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de Souza W, Sant'Anna C, Cunha-e-Silva NL. Electron microscopy and cytochemistry analysis of the endocytic pathway of pathogenic protozoa. ACTA ACUST UNITED AC 2009; 44:67-124. [PMID: 19410686 DOI: 10.1016/j.proghi.2009.01.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Endocytosis is essential for eukaryotic cell survival and has been well characterized in mammal and yeast cells. Among protozoa it is also important for evading from host immune defenses and to support intense proliferation characteristic of some life cycle stages. Here we focused on the contribution of morphological and cytochemical studies to the understanding of endocytosis in Trichomonas, Giardia, Entamoeba, Plasmodium, and trypanosomatids, mainly Trypanosoma cruzi, and also Trypanosoma brucei and Leishmania.
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Affiliation(s)
- Wanderley de Souza
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Rio de Janeiro 21941-902, Brazil.
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52
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Lacomble S, Vaughan S, Gadelha C, Morphew MK, Shaw MK, McIntosh JR, Gull K. Three-dimensional cellular architecture of the flagellar pocket and associated cytoskeleton in trypanosomes revealed by electron microscope tomography. J Cell Sci 2009; 122:1081-90. [PMID: 19299460 DOI: 10.1242/jcs.045740] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
This study uses electron tomography linked to a variety of other EM methods to provide an integrated view of the flagellar pocket and basal body area of the African trypanosome procyclic trypomastigote. We reveal the pocket as an asymmetric membranous 'balloon' with two boundary structures. One of these - the collar - defines the flagellum exit point. The other defines the entry point of the flagellum into the pocket and consists of both an internal transitional fibre array and an external membrane collarette. A novel set of nine radial fibres is described in the basal body proximal zone. The pocket asymmetry is invariably correlated with the position of the probasal body and Golgi. The neck region, just distal to the flagellum exit site, is a specialised area of membrane associated with the start of the flagellum attachment zone and signifies the point where a special set of four microtubules, nucleated close to the basal bodies, joins the subpellicular array. The neck region is also associated with the single Golgi apparatus of the cell. The flagellar exit point interrupts the subpellicular microtubule array with discrete endings of microtubules at the posterior side. Overall, our studies reveal a highly organised, yet dynamic, area of cytoplasm and will be informative in understanding its function.
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Affiliation(s)
- Sylvain Lacomble
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, UK
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53
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Jetton N, Rothberg KG, Hubbard JG, Wise J, Li Y, Ball HL, Ruben L. The cell cycle as a therapeutic target against Trypanosoma brucei: Hesperadin inhibits Aurora kinase-1 and blocks mitotic progression in bloodstream forms. Mol Microbiol 2009; 72:442-58. [PMID: 19320832 DOI: 10.1111/j.1365-2958.2009.06657.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Aurora kinase family members co-ordinate a range of events associated with mitosis and cytokinesis. Anti-cancer therapies are currently being developed against them. Here, we evaluate whether Aurora kinase-1 (TbAUK1) from pathogenic Trypanosoma brucei might be targeted in anti-parasitic therapies as well. Conditional knockdown of TbAUK1 within infected mice demonstrated its essential contribution to infection. An in vitro kinase assay was developed which used recombinant trypanosome histone H3 as a substrate. Tandem mass spectroscopy identified a novel phosphorylation site in the carboxyl-tail of recombinant trypanosome histone H3. Hesperadin, an inhibitor of human Aurora B, prevented the phosphorylation of substrate with IC(50) of 40 nM. Growth of cultured bloodstream forms was also sensitive to Hesperadin (IC(50) of 50 nM). Hesperadin blocked nuclear division and cytokinesis but not other aspects of the cell cycle. Consequently, growth arrested cells accumulated multiple kinetoplasts, flagella and nucleoli, similar to the effects of RNAi-dependent knockdown of TbAUK1 in cultured bloodstream forms cells. Molecular models predicted high-affinity binding of Hesperadin to both conserved and novel sites in TbAUK1. Collectively, these data demonstrate that cell cycle progression is essential for infections with T. brucei and that parasite Aurora kinases can be targeted with small-molecule inhibitors.
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Affiliation(s)
- Neal Jetton
- Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275, USA
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54
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Field MC, Lumb JH, Adung'a VO, Jones NG, Engstler M. Chapter 1 Macromolecular Trafficking and Immune Evasion in African Trypanosomes. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2009; 278:1-67. [DOI: 10.1016/s1937-6448(09)78001-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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55
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Mechanisms regulating targeting of recycling endosomes to the cleavage furrow during cytokinesis. Biochem Soc Trans 2008; 36:391-4. [PMID: 18481966 DOI: 10.1042/bst0360391] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Recently, recycling endosomes have emerged as a key components required for the successful completion of cytokinesis. Furthermore, FIP3 (family of Rab11-interacting protein 3), a Rab11 GTPase-binding protein, has been implicated in targeting the recycling endosomes to the midbody of dividing cells. Previously, we have shown that FIP3/Rab11-containing endosomes associate with centrosomes until anaphase, at which time they translocate to the cleavage furrow. At telophase, FIP3/Rab11-containing endosomes move from the furrow into the midbody, and this step is required for abscission. While several other proteins were implicated in regulating FIP3 targeting to the cleavage furrow, the mechanisms regulating the dynamics of FIP3-containing endosomes during mitosis have not been defined. To identify the factors regulating FIP3 targeting to the furrow, we used a combination of siRNA (small interfering RNA) screens and proteomic analysis to identify Cyk-4/MgcRacGAP (GTPase-activating protein) and kinesin I as FIP3-binding proteins. Furthermore, kinesin I mediates the transport of FIP3-containing endosomes to the cleavage furrow. Once in the furrow, FIP3 binds to Cyk-4 as part of centralspindlin complex and accumulates at the midbody. Finally, we demonstrated that ECT2 regulates FIP3 association with the centralspindlin complex. Thus we propose that kinesin I, in concert with centralspindlin complex, plays a role in temporal and spatial regulation of endosome transport to the cleavage furrow during cytokinesis.
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56
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Stem-loop silencing reveals that a third mitochondrial DNA polymerase, POLID, is required for kinetoplast DNA replication in trypanosomes. EUKARYOTIC CELL 2008; 7:2141-6. [PMID: 18849470 DOI: 10.1128/ec.00199-08] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Kinetoplast DNA (kDNA), the mitochondrial genome of trypanosomes, is a catenated network containing thousands of minicircles and tens of maxicircles. The topological complexity dictates some unusual features including a topoisomerase-mediated release-and-reattachment mechanism for minicircle replication and at least six mitochondrial DNA polymerases (Pols) for kDNA transactions. Previously, we identified four family A DNA Pols from Trypanosoma brucei with similarity to bacterial DNA Pol I and demonstrated that two (POLIB and POLIC) were essential for maintaining the kDNA network, while POLIA was not. Here, we used RNA interference to investigate the function of POLID in procyclic T. brucei. Stem-loop silencing of POLID resulted in growth arrest and the progressive loss of the kDNA network. Additional defects in kDNA replication included a rapid decline in minicircle and maxicircle abundance and a transient accumulation of minicircle replication intermediates before loss of the kDNA network. These results demonstrate that POLID is a third essential DNA Pol required for kDNA replication. While other eukaryotes utilize a single DNA Pol (Pol gamma) for replication of mitochondrial DNA, T. brucei requires at least three to maintain the complex kDNA network.
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57
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Evolutionary linkage between eukaryotic cytokinesis and chloroplast division by dynamin proteins. Proc Natl Acad Sci U S A 2008; 105:15202-7. [PMID: 18809930 DOI: 10.1073/pnas.0802412105] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chloroplasts have evolved from a cyanobacterial endosymbiont and been retained for more than 1 billion years by coordinated chloroplast division in multiplying eukaryotic cells. Chloroplast division is performed by ring structures at the division site, encompassing both the inside and the outside of the two envelopes. A part of the division machinery is derived from the cyanobacterial cytokinetic activity based on the FtsZ protein. In contrast, other parts of the division machinery involve proteins specific to eukaryotes, including a member of the dynamin family. Each member of the dynamin family is involved in the division or fusion of a distinct eukaryotic membrane system. To gain insight into the kind of ancestral dynamin protein and eukaryotic membrane activity that evolved to regulate chloroplast division, we investigated the functions of the dynamin proteins that are most closely related to chloroplast division proteins. These proteins in the amoeba Dictyostelium discoideum and Arabidopsis thaliana localize at the sites of cell division, where they are involved in cytokinesis. Our results suggest that the dynamin for chloroplast division is derived from that involved in eukaryotic cytokinesis. Therefore, the chloroplast division machinery is a mixture of bacterial and eukaryotic cytokinesis components, with the latter a key factor in the synchronization of endosymbiotic cell division with host cell division, thus helping to establish the permanent endosymbiotic relationship.
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58
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Regmi S, Rothberg KG, Hubbard JG, Ruben L. The RACK1 signal anchor protein from Trypanosoma brucei associates with eukaryotic elongation factor 1A: a role for translational control in cytokinesis. Mol Microbiol 2008; 70:724-45. [PMID: 18786142 PMCID: PMC2581647 DOI: 10.1111/j.1365-2958.2008.06443.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
RACK1 is a WD-repeat protein that forms signal complexes at appropriate locations in the cell. RACK1 homologues are core components of ribosomes from yeast, plants and mammals. In contrast, a cryo-EM analysis of trypanosome ribosomes failed to detect RACK1, thus eliminating an important translational regulatory mechanism. Here we report that TbRACK1 from Trypanosoma brucei associates with eukaryotic translation elongation factor-1a (eEF1A) as determined by tandem MS of TAP-TbRACK1 affinity eluates, co-sedimentation in a sucrose gradient, and co-precipitation assays. Consistent with these observations, sucrose gradient purified 80S monosomes and translating polysomes each contained TbRACK1. When RNAi was used to deplete cells of TbRACK1, a shift in the polysome profile was observed, while the phosphorylation of a ribosomal protein increased. Under these conditions, cell growth became hypersensitive to the translational inhibitor anisomycin. The kinetoplasts and nuclei were misaligned in the postmitotic cells, resulting in partial cleavage furrow ingression during cytokinesis. Overall, these findings identify eEF1A as a novel TbRACK1 binding partner and establish TbRACK1 as a component of the trypanosome translational apparatus. The synergy between anisomycin and TbRACK1 RNAi suggests that continued translation is required for complete ingression of the cleavage furrow.
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Affiliation(s)
- Sandesh Regmi
- Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275, USA
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59
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Rahaman A, Elde NC, Turkewitz AP. A dynamin-related protein required for nuclear remodeling in Tetrahymena. Curr Biol 2008; 18:1227-33. [PMID: 18701286 DOI: 10.1016/j.cub.2008.07.042] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2008] [Revised: 07/08/2008] [Accepted: 07/10/2008] [Indexed: 10/21/2022]
Abstract
Dynamin-related proteins (DRPs) are GTPases that reversibly assemble on cellular membranes [1]. Individual DRPs (here "DRP" includes authentic dynamins) function in fission or tubulation of the plasma membrane, trans-Golgi network, mitochondria, peroxisomes, chloroplasts, and endosomes [1] and in mitochondrial fusion [2]. Many of these functions are widespread; they are present in animals, plants, trypanosomes, Giardia, ciliates, alga, and slime molds [3-8]. Lineage-specific expansions of the gene family created specialized DRPs. In animals, such DRPs include MxB, which has been reported to regulate nuclear-pore transport [9]. Whereas many unicellular organisms possess a small number of DRPs, expansions occurred in some protist lineages. The eight DRPs in the ciliate Tetrahymena thermophila might contribute to aspects of ciliate complexity. Each ciliate cell contains distinct germline and somatic nuclei, whose differentiation and maintenance must require distinct machinery [10, 11]. Here we show that Drp6p, previously shown to be targeted to the nuclear envelope [3], is required for macronuclear development. Drp6p activity, which is distinct from that of the only other known nuclear DRP, is modulated by a combination of stage-specific subcellular targeting and assembly dynamics. This work demonstrates a novel DRP activity and presents a system in which environmental and developmental cues can be used for manipulating key aspects of regulation.
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Affiliation(s)
- Abdur Rahaman
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA
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60
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Wloga D, Strzyzewska-Jówko I, Gaertig J, Jerka-Dziadosz M. Septins stabilize mitochondria in Tetrahymena thermophila. EUKARYOTIC CELL 2008; 7:1373-86. [PMID: 18586950 PMCID: PMC2519767 DOI: 10.1128/ec.00085-08] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2008] [Accepted: 06/18/2008] [Indexed: 01/02/2023]
Abstract
We describe phylogenetic and functional studies of three septins in the free-living ciliate Tetrahymena thermophila. Both deletion and overproduction of septins led to vacuolization of mitochondria, destabilization of the nuclear envelope, and increased autophagy. All three green fluorescent protein-tagged septins localized to mitochondria. Specific septins localized to the outer mitochondrial membrane, to septa formed during mitochondrial scission, or to the mitochondrion-associated endoplasmic reticulum. The only other septins known to localize to mitochondria are human ARTS and murine M-septin, both alternatively spliced forms of Sep4 (S. Larisch, Cell Cycle 3:1021-1023, 2004; S. Takahashi, R. Inatome, H. Yamamura, and S. Yanagi, Genes Cells 8:81-93, 2003). It therefore appears that septins have been recruited to mitochondrial functions independently in at least two eukaryotic lineages and in both cases are involved in apoptotic events.
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Affiliation(s)
- D Wloga
- Department of Cellular Biology, University of Georgia, Athens, GA 30602-2607, USA
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61
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Bisaggio DFR, Adade CM, Souto-Padrón T. In vitro effects of suramin on Trypanosoma cruzi. Int J Antimicrob Agents 2008; 31:282-6. [DOI: 10.1016/j.ijantimicag.2007.11.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2007] [Revised: 11/05/2007] [Accepted: 11/06/2007] [Indexed: 10/22/2022]
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62
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The direct route: a simplified pathway for protein import into the mitochondrion of trypanosomes. Trends Cell Biol 2008; 18:12-8. [DOI: 10.1016/j.tcb.2007.09.009] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Revised: 09/09/2007] [Accepted: 09/14/2007] [Indexed: 01/23/2023]
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63
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Mitochondrial origin-binding protein UMSBP mediates DNA replication and segregation in trypanosomes. Proc Natl Acad Sci U S A 2007; 104:19250-5. [PMID: 18048338 DOI: 10.1073/pnas.0706858104] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Kinetoplast DNA (kDNA) is the remarkable mitochondrial genome of trypanosomatids. Its major components are several thousands of topologically linked DNA minicircles, whose replication origins are bound by the universal minicircle sequence-binding protein (UMSBP). The cellular function of UMSBP has been studied in Trypanosoma brucei by using RNAi analysis. Silencing of the trypanosomal UMSBP genes resulted in remarkable effects on the trypanosome cell cycle. It significantly inhibited the initiation of minicircle replication, blocked nuclear DNA division, and impaired the segregation of the kDNA network and the flagellar basal body, resulting in growth arrest. These observations, revealing the function of UMSBP in kDNA replication initiation and segregation as well as in mitochondrial and nuclear division, imply a potential role for UMSBP in linking kDNA replication and segregation to the nuclear S-phase control during the trypanosome cell cycle.
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64
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Hammarton TC, Monnerat S, Mottram JC. Cytokinesis in trypanosomatids. Curr Opin Microbiol 2007; 10:520-7. [PMID: 18023244 DOI: 10.1016/j.mib.2007.10.005] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Revised: 10/10/2007] [Accepted: 10/11/2007] [Indexed: 11/15/2022]
Abstract
The process of cytokinesis, where the cytoplasm of one cell is divided to produce two daughter cells, is intricate in trypanosomatids because of the requirement to replicate and segregate a number of single copy organelles, including the nucleus, kinetoplast, Golgi apparatus, and flagellum. Identifying regulators of the three stages of cytokinesis, initiation, furrow ingression, and abscission is complicated by the fact that cell division in trypanosomatids is easily perturbed and aberrant cells are readily produced during functional characterization of gene products. In this review, we discuss direct and indirect effects on cytokinesis, using Trypanosoma brucei as a model.
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Affiliation(s)
- Tansy C Hammarton
- Wellcome Centre for Molecular Parasitology, University of Glasgow, 120 University Place, Glasgow G12 8TA, United Kingdom
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65
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Gaechter V, Schraner E, Wild P, Hehl AB. The single dynamin family protein in the primitive protozoan Giardia lamblia is essential for stage conversion and endocytic transport. Traffic 2007; 9:57-71. [PMID: 17892527 DOI: 10.1111/j.1600-0854.2007.00657.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Dynamins are universally conserved large guanosine triphosphatases, which function as mechanoenzymes in membrane scission. The primitive protozoan Giardia lamblia has a single dynamin-related protein (GlDRP) with an unusual domain structure. Giardia lacks a Golgi apparatus but generates transient Golgi-like delay compartments dubbed encystation-specific vesicles (ESVs), which serve to accumulate and mature cyst wall proteins during differentiation to infectious cyst forms. Here, we analyze the function of GlDRP during growth and encystation and demonstrate that it relocalizes from peripheral endosomal-lysosomal compartments to nascent ESVs. We show that GlDRP is necessary for secretion of the cyst wall material and ESV homeostasis. Expression of a dominant-negative GlDRP variant does not interfere with ESV formation but blocks cyst formation completely prior to regulated exocytosis. GlDRP colocalizes with clathrin at the cell periphery and is necessary for endocytosis of surface proteins to endosomal-lysosomal organelles in trophozoites. Electron microscopy and live cell imaging reveal gross morphological changes as well as functional impairment of the endocytic system in cells expressing the dominant-negative GlDRP. Thus, giardial DRP plays a key role in two distinct trafficking pathways and in organelle homeostasis, both essential functions for the proliferation of the parasite in the gut and its transmission to a new host.
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Affiliation(s)
- Verena Gaechter
- Institute of Parasitology, University of Zürich, Winterthurerstrasse 266a, 8057 Zürich, Switzerland
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66
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Hehl AB, Regos A, Schraner E, Schneider A. Bax function in the absence of mitochondria in the primitive protozoan Giardia lamblia. PLoS One 2007; 2:e488. [PMID: 17534438 PMCID: PMC1871612 DOI: 10.1371/journal.pone.0000488] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Accepted: 05/05/2007] [Indexed: 11/18/2022] Open
Abstract
Bax-induced permeabilization of the mitochondrial outer membrane and release of cytochrome c are key events in apoptosis. Although Bax can compromise mitochondria in primitive unicellular organisms that lack a classical apoptotic machinery, it is still unclear if Bax alone is sufficient for this, or whether additional mitochondrial components are required. The protozoan parasite Giardia lamblia is one of the earliest branching eukaryotes and harbors highly degenerated mitochondrial remnant organelles (mitosomes) that lack a genome. Here we tested whether human Bax expressed in Giardia can be used to ablate mitosomes. We demonstrate that these organelles are neither targeted, nor compromised, by Bax. However, specialized compartments of the regulated secretory pathway are completely ablated by Bax. As a consequence, maturing cyst wall proteins that are sorted into these organelles are released into the cytoplasm, causing a developmental arrest and cell death. Interestingly, this ectopic cargo release is dependent on the carboxy-terminal 22 amino acids of Bax, and can be prevented by the Bax-inhibiting peptide Ku70. A C-terminally truncated Bax variant still localizes to secretory organelles, but is unable to permeabilize these membranes, uncoupling membrane targeting and cargo release. Even though mitosomes are too diverged to be recognized by Bax, off-target membrane permeabilization appears to be conserved and leads to cell death completely independently of mitochondria.
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Affiliation(s)
- Adrian B Hehl
- Institute of Parasitology, University of Zürich, Zurich, Switzerland.
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67
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Rodgers MJ, Albanesi JP, Phillips MA. Phosphatidylinositol 4-kinase III-beta is required for Golgi maintenance and cytokinesis in Trypanosoma brucei. EUKARYOTIC CELL 2007; 6:1108-18. [PMID: 17483288 PMCID: PMC1951100 DOI: 10.1128/ec.00107-07] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The parasitic protozoan Trypanosoma brucei contains two type III phosphatidylinositol 4-kinases (alpha and beta). We have cloned the gene encoding the T. brucei type III phosphatidylinositol 4-kinase beta (TbPI4KIII-beta), expressed the protein in COS-7 cells, and confirmed that the protein catalyzes the phosphorylation of phosphatidylinositol. Depletion of TbPI4KIII-beta in procyclic T. brucei by RNA interference (RNAi) resulted in inhibition of cell growth and a distorted cellular morphology. RNAi cells had a distorted Golgi apparatus, and lysosomal and flagellar pocket proteins were mislocalized. Ultrastructural analysis revealed the internal accumulation of a heterogeneous population of vesicles, abnormal positioning of organelles, and a loss of cell polarity. Scanning electron microcopy revealed a twisted phenotype, and dividing cells often exhibited a detached daughter flagellum and lacked a cleavage furrow. Cell cycle analysis confirmed that cells depleted of TbPI4KIII-beta have a postmitotic cytokinesis block that occurs after a single round of mitosis, suggestive of a specific cell cycle block. In summary, TbPI4KIII-beta is an essential protein in procyclic T. brucei, required for maintenance of Golgi structure, protein trafficking, normal cellular shape, and cytokinesis.
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Affiliation(s)
- Melissa J Rodgers
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9041, USA
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68
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Abstract
Trypanosomes are members of the kinetoplastida, a group of divergent protozoan parasites responsible for considerable morbidity and mortality worldwide. These organisms have highly complex life cycles requiring modification of their cell surface together with engagement of immune evasion systems to effect survival; both processes intimately involve the membrane trafficking system. The completion of three trypanosomatid and several additional protist genomes in the last few years is providing an exciting opportunity to evaluate, at the molecular level, the evolution and diversity of membrane trafficking across deep evolutionary time as well as to analyse in unprecedented detail the membrane trafficking systems of trypanosomes.
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Affiliation(s)
- Mark C Field
- Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QP, UK.
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69
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Charneau S, Bastos IMD, Mouray E, Ribeiro BM, Santana JM, Grellier P, Florent I. Characterization of PfDYN2, a dynamin-like protein of Plasmodium falciparum expressed in schizonts. Microbes Infect 2007; 9:797-805. [PMID: 17533148 DOI: 10.1016/j.micinf.2007.02.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2006] [Revised: 02/14/2007] [Accepted: 02/21/2007] [Indexed: 10/23/2022]
Abstract
Dynamin superfamily members are large GTPases conserved through evolution mainly described as mechanochemical enzymes involved in membrane scission events. The Plasmodium falciparum dynamin-2 (Pfdyn2) gene was cloned from the FcB1 strain. PfDYN2 belongs to the dynamin-like protein subgroup of the dynamin superfamily since it possesses a large GTPase domain together with the conserved dynamin_M and GED domains. Recombinant PfDYN2 was able to bind GTP, to hydrolyze GTP into GDP and to self-associate in low-salt conditions. PfDYN2 expression was restricted to schizonts where it localized in punctuate structures within the parasite cytoplasm. PfDYN2 partly co-localized with markers of the parasite endoplasmic reticulum, Golgi apparatus and apicoplast, suggesting it could be implicated in vesicular trafficking and/or organelle fission events known to occur during the last hours of the parasite development in erythrocytes. PfDYN2 and the previously described PfDYN1 are the only two dynamin superfamily members identified in the P. falciparum genome and the available data suggest that this situation is conserved in the Apicomplexa phylum.
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Affiliation(s)
- Sébastien Charneau
- USM504-EA3335, RDDM, Muséum National d'Histoire Naturelle, 61, rue Buffon, CP52, 75231 Paris cedex 05, France
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70
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Hammarton TC. Cell cycle regulation in Trypanosoma brucei. Mol Biochem Parasitol 2007; 153:1-8. [PMID: 17335918 PMCID: PMC1914216 DOI: 10.1016/j.molbiopara.2007.01.017] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Revised: 01/25/2007] [Accepted: 01/26/2007] [Indexed: 01/23/2023]
Abstract
Cell division is regulated by intricate and interconnected signal transduction pathways that precisely coordinate, in time and space, the complex series of events involved in replicating and segregating the component parts of the cell. In Trypanosoma brucei, considerable progress has been made over recent years in identifying molecular regulators of the cell cycle and elucidating their functions, although many regulators undoubtedly remain to be identified, and there is still a long way to go with respect to determining signal transduction pathways. However, it is clear that cell cycle regulation in T. brucei is unusual in many respects. Analyses of trypanosome orthologues of conserved eukaryotic cell cycle regulators have demonstrated divergence of their function in the parasite, and a number of other key regulators are missing from T. brucei. Cell cycle regulation differs in different parasite life cycle stages, and T. brucei appears to use different checkpoint control strategies compared to model eukaryotes. It is therefore probable that T. brucei has evolved novel pathways to control its cell cycle.
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Affiliation(s)
- Tansy C Hammarton
- Division of Infection & Immunity and Wellcome Centre for Molecular Parasitology, University of Glasgow, Biomedical Research Centre, 120 University Place, Glasgow G12 8TA, United Kingdom.
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