1
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Cheng C. Tissue, cellular, and molecular level determinants for eye lens stiffness and elasticity. FRONTIERS IN OPHTHALMOLOGY 2024; 4:1456474. [PMID: 39176256 PMCID: PMC11339033 DOI: 10.3389/fopht.2024.1456474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/28/2024] [Accepted: 07/26/2024] [Indexed: 08/24/2024]
Abstract
The eye lens is a transparent, ellipsoid tissue in the anterior chamber that is required for the fine focusing of light onto the retina to transmit a clear image. The focusing function of the lens is tied to tissue transparency, refractive index, and biomechanical properties. The stiffness and elasticity or resilience of the human lens allows for shape changes during accommodation to focus light from objects near and far. It has long been hypothesized that changes in lens biomechanical properties with age lead to the loss of accommodative ability and the need for reading glasses with age. However, the cellular and molecular mechanisms that influence lens biomechanical properties and/or change with age remain unclear. Studies of lens stiffness and resilience in mouse models with genetic defects or at advanced age inform us of the cytoskeletal, structural, and morphometric parameters that are important for biomechanical stability. In this review, we will explore whether: 1) tissue level changes, including the capsule, lens volume, and nucleus volume, 2) cellular level alterations, including cell packing, suture organization, and complex membrane interdigitations, and 3) molecular scale modifications, including the F-actin and intermediate filament networks, protein modifications, lipids in the cell membrane, and hydrostatic pressure, influence overall lens biomechanical properties.
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Affiliation(s)
- Catherine Cheng
- School of Optometry and Vision Science Program, Indiana University, Bloomington, IN, United States
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2
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Aboelnour A, Gewaily MS, Noreldin AE. Comparative light and scanning electron microscopic studies of the lenses in the insectivorous bat (Pipistrellus kuhlii) and Egyptian fruit bat (Rousettus aegyptiacus). Microsc Res Tech 2024; 87:1436-1442. [PMID: 38400686 DOI: 10.1002/jemt.24532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Revised: 01/22/2024] [Accepted: 02/14/2024] [Indexed: 02/25/2024]
Abstract
Bats have the ability to fly without eye application in the darkness. In this study, we aimed to characterize the functional and structural acclimations of the lenses of two common bats with a various lifestyle in the Egyptian environment: the insectivorous bat (IB) (Pipistrellus kuhlii) and Egyptian fruit bat (FB) (Rousettus aegyptiacus). From each species, seven lenses were extracted from adult eyes. The scanning electron microscopic (SEM) and light microscopic examination of the lens were carried out. FB lenses were made up primarily of fiber cells and sheets, which were encapsulated by a thin collagenous capsule and covered by single epithelial layer anteriorly. On the other hand, the IB lens had two poles and was visibly oval shaped. Both lenses had epithelial cells of the same cuboidal form that were subjected to continuous division and differentiation into new fiber cells at the center. SEM revealed that the normal FB lens had regularly organized shells of fiber cells of intact lens fibers which were connected by membrane interdigitations with different shapes mainly ball-and-socket junctions through the superficial cortical fiber cells. The IB lens was composed of parallel, evenly spaced fibers with various types of interdigitations between fibers that can be seen and increased close to the middle region revealing tiny bumps along the scrubby portions and sockets and balls in the center of the wide portions. Near the center of both lenses, there were large interlocking paddles with little and lengthy protrusions along their short sides. In conclusion, our study discovered several ultrastructural and structural variations among the investigated species. The detection of specialized membrane interdigitations with different shapes protruding from the lens fiber sheets is considered the most characteristic of the FB lens. RESEARCH HIGHLIGHTS: FB lens has more organized sheets of fibers parallel to each other than IB lens. Different shapes of interdigitations protruded from the FB lens have been detected. Interlocking paddles, balls, and sockets with tongue-like fiber flabs are characteristic to FB lens.
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Affiliation(s)
- Asmaa Aboelnour
- Department of Histology and Cytology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt
| | - Mahmoud S Gewaily
- Department of Anatomy and Embryology, Faculty of Veterinary Medicine, Kafrelsheikh University, Kafrelsheikh, Egypt
| | - Ahmed E Noreldin
- Department of Histology and Cytology, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt
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3
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Cheng C, Wang K, Hoshino M, Uesugi K, Yagi N, Pierscionek B. EphA2 Affects Development of the Eye Lens Nucleus and the Gradient of Refractive Index. Invest Ophthalmol Vis Sci 2022; 63:2. [PMID: 34978559 PMCID: PMC8742528 DOI: 10.1167/iovs.63.1.2] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Purpose Our studies in mouse eye lenses demonstrate that ephrin-A5 and EphA2 are needed for normal epithelial cells and lens transparency. We sought to determine whether EphA2 and ephrin-A5 are important for lens morphometrics, nucleus formation, and refractive index. Methods We performed tissue morphometric measurements, electron microscopy, Western blots, and interferometric measurements using an X-ray synchrotron beam source to measure the gradient of refractive index (GRIN) to compare mouse lenses with genetic disruption of EphA2 or ephrin-A5. Results Morphometric analysis revealed that although there is no change in the overall lens volume, there is a change in lens shape in both EphA2-/- lenses and ephrin-A5-/- lenses. Surprisingly, EphA2-/- lenses had small and soft lens nuclei different from hard lens nuclei of control lenses. SEM images revealed changes in cell morphology of EphA2-/- fiber cells close to the center of the lens. Inner EphA2-/- lens fibers had more pronounced tongue-and-groove interdigitations and formed globular membrane morphology only in the deepest layers of the lens nucleus. We did not observe nuclear defects in ephrin-A5-/- lenses. There was an overall decrease in magnitude of refractive index across EphA2-/- lenses, which is most pronounced in the nucleus. Conclusions This work reveals that Eph-ephrin signaling plays a role in fiber cell maturation, nuclear compaction, and lens shape. Loss of EphA2 disrupts the nuclear compaction resulting in a small lens nucleus. Our data suggest that Eph-ephrin signaling may be required for fiber cell membrane reorganization and compaction and for establishing a normal GRIN.
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Affiliation(s)
- Catherine Cheng
- School of Optometry, Indiana University, Bloomington, IN, United States
| | - Kehao Wang
- Beijing Advanced Innovation Centre for Biomedical Engineering, Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Engineering Medicine, Beihang University, Beijing, China
| | - Masato Hoshino
- Japan Synchrotron Radiation Research Institute (Spring-8), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
| | - Kentaro Uesugi
- Japan Synchrotron Radiation Research Institute (Spring-8), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
| | - Naoto Yagi
- Japan Synchrotron Radiation Research Institute (Spring-8), 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 Japan
| | - Barbara Pierscionek
- Faculty of Health, Education, Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Chelmsford Campus, United Kingdom
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4
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Costello MJ, Gilliland KO, Mohamed A, Schey KL, Johnsen S, Brennan LA, Kantorow M. Novel mitochondrial derived Nuclear Excisosome degrades nuclei during differentiation of prosimian Galago (bush baby) monkey lenses. PLoS One 2020; 15:e0241631. [PMID: 33180800 PMCID: PMC7660580 DOI: 10.1371/journal.pone.0241631] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Accepted: 10/16/2020] [Indexed: 11/18/2022] Open
Abstract
The unique cellular organization and transparent function of the ocular lens depend on the continuous differentiation of immature epithelial cells on the lens anterior surface into mature elongated fiber cells within the lens core. A ubiquitous event during lens differentiation is the complete elimination of organelles required for mature lens fiber cell structure and transparency. Distinct pathways have been identified to mediate the elimination of non-nuclear organelles and nuclei. Recently, we reported the discovery of a unique structure in developing fiber cells of the chick embryo lens, called the Nuclear Excisosome, that is intractably associated with degrading nuclei during lens fiber cell differentiation. In the chick lens, the Nuclear Excisosome is derived from projections of adjacent cells contacting the nuclear envelope during nuclear elimination. Here, we demonstrate that, in contrast to the avian model, Nuclear Excisosomes in a primate model, Galago (bush baby) monkeys, are derived through the recruitment of mitochondria to form unique linear assemblies that define a novel primate Nuclear Excisosome. Four lenses from three monkeys aged 2–5 years were fixed in formalin, followed by paraformaldehyde, then processed for Airyscan confocal microscopy or transmission electron microscopy. For confocal imaging, fluorescent dyes labelled membranes, carbohydrate in the extracellular space, filamentous actin and nuclei. Fiber cells from Galago lenses typically displayed prominent linear structures within the cytoplasm with a distinctive cross-section of four membranes and lengths up to 30 μm. The outer membranes of these linear structures were observed to attach to the outer nuclear envelope membrane to initiate degradation near the organelle-free zone. The origin of these unique structures was mitochondria in the equatorial epithelium (not from plasma membranes of adjacent cells as in the chick embryo model). Early changes in mitochondria appeared to be the collapse of the cristae and modification of one side of the mitochondrial outer membrane to promote accumulation of protein in a dense cluster. As a mitochondrion surrounded the dense protein cluster, an outer mitochondrial membrane enclosed the protein to form a core and another outer mitochondrial membrane formed the outermost layer. The paired membranes of irregular texture between the inner core membrane and the outer limiting membrane appeared to be derived from modified mitochondrial cristae. Several mitochondria were involved in the formation and maturation of these unique complexes that apparently migrated around the fulcrum into the cytoplasm of nascent fiber cells where they were stabilized until the nuclear degradation was initiated. Thus, unlike in the chick embryo, the Galago lenses degraded nuclear envelopes with a Nuclear Excisosome derived from multiple mitochondria in the epithelium that formed novel linear assemblies in developing fiber cells. These findings suggest that recruitment of distinct structures is required for Nuclear Excisosome formation in different species.
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Affiliation(s)
- M Joseph Costello
- Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC, United States of America
| | - Kurt O Gilliland
- Department of Cell Biology and Physiology, University of North Carolina, Chapel Hill, NC, United States of America
| | - Ashik Mohamed
- Ophthalmic Biophysics, L V Prasad Eye Institute, Hyderabad, Telangana, India
| | - Kevin L Schey
- Biochemistry Department, Vanderbilt University, Nashville, TN, United States of America
| | - Sönke Johnsen
- Biology Department, Duke University, Durham, NC, United States of America
| | - Lisa A Brennan
- Department of Biomedical Science, Florida Atlantic University, Boca Raton, FL, United States of America
| | - Marc Kantorow
- Department of Biomedical Science, Florida Atlantic University, Boca Raton, FL, United States of America
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Liu S, Hu C, Luo Y, Yao K. Genome-wide DNA methylation profiles may reveal new possible epigenetic pathogenesis of sporadic congenital cataract. Epigenomics 2020; 12:771-788. [PMID: 32516005 DOI: 10.2217/epi-2019-0254] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Aim: To investigate the possible epigenetic pathogenesis of sporadic congenital cataract. Materials & methods: We conducted whole genome bisulfite sequencing on peripheral blood from sporadic binocular or monocular congenital cataract patients and cataract-free participants. Results: We found massive differentially methylated regions within the whole genomes between any two groups. Meanwhile, we identified five genes (ACTN4, ACTG1, TUBA1A, TUBA1C, TUBB4B) for the binocular and control groups and TUBA1A for the monocular and control groups as the core differentially methylated region-related genes. The proteins encoded by these core genes are involved in building cytoskeleton and intercellular junctions. Conclusion: Changes in the methylation levels of core genes may disturb the function of cytoskeleton and intercellular junctions, eventually leading to sporadic congenital cataract.
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Affiliation(s)
- Siyu Liu
- Eye Center of The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310031, PR China.,Zhejiang Provincial Key Lab of Ophthalmology, Hangzhou, Zhejiang Province 310031, PR China
| | - Chenyang Hu
- Eye Center of The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310031, PR China.,Zhejiang Provincial Key Lab of Ophthalmology, Hangzhou, Zhejiang Province 310031, PR China
| | - Yueqiu Luo
- Eye Center of The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310031, PR China.,Zhejiang Provincial Key Lab of Ophthalmology, Hangzhou, Zhejiang Province 310031, PR China
| | - Ke Yao
- Eye Center of The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou 310031, PR China.,Zhejiang Provincial Key Lab of Ophthalmology, Hangzhou, Zhejiang Province 310031, PR China
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Zhang N, Zhang C, Wang X, Qi Y. High-throughput sequencing reveals novel lincRNA in age-related cataract. Int J Mol Med 2017; 40:1829-1839. [PMID: 29039457 PMCID: PMC5716429 DOI: 10.3892/ijmm.2017.3185] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Accepted: 10/02/2017] [Indexed: 12/14/2022] Open
Abstract
Age-related cataract (ARC) is a major cause of blindness. Long non-coding RNAs (lncRNAs) are a heterogeneous class of RNAs that are non-protein-coding transcripts >200 nucleotides in length. LncRNAs are involved in various critical biological processes, such as chromatin remodeling, gene transcription, and protein transport and trafficking. Furthermore, the dysregulation of lncRNAs causes a number of complex human diseases, including coronary artery diseases, autoimmune diseases, neurological disorders and various cancers. However, the role of lncRNA in cataract remains unclear. Therefore, in the present study, lens anterior capsular membrane was collected from normal subjects and patients with ARC and total RNA was extracted. High-throughput sequencing was applied to detect differentially expressed lncRNAs and mRNAs. The analysis identified a total of 42,556 candidate differentially expressed mRNAs (27,447 +15,109) and a total of 7,041 candidate differentially expressed lncRNAs (4,146 + 2,895). Through bioinformatics analysis, the significant differential expression of novel lincRNA was observed and its possible molecular mechanism was explored. Reverse transcription-quantitative polymerase chain reaction was used to validate the different expression levels of selected lncRNAs. These findings may lead to the development of novel strategies for genetic diagnosis and gene therapy.
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Affiliation(s)
- Na Zhang
- Department of Ophthalmology, The Second Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang 150081, P.R. China
| | - Chunmei Zhang
- Department of Ophthalmology, The Second Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang 150081, P.R. China
| | - Xu Wang
- Department of Ophthalmology, The Second Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang 150081, P.R. China
| | - Yanhua Qi
- Department of Ophthalmology, The Second Affiliated Hospital of Harbin Medical University, Harbin, Heilongjiang 150081, P.R. China
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7
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Wang E, Geng A, Maniar AM, Mui BWH, Gong X. Connexin 50 Regulates Surface Ball-and-Socket Structures and Fiber Cell Organization. Invest Ophthalmol Vis Sci 2017; 57:3039-46. [PMID: 27281269 PMCID: PMC4913802 DOI: 10.1167/iovs.16-19521] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Purpose The roles of gap junction protein connexin 50 (Cx50) encoded by Gja8, during lens development are not fully understood. Connexin 50 knockout (KO) lenses have decreased proliferation of epithelial cells and altered fiber cell denucleation. We further investigated the mechanism for cellular defects in Cx50 KO (Gja8−/−) lenses. Methods Fiber cell morphology and subcellular distribution of various lens membrane/cytoskeleton proteins from wild-type and Cx50 KO mice were visualized by immunofluorescent staining and confocal microscopy. Results We observed multiple morphological defects in the cortical fibers of Cx50 KO lenses, including abnormal fiber cell packing geometry, decreased F-actin enrichment at tricellular vertices, and disrupted ball-and-socket (BS) structures on the long sides of hexagonal fibers. Moreover, only small gap junction plaques consisting of Cx46 (α3 connexin) were detected in cortical fibers and the distributions of the BS-associated beta-dystroglycan and ZO-1 proteins were altered. Conclusions Connexin 50 gap junctions are important for BS structure maturation and cortical fiber cell organization. Connexin 50–based gap junction plaques likely form structural domains with an array of membrane/cytoskeletal proteins to stabilize BS. Loss of Cx50-mediated coupling, BS disruption, and altered F-actin in Cx50 KO fibers, thereby contribute to the small lens and mild cataract phenotypes.
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8
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Cheng C, Nowak RB, Biswas SK, Lo WK, FitzGerald PG, Fowler VM. Tropomodulin 1 Regulation of Actin Is Required for the Formation of Large Paddle Protrusions Between Mature Lens Fiber Cells. Invest Ophthalmol Vis Sci 2017; 57:4084-99. [PMID: 27537257 PMCID: PMC4986768 DOI: 10.1167/iovs.16-19949] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Purpose To elucidate the proteins required for specialized small interlocking protrusions and large paddle domains at lens fiber cell tricellular junctions (vertices), we developed a novel method to immunostain single lens fibers and studied changes in cell morphology due to loss of tropomodulin 1 (Tmod1), an F-actin pointed end–capping protein. Methods We investigated F-actin and F-actin–binding protein localization in interdigitations of Tmod1+/+ and Tmod1−/− single mature lens fibers. Results F-actin–rich small protrusions and large paddles were present along cell vertices of Tmod1+/+ mature fibers. In contrast, Tmod1−/− mature fiber cells lack normal paddle domains, while small protrusions were unaffected. In Tmod1+/+ mature fibers, Tmod1, β2-spectrin, and α-actinin are localized in large puncta in valleys between paddles; but in Tmod1−/− mature fibers, β2-spectrin was dispersed while α-actinin was redistributed at the base of small protrusions and rudimentary paddles. Fimbrin and Arp3 (actin-related protein 3) were located in puncta at the base of small protrusions, while N-cadherin and ezrin outlined the cell membrane in both Tmod1+/+ and Tmod1−/− mature fibers. Conclusions These results suggest that distinct F-actin organizations are present in small protrusions versus large paddles. Formation and/or maintenance of large paddle domains depends on a β2-spectrin–actin network stabilized by Tmod1. α-Actinin–crosslinked F-actin bundles are enhanced in absence of Tmod1, indicating altered cytoskeleton organization. Formation of small protrusions is likely facilitated by Arp3-branched and fimbrin-bundled F-actin networks, which do not depend on Tmod1. This is the first work to reveal the F-actin–associated proteins required for the formation of paddles between lens fibers.
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Affiliation(s)
- Catherine Cheng
- Department of Cell and Molecular Biology The Scripps Research Institute, La Jolla, California, United States
| | - Roberta B Nowak
- Department of Cell and Molecular Biology The Scripps Research Institute, La Jolla, California, United States
| | - Sondip K Biswas
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia, United States
| | - Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia, United States
| | - Paul G FitzGerald
- Department of Cell Biology and Human Anatomy, University of California, Davis, California, United States
| | - Velia M Fowler
- Department of Cell and Molecular Biology The Scripps Research Institute, La Jolla, California, United States
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9
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Lens Biology is a Dimension of Neurobiology. Neurochem Res 2017; 42:933-942. [DOI: 10.1007/s11064-016-2156-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Revised: 12/12/2016] [Accepted: 12/19/2016] [Indexed: 01/02/2023]
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10
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Identification and Ultrastructural Characterization of a Novel Nuclear Degradation Complex in Differentiating Lens Fiber Cells. PLoS One 2016; 11:e0160785. [PMID: 27536868 PMCID: PMC4990417 DOI: 10.1371/journal.pone.0160785] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 07/25/2016] [Indexed: 01/18/2023] Open
Abstract
An unresolved issue in structural biology is how the encapsulated lens removes membranous organelles to carry out its role as a transparent optical element. In this ultrastructural study, we establish a mechanism for nuclear elimination in the developing chick lens during the formation of the organelle-free zone. Day 12-15 chick embryo lenses were examined by high-resolution confocal light microscopy and thin section transmission electron microscopy (TEM) following fixation in 10% formalin and 4% paraformaldehyde, and then processing for confocal or TEM as described previously. Examination of developing fiber cells revealed normal nuclei with dispersed chromatin and clear nucleoli typical of cells in active ribosome production to support protein synthesis. Early signs of nuclear degradation were observed about 300 μm from the lens capsule in Day 15 lenses where the nuclei display irregular nuclear stain and prominent indentations that sometimes contained a previously undescribed macromolecular aggregate attached to the nuclear envelope. We have termed this novel structure the nuclear excisosome. This complex by confocal is closely adherent to the nuclear envelope and by TEM appears to degrade the outer leaflet of the nuclear envelope, then the inner leaflet up to 500 μm depth. The images suggest that the nuclear excisosome separates nuclear membrane proteins from lipids, which then form multilamellar assemblies that stain intensely in confocal and in TEM have 5 nm spacing consistent with pure lipid bilayers. The denuded nucleoplasm then degrades by condensation and loss of structure in the range 600 to 700 μm depth producing pyknotic nuclear remnants. None of these stages display any classic autophagic vesicles or lysosomes associated with nuclei. Uniquely, the origin of the nuclear excisosome is from filopodial-like projections of adjacent lens fiber cells that initially contact, and then appear to fuse with the outer nuclear membrane. These filopodial-like projections appear to be initiated with a clathrin-like coat and driven by an internal actin network. In summary, a specialized cellular organelle, the nuclear excisosome, generated in part by adjacent fiber cells degrades nuclei during fiber cell differentiation and maturation.
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11
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Rao PV, Maddala R. Ankyrin-B in lens architecture and biomechanics: Just not tethering but more. BIOARCHITECTURE 2016; 6:39-45. [PMID: 27044909 DOI: 10.1080/19490992.2016.1156284] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The ankyrins are a family of well-characterized metazoan adaptor proteins that play a key role in linking various membrane-spanning proteins to the underlying spectrin-actin cytoskeleton; a mechanistic understanding of their role in tissue architecture and mechanics, however, remains elusive. Here we comment on a recent study demonstrating a key role for ankyrin-B in maintaining the hexagonal shape and radial alignment of ocular lens fiber cells by regulating the membrane organization of periaxin, dystrophins/dystroglycan, NrCAM and spectrin-actin network of proteins, and revealing that ankyrin-B deficiency impairs fiber cell shape and mechanical properties of the ocular lens. These observations indicate that ankyrin-B plays an important role in maintaining tissue cytoarchitecture, cell shape and biomechanical properties via engaging in key protein: protein interactions required for membrane anchoring and organization of the spectrin-actin skeleton, scaffolding proteins and cell adhesive proteins.
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Affiliation(s)
- Ponugoti Vasantha Rao
- a Department of Ophthalmology , Duke University School of Medicine , Durham , NC , USA.,b Department of Pharmacology & Cancer Biology , Duke University School of Medicine , Durham , NC , USA
| | - Rupalatha Maddala
- a Department of Ophthalmology , Duke University School of Medicine , Durham , NC , USA
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12
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Wenke JL, McDonald WH, Schey KL. Spatially Directed Proteomics of the Human Lens Outer Cortex Reveals an Intermediate Filament Switch Associated With the Remodeling Zone. Invest Ophthalmol Vis Sci 2016; 57:4108-14. [PMID: 27537260 PMCID: PMC4991037 DOI: 10.1167/iovs.16-19791] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/15/2016] [Indexed: 01/25/2023] Open
Abstract
PURPOSE To quantify protein changes in the morphologically distinct remodeling zone (RZ) and adjacent regions of the human lens outer cortex using spatially directed quantitative proteomics. METHODS Lightly fixed human lens sections were deparaffinized and membranes labeled with fluorescent wheat germ agglutinin (WGA-TRITC). Morphology directed laser capture microdissection (LCM) was used to isolate tissue from four distinct regions of human lens outer cortex: differentiating zone (DF), RZ, transition zone (TZ), and inner cortex (IC). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) of the plasma membrane fraction from three lenses (21-, 22-, and 27-year) revealed changes in major cytoskeletal proteins including vimentin, filensin, and phakinin. Peptides from proteins of interest were quantified using multiple reaction monitoring (MRM) mass spectrometry and isotopically-labeled internal peptide standards. RESULTS Results revealed an intermediate filament switch from vimentin to beaded filament proteins filensin and phakinin that occurred at the RZ. Several other cytoskeletal proteins showed significant changes between regions, while most crystallins remained unchanged. Targeted proteomics provided accurate, absolute quantification of these proteins and confirmed vimentin, periplakin, and periaxin decrease from the DF to the IC, while filensin, phakinin, and brain acid soluble protein 1 (BASP1) increase significantly at the RZ. CONCLUSIONS Mass spectrometry-compatible fixation and morphology directed laser capture enabled proteomic analysis of narrow regions in the human lens outer cortex. Results reveal dramatic cytoskeletal protein changes associated with the RZ, suggesting that one role of these proteins is in membrane deformation and/or the establishment of ball and socket joints in the human RZ.
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13
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Audette DS, Scheiblin DA, Duncan MK. The molecular mechanisms underlying lens fiber elongation. Exp Eye Res 2016; 156:41-49. [PMID: 27015931 DOI: 10.1016/j.exer.2016.03.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Revised: 03/14/2016] [Accepted: 03/16/2016] [Indexed: 12/28/2022]
Abstract
Lens fiber cells are highly elongated cells with complex membrane morphologies that are critical for the transparency of the ocular lens. Investigations into the molecular mechanisms underlying lens fiber cell elongation were first reported in the 1960s, however, our understanding of the process is still poor nearly 50 years later. This review summarizes what is currently hypothesized about the regulation of lens fiber cell elongation along with the available experimental evidence, and how this information relates to what is known about the regulation of cell shape/elongation in other cell types, particularly neurons.
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Affiliation(s)
- Dylan S Audette
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - David A Scheiblin
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Melinda K Duncan
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA.
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14
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Cheng C, Nowak RB, Fowler VM. The lens actin filament cytoskeleton: Diverse structures for complex functions. Exp Eye Res 2016; 156:58-71. [PMID: 26971460 DOI: 10.1016/j.exer.2016.03.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2015] [Revised: 03/01/2016] [Accepted: 03/07/2016] [Indexed: 01/05/2023]
Abstract
The eye lens is a transparent and avascular organ in the front of the eye that is responsible for focusing light onto the retina in order to transmit a clear image. A monolayer of epithelial cells covers the anterior hemisphere of the lens, and the bulk of the lens is made up of elongated and differentiated fiber cells. Lens fiber cells are very long and thin cells that are supported by sophisticated cytoskeletal networks, including actin filaments at cell junctions and the spectrin-actin network of the membrane skeleton. In this review, we highlight the proteins that regulate diverse actin filament networks in the lens and discuss how these actin cytoskeletal structures assemble and function in epithelial and fiber cells. We then discuss methods that have been used to study actin in the lens and unanswered questions that can be addressed with novel techniques.
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Affiliation(s)
- Catherine Cheng
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Roberta B Nowak
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Velia M Fowler
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
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Biswas S, Son A, Yu Q, Zhou R, Lo WK. Breakdown of interlocking domains may contribute to formation of membranous globules and lens opacity in ephrin-A5(-/-) mice. Exp Eye Res 2015; 145:130-139. [PMID: 26643403 DOI: 10.1016/j.exer.2015.11.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Revised: 11/05/2015] [Accepted: 11/24/2015] [Indexed: 01/17/2023]
Abstract
Ephrin-A5, a ligand of the Eph family of receptor tyrosine kinases, plays a key role in lens fiber cell packing and cell-cell adhesion, with approximately 87% of ephrin-A5(-/-) mice develop nuclear cataracts. Here, we investigated the extensive formation of light-scattering globules associated with breakdown of interlocking protrusions during lens opacification in ephrin-A5(-/-) mice. Lenses from wild-type (WT) and ephrin-A5(-/-) mice between 2 and 21 weeks old were studied with light and electron microscopy, immunofluorescence labeling, freeze-fracture TEM and filipin cytochemistry for membrane cholesterol detection. Lens opacities with various densities were first observed in ephrin-A5(-/-) mice at around 60 days old. Dense cataracts in the mutant lenses were seen primarily in the nuclear region surrounded by transparent cortices from all eyes examined. We confirmed that a majority of nuclear cataracts were dislocated posteriorly and ruptured the thinner posterior lens capsule. SEM analysis indicated that numerous interlocking protrusions and wavy ridge-and-valley membrane surfaces in deep cortical and nuclear fibers did not cause lens opacity in both transparent ephrin-A5(-/-) and WT mice. In contrast, abundant isolated membranous globules of approximately 1000 nm in size were distributed randomly along the intact fiber cells during early stage of all ephrin-A5(-/-) cataracts examined. A further examination using both SEM and TEM revealed that isolated globules were generated from the disintegrated interlocking protrusions originally located along the corners of hexagonal fiber cells. Freeze-fracture TEM further revealed the association of square-array aquaporin junctions with both isolated globules and interlocking membrane domains. This study reports for the first time that disrupted interlocking protrusions are the source of numerous large membranous globules that contribute to light scattering and nuclear cataracts in the ephrin-A5(-/-) mice. Our results further suggest that dissociations of N-cadherin and adherens junctions in the associated interlocking domains may result in the formation of isolated globules and nuclear opacities in the ephrin-A5(-/-) mice.
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Affiliation(s)
- Sondip Biswas
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, USA
| | - Alexander Son
- Department of Chemical Biology, College of Pharmacy, Rutgers University, Piscataway, NJ, USA
| | - Qili Yu
- Department of Chemical Biology, College of Pharmacy, Rutgers University, Piscataway, NJ, USA
| | - Renping Zhou
- Department of Chemical Biology, College of Pharmacy, Rutgers University, Piscataway, NJ, USA.
| | - Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, USA.
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16
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Fragile X Syndrome FMRP Co-localizes with Regulatory Targets PSD-95, GABA Receptors, CaMKIIα, and mGluR5 at Fiber Cell Membranes in the Eye Lens. Neurochem Res 2015; 40:2167-76. [PMID: 26298628 DOI: 10.1007/s11064-015-1702-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 07/27/2015] [Accepted: 08/13/2015] [Indexed: 01/01/2023]
Abstract
Fmr1 and FMRP underlie Fragile X Syndrome (FXS) and are linked with related autism spectrum disorders (ASD). Fmr1 also has an essential role in eye and lens development. Lenses express FMRP along with γ-aminobutyric acid (GABA) receptors (GABARs), post-synaptic density protein 95 (PSD-95), Tyr-phosphatase STEP, CaMKIIα and Alzheimer's disease Aβ precursor protein, which are verified targets of FMRP regulation in neurons and outline major topics in FXS/ASD research. PSD-95 as well as CaMKIIα transcripts undergo polypryimidine tract binding protein dependent alternative splicing in lens, consistent with PSD-95 translation in lens. At least 13 GABAR subunits and GAD25/65/67 GABA metabolism enzymes are expressed in lenses beginning in embryonic development, matching neural development. Interestingly, GABAergic drugs (e.g. baclofen) studied as FXS/ASD therapeutics are shown to resolve developmental vision defects in experimental myopia. Here, we demonstrated that FMRP co-localizes at fiber cell membranes with PSD-95, GABAAδ, GABAAβ3, GABBR1, STEP, CaMKIIα, and mGluR5 in young adult lenses. GAD65 and GABA detection was greatest at the peri-nuclear lens region where fiber cell terminal differentiation occurs. These findings add to an extensive list of detailed parallels between fiber cell and neuron morphology and their lateral membrane spine/protrusions, also reflected in the shared expression of genes involved in the morphogenesis and function of these membrane structures, and shared use of associated regulatory mechanisms first described as distinguishing the neuronal phenotype. Future studies can determine if GABA levels currently studied as a FXS/ASD biomarker in the brain, and generated by GAD25/65/67 in a comparable cell environment in the lens, may be similarly responsive to Fmr1 mutation in lens. The present demonstration of FMRP and key regulatory targets in the lens identifies a potential for the lens to provide a new research venue, in the same individual, to inform about Fmr1/FMRP pathobiology in brain as well as lens.
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17
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Caster DJ, Korte EA, Merchant ML, Klein JB, Wilkey DW, Rovin BH, Birmingham DJ, Harley JB, Cobb BL, Namjou B, McLeish KR, Powell DW. Autoantibodies targeting glomerular annexin A2 identify patients with proliferative lupus nephritis. Proteomics Clin Appl 2015; 9:1012-20. [PMID: 25824007 DOI: 10.1002/prca.201400175] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 02/10/2015] [Accepted: 03/26/2015] [Indexed: 11/09/2022]
Abstract
PURPOSE Patients with systemic lupus erythematosus (SLE) frequently develop lupus nephritis (LN), a complication frequently leading to end stage kidney disease. Immune complex deposition in the glomerulus is central to the development of LN. Using a targeted proteomic approach, we tested the hypothesis that autoantibodies targeting glomerular antigens contribute to the development of LN. EXPERIMENTAL DESIGN Human podocyte and glomerular proteins were separated by SDS-PAGE and immunoblotted with sera from SLE patients with and without LN. The regions of those gels corresponding to reactive bands observed with sera from LN patients were analyzed using LC-MS/MS. RESULTS LN reactive bands were seen at approximately 50 kDa in podocyte extracts and between 36 and 50 kDa in glomerular extracts. Those bands were analyzed by LC-MS/MS and 102 overlapping proteins were identified. Bioinformatic analysis determined that 36 of those proteins were membrane associated, including a protein previously suggested to contribute to glomerulonephritis and LN, annexin A2. By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against annexin A2. CONCLUSION AND CLINICAL RELEVANCE Proteomic approaches identified multiple candidate antigens for autoantibodies in patients with LN. Serum antibodies against annexin A2 were significantly elevated in subjects with proliferative LN, validating those antibodies as potential biomarkers.
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Affiliation(s)
- Dawn J Caster
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY, USA.,Robley Rex Veterans Affairs Medical Center, Louisville, KY, USA
| | - Erik A Korte
- Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, Louisville, KY, USA
| | - Michael L Merchant
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY, USA
| | - Jon B Klein
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY, USA.,Robley Rex Veterans Affairs Medical Center, Louisville, KY, USA
| | - Daniel W Wilkey
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY, USA
| | - Brad H Rovin
- Department of Medicine, the Ohio State University, Columbus, OH, USA
| | - Dan J Birmingham
- Department of Medicine, the Ohio State University, Columbus, OH, USA
| | - John B Harley
- Center for Autoimmune Genomics and Etiology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center and the University of Cincinnati, Cincinnati, OH, USA.,US Department of Veterans Affairs Medical Center, Cincinnati, OH, USA
| | - Beth L Cobb
- Center for Autoimmune Genomics and Etiology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center and the University of Cincinnati, Cincinnati, OH, USA
| | - Bahram Namjou
- Center for Autoimmune Genomics and Etiology, Department of Pediatrics, Cincinnati Children's Hospital Medical Center and the University of Cincinnati, Cincinnati, OH, USA
| | - Kenneth R McLeish
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY, USA.,Robley Rex Veterans Affairs Medical Center, Louisville, KY, USA
| | - David W Powell
- Department of Medicine, University of Louisville School of Medicine, Louisville, KY, USA.,Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, Louisville, KY, USA
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18
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Frederikse PH, Kasinathan C. Lens GABA receptors are a target of GABA-related agonists that mitigate experimental myopia. Med Hypotheses 2015; 84:589-92. [PMID: 25841296 DOI: 10.1016/j.mehy.2015.03.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Revised: 02/12/2015] [Accepted: 03/04/2015] [Indexed: 12/16/2022]
Abstract
Coordinated growth of eye tissues is required to achieve visual acuity. However, visual experience also guides this process. Experimental myopia can be produced by altering light entering the eye, but also by changing light/dark regimens. Drug discovery studies demonstrated that γ-aminobutyric acid (GABA)-related agonists (e.g., baclofen) will mitigate experimental myopia, and are also drugs studied for their capacity to affect neurodevelopmental disorders that include Fragile X Syndrome and related autism spectrum disorders. GABA receptors thought to mediate these responses in the eye have been studied in the neural retina as well as the cornea and sclera which are both innervated tissues. In addition to neurons, lenses express GAD25/65/67 GABA metabolic enzymes and at least 13 GABA receptor subunits with developmental expression profiles that match neural development. Evidence that lens GABA receptors are expressed in a cell environment comparable to neurons is seen in the lens expression of AMPA and NMDA glutamate receptors together with an unexpectedly comprehensive array of associated signaling proteins that include post-synaptic-density 95 (PSD95), calcium calmodulin kinase IIα (CaMKIIα), Fragile X Syndrome mental retardation protein (FMRP), ephrin receptors, Ca(V)1.2, 1.3 channels, cyclin-dependent kinase 5 (Cdk5), and neuronal C-src among others. Moreover, lens cells share fundamental molecular regulatory mechanisms that integrate the regulation and function of these genes at the DNA, RNA, and protein levels in neurons. GABA has trophic, growth promoting effects early in neuron development and later assumes its classic inhibitory role in the adult neural system. We hypothesize that the extensive parallels between GABA and glutamate receptor biology in lens and brain identifies the lens as a site of GABA agonist drug action affecting experimental myopia, acting through lens GABA receptors to similarly affect growth in both elongated cell types.
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Affiliation(s)
- Peter H Frederikse
- Department of Oral Biology, Rutgers SDM and BHS, New Jersey, Newark, NJ 07103, USA; Department of Pharmacology & Physiology, Rutgers SDM and BHS, New Jersey, Newark, NJ 07103, USA.
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19
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Frederikse PH, Nandanoor A, Kasinathan C. "Moonlighting" GAPDH Protein Localizes with AMPA Receptor GluA2 and L1 Axonal Cell Adhesion Molecule at Fiber Cell Borders in the Lens. Curr Eye Res 2015; 41:41-9. [PMID: 25614994 DOI: 10.3109/02713683.2014.997886] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
PURPOSE The canonical role of glyceraldehyde phosphate dehydrogenase (GAPDH) is as an enzyme in glycolysis. GAPDH is also a principal "moonlighting" protein with additional roles at diverse sites in a variety of cells. Surface GAPDH on mammalian, yeast, and bacterial cells acts as a receptor and also mediates cell contacts. In neurons, extracellular GAPDH localizes at synapses. Two GAPDH binding partners at synapses are α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptor (AMPA) GluA2 subunit at dendritic spines and L1 cell adhesion molecule at pre-synaptic membranes, and both proteins are also expressed in lenses. Fiber cell membrane protrusions and dendritic spines have similar size, shape, and spacing, contain F-actin, and express clathrin/AP-2 Adaptor at their surfaces linked with Tyr-phosphatase STEP-regulated endocytosis of AMPA/GluA2 receptors. AMPA receptors work with NMDA (N-methyl-d-aspartate) and GABA (γ-aminobutyric acid) receptors, calcium calmodulin kinase II (CaMKIIα), channel proteins, STEP, and ephrin receptors, which are also expressed in lenses. In neurons, coordinate AMPA/GluA2 receptor endocytosis with GAPDH is linked with disease. GAPDH was previously characterized as a fiber cell membrane protein and shown to decrease substantially in interior fiber cells in human age-related cataract. Here, we examined GAPDH spatial expression in healthy lenses in two vertebrate species. METHODS In situ methods were used to examine GAPDH expression in lenses of healthy young adult rabbits and chickens. Immunoblots were used to detect L1 in lenses. RESULTS The present study demonstrated that GAPDH is present at fiber cell borders in adult rabbit and chicken lenses with evidence of focal concentrations along the fiber cell perimeter, and overlapped with detection of p-Tyr-GluA2, L1, STEP, actin and clathrin. We observed that L1-140 kDa was the prominent form in lens. CONCLUSIONS Our findings indicate investigations into GAPDH "moonlighting" activities similar to its role in cell-cell interactions at neuron surfaces are warranted in the lens.
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Affiliation(s)
- Peter H Frederikse
- a Department of Oral Biology and.,b Department of Pharmacology & Physiology , Rutgers SDM/BHS , Newark , NJ , USA
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20
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Battacharya M, Nandanoor A, Osman M, Kasinathan C, Frederikse P. NMDA Glutamate Receptor NR1, NR2A and NR2B Expression and NR2B Tyr-1472 Phosphorylation in the Lens. Neurochem Res 2014; 39:1825-32. [DOI: 10.1007/s11064-014-1394-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2014] [Revised: 07/15/2014] [Accepted: 07/17/2014] [Indexed: 12/19/2022]
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21
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Scheiblin DA, Gao J, Caplan JL, Simirskii VN, Czymmek KJ, Mathias RT, Duncan MK. Beta-1 integrin is important for the structural maintenance and homeostasis of differentiating fiber cells. Int J Biochem Cell Biol 2014; 50:132-45. [PMID: 24607497 DOI: 10.1016/j.biocel.2014.02.021] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2013] [Revised: 02/04/2014] [Accepted: 02/21/2014] [Indexed: 11/19/2022]
Abstract
β1-Integrin is a heterodimeric transmembrane protein that has roles in both cell-extra-cellular matrix and cell-cell interactions. Conditional deletion of β1-integrin from all lens cells during embryonic development results in profound lens defects, however, it is less clear whether this reflects functions in the lens epithelium alone or whether this protein plays a role in lens fibers. Thus, a conditional approach was used to delete β1-integrin solely from the lens fiber cells. This deletion resulted in two distinct phenotypes with some lenses exhibiting cataracts while others were clear, albeit with refractive defects. Analysis of "clear" conditional knockout lenses revealed that they had profound defects in fiber cell morphology associated with the loss of the F-actin network. Physiological measurements found that the lens fiber cells had a twofold increase in gap junctional coupling, perhaps due to differential localization of connexins 46 and 50, as well as increased water permeability. This would presumably facilitate transport of ions and nutrients through the lens, and may partially explain how lenses with profound structural abnormalities can maintain transparency. In summary, β1-integrin plays a role in maintaining the cellular morphology and homeostasis of the lens fiber cells.
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Affiliation(s)
- David A Scheiblin
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, United States
| | - Junyuan Gao
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York, NY 11794-8661, United States
| | - Jeffrey L Caplan
- Delaware Biotechnology Institute, University of Delaware, Newark, DE 19716, United States
| | - Vladimir N Simirskii
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, United States
| | - Kirk J Czymmek
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, United States
| | - Richard T Mathias
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York, NY 11794-8661, United States
| | - Melinda K Duncan
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, United States.
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22
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Lo WK, Biswas SK, Brako L, Shiels A, Gu S, Jiang JX. Aquaporin-0 targets interlocking domains to control the integrity and transparency of the eye lens. Invest Ophthalmol Vis Sci 2014; 55:1202-12. [PMID: 24458158 DOI: 10.1167/iovs.13-13379] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Lens fiber cell membranes contain aquaporin-0 (AQP0), which constitutes approximately 50% of the total fiber cell membrane proteins and has a dual function as a water channel protein and an adhesion molecule. Fiber cell membranes also develop an elaborate interlocking system that is required for maintaining structural order, stability, and lens transparency. Herein, we used an AQP0-deficient mouse model to investigate an unconventional adhesion role of AQP0 in maintaining a normal structure of lens interlocking protrusions. METHODS The loss of AQP0 in AQP0(-/-) lens fibers was verified by Western blot and immunofluorescence analyses. Changes in membrane surface structures of wild-type and AQP0(-/-) lenses at age 3 to 12 weeks were examined with scanning electron microscopy. Preferential distribution of AQP0 in wild-type fiber cell membranes was analyzed with immunofluorescence and immunogold labeling using freeze-fracturing transmission electron microscopy. RESULTS Interlocking protrusions in young differentiating fiber cells developed normally but showed minor abnormalities at approximately 50 μm deep in the absence of AQP0 in all ages studied. Strikingly, protrusions in maturing fiber cells specifically underwent uncontrolled elongation, deformation, and fragmentation, while cells still retained their overall shape. Later in the process, these changes eventually resulted in fiber cell separation, breakdown, and cataract formation in the lens core. Immunolabeling at the light microscopy and transmission electron microscopy levels demonstrated that AQP0 was particularly enriched in interlocking protrusions in wild-type lenses. CONCLUSIONS This study suggests that AQP0 exerts its primary adhesion or suppression role specifically to maintain the normal structure of interlocking protrusions that is critical to the integrity and transparency of the lens.
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Affiliation(s)
- Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia
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23
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Costello MJ, Mohamed A, Gilliland KO, Fowler WC, Johnsen S. Ultrastructural analysis of the human lens fiber cell remodeling zone and the initiation of cellular compaction. Exp Eye Res 2013; 116:411-8. [PMID: 24183661 DOI: 10.1016/j.exer.2013.10.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 10/18/2013] [Accepted: 10/21/2013] [Indexed: 10/26/2022]
Abstract
The purpose is to determine the nature of the cellular rearrangements occurring through the remodeling zone (RZ) in human donor lenses, identified previously by confocal microscopy to be about 100 μm from the capsule. Human donor lenses were fixed with 10% formalin followed by 4% paraformaldehyde prior to processing for transmission electron microscopy. Of 27 fixed lenses, ages 22, 55 and 92 years were examined in detail. Overview electron micrographs confirmed the loss of cellular organization present in the outer cortex (80 μm thick) as the cells transitioned into the RZ. The transition occurred within a few cell layers and fiber cells in the RZ completely lost their classical hexagonal cross-sectional appearance. Cell interfaces became unusually interdigitated and irregular even though the radial cell columns were retained. Gap junctions appeared to be unaffected. After the RZ (40 μm thick), the cells were still irregular but more recognizable as fiber cells with typical interdigitations and the appearance of undulating membranes. Cell thickness was irregular after the RZ with some cells compacted, while others were not, up to the zone of full compaction in the adult nucleus. Similar dramatic cellular changes were observed within the RZ for each lens regardless of age. Because the cytoskeleton controls cell shape, dramatic cellular rearrangements that occur in the RZ most likely are due to alterations in the associations of crystallins to the lens-specific cytoskeletal beaded intermediate filaments. It is also likely that cytoskeletal attachments to membranes are altered to allow undulating membranes to develop.
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Affiliation(s)
- M Joseph Costello
- Department of Cell Biology and Physiology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA.
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24
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Frederikse PH, Kasinathan C, Kleiman NJ. Parallels between neuron and lens fiber cell structure and molecular regulatory networks. Dev Biol 2012; 368:255-60. [PMID: 22641011 DOI: 10.1016/j.ydbio.2012.05.022] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Revised: 05/18/2012] [Accepted: 05/19/2012] [Indexed: 11/26/2022]
Abstract
Studies over the past fifty years have identified extensive similarities between neurons and elongated fiber cells that make up in the interior of the ocular lens. Electron micrographs showed parallels in the organization of their intracellular vesicle transport machinery and between lens fiber cell lateral protrusions and dendritic spines. Consistent with those observations, a number of gene products first characterized as highly neuron-preferred in their expression were also demonstrated in lens fiber cells. Going further, a fundamental network of regulatory factors with critical roles in determining the neuronal phenotype were also identified in lenses, and showed a corresponding mutually exclusive distribution of neural and non-neural factor isoforms in mitotic lens epithelial cells and post-mitotic fiber cells consistent with their interlocking functions in neural cells. These included REST/NRSF transcription factors, members of major RNA binding protein families, and "brain-specific" miRNAs that were each shown to have global roles in governing neural and non-neural gene expression and alternative transcript splicing in vertebrates. This review discusses these extensive parallels between neurons and fiber cells and implications regarding common themes in lens and neural cell physiology and disease, which may also suggest related evolutionary processes.
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Affiliation(s)
- Peter H Frederikse
- Department of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, 185 South Orange Avenue, MSB H645, Newark, NJ 07103, United States.
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25
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Bitel CL, Singh V, Frederikse PH. miR-124, miR-125b, let-7 and vesicle transport proteins in squid lenses in L. pealei. Curr Eye Res 2012; 37:388-94. [PMID: 22257219 DOI: 10.3109/02713683.2011.635833] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
PURPOSE Studies over the past several decades identified parallels between neuron and lens fiber cell morphology, development, and physiology. Consistent with this, mammalian lens fiber cells were shown to express a substantial complement of genes that cluster with respect to synaptic vesicle transport and exocytosis. Expression of these genes in these two cell types also appears consistent with similarities described between lens fiber cell lateral protrusions and neuronal dendrites. Recently, we showed vertebrate neurons and lens fiber cells share expression of a core set of factors that form an interlocking regulatory network which has a fundamental role in determining neural cell identity. These included the REST/NRSF transcription factor, neural RNA binding proteins and miR-124. In addition, we identified miR-125 and let-7 in mammalian lenses that have been shown to regulate dendrite formation in neurons. The present study examined expression of miR-124, miR-125, and let-7 as well as genes involved in vesicle transport in lens in the squid Loligo (also referred to as Doryteuthis) pealei. METHODS Northern blot, RT-PCR, immunoblots, and in situ detection were used to analyze expression in squid and vertebrate tissues. RESULTS The present study provided evidence that miR-124, miR-125, let-7 and vesicle transport-related proteins are produced in squid lenses. Consistent with these mRNAs and miRNAs in squid lenses, and polyribosomes shown by others, we detected substantial levels of tRNA and rRNA in anuclear squid lenses which do not produce an epithelial cell layer that would be analogous to vertebrate lenses. CONCLUSIONS Our study provided evidence that miR-124, miR-125, and let-7, as well as proteins involved in vesicle transport linked with synaptic and cargo vesicle transport in vertebrates are also expressed in squid lenses.
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Affiliation(s)
- Claudine L Bitel
- Department of Pharmacology and Physiology and the Rutgers-UMDNJ Integrative Neurosciences Program, Newark, NJ 07103, USA
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Farooq M, Kaswala RH, Kleiman NJ, Kasinathan C, Frederikse PH. GluA2 AMPA glutamate receptor subunit exhibits codon 607 Q/R RNA editing in the lens. Biochem Biophys Res Commun 2012; 418:273-7. [PMID: 22266371 DOI: 10.1016/j.bbrc.2012.01.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2012] [Accepted: 01/04/2012] [Indexed: 11/19/2022]
Abstract
Regulated GluA2 AMPA receptor subunit expression, RNA editing, and membrane localization are fundamental determinants of neuronal Ca(2+) influx, and underlie basic functions such as memory and the primary brain disorder epilepsy. Consistent with this, AMPARs, and specifically GluA2, are targets of common antiepileptic drugs (AEDs) and antidepressants. Recently, epidemiological associations between epilepsy and increased cataract prevalence were found comparable to cataract links with diabetes and smoking. Similarly, use of AEDs and several antidepressants also showed links with increased cataract. Here, we demonstrated GluA2 in lenses, consistent with REST/NRSF and REST4 we described previously in lenses, as well as GluA1 and ADAR2 in the lens. Surprisingly, we found predominant neuron-like Q/R editing of GluA2 RNAs also occurs in the lens and evidence of lens GluA2 phosphorylation and STEP phosphatases linked with GluA2 membrane localization in neurons. This study is among the first to show GluA2 expression and predominant Q/R RNA editing in a non-neural cell. Our results suggest GluA2 AMPARs have related roles in lens physiology and disease processes, and provide evidence these anticonvulsant and antidepressant drug targets also occur in the lens.
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Affiliation(s)
- Mohammed Farooq
- Department of Pharmacology and Physiology, UMDNJ-New Jersey Medical School, Newark, NJ, USA
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Dahm R, van Marle J, Quinlan RA, Prescott AR, Vrensen GFJM. Homeostasis in the vertebrate lens: mechanisms of solute exchange. Philos Trans R Soc Lond B Biol Sci 2011; 366:1265-77. [PMID: 21402585 DOI: 10.1098/rstb.2010.0299] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The eye lens is avascular, deriving nutrients from the aqueous and vitreous humours. It is, however, unclear which mechanisms mediate the transfer of solutes between these humours and the lens' fibre cells (FCs). In this review, we integrate the published data with the previously unpublished ultrastructural, dye loading and magnetic resonance imaging results. The picture emerging is that solute transfer between the humours and the fibre mass is determined by four processes: (i) paracellular transport of ions, water and small molecules along the intercellular spaces between epithelial and FCs, driven by Na(+)-leak conductance; (ii) membrane transport of such solutes from the intercellular spaces into the fibre cytoplasm by specific carriers and transporters; (iii) gap-junctional coupling mediating solute flux between superficial and deeper fibres, Na(+)/K(+)-ATPase-driven efflux of waste products in the equator, and electrical coupling of fibres; and (iv) transcellular transfer via caveoli and coated vesicles for the uptake of macromolecules and cholesterol. There is evidence that the Na(+)-driven influx of solutes occurs via paracellular and membrane transport and the Na(+)/K(+)-ATPase-driven efflux of waste products via gap junctions. This micro-circulation is likely restricted to the superficial cortex and nearly absent beyond the zone of organelle loss, forming a solute exchange barrier in the lens.
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Affiliation(s)
- Ralf Dahm
- Center for Brain Research, Medical University of Vienna, Spitalgasse 4, A-1090 Vienna, Austria.
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Bitel CL, Nathan R, Wong P, Kuppasani S, Matsushita M, Kanazawa H, Frederikse PH. Evidence That ‘Brain-Specific’ Fox-1, Fox-2, and nPTB Alternatively Spliced Isoforms Are Produced in the Lens. Curr Eye Res 2010; 35:1002-11. [DOI: 10.3109/02713683.2010.500114] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Jungbluth H, Cullup T, Lillis S, Zhou H, Abbs S, Sewry C, Muntoni F. Centronuclear myopathy with cataracts due to a novel dynamin 2 (DNM2) mutation. Neuromuscul Disord 2009; 20:49-52. [PMID: 19932620 DOI: 10.1016/j.nmd.2009.10.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2009] [Revised: 10/12/2009] [Accepted: 10/16/2009] [Indexed: 10/20/2022]
Abstract
Dynamin 2 (DNM2)-related dominant centronuclear myopathy is usually a mild disorder, but more severe variants have been associated with mutations affecting the pleckstrin homology (PH) domain of the protein, mainly implicated in different forms of Charcot-Marie-Tooth Disease (CMT). Whilst DNM2-related CMT may feature non-neurological findings including cataracts, this has not been reported in DNM2-related centronuclear myopathy. We report a girl presenting from birth with hypotonia, respiratory and feeding difficulties. Motor development was delayed and at 9years she lost the ability to walk. She had ptosis, external ophthalmoplegia and bilateral cataracts. Muscle biopsy showed increase in central nuclei with type 1 hypotrophy and fibrosis. DNM2 screening revealed a novel heterozygous substitution (c.1862T>C; p.Leu621Pro) affecting the PH domain of the protein. Her further course was progressive and at 14years she died from respiratory failure. Our findings expand the phenotypical spectrum associated with DNM2 mutations and provide a new clinical indicator for involvement of this gene in patients with centronuclear myopathy.
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Wnt signaling is required for organization of the lens fiber cell cytoskeleton and development of lens three-dimensional architecture. Dev Biol 2008; 324:161-76. [PMID: 18824165 DOI: 10.1016/j.ydbio.2008.09.002] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Revised: 09/03/2008] [Accepted: 09/03/2008] [Indexed: 12/12/2022]
Abstract
How an organ develops its characteristic shape is a major issue. This is particularly critical for the eye lens as its function depends on having appropriately ordered three-dimensional cellular architecture. Recent in vitro studies indicate that Wnt signaling plays key roles in regulating morphological events in FGF-induced fiber cell differentiation in the mammalian lens. To further investigate this the Wnt signaling antagonist, secreted frizzled-related protein 2 (Sfrp2), was overexpressed in lens fiber cells of transgenic mice. In these mice fiber cell elongation was attenuated and individual fibers exhibited irregular shapes and consequently did not align or pack regularly; microtubules, microfilaments and intermediate filaments were clearly disordered in these fibers. Furthermore, a striking feature of transgenic lenses was that fibers did not develop the convex curvature typically seen in normal lenses. This appears to be related to a lack of protrusive processes that are required for directed migratory activity at their apical and basal tips as well as for the formation of interlocking processes along their lateral margins. Components of the Wnt/Planar Cell Polarity (PCP) pathway were downregulated or inhibited. Taken together this supports a role for Wnt/PCP signaling in orchestrating the complex organization and dynamics of the fiber cell cytoskeleton.
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Ramalingam A, Duhadaway JB, Sutanto-Ward E, Wang Y, Dinchuk J, Huang M, Donover PS, Boulden J, McNally LM, Soler AP, Muller AJ, Duncan MK, Prendergast GC. Bin3 Deletion Causes Cataracts and Increased Susceptibility to Lymphoma during Aging. Cancer Res 2008; 68:1683-90. [DOI: 10.1158/0008-5472.can-07-6072] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Rao PV, Maddala R. The role of the lens actin cytoskeleton in fiber cell elongation and differentiation. Semin Cell Dev Biol 2006; 17:698-711. [PMID: 17145190 PMCID: PMC1803076 DOI: 10.1016/j.semcdb.2006.10.011] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The vertebrate ocular lens is a fascinating and unique transparent tissue that grows continuously throughout life. During the process of differentiation into fiber cells, lens epithelial cells undergo dramatic morphological changes, membrane remodeling, polarization, transcriptional activation and elimination of cellular organelles including nuclei, concomitant with migration towards the lens interior. Most of these events are presumed to be influenced in large part, by dynamic reorganization of the cellular actin cytoskeleton and by intercellular and cell: extracellular matrix interactions. In light of recent and unprecedented advancement in our understanding of the mechanistic bases underlying regulation of actin cytoskeletal dynamics and the role of the actin cytoskeleton in cell function, this review attempts to summarize current knowledge regarding the role of the cellular actin cytoskeleton, in lens fiber cell elongation and differentiation, and regulation of actin cytoskeletal organization in the lens.
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Affiliation(s)
- P Vasantha Rao
- Departments of Ophthalmology, Pharmacology and Cancer Biology, Duke University School of Medicine, Durham, NC, USA.
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