PT - JOURNAL ARTICLE AU - Tommi Anttonen AU - Ilya Belevich AU - Maarja Laos AU - Anni Herranen AU - Eija Jokitalo AU - Cord Brakebusch AU - Ulla Pirvola TI - Cytoskeletal Stability in the Auditory Organ <em>in Vivo</em>: RhoA Is Dispensable for Wound Healing, but Essential for Hair Cell Development AID - 10.1523/ENEURO.0149-17.2017 DP - 2017 Sep 07 TA - eneuro PG - ENEURO.0149-17.2017 4099 - http://www.eneuro.org/content/early/2017/09/07/ENEURO.0149-17.2017.short 4100 - http://www.eneuro.org/content/early/2017/09/07/ENEURO.0149-17.2017.full AB - Wound healing in the inner ear sensory epithelia is performed by the apical domains of supporting cells (SCs). Junctional F-actin belts of SCs are thin during development, but become exceptionally thick during maturation. Functional significance of the thick belts is not fully understood. We have studied the role of F-actin belts during wound healing in the developing and adult cochlea of the mouse in vivo. We show that the thick belts serve as intracellular scaffolds that preserve the positions of surviving cells in the cochlear sensory epithelium. Junctions associated with the thick F-actin belts did not readily disassemble during wound healing. To compensate for this, basolateral membranes of SCs participated in the closure of surface breach. Since not only neighboring but also distant SCs contributed to wound healing by basolateral protrusions, this event appears to be triggered by contact-independent diffusible signals. In search for regulators of wound healing, we inactivated RhoA in SCs, which, however, did not limit wound healing. RhoA inactivation in developing outer hair cells (OHCs) caused myosin II delocalization from the perijunctional domain and apical cell-surface enlargement. These abnormalities led to the extrusion of OHCs from the epithelium. These results demonstrate the importance of stability of the apical domain, both in wound repair by SCs and in development of OHCs, and that only this latter function is regulated by RhoA. As correct cytoarchitecture of the cochlear sensory epithelium is required for normal hearing, stability of cell apices should be maintained in regenerative and protective interventions.Significance Statement We show that the stability of the apical domain is required for the development of cochlear hair cells and that it is regulated by the GTPase RhoA. We also show that the apical stability of supporting cells is critical for wound healing in the adult cochlea, as it maintains cellular topology and dimensions at the surface of the sensory epithelium. Surprisingly, although RhoA is known to regulate wound healing in several cell contexts, the wound repair process in the cochlear sensory epithelium does not depend on it. Our results point to the importance of preservation of apical stability of cochlear sensory epithelial cells in future therapeutic interventions aiming at treating hearing loss.