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Reuter C, Hauf L, Imdahl F, Sen R, Vafadarnejad E, Fey P, Finger T, Jones NG, Walles H, Barquist L, Saliba AE, Groeber-Becker F, Engstler M. Vector-borne Trypanosoma brucei parasites develop in artificial human skin and persist as skin tissue forms. Nat Commun 2023; 14:7660. [PMID: 37996412 PMCID: PMC10667367 DOI: 10.1038/s41467-023-43437-2] [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: 07/10/2021] [Accepted: 11/08/2023] [Indexed: 11/25/2023] Open
Abstract
Transmission of Trypanosoma brucei by tsetse flies involves the deposition of the cell cycle-arrested metacyclic life cycle stage into mammalian skin at the site of the fly's bite. We introduce an advanced human skin equivalent and use tsetse flies to naturally infect the skin with trypanosomes. We detail the chronological order of the parasites' development in the skin by single-cell RNA sequencing and find a rapid activation of metacyclic trypanosomes and differentiation to proliferative parasites. Here we show that after the establishment of a proliferative population, the parasites enter a reversible quiescent state characterized by slow replication and a strongly reduced metabolism. We term these quiescent trypanosomes skin tissue forms, a parasite population that may play an important role in maintaining the infection over long time periods and in asymptomatic infected individuals.
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Affiliation(s)
- Christian Reuter
- Department of Cell and Developmental Biology, Biocenter, Julius-Maximilians-Universitaet of Wuerzburg, Wuerzburg, Germany
- Department of Tissue Engineering and Regenerative Medicine (TERM), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Laura Hauf
- Department of Cell and Developmental Biology, Biocenter, Julius-Maximilians-Universitaet of Wuerzburg, Wuerzburg, Germany
| | - Fabian Imdahl
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz Center for Infection Research (HZI), Wuerzburg, Germany
- Core Unit Systems Medicine, Julius-Maximilians-Universitaet of Wuerzburg, Wuerzburg, Germany
| | - Rituparno Sen
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz Center for Infection Research (HZI), Wuerzburg, Germany
| | - Ehsan Vafadarnejad
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz Center for Infection Research (HZI), Wuerzburg, Germany
| | - Philipp Fey
- Translational Center Regenerative Therapies, Fraunhofer ISC, Wuerzburg, Germany
| | - Tamara Finger
- Translational Center Regenerative Therapies, Fraunhofer ISC, Wuerzburg, Germany
| | - Nicola G Jones
- Department of Cell and Developmental Biology, Biocenter, Julius-Maximilians-Universitaet of Wuerzburg, Wuerzburg, Germany
| | - Heike Walles
- Translational Center Regenerative Therapies, Fraunhofer ISC, Wuerzburg, Germany
- Core Facility Tissue Engineering, Otto-von-Guericke University, Magdeburg, Germany
| | - Lars Barquist
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz Center for Infection Research (HZI), Wuerzburg, Germany
| | - Antoine-Emmanuel Saliba
- Helmholtz Institute for RNA-based Infection Research (HIRI), Helmholtz Center for Infection Research (HZI), Wuerzburg, Germany
- Institute of Molecular Infection Biology (IMIB), Faculty of Medicine, Julius-Maximilians-Universitaet of Wuerzburg, Wuerzburg, Germany
| | - Florian Groeber-Becker
- Department of Tissue Engineering and Regenerative Medicine (TERM), University Hospital Wuerzburg, Wuerzburg, Germany
- Translational Center Regenerative Therapies, Fraunhofer ISC, Wuerzburg, Germany
| | - Markus Engstler
- Department of Cell and Developmental Biology, Biocenter, Julius-Maximilians-Universitaet of Wuerzburg, Wuerzburg, Germany.
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Affiliation(s)
- Lauren L. Prister
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
| | - H. Steven Seifert
- Department of Microbiology-Immunology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America
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3
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Pinger J, Chowdhury S, Papavasiliou FN. Variant surface glycoprotein density defines an immune evasion threshold for African trypanosomes undergoing antigenic variation. Nat Commun 2017; 8:828. [PMID: 29018220 PMCID: PMC5635023 DOI: 10.1038/s41467-017-00959-w] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2017] [Accepted: 08/02/2017] [Indexed: 11/15/2022] Open
Abstract
Trypanosoma brucei is a protozoan parasite that evades its host's adaptive immune response by repeatedly replacing its dense variant surface glycoprotein (VSG) coat from its large genomic VSG repertoire. While the mechanisms regulating VSG gene expression and diversification have been examined extensively, the dynamics of VSG coat replacement at the protein level, and the impact of this process on successful immune evasion, remain unclear. Here we evaluate the rate of VSG replacement at the trypanosome surface following a genetic VSG switch, and show that full coat replacement requires several days to complete. Using in vivo infection assays, we demonstrate that parasites undergoing coat replacement are only vulnerable to clearance via early IgM antibodies for a limited time. Finally, we show that IgM loses its ability to mediate trypanosome clearance at unexpectedly early stages of coat replacement based on a critical density threshold of its cognate VSGs on the parasite surface. Trypanosoma brucei evades the host immune system through replacement of a variant surface glycoprotein (VSG) coat. Here, the authors show that VSG replacement takes several days to complete, and the parasite is vulnerable to the host immune system for a short period of time during the process.
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Affiliation(s)
- Jason Pinger
- The Rockefeller University, Laboratory of Lymphocyte Biology, 1230 York Avenue, New York, NY, 10065, USA.
- The David Rockefeller Graduate School, 1230 York Avenue, New York, NY, 10065, USA.
| | - Shanin Chowdhury
- The Rockefeller University, Laboratory of Lymphocyte Biology, 1230 York Avenue, New York, NY, 10065, USA
| | - F Nina Papavasiliou
- The Rockefeller University, Laboratory of Lymphocyte Biology, 1230 York Avenue, New York, NY, 10065, USA.
- Division of Immune Diversity, German Cancer Research Center, Im Neuenheimer Feld 280, Heidelberg, 69120, Germany.
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4
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Abstract
Studies on Variant Surface Glycoproteins (VSGs) and antigenic variation in the African trypanosome, Trypanosoma brucei, have yielded a remarkable range of novel and important insights. The features first identified in T. brucei extend from unique to conserved-among-trypanosomatids to conserved-among-eukaryotes. Consequently, much of what we now know about trypanosomatid biology and much of the technology available has its origin in studies related to VSGs. T. brucei is now probably the most advanced early branched eukaryote in terms of experimental tractability and can be approached as a pathogen, as a model for studies on fundamental processes, as a model for studies on eukaryotic evolution or often all of the above. In terms of antigenic variation itself, substantial progress has been made in understanding the expression and switching of the VSG coat, while outstanding questions continue to stimulate innovative new approaches. There are large numbers of VSG genes in the genome but only one is expressed at a time, always immediately adjacent to a telomere. DNA repair processes allow a new VSG to be copied into the single transcribed locus. A coordinated transcriptional switch can also allow a new VSG gene to be activated without any detectable change in the DNA sequence, thereby maintaining singular expression, also known as allelic exclusion. I review the story behind VSGs; the genes, their expression and switching, their central role in T. brucei virulence, the discoveries that emerged along the way and the persistent questions relating to allelic exclusion in particular.
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Affiliation(s)
- David Horn
- Division of Biological Chemistry & Drug Discovery, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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5
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Fichtner L, Schulze F, Braus GH. Differential Flo8p-dependent regulation of FLO1 and FLO11 for cell-cell and cell-substrate adherence of S. cerevisiae S288c. Mol Microbiol 2008; 66:1276-89. [PMID: 18001350 PMCID: PMC2780560 DOI: 10.1111/j.1365-2958.2007.06014.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cell–cell and cell–surface adherence represents initial steps in forming multicellular aggregates or in establishing cell–surface interactions. The commonly used Saccharomyces cerevisiae laboratory strain S288c carries a flo8 mutation, and is only able to express the flocculin-encoding genes FLO1 and FLO11, when FLO8 is restored. We show here that the two flocculin genes exhibit differences in regulation to execute distinct functions under various environmental conditions. In contrast to the laboratory strain Σ1278b, haploids of the S288c genetic background require FLO1 for cell–cell and cell–substrate adhesion, whereas FLO11 is required for pseudohyphae formation of diploids. In contrast to FLO11, FLO1 repression requires the Sin4p mediator tail component, but is independent of the repressor Sfl1p. FLO1 regulation also differs from FLO11, because it requires neither the KSS1 MAP kinase cascade nor the pathways which lead to the transcription factors Gcn4p or Msn1p. The protein kinase A pathway and the transcription factors Flo8p and Mss11p are the major regulators for FLO1 expression. Therefore, S. cerevisiae is prepared to simultaneously express two genes of its otherwise silenced FLO reservoir resulting in an appropriate cellular surface for different environments.
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Affiliation(s)
- Lars Fichtner
- Institut für Mikrobiologie und Genetik, DFG Research Center for Molecular Physiology of the Brain (CMPB), Georg-August Universität Göttingen, Grisebachstr. 8, D-37077 Göttingen, Germany
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6
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Mansfield JM, Paulnock DM. Genetic manipulation of African trypanosomes as a tool to dissect the immunobiology of infection. Parasite Immunol 2008; 30:245-53. [PMID: 18208450 DOI: 10.1111/j.1365-3024.2007.01003.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The variant surface glycoprotein (VSG) coat of African trypanosomes exhibits immunobiological functions distinct from its prominent role as a variant surface antigen. In order to address questions regarding immune stealth effects of VSG switch-variant coats, and the innate immune system activating effects of shed VSG substituents, several groups have genetically modified the ability of trypanosomes to express or release VSG during infection of the mammalian host. The role of mosaic surface coats expressed by VSG switch-variants (VSG double-expressors) in escaping early immune detection, and the role of VSG glycosylphosphatidylinositol (GPI) anchor substituents in regulating host immunity have been revealed, respectively, by stable co-expression of an exogenous VSG gene in trypanosomes expressing an endogenous VSG gene, and by knocking out the genetic locus for GPI-phospholipase C (PLC) that releases VSG from the membrane. Both approaches to genetic modification of African trypanosomes have suggested interesting and unexpected immunobiological effects associated with surface coat molecules.
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Affiliation(s)
- J M Mansfield
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA.
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7
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Abstract
African trypanosomes are well known for their ability to avoid immune elimination by switching the immunodominant variant surface glycoprotein (VSG) coat during infection. However, antigenic variation is only one of several means by which trypanosomes manipulate the immune system of their hosts. In this article, the role of parasite factors such as GPI anchor residues of the shed VSG molecule and the release of CpG DNA, in addition to host factors such as IFN-gamma, in regulating key aspects of innate and acquired immunity during infection is examined. The biological relevance of these immunoregulatory events is discussed in the context of host and parasite survival.
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Affiliation(s)
- J M Mansfield
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA.
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8
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Dubois ME, Demick KP, Mansfield JM. Trypanosomes expressing a mosaic variant surface glycoprotein coat escape early detection by the immune system. Infect Immun 2005; 73:2690-7. [PMID: 15845470 PMCID: PMC1087325 DOI: 10.1128/iai.73.5.2690-2697.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Host resistance to African trypanosomiasis is partially dependent on an early and strong T-independent B-cell response against the variant surface glycoprotein (VSG) coat expressed by trypanosomes. The repetitive array of surface epitopes displayed by a monotypic surface coat, in which identical VSG molecules are closely packed together in a uniform architectural display, cross-links cognate B-cell receptors and initiates T-independent B-cell activation events. However, this repetitive array of identical VSG epitopes is altered during the process of antigenic variation, when former and nascent VSG proteins are transiently expressed together in a mosaic surface coat. Thus, T-independent B-cell recognition of the trypanosome surface coat may be disrupted by the introduction of heterologous VSG molecules into the coat structure. To address this hypothesis, we transformed Trypanosoma brucei rhodesiense LouTat 1 with the 117 VSG gene from Trypanosoma brucei brucei MiTat 1.4 in order to produce VSG double expressers; coexpression of the exogenous 117 gene along with the endogenous LouTat 1 VSG gene resulted in the display of a mosaic VSG coat. Results presented here demonstrate that the host's ability to produce VSG-specific antibodies and activate B cells during early infection with VSG double expressers is compromised relative to that during infection with the parental strain, which displays a monotypic coat. These findings suggest a previously unrecognized mechanism of immune response evasion in which coat-switching trypanosomes fail to directly activate B cells until coat VSG homogeneity is achieved. This process affords an immunological advantage to trypanosomes during the process of antigenic variation.
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Affiliation(s)
- Melissa E Dubois
- Department of Bacteriology, University of Wisconsin-Madison, 1925 Willow Drive, Madison, WI 53706, USA
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9
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Barry JD, Turner CM. The dynamics of antigenic variation and growth of African trypanosomes. ACTA ACUST UNITED AC 2005; 7:207-11. [PMID: 15463498 DOI: 10.1016/0169-4758(91)90143-c] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Antigenic variation in African trypanosomes, which is a simple strategy for survival in the immune host, is rendered complex by its magnitude. For protection from nonspecific immunity and escape from specific immunity, each trypanosome is covered by a replaceable surface coat composed of the variant surface glycoprotein (VSG), which specifies the variable antigen type (VAT) of the trypanosome. Antigenic variation is the process by which the trypanosome switches from one coat to another. Here, David Barry and Michael Turner consider this phenomenon within the context of the course of trypanosome infection.
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Affiliation(s)
- J D Barry
- Wellcome Unit of Molecular Parasitology and Institute of Genetics, University of Glasgow, Church Street, Glasgow G11 5JS, UK
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10
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Abstract
African trypanosomes are protozoan parasites that reside in the mammalian bloodstream where they constantly confront the immune responses directed against them. They keep one-step-ahead of the immune system by continually switching from the expression of one variant surface glycoprotein (VSG) on their surface to the expression of another immunologically distinct VSG-a phenomenon called antigenic variation. About 1000 VSG genes (VSGs) and pseudo-VSGs are scattered throughout the trypanosome genome, all of which are transcriptionally silent except for one. Usually, the active VSG has been recently duplicated and translocated to one of about 20 potential bloodstream VSG expression sites (B-ESs). Each of the 20 potential B-ESs is adjacent to a chromosomal telomere, but only one B-ES is actively transcribed in a given organism. Recent evidence suggests the active B-ES is situated in an extra-nucleolar body of the nucleus where it is transcribed by RNA polymerase I. Members of another group of about 20 telomere-linked VSG expression sites (the M-ESs) are expressed only during the metacyclic stage of the parasite in its tsetse fly vector. Progress in sequencing the African trypanosome genome has led to additional insights on the organization of genes within both groups of ESs that may ultimately suggest better ways to control or eliminate this deadly pathogen.
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Affiliation(s)
- John E Donelson
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA.
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11
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Nash TE, Luján HT, Mowatt MR, Conrad JT. Variant-specific surface protein switching in Giardia lamblia. Infect Immun 2001; 69:1922-3. [PMID: 11179375 PMCID: PMC98104 DOI: 10.1128/iai.69.3.1922-1923.2001] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Surface antigen switching in Giardia lamblia was analyzed using monoclonal antibodies specific for two variant-specific surface proteins (VSPs). Two VSPs were detected on the surface of single trophozoites. Dual expression persisted for 13 h but disappeared at 36 h, as in other parasites that undergo surface antigenic variation.
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Affiliation(s)
- T E Nash
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
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12
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Abstract
The haploid nuclear genome of the African trypanosome, Trypanosoma brucei, is about 35 Mb and varies in size among different trypanosome isolates by as much as 25%. The nuclear DNA of this diploid organism is distributed among three size classes of chromosomes: the megabase chromosomes of which there are at least 11 pairs ranging from 1 Mb to more than 6 Mb (numbered I-XI from smallest to largest); several intermediate chromosomes of 200-900 kb and uncertain ploidy; and about 100 linear minichromosomes of 50-150 kb. Size differences of as much as four-fold can occur, both between the two homologues of a megabase chromosome pair in a specific trypanosome isolate and among chromosome pairs in different isolates. The genomic DNA sequences determined to date indicated that about 50% of the genome is coding sequence. The chromosomal telomeres possess TTAGGG repeats and many, if not all, of the telomeres of the megabase and intermediate chromosomes are linked to expression sites for genes encoding variant surface glycoproteins (VSGs). The minichromosomes serve as repositories for VSG genes since some but not all of their telomeres are linked to unexpressed VSG genes. A gene discovery program, based on sequencing the ends of cloned genomic DNA fragments, has generated more than 20 Mb of discontinuous single-pass genomic sequence data during the past year, and the complete sequences of chromosomes I and II (about 1 Mb each) in T. brucei GUTat 10.1 are currently being determined. It is anticipated that the entire genomic sequence of this organism will be known in a few years. Analysis of a test microarray of 400 cDNAs and small random genomic DNA fragments probed with RNAs from two developmental stages of T. brucei demonstrates that the microarray technology can be used to identify batteries of genes differentially expressed during the various life cycle stages of this parasite.
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Affiliation(s)
- N M El-Sayed
- The Institute for Genomic Research (TIGR), 9712 Medical Center Drive, Rockville, MD 20850, USA.
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13
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Cardoso De Almeida ML, Geuskens M, Pays E. Cell lysis induces redistribution of the GPI-anchored variant surface glycoprotein on both faces of the plasma membrane of Trypanosoma brucei. J Cell Sci 1999; 112 ( Pt 23):4461-73. [PMID: 10564663 DOI: 10.1242/jcs.112.23.4461] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
African trypanosomes are coated by 10 million copies of a single variant specific glycoprotein (VSG) which are anchored in the plasma membrane by glycosylphosphatidylinositol (GPI). A GPI-specific phospholipase C (GPI-PLC) triggers fast VSG release upon cell lysis but in vivo it is safely controlled and topologically concealed from its substrate by being intracellular. One enigmatic aspect of GPI-PLC action therefore consists of how it could gain access to the VSG in the exoplasmic leaflet of the membrane. The data presented herewith disclose an unexpected possible solution for this puzzle: upon cell rupture the VSG invades the cytoplasmic face of the plasma membrane which thus becomes double coated. This unusual VSG rearrangement was stable in ruptured plasma membrane from GPI-PLC null mutant trypanosomes but transiently preceded VSG release in wild-type parasites. The formation of double coat membrane (DCM) was independent of the presence or activation of GPI-PLC, occurred both at 4 degrees C and 30 degrees C and was unaffected by the classical inhibitor of VSG release, p-choromercuryphenylsulfonic acid (PCM). DCMs conserved the same coat thickness and association with subpellicular microtubules as in intact cells and were prone to form vesicles following gradual detachment of the latter. Our data also demonstrate that: (i) GPI-PLC expressed by one trypanosome only targets its own plasma membrane, being unable to release VSG of another parasite; (ii) DCMs concomitantly formed from trypanosomes expressing different VSGs do not intermix, an indication that DCM might be refractory to membrane fusion.
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Affiliation(s)
- M L Cardoso De Almeida
- Laboratory of Molecular Parasitology, Free University of Brussels, rue des Chevaux, B-1640 Rhode-St-Genèse, Belgium. mlcalmei@alize. ulb.ac.be
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14
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Alarcon CM, Pedram M, Donelson JE. Leaky transcription of variant surface glycoprotein gene expression sites in bloodstream african trypanosomes. J Biol Chem 1999; 274:16884-93. [PMID: 10358034 DOI: 10.1074/jbc.274.24.16884] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Trypanosoma brucei undergoes antigenic variation by periodically switching the expression of its variant surface glycoprotein (VSG) genes (vsg) among an estimated 20-40 telomere-linked expression sites (ES), only one of which is fully active at a given time. We found that in bloodstream trypanosomes one ES is transcribed at a high level and other ESs are expressed at low levels, resulting in organisms containing one abundant VSG mRNA and several rare VSG RNAs. Some of the rare VSG mRNAs come from monocistronic ESs in which the promoters are situated about 2 kilobases upstream of the vsg, in contrast to the polycistronic ESs in which the promoters are located 45-60 kilobases upstream of the vsg. The monocistronic ES containing the MVAT4 vsg does not include the ES-associated genes (esag) that occur between the promoter and the vsg in polycistronic ESs. However, bloodstream MVAT4 trypanosomes contain the mRNAs for many different ESAGs 6 and 7 (transferrin receptors), suggesting that polycistronic ESs are partially active in this clone. To explain these findings, we propose a model in which both mono- and polycistronic ESs are controlled by a similar mechanism throughout the parasite's life cycle. Certain VSGs are preferentially expressed in metacyclic versus bloodstream stages as a result of differences in ESAG expression and the proximity of the promoters to the vsg and telomere.
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Affiliation(s)
- C M Alarcon
- Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA
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15
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Abstract
Recent advances in transfection technology have been exploited to address fundamental questions relating to secretory trafficking in African trypanosomes. Targeted gene disruptions and ectopic expression of the major stage-specific surface proteins have provided unexpected insights into both the function and assembly of the essential parasite surface coats. A growing list of novel secretory cargo molecules, as well as advances in the characterization of trypanosomal secretory machinery, provide a unique model system for the study of eukaryotic secretory processes.
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Affiliation(s)
- J D Bangs
- Department of Medical Microbiology, University of Wisconsin-Madison, 1300 University Avenue, Madison, WI 53706, USA.
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16
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Rudenko G, Cross M, Borst P. Changing the end: antigenic variation orchestrated at the telomeres of African trypanosomes. Trends Microbiol 1998; 6:113-6. [PMID: 9582937 DOI: 10.1016/s0966-842x(97)01200-6] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
African trypanosomes express the gene encoding their variant surface glycoprotein (VSG) surface coat from one of many telomeric expression sites. This genomic location at chromosome ends not only allows easy exchange of VSG gene cassettes using various mechanisms of DNA recombination but also appears to play a role in VSG gene expression site control.
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Affiliation(s)
- G Rudenko
- Dept of Molecular Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
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17
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Horn D, Cross GA. Position-dependent and promoter-specific regulation of gene expression in Trypanosoma brucei. EMBO J 1997; 16:7422-31. [PMID: 9405371 PMCID: PMC1170342 DOI: 10.1093/emboj/16.24.7422] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Trypanosoma brucei evades the mammalian immune response by a process of antigenic variation. This involves mutually exclusive and alternating expression of telomere-proximal variant surface glycoprotein genes (vsgs), which is controlled at the level of transcription. To examine transcription repression in T.brucei we inserted reporter genes, under the control of either rRNA or vsg expression site (ES) promoters, into various chromosomal loci. Position-dependent repression of both promoters was observed in the mammalian stage of the life cycle (bloodstream forms). Repression of promoters inserted into a silent ES was more pronounced closer to the telomere and was bi-directional. Transcription from both ES and rRNA promoters was also efficiently repressed at a non-telomeric vsg locus in bloodstream-form trypanosomes. In cultured tsetse fly midgut-stage (procyclic) trypanosomes, in which vsg is not normally expressed, all inserted rRNA promoters were derepressed but ES promoters remained silent. Our results suggest that vsg promoters and ectopic rRNA promoters in bloodstream-form T.brucei are restrained by position effects related to their proximity to vsgs or other features of the ES. Sequences present in rRNA promoters but absent from vsg ES promoters appear to be responsible for rRNA promoter-specific derepression in procyclic cells.
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Affiliation(s)
- D Horn
- Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6399, USA
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18
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Webb H, Carnall N, Vanhamme L, Rolin S, Van Den Abbeele J, Welburn S, Pays E, Carrington M. The GPI-phospholipase C of Trypanosoma brucei is nonessential but influences parasitemia in mice. J Cell Biol 1997; 139:103-14. [PMID: 9314532 PMCID: PMC2139819 DOI: 10.1083/jcb.139.1.103] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/1996] [Revised: 07/17/1997] [Indexed: 02/05/2023] Open
Abstract
In the mammalian host, the cell surface of Trypanosoma brucei is protected by a variant surface glycoprotein that is anchored in the plasma membrane through covalent attachment of the COOH terminus to a glycosylphosphatidylinositol. The trypanosome also contains a phospholipase C (GPI-PLC) that cleaves this anchor and could thus potentially enable the trypanosome to shed the surface coat of VSG. Indeed, release of the surface VSG can be observed within a few minutes on lysis of trypanosomes in vitro. To investigate whether the ability to cleave the membrane anchor of the VSG is an essential function of the enzyme in vivo, a GPI-PLC null mutant trypanosome has been generated by targeted gene deletion. The mutant trypanosomes are fully viable; they can go through an entire life cycle and maintain a persistent infection in mice. Thus the GPI-PLC is not an essential activity and is not necessary for antigenic variation. However, mice infected with the mutant trypanosomes have a reduced parasitemia and survive longer than those infected with control trypanosomes. This phenotype is partially alleviated when the null mutant is modified to express low levels of GPI-PLC.
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Affiliation(s)
- H Webb
- Department of Biochemistry, Cambridge University, United Kingdom
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19
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Turner CM. Trypanosomes with multicoloured coats. ACTA ACUST UNITED AC 1997; 13:247-8. [PMID: 15275060 DOI: 10.1016/s0169-4758(97)01071-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- C M Turner
- Division of Infection and Immunity, IBLS, Joseph Black Building, University of Glasgow, Glasgow, UK.
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20
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Davies KP, Carruthers VB, Cross GA. Manipulation of the vsg co-transposed region increases expression-site switching in Trypanosoma brucei. Mol Biochem Parasitol 1997; 86:163-77. [PMID: 9200123 DOI: 10.1016/s0166-6851(97)02853-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Disruption of a region of DNA in Trypanosoma brucei immediately upstream of the expressed telomere-proximal variant surface glycoprotein gene (vsg), known as the co-transposed region (CTR), can cause a dramatic increase in the rate at which the active expression site (ES) is switched off and a new ES is switched on. Deletion of most of the CTR in two ESs caused a greater than 100-fold increase in the rate of ES switching, to about 1.3 x 10(-4) per generation. A more dramatic effect was observed when the entire CTR and the 5' coding region of the expressed vsg221 were deleted. In this case a new ES was activated within a few cell divisions. This switch also occurred in cell lines where a second vsg had been inserted into the ES, prior to CTR deletion. These cell lines, which stably co-expressed the inserted and endogenous Vsgs, in equal amounts, did not differ from the wild-type in growth rate or switching frequency, suggesting that simultaneous expression of two Vsgs has no intrinsic effect. CTR deletion did not disturb the inserted vsg117. We tentatively conclude that it was not the disruption of the vsg221 in itself that destabilized the ES. All of the observed switches occurred without additional detectable DNA rearrangements in the switched ES. Deletion of the 70-bp repeats and/or a vsg pseudogene upstream of the CTR did not affect ES stability. Several speculative interpretations of these observation are offered, the most intriguing of which is that the CTR plays some role in modulating chromatin conformation at an ES.
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Affiliation(s)
- K P Davies
- Laboratory of Molecular Parasitology, Rockefeller University, New York, NY 10021, USA
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21
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Abstract
Trypanosoma brucei can undergo antigenic variation by switching between distinct telomeric variant surface glycoprotein gene (vsg) expression sites (ESs) or by replacing the active vsg. DNA rearrangements have often been associated with ES switching, but it is unclear if such rearrangements are necessary or whether ES inactivation always accompanies ES activation. To explore these issues, we derived ten independent clones, from the same parent, that had undergone a similar vsg activation event. This was achieved in the absence of an immune response, in vitro, using cells with selectable markers integrated into an ES. Nine of the ten clones had undergone ES switching. Such heritable changes in transcription state occurred at a frequency of approximately 6 x 10(-7). Comparison of switched and un-switched clones highlighted the dynamic nature of T. brucei telomeres, but changes in telomere length were not specifically associated with ES switching. Mapping within and beyond the ESs revealed no detectable DNA rearrangements, indicating that rearrangements are not necessary for ES activation/inactivation. Examination of individual cells indicated that ES activation consistently accompanied inactivation of the previously active ES. In some cases, however, we found cells that appeared to have efficiently established the switched state but which subsequently, at a frequency of approximately 2 x 10(-3), generated cells expressing both pre- and post-switch vsgs. These results show that ES activation/inactivation is usually a coupled process but that cells can inherit a propensity to uncouple these events.
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Affiliation(s)
- D Horn
- Laboratory of Molecular Parasitology, Rockefeller University, New York, NY 10021-6399, USA
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22
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Muñoz-Jordán JL, Davies KP, Cross GA. Stable expression of mosaic coats of variant surface glycoproteins in Trypanosoma brucei. Science 1996; 272:1795-7. [PMID: 8650579 DOI: 10.1126/science.272.5269.1795] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The paradigm of antigenic variation in parasites is the variant surface glycoprotein (VSG) of African trypanosomes. Only one VSG is expressed at any time, except for short periods during switching. The reasons for this pattern of expression and the consequences of expressing more than one VSG are unknown. Trypanosoma brucei was genetically manipulated to generate cell lines that expressed two VSGs simultaneously. These VSGs were produced in equal amounts and were homogeneously distributed on the trypanosome surface. The double-expressor cells had similar population doubling times and were as infective as wild-type cells. Thus, the simultaneous expression of two VSGs is not intrinsically harmful.
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Affiliation(s)
- J L Muñoz-Jordán
- Laboratory of Molecular Parasitology, Rockefeller University, New York 10012, USA
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23
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Abstract
Among pathogenic micro-organisms that evade the mammalian immune responses. Trypanosoma brucei has developed the most elaborate capacity for antigenic variation. Trypanosomes branched early during eukaryotic evolution. They are characterized by many aberrations, ranging from the unusual compartmentation of metabolic pathways to the heresy of RNA editing. The ubiquitous phenomenon of glycosylphosphatidylinositol-anchoring of eukaryotic plasma membrane proteins and RNA trans-splicing (trypanosome genes contain no introns), which adds an identical leader sequence to all trypanosome mRNAs, were first defined during studies of antigenic variation. Genetic transformation of trypanosomes and the high efficiency of gene targeting provide new opportunities to investigate the regulation of antigenic variation. There is every reason to expect trypanosomes to provide further surprises and insights into the evolution of genetic regulatory mechanisms.
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Affiliation(s)
- G A Cross
- Rockefeller University, New York, NY 10021-6399, USA
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24
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Donelson JE. Mechanisms of antigenic variation in Borrelia hermsii and African trypanosomes. J Biol Chem 1995; 270:7783-6. [PMID: 7713867 DOI: 10.1074/jbc.270.14.7783] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Affiliation(s)
- J E Donelson
- Department of Biochemistry, University of Iowa, Iowa City 52242, USA
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25
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Abstract
African trypanosomes evade the humoral immune response by periodically changing the antigenic identity of their variant cell-surface glycoprotein (VSG) coat. Antigenic variation relies on DNA rearrangement events that can translocate a silent VSG gene to a telomerically located VSG gene expression site. Antigenic switches can also be brought about by the differential transcriptional control of the expression sites, only one of which is transcribed at any time.
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Affiliation(s)
- L H Van der Ploeg
- Department of Genetics and Molecular Biology, Merck Research Laboratories, Rahway, NJ 07065
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26
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Eshita Y, Urakawa T, Hirumi H, Fish WR, Majiwa PA. Metacyclic form-specific variable surface glycoprotein-encoding genes of Trypanosoma (Nannomonas) congolense. Gene 1992; 113:139-48. [PMID: 1572537 DOI: 10.1016/0378-1119(92)90389-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A complementary DNA expression library in phage lambda gt11 was synthesized using mRNA from in vitro-produced metacyclic forms of a clone of Trypanosoma (Nannomonas) congolense. The unamplified library was screened with antiserum from a goat immune to infection with metacyclic (m)-forms of T. congolense ILRAD Nannomonas antigen repertoire 2(ILNaR2). Of the 100 antiserum-reactive phage clones identified, 22 were analyzed further: 21 of the clones contained overlapping portions of a single transcript, while one other contained a different transcript. Northern blot analyses indicated that the sequences contained in the clones were transcribed only by m-forms of ILNaR2. Immunological and sequence analyses indicated that the two different cloned sequences encode m-form-specific variable surface glycoproteins.
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Affiliation(s)
- Y Eshita
- International Laboratory for Research on Animal Diseases (ILRAD), Nairobi, Kenya
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27
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Turner CM, Aslam N, Smith E, Buchanan N, Tait A. The effects of genetic exchange on variable antigen expression in Trypanosoma brucei. Parasitology 1991; 103 Pt 3:379-86. [PMID: 1780175 DOI: 10.1017/s0031182000059898] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The inheritance of variant surface antigens in Trypanosoma brucei has been determined by identifying variable antigen types (VATs) in each of two cloned parental stocks and then examining the presence and abundance of these VATs in hybrid progeny produced when these stocks undergo genetic exchange during co-transmission through tsetse flies. Nine VATs have been identified from the repertoire of the parental stock STIB 247L and 5 VATs have been identified from the parental stock STIB 386AA; the identified VATs were exclusive to each stock. Their inheritance was elucidated using two assays. In the first, repertoire antisera (RAS) containing antibody specificities to many different VATs were raised in rabbits to the 2 parental stocks and 6 progeny clones. The presence of VAT-specific antibodies in these RAS was then determined by antibody-dependent complement-mediated lysis. In the second assay, the 2 parental stocks and 4 hybrid progeny clones were each independently transmitted through tsetse flies and VATs observed using VAT-specific antisera in indirect immunofluorescence of metacyclic trypanosomes and in bloodstream forms of fly-bitten mice. The results from both assays showed that (1) both metacyclic- and bloodstream-VATs were inherited into the progeny, (2) each hybrid progeny clone contained some VATs from both parents, (3) hybrids did not express all the VATs from either parent, (4) there was little apparent pattern as to which VATs had been inherited and which had not and (5) the VAT repertoires of the hybrid progeny appeared to be larger than those of the parents. In addition, two results indicated that control of VAT expression remains unaltered after genetic exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- C M Turner
- Department of Zoology, University of Glasgow
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28
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Modespacher UP, Rudin W, Hecker H. Surface coat synthesis and turnover from epimastigote to bloodstream forms of Trypanosoma brucei. Acta Trop 1991; 50:67-78. [PMID: 1686146 DOI: 10.1016/0001-706x(91)90074-t] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Monoclonal antibodies to metacyclic surface coat glycoproteins of Trypanosoma brucei brucei STIB 247LG were produced for a study of the synthesis of metacyclic variable surface glycoproteins (VSGs) within the salivary gland of Glossina morsitans morsitans, and of the first exchange of the surface glycoproteins after infection in mice. Immunofluorescence antibody tests and protein A-gold labelling revealed that the VSGs are continuously integrated into the whole surface of the trypanosome while it is still attached to the gland epithelium. A pool of 8 antibodies recognized about 50% of the metacyclic forms present in the saliva of an infected tsetse fly, which confirmed the heterogeneity of the metacyclic VSG-generation. The labelling experiments showed that the integration of the first VSG-generation into the surface of bloodstream forms takes place in the same way as in the metacyclics. This process started on day 3 after infection and was finished on day 6.
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29
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Abstract
Antigenic variation is one of the most effective strategies developed by parasites to escape immune destruction. It requires a large wardrobe of surface coats and mechanisms to exchange one coat for an unrelated one. The molecular principles of antigenic variation are now largely known in the bacterial species Borrelia and Neisseria and in the protozoa of the African trypanosome group and these three examples are discussed here by Piet Borst.
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MESH Headings
- Amino Acid Sequence
- Animals
- Antigenic Variation/genetics
- Antigens, Bacterial/genetics
- Antigens, Bacterial/immunology
- Antigens, Protozoan/genetics
- Antigens, Protozoan/immunology
- Antigens, Surface/genetics
- Antigens, Surface/immunology
- Bacterial Outer Membrane Proteins/genetics
- Bacterial Outer Membrane Proteins/immunology
- Base Sequence
- Borrelia/genetics
- Borrelia/immunology
- Fimbriae Proteins
- Gene Expression Regulation
- Gene Expression Regulation, Bacterial
- Genes
- Genes, Bacterial
- Host-Parasite Interactions
- Mice
- Molecular Sequence Data
- Neisseria/genetics
- Neisseria/immunology
- Trypanosoma brucei brucei/genetics
- Trypanosoma brucei brucei/immunology
- Variant Surface Glycoproteins, Trypanosoma/genetics
- Variant Surface Glycoproteins, Trypanosoma/immunology
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Affiliation(s)
- P Borst
- The Netherlands Cancer Institute, Amsterdam
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31
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Matthews KR, Shiels PG, Graham SV, Cowan C, Barry JD. Duplicative activation mechanisms of two trypanosome telomeric VSG genes with structurally simple 5' flanks. Nucleic Acids Res 1990; 18:7219-27. [PMID: 2175429 PMCID: PMC332856 DOI: 10.1093/nar/18.24.7219] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
In the mammalian bloodstream, African trypanosomes express variant surface glycoprotein (VSG) genes from a family of long and complex telomeric expression sites. VSG switching generally occurs by the duplication of different VSG genes into these sites by gene conversion involving a series of 70 base pair (70bp) repeats in the 5' flank. In contrast, when VSG is first synthesised by trypanosomes in the tsetse fly at the metacyclic stage, a separate set of telomeric expression sites is activated. These latter telomeres appear not to act as recipients in gene conversion. We have found that the structure of two such expression sites is simple, with very short 70bp repeat regions and very little other sequence in common with bloodstream expression sites. However, the two telomeres readily act as donors in VSG gene conversion in the bloodstream and we show for one a consistent association of the conversion 5' end point with the short 70bp repeat region. These findings help explain why a very predictable set of VSGs is expressed in the tsetse fly and have implications for VSG gene conversion mechanisms.
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32
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Seyfang A, Mecke D, Duszenko M. Degradation, recycling, and shedding of Trypanosoma brucei variant surface glycoprotein. THE JOURNAL OF PROTOZOOLOGY 1990; 37:546-52. [PMID: 2086784 DOI: 10.1111/j.1550-7408.1990.tb01263.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Trypanosoma brucei bloodstream forms express a densely packed surface coat consisting of identical variant surface glycoprotein (VSG) molecules. This surface coat is subject to antigenic variation by sequential expression of different VSG genes and thus enables the cells to escape the mammalian host's specific immune response. VSG turnover was investigated and compared with the antigen switching rate. Living cells were radiochemically labeled with either 125I-Bolton-Hunter reagent or 35S-methionine, and immunogold-surface labeled for electron microscopy studies. The fate of labeled VSG was studied during subsequent incubation or cultivation of labeled trypanosomes. Our data show that living cells slowly released VSG into the medium with a shedding rate of 2.2 +/- 0.6% h-1 (t1/2 = 33 +/- 9 h). In contrast, VSG degradation accounted for only 0.3 +/- 0.06% h-1 (t1/2 = 237 +/- 45 h) and followed the classical lysosomal pathway as judged by electron microscopy. Since VSG uptake by endocytosis was rather high, our data suggest that most of the endocytosed VSG was recycled to the surface membrane. These results indicate that shedding of VSG at a regular turnover rate is sufficient to remove the old VSG coat within one week, and no increase of the VSG turnover rate seems to be necessary during antigenic variation.
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Affiliation(s)
- A Seyfang
- Physiologisch-chemisches Institut, Tübingen, Federal Republic of Germany
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34
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Agur Z, Abiri D, Van der Ploeg LH. Ordered appearance of antigenic variants of African trypanosomes explained in a mathematical model based on a stochastic switch process and immune-selection against putative switch intermediates. Proc Natl Acad Sci U S A 1989; 86:9626-30. [PMID: 2594790 PMCID: PMC298551 DOI: 10.1073/pnas.86.23.9626] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Antigenic variation of African trypanosomes results from the periodic activation of a single new variant cell surface glycoprotein (VSG) gene out of a repertoire of about a 1000 VSG genes. In spite of the apparently random genetic basis of the process of antigenic variation, the relapsing parasitemias are characterized by an as yet unexplained order of appearance of major VSG variants. Here we mathematically test hypotheses concerning the blood-based parasitemia. In our model the antigenic switches occur at random at the DNA level. A variable proportion of the switches has a short intermediate phase in which two different VSGs simultaneously occur on the cell surface. We show that, in a theoretical population of 230 single expressor variants in an immunocompetent or in an immunodeficient host, it is not possible to explain the ordered appearance of variants by affecting the growth coefficients of single expressors or double expressors or by affecting the antigen switch probabilities. Rather, a realistic parasitemia can be obtained if the majority of switches has a double expressor switch-intermediate phase and if the double expressors have a differential susceptibility to the immune control. This study is significant in providing a theoretical basis for the ordered appearance of variants and in explaining previously unresolved discrepancies between the rate of appearance of new variants in culture and in vivo. In addition, testable predictions as to the development of the infections, switch rate of variants, fraction of double expressors, and parasite mortality coefficients are generated.
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Affiliation(s)
- Z Agur
- Department of Applied Mathematics, Weizmann Institute of Science, Rehovot, Israel
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35
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Abstract
Survival of the trypanosome (Trypanosoma brucei) population in the mammalian body depends upon paced stimulation of the host's humoral immune response by different antigenic variants and serial sacrifice of the dominant variant (homotype) so that minority variants (heterotypes) can continue the infection and each become a homotype in its turn. New variants are generated by a spontaneous switch in gene expression so that the trypanosome puts on a surface coat of a glycoprotein differing in antigenic specificity from its predecessor. Homotypes appear in a characteristic order for a given trypanosome clone but what determines this order and the pacing of homotype generation so that the trypanosome does not quickly exhaust its repertoire of variable antigens, is not clear. The tendency of some genes to be expressed more frequently than others may reflect the location within the genome and mode of expression of the genes concerned and may influence homotype succession. Differences in the doubling time of different variants or in the rate at which trypanosomes belonging to a particular variant differentiate into non-dividing (vector infective) stumpy forms have also been invoked to explain how a heterotype's growth characteristics may determine when it becomes a homotype. Recent estimations of the frequency of variable antigen switching in trypanosome populations after transmission through the tsetse fly vector, however, suggest a much higher figure (0.97-2.2 x 10(-3) switches per cell per generation) than that obtained for syringe-passed infections (10(-5)-10(-7) switches per cell per generation) and it seems probable that most of the variable antigen genes are expressed as minority variable antigen types very early in the infection. Instability of expression is a feature of trypanosome clones derived from infective tsetse salivary gland (metacyclic) trypanosomes and it is suggested that high switching rates in tsetse-transmitted infections may delay the growth of certain variants to homotype status until later in the infection.
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Affiliation(s)
- K Vickerman
- Department of Zoology, University of Glasgow
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36
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Abstract
To understand the control of differential variant cell surface glycoprotein (VSG) gene expression in T. brucei, we studied VSG gene and expression site transcription regulation. We show that the interchromosomal duplicative transposition of VSG gene 118, on an unusually large transposed segment, results in the transcriptional activation of a cotransposed RNA polymerase I-like (pol I) promoter, from which the VSG gene is transcribed. Transcription of VSG genes by pol I can therefore be regulated by DNA rearrangements that affect positional control of gene expression. A 5' cap is added in trans to the pol I-derived pre-mRNA, by addition of a pol II-derived 35 nucleotide mini-exon. A second gene (ESAG1) is located 25 kb upstream of the VSG 118 gene and is also transcribed. This expression site therefore contains at least two independently regulated genes. We discuss the putative importance of a nucleolar location for VSG gene and expression site transcription regulation.
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Abstract
The expression of several surface antigen genes in Trypanosoma brucei is mediated by the duplicative transposition of a basic-copy variant surface glycoprotein (VSG) gene into an expression site. We determined that the appearance of variant 118, in a parasitemia, resulted from at least four independent duplicative transpositions of the same VSG 118 gene. Variants 117 and 118 both appeared at specific periods but resulted from multiple independent activations. Antigenic variants thus occur in an ordered manner. We show that in the duplicative transpositions of VSG genes, the ends of the transposed segments were homologous between the basic copy and the expression site. Sequences other than the previously reported 70-base-pair (bp) repeats could be involved. In one variant, 118 clone 1, the homology was between a sequence previously transposed into the expression site and a sequence located 6 kilobases upstream of the VSG 118 gene. In variant 118b the homology was presumably in 70-bp repeat arrays, while in a third 118 variant yet another sequence was involved. The possibility that the 70-bp repeats are important in the initial steps of the recombinational events was illustrated by a rearrangement involving a 70-bp repeat array. The data provide strong evidence for the notion that gene conversion mediates the duplicative transposition of VSG genes. We discuss a model that explains how the process of duplicative transposition can occur at random and still produce an ordered appearance of variants.
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Timmers HT, de Lange T, Kooter JM, Borst P. Coincident multiple activations of the same surface antigen gene in Trypanosoma brucei. J Mol Biol 1987; 194:81-90. [PMID: 3612801 DOI: 10.1016/0022-2836(87)90717-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Trypanosomes with a coat of variant surface glycoprotein (VSG) 118, consistently appear around day 20 when a rabbit is infected with Trypanosoma brucei strain 427. There is a single chromosome-internal gene for VSG 118 and this is activated by duplicative transposition to a telomeric expression site. We show here that the expression-linked extra copy of VSG gene 118 in a day 18 population of a chronic infection is heterogeneous, and we infer that the population is not monoclonal but is the result of multiple independent activations of the 118 gene. We show that the heterogeneity of expression-linked extra copies is also present in other trypanosome populations expressing chromosome-internal VSG genes. We present a model for the timing of VSG gene activation during chronic infection that emphasizes two features: the relative activation and inactivation frequencies of different expression sites, and the degree of homology of the sequences flanking VSG genes with expression sites.
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39
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Lee MG, Van der Ploeg LH. Frequent independent duplicative transpositions activate a single VSG gene. Mol Cell Biol 1987; 7:357-64. [PMID: 3031467 PMCID: PMC365076 DOI: 10.1128/mcb.7.1.357-364.1987] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The expression of several surface antigen genes in Trypanosoma brucei is mediated by the duplicative transposition of a basic-copy variant surface glycoprotein (VSG) gene into an expression site. We determined that the appearance of variant 118, in a parasitemia, resulted from at least four independent duplicative transpositions of the same VSG 118 gene. Variants 117 and 118 both appeared at specific periods but resulted from multiple independent activations. Antigenic variants thus occur in an ordered manner. We show that in the duplicative transpositions of VSG genes, the ends of the transposed segments were homologous between the basic copy and the expression site. Sequences other than the previously reported 70-base-pair (bp) repeats could be involved. In one variant, 118 clone 1, the homology was between a sequence previously transposed into the expression site and a sequence located 6 kilobases upstream of the VSG 118 gene. In variant 118b the homology was presumably in 70-bp repeat arrays, while in a third 118 variant yet another sequence was involved. The possibility that the 70-bp repeats are important in the initial steps of the recombinational events was illustrated by a rearrangement involving a 70-bp repeat array. The data provide strong evidence for the notion that gene conversion mediates the duplicative transposition of VSG genes. We discuss a model that explains how the process of duplicative transposition can occur at random and still produce an ordered appearance of variants.
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40
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Metacyclic variant surface glycoprotein genes of Trypanosoma brucei subsp. rhodesiense are activated in situ, and their expression is transcriptionally regulated. Mol Cell Biol 1986. [PMID: 3785186 DOI: 10.1128/mcb.6.6.1991] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During the metacyclic stage in the life cycle of Trypanosoma brucei subsp. rhodesiense, the expression of variant surface glycoproteins (VSGs) is restricted to a small subset of antigenic types. Previously we identified cDNAs for the VSGs expressed in metacyclic variant antigen types (MVATs) 4 and 7 and found that these VSG genes do not rearrange when expressed at the metacyclic stage (M. J. Lenardo, A. C. Rice-Ficht, G. Kelly, K. Esser, and J. E. Donelson, Proc. Nathl. Acad Sci. USA 81:6642-6646, 1984). We now provide further evidence that these genes do not rearrange and demonstrate that their 5' upstream regions lack the 72 to 76-base-pair repeats which are considered the substrate for duplication and transposition events. Pulsed field gradient electrophoresis showed that the MVAT VSG genes were located on the largest chromosome-sized DNA molecules, and the lack of the MVAT 4 gene in one of two different serodemes suggested that one mechanism for the evolution of MVAT repertoires is gene deletion. When MVATs were inoculated into the bloodstream of a mammalian host by a bite from the insect vector, they rapidly switched into nonmetacyclic VSG types. We found that this switch was accomplished by a loss of MVAT RNA concomitant with the loss of metacyclic VSGs. Transcription studies with isolated metacyclic nuclei showed that the MVAT genes were expressed in situ from a single locus and were regulated at the level of transcription.
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41
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Purification and characterization of the membrane-form variant surface glycoprotein hydrolase of Trypanosoma brucei. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(18)67328-4] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Diffley P, Straus DC. Biochemical and immunological characterization of the variant surface coat glycoprotein shed by African trypanosomes. Infect Immun 1986; 53:166-72. [PMID: 3721578 PMCID: PMC260092 DOI: 10.1128/iai.53.1.166-172.1986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
As the variant surface coat glycoprotein (VSG) was shed from Trypanosoma brucei rhodesiense into the blood of infected rats, it was biochemically characterized and compared with VSG that had been purified from trypanosomal homogenates. To determine if VSG was in association with lipid, membranes and lipoproteins in plasma of infected rats (IRP), VSG isolated from plasma (PVSG), and VSG isolated from trypanosomal homogenates (HVSG) were all concentrated by ultracentrifugation and assayed for the presence of VSG by radial immunodiffusion (minimum level of detection, 25 micrograms/ml) and by immunoelectroblots (minimum level of detection, 1 microgram/ml). Crimson red was used to detect lipid (minimum level of detection, 10 micrograms per sample) in electrophoresed samples. The VSG was neither concentrated with membrane or lipoprotein fractions nor stained by lipid crimson. Lipids from normal rat plasma, IRP, trypanosomal homogenates, HVSG, and PVSG were also extracted and separated by thin-layer chromatography (minimum level of detection, 20 micrograms of trypanosomal phospholipid per sample). The trypanosomal homogenates had five bands as detected by iodine vapors, of which three were phospholipids as detected by molybdenum blue. Both normal rat plasma and IRP had identical patterns of bands with a single phospholipid. The PVSG had one neutral lipid contaminant that apparently was not physically associated with the shed surface coat. The HVSG contained no lipids at all. Therefore, no evidence was obtained to implicate an association between membranes and VSG, once the latter had been shed into the blood of infected hosts. From immunoelectroblots of denatured material, it was determined that both HVSG and PVSG had the same reduced molecular weight. From molecular sieve column chromatography, however, it was determined that VSG released during the homogenization of trypanosomes is a noncovalently linked dimer, whereas that shed in the blood is apparently a trimer. This difference in native structure made no difference in immunological effect. Administered in a regimen that mimicked what the host encounters during a first peak of parasitemia, both HVSG and PVSG induced nonspecific proliferation of splenic lymphocytes and production of unelicited antibodies without the generation of nonspecific immunosuppression. This polyclonal activation of lymphocytes was not the result of contamination by exogenous pyrogen, because the activity was lost if VSG was immunologically absorbed from plasma.(ABSTRACT TRUNCATED AT 400 WORDS)
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Lenardo MJ, Esser KM, Moon AM, Van der Ploeg LH, Donelson JE. Metacyclic variant surface glycoprotein genes of Trypanosoma brucei subsp. rhodesiense are activated in situ, and their expression is transcriptionally regulated. Mol Cell Biol 1986; 6:1991-7. [PMID: 3785186 PMCID: PMC367738 DOI: 10.1128/mcb.6.6.1991-1997.1986] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
During the metacyclic stage in the life cycle of Trypanosoma brucei subsp. rhodesiense, the expression of variant surface glycoproteins (VSGs) is restricted to a small subset of antigenic types. Previously we identified cDNAs for the VSGs expressed in metacyclic variant antigen types (MVATs) 4 and 7 and found that these VSG genes do not rearrange when expressed at the metacyclic stage (M. J. Lenardo, A. C. Rice-Ficht, G. Kelly, K. Esser, and J. E. Donelson, Proc. Nathl. Acad Sci. USA 81:6642-6646, 1984). We now provide further evidence that these genes do not rearrange and demonstrate that their 5' upstream regions lack the 72 to 76-base-pair repeats which are considered the substrate for duplication and transposition events. Pulsed field gradient electrophoresis showed that the MVAT VSG genes were located on the largest chromosome-sized DNA molecules, and the lack of the MVAT 4 gene in one of two different serodemes suggested that one mechanism for the evolution of MVAT repertoires is gene deletion. When MVATs were inoculated into the bloodstream of a mammalian host by a bite from the insect vector, they rapidly switched into nonmetacyclic VSG types. We found that this switch was accomplished by a loss of MVAT RNA concomitant with the loss of metacyclic VSGs. Transcription studies with isolated metacyclic nuclei showed that the MVAT genes were expressed in situ from a single locus and were regulated at the level of transcription.
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Affiliation(s)
- J D Barry
- Institute of Genetics, University of Glasgow, Glasgow G11 5JS, UK
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Abstract
Substantial progress has been made in the last ten years in understanding the structural and functional organization of parasitic protozoa and helminths and the complex physiological relationships that exist between these organisms and their hosts. By employing the new powerful techniques of biochemistry, molecular biology and immunology the genomic organization in parasites, the molecular basis of parasite's variation in surface antigens and the biosynthesis, processing, transport and membrane anchoring of these and other surface proteins were extensively investigated. Significant advances have also been made in our knowledge of the specific and often peculiar strategies of intermediary metabolism, cell compartmentation, the role of oxygen for parasites and the mechanisms of antiparasitic drug action. Further major fields of interest are currently the complex processes which enables parasites to evade the host's immune defense system and other mechanisms which have resulted in the specific adaptations which enabled parasites to survive within their host environments. Various approaches in molecular and biochemical parasitology and in immunoparasitology have been proven to be of high potential for serodiagnosis, immunoprophylaxis and drug design.
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Abstract
Previously quoted figures for the frequency of antigen switching in Trypanosoma brucei are based on incorrect assumptions. In order to determine the correct switching frequency, an equation was derived that takes the growth rates of the newly expressed antigen types into consideration as well as the proportion of switched trypanosomes and the number of generations since the population was antigenically homogeneous. When this equation was applied to published in vitro data, variable values were obtained for the switching frequency in clonal populations originally expressing one antigen type. The calculated most likely switching frequencies ranged from 1.4 X 10(-7) to 3.5 X 10(-6). This variation was probably caused by differences in the growth rates of the new antigen types in the population and failure to detect slow growing variants. To overcome these problems, an experimental procedure was developed to analyse the switching frequency in vitro. Trypanosomes were cloned and grown in parallel cultures. After an appropriate number of generations, cells expressing the original antigen type were destroyed and, from the proportion of cultures that contained new antigen types, the switching frequency was calculated. The technique minimized subculturing or other procedures that could distort the results. Although the method was optimized for analysing switching frequency, the values differed between experiments, ranging from 2.2 X 10(-7) to 2.6 X 10(-6) for one variant. Possible causes for the variations in switching frequency are discussed.
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