1
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Füllbrunn N, Nicastro R, Mari M, Griffith J, Herrmann E, Rasche R, Borchers AC, Auffarth K, Kümmel D, Reggiori F, De Virgilio C, Langemeyer L, Ungermann C. The GTPase activating protein Gyp7 regulates Rab7/Ypt7 activity on late endosomes. J Cell Biol 2024; 223:e202305038. [PMID: 38536036 PMCID: PMC10978497 DOI: 10.1083/jcb.202305038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 01/22/2024] [Accepted: 03/08/2024] [Indexed: 04/01/2024] Open
Abstract
Organelles of the endomembrane system contain Rab GTPases as identity markers. Their localization is determined by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). It remains largely unclear how these regulators are specifically targeted to organelles and how their activity is regulated. Here, we focus on the GAP Gyp7, which acts on the Rab7-like Ypt7 protein in yeast, and surprisingly observe the protein exclusively in puncta proximal to the vacuole. Mistargeting of Gyp7 to the vacuole strongly affects vacuole morphology, suggesting that endosomal localization is needed for function. In agreement, efficient endolysosomal transport requires Gyp7. In vitro assays reveal that Gyp7 requires a distinct lipid environment for membrane binding and activity. Overexpression of Gyp7 concentrates Ypt7 in late endosomes and results in resistance to rapamycin, an inhibitor of the target of rapamycin complex 1 (TORC1), suggesting that these late endosomes are signaling endosomes. We postulate that Gyp7 is part of regulatory machinery involved in late endosome function.
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Affiliation(s)
- Nadia Füllbrunn
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytics, Osnabrück University, Osnabrück, Germany
| | - Raffaele Nicastro
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Muriel Mari
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Janice Griffith
- Department of Cell Biology, University Medical Center Utrecht, Utrecht, Netherlands
| | - Eric Herrmann
- Institute of Biochemistry, University of Münster, Münster, Germany
| | - René Rasche
- Institute of Biochemistry, University of Münster, Münster, Germany
| | - Ann-Christin Borchers
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Kathrin Auffarth
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Daniel Kümmel
- Institute of Biochemistry, University of Münster, Münster, Germany
| | - Fulvio Reggiori
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
- Department of Cell Biology, University Medical Center Utrecht, Utrecht, Netherlands
| | | | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytics, Osnabrück University, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
- Center of Cellular Nanoanalytics, Osnabrück University, Osnabrück, Germany
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2
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Yong X, Jia G, Liu Z, Zhou C, Yi J, Tang Y, Chen L, Chen L, Wang Y, Sun Q, Billadeau D, Su Z, Jia D. Cryo-EM structure of the Mon1-Ccz1-RMC1 complex reveals molecular basis of metazoan RAB7A activation. Proc Natl Acad Sci U S A 2023; 120:e2301725120. [PMID: 37216550 PMCID: PMC10235969 DOI: 10.1073/pnas.2301725120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 04/18/2023] [Indexed: 05/24/2023] Open
Abstract
Understanding of the evolution of metazoans from their unicellular ancestors is a fundamental question in biology. In contrast to fungi which utilize the Mon1-Ccz1 dimeric complex to activate the small GTPase RAB7A, metazoans rely on the Mon1-Ccz1-RMC1 trimeric complex. Here, we report a near-atomic resolution cryogenic-electron microscopy structure of the Drosophila Mon1-Ccz1-RMC1 complex. RMC1 acts as a scaffolding subunit and binds to both Mon1 and Ccz1 on the surface opposite to the RAB7A-binding site, with many of the RMC1-contacting residues from Mon1 and Ccz1 unique to metazoans, explaining the binding specificity. Significantly, the assembly of RMC1 with Mon1-Ccz1 is required for cellular RAB7A activation, autophagic functions and organismal development in zebrafish. Our studies offer a molecular explanation for the different degree of subunit conservation across species, and provide an excellent example of how metazoan-specific proteins take over existing functions in unicellular organisms.
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Affiliation(s)
- Xin Yong
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Guowen Jia
- Department of Geriatrics and National Clinical Research Center for Geriatrics, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University610044Chengdu, China
| | - Zhe Liu
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Chunzhuang Zhou
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Jiamin Yi
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Yingying Tang
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Li Chen
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Lu Chen
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
| | - Yuan Wang
- Department of Geriatrics and National Clinical Research Center for Geriatrics, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University610044Chengdu, China
| | - Qingxiang Sun
- Department of Geriatrics and National Clinical Research Center for Geriatrics, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University610044Chengdu, China
| | - Daniel D. Billadeau
- Division of Oncology Research and Schulze Center for Novel Therapeutics, Mayo Clinic, Rochester, MN55905
| | - Zhaoming Su
- Department of Geriatrics and National Clinical Research Center for Geriatrics, State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University610044Chengdu, China
| | - Da Jia
- Key Laboratory of Birth Defects and Related Diseases of Women and Children, Department of Paediatrics, West China Second University Hospital, State Key Laboratory of Biotherapy and Collaborative Innovation Center of Biotherapy, Sichuan University, Chengdu610041, China
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3
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Schleinitz A, Pöttgen LA, Keren-Kaplan T, Pu J, Saftig P, Bonifacino JS, Haas A, Jeschke A. Consecutive functions of small GTPases guide HOPS-mediated tethering of late endosomes and lysosomes. Cell Rep 2023; 42:111969. [PMID: 36640308 PMCID: PMC10018218 DOI: 10.1016/j.celrep.2022.111969] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Revised: 10/12/2022] [Accepted: 12/20/2022] [Indexed: 01/06/2023] Open
Abstract
The transfer of endocytosed cargoes to lysosomes (LYSs) requires HOPS, a multiprotein complex that tethers late endosomes (LEs) to LYSs before fusion. Many proteins interact with HOPS on LEs/LYSs. However, it is not clear whether these HOPS interactors localize to LEs or LYSs or how they participate in tethering. Here, we biochemically characterized endosomes purified from untreated or experimentally manipulated cells to put HOPS and interacting proteins in order and to establish their functional interdependence. Our results assign Rab2a and Rab7 to LEs and Arl8 and BORC to LYSs and show that HOPS drives LE-LYS fusion by bridging late endosomal Rab2a with lysosomal BORC-anchored Arl8. We further show that Rab7 is absent from sites of HOPS-dependent tethering but promotes fusion by moving LEs toward LYSs via dynein. Thus, our study identifies the topology of the machinery for LE-LYS tethering and elucidates the role of different small GTPases in the process.
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Affiliation(s)
| | | | - Tal Keren-Kaplan
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jing Pu
- Department of Molecular Genetics and Microbiology, and Autophagy, Inflammation, and Metabolism, Center of Biomedical Research Excellence, University of New Mexico, Albuquerque, NM 87131, USA
| | - Paul Saftig
- Biochemical Institute, University of Kiel, 24118 Kiel, Germany
| | - Juan S Bonifacino
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | - Albert Haas
- Cell Biology Institute, University of Bonn, 53121 Bonn, Germany.
| | - Andreas Jeschke
- Cell Biology Institute, University of Bonn, 53121 Bonn, Germany.
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4
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Kümmel D, Herrmann E, Langemeyer L, Ungermann C. Molecular insights into endolysosomal microcompartment formation and maintenance. Biol Chem 2022; 404:441-454. [PMID: 36503831 DOI: 10.1515/hsz-2022-0294] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Accepted: 11/22/2022] [Indexed: 12/14/2022]
Abstract
Abstract
The endolysosomal system of eukaryotic cells has a key role in the homeostasis of the plasma membrane, in signaling and nutrient uptake, and is abused by viruses and pathogens for entry. Endocytosis of plasma membrane proteins results in vesicles, which fuse with the early endosome. If destined for lysosomal degradation, these proteins are packaged into intraluminal vesicles, converting an early endosome to a late endosome, which finally fuses with the lysosome. Each of these organelles has a unique membrane surface composition, which can form segmented membrane microcompartments by membrane contact sites or fission proteins. Furthermore, these organelles are in continuous exchange due to fission and fusion events. The underlying machinery, which maintains organelle identity along the pathway, is regulated by signaling processes. Here, we will focus on the Rab5 and Rab7 GTPases of early and late endosomes. As molecular switches, Rabs depend on activating guanine nucleotide exchange factors (GEFs). Over the last years, we characterized the Rab7 GEF, the Mon1-Ccz1 (MC1) complex, and key Rab7 effectors, the HOPS complex and retromer. Structural and functional analyses of these complexes lead to a molecular understanding of their function in the context of organelle biogenesis.
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Affiliation(s)
- Daniel Kümmel
- Institute of Biochemistry, University of Münster , Corrensstraße 36 , D-48149 Münster , Germany
| | - Eric Herrmann
- Institute of Biochemistry, University of Münster , Corrensstraße 36 , D-48149 Münster , Germany
| | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry section , Osnabrück University , Barbarastraße 13 , D-49076 Osnabrück , Germany
- Center of Cellular Nanoanalytics (CellNanOs) , Osnabrück University , Barbarastraße 11 , D-49076 Osnabrück , Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry section , Osnabrück University , Barbarastraße 13 , D-49076 Osnabrück , Germany
- Center of Cellular Nanoanalytics (CellNanOs) , Osnabrück University , Barbarastraße 11 , D-49076 Osnabrück , Germany
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5
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Meyer C, Breitsprecher L, Bataille L, Vincent AJM, Drechsler M, Meyer H, Paululat A. Formation and function of a highly specialised type of organelle in cardiac valve cells. Development 2022; 149:276991. [DOI: 10.1242/dev.200701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Accepted: 08/23/2022] [Indexed: 11/06/2022]
Abstract
ABSTRACT
Within a cell, vesicles play a crucial role in the transport of membrane material and proteins to a given target membrane, and thus regulate a variety of cellular functions. Vesicular transport occurs by means of, among others, endocytosis, where cargoes are taken up by the cell and are processed further upon vesicular trafficking, i.e. transported back to the plasma membrane via recycling endosomes or the degraded by fusion of the vesicles with lysosomes. During evolution, a variety of vesicles with individual functions arose, with some of them building up highly specialised subcellular compartments. In this study, we have analysed the biosynthesis of a new vesicular compartment present in the valve cells of Drosophila melanogaster. We show that the compartment is formed by invaginations of the plasma membrane and grows via re-routing of the recycling endosomal pathway. This is achieved by inactivation of other membrane-consuming pathways and a plasma membrane-like molecular signature of the compartment in these highly specialised heart cells.
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Affiliation(s)
- Christian Meyer
- University of Osnabrück 1 , Department of Biology and Chemistry, Zoology and Developmental Biology, Barbarastraße 11, 49076 Osnabrück , Germany
| | - Leonhard Breitsprecher
- University of Osnabrück 1 , Department of Biology and Chemistry, Zoology and Developmental Biology, Barbarastraße 11, 49076 Osnabrück , Germany
- Center of Cellular Nanoanalytics (CellNanOs), integrated Bioimaging Facility (iBiOs), University of Osnabrück 2 , Barbarastrasse 11, 49076 Osnabrück , Germany
| | - Laetitia Bataille
- Unité de Biologie Moléculaire et Cellulaire et du Développement (MCD), Centre de Biologie Intégrative (CBI) 3 , Université de Toulouse UMR 5077/CNRS, F-31062 Toulouse , France
| | - Alain J. M. Vincent
- Unité de Biologie Moléculaire et Cellulaire et du Développement (MCD), Centre de Biologie Intégrative (CBI) 3 , Université de Toulouse UMR 5077/CNRS, F-31062 Toulouse , France
| | - Maik Drechsler
- University of Osnabrück 1 , Department of Biology and Chemistry, Zoology and Developmental Biology, Barbarastraße 11, 49076 Osnabrück , Germany
| | - Heiko Meyer
- University of Osnabrück 1 , Department of Biology and Chemistry, Zoology and Developmental Biology, Barbarastraße 11, 49076 Osnabrück , Germany
- Center of Cellular Nanoanalytics (CellNanOs), integrated Bioimaging Facility (iBiOs), University of Osnabrück 2 , Barbarastrasse 11, 49076 Osnabrück , Germany
| | - Achim Paululat
- University of Osnabrück 1 , Department of Biology and Chemistry, Zoology and Developmental Biology, Barbarastraße 11, 49076 Osnabrück , Germany
- Center of Cellular Nanoanalytics (CellNanOs), integrated Bioimaging Facility (iBiOs), University of Osnabrück 2 , Barbarastrasse 11, 49076 Osnabrück , Germany
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6
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Paradis M, Kucharowski N, Edwards Faret G, Maya Palacios SJ, Meyer C, Stümpges B, Jamitzky I, Kalinowski J, Thiele C, Bauer R, Paululat A, Sellin J, Bülow MH. The ER protein Creld regulates ER-mitochondria contact dynamics and respiratory complex 1 activity. SCIENCE ADVANCES 2022; 8:eabo0155. [PMID: 35867795 PMCID: PMC9307246 DOI: 10.1126/sciadv.abo0155] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 06/07/2022] [Indexed: 05/26/2023]
Abstract
Dynamic contacts are formed between endoplasmic reticulum (ER) and mitochondria that enable the exchange of calcium and phospholipids. Disturbed contacts between ER and mitochondria impair mitochondrial dynamics and are a molecular hallmark of Parkinson's disease, which is also characterized by impaired complex I activity and dopaminergic neuron degeneration. Here, we analyzed the role of cysteine-rich with EGF-like domain (Creld), a poorly characterized risk gene for Parkinson's disease, in the regulation of mitochondrial dynamics and function. We found that loss of Creld leads to mitochondrial hyperfusion and reduced ROS signaling in Drosophila melanogaster, Xenopus tropicalis, and human cells. Creld fly mutants show differences in ER-mitochondria contacts and reduced respiratory complex I activity. The resulting low-hydrogen peroxide levels are linked to disturbed neuronal activity and lead to impaired locomotion, but not neurodegeneration, in Creld mutants. We conclude that Creld regulates ER-mitochondria communication and thereby hydrogen peroxide formation, which is required for normal neuron function.
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Affiliation(s)
- Marie Paradis
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Nicole Kucharowski
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Gabriela Edwards Faret
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
- VIB-KU Leuven Center for Brain and Disease Research, Leuven, Belgium
| | | | - Christian Meyer
- Department of Zoology and Developmental Biology, University of Osnabrück, Barbarastr. 11, 49076 Osnabrück, Germany
| | - Birgit Stümpges
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Isabell Jamitzky
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Julia Kalinowski
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Christoph Thiele
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Reinhard Bauer
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
| | - Achim Paululat
- Department of Zoology and Developmental Biology, University of Osnabrück, Barbarastr. 11, 49076 Osnabrück, Germany
| | - Julia Sellin
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
- Institute for Digitalization and General Medicine, University Hospital Aachen, Pauwelsstr. 30, 52074 Aachen
| | - Margret Helene Bülow
- Life and Medical Sciences (LIMES) Institute, University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany
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7
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Structure of the Mon1-Ccz1 complex reveals molecular basis of membrane binding for Rab7 activation. Proc Natl Acad Sci U S A 2022; 119:2121494119. [PMID: 35105815 PMCID: PMC8833172 DOI: 10.1073/pnas.2121494119] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/22/2021] [Indexed: 01/02/2023] Open
Abstract
Activation of the GTPase Rab7/Ypt7 by its cognate guanine nucleotide exchange factor (GEF) Mon1-Ccz1 marks organelles such as endosomes and autophagosomes for fusion with lysosomes/vacuoles and degradation of their content. Here, we present a high-resolution cryogenic electron microscopy structure of the Mon1-Ccz1 complex that reveals its architecture in atomic detail. Mon1 and Ccz1 are arranged side by side in a pseudo-twofold symmetrical heterodimer. The three Longin domains of each Mon1 and Ccz1 are triangularly arranged, providing a strong scaffold for the catalytic center of the GEF. At the opposite side of the Ypt7-binding site, a positively charged and relatively flat patch stretches the Longin domains 2/3 of Mon1 and functions as a phosphatidylinositol phosphate-binding site, explaining how the GEF is targeted to membranes. Our work provides molecular insight into the mechanisms of endosomal Rab activation and serves as a blueprint for understanding the function of members of the Tri Longin domain Rab-GEF family.
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8
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Psathaki OE, Paululat A. Preparation of Drosophila Tissues and Organs for Transmission Electron Microscopy. Methods Mol Biol 2022; 2540:361-385. [PMID: 35980589 DOI: 10.1007/978-1-0716-2541-5_19] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Transmission electron microscopy (TEM) is the method of choice to image the ultrastructure of cells or tissues. TEM allows the visualization of molecular complexes up to an atomic resolution. Thus, TEM data have led to important conclusions about cellular processes and supported findings obtained by functional analyses. In this chapter, we describe the preparation of Drosophila tissues for TEM and provide reliable step-by-step protocols for applying classical chemical fixation or high-pressure freezing-freeze substitution (HPF-FS) to preserve cellular structures.
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Affiliation(s)
- Olympia-Ekaterini Psathaki
- University of Osnabrück, Department of Zoology and Developmental Biology, Osnabrück, Germany
- University of Osnabrück, Center of Cellular Nanoanalytics, Integrated Bioimaging Facility Osnabrück (iBiOs), Osnabrück, Germany
| | - Achim Paululat
- University of Osnabrück, Department of Zoology and Developmental Biology, Osnabrück, Germany.
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9
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Borchers AC, Langemeyer L, Ungermann C. Who's in control? Principles of Rab GTPase activation in endolysosomal membrane trafficking and beyond. J Cell Biol 2021; 220:212549. [PMID: 34383013 PMCID: PMC8366711 DOI: 10.1083/jcb.202105120] [Citation(s) in RCA: 68] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 07/08/2021] [Accepted: 07/08/2021] [Indexed: 12/12/2022] Open
Abstract
The eukaryotic endomembrane system consists of multiple interconnected organelles. Rab GTPases are organelle-specific markers that give identity to these membranes by recruiting transport and trafficking proteins. During transport processes or along organelle maturation, one Rab is replaced by another, a process termed Rab cascade, which requires at its center a Rab-specific guanine nucleotide exchange factor (GEF). The endolysosomal system serves here as a prime example for a Rab cascade. Along with endosomal maturation, the endosomal Rab5 recruits and activates the Rab7-specific GEF Mon1-Ccz1, resulting in Rab7 activation on endosomes and subsequent fusion of endosomes with lysosomes. In this review, we focus on the current idea of Mon1-Ccz1 recruitment and activation in the endolysosomal and autophagic pathway. We compare identified principles to other GTPase cascades on endomembranes, highlight the importance of regulation, and evaluate in this context the strength and relevance of recent developments in in vitro analyses to understand the underlying foundation of organelle biogenesis and maturation.
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Affiliation(s)
- Ann-Christin Borchers
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Lars Langemeyer
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany
| | - Christian Ungermann
- Department of Biology/Chemistry, Biochemistry Section, Osnabrück University, Osnabrück, Germany.,Center of Cellular Nanoanalytics Osnabrück (CellNanOs), Osnabrück University, Osnabrück, Germany
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