TMC1 and TMC2 Are Components of the Mechanotransduction Channel in Hair Cells of the Mammalian Inner Ear

Abstract

SUMMARY Sensory transduction in auditory and vestibular hair cells requires expression of transmembrane channel-like (Tmc) 1 and 2 genes, but the function of these genes is unknown. To investigate the hypothesis that TMC1 and TMC2 proteins are components of the mechanosensitive ion channels that convert mechanical information into electrical signals, we recorded whole-cell and single-channel currents from mouse hair cells that expressed Tmc1, Tmc2 or mutant Tmc1. Cells that expressed mutant Tmc1 had reduced calcium permeability and reduced single-channel currents, while Tmc2 cells had high calcium permeability and large single-channel currents. Cells that expressed both Tmc1 and Tmc2 had a broad range of single-channel currents, suggesting multiple heteromeric assemblies of TMC subunits. The data demonstrate TMC1 and TMC2 are components of hair cell transduction channels and contribute to permeation properties. Gradients in TMC channel composition may also contribute to variation in sensory transduction along the tonotopic axis of the mammalian cochlea.

Treatment of autosomal dominant hearing loss by in vivo delivery of genome editing agents

“…All mice were genotyped by Transnetyx (Cordova, TN). For mechanotransduction experiments, two genotypes of Tmc mutant mice were used: Tmc1 Bth/Bth;Tmc2 Δ/Δ and Tmc1 Δ/Δ;Tmc2 Δ/Δ as previously reported 16 .…”

“…Tmc1 protein is an essential component of mechanotransduction channels in mammalian hair cells 16 . Mutations in TMC1 have been linked to recessive and dominant genetic deafness 17 .…”

“…Mutations in TMC1 have been linked to recessive and dominant genetic deafness 17 . A dominant-negative missense mutation in TMC1 (p.M418K, c.T1253A) causes reduced single-channel current levels and calcium permeability 16 and progressive post-lingual sensorineural hearing loss in humans 18–20 . The Bth/+ mouse model carries the orthologous missense mutation (p.M412K, c.T1235A) in the mouse Tmc1 gene and exhibits progressive auditory response threshold elevation and progressive hair cell loss beginning at one month 21 .…”

“…Neonatal cochlear hair cells express Tmc1 and Tmc2, both of which can enable sensory transduction. To isolate the effect of editing the Bth allele, we injected the Cas9:Tmc1-mut3 sgRNA:lipid complex into Tmc1 Bth/Δ;Tmc2 Δ/Δ mice 16 to avoid transduction current contributions from Tmc2 and from wild-type Tmc1. We recorded sensory transduction currents from inner hair cells (IHCs) after injection with Cas9:Tmc1-mut3:lipid complex, or with a control targeting an unrelated gfp gene.…”

Morin hydrate promotes inner ear neural stem cell survival and differentiation and protects cochlea against neuronal hearing loss

“…Isolated cochlea were divided into three experimental groups ( n = 10 each): ( i ) control, 0 mM gentamicin + 0 mg/l morin hydrate; ( ii ) GM, 3 mM gentamicin + 0 mg/l morin hydrate; and ( iii ) GM+morin, 3 mM gentamicin + 2 mg/l morin hydrate. After 24 hrs of respective treatments, they were then subjected to mechanotransduction measurements following previously established methods 19, 20. Briefly, utricles and cochleae were separated and mounted on glass coverslips and viewed using Axioskop FS upright microscope (Zeiss, Oberkochen, Germany) equipped with a 633 water‐immersion objective and differential interference contrast optics.…”