Mechanotransduction in mouse inner ear hair cells requires transmembrane channel–like genes
Yoshiyuki Kawashima, Gwenaëlle S.G. Géléoc, Kiyoto Kurima, Valentina Labay, Andrea Lelli, Yukako Asai, Tomoko Makishima, Doris K. Wu, Charles C. Della Santina, Jeffrey R. Holt, Andrew J. Griffith
Yoshiyuki Kawashima, Gwenaëlle S.G. Géléoc, Kiyoto Kurima, Valentina Labay, Andrea Lelli, Yukako Asai, Tomoko Makishima, Doris K. Wu, Charles C. Della Santina, Jeffrey R. Holt, Andrew J. Griffith
View: Text | PDF
Research Article

Mechanotransduction in mouse inner ear hair cells requires transmembrane channel–like genes

Abstract

Inner ear hair cells convert the mechanical stimuli of sound, gravity, and head movement into electrical signals. This mechanotransduction process is initiated by opening of cation channels near the tips of hair cell stereocilia. Since the identity of these ion channels is unknown, and mutations in the gene encoding transmembrane channel–like 1 (TMC1) cause hearing loss without vestibular dysfunction in both mice and humans, we investigated the contribution of Tmc1 and the closely related Tmc2 to mechanotransduction in mice. We found that Tmc1 and Tmc2 were expressed in mouse vestibular and cochlear hair cells and that GFP-tagged TMC proteins localized near stereocilia tips. Tmc2 expression was transient in early postnatal mouse cochlear hair cells but persisted in vestibular hair cells. While mice with a targeted deletion of Tmc1 (Tmc1Δ mice) were deaf and those with a deletion of Tmc2 (Tmc2Δ mice) were phenotypically normal, Tmc1ΔTmc2Δ mice had profound vestibular dysfunction, deafness, and structurally normal hair cells that lacked all mechanotransduction activity. Expression of either exogenous TMC1 or TMC2 rescued mechanotransduction in Tmc1ΔTmc2Δ mutant hair cells. Our results indicate that TMC1 and TMC2 are necessary for hair cell mechanotransduction and may be integral components of the mechanotransduction complex. Our data also suggest that persistent TMC2 expression in vestibular hair cells may preserve vestibular function in humans with hearing loss caused by TMC1 mutations.

Authors

Yoshiyuki Kawashima, Gwenaëlle S.G. Géléoc, Kiyoto Kurima, Valentina Labay, Andrea Lelli, Yukako Asai, Tomoko Makishima, Doris K. Wu, Charles C. Della Santina, Jeffrey R. Holt, Andrew J. Griffith

×

Figure 1

Hair cell expression of Tmc1 and Tmc2.

Options: View larger image (or click on image) Download as PowerPoint
Hair cell expression of Tmc1 and Tmc2. (A) qPCR analysis of Tmc1 and...
(A) qPCR analysis of Tmc1 and Tmc2 in RNA extracted from mouse utricles at developmental ages between E15 and P21. We used primers that amplify a fragment of Tmc1 common to both Tmc1ex1 and Tmc1ex2. Each sample was analyzed 6–9 times. Expression levels were normalized, using the ΔΔCt method, first to Actb (encoding β-actin) expression and then to the Tmc expression level at E15. Error bars indicate ± SD. (B) qPCR analysis of mouse cochlear RNA showed a steady rise in Tmc1 expression through P5 and in the P22 apical sample. Other portions of P22 cochleae were not harvested due to rapid degradation of hair cell integrity and mRNA quality. Tmc2 RNA was transiently expressed in mouse cochleae during the postnatal period. Error bars indicate SD. (C) In situ hybridization analysis of Tmc2 in P1 mouse vestibule and cochlea. Tmc2 expression was detected in wild-type crista ampullaris (CA), utricular macula (UM), hair cells of the basal cochlear turn, and, to a lesser extent, in the middle turn at P1. Tmc2 expression was not detected in hair cells of the apical turn. Adjacent sections probed for Myo15 transcripts are shown as a control for hair cell hybridization (52). Scale bar: 100 μm. See also Supplemental Figure 1.