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First published online on September 14, 2006.
Copyright © 2006 by The Physiological Society
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jphysiol.2006.118547v1
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Received August 2, 2006
Revised August 26, 2006
Accepted after revision September 11, 2006

Auditory mechanotransduction in the absence of functional myosin-XVa

Ruben Stepanyan1, Inna A Belyantseva2, Andrew J Griffith2, Thomas B Friedman2, and Gregory I Frolenkov1*

1 Department of Physiology, University of Kentucky
2 National Institute on Deafness and Other Communication Disorders, NIH

* To whom correspondence should be addressed. E-mail: gregory.frolenkov{at}uky.edu.

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.


Key words: Cochlea • Mechano-electrical transduction • Myosin







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