REST mRNA expression in normal and regenerating avian auditory epithelium

Repressor element 1-silencing transcription factor deficiency yields profound hearing loss through Kv7.4 channel upsurge in auditory neurons and hair cells

Repressor element 1-silencing transcription factor (REST) is a transcriptional repressor that recognizes neuron-restrictive silencer elements in the mammalian genomes in a tissue- and cell-specific manner. The identity of REST target genes and molecular details of how REST regulates them are emerging. We performed conditional null deletion of Rest (cKO), mainly restricted to murine hair cells (HCs) and auditory neurons (aka spiral ganglion neurons [SGNs]). Null inactivation of full-length REST did not affect the development of normal HCs and SGNs but manifested as progressive hearing loss in adult mice. We found that the inactivation of REST resulted in an increased abundance of K_v7.4 channels at the transcript, protein, and functional levels. Specifically, we found that SGNs and HCs from Rest cKO mice displayed increased K_v7.4 expression and augmented K_v7 currents; SGN’s excitability was also significantly reduced. Administration of a compound with K_v7.4 channel activator activity, fasudil, recapitulated progressive hearing loss in mice. In contrast, inhibition of the K_v7 channels by XE991 rescued the auditory phenotype of Rest cKO mice. Previous studies identified some loss-of-function mutations within the K_v7.4-coding gene, Kcnq4, as a causative factor for progressive hearing loss in mice and humans. Thus, the findings reveal that a critical homeostatic K_v7.4 channel level is required for proper auditory functions.

A DNA variant within the MYO7A promoter regulates YY1 transcription factor binding and gene expression serving as a potential dominant DFNA11 auditory genetic modifier

Mutations within MYO7A can lead to recessive and dominant forms of inherited hearing loss. We previously identified a large pedigree (referred to as the HL2 family) with hearing loss that first impacts the low and mid frequencies segregating a dominant MYO7A mutation in exon 17 at DNA residue G2164C. The MYO7A(G2164C) mutation predicts a nonconservative glycine-to-arginine (G722R) amino acid substitution at a highly conserved glycine residue. The degree of low and mid frequency hearing loss varies markedly in the family, suggesting the presence of a genetic modifier that either rescues or exacerbates the primary MYO7A(G2164C) mutation. Here we describe a single nucleotide polymorphism (SNP) T/C at position -4128 in the wild-type MYO7A promoter allele that sorts with the degree of hearing loss severity in the pedigree. Electrophoretic mobility shift assay analysis indicates that the SNP differentially regulates the binding of the YY1 transcription factor with the T(-4128) allele creating an YY1 binding site. Immunocytochemistry demonstrates that Yy1 is expressed in hair cell nuclei within the cochlea. Given that Myo7a is also expressed in cochlear hair cells, Yy1 shows the appropriate localization to regulate Myo7a transcription within the inner ear. YY1 appears to be acting as a transcriptional repressor as the MYO7A promoter allele containing the T(-4128) SNP drives 41 and 46% less reporter gene expression compared with the C(-4128) SNP in the ARPE-19 and HeLa cell lines, respectively. The T(-4128) SNP may be contributing to the severe hearing loss phenotype in the HL2 pedigree by reducing expression of the wild-type MYO7A allele.

The histone deacetylase inhibitor sodium butyrate protects against cisplatin-induced hearing loss in guinea pigs

OBJECTIVE

There is a need for otoprotective agents that can be administered systemically without compromising cancer treatment. Histone deacetylase inhibitors are anticancer agents that act by upregulating the expression of cell-cycle control genes. They are also neuroprotective, leading us to hypothesize that they might be otoprotective. The goal of this study was to determine if the antitumor agent sodium butyrate (a histone deacetylase inhibitor) protects against cisplatin ototoxicity when administered systemically.

STUDY DESIGN

This was an animal study.

METHODS

: Cisplatin was administered to guinea pigs who received either 12 days of sodium butyrate (7 d before and 5 d after cisplatin) or equivolume saline injections. Hearing was tested with distortion product otoacoustic emission (DPOAE) analysis before the start of the study and 2 weeks after cisplatin treatment.

RESULTS

Guinea pigs given a single intraperitoneal injection of 14 mg/kg cisplatin experience a mean hearing loss of 8 dB across the frequencies of 3.5, 5, 7, 10, 14, and 20 kHz. Intraperitoneal injection of 1.2 mg/kg sodium butyrate per day for 7 days before and 5 days after cisplatin almost completely eliminates this threshold shift (P=.0011).

CONCLUSIONS

The histone deacetylase inhibitor sodium butyrate gives almost complete protection in a single-dose model of cisplatin ototoxicity in guinea pigs. Because histone deacetylase inhibitors are anticancer agents with very few side effects, they may be candidates for clinical use during cisplatin chemotherapy.

Localization of a novel autosomal recessive non-syndromic hearing impairment locus DFNB55 to chromosome 4q12-q13.2

Hereditary hearing impairment (HI) is the most genetically heterogeneous trait known in humans. So far, 54 autosomal recessive non-syndromic hearing impairment (ARNSHI) loci have been mapped, and 21 ARNSHI genes have been identified. Here is reported the mapping of a novel ARNSHI locus, DFNB55, to chromosome 4q12-q13.2 in a consanguineous Pakistani family. A maximum multipoint LOD score of 3.5 was obtained at marker D4S2638. The region of homozygosity and the 3-unit support interval are flanked by markers D4S2978 and D4S2367. The region spans 8.2 cm on the Rutgers combined linkage-physical map and contains 11.5 Mb. DFNB55 represents the third ARNSHI locus mapped to chromosome 4.

Age effects and size effects in the ears of gekkonomorph lizards: inner ear

Audiograms have indicated greater auditory sensitivity in larger than in smaller geckos; part of this difference, interspecifically and intraspecifically, is explained by middle-ear proportions. To investigate the contribution of the inner ear to the variation in sensitivity, we examined it in museum specimens representing 11 species and three subfamilies. We measured papilla basilaris length, and, when intact, the saccular otoconial mass. Papilla length approximated 1% of rostrum-anus length in large geckos but 2% in small geckos; in some species some inter-aural difference was indicated. Over the lumped material, relative papilla length varied as a function of body length, with highly significant correlation. Similar relations prevailed within each subfamily. However, intraspecifically the correlation of papilla basilaris length with animal size was usually nonsignificant. Hair cell populations assessed from SEM photographs were larger in the larger species but intraspecifically did not relate to an individual's size. Hence interspecifically, the dependence of auditory sensitivity on animal size seems supported by inner-ear differences but intraspecifically this relation derives only from the middle ear. Otoconial mass, as measured by its volume, was correlated with animal length both interspecifically and intraspecifically.