One of the most remarkable features of Apicomplexan parasites is their ability to infect another eukaryotic cell and co-opt the functions of such a cell once inside. For many years, Toxoplasma gondii has served as an important and informative model for dissecting these processes. The act of invasion is associated with injection into the host cell of key components of the apical secretory organelles known as rhoptries. These organelles contain many parts of the invasion machinery itself, located within the rhoptry necks and therefore known as RONs, as well as an assortment of effector proteins known as ROPs that are located within the rhoptry bulbs and serve to co-opt host cell functions. Much work by us and others has revealed the identity of many of these RON and ROP proteins but the function of only a few has emerged from biochemical and genetic studies and nothing is known about how they are introduced. The goal of this current application is to determine the mechanism of how rhoptries introduce their contents into the host cell and how this injection sets up the infection in its earliest stages in vivo. To accomplish these goals, we will use innovative approaches involving genetic screens with specifically engineered parasites and in vivo studies with specifically engineered reporter mice. The identification of the injection apparatus, which appears to be conserved between Toxoplasma and its important cousin, Plasmodium, will allow novel strategies for interrupting this crucial step in invasion. Similarly, he determination of the first changes that occur within the intestinal epithelium of animals acquiring an oral infection with encysted bradyzoites will reveal how Toxoplasma has evolved to establish the infection in its earliest stages. This crucial interaction between the parasite and host is pivotal but no method has previously existed to explore it in vivo. The work we propose here will, therefore, address two important, unanswered questions.

Public Health Relevance

Toxoplasma is a parasitic pathogen of great medical importance as infections of the developing fetus and of immunocompromised individuals, including AIDS, cancer and transplant patients, can lead to serious illness. This work concerns the mechanism by which Toxoplasma first infects and co-opts host cells, both crucial steps in the infection. These processes are shared among many related parasites, including the causative agent of malaria, Plasmodium sp. The results of this work will inform novel approaches for the control and treatment of the diseases these important parasites cause.

National Institute of Health (NIH)
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Pathogenic Eukaryotes Study Section (PTHE)
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Wali, Tonu M
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Stanford University
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Christian, David A; Koshy, Anita A; Reuter, Morgan A et al. (2014) Use of transgenic parasites and host reporters to dissect events that promote interleukin-12 production during toxoplasmosis. Infect Immun 82:4056-67
Franco, Magdalena; Shastri, Anjali J; Boothroyd, John C (2014) Infection by Toxoplasma gondii specifically induces host c-Myc and the genes this pivotal transcription factor regulates. Eukaryot Cell 13:483-93
Poukchanski, Anna; Fritz, Heather M; Tonkin, Michelle L et al. (2013) Toxoplasma gondii sporozoites invade host cells using two novel paralogues of RON2 and AMA1. PLoS One 8:e70637
Child, Matthew A; Hall, Carolyn I; Beck, Josh R et al. (2013) Small-molecule inhibition of a depalmitoylase enhances Toxoplasma host-cell invasion. Nat Chem Biol 9:651-6
Boothroyd, John C (2013) Have it your way: how polymorphic, injected kinases and pseudokinases enable toxoplasma to subvert host defenses. PLoS Pathog 9:e1003296
Jensen, Kirk D C; Wang, Yiding; Wojno, Elia D Tait et al. (2011) Toxoplasma polymorphic effectors determine macrophage polarization and intestinal inflammation. Cell Host Microbe 9:472-83
Tyler, Jessica S; Boothroyd, John C (2011) The C-terminus of Toxoplasma RON2 provides the crucial link between AMA1 and the host-associated invasion complex. PLoS Pathog 7:e1001282
Caffaro, Carolina E; Boothroyd, John C (2011) Evidence for host cells as the major contributor of lipids in the intravacuolar network of Toxoplasma-infected cells. Eukaryot Cell 10:1095-9
Tyler, Jessica S; Treeck, Moritz; Boothroyd, John C (2011) Focus on the ringleader: the role of AMA1 in apicomplexan invasion and replication. Trends Parasitol 27:410-20
Morgado, Pedro; Ong, Yi-Ching; Boothroyd, John C et al. (2011) Toxoplasma gondii induces B7-2 expression through activation of JNK signal transduction. Infect Immun 79:4401-12

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