The 133-kDa N-terminal domain enables myosin 15 to maintain mechanotransducing stereocilia and is essential for hearing

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Abstract

The precise assembly of inner ear hair cell stereocilia into rows of increasing height is critical for mechanotransduction and the sense of hearing. Yet, how the lengths of actin-based stereocilia are regulated remains poorly understood. Mutations of the molecular motor myosin-15 stunt stereocilia growth and cause deafness. We found that hair cells express two isoforms of myosin-15 through alternative splicing of an N-terminal domain, and that these isoforms selectively traffic to different stereocilia rows. Using an isoform-specific knockout mouse, hair cells expressing only the small isoform remarkably develop normal stereocilia bundles. However, a critical subset of stereocilia with active mechanotransducer channels subsequently retracts. The larger isoform with the N-terminal domain traffics to these specialized stereocilia and prevents disassembly of their actin core. Our results show that myosin-15 isoforms can navigate between functionally distinct classes of stereocilia, and are independently required to assemble and then maintain the intricate hair bundle architecture.

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Qing Fang

Department of Human Genetics, University of Michigan, Ann Arbor, United States

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The authors declare that no competing interests exist.
Artur A Indzhykulian

Department of Neurobiology, Harvard Medical School, Boston, United States

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The authors declare that no competing interests exist.
Mirna Mustapha

Department of Otolaryngology - Head and Neck Surgery, Stanford University, Stanford, United States

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The authors declare that no competing interests exist.
Gavin P Riordan

Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, Bethesda, United States

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The authors declare that no competing interests exist.
David F Dolan

Department of Otolaryngology, University of Michigan Medical School, Ann Arbor, United States

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The authors declare that no competing interests exist.
Thomas B Friedman

Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, Bethesda, United States

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The authors declare that no competing interests exist.
Inna A Belyantseva

Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, Bethesda, United States

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The authors declare that no competing interests exist.
Gregory I Frolenkov

Department of Physiology, University of Kentucky, Lexington, United States

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The authors declare that no competing interests exist.
Sally A Camper

Department of Human Genetics, University of Michigan, Ann Arbor, United States

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The authors declare that no competing interests exist.
Jonathan E Bird

Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, Bethesda, United States

For correspondence
jonathan.bird@nih.gov

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The authors declare that no competing interests exist.

Ethics

Animal experimentation: All animal procedures were approved by the institutional animal care and use committees (IACUC) at the University of Michigan (#PRO00004639, #PRO00005913, #PRO00005128), the University of Kentucky (#903M2005) and at the NIDCD (#1263-12).

Copyright

This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.