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Triffo WJ, Palsdottir H, Song J, Morgan DG, McDonald KL, Auer M, Raphael RM. 3D Ultrastructure of the Cochlear Outer Hair Cell Lateral Wall Revealed By Electron Tomography. Front Cell Neurosci 2019; 13:560. [PMID: 31920560 PMCID: PMC6933316 DOI: 10.3389/fncel.2019.00560] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 12/04/2019] [Indexed: 11/17/2022] Open
Abstract
Outer Hair Cells (OHCs) in the mammalian cochlea display a unique type of voltage-induced mechanical movement termed electromotility, which amplifies auditory signals and contributes to the sensitivity and frequency selectivity of mammalian hearing. Electromotility occurs in the OHC lateral wall, but it is not fully understood how the supramolecular architecture of the lateral wall enables this unique form of cellular motility. Employing electron tomography of high-pressure frozen and freeze-substituted OHCs, we visualized the 3D structure and organization of the membrane and cytoskeletal components of the OHC lateral wall. The subsurface cisterna (SSC) is a highly prominent feature, and we report that the SSC membranes and lumen possess hexagonally ordered arrays of particles. We also find the SSC is tightly connected to adjacent actin filaments by short filamentous protein connections. Pillar proteins that join the plasma membrane to the cytoskeleton appear as variable structures considerably thinner than actin filaments and significantly more flexible than actin-SSC links. The structurally rich organization and rigidity of the SSC coupled with apparently weaker mechanical connections between the plasma membrane (PM) and cytoskeleton reveal that the membrane-cytoskeletal architecture of the OHC lateral wall is more complex than previously appreciated. These observations are important for our understanding of OHC mechanics and need to be considered in computational models of OHC electromotility that incorporate subcellular features.
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Affiliation(s)
- William Jeffrey Triffo
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States.,Department of Bioengineering, George R. Brown School of Engineering, Rice University, Houston, TX, United States.,Department of Radiology, Geisinger, Danville, PA, United States
| | - Hildur Palsdottir
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - Junha Song
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - David Gene Morgan
- Interdisciplinary Center for Electron Microscopy, University of California, Davis, Davis, CA, United States
| | - Kent L McDonald
- Electron Microscope Laboratory, University of California, Berkeley, Berkeley, CA, United States
| | - Manfred Auer
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - Robert M Raphael
- Department of Bioengineering, George R. Brown School of Engineering, Rice University, Houston, TX, United States
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Khanna MR, Mattie FJ, Browder KC, Radyk MD, Crilly SE, Bakerink KJ, Harper SL, Speicher DW, Thomas GH. Spectrin tetramer formation is not required for viable development in Drosophila. J Biol Chem 2014; 290:706-15. [PMID: 25381248 DOI: 10.1074/jbc.m114.615427] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The dominant paradigm for spectrin function is that (αβ)2-spectrin tetramers or higher order oligomers form membrane-associated two-dimensional networks in association with F-actin to reinforce the plasma membrane. Tetramerization is an essential event in such structures. We characterize the tetramerization interaction between α-spectrin and β-spectrins in Drosophila. Wild-type α-spectrin binds to both β- and βH-chains with high affinity, resembling other non-erythroid spectrins. However, α-spec(R22S), a tetramerization site mutant homologous to the pathological α-spec(R28S) allele in humans, eliminates detectable binding to β-spectrin and reduces binding to βH-spectrin ∼1000-fold. Even though spectrins are essential proteins, α-spectrin(R22S) rescues α-spectrin mutants to adulthood with only minor phenotypes indicating that tetramerization, and thus conventional network formation, is not the essential function of non-erythroid spectrin. Our data provide the first rigorous test for the general requirement for tetramer-based non-erythroid spectrin networks throughout an organism and find that they have very limited roles, in direct contrast to the current paradigm.
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Affiliation(s)
- Mansi R Khanna
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Floyd J Mattie
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Kristen C Browder
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Megan D Radyk
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Stephanie E Crilly
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Katelyn J Bakerink
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
| | - Sandra L Harper
- the Systems Biology Division, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - David W Speicher
- the Systems Biology Division, The Wistar Institute, Philadelphia, Pennsylvania 19104
| | - Graham H Thomas
- From the Department of Biology and the Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802 and
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Microdomains shift and rotate in the lateral wall of cochlear outer hair cells. Biophys J 2013; 104:8-18. [PMID: 23332054 DOI: 10.1016/j.bpj.2012.11.3828] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 11/26/2012] [Accepted: 11/29/2012] [Indexed: 12/26/2022] Open
Abstract
Outer hair cell (OHC) electromotility, a response consisting of reversible changes in cell length and diameter induced by electrical stimulation, confers remarkable sensitivity and frequency resolution to the mammalian inner ear. Looking for a better understanding of this mechanism, we labeled isolated guinea pig OHCs with microspheres and, using high-speed video recording, investigated their movements at the apical, mid, and basal regions of osmotically and electrically stimulated cells. After hypoosmotic challenge, OHCs shortened and their diameter increased, with microspheres moving always toward the central plane; iso-osmolarity returned OHCs to their original shape and microspheres to their original positions. Under electrical stimulation, microspheres exhibited robust movements, with their displacement vectors changing in direction from random to parallel to the longitudinal axis of the cells with peak reorientation speeds of up to 6 rad/s and returning to random after 5 min without stimulation. Alterations in plasma-membrane cholesterol levels as well as cytoskeleton integrity affected microsphere responses. We concluded that microspheres attach to different molecular microdomains, and these microdomains are able to shift and rotate in the plane of the OHC lateral wall with a dynamics tightly regulated by membrane lipid composition and the cortical cytoskeleton.
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Kamar RI, Organ-Darling LE, Raphael RM. Membrane cholesterol strongly influences confined diffusion of prestin. Biophys J 2012; 103:1627-36. [PMID: 23083705 DOI: 10.1016/j.bpj.2012.07.052] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Revised: 07/18/2012] [Accepted: 07/25/2012] [Indexed: 01/04/2023] Open
Abstract
Prestin is the membrane motor protein that drives outer hair cell (OHC) electromotility, a process that is essential for mammalian hearing. Prestin function is sensitive to membrane cholesterol levels, and numerous studies have suggested that prestin localizes in cholesterol-rich membrane microdomains. Previously, fluorescence recovery after photobleaching experiments were performed in HEK cells expressing prestin-GFP after cholesterol manipulations, and revealed evidence of transient confinement. To further characterize this apparent confined diffusion of prestin, we conjugated prestin to a photostable fluorophore (tetramethylrhodamine) and performed single-molecule fluorescence microscopy. Using single-particle tracking, we determined the microscopic diffusion coefficient from the full time course of the mean-squared deviation. Our results indicate that prestin undergoes diffusion in confinement regions, and that depletion of membrane cholesterol increases confinement size and decreases confinement strength. By interpreting the data in terms of a mathematical model of hop-diffusion, we quantified these cholesterol-induced changes in membrane organization. A complementary analysis of the distribution of squared displacements confirmed that cholesterol depletion reduces prestin confinement. These findings support the hypothesis that prestin function is intimately linked to membrane organization, and further promote a regulatory role for cholesterol in OHC and auditory function.
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Affiliation(s)
- R I Kamar
- Department of Physics and Astronomy, Rice University, Houston, Texas, USA
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Sinha GP, Sabri F, Dimitriadis EK, Iwasa KH. Organization of membrane motor in outer hair cells: an atomic force microscopic study. Pflugers Arch 2009; 459:427-39. [PMID: 19809831 PMCID: PMC2810367 DOI: 10.1007/s00424-009-0742-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 09/17/2009] [Accepted: 09/22/2009] [Indexed: 11/25/2022]
Abstract
Using atomic force microscopy, we imaged the cytosolic surface of the lateral plasma membrane of outer hair cells from guinea pigs’ inner ear. We used a “cell-free” preparation, in which a patch of plasma membrane was firmly attached to a substrate and the cytoplasmic face was exposed. The membrane patches contained densely packed particles whose diameter, after correcting for the geometry of the probing tip, was ∼10 nm. The particles were predominantly aligned unidirectionally with spacing of ∼36 nm. The density of the particle was ∼850 μm−2, which could be an underestimate presumably due to the method of sample preparation. Antibody-labeled specimens showed particles more elevated than unlabeled preparation indicative of primary and secondary antibody complexes. The corrected diameters of these particles labeled with anti-actin were ∼12 nm while that with antiprestin were ∼8 nm. The alignment pattern in antiprestin-labeled specimens resembled that of the unlabeled preparation. Specimens labeled with actin antibodies did not show such alignment. We interpret that the particles observed in the unlabeled membranes correspond to the 10-nm particles reported by electron microscopy and that these particles contain prestin, a member of the SLC26 family, which is essential for electromotility.
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Affiliation(s)
- Ghanshyam P. Sinha
- Biophysics Section, Laboratory of Cellular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, 5 Research Court, Rockville, MD 20850-3211 USA
| | - Firouzeh Sabri
- Biophysics Section, Laboratory of Cellular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, 5 Research Court, Rockville, MD 20850-3211 USA
| | - Emilios K. Dimitriadis
- Laboratory of Bioengineering and Physical Sciences, National Institute of Biomedical Imaging Bioengineering, National Institutes of Health, 13 South Drive, Bethesda, MD 20892-5766 USA
| | - Kuni H. Iwasa
- Biophysics Section, Laboratory of Cellular Biology, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, 5 Research Court, Rockville, MD 20850-3211 USA
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Abstract
The high sensitivity of mammalian hearing is achieved by amplification of the motion of the cochlear partition. The origin of this cochlear amplification is the elongation and contraction of outer hair cells (OHCs) in response to acoustical stimulation. This motility is made possible by a membrane protein embedded in the lateral membrane of OHCs. The gene of this protein has been identified and termed prestin. We, herein, present a method for observation by atomic force microscopy (AFM) of prestin expressed in the Chinese hamster ovary (CHO) cell plasma membrane. To obtain a stable sample for AFM imaging in liquid, we used as an example in the protocol provide here, CHO cells transfected with prestin or FLAG-tagged prestin, and untransfected CHO cells. The cells attached to a substrate were subjected to ultrasonic waves generated from a sonicator probe so that the inside-out plasma membranes remained on the substrate. Prestin was immunostained with mouse anti-FLAG primary antibody and FITC-conjugated goat anti-mouse IgG secondary antibody. The lipid of the plasma membrane was labeled with fluorescence probes. The cytoplasmic faces of the cells were then observed in liquid by the tapping mode of AFM at low and high magnifications. More particle-like structures 8-12 nm in diameter were observed in the plasma membranes of the prestin-transfected CHO cells than in those of the untransfected CHO cells. Since the difference between these two types of cells is due to the existence of prestin, such particle-like structures in the prestin-transfected CHO cells are possibly constituted by prestin.
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Affiliation(s)
- Michio Murakoshi
- Department of Bioengineering and Robotics, Graduate School of Engineering Tohoku University, Sendai, Japan
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Kasas S, Dietler G. Probing nanomechanical properties from biomolecules to living cells. Pflugers Arch 2008; 456:13-27. [DOI: 10.1007/s00424-008-0448-y] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2008] [Accepted: 01/09/2008] [Indexed: 12/27/2022]
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Murakoshi M, Gomi T, Iida K, Kumano S, Tsumoto K, Kumagai I, Ikeda K, Kobayashi T, Wada H. Imaging by atomic force microscopy of the plasma membrane of prestin-transfected Chinese hamster ovary cells. J Assoc Res Otolaryngol 2006; 7:267-78. [PMID: 16761115 PMCID: PMC2504612 DOI: 10.1007/s10162-006-0041-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Accepted: 04/26/2006] [Indexed: 11/27/2022] Open
Abstract
The high sensitivity of mammalian hearing is achieved by amplification of the motion of the cochlear partition. This cochlear amplification is thought to be generated by the elongation and contraction of outer hair cells (OHCs) in response to acoustical stimulation. This motility is made possible by a membrane protein embedded in the lateral membrane of OHCs. Although a fructose transporter, GLUT-5, was initially proposed to be this protein, a later study identified the gene of the motor protein distributed throughout the OHC plasma membrane. This protein has been named "prestin." However, although previous morphological studies by electron microscopy and atomic force microscopy (AFM) found the lateral wall of OHCs to be covered with 10-nm particles, believed to be motor proteins, it is unknown whether such particles consist only of prestin or are a complex of GLUT-5 and prestin molecules. To determine if the 10-nm particles are indeed constituted only of prestin, plasma membranes of prestin-transfected and untransfected Chinese hamster ovary (CHO) cells, which do not express GLUT-5, were observed by AFM. First, the cells attached to a substrate were sonicated so that only the plasma membrane remained on the substrate. The cytoplasmic face of the cell was observed by the tapping mode of the AFM in liquid. As a result, particle-like structures were recognized on the plasma membranes of both the prestin-transfected and untransfected CHO cells. Comparison of the difference in the frequency distribution of these structures between those two cells showed approximately 75% of the particle-like structures with a diameter of 8-12 nm in the prestin-transfected CHO cells to be possibly constituted only by prestin molecules. Our data suggest that the densely packed 10-nm particles observed on the OHC lateral wall are likely to be constituted only of prestin molecules.
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Affiliation(s)
- Michio Murakoshi
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Takashi Gomi
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Koji Iida
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Shun Kumano
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Kouhei Tsumoto
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8652 Japan
| | - Izumi Kumagai
- Department of Biomolecular Engineering, Tohoku University, 6-6-11 Aoba-yama, Sendai, 980-8579 Japan
| | - Katsuhisa Ikeda
- Department of Otorhinolaryngology, Juntendo University School of Medicine, 2-1-1 Hongo, Tokyo, 113-8421 Japan
| | - Toshimitsu Kobayashi
- Department of Otorhinolaryngology–Head and Neck Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Sendai, 980-8574 Japan
| | - Hiroshi Wada
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
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Murakoshi M, Yoshida N, Iida K, Kumano S, Kobayashi T, Wada H. Local mechanical properties of mouse outer hair cells: atomic force microscopic study. Auris Nasus Larynx 2006; 33:149-57. [PMID: 16436324 DOI: 10.1016/j.anl.2005.11.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2005] [Revised: 10/07/2005] [Accepted: 11/11/2005] [Indexed: 11/24/2022]
Abstract
OBJECTIVES Outer hair cells (OHCs) are capable of altering their cell length in response to changes in membrane potential. Due to this electromotility, OHCs probably subject the basilar membrane to force, resulting in cochlear amplification. To understand the mechanism of such amplification, knowledge of the mechanical properties of OHCs is required since the force produced by OHC electromotility is thought to depend on such properties. Various studies have been conducted to investigate the mechanical properties of guinea pig OHCs. With regard to mice, however, although various kinds of transgenic and knockout mice possess great potential as research models, the mechanical properties of mouse OHCs have not as yet been reported since the cells and/or tissues in the mouse hearing organ are relatively small and vulnerable to external stimuli, rendering sample preparation difficult. In this study, therefore, to establish indicators of the mechanical properties of OHCs in mice, such properties were measured by atomic force microscopy (AFM). METHODS CBA/JNCrj strain male mice aged 10-12 weeks (25-30 g) were used. Cochleae were dissected out from the animal and both the basilar membrane and the organ of Corti were simultaneously unwrapped from the modiolus with forceps. Dissected coiled tissue was then incubated with an enzymatic digestion medium for 15 min. After digestion, OHCs were isolated by gently triturating the coiled tissue. Local mechanical properties of the OHCs were then measured by an indentation test using an AFM. RESULTS Young's modulus and stiffness of the OHC in the apical turn of the mouse cochlea were 2.1+/-0.5 kPa and 4.4+/-1.2 mN/m, respectively. CONCLUSIONS Young's modulus of the OHC in the apical turn of the cochlea in mice was roughly the same as that in the apical turn of the cochlea in guinea pigs; however, the stiffness of the former was about two times greater than that of the latter because the cell length of the former was shorter than that of the latter.
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Affiliation(s)
- Michio Murakoshi
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai 980-8579, Japan.
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Zelenskaya A, de Monvel JB, Pesen D, Radmacher M, Hoh JH, Ulfendahl M. Evidence for a highly elastic shell-core organization of cochlear outer hair cells by local membrane indentation. Biophys J 2005; 88:2982-93. [PMID: 15653728 PMCID: PMC1305392 DOI: 10.1529/biophysj.104.052225] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2004] [Accepted: 01/03/2005] [Indexed: 11/18/2022] Open
Abstract
Cochlear outer hair cells (OHCs) are thought to play an essential role in the high sensitivity and sharp frequency selectivity of the hearing organ by generating forces that amplify the vibrations of this organ at frequencies up to several tens of kHz. This tuning process depends on the mechanical properties of the cochlear partition, which OHC activity has been proposed to modulate on a cycle-by-cycle basis. OHCs have a specialized shell-core ultrastructure believed to be important for the mechanics of these cells and for their unique electromotility properties. Here we use atomic force microscopy to investigate the mechanical properties of isolated living OHCs and to show that indentation mechanics of their membrane is consistent with a shell-core organization. Indentations of OHCs are also found to be highly nonhysteretic at deformation rates of more than 40 microm/s, which suggests the OHC lateral wall is a highly elastic structure, with little viscous dissipation, as would appear to be required in view of the very rapid changes in shape and mechanics OHCs are believed to undergo in vivo.
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Affiliation(s)
- Alexandra Zelenskaya
- Department of Clinical Neuroscience and Center for Hearing and Communication Research, Karolinska Institutet, SE-171 76 Stockholm, Sweden
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