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Affiliation(s)
- P Borst
- Division of Molecular Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
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2
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Matthews RA. Ichthyophthirius multifiliis Fouquet and Ichthyophthiriosis in Freshwater Teleosts. ADVANCES IN PARASITOLOGY 2005; 59:159-241. [PMID: 16182866 DOI: 10.1016/s0065-308x(05)59003-1] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The ciliate Ichthyophthirius multifiliis is an important pathogen of freshwater teleosts occurring in both temperate and tropical regions throughout the world. The disease, ichthyophthiriosis, accounts for significant economic losses to the aquaculture industry, including the ornamental fish trade, and epizootics in wild fish populations can result in mass kills. This review attempts to provide a comprehensive overview of the biology of the parasite, covering the free-living and parasitic stages in the life cycle, host-parasite interactions, and the immune response of host and immune evasion strategies by the parasite. Emphasis on the immunological aspects of infection within the fish host, including molecular studies of i-antigens, reflects the current interest in this subject area and the quest to develop a recombinant vaccine against the disease. The current status of methods for the control of ichthyophthiriosis is discussed, together with new approaches in combating this important disease.
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Affiliation(s)
- R A Matthews
- School of Biological Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK.
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3
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Abstract
Many pathogens that either rely on an insect vector to complete their life cycle (e.g., Trypanosoma spp. and Borrelia spp.) or exist in a unique ecological niche where transmission from host to host is sporadic (e.g., Neisseria spp.) have evolved strategies to maintain infection of their mammalian hosts for long periods of time in order to ensure their survival. Because they have to survive in the face of a fully functional immune system, a common feature of many of these organisms is their development of sophisticated strategies for immune evasion. For the above organisms and for malaria parasites of the genus Plasmodium, a common theme is the ability to undergo clonal antigenic variation. In all cases, surface molecules that are important targets of the humoral immune response are encoded in the genome as multicopy, nonallelic gene families. Antigenic variation is accomplished by the successive expression of members of these gene families that show little or no immunological cross-reactivity. In the case of malaria parasites, however, some of the molecules that undergo antigenic variation are also major virulence factors, adding an additional level of complication to the host-parasite interaction. In this review, we cover the history of antigenic variation in malaria and then summarize the more recent data with particular emphasis on Plasmodium falciparum, the etiological agent of the most severe form of human malaria.
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Affiliation(s)
- S Kyes
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, Headington, Oxford OX3 9DS United Kingdom.
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Yang H, Russell DG, Zheng B, Eiki M, Lee MG. Sequence requirements for trafficking of the CRAM transmembrane protein to the flagellar pocket of African trypanosomes. Mol Cell Biol 2000; 20:5149-63. [PMID: 10866671 PMCID: PMC85964 DOI: 10.1128/mcb.20.14.5149-5163.2000] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
CRAM is a cysteine-rich acidic transmembrane protein, highly expressed in the procyclic form of Trypanosoma brucei. Cell surface expression of CRAM is restricted to the flagellar pocket of trypanosomes, the only place where receptor mediated endocytosis takes place in the parasite. CRAM can function as a receptor and was hypothesized to be a lipoprotein receptor of trypanosomes. We study mechanisms involved in the presentation and routing of CRAM to the flagellar pocket of insect- and bloodstream-form trypanosomes. By deletional mutagenesis, we found that deleting up to four amino acids from the C terminus of CRAM did not affect the localization of CRAM at the flagellar pocket. Shortening the CRAM protein by 8 and 19 amino acids from the C terminus resulted in the distribution of the CRAM protein in the endoplasmic reticulum (ER) (the CRAM protein is no longer uniquely sequestered at the flagellar pocket). This result indicates that the truncation of the CRAM C terminus affected the transport efficiency of CRAM from the ER to the flagellar pocket. However, when CRAM was truncated between 29 and 40 amino acids from the C terminus, CRAM was not only distributed in the ER but also located to the flagellar pocket and spread to the cell surface and the flagellum. Replacing the CRAM transmembrane domain with the invariant surface glycoprotein 65-derived transmembrane region did not affect the flagellar pocket location of CRAM. These results indicate that the CRAM cytoplasmic extension may exhibit two functional domains: one domain near the C terminus is important for efficient export of CRAM from the ER, while the second domain is of importance for confining CRAM to the flagellar pocket membrane.
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Affiliation(s)
- H Yang
- Department of Pathology, New York University School of Medicine, New York, New York 10016, USA
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5
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Lee MG, Van der Ploeg LH. Transcription of protein-coding genes in trypanosomes by RNA polymerase I. Annu Rev Microbiol 1997; 51:463-89. [PMID: 9343357 DOI: 10.1146/annurev.micro.51.1.463] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In eukaryotes, RNA polymerase (pol) II transcribes the protein-coding genes, whereas RNA pol I transcribes the genes that encode the three RNA species of the ribosome [the ribosomal RNAs (rRNAs)] at the nucleolus. Protozoan parasites of the order Kinetoplastida may represent an exception, because pol I can mediate the expression of exogenously introduced protein-coding genes in these single-cell organisms. A unique molecular mechanism, which leads to pre-mRNA maturation by trans-splicing, facilitates pol I-mediated protein-coding gene expression in trypanosomes. Trans-splicing adds a capped 39-nucleotide mini-exon, or spliced leader transcript, to the 5' end of the main coding exon posttranscriptionally. In other eukaryotes, the addition of a 5' cap, which is essential for mRNA function, occurs exclusively as a result of RNA pol II-mediated transcription. Given the assumption that cap addition represents the limiting factor, trans-splicing may have uncoupled the requirement for RNA pol II-mediated mRNA production. A comparison of the alpha-amanitin sensitivity of transcription in naturally occurring trypanosome protein-coding genes reveals that a unique subset of protein-coding genes-the variant surface glycoprotein (VSG) expression sites and the procyclin or the procyclic acidic repetitive protein (PARP) genes-are transcribed by an RNA polymerase that is resistant to the mushroom toxin alpha-amanitin, a characteristic of transcription by RNA pol I. Promoter analysis and a pharmacological characterization of the RNA polymerase that transcribes these genes have strengthened the proposal that the VSG expression sites and the PARP genes represent naturally occurring protein-coding genes that are transcribed by RNA pol I.
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Affiliation(s)
- M G Lee
- Department of Pathology, New York University, New York 10016, USA
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Blundell PA, Rudenko G, Borst P. Targeting of exogenous DNA into Trypanosoma brucei requires a high degree of homology between donor and target DNA. Mol Biochem Parasitol 1996; 76:215-29. [PMID: 8920008 DOI: 10.1016/0166-6851(95)02560-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Integration of exogenous DNA into the trypanosome genome occurs by homologous recombination only. To test whether a high degree of homology between donor and target DNA is required, we have inserted marker genes for drug resistance into the promoter area of variant surface glycoprotein (VSG) gene expression sites of Trypanosoma brucei, using targeting fragments from two expression sites that are 92% identical. We observed integrations into expression sites that are known to be perfectly matched to the donor flanks, and into subsets of uncharacterized expression sites that are specific for each type of targeting fragment, and that could be similar or identical to the donor flanks. This requirement for very high homology was found in both procyclic and bloodstream-form trypanosomes. We speculate that trypanosomes have a mismatch repair system that suppresses recombination between divergent DNA sequences, and we discuss ways in which the trypanosome might circumvent the requirement for perfect DNA homology in the duplicative transposition of a VSG gene into a VSG gene expression site.
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Affiliation(s)
- P A Blundell
- Division of Molecular Biology, Netherlands Cancer Institute, Amsterdam
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7
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Bracha R, Nuchamowitz Y, Mirelman D. Molecular cloning of a 30-kilodalton lysine-rich surface antigen from a nonpathogenic Entamoeba histolytica strain and its expression in a pathogenic strain. Infect Immun 1995; 63:917-25. [PMID: 7868264 PMCID: PMC173090 DOI: 10.1128/iai.63.3.917-925.1995] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
A monoclonal antibody (MAb), 318-28, that specifically reacts with a 30-kDa antigen present on membrane surfaces of all nonpathogenic (NP) Entamoeba histolytica strains tested and which did not react with pathogenic (P) strains was used for the isolation of the cDNA coding for this antigen from an expression library of an NP E. histolytica strain. The deduced amino acid composition was rich in lysine residues (14.5%), with some sequence similarity to a polyadenylate-binding protein. Southern and Northern (RNA) blot analyses, as well as amplifications of DNA segments by PCR, indicate that a very similar gene (identity of 96.5%) exists in P strains of E. histolytica. Unexpectedly, the NP-specific antigen was also identified by MAb 318-28 on the surfaces of a cloned, xenically cultivated and well-characterized P strain (BNI:0591) that was recently isolated from a human liver abscess. Binding of the MAb, both to the cell surfaces and to Western blots (immunoblots), was abolished, however, upon axenization of the BNI:0591 cultures. Oligonucleotide primers, designed to anneal only to specific DNA sequences of the NP 30-kDa protein gene copy, amplified a DNA segment from P strain BNI:0591 which was identical in sequence to that of the NP 30-kDa protein gene. Our findings indicate that a P strain of E. histolytica can possess and express, under certain growth conditions, an antigen that is usually detected only in NP strains.
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Affiliation(s)
- R Bracha
- Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel
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Orozco E, Benitez-Bibriesca L, Hernandez R. Invasion and metastasis mechanisms in Entamoeba histolytica and cancer cells. Some common cellular and molecular features. Mutat Res 1994; 305:229-39. [PMID: 7510034 DOI: 10.1016/0027-5107(94)90243-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- E Orozco
- Department of Experimental Pathology, Centro de Investigacion y de Estudios Avanzados IPN, México, D.F., Mexico
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9
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Aline RF, Myler PJ, Gobright E, Stuart KD. Early expression of a Trypanosoma brucei VSG gene duplicated from an incomplete basic copy. J Eukaryot Microbiol 1994; 41:71-8. [PMID: 8124269 DOI: 10.1111/j.1550-7408.1994.tb05937.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Intrachromosomal variant surface glycoprotein (VSG) genes in Trypanosoma brucei are expressed by a mechanism involving gene conversion. The 3' boundary of gene conversion is usually within the last 130 bp of the VSG gene, a region of partially conserved sequences. We report here the loss of the predominant telomeric A VSG gene in the cloned variant antigenic type (VAT) 5A3, leaving only an intrachromosomal A VSG gene (the A-B gene). The nucleotide sequence of the A-B VSG gene reveals that it lacks the normal VSG 3' sequence. Surprisingly, we find cells expressing this A-B VSG gene in relapse populations arising from VAT 5A3. Since the A VSG mRNAs from these cells have a normal 3' sequence, the incomplete A-B VSG gene must be expressed via a partial gene conversion that supplies the functional 3' end. Although the A-B VSG gene is no longer predominant like the telomeric A VSG gene, it is still expressed more frequently than other intrachromosomal VSG genes, suggesting that factors other than a telomeric location determine whether a VSG gene is expressed early in a serodeme.
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Affiliation(s)
- R F Aline
- Seattle Biomedical Research Institute, Washington 98109-1651
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10
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Beals TP, Boothroyd JC. Genomic organization and context of a trypanosome variant surface glycoprotein gene family. J Mol Biol 1992; 225:961-71. [PMID: 1613802 DOI: 10.1016/0022-2836(92)90097-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We have defined the genomic organization and genomic context of a Trypanosoma brucei brucei gene family encoding variant surface glycoproteins (VSGs). This gene family is neither tandemly repeated nor closely linked in the genome, and is not located on small or intermediate size chromosomes. Two dispersed repeated sequence elements, RIME-ingi and the upstream repeat sequence, are linked to members of this gene family; however, the upstream repeat sequences are closely linked only to the basic copy. In other isolates of T.b. brucei this gene family appears conserved with some variation; a restriction fragment length polymorphism found among these isolates suggests the hypothesis that VSG genes may occasionally be diploid. A model accounting for both the generation of dispersed families of VSG genes, and for the interstrain variability of VSG genes, is proposed.
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Affiliation(s)
- T P Beals
- Department of Microbiology and Immunology, Stanford University School of Medicine, CA 94305
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Mercereau-Puijalon O, Fandeur T, Guillotte M, Bonnefoy S. Parasite features impeding malaria immunity: antigenic diversity, antigenic variation and poor immunogenicity. RESEARCH IN IMMUNOLOGY 1991; 142:690-7. [PMID: 1817299 DOI: 10.1016/0923-2494(91)90151-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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