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Barcons-Simon A, Carrington M, Siegel TN. Decoding the impact of nuclear organization on antigenic variation in parasites. Nat Microbiol 2023; 8:1408-1418. [PMID: 37524976 DOI: 10.1038/s41564-023-01424-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 06/13/2023] [Indexed: 08/02/2023]
Abstract
Antigenic variation as a strategy to evade the host adaptive immune response has evolved in divergent pathogens. Antigenic variation involves restricted, and often mutually exclusive, expression of dominant antigens and a periodic switch in antigen expression during infection. In eukaryotes, nuclear compartmentalization, including three-dimensional folding of the genome and physical separation of proteins in compartments or condensates, regulates mutually exclusive gene expression and chromosomal translocations. In this Review, we discuss the impact of nuclear organization on antigenic variation in the protozoan pathogens Trypanosoma brucei and Plasmodium falciparum. In particular, we highlight the relevance of nuclear organization in both mutually exclusive antigen expression and genome stability, which underlie antigenic variation.
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Affiliation(s)
- Anna Barcons-Simon
- Division of Experimental Parasitology, Faculty of Veterinary Medicine, Ludwig-Maximilians-Universität München, Munich, Germany
- Biomedical Center, Division of Physiological Chemistry, Faculty of Medicine, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - T Nicolai Siegel
- Division of Experimental Parasitology, Faculty of Veterinary Medicine, Ludwig-Maximilians-Universität München, Munich, Germany.
- Biomedical Center, Division of Physiological Chemistry, Faculty of Medicine, Ludwig-Maximilians-Universität München, Munich, Germany.
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2
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Toh JY, Nkouawa A, Dong G, Kolev NG, Tschudi C. Two cold shock domain containing proteins trigger the development of infectious Trypanosoma brucei. PLoS Pathog 2023; 19:e1011438. [PMID: 37276216 PMCID: PMC10270622 DOI: 10.1371/journal.ppat.1011438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Accepted: 05/22/2023] [Indexed: 06/07/2023] Open
Abstract
Cold shock proteins are members of a family of DNA- and RNA-binding proteins with one or more evolutionarily conserved cold shock domain (CSD). These proteins have a wide variety of biological functions, including DNA-damage repair, mRNA stability, and regulation of transcription, splicing and translation. We previously identified two CSD containing proteins, CSD1 and CSD2, in the protozoan parasite Trypanosoma brucei to be required for RBP6-driven metacyclic production, albeit at different steps of the developmental program. During metacyclogenesis T. brucei undergoes major morphological and metabolic changes that culminate in the establishment of quiescent metacyclic parasites and the acquisition of mammalian infectivity. To investigate the specific role of CSD1 and CSD2 in this process, we ectopically expressed CSD1 or CSD2 in non-infectious procyclic parasites and discovered that each protein is sufficient to produce infectious metacyclic parasites in 24 hours. Domain truncation assays determined that the N-terminal domain, but not the C-terminal domain, of CSD1 and CSD2 was required for metacyclic development. Furthermore, conserved amino acid residues in the CSD of CSD1 and CSD2, known to be important for binding nucleic acids, were found to be necessary for metacyclic production. Using single-end enhanced crosslinking and immunoprecipitation (seCLIP) we identified the specific binding motif of CSD1 and CSD2 as "ANACAU" and the bound mRNAs were enriched for biological processes, including lipid metabolism, microtubule-based movement and nucleocytoplasmic transport that are likely involved in the transition to bloodstream form-like cells.
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Affiliation(s)
- Justin Y Toh
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America
| | - Agathe Nkouawa
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America
| | - Gang Dong
- Max Perutz Labs, Vienna Biocenter, Center for Medical Biochemistry, Medical University of Vienna, Vienna, Austria
| | - Nikolay G Kolev
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America
| | - Christian Tschudi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America
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3
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Tihon E, Rubio-Peña K, Dujeancourt-Henry A, Crouzols A, Rotureau B, Glover L. VEX1 Influences mVSG Expression During the Transition to Mammalian Infectivity in Trypanosoma brucei. Front Cell Dev Biol 2022; 10:851475. [PMID: 35450294 PMCID: PMC9017762 DOI: 10.3389/fcell.2022.851475] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 02/28/2022] [Indexed: 11/28/2022] Open
Abstract
The Trypanosoma (T) brucei life cycle alternates between the tsetse fly vector and the mammalian host. In the insect, T. brucei undergoes several developmental stages until it reaches the salivary gland and differentiates into the metacyclic form, which is capable of infecting the next mammalian host. Mammalian infectivity is dependent on expression of the metacyclic variant surface glycoprotein genes as the cells develop into mature metacyclics. The VEX complex is essential for monoallelic variant surface glycoprotein expression in T. brucei bloodstream form, however, initiation of expression of the surface proteins genes during metacyclic differentiation is poorly understood. To better understand the transition to mature metacyclics and the control of metacyclic variant surface glycoprotein expression we examined the role of VEX1 in this process. We show that modulating VEX1 expression leads to a dysregulation of variant surface glycoprotein expression during metacyclogenesis, and that following both in vivo and in vitro metacyclic differentiation VEX1 relocalises from multiple nuclear foci in procyclic cells to one to two distinct nuclear foci in metacyclic cells - a pattern like the one seen in mammalian infective bloodstream forms. Our data suggest a role for VEX1 in the metacyclic differentiation process and their capacity to become infectious to the mammalian host.
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Affiliation(s)
- Eliane Tihon
- Trypanosome Molecular Biology, Institut Pasteur, Université Paris Cité, Paris, France
| | - Karinna Rubio-Peña
- Trypanosome Molecular Biology, Institut Pasteur, Université Paris Cité, Paris, France
| | | | - Aline Crouzols
- Trypanosome Transmission Group, Trypanosome Cell Biology Unit, INSERM U1201 and, Institut Pasteur, Paris, France
| | - Brice Rotureau
- Trypanosome Transmission Group, Trypanosome Cell Biology Unit, INSERM U1201 and, Institut Pasteur, Paris, France
- Parasitology Lab, Institut Pasteur of Guinea, Conakry, Guinea
| | - Lucy Glover
- Trypanosome Molecular Biology, Institut Pasteur, Université Paris Cité, Paris, France
- *Correspondence: Lucy Glover,
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4
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Florini F, Visone JE, Deitsch KW. Shared Mechanisms for Mutually Exclusive Expression and Antigenic Variation by Protozoan Parasites. Front Cell Dev Biol 2022; 10:852239. [PMID: 35350381 PMCID: PMC8957917 DOI: 10.3389/fcell.2022.852239] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 02/17/2022] [Indexed: 01/05/2023] Open
Abstract
Cellular decision-making at the level of gene expression is a key process in the development and evolution of every organism. Variations in gene expression can lead to phenotypic diversity and the development of subpopulations with adaptive advantages. A prime example is the mutually exclusive activation of a single gene from within a multicopy gene family. In mammals, this ranges from the activation of one of the two immunoglobulin (Ig) alleles to the choice in olfactory sensory neurons of a single odorant receptor (OR) gene from a family of more than 1,000. Similarly, in parasites like Trypanosoma brucei, Giardia lamblia or Plasmodium falciparum, the process of antigenic variation required to escape recognition by the host immune system involves the monoallelic expression of vsg, vsp or var genes, respectively. Despite the importance of this process, understanding how this choice is made remains an enigma. The development of powerful techniques such as single cell RNA-seq and Hi-C has provided new insights into the mechanisms these different systems employ to achieve monoallelic gene expression. Studies utilizing these techniques have shown how the complex interplay between nuclear architecture, physical interactions between chromosomes and different chromatin states lead to single allele expression. Additionally, in several instances it has been observed that high-level expression of a single gene is preceded by a transient state where multiple genes are expressed at a low level. In this review, we will describe and compare the different strategies that organisms have evolved to choose one gene from within a large family and how parasites employ this strategy to ensure survival within their hosts.
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Howick VM, Peacock L, Kay C, Collett C, Gibson W, Lawniczak MKN. Single-cell transcriptomics reveals expression profiles of Trypanosoma brucei sexual stages. PLoS Pathog 2022; 18:e1010346. [PMID: 35255094 PMCID: PMC8939820 DOI: 10.1371/journal.ppat.1010346] [Citation(s) in RCA: 7] [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: 11/01/2021] [Revised: 03/22/2022] [Accepted: 02/06/2022] [Indexed: 01/26/2023] Open
Abstract
Early diverging lineages such as trypanosomes can provide clues to the evolution of sexual reproduction in eukaryotes. In Trypanosoma brucei, the pathogen that causes Human African Trypanosomiasis, sexual reproduction occurs in the salivary glands of the insect host, but analysis of the molecular signatures that define these sexual forms is complicated because they mingle with more numerous, mitotically-dividing developmental stages. We used single-cell RNA-sequencing (scRNAseq) to profile 388 individual trypanosomes from midgut, proventriculus, and salivary glands of infected tsetse flies allowing us to identify tissue-specific cell types. Further investigation of salivary gland parasite transcriptomes revealed fine-scale changes in gene expression over a developmental progression from putative sexual forms through metacyclics expressing variant surface glycoprotein genes. The cluster of cells potentially containing sexual forms was characterized by high level transcription of the gamete fusion protein HAP2, together with an array of surface proteins and several genes of unknown function. We linked these expression patterns to distinct morphological forms using immunofluorescence assays and reporter gene expression to demonstrate that the kinetoplastid-conserved gene Tb927.10.12080 is exclusively expressed at high levels by meiotic intermediates and gametes. Further experiments are required to establish whether this protein, currently of unknown function, plays a role in gamete formation and/or fusion.
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Affiliation(s)
- Virginia M. Howick
- Institute of Biodiversity, Animal Health, and Comparative Medicine, University of Glasgow, Glasgow, United Kingdom
- Wellcome Centre for Integrative Parasitology, University of Glasgow, Glasgow, United Kingdom
- Parasites and Microbes Programme, Wellcome Sanger Institute, Hinxton, United Kingdom
| | - Lori Peacock
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
- Bristol Veterinary School, University of Bristol, Langford, United Kingdom
| | - Chris Kay
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
| | - Clare Collett
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
| | - Wendy Gibson
- School of Biological Sciences, University of Bristol, Bristol, United Kingdom
| | - Mara K. N. Lawniczak
- Parasites and Microbes Programme, Wellcome Sanger Institute, Hinxton, United Kingdom
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6
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Hutchinson S, Foulon S, Crouzols A, Menafra R, Rotureau B, Griffiths AD, Bastin P. The establishment of variant surface glycoprotein monoallelic expression revealed by single-cell RNA-seq of Trypanosoma brucei in the tsetse fly salivary glands. PLoS Pathog 2021; 17:e1009904. [PMID: 34543350 PMCID: PMC8509897 DOI: 10.1371/journal.ppat.1009904] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Revised: 10/12/2021] [Accepted: 08/17/2021] [Indexed: 12/27/2022] Open
Abstract
The long and complex Trypanosoma brucei development in the tsetse fly vector culminates when parasites gain mammalian infectivity in the salivary glands. A key step in this process is the establishment of monoallelic variant surface glycoprotein (VSG) expression and the formation of the VSG coat. The establishment of VSG monoallelic expression is complex and poorly understood, due to the multiple parasite stages present in the salivary glands. Therefore, we sought to further our understanding of this phenomenon by performing single-cell RNA-sequencing (scRNA-seq) on these trypanosome populations. We were able to capture the developmental program of trypanosomes in the salivary glands, identifying populations of epimastigote, gamete, pre-metacyclic and metacyclic cells. Our results show that parasite metabolism is dramatically remodeled during development in the salivary glands, with a shift in transcript abundance from tricarboxylic acid metabolism to glycolytic metabolism. Analysis of VSG gene expression in pre-metacyclic and metacyclic cells revealed a dynamic VSG gene activation program. Strikingly, we found that pre-metacyclic cells contain transcripts from multiple VSG genes, which resolves to singular VSG gene expression in mature metacyclic cells. Single molecule RNA fluorescence in situ hybridisation (smRNA-FISH) of VSG gene expression following in vitro metacyclogenesis confirmed this finding. Our data demonstrate that multiple VSG genes are transcribed before a single gene is chosen. We propose a transcriptional race model governs the initiation of monoallelic expression. African trypanosomes are parasitic protists which cause endemic disease in sub-Saharan Africa. To evade mammalian immune responses the parasite has developed a system of antigenic variation, where the surface of the cell is covered in a tightly packed coat of variant surface glycoproteins (VSGs). Each cell expresses only one variant surface glycoprotein at a time, and this is periodically switched to evade new antibodies. The process of singular gene expression is termed monoallelic expression and this has two components, establishment and maintenance, i.e. how a single gene is selected for expression and how its singular expression is maintained throughout successive generations. The establishment of monoallelic VSG gene expression occurs in the salivary gland of the tsetse fly vector, although this process is not well understood. We used single cell gene expression profiling applied to thousands of single cells in the salivary gland of the fly. We show that in order to select a single gene, trypanosomes initially transcribe multiple VSGs before a single gene is selected for high-level expression. We propose a model where this process is driven by a race to accumulate transcription factors at a single VSG gene.
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Affiliation(s)
- Sebastian Hutchinson
- Trypanosome Cell Biology Unit and INSERM U1201, Institut Pasteur, Paris, France
- * E-mail:
| | - Sophie Foulon
- Laboratoire de Biochimie, CBI, ESPCI Paris, Université PSL, CNRS UMR 8231, Paris, France
| | - Aline Crouzols
- Trypanosome Cell Biology Unit and INSERM U1201, Institut Pasteur, Paris, France
| | - Roberta Menafra
- Laboratoire de Biochimie, CBI, ESPCI Paris, Université PSL, CNRS UMR 8231, Paris, France
| | - Brice Rotureau
- Trypanosome Cell Biology Unit and INSERM U1201, Institut Pasteur, Paris, France
| | - Andrew D. Griffiths
- Laboratoire de Biochimie, CBI, ESPCI Paris, Université PSL, CNRS UMR 8231, Paris, France
| | - Philippe Bastin
- Trypanosome Cell Biology Unit and INSERM U1201, Institut Pasteur, Paris, France
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7
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Identification of positive and negative regulators in the stepwise developmental progression towards infectivity in Trypanosoma brucei. Sci Rep 2021; 11:5755. [PMID: 33707699 PMCID: PMC7952579 DOI: 10.1038/s41598-021-85225-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 02/25/2021] [Indexed: 11/17/2022] Open
Abstract
Trypanosoma brucei is a protozoan parasite that causes important human and livestock diseases in sub-Saharan Africa. By overexpressing a single RNA-binding protein, RBP6, in non-infectious procyclics trypanosomes, we previously recapitulated in vitro the events occurring in the tsetse fly vector, namely the development of epimastigotes and infectious, quiescent metacyclic parasites. To identify genes involved in this developmental progression, we individually targeted 86 transcripts by RNAi in the RBP6 overexpression cell line and assessed the loss-of-function phenotypes on repositioning the kinetoplast, an organelle that contains the mitochondrial genome, the expression of BARP or brucei alanine rich protein, a marker for epimastigotes, and metacyclic variant surface glycoprotein. This screen identified 22 genes that positively or negatively regulate the stepwise progression towards infectivity at different stages. Two previously uncharacterized putative nucleic acid binding proteins emerged as potent regulators, namely the cold shock domain-containing proteins CSD1 and CSD2. RNA-Seq data from a selected group of cell lines further revealed that the components of gene expression regulatory networks identified in this study affected the abundance of a subset of transcripts in very similar fashion. Finally, our data suggest a considerable overlap between the genes that regulate the formation of stumpy bloodstream form trypanosomes and the genes that govern the development of metacyclic form parasites.
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Saha A, Nanavaty VP, Li B. Telomere and Subtelomere R-loops and Antigenic Variation in Trypanosomes. J Mol Biol 2019; 432:4167-4185. [PMID: 31682833 DOI: 10.1016/j.jmb.2019.10.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2019] [Revised: 10/02/2019] [Accepted: 10/21/2019] [Indexed: 12/12/2022]
Abstract
Trypanosoma brucei is a kinetoplastid parasite that causes African trypanosomiasis, which is fatal if left untreated. T. brucei regularly switches its major surface antigen, VSG, to evade the host immune responses. VSGs are exclusively expressed from subtelomeric expression sites (ESs) where VSG genes are flanked by upstream 70 bp repeats and downstream telomeric repeats. The telomere downstream of the active VSG is transcribed into a long-noncoding RNA (TERRA), which forms RNA:DNA hybrids (R-loops) with the telomeric DNA. At an elevated level, telomere R-loops cause more telomeric and subtelomeric double-strand breaks (DSBs) and increase VSG switching rate. In addition, stabilized R-loops are observed at the 70 bp repeats and immediately downstream of ES-linked VSGs in RNase H defective cells, which also have an increased amount of subtelomeric DSBs and more frequent VSG switching. Although subtelomere plasticity is expected to be beneficial to antigenic variation, severe defects in subtelomere integrity and stability increase cell lethality. Therefore, regulation of the telomere and 70 bp repeat R-loop levels is important for the balance between antigenic variation and cell fitness in T. brucei. In addition, the high level of the active ES transcription favors accumulation of R-loops at the telomere and 70 bp repeats, providing an intrinsic mechanism for local DSB formation, which is a strong inducer of VSG switching.
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Affiliation(s)
- Arpita Saha
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Science and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
| | - Vishal P Nanavaty
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Science and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
| | - Bibo Li
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Science and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA; Case Comprehensive Cancer Center, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
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Shi H, Butler K, Tschudi C. Differential expression analysis of transcriptome data of Trypanosoma brucei RBP6 induction in procyclics leading to infectious metacyclics and bloodstream forms in vitro. Data Brief 2018; 20:978-980. [PMID: 30225310 PMCID: PMC6139001 DOI: 10.1016/j.dib.2018.08.169] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 08/27/2018] [Indexed: 02/02/2023] Open
Abstract
We used an in vitro system based on the inducible expression of the RNA binding protein 6 (RBP6) to monitor transcriptome changes during the differentiation of Trypanosoma brucei from non-infectious procyclics to infectious metacyclics and from metacyclics to bloodstream forms. This data file describes the bioinformatics analysis of 20 distinct RNA-Seq samples, with four biological replicates each, highlighting differential transcript abundance. Additional functional annotation analysis using Gene Ontology is also presented. Complete raw data files were deposited at the NCBI Sequence Read Archive - SRA at http://www.ncbi.nlm.nih.gov/Traces/sra/sra.cgi with accession numbers: SRP153824, SRP153562, and SRP152737.
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Affiliation(s)
- Huafang Shi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA
| | - Kiantra Butler
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA
| | - Christian Tschudi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA
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Shi H, Butler K, Tschudi C. A single-point mutation in the RNA-binding protein 6 generates Trypanosoma brucei metacyclics that are able to progress to bloodstream forms in vitro. Mol Biochem Parasitol 2018; 224:50-56. [PMID: 30055184 DOI: 10.1016/j.molbiopara.2018.07.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 07/20/2018] [Accepted: 07/22/2018] [Indexed: 01/27/2023]
Abstract
We previously established an in vitro differentiation system based on the inducible expression of the RNA binding protein 6 (RBP6), which initiated differentiation of Trypanosoma brucei non-infectious procyclics to infectious metacyclics (MFs). However, further differentiation to bloodstream forms (BFs) required infection of mice. Here we report the serendipitous isolation of a single point mutation in RBP6 (Q109K), whose expression not only generated MFs, but purified MFs continued the developmental cycle in vitro to BFs expressing variant surface glycoprotein-2 (VSG-2), formerly known as VSG 221. This transition occurred over a period of 11 days and by RNA-Seq, VSG-2 was first measureable on day 1, whereas metacyclic VSGs were detected up to 8 days. We further showed that inducible expression of mutant RBP6 appeared to skip the intermediate epimastigote stage and we highlight the potential involvement of RBP33 in the establishment of metacyclics and in particular in the generation of metacyclics uncharacteristically arrested at the G2/M checkpoint.
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Affiliation(s)
- Huafang Shi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, Connecticut 06520, USA
| | - Kiantra Butler
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, Connecticut 06520, USA
| | - Christian Tschudi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, Connecticut 06520, USA.
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Cestari I, Stuart K. Transcriptional Regulation of Telomeric Expression Sites and Antigenic Variation in Trypanosomes. Curr Genomics 2018; 19:119-132. [PMID: 29491740 PMCID: PMC5814960 DOI: 10.2174/1389202918666170911161831] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 04/03/2017] [Accepted: 05/04/2017] [Indexed: 12/29/2022] Open
Abstract
INTRODUCTION Trypanosoma brucei uses antigenic variation to evade the host antibody clearance by periodically changing its Variant Surface Glycoprotein (VSGs) coat. T. brucei encode over 2,500 VSG genes and pseudogenes, however they transcribe only one VSG gene at time from one of the 20 telomeric Expression Sites (ESs). VSGs are transcribed in a monoallelic fashion by RNA polymerase I from an extranucleolar site named ES body. VSG antigenic switching occurs by transcriptional switching between telomeric ESs or by recombination of the VSG gene expressed. VSG expression is developmentally regulated and its transcription is controlled by epigenetic mechanisms and influenced by a telomere position effect. CONCLUSION Here, we discuss 1) the molecular basis underlying transcription of telomeric ESs and VSG antigenic switching; 2) the current knowledge of VSG monoallelic expression; 3) the role of inositol phosphate pathway in the regulation of VSG expression and switching; and 4) the developmental regulation of Pol I transcription of procyclin and VSG genes.
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Affiliation(s)
- Igor Cestari
- Center for Infectious Disease Research, Seattle, WA98109, USA
| | - Ken Stuart
- Center for Infectious Disease Research, Seattle, WA98109, USA
- Department of Global Health, University of Washington, Seattle, WA98195, USA
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12
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Expression of the RNA-binding protein RBP10 promotes the bloodstream-form differentiation state in Trypanosoma brucei. PLoS Pathog 2017; 13:e1006560. [PMID: 28800584 PMCID: PMC5568443 DOI: 10.1371/journal.ppat.1006560] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 08/23/2017] [Accepted: 07/29/2017] [Indexed: 01/06/2023] Open
Abstract
In nearly all eukaryotes, cellular differentiation is governed by changes in transcription, and stabilized by chromatin and DNA modification. Gene expression control in the pathogen Trypanosoma brucei, in contrast, relies almost exclusively on post-transcriptional mechanisms, so RNA binding proteins must assume the burden that is usually borne by transcription factors. T. brucei multiply in the blood of mammals as bloodstream forms, and in the midgut of Tsetse flies as procyclic forms. We show here that a single RNA-binding protein, RBP10, promotes the bloodstream-form trypanosome differentiation state. Depletion of RBP10 from bloodstream-form trypanosomes gives cells that can grow only as procyclic forms; conversely, expression of RBP10 in procyclic forms converts them to bloodstream forms. RBP10 binds to procyclic-specific mRNAs containing an UAUUUUUU motif, targeting them for translation repression and destruction. Products of RBP10 target mRNAs include not only the major procyclic surface protein and enzymes of energy metabolism, but also protein kinases and stage-specific RNA-binding proteins: this suggests that alterations in RBP10 trigger a regulatory cascade.
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13
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Christiano R, Kolev NG, Shi H, Ullu E, Walther TC, Tschudi C. The proteome and transcriptome of the infectious metacyclic form of Trypanosoma brucei define quiescent cells primed for mammalian invasion. Mol Microbiol 2017; 106:74-92. [PMID: 28742275 DOI: 10.1111/mmi.13754] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/20/2017] [Indexed: 01/22/2023]
Abstract
The infectious metacyclic forms of Trypanosoma brucei result from a complex development in the tsetse fly vector. When they infect mammals, they cause African sleeping sickness in humans. Due to scarcity of biological material and difficulties of the tsetse fly as an experimental system, very limited information is available concerning the gene expression profile of metacyclic forms. We used an in vitro system based on expressing the RNA binding protein 6 to obtain infectious metacyclics and determined their protein and mRNA repertoires by mass-spectrometry (MS) based proteomics and mRNA sequencing (RNA-Seq) in comparison to non-infectious procyclic trypanosomes. We showed that metacyclics are quiescent cells, and propose this influences the choice of a monocistronic variant surface glycoprotein expression site. Metacyclics have a largely bloodstream-form type transcriptome, and thus are programmed to translate a bloodstream-form type proteome upon entry into the mammalian host and resumption of cell division. Genes encoding cell surface components showed the largest changes between procyclics and metacyclics, observed at both the transcript and protein levels. Genes encoding metabolic enzymes exhibited expression in metacyclics with features of both procyclic and bloodstream forms, suggesting that this intermediate-type metabolism is dictated by the availability of nutrients in the tsetse fly vector.
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Affiliation(s)
- Romain Christiano
- Department of Cell Biology, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - Nikolay G Kolev
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA
| | - Huafang Shi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA
| | - Elisabetta Ullu
- Department of Cell Biology, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA.,Department of Internal Medicine, School of Medicine, Yale University, 330 Cedar St, Boardman 110, New Haven, CT 06520, USA
| | - Tobias C Walther
- Department of Cell Biology, School of Medicine, Yale University, 333 Cedar Street, New Haven, CT 06520, USA.,Howard Hughes Medical Institute, Harvard T.H. Chan School of Public Health Boston, MA 02115, USA
| | - Christian Tschudi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, 60 College Street, New Haven, CT 06520, USA
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Kolev NG, Günzl A, Tschudi C. Metacyclic VSG expression site promoters are recognized by the same general transcription factor that is required for RNA polymerase I transcription of bloodstream expression sites. Mol Biochem Parasitol 2017; 216:52-55. [PMID: 28716719 DOI: 10.1016/j.molbiopara.2017.07.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 07/12/2017] [Accepted: 07/13/2017] [Indexed: 11/25/2022]
Abstract
Infectious metacyclic Trypanosoma brucei cells develop in the salivary glands of tsetse flies. A critical aspect of the developmental program leading to acquisition of infectivity is the synthesis of a variant surface glycoprotein (VSG) coat. Metacyclic VSG genes are transcribed from a set of specialized VSG expression sites (ESs) that differ from bloodstream VSG ESs by being monocistronic, being significantly shorter, lacking long stretches of 70-bp repeats, and having distinct promoter sequences. Both metacyclic and bloodstream VSG ESs are transcribed by the multifunctional T. brucei RNA polymerase I (Pol I), however the factor that recognizes the divergent metacyclic VSG ES promoters and recruits Pol I during the development to infectious cells remains unknown. We used an in vitro assay to show that the promoters for both metacyclic and bloodstream VSG ESs are recognized by the same class I transcription factor A (CITFA). This general Pol I transcription initiation factor was previously shown to be essential for the transcription of bloodstream VSG genes, procyclin genes and rRNA genes, and was demonstrated to have distinct binding affinities for these three types of promoters. We now show that differences in the sequence of individual metacyclic VSG ESs promoters determine different affinities for CITFA.
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Affiliation(s)
- Nikolay G Kolev
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT 06536, USA.
| | - Arthur Günzl
- Department of Genetics and Genome Sciences, University of Connecticut Health Center, Farmington, CT 06030, USA
| | - Christian Tschudi
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT 06536, USA
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15
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Mugo E, Egler F, Clayton C. Conversion of procyclic-form Trypanosoma brucei to the bloodstream form by transient expression of RBP10. Mol Biochem Parasitol 2017; 216:49-51. [PMID: 28651963 DOI: 10.1016/j.molbiopara.2017.06.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 06/22/2017] [Accepted: 06/23/2017] [Indexed: 12/22/2022]
Abstract
Bloodstream-form Trypanosoma brucei can lose the ability to differentiate to the procyclic form during prolonged in vitro culture. This can pose a problem during complicated genetic manipulation experiments, especially when the differentiation phenotype is under investigation. Ideally, to preserve differentiation competence, parasites should be cycled after every genetic manipulation step. Conversion of bloodstream-form Trypanosoma brucei to the procyclic form in vitro is routine, but conversion of procyclic forms to bloodstream forms has hitherto only been achieved in transgenic parasites with tetracycline-inducible expression of proteins with RNA-binding domains - either RBP6 or RBP10. This method, however, requires use of a selectable marker which might be needed for other purposes, and restricts options for tetracycline-inducible expression or repression of other genes. A simple method for inter-conversion that does not require permanent genetic manipulation would therefore be useful. Induced expression of RBP10 in procyclic forms gives faster differentiation than expression of RBP6, with a switch towards bloodstream forms within 48h. We here show that bloodstream forms can be obtained by transient transfection of procyclic forms with a circular plasmid designed for expression of RBP10 from an rRNA promoter. This method enables routine cycling of T. brucei without permanent genetic manipulation.
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Affiliation(s)
- Elisha Mugo
- Centre for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, D69120 Heidelberg, Germany
| | - Franziska Egler
- Centre for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, D69120 Heidelberg, Germany
| | - Christine Clayton
- Centre for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, D69120 Heidelberg, Germany.
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