Toxoplasma gondii (Tg), causative agent of the disease toxoplasmosis in humans is an opportunistic pathogen belonging to the phylum Apicomplexa, which includes many medically important pathogens such as Plasmodium. Tg life cycle is characterized by two cysts stages: tissue cysts containing bradyzoites and oocysts. Taken together tissue cysts in contaminated food/water and oocysts shed into the environment are responsible for nearly 25% of the adult population worldwide being chronically infected with this parasite. Clinically, encystation by Tg presents the greatest challenge towards treatment of Tg as the cyst form is currently untreatable. Our aim is to identify genes and regulatory networks that regulate Tg oocyst/tissue cyst production. Isolation of such global regulators, which regulate encystation will be crucial for designing therapeutic strategies which effectively prevent cyst formation and block transmission of the disease by felines. Using a forward genetics approach, we have isolated a unique Tg mutant, named 11BE9, that under normal growing conditions (tachyzoite stage) in vitro dramatically expresses more than 100 genes, that are usually expressed in the oocyst/bradyzoite stages. Our hypothesis is that a global regulator(s) has been deregulated in this mutant, which is responsible for the over-expression of cyst-associated genes in the tachyzoite stage in the mutant. To identify this regulatory gene, we compared the transcriptome of this mutant to wild type Tg using microarrays, and Tg FIKK kinase gene was identified as a potential candidate. FIKK kinases are novel serine threonine kinases that share a conserved stretch of amino acids and are hypothesized as drug targets due to their unique expression in Apicomplexa. Our preliminary studies show that deletion of the FIKK gene in Tg leads to an impaired in vitro conversion of the tachyzoites to bradyzoites which is required for the establishment of the chronic cyst stage of the parasite during toxoplasmosis. Currently we are in the process of complementing the gene deletion clone to confirm the role of Tg FIKK kinase on cyst formation.


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