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Initial Characterization of CST1, a Toxoplasma gondii Cyst Wall Glycoprotein
Infection and Immunity, 2001
Toxoplasma gondii is an important protozoan pathogen of humans that can cause encephalitis in immunocompromised individuals such as those with AIDS. This encephalitis is due to reactivation of latent infection in T. gondii-seropositive patients. Latent organisms survive within tissue cysts, which are specialized parasitophorous vacuoles containing bradyzoites. The cyst wall of this structure is produced by modification of the parasitophorous vacuole by the parasite and is important in cyst survival. The components of the cyst wall have been poorly characterized. By using immunofluorescence and immunoelectron microscopy, we have identified a monoclonal antibody (MAb 93.18) that reacts with the cyst wall. This antibody recognizes a 116-kDa glycoprotein, which we have termed CST1, containing sugar residues that bind Dolichos biflorans lectin (DBA). CST1 is distinct from T. gondii antigen labeled with succinyl Triticum vulgare lectin (S-WGA) and represents the major DBA-binding component in T. gondii. The carbohydrate components of the tissue cyst, such as CST1, are probably important in both providing stability and facilitating persistence in its host. As is seen in the carbohydrate capsules of fungi, glycoproteins in the T. gondii cyst wall may protect cysts from the immune response of the host. Further characterization of the formation of the cyst wall and its components should lead to insights into the mechanism of tissue cyst persistence and may suggest novel therapeutic approaches to eliminate tissue cysts of this organism.
2021
Toxoplasma gondii has evolved different developmental stages for disseminating during acute infection (i.e. tachyzoites) and for establishing chronic infection (i.e. bradyzoites). Calcium ion (Ca2+) signaling tightly regulates the lytic cycle of tachyzoites by controlling microneme secretion and motility to drive egress and cell invasion. However, the roles of Ca2+ signaling pathways in bradyzoites remain largely unexplored. Here we show that Ca2+ responses are highly restricted in bradyzoites and that they fail to egress in response to agonists. Development of dual-reporter parasites revealed dampened calcium responses and minimal microneme secretion by bradyzoites induced in vitro or harvested from infected mice and tested ex vivo. Ratiometric Ca2+ imaging demonstrated lower Ca2+ basal levels, reduced magnitude, and slower Ca2+ kinetics in bradyzoites compared with tachyzoites stimulated with agonists. Diminished responses in bradyzoites were associated with down-regulation of cal...
Experimental Parasitology, 2011
The DnaK-tetratricopeptide repeat (DnaK-TPR) gene (ToxoDB ID, TGME49_002020) is expressed predominantly at the bradyzoite stage. DnaK-TPR protein has a heat shock protein (DnaK) and tetratricopeptide repeat (TPR) domains with amino acid sequence similarity to the counterparts of other organisms (40.2-43.7% to DnaK domain and 41.1-66.0% to TPR domain). These findings allowed us to infer that DnaK-TPR protein is important in the tachyzoite-to-bradyzoite development or maintenance of cyst structure although the function of this gene is still unknown. An immunofluorescence assay (IFA) revealed that DnaK-TPR protein was expressed in Toxoplasma gondii-encysted and in vitro-induced bradyzoites and distributed in the whole part of parasite cells. We conducted yeast two-hybrid screening to identify proteins interacting with DnaK-TPR protein, and demonstrated that DnaK-TPR protein interacts with p23 co-chaperone protein (Tgp23). It was expected that DnaK-TPR protein would have a function as a molecular chaperon in bradyzoite cells associated with Tgp23. Possible mechanisms for this gene are discussed.
A novel rhoptry protein in Toxoplasma gondii bradyzoites and merozoites
Molecular and Biochemical Parasitology, 2005
The secretory organelles of Toxoplasma gondii orchestrate invasion of the host cell and establish the parasitophorous vacuole. Although much has been learned about the roles played by these organelles in invasion by the tachyzoite stage, little is known about the contents or functions of these organelles during bradyzoite development or pathogenesis. We identified a novel protein that localizes to the rhoptries of the bradyzoite stage, but is absent from the tachyzoite stage. This protein, BRP1, first appears in the nascent rhoptries during the first division of bradyzoite stage development. We observed secretion of BRP1 and other rhoptry proteins into the parasitophorous vacuole during bradyzoite development in vitro, but there was no evidence that this occurs in vivo. Brp1 knockout parasites did not appear to have any developmental or growth defects in vitro, and were able to establish infections in mice both as tachyzoites (via intraperitoneal injection of in vitro-derived tachyzoites) or bradyzoites (via oral gavage using cysts harvested from mouse brain). Mice infected using brain cysts from the brp1 knockout or the control strain developed similar numbers and sizes of brain cysts. Thus BRP1 does not appear to play an essential role in development of the bradyzoite stage, development of brain cysts, or oral infection of new hosts, at least in the mouse model used here. Since we also observed that BRP1 is expressed in the merozoite stages in the gut of infected cats, the coccidian phase of the life cycle may be where BRP1 plays its most important role.
Infection and immunity, 1998
The virulent RH strain of Toxoplasma gondii is acutely lethal in mice and fails to establish chronic infection. Vaccination of BALB/c mice with a soluble tachyzoite antigen preparation, STAg, in combination with the immunostimulatory cytokine interleukin-12 results in partial protection against RH lethal challenge. Nevertheless, brain tissue obtained from surviving, vaccinated mice as late as 1 year after RH infection contained latent parasite forms as demonstrated by subinoculation into naive recipients. The tachyzoites arising in the subinoculated animals were genetically indistinguishable from the original RH inoculum. Microscopic examination revealed that the persistent parasite forms present in the brains of vaccinated and challenged mice have a tissue cyst-like morphology and express the bradyzoite antigen BAG-1 but not the tachyzoite-specific antigen SAG-2 but are different from the cysts formed by avirulent T. gondii strains in that the internal parasite stages display ultra...
Bradyzoite development in Toxoplasma gondii and the hsp70 stress response
Infection and immunity, 1998
Toxoplasma gondii is a well-described ubiquitous Apicomplexan protozoan parasite that is an important opportunistic pathogen. The factors affecting the transition of tachyzoites to the latent bradyzoite stage remain to be defined. The induction of bradyzoite development in vitro has been linked to temperature, pH, mitochondrial inhibitors, sodium arsenite, and many of the other stressors associated with heat shock protein (hsp) induction. There is evidence for other organisms that hsps are developmentally regulated. Therefore, we examined whether hsp induction is an early event in bradyzoite differentiation. Extracellular and intracellular T. gondii cells, after exposure to pH 8.1 or 7.1, were analyzed for the expression of inducible hsp70 by using monoclonal antibody C92F3A-5 (specific to hsp70). Western blotting demonstrated that a 72-kDa protein reactive with C92F3A-5 (hsp70), which we believe is part of the hsp70 family, is induced during bradyzoite development. By immunofluores...
Infection and immunity, 1998
Toxoplasma gondii is a protozoan parasite responsible for widespread infections in humans and animals. Two major asexual forms are produced during the life cycle of this parasite: the rapidly dividing tachyzoite and the more slowly dividing, encysted bradyzoite. To further study the differentiation between these two forms, we have generated a large number of expressed sequence tags (ESTs) from both asexual stages. Previously, we obtained data on approximately 7,400 ESTs from tachyzoites (J. Ajioka et al., Genome Res. 8:18-28, 1998). Here, we report the results from analysis of approximately 2,500 ESTs from bradyzoites purified from the cysts of infected mice. We also report the results from analysis of 760 ESTs from parasites induced to differentiate from tachyzoites to bradyzoites in vitro. Comparison of the data sets from bradyzoites and tachyzoites reveals many previously uncharacterized sequence clusters which are largely or completely specific to one or other developmental stag...