Direct mechanical stimulation of tip links in hair cells through DNA tethers.

Aakash Basu,Aj Hudspeth,Samuel Lagier,Brian A Fabella,Maria Vologodskaia

doi:10.7554/elife.16041

Abstract

Mechanoelectrical transduction by hair cells commences with hair-bundle deflection, which is postulated to tense filamentous tip links connected to transduction channels. Because direct mechanical stimulation of tip links has not been experimentally possible, this hypothesis has not been tested. We have engineered DNA tethers that link superparamagnetic beads to tip links and exert mechanical forces on the links when exposed to a magnetic-field gradient. By pulling directly on tip links of the bullfrog's sacculus we have evoked transduction currents from hair cells, confirming the hypothesis that tension in the tip links opens transduction channels. This demonstration of direct mechanical access to tip links additionally lays a foundation for experiments probing the mechanics of individual channels.

Highlights

Hair cells occur universally in the auditory and vestibular systems of vertebrates, where they transduce mechanical stimuli into electrical responses and initiate the perception of sounds and accelerations (Hudspeth, 2008, 2014)
The upper two-thirds of this link comprises a parallel dimer of cadherin 23 (CDH23) molecules whereas the lower third encompasses a parallel dimer of protocadherin 15 (PCDH15) molecules (Kazmierczak et al, 2007)
We have developed a method of applying mechanical force to tip links, allowing us to test directly the hypothesis that tip-link tension gates the transduction channels

Summary

Introduction

Hair cells occur universally in the auditory and vestibular systems of vertebrates, where they transduce mechanical stimuli into electrical responses and initiate the perception of sounds and accelerations (Hudspeth, 2008, 2014). Deflection of a hair bundle toward its tall edge opens mechanoelectrical-transduction channels that allow an influx of cations, predominantly K+ and Ca2+, and depolarizes the hair cell. Electrophysiological and mechanical evidence suggests that deflection increases the tension in an elastic structure, the gating spring, that communicates force to the transduction channels (Corey and Hudspeth, 1983a). Several lines of circumstantial evidence support the hypothesis that the tip link constitutes at least a portion of the gating spring: the stereociliary tips are the site of transduction (Hudspeth, 1982; Beurg et al, 2009); the orientation of the tip links corresponds to the hair bundle’s axis of maximal sensitivity (Shotwell et al, 1981); and the responsiveness vanishes when the tip links are disrupted (Assad et al, 1991). The critical role of tip-link tension in gating mechanoelectrical-transduction channels has never been tested directly

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Conclusion