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van der Watt ME, Reader J, Birkholtz LM. Adapt or Die: Targeting Unique Transmission-Stage Biology for Malaria Elimination. Front Cell Infect Microbiol 2022; 12:901971. [PMID: 35755845 PMCID: PMC9218253 DOI: 10.3389/fcimb.2022.901971] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Accepted: 05/06/2022] [Indexed: 12/25/2022] Open
Abstract
Plasmodium parasites have a complex life cycle that includes development in the human host as well as the Anopheles vector. Successful transmission of the parasite between its host and vector therefore requires the parasite to balance its investments in asexual replication and sexual reproduction, varying the frequency of sexual commitment to persist within the human host and generate future opportunities for transmission. The transmission window is extended further by the ability of stage V gametocytes to circulate in peripheral blood for weeks, whereas immature stage I to IV gametocytes sequester in the bone marrow and spleen until final maturation. Due to the low gametocyte numbers in blood circulation and with the ease of targeting such life cycle bottlenecks, transmission represents an efficient target for therapeutic intervention. The biological process of Plasmodium transmission is a multistage, multifaceted process and the past decade has seen a much deeper understanding of the molecular mechanisms and regulators involved. Clearly, specific and divergent processes are used during transmission compared to asexual proliferation, which both poses challenges but also opportunities for discovery of transmission-blocking antimalarials. This review therefore presents an update of our molecular understanding of gametocyte and gamete biology as well as the status of transmission-blocking activities of current antimalarials and lead development compounds. By defining the biological components associated with transmission, considerations for the development of new transmission-blocking drugs to target such untapped but unique biology is suggested as an important, main driver for transmission-blocking drug discovery.
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Affiliation(s)
- Mariëtte E van der Watt
- Institute for Sustainable Malaria Control, School of Health Systems and Public Health, University of Pretoria, Pretoria, South Africa
| | - Janette Reader
- Institute for Sustainable Malaria Control, School of Health Systems and Public Health, University of Pretoria, Pretoria, South Africa.,Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria, South Africa
| | - Lyn-Marié Birkholtz
- Institute for Sustainable Malaria Control, School of Health Systems and Public Health, University of Pretoria, Pretoria, South Africa.,Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria, South Africa
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2
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Henry NB, Sermé SS, Siciliano G, Sombié S, Diarra A, Sagnon N, Traoré AS, Sirima SB, Soulama I, Alano P. Biology of Plasmodium falciparum gametocyte sex ratio and implications in malaria parasite transmission. Malar J 2019; 18:70. [PMID: 30866941 PMCID: PMC6417185 DOI: 10.1186/s12936-019-2707-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 03/05/2019] [Indexed: 11/10/2022] Open
Abstract
While significant advances have been made in understanding Plasmodium falciparum gametocyte biology and its relationship with malaria parasite transmission, the gametocyte sex ratio contribution to this process still remains a relevant research question. The present review discusses the biology of sex determination in P. falciparum, the underlying host and parasite factors, the sex specific susceptibility to drugs, the effect of sex ratio dynamics on malaria parasite transmission and the development of gametocyte sex specific diagnosis tools. Despite the inherent differences across several studies and approaches, the emerging picture highlights a potentially relevant contribution of the P. falciparum gametocyte sex ratio in the modulation of malaria parasite transmission. The increasing availability of molecular methods to measure gametocyte sex ratio will enable evaluation of important parameters, such as the impact of drug treatment on gametocyte sex ratio in vitro and in vivo as well as the changes of gametocyte sex ratios in natural infections, key steps towards elucidating how these parameters affect parasite infectiousness to the mosquito vectors.
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Affiliation(s)
- Noëlie Béré Henry
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | - Samuel Sindié Sermé
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | - Giulia Siciliano
- Dipartimento di Malattie Infettive, Istituto Superiore di Sanità, Rome, Italy
| | - Salif Sombié
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | - Amidou Diarra
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | - N'fale Sagnon
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | | | - Sodiomon Bienvenu Sirima
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso.,Groupe de Recherche Action Santé, Ouagadougou, Burkina Faso
| | - Issiaka Soulama
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso.
| | - Pietro Alano
- Dipartimento di Malattie Infettive, Istituto Superiore di Sanità, Rome, Italy.
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3
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Ortega C, Frando A, Webb-Robertson BJ, Anderson LN, Fleck N, Flannery EL, Fishbaugher M, Murphree TA, Hansen JR, Smith RD, Kappe SHI, Wright AT, Grundner C. A Global Survey of ATPase Activity in Plasmodium falciparum Asexual Blood Stages and Gametocytes. Mol Cell Proteomics 2017; 17:111-120. [PMID: 29079720 DOI: 10.1074/mcp.ra117.000088] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 10/03/2017] [Indexed: 01/12/2023] Open
Abstract
Effective malaria control and elimination in hyperendemic areas of the world will require treatment of the Plasmodium falciparum (Pf) blood stage that causes disease as well as the gametocyte stage that is required for transmission from humans to the mosquito vector. Most currently used therapies do not kill gametocytes, a highly specialized, non-replicating sexual parasite stage. Further confounding next generation drug development against Pf is the unknown metabolic state of the gametocyte and the lack of known biochemical activity for most parasite gene products in general. Here, we take a systematic activity-based proteomics approach to survey the activity of the large and druggable ATPase family in replicating blood stage asexual parasites and transmissible, non-replicating sexual gametocytes. ATPase activity broadly changes during the transition from asexual schizonts to sexual gametocytes, indicating altered metabolism and regulatory roles of ATPases specific for each lifecycle stage. We further experimentally confirm existing annotation and predict ATPase function for 38 uncharacterized proteins. By mapping the activity of ATPases associated with gametocytogenesis, we assign biochemical activity to a large number of uncharacterized proteins and identify new candidate transmission blocking targets.
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Affiliation(s)
- Corrie Ortega
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109
| | - Andrew Frando
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109.,§Department of Global Health, University of Washington, Seattle, Washington 98195
| | - Bobbie-Jo Webb-Robertson
- ¶Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Lindsey N Anderson
- ¶Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Neil Fleck
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109
| | - Erika L Flannery
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109
| | - Matthew Fishbaugher
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109
| | - Taylor A Murphree
- ¶Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Joshua R Hansen
- ¶Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Richard D Smith
- ¶Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Stefan H I Kappe
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109.,§Department of Global Health, University of Washington, Seattle, Washington 98195
| | - Aaron T Wright
- ¶Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Christoph Grundner
- From the ‡Center for Infectious Disease Research (formerly Seattle Biomedical Research Institute), Seattle, Washington 98109; .,§Department of Global Health, University of Washington, Seattle, Washington 98195
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4
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Josling GA, Llinás M. Sexual development in Plasmodium parasites: knowing when it's time to commit. Nat Rev Microbiol 2015; 13:573-87. [DOI: 10.1038/nrmicro3519] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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5
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Ariey F, Witkowski B, Amaratunga C, Beghain J, Langlois AC, Khim N, Kim S, Duru V, Bouchier C, Ma L, Lim P, Leang R, Duong S, Sreng S, Suon S, Chuor CM, Bout DM, Ménard S, Rogers WO, Genton B, Fandeur T, Miotto O, Ringwald P, Le Bras J, Berry A, Barale JC, Fairhurst RM, Benoit-Vical F, Mercereau-Puijalon O, Ménard D. A molecular marker of artemisinin-resistant Plasmodium falciparum malaria. Nature 2014; 505:50-5. [PMID: 24352242 PMCID: PMC5007947 DOI: 10.1038/nature12876] [Citation(s) in RCA: 1406] [Impact Index Per Article: 140.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 11/12/2013] [Indexed: 12/24/2022]
Abstract
Plasmodium falciparum resistance to artemisinin derivatives in southeast Asia threatens malaria control and elimination activities worldwide. To monitor the spread of artemisinin resistance, a molecular marker is urgently needed. Here, using whole-genome sequencing of an artemisinin-resistant parasite line from Africa and clinical parasite isolates from Cambodia, we associate mutations in the PF3D7_1343700 kelch propeller domain ('K13-propeller') with artemisinin resistance in vitro and in vivo. Mutant K13-propeller alleles cluster in Cambodian provinces where resistance is prevalent, and the increasing frequency of a dominant mutant K13-propeller allele correlates with the recent spread of resistance in western Cambodia. Strong correlations between the presence of a mutant allele, in vitro parasite survival rates and in vivo parasite clearance rates indicate that K13-propeller mutations are important determinants of artemisinin resistance. K13-propeller polymorphism constitutes a useful molecular marker for large-scale surveillance efforts to contain artemisinin resistance in the Greater Mekong Subregion and prevent its global spread.
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Affiliation(s)
- Frédéric Ariey
- 1] Institut Pasteur, Parasite Molecular Immunology Unit, 75724 Paris Cedex 15, France [2] Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 75724 Paris Cedex 15, France [3] Institut Pasteur, Genetics and Genomics of Insect Vectors Unit, 75724 Paris Cedex 15, France (F.A.); Institut Pasteur, Functional Genetics of Infectious Diseases Unit, 75724 Paris Cedex 15, France (J.B.); Centre de Physiopathologie de Toulouse-Purpan, Institut National de la Santé et de la Recherche Médicale UMR1043, Centre National de la Recherche Scientifique UMR5282, Université Toulouse III, 31024 Toulouse Cedex 3, France Institut Pasteur, Unité de Biologie et Génétique du Paludisme, Team Malaria Targets and Drug Development, 75724 Paris Cedex 15, France (J.-C.B.)
| | - Benoit Witkowski
- Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia
| | - Chanaki Amaratunga
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Johann Beghain
- 1] Institut Pasteur, Parasite Molecular Immunology Unit, 75724 Paris Cedex 15, France [2] Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 75724 Paris Cedex 15, France [3] Institut Pasteur, Genetics and Genomics of Insect Vectors Unit, 75724 Paris Cedex 15, France (F.A.); Institut Pasteur, Functional Genetics of Infectious Diseases Unit, 75724 Paris Cedex 15, France (J.B.); Centre de Physiopathologie de Toulouse-Purpan, Institut National de la Santé et de la Recherche Médicale UMR1043, Centre National de la Recherche Scientifique UMR5282, Université Toulouse III, 31024 Toulouse Cedex 3, France Institut Pasteur, Unité de Biologie et Génétique du Paludisme, Team Malaria Targets and Drug Development, 75724 Paris Cedex 15, France (J.-C.B.)
| | - Anne-Claire Langlois
- 1] Institut Pasteur, Parasite Molecular Immunology Unit, 75724 Paris Cedex 15, France [2] Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 75724 Paris Cedex 15, France
| | - Nimol Khim
- Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia
| | - Saorin Kim
- Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia
| | - Valentine Duru
- Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia
| | - Christiane Bouchier
- Institut Pasteur, Plate-forme Génomique, Département Génomes et Génétique, 75724 Paris Cedex 15, France
| | - Laurence Ma
- Institut Pasteur, Plate-forme Génomique, Département Génomes et Génétique, 75724 Paris Cedex 15, France
| | - Pharath Lim
- 1] Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia [2] Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA [3] National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Rithea Leang
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Socheat Duong
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Sokunthea Sreng
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Seila Suon
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Char Meng Chuor
- National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Denis Mey Bout
- SSA WHO, Drug Monitoring in Cambodia, National Center for Parasitology, Entomology and Malaria Control, Phnom Penh, Cambodia
| | - Sandie Ménard
- 1] Service de Parasitologie et Mycologie, Centre Hospitalier Universitaire de Toulouse, 31059 Toulouse Cedex 9, France [2] Institut Pasteur, Genetics and Genomics of Insect Vectors Unit, 75724 Paris Cedex 15, France (F.A.); Institut Pasteur, Functional Genetics of Infectious Diseases Unit, 75724 Paris Cedex 15, France (J.B.); Centre de Physiopathologie de Toulouse-Purpan, Institut National de la Santé et de la Recherche Médicale UMR1043, Centre National de la Recherche Scientifique UMR5282, Université Toulouse III, 31024 Toulouse Cedex 3, France Institut Pasteur, Unité de Biologie et Génétique du Paludisme, Team Malaria Targets and Drug Development, 75724 Paris Cedex 15, France (J.-C.B.)
| | | | - Blaise Genton
- Swiss Tropical and Public Health Institute, 4051 Basel, Switzerland
| | - Thierry Fandeur
- 1] Institut Pasteur, Parasite Molecular Immunology Unit, 75724 Paris Cedex 15, France [2] Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia
| | - Olivo Miotto
- 1] MRC Centre for Genomics and Global Health, University of Oxford, Oxford OX3 7BN, UK [2] Mahidol-Oxford Tropical Medicine Research Unit, Mahidol University, Bangkok 10400, Thailand [3] Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK
| | - Pascal Ringwald
- Global Malaria Program, World Health Organization, 1211 Geneva, Switzerland
| | - Jacques Le Bras
- Centre National de Référence du Paludisme, CHU Bichat-Claude Bernard, APHP, PRES Sorbonne Paris Cité, 75018 Paris, France
| | - Antoine Berry
- 1] Service de Parasitologie et Mycologie, Centre Hospitalier Universitaire de Toulouse, 31059 Toulouse Cedex 9, France [2] Institut Pasteur, Genetics and Genomics of Insect Vectors Unit, 75724 Paris Cedex 15, France (F.A.); Institut Pasteur, Functional Genetics of Infectious Diseases Unit, 75724 Paris Cedex 15, France (J.B.); Centre de Physiopathologie de Toulouse-Purpan, Institut National de la Santé et de la Recherche Médicale UMR1043, Centre National de la Recherche Scientifique UMR5282, Université Toulouse III, 31024 Toulouse Cedex 3, France Institut Pasteur, Unité de Biologie et Génétique du Paludisme, Team Malaria Targets and Drug Development, 75724 Paris Cedex 15, France (J.-C.B.)
| | - Jean-Christophe Barale
- 1] Institut Pasteur, Parasite Molecular Immunology Unit, 75724 Paris Cedex 15, France [2] Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 75724 Paris Cedex 15, France [3] Institut Pasteur, Genetics and Genomics of Insect Vectors Unit, 75724 Paris Cedex 15, France (F.A.); Institut Pasteur, Functional Genetics of Infectious Diseases Unit, 75724 Paris Cedex 15, France (J.B.); Centre de Physiopathologie de Toulouse-Purpan, Institut National de la Santé et de la Recherche Médicale UMR1043, Centre National de la Recherche Scientifique UMR5282, Université Toulouse III, 31024 Toulouse Cedex 3, France Institut Pasteur, Unité de Biologie et Génétique du Paludisme, Team Malaria Targets and Drug Development, 75724 Paris Cedex 15, France (J.-C.B.)
| | - Rick M Fairhurst
- 1] Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA [2]
| | - Françoise Benoit-Vical
- 1] Centre National de la Recherche Scientifique, Laboratoire de Chimie de Coordination UPR8241, 31077 Toulouse Cedex 4, France [2] Université de Toulouse, UPS, Institut National Polytechnique de Toulouse, 31077 Toulouse Cedex 4, France [3]
| | - Odile Mercereau-Puijalon
- 1] Institut Pasteur, Parasite Molecular Immunology Unit, 75724 Paris Cedex 15, France [2] Centre National de la Recherche Scientifique, Unité de Recherche Associée 2581, 75724 Paris Cedex 15, France [3]
| | - Didier Ménard
- 1] Institut Pasteur du Cambodge, Malaria Molecular Epidemiology Unit, Phnom Penh, Cambodia [2]
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Aberrant sporogonic development of Dmc1 (a meiotic recombinase) deficient Plasmodium berghei parasites. PLoS One 2012; 7:e52480. [PMID: 23285059 PMCID: PMC3528682 DOI: 10.1371/journal.pone.0052480] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Accepted: 11/19/2012] [Indexed: 11/19/2022] Open
Abstract
Background In Plasmodium, meiosis occurs in diploid zygotes as they develop into haploid motile ookinetes inside the mosquito. Further sporogonic development involves transformation of ookinetes into oocysts and formation of infective sporozoites. Methodology/Principal Findings Reverse genetics was employed to examine the role of the meiotic specific recombinase Dmc1, a bacterial RecA homolog during sporogony in Plasmodium berghei. PbDmc1 knockout (KO) parasites showed normal asexual growth kinetics compared to WT parasites; however oocyst formation in mosquitoes was reduced by 50 to 80%. Moreover, the majority of oocysts were retarded in their growth and were smaller in size compared to WT parasites. Only a few Dmc1 KO parasites completed maturation resulting in formation of fewer sporozoites which were incapable of infecting naive mice or hepatocytes in vitro. PbDmc1 KO parasites were shown to be approximately 18 times more sensitive to Bizelesin, a DNA alkylating drug compared to WT parasites as reflected by impairment of oocyst formation and sporogonic development in the mosquito vector. Conclusions/Significance Our findings suggest that PbDmc1 plays a critical role in malaria transmission biology.
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Liu Z, Miao J, Cui L. Gametocytogenesis in malaria parasite: commitment, development and regulation. Future Microbiol 2012; 6:1351-69. [PMID: 22082293 DOI: 10.2217/fmb.11.108] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Malaria parasites have evolved a complicated life cycle alternating between two hosts. Gametocytes are produced in the vertebrate hosts and are obligatory for natural transmission of the parasites through mosquito vectors. The mechanism of sexual development in Plasmodium has been the focus of extensive studies. In the postgenomic era, the advent of genome-wide analytical tools and genetic manipulation technology has enabled rapid advancement of our knowledge in this area. Patterns of gene expression during sexual development, molecular distinction of the two sexes, and mechanisms underlying subsequent formation of gametes and their fertilization have been progressively elucidated. However, the triggers and mechanism of sexual development remain largely unknown. This article provides an update of our understanding of the molecular and cellular events associated with the decision for commitment to sexual development and regulation of gene expression during gametocytogenesis. Insights into the molecular mechanisms of gametocyte development are essential for designing proper control strategies for interruption of malaria transmission and ultimate elimination.
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Affiliation(s)
- Zhenyu Liu
- Department of Entomology, The Pennsylvania State University, 537 ASI Building University Park, PA 16802, USA
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8
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Boisson B, Lacroix C, Bischoff E, Gueirard P, Bargieri DY, Franke-Fayard B, Janse CJ, Ménard R, Baldacci P. The novel putative transporter NPT1 plays a critical role in early stages of Plasmodium berghei sexual development. Mol Microbiol 2011; 81:1343-57. [PMID: 21752110 DOI: 10.1111/j.1365-2958.2011.07767.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Transmission of Plasmodium species from a mammalian host to the mosquito vector requires the uptake, during an infected blood meal, of gametocytes, the precursor cells of the gametes. Relatively little is known about the molecular mechanisms involved in the developmental switch from asexual development to sexual differentiation or the maturation and survival of gametocytes. Here, we show that a gene coding for a novel putative transporter, NPT1, plays a crucial role in the development of Plasmodium berghei gametocytes. Parasites lacking NPT1 are severely compromised in the production of gametocytes and the rare gametocytes produced are unable to differentiate into fertile gametes. This is the earliest block in gametocytogenesis obtained by reverse genetics and the first to demonstrate the role of a protein with a putative transport function in sexual development. These results and the high degree of conservation of NPT1 in Plasmodium species suggest that this protein could be an attractive target for the development of novel drugs to block the spread of malaria.
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Affiliation(s)
- Bertrand Boisson
- Institut Pasteur, Biologie et Génétique du Paludisme, 75724 Paris, France.
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Bousema T, Drakeley C. Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination. Clin Microbiol Rev 2011; 24:377-410. [PMID: 21482730 PMCID: PMC3122489 DOI: 10.1128/cmr.00051-10] [Citation(s) in RCA: 508] [Impact Index Per Article: 39.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Malaria remains a major cause of morbidity and mortality in the tropics, with Plasmodium falciparum responsible for the majority of the disease burden and P. vivax being the geographically most widely distributed cause of malaria. Gametocytes are the sexual-stage parasites that infect Anopheles mosquitoes and mediate the onward transmission of the disease. Gametocytes are poorly studied despite this crucial role, but with a recent resurgence of interest in malaria elimination, the study of gametocytes is in vogue. This review highlights the current state of knowledge with regard to the development and longevity of P. falciparum and P. vivax gametocytes in the human host and the factors influencing their distribution within endemic populations. The evidence for immune responses, antimalarial drugs, and drug resistance influencing infectiousness to mosquitoes is reviewed. We discuss how the application of molecular techniques has led to the identification of submicroscopic gametocyte carriage and to a reassessment of the human infectious reservoir. These components are drawn together to show how control measures that aim to reduce malaria transmission, such as mass drug administration and a transmission-blocking vaccine, might better be deployed.
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Affiliation(s)
- Teun Bousema
- Department of Immunology & Infection, London School of Hygiene and Tropical Medicine, London W1CE 7HT, United Kingdom
| | - Chris Drakeley
- Department of Immunology & Infection, London School of Hygiene and Tropical Medicine, London W1CE 7HT, United Kingdom
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Blocking Plasmodium falciparum Malaria Transmission with Drugs: The Gametocytocidal and Sporontocidal Properties of Current and Prospective Antimalarials. Pharmaceuticals (Basel) 2010. [PMCID: PMC4052541 DOI: 10.3390/ph4010044] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Drugs that kill or inhibit the sexual stages of Plasmodium could potentially amplify or synergize the impact of other interventions by blocking transmission to mosquitoes. Primaquine and other 8-aminoquinolines have long offered such potential, but safety and other concerns have limited their use. Although transmission-blocking properties are not often a priority of drug discovery efforts, a number of interesting gametocytocidal and/or sporontocidal drug candidates have emerged in recent years. Some still bear significant technical and safety concerns, while others have passed clinical trials and are on the verge of entering the antimalarial armamentarium. Recent advances in our knowledge of gametocyte differentiation, gametogenesis and sporogony have also led to the identification of a large array of potential new targets for drugs that might interfere with malaria transmission. This review examines the properties of existing and prospective drugs, mechanisms of action, counter-indications and their potential role in regional malaria elimination efforts.
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Miao J, Li J, Fan Q, Li X, Li X, Cui L. The Puf-family RNA-binding protein PfPuf2 regulates sexual development and sex differentiation in the malaria parasite Plasmodium falciparum. J Cell Sci 2010; 123:1039-49. [PMID: 20197405 DOI: 10.1242/jcs.059824] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Translation regulation plays an important role during gametocytogenesis in the malaria parasite, a process that is obligatory for the transmission of the parasite through mosquito vectors. In this study we determined the function of PfPuf2, a member of the Puf family of translational repressors, in gametocytogenesis of Plasmodium falciparum. Tagging of the endogenous PfPuf2 protein with green fluorescent protein showed that PfPuf2 was expressed in both male and female gametocytes, and the protein was localized in the cytoplasm of the parasite. Targeted disruption of the PfPuf2 gene did not affect asexual growth of the parasite, but promoted the formation of gametocytes and differentiation of male gametocytes. Complementation studies were performed to confirm that the resultant phenotypic changes were due to disruption of the PfPuf2 gene. Episomal expression of PfPuf2 under its cognate promoter almost restored the gametocytogenesis rate in a PfPuf2 disruptant to the level of the wild-type parasite. It also partially restored the effect of PfPuf2 disruption on male-female sex ratio. In addition, episomal overexpression of PfPuf2 under its cognate promoter but with a higher concentration of the selection drug or under the constitutive hsp86 promoter in both the PfPuf2-disruptant and wild-type 3D7 lines, further dramatically reduced gametocytogenesis rates and sex ratios. These findings suggest that in this early branch of eukaryotes the function of PfPuf2 is consistent with the ancestral function of suppressing differentiation proposed for Puf-family proteins.
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Affiliation(s)
- Jun Miao
- Department of Entomology, The Pennsylvania State University, University Park, PA 16802, USA
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12
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Regulated oligomerisation and molecular interactions of the early gametocyte protein Pfg27 in Plasmodium falciparum sexual differentiation. Int J Parasitol 2009; 40:663-73. [PMID: 19968995 DOI: 10.1016/j.ijpara.2009.11.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 10/12/2009] [Accepted: 11/02/2009] [Indexed: 11/22/2022]
Abstract
Gametocytes of the protozoan Plasmodium falciparum ensure malaria parasite transmission from humans to the insect vectors. In their development, they produce the abundant specific protein Pfg27, the function and in vivo molecular interactions of which are unknown. Here we reveal a previously unreported localisation of Pfg27 in the gametocyte nucleus by immunoelectron microscopy and studies with HaloTag and Green Fluorescent Protein fusions, and identify a network of interactions established by the protein during gametocyte development. We report the ability of endogenous Pfg27 to form oligomeric complexes that are affected by phosphorylation of the protein, possibly through the identified phosphorylation sites, Ser32 and Thr208. We show that Pfg27 binds RNA molecules through specific residues and that the protein interacts with parasite RNA-binding proteins such as EF1alpha and PfH45. We propose a structural model for Pfg27 oligomerisation, based on the sequence and structural conservation here recognised between Pfg27 and sterile alpha motif. This study provides a molecular basis for Pfg27 to establish an interaction network with RNA and RNA-binding proteins and to govern its dynamic oligomerisation in developing gametocytes.
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13
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Olivieri A, Camarda G, Bertuccini L, van de Vegte-Bolmer M, Luty AJF, Sauerwein R, Alano P. The Plasmodium falciparum protein Pfg27 is dispensable for gametocyte and gamete production, but contributes to cell integrity during gametocytogenesis. Mol Microbiol 2009; 73:180-93. [PMID: 19570101 DOI: 10.1111/j.1365-2958.2009.06762.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
In the human malaria parasite Plasmodium falciparum, gametocyte maturation is a process remarkably longer than in other malaria species, accompanied by expression of 2-300 sexual stage-specific proteins. Disruption of several of their encoding genes so far showed that only the abundant protein Pfg27, produced at the onset of sexual differentiation, is essential for gametocyte production. In contrast with what has been previously described, here we show that P. falciparum pfg27 disruptant lines are able to undergo all stages of gametocyte maturation, and are able to mature into gametes. A fraction of Pfg27-defective gametocytes show, however, distinct abnormalities in intra- and extra-cellular membranous compartments, such as accumulation of parasitophorous vacuole-derived vesicles in the erythrocyte cytoplasm, large intracellular vacuoles and discontinuities in their trilaminar cell membrane. This work revises current knowledge on the role of Pfg27, indicating that the protein is not required for parasite entry into sexual differentiation, and suggesting that it is instead involved in maintaining cell integrity in the uniquely long gametocytogenesis of P. falciparum.
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Affiliation(s)
- Anna Olivieri
- Dipartimento di Malattie Infettive, Parassitarie e Immunomediate, Istituto Superiore di Sanità, 00161, Rome, Italy
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14
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Lal K, Delves MJ, Bromley E, Wastling JM, Tomley FM, Sinden RE. Plasmodium male development gene-1 (mdv-1) is important for female sexual development and identifies a polarised plasma membrane during zygote development. Int J Parasitol 2008; 39:755-61. [PMID: 19136003 DOI: 10.1016/j.ijpara.2008.11.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 11/18/2008] [Accepted: 11/30/2008] [Indexed: 12/20/2022]
Abstract
Successful development of Plasmodium sexual stages is essential for parasite survival, but the genes involved are poorly understood. We 'knocked out' the male development gene-1 (mdv-1) locus in Plasmodium berghei and found it to be important in female gametocyte activation. Indirect immunofluorescence assays show MDV-1 has a punctate cytoplasmic distribution in gametocytes. After activation of both females and males, MDV-1 is more peripherally located but in males exclusively it becomes concentrated in a few large foci. In vitro ookinete conversion assays that test the ability of activated female gametocytes to develop into retort stage ookinetes, suggests a complicit role for MDV-1, with the knock-out parasite producing 86% reduction in ookinetes. The retort stage ookinete develops from the zygote by increasing growth of an apical protrusion and MDV-1 locates at the 'leading' extracellular apical pole of this protrusion. In the fully developed ookinete MDV-1 is localised to the posterior pole. In vivo, the knock-out parasites demonstrate a phenotype in which there is a 90% reduction of parasite transmission to oocysts in mosquitoes.
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Affiliation(s)
- Kalpana Lal
- The Division of Cell and Molecular Biology, Imperial College London, London, UK.
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15
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Hayton K, Su XZ. Drug resistance and genetic mapping in Plasmodium falciparum. Curr Genet 2008; 54:223-39. [PMID: 18802698 DOI: 10.1007/s00294-008-0214-x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2008] [Revised: 08/27/2008] [Accepted: 08/28/2008] [Indexed: 11/30/2022]
Abstract
Drug resistance in malaria parasites is a serious public health burden, and resistance to most of the antimalarial drugs currently in use has been reported. A better understanding of the molecular mechanisms of drug resistance is urgently needed to slow or circumvent the spread of resistance, to allow local treatments to be deployed more effectively to prolong the life span of the current drugs, and to develop new drugs. Although mutations in genes determining resistance to drugs such as chloroquine and the antifolates have been identified, we still do not have a full understanding of the resistance mechanisms, and genes that contribute to resistance to many other drugs remain to be discovered. Genetic mapping is a powerful tool for the identification of mutations conferring drug resistance in malaria parasites because most drug-resistant phenotypes were selected within the past 60 years. High-throughput methods for genotyping large numbers of single nucleotide polymorphisms (SNPs) and microsatellites (MSs) are now available or are being developed, and genome-wide association studies for malaria traits will soon become a reality. Here we discuss strategies and issues related to mapping genes contributing to drug resistance in the human malaria parasite Plasmodium falciparum.
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Affiliation(s)
- Karen Hayton
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 9000 Rockville Pike, Bethesda, MD 20892, USA.
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16
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Cortés A, Carret C, Kaneko O, Yim Lim BYS, Ivens A, Holder AA. Epigenetic silencing of Plasmodium falciparum genes linked to erythrocyte invasion. PLoS Pathog 2007; 3:e107. [PMID: 17676953 PMCID: PMC1937010 DOI: 10.1371/journal.ppat.0030107] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2007] [Accepted: 06/11/2007] [Indexed: 11/20/2022] Open
Abstract
The process of erythrocyte invasion by merozoites of Plasmodium falciparum involves multiple steps, including the formation of a moving junction between parasite and host cell, and it is characterised by the redundancy of many of the receptor–ligand interactions involved. Several parasite proteins that interact with erythrocyte receptors or participate in other steps of invasion are encoded by small subtelomerically located gene families of four to seven members. We report here that members of the eba, rhoph1/clag, acbp, and pfRh multigene families exist in either an active or a silenced state. In the case of two members of the rhoph1/clag family, clag3.1 and clag3.2, expression was mutually exclusive. Silencing was clonally transmitted and occurred in the absence of detectable DNA alterations, suggesting that it is epigenetic. This was demonstrated for eba-140. Our data demonstrate that variant or mutually exclusive expression and epigenetic silencing in Plasmodium are not unique to genes such as var, which encode proteins that are exported to the surface of the erythrocyte, but also occur for genes involved in host cell invasion. Clonal variant expression of invasion-related ligands increases the flexibility of the parasite to adapt to its human host. Plasmodium falciparum is responsible for the most severe forms of human malaria. Invasion of host erythrocytes is an essential step of the complex life cycle of this parasite. There is redundancy in many of the interactions involved in this process, such that the parasite can use different sets of receptor–ligand interactions to invade. Here, we demonstrate that the parasite can turn off the expression of some of the proteins that mediate invasion of erythrocytes. Expression can be turned off without alterations in the genetic information of the parasite by using a mechanism known as epigenetic silencing. This is far more flexible than genetic changes, and permits fast, reversible adaptation. Turning on or off the expression of these proteins did not affect the capacity of the parasite to invade normal or modified red cells, which suggests that the variant expression of these genes may be used by the parasite to escape immune responses from the host. Parasite proteins that participate in erythrocyte invasion are important vaccine candidates. Determining which proteins can be turned off is important because vaccines based on single antigens of the parasite that can be turned off without affecting its growth would have little chance of inducing protective immunity.
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Affiliation(s)
- Alfred Cortés
- Division of Parasitology, Medical Research Council National Institute for Medical Research (NIMR), London, United Kingdom.
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17
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Abstract
Sexual differentiation and parasite transmission are intimately linked in the life cycle of malaria parasites. The specialized cells providing this crucial link are the Plasmodium gametocytes. These are formed in the vertebrate host and are programmed to mature into gametes emerging from the erythrocytes in the midgut of a blood-feeding mosquito. The ensuing fusion into a zygote establishes parasite infection in the insect vector. Although key mechanisms of gametogenesis and fertilization are becoming progressively clear, the fundamental biology of gametocyte formation still presents open questions, some of which are specific to the human malaria parasite Plasmodium falciparum. Developmental commitment to sexual differentiation, regulation of stage-specific gene expression, the profound molecular and cellular changes accompanying gametocyte specialization, the requirement for tissue-specific sequestration in P. falciparum gametocytogenesis are proposed here as areas for future investigation. The epidemiological relevance of parasite transmission from humans to mosquito in the spread of malaria and of Plasmodium drug resistance genes indicates that understanding molecular mechanisms of gametocyte formation is highly relevant to design strategies able to interfere with the transmission of this disease.
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Affiliation(s)
- Pietro Alano
- Dipartimento di Malattie Infettive, Parassitarie ed Immunomediate, Istituto Superiore di Sanità, Viale Regina Elena n. 299, 00161 Rome, Italy.
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18
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Pradel G. Proteins of the malaria parasite sexual stages: expression, function and potential for transmission blocking strategies. Parasitology 2007; 134:1911-29. [PMID: 17714601 DOI: 10.1017/s0031182007003381] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SUMMARYThe sexual phase of the malaria pathogen,Plasmodium falciparum, culminates in fertilization within the midgut of the mosquito and represents a crucial step in the completion of the parasite's life-cycle and transmission of the disease. Two decades ago, the first sexual stage-specific surface proteins were identified, among themPfs230,Pfs48/45, andPfs25, which were of scientific interest as candidates for the development of transmission blocking vaccines. A decade later, gene information gained from the sequencing of theP. falciparumgenome led to the identification of numerous additional sexual-stage proteins with antigenic properties and novel enzymes that putatively possess regulatory functions during sexual-stage development. This review aims to summarize the sexual-stage proteins identified to date, to compare their stage specificities and expression patterns and to highlight novel regulative mechanisms of sexual differentiation. The prospective candidacy of select sexual-stage proteins as targets for transmission blocking strategies will be discussed.
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Affiliation(s)
- G Pradel
- University of Würzburg, Research Center for Infectious Diseases, Röntgenring 11, 97070 Würzburg, Germany.
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19
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Nkrumah LJ, Muhle RA, Moura PA, Ghosh P, Hatfull GF, Jacobs WR, Fidock DA. Efficient site-specific integration in Plasmodium falciparum chromosomes mediated by mycobacteriophage Bxb1 integrase. Nat Methods 2006; 3:615-21. [PMID: 16862136 PMCID: PMC2943413 DOI: 10.1038/nmeth904] [Citation(s) in RCA: 205] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Accepted: 06/19/2006] [Indexed: 01/03/2023]
Abstract
Here we report an efficient, site-specific system of genetic integration into Plasmodium falciparum malaria parasite chromosomes. This is mediated by mycobacteriophage Bxb1 integrase, which catalyzes recombination between an incoming attP and a chromosomal attB site. We developed P. falciparum lines with the attB site integrated into the glutaredoxin-like cg6 gene. Transfection of these attB(+) lines with a dual-plasmid system, expressing a transgene on an attP-containing plasmid together with a drug resistance gene and the integrase on a separate plasmid, produced recombinant parasites within 2 to 4 weeks that were genetically uniform for single-copy plasmid integration. Integrase-mediated recombination resulted in proper targeting of parasite proteins to intra-erythrocytic compartments, including the apicoplast, a plastid-like organelle. Recombinant attB x attP parasites were genetically stable in the absence of drug and were phenotypically homogeneous. This system can be exploited for rapid genetic integration and complementation analyses at any stage of the P. falciparum life cycle, and it illustrates the utility of Bxb1-based integrative recombination for genetic studies of intracellular eukaryotic organisms.
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Affiliation(s)
- Louis J Nkrumah
- Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA
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20
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Gupta A, Mehra P, Nitharwal R, Sharma A, Biswas AK, Dhar SK. Analogous expression pattern ofPlasmodium falciparumreplication initiation proteins PfMCM4 and PfORC1 during the asexual and sexual stages of intraerythrocytic developmental cycle. FEMS Microbiol Lett 2006; 261:12-8. [PMID: 16842352 DOI: 10.1111/j.1574-6968.2006.00324.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
DNA replication takes place at five different stages during the life cycle of Plasmodium falciparum including the human and mosquito hosts. DNA replication initiation, the rate-determining step is poorly understood in Plasmodium. Here we show that PfMCM4 and PfORC1, two members of prereplication initiation complex are expressed specifically in the nucleus during the trophozoite and schizont stages of the asexual parasitic life cycle where maximum amount of DNA replication takes place. Further, we show that these proteins are also expressed in gametocytes, where DNA replication also occurs. These results expand our knowledge on these proteins and resolves discrepancies arising from previous studies with respect to the expression pattern of replication initiation proteins during the parasite's life cycle.
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Affiliation(s)
- Ashish Gupta
- Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi, India
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21
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Oguariri RM, Dunn JM, Golightly LM. 3' gene regulatory elements required for expression of the Plasmodiumfalciparum developmental protein, Pfs25. Mol Biochem Parasitol 2006; 146:163-72. [PMID: 16439031 DOI: 10.1016/j.molbiopara.2005.12.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Revised: 07/21/2005] [Accepted: 12/09/2005] [Indexed: 11/29/2022]
Abstract
Development of sexual stage parasites within the mosquito vector is a crucial step in the transmission of Plasmodium parasites. The expression of the P25 and P28 proteins on the surface of Plasmodium parasites in the mosquito midgut is required for development and hence disease transmission. 3' gene-flanking sequences are essential for expression of these critical proteins but the nucleotide elements required are poorly defined. Transient gene transfection experiments using constructs containing deletions of the 3' gene-flanking region of the Plasmodium falciparum P25 homologue, pfs25, reveal that elements necessary for protein expression are within 315 nucleotides (nt) of the stop codon. A T-rich region 137-231 nt from the stop codon is required for expression. The nonamer AATAAAATG, 360 nt downstream from the stop codon, enhances expression by 51 percent. Using 3' RACE analysis, multiple polyadenylation sites from endogenous and plasmid-derived pfs25 transcripts were identified. Dissimilarities between the identified elements and those of metazoans support the hypothesis that definition of P25/28 3' gene regulatory processes may eventually permit the development of agents which block malaria transmission but are non-toxic to humans.
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Affiliation(s)
- Raphael M Oguariri
- Department of Medicine, Division of International Medicine and Infectious Diseases, Weill Medical College of Cornell University, New York, NY 10021, USA
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22
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Eksi S, Haile Y, Furuya T, Ma L, Su X, Williamson KC. Identification of a subtelomeric gene family expressed during the asexual-sexual stage transition in Plasmodium falciparum. Mol Biochem Parasitol 2005; 143:90-9. [PMID: 15996767 DOI: 10.1016/j.molbiopara.2005.05.010] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2005] [Revised: 05/05/2005] [Accepted: 05/25/2005] [Indexed: 11/24/2022]
Abstract
For malaria transmission, the parasite must undergo sexual differentiation into mature gametocytes. However, the molecular basis for this critical transition in the parasites life cycle is unknown. Six previously uncharacterized genes, Pfg14.744, Pfg14.745, Pfg14.748, Pfg14.763, Pfg14.752 and Pfg6.6 that are members of a 36 gene Plasmodium falciparum-specific subtelomeric superfamily were found to be expressed in parasites that are committed to sexual development as suggested by co-expression of Pfs16 and Pfg27. Northern blots demonstrated that Pfg14.744 and Pfg14.748 were first expressed before the parasites differentiated into morphologically distinct gametocytes, transcription continued to increase until stage II gametocytes were formed and then rapidly decreased. Immunofluorescence assays indicated that both proteins were only produced in the subpopulation of ring stage parasites that are committed to gametocytogenesis and both localized to the parasitophorous vacuole (PV)b of the early ring stage parasites. As the parasites continued to develop Pfg14.748 remained within the parasitophorous vacuole, while Pfg14.744 was detected in the erythrocyte. The 5' flanking region of either gene alone was sufficient to drive early gametocyte specific expression of green fluorescent protein (GFP). In parasites transfected with a plasmid containing the Pfg14.748 5' flanking region immediately upstream of GFP, fluorescence was observed in a small number of schizonts the cycle before stage I gametocytes were observed. This expression pattern is consistent with commitment to sexual differentiation prior to merozoite release and erythrocyte invasion. Further investigation into the role of these genes in the transition from asexual to sexual differentiation could provide new strategies to block malaria transmission.
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Affiliation(s)
- Saliha Eksi
- Loyola University Chicago, Department of Biology, 6525 North Sheridan Road, Chicago, IL 60626, USA
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23
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Silvestrini F, Bozdech Z, Lanfrancotti A, Di Giulio E, Bultrini E, Picci L, Derisi JL, Pizzi E, Alano P. Genome-wide identification of genes upregulated at the onset of gametocytogenesis in Plasmodium falciparum. Mol Biochem Parasitol 2005; 143:100-10. [PMID: 16026866 DOI: 10.1016/j.molbiopara.2005.04.015] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2005] [Revised: 04/19/2005] [Accepted: 04/21/2005] [Indexed: 11/23/2022]
Abstract
A genome-wide expression analysis was undertaken to identify novel genes specifically activated from early stages of gametocytogenesis in Plasmodium falciparum. A comparative analysis was conducted on sexually induced cultures of reference parasite clone 3D7 and its gametocyteless derivative clone F12. Competitive hybridisations on long-oligomer microarrays representing 4488 P. falciparum genes identified a remarkably small number of transcripts differentially produced in the two clones. Upregulation of the mRNAs for the early gametocyte markers Pfs16 and Pfg27 was however readily detected in 3D7, and such genes were used as reference transcripts in a comparative time course analysis of 3D7 and F12 parasites between 30 and 40 h post-invasion in cultures induced to enter gametocytogenesis. One hundred and seventeen genes had expression profiles which correlated to those of pfs16 and pfg27, and Northern blot analysis and published proteomic data identified those whose expression was gametocyte-specific. Immunofluorescence analysis with antibodies against two of these gene products identified two novel parasite membrane associated, sexual stage-specific proteins. One was produced from stage I gametocytes and the second showed peak production in stage II gametocytes. The two proteins were named Pfpeg-3 and Pfpeg-4, for P. falciparum proteins of early gametocytes.
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Affiliation(s)
- Francesco Silvestrini
- Dipartimento di Malattie Infettive Parassitarie e Immunomediate, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
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24
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Cann H, Brown SV, Oguariri RM, Golightly LM. 3' UTR signals necessary for expression of the Plasmodium gallinaceum ookinete protein, Pgs28, share similarities with those of yeast and plants. Mol Biochem Parasitol 2005; 137:239-45. [PMID: 15383294 DOI: 10.1016/j.molbiopara.2004.06.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2004] [Revised: 06/15/2004] [Accepted: 06/18/2004] [Indexed: 11/15/2022]
Abstract
During metazoan development, 3' UTR signals mediate the time and place of gene expression. For protozoan Plasmodium parasites, the formation of ookinetes from gametes in the mosquito midgut is an analogous developmental process. Previous studies of the 3' UTR signals necessary for expression of Pgs28, the major surface protein of Plasmodium gallinaceum ookinetes, suggested that a 3' UTR T-rich region and DNA sequences containing an ATTAAA eukaryotic polyadenylation consensus motif were necessary for its expression. During metazoan development, U-rich elements may function in conjunction with eukaryotic polyadenylation consensus signals to mediate developmental protein expression. To define whether the putative Plasmodium elements were mediators of Pgs28 expression mutations of these nucleotide sequences were made in plasmid constructs. The effect of the mutations on Pgs28 expression was tested by the transient gene transfection of sexual stage P. gallinaceum parasites. These studies reveal that two different mutations of the ATTAAA motif, which alter gene expression in higher eukaryotes and yeast, do not alter the expression of Pgs28. However, the U-rich element, adjacent nucleotides UUUACAAAAUUGUUUUAACU and downstream nucleotides UAUAUAAAA are able to mediate expression to varying degrees. The organization and overlapping function of these elements appears to more closely resemble that of yeasts or plants than those of metazoans.
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Affiliation(s)
- Helen Cann
- Department of Medicine, Division of International Medicine and Infectious Diseases, Weill Medical College of Cornell University, 1300 York Avenue, Room A421, New York, NY 10021, USA
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25
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Abstract
The Molecular Approaches to Malaria 2004 meeting provided an opportunity to see the impressive progress in all research fields and in the four years since the previous Molecular Approaches to Malaria meeting, when much of the Plasmodium falciparum genome sequence was already available. Study of the part of the Plasmodium life cycle associated with transmission through the vector, which begins with the commitment of blood-stage forms to sexual development, has been especially fruitful. This success is a result of several reasons including: (i) the availability of the genome sequence; (ii) the availability of good animal models that allow parasite culture and facile in vivo studies of many of the life cycle stages involved in transmission; (iii) the availability of genetic manipulation technologies for the animal models of malaria, as well as P. falciparum; and (iv) the ability to study lethal gene knockouts at this stage of the life cycle.
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Affiliation(s)
- Shahid M Khan
- Department of Parasitology, Centre of Infectious Disease, Leiden University Medical Centre, Albinusdreef 1, 2333 ZA Leiden, The Netherlands
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26
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Moreira CK, Marrelli MT, Jacobs-Lorena M. Gene expression in Plasmodium: from gametocytes to sporozoites. Int J Parasitol 2004; 34:1431-40. [PMID: 15582520 DOI: 10.1016/j.ijpara.2004.10.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Revised: 09/17/2004] [Accepted: 10/05/2004] [Indexed: 02/06/2023]
Abstract
Completion of the complex developmental program of Plasmodium in the mosquito is essential for parasite transmission, yet this part of its life cycle is still poorly understood. In recent years, considerable progress has been made in the identification and characterization of genes expressed during parasite development in the mosquito. This line of investigation was greatly facilitated by the availability of the genome sequence of several Plasmodium, and by the application of approaches such as proteomics, microarrays, gene disruption by homologous recombination (gene knockout) and by use of subtraction libraries. Here, we review what is presently known about genes expressed in gametocytes and during the Plasmodium life cycle in the mosquito.
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Affiliation(s)
- C K Moreira
- Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Malaria Research Institute, The Johns Hopkins University, 615 N Wolfe St., Baltimore, MD 21205, USA
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27
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Kumar N, Cha G, Pineda F, Maciel J, Haddad D, Bhattacharyya M, Nagayasu E. Molecular complexity of sexual development and gene regulation in Plasmodium falciparum. Int J Parasitol 2004; 34:1451-8. [PMID: 15582522 DOI: 10.1016/j.ijpara.2004.10.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2004] [Revised: 10/19/2004] [Accepted: 10/19/2004] [Indexed: 11/28/2022]
Abstract
The malaria parasite, Plasmodium falciparum, has a complex life cycle which alternates between the vertebrate host and the invertebrate vector. Various morphological changes as well as stage-specific transcripts and gene expression profiles that accompany parasite's asexual and sexual life cycle suggest that gene regulation is crucial for the parasite's continual adaptations to survive the changing environments as well as for pathogenesis. Development of sexual stages is crucial for malaria transmission and relatively little is known about the role of specific gene products during asexual to sexual differentiation and further development. Therefore, in order to have a full understanding of the biology of the malaria parasite, gene regulation on a genome-wide global level must be understood, an area remaining to be elucidated in P. falciparum. Parasite features, such as A-T bias, difficulties in cloning, labor-intensive culture and purification of specific stages of the parasite, all contribute to the difficulties to investigate many aspects of parasite biology. However, despite these challenges, limited studies have revealed a number of parallelisms with eukaryotic transcription. For example, the parasite's genes are organised in a similar fashion, contain promoter elements and upstream activation sequences, as shown by structural searches and functional assays, and some of the basal machinery and general transcription factors have been found in Plasmodium. The completion of the full genome sequence of P. falciparum and other species of Plasmodium has resulted in the search for specific transcription factors through genome mining. Although genome mining may identify some of the factors, search for these factors solely by primary sequence homology would result in a non-comprehensive list for transcription factors present in the genome. Here, we present further discussion on putative transcription factors like activities detected in the asexual and sexual stages of P. falciparum.
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Affiliation(s)
- Nirbhay Kumar
- Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins Malaria Research Institute, Johns Hopkins University, 615 N. Wolfe Street, Baltimore, MD 21205, USA.
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28
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Shue P, Brown SV, Cann H, Singer EF, Appleby S, Golightly LM. The 3′ UTR elements of P. gallinaceum protein Pgs28 are functionally distinct from those of human cells. Mol Biochem Parasitol 2004; 137:355-9. [PMID: 15383307 DOI: 10.1016/j.molbiopara.2004.07.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2004] [Revised: 06/30/2004] [Accepted: 07/06/2004] [Indexed: 11/23/2022]
Affiliation(s)
- Peter Shue
- Department of Medicine, Division of International Medicine and Infectious Diseases, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA
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29
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Gissot M, Refour P, Briquet S, Boschet C, Coupé S, Mazier D, Vaquero C. Transcriptome of 3D7 and its gametocyte-less derivative F12 Plasmodium falciparum clones during erythrocytic development using a gene-specific microarray assigned to gene regulation, cell cycle and transcription factors. Gene 2004; 341:267-77. [PMID: 15474309 DOI: 10.1016/j.gene.2004.07.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2004] [Revised: 06/21/2004] [Accepted: 07/05/2004] [Indexed: 11/19/2022]
Abstract
During the complex life cycle of Plasmodium falciparum, through mosquito and human, the erythrocytic cycle is responsible for malarial disease and transmission. The regulation of events that occur during parasite development, such as proliferation and differentiation, implies a fine control of transcriptional activities that in turn governs the expression profiles of sets of genes. Pathways that underline gametocyte commitment are yet poorly understood even though kinases and transcription factors have been assumed to play a crucial role in this event. In order to understand the molecular mechanisms controlling the variation of gene expression profiles that might participate in early gametocytogenesis, the transcriptome of two clones, 3D7 and its gametocyte-less derivative F12, was compared at five time points of the erythrocytic asexual development. We have used a thematic DNA microarray containing 150 PCR fragments, representative of P. falciparum genes involved in signal transduction, cell cycle and transcriptional regulation. We identified several genes eliciting different expression profiles among which some implicated in gene regulation or encoding putative transcription factors. The differential expression of transcription factor and kinase transcripts observed in the two clones may enlighten genes that might have a role in impairment of the early gametocytogenesis of the F12 clone.
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Affiliation(s)
- Mathieu Gissot
- INSERM U511, CHU Pitié-Salpêtrière, Université Paris 6, 91 boulevard de l'Hôpital, 75013 Paris, France
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30
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Mosqueda J, Falcon A, Antonio Alvarez J, Alberto Ramos J, Oropeza-Hernandez LF, Figueroa JV. Babesia bigemina sexual stages are induced in vitro and are specifically recognized by antibodies in the midgut of infected Boophilus microplus ticks. Int J Parasitol 2004; 34:1229-36. [PMID: 15491585 DOI: 10.1016/j.ijpara.2004.07.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2004] [Revised: 07/06/2004] [Accepted: 07/06/2004] [Indexed: 11/17/2022]
Abstract
Babesia bigemina, a causative agent of bovine babesiosis, is transmitted from one bovine to another only by infected ticks. The life cycle of B. bigemina includes a sexual phase in the tick host; however, molecules from sexual stages of any Babesia species have not been characterized. This is the first report of the induction of sexual stages of any Babesia species in vitro, free of tick antigens. Intraerythrocytic parasites were cultured in vitro for 20h using an induction medium. Extraerythrocytic parasites were first seen 3h post induction; elongated stages with long projections appeared at 6h post induction and by 9h they paired and fused to form larger stages. Round zygotes appeared 20h post induction. Moreover, by using Percoll gradients, sexual stages were purified free of contaminating intraerythrocytic stages. Purified parasites were used to generate polyclonal antibodies, which specifically bound to antigens expressed in sexual stages induced in vitro, but not to antigens expressed in intraerythrocytic stages. Importantly, these antibodies specifically identified sexual stages from midguts of female Boophilus microplus ticks fed on infected cattle.
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Affiliation(s)
- Juan Mosqueda
- Centro Nacional de Investigacion Disciplinaria en Parasitologia Veterinaria, INIFAP, Col Progreso, Jiutepec, Morelos, Mexico.
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31
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Talman AM, Domarle O, McKenzie FE, Ariey F, Robert V. Gametocytogenesis: the puberty of Plasmodium falciparum. Malar J 2004; 3:24. [PMID: 15253774 PMCID: PMC497046 DOI: 10.1186/1475-2875-3-24] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2004] [Accepted: 07/14/2004] [Indexed: 11/16/2022] Open
Abstract
The protozoan Plasmodium falciparum has a complex life cycle in which asexual multiplication in the vertebrate host alternates with an obligate sexual reproduction in the anopheline mosquito. Apart from the apparent recombination advantages conferred by sex, P. falciparum has evolved a remarkable biology and adaptive phenotypes to insure its transmission despite the dangers of sex. This review mainly focuses on the current knowledge on commitment to sexual development, gametocytogenesis and the evolutionary significance of various aspects of gametocyte biology. It goes further than pure biology to look at the strategies used to improve successful transmission. Although gametocytes are inevitable stages for transmission and provide a potential target to fight malaria, they have received less attention than the pathogenic asexual stages. There is a need for research on gametocytes, which are a fascinating stage, responsible to a large extent for the success of P. falciparum.
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Affiliation(s)
- Arthur M Talman
- Groupe de Recherche sur le Paludisme, Institut Pasteur de Madagascar, B.P.1274 Antananarivo 101, Madagascar
- Department of Biological Sciences, Imperial College London, Exhibition Road, SW7 2AZ London, UK
| | - Olivier Domarle
- Groupe de Recherche sur le Paludisme, Institut Pasteur de Madagascar, B.P.1274 Antananarivo 101, Madagascar
| | - F Ellis McKenzie
- Fogarty International Centre, National Institutes of Health, Bethesda, MD 20892, USA
| | - Frédéric Ariey
- Groupe de Recherche sur le Paludisme, Institut Pasteur de Madagascar, B.P.1274 Antananarivo 101, Madagascar
| | - Vincent Robert
- Groupe de Recherche sur le Paludisme, Institut Pasteur de Madagascar, B.P.1274 Antananarivo 101, Madagascar
- UR 77 Paludisme Afro-tropical, Institut de Recherche pour le Développement, Madagascar
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32
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Wel AVD, Kocken CHM, Pronk TC, Franke-Fayard B, Thomas AW. New selectable markers and single crossover integration for the highly versatile Plasmodium knowlesi transfection system. Mol Biochem Parasitol 2004; 134:97-104. [PMID: 14747147 DOI: 10.1016/j.molbiopara.2003.10.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Plasmodium knowlesi provides a highly versatile transfection system for malaria, since it enables rapid genetic modification of the parasite both in vivo as well as in vitro. However, it is not possible to perform multiple genetic manipulations within one parasite line because of a lack of selectable markers. In an effort to develop additional selectable markers for this parasite, positive and negative selectable markers that have recently been successfully used in Plasmodium falciparum were tested. It was shown that the positive selectable markers human dihydrofolate reductase (hdhfr), blasticidin S deaminase (bsd) and neomycin phosphotransferase II (neo) all conferred drug resistance to P. knowlesi when introduced as episomes. The plasmid containing the hdhfr selectable marker was not only successfully introduced as circular form, but also as linear fragment, demonstrating for the first time single crossover integration in P. knowlesi. Thymidine kinase was tested for its potential as negative selectable marker and it was shown that recombinant P. knowlesi parasites expressing thymidine kinase from episomes were highly sensitive to ganciclovir compared to wild-type P. knowlesi. The availability of new positive selectable markers and a strong candidate for a negative selectable marker for P. knowlesi, in combination with the opportunity to perform targeted single crossover integration in P. knowlesi, significantly increases the flexibility of this transfection system, making it one of the most versatile systems available for Plasmodium.
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Affiliation(s)
- Annemarie v d Wel
- Department of Parasitology, Biomedical Primate Research Centre, P.O. Box 3306, 2280 GH, Rijswijk, The Netherlands
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33
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Kongkasuriyachai D, Fujioka H, Kumar N. Functional analysis of Plasmodium falciparum parasitophorous vacuole membrane protein (Pfs16) during gametocytogenesis and gametogenesis by targeted gene disruption. Mol Biochem Parasitol 2004; 133:275-85. [PMID: 14698439 DOI: 10.1016/j.molbiopara.2003.10.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Gametocytogenesis is a tightly regulated process marked by differentiation through distinct morphological forms and coordinated expression of sexual stage gene products. The earliest known gene product expressed at the onset of Plasmodium falciparum gametocytogenesis is Pfs16 localized on the parasitophorous vacuole membrane (PVM). Targeted gene disruption was undertaken to disrupt expression of Pfs16 and examine its potential role during sexual development. Three independent clones were demonstrated to have the coding sequence of Ps16 gene disrupted by the targeting plasmid by homologous recombination. No full-length transcripts and PVM localized 16 kDa protein were detected. Instead, all three "16ko" clones expressed a protein of 14 kDa recognized by Pfs16 specific antibodies that was mislocalized to an unidentified double membrane compartment in the parasites. Disruption of Pfs16 gene resulted in a significant reduction in gametocyte production, although the small number of gametocytes produced appeared to be normal by molecular and phenotypic evidences. Preliminary observation also suggested impaired ability of male gametocytes to exflagellate in vitro. Pfs16 does not appear to be essential for sexual development, instead may be required for optimal production of sexual parasites. Understanding mechanisms involved in the development of sexual stages of P. falciparum may identify novel targets for drugs and vaccines effective in reducing malaria transmission.
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Affiliation(s)
- Darin Kongkasuriyachai
- Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins Malaria Research Institute, Baltimore, MD 21205, USA
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34
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Bhattacharyya MK, Kumar N. Identification and molecular characterisation of DNA damaging agent induced expression of Plasmodium falciparum recombination protein PfRad51. Int J Parasitol 2003; 33:1385-92. [PMID: 14527521 DOI: 10.1016/s0020-7519(03)00212-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Rad51 protein, the eukaryotic homologue of Escherichia coli RecA protein plays a pivotal role in recombinational repair mechanism. We have identified a new homologue of Rad51 from the apicomplexan parasite Plasmodium falciparum, designated PfRad51. The PfRad51 gene codes for a 351 amino acid polypeptide with a predicted molecular mass of 38720, and shares 66-75% sequence identity within the catalytic region with Rad51 from human, yeast and other protozoan parasites such as Trypanosoma and Leishmania. The expression of PfRad51 transcript as well as protein in the intra-erythrocytic in vitro culture of P. flalciparum was found to be up-regulated in response to the DNA damaging agent methyl methanesulfonate, suggesting its functional involvement in recombinational repair process. PfRad51 is the first apicomplexan gene identified that codes for a recombination protein, and it offers an excellent model for studying DNA damage inducible gene expression in such parasites.
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Affiliation(s)
- Mrinal Kanti Bhattacharyya
- Johns Hopkins University Bloomberg School of Public Health, 615 N. Wolfe Street, Baltimore, MD 21205, USA
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35
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Sharma A, Sharma I, Kogkasuriyachai D, Kumar N. Structure of a gametocyte protein essential for sexual development in Plasmodium falciparum. Nat Struct Mol Biol 2003; 10:197-203. [PMID: 12577051 DOI: 10.1038/nsb899] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2002] [Accepted: 01/02/2003] [Indexed: 11/08/2022]
Abstract
Malaria transmission is dependent on the development of sexual forms of Plasmodium falciparum, called gametocytes, in the vertebrate host. Pfg27 is an abundantly expressed sexual stage-specific protein that is essential for gametocytogenesis in P. falciparum. We describe the crystal structure of Pfg27, which reveals a novel fold composed of two pseudo dyad-related repeats of the helix-turn-helix motif. Structurally equivalent helices of each repeat either form a dimer interface or interact with RNA in vitro. One side of the dimer presents an unprecedented juxtaposition of four polyproline (PXXP) motifs. Preliminary binding data indicate that these sites are capable of binding Src homology-3 (SH3) modules. Molecular modeling suggests that the dimer can accommodate two SH3 modules simultaneously, potentially enabling molecular crosstalk between SH3-containing proteins. The structural and initial biochemical evidence suggests that Pfg27 may serve as a platform for RNA and SH3 binding.
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Affiliation(s)
- Amit Sharma
- Malaria group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi 110067, India.
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36
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Kongkasuriyachai D, Kumar N. Functional characterisation of sexual stage specific proteins in Plasmodium falciparum. Int J Parasitol 2002; 32:1559-66. [PMID: 12435440 DOI: 10.1016/s0020-7519(02)00184-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The various stages of the malaria parasites in the vertebrate host and in the mosquito vector offer numerous candidates for vaccine and drug development. However, the biological complexity of the parasites and the interaction with the immune system of the host continue to frustrate all such efforts thus far. While most of the targets for drug and vaccine design have focused on the asexual stages, the sexual stages of the parasite are critical for transmission and maintenance of parasites among susceptible vertebrate hosts. Sexual stage parasites undergo a series of morphological and biochemical changes during their development, accompanied by a co-ordinated cascade of a distinct expression pattern of sexual stage specific proteins. Mechanisms underlying the developmental switch from asexual parasite to sexual parasite still remain elusive. Methods that can break the malaria transmission cycle thus occupy a central place in the overall malaria control strategies. This paper provides a review of genes expressed in sexually differentiated Plasmodium. In the past few years, a molecular approach based on targeted gene disruption has revealed fascinating biological roles for many of the sexual stage gene products. In addition, we will briefly discuss other functional genomic approaches employed to study not only sexual but also other aspects of host-parasite biology.
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Affiliation(s)
- Darin Kongkasuriyachai
- Johns Hopkins Malaria Research Institute, Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
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37
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Sati SP, Singh SK, Kumar N, Sharma A. Extra terminal residues have a profound effect on the folding and solubility of a Plasmodium falciparum sexual stage-specific protein over-expressed in Escherichia coli. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:5259-63. [PMID: 12392558 DOI: 10.1046/j.1432-1033.2002.03237.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The presence of extra N- and C- terminal residues can play a major role in the stability, solubility and yield of recombinant proteins. Pfg27 is a 27K soluble protein that is essential for sexual development in Plasmodium falciparum. It was over-expressed using the pMAL-p2 vector as a fusion protein with the maltose binding protein. Six different constructs were made and each of the fusion proteins were expressed and purified. Our results show that the fusion proteins were labile and only partially soluble in five of the constructs resulting in very poor yields. Intriguingly, in the sixth construct, the yield of soluble fusion protein with an extended carboxyl terminus of 17 residues was several fold higher. Various constructs with either N-terminal or smaller C-terminal extensions failed to produce any soluble fusion protein. Furthermore, all five constructs produced Pfg27 that precipitated after protease cleavage from its fusion partner. The sixth construct, which produced soluble protein in high yields, also gave highly stable and soluble Pfg27 after cleavage of the fusion. These results indicate that extra amino acid residues at the termini of over-expressed proteins can have a significant effect on the folding of proteins expressed in E. coli. Our data suggest the potential for development of a novel methodology, which will entail construction of fusion proteins with maltose binding protein as a chaperone on the N-terminus and a C-terminal 'solubilization tag'. This system may allow large-scale production of those proteins that have a tendency to misfold during expression.
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Affiliation(s)
- Sushil Prasad Sati
- Malaria Group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India
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38
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Crabb BS. Transfection technology and the study of drug resistance in the malaria parasite Plasmodium falciparum. Drug Resist Updat 2002; 5:126-30. [PMID: 12237080 DOI: 10.1016/s1368-7646(02)00085-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Numerous approaches have been employed to identify the molecules responsible for drug resistance in the human malaria parasite Plasmodium falciparum. However, it was not until the recent development of stable transfection in this parasite that it became possible to prove the role of particular genes in drug resistance and, perhaps more importantly, to characterise the nature of the specific mutations that contribute the resistance phenotype. In this review, the contribution of various molecular genetic approaches to the dissection of drug resistance in P. falciparum is described. Future possibilities in this field are also outlined in the light of recent technological advances.
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Affiliation(s)
- Brendan S Crabb
- The Walter and Eliza Hall Institute of Medical Research, PO Royal Melbourne Hospital, Vic., Australia.
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39
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Eksi S, Williamson KC. Male-specific expression of the paralog of malaria transmission-blocking target antigen Pfs230, PfB0400w. Mol Biochem Parasitol 2002; 122:127-30. [PMID: 12106866 DOI: 10.1016/s0166-6851(02)00091-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Malaria transmission requires that Plasmodium parasites circulating in the vertebrate host develop into male and female gametocytes, which are then taken up by a mosquito to undergo fertilization and further development into infectious sporozoites. To understand the malaria specific events involved in this process, the gene products involved require identification and characterization. This work demonstrates that antibodies generated against the paralog of malaria transmission-blocking antigen Pfs230, PfB0400w, react only with stage V male gametocytes, not gametes or asexual parasites. In contrast, Pfs230 is expressed on the surface of all gametocytes and remains associated with emerged gametes as one of the primary surface antigens for several hours. Consistent with the localization findings, a high molecular weight band is recognized by anti-PfB0400w antibodies on western blots of extracts of late stage gametocytes, not asexual parasites, early (stage II/III) gametocytes, or gametes. PfB0400w mRNA is also not observed in asexual parasites. The transcript levels peak in stage III/IV gametocytes, then sharply decline in gametes. This work identifies a novel male-specific protein with an expression pattern that is distinctly different than its paralog.
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Affiliation(s)
- Saliha Eksi
- Department of Biology, Loyola University, 6525 North Sheridan Road, Chicago, IL 60626, USA
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40
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Bhattacharyya MK, Hong Z, Kongkasuriyachai D, Kumar N. Plasmodium falciparum protein phosphatase type 1 functionally complements a glc7 mutant in Saccharomyces cerevisiae. Int J Parasitol 2002; 32:739-47. [PMID: 12062492 DOI: 10.1016/s0020-7519(02)00007-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We have identified a new homologue of protein phosphatase type 1 from Plasmodium falciparum, designated PfPP1, which shows 83-87% sequence identity with yeast and mammalian PP1s at the amino acid level. The PfPP1 sequence is strikingly different from all other P. falciparum Ser/Thr phosphatases cloned so far. The deduced 304 amino acid sequence revealed the signature sequence of Ser/Thr phosphatase LRGNHE, and two putative protein kinase C and five putative casein kinase II phosphorylation sites. Calyculin A, a potent inhibitor of Ser/Thr phosphatase 1 and 2A showed hyperphosphorylation of a 51kDa protein among other parasite proteins. Okadaic acid on the other hand, was without any effect suggesting that PP1 activity might predominate over PP2A activity in intra-erythrocytic P. falciparum. Complementation studies showed that PfPP1 could rescue low glycogen phenotype of Saccharomyces cerevisiae glc7 (PP1) mutant, strongly suggesting functional interaction of PfPP1 and yeast proteins involved in glycogen metabolism.
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Affiliation(s)
- Mrinal K Bhattacharyya
- Johns Hopkins Malaria Research Institute, The W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA
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41
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Delrieu I, Waller CC, Mota MM, Grainger M, Langhorne J, Holder AA. PSLAP, a protein with multiple adhesive motifs, is expressed in Plasmodium falciparum gametocytes. Mol Biochem Parasitol 2002; 121:11-20. [PMID: 11985859 DOI: 10.1016/s0166-6851(02)00016-6] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A gene coding for a protein containing two Scavenger Receptor Cysteine-Rich (SRCR) motifs, four Limulus factor C, Coch-5b2 and Lgl1 (LCCL) motifs; and one Polycystin-1, Lipoxygenase and Alpha Toxin (PLAT) motif was cloned from Plasmodium chabaudi and homologues identified in the P. falciparum and P. yoelii genome data bases. At least one of these sequence motifs (SRCR) has adhesive properties in other proteins, therefore, we propose to name this protein PSLAP for Plasmodium SRCR, LCCL Adhesive-like Protein. Southern blotting and chromosome analysis showed that pslap is a single copy gene on chromosome 14 in P. falciparum 3D7. pslap mRNA is strongly expressed in P. falciparum gametocytes, but was undetectable on Northern blots of RNA from the asexual blood stages. Polyclonal antibodies raised to different parts of PSLAP detected a protein expressed in late gametocytes, but not in the early stages of gametocytogenesis or asexual blood stages of P. falciparum. We suggest that PSLAP functions in the mosquito, for example, in modulation of the invertebrate host immune response or in protection against complement factors in the blood meal.
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Affiliation(s)
- Isabelle Delrieu
- Division of Parasitology, National Institute for Medical Research, The Ridgeway, London, UK
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42
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Patankar S, Munasinghe A, Shoaibi A, Cummings LM, Wirth DF. Serial analysis of gene expression in Plasmodium falciparum reveals the global expression profile of erythrocytic stages and the presence of anti-sense transcripts in the malarial parasite. Mol Biol Cell 2001; 12:3114-25. [PMID: 11598196 PMCID: PMC60160 DOI: 10.1091/mbc.12.10.3114] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Serial analysis of gene expression (SAGE) was applied to the malarial parasite Plasmodium falciparum to characterize the comprehensive transcriptional profile of erythrocytic stages. A SAGE library of approximately 8335 tags representing 4866 different genes was generated from 3D7 strain parasites. Basic local alignment search tool analysis of high abundance SAGE tags revealed that a majority (88%) corresponded to 3D7 sequence, and despite the low complexity of the genome, 70% of these highly abundant tags matched unique loci. Characterization of these suggested the major metabolic pathways that are used by the organism under normal culture conditions. Furthermore several tags expressed at high abundance (30% of tags matching to unique loci of the 3D7 genome) were derived from previously uncharacterized open reading frames, demonstrating the use of SAGE in genome annotation. The open platform "profiling" nature of SAGE also lead to the important discovery of a novel transcriptional phenomenon in the malarial pathogen: a significant number of highly abundant tags that were derived from annotated genes (17%) corresponded to antisense transcripts. These SAGE data were validated by two independent means, strand specific reverse transcription-polymerase chain reaction and Northern analysis, where antisense messages were detected in both asexual and sexual stages. This finding has implications for transcriptional regulation of Plasmodium gene expression.
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Affiliation(s)
- S Patankar
- Department of Immunology and Infectious Diseases, Harvard School of Public Health, Harvard University, Boston, MA 02115, USA
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43
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de Koning-Ward TF, Waters AP, Crabb BS. Puromycin-N-acetyltransferase as a selectable marker for use in Plasmodium falciparum. Mol Biochem Parasitol 2001; 117:155-60. [PMID: 11606225 DOI: 10.1016/s0166-6851(01)00344-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The limited number of selectable markers available for malaria transfection has hindered extensive manipulation of the Plasmodium falciparum genome and subsequently thorough genetic analysis of this organism. In this paper, we demonstrate that P. falciparum is highly sensitive to the drug puromycin, but that transgenic expression of the puromycin-N-acetyltransferase (PAC) gene from Streptomyces alboninger confers resistance to this drug with the IC(50) and IC(90) values increasing approximately 3- and 7-fold, respectively in PAC-expressing parasites. Despite this relatively low level of resistance, parasite populations transfected with the PAC selectable marker and selected directly on puromycin emerged at the same rate post-transfection as human dihydrofolate reductase (hDHFR)-expressing parasites, selected independently with the anti-folate drug WR99210. Transfected parasites generally maintained the PAC expression plasmid episomally at between two and six copies per parasite. We also demonstrate by cycling transfected parasites in the presence and absence of puromycin for several weeks, that the PAC selectable marker can be used for gene-targeting. Since the mode of action of puromycin is distinct from other drugs currently used for the stable transfection of P. falciparum, the PAC selectable marker should also have applicability for use in conjunction with other positive selectable markers, thereby increasing the possibilities for more complex functional studies of this organism.
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Affiliation(s)
- T F de Koning-Ward
- The Walter and Eliza Hall Institute of Medical Research, PO Royal Melbourne Hospital, Melbourne, Vic. 3050, Australia
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44
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Abstract
Malaria is still a leading cause of morbidity and mortality in human populations. Problems, including drug-resistant parasites and insecticide resistant mosquitoes, ensure the continued hold of malaria in the tropics and sub-tropics. Each year around 100 million cases of malaria result in at least 50,000 deaths outside of sub-Saharan Africa; within sub-Saharan Africa itself, malaria causes around one million child deaths per year. New approaches for malaria control are badly needed and much effort has gone to develop malaria vaccines. In addition to giving personal protection, most such vaccines would also tend to reduce the transmission of malaria. One class of vaccine is being developed specifically for this purpose--the malaria transmission-blocking vaccines (TBV). TBVs are based upon antigens expressed on the surface of the sexual and mosquito mid-gut stages of malaria parasites. These antigens are the targets of antibodies induced by vaccination of the host and ingested with the parasites in a mosquito blood meal. The antibodies act by inhibiting the parasite's development within the mosquito itself and they thereby prevent the onward transmission of the parasites. TBVs could contribute to the total interruption of malaria transmission in many locations with relatively low transmission rates, mostly outside sub-Saharan Africa. Under almost all transmission rates, however, TBVs would help reduce malaria incidence and malaria-related morbidity and mortality. Promising recombinant TBV candidate antigens for the two main human malaria parasite species, Plasmodium falciparum and Plasmodium vivax, have been produced and tested in the laboratory; one has undergone early clinical trials.
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Affiliation(s)
- A Stowers
- Malaria Vaccine Development Unit, Laboratory of Parasitic Diseases, NIAID/NIH, 5640 Fishers Lane, Rockville, MD 20852, USA
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45
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de Koning-Ward TF, Janse CJ, Waters AP. The development of genetic tools for dissecting the biology of malaria parasites. Annu Rev Microbiol 2001; 54:157-85. [PMID: 11018127 DOI: 10.1146/annurev.micro.54.1.157] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Plasmodium parasites are haploid unicellular organisms that cause malaria. In the last decade, transfection systems have been developed for both human and animal model species of Plasmodium, providing a broad range of genetic tools for the study of malaria parasite biology. Transient transfection has been used to provide insight into the regulation of gene expression by Plasmodium spp. The development of stable transfection technologies has provided the opportunity to express transgenes in Plasmodium spp., as well as elucidate the function of proteins by disrupting, modifying, or replacing the genes encoding them. These genetic tools represent an important breakthrough for malaria research and will significantly contribute to our understanding of the biology of the parasite. However, further developments in this technology are still required, especially because the full genome sequence of the major human malaria parasite Plasmodium falciparum will shortly be available. Ultimately, the biological information obtained through genetic manipulation of Plasmodium spp. will facilitate a more rational approach to vaccine and drug design.
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Affiliation(s)
- T F de Koning-Ward
- Department of Parasitology, Leiden University Medical Centre, Leiden, The Netherlands
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46
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O'Donnell RA, Preiser PR, Williamson DH, Moore PW, Cowman AF, Crabb BS. An alteration in concatameric structure is associated with efficient segregation of plasmids in transfected Plasmodium falciparum parasites. Nucleic Acids Res 2001; 29:716-24. [PMID: 11160894 PMCID: PMC30406 DOI: 10.1093/nar/29.3.716] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Transfection of the human malaria parasite Plasmodium falciparum is currently performed with circularised plasmids that are maintained episomally in parasites under drug selection but which are rapidly lost when selection pressure is removed. In this paper, we show that in instances where gene targeting is not favoured, transfected plasmids can change to stably replicating forms (SRFs) that are maintained episomally in the absence of drug selection. SRF DNA is a large concatamer of the parental plasmid comprising at least nine plasmids arranged in a head-to-tail array. We show as well that the original unstable replicating forms (URFs) are also present as head-to-tail concatamers, but only comprise three plasmids. Limited digestion and gamma irradiation experiments revealed that while URF concatamers are primarily circular, as expected, SRF concatamers form a more complex structure that includes extensive single-stranded DNA. No evidence of sequence rearrangement or additional sequence was detected in SRF DNA, including in transient replication experiments designed to select for more efficiently replicating plasmids. Surprisingly, these experiments revealed that the bacterial plasmid alone can replicate in parasites. Together, these results imply that transfected plasmids are required to form head-to-tail concatamers to be maintained in parasites and implicate both rolling-circle and recombination-dependent mechanisms in their replication.
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Affiliation(s)
- R A O'Donnell
- Department of Microbiology and Immunology and the CRC for Vaccine Technology, The University of Melbourne, VIC 3010, Australia
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47
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Kadekoppala M, Cheresh P, Catron D, Ji DD, Deitsch K, Wellems TE, Seifert HS, Haldar K. Rapid recombination among transfected plasmids, chimeric episome formation and trans gene expression in Plasmodium falciparum. Mol Biochem Parasitol 2001; 112:211-8. [PMID: 11223128 DOI: 10.1016/s0166-6851(00)00368-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Although recombination is known to be important to generating diversity in the human malaria parasite P. falciparum, the low efficiencies of transfection and the fact that integration of transfected DNA into chromosomes is observed only after long periods (typically 12 weeks or more) have made it difficult to genetically manipulate the blood stages of this major human pathogen. Here we show that co-transfection of a P. falciparum line with two plasmids, one expressing a green fluorescent protein (gfp) reporter and the other expressing a drug resistance marker (Tgdhfr-ts M23), allowed selection of a population in which about approximately 30% of the parasites produce GFP. In these GFP-producing parasites, the transfected plasmids had recombined into chimeric episomes as large as 20 kb and could be maintained under drug pressure for at least 16 weeks. Our data suggest that chimera formation occurs early (detected by 7--14 days) and that it involves homologous recombination favored by presence of the same P. falciparum 5'hrp3 UTR promoting transcription from each plasmid. This indicates the presence of high levels of homologous recombination activity in blood stage parasites that can be used to drive rapid recombination of newly introduced DNA, study mechanisms of recombination, and introduce genes for trans expression in P. falciparum.
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Affiliation(s)
- M Kadekoppala
- Department of Pathology, Northwestern University Medical School, 303 E. Chicago Ave., Chicago, IL 60611-3008, USA
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48
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van Dijk MR, Janse CJ, Thompson J, Waters AP, Braks JA, Dodemont HJ, Stunnenberg HG, van Gemert GJ, Sauerwein RW, Eling W. A central role for P48/45 in malaria parasite male gamete fertility. Cell 2001; 104:153-64. [PMID: 11163248 DOI: 10.1016/s0092-8674(01)00199-4] [Citation(s) in RCA: 302] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Fertilization and zygote development are obligate features of the malaria parasite life cycle and occur during parasite transmission to mosquitoes. The surface protein PFS48/45 is expressed by male and female gametes of Plasmodium falciparum and PFS48/45 antibodies prevent zygote development and transmission. Here, gene disruption was used to show that Pfs48/45 and the ortholog Pbs48/45 from a rodent malaria parasite P. berghei play a conserved and important role in fertilization. p48/45- parasites had a reduced capacity to produce oocysts in mosquitoes due to greatly reduced zygote formation. Unexpectedly, only male gamete fertility of p48/45- parasites was affected, failing to penetrate otherwise fertile female gametes. P48/45 is shown to be a surface protein of malaria parasites with a demonstrable role in fertilization.
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Affiliation(s)
- M R van Dijk
- Laboratory for Parasitology, Leiden University Medical Center, P.O. Box 9600, 2300 RC Leiden, The Netherlands
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49
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Ben Mamoun C, Gluzman IY, Hott C, MacMillan SK, Amarakone AS, Anderson DL, Carlton JM, Dame JB, Chakrabarti D, Martin RK, Brownstein BH, Goldberg DE. Co-ordinated programme of gene expression during asexual intraerythrocytic development of the human malaria parasite Plasmodium falciparum revealed by microarray analysis. Mol Microbiol 2001; 39:26-36. [PMID: 11123685 DOI: 10.1046/j.1365-2958.2001.02222.x] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Plasmodium falciparum is a protozoan parasite responsible for the most severe forms of human malaria. All the clinical symptoms and pathological changes seen during human infection are caused by the asexual blood stages of Plasmodium. Within host red blood cells, the parasite undergoes enormous developmental changes during its maturation. In order to analyse the expression of genes during intraerythrocytic development, DNA microarrays were constructed and probed with stage-specific cDNA. Developmental upregulation of specific mRNAs was found to cluster into functional groups and revealed a co-ordinated programme of gene expression. Those involved in protein synthesis (ribosomal proteins, translation factors) peaked early in development, followed by those involved in metabolism, most dramatically glycolysis genes. Adhesion/invasion genes were turned on later in the maturation process. At the end of intraerythrocytic development (late schizogony), there was a general shut-off of gene expression, although a small set of genes, including a number of protein kinases, were turned on at this stage. Nearly all genes showed some regulation over the course of development. A handful of genes remained constant and should be useful for normalizing mRNA levels between stages. These data will facilitate functional analysis of the P. falciparum genome and will help to identify genes with a critical role in parasite progression and multiplication in the human host.
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Affiliation(s)
- C Ben Mamoun
- Washington University School of Medicine, 660 S. Euclid Avenue, Box 8230, St Louis, MO 63110. USA
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50
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Sallicandro P, Paglia MG, Hashim SO, Silvestrini F, Picci L, Gentile M, Mulaa F, Alano P. Repetitive sequences upstream of the pfg27/25 gene determine polymorphism in laboratory and natural lines of Plasmodium falciparum. Mol Biochem Parasitol 2000; 110:247-57. [PMID: 11071280 DOI: 10.1016/s0166-6851(00)00274-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The structure of the genomic region located upstream of the gametocyte-specific gene pfg27/25 of Plasmodium falciparum was analysed in laboratory lines and field isolates of the parasite. The gene is located in a subtelomeric region of chromosome 13 in parasite clones 3D7 and HB3. Analysis of laboratory lines and field isolates of P. falciparum indicated that polymorphism upstream of pfg27/25 is mainly due to the structure of a repetitive DNA region located at about half a kilobase from the pfg27/25 coding sequence. Different types of repetitive sequences are present in this region, whose copy number is variable in different parasite lines. In addition a GC-rich sequence element contained in this region, which is proposed to be the startpoint of pfg27/25 mRNA, presents either a direct or a reverse orientation in different parasite lines. Genomic deletions upstream of the pfg27/25 gene are also described in two laboratory lines of the parasite, which eliminate two newly identified malaria genes. orf P and orf Gap, from the genome of these parasites. One of them, orf Gap, deleted from the reference parasite clone 3D7, is abundantly expressed as mature mRNA in asexual parasites. PCR analysis on 64 field isolates of P. falciparum indicated that orf P and orf Gap sequences are present in all tested samples of naturally propagating parasites.
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Affiliation(s)
- P Sallicandro
- Laboratorio di Biologia Cellulare, Instituto Superiore di Sanità, Rome, Italy
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