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Schmid-Hempel P, Aebi M, Barribeau S, Kitajima T, du Plessis L, Schmid-Hempel R, Zoller S. The genomes of Crithidia bombi and C. expoeki, common parasites of bumblebees. PLoS One 2018; 13:e0189738. [PMID: 29304093 PMCID: PMC5755769 DOI: 10.1371/journal.pone.0189738] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Accepted: 11/30/2017] [Indexed: 11/19/2022] Open
Abstract
Trypanosomatids (Trypanosomatidae, Kinetoplastida) are flagellated protozoa containing many parasites of medical or agricultural importance. Among those, Crithidia bombi and C. expoeki, are common parasites in bumble bees around the world, and phylogenetically close to Leishmania and Leptomonas. They have a simple and direct life cycle with one host, and partially castrate the founding queens greatly reducing their fitness. Here, we report the nuclear genome sequences of one clone of each species, extracted from a field-collected infection. Using a combination of Roche 454 FLX Titanium, Pacific Biosciences PacBio RS, and Illumina GA2 instruments for C. bombi, and PacBio for C. expoeki, we could produce high-quality and well resolved sequences. We find that these genomes are around 32 and 34 MB, with 7,808 and 7,851 annotated genes for C. bombi and C. expoeki, respectively-which is somewhat less than reported from other trypanosomatids, with few introns, and organized in polycistronic units. A large fraction of genes received plausible functional support in comparison primarily with Leishmania and Trypanosoma. Comparing the annotated genes of the two species with those of six other trypanosomatids (C. fasciculata, L. pyrrhocoris, L. seymouri, B. ayalai, L. major, and T. brucei) shows similar gene repertoires and many orthologs. Similar to other trypanosomatids, we also find signs of concerted evolution in genes putatively involved in the interaction with the host, a high degree of synteny between C. bombi and C. expoeki, and considerable overlap with several other species in the set. A total of 86 orthologous gene groups show signatures of positive selection in the branch leading to the two Crithidia under study, mostly of unknown function. As an example, we examined the initiating glycosylation pathway of surface components in C. bombi, finding it deviates from most other eukaryotes and also from other kinetoplastids, which may indicate rapid evolution in the extracellular matrix that is involved in interactions with the host. Bumble bees are important pollinators and Crithidia-infections are suspected to cause substantial selection pressure on their host populations. These newly sequenced genomes provide tools that should help better understand host-parasite interactions in these pollinator pathogens.
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Affiliation(s)
| | - Markus Aebi
- Institute of Microbiology, ETH Zurich, Zürich, Switzerland
| | - Seth Barribeau
- Institute of Integrative Biology (IBZ), ETH Zurich, Zürich, Switzerland
| | | | - Louis du Plessis
- Institute of Integrative Biology (IBZ), ETH Zurich, Zürich, Switzerland
| | | | - Stefan Zoller
- Genetic Diversity Centre (GDC), ETH Zurich, Zürich, Switzerland
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2
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Abstract
Faithful transmission of genetic material is essential for the survival of all organisms. Eukaryotic chromosome segregation is driven by the kinetochore that assembles onto centromeric DNA to capture spindle microtubules and govern the movement of chromosomes. Its molecular mechanism has been actively studied in conventional model eukaryotes, such as yeasts, worms, flies and human. However, these organisms are closely related in the evolutionary time scale and it therefore remains unclear whether all eukaryotes use a similar mechanism. The evolutionary origins of the segregation apparatus also remain enigmatic. To gain insights into these questions, it is critical to perform comparative studies. Here, we review our current understanding of the mitotic mechanism in Trypanosoma brucei, an experimentally tractable kinetoplastid parasite that branched early in eukaryotic history. No canonical kinetochore component has been identified, and the design principle of kinetochores might be fundamentally different in kinetoplastids. Furthermore, these organisms do not appear to possess a functional spindle checkpoint that monitors kinetochore-microtubule attachments. With these unique features and the long evolutionary distance from other eukaryotes, understanding the mechanism of chromosome segregation in T. brucei should reveal fundamental requirements for the eukaryotic segregation machinery, and may also provide hints about the origin and evolution of the segregation apparatus.
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Affiliation(s)
- Bungo Akiyoshi
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK
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3
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Abstract
SUMMARYHuman sleeping sickness in Africa, caused by Trypanosoma brucei spp. raises a number of questions. Despite the widespread distribution of the tsetse vectors and animal trypanosomiasis, human disease is only found in discrete foci which periodically give rise to epidemics followed by periods of endemicity A key to unravelling this puzzle is a detailed knowledge of the aetiological agents responsible for different patterns of disease – knowledge that is difficult to achieve using traditional microscopy. The science of molecular epidemiology has developed a range of tools which have enabled us to accurately identify taxonomic groups at all levels (species, subspecies, populations, strains and isolates). Using these tools, we can now investigate the genetic interactions within and between populations of Trypanosoma brucei and gain an understanding of the distinction between human- and nonhuman-infective subspecies. In this review, we discuss the development of these tools, their advantages and disadvantages and describe how they have been used to understand parasite genetic diversity, the origin of epidemics, the role of reservoir hosts and the population structure. Using the specific case of T.b. rhodesiense in Uganda, we illustrate how molecular epidemiology has enabled us to construct a more detailed understanding of the origins, generation and dynamics of sleeping sickness epidemics.
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4
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Delespaux V, Dinka H, Masumu J, Van den Bossche P, Geerts S. Five-fold increase in Trypanosoma congolense isolates resistant to diminazene aceturate over a seven-year period in Eastern Zambia. Drug Resist Updat 2008; 11:205-9. [PMID: 18993109 DOI: 10.1016/j.drup.2008.10.002] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Two groups of Trypanosoma congolense isolates collected from cattle in 1996 (n=39) and 2003 (n=38) in the Eastern Province of Zambia were analyzed by BclI-PCR-RFLP to assess the evolution of diminazene aceturate (DA) resistance over a period of seven years. The results show a significant increase of DA resistance in this relatively short period of time. In 1996, among the 39 isolates, 61.5% were found sensitive, 12.8% resistant and 25.7% had a mixed BclI-PCR-RFLP profile. In 2004, among the 38 isolates, 10.5% were found sensitive, 63.2% were resistant and 26.3% showed a mixed BclI-PCR-RFLP profile. In vivo tests in mice showed that isolates with a sensitive or mixed RFLP profile were sensitive to DA whereas isolates with a resistant RFLP profile were resistant. Since there are no indications that the drug pressure has increased between 1996 and 2003, it is suggested that genetic exchange of resistance genes might explain the increased frequency of resistance to DA.
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Affiliation(s)
- Vincent Delespaux
- Animal Health Department, Institute of Tropical Medicine (Antwerp), Nationalestraat 155, B-2000 Antwerp, Belgium.
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5
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MacLeod A, Tweedie A, McLellan S, Hope M, Taylor S, Cooper A, Sweeney L, Turner CMR, Tait A. Allelic segregation and independent assortment in T. brucei crosses: Proof that the genetic system is Mendelian and involves meiosis. Mol Biochem Parasitol 2005; 143:12-9. [PMID: 15941603 DOI: 10.1016/j.molbiopara.2005.04.009] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2005] [Revised: 04/26/2005] [Accepted: 04/26/2005] [Indexed: 11/27/2022]
Abstract
The genetic system on Trypanosoma brucei has been analysed by generating large numbers of independent progeny clones from two crosses, one between two cloned isolates of Trypanosoma brucei brucei and one between cloned isolates of T. b. brucei and Trypanosoma brucei gambiense, Type 2. Micro and minisatellite markers (located on each of the 11 megabase housekeeping chromosomes) were identified, that are heterozygous in one or more of the parental strains and the segregation of alleles at each locus was then determined in each of the progeny clones. The results unequivocally show that alleles segregate in the predicted ratios and that alleles at loci on different chromosomes segregate independently. These data provide statistically robust proof that the genetic system is Mendelian and that meiosis occurs. Segregation distortion is observed with the minisatellite locus located on chromosome I of T. b. gambiense Type 2 and neighboring markers, but analysis of markers further along this chromosome did not show distortion leading to the conclusion that this is due to selection acting on one part of this chromosome. The results obtained are discussed in relation to previously proposed models of mating and support the occurrence of meiosis to form haploid gametes that then fuse to form the diploid progeny in a single round of mating.
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Affiliation(s)
- Annette MacLeod
- Wellcome Centre for Molecular Parasitology, Anderson College, University of Glasgow, 56 Dumbarton Road, Glasgow G11 6NU, UK
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6
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Abstract
In a highly controversial paper(1), Tibayrenc and colleagues have argued that clonal (asexual) reproduction may be a general phenomenon among protozoan parasites. Many parasitologists would be quite comfortable with a theory applied to Leishmania, Trypanosoma, Entamoeba and Giardia which proposes 'that uniparental reproduction is ... predominant enough in natural populations to generate clones that are stable in space and time ...' The current view is that these parasites can reproduce sexually some of the time (eg. Refs 2,3) but may not do so most of the time. What has provoked the most controversy(4-7) is the suggestion that malaria parasites can be considered as bedfellows of the above, for Plasmodium are generally thought to undergo obligate sexual reproduction in each generation. Here, Christopher Dye focuses on Tibayrenc's arguments for clonal reproduction in Plasmodium, not only because malaria parasites are at the heart of the dispute but also because an analysis of his arguments about sexually reproducing parasites carries implications for his assertions in general.
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Affiliation(s)
- C Dye
- Department of Medical Parasitology, London School of Hygiene and Tropical Medicine, Keppel Street, London WCIE 7HT, UK
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7
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Abstract
The exploration of the genome of the tryponosomotid protozoan Leishmania has been difficult until recently owing to a number of obstacles, not least our ignorance of the ploidy and of the number of chromosomes (as in many other protozoa, the latter do not condense during mitosis), the uncertainty of the species concept in these allegedly asexual protozoa and the absence of classical genetic studies. Here, Patrick Bastien, Christine Bloineou and Michel Pages discuss the advances in this field brought about by the advent of molecular biology and its techniques, with on emphasis on ploidy and genetic exchange. In particular, they discuss the data from pulsed field gel electrophoresis (PFGE). When coupled with DNA restriction analysis, PFGE constitutes a powerful tool for the direct examination o f chromosomes of protozoa.
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Affiliation(s)
- P Bastien
- Laboratoire de Parasitologie, Faculté de Médecine, Montpellier, France
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Hide G, Tait A, Maudlin I, Welburn SC. The origins, dynamics and generation of Trypanosoma brucei rhodesiense epidemics in East Africa. ACTA ACUST UNITED AC 2005; 12:50-5. [PMID: 15275254 DOI: 10.1016/0169-4758(96)80654-5] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The history of sleeping sickness in East Africa has provoked controversy not only about the origins and spread of the disease, but also the identity of the causative organisms involved. Molecular methodology(1) has shed new light on the genetic makeup of the organisms involved in recent epidemics. Here, Geoff Hide, Andrew Tait, Ian Maudlin and Susan Welburn discuss these new data in relation to previous theories about the origins of epidemics in East Africa which emphasized the importance of the introduction of new strains.
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Affiliation(s)
- G Hide
- Welcome Unit of Molecular Parasitology, The Anderson College, University of Glasgow, Glasgow, UK
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9
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Tait A, Masiga D, Ouma J, MacLeod A, Sasse J, Melville S, Lindegard G, McIntosh A, Turner M. Genetic analysis of phenotype in Trypanosoma brucei: a classical approach to potentially complex traits. Philos Trans R Soc Lond B Biol Sci 2002; 357:89-99. [PMID: 11839186 PMCID: PMC1692923 DOI: 10.1098/rstb.2001.1050] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The genome of the African trypanosome, Trypanosoma brucei, is currently being sequenced, raising the question of how the data generated can be used to determine the function of the large number of genes that will be identified. There is a range of possible approaches, and in this paper we discuss the use of a classical genetic approach coupled with positional cloning based on the ability of trypanosomes to undergo genetic exchange. The genetics of these parasites is essentially similar to a conventional diploid Mendelian system with allelic segregation and an independent assortment of markers on different chromosomes. Data are presented showing that recombination occurs between markers on the same chromosome allowing the physical size of the unit of recombination to be determined. Analysis of the available progeny clones from a series of crosses shows that, in principal, large numbers of progeny can readily be isolated from existing cryopreserved products of mating and, taking these findings together, it is clear that genetic mapping of variable phenotypes is feasible. The available phenotypes for analysis are outlined and most are relevant to the transmission and pathogenesis of the parasite. Genetic maps from two crosses are presented based on the use of the technique of AFLP; these maps comprise 146 and 139 markers in 30 and 21 linkage groups respectively. Segregation distortion is exhibited by some of the linkage groups and the possible reasons for this are discussed. The general conclusion, from the results presented, is that a genetic-mapping approach is feasible and will, in the future, allow the genes determining a number of important traits to be identified.
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Affiliation(s)
- Andy Tait
- Wellcome Centre for Molecular Parasitology, University of Glasgow, 56 Dumbarton Road, Glasgow G11 6NU, UK.
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10
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Welburn SC, Fèvre EM, Coleman PG, Odiit M, Maudlin I. Sleeping sickness: a tale of two diseases. Trends Parasitol 2001; 17:19-24. [PMID: 11137736 DOI: 10.1016/s1471-4922(00)01839-0] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Sleeping sickness presents clinically as two distinct diseases, reflecting the fact that two very different trypanosomes are responsible. The African Rift separating East and West Africa defines the distribution of the two diseases. In this review, Susan Welburn, Eric Fèvre, Paul Coleman, Martin Odiit and Ian Maudlin discuss the biology and distribution of these two diseases in relation to the evolution of hominids in Africa.
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Affiliation(s)
- S C Welburn
- Sir Alexander Robertson Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Roslin, EH25 9RG., Midlothian, UK.
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11
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Welburn SC, Maudlin I. Tsetse-trypanosome interactions: rites of passage. PARASITOLOGY TODAY (PERSONAL ED.) 1999; 15:399-403. [PMID: 10481151 DOI: 10.1016/s0169-4758(99)01512-4] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Trypanosomes that cause sleeping sickness (Trypanosoma brucei rhodesiense and T. b. gambiense) are entirely dependent on tsetse for their transmission between hosts, but the flies are not easily infected. This situation has not arisen by chance - the tsetse has evolved an efficient defence system against trypanosome invasion. In this review, Susan Welburn and Ian Maudlin chart the progress of trypanosomes through the fly and identify some of the hazards faced by both parasite and fly that affect vector competence of tsetse.
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Affiliation(s)
- S C Welburn
- Centre for Tropical Veterinary Medicine, University of Edinburgh, Easter Bush, Roslin, Midlothian, UK EH25 9RG.
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12
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13
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Abstract
The history of human sleeping sickness in East Africa is characterized by the appearance of disease epidemics interspersed by long periods of endemicity. Despite the presence of the tsetse fly in large areas of East Africa, these epidemics tend to occur multiply in specific regions or foci rather than spreading over vast areas. Many theories have been proposed to explain this phenomenon, but recent molecular approaches and detailed analyses of epidemics have highlighted the stability of human-infective trypanosome strains within these foci. The new molecular data, taken alongside the history and biology of human sleeping sickness, are beginning to highlight the important factors involved in the generation of epidemics. Specific, human-infective trypanosome strains may be associated with each focus, which, in the presence of the right conditions, can be responsible for the generation of an epidemic. Changes in agricultural practice, favoring the presence of tsetse flies, and the important contribution of domestic animals as a reservoir for the parasite are key factors in the maintenance of such epidemics. This review examines the contribution of molecular and genetic data to our understanding of the epidemiology and history of human sleeping sickness in East Africa.
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Affiliation(s)
- G Hide
- Centre for Molecular Epidemiology and Ecology, Department of Biological Sciences, University of Salford, Salford M5 4WT, United Kingdom.
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14
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Morphological features suggesting a sexual process in a trypanosomatid of the genus Herpetomonas. Eur J Protistol 1997. [DOI: 10.1016/s0932-4739(97)80047-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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15
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Barrett MP, MacLeod A, Tovar J, Sweetman JP, Tait A, Le Page RW, Melville SE. A single locus minisatellite sequence which distinguishes between Trypanosoma brucei isolates1Note: Nucleotide sequence data reported in this paper have been submitted to the EMBL data base with the accession number X70187.1. Mol Biochem Parasitol 1997. [DOI: 10.1016/s0166-6851(97)02832-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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16
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Sousa MAD. Cytological Findings Suggesting Sexuality in Phytomonas davidi (Protozoa: Kinetoplastida). Mem Inst Oswaldo Cruz 1997. [DOI: 10.1590/s0074-02761997000200007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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17
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el-Sayed NM, Donelson JE. A survey of the Trypanosoma brucei rhodesiense genome using shotgun sequencing. Mol Biochem Parasitol 1997; 84:167-78. [PMID: 9084037 DOI: 10.1016/s0166-6851(96)02792-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A comparison of the efficiency of sequencing random genomic DNA fragments versus random cDNAs for the discovery of new genes in African trypanosomes was undertaken. Trypanosome DNA was sheared to a 1.5-2.5 kb size distribution, cloned into a plasmid and the sequences at both ends of 183 cloned fragments determined. Sequences of both kinetoplast and nuclear DNA were identified. New coding regions were discovered for a variety of proteins, including cell division proteins, an RNA-binding protein and a homologue of the Leishmania surface protease GP63. In some cases, each end of a fragment was found to contain a different gene, demonstrating the proximity of those genes and suggesting that the density of genes in the African trypanosome genome is quite high. Repetitive sequence elements found included telomeric hexamer repeats, 76 bp repeats associated with VSG gene expression sites, 177 bp satellite repeats in minichromosomes and the Ingi transposon-like elements. In contrast to cDNA sequencing, no ribosomal protein genes were detected. For the sake of comparison, the sequences of 190 expressed sequence tags (ESTs) were also determined, and a similar number of new trypanosomal homologues were found including homologues of another putative surface protein and a human leucine-rich repeat-containing protein. We conclude from this analysis and our previous work that sequencing random DNA fragments in African trypanosomes is as efficient for gene discovery as is sequencing random cDNA clones.
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Affiliation(s)
- N M el-Sayed
- Department of Biochemistry, University of Iowa, Iowa City 52242, USA
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18
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Cornelissen AW, Schetters TP. Vaccines against protozoal diseases of veterinary importance. FEMS IMMUNOLOGY AND MEDICAL MICROBIOLOGY 1996; 15:61-72. [PMID: 8880130 DOI: 10.1111/j.1574-695x.1996.tb00055.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Protozoan parasites are important animal and human pathogens. At present, most of these infections are controlled by chemotherapy. In addition, vaccines are available for some of these diseases. There is, however, still an urgent need for the development of vaccines against protozoal diseases, since the current array of available vaccines is very limited. This review describes the different approaches that have been taken to develop such vaccines and discusses the difficulties that hampered vaccine development. Many of the problems are related to the complex life cycle of these parasites and the virtual lack of mass in vitro culture systems. We also give an overview of the commercial and non-commercial vaccines that do exist at present. Finally, we describe the future directions of this interesting field. New techniques and strategies include parasite cultivation methods and recombinant-DNA techniques, such as vector vaccines and DNA-vaccines. Moreover, these approaches are complemented by the development of sophisticated adjuvants; the coupling of immunoprotective molecules to entities with adjuvant activity or the use of cytokines, e.g. IL-12. Through these innovations new vaccines against protozoal diseases will become available in the near future.
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Affiliation(s)
- A W Cornelissen
- Utrecht University, Faculty of Veterinary Medicine, Department of Parasitology and Tropical Veterinary Medicine, The Netherlands
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19
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Hill WG, Babiker HA, Ranford-Cartwright LC, Walliker D. Estimation of inbreeding coefficients from genotypic data on multiple alleles, and application to estimation of clonality in malaria parasites. Genet Res (Camb) 1995; 65:53-61. [PMID: 7750746 DOI: 10.1017/s0016672300033000] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Methods for estimating probability of identity by descent (f) are derived for data on numbers of genotypes at single loci and at pairs of loci with many alleles at each locus. The methods are general, but are specifically applied to data on genotype frequencies in zygotes of the malaria parasite sampled from its mosquito host in order to find the extent of outcrossing in the parasite and the degree of clonality in populations. It is assumed that zygotes are the outcome either of gametes of the same clone, in which they are identical at all loci, or are products of two random, unrelated clones. From the estimate of f an effective number of clones per human host can also be derived. For Plasmodium falciparum from a Tanzanian village, estimates of f are 0.33 from data on zygote frequencies at two multiallelic loci, indicating that two-thirds of zygotes produce recombinant type.
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Affiliation(s)
- W G Hill
- Institute of Cell, Animal and Population Biology, University of Edinburgh
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20
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Wu Y, Deford J, Benjamin R, Lee MG, Ruben L. The gene family of EF-hand calcium-binding proteins from the flagellum of Trypanosoma brucei. Biochem J 1994; 304 ( Pt 3):833-41. [PMID: 7818488 PMCID: PMC1137409 DOI: 10.1042/bj3040833] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The flagellum of Trypanosoma brucei contains calmodulin, and a separate family of antigenically related EF-hand calcium-binding proteins which we call calflagins. The following study evaluates the structure and genomic organization of the calflagin family. Genomic Southern blots indicated that multiple copies of calflagin genes occurred in T. brucei, and that all of these copies were contained in a single 23 kb XhoI-XhoI fragment on chromosomes 15 and 16 mRNAs of 1.2 and 1.6 kb were identified in bloodstream and procyclic life-cycle stages. Genomic fragments of 2.5 and 1.7 kb were cloned that encoded calflagin sequences. The calflagin genes were arranged tandemly along the genomic fragments. Three new members of the calflagin family were sequenced from a cDNA clone and the two genomic clones. Two unrelated families of 3' flanking sequences were downstream from the calflagin genes. An open reading frame that was unrelated to any calflagin sequence was at the 5' end of the 2.5 kb genomic fragment. The deduced amino acid sequences of the genomic clones (called Tb-24 and Tb-1.7g) were similar to the previously described Tb-17. Each encoded an approximately 24 kDa protein which contained three EF-hand calcium-binding motifs and one degenerate EF-hand motif. The cDNA encoded a protein (called Tb-44A) which was approximately twice as large as the other calflagins. The large size resulted from a nearly direct repeat of 186 amino acids. In general, variability among the T. brucei calflagins was greater than observed for related proteins from Trypanosoma cruzi. We demonstrate that this variability resulted from amino acid substitutions at the N-terminus, C-terminal extensions, and duplication of internal segments.
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Affiliation(s)
- Y Wu
- Department of Biological Sciences, Southern Methodist University, Dallas, TX 75235
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21
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Schweizer J, Pospichal H, Hide G, Buchanan N, Tait A, Jenni L. Analysis of a new genetic cross between two East African Trypanosoma brucei clones. Parasitology 1994; 109 ( Pt 1):83-93. [PMID: 7914691 DOI: 10.1017/s0031182000077799] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Two clones of East African Trypanosoma brucei, with distinct homozygous isoenzyme patterns for one of three enzymes examined, were cotransmitted through the tsetse fly vector Glossina morsitans centralis. Flies with mature infections were individually fed on mice and the subsequent bloodstream from populations analysed for the presence of hybrid trypanosomes by isoenzyme analysis. Several combinations have previously been detected using this approach (Schweizer, Tait & Jenni, 1988; Sternberg et al. 1989). Four clones were isolated from one of the hybrid-containing populations. They showed a hybrid phenotype, as would be expected for the F1 progeny in a diploid Mendelian system. The analysis of the progeny clones, using two gene probes which detect restriction fragment length polymorphisms between the two parental stocks, showed that alleles had segregated at each locus and given rise to three different non-parental combinations of alleles in the hybrid progeny. Characterization of the hybrid progeny clones by PFGE (pulsed field gradient gel electrophoresis) revealed that all progeny clones were recombinant for the intermediate size chromosomes. From the analysis of the segregation of the larger chromosomes, marked by PGK (phosphoglycerate kinase) and CP (cysteine protease) gene probes, it was inferred that the progeny clones did not result from a direct fusion of diploid cells. Results with the PGK probe fit into a classical system with meiosis and subsequent fusion of the nuclei to form diploid progeny. On the other hand, blots with the CP probe as well as some of the ethidium bromide stained PFGE gels revealed the existence of non-parental size chromosomes in some of the hybrid progeny. This phenomenon was observed previously (Gibson, 1989) and further investigation is required to elucidate the mechanism.
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MESH Headings
- Africa, Eastern
- Animals
- Blotting, Southern
- Cloning, Molecular
- Crosses, Genetic
- Cysteine Endopeptidases/genetics
- DNA Probes
- DNA, Protozoan/analysis
- Electrophoresis, Gel, Pulsed-Field
- Electrophoresis, Starch Gel
- Genes, Protozoan
- Hybridization, Genetic
- Isoenzymes/analysis
- Isoenzymes/genetics
- Karyotyping
- Mice
- Mice, Inbred ICR
- Phenotype
- Phosphoglycerate Kinase/genetics
- Polymorphism, Restriction Fragment Length
- Trypanosoma brucei brucei/classification
- Trypanosoma brucei brucei/enzymology
- Trypanosoma brucei brucei/genetics
- Tsetse Flies
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22
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Hide G, Welburn SC, Tait A, Maudlin I. Epidemiological relationships of Trypanosoma brucei stocks from south east Uganda: evidence for different population structures in human infective and non-human infective isolates. Parasitology 1994; 109 ( Pt 1):95-111. [PMID: 7914692 DOI: 10.1017/s0031182000077805] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This study represents an analysis of trypanosome strains circulating within a confined location over a short period of time during a sleeping sickness epidemic in S.E. Uganda. A large number of Trypanosoma brucei isolates (88) were collected from a variety of hosts (man, cattle, pigs and tsetse) from villages within a 10 km radius and were analysed for variation in isoenzyme patterns, restriction fragment length polymorphism (RFLP) in repetitive DNA sequences and susceptibility to human serum. The human infective stocks form a clearly distinguishable population when compared with other stocks circulating in the domestic cattle reservoir. The data here support the occurrence of genetic exchange between the cattle stocks while an 'epidemic' population structure involving limited genetic exchange is a characteristic of the human infective stocks. Furthermore, it is shown that when both RFLP and isoenzyme analysis are carried out most stocks appear to have individual genotypes. Stocks which were formerly grouped as zymodemes are better considered as a collected of distinct individuals.
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Affiliation(s)
- G Hide
- Department of Veterinary Parasitology, Glasgow University Veterinary School
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23
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Sousa MA. Cell-to-cell interactions suggesting a sexual process in Herpetomonas megaseliae (Kinetoplastida: Trypanosomatidae). Parasitol Res 1994; 80:112-6. [PMID: 8202449 DOI: 10.1007/bf00933777] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Giemsa-stained smears of Herpetomonas megaseliae cultures in LIT medium displayed on several occasions not only the typically dividing promastigotes but also pairs of apposed parasites attached by their posterior ends, where a cellular enlargement and a ring-like border generally occurred; other pairs formed by an elongated promastigote and a bell-shaped cell were also found. In both cases, either each of the joined cells could have its own nucleus or one of them was anucleate and the other presented two nuclei that were sometimes so close that they appeared to be a single nucleus. These findings, along with others seeming to be intermediate steps between them, strongly suggested that a sexual process, involving parasite union followed by nuclear migration from one cell to the other and then by fusion, was taking place in such cultures.
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Affiliation(s)
- M A Sousa
- Departamento de Protozoologia, Instituto Oswaldo Cruz, Rio de Janeiro, Brasil
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24
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Breunig A, König H, Brugerolle G, Vickerman K, Hertel H. Isolation and ultrastructural features of a new strain of Dimastigella trypaniformis Sandon 1928 (Bodonina, Kinetoplastida) and comparison with a previously isolated strain. Eur J Protistol 1993. [DOI: 10.1016/s0932-4739(11)80404-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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25
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Truc P, Tibayrenc M. Population genetics of Trypanosoma brucei in central Africa: taxonomic and epidemiological significance. Parasitology 1993; 106 ( Pt 2):137-49. [PMID: 8095328 DOI: 10.1017/s003118200007493x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
In order to estimate the value of population genetics for both the taxonomy of trypanosomes belonging to the species Trypanosoma brucei and a better understanding of Human African Trypanosomiasis (HAT), we undertook a cellulose acetate electrophoresis isoenzyme study involving 55 stocks isolated from man and animals in Congo, Zaire and Cameroun. Out of the 24 loci surveyed, 15 exhibited variability, which made it possible to delimit 23 zymodemes, divided into 2 groups. The first group equated to the classical subspecies Trypanosoma brucei gambiense, while the second corresponded to the classical subspecies Trypanosoma brucei brucei. These results broadly agree with the current taxonomy, and are corroborated by RFLP analysis of kDNA. Statistical analysis indicates a basically clonal reproduction system of the trypanosomes in the area studied; the zymodemes are equivalent to natural clones (or a family of closely related clones), stable in space and time. Epidemiological hypotheses are proposed according to the geographic distribution of the clones in this area.
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Affiliation(s)
- P Truc
- UMR CNRS/ORSTOM 9926, Génétique moléculaire des parasites et des vecteurs, Montpellier, France
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26
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Dirie MF, Otte MJ, Thatthi R, Gardiner PR. Comparative studies of Trypanosoma (Duttonella) vivax isolates from Colombia. Parasitology 1993; 106 ( Pt 1):21-9. [PMID: 8097584 DOI: 10.1017/s0031182000074771] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The characterization of four Trypanosoma vivax isolates from Colombia in South America showed that although minor phenotypic differences existed between them, these parasites are antigenically related and belong to a single serodeme. Characterization by isoenzyme assay, karyotyping and DNA probe analysis, showed the Colombian isolates to be more similar to the West African than to Kenyan T. vivax. There was, however, little serological cross-reactivity between South American and African groups of T. vivax. Although the T. vivax isolates from Colombia were pathogenic for dairy calves which showed the typical sign of progressive emaciation, these parasites failed to infect mice or tsetse and could not be cultivated as bloodstream forms in vitro. This study represents initial attempts to establish the phenotypic and serological diversity amongst T. vivax isolates from South America.
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Affiliation(s)
- M F Dirie
- International Laboratory for Research on Animal Diseases (ILRAD), Nairobi, Kenya
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27
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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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28
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Cibulskis RE. Genetic variation in Trypanosoma brucei and the epidemiology of sleeping sickness in the Lambwe Valley, Kenya. Parasitology 1992; 104 Pt 1:99-109. [PMID: 1614744 DOI: 10.1017/s0031182000060844] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A contingency table approach was used to explore the influence of location, host species and time on the genetic composition of a Trypanosoma brucei population in Lambwe Valley, Kenya. Significant differences in zymodeme frequencies were noticed over comparatively short geographical distances suggesting that transmission of T. brucei is somewhat localized. A significant association was observed between zymodeme and the mammalian host from which T. brucei was derived. The association was consistent in different localities in Lambwe valley and remained stable for at least 32 months. These observations indicate that zymodemes are adapted to different host species and that genetic exchange has not disrupted host associations over this time-scale. A major change in the composition of the T. brucei population during a sleeping sickness outbreak in 1980 was confirmed. But while new zymodemes emerged, a decline in overall diversity was noted during times of high sleeping sickness incidence. The results can be explained by selection of T. brucei zymodemes for particular transmission cycles. Although it is not necessary to invoke genetic exchange, sex may help T. brucei to adapt to changes in selection pressures. Such a hypothesis helps to explain why T. brucei appears largely clonal in the short term, even though population studies indicate that sex is responsible for much genetic diversity in the long term. It also explains why neighbouring populations of T. brucei are composed of a different range of zymodemes formed from the same alleles. Such a view implies that genetic exchange has an important role in the microevolution of T. brucei populations.
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Affiliation(s)
- R E Cibulskis
- Department of International Community Health, Liverpool School of Tropical Medicine, UK
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29
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Abstract
The advent of pulsed field electrophoresis has allowed a direct approach to the karyotype of Leishmania. The molecular karyotype thus obtained is a stable characteristic of a given strain, although minor modifications may occur during in vitro maintenance. Between 20 and 28 chromosomal bands can be resolved depending on the strain, ranging in size from approximately 250 to 2600 kb. The technique has revealed a striking degree of polymorphism in the size and number of the chromosomal bands between different strains, and this seems independent of the category (species, zymodeme, population) to which the strains belong. It appears that only certain strains originating from the same geographic area may share extensive similarities. This polymorphism can largely be accounted for by chromosome size variations, which can involve up to 25% of the chromosome length. As a result, homologous chromosomes can exist in versions of markedly different size within the same strain. When this occurs with several different chromosomes, the interpretation of PFE patterns appears difficult without prior identification of the size-variable chromosomes and of the chromosome homologies. DNA deletions and amplifications have been shown to account for some of these size modifications, but other mechanisms are probably involved; nevertheless, interchromosomal exchange does not seem to play a major role in these polymorphisms. These chromosomal rearrangements, yet in an early stage of characterization, exhibit two relevant features: they seem (1) to affect essentially the subtelomeric regions and (2) to occur in a recurrent nonrandom manner. Chromosomal rearrangements sharing the same characteristics have been identified in yeast and other protozoa such as Trypanosoma and Plasmodium. The significance of this hypervariability for the biology of the parasite remains unknown, but it can be expected that such mechanisms have been maintained for some purpose; genes specifically located near chromosome ends might benefit from rapid sequence change, alternating activation, or polymorphism of expression. The chromosomal plasticity could represent a general mode of mutation in these parasites, in parallel with genetic exchange which may be uncommon in nature. The molecular characterization of these rearrangements, the identification of each chromosome with the help of physical restriction maps and linkage maps, and the collation of such data on a number of strains and species should allow a significant progress in the understanding of the genetics of Leishmania, in particular as regards ploidy, generation of phenotypic diversity, and genome evolution. Finally, like other models, this is susceptible to improve our knowledge of DNA-DNA interactions and of the chromosome functional structure and dynamics.
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Affiliation(s)
- P Bastien
- Laboratoire d'Ecologie Médicale et Pathologie Parasitaire, Annexe de la Faculté de Médecine, Montpellier, France
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30
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Affiliation(s)
- C M Turner
- Laboratory for Biochemical Parasitology, Department of Zoology, University of Glasgow, Glasgow G12 8QQ, UK
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Turner CM, Aslam N, Smith E, Buchanan N, Tait A. The effects of genetic exchange on variable antigen expression in Trypanosoma brucei. Parasitology 1991; 103 Pt 3:379-86. [PMID: 1780175 DOI: 10.1017/s0031182000059898] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The inheritance of variant surface antigens in Trypanosoma brucei has been determined by identifying variable antigen types (VATs) in each of two cloned parental stocks and then examining the presence and abundance of these VATs in hybrid progeny produced when these stocks undergo genetic exchange during co-transmission through tsetse flies. Nine VATs have been identified from the repertoire of the parental stock STIB 247L and 5 VATs have been identified from the parental stock STIB 386AA; the identified VATs were exclusive to each stock. Their inheritance was elucidated using two assays. In the first, repertoire antisera (RAS) containing antibody specificities to many different VATs were raised in rabbits to the 2 parental stocks and 6 progeny clones. The presence of VAT-specific antibodies in these RAS was then determined by antibody-dependent complement-mediated lysis. In the second assay, the 2 parental stocks and 4 hybrid progeny clones were each independently transmitted through tsetse flies and VATs observed using VAT-specific antisera in indirect immunofluorescence of metacyclic trypanosomes and in bloodstream forms of fly-bitten mice. The results from both assays showed that (1) both metacyclic- and bloodstream-VATs were inherited into the progeny, (2) each hybrid progeny clone contained some VATs from both parents, (3) hybrids did not express all the VATs from either parent, (4) there was little apparent pattern as to which VATs had been inherited and which had not and (5) the VAT repertoires of the hybrid progeny appeared to be larger than those of the parents. In addition, two results indicated that control of VAT expression remains unaltered after genetic exchange.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- C M Turner
- Department of Zoology, University of Glasgow
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32
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Zajícek P. Trypanosoma cf. carassii: the combination of malic enzyme patterns supports the theory of diploidy in trypanosomes. Int J Parasitol 1991; 21:753-5. [PMID: 1757208 DOI: 10.1016/0020-7519(91)90093-m] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Electrophoretic analysis of Trypanosoma cf. carassii strains from cyprinid fish revealed three basic types of enzyme patterns of malic enzyme (ME) in forms from culture. Two enzyme patterns were one-banded and differed only slightly in electrophoretic mobility. The third pattern consisted of three bands, the two marginals corresponding to respective bands of one-banded patterns and the third located in the middle. ME is thought to be dimeric in trypanosomes and therefore the triple-banded pattern may be regarded as the hybrid from combination of the former two. This fact supports the concept of diploidy in fish trypanosomes.
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Affiliation(s)
- P Zajícek
- Czechoslovak Academy of Sciences, Institute of Parasitology, Ceské Budĕjovice
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33
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Kelly JM, Law JM, Chapman CJ, Van Eys GJ, Evans DA. Evidence of genetic recombination in Leishmania. Mol Biochem Parasitol 1991; 46:253-63. [PMID: 1656255 DOI: 10.1016/0166-6851(91)90049-c] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In the genus Leishmania there has been no convincing demonstration of genetic exchange, and it has been proposed that reproduction is clonal. However, preliminary characterization of two strains of Leishmania isolated from wild animals in a zoonotic focus of cutaneous leishmaniasis in the Eastern Province of Saudi Arabia, has suggested that they may represent hybrids of Leishmania major and Leishmania arabica. Evidence presented here strongly supports this hypothesis. Isoenzyme analysis and molecular karyotyping of cloned organisms indicated that the putative hybrids are distinct from other species of Leishmania, and possess characteristics of both L. major and L. arabica. Experiments using highly specific probes demonstrated that kinetoplast minicircle DNA from the putative hybrid contained L. major-specific, but not L. arabica-specific sequences. DNA fingerprinting data obtained using 6 genomic DNA probes were consistent in all cases with a L. major/L. arabica recombinant genotype, and implied both diploidy and allelic segregation. These observations suggest that sexual reproduction may generate genetic diversity within natural Leishmania populations.
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Affiliation(s)
- J M Kelly
- Department of Medical Parasitology, London School of Hygiene and Tropical Medicine, U.K
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Coburn CM, Otteman KM, McNeely T, Turco SJ, Beverley SM. Stable DNA transfection of a wide range of trypanosomatids. Mol Biochem Parasitol 1991; 46:169-79. [PMID: 1906580 DOI: 10.1016/0166-6851(91)90210-w] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We have shown that the Leishmania major transfection vector pR-NEO (or derivatives thereof) can be introduced and stably maintained in four species complexes of pathogenic Leishmania (L. tropica, L. mexicana, L. donovani, L. braziliensis), and the genera Endotrypanum and Crithidia; transfection of Trypanosoma cruzi or Trypanosoma brucei was not successful. Quantitative plating assays showed that the transfection efficiencies were high in L. major and Leishmania amazonensis (5x10(-5)/cell) and about 10-fold less for Leishmania panamaensis and Crithidia. Leishmania donovani transfected with pR-NEO retained the ability to infect hamsters, and amastigotes recovered after 2 months yielded G418-resistant promastigotes which retained high levels of extrachromosomal pR-NEO DNA. In promastigotes, the transfected DNA existed as extrachromosomal circles, and expressed the predicted 2.4-kb hybrid NEO/DHFR-TS mRNA bearing the trans-spliced miniexon. Large quantitative differences were observed only in Crithidia: relative to transfected Leishmania species, the copy number of pR-NEO was elevated 20-fold, while the levels of the NEO/DHRFR-TS mRNA or Escherichia coli beta-galactosidase (synthesized from the expression vector pX-beta GAL) were reduced 80 and more than 1000-fold, respectively. Thus, genetic signals derived from L. major DNA that mediate RNA expression or stability are recognized by the heterologous Leishmania species but less efficiently by Crithidia. These studies suggest that pR-NEO derived vectors may be applied to the study of genes expressed throughout the life cycle in a wide range of pathogenic trypanosomatids.
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Affiliation(s)
- C M Coburn
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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Panton LJ, Tesh RB, Nadeau KC, Beverley SM. A test for genetic exchange in mixed infections of Leishmania major in the sand fly Phlebotomus papatasi. THE JOURNAL OF PROTOZOOLOGY 1991; 38:224-8. [PMID: 1880760 DOI: 10.1111/j.1550-7408.1991.tb04433.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We tested if genetic exchange was observable between two strains of Leishmania major (Trypanosomatidae) during mixed infection of the sand fly Phlebotomus papatasi. Previous studies suggested that genetic exchange may occur in natural populations of Leishmania at a low frequency, but experimental crosses examining small numbers of progeny (less than 60) did not reveal hybrid parasites. Accordingly, a strategy was devised to increase the number of progeny that could be screened by 100-fold. Clonal derivatives from two strains that were infective to flies and contained numerous restriction fragment length polymorphisms were characterized and selected for resistance to methotrexate or tunicamycin by gene amplification. A successfully mixed infection of P. papatasi was obtained, and a method was developed for directly plating promastigotes from the gut contents of infected flies onto selective media. Twenty-five hundred independent progeny were scored for the presence of both drug resistance markers. No hybrid parasites were observed, indicating that the frequency of genetic exchange in this cross must be less than 4 x 10(-4). The lines and methods established in this work may prove useful in future studies of the mechanism and frequency of gene exchange in Leishmania.
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Affiliation(s)
- L J Panton
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
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Evidence that the mechanism of gene exchange in Trypanosoma brucei involves meiosis and syngamy. Parasitology 1990; 101 Pt 3:377-86. [PMID: 1982633 DOI: 10.1017/s0031182000060571] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
All pairwise combinations of three cloned stocks of Trypanosoma brucei (STIB 247L, STIB 386AA and TREU 927/4) were co-transmitted through tsetse flies (Glossina morsitans) and screened for the production of hybrid trypanosomes. Clones of metacyclic and bloodstream trypanosomes from flies harbouring mature infections containing hybrid trypanosomes were established and screened for several isoenzyme and restriction fragment length polymorphisms. For each of the three combinations of parents, some progeny clones were observed to be of a phenotype and genotype indicating that genetic exchange had occurred during development of the trypanosomes in flies. These hybrid clones shared three salient features: (1) where the parents were homozygous variants the progeny were heterozygous, (2) where one of the parents was heterozygous, allelic segregation was observed and (3) the progeny clones were shown to be recombinant when two or more markers for which one of the parents was heterozygous were examined. These results are consistent with the progeny being an F1 in a diploid mendelian genetic system involving meiosis and syngamy. Our observations show that all possible combinations of the three stocks may undergo genetic exchange. A marker analysis of a series of clones each derived from single metacyclic trypanosomes showed that individual flies transmit a mixture of trypanosome genotypes corresponding to F1 progeny and to parental types, indicating that genetic exchange was a non-obligatory event in the life-cycle of the trypanosome. In addition, a preliminary analysis of the phenotype of procyclic stage trypanosomes derived from flies infected with two stocks, indicates that genetic exchange is unlikely to occur at this stage.
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Abstract
African trypanosomes are important pathogens of humans and domestic animals, but little was known, until recently, of the genetic system of these parasites. Recent results demonstrate the existence of nonobligatory genetic exchange between different stocks of T. brucei. A number of models have been put forward for the mechanism of genetic exchange, including a fusion model with subsequent random loss of chromosomes and a more conventional mendelian system.
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Affiliation(s)
- J Sternberg
- Department of Zoology, University of Aberdeen, UK
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Tait A. Genetic exchange and evolutionary relationships in protozoan and helminth parasites. Parasitology 1990; 100 Suppl:S75-87. [PMID: 2235065 DOI: 10.1017/s0031182000073030] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The study of genetic exchange systems and the use of genetic analysis has been relatively limited in parasites leading to considerable gaps in our basic knowledge. This lack of knowledge makes it difficult to draw firm conclusions as to how these systems evolved. An additional problem is also raised by the difficulties in defining evolutionary distances particularly with the unicellular protozoa, using classical ultrastructural and cytological criteria. While these difficulties have by no means been overcome, the use of rapid sequencing techniques applied to the ribosomal genes has allowed measurement of evolutionary distances, and considerable advances in our understanding of the genetic exchange systems in a few parasitic protozoa have recently been made. The conclusions from these recent sets of analyses are reviewed and then examined together in order to discuss the evolution of genetic exchange systems in parasitic protozoa. The evolutionary distances defined by ribosome sequence analysis show that parasites are an extremely divergent group, with distances which, in some cases, are orders of magnitude greater than the distances between mammals and fish; furthermore these studies suggest that the parasitic protozoa or their free-living ancestors are extremely ancient. These findings support the view that parasitism has occurred independently many times and that the parasitic life-style has been adopted by evolutionarily distinct groups. The recent observation of a non-obligatory genetic system in the diploid but evolutionary ancient kinetoplastid Trypanosoma brucei suggests that diploidy and meiosis are extremely old. The observation, in parasitic protozoa and helminths, that selfing or non-obligatory mating is a common feature suggests that these processes may be strategies to overcome the cost of meiosis. In this context, the question of what selective forces maintain genetic exchange is discussed.
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Affiliation(s)
- A Tait
- Wellcome Unit of Molecular Parasitology, University of Glasgow
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40
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Affiliation(s)
- W Gibson
- Department of Pathology and Microbiology, University of Bristol Veterinary School, Longford, Bristol BS18 7DU, UK
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