title: Maintenance of stereocilia and apical junctional complexes by Cdc42 in cochlear hair cells.
abstract: Cdc42 is a key regulator of dynamic actin organization. However, little is known about how Cdc42-dependent actin regulation influences steady-state actin structures in differentiated epithelia. We employed inner ear hair-cell-specific conditional knockout to analyze the role of Cdc42 in hair cells possessing highly elaborate stable actin protrusions (stereocilia). Hair cells of Atoh1-Cre;Cdc42(flox/flox) mice developed normally but progressively degenerated after maturation, resulting in progressive hearing loss particularly at high frequencies. Cochlear hair cell degeneration was more robust in inner hair cells than in outer hair cells, and began as stereocilia fusion and depletion, accompanied by a thinning and waving circumferential actin belt at apical junctional complexes (AJCs). Adenovirus-encoded GFP-Cdc42 expression in hair cells and fluorescence resonance energy transfer (FRET) imaging of hair cells from transgenic mice expressing a Cdc42-FRET biosensor indicated Cdc42 presence and activation at stereociliary membranes and AJCs in cochlear hair cells. Cdc42-knockdown in MDCK cells produced phenotypes similar to those of Cdc42-deleted hair cells, including abnormal microvilli and disrupted AJCs, and downregulated actin turnover represented by enhanced levels of phosphorylated cofilin. Thus, Cdc42 influenced the maintenance of stable actin structures through elaborate tuning of actin turnover, and maintained function and viability of cochlear hair cells.
authors.affiliation: Laboratory of Molecular Pharmacology, Biosignal Research Center, Kobe University, Kobe 657-8501, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Ueyama
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Sakaguchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakamura
authors.forename: Akihiro
authors.initials: A
authors.lastname: Goto
authors.forename: Shigefumi
authors.initials: S
authors.lastname: Morioka
authors.forename: Aya
authors.initials: A
authors.lastname: Shimizu
authors.forename: Kazuki
authors.initials: K
authors.lastname: Nakao
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Hishikawa
authors.forename: Yuzuru
authors.initials: Y
authors.lastname: Ninoyu
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Kassai
authors.forename: Shiro
authors.initials: S
authors.lastname: Suetsugu
authors.forename: Takehiko
authors.initials: T
authors.lastname: Koji
authors.forename: Bernd
authors.initials: B
authors.lastname: Fritzsch
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Yonemura
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Hisa
authors.forename: Michiyuki
authors.initials: M
authors.lastname: Matsuda
authors.forename: Atsu
authors.initials: A
authors.lastname: Aiba
authors.forename: Naoaki
authors.initials: N
authors.lastname: Saito
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D015374:Biosensing Techniques; D003051:Cochlea / Q000166:cytology / Q000378:metabolism; D004285:Dogs; D031541:Fluorescence Resonance Energy Transfer; D006198:Hair Cells, Auditory / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D061985:Madin Darby Canine Kidney Cells; D051379:Mice; D064347:Microscopy, Electrochemical, Scanning; D046529:Microscopy, Electron, Transmission; D009924:Organ Culture Techniques / Q000379:methods; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D020764:cdc42 GTP-Binding Protein
keywords: Actin turnover; Apical junctional complex; Cdc42; Deafness; FRET; Hair cell; Stereocilia