Calcium dependence of conoid extrusion in Toxoplasma gondii tachyzoites

Mondragón, Ricardo; Frixione, Eugenio

doi:10.1016/s1383-5769(98)80363-2

Cited by 40 publications

(90 citation statements)

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“…Conoid extension was assayed as previously described (Mondragon and Frixione, 1996;Carey et al, 2004b). At least 200 parasites from each parasite line (grown with or without Atc) were counted blindly, in each of two independent experiments.…”

Section: Secondary Assaysmentioning

confidence: 99%

“…The function of the conoid is unknown, but a recently described small molecule inhibitor of conoid extension inhibits invasion (Carey et al, 2004b). Conoid extension can also be inhibited by chelators of intracellular calcium, and extension can be induced by the calcium ionophore ionomycin (Mondragon and Frixione, 1996;Hu et al, 2002;Morrissette and Sibley, 2002). Conoid extension was compared in the AMA1/AMA1-myc and ⌬ama1/AMA1-myc parasites, grown with or without Atc.…”

Section: Conoid Extensionmentioning

confidence: 99%

“…Gliding motility was visualized at 37°C on a Nikon TE300 inverted microscope with Nomarski optics (Melville, NY). Video data were collected with a VE1000SIT camera (Dage-MTI, Michigan City, IN).Conoid extension was assayed as previously described (Mondragon and Frixione, 1996;Carey et al, 2004b). At least 200 parasites from each parasite line (grown with or without Atc) were counted blindly, in each of two independent experiments.…”

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confidence: 99%

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Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Mital

Meissner

Soldati

et al. 2005

MBoC

227

250

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Toxoplasma gondii is an obligate intracellular parasite and an important human pathogen. Relatively little is known about the proteins that orchestrate host cell invasion by T. gondii or related apicomplexan parasites (including Plasmodium spp., which cause malaria), due to the difficulty of studying essential genes in these organisms. We have used a recently developed regulatable promoter to create a conditional knockout of T. gondii apical membrane antigen-1 (TgAMA1). TgAMA1 is a transmembrane protein that localizes to the parasite's micronemes, secretory organelles that discharge during invasion. AMA1 proteins are conserved among apicomplexan parasites and are of intense interest as malaria vaccine candidates. We show here that T. gondii tachyzoites depleted of TgAMA1 are severely compromised in their ability to invade host cells, providing direct genetic evidence that AMA1 functions during invasion. The TgAMA1 deficiency has no effect on microneme secretion or initial attachment of the parasite to the host cell, but it does inhibit secretion of the rhoptries, organelles whose discharge is coupled to active host cell penetration. The data suggest a model in which attachment of the parasite to the host cell occurs in two distinct stages, the second of which requires TgAMA1 and is involved in regulating rhoptry secretion. INTRODUCTIONToxoplasma gondii is one of the one most common protozoan parasites of humans, infecting approximately one-third of the world's population. The disease caused by an acute T. gondii infection, toxoplasmosis, can be life threatening in the congenitally infected fetus and immunocompromised hosts. Like all members of the Phylum Apicomplexa, including Plasmodium spp. (the causative agents of malaria) and Cryptosporidium parvum (a significant worldwide cause of waterborne illness), T. gondii is an obligate intracellular parasite. Host cell invasion is a critical step in the pathogenesis of the diseases caused by apicomplexan parasites, including toxoplasmosis. T. gondii represents an excellent model system for studying the relatively conserved process of apicomplexan invasion, because of the ease with which this parasite can be cultured and genetically manipulated (Roos et al., 1994;Black and Boothroyd, 2000;Kim and Weiss, 2004).Host cell invasion by apicomplexan parasites is a complex, multistep process (reviewed in Black and Boothroyd, 2000;Chitnis and Blackman, 2000). In T. gondii, the asexual stage tachyzoites move over solid surfaces, including cells, by an unusual form of substrate-dependent gliding motility (Sibley et al., 1998;Hakansson et al., 1999). After the apical end of a parasite comes in contact with the host cell membrane, apical secretory organelles (micronemes and rhoptries) sequentially discharge their contents (Dubremetz et al., 1993;Carruthers and Sibley, 1997) and a zone of tight interaction forms between the two cells (Nichols and O'Connor, 1981;Dubremetz et al., 1985;Grimwood and Smith, 1995). An invagination in the host cell plasma membrane develops at the point ...

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Section: Secondary Assaysmentioning

confidence: 99%

Section: Conoid Extensionmentioning

confidence: 99%

mentioning

confidence: 99%

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Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Mital

Meissner

Soldati

et al. 2005

MBoC

227

250

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“…Geometrically, it is a hollow truncated cone of 280 nm in length and 380 nm in diameter, formed by 10-12 helical subunits composed of at least a-tubuline (Nichols and Chiappino, 1987;Mondragón and Frixione, 1996;Hu et al, 2002). The conoid is associated to the anterior polar ring, a microtubule organizing centre for 22 subpellicular microtubules (Nichols and Chiappino, 1987).…”

Section: Introductionmentioning

confidence: 99%

Induction and regulation of conoid extrusion inToxoplasma gondii

Carmen

Mondragón

González

et al. 2009

Cellular Microbiology

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SummaryCell invasion by the intracellular parasite Toxoplasma gondii occurs through an active process that involves dynamic events, such as gliding motility and conoid extrusion, followed by a sequential secretion from specialized secretory organelles. Increase of intracellular Ca2+ by ionophores induces conoid extrusion, although in an irreversible way, thus limiting the characterization of the regulatory pathways. In this report we studied the effect of different activating conoid conditions to characterize the regulatory mechanisms involved. Exposure of tachyzoites to ethanol, a well-known activator of microneme secretion through the increase of intracellular Ca 2+, induced conoid extrusion without affecting parasite viability nor its in vitro invasive capability, in a process that could be completely reverted and repeatedly reactivated. A temporal relationship between conoid extrusion and microneme secretion was here studied. Under this condition, signal transduction pathways and the precise role of the parasite cytoskeleton were characterized. Our results indicate that phospholipase C, Ca 2+ released through channels sensitive to inositol-3-phosphate and ryanodine, as well as myosin together with actin filaments, but not microtubules, all participate in conoid extrusion. Specific inhibitors for serine-threonine kinases blocked conoid extrusion; in contrast, calmodulin inhibitors did not affect the induction. A regulatory model for conoid activation is here proposed.

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“…Because the secretion of GRA2 (P28) was enhanced by increasing Ca levels (Sibley, 1993), the presence of CaATPase in these organelles seems to be possible and important. Mondragon and Frixione (1996) showed no conoid extrusion in calcium-free medium, but exposure of tachyzoites in a medium with calcium and thapsigargin (0.5-1 mM) produced a significant extrusion of the conoid. These observation suggest the presence of a Ca-pump (thapsigargin is a Ca 2+ -ATPase inhibitor), which is in agreement with our results.…”

Section: Discussionmentioning

confidence: 87%

Detection and Localization of a Ca2+-ATPase Activity in Toxoplasma gondii.

Bouchot

Jaillet

Bonhomme

et al. 2001

Cell Struct. Funct.

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ABSTRACT. Toxoplasma gondii, the agent causing toxoplasmosis, is an obligate intracellular protozoan parasite.A calcium signal appears to be essential for intracellular transduction during the active process of host cell invasion. We have looked for a Ca 2+ -transport ATPase in tachyzoites and found Ca 2+ -ATPase activity (11-22 nmol Pi liberated/mg protein/min) in the tachyzoite membrane fraction. This ATP-dependent activity was stimulated by Ca 2+ and Mg 2+ ions and by calmodulin, and was inhibited by pump inhibitors (sodium orthovanadate or thapsigargin). We used cytochemistry and X-ray microanalysis of cerium phosphate precipitates and immunolabelling to find the Ca 2+ , Mg 2+ -ATPase. It was located mainly in the membrane complex, the conoid, nucleus, secretory organelles (rhoptries, dense granules) and in vesicles with a high calcium concentration. Thus, Toxoplasma gondii possesses Ca 2+ -pump ATPase (Ca 2+ , Mg 2+ -ATPase) as do eukaryotic cells.

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Calcium dependence of conoid extrusion in Toxoplasma gondii tachyzoites

Cited by 40 publications

References 0 publications

Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Induction and regulation of conoid extrusion inToxoplasma gondii

Detection and Localization of a Ca2+-ATPase Activity in Toxoplasma gondii.

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