Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2006 Nov 1;576(Pt 3):801-8.
doi: 10.1113/jphysiol.2006.118547. Epub 2006 Sep 14.

Auditory mechanotransduction in the absence of functional myosin-XVa

Ruben Stepanyan  1 , Inna A Belyantseva, Andrew J Griffith, Thomas B Friedman, Gregory I Frolenkov
Affiliations

Auditory mechanotransduction in the absence of functional myosin-XVa

Ruben Stepanyan et al. J Physiol. .

Abstract

In hair cells of all vertebrates, a mechanosensory bundle is formed by stereocilia with precisely graded heights. Unconventional myosin-XVa is critical for formation of this bundle because it transports whirlin and perhaps other molecular components responsible for programmed elongation of stereocilia to the stereocilia tips. A tip of a stereocilium is the site of stereocilia growth and one of the proposed sites of mechano-electrical transduction. In adult shaker 2 mice, a mutation that disables the motor function of myosin-XVa results in profound deafness and abnormally short stereocilia that lack stereocilia links, an indispensable component of mechanotransduction machinery. Therefore, it was assumed that myosin-XVa is required for proper formation of the mechanotransduction apparatus. Here we show that in young postnatal shaker 2 mice, abnormally short stereocilia bundles of auditory hair cells have numerous stereocilia links and 'wild type' mechano-electrical transduction. We compared the mechanotransduction current in auditory hair cells of young normal-hearing littermates, myosin-XVa-deficient shaker 2 mice, and whirler mice that have similarly short stereocilia but intact myosin-XVa at the stereocilia tips. This comparison revealed that the absence of functional myosin-XVa does not disrupt adaptation of the mechanotransduction current during sustained bundle deflection. Thus, the hair cell mechanotransduction complex forms and functions independently from myosin-XVa-based hair bundle morphogenesis.

PubMed Disclaimer

Figures

Figure 2
Figure 2. Intact mechano-electrical transduction in young Myo15sh2/sh2 OHCs
A, organ of Corti explant with a piezo-driven probe (left) and a patch pipette (right). B and C, typical SEM images of OHC stereocilia bundles at the end of the first (apical) cochlear turn in Myo15sh2/sh2 (B) and Myo15+/sh2 (C) organ of Corti explants. D and E, representative whole-cell currents (top traces) evoked by the graded deflections of stereocilia at a holding potential of −90 mV in Myo15sh2/sh2 (D) and Myo15+/sh2 (E) mice. Mechanotransduction current rapidly reaches a peak (black arrows) and then decays on a fast and then slow (open arrows) time scale. Responses to the inhibitory bundle deflections are shown in bold. Relatively large access resistances (D −74 MΩ, E −73.5 MΩ) may somewhat decrease the driving force and maximum amplitude of transduction current. F, average relationships between peak transduction current and probe displacement in Myo15+/sh2 (○, n = 7) and Myo15sh2/sh2 (•, n = 7) OHCs. Data were fitted with a second order Boltzmann function: I = Imax/[1 + exp(α2*(p2 −Δx))*(1 + exp(α1*(p1 −Δx)))] − Imin. Parameters of the fit (Myo15+/sh2/Myo15sh2/sh2): Imax = 285/240 pA; Imin = 14.4/6.9 pA; α1 = 12.6/11.7 μm−1; p1 = 0.11/0.18 μm; α2 = 4.5/3.7 μm−1; p2 = 0.28/0.18 μm. Access resistances (Myo15+/sh2/Myo15sh2/sh2): 53 ± 6/51 ± 4 MΩ. G, normalized current-displacement relationships in OHCs of Myo15+/sh2 and Myo15sh2/sh2 mice at −90 mV holding potential. The averages of individual normalized current-displacement curves are shown. Parameters of the fit (Myo15+/sh2/Myo15sh2/sh2): α1 = 10.7/10.5 μm−1; p1 = 0.14/0.18 μm; α2 = 3.8/3.6 μm−1; p2 = 0.26/0.19 μm. The same OHCs contributed to F and G. Vertical bars indicate Standard Errors. Scale bars: 10 μm (A); 1 μm (B and C). Hair cell ages: B–E: P2 plus 3–4 days in vitro, F and G: P2–3 plus 2–4 days in vitro.
Figure 1
Figure 1. Auditory mechanotransduction phenotype of young postnatal Myo15sh2/sh2 mice
A and B, SEM images of Myo15sh2/sh2 OHCs at postnatal day 9 (P9) (A) and 19 (B). Insets show magnified images of stereocilia. Note stereocilia links in A and their absence in B. C, auditory brainstem responses in P16 homozygous (left) and heterozygous (right) Myo15sh2 mice. Stimulus type and intensity (dB SPL, sound pressure level) are indicated. Arrows mark the stimulus onset. D, epifluorescent images of Myo15sh2/sh2 organ of Corti explants (harvested at P3 and kept 3 days in vitro) after incubations with 5 μm FM1-43 for 60 s (left), FM1-43 and 1 mm GdCl3 for 60 s (middle), or FM3-25 for 6 min (right). E, time course of FM1-43 uptake in Myo15sh2/sh2 hair cells measured at the confocal optical plane below the cuticular plate. Insets show the actual fluorescent images before and immediately after application of 5 μm of the dye to the apical surface of OHCs. Scale bars: 1 μm (A, B); 10 μm (D). All cells (A and B, D and E) were located approximately at the end of the first (apical) cochlear turn.
Figure 3
Figure 3. Properties of mechano-electrical transduction in Myo15sh2/sh2 OHCs
A, voltage–current relationship of the maximal mechanotransduction current evoked by ramp deflections of the bundle at different holding potentials (inset). B, mechanotransduction currents recorded at −90 mV and +90 mV holding potentials in the same cell. C, mechanotransduction current (left) evoked by a brief bundle deflection before (○) and after (▪) a longer step-like deflection of stereocilia by 0.6 μm at −70 mV holding potential. Displacement–current relationships (right) were fitted to a first order Boltzmann function to determine a shift due to adaptation (0.5 μm, indicated by arrow). Access resistances (MΩ): A −40.6; B −37.8; C −74.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Assad JA, Hacohen N, Corey DP. Voltage dependence of adaptation and active bundle movement in bullfrog saccular hair cells. Proc Natl Acad Sci U S A. 1989;86:2918–2922. - PMC - PubMed
    1. Assad JA, Shepherd GM, Corey DP. Tip-link integrity and mechanical transduction in vertebrate hair cells. Neuron. 1991;7:985–994. - PubMed
    1. Belyantseva IA, Boger ET, Friedman TB. Myosin XVa localizes to the tips of inner ear sensory cell stereocilia and is essential for staircase formation of the hair bundle. Proc Natl Acad Sci U S A. 2003;100:13958–13963. - PMC - PubMed
    1. Belyantseva IA, Boger ET, Naz S, Frolenkov GI, Sellers JR, Ahmed ZM, Griffith AJ, Friedman TB. Myosin-XVa is required for tip localization of whirlin and differential elongation of hair-cell stereocilia. Nat Cell Biol. 2005;7:148–156. - PubMed
    1. Beyer LA, Odeh H, Probst FJ, Lambert EH, Dolan DF, Camper SA, Kohrman DC, Raphael Y. Hair cells in the inner ear of the pirouette and shaker 2 mutant mice. J Neurocytol. 2000;29:227–240. - PubMed

Publication types

MeSH terms

LinkOut - more resources