutations from 81 genes related to nonsyndromic hearing loss in this family. A novel nonsense mutation of POU4F3, c.337C>T (p. Gln113^⁎), was identified in a Chinese family characterized by late-onset progressive nonsyndromic hearing loss. The novel mutation cosegregated with hearing loss in this family and was absent in 200 ethnicity-matched controls. The mutation led to a stop codon and thus a truncated protein with no functional domains remained. Transient transfection and immunofluorescence assay revealed that the subcellular localization of the truncated protein differed markedly from normal protein, which could be the underlying reason for complete loss of its normal function. Here, we report the first nonsense mutation of POU4F3 associated with progressive hearing loss and explored the possible underlying mechanism. Routine examination of POU4F3 is necessary for the genetic diagnosis of hereditary hearing loss in the future.

Exome sequencing identifies POU4F3 as the causative gene for a large Chinese family with non-syndromic hearing loss

Hearing impairment, or deafness (in its most severe form), is one of the most common human sensory disorders. There have been several reports of autosomal dominant mutations in the POU4F3 gene, which is associated with non-syndromic hearing loss. In this study, we identified a novel heterozygous mutation (c.602delT, p.L201fs) in the gene POU4F3 by taking advantage of whole-exome sequencing, which was validated by Sanger sequencing and completely co-segregated within a large hearing impaired Chinese family. We have focused on this pedigree since 2002, and we have mapped a deafness locus named DFNA42 (which has been renamed DFNA52, OMIM entry 607683) via a genome-wide scan. Furthermore, we analyzed this mutational variant and found that it was located at the beginning of the first functional domain of POU4F3, which could theoretically impair the function of POU4F3. We have identified a novel frameshift mutation in the POU4F3 gene. Further functional studies of variants of this specific gene are needed to illustrate the pathogenic mechanism(s) that underlie hearing impairment.

Genetic Variation in POU4F3 and GRHL2 Associated with Noise-Induced Hearing Loss in Chinese Population: A Case-Control Study

Noise-induced hearing loss (NIHL) is an important occupational disease worldwide resulting from interactions between genetic and environmental factors. The purpose of this study was to examine whether genetic variations in POU4F3 and GRHL2 may influence susceptibility to NIHL in the Chinese population. A matched case-control study was carried out among 293 hearing loss individuals and 293 normal hearing workers drawn from a population of 3790 noise-exposed workers. Ten single-nucleotide polymorphisms (SNPs) in POU4F3 and GRHL2 were selected and genotyped. Logistic regression was performed to analyze the main effects of SNPs and the interactions between noise exposure and SNPs. Moreover, the interactions between predictor haplotypes and noise exposure were also analyzed. Analysis revealed that the CC genotype of rs1981361 in the GRHL2 gene was associated with a higher risk of NIHL (adjusted OR = 1.59; 95% CI: 1.08–2.32, p = 0.018). Additionally, the GG genotype of rs3735715 in the GRHL2 gene was also a risk genotype (adjusted OR = 1.48; 95% CI: 1.01–2.19, p = 0.046). Significant interactions were found between rs3735715, rs1981361 (GRHL2), rs1368402 as well as rs891969 (POU4F3) and noise exposure in the high-level exposure groups. Furthermore, the protective haplotype CA in the POU4F3 gene and the risk haplotype GCCG in the GRHL2 gene were identified combined with noise exposure. These results indicated that GRHL2 might be an NIHL susceptibility gene, but the effect of POU4F3 on NIHL could only be detected when taking noise exposure into account, and their effects were enhanced by higher levels of noise exposure. However, the differences were not significant after the Bonferroni correction was applied. These results should be seen as suggestive.

Effects of genetic correction on the differentiation of hair cell-like cells from iPSCs with MYO15A mutation

Deafness or hearing loss is a major issue in human health. Inner ear hair cells are the main sensory receptors responsible for hearing. Defects in hair cells are one of the major causes of deafness. A combination of induced pluripotent stem cell (iPSC) technology with genome-editing technology may provide an attractive cell-based strategy to regenerate hair cells and treat hereditary deafness in humans. Here, we report the generation of iPSCs from members of a Chinese family carrying MYO15A c.4642G>A and c.8374G>A mutations and the induction of hair cell-like cells from those iPSCs. The compound heterozygous MYO15A mutations resulted in abnormal morphology and dysfunction of the derived hair cell-like cells. We used a CRISPR/Cas9 approach to genetically correct the MYO15A mutation in the iPSCs and rescued the morphology and function of the derived hair cell-like cells. Our data demonstrate the feasibility of generating inner ear hair cells from human iPSCs and the functional rescue of gene mutation-based deafness by using genetic correction.

Pou4f1 and pou4f2 are dispensable for the long-term survival of adult retinal ganglion cells in mice

PURPOSE

To investigate the role of Pou4f1 and Pou4f2 in the survival of adult retinal ganglion cells (RGCs).

METHODS

Conditional alleles of Pou4f1 and Pou4f2 were generated (Pou4f1loxP and Pou4f2loxP respectively) for the removal of Pou4f1 and Pou4f2 in adult retinas. A tamoxifen-inducible Cre was used to delete Pou4f1 and Pou4f2 in adult mice and retinal sections and flat mounts were subjected to immunohistochemistry to confirm the deletion of both alleles and to quantify the changes in the number of RGCs and other retinal neurons. To determine the effect of loss of Pou4f1 and Pou4f2 on RGC survival after axonal injury, controlled optic nerve crush (CONC) was performed and RGC death was assessed.

RESULTS

Pou4f1 and Pou4f2 were ablated two weeks after tamoxifen treatment. Retinal interneurons and Müller glial cells are not affected by the ablation of Pou4f1 or Pou4f2 or both. Although the deletion of both Pou4f1 and Pou4f2 slightly delays the death of RGCs at 3 days post-CONC in adult mice, it does not affect the cell death progress afterwards. Moreoever, deletion of Pou4f1 or Pou4f2 or both has no impact on the long-term viability of RGCs at up to 6 months post-tamoxifen treatment.

CONCLUSION

Pou4f1 and Pou4f2 are involved in the acute response to damage to RGCs but are dispensable for the long-term survival of adult RGC in mice.

Inhibition of Myo6 gene expression by co‑expression of a mutant of transcription factor POU4F3 (BRN‑3C) in hair cells

An eight‑base pair (bp) deletion in the Pou4f3 gene in hair cells is associated with DFNA15, a hereditary form of hearing loss. To explore the pathological mechanisms underlying the development of DFNA15, the effect of the mutation in Pou4f3 on the activity of the myosin VI (Myo6) promoter, was investigated. The upstream regulatory sequence of Myo6 (2625 bp), consisting of an 1899 bp upstream sequence and a 727 bp intron 1 sequence, was amplified using polymerase chain reaction and subcloned into the pGL3‑Basic vector expressing firefly luciferase. For verification of inserted fragments, plasmids were subjected to restriction analysis and then sequenced. HEK293T human embryonic kidney cells were transiently transfected with renilla luciferase‑thymidine kinase vectors expressing Renilla luciferase and the Myo6 promoter‑driven firefly luciferase expressing vectors along with pIRES2‑enhanced green fluorescent protein (EGFP)‑Pou4f3 (expressing wild‑type Pou4f3) or pIRES2‑EGFP‑Pou4f3 (expressing the truncation mutant of Pou4f3). The relative luciferase activities were measured to determine the activity of the Myo6 promoter. The Myo6 promoter activity was not affected by co‑expression of wild‑type Pou4f3, as indicated by the comparable relative luciferase activities in the presence of the pIRES2‑EGFP‑Pou4f3 and the empty control vectors. However, co‑expression of mutated Pou4f3 significantly inhibited the activity of the Myo6 promoter to almost half of that of the control (P<0.001). The data suggests that mutated Pou4f3 has a negative role in the promoter activity of Myo6, and by extension, the expression of myosin VI, and this may be an underlying mechanism of DFNA15 hearing loss.

SNP linkage analysis and whole exome sequencing identify a novel POU4F3 mutation in autosomal dominant late-onset nonsyndromic hearing loss (DFNA15)

Autosomal dominant non-syndromic hearing loss (AD-NSHL) is one of the most common genetic diseases in human and is well-known for the considerable genetic heterogeneity. In this study, we utilized whole exome sequencing (WES) and linkage analysis for direct genetic diagnosis in AD-NSHL. The Korean family had typical AD-NSHL running over 6 generations. Linkage analysis was performed by using genome-wide single nucleotide polymorphism (SNP) chip and pinpointed a genomic region on 5q31 with a significant linkage signal. Sequential filtering of variants obtained from WES, application of the linkage region, bioinformatic analyses, and Sanger sequencing validation identified a novel missense mutation Arg326Lys (c.977G>A) in the POU homeodomain of the POU4F3 gene as the candidate disease-causing mutation in the family. POU4F3 is a known disease gene causing AD-HSLH (DFNA15) described in 5 unrelated families until now each with a unique mutation. Arg326Lys was the first missense mutation affecting the 3(rd) alpha helix of the POU homeodomain harboring a bipartite nuclear localization signal sequence. The phenotype findings in our family further supported previously noted intrafamilial and interfamilial variability of DFNA15. This study demonstrated that WES in combination with linkage analysis utilizing bi-allelic SNP markers successfully identified the disease locus and causative mutation in AD-NSHL.

Cytoplasmic mislocalization of POU3F4 due to novel mutations leads to deafness in humans and mice

POU3F4 is a POU domain transcription factor that is required for hearing. In the ear, POU3F4 is essential for mesenchymal remodeling of the bony labyrinth and is the causative gene for DFNX2 human nonsyndromic deafness. Ear abnormalities underlie this form of deafness, characterized previously in multiple spontaneous, radiation-induced and transgenic mouse mutants. Here, we report three novel mutations in the POU3F4 gene that result in profound hearing loss in both humans and mice. A p.Gln79* mutation was identified in a child from an Israeli family, revealed by massively parallel sequencing (MPS). This strategy demonstrates the strength of MPS for diagnosis with only one affected individual. A second mutation, p.Ile285Argfs*43, was identified by Sanger sequencing. A p.Cys300* mutation was found in an ENU-induced mutant mouse, schwindel (sdl), by positional cloning. The mutation leads to a predicted truncated protein, similar to the human mutations, providing a relevant mouse model. The p.Ile285Argfs*43 and p.Cys300* mutations lead to a shift of Pou3f4 nuclear localization to the cytoplasm, demonstrated in cellular localization studies and in the inner ears of the mutant mice. The discovery of these mutations facilitates a deeper comprehension of the molecular basis of inner ear defects due to mutations in the POU3F4 transcription factor.

Caprin-1 is a target of the deafness gene Pou4f3 and is recruited to stress granules in cochlear hair cells in response to ototoxic damage

The POU4 family of transcription factors are required for survival of specific cell types in different sensory systems. Pou4f3 is essential for the survival of auditory sensory hair cells and several mutations in human POU4F3 cause hearing loss. Thus, genes regulated by Pou4f3 are likely to be essential for hair cell survival. We performed a subtractive hybridisation screen in an inner-ear-derived cell line to find genes with differential expression in response to changes in Pou4f3 levels. The screen identified the stress-granule-associated protein Caprin-1 as being downregulated by Pou4f3. We demonstrated that this regulation occurs through the direct interaction of Pou4f3 with binding sites in the Caprin-1 5' flanking sequence, and describe the expression pattern of Caprin-1 mRNA and protein in the cochlea. Moreover, we found Caprin-1-containing stress granules are induced in cochlear hair cells following aminoglycoside-induced damage. This is the first report of stress granule formation in mammalian hair cells and suggests that the formation of Caprin-1-containing stress granules is a key damage response to a clinically relevant ototoxic agent. Our results have implications for the understanding of aminoglycoside-induced hearing loss and provide further evidence that stress granule formation is a fundamental cellular stress response.

A novel frameshift mutation of POU4F3 gene associated with autosomal dominant non-syndromic hearing loss

Autosomal dominant mutations in the transcription factor POU4F3 gene are associated with non-syndromic hearing loss in humans; however, there have been few reports of mutations in this gene worldwide. We performed a mutation analysis of the POU4F3 gene in 42 unrelated Koreans with autosomal dominant non-syndromic hearing loss, identifying a novel 14-bp deletion mutation in exon 2 (c.662del14) in one patient. Audiometric examination revealed severe bilateral sensorineural hearing loss in this patient. The novel mutation led to a truncated protein that lacked both functional POU domains. We further investigated the functional distinction between wild-type and mutant POU4F3 proteins using in vitro assays. The wild-type protein was completely localized in the nucleus, while the truncation of protein seriously affected its nuclear localization. In addition, the mutant failed to activate reporter gene expression. This is the first report of a POU4F3 mutation in Asia, and moreover our data suggest that further investigation will need to delineate ethnicity-specific genetic background for autosomal dominant non-syndromic hearing loss within Asian populations.

Hearing loss: mechanisms revealed by genetics and cell biology

Hearing loss (HL), or deafness in its most severe form, affects an estimated 28 and 22.5 million Americans and Europeans, respectively. The numbers are higher in regions such as India and the Middle East, where consanguinity contributes to larger numbers of recessively inherited hearing impairment (HI). As a result of work-related difficulties, educational and developmental delays, and social stigmas and exclusion, the economic impact of HL is very high. At the other end of the spectrum, a rich deaf culture, particularly for individuals whose parents and even grandparents were deaf, is a social movement that believes that deafness is a difference in human experience rather than a disability. This review attempts to cover the remarkable progress made in the field of the genetics of HL over the past 20 years. Mutations in a significant number of genes have been discovered over the years that contribute to clinically heterogeneous forms of HL, enabling genetic counseling and prediction of progression of HL. Cell biological assays, protein localization in the inner ear, and detailed analysis of spontaneous and transgenic mouse models have provided an incredibly rich resource for elucidating mechanisms of hereditary hearing loss (HHL). This knowledge is providing answers for the families with HL, who contribute a great deal to the research being performed worldwide.

Clinical and molecular characterizations of novel POU3F4 mutations reveal that DFN3 is due to null function of POU3F4 protein

X-linked deafness type 3 (DFN3), the most prevalent X-linked form of hereditary deafness, is caused by mutations in the POU3F4 locus, which encodes a member of the POU family of transcription factors. Despite numerous reports on clinical evaluations and genetic analyses describing novel POU3F4 mutations, little is known about how such mutations affect normal functions of the POU3F4 protein and cause inner ear malformations and deafness. Here we describe three novel mutations of the POU3F4 gene and their clinical characterizations in three Korean families carrying deafness segregating at the DFN3 locus. The three mutations cause a substitution (p.Arg329Pro) or a deletion (p.Ser310del) of highly conserved amino acid residues in the POU homeodomain or a truncation that eliminates both DNA-binding domains (p.Ala116fs). In an attempt to better understand the molecular mechanisms underlying their inner ear defects, we examined the behavior of the normal and mutant forms of the POU3F4 protein in C3H/10T1/2 mesodermal cells. Protein modeling as well as in vitro assays demonstrated that these mutations are detrimental to the tertiary structure of the POU3F4 protein and severely affect its ability to bind DNA. All three mutated POU3F4 proteins failed to transactivate expression of a reporter gene. In addition, all three failed to inhibit the transcriptional activity of wild-type proteins when both wild-type and mutant proteins were coexpressed. Since most of the mutations reported for DFN3 thus far are associated with regions that encode the DNA binding domains of POU3F4, our results strongly suggest that the deafness in DFN3 patients is largely due to the null function of POU3F4.

Deafness genes in Israel: implications for diagnostics in the clinic

The identification of the molecular basis of deafness in the last decade has made a remarkable impact on genetic counseling and diagnostics for the hearing impaired population. Since the discovery of the most prevalent form of deafness associated with mutations in the GJB2 (connexin 26) gene, many other genes have been found worldwide, with a subset of these, including unique mutations, in Israel. Here, we review the current status of deafness genes in Israel and report one known mutation in a syndromic form of deafness, Usher syndrome, described in the Jewish Israeli population for the first time. In the future, the identification of specific mutations may be relevant for specific types of treatment.

Mild and Variable Audiometric and Vestibular Features in a Third DFNA15 Family with a Novel Mutation in POU4F3

Objectives:

Cochleovestibular characteristics were investigated in a Dutch DFNA15 family with a novel POU4F3 mutation, L223P

Methods:

A 4-generation pedigree was constructed of the Dutch family with the novel L223P POU4F3 mutation. Pure tone audiometric data were collected and analyzed cross-sectionally in mutation carriers. Age-related typical audiograms were derived. Vestibular examination was performed in most of the mutation carriers. The results were compared to those obtained from previously identified 884del8 and L289F POU4F3 mutation carriers.

Results:

A novel mutation (L223P) in POU4F3 segregated with hearing impairment in the present family. Audiometric analysis generally showed an early-adult to midlife onset of hearing impairment. High-frequency hearing impairment was observed most frequently. Age-related typical audiograms showed a down-sloping configuration at ages of more than 30 years, with the fastest rate of progression at the high frequencies. Vestibular function tests revealed hypofunction of the vestibular labyrinth in 2 mutation carriers (not statistically significant).

Conclusions:

The clinical features in the present family with a POU4F3 mutation were fairly similar to those in the 2 previously described DFNA15 families, but the level of hearing impairment was milder, and there was no substantial vestibular dysfunction.

Missense mutations in POU4F3 cause autosomal dominant hearing impairment DFNA15 and affect subcellular localization and DNA binding

In a Dutch pedigree suffering from autosomal dominant nonsyndromic hearing impairment (ADNSHI), linkage was found to the locus for DFNA15, with a two-point logarithm of the odds (LOD) score of 5.1. Sequence analysis of the POU4F3 gene that is involved in DFNA15 revealed the presence of a missense mutation (c.865C>T), segregating with the deafness in this family. The mutation is predicted to result in the substitution of a phenylalanine residue for a leucine residue (p.L289F) in the POU homeodomain of the transcription factor POU4F3. Mutation analysis of the POU4F3 gene in 30 patients suffering from dominantly inherited hearing impairment revealed a second novel missense mutation (c.668T>C), resulting in the substitution of a proline for a leucine residue (p.L223P) within the POU-specific DNA-binding domain of the protein. In a computer model describing the structure of the two DNA-binding domains, the alterations are predicted to affect the tertiary structure of these domains. Transient transfection studies showed that whereas the wild-type POU4F3 is located almost exclusively in the nucleus, part of the mutant proteins was also present in the cytoplasm. In addition, both mutant proteins showed greatly reduced capability for binding to DNA as well as transcriptionally activating reporter gene expression. Together, our results describe the identification of the first missense mutations in POU4F3 causing DFNA15. Furthermore, mutations in this gene do not seem to be a rare cause of hearing impairment in the Dutch population, and the POU4F3 gene may thus be suitable for implementation in diagnostic testing.

Specific amino acid residues in the basic helix-loop-helix domain of SRC-3 are essential for its nuclear localization and proteasome-dependent turnover

SRC-3/AIB1/ACTR/pCIP/RAC3/TRAM-1 is a primary transcriptional coactivator for the estrogen receptor. Here we report that deletion of the SRC-3 basic helix-loop-helix (bHLH) domain blocks its proteasome-dependent turnover. We further identified two residues (K17 and R18) in the SRC-3 bHLH domain that are essential for its stability. Moreover, we found that the bHLH domain contains a bipartite nuclear localization signal (NLS). SRC-3 NLS mutants block its translocation into the nucleus, and this correlates with its insensitivity to proteasome-dependent turnover. SRC-3 shows a time-dependent decay in the presence of cycloheximide which is not apparent for the cytoplasmic mutant. Fusion of a simian virus 40 T antigen NLS to the cytoplasmic localized SRC-3 mutant drives it back into the nucleus and restores its proteasomal sensitivity. In addition, the cytoplasmic mutants are inactive for transcriptional coactivation and cancer cell growth. Taken together, our data indicate that proteasome-dependent turnover of SRC-3 occurs in the nucleus and that two amino acid residues in the bHLH domain provide a signal for its nuclear localization and proteasome-dependent degradation as well as for regulation of SRC-3 transcriptional coactivator capacity.

Molecular genetics of non-syndromic deafness

One in every 1,000 newborn suffers from congenital hearing impairment. More than 60% of the congenital cases are caused by genetic factors. In most cases, hearing loss is a multifactorial disorder caused by both genetic and environmental factors. Molecular genetics of deafness has experienced remarkable progress in the last decade. Genes responsible for hereditary hearing impairment are being mapped and cloned progressively. This review focuses on non-syndromic hearing loss, since the gene involved in this type of hearing loss have only recently begun to be identified.

Nuclear and mitochondrial genes mutated in nonsyndromic impaired hearing

Half of the cases with congenital impaired hearing are hereditary (HIH). HIH may occur as part of a multisystem disease (syndromic HIH) or as disorder restricted to the ear and vestibular system (nonsyndromic HIH). Since nonsyndromic HIH is almost exclusively caused by cochlear defects, affected patients suffer from sensorineural hearing loss. One percent of the total human genes, i.e. 300-500, are estimated to cause syndromic and nonsyndromic HIH. Of these, approximately 120 genes have been cloned thus far, approximately 80 for syndromic HIH and 42 for nonsyndromic HIH. In the majority of the cases, HIH manifests before (prelingual), and rarely after (postlingual) development of speech. Prelingual, nonsyndromic HIH follows an autosomal recessive trait (75-80%), an autosomal dominant trait (10-20%), an X-chromosomal, recessive trait (1-5%), or is maternally inherited (0-20%). Postlingual nonsyndromic HIH usually follows an autosomal dominant trait. Of the 41 mutated genes that cause nonsyndromic HIH, 15 cause autosomal dominant HIH, 15 autosomal recessive HIH, 6 both autosomal dominant and recessive HIH, 2 X-linked HIH, and 3 maternally inherited HIH. Mutations in a single gene may not only cause autosomal dominant, nonsyndromic HIH, but also autosomal recessive, nonsyndromic HIH (GJB2, GJB6, MYO6, MYO7A, TECTA, TMC1), and even syndromic HIH (CDH23, COL11A2, DPP1, DSPP, GJB2, GJB3, GJB6, MYO7A, MYH9, PCDH15, POU3F4, SLC26A4, USH1C, WFS1). Different mutations in the same gene may cause variable phenotypes within a family and between families. Most cases of recessive HIH result from mutations in a single locus, but an increasing number of disorders is recognized, in which mutations in two different genes (GJB2/GJB6, TECTA/KCNQ4), or two different mutations in a single allele (GJB2) are involved. This overview focuses on recent advances in the genetic background of nonsyndromic HIH.

Genética molecular da deficiência auditiva não-sindrômica

Aproximadamente 1/1000 recém-nascidos apresentam deficiência auditiva congênita, sendo 60% dessas de etiologia genética. Na maioria dos casos, a deficiência auditiva é uma doença multifatorial causada por ambos os fatores, genéticos e ambientais. A genética molecular da deficiência auditiva tem apresentado grandes avanços na última década, pois os genes responsáveis pela deficiência auditiva hereditária vêm sendo progressivamente mapeados e clonados. Esta revisão enfatiza a deficiência auditiva não-sindrômica, uma vez que, os genes envolvidos nesse tipo de deficiência foram identificados recentemente.

Inner hair cell Cre-expressing transgenic mouse

Cochlear hair cells of the inner ear are mechanosensory transducers critical for sound reception in mammals. A mouse with a specific expression of Cre recombinase activity in hair cells is essential for hair cell-specific gene targeting. Here we report a transgenic mouse in which Cre activity is detected in inner hair cells, not in supporting cells, in the cochlea. The Cre activity was visualized with both X-gal staining and beta-galactosidase immunostaining in progeny of a cross between our Cre line and the reporter ROSA26R line. In inner hair cells, the Cre activity started at postnatal day 14 and was maintained throughout adulthood. Starting at postnatal day 50, a few outer hair cells in the outermost row of cochlear apical and middle turns displayed the Cre activity. In vestibular hair cells and spiral ganglia, the Cre activity was also detected. Cre activity was present in cells widely distributed throughout brain, testis, and retina, but was absent in many other tissues such as kidney, heart, liver, and intestine. This Cre mouse line can thus be used for conditional gene targeting in mature inner hair cells of the cochlea. genesis 39:173-177, 2004.

Brn-3c (POU4F3) regulates BDNF and NT-3 promoter activity

Brn-3c is a transcription factor necessary for maturation and survival of hair cells in the inner ear. Mutations in Brn-3c are associated with deafness in mice and with hearing loss in humans. Mice lacking Brn-3c also show reduced innervation and loss of sensory neurons presumed to be an indirect effect of hair cell loss potentially through lower BDNF and NT-3 expression. Using transient transfection assays we show that Brn-3c is capable of activating both BDNF and NT-3 promoters in inner ear sensory epithelial cell lines. In vitro analysis shows that Brn-3c binds to specific elements within the promoters of both genes and these elements are sufficient to confer Brn-3c regulation on a heterologous promoter. Additionally, BDNF expression is reduced in the inner ear of a Brn-3c mutant mouse during embryogenesis. Our data suggest that Brn-3c may play a role in regulating neurotrophin gene expression in the inner ear.

Targeting hearing genes in mice

The rate of identification of genes for hearing has clearly outpaced the rate of determination of the functions of these genes' products. The use of transgenic and knock-out mouse models is a powerful approach to the elucidation of gene function in the ear. A large number of gene-targeted mice with auditory defects have recently been created and characterized, and nine independent mouse lines in which Cre recombinase activity begins to be expressed during early embryonic development of the ear or is specifically expressed in hair cells during postnatal development will be useful for ear-specific gene manipulation when combined with mouse lines that have loxP sites flanking the genes of interest. Existing gene-trapped embryonic stem (ES) cells and existing targeting constructs are readily available; new targeting constructs can easily be created by modifying bacterial artificial chromosomes and using them to directly transfect and screen ES cells; and N-ethyl-N-nitrosourea mutagenesis of ES cells can create point mutations in specific genes. To minimize variation in hearing phenotypes and avoid undesired hearing defects, mutant mice in the common gene-targeting background strains (129 and C57BL/6) should be transferred into congenic CBA/CaJ, a strain with "gold standard" normal hearing. Valuable mutant strains can be maintained, distributed, and cryopreserved in one of four NIH-sponsored Mutant Mouse Regional Resource Centers. Targeting hearing genes in mice will provide unprecedented opportunities for collaboration and new directions in the hearing research community.

Transcription profiling of inner ears from Pou4f3(ddl/ddl) identifies Gfi1 as a target of the Pou4f3 deafness gene

Pou4f3 (Brn3.1, Brn3c) is a class IV POU domain transcription factor that has a central function in the development of all hair cells in the human and mouse inner ear sensory epithelia. A mutation of POU4F3 underlies human autosomal dominant non-syndromic progressive hearing loss DFNA15. Through a comparison of inner ear gene expression profiles of E16.5 wild-type and Pou4f3 mutant deaf mice using a high density oligonucleotide microarray, we identified the gene encoding growth factor independence 1 (Gfi1) as a likely in vivo target gene regulated by Pou4f3. To validate this result, we performed semi-quantitative RT-PCR and in situ hybridizations for Gfi1 on wild-type and Pou4f3 mutant mice. Our results demonstrate that a deficiency of Pou4f3 leads to a statistically significant reduction in Gfi1 expression levels and that the dynamics of Gfi1 mRNA abundance closely follow the pattern of expression for Pou4f3. To examine the role of Gfi1 in the pathogenesis of Pou4f3-related deafness, we performed comparative analyses of the embryonic inner ears of Pou4f3 and Gfi1 mouse mutants using immunohistochemistry and scanning electron microscopy. The loss of Gfi1 results in outer hair cell degeneration, which appears comparable to that observed in Pou4f3 mutants. These results identify Gfi1 as the first downstream target of a hair cell specific transcription factor and suggest that outer hair cell degeneration in Pou4f3 mutants is largely or entirely a result of the loss of expression of Gfi1.