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Infection and Immunity. Clin Immunol 2023. [DOI: 10.1016/b978-0-12-818006-8.00007-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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Garzon T, Ortega-Tirado D, Lopez-Romero G, Alday E, Robles-Zepeda RE, Garibay-Escobar A, Velazquez C. "Immunoinformatic Identification of T-Cell and B-Cell Epitopes From Giardia lamblia Immunogenic Proteins as Candidates to Develop Peptide-Based Vaccines Against Giardiasis". Front Cell Infect Microbiol 2021; 11:769446. [PMID: 34778111 PMCID: PMC8579046 DOI: 10.3389/fcimb.2021.769446] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 10/08/2021] [Indexed: 11/19/2022] Open
Abstract
Giardiasis is one of the most common gastrointestinal infections worldwide, mainly in developing countries. The etiological agent is the Giardia lamblia parasite. Giardiasis mainly affects children and immunocompromised people, causing symptoms such as diarrhea, dehydration, abdominal cramps, nausea, and malnutrition. In order to develop an effective vaccine against giardiasis, it is necessary to understand the host-Giardia interactions, the immunological mechanisms involved in protection against infection, and to characterize the parasite antigens that activate the host immune system. In this study, we identify and characterize potential T-cell and B-cell epitopes of Giardia immunogenic proteins by immunoinformatic approaches, and we discuss the potential role of those epitopes to stimulate the host´s immune system. We selected the main immunogenic and protective proteins of Giardia experimentally investigated. We predicted T-cell and B-cell epitopes using immunoinformatic tools (NetMHCII and BCPREDS). Variable surface proteins (VSPs), structural (giardins), metabolic, and cyst wall proteins were identified as the more relevant immunogens of G. lamblia. We described the protein sequences with the highest affinity to bind MHC class II molecules from mouse (I-Ak and I-Ad) and human (DRB1*03:01 and DRB1*13:01) alleles, as well as we selected promiscuous epitopes, which bind to the most common range of MHC class II molecules in human population. In addition, we identified the presence of conserved epitopes within the main protein families (giardins, VSP, CWP) of Giardia. To our knowledge, this is the first in silico study that analyze immunogenic proteins of G. lamblia by combining bioinformatics strategies to identify potential T-cell and B-cell epitopes, which can be potential candidates in the development of peptide-based vaccines. The bioinformatics analysis demonstrated in this study provides a deeper understanding of the Giardia immunogens that bind to critical molecules of the host immune system, such as MHC class II and antibodies, as well as strategies to rational design of peptide-based vaccine against giardiasis.
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Affiliation(s)
- Thania Garzon
- Department of Chemistry-Biology, University of Sonora, Hermosillo, Mexico
| | | | | | - Efrain Alday
- Department of Chemistry-Biology, University of Sonora, Hermosillo, Mexico
| | | | | | - Carlos Velazquez
- Department of Chemistry-Biology, University of Sonora, Hermosillo, Mexico
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Onyilagha C, Uzonna JE. Host Immune Responses and Immune Evasion Strategies in African Trypanosomiasis. Front Immunol 2019; 10:2738. [PMID: 31824512 PMCID: PMC6883386 DOI: 10.3389/fimmu.2019.02738] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 11/08/2019] [Indexed: 01/11/2023] Open
Abstract
Parasites, including African trypanosomes, utilize several immune evasion strategies to ensure their survival and completion of their life cycles within their hosts. The defense factors activated by the host to resolve inflammation and restore homeostasis during active infection could be exploited and/or manipulated by the parasites in an attempt to ensure their survival and propagation. This often results in the parasites evading the host immune responses as well as the host sustaining some self-inflicted collateral tissue damage. During infection with African trypanosomes, both effector and suppressor cells are activated and the balance between these opposing arms of immunity determines susceptibility or resistance of infected host to the parasites. Immune evasion by the parasites could be directly related to parasite factors, (e.g., antigenic variation), or indirectly through the induction of suppressor cells following infection. Several cell types, including suppressive macrophages, myeloid-derived suppressor cells (MDSCs), and regulatory T cells have been shown to contribute to immunosuppression in African trypanosomiasis. In this review, we discuss the key factors that contribute to immunity and immunosuppression during T. congolense infection, and how these factors could aid immune evasion by African trypanosomes. Understanding the regulatory mechanisms that influence resistance and/or susceptibility during African trypanosomiasis could be beneficial in designing effective vaccination and therapeutic strategies against the disease.
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Affiliation(s)
- Chukwunonso Onyilagha
- Department of Immunology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, MB, Canada
| | - Jude Ezeh Uzonna
- Department of Immunology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, MB, Canada.,Department of Medical Microbiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, MB, Canada
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Zimmermann H, Subota I, Batram C, Kramer S, Janzen CJ, Jones NG, Engstler M. A quorum sensing-independent path to stumpy development in Trypanosoma brucei. PLoS Pathog 2017; 13:e1006324. [PMID: 28394929 PMCID: PMC5398725 DOI: 10.1371/journal.ppat.1006324] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 04/20/2017] [Accepted: 03/29/2017] [Indexed: 11/19/2022] Open
Abstract
For persistent infections of the mammalian host, African trypanosomes limit their population size by quorum sensing of the parasite-excreted stumpy induction factor (SIF), which induces development to the tsetse-infective stumpy stage. We found that besides this cell density-dependent mechanism, there exists a second path to the stumpy stage that is linked to antigenic variation, the main instrument of parasite virulence. The expression of a second variant surface glycoprotein (VSG) leads to transcriptional attenuation of the VSG expression site (ES) and immediate development to tsetse fly infective stumpy parasites. This path is independent of SIF and solely controlled by the transcriptional status of the ES. In pleomorphic trypanosomes varying degrees of ES-attenuation result in phenotypic plasticity. While full ES-attenuation causes irreversible stumpy development, milder attenuation may open a time window for rescuing an unsuccessful antigenic switch, a scenario that so far has not been considered as important for parasite survival.
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Affiliation(s)
- Henriette Zimmermann
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Ines Subota
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Christopher Batram
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Susanne Kramer
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Christian J. Janzen
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Nicola G. Jones
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
| | - Markus Engstler
- Department of Cell and Developmental Biology, Biocenter, University of Würzburg, Würzburg, Germany
- * E-mail:
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Hovel-Miner G, Mugnier MR, Goldwater B, Cross GAM, Papavasiliou FN. A Conserved DNA Repeat Promotes Selection of a Diverse Repertoire of Trypanosoma brucei Surface Antigens from the Genomic Archive. PLoS Genet 2016; 12:e1005994. [PMID: 27149665 PMCID: PMC4858185 DOI: 10.1371/journal.pgen.1005994] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 03/28/2016] [Indexed: 12/02/2022] Open
Abstract
African trypanosomes are mammalian pathogens that must regularly change their protein coat to survive in the host bloodstream. Chronic trypanosome infections are potentiated by their ability to access a deep genomic repertoire of Variant Surface Glycoprotein (VSG) genes and switch from the expression of one VSG to another. Switching VSG expression is largely based in DNA recombination events that result in chromosome translocations between an acceptor site, which houses the actively transcribed VSG, and a donor gene, drawn from an archive of more than 2,000 silent VSGs. One element implicated in these duplicative gene conversion events is a DNA repeat of approximately 70 bp that is found in long regions within each BES and short iterations proximal to VSGs within the silent archive. Early observations showing that 70-bp repeats can be recombination boundaries during VSG switching led to the prediction that VSG-proximal 70-bp repeats provide recombinatorial homology. Yet, this long held assumption had not been tested and no specific function for the conserved 70-bp repeats had been demonstrated. In the present study, the 70-bp repeats were genetically manipulated under conditions that induce gene conversion. In this manner, we demonstrated that 70-bp repeats promote access to archival VSGs. Synthetic repeat DNA sequences were then employed to identify the length, sequence, and directionality of repeat regions required for this activity. In addition, manipulation of the 70-bp repeats allowed us to observe a link between VSG switching and the cell cycle that had not been appreciated. Together these data provide definitive support for the long-standing hypothesis that 70-bp repeats provide recombinatorial homology during switching. Yet, the fact that silent archival VSGs are selected under these conditions suggests the 70-bp repeats also direct DNA pairing and recombination machinery away from the closest homologs (silent BESs) and toward the rest of the archive. Chromosomal translocations can fuel genetic change or cause catastrophic genomic damage. African trypanosomes, exemplified by Trypanosoma brucei sub-species, are unicellular parasites that can chronically infect their human and livestock hosts by using a strategy of antigenic variation by which they repeatedly change their protein coats. Switching the surface coat requires the accurate selection and translocation of a single silent coat gene, from a large genomic archive, into an actively transcribed site. How the coat genes from within this deep archive are selected and activated was unproven. Here we show that a specific repetitive DNA sequence is required to access coat genes from diverse sites within the genome. The likely outcome of restricting this process of coat gene selection in natural infections would be a reduction in the chronic nature of African trypanosomiasis.
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Affiliation(s)
- Galadriel Hovel-Miner
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
- The George Washington University, Department of Microbiology Immunology, and Tropical Medicine, Washington, DC, United States of America
- * E-mail:
| | - Monica R. Mugnier
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
| | - Benjamin Goldwater
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
| | - George A. M. Cross
- The Rockefeller University, Laboratory of Molecular Parasitology, New York, New York, United States of America
| | - F. Nina Papavasiliou
- The Rockefeller University, Laboratory of Lymphocyte Biology, New York, New York, United States of America
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DNA Recombination Strategies During Antigenic Variation in the African Trypanosome. Microbiol Spectr 2016; 3:MDNA3-0016-2014. [PMID: 26104717 DOI: 10.1128/microbiolspec.mdna3-0016-2014] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Survival of the African trypanosome in its mammalian hosts has led to the evolution of antigenic variation, a process for evasion of adaptive immunity that has independently evolved in many other viral, bacterial and eukaryotic pathogens. The essential features of trypanosome antigenic variation have been understood for many years and comprise a dense, protective Variant Surface Glycoprotein (VSG) coat, which can be changed by recombination-based and transcription-based processes that focus on telomeric VSG gene transcription sites. However, it is only recently that the scale of this process has been truly appreciated. Genome sequencing of Trypanosoma brucei has revealed a massive archive of >1000 VSG genes, the huge majority of which are functionally impaired but are used to generate far greater numbers of VSG coats through segmental gene conversion. This chapter will discuss the implications of such VSG diversity for immune evasion by antigenic variation, and will consider how this expressed diversity can arise, drawing on a growing body of work that has begun to examine the proteins and sequences through which VSG switching is catalyzed. Most studies of trypanosome antigenic variation have focused on T. brucei, the causative agent of human sleeping sickness. Other work has begun to look at antigenic variation in animal-infective trypanosomes, and we will compare the findings that are emerging, as well as consider how antigenic variation relates to the dynamics of host-trypanosome interaction.
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Bargul JL, Jung J, McOdimba FA, Omogo CO, Adung’a VO, Krüger T, Masiga DK, Engstler M. Species-Specific Adaptations of Trypanosome Morphology and Motility to the Mammalian Host. PLoS Pathog 2016; 12:e1005448. [PMID: 26871910 PMCID: PMC4752354 DOI: 10.1371/journal.ppat.1005448] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 01/20/2016] [Indexed: 11/24/2022] Open
Abstract
African trypanosomes thrive in the bloodstream and tissue spaces of a wide range of mammalian hosts. Infections of cattle cause an enormous socio-economic burden in sub-Saharan Africa. A hallmark of the trypanosome lifestyle is the flagellate's incessant motion. This work details the cell motility behavior of the four livestock-parasites Trypanosoma vivax, T. brucei, T. evansi and T. congolense. The trypanosomes feature distinct swimming patterns, speeds and flagellar wave frequencies, although the basic mechanism of flagellar propulsion is conserved, as is shown by extended single flagellar beat analyses. Three-dimensional analyses of the trypanosomes expose a high degree of dynamic pleomorphism, typified by the 'cellular waveform'. This is a product of the flagellar oscillation, the chirality of the flagellum attachment and the stiffness of the trypanosome cell body. The waveforms are characteristic for each trypanosome species and are influenced by changes of the microenvironment, such as differences in viscosity and the presence of confining obstacles. The distinct cellular waveforms may be reflective of the actual anatomical niches the parasites populate within their mammalian host. T. vivax displays waveforms optimally aligned to the topology of the bloodstream, while the two subspecies T. brucei and T. evansi feature distinct cellular waveforms, both additionally adapted to motion in more confined environments such as tissue spaces. T. congolense reveals a small and stiff waveform, which makes these parasites weak swimmers and destined for cell adherence in low flow areas of the circulation. Thus, our experiments show that the differential dissemination and annidation of trypanosomes in their mammalian hosts may depend on the distinct swimming capabilities of the parasites.
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Affiliation(s)
- Joel L. Bargul
- Lehrstuhl für Zell- und Entwicklungsbiologie, Biozentrum, Julius-Maximilians-Universität Würzburg, Am Hubland, Würzburg, Germany
- Department of Biochemistry, Jomo Kenyatta University of Agriculture and technology, Nairobi, Kenya
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
| | - Jamin Jung
- Lehrstuhl für Zell- und Entwicklungsbiologie, Biozentrum, Julius-Maximilians-Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Francis A. McOdimba
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
| | - Collins O. Omogo
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
| | - Vincent O. Adung’a
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
- Department of Biochemistry and Molecular Biology, Egerton University, Egerton, Kenya
| | - Timothy Krüger
- Lehrstuhl für Zell- und Entwicklungsbiologie, Biozentrum, Julius-Maximilians-Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Daniel K. Masiga
- Molecular Biology and Bioinformatics Unit, International Centre of Insect Physiology and Ecology, Nairobi, Kenya
| | - Markus Engstler
- Lehrstuhl für Zell- und Entwicklungsbiologie, Biozentrum, Julius-Maximilians-Universität Würzburg, Am Hubland, Würzburg, Germany
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Cardoso MS, Reis-Cunha JL, Bartholomeu DC. Evasion of the Immune Response by Trypanosoma cruzi during Acute Infection. Front Immunol 2016; 6:659. [PMID: 26834737 PMCID: PMC4716143 DOI: 10.3389/fimmu.2015.00659] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 12/24/2015] [Indexed: 12/11/2022] Open
Abstract
Trypanosoma cruzi is the etiologic agent of Chagas disease, a neglected tropical disease that affects millions of people mainly in Latin America. To establish a life-long infection, T. cruzi must subvert the vertebrate host's immune system, using strategies that can be traced to the parasite's life cycle. Once inside the vertebrate host, metacyclic trypomastigotes rapidly invade a wide variety of nucleated host cells in a membrane-bound compartment known as the parasitophorous vacuole, which fuses to lysosomes, originating the phagolysosome. In this compartment, the parasite relies on a complex network of antioxidant enzymes to shield itself from lysosomal oxygen and nitrogen reactive species. Lysosomal acidification of the parasitophorous vacuole is an important factor that allows trypomastigote escape from the extremely oxidative environment of the phagolysosome to the cytoplasm, where it differentiates into amastigote forms. In the cytosol of infected macrophages, oxidative stress instead of being detrimental to the parasite, favors amastigote burden, which then differentiates into bloodstream trypomastigotes. Trypomastigotes released in the bloodstream upon the rupture of the host cell membrane express surface molecules, such as calreticulin and GP160 proteins, which disrupt initial and key components of the complement pathway, while others such as glycosylphosphatidylinositol-mucins stimulate immunoregulatory receptors, delaying the progression of a protective immune response. After an immunologically silent entry at the early phase of infection, T. cruzi elicits polyclonal B cell activation, hypergammaglobulinemia, and unspecific anti-T. cruzi antibodies, which are inefficient in controlling the infection. Additionally, the coexpression of several related, but not identical, epitopes derived from trypomastigote surface proteins delays the generation of T. cruzi-specific neutralizing antibodies. Later in the infection, the establishment of an anti-T. cruzi CD8(+) immune response focused on the parasite's immunodominant epitopes controls parasitemia and tissue infection, but fails to completely eliminate the parasite. This outcome is not detrimental to the parasite, as it reduces host mortality and maintains the parasite infectivity toward the insect vectors.
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Affiliation(s)
- Mariana S Cardoso
- Laboratório de Imunologia e Genômica de Parasitos, Departamento de Parasitologia, Universidade Federal de Minas Gerais , Belo Horizonte , Minas Gerais, Brazil
| | - João Luís Reis-Cunha
- Laboratório de Imunologia e Genômica de Parasitos, Departamento de Parasitologia, Universidade Federal de Minas Gerais , Belo Horizonte , Minas Gerais, Brazil
| | - Daniella C Bartholomeu
- Laboratório de Imunologia e Genômica de Parasitos, Departamento de Parasitologia, Universidade Federal de Minas Gerais , Belo Horizonte , Minas Gerais, Brazil
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Hovel-Miner G, Mugnier M, Papavasiliou FN, Pinger J, Schulz D. A Host-Pathogen Interaction Reduced to First Principles: Antigenic Variation in T. brucei. Results Probl Cell Differ 2015; 57:23-46. [PMID: 26537376 DOI: 10.1007/978-3-319-20819-0_2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Antigenic variation is a common microbial survival strategy, powered by diversity in expressed surface antigens across the pathogen population over the course of infection. Even so, among pathogens, African trypanosomes have the most comprehensive system of antigenic variation described. African trypanosomes (Trypanosoma brucei spp.) are unicellular parasites native to sub-Saharan Africa, and the causative agents of sleeping sickness in humans and of n'agana in livestock. They cycle between two habitats: a specific species of fly (Glossina spp. or, colloquially, the tsetse) and the bloodstream of their mammalian hosts, by assuming a succession of proliferative and quiescent developmental forms, which vary widely in cell architecture and function. Key to each of the developmental forms that arise during these transitions is the composition of the surface coat that covers the plasma membrane. The trypanosome surface coat is extremely dense, covered by millions of repeats of developmentally specified proteins: procyclin gene products cover the organism while it resides in the tsetse and metacyclic gene products cover it while in the fly salivary glands, ready to make the transition to the mammalian bloodstream. But by far the most interesting coat is the Variant Surface Glycoprotein (VSG) coat that covers the organism in its infectious form (during which it must survive free living in the mammalian bloodstream). This coat is highly antigenic and elicits robust VSG-specific antibodies that mediate efficient opsonization and complement mediated lysis of the parasites carrying the coat against which the response was made. Meanwhile, a small proportion of the parasite population switches coats, which stimulates a new antibody response to the prevalent (new) VSG species and this process repeats until immune system failure. The disease is fatal unless treated, and treatment at the later stages is extremely toxic. Because the organism is free living in the blood, the VSG:antibody surface represents the interface between pathogen and host, and defines the interaction of the parasite with the immune response. This interaction (cycles of VSG switching, antibody generation, and parasite deletion) results in stereotypical peaks and troughs of parasitemia that were first recognized more than 100 years ago. Essentially, the mechanism of antigenic variation in T. brucei results from a need, at the population level, to maintain an extensive repertoire, to evade the antibody response. In this chapter, we will examine what is currently known about the VSG repertoire, its depth, and the mechanisms that diversify it both at the molecular (DNA) and at the phenotypic (surface displayed) level, as well as how it could interact with antibodies raised specifically against it in the host.
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Affiliation(s)
- Galadriel Hovel-Miner
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
| | - Monica Mugnier
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
| | - F Nina Papavasiliou
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA.
| | - Jason Pinger
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
| | - Danae Schulz
- Laboratory of Lymphocyte Biology, The Rockefeller University, 1230 York Avenue, New York, NY, 10065, USA
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Alsing AK, Sneppen K. Differentiation of developing olfactory neurons analysed in terms of coupled epigenetic landscapes. Nucleic Acids Res 2013; 41:4755-64. [PMID: 23519617 PMCID: PMC3643594 DOI: 10.1093/nar/gkt181] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Revised: 02/26/2013] [Accepted: 02/26/2013] [Indexed: 02/06/2023] Open
Abstract
The olfactory system integrates signals from receptors expressed in olfactory sensory neurons. Each sensory neuron expresses only one of many similar olfactory receptors (ORs). The choice of receptor is made stochastically early in the differentiation process and is maintained throughout the life of the neuron. The underlying mechanism of this stochastic commitment to one of multiple similar OR genes remains elusive. We present a theoretical analysis of a mechanism that invokes important epigenetic properties of the system. The proposed model combines nucleosomes and associated read-write enzymes as mediators of a cis-acting positive feedback with a trans-acting negative feedback, thereby coupling the local epigenetic landscape of the individual OR genes in a way that allow one and only one gene to be active at any time. The model pinpoint that singular gene selection does not require transient mechanisms, enhancer elements or transcription factors to separate choice from maintenance. In addition, our hypothesis allow us to combine all reported characteristics of singular OR gene selection, in particular that OR genes are silenced from OR transgenes. Intriguingly, it predicts that OR transgenes placed in close proximity should always be expressed simultaneously, though rarely.
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Affiliation(s)
| | - Kim Sneppen
- Center for Models of Life, Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen, Denmark
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Telomere length affects the frequency and mechanism of antigenic variation in Trypanosoma brucei. PLoS Pathog 2012; 8:e1002900. [PMID: 22952449 PMCID: PMC3431348 DOI: 10.1371/journal.ppat.1002900] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Accepted: 07/26/2012] [Indexed: 11/19/2022] Open
Abstract
Trypanosoma brucei is a master of antigenic variation and immune response evasion. Utilizing a genomic repertoire of more than 1000 Variant Surface Glycoprotein-encoding genes (VSGs), T. brucei can change its protein coat by “switching” from the expression of one VSG to another. Each active VSG is monoallelically expressed from only one of approximately 15 subtelomeric sites. Switching VSG expression occurs by three predominant mechanisms, arguably the most significant of which is the non-reciprocal exchange of VSG containing DNA by duplicative gene conversion (GC). How T. brucei orchestrates its complex switching mechanisms remains to be elucidated. Recent work has demonstrated that an exogenous DNA break in the active site could initiate a GC based switch, yet the source of the switch-initiating DNA lesion under natural conditions is still unknown. Here we investigated the hypothesis that telomere length directly affects VSG switching. We demonstrate that telomerase deficient strains with short telomeres switch more frequently than genetically identical strains with long telomeres and that, when the telomere is short, switching preferentially occurs by GC. Our data supports the hypothesis that a short telomere at the active VSG expression site results in an increase in subtelomeric DNA breaks, which can initiate GC based switching. In addition to their significance for T. brucei and telomere biology, the findings presented here have implications for the many diverse pathogens that organize their antigenic genes in subtelomeric regions. A broad array of human pathogens (including bacteria, fungi and parasites) vary the proteins on their cell surface to escape the immune response of their hosts. This process, called antigenic variation, relies on a repertoire of variant protein encoding genes in the genome and the organism's ability to accurately switch from the expression of one variant gene to another. A common theme in both the diversification of these variant genes and the mechanisms required for their expression is that they are often located near the ends of chromosomes. The ends of chromosomes are protected by structures called telomeres. Regions near the telomere are referred to as subtelomeric and are commonly thought to be comparatively unstable DNA sites. It is therefore intriguing that organisms that rely on antigenic variation for survival would organize their critical survival genes in these sites. Trypanosoma brucei is a model organism for the study of antigenic variation. The causative agent of African sleeping sickness, this unicellular parasite possesses an antigenic repertoire of unparalleled diversity, which can only be expressed from specific subtelomeric sites. Here we use the power of the T. brucei model to investigate the effect of telomere length on antigenic variation.
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Haanstra JR, Kerkhoven EJ, van Tuijl A, Blits M, Wurst M, van Nuland R, Albert MA, Michels PAM, Bouwman J, Clayton C, Westerhoff HV, Bakker BM. A domino effect in drug action: from metabolic assault towards parasite differentiation. Mol Microbiol 2010; 79:94-108. [DOI: 10.1111/j.1365-2958.2010.07435.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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13
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Adam RD, Nigam A, Seshadri V, Martens CA, Farneth GA, Morrison HG, Nash TE, Porcella SF, Patel R. The Giardia lamblia vsp gene repertoire: characteristics, genomic organization, and evolution. BMC Genomics 2010; 11:424. [PMID: 20618957 PMCID: PMC2996952 DOI: 10.1186/1471-2164-11-424] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Accepted: 07/09/2010] [Indexed: 11/10/2022] Open
Abstract
Background Giardia lamblia trophozoites colonize the intestines of susceptible mammals and cause diarrhea, which can be prolonged despite an intestinal immune response. The variable expression of the variant-specific surface protein (VSP) genes may contribute to this prolonged infection. Only one is expressed at a time, and switching expression from one gene to another occurs by an epigenetic mechanism. Results The WB Giardia isolate has been sequenced at 10× coverage and assembled into 306 contigs as large as 870 kb in size. We have used this assembly to evaluate the genomic organization and evolution of the vsp repertoire. We have identified 228 complete and 75 partial vsp gene sequences for an estimated repertoire of 270 to 303, making up about 4% of the genome. The vsp gene diversity includes 30 genes containing tandem repeats, and 14 vsp pairs of identical genes present in either head to head or tail to tail configurations (designated as inverted pairs), where the two genes are separated by 2 to 4 kb of non-coding DNA. Interestingly, over half the total vsp repertoire is present in the form of linear gene arrays that can contain up to 10 vsp gene members. Lastly, evidence for recombination within and across minor clades of vsp genes is provided. Conclusions The data we present here is the first comprehensive analysis of the vsp gene family from the Genotype A1 WB isolate with an emphasis on vsp characterization, function, evolution and contributions to pathogenesis of this important pathogen.
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Affiliation(s)
- Rodney D Adam
- Departments of Medicine and Immunobiology, University of Arizona College of Medicine, Tucson, AZ, USA.
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14
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Abstract
Parasitic infections previously seen only in developing tropical settings can be currently diagnosed worldwide due to travel and population migration. Some parasites may directly or indirectly affect various anatomical structures of the heart, with infections manifested as myocarditis, pericarditis, pancarditis, or pulmonary hypertension. Thus, it has become quite relevant for clinicians in developed settings to consider parasitic infections in the differential diagnosis of myocardial and pericardial disease anywhere around the globe. Chagas' disease is by far the most important parasitic infection of the heart and one that it is currently considered a global parasitic infection due to the growing migration of populations from areas where these infections are highly endemic to settings where they are not endemic. Current advances in the treatment of African trypanosomiasis offer hope to prevent not only the neurological complications but also the frequently identified cardiac manifestations of this life-threatening parasitic infection. The lack of effective vaccines, optimal chemoprophylaxis, or evidence-based pharmacological therapies to control many of the parasitic diseases of the heart, in particular Chagas' disease, makes this disease one of the most important public health challenges of our time.
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15
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Jackson AP, Sanders M, Berry A, McQuillan J, Aslett MA, Quail MA, Chukualim B, Capewell P, MacLeod A, Melville SE, Gibson W, Barry JD, Berriman M, Hertz-Fowler C. The genome sequence of Trypanosoma brucei gambiense, causative agent of chronic human african trypanosomiasis. PLoS Negl Trop Dis 2010; 4:e658. [PMID: 20404998 PMCID: PMC2854126 DOI: 10.1371/journal.pntd.0000658] [Citation(s) in RCA: 118] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Accepted: 03/02/2010] [Indexed: 12/03/2022] Open
Abstract
Background Trypanosoma brucei gambiense is the causative agent of chronic Human African Trypanosomiasis or sleeping sickness, a disease endemic across often poor and rural areas of Western and Central Africa. We have previously published the genome sequence of a T. b. brucei isolate, and have now employed a comparative genomics approach to understand the scale of genomic variation between T. b. gambiense and the reference genome. We sought to identify features that were uniquely associated with T. b. gambiense and its ability to infect humans. Methods and Findings An improved high-quality draft genome sequence for the group 1 T. b. gambiense DAL 972 isolate was produced using a whole-genome shotgun strategy. Comparison with T. b. brucei showed that sequence identity averages 99.2% in coding regions, and gene order is largely collinear. However, variation associated with segmental duplications and tandem gene arrays suggests some reduction of functional repertoire in T. b. gambiense DAL 972. A comparison of the variant surface glycoproteins (VSG) in T. b. brucei with all T. b. gambiense sequence reads showed that the essential structural repertoire of VSG domains is conserved across T. brucei. Conclusions This study provides the first estimate of intraspecific genomic variation within T. brucei, and so has important consequences for future population genomics studies. We have shown that the T. b. gambiense genome corresponds closely with the reference, which should therefore be an effective scaffold for any T. brucei genome sequence data. As VSG repertoire is also well conserved, it may be feasible to describe the total diversity of variant antigens. While we describe several as yet uncharacterized gene families with predicted cell surface roles that were expanded in number in T. b. brucei, no T. b. gambiense-specific gene was identified outside of the subtelomeres that could explain the ability to infect humans. Sleeping sickness, or Human African Trypanosomiasis, is a disease affecting the health and productivity of poor people in many rural areas of sub-Saharan Africa. The disease is caused by a single-celled flagellate, Trypanosoma brucei, which evades the immune system by periodically switching the proteins on its surface. We have produced a genome sequence for T. brucei gambiense, which is the particular subspecies causing most disease in humans. We compared this with an existing reference genome for a non-human infecting strain (T. b. brucei 927) to identify genes in T. b. gambiense that might explain its ability to infect humans and to assess how well the reference performs as a universal plan for all T. brucei. The genome sequences differ only due to rare insertions and duplications and homologous genes are over 95% identical on average. The archive of surface antigens that enable the parasite to switch its protein coat is remarkably consistent, even though it evolves very quickly. We identified genes with predicted cell surface functions that are only present in T. b. brucei and have evolved rapidly in recent time. These genes might help to explain variation in disease pathology between different T. brucei strains in different hosts.
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Affiliation(s)
- Andrew P. Jackson
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Mandy Sanders
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Andrew Berry
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Jacqueline McQuillan
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Martin A. Aslett
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Michael A. Quail
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | | | - Paul Capewell
- Wellcome Centre for Molecular Parasitology, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow, United Kingdom
| | - Annette MacLeod
- Wellcome Centre for Molecular Parasitology, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow, United Kingdom
| | | | - Wendy Gibson
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
| | - J. David Barry
- Wellcome Centre for Molecular Parasitology, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow, United Kingdom
| | - Matthew Berriman
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Christiane Hertz-Fowler
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
- * E-mail:
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16
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Immunobiology of African trypanosomes: need of alternative interventions. J Biomed Biotechnol 2010; 2010:389153. [PMID: 20182644 PMCID: PMC2826769 DOI: 10.1155/2010/389153] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 10/29/2009] [Accepted: 12/23/2009] [Indexed: 02/08/2023] Open
Abstract
Trypanosomiasis is one of the major parasitic diseases for which control is still far from reality. The vaccination approaches by using dominant surface proteins have not been successful, mainly due to antigenic variation of the parasite surface coat. On the other hand, the chemotherapeutic drugs in current use for the treatment of this disease are toxic and problems of resistance are increasing (see Kennedy (2004) and Legros et al. (2002)). Therefore, alternative approaches in both treatment and vaccination against trypanosomiasis are needed at this time. To be able to design and develop such alternatives, the biology of this parasite and the host response against the pathogen need to be studied. These two aspects of this disease with few examples of alternative approaches are discussed here.
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Verstrepen KJ, Fink GR. Genetic and epigenetic mechanisms underlying cell-surface variability in protozoa and fungi. Annu Rev Genet 2009; 43:1-24. [PMID: 19640229 DOI: 10.1146/annurev-genet-102108-134156] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Eukaryotic microorganisms have evolved ingenious mechanisms to generate variability at their cell surface, permitting differential adherence, rapid adaptation to changing environments, and evasion of immune surveillance. Fungi such as Saccharomyces cerevisiae and the pathogen Candida albicans carry a family of mucin and adhesin genes that allow adhesion to various surfaces and tissues. Trypanosoma cruzi, T. brucei, and Plasmodium falciparum likewise contain large arsenals of different cell surface adhesion genes. In both yeasts and protozoa, silencing and differential expression of the gene family results in surface variability. Here, we discuss unexpected similarities in the structure and genomic location of the cell surface genes, the role of repeated DNA sequences, and the genetic and epigenetic mechanisms-all of which contribute to the remarkable cell surface variability in these highly divergent microbes.
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18
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Landeira D, Bart JM, Van Tyne D, Navarro M. Cohesin regulates VSG monoallelic expression in trypanosomes. J Cell Biol 2009; 186:243-54. [PMID: 19635842 PMCID: PMC2717648 DOI: 10.1083/jcb.200902119] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Accepted: 06/25/2009] [Indexed: 11/22/2022] Open
Abstract
Antigenic variation allows Trypanosoma brucei to evade the host immune response by switching the expression of 1 out of approximately 15 telomeric variant surface glycoprotein (VSG) expression sites (ESs). VSG ES transcription is mediated by RNA polymerase I in a discrete nuclear site named the ES body (ESB). However, nothing is known about how the monoallelic VSG ES transcriptional state is maintained over generations. In this study, we show that during S and G2 phases and early mitosis, the active VSG ES locus remains associated with the single ESB and exhibits a delay in the separation of sister chromatids relative to control loci. This delay is dependent on the cohesin complex, as partial knockdown of cohesin subunits resulted in premature separation of sister chromatids of the active VSG ES. Cohesin depletion also prompted transcriptional switching from the active to previously inactive VSG ESs. Thus, in addition to maintaining sister chromatid cohesion during mitosis, the cohesin complex plays an essential role in the correct epigenetic inheritance of the active transcriptional VSG ES state.
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Affiliation(s)
- David Landeira
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Cientificas, 18100 Granada, Spain
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19
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A yeast-endonuclease-generated DNA break induces antigenic switching in Trypanosoma brucei. Nature 2009; 459:278-81. [PMID: 19369939 PMCID: PMC2688456 DOI: 10.1038/nature07982] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2008] [Accepted: 03/10/2009] [Indexed: 11/10/2022]
Abstract
Trypanosoma brucei is the causative agent of African Sleeping Sickness in humans and one of the causes of Nagana in cattle. This protozoan parasite evades the host immune system by antigenic variation, a periodic switching of its variant surface glycoprotein (VSG) coat. VSG switching is spontaneous and occurs at a rate of about 10-2 –10-3 per population doubling in recent isolates from nature, but at a dramatically reduced rate (10-5-10-6) in laboratory-adapted strains1-3. VSG switching is thought to occur predominantly through gene conversion, a form of homologous recombination (HR) initiated by a DNA lesion that is used by other pathogens (e.g. Candida albicans, Borrelia sp. and Neisseria gonorrhoeae) to generate surface protein diversity, and by B lymphocytes of the vertebrate immune system to generate antibody diversity. Very little is known about the molecular mechanism of VSG switching in T. brucei. Here we demonstrate that the introduction of a DNA double-stranded break (DSB) adjacent to the ∼70-bp repeats upstream of the transcribed VSG increases switching in vitro ∼250-fold, producing switched clones with a frequency and features similar to those generated early in an infection. We were also able to detect spontaneous DSBs within the 70-bp repeats upstream of the actively transcribed VSG, suggesting that a DSB is a natural intermediate of VSG gene conversion and that VSG switching is the result of the resolution of this DSB by break-induced replication (BIR).
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20
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Schmuckli-Maurer J, Casanova C, Schmied S, Affentranger S, Parvanova I, Kang'a S, Nene V, Katzer F, McKeever D, Müller J, Bishop R, Pain A, Dobbelaere DAE. Expression analysis of the Theileria parva subtelomere-encoded variable secreted protein gene family. PLoS One 2009; 4:e4839. [PMID: 19325907 PMCID: PMC2657828 DOI: 10.1371/journal.pone.0004839] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 02/04/2009] [Indexed: 11/23/2022] Open
Abstract
Background The intracellular protozoan parasite Theileria parva transforms bovine lymphocytes inducing uncontrolled proliferation. Proteins released from the parasite are assumed to contribute to phenotypic changes of the host cell and parasite persistence. With 85 members, genes encoding subtelomeric variable secreted proteins (SVSPs) form the largest gene family in T. parva. The majority of SVSPs contain predicted signal peptides, suggesting secretion into the host cell cytoplasm. Methodology/Principal Findings We analysed SVSP expression in T. parva-transformed cell lines established in vitro by infection of T or B lymphocytes with cloned T. parva parasites. Microarray and quantitative real-time PCR analysis revealed mRNA expression for a wide range of SVSP genes. The pattern of mRNA expression was largely defined by the parasite genotype and not by host background or cell type, and found to be relatively stable in vitro over a period of two months. Interestingly, immunofluorescence analysis carried out on cell lines established from a cloned parasite showed that expression of a single SVSP encoded by TP03_0882 is limited to only a small percentage of parasites. Epitope-tagged TP03_0882 expressed in mammalian cells was found to translocate into the nucleus, a process that could be attributed to two different nuclear localisation signals. Conclusions Our analysis reveals a complex pattern of Theileria SVSP mRNA expression, which depends on the parasite genotype. Whereas in cell lines established from a cloned parasite transcripts can be found corresponding to a wide range of SVSP genes, only a minority of parasites appear to express a particular SVSP protein. The fact that a number of SVSPs contain functional nuclear localisation signals suggests that proteins released from the parasite could contribute to phenotypic changes of the host cell. This initial characterisation will facilitate future studies on the regulation of SVSP gene expression and the potential biological role of these enigmatic proteins.
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Affiliation(s)
| | - Carlo Casanova
- Molecular Pathobiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland
| | - Stéfanie Schmied
- Molecular Pathobiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland
| | - Sarah Affentranger
- Molecular Pathobiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland
| | - Iana Parvanova
- Molecular Pathobiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland
| | - Simon Kang'a
- The Institute for Genomic Research (TIGR), Rockville, Maryland, United States of America
| | - Vishvanath Nene
- The Institute for Genomic Research (TIGR), Rockville, Maryland, United States of America
| | - Frank Katzer
- Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian, United Kingdom
| | - Declan McKeever
- Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian, United Kingdom
| | - Joachim Müller
- Institute of Parasitology, University of Bern, Bern, Switzerland
| | - Richard Bishop
- International Livestock Research Institute, Nairobi, Kenya
| | - Arnab Pain
- Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Dirk A. E. Dobbelaere
- Molecular Pathobiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland
- * E-mail:
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21
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Universal primers suitable to assess population dynamics reveal apparent mutually exclusive transcription of the Babesia bovis ves1alpha gene. Mol Biochem Parasitol 2009; 166:47-53. [PMID: 19428672 DOI: 10.1016/j.molbiopara.2009.02.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 02/11/2009] [Accepted: 02/16/2009] [Indexed: 11/23/2022]
Abstract
Babesia bovis is an intraerythrocytic hemoparasite of widespread distribution, which adversely affects livestock production in many regions of the world. This parasite establishes persistent infections of long duration, at least in part through rapid antigenic variation of the VESA1 protein on the infected-erythrocyte surface. To understand the dynamics of in vivo antigenic variation among the parasite population it is necessary to have sensitive and broadly applicable tools enabling monitoring of variation events in parasite antigen genes. To address this need for B. bovis, "universal" primers for the polymerase chain reaction have been designed for the ves1alpha gene, spanning from exon 2 to near the 3' end of cysteine-lysine-rich domain (CKRD) sequences in exon 3. These primers robustly amplified this segment, with minimal bias, from essentially the entire repertoire of full-length ves1alpha sequences in the B. bovis Mexico isolate genome, and are equivalently present in other isolates. On purified genomic DNA, this primer set can achieve a sensitivity of 10 genome equivalents or less. When applied to the amplification of cDNA derived from the B. bovis C9.1 clonal line evidence consistent with mutually exclusive transcription of the ves1alpha gene was obtained, concomitant with detection of numerous mutational events among members of the parasite population. These characteristics of the primers will facilitate the application of polymerase chain reaction-based methodologies to the study of B. bovis population and antigenic switching dynamics.
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22
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Peñate X, López-Farfán D, Landeira D, Wentland A, Vidal I, Navarro M. RNA pol II subunit RPB7 is required for RNA pol I-mediated transcription in Trypanosoma brucei. EMBO Rep 2009; 10:252-7. [PMID: 19165144 DOI: 10.1038/embor.2008.244] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 11/27/2008] [Accepted: 12/03/2008] [Indexed: 01/11/2023] Open
Abstract
In the protozoan parasite Trypanosoma brucei, the two main surface glycoprotein genes are transcribed by RNA polymerase I (pol I) instead of RNA pol II, the polymerase committed to the production of mRNA in eukaryotes. This unusual feature might be accomplished by the recruitment of specific subunits or cofactors that allow pol I to transcribe protein-coding RNAs. Here, we report that transcription mediated by pol I requires TbRPB7, a dissociable subunit of the pol II complex. TbRPB7 was found to interact with two pol I-specific subunits, TbRPA1 and TbRPB6z. Pol I-specific transcription was affected on depletion of TbRPB7 in run-on assays, whereas recombinant TbRPB7 increased transcription driven by a pol I promoter. These results represent a unique example of a functional RNA polymerase chimaera consisting of a core pol I complex that recruits a specific pol II subunit.
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Affiliation(s)
- Xenia Peñate
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Científicas, CSIC (Spanish National Research Council), Avda. del Conocimiento s/n, 18100 Granada, Spain
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23
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SnSAG5 is an alternative surface antigen of Sarcocystis neurona strains that is mutually exclusive to SnSAG1. Vet Parasitol 2008; 158:36-43. [DOI: 10.1016/j.vetpar.2008.08.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2008] [Revised: 08/18/2008] [Accepted: 08/18/2008] [Indexed: 11/20/2022]
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Figueiredo LM, Janzen CJ, Cross GA. A histone methyltransferase modulates antigenic variation in African trypanosomes. PLoS Biol 2008; 6:e161. [PMID: 18597556 PMCID: PMC2443197 DOI: 10.1371/journal.pbio.0060161] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2008] [Accepted: 05/23/2008] [Indexed: 11/18/2022] Open
Abstract
To evade the host immune system, several pathogens periodically change their cell-surface epitopes. In the African trypanosomes, antigenic variation is achieved by tightly regulating the expression of a multigene family encoding a large repertoire of variant surface glycoproteins (VSGs). Immune evasion relies on two important features: exposing a single type of VSG at the cell surface and periodically and very rapidly switching the expressed VSG. Transcriptional switching between resident telomeric VSG genes does not involve DNA rearrangements, and regulation is probably epigenetic. The histone methyltransferase DOT1B is a nonessential protein that trimethylates lysine 76 of histone H3 in Trypanosoma brucei. Here we report that transcriptionally silent telomeric VSGs become partially derepressed when DOT1B is deleted, whereas nontelomeric loci are unaffected. DOT1B also is involved in the kinetics of VSG switching: in ΔDOT1B cells, the transcriptional switch is so slow that cells expressing two VSGs persist for several weeks, indicating that monoallelic transcription is compromised. We conclude that DOT1B is required to maintain strict VSG silencing and to ensure rapid transcriptional VSG switching, demonstrating that epigenetics plays an important role in regulating antigenic variation in T. brucei. The surface of Trypanosoma brucei, a unicellular parasite that lives in the bloodstream of its mammalian host, is coated with glycoprotein (VSG) molecules. To evade elimination by the immune system, this parasite replaces its coat with one tailored from another glycoprotein variant. Even though there are hundreds of VSG genes in the genome, this process, called antigenic variation, works because all are silenced except for the one that encodes the current coat. In this work, we show that the chromatin-modifying enzyme DOT1B helps to epigenetically regulate the number of VSGs each parasite can have at a time at the surface and how fast each parasite can switch from one coat to another. In parasites lacking DOT1B, silent VSG genes become partially active and the switch from one VSG to another slows down, allowing two different VSGs to appear on the surface of an individual parasite at the same time. Our studies reveal the importance of epigenetics in regulating VSG genes and provide new insights toward the understanding of this unique survival device. Antigenic variation in Trypanosoma brucei relies on monoallelic expression of a multigene family. New evidence shows that a chromatin-modifying enzyme prevents simultaneous expression of different proteins at the parasite's surface.
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Affiliation(s)
- Luisa M Figueiredo
- Laboratory of Molecular Parasitology, the Rockefeller University, New York, New York, United States of America
| | | | - George A.M Cross
- Laboratory of Molecular Parasitology, the Rockefeller University, New York, New York, United States of America
- * To whom correspondence should be addressed. E-mail:
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Mansfield JM, Paulnock DM. Genetic manipulation of African trypanosomes as a tool to dissect the immunobiology of infection. Parasite Immunol 2008; 30:245-53. [PMID: 18208450 DOI: 10.1111/j.1365-3024.2007.01003.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The variant surface glycoprotein (VSG) coat of African trypanosomes exhibits immunobiological functions distinct from its prominent role as a variant surface antigen. In order to address questions regarding immune stealth effects of VSG switch-variant coats, and the innate immune system activating effects of shed VSG substituents, several groups have genetically modified the ability of trypanosomes to express or release VSG during infection of the mammalian host. The role of mosaic surface coats expressed by VSG switch-variants (VSG double-expressors) in escaping early immune detection, and the role of VSG glycosylphosphatidylinositol (GPI) anchor substituents in regulating host immunity have been revealed, respectively, by stable co-expression of an exogenous VSG gene in trypanosomes expressing an endogenous VSG gene, and by knocking out the genetic locus for GPI-phospholipase C (PLC) that releases VSG from the membrane. Both approaches to genetic modification of African trypanosomes have suggested interesting and unexpected immunobiological effects associated with surface coat molecules.
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Affiliation(s)
- J M Mansfield
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA.
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Denninger V, Koopmann R, Muhammad K, Barth T, Bassarak B, Schönfeld C, Kilunga BK, Duszenko M. Chapter Twenty‐Five Kinetoplastida. Methods Enzymol 2008; 451:373-408. [DOI: 10.1016/s0076-6879(08)03225-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Ottaviani A, Gilson E, Magdinier F. Telomeric position effect: from the yeast paradigm to human pathologies? Biochimie 2007; 90:93-107. [PMID: 17868970 DOI: 10.1016/j.biochi.2007.07.022] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Accepted: 07/25/2007] [Indexed: 01/28/2023]
Abstract
Alteration of the epigenome is associated with a wide range of human diseases. Therefore, deciphering the pathways that regulate the epigenetic modulation of gene expression is a major milestone for the understanding of diverse biological mechanisms and subsequently human pathologies. Although often evoked, little is known on the implication of telomeric position effect, a silencing mechanism combining telomere architecture and classical heterochromatin features, in human cells. Nevertheless, this particular silencing mechanism has been investigated in different organisms and several ingredients are likely conserved during evolution. Subtelomeres are highly dynamic regions near the end of the chromosomes that are prone to recombination and may buffer or facilitate the spreading of silencing that emanates from the telomere. Therefore, the composition and integrity of these regions also concur to the propensity of telomeres to regulate the expression, replication and recombination of adjacent regions. Here we describe the similarities and disparities that exist among the different species at chromosome ends with regard to telomeric silencing regulation with a special accent on its implication in numerous human pathologies.
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Affiliation(s)
- Alexandre Ottaviani
- Laboratoire de Biologie Moléculaire de la Cellule, CNRS UMR5239, Ecole Normale Supérieure de Lyon, UCBL1, IFR128, 46 allée d'Italie, 69364 Lyon Cedex 07, France
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Navarro M, Peñate X, Landeira D. Nuclear architecture underlying gene expression in Trypanosoma brucei. Trends Microbiol 2007; 15:263-70. [PMID: 17481901 DOI: 10.1016/j.tim.2007.04.004] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 03/26/2007] [Accepted: 04/16/2007] [Indexed: 11/24/2022]
Abstract
The influence of nuclear architecture on the regulation of developmental gene expression has recently become evident in many organisms ranging from yeast to humans. During interphase, chromosomes and nuclear structures are in constant motion; therefore, correct temporal association is needed to meet the requirements of gene expression. Trypanosoma brucei is an excellent model system in which to analyze nuclear spatial implications in the regulation of gene expression because the two main surface-protein genes (procyclin and VSG) are transcribed by the highly compartmentalized RNA polymerase I and undergo distinct transcriptional activation or downregulation during developmental differentiation. Furthermore, the infective bloodstream form of the parasite undergoes antigenic variation, displaying sequentially different types of VSG by allelic exclusion. Here, we discuss recent advances in understanding the role of chromosomal nuclear positioning in the regulation of gene expression in T. brucei.
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Affiliation(s)
- Miguel Navarro
- Instituto de Parasitología y Biomedicina López-Neyra, Consejo Superior de Investigaciones Científicas (Spanish National Research Council), Avda. del Conocimiento s/n, 18100 Granada, Spain.
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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] [Abstract] [Key Words] [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.
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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
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Prabhu A, Morrison HG, Martinez CR, Adam RD. Characterisation of the subtelomeric regions of Giardia lamblia genome isolate WBC6. Int J Parasitol 2007; 37:503-13. [PMID: 17275000 DOI: 10.1016/j.ijpara.2006.12.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 11/13/2006] [Accepted: 12/04/2006] [Indexed: 11/19/2022]
Abstract
Giardia trophozoites are polyploid and have five chromosomes. The chromosome homologues demonstrate considerable size heterogeneity due to variation in the subtelomeric regions. We used clones from the genome project with telomeric sequence at one end to identify six subtelomeric regions in addition to previously identified subtelomeric regions, to study the telomeric arrangement of the chromosomes. The subtelomeric regions included two retroposons, one retroposon pseudogene, and two vsp genes, in addition to the previously identified subtelomeric regions that include ribosomal DNA repeats. The presence of vsp genes in a subtelomeric region suggests that telomeric rearrangements may contribute to the generation of vsp diversity. These studies of the subtelomeric regions of Giardia may contribute to our understanding of the factors that maintain stability, while allowing diversity in chromosome structure.
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Affiliation(s)
- Anjali Prabhu
- Department of Immunobiology, University of Arizona College of Medicine, 1501 N. Campbell, Tucson, AZ 85724-5049, USA
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31
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Genest PA, ter Riet B, Cijsouw T, van Luenen HG, Borst P. Telomeric localization of the modified DNA base J in the genome of the protozoan parasite Leishmania. Nucleic Acids Res 2007; 35:2116-24. [PMID: 17329373 PMCID: PMC1874636 DOI: 10.1093/nar/gkm050] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Base J or β-d-glucosylhydroxymethyluracil is a DNA modification replacing a fraction of thymine in the nuclear DNA of kinetoplastid parasites and of Euglena. J is located in the telomeric sequences of Trypanosoma brucei and in other simple repeat DNA sequences. In addition, J was found in the inactive variant surface glycoprotein (VSG) expression sites, but not in the active expression site of T. brucei, suggesting that J could play a role in transcription silencing in T. brucei. We have now looked at the distribution of J in the genomes of other kinetoplastid parasites. First, we analyzed the DNA sequences immunoprecipitated with a J-antiserum in Leishmania major Friedlin. Second, we investigated the co-migration of J- and telomeric repeat-containing DNA sequences of various kinetoplastids using J-immunoblots and Southern blots of fragmented DNA. We find only ∼1% of J outside the telomeric repeat sequences of Leishmania sp. and Crithidia fasciculata, in contrast to the substantial fraction of non-telomeric J found in T. brucei, Trypanosoma equiperdum and Trypanoplasma borreli. Our results suggest that J is a telomeric base modification, recruited for other (unknown) functions in some kinetoplastids and Euglena.
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Affiliation(s)
| | | | | | | | - Piet Borst
- *To whom Correspondence should be addressed. +31 20 512 2880+31 20 669 1383
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32
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Faulkner SD, Oli MW, Kieft R, Cotlin L, Widener J, Shiflett A, Cipriano MJ, Pacocha SE, Birkeland SR, Hajduk SL, McArthur AG. In vitro generation of human high-density-lipoprotein-resistant Trypanosoma brucei brucei. EUKARYOTIC CELL 2007; 5:1276-86. [PMID: 16896212 PMCID: PMC1539141 DOI: 10.1128/ec.00116-06] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The host range of African trypanosomes is influenced by innate protective molecules in the blood of primates. A subfraction of human high-density lipoprotein (HDL) containing apolipoprotein A-I, apolipoprotein L-I, and haptoglobin-related protein is toxic to Trypanosoma brucei brucei but not the human sleeping sickness parasite Trypanosoma brucei rhodesiense. It is thought that T. b. rhodesiense evolved from a T. b. brucei-like ancestor and expresses a defense protein that ablates the antitrypanosomal activity of human HDL. To directly investigate this possibility, we developed an in vitro selection to generate human HDL-resistant T. b. brucei. Here we show that conversion of T. b. brucei from human HDL sensitive to resistant correlates with changes in the expression of the variant surface glycoprotein (VSG) and abolished uptake of the cytotoxic human HDLs. Complete transcriptome analysis of the HDL-susceptible and -resistant trypanosomes confirmed that VSG switching had occurred but failed to reveal the expression of other genes specifically associated with human HDL resistance, including the serum resistance-associated gene (SRA) of T. b. rhodesiense. In addition, we found that while the original active expression site was still utilized, expression of three expression site-associated genes (ESAG) was altered in the HDL-resistant trypanosomes. These findings demonstrate that resistance to human HDLs can be acquired by T. b. brucei.
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Affiliation(s)
- Sara D Faulkner
- Josephine Bay Paul Center, Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA
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Abstract
In recent years, the sequencing and annotation of complete genomes, together with the development of genetic and proteomic techniques to study previously intractable eukaryotic microbes, has revealed interesting new themes in the control of virulence gene expression. Families of variantly expressed genes are found adjacent to telomeres in the genomes of both pathogenic and non-pathogenic organisms. This subtelomeric DNA is normally heterochromatic and higher-order chromatin structure has now come to be recognized as an important factor controlling both the evolution and expression dynamics of these multigene families. In eukaryotic cells, higher-order chromatin structure plays a central role in many DNA processes including the control of chromosome integrity and recombination, DNA partitioning during cell division, and transcriptional control. DNA can be packaged in two distinct forms: euchromatin is relatively accessible to DNA binding proteins and generally contains active genes, while heterochromatin is densely packaged, relatively inaccessible and usually transcriptionally silent. These features of chromatin are epigenetically inherited from cell cycle to cell cycle. This review will focus on the epigenetic mechanisms used to control expression of virulence genes in medically important microbial pathogens. Examples of such control have now been reported in several evolutionarily distant species, revealing what may be a common strategy used to regulate many very different families of genes.
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Affiliation(s)
- Catherine J Merrick
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, 665 Huntington Ave, Building I, Rm 706, Boston, MA 02115, USA
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Abstract
Telomeres are specialized DNA-protein complexes that stabilize chromosome ends, protecting them from nucleolytic degradation and illegitimate recombination. Telomeres form a heterochromatic structure that can suppress the transcription of adjacent genes. These structures might have additional roles in Trypanosoma brucei, as the major surface antigens of this parasite are expressed during its infectious stages from subtelomeric loci. We propose that the telomere protein complexes of trypanosomes and vertebrates are conserved and offer the hypothesis that growth and breakage of telomeric repeats has an important role in regulating parasite antigenic variation in trypanosomes.
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Affiliation(s)
- Oliver Dreesen
- The Rockefeller University, 1230 York Avenue, New York, New York 10021, USA
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35
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Abstract
Protozoan parasites are early branching eukaryotes causing significant morbidity and mortality in humans and livestock. Single-celled parasites have evolved complex life cycles, which may involve multiple host organisms, and strategies to evade host immune responses. Consequently, two key aspects of virulence that underlie pathogenesis are parasite differentiation and antigenic variation, both of which require changes in the expressed genome. Complicating these requisite alterations in the parasite transcriptome is chromatin, which serves as a formidable barrier to DNA processes including transcription, repair, replication and recombination. Considerable progress has been made in the study of chromatin dynamics in other eukaryotes, and there is much to be gained in extending these analyses to protozoan parasites. Much of the work completed to date has focused on histone acetylation and methylation in the apicomplexans and trypanosomatids. As we describe in this review, such studies provide a unique vantage point of the evolutionary picture of eukaryotic cell development, and reveal unique phenomena that could be exploited pharmacologically to treat protozoal diseases.
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Affiliation(s)
- William J Sullivan
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
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Dreesen O, Cross GAM. Telomerase-independent stabilization of short telomeres in Trypanosoma brucei. Mol Cell Biol 2006; 26:4911-9. [PMID: 16782879 PMCID: PMC1489180 DOI: 10.1128/mcb.00212-06] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In cancer cells and germ cells, shortening of chromosome ends is prevented by telomerase. Telomerase-deficient cells have a replicative life span, after which they enter senescence. Senescent cells can give rise to survivors that maintain chromosome ends through recombination-based amplification of telomeric or subtelomeric repeats. We found that in Trypanosoma brucei, critically short telomeres are stable in the absence of telomerase. Telomere stabilization ensured genomic integrity and could have implications for telomere maintenance in human telomerase-deficient cells. Cloning and sequencing revealed 7 to 27 TTAGGG repeats on stabilized telomeres and no changes in the subtelomeric region. Clones with short telomeres were used to study telomere elongation dynamics, which differed dramatically at transcriptionally active and silent telomeres, after restoration of telomerase. We propose that transcription makes the termini of short telomeres accessible for rapid elongation by telomerase and that telomere elongation in T. brucei is not regulated by a protein-counting mechanism. Many minichromosomes were lost after long-term culture in the absence of telomerase, which may reflect their different mitotic segregation properties.
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Affiliation(s)
- Oliver Dreesen
- Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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38
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Haag KL, Gottstein B, Müller N, Schnorr A, Ayala FJ. Redundancy and recombination in the Echinococcus AgB multigene family: is there any similarity with protozoan contingency genes? Parasitology 2006; 133:411-9. [PMID: 16817991 DOI: 10.1017/s0031182006000564] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2006] [Revised: 04/24/2006] [Accepted: 04/25/2006] [Indexed: 11/06/2022]
Abstract
Numerous genetic variants of the Echinococcus antigen B (AgB) are encountered within a single metacestode. This could be a reflection of gene redundancy or the result of a somatic hypermutation process. We evaluate the complexity of the AgB multigene family by characterizing the upstream promoter regions of the 4 already known genes (EgAgB1-EgAgB4) and evaluating their redundancy in the genome of 3 Echinococcus species (E. granulosus, E. ortleppi and E. multilocularis) using PCR-based approaches. We have ascertained that the number of AgB gene copies is quite variable, both within and between species. The most repetitive gene seems to be AgB3, of which there are more than 110 copies in E. ortleppi. For E. granulosus, we have cloned and characterized 10 distinct upstream promoter regions of AgB3 from a single metacestode. Our sequences suggest that AgB1 and AgB3 are involved in gene conversion. These results are discussed in light of the role of gene redundancy and recombination in parasite evasion mechanisms of host immunity, which at present are known for protozoan organisms, but virtually unknown for multicellular parasites.
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Affiliation(s)
- K L Haag
- Department of Genetics, Institute of Biological Sciences, UFRGS, Porto Alegre, 91501-970 RS, Brazil.
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39
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Janzen CJ, van Deursen F, Shi H, Cross GA, Matthews KR, Ullu E. Expression site silencing and life-cycle progression appear normal in Argonaute1-deficient Trypanosoma brucei. Mol Biochem Parasitol 2006; 149:102-107. [PMID: 16735068 PMCID: PMC3904126 DOI: 10.1016/j.molbiopara.2006.04.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2006] [Revised: 04/01/2006] [Accepted: 04/07/2006] [Indexed: 11/19/2022]
Affiliation(s)
- Christian J. Janzen
- Laboratory of Molecular Parasitology, The Rockefeller University, Box 185, 1230 York Avenue, New York, NY 10021-6399, USA
| | - Frederick van Deursen
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, UK
| | - Huafang Shi
- Department of Internal Medicine, Yale Medical School, BCMM 136D, 295 Congress Avenue, Box 9812, New Haven, CT, 06536-8012, USA
| | - George A.M. Cross
- Laboratory of Molecular Parasitology, The Rockefeller University, Box 185, 1230 York Avenue, New York, NY 10021-6399, USA
| | - Keith R. Matthews
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, UK
| | - Elisabetta Ullu
- Department of Internal Medicine, Yale Medical School, BCMM 136D, 295 Congress Avenue, Box 9812, New Haven, CT, 06536-8012, USA
- Department of Cell Biology, Yale Medical School, BCMM 136D, 295 Congress Avenue, Box 9812, New Haven, CT, 06536-8012, USA
- Corresponding author. Tel.: +203 785 3563; fax: +203 785 7329.
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40
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van Luenen HGAM, Kieft R, Mussmann R, Engstler M, ter Riet B, Borst P. Trypanosomes change their transferrin receptor expression to allow effective uptake of host transferrin. Mol Microbiol 2006; 58:151-65. [PMID: 16164555 DOI: 10.1111/j.1365-2958.2005.04831.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In its mammalian host, Trypanosoma brucei covers its iron requirements by receptor-mediated uptake of host transferrin (Tf). The Tf-receptor (Tf-R) is a heterodimeric membrane protein encoded by expression site-associated gene (ESAG) 6 and 7 located promoter-proximal in a polycistronic expression site (ES). Each of the 20 ESs encodes a slightly different Tf-R; these differences strongly affect the binding affinity for Tfs of different hosts. The Tf-R encoded in the 221 ES has a low affinity for dog Tf. Transfer of trypanosomes with an active 221 ES to dilute dog serum leads to growth arrest, which they can overcome by switching to another ES encoding a Tf-R with higher affinity for dog Tf. Here we show that trypanosomes can also adapt to dilute dog serum without switching but by replacing the ESAG7 gene in the 221 ES by one from another ES, by deleting ESAG7 from the 221 ES with concomitant upregulation of transcription of ESAG7 in 'silent' ESs, by grossly overproducing the 221 Tf-R or by combinations of these alterations. Our results illustrate the striking genetic flexibility of trypanosomes.
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Affiliation(s)
- Henri G A M van Luenen
- The Netherlands Cancer Institute, Division of Molecular Biology and Centre for Biomedical Genetics, Plesmanlaan 121, 1060 CX Amsterdam, the Netherlands
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41
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Dzikowski R, Frank M, Deitsch K. Mutually exclusive expression of virulence genes by malaria parasites is regulated independently of antigen production. PLoS Pathog 2006; 2:e22. [PMID: 16518466 PMCID: PMC1386720 DOI: 10.1371/journal.ppat.0020022] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2005] [Accepted: 01/31/2006] [Indexed: 12/04/2022] Open
Abstract
The primary virulence determinant of Plasmodium falciparum malaria parasite–infected cells is a family of heterogeneous surface receptors collectively referred to as PfEMP1. These proteins are encoded by a large, polymorphic gene family called var. The family contains approximately 60 individual genes, which are subject to strict, mutually exclusive expression, with the single expressed var gene determining the antigenic, cytoadherent, and virulence phenotype of the infected cell. The mutually exclusive expression pattern of var genes is imperative for the parasite's ability to evade the host's immune response and is similar to the process of “allelic exclusion” described for mammalian Ig and odorant receptor genes. In mammalian systems, mutually exclusive expression is ensured by negative feedback inhibition mediated by production of a functional protein. To investigate how expression of the var gene family is regulated, we have created transgenic lines of parasites in which expression of individual var loci can be manipulated. Here we show that no such negative feedback system exists in P. falciparum and that this process is dependent solely on the transcriptional regulatory elements immediately adjacent to each gene. Transgenic parasites that are selected to express a var gene in which the PfEMP1 coding region has been replaced by a drug-selectable marker silence all other var genes in the genome, thus effectively knocking out all PfEMP1 expression and indicating that the modified gene is still recognized as a member of the var gene family. Mutually exclusive expression in P. falciparum is therefore regulated exclusively at the level of transcription, and a functional PfEMP1 protein is not necessary for viability or for proper gene regulation in cultured parasites. Mutually exclusive gene expression refers to the ability of an organism to select one member of a large, multicopy gene family for expression while simultaneously silencing all other members of the family. Human malaria parasites utilize this process in regulating the expression of the major antigenic and virulence-determining proteins encoded by a multicopy gene family called var. In any given parasite, only a single var gene is expressed at a time, while all other members of the family are transcriptionally silenced. The mechanism that regulates this tightly controlled process and coordinates switches in gene expression is largely unknown. Here Dzikowski and colleagues show that this process is regulated entirely at the level of transcription, and that protein production and chromosomal context of the genes are not involved. In addition, they identify the DNA elements required for a var gene promoter to be recognized and co-regulated along with the rest of the family. This knowledge has enabled the authors to create transgenic parasites in which they can manipulate expression of the entire var gene family through selection for expression of specific, modified var genes, thus knocking out expression of the main virulence factor of malaria.
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Affiliation(s)
- Ron Dzikowski
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
| | - Matthias Frank
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
- Division of International Health and Infectious Diseases, Weill Medical College of Cornell University, New York, New York, United States of America
| | - Kirk Deitsch
- Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
- * To whom correspondence should be addressed. E-mail:
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42
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Al-Khedery B, Allred DR. Antigenic variation inBabesia bovisoccurs through segmental gene conversion of thevesmultigene family, within a bidirectional locus of active transcription. Mol Microbiol 2005; 59:402-14. [PMID: 16390438 DOI: 10.1111/j.1365-2958.2005.04993.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Antigenic variation in Babesia bovis is one aspect of a multifunctional virulence/survival mechanism mediated by the heterodimeric variant erythrocyte surface antigen 1 (VESA1) protein that also involves endothelial cytoadhesion with sequestration of mature parasitized erythrocytes. The ves1alpha gene encoding the VESA1a subunit was previously identified. In this study, we present the unique organization of the genomic locus from which ves1alpha is transcribed, and identify a novel branch of the ves multigene family, ves1beta. These genes are found together, closely juxtaposed and divergently oriented, at the locus of active transcription. We provide compelling evidence that variation of both transcriptionally active genes occurs through a mechanism of segmental gene conversion involving sequence donor genes of similar organization. These results also suggest the possibility of epigenetic regulation through in situ switching among gene loci, further expanding the potential repertoire of variant proteins.
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Affiliation(s)
- Basima Al-Khedery
- Department of Pathobiology, University of Florida, Gainesville, 32611, USA.
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43
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Proudfoot C, McCulloch R. Distinct roles for two RAD51-related genes in Trypanosoma brucei antigenic variation. Nucleic Acids Res 2005; 33:6906-19. [PMID: 16326865 PMCID: PMC1301600 DOI: 10.1093/nar/gki996] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2005] [Revised: 11/07/2005] [Accepted: 11/16/2005] [Indexed: 12/21/2022] Open
Abstract
In Trypanosoma brucei, DNA recombination is crucial in antigenic variation, a strategy for evading the mammalian host immune system found in a wide variety of pathogens. T.brucei has the capacity to encode >1000 antigenically distinct variant surface glycoproteins (VSGs). By ensuring that only one VSG is expressed on the cell surface at one time, and by periodically switching the VSG gene that is expressed, T.brucei can evade immune killing for prolonged periods. Much of VSG switching appears to rely on a widely conserved DNA repair pathway called homologous recombination, driven by RAD51. Here, we demonstrate that T.brucei encodes a further five RAD51-related proteins, more than has been identified in other single-celled eukaryotes to date. We have investigated the roles of two of the RAD51-related proteins in T.brucei, and show that they contribute to DNA repair, homologous recombination and RAD51 function in the cell. Surprisingly, however, only one of the two proteins contributes to VSG switching, suggesting that the family of diverged RAD51 proteins present in T.brucei have assumed specialized functions in homologous recombination, analogous to related proteins in metazoan eukaryotes.
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Affiliation(s)
- Chris Proudfoot
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, Anderson College56 Dumbarton Road, Glasgow, G11 6NU, UK
| | - Richard McCulloch
- The Wellcome Centre for Molecular Parasitology, University of Glasgow, Anderson College56 Dumbarton Road, Glasgow, G11 6NU, UK
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44
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Aitcheson N, Talbot S, Shapiro J, Hughes K, Adkin C, Butt T, Sheader K, Rudenko G. VSG switching in Trypanosoma brucei: antigenic variation analysed using RNAi in the absence of immune selection. Mol Microbiol 2005; 57:1608-22. [PMID: 16135228 PMCID: PMC1618954 DOI: 10.1111/j.1365-2958.2005.04795.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Trypanosoma brucei relies on antigenic variation of its variant surface glycoprotein (VSG) coat for survival. We show that VSG switching can be efficiently studied in vitro using VSG RNAi in place of an immune system to select for switch variants. Contrary to models predicting an instant switch after inhibition of VSG synthesis, switching was not induced by VSG RNAi and occurred at a rate of 10(-4) per division. We find a highly reproducible hierarchy of VSG activation, which appears to be capable of resetting, whereby more than half of the switch events over 12 experiments were to one of two VSGs. We characterized switched clones according to switch mechanism using marker genes in the active VSG expression site (ES). Transcriptional switches between ESs were the preferred switching mechanism, whereby at least 10 of the 17 ESs identified in T. brucei 427 can be functionally active in vitro. We could specifically select for switches mediated by DNA rearrangements by inducing VSG RNAi in the presence of drug selection for the active ES. Most of the preferentially activated VSGs could be activated by multiple mechanisms. This VSG RNAi-based procedure provides a rapid and powerful means for analysing VSG switching in African trypanosomes entirely in vitro.
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Affiliation(s)
| | | | | | | | | | | | | | - Gloria Rudenko
- * To whom correspondence should be addressed. Tel: +44 1865 281 548, FAX: +44 1865 281 894, E-mail:
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45
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Ralph SA, Scherf A. The epigenetic control of antigenic variation in Plasmodium falciparum. Curr Opin Microbiol 2005; 8:434-40. [PMID: 15979386 DOI: 10.1016/j.mib.2005.06.007] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Accepted: 06/14/2005] [Indexed: 11/16/2022]
Abstract
Much of what is known about antigenic variation in the human malaria parasite Plasmodium falciparum has been established by the study of phenotypic changes at the surface of parasitized red blood cells. Although this has contributed to our fundamental understanding of immune escape, nothing conclusive has been elucidated about the molecular mechanisms that determine activation and silencing of members of the antigenic variation var gene family. Recent findings indicate that reversible chromatin modifications and perinuclear gene movement are epigenetic factors that define the silent and active states of telomere-adjacent var genes.
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Affiliation(s)
- Stuart A Ralph
- Institut Pasteur, Biology of Host-Parasite Interactions, URA 2581, 25 Rue du Docteur Roux, Paris, 75015, France.
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46
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Figueiredo L, Scherf A. Plasmodium telomeres and telomerase: the usual actors in an unusual scenario. Chromosome Res 2005; 13:517-24. [PMID: 16132816 DOI: 10.1007/s10577-005-0996-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
In the last decade, telomeres of malaria parasites have been in the spotlight. A number of different host-parasite interactions involve genes that are regulated through processes unique to telomeres. In the highly proliferative human pathogen, Plasmodium falciparum, telomerase appears to not only promote telomere maintenance but also to repair broken chromosome ends. The characterization of the plasmodial gene that encodes the telomerase reverse transcriptase protein has revealed several unusual features. For example, the predicted protein is approximately three times larger than the yeast homologue, due to many insertions of stretches of basic amino acids. Other telomere-associated proteins have also been identified. One of them, the P. falciparum gene homologous to yeast Sir2, seems to be required for the establishment of a heterochromatin-like structure at the telomeres, which leads to the silencing of subtelomeric genes. It has been shown that PfSir2 associates with promoter regions of silenced genes involved in antigenic variation.
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Affiliation(s)
- Luisa Figueiredo
- Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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Dubois ME, Demick KP, Mansfield JM. Trypanosomes expressing a mosaic variant surface glycoprotein coat escape early detection by the immune system. Infect Immun 2005; 73:2690-7. [PMID: 15845470 PMCID: PMC1087325 DOI: 10.1128/iai.73.5.2690-2697.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Host resistance to African trypanosomiasis is partially dependent on an early and strong T-independent B-cell response against the variant surface glycoprotein (VSG) coat expressed by trypanosomes. The repetitive array of surface epitopes displayed by a monotypic surface coat, in which identical VSG molecules are closely packed together in a uniform architectural display, cross-links cognate B-cell receptors and initiates T-independent B-cell activation events. However, this repetitive array of identical VSG epitopes is altered during the process of antigenic variation, when former and nascent VSG proteins are transiently expressed together in a mosaic surface coat. Thus, T-independent B-cell recognition of the trypanosome surface coat may be disrupted by the introduction of heterologous VSG molecules into the coat structure. To address this hypothesis, we transformed Trypanosoma brucei rhodesiense LouTat 1 with the 117 VSG gene from Trypanosoma brucei brucei MiTat 1.4 in order to produce VSG double expressers; coexpression of the exogenous 117 gene along with the endogenous LouTat 1 VSG gene resulted in the display of a mosaic VSG coat. Results presented here demonstrate that the host's ability to produce VSG-specific antibodies and activate B cells during early infection with VSG double expressers is compromised relative to that during infection with the parental strain, which displays a monotypic coat. These findings suggest a previously unrecognized mechanism of immune response evasion in which coat-switching trypanosomes fail to directly activate B cells until coat VSG homogeneity is achieved. This process affords an immunological advantage to trypanosomes during the process of antigenic variation.
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Affiliation(s)
- Melissa E Dubois
- Department of Bacteriology, University of Wisconsin-Madison, 1925 Willow Drive, Madison, WI 53706, USA
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Li H, Tschudi C. Novel and essential subunits in the 300-kilodalton nuclear cap binding complex of Trypanosoma brucei. Mol Cell Biol 2005; 25:2216-26. [PMID: 15743819 PMCID: PMC1061625 DOI: 10.1128/mcb.25.6.2216-2226.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
One of the unique aspects of RNA processing in trypanosomatid protozoa is the presence of a cap 4 structure (m7Gpppm2(6)AmpAmpCmpm3Um) at the 5' end of all mRNAs. The cap 4 becomes part of the mRNA through trans-splicing of a 39-nucleotide-long sequence donated by the spliced leader RNA. Although the cap 4 modifications are required for trans-splicing to occur, the underlying mechanism remains to be determined. We now describe an unconventional nuclear cap binding complex (CBC) in Trypanosoma brucei with an apparent molecular mass of 300 kDa and consisting of five protein components: the known CBC subunits CBP20 and importin-alpha and three novel proteins that are only present in organisms featuring a cap 4 structure and trans-splicing. Competitive binding studies are consistent with a specific interaction between the CBC and the cap 4 structure. Downregulation of several individual components of the T. brucei CBC by RNA interference demonstrated an essential function at an early step in trans-splicing. Thus, our studies are consistent with the CBC providing a mechanistic link between cap 4 modifications and trans-splicing.
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Affiliation(s)
- Hongjie Li
- Department of Epidemiology and Public Health, Yale University Medical School, BCMM 136C, 295 Congress Ave., New Haven, CT 06536-0812, USA
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49
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Vanhamme L, Pays E. The trypanosome lytic factor of human serum and the molecular basis of sleeping sickness. Int J Parasitol 2004; 34:887-98. [PMID: 15217727 DOI: 10.1016/j.ijpara.2004.04.008] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2004] [Revised: 04/20/2004] [Accepted: 04/20/2004] [Indexed: 02/08/2023]
Abstract
Trypanosoma brucei brucei infects a wide range of mammals but is unable to infect humans because this subspecies is lysed by normal human serum (NHS). The trypanosome lytic factor is associated with High Density Lipoproteins (HDLs). Several HDL-associated components have been proposed as candidate lytic factors, and contradictory hypotheses concerning the mechanism of lysis have been suggested. Elucidation of the process by which Trypanosoma brucei rhodesiense resists lysis and causes human sleeping sickness has indicated that the HDL-bound apolipoprotein L-I (apoL-I) could be the long-sought after lytic component of NHS. This research also allowed the identification of a specific diagnostic DNA probe for T. b. rhodesiense, and may lead to the development of novel anti-trypanosome strategies for use in the field.
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Affiliation(s)
- Luc Vanhamme
- Department of Molecular Biology, Laboratory of Molecular Parasitology, IBMM, University of Brussels, 12, rue des Professeurs Jeener et Brachet, B6041 Gosselies, Belgium
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50
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Lowell JE, Cross GAM. A variant histone H3 is enriched at telomeres in Trypanosoma brucei. J Cell Sci 2004; 117:5937-47. [PMID: 15522895 DOI: 10.1242/jcs.01515] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Variant histones play critical roles in transcriptional activation and repression, DNA repair and chromosome segregation. We have identified HTV, a single-copy gene in Trypanosoma brucei encoding a variant form of histone H3 (H3V). H3V is present at discrete nuclear foci that shift over the course of the cell cycle and associate with the mitotic spindle, a pattern of localization reminiscent of that described previously for both mini-chromosomes and telomeres. By combining fluorescence in situ hybridization with indirect immunofluorescence, we confirmed that the H3V foci overlap with a 177-bp repetitive sequence element found predominantly in mini-chromosomes, as well as with the TTAGGG repeats that compose telomeres. Chromatin immunoprecipitation studies, however, reveal that only the telomeric repeat DNA is substantially enriched with H3V. HTV is not essential for viability, mini-chromosome segregation, telomere maintenance or transcriptional silencing at the telomere-proximal expression sites from which bloodstream-form T. brucei controls antigenic variation. We propose that H3V represents a novel class of histone H3 variant, a finding that has evolutionary implications.
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Affiliation(s)
- Joanna E Lowell
- Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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