title: Unconventional myosins in inner-ear sensory epithelia.
abstract: To understand how cells differentially use the dozens of myosin isozymes present in each genome, we examined the distribution of four unconventional myosin isozymes in the inner ear, a tissue that is particularly reliant on actin-rich structures and unconventional myosin isozymes. Of the four isozymes, each from a different class, three are expressed in the hair cells of amphibia and mammals. In stereocilia, constructed of cross-linked F-actin filaments, myosin-Ibeta is found mostly near stereociliary tips, myosin-VI is largely absent, and myosin-VIIa colocalizes with crosslinks that connect adjacent stereocilia. In the cuticular plate, a meshwork of actin filaments, myosin-Ibeta is excluded, myosin-VI is concentrated, and modest amounts of myosin-VIIa are present. These three myosin isozymes are excluded from other actin-rich domains, including the circumferential actin belt and the cortical actin network. A member of a fourth class, myosin-V, is not expressed in hair cells but is present at high levels in afferent nerve cells that innervate hair cells. Substantial amounts of myosins-Ibeta, -VI, and -VIIa are located in a pericuticular necklace that is largely free of F-actin, squeezed between (but not associated with) actin of the cuticular plate and the circumferential belt. Our localization results suggest specific functions for three hair-cell myosin isozymes. As suggested previously, myosin-Ibeta probably plays a role in adaptation; concentration of myosin-VI in cuticular plates and association with stereociliary rootlets suggest that this isozyme participates in rigidly anchoring stereocilia; and finally, colocalization with cross-links between adjacent stereocilia indicates that myosin-VIIa is required for the structural integrity of hair bundles.
authors.affiliation: Department of Biology, Department of Cell Biology, Department of Pathology, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: T
authors.initials: T
authors.lastname: Hasson
authors.forename: P G
authors.initials: PG
authors.lastname: Gillespie
authors.forename: J A
authors.initials: JA
authors.lastname: Garcia
authors.forename: R B
authors.initials: RB
authors.lastname: MacDonald
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: A G
authors.initials: AG
authors.lastname: Yee
authors.forename: M S
authors.initials: MS
authors.lastname: Mooseker
authors.forename: D P
authors.initials: DP
authors.lastname: Corey
mesh_terms: D000818:Animals; D004398:Dyneins; D004423:Ear; D007758:Ear, Inner / Q000201:enzymology*; D004848:Epithelium / Q000201:enzymology; D006801:Humans; D007527:Isoenzymes / Q000032:analysis*; D051379:Mice; D018995:Myosin Heavy Chains / Q000032:analysis; D000081412:Myosin VIIa; D009218:Myosins / Q000032:analysis*; D011817:Rabbits; D011892:Rana catesbeiana
chemical_list: D007527:Isoenzymes; C000631455:MYO7A protein, human; C000631456:Myo7a protein, mouse; D000081412:Myosin VIIa; C089785:myosin VI; D018995:Myosin Heavy Chains; D009218:Myosins; D004398:Dyneins