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Chowdhury SP, Solley SC, Polishchuk E, Bacal J, Conrad JE, Gardner BM, Acosta-Alvear D, Zappa F. Baseline unfolded protein response signaling adjusts the timing of the mammalian cell cycle. Mol Biol Cell 2024; 35:br12. [PMID: 38656789 DOI: 10.1091/mbc.e23-11-0419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/26/2024] Open
Abstract
The endoplasmic reticulum (ER) is a single-copy organelle that cannot be generated de novo, suggesting coordination between the mechanisms overseeing ER integrity and those controlling the cell cycle to maintain organelle inheritance. The Unfolded Protein Response (UPR) is a conserved signaling network that regulates ER homeostasis. Here, we show that pharmacological and genetic inhibition of the UPR sensors IRE1, ATF6, and PERK in unstressed cells delays the cell cycle, with PERK inhibition showing the most penetrant effect, which was associated with a slowdown of the G1-to-S/G2 transition. Treatment with the small molecule ISRIB to bypass the effects of PERK-dependent phosphorylation of the translation initiation factor eIF2α had no such effect, suggesting that cell cycle timing depends on PERK's kinase activity but is independent of eIF2α phosphorylation. Using complementary light and electron microscopy and flow cytometry-based analyses, we also demonstrate that the ER enlarges before mitosis. Together, our results suggest coordination between UPR signaling and the cell cycle to maintain ER physiology during cell division.
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Affiliation(s)
- Soham P Chowdhury
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106
| | - Sabrina C Solley
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106
| | - Elena Polishchuk
- Telethon Institute of Genetics and Medicine (TIGEM), 80078 Pozzuoli, Naples, Italy
| | - Julien Bacal
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106
| | - Julia E Conrad
- Altos Labs Bay Area Institute of Science, Altos Labs, Redwood City, CA 94065
| | - Brooke M Gardner
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106
| | - Diego Acosta-Alvear
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106
| | - Francesca Zappa
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, Santa Barbara, CA 93106
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2
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Walton K, Nawara TJ, Angermeier AR, Rosengrant H, Lee E, Wynn B, Victorova E, Belov G, Sztul E. Site-specific phosphorylations of the Arf activator GBF1 differentially regulate GBF1 function in Golgi homeostasis and secretion versus cytokinesis. Sci Rep 2023; 13:13609. [PMID: 37604968 PMCID: PMC10442430 DOI: 10.1038/s41598-023-40705-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 08/16/2023] [Indexed: 08/23/2023] Open
Abstract
Diverse cellular processes, including membrane traffic, lipid homeostasis, cytokinesis, mitochondrial positioning, and cell motility are critically dependent on the Sec7 domain guanine nucleotide exchange factor GBF1. Yet, how the participation of GBF1 in a particular cellular function is regulated is unknown. Here, we show that the phosphorylation of specific highly conserved serine and tyrosine residues within the N-terminal domain of GBF1 differentially regulates its function in maintaining Golgi homeostasis and facilitating secretion versus its role in cytokinesis. Specifically, GBF1 mutants containing single amino acid substitutions that mimic a stably phosphorylated S233, S371, Y377, and Y515 or the S233A mutant that can't be phosphorylated are fully able to maintain Golgi architecture and support cargo traffic through the secretory pathway when assessed in multiple functional assays. However, the same mutants cause multi-nucleation when expressed in cells, and appear to inhibit the progression through mitosis and the resolution of cytokinetic bridges. Thus, GBF1 participates in distinct interactive networks when mediating Golgi homeostasis and secretion versus facilitating cytokinesis, and GBF1 integration into such networks is differentially regulated by the phosphorylation of specific GBF1 residues.
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Affiliation(s)
- Kendall Walton
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA.
| | - Tomasz J Nawara
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA
| | - Allyson R Angermeier
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA
| | - Hadley Rosengrant
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA
| | - Eunjoo Lee
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA
| | - Bridge Wynn
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA
| | - Ekaterina Victorova
- Department of Veterinary Medicine, Virginia-Maryland College of Veterinary Medicine, University of Maryland, College Park, MD, 20742, USA
| | - George Belov
- Department of Veterinary Medicine, Virginia-Maryland College of Veterinary Medicine, University of Maryland, College Park, MD, 20742, USA
| | - Elizabeth Sztul
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, 1918 University Boulevard, MCLM 668, Birmingham, AL, 35233-2008, USA
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3
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Jasinski J, Völkl M, Hahn J, Jérôme V, Freitag R, Scheibel T. Polystyrene microparticle distribution after ingestion by murine macrophages. JOURNAL OF HAZARDOUS MATERIALS 2023; 457:131796. [PMID: 37307726 DOI: 10.1016/j.jhazmat.2023.131796] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Revised: 05/28/2023] [Accepted: 06/05/2023] [Indexed: 06/14/2023]
Abstract
The impact of microplastic particles on organisms is currently intensely researched. Although it is well established that macrophages ingest polystyrene (PS) microparticles, little is known about the subsequent fate of the particles, such as entrapment in organelles, distribution during cell division, as well as possible mechanisms of excretion. Here, submicrometer (0.2 and 0.5 µm) and micron-sized (3 µm) particles were used to analyze particle fate upon ingestion of murine macrophages (J774A.1 and ImKC). Distribution and excretion of PS particles was investigated over cycles of cellular division. The distribution during cell division seems cell-specific upon comparing two different macrophage cell lines, and no apparent active excretion of microplastic particles could be observed. Using polarized cells, M1 polarized macrophages show higher phagocytic activity and particle uptake than M2 polarized ones or M0 cells. While particles with all tested diameters were found in the cytoplasm, submicron particles were additionally co-localized with the endoplasmic reticulum. Further, 0.5 µm particles were occasionally found in endosomes. Our results indicate that a possible reason for the previously described low cytotoxicity upon uptake of pristine PS microparticles by macrophages may be due to the preferential localization in the cytoplasm.
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Affiliation(s)
- Julia Jasinski
- Biomaterials, Faculty of Engineering Sciences, University of Bayreuth, Bayreuth, Germany
| | - Matthias Völkl
- Process Biotechnology, Faculty of Engineering Sciences, University of Bayreuth, Bayreuth, Germany
| | - Jonas Hahn
- Biomaterials, Faculty of Engineering Sciences, University of Bayreuth, Bayreuth, Germany
| | - Valérie Jérôme
- Process Biotechnology, Faculty of Engineering Sciences, University of Bayreuth, Bayreuth, Germany
| | - Ruth Freitag
- Process Biotechnology, Faculty of Engineering Sciences, University of Bayreuth, Bayreuth, Germany; Bayreuth Center for Molecular Biosciences (BZMB), University of Bayreuth, Bayreuth, Germany
| | - Thomas Scheibel
- Biomaterials, Faculty of Engineering Sciences, University of Bayreuth, Bayreuth, Germany; Bayreuth Center for Colloids and Interfaces (BZKG), University of Bayreuth, Bayreuth, Germany; Bayreuth Center for Molecular Biosciences (BZMB), University of Bayreuth, Bayreuth, Germany; Bayreuth Center for Material Science (BayMAT), University of Bayreuth, Bayreuth, Germany; Bavarian Polymer Institute (BPI), University of Bayreuth, Bayreuth, Germany.
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4
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Yasuno Y, Kawano JI, Inoue YH, Yamamoto MT. Distribution and morphological changes of the Golgi apparatus during Drosophila spermatogenesis. Dev Growth Differ 2013; 55:635-47. [PMID: 23855356 DOI: 10.1111/dgd.12070] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Revised: 05/19/2013] [Accepted: 05/20/2013] [Indexed: 12/01/2022]
Abstract
In spermatogenesis, the Golgi apparatus is important for the formation of the acrosome, which is a sperm-specific organelle essential for fertilization. Comprehensive examinations of the spatiotemporal distribution and morphological characterizations of the Golgi in various cells during spermatogenesis are necessary for functional analyses and mutant screenings in the model eukaryote Drosophila. Here, we examined the distribution and morphology of the Golgi during Drosophila spermatogenesis with immunofluorescence and electron microscopy. In pre-meiotic germ cells, the Golgi apparatuses were distributed evenly in the cytoplasm. In contrast, they were located exclusively in two regions near the poles during the meiotic metaphase, where they were segregated prior to the chromosomes. In cells in anaphase to telophase, the Golgi were predominantly left behind in the equatorial region between the separating daughter nuclei. After completion of meiosis, the dispersed Golgi were assembled at the apical side of the spermatid nucleus to form the acrosome. Further investigation of the Golgi distribution in β2-tubulin mutants showed aberrant and uneven distributions of the Golgi among sister cells in the meiotic spermatocytes and in the post-meiotic spermatids. At the ultrastructural level, the Golgi apparatus in pre-meiotic spermatocytes comprised a pair of stacks. The two stacks were situated adjacent to each other, as if they had duplicated before entering into meiotic division. These results highlight the dynamic nature of the Golgi during spermatogenesis and provide a framework for analyzing the correlations between the dynamics of the Golgi and its function in sperm development.
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Affiliation(s)
- Yusaku Yasuno
- Drosophila Genetic Resource Center, Kyoto Institute of Technology, Saga-Ippongi-cho, Ukyo-ku, Kyoto, Japan.
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5
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Gaietta GM, Giepmans BNG, Deerinck TJ, Smith WB, Ngan L, Llopis J, Adams SR, Tsien RY, Ellisman MH. Golgi twins in late mitosis revealed by genetically encoded tags for live cell imaging and correlated electron microscopy. Proc Natl Acad Sci U S A 2006; 103:17777-82. [PMID: 17101980 PMCID: PMC1635977 DOI: 10.1073/pnas.0608509103] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Combinations of molecular tags visible in light and electron microscopes become particularly advantageous in the analysis of dynamic cellular components like the Golgi apparatus. This organelle disassembles at the onset of mitosis and, after a sequence of poorly understood events, reassembles after cytokinesis. The precise location of Golgi membranes and resident proteins during mitosis remains unclear, partly due to limitations of molecular markers and the resolution of light microscopy. We generated a fusion consisting of the first 117 residues of alpha-mannosidase II tagged with a fluorescent protein and a tetracysteine motif. The mannosidase component guarantees docking into the Golgi membrane, with the tags exposed in the lumen. The fluorescent protein is optically visible without further treatment, whereas the tetracysteine tag can be reduced acutely with a membrane-permeant phosphine, labeled with ReAsH, monitored in the light microscope, and used to trigger the photoconversion of diaminobenzidine, allowing 4D optical recording on live cells and correlated ultrastructural analysis by electron microscopy. These methods reveal that Golgi reassembly is preceded by the formation of four colinear clusters at telophase, two per daughter cell. Within each daughter, the smaller cluster near the midbody gradually migrates to rejoin the major cluster on the far side of the nucleus and asymmetrically reconstitutes a single Golgi apparatus, first in one daughter cell and then in the other. Our studies provide previously undescribed insights into Golgi disassociation and reassembly during mitosis and offer a powerful approach to follow recombinant protein distribution in 4D imaging and correlated high-resolution analysis.
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Affiliation(s)
- Guido M. Gaietta
- *National Center for Microscopy and Imaging Research, Center for Research on Biological Structure, and
| | - Ben N. G. Giepmans
- *National Center for Microscopy and Imaging Research, Center for Research on Biological Structure, and
- Department of Pharmacology and
| | - Thomas J. Deerinck
- *National Center for Microscopy and Imaging Research, Center for Research on Biological Structure, and
| | - W. Bryan Smith
- *National Center for Microscopy and Imaging Research, Center for Research on Biological Structure, and
| | - Lucy Ngan
- *National Center for Microscopy and Imaging Research, Center for Research on Biological Structure, and
| | - Juan Llopis
- Facultad de Medicina y Centro Regional de Investigaciones Biomédicas, Universidad de Castilla-La Mancha, C/Almansa s/n, 02006 Albacete, Spain
| | | | - Roger Y. Tsien
- Department of Pharmacology and
- Howard Hughes Medical Institute, Department Code 0648, University of California at San Diego, La Jolla, CA 92093; and
- To whom correspondence should be addressed. E-mail:
| | - Mark H. Ellisman
- *National Center for Microscopy and Imaging Research, Center for Research on Biological Structure, and
- Department of Neurosciences, Department Code 0608, University of California at San Diego, La Jolla, CA 92093
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6
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Hollande E, Salvador-Cartier C, Alvarez L, Fanjul M. Expression of a wild-type CFTR maintains the integrity of the biosynthetic/secretory pathway in human cystic fibrosis pancreatic duct cells. J Histochem Cytochem 2005; 53:1539-52. [PMID: 15956032 PMCID: PMC3957539 DOI: 10.1369/jhc.4a6587.2005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The structural integrity of the Golgi complex is essential to its functions in the maturation, sorting, and transport of plasma membrane proteins. Previously, we demonstrated that in pancreatic duct CFPAC-1 cells, which express DeltaF508 CFTR (cystic fibrosis transmembrane conductance regulator), the intracellular trafficking of carbonic anhydrase IV (CA IV), a membrane protein involved in HCO(3)(-) secretion, was impaired. To determine whether these abnormalities were related to changes in the Golgi complex, we examined the ultrastructure and distribution of Golgi compartments with regard to the microtubule cytoskeleton in CFPAC-1 cells transfected or not with the wild-type CFTR. Ultrastructural and immunocytochemical analysis showed that in polarized CFPAC-1 cells, Golgi stacks were disconnected from one another and scattered throughout the cytoplasm. The colocalization of CA IV with markers of Golgi compartments indicated the ability of stacks to transfer this enzyme. This Golgi dispersal was associated with abnormal microtubule distribution and multiplicity of the microtubule-organizing centers (MTOCs). In reverted cells, the normalization of Golgi structure, microtubule distribution, and MTOC number was observed. These observations suggest that the entire biosynthetic/secretory pathway is disrupted in CFPAC-1 cells, which might explain the abnormal intracellular transport of CA IV. Taken together, these results point to the fact that the expression of DeltaF508 CFTR affects the integrity of the secretory pathway.
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Affiliation(s)
- Etienne Hollande
- Laboratoire de Biologie Cellulaire et Moléculaire des Epithéliums, Université Paul Sabatier, Toulouse, France.
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7
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Fan J, Beck KA. A role for the spectrin superfamily member Syne-1 and kinesin II in cytokinesis. J Cell Sci 2004; 117:619-29. [PMID: 14709720 DOI: 10.1242/jcs.00892] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Expression of a dominant negative fragment of the spectrin family member Syne-1 causes an accumulation of binucleate cells, suggesting a role for this protein in cytokinesis. An association of this fragment with the C-terminal tail domain of the kinesin II subunit KIF3B was identified by yeast two-hybrid and co-precipitation assays, suggesting that the role of Syne-1 in cytokinesis involves an interaction with kinesin II. In support of this we found that (1) expression of KIF3B tail domain also gives rise to multinucleate cells, (2) both Syne-1 and KIF3B localize to the central spindle and midbody during cytokinesis in a detergent resistant and ATP sensitive manner and (3) Syne-1 localization is blocked by expression of KIF3B tail. Also, membrane vesicles containing syntaxin associate with the spindle midbody with identical properties. We conclude that Syne-1 and KIF3B function together in cytokinesis by facilitating the accumulation of membrane vesicles at the spindle midbody.
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Affiliation(s)
- Jun Fan
- Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis, CA 95616, USA
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8
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Rossanese OW, Reinke CA, Bevis BJ, Hammond AT, Sears IB, O'Connor J, Glick BS. A role for actin, Cdc1p, and Myo2p in the inheritance of late Golgi elements in Saccharomyces cerevisiae. J Cell Biol 2001; 153:47-62. [PMID: 11285273 PMCID: PMC2185536 DOI: 10.1083/jcb.153.1.47] [Citation(s) in RCA: 175] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In Saccharomyces cerevisiae, Golgi elements are present in the bud very early in the cell cycle. We have analyzed this Golgi inheritance process using fluorescence microscopy and genetics. In rapidly growing cells, late Golgi elements show an actin-dependent concentration at sites of polarized growth. Late Golgi elements are apparently transported into the bud along actin cables and are also retained in the bud by a mechanism that may involve actin. A visual screen for mutants defective in the inheritance of late Golgi elements yielded multiple alleles of CDC1. Mutations in CDC1 severely depolarize the actin cytoskeleton, and these mutations prevent late Golgi elements from being retained in the bud. The efficient localization of late Golgi elements to the bud requires the type V myosin Myo2p, further suggesting that actin plays a role in Golgi inheritance. Surprisingly, early and late Golgi elements are inherited by different pathways, with early Golgi elements localizing to the bud in a Cdc1p- and Myo2p-independent manner. We propose that early Golgi elements arise from ER membranes that are present in the bud. These two pathways of Golgi inheritance in S. cerevisiae resemble Golgi inheritance pathways in vertebrate cells.
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Affiliation(s)
- Olivia W. Rossanese
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
| | - Catherine A. Reinke
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
| | - Brooke J. Bevis
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
| | - Adam T. Hammond
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
| | - Irina B. Sears
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
| | - James O'Connor
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
| | - Benjamin S. Glick
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637
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9
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Hammond AT, Glick BS. Dynamics of transitional endoplasmic reticulum sites in vertebrate cells. Mol Biol Cell 2000; 11:3013-30. [PMID: 10982397 PMCID: PMC14972 DOI: 10.1091/mbc.11.9.3013] [Citation(s) in RCA: 213] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
A typical vertebrate cell contains several hundred sites of transitional ER (tER). Presumably, tER sites generate elements of the ER-Golgi intermediate compartment (ERGIC), and ERGIC elements then generate Golgi cisternae. Therefore, characterizing the mechanisms that influence tER distribution may shed light on the dynamic behavior of the Golgi. We explored the properties of tER sites using Sec13 as a marker protein. Fluorescence microscopy confirmed that tER sites are long-lived ER subdomains. tER sites proliferate during interphase but lose Sec13 during mitosis. Unlike ERGIC elements, tER sites move very little. Nevertheless, when microtubules are depolymerized with nocodazole, tER sites redistribute rapidly to form clusters next to Golgi structures. Hence, tER sites have the unusual property of being immobile, yet dynamic. These findings can be explained by a model in which new tER sites are created by retrograde membrane traffic from the Golgi. We propose that the tER-Golgi system is organized by mutual feedback between these two compartments.
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Affiliation(s)
- A T Hammond
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637, USA
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10
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Abstract
The Golgi complex of mammalian cells is composed of cisternal stacks that function in processing and sorting of membrane and luminal proteins during transport from the site of synthesis in the endoplasmic reticulum to lysosomes, secretory vacuoles, and the cell surface. Even though exceptions are found, the Golgi stacks are usually arranged as an interconnected network in the region around the centrosome, the major organizing center for cytoplasmic microtubules. A close relation thus exists between Golgi elements and microtubules (especially the stable subpopulation enriched in detyrosinated and acetylated tubulin). After drug-induced disruption of microtubules, the Golgi stacks are disconnected from each other, partly broken up, dispersed in the cytoplasm, and redistributed to endoplasmic reticulum exit sites. Despite this, intracellular protein traffic is only moderately disturbed. Following removal of the drugs, scattered Golgi elements move along reassembling microtubules back to the centrosomal region and reunite into a continuous system. The microtubule-dependent motor proteins cytoplasmic dynein and kinesin bind to Golgi membranes and have been implicated in vesicular transport to and from the Golgi complex. Microinjection of dynein heavy chain antibodies causes dispersal of the Golgi complex, and the Golgi complex of cells lacking cytoplasmic dynein is likewise spread throughout the cytoplasm. In a similar manner, kinesin antibodies have been found to inhibit Golgi-to-endoplasmic reticulum transport in brefeldin A-treated cells and scattering of Golgi elements along remaining microtubules in cells exposed to a low concentration of nocodazole. The molecular mechanisms in the interaction between microtubules and membranes are, however, incompletely understood. During mitosis, the Golgi complex is extensively reorganized in order to ensure an equal partitioning of this single-copy organelle between the daughter cells. Mitosis-promoting factor, a complex of cdc2 kinase and cyclin B, is a key regulator of this and other events in the induction of cell division. Cytoplasmic microtubules depolymerize in prophase and as a result thereof, the Golgi stacks become smaller, disengage from each other, and take up a perinuclear distribution. The mitotic spindle is thereafter put together, aligns the chromosomes in the metaphase plate, and eventually pulls the sister chromatids apart in anaphase. In parallel, the Golgi stacks are broken down into clusters of vesicles and tubules and movement of protein along the exocytic and endocytic pathways is inhibited. Using a cell-free system, it has been established that the fragmentation of the Golgi stacks is due to a continued budding of transport vesicles and a concomitant inhibition of the fusion of the vesicles with their target membranes. In telophase and after cytokinesis, a Golgi complex made up of interconnected cisternal stacks is recreated in each daughter cell and intracellular protein traffic is resumed. This restoration of a normal interphase morphology and function is dependent on reassembly of a radiating array of cytoplasmic microtubules along which vesicles can be carried and on reactivation of the machinery for membrane fusion.
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Affiliation(s)
- J Thyberg
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, Stockholm, S-171 77, Sweden.
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