Ripor2 is involved in auditory hair cell stereociliary bundle structure and orientation
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RIPOR2 (previously known as FAM65B) localizes to stereocilia of auditory hair cells and causes deafness when its function is disturbed by mutations. Here, we demonstrate that during the morphogenesis of the hair cell bundle, absence of Ripor2 affects the orientation of this key subcellular structure. We show that Ripor2 interacts with Myh9, a protein encoded by a known deafness gene. Absence of Ripor2 is associated with low Myh9 abundance in the mouse cochlea despite increased amount of Myh9 transcripts. While Myh9 is mainly expressed in stereocilia, a phosphorylated form of Myh9 is particularly enriched in the kinocilium. In Ripor2-deficient mice, kinocilium shows an aberrant localization which associates with a reduced content of phosphorylated Myh9. Acetylated alpha tubulin, another specific kinociliary protein which contributes to microtubule stabilization, is reduced in the absence of Ripor2 as well. We propose that Ripor2 deficiency influences abundance and/or post-translational modifications of proteins expressed in both stereocilia and kinocilia. This effect may have a negative impact on the structure and function of the auditory hair cell bundle.
KeywordsDeafness Hair cells Kinocilium Myh9 Ripor2 Stereocilia
The Ripor2tm1(KOMP)Vlcg mouse strain used for this research project was created from ES cell clone 15686A-B6, generated by Regeneron Pharmaceuticals, Inc. and made into live mice by the KOMP Repository (www.komp.org) and the Mouse Biology Program (www.mousebiology.org) at the University of California Davis. Dr. Oscar Diaz-Horta was a molecular biologist who made significant contributions to the biology of hearing and deafness. He passed away on August 26, 2018, before the acceptance of this article. He will be missed sorely and remembered fondly by all who knew him.
This study was supported by NIH grant R01DC009645 to M.T and by the Hearing Health Foundation’s Emerging Research Grants program to O.D-H.
Compliance with ethical standards
All procedures were approved by the University of Miami Institutional Animal Care and Use Committee and followed the National Institutes of Health guidelines “Using Animals in Intramural Research (http://oacu.od.nih.gov/training/PI/main_menu.htm).”
Conflict of interest
The authors declare that they have no conflict of interest.
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