1
|
Trenaman A, Glover L, Hutchinson S, Horn D. A post-transcriptional respiratome regulon in trypanosomes. Nucleic Acids Res 2019; 47:7063-7077. [PMID: 31127277 PMCID: PMC6648352 DOI: 10.1093/nar/gkz455] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 04/25/2019] [Accepted: 05/10/2019] [Indexed: 12/21/2022] Open
Abstract
Post-transcriptional regulons coordinate the expression of groups of genes in eukaryotic cells, yet relatively few have been characterized. Parasitic trypanosomatids are particularly good models for studies on such mechanisms because they exhibit almost exclusive polycistronic, and unregulated, transcription. Here, we identify the Trypanosoma brucei ZC3H39/40 RNA-binding proteins as regulators of the respiratome; the mitochondrial electron transport chain (complexes I-IV) and the FoF1-ATP synthase (complex V). A high-throughput RNAi screen initially implicated both ZC3H proteins in variant surface glycoprotein (VSG) gene silencing. This link was confirmed and both proteins were shown to form a cytoplasmic ZC3H39/40 complex. Transcriptome and mRNA-interactome analyses indicated that the impact on VSG silencing was indirect, while the ZC3H39/40 complex specifically bound and stabilized transcripts encoding respiratome-complexes. Quantitative proteomic analyses revealed specific positive control of >20 components from complexes I, II and V. Our findings establish a link between the mitochondrial respiratome and VSG gene silencing in bloodstream form T. brucei. They also reveal a major respiratome regulon controlled by the conserved trypanosomatid ZC3H39/40 RNA-binding proteins.
Collapse
Affiliation(s)
- Anna Trenaman
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Lucy Glover
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Sebastian Hutchinson
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - David Horn
- The Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| |
Collapse
|
2
|
Müller LSM, Cosentino RO, Förstner KU, Guizetti J, Wedel C, Kaplan N, Janzen CJ, Arampatzi P, Vogel J, Steinbiss S, Otto TD, Saliba AE, Sebra RP, Siegel TN. Genome organization and DNA accessibility control antigenic variation in trypanosomes. Nature 2018; 563:121-125. [PMID: 30333624 PMCID: PMC6784898 DOI: 10.1038/s41586-018-0619-8] [Citation(s) in RCA: 113] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 09/03/2018] [Indexed: 01/15/2023]
Abstract
Many evolutionarily distant pathogenic organisms have evolved similar survival strategies to evade the immune responses of their hosts. These include antigenic variation, through which an infecting organism prevents clearance by periodically altering the identity of proteins that are visible to the immune system of the host1. Antigenic variation requires large reservoirs of immunologically diverse antigen genes, which are often generated through homologous recombination, as well as mechanisms to ensure the expression of one or very few antigens at any given time. Both homologous recombination and gene expression are affected by three-dimensional genome architecture and local DNA accessibility2,3. Factors that link three-dimensional genome architecture, local chromatin conformation and antigenic variation have, to our knowledge, not yet been identified in any organism. One of the major obstacles to studying the role of genome architecture in antigenic variation has been the highly repetitive nature and heterozygosity of antigen-gene arrays, which has precluded complete genome assembly in many pathogens. Here we report the de novo haplotype-specific assembly and scaffolding of the long antigen-gene arrays of the model protozoan parasite Trypanosoma brucei, using long-read sequencing technology and conserved features of chromosome folding4. Genome-wide chromosome conformation capture (Hi-C) reveals a distinct partitioning of the genome, with antigen-encoding subtelomeric regions that are folded into distinct, highly compact compartments. In addition, we performed a range of analyses-Hi-C, fluorescence in situ hybridization, assays for transposase-accessible chromatin using sequencing and single-cell RNA sequencing-that showed that deletion of the histone variants H3.V and H4.V increases antigen-gene clustering, DNA accessibility across sites of antigen expression and switching of the expressed antigen isoform, via homologous recombination. Our analyses identify histone variants as a molecular link between global genome architecture, local chromatin conformation and antigenic variation.
Collapse
Affiliation(s)
- Laura S M Müller
- Department of Veterinary Sciences, Experimental Parasitology, Ludwig-Maximilians-Universität München, Munich, Germany
- Biomedical Center Munich, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
- Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany
| | - Raúl O Cosentino
- Department of Veterinary Sciences, Experimental Parasitology, Ludwig-Maximilians-Universität München, Munich, Germany
- Biomedical Center Munich, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
- Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany
| | - Konrad U Förstner
- ZB MED - Information Centre for Life Sciences, Cologne, Germany
- TH Köln, Faculty of Information Science and Communication Studies, Cologne, Germany
- Core Unit Systems Medicine, Institute of Molecular Infection Biology, University of Würzburg, Würzburg, Germany
| | - Julien Guizetti
- Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany
- Centre for Infectious Diseases, Parasitology, Heidelberg University Hospital, Heidelberg, Germany
| | - Carolin Wedel
- Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany
| | - Noam Kaplan
- Department of Physiology, Biophysics & Systems Biology, Rappaport Faculty of Medicine, Technion Israel Institute of Technology, Haifa, Israel
| | - Christian J Janzen
- Department of Cell & Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Panagiota Arampatzi
- Core Unit Systems Medicine, Institute of Molecular Infection Biology, University of Würzburg, Würzburg, Germany
| | - Jörg Vogel
- Helmholtz Institute for RNA-based Infection Research, Würzburg, Germany
- RNA Biology Group, Institute of Molecular Infection Biology, University of Würzburg, Würzburg, Germany
| | | | - Thomas D Otto
- Wellcome Trust Sanger Institute, Hinxton, Cambridge, UK
- Centre of Immunobiology, Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK
| | | | - Robert P Sebra
- Icahn Institute and Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - T Nicolai Siegel
- Department of Veterinary Sciences, Experimental Parasitology, Ludwig-Maximilians-Universität München, Munich, Germany.
- Biomedical Center Munich, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany.
- Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany.
| |
Collapse
|
3
|
Cheung JLY, Wand NV, Ooi CP, Ridewood S, Wheeler RJ, Rudenko G. Blocking Synthesis of the Variant Surface Glycoprotein Coat in Trypanosoma brucei Leads to an Increase in Macrophage Phagocytosis Due to Reduced Clearance of Surface Coat Antibodies. PLoS Pathog 2016; 12:e1006023. [PMID: 27893860 PMCID: PMC5125712 DOI: 10.1371/journal.ppat.1006023] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 10/25/2016] [Indexed: 11/19/2022] Open
Abstract
The extracellular bloodstream form parasite Trypanosoma brucei is supremely adapted to escape the host innate and adaptive immune system. Evasion is mediated through an antigenically variable Variant Surface Glycoprotein (VSG) coat, which is recycled at extraordinarily high rates. Blocking VSG synthesis triggers a precytokinesis arrest where stalled cells persist for days in vitro with superficially intact VSG coats, but are rapidly cleared within hours in mice. We therefore investigated the role of VSG synthesis in trypanosome phagocytosis by activated mouse macrophages. T. brucei normally effectively evades macrophages, and induction of VSG RNAi resulted in little change in phagocytosis of the arrested cells. Halting VSG synthesis resulted in stalled cells which swam directionally rather than tumbling, with a significant increase in swim velocity. This is possibly a consequence of increased rigidity of the cells due to a restricted surface coat in the absence of VSG synthesis. However if VSG RNAi was induced in the presence of anti-VSG221 antibodies, phagocytosis increased significantly. Blocking VSG synthesis resulted in reduced clearance of anti-VSG antibodies from the trypanosome surface, possibly as a consequence of the changed motility. This was particularly marked in cells in the G2/ M cell cycle stage, where the half-life of anti-VSG antibody increased from 39.3 ± 4.2 seconds to 99.2 ± 15.9 seconds after induction of VSG RNAi. The rates of internalisation of bulk surface VSG, or endocytic markers like transferrin, tomato lectin or dextran were not significantly affected by the VSG synthesis block. Efficient elimination of anti-VSG-antibody complexes from the trypanosome cell surface is therefore essential for trypanosome evasion of macrophages. These experiments highlight the essentiality of high rates of VSG recycling for the rapid removal of host opsonins from the parasite surface, and identify this process as a key parasite virulence factor during a chronic infection.
Collapse
Affiliation(s)
- Jackie L. Y. Cheung
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Nadina V. Wand
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Cher-Pheng Ooi
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Sophie Ridewood
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
| | - Richard J. Wheeler
- Department of Pathology, Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Gloria Rudenko
- Department of Life Sciences, Sir Alexander Fleming Building, Imperial College London, South Kensington, London, United Kingdom
- * E-mail:
| |
Collapse
|
4
|
Manna PT, Boehm C, Leung KF, Natesan SK, Field MC. Life and times: synthesis, trafficking, and evolution of VSG. Trends Parasitol 2014; 30:251-8. [PMID: 24731931 PMCID: PMC4007029 DOI: 10.1016/j.pt.2014.03.004] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Revised: 03/14/2014] [Accepted: 03/14/2014] [Indexed: 11/30/2022]
Abstract
Evasion of the acquired immune response in African trypanosomes is principally mediated by antigenic variation, the sequential expression of distinct variant surface glycoproteins (VSGs) at extremely high density on the cell surface. Sequence diversity between VSGs facilitates escape of a subpopulation of trypanosomes from antibody-mediated killing. Significant advances have increased understanding of the mechanisms underpinning synthesis and maintenance of the VSG coat. In this review, we discuss the biosynthesis, trafficking, and turnover of VSG, emphasising those unusual mechanisms that act to maintain coat integrity and to protect against immunological attack. We also highlight new findings that suggest the presence of unique or highly divergent proteins that may offer therapeutic opportunities, as well as considering aspects of VSG biology that remain to be fully explored.
Collapse
Affiliation(s)
- Paul T Manna
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, DD1 5EH, UK
| | - Cordula Boehm
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, DD1 5EH, UK
| | - Ka Fai Leung
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Senthil Kumar Natesan
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK
| | - Mark C Field
- Division of Biological Chemistry and Drug Discovery, University of Dundee, Dundee, DD1 5EH, UK.
| |
Collapse
|
5
|
Povelones ML, Gluenz E, Dembek M, Gull K, Rudenko G. Histone H1 plays a role in heterochromatin formation and VSG expression site silencing in Trypanosoma brucei. PLoS Pathog 2012; 8:e1003010. [PMID: 23133390 PMCID: PMC3486875 DOI: 10.1371/journal.ppat.1003010] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 09/20/2012] [Indexed: 11/30/2022] Open
Abstract
The African sleeping sickness parasite Trypanosoma brucei evades the host immune system through antigenic variation of its variant surface glycoprotein (VSG) coat. Although the T. brucei genome contains ∼1500 VSGs, only one VSG is expressed at a time from one of about 15 subtelomeric VSG expression sites (ESs). For antigenic variation to work, not only must the vast VSG repertoire be kept silent in a genome that is mainly constitutively transcribed, but the frequency of VSG switching must be strictly controlled. Recently it has become clear that chromatin plays a key role in silencing inactive ESs, thereby ensuring monoallelic expression of VSG. We investigated the role of the linker histone H1 in chromatin organization and ES regulation in T. brucei. T. brucei histone H1 proteins have a different domain structure to H1 proteins in higher eukaryotes. However, we show that they play a key role in the maintenance of higher order chromatin structure in bloodstream form T. brucei as visualised by electron microscopy. In addition, depletion of histone H1 results in chromatin becoming generally more accessible to endonucleases in bloodstream but not in insect form T. brucei. The effect on chromatin following H1 knock-down in bloodstream form T. brucei is particularly evident at transcriptionally silent ES promoters, leading to 6–8 fold derepression of these promoters. T. brucei histone H1 therefore appears to be important for the maintenance of repressed chromatin in bloodstream form T. brucei. In particular H1 plays a role in downregulating silent ESs, arguing that H1-mediated chromatin functions in antigenic variation in T. brucei. Trypanosoma brucei causes African sleeping sickness, endemic to sub-Saharan Africa. Bloodstream form T. brucei is covered with a dense coat of variant surface glycoprotein (VSG). Only one VSG is expressed at a time out of a vast repertoire of ∼1500 VSGs. The active VSG is transcribed in a telomeric VSG expression site (ES), and VSG switching allows immune evasion. Exactly how monoallelic exclusion of VSG ESs operates, and how switching between ESs is mediated remains mysterious, although epigenetics and chromatin structure clearly play a major role. The linker histone H1 is thought to orchestrate higher order chromatin structure in eukaryotes, but its exact function is unclear. We investigated the role of histone H1 in the regulation of antigenic variation in T. brucei. We show that histone H1 is associated with chromatin and is required for higher order chromatin structure. Depletion of histone H1 results in derepression of silent VSG ES promoters, indicating that H1-mediated chromatin functions in antigenic variation in T. brucei.
Collapse
Affiliation(s)
- Megan L. Povelones
- Division of Cell and Molecular Biology, Imperial College London, South Kensington, London, United Kingdom
| | - Eva Gluenz
- The Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Marcin Dembek
- Division of Cell and Molecular Biology, Imperial College London, South Kensington, London, United Kingdom
| | - Keith Gull
- The Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Gloria Rudenko
- Division of Cell and Molecular Biology, Imperial College London, South Kensington, London, United Kingdom
- * E-mail:
| |
Collapse
|
6
|
Bayer-Santos E, Gentil LG, Cordero EM, Corrêa PRC, da Silveira JF. Regulatory elements in the 3' untranslated region of the GP82 glycoprotein are responsible for its stage-specific expression in Trypanosoma cruzi metacyclic trypomastigotes. Acta Trop 2012; 123:230-3. [PMID: 22579673 DOI: 10.1016/j.actatropica.2012.03.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/13/2012] [Accepted: 03/14/2012] [Indexed: 11/29/2022]
Abstract
Gene expression in Trypanosoma cruzi is regulated at the post-transcriptional level and cis-acting elements present in the 3' untranslated region (3'UTR) play an important role by interacting with regulatory proteins. Previous studies demonstrated that the GP82 surface glycoprotein, which is involved in host cell invasion, is up-regulated in the infective metacyclic trypomastigote form, and that GP82 mRNA half-life is longer in this form compared to the non-infective epimastigote form. Here, we demonstrate that the 3'UTR of the GP82 transcript is involved in this developmental regulation, promoting higher expression of the green fluorescent protein (GFP) reporter in metacyclic trypomastigotes than in epimastigotes. A series of stepwise deletions in the 3'UTR was created and results suggest that the mechanism regulating GP82 expression involves multiple elements in the 3'UTR.
Collapse
Affiliation(s)
- Ethel Bayer-Santos
- Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, UNIFESP, Rua Botucatu 862, CEP 04023-062 São Paulo, Brazil
| | | | | | | | | |
Collapse
|
7
|
Abstract
African trypanosomes evade the host immune response through antigenic variation, which is achieved by periodically expressing different variant surface glycoproteins (VSGs). VSG expression is monoallelic such that only one of approximately 15 telomeric VSG expression sites (ESs) is transcribed at a time. Epigenetic regulation is involved in VSG control but our understanding of the mechanisms involved remains incomplete. Histone deacetylases are potential drug targets for diseases caused by protozoan parasites. Here, using recombinant expression we show that the essential Trypanosoma brucei deacetylases, DAC1 (class I) and DAC3 (class II) display histone deacetylase activity. Both DAC1 and DAC3 are nuclear proteins in the bloodstream stage parasite, while only DAC3 remains concentrated in the nucleus in insect-stage cells. Consistent with developmentally regulated localization, DAC1 antagonizes SIR2rp1-dependent telomeric silencing only in the bloodstream form, indicating a conserved role in the control of silent chromatin domains. In contrast, DAC3 is specifically required for silencing at VSG ES promoters in both bloodstream and insect-stage cells. We conclude that DAC1 and DAC3 play distinct roles in subtelomeric gene silencing and that DAC3 represents the first readily druggable target linked to VSG ES control in the African trypanosome.
Collapse
Affiliation(s)
- Qiao-Ping Wang
- London School of Hygiene and Tropical MedicineKeppel Street, London WC1E 7HT, UK
- Center for Parasitic Organisms, State Key Laboratory of Biocontrol, School of Life Sciences, Key Laboratory of Tropical Diseases Control, Ministry of Education, Zhongshan Medical College, Sun Yat-Sen UniversityGuangzhou 510275, China
| | - Taemi Kawahara
- London School of Hygiene and Tropical MedicineKeppel Street, London WC1E 7HT, UK
| | - David Horn
- London School of Hygiene and Tropical MedicineKeppel Street, London WC1E 7HT, UK
| |
Collapse
|
8
|
Wang YN, Wang M, Field MC. Trypanosoma brucei: trypanosome-specific endoplasmic reticulum proteins involved in variant surface glycoprotein expression. Exp Parasitol 2010; 125:208-21. [PMID: 20109450 PMCID: PMC2877885 DOI: 10.1016/j.exppara.2010.01.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Revised: 01/13/2010] [Accepted: 01/18/2010] [Indexed: 12/22/2022]
Abstract
In Trypanosoma brucei the GPI-anchored variant surface glycoprotein (VSG) represents approximately 90% of cell surface protein and a major proportion of endoplasmic reticulum (ER) biosynthetic output. We identified four trypanosomatid-specific genes encoding candidate ER-resident proteins; all were required for normal proliferation. For Tb11.01.2640 and Tb11.01.8120, an increase in VSG abundance was found on silencing, while the protein products localized to the ER; we designated these ERAP32 and ERAP18 for ER-associated protein of 32kDa and 18kDa. Silencing ERAP32 or ERAP18 did not alter expression levels of ISG65 or ISG75, the major surface trans-membrane domain proteins. Surface biotinylation or immunoflorescence did not identify intracellular VSG accumulation, while FACS and fluorescence microscopy indicated that the cells were not increased in size, arguing for increased VSG density on the cell surface. Therefore, ERAP32 and ERAP18 are trypanosome-specific ER-localized proteins with a major role in VSG protein export and, contrary to current paradigms, VSG is not saturated on the cell surface.
Collapse
Affiliation(s)
- Ya-Nan Wang
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Ming Wang
- College of Veterinary Medicine, China Agricultural University, Beijing 100193, China
| | - Mark C. Field
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| |
Collapse
|
9
|
Field MC, Sergeenko T, Wang YN, Böhm S, Carrington M. Chaperone requirements for biosynthesis of the trypanosome variant surface glycoprotein. PLoS One 2010; 5:e8468. [PMID: 20052285 PMCID: PMC2797082 DOI: 10.1371/journal.pone.0008468] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2009] [Accepted: 12/03/2009] [Indexed: 11/27/2022] Open
Abstract
Background Trypanosoma brucei does not respond transcriptionally to several endoplasmic reticulum (ER) stress conditions, including tunicamycin or dithiothreitol, indicating the absence of a conventional unfolded protein response. This suggests divergent mechanisms for quality control (QC) of ER protein folding and export may be present in trypanosomes. As the variant surface glycoprotein (VSG) represents ∼90% of trypanosome plasma membrane protein, it is possible that VSG has evolved to fold efficiently to minimize ER folding burden. Methodology/Principal Findings We demonstrate the presence of a QC system by pharmacological inhibition of the trypanosome 26S proteasome. This indicates active proteasome-mediated VSG turnover as ∼2.5 fold more VSG is recovered from cell lysates following MG132 inhibition. An in silico scan of the trypanosome genome identified 28 open reading frames likely to encode polypeptides participating in ER nascent chain maturation. By RNA interference we monitored the importance of these gene products to proliferation, VSG abundance and cell morphology. 68% of the cohort were required for normal proliferation, and depletion of most of these factors resulted in increased VSG abundance, suggesting involvement in ERQC and degradation. Conclusions/Significance The retention of genes for, and the involvement of many gene products in, VSG folding indicates a substantial complexity within the pathways required to perform this role. Counterintuitively, for a super-abundant antigen VSG is apparently made in excess. The biosynthetic excess VSG appears to be turned over efficiently by the proteasome, implying that considerable VSG is rejected by the trypanosome ERQC mechanism. Accordingly, the VSG polypeptide is not well optimized for folding, as only ∼30% attains the native state. Finally as much of the core ERQC system is functionally conserved in trypanosomes, the pathway has an ancient evolutionary origin, and was present in the last common eukaryotic ancestor.
Collapse
Affiliation(s)
- Mark C Field
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom.
| | | | | | | | | |
Collapse
|
10
|
Gentil LG, Cordero EM, do Carmo MS, dos Santos MRM, da Silveira JF. Posttranscriptional mechanisms involved in the control of expression of the stage-specific GP82 surface glycoprotein in Trypanosoma cruzi. Acta Trop 2009; 109:152-8. [PMID: 19013421 DOI: 10.1016/j.actatropica.2008.10.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Revised: 09/29/2008] [Accepted: 10/14/2008] [Indexed: 01/08/2023]
Abstract
Trypanosoma cruzi metacyclic trypomastigotes express the developmentally regulated GP82 glycoprotein, which is implicated in host cell invasion. Although GP82 mRNA and protein are not present and the mRNAs barely detectable in epimastigotes, nuclear run-on analysis showed that it is transcribed in both stages. This result indicates that accumulation of transcripts in metacyclic forms is not due to increased transcription of the GP82 gene. To investigate whether mRNA stability may be responsible for the differences in the steady-state levels of this mRNA, parasites were treated with actinomycin D or cycloheximide. When treated with actinomycin D, the half-lives estimated for GP82 transcripts were about 6h in metacyclic trypomastigotes and 0.5h in epimastigotes. In the presence of cycloheximide, the levels of GP82 mRNA decayed slightly after 8h in metacyclic trypomastigotes, whereas in epimastigotes the levels of this mRNA increased. This effect suggests a stabilizing mechanism acting in metacyclic trypomastigotes and a destabilizing mechanism in epimastigotes which could be mediated by an element present in the 3'-UTR of the transcripts. Consistent with this finding, northern blot analysis showed that GP82 mRNAs were mobilized to polysomes and consequently translated, but only in metacyclic trypomastigotes.
Collapse
Affiliation(s)
- Luciana Girotto Gentil
- Department of Microbiology, Immunology and Parasitology, Escola Paulista de Medicina, UNIFESP, Rua Botucatu, São Paulo, Brazil
| | | | | | | | | |
Collapse
|
11
|
Cordero EM, Gentil LG, Crisante G, Ramírez JL, Yoshida N, Añez N, Franco da Silveira J. Expression of GP82 and GP90 surface glycoprotein genes of Trypanosoma cruzi during in vivo metacyclogenesis in the insect vector Rhodnius prolixus. Acta Trop 2008; 105:87-91. [PMID: 17889817 DOI: 10.1016/j.actatropica.2007.08.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2007] [Accepted: 08/14/2007] [Indexed: 10/22/2022]
Abstract
Trypanosoma cruzi, the parasite causing Chagas' disease, relies on triatomines for its transmission. T. cruzi metacyclic trypomastigotes express GP82 and GP90, which are developmentally regulated surface proteins that have been implicated in host cell invasion. We used quantitative RT-PCR to quantify GP90 and GP82 mRNA levels expressed by T. cruzi in the digestive tract of experimentally infected Rhodnius prolixus at different times post infection. Translation of these transcripts was assessed by immunofluorescence using specific monoclonal antibodies against GP90 and GP82. We found that although GP82 and GP90 proteins were not detected in epimastigote cells by immunofluorescence, transcripts were present at lower levels. Increased levels of GP90 and GP82 transcripts and the appearance of these proteins on the parasite surface were accompanied by morphological differentiation from epimastigotes into metacyclic forms. Our data suggest that during in vivo metacyclogenesis there is a coordinated mechanism that links stabilization of GP90 and GP82 mRNAs with their translation.
Collapse
Affiliation(s)
- Esteban M Cordero
- Departamento de Microbiologia, Imunologia e Parasitologia, Escola Paulista de Medicina, UNIFESP, Rua Botucatu 862, CEP 04023-062, São Paulo, Brazil
| | | | | | | | | | | | | |
Collapse
|
12
|
Grandgenett PM, Otsu K, Wilson HR, Wilson ME, Donelson JE. A function for a specific zinc metalloprotease of African trypanosomes. PLoS Pathog 2007; 3:1432-45. [PMID: 17953481 PMCID: PMC2034397 DOI: 10.1371/journal.ppat.0030150] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2007] [Accepted: 09/04/2007] [Indexed: 11/19/2022] Open
Abstract
The Trypanosoma brucei genome encodes three groups of zinc metalloproteases, each of which contains approximately 30% amino acid identity with the major surface protease (MSP, also called GP63) of Leishmania. One of these proteases, TbMSP-B, is encoded by four nearly identical, tandem genes transcribed in both bloodstream and procyclic trypanosomes. Earlier work showed that RNA interference against TbMSP-B prevents release of a recombinant variant surface glycoprotein (VSG) from procyclic trypanosomes. Here, we used gene deletions to show that TbMSP-B and a phospholipase C (GPI-PLC) act in concert to remove native VSG during differentiation of bloodstream trypanosomes to procyclic form. When the four tandem TbMSP-B genes were deleted from both chromosomal alleles, bloodstream B (-/-) trypanosomes could still differentiate to procyclic form, but VSG was removed more slowly and in a non-truncated form compared to differentiation of wild-type organisms. Similarly, when both alleles of the single-copy GPI-PLC gene were deleted, bloodstream PLC (-/-) cells could still differentiate. However, when all the genes for both TbMSP-B and GPI-PLC were deleted from the diploid genome, the bloodstream B (-/-) PLC (-/-) trypanosomes did not proliferate in the differentiation medium, and 60% of the VSG remained on the cell surface. Inhibitors of cysteine proteases did not affect this result. These findings demonstrate that removal of 60% of the VSG during differentiation from bloodstream to procyclic form is due to the synergistic activities of GPI-PLC and TbMSP-B.
Collapse
Affiliation(s)
- Paul M Grandgenett
- Interdepartmental Genetics Program, University of Iowa, Iowa City, Iowa, United States of America
| | - Keiko Otsu
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Helen R Wilson
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Mary E Wilson
- Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Department of Microbiology, University of Iowa, Iowa City, Iowa, United States of America
- Veterans Affairs Medical Center, Iowa City, Iowa, United States of America
| | - John E Donelson
- Interdepartmental Genetics Program, University of Iowa, Iowa City, Iowa, United States of America
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
- * To whom correspondence should be addressed. E-mail:
| |
Collapse
|
13
|
Hughes K, Wand M, Foulston L, Young R, Harley K, Terry S, Ersfeld K, Rudenko G. A novel ISWI is involved in VSG expression site downregulation in African trypanosomes. EMBO J 2007; 26:2400-10. [PMID: 17431399 PMCID: PMC1864976 DOI: 10.1038/sj.emboj.7601678] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2007] [Accepted: 03/15/2007] [Indexed: 11/08/2022] Open
Abstract
African trypanosomes show monoallelic expression of one of about 20 telomeric variant surface glycoprotein (VSG) gene-expression sites (ESs) while multiplying in the mammalian bloodstream. We screened for genes involved in ES silencing using flow cytometry and RNA interference (RNAi). We show that a novel member of the ISWI family of SWI2/SNF2-related chromatin-remodelling proteins (TbISWI) is involved in ES downregulation in Trypanosoma brucei. TbISWI has an atypical protein architecture for an ISWI, as it lacks characteristic SANT domains. Depletion of TbISWI by RNAi leads to 30-60-fold derepression of ESs in bloodstream-form T. brucei, and 10-17-fold derepression in insect form T. brucei. We show that although blocking synthesis of TbISWI leads to derepression of silent VSG ES promoters, this does not lead to fully processive transcription of silent ESs, or an increase in ES-activation rates. VSG ES activation in African trypanosomes therefore appears to be a multistep process, whereby an increase in transcription from a silent ES promoter is necessary but not sufficient for full ES activation.
Collapse
Affiliation(s)
- Katie Hughes
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
| | - Matthew Wand
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
| | - Lucy Foulston
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
| | - Rosanna Young
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
| | - Kate Harley
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
| | - Stephen Terry
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
| | - Klaus Ersfeld
- Department of Biological Sciences, University of Hull, Hull, UK
| | - Gloria Rudenko
- Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, UK
- The Peter Medawar Building for Pathogen Research, University of Oxford, South Parks Road, Oxford OX1 3SY, UK. Tel.: +44 1865 281 548; Fax: +44 1865 281 894; E-mail:
| |
Collapse
|
14
|
Janzen CJ, Lander F, Dreesen O, Cross GAM. Telomere length regulation and transcriptional silencing in KU80-deficient Trypanosoma brucei. Nucleic Acids Res 2004; 32:6575-84. [PMID: 15602000 PMCID: PMC545459 DOI: 10.1093/nar/gkh991] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
KU is a heterodimer, consisting of approximately 70 and approximately 80 kDa subunits (KU70 and KU80, respectively), which is involved in a variety of nuclear functions. We generated tbKU80-deficient trypanosomes to explore the potential role of the tbKU complex in telomere maintenance and transcriptional regulation of variant surface glycoprotein (VSG) genes in Trypanosoma brucei. Using real-time PCR, we demonstrated that the expression of several different VSG genes remains tightly regulated in tbKU80-deficient bloodstream-form cell lines, suggesting that VSG transcription profiles do not change in these cells. Owing to developmental silencing of the VSG Expression Sites (ES), no VSG is transcribed in the insect procyclic stage. With a green fluorescent protein reporter system, we showed that tbKU80-deficient mutants are fully capable of ES silencing after differentiation into procyclic forms. Using T7 RNA polymerase to explore the transcriptional accessibility of ES chromatin in vivo, we demonstrated that tbKU80-deficient bloodstream-form cells were able to generate transcriptionally repressed ES chromatin after differentiation into procyclic cells. Finally, we demonstrated progressive telomere shortening in tbKU80-deficient mutants. The possible function of tbKU80 in telomere maintenance and regulation of telomerase is discussed.
Collapse
Affiliation(s)
- Christian J Janzen
- Laboratory of Molecular Parasitology, The Rockefeller University, Box 185, 1230 York Avenue, New York, NY 10021-6399, USA
| | | | | | | |
Collapse
|
15
|
Staalsoe T, Nielsen MA, Vestergaard LS, Jensen ATR, Theander TG, Hviid L. In vitro selection of Plasmodium falciparum 3D7 for expression of variant surface antigens associated with severe malaria in African children. Parasite Immunol 2004; 25:421-7. [PMID: 14651589 DOI: 10.1111/j.1365-3024.2003.00652.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
P. falciparum-infected red blood cells (IRBC) can adhere to endothelial host receptors through parasite-encoded, clonally variant surface antigens (VSA). The VSA-mediated IRBC adhesion and the acquired VSA-specific antibody response have both been linked to IRBC organ tropism and disease severity. Parasites isolated from young children with severe malaria (SM) tend to express a limited and conserved set of VSA (VSASM) that are both stronger and more commonly recognized by IgG in the plasma of malaria-exposed individuals than VSA (VSAUM) expressed by parasites causing uncomplicated malaria (UM) in older semi-immune children. Establishment of the genetic mechanism underlying changes in VSA expression in response to in vitro selective pressure is now possible because of the availability of the entire genomic sequence of the P. falciparum clone 3D7. As a first step towards direct molecular identification of VSASM-encoding genes in 3D7, we report here a method of enforcing expression of VSASM-like antigens in this parasite clone by a novel selection method using plasma from semi-immune children with low VSAUM-specific, but high VSASM-specific, IgG reactivity. In addition to the resulting increase in VSA-specific IgG recognition, VSASM-expressing 3D7(3D7-Dodowa1) showed reduced adhesion to CD36. Finally, levels of IgG specific for the VSA expressed by 3D7-Dodowa1 were uniformly higher than those of IgG with specificity for VSA expressed by the unselected 3D7 in plasma samples from geographically and epidemiologically diverse areas of endemic parasite transmission. The described selection method appears a useful tool in the identification of genes encoding VSA involved in severe and life-threatening P. falciparum malaria.
Collapse
MESH Headings
- Adolescent
- Adult
- Africa
- Animals
- Antibodies, Protozoan/blood
- Antibodies, Protozoan/immunology
- Antigens, Protozoan/genetics
- Antigens, Protozoan/immunology
- CD36 Antigens/physiology
- CHO Cells
- Cell Adhesion
- Child
- Cricetinae
- Erythrocytes/parasitology
- Erythrocytes/physiology
- Gene Expression
- Humans
- Immunoglobulin G/blood
- Malaria, Falciparum/epidemiology
- Malaria, Falciparum/immunology
- Malaria, Falciparum/parasitology
- Middle Aged
- Plasmodium falciparum/genetics
- Plasmodium falciparum/immunology
- Selection, Genetic
- Variant Surface Glycoproteins, Trypanosoma/biosynthesis
- Variant Surface Glycoproteins, Trypanosoma/classification
- Variant Surface Glycoproteins, Trypanosoma/genetics
- Variant Surface Glycoproteins, Trypanosoma/immunology
Collapse
Affiliation(s)
- Trine Staalsoe
- Centre for Medical Parasitology at Department of Infectious Diseases, Copenhagen University Hospital, Copenhagen, Denmark.
| | | | | | | | | | | |
Collapse
|
16
|
te Vruchte D, Aitcheson N, Rudenko G. Downregulation of Trypanosoma brucei VSG expression site promoters on circular bacterial artificial chromosomes. Mol Biochem Parasitol 2003; 128:123-33. [PMID: 12742579 DOI: 10.1016/s0166-6851(03)00053-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Trypanosoma brucei has about 20 telomeric variant surface glycoprotein (VSG) gene expression sites (ESs), which are downregulated in the insect form. We investigated the transcriptional behaviour of ES promoters on bacterial artificial chromosomes (BACs) containing two different ESs and their flanking regions on fragments of about 140kb. Four different BACs containing either the 221 or the VO2 ES were introduced into insect form T. brucei. The BACs replicated as circular episomes as shown using pulsed field gel (PFG) analysis of DNA exposed to increasing doses of gamma radiation, and digestion with Dam methylation-sensitive restriction enzymes. BAC copy number per cell varied from about 3 for the 221 ES BACs to about 15 for the VO2 ES BACs. Increasing drug selection pressure on the VO2 BAC T. brucei transformants resulted in amplification to about 80 BACs per cell. Although BACs were maintained in the absence of drug selection for at least 56 days, copy number fell and there was no evidence for centromere activity. ES promoters on small plasmid episomes introduced into insect form T. brucei in transient transfections are derepressed. In contrast, ES promoters on large BAC episomes are downregulated both on the original ES BACs, and on ES BACs selected for a drug marker driven by a rDNA promoter fused to the BAC vector. This indicates that downregulation of ES promoters in insect form T. brucei is influenced by genomic context, but does not necessitate proximity to a chromosome end.
Collapse
Affiliation(s)
- Daniëlle te Vruchte
- The Peter Medawar Building for Pathogen Research, University of Oxford, South Parks Road, Oxford OX1 3SY, UK
| | | | | |
Collapse
|
17
|
Ginger ML, Blundell PA, Lewis AM, Browitt A, Günzl A, Barry JD. Ex vivo and in vitro identification of a consensus promoter for VSG genes expressed by metacyclic-stage trypanosomes in the tsetse fly. Eukaryot Cell 2002; 1:1000-9. [PMID: 12477800 PMCID: PMC138762 DOI: 10.1128/ec.1.6.1000-1009.2002] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The trypanosome variant surface glycoprotein (VSG) is first expressed during differentiation to the infective, metacyclic population in tsetse fly salivary glands. Unlike the VSG genes expressed by bloodstream form trypanosomes, metacyclic VSGs (MVSGs) have their own promoters. The scarcity of metacyclic cells has meant that only indirect approaches have been used to study these promoters, and not even their identities have been agreed on. Here, we isolated trypanosomes by dissection from salivary glands and used an approach involving 5' rapid amplification of cDNA ends to identify the transcription start site of three MVSGs. This shows that the authentic start site is that proposed for the MVAT series of MVSGs (K. S. Kim and J. E. Donelson, J. Biol. Chem. 272:24637-24645, 1997). In the more readily accessible procyclic trypanosome stage, where MVSGs are normally silent, we used reporter gene assays and linker scanning analysis to confirm that the 67 bp upstream of the start site is a promoter. This is confirmed further by accurate initiation in a homologous in vitro transcription system. We show also that MVSG promoters become derepressed when tested outwith their endogenous, subtelomeric loci. The MVSG promoters are only loosely conserved with bloodstream VSG promoters, and our detailed analysis of the 1.63 MVSG promoter reveals that its activity depends on the start site itself and sequences 26 to 49 bp and 56 to 60 bp upstream. These are longer than those necessary for the bloodstream promoter.
Collapse
Affiliation(s)
- Michael L Ginger
- Wellcome Centre for Molecular Parasitology, Anderson College, University of Glasgow, Glasgow G11 6NU, United Kingdom
| | | | | | | | | | | |
Collapse
|
18
|
Abstract
The glycosyl phosphatidylinositol anchor of the trypanosome variant surface glycoprotein contains myristate as its sole fatty acid component. Surprisingly, there does not appear to be enough myristate in either the parasite or its host's bloodstream to sustain myristoylation of the enormous quantity of variant surface glycoprotein produced. Here, we discuss how the trypanosome solves its myristate dilemma. The parasite not only efficiently salvages and processes myristate from the bloodstream, but it also makes myristate de novo using a recently discovered specialized fatty acid synthesis system.
Collapse
Affiliation(s)
- K S Paul
- Dept Biological Chemistry, Johns Hopkins Medical School, 725 N. Wolfe Street, Baltimore, MD 21205, USA
| | | | | | | |
Collapse
|
19
|
Duszenko M, Kang X, Böhme U, Hömke R, Lehner M. In vitro translation in a cell-free system from Trypanosoma brucei yields glycosylated and glycosylphosphatidylinositol-anchored proteins. Eur J Biochem 1999; 266:789-97. [PMID: 10583372 DOI: 10.1046/j.1432-1327.1999.00897.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
African trypanosomes escape many cellular and unspecific immune reactions by the expression of a protective barrier formed from a repertoire of several hundred genes encoding immunologically distinct variant surface glycoproteins (VSGs). All mature VSGs are glycosylphosphatidylionositol-anchored and N-glycosylated. To study trypanosome-specific post-translational modifications of VSG, a cell-free system capable of in vitro translation, translocation into the rough endoplasmic reticulum, N-glycosylation and glycosylphosphatidylinositol-anchor addition was established using lysates of the bloodstream form of Trypanosoma brucei. Monitoring protein synthesis by [35S]methionine incorporation, labeled protein bands were readily detected by fluorography following SDS/PAGE. Appearance of these bands increased during a time-course of 45 min and was sensitive to cycloheximide but not chloramphenicol treatment. Efficiency of this system, in terms of incorporation of radiolabeled amino acids into newly formed proteins, is similar to reticulocyte lysates. The system does not, however, allow initiation of protein synthesis. Depending on the clone used, immunoprecipitation revealed one or two newly formed VSG bands. Upon digestion with N-glycosidase F these bands resulted in a single band of a lower apparent molecular mass, indicating that newly synthesized VSG underwent translocation and glycosylation in the cell-free system. Biotinylation of VSG and a combination of precipitation with immobilized avidin and detection of VSG using antibodies specific for clones and cross-reacting determinants revealed that newly formed VSG contained the glycosylphosphatidylinositol anchor.
Collapse
Affiliation(s)
- M Duszenko
- Physiologisch-chemisches Institut der Universität Tübingen, Germany.
| | | | | | | | | |
Collapse
|
20
|
Graham SV, Terry S, Barry JD. A structural and transcription pattern for variant surface glycoprotein gene expression sites used in metacyclic stage Trypanosoma brucei. Mol Biochem Parasitol 1999; 103:141-54. [PMID: 10551359 DOI: 10.1016/s0166-6851(99)00128-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
African trypanosomes first express the variant surface glycoprotein (VSG) at the metacyclic stage in the tsetse fly vector, in preparation for transfer into the mammal. Metacyclic (M)VSGs comprise a specific VSG repertoire subset and their expression is regulated differently from that of bloodstream VSGs, involving exclusively transcriptional regulation during the life cycle. To identify basic structural and functional features that may be common to MVSG telomeric transcription units, we have characterized the anatomy and transcription of the telomere containing the ILTat 1.61 MVSG gene. This telomere contains pseudogenes of the ESAG1 and ESAG9 families found in bloodstream VSG transcription units. The 1.61 MVSG occupies a monocistronic transcription unit and is transcriptionally controlled through the life cycle. The 1.61, and also the 1.22, MVSG transcription initiation site sequences resemble eukaryotic initiator elements. Sequence comparison reveals that four out of five characterized MVSG expression sites have a conserved region 2.0-4.7 kb long upstream of the MVSG. In some cases, this region contains not only the transcription initiation site that we have observed to be active in fly-transmitted trypanosomes but also, upstream, another sequence, described elsewhere as a 'putative promoter' for the MVAT set of M/VSGs (Nagoshi YL, Alarcon CM, Donelson JE. A monocistronic transcript for a trypanosome variant surface glycoprotein, Mol Biochem Parasitol 1995;72:33-45). In fly-transmitted trypanosomes, the latter element is transcriptionally silent. Our analysis of the structure of MVSG telomeres suggests that metacyclic expression sites arose from bloodstream expression sites.
Collapse
Affiliation(s)
- S V Graham
- Wellcome Centre for Molecular Parasitology, The Anderson College, University of Glasgow, Scotland, UK
| | | | | |
Collapse
|
21
|
Ferguson MA, Brimacombe JS, Brown JR, Crossman A, Dix A, Field RA, Güther ML, Milne KG, Sharma DK, Smith TK. The GPI biosynthetic pathway as a therapeutic target for African sleeping sickness. Biochim Biophys Acta 1999; 1455:327-40. [PMID: 10571022 DOI: 10.1016/s0925-4439(99)00058-7] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
African sleeping sickness is a debilitating and often fatal disease caused by tsetse fly transmitted African trypanosomes. These extracellular protozoan parasites survive in the human bloodstream by virtue of a dense cell surface coat made of variant surface glycoprotein. The parasites have a repertoire of several hundred immunologically distinct variant surface glycoproteins and they evade the host immune response by antigenic variation. All variant surface glycoproteins are anchored to the plasma membrane via glycosylphosphatidylinositol membrane anchors and compounds that inhibit the assembly or transfer of these anchors could have trypanocidal potential. This article compares glycosylphosphatidylinositol biosynthesis in African trypanosomes and mammalian cells and identifies several steps that could be targets for the development of parasite-specific therapeutic agents.
Collapse
Affiliation(s)
- M A Ferguson
- Department of Biochemistry, University of Dundee, UK.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Ferguson MA. The structure, biosynthesis and functions of glycosylphosphatidylinositol anchors, and the contributions of trypanosome research. J Cell Sci 1999; 112 ( Pt 17):2799-809. [PMID: 10444375 DOI: 10.1242/jcs.112.17.2799] [Citation(s) in RCA: 418] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The discovery of glycosylphosphatidylinositol (GPI) membrane anchors has had a significant impact on several areas of eukaryote cell biology. Studies of the African trypanosome, which expresses a dense surface coat of GPI-anchored variant surface glycoprotein, have played important roles in establishing the general structure of GPI membrane anchors and in delineating the pathway of GPI biosynthesis. The major cell-surface molecules of related parasites are also rich in GPI-anchored glycoproteins and/or GPI-related glycophospholipids, and differences in substrate specificity between enzymes of trypanosomal and mammalian GPI biosynthesis may have potential for the development of anti-parasite therapies. Apart from providing stable membrane anchorage, GPI anchors have been implicated in the sequestration of GPI-anchored proteins into specialised membrane microdomains, known as lipid rafts, and in signal transduction events.
Collapse
Affiliation(s)
- M A Ferguson
- Division of Molecular Parasitology and Biological Chemistry, Department of Biochemistry, The Wellcome Trust Building, University of Dundee, Dundee DD1 5EH, UK.
| |
Collapse
|
23
|
Laufer G, Schaaf G, Bollgönn S, Günzl A. In vitro analysis of alpha-amanitin-resistant transcription from the rRNA, procyclic acidic repetitive protein, and variant surface glycoprotein gene promoters in Trypanosoma brucei. Mol Cell Biol 1999; 19:5466-73. [PMID: 10409736 PMCID: PMC84388 DOI: 10.1128/mcb.19.8.5466] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In Trypanosoma brucei, transcription resistant to the mushroom toxin alpha-amanitin is not restricted to the rRNA genes (rDNA), as in higher eukaryotes, but extends to genes encoding the major cell surface proteins variant surface glycoprotein (VSG) and procyclin or procyclic acidic repetitive protein (PARP). Here, we report the development of a homologous cell extract from procyclic T. brucei cells in which rDNA and PARP A and VSG gene promoters drive efficient, accurate, and alpha-amanitin-resistant transcription. A comparative analysis revealed that transcription from the three promoters generally required identical reaction conditions for maximal efficiency. Nevertheless, PARP promoter transcription proved to be exceptional by its high efficiency, its lag phase, a high template DNA concentration optimum, and its tolerance to increasing concentrations of Mn(2+). Mutational analysis for both the PARP and rDNA promoters showed that the proximal and distal core elements were essential for efficient transcription in vitro. Deletion of the upstream control regions (UCRs), however, had a different effect. Whereas PARP UCR deletion reduced transcription efficiency almost 10-fold, deletion of the rDNA UCR had only a minor effect on transcription efficiency.
Collapse
Affiliation(s)
- G Laufer
- Abteilung Zellbiologie, Zoologisches Institut der Universität Tübingen, D-72076 Tübingen, Germany
| | | | | | | |
Collapse
|
24
|
McAndrew M, Graham S, Hartmann C, Clayton C. Testing promoter activity in the trypanosome genome: isolation of a metacyclic-type VSG promoter, and unexpected insights into RNA polymerase II transcription. Exp Parasitol 1998; 90:65-76. [PMID: 9709032 DOI: 10.1006/expr.1998.4317] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In trypanosomes, most genes are arranged in polycistronic transcription units. Individual mRNAs are generated by 5'-trans splicing and 3' polyadenylation. Remarkably, no regulation of RNA polymerase II transcription has been detected although many RNAs are differentially expressed during kinetoplastid life cycles. Demonstration of specific class II promoters is complicated by the difficulty in distinguishing between genuine promoter activity and stimulation of trans splicing. Using vectors that were designed to allow the detection of low promoter activities in a transcriptionally silent chromosomal context, we isolated a novel trypanosome RNA polymerase I promoter. We were however unable to detect class II promoter activity in any tested DNA fragment. We also integrated genes which were preceded by a T3 promoter into the genome of cells expressing bacteriophage T3 polymerase: surprisingly, transcription was alpha-amanitin sensitive. One possible interpretation of these results is that in trypanosomes, RNA polymerase II initiation is favored by genomic accessibility and double-strand melting.
Collapse
Affiliation(s)
- M McAndrew
- Zentrum für Molekulare Biologie, Heidelberg, Im Neuenheimer Feld 282, D-69120, Heidelberg, Germany
| | | | | | | |
Collapse
|
25
|
Blundell PA, van Leeuwen F, Brun R, Borst P. Changes in expression site control and DNA modification in Trypanosoma brucei during differentiation of the bloodstream form to the procyclic form. Mol Biochem Parasitol 1998; 93:115-30. [PMID: 9662033 DOI: 10.1016/s0166-6851(98)00030-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We have adapted a system for in vitro differentiation of a monomorphic trypanosome strain to monitor changes in transcription and DNA modification in expression sites during the transition of the bloodstream-form to the procyclic trypanosome. We have used trypanosomes that have a gene for drug resistance integrated in an expression site, just downstream of either an expression site promoter, or a ribosomal promoter replacing the endogenous promoter. During the transition from bloodstream-form to procyclic, the promoters in an active expression site behave as expected on the basis of previous work on these promoters in procyclics, i.e. the ribosomal replacement promoter remains fully active, whereas the expression site promoter is (incompletely) down-regulated. A silent bloodstream-form expression site promoter does not remain tightly silenced, however. There is a transient increase of transcription of the marker gene during the transition from bloodstream-form to procyclic, indicating that the control of silent expression sites differs between the bloodstream-form and the procyclic trypanosome, and that a short time is required to reset the silencing mechanisms. One of the differences between bloodstream-form and procyclic trypanosomes is the presence of the modified base beta-D-glucosyl-hydroxymethyluracil (J) in and around bloodstream-form expression sites. We have studied loss of this DNA modification and find that the change in expression site control from bloodstream-form to procyclic does not require active removal of J. Base J is lost by synthesis of new, unmodified DNA, which happens after the major changes in expression site transcription have occurred.
Collapse
Affiliation(s)
- P A Blundell
- Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam
| | | | | | | |
Collapse
|
26
|
Graham SV, Wymer B, Barry JD. A trypanosome metacyclic VSG gene promoter with two functionally distinct, life cycle stage-specific activities. Nucleic Acids Res 1998; 26:1985-90. [PMID: 9518493 PMCID: PMC147490 DOI: 10.1093/nar/26.8.1985] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In the mammalian bloodstream, African trypanosomes express the variant surface glycoprotein (VSG), continual switching of which allows evasion of the host immune response. Bloodstream VSG genes are transcribed from polycistronic bloodstream expression sites with promoters which are located 45-60 kb upstream. These promoters are not exclusively stage-regulated, being active in the insect midgut stage where VSG is not expressed. However, the metacyclic VSG (M-VSG) genes, a small subset activated when VSG synthesis begins in the metacyclic stage in the tsetse fly salivary glands, are transcriptionally activated specifically in that stage from promoters <3 kb upstream. Using deletion mapping and transient transfection, we show that the entire 1.22 M-VSG gene promoter region (171 bp) is required for full activity in metacyclic-derived trypanosomes. However, a subsidiary, bloodstream stage-specific activity is present in its 5' half which directs transcription initiation very close to the initiation site used in metacyclic-derived trypanosomes. Our results imply that the M-VSG gene promoter is longer and more complex than other VSG gene promoters.
Collapse
Affiliation(s)
- S V Graham
- Wellcome Unit of Molecular Parasitology, University of Glasgow, Anderson College, 56 Dumbarton Road, Glasgow G11 6NU, UK
| | | | | |
Collapse
|
27
|
Affiliation(s)
- L Simpson
- Howard Hughes Medical Institute and Department of Cell, Molecular, and Developmental Biology, University of California at Los Angeles, Los Angeles, CA 90095, USA
| |
Collapse
|
28
|
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.
Collapse
Affiliation(s)
- D Horn
- Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6399, USA
| | | |
Collapse
|
29
|
Paturiaux-Hanocq F, Zitzmann N, Hanocq-Quertier J, Vanhamme L, Rolin S, Geuskens M, Ferguson MA, Pays E. Expression of a variant surface glycoprotein of Trypanosoma gambiense in procyclic forms of Trypanosoma brucei shows that the cell type dictates the nature of the glycosylphosphatidylinositol membrane anchor attached to the glycoprotein. Biochem J 1997; 324 ( Pt 3):885-95. [PMID: 9210413 PMCID: PMC1218505 DOI: 10.1042/bj3240885] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Procyclic forms of Trypanosoma brucei have been genetically modified to express the major metacyclic variant surface glycoprotein (VSG variant AnTat 11.17) of Trypanosoma gambiense. The VSG is expressed in an intact membrane-bound form that can be detected over the entire plasma membrane, together with procyclin, and as a series of lower-molecular-mass fragments that are mostly soluble degradation products. The presence of degraded VSG in the cells and the culture medium suggests that VSG is not efficiently processed and/or efficiently folded when expressed in procyclic cells. The level of procyclin expressed on the surface of these cells is slightly reduced, although there is no difference in procyclin mRNA levels. The intact membrane-bound form of the VSG is N-glycosylated with oligomannose structures and contains a glycosylphosphatidylinositol (GPI) membrane anchor that can be biosynthetically labelled with [3H]ethanolamine. The anchor is sensitive to mammalian GPI-specific phospholipase D but, like the anchor of procyclin, it is resistant to the action of bacterial phosphatidylinositol-specific phospholipase C. This pattern of phospholipase sensitivity suggests that the GPI anchor acquired by VSG when expressed in procyclics is acylated on the inositol ring and therefore resembles a procyclic procyclin-type anchor rather than a trypomastigote VSG-type anchor with respect to the lipid structure. The VSG expressed in procyclics was sensitive to the action of a mixture of sialidase, beta-galactosidase and beta-hexosaminidase, suggesting that the VSG GPI anchor also contains a sialylated polylactosamine side-chain modification similar to that described for procyclin. These results indicate that the nature of the protein expressed has little influence on the post-translational modifications performed in the secretory pathway of procyclic trypanosomes.
Collapse
Affiliation(s)
- F Paturiaux-Hanocq
- Department of Molecular Biology, Free University of Brussels, 67, rue des Chevaux, B1640 Rhode Saint Genèse, Belgium
| | | | | | | | | | | | | | | |
Collapse
|
30
|
Borst P, Rudenko G, Blundell PA, van Leeuwen F, Cross MA, McCulloch R, Gerrits H, Chaves IM. Mechanisms of antigenic variation in African trypanosomes. Behring Inst Mitt 1997:1-15. [PMID: 9303197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
African trypanosomes can escape destruction by the immune system of their mammalian host by antigenic variation of the trypanosome surface coat. This coat is mainly composed of a single protein species, the Variant Surface Glycoprotein or VSG. The genes for VSGs are expressed in a polycistronic telomeric expression site together with at least eight expression site-associated genes (ESAGs). Trypanosomes may switch coat either by replacing the VSG gene in the active expression site by a different one, or by activating another expression site with concomitant silencing of the previously active one. Here we review our present knowledge of antigenic variation in Trypanosome brucei. We focus on four questions: How do trypanosomes switch from one VSG gene expression site to another one? What is the role of the novel base J in silencing expression sites? What is the functional significance of the antigenic variation of the heterodimeric transferrin receptor encoded by two ESAG genes? Why do trypanosomes have multiple expression sites at all?
Collapse
Affiliation(s)
- P Borst
- Netherlands Cancer Institute, Division of Molecular Biology, Amsterdam, The Netherlands
| | | | | | | | | | | | | | | |
Collapse
|
31
|
Werbovetz KA, Englund PT. Lipid metabolism in Trypanosoma brucei: utilization of myristate and myristoyllysophosphatidylcholine for myristoylation of glycosyl phosphatidylinositols. Biochem J 1996; 318 ( Pt 2):575-81. [PMID: 8809049 PMCID: PMC1217659 DOI: 10.1042/bj3180575] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Myristate is the exclusive fatty acid species in the glycosyl phosphatidylinositol (GPI) anchor of the Trypanosoma brucei variant surface glycoprotein (VSG). [3H]Myristate can be incorporated into T. brucei GPIs by two distinct processes known as fatty acid remodelling and myristate exchange. Myristoyllysophosphatidylcholine (M-LPC) can also serve as a myristate donor for VSG in trypanosomes [Bowes, Samad, Jiang, Weaver and Mellors (1993) J. Biol. Chem. 268, 13885-13892]. We have studied in detail the myristoylation of GPIs using a [3H]M-LPC substrate. Labelling of VSG and free GPIs by [3H]M-LPC in cultured trypanosomes occurred at the same rate as with [3H]myristate. Concurrent with GPI labelling, there was rapid hydrolysis of [3H]M-LPC to generate extracellular [3H]myristate. Experiments in a trypanosomal cell-free system indicated that GPI labelling by fatty acid remodelling and myristate exchange was also equally efficient with [3H]M-LPC and [3H]myristate. Furthermore, both ATP and CoA are required for the myristoylation of GPIs by [3H]M-LPC. These experiments suggest that GPI myristoylation from M-LPC involves hydrolysis of M-LPC to free myristate. To address the physiological importance of myristate and M-LPC in VSG myristoylation, we radiolabelled trypanosomes in vivo with both substrates in medium containing serum, and found that [3H]myristate labelled VSG and GPIs more efficiently. Thus, VSG myristoylation by free myristate may be favoured in bloodstream trypanosome infections.
Collapse
Affiliation(s)
- K A Werbovetz
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, U.S.A
| | | |
Collapse
|
32
|
Gerold P, Striepen B, Reitter B, Geyer H, Geyer R, Reinwald E, Risse HJ, Schwarz RT. Glycosyl-phosphatidylinositols of Trypanosoma congolense: two common precursors but a new protein-anchor. J Mol Biol 1996; 261:181-94. [PMID: 8757286 DOI: 10.1006/jmbi.1996.0451] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The parasitic protozoan Trypanosoma congolense exhibits a dense surface coat which is pivotal for immunoevasion of the parasite. This dense surface coat is made of a single protein species, the variant surface glycoprotein, which is present in a high copy number. The protein is anchored to the plasma membrane by a glycosyl-phosphatidylinositol membrane anchor. A detailed study of the structure of T. congolense strain 423 (clone BENat 1.3) variant surface glycoprotein glycosyl-phosphatidylinositol membrane anchor was performed. Radioactively labelled core-glycan prepared by dephosphorylation, deamination and reduction was analysed by high-pH anion-exchange chromatography, size-exclusion and lectin affinity chromatography. Additionally the glycosyl-phosphatidylinositol membrane anchor core-glycan was purified from a bulk preparation of variant surface glycoprotein and subjected to mass spectrometry and methylation analysis. Using these methods we could identify a novel galactose-beta 1,6-N-acetyl-glucosamine-beta 1,4-branch modifying the mannose adjacent to the glucosamine of the mannose-alpha 1,2-mannose-alpha 1,6-mannose-alpha 1,4-glucosamine core-glycan of the variant surface glycoprotein glycosyl-phosphatidylinositol membrane anchor. Furthermore the biosynthetic pathway leading to this novel structure was investigated. Two putative glycosyl-phosphatidylinositol anchor precursors were identified having structures identical to the previously characterized Trypanosoma brucei brucei glycolipids P2 and P3 (also designated glycolipid A and C) consistent with a trimannosyl core and a dimyristoyl-glycerol. Both glycosyl-phosphatidylinositol anchor precursors of T. congolense do not possess the side-branch modification found on the mature protein membrane anchor, implying that the sugar side-chain is added to the anchor during its passage through the Golgi-apparatus.
Collapse
Affiliation(s)
- P Gerold
- Zentrum für Hygiene und Medizinische Mikrobiologie, Philipps-Universität Marburg, Germany
| | | | | | | | | | | | | | | |
Collapse
|
33
|
Abstract
Amastigote forms of T. cruzi express the specific Ssp-4 surface antigen which is progressively shed, by the action of an endogenous phosphatidylinositol-phospholipase C, during their development into epimastigotes (Andrews et al., J. Exp. Med., 167 (1988) 300-314). We show now that the lipid moiety of the anchor of Ssp-4 is a ceramide which was metabolically labelled with [3H]palmitic acid. The lipid could be cleaved by PI-PLC digestion in vitro, and was identified by methanolysis and reverse phase thin layer chromatography of the products, as palmitoyldihydrosphingosine. Also, the free biosynthesized lipids were investigated in parasites obtained after 0, 24, 48 and 72 h differentiation of trypomastigotes and further incubated with [3H]palmitic acid for 2 h. A maximum of free ceramide was found in the 24 h point, in accordance with the maximum of amastigote forms. In contrast only traces of free ceramide were found in trypomastigotes. The major ceramide (more than 90%) is palmitoyldihydrosphingosine, which is the same as found in the anchor of Ssp-4. The ceramide could play an important role in the cell biology of the parasite as previously found for mammalian cells.
Collapse
Affiliation(s)
- L E Bertello
- Departamento de Química Orgánica, Facultad de Ciencias Exactos y Naturales, Universidad de Buenos Aires, Citudad Universitaria, Argentina
| | | | | |
Collapse
|
34
|
Abstract
Changes in variant surface glycoprotein (Vsg) expression allow Trypanosoma brucei to elude the immune response. The expressed vsg is always located at the telomeric end of a polycistronic transcription unit known as an expression site (ES). Although there are many ESs, only one is active at any particular time. The mechanisms regulating ES transcription and switching are unknown. Chromosome rearrangements within or upstream of the ES have been described to occur in occasional switch events, but no changes have been consistently associated with switching. We inserted the drug resistance genes neo and ble, conferring resistance to G418 and phleomycin, respectively, 1 kb downstream of "silent" ES promoters. This demonstrated that short-range transcription could be achieved from a silent ES promoter. From one initial transformant clone, panels of independent consecutive on-off-on switch clones were generated and analyzed. The first activation of the neo-targeted ES was always associated with deletion of the upstream tandem promoter in this ES, but no further rearrangements were detected in consecutive off-on switches of this ES. On the other hand, direct analysis of ES promoters showed that deletions and duplications occurred elsewhere. Activation of a ble-tagged 300-kb chromosome could not be achieved, but phleomycin-resistant clones could be obtained. One such clone arose from recombination between three ESs. Taken together, our experiments suggest that ES switching may occur after a period of chromosomal interactivity that may or may not leave tangible evidence in the form of detectable sequence changes.
Collapse
Affiliation(s)
- M Navarro
- Laboratory of Molecular Parasitology, The Rockefeller University, New York, New York 10021-6399, USA
| | | |
Collapse
|
35
|
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.
Collapse
Affiliation(s)
- J L Muñoz-Jordán
- Laboratory of Molecular Parasitology, Rockefeller University, New York 10012, USA
| | | | | |
Collapse
|
36
|
Abstract
The highly regulated intracellular concentration of calcium (Ca2+) is a well-described regulator of diverse cellular events, including cell cycle control. In the present study we have addressed the regulation of cytosolic Ca2+ in differentiation events in the life cycle of the protozoan parasite Trypanosoma brucei. Bloodstream form (BSF) trypanosomes include the mitotically active long slender forms (LS) which differentiate to two nondividing stages--intermediate (INT) which transform into short stumpy (SS) forms. An axenic in vitro culture system was used to cultivate LS to a density greater than 1.0 x 10(6) cells/ml/day. Populations of the intermediate BSF (INT) and SS were derived from cultured LS by treatment with difluoromethyl ornithine (DFMO, 100 microM) for 2 and 4 days, respectively. A semiquantitative reverse transcriptase-coupled polymerase chain reaction protocol (SQ-RT-PCR) was developed to objectively distinguish the three BSF by monitoring the relative levels of stage-specific mRNAs--cytochrome oxidase II (COXII), variant surface glycoprotein, and procyclin during the differentiation of LS to SS, showing an increase in COXII and procyclin mRNA expression during this process of differentiation. Basal cytosolic Ca2+ levels [Ca2+]i of populations of LS, INT, and SS were studied using Indo-1 dual emission fluorometry. [Ca2+]i was maximal in dividing LS cells and was shown to decrease coincidentally with early events in the process of differentiation to INT and SS. Thapsigargin (1 microM), reported to cause the release of Ca2+ from the endoplasmic reticulum, elevated [Ca2+]i by about 30-60 nM in all BSF; however, the total thapsigargin-releasable stores decreased in parallel with the decrease in basal [Ca2+]i. Control treatments verified that elevations in [Ca2+]i in response to thapsigargin were intracellular in origin. These results may reflect the cessation of cytosolic Ca2+ transients involved in the regulation of mitosis as the parasite exits from the cell cycle and differentiates from rapidly dividing LS to the nondividing SS.
Collapse
Affiliation(s)
- D F Stojdl
- Department of Microbiology and Immunology, University of Western Ontario, London, Canada
| | | |
Collapse
|
37
|
Morgan RW, El-Sayed NM, Kepa JK, Pedram M, Donelson JE. Differential expression of the expression site-associated gene I family in African trypanosomes. J Biol Chem 1996; 271:9771-7. [PMID: 8621657 DOI: 10.1074/jbc.271.16.9771] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
A minimum of 20 different mRNA species encoding related members of the expression site-associated gene I (ESAG-I) family occur in metacyclic variant antigen type 4 bloodstream trypanosomes. None of these ESAG-I mRNAs are derived from the metacyclic variant antigen type 4 variant surface glycoprotein (VSG) gene expression site, and some appear to come from pseudogenes. The ESAG-Is are transcribed in both procyclic and bloodstream trypanosomes, but their mRNAs accumulate to a detectable steady state level only in bloodstream trypanosomes. At least five different groups of 3'-untranslated regions (3'-UTRs) are represented among these ESAG-I mRNAs, suggesting that the 3'-UTR does not contribute to their differential expression. Some ESAG-I mRNAs completely lack a 3'-UTR or have only a single nucleotide as a 3'-UTR. Transcription of the ESAG-Is is sensitive to alpha-amanitin, indicating that they are transcribed by a different RNA polymerase than the VSG genes. These results collectively demonstrate that ESAG-I's are a heterogeneous population that can be expressed independently of VSG genes, but like the VSG genes, their mRNAs are present in the bloodstream stage of the parasite and not in the procyclic stage.
Collapse
Affiliation(s)
- R W Morgan
- Department of Biochemistry, University of Iowa, Iowa City 52242, USA
| | | | | | | | | |
Collapse
|
38
|
Abuin G, Colli W, Alves MJ. Turnover and shedding of the Tc-85 surface glycoprotein of Trypanosoma cruzi trypomastigotes. Braz J Med Biol Res 1996; 29:335-41. [PMID: 8736126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Tc-85 is an 85-kDa surface glycoprotein specific for the trypomastigote stage of Trypanosoma cruzi which has been implicated in the invasion of host cells by the parasite. Tc-85 has a half-life of 3.5-4 h and is synthesized as a 95-kDa precursor. Processing of the 95-kDa precursor is inhibited by N-p-tosyl-L-lysine chloromethyl ketone, p-chloromercuriphenylsulfonic acid, iodoacetamide or N-ethylmaleimide, but not by aprotinin, antipain or phenylmethylsulfonil fluoride. Tc-85, but not the precursor, is rapidly shed into the medium, allowing a correlation between the decrease of Tc-85 in trypomastigotes and its increase in the culture medium. The shedding of Tc-85 was inhibited 50% by 1 microM tunicamycin, but not by 10 microM swainsonine or 10 microM 1-deoxynojirimycin under the experimental conditions employed. This suggests that N-linked oligosaccharides are important for the shedding phenomenon, although it appears that they do not have to be fully processed for shedding to occur.
Collapse
Affiliation(s)
- G Abuin
- Departamento de Bioquímica, Universidade de São Paulo, Brasil
| | | | | |
Collapse
|
39
|
Abstract
The glycosyl-phosphatidylinositol (GPI) anchor of the Trypanosoma brucei variant surface glycoprotein (VSG) is unique in having exclusively myristate as its fatty acid component. We previously demonstrated that the myristate specificity is the result of two independent pathways. First, the newly synthesized free GPI, which is not myristoylated, undergoes fatty acid remodeling to replace both its fatty acids with myristate. Second, the myristoylated precursor, glycolipid A, undergoes a myristate exchange reaction, detected by the replacement of unlabeled myristate by [3H]myristate. Remodeling and exchange have different enzymatic properties and apparently occur in different subcellular compartments. We now demonstrate that the GPI anchor linked to VSG is the major substrate for myristate exchange. VSG can be efficiently labeled with [3H]myristate by exchange in the presence of cycloheximide, an inhibitor that prevents new VSG synthesis and thus anchor addition to protein. Not only is newly synthesized VSG subject to exchange, but mature VSG, possibly recycling from the cell surface, also undergoes myristate exchange.
Collapse
Affiliation(s)
- L U Buxbaum
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | | | | | | |
Collapse
|
40
|
Urakawa T, Eshita Y, Fukuma T, Hirumi H, Hirumi K, Majiwa PA. Expression of Trypanosoma congolense antigens in Spodoptera frugiperda insect cells. Exp Parasitol 1995; 80:633-44. [PMID: 7758544 DOI: 10.1006/expr.1995.1079] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Transcripts which encode two metacyclic-form-specific variable surface glycoproteins (mVSGs) of Trypanosoma congolense IL3000 have been cloned into baculovirus expression vectors using a novel transfer vector, pAcL11. One of the recombinant baculoviruses (AcVSG1) expressed a mVSG as a glycoprotein with a signal peptide which was cleaved in this expression system, whereas the other one (AcVSG2) expressed an unprocessed protein. From 1 liter of culture containing 10(9) Spodoptera frugiperda cells infected with the recombinant baculoviruses, 10 and 30 mg of mVSG1 and mVSG2, respectively, were obtained. Monospecific polyclonal antibodies produced by immunization of mice with the recombinant proteins reacted specifically with the respective proteins and showed no cross-reactivities between mVSG1 and mVSG2 in immunoblot assays. The antibodies to each of the proteins stained only the surface of a proportion of intact fixed T. congolense IL3000 metacyclic forms. It was possible to determine from these studies that, on the average, the parasites expressing mVSG1 constitute approximately 45% of the metacyclic population of T. congolense IL3000 maintained in in vitro cultures, whereas those that express mVSG2 constitute approximately 20%.
Collapse
Affiliation(s)
- T Urakawa
- Chemo-Sero-Therapeutic Research Institute, Kikuchi Laboratories, Kumamoto, Japan
| | | | | | | | | | | |
Collapse
|
41
|
Abstract
During their metacyclic developmental stage, African trypanosomes are coated with one of 12-15 variant surface glycoproteins (VSGs) that define different metacyclic variant antigen types (MVATs). The MVAT VSG genes are located near telomeres of large chromosomes and are expressed without rearrangement in the metacyclic stage. We have cloned and examined the telomere-linked MVAT5 VSG gene and its upstream expression site associated gene (ESAG I) which are separated by 4.5 kb. Within this 4.5-kb intergenic region is an 87-bp sequence that serves as a strong promoter for a luciferase reporter gene in transient transfection assays. This 87-bp sequence is similar, but not identical, to the promoter for another MVAT VSG gene. UV irradiation experiments were used to detect RNA synthesis from this MVAT5 promoter in bloodstream trypanosomes expressing an unrelated VSG. We propose that this sequence is a specific promoter for the MVAT5 VSG mRNA that occurs in about 10% of the trypanosome population during the metacyclic stage of the parasites' life cycle.
Collapse
Affiliation(s)
- Y L Nagoshi
- Genetics Ph.D. Program, University of Iowa, Iowa City 52242, USA
| | | | | |
Collapse
|
42
|
Abstract
When the African trypanosome Trypanosoma brucei is taken up from mammals by a tse-tse fly, it replaces its variant surface glycoprotein (VSG) coat by a procyclin coat. Transcription of VSG genes stops in the fly, but transcription of sequences derived from the promoter area of the VSG expression site(s) remains high. Whether this is due to continuing high activity of one promoter or to low activity of many promoters was unclear. We have used the small differences between the sequences of different expression sites to show that multiple expression site promoters are active in insect form trypanosomes. This is confirmed by the low expression of single copy marker genes introduced into the transcribed area. However, if the expression site promoter is removed from the genomic location of the expression site and inserted in the non-transcribed spacer of the ribosomal DNA (rDNA), it is derepressed. Derepression of transcription can also be accomplished by replacing the promoter of an expression site by an rDNA promoter. We conclude that the down-regulation of VSG gene expression site promoters in insect form trypanosomes is affected by both the DNA sequence of the promoter and the genomic context in which it resides.
Collapse
Affiliation(s)
- G Rudenko
- The Netherlands Cancer Institute, Amsterdam
| | | | | | | | | |
Collapse
|
43
|
Lu Y, Alarcon CM, Hall T, Reddy LV, Donelson JE. A strand bias occurs in point mutations associated with variant surface glycoprotein gene conversion in Trypanosoma rhodesiense. Mol Cell Biol 1994; 14:3971-80. [PMID: 8196636 PMCID: PMC358763 DOI: 10.1128/mcb.14.6.3971-3980.1994] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
We previously described a bloodstream Trypansoma rhodesiense clone, MVAT5-Rx2, whose isolation was based on its cross-reactivity with a monoclonal antibody (MAb) directed against a metacyclic variant surface glycoprotein (VSG). When the duplicated, expressed VSG gene in MVAT5-Rx2 was compared with its donor (basic copy) gene, 11 nucleotide differences were found in the respective 1.5-kb coding regions (Y. Lu, T. Hall, L. S. Gay, and J. E. Donelson, Cell 72:397-406, 1993). Here we describe a characterization of two additional bloodstream trypanosome clones, MVAT5-Rx1 and MVAT5-Rx3, whose VSGs are expressed from duplicated copies of the same donor VSG gene. The three trypanosome clones each react with the MVAT5-specific MAb, but they have different cross-reactivities with a panel of other MAbs, suggesting that their surface epitopes are similar but nonidentical. Each of the three gene duplication events occurs at a different 5' crossover site within a 76-bp repeat and is associated with a different set of point mutations. The 35, 11, and 28 point mutations in the duplicated VSG coding regions of Rx1, Rx2, and Rx3, respectively, exhibit a strand bias. In the sense strand, of the 74 total mutations generated in the three duplications, 54% are A-to-G or G-to-A (A:G) transitions and 7% are C:T transitions, while 26% are C:A transversions and 13% are C:G transversions. No T:G or T:A transversions occurred. Possible models for the generation of these point mutations are discussed.
Collapse
MESH Headings
- Amino Acid Sequence
- Animals
- Antibodies, Monoclonal
- Base Sequence
- Blotting, Southern
- Cloning, Molecular
- Cross Reactions
- Crossing Over, Genetic
- DNA Primers
- DNA, Protozoan/analysis
- DNA, Protozoan/genetics
- Fluorescent Antibody Technique
- Gene Conversion
- Gene Expression
- Molecular Sequence Data
- Point Mutation
- Polymerase Chain Reaction
- Repetitive Sequences, Nucleic Acid
- Sequence Homology, Amino Acid
- Sequence Homology, Nucleic Acid
- Trypanosoma brucei rhodesiense/genetics
- Variant Surface Glycoproteins, Trypanosoma/analysis
- Variant Surface Glycoproteins, Trypanosoma/biosynthesis
- Variant Surface Glycoproteins, Trypanosoma/genetics
Collapse
Affiliation(s)
- Y Lu
- Genetics Ph.D. Program, University of Iowa, Iowa City 52242
| | | | | | | | | |
Collapse
|
44
|
Vassella E, Braun R, Roditi I. Control of polyadenylation and alternative splicing of transcripts from adjacent genes in a procyclin expression site: a dual role for polypyrimidine tracts in trypanosomes? Nucleic Acids Res 1994; 22:1359-64. [PMID: 8190625 PMCID: PMC307990 DOI: 10.1093/nar/22.8.1359] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The procyclin-associated genes (PAGs) of Trypanosoma brucei are located downstream of tandemly repeated procyclin genes and belong to the same alpha-amanitin-resistant polycistronic transcription units. In procyclic form trypanosomes the PAG 1 pre-mRNA is alternatively spliced to give rise to three transcripts of 2.7 kb, 1.8 kb and 1.3 kb. The two larger transcripts contain additional short open reading frames (ORFs) upstream of the major ORF. Trans-splicing to generate these transcripts occurs downstream of three different polypyrimidine tracts. A minor population of procyclin mRNAs is also generated by alternative splicing at a polypyrimidine tract that begins 524 bp upstream of the major splice acceptor site of the procyclin beta-gene. The same polypyrimidine tract is also required for accurate polyadenylation of mRNAs from the upstream procyclin alpha-gene (1). Alternatively polyadenylated forms of PAG 1 mRNAs can also be detected. All polyadenylation sites are found at a similar distance upstream of splice-acceptor sites, in each case with a polypyrimidine tract between them. Our results point to a dual role for polypyrimidine tracts in the maturation of trypanosome mRNAs.
Collapse
Affiliation(s)
- E Vassella
- Institut für Allgemeine Mikrobiologie, Universität Bern, Switzerland
| | | | | |
Collapse
|
45
|
Gommers-Ampt JH, Van Leeuwen F, de Beer AL, Vliegenthart JF, Dizdaroglu M, Kowalak JA, Crain PF, Borst P. beta-D-glucosyl-hydroxymethyluracil: a novel modified base present in the DNA of the parasitic protozoan T. brucei. Cell 1993; 75:1129-36. [PMID: 8261512 DOI: 10.1016/0092-8674(93)90322-h] [Citation(s) in RCA: 148] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We have previously shown that the DNA of the unicellular eukaryote T. brucei contains about 0.1% of a novel modified base, called J. The presence of J correlates with a DNA modification associated with the silencing of telomeric expression sites for the variant surface antigens of trypanosomes. Here we show that J is 5-((beta-D-glucopyranosyloxy)-methyl)-uracil (shortened to beta-D-glucosyl-hydroxymethyluracil), a base not previously found in DNA. We discuss putative pathways for the introduction of this base modification at specific positions in the DNA and the possible contribution of this modification to repression of surface antigen gene expression.
Collapse
Affiliation(s)
- J H Gommers-Ampt
- Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam
| | | | | | | | | | | | | | | |
Collapse
|
46
|
Doering TL, Pessin MS, Hoff EF, Hart GW, Raben DM, Englund PT. Trypanosome metabolism of myristate, the fatty acid required for the variant surface glycoprotein membrane anchor. J Biol Chem 1993; 268:9215-22. [PMID: 8486622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The trypanosome variant surface glycoprotein (VSG) is anchored to the outer leaflet of the parasite plasma membrane by a glycosyl phosphatidylinositol (GPI). The VSG anchor is unique among GPIs in containing exclusively dimyristoylglycerol as its lipid moiety. Myristate is incorporated into the anchor precursor by sequential deacylation and specific reacylation with myristate. Although myristate is required for the VSG anchor, trypanosomes cannot synthesize this fatty acid and must import their entire supply from the host bloodstream, where it exists in low abundance. Chemical analysis of these parasites reveals that most of their myristate is in VSG protein, with no major lipid storage form. Unexpectedly, when these cells are radiolabeled with [3H]myristate in culture, most of the label is incorporated into phospholipids, with little into VSG. This apparent contradiction is explained by the fact that trypanosomes in culture medium elongate much of the [3H]myristate into palmitate and stearate, probably because the medium (with only 5% serum) contains limiting amounts of these fatty acids. In contrast, trypanosomes radiolabeled in whole blood (with higher concentrations of palmitate and stearate) do not modify most of the [3H]myristate, and instead utilize the major portion of it for GPI synthesis. Our studies suggest that bloodstream trypanosomes have evolved highly efficient means of directing myristate into the GPI biosynthetic pathway.
Collapse
Affiliation(s)
- T L Doering
- Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | | | | | | | | | | |
Collapse
|
47
|
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.
Collapse
|
48
|
Abstract
Expression site-associated genes (ESAGs) of Trypanosoma brucei are found upstream of variant surface glycoprotein (VSG) genes in bloodstream expression sites. There are at least 6 different ESAGs in each of these expression sites, and each ESAG is repetitive in the genome. ESAGs are believed to reside only in VSG expression sites and to be co-transcribed with the VSG gene from a common alpha-amanitin-insensitive promoter. Our results show that this is not always true. The transcriptionally active 1.22 metacyclic expression site contains no ESAGs, but ESAGs are highly transcribed in these cells. The level of transcription indicates that more than one copy of each of these genes is active. Furthermore, some of these genes are transcribed, to produce steady state RNA, in procyclic culture cells which do not express the VSG gene: there is differential expression of ESAGs between the bloodstream and procyclic phases of the trypanosome life cycle. Thus ESAGs can be transcribed outwith an active VSG gene expression site and in the absence of expression of the VSG.
Collapse
Affiliation(s)
- S V Graham
- Institute of Genetics, University of Glasgow, Scotland, U.K
| | | |
Collapse
|
49
|
Wirtz E, Sylvester D, Hill GC. Characterization of a novel developmentally regulated gene from Trypanosoma brucei encoding a potential phosphoprotein. Mol Biochem Parasitol 1991; 47:119-28. [PMID: 1857381 DOI: 10.1016/0166-6851(91)90154-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We have isolated a cDNA clone corresponding to a single-copy nuclear gene that is upregulated at the mRNA level during in vitro differentiation of bloodstream trypomastigotes of strains of both Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense to procyclic forms. Transcript levels begin to increase within minutes of introduction of bloodstream forms into culture and peak well before cultures exhibit a procyclic morphology. This increase in transcript levels was found to occur both in the absence of protein synthesis and in a nontransforming strain blocked very early in the developmental program, both conditions under which accumulation of procyclic acidic repetitive protein (PARP) transcripts did not occur in control experiments. DNA sequence analysis reveals an open reading frame sufficient to encode a protein of approximately 50 kDa within the cDNA, but data base searches for homology at either the amino acid or nucleotide level revealed no related sequences. A high density of kinase consensus target sites in the deduced amino acid sequence suggests that the gene product may be a phosphoprotein.
Collapse
Affiliation(s)
- E Wirtz
- Division of Biomedical Sciences, Meharry Medical College, Nashville, TN 37208
| | | | | |
Collapse
|
50
|
Abstract
We have demonstrated efficient protein synthesis in a cell-free system from the bloodstream form of Trypanosoma brucei. This system was able to translate endogenous mRNA, added mRNA, or (apparently at much lower efficiency) three synthetic RNA transcripts lacking 5' mini-exon and 3' poly(A) sequences. Translation was resistant to chloramphenicol and greater than 95% inhibited by low concentrations of anisomycin and puromycin, but only partially inhibited by cycloheximide. Variant surface glycoprotein synthesized from endogenous mRNA was sensitive to endoglycosidase H, indicating the co-translational glycosylation potential of the system. Two proteins translated ab initio from the corresponding in vitro-transcribed RNAs showed no evidence of signal sequence cleavage or glycosylation. Efficient processing occurred when the same RNAs were translated in a rabbit reticulocyte lysate supplemented with canine pancreatic microsomes but not with trypanosome microsomes.
Collapse
Affiliation(s)
- S N Moreno
- Rockefeller University, New York, NY 10021-6399
| | | | | |
Collapse
|