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Narangifard A, Wennberg CL, den Hollander L, Iwai I, Han H, Lundborg M, Masich S, Lindahl E, Daneholt B, Norlén L. Molecular Reorganization during the Formation of the Human Skin Barrier Studied In Situ. J Invest Dermatol 2021; 141:1243-1253.e6. [DOI: 10.1016/j.jid.2020.07.040] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 07/01/2020] [Accepted: 07/13/2020] [Indexed: 12/25/2022]
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Hernández-Hernández A, Masich S, Fukuda T, Kouznetsova A, Sandin S, Daneholt B, Höög C. The central element of the synaptonemal complex in mice is organized as a bilayered junction structure. J Cell Sci 2016; 129:2239-49. [PMID: 27103161 DOI: 10.1242/jcs.182477] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 04/14/2016] [Indexed: 01/25/2023] Open
Abstract
The synaptonemal complex transiently stabilizes pairing interactions between homologous chromosomes during meiosis. Assembly of the synaptonemal complex is mediated through integration of opposing transverse filaments into a central element, a process that is poorly understood. We have, here, analyzed the localization of the transverse filament protein SYCP1 and the central element proteins SYCE1, SYCE2 and SYCE3 within the central region of the synaptonemal complex in mouse spermatocytes using immunoelectron microscopy. Distribution of immuno-gold particles in a lateral view of the synaptonemal complex, supported by protein interaction data, suggest that the N-terminal region of SYCP1 and SYCE3 form a joint bilayered central structure, and that SYCE1 and SYCE2 localize in between the two layers. We find that disruption of SYCE2 and TEX12 (a fourth central element protein) localization to the central element abolishes central alignment of the N-terminal region of SYCP1. Thus, our results show that all four central element proteins, in an interdependent manner, contribute to stabilization of opposing N-terminal regions of SYCP1, forming a bilayered transverse-filament-central-element junction structure that promotes synaptonemal complex formation and synapsis.
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Affiliation(s)
| | - Sergej Masich
- Department of Cell and Molecular Biology, Karolinska Institutet Berzelius väg 35, Stockholm 171 77, Sweden
| | - Tomoyuki Fukuda
- Department of Cell and Molecular Biology, Karolinska Institutet Berzelius väg 35, Stockholm 171 77, Sweden Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan
| | - Anna Kouznetsova
- Department of Cell and Molecular Biology, Karolinska Institutet Berzelius väg 35, Stockholm 171 77, Sweden
| | - Sara Sandin
- School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, 637551, Singapore
| | - Bertil Daneholt
- Department of Cell and Molecular Biology, Karolinska Institutet Berzelius väg 35, Stockholm 171 77, Sweden
| | - Christer Höög
- Department of Cell and Molecular Biology, Karolinska Institutet Berzelius väg 35, Stockholm 171 77, Sweden
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den Hollander L, Han H, de Winter M, Svensson L, Masich S, Daneholt B, Norlén L. Skin Lamellar Bodies are not Discrete Vesicles but Part of a Tubuloreticular Network. Acta Derm Venereol 2016; 96:303-8. [PMID: 26439096 DOI: 10.2340/00015555-2249] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Improved knowledge of the topology of lamellar bodies is a prerequisite for a molecular-level understanding of skin barrier formation, which in turn may provide clues as to the underlying causes of barrier-deficient skin disease. The aim of this study was to examine the key question of continuity vs. discreteness of the lamellar body system using 3 highly specialized and complementary 3-dimensional (3D) electron microscopy methodologies; tomography of vitreous sections (TOVIS), freeze-substitution serial section electron tomography (FS-SET), and focused ion beam scanning electron microscopy (FIB-SEM) tomography. We present here direct evidence that lamellar bodies are not discrete vesicles, but are part of a tubuloreticular membrane network filling out the cytoplasm and being continuous with the plasma membrane of stratum granulosum cells. This implies that skin barrier formation could be regarded as a membrane folding/unfolding process, but not as a lamellar body fusion process.
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Affiliation(s)
- Lianne den Hollander
- Department of Cell and Molelcular Biology, Karolinska Institutet, 17177 Stockholm, Sweden
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Khatibi Shahidi M, Krivanek J, Kaukua N, Ernfors P, Hladik L, Kostal V, Masich S, Hampl A, Chubanov V, Gudermann T, Romanov R, Harkany T, Adameyko I, Fried K. Three-dimensional Imaging Reveals New Compartments and Structural Adaptations in Odontoblasts. J Dent Res 2015; 94:945-54. [DOI: 10.1177/0022034515580796] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
In organized tissues, the precise geometry and the overall shape are critical for the specialized functions that the cells carry out. Odontoblasts are major matrix-producing cells of the tooth and have also been suggested to participate in sensory transmission. However, refined morphologic data on these important cells are limited, which hampers the analysis and understanding of their cellular functions. We took advantage of fluorescent color-coding genetic tracing to visualize and reconstruct in 3 dimensions single odontoblasts, pulp cells, and their assemblages. Our results show distinct structural features and compartments of odontoblasts at different stages of maturation, with regard to overall cellular shape, formation of the main process, orientation, and matrix deposition. We demonstrate previously unanticipated contacts between the processes of pulp cells and odontoblasts. All reported data are related to mouse incisor tooth. We also show that odontoblasts express TRPM5 and Piezo2 ion channels. Piezo2 is expressed ubiquitously, while TRPM5 is asymmetrically distributed with distinct localization to regions proximal to and within odontoblast processes.
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Affiliation(s)
| | - J. Krivanek
- Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - N. Kaukua
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - P. Ernfors
- Unit of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden
| | - L. Hladik
- TESCAN ORSAY Holding, Brno, Czech Republic
| | - V. Kostal
- TESCAN ORSAY Holding, Brno, Czech Republic
| | - S. Masich
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
| | - A. Hampl
- Department of Histology and Embryology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - V. Chubanov
- Ludwig-Maximilians-Universität München, Walther-Straub-Institut für Pharmakologie und Toxikologie, München, Germany
| | - T. Gudermann
- Ludwig-Maximilians-Universität München, Walther-Straub-Institut für Pharmakologie und Toxikologie, München, Germany
| | - R.A. Romanov
- Unit of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden
| | - T. Harkany
- Unit of Molecular Neurobiology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden
- Department of Molecular Neurosciences, Center of Brain Research, Medical University of Vienna, Vienna, Austria
| | - I. Adameyko
- Department of Molecular Neurosciences, Center of Brain Research, Medical University of Vienna, Vienna, Austria
- Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
| | - K. Fried
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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5
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Leitinger G, Masich S, Neumüller J, Pabst MA, Pavelka M, Rind FC, Shupliakov O, Simmons PJ, Kolb D. Structural organization of the presynaptic density at identified synapses in the locust central nervous system. J Comp Neurol 2012; 520:384-400. [PMID: 21826661 PMCID: PMC3263340 DOI: 10.1002/cne.22744] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In a synaptic active zone, vesicles aggregate around a densely staining structure called the presynaptic density. We focus on its three-dimensional architecture and a major molecular component in the locust. We used electron tomography to study the presynaptic density in synapses made in the brain by identified second-order neuron of the ocelli. Here, vesicles close to the active zone are organized in two rows on either side of the presynaptic density, a level of organization not previously reported in insect central synapses. The row of vesicles that is closest to the density's base includes vesicles docked with the presynaptic membrane and thus presumably ready for release, whereas the outer row of vesicles does not include any that are docked. We show that a locust ortholog of the Drosophila protein Bruchpilot is localized to the presynaptic density, both in the ocellar pathway and compound eye visual neurons. An antibody recognizing the C-terminus of the Bruchpilot ortholog selectively labels filamentous extensions of the presynaptic density that reach out toward vesicles. Previous studies on Bruchpilot have focused on its role in neuromuscular junctions in Drosophila, and our study shows it is also a major functional component of presynaptic densities in the central nervous system of an evolutionarily distant insect. Our study thus reveals Bruchpilot executes similar functions in synapses that can sustain transmission of small graded potentials as well as those relaying large, spike-evoked signals.
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Affiliation(s)
- Gerd Leitinger
- Institute of Cell Biology, Histology and Embryology, Center for Molecular Medicine (ZMM), Medical University of Graz, Austria. Gerd.Leitinger@medunigraz
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Abstract
We present a new approach to simulate electron cryo-microscope images of biological specimens. The framework for simulation consists of two parts; the first is a phantom generator that generates a model of a specimen suitable for simulation, the second is a transmission electron microscope simulator. The phantom generator calculates the scattering potential of an atomic structure in aqueous buffer and allows the user to define the distribution of molecules in the simulated image. The simulator includes a well defined electron-specimen interaction model based on the scalar Schrödinger equation, the contrast transfer function for optics, and a noise model that includes shot noise as well as detector noise including detector blurring. To enable optimal performance, the simulation framework also includes a calibration protocol for setting simulation parameters. To test the accuracy of the new framework for simulation, we compare simulated images to experimental images recorded of the Tobacco Mosaic Virus (TMV) in vitreous ice. The simulated and experimental images show good agreement with respect to contrast variations depending on dose and defocus. Furthermore, random fluctuations present in experimental and simulated images exhibit similar statistical properties. The simulator has been designed to provide a platform for development of new instrumentation and image processing procedures in single particle electron microscopy, two-dimensional crystallography and electron tomography with well documented protocols and an open source code into which new improvements and extensions are easily incorporated.
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Affiliation(s)
- H Rullgård
- Department of Mathematics, Stockholm University, Stockholm, Sweden
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Jiao W, Masich S, Franzén O, Shupliakov O. Two pools of vesicles associated with the presynaptic cytosolic projection in Drosophila neuromuscular junctions. J Struct Biol 2010; 172:389-94. [PMID: 20678577 DOI: 10.1016/j.jsb.2010.07.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Revised: 07/19/2010] [Accepted: 07/24/2010] [Indexed: 10/19/2022]
Abstract
Synapses that sustain neurotransmitter release at high rates often contain special presynaptic cytosolic projections (PCPs) that are believed to facilitate synaptic vesicle (SV) movements to the sites of fusion. The genetically modifiable Drosophila neuromuscular junction (NMJ) serves as one of the model systems to investigate the functions of these structures. Using electron microscope tomography we determined the three-dimensional organization of the Drosophila PCP immobilized by high-pressure freezing, followed by cryo-substitution. We show that it is composed of three structural components: (1) the central core, (2) legs, organized in a regular grid at the bottom of the central core, and (3) cytoplasmic extensions. The extensions are comprised of thin filaments emerging from the central core. SVs connected to the extensions are either linked to the vesicles accumulated around the PCP or to the presynaptic membrane. This suggests that SVs associated with the PCP loose their connections with other vesicles in the cluster during translocation to the site of fusion.
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Affiliation(s)
- Wei Jiao
- Department of Neuroscience, DBRM, Karolinska Institutet, 17177 Stockholm, Sweden
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Barrau S, Andersson V, Zhang F, Masich S, Bijleveld J, Andersson MR, Inganäs O. Nanomorphology of Bulk Heterojunction Organic Solar Cells in 2D and 3D Correlated to Photovoltaic Performance. Macromolecules 2009. [DOI: 10.1021/ma802457v] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Sophie Barrau
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
- Center of Organic Electronics (COE), Linköping University, SE-58183 Linköping, Sweden
| | - Viktor Andersson
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
- Center of Organic Electronics (COE), Linköping University, SE-58183 Linköping, Sweden
| | - Fengling Zhang
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
- Center of Organic Electronics (COE), Linköping University, SE-58183 Linköping, Sweden
| | - Sergej Masich
- Department of Cell and Molecular Biology, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Johan Bijleveld
- Polymer Chemistry, Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
| | - Mats R. Andersson
- Polymer Chemistry, Department of Chemical and Biological Engineering/Polymer Technology, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
| | - Olle Inganäs
- Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology, Linköping University, SE-58183 Linköping, Sweden
- Center of Organic Electronics (COE), Linköping University, SE-58183 Linköping, Sweden
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Abstract
Electron tomography has been used for analyzing the active layer in a polymer solar cell, a bulk heterojunction of an alternating copolymer of fluorene and a derivative of fullerene. The method supplies a three-dimensional representation of the morphology of the film, where domains with different scattering properties may be distinguished. The reconstruction shows good contrast between the two phases included in the film and demonstrates that electron tomography is an adequate tool for investigations of the three-dimensional nanostructure of the amorphous materials used in polymer solar cells.
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Affiliation(s)
- B Viktor Andersson
- Biomolecular and Organic Electronics, IFM, Linkoping University, SE-581 83 Linkoping, Sweden.
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Norlén L, Masich S, Goldie KN, Hoenger A. Structural analysis of vimentin and keratin intermediate filaments by cryo-electron tomography. Exp Cell Res 2007; 313:2217-27. [PMID: 17499715 DOI: 10.1016/j.yexcr.2007.03.037] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2007] [Revised: 03/20/2007] [Accepted: 03/26/2007] [Indexed: 11/25/2022]
Abstract
Intermediate filaments are a large and structurally diverse group of cellular filaments that are classified into five different groups. They are referred to as intermediate filaments (IFs) because they are intermediate in diameter between the two other cytoskeletal filament systems that is filamentous actin and microtubules. The basic building block of IFs is a predominantly alpha-helical rod with variable length globular N- and C-terminal domains. On the ultra-structural level there are two major differences between IFs and microtubules or actin filaments: IFs are non-polar, and they do not exhibit large globular domains. IF molecules associate via a coiled-coil interaction into dimers and higher oligomers. Structural investigations into the molecular building plan of IFs have been performed with a variety of biophysical and imaging methods such as negative staining and metal-shadowing electron microscopy (EM), mass determination by scanning transmission EM, X-ray crystallography on fragments of the IF stalk and low-angle X-ray scattering. The actual packing of IF dimers into a long filament varies between the different families. Typically the dimers form so called protofibrils that further assemble into a filament. Here we introduce new cryo-imaging methods for structural investigations of IFs in vitro and in vivo, i.e., cryo-electron microscopy and cryo-electron tomography, as well as associated techniques such as the preparation and handling of vitrified sections of cellular specimens.
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Affiliation(s)
- Lars Norlén
- Medical Nobel Institute, Department of Cellular and Molecular Biology (CMB), Karolinska Institute, and Dermatology Clinic, Karolinska University Hospital, Stockholm, Sweden.
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Nashchekin D, Masich S, Soop T, Kukalev A, Kovrigina E, Nashchekina O, Daneholt B. Two splicing isoforms of the Y-box protein ctYB-1 appear on the same mRNA molecule. FEBS J 2007; 274:202-11. [PMID: 17222182 DOI: 10.1111/j.1742-4658.2006.05576.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Y-box proteins constitute an evolutionarily conserved family of DNA- and RNA-binding proteins involved in the regulation of transcription and translation. In the dipteran Chironomus tentans, a homologue to the vertebrate Y-box protein YB-1 was recently characterized and designated ctYB-1. It is transferred from nucleus to cytoplasm bound to mRNA and is likely to affect translation. It appears in two size variants, p40 and p50. We further analysed the two size variants and their interaction with mRNA. Southern blot analysis, in situ hybridization and RT-PCR analysis suggested that there is just one YB-1 gene, and that the two size variants represent splicing isoforms. In a C. tentans epithelial cell line, only p40 is present, whereas both variants appear together in eight tissues from fourth-instar larvae, although in somewhat different proportions. Furthermore, the appearance of the two isoforms was studied in relation to a specific 35-40 kb mRNA transcript in the salivary glands, the Balbiani ring mRNA. Because of their exceptional size, Balbiani ring messenger ribonucleoprotein particles in nucleoplasm and Balbiani ring polysomes in cytoplasm could be identified and selectively studied. We were able to establish that both isoforms are associated with both nuclear and cytoplasmic Balbiani ring mRNA. In addition, a p50-specific antibody coimmunoprecipitated p40 from Balbiani ring polysomes, suggesting that the two splicing isoforms are located along the same Balbiani ring mRNA molecule. The functional significance of the two isoforms is being discussed.
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Affiliation(s)
- Dmitry Nashchekin
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, Stockholm, Sweden
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12
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Masich S, Ostberg T, Norlén L, Shupliakov O, Daneholt B. A procedure to deposit fiducial markers on vitreous cryo-sections for cellular tomography. J Struct Biol 2006; 156:461-8. [PMID: 16859924 DOI: 10.1016/j.jsb.2006.05.010] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2006] [Revised: 05/29/2006] [Accepted: 05/31/2006] [Indexed: 11/21/2022]
Abstract
We describe a novel approach for the accurate alignment of images in electron tomography of vitreous cryo-sections. Quantum dots, suspended in organic solvents at cryo-temperatures, are applied directly onto the sections and are subsequently used as fiducial markers to align the tilt series. Data collection can be performed from different regions of the vitreous sections, even when the sections touch the grid only at a few places. We present high-resolution tomograms of some organelles in cryo-sections of human skin cells using this method. The average error in image alignment was about 1nm and the resolution was estimated to be 5-7nm. Thus, the use of section-attached quantum dots as fiducial markers in electron tomography of vitreous cryo-sections facilitates high-resolution in situ 3D imaging of organelles and macromolecular complexes in their native hydrated state.
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Affiliation(s)
- Sergej Masich
- Department of Cell and Molecular Biology, Karolinska Institutet, Box 285, SE-17177 Stockholm, Sweden
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Soop T, Ivarsson B, Björkroth B, Fomproix N, Masich S, Cordes VC, Daneholt B. Nup153 affects entry of messenger and ribosomal ribonucleoproteins into the nuclear basket during export. Mol Biol Cell 2005; 16:5610-20. [PMID: 16195343 PMCID: PMC1289406 DOI: 10.1091/mbc.e05-08-0715] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A specific messenger ribonucleoprotein (RNP) particle, Balbiani ring (BR) granules in the dipteran Chironomus tentans, can be visualized during passage through the nuclear pore complex (NPC). We have now examined the transport through the nuclear basket preceding the actual translocation through the NPC. The basket consists of eight fibrils anchored to the NPC core by nucleoprotein Nup153. On nuclear injection of anti-Nup153, the transport of BR granules is blocked. Many granules are retained on top of the nuclear basket, whereas no granules are seen in transit through NPC. Interestingly, the effect of Nup153 seems distant from the antibody-binding site at the base of the basket. We conclude that the entry into the basket is a two-step process: an mRMP first binds to the tip of the basket fibrils and only then is it transferred into the basket by a Nup153-dependent process. It is indicated that ribosomal subunits follow a similar pathway.
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Affiliation(s)
- Teresa Soop
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, S-171 77 Stockholm, Sweden
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Bear DG, Fomproix N, Soop T, Björkroth B, Masich S, Daneholt B. Nuclear poly(A)-binding protein PABPN1 is associated with RNA polymerase II during transcription and accompanies the released transcript to the nuclear pore. Exp Cell Res 2003; 286:332-44. [PMID: 12749861 DOI: 10.1016/s0014-4827(03)00123-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The nuclear poly(A)-binding protein, PABPN1, has been previously shown to regulate mRNA poly(A) tail length and to interact with selected proteins involved in mRNA synthesis and trafficking. To further understand the role of PABPN1 in mRNA metabolism, we used cryo-immunoelectron microscopy to determine the fate of PABPN1 at various stages in the assembly and transport of the Chironomus tentans salivary gland Balbiani ring (BR) mRNA ribonucleoprotein (mRNP) complex. PABPN1 is found on BR mRNPs within the nucleoplasm as well as on mRNPs docked at the nuclear pore. Very little PABPN1 is detected on the cytoplasmic side of the nuclear envelope, suggesting that PABPN1 is displaced from mRNPs during or shortly after passage through the nuclear pore. Surprisingly, we also find PABPN1 associated with RNA polymerase II along the chromatin axis of the BR gene. Our results suggest that PABPN1 binds to the polymerase before, at, or shortly after the start of transcription, and that the assembly of PABPN1 onto the poly(A) tail may be coupled to transcription. Furthermore, PABPN1 remains associated with the released BR mRNP until the mRNP is translocated from the nucleus to the cytoplasm.
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Affiliation(s)
- David G Bear
- Department of Cell Biology and Physiology and the UNM Cancer Research and Treatment Center, University of New Mexico Health Sciences Center, Albuquerque, NM 87131, USA.
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15
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Wetterberg I, Zhao J, Masich S, Wieslander L, Skoglund U. In situ transcription and splicing in the Balbiani ring 3 gene. EMBO J 2001; 20:2564-74. [PMID: 11350946 PMCID: PMC125468 DOI: 10.1093/emboj/20.10.2564] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2001] [Revised: 03/26/2001] [Accepted: 03/27/2001] [Indexed: 11/13/2022] Open
Abstract
The Balbiani ring 3 (BR3) gene contains 38 introns, and more than half of them are co-transcriptionally excised. We have determined the in situ structure of the active BR3 gene by electron tomography. Each of the 20-25 nascent transcripts on the gene is present together with splicing factors and the RNA polymerase II in a nascent transcript and splicing complex, here called the NTS complex. The results indicate that extensive changes in overall shape, substructure and molecular mass take place repeatedly within an NTS complex as it moves along the gene. The volume and calculated mass of the NTS complexes show that, maximally, one complete spliceosome is assembled on the multi-intron transcript at any given time point. The structural data show that the spliceosome is not a structurally well-defined unit in situ and that the C-terminal domain of the elongating RNA polymerase II cannot carry spliceosomal components for all introns in the BR3 transcript. Our data indicate that spliceosomal factors are continuously added to and released from the NTS complexes during transcription elongation.
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Affiliation(s)
- Ingela Wetterberg
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institute, SE-171 77 Stockholm and Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden Corresponding author e-mail:
| | - Jian Zhao
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institute, SE-171 77 Stockholm and Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden Corresponding author e-mail:
| | - Sergej Masich
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institute, SE-171 77 Stockholm and Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden Corresponding author e-mail:
| | - Lars Wieslander
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institute, SE-171 77 Stockholm and Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden Corresponding author e-mail:
| | - Ulf Skoglund
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institute, SE-171 77 Stockholm and Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden Corresponding author e-mail:
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16
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Abstract
Specific premessenger ribonucleoprotein (pre-mRNP) particles, the Balbiani ring (BR) granules in the salivary glands of the dipteran Chironomus tentans, can be visualized in the electron microscope when they assemble on the genes, move through nucleoplasm, and bind to and translocate through the nuclear pores. As shown by BrUTP labeling and immunoelectron microscopy, newly synthesized BR RNP particles, released from the BR genes, appear early in all nucleoplasmic regions of the cell nucleus and they saturate the nucleoplasmic pool of BR particles after 2 h of labelling. It is concluded that within the nucleus the BR particles move randomly. Furthermore, estimates of minimum diffusion coefficients for the BR particles are compatible with the view that the particles diffuse freely in the interchromosomal space, although it is not excluded that the random movement could be slightly retarded. Once the particles get bound to the nuclear pore complexes, they seem committed to translocation through the nuclear pores.
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Affiliation(s)
- O P Singh
- Medical Nobel Institute, Karolinska Institutet, Stockholm, SE-17177, Sweden
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