Kinetics and pattern of organelle exocytosis duringToxoplasma gondii/host-cell interaction

Abstract

The fate of Toxoplasma gondii dense-granule (GRA2, GRA3), rhoptry (ROP1), and surface (SAG1) proteins was followed by immunofluorescence assay (IFA) and immunoelectron microscopy at different stages after infection. Dense-granule exocytosis occurred in the apical area of the tachyzoite within minutes of invasion. Several exocytic events were found simultaneously in the same organism, both by serial sectioning and by freeze-fracture studies. Dense-granule contents were first found as a dense material trapped between parasite and vacuole membranes before either the vacuolar network or the vacuole membrane could be immunolabeled with specific antibodies. The vacuolar network was strongly labeled with dense-granule antibodies but not with the SAG1-specific probe, which suggests that the network is not enriched in membrane proteins. In addition to strongly labeling the vacuole membrane, GRA3 antibodies also labeled strands extending from the parasitophorous vacuoles into the host-cell cytoplasm.

Gene Discovery in the Apicomplexa as Revealed by EST Sequencing and Assembly of a Comparative Gene Database

“…1), but is also a reflection of the biological specialization of the Apicomplexa, as such secretory components were also abundant in E. tenella and P. falciparum. These secretory components are sequentially discharged during cell invasion and participate in attachment, entry, and intracellular survival of the parasites (Dubremetz et al 1993;Carruthers and Sibley 1997). A second major class of abundant ESTs was a surface antigen family known as SAGs, first identified in T. gondii (Manger et al 1998a;Boothroyd et al 1997;Lekutis et al 2000).…”

Host cell manipulation by the human pathogen Toxoplasma gondii

“…T. gondii presents three organelles involved in host cell attachment, penetration, and in the formation of the parasitophorous vacuole (PV). Micronemes, rhoptries, and dense granules fuse alternately with the parasite membrane, discharging their (protein) contents in a well-orchestrated, rapid series of deployments [6,7]. Microneme proteins (MICs) play a central role in attachment to host through the binding of specific receptors [8,9].…”

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

“…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 of entry and progressively deepens, ultimately surrounding the fully internalized parasite (Suss-Toby et al, 1996).…”