|About the Book|
Toxoplasma gondii is an obligate intracellular parasite of all mammalian hosts. During asexual development, the parasite actively replicates as a tachyzoite within a parasitophorous vacuole (PV) until undergoing development into a slow growingMoreToxoplasma gondii is an obligate intracellular parasite of all mammalian hosts. During asexual development, the parasite actively replicates as a tachyzoite within a parasitophorous vacuole (PV) until undergoing development into a slow growing encysted bradyzoite form in an immunocompetent hosts brain and muscle tissues. Little is known about the genes important for bradyzoite development and cyst wall formation. There is great interest in understanding the tachyzoite to bradyzoite development cycle because the bradyzoite form is an important source of transmission, and there currently are no treatment options for chronic infection by the parasite. This current study identified nine bradyzoite development mutants by using a forward genetic screen of a T. gondii insertional mutant library. Characterization of one of these mutants, 42-F5, identified a new gene important for bradyzoite development. Specifically, this gene, CWE1, is upregulated in bradyzoites and appears to be important for enhancing cyst wall component expression and secretion during the formation of the cyst wall. Further analysis of CWE1 indicates a separation of the signaling pathways for cyst wall component expression from other bradyzoite developmental pathways.-Another mutant identified in the screen, 76-E2, is disrupted at the Dense Granule 3 locus (GRA3). Dense granule proteins have been characterized in tachyzoites as important for the development and maturation of the parasitophorous vacuole, where the parasite resides within an infected cell. These proteins have also been hypothesized to be involved in the modification of the parasitophorous vacuole during bradyzoite development to contain a cyst wall. 76-E2 is disrupted in the GRA3 3UTR- however, it was found that disruption of the GRA3 locus and protein is not responsible for the development phenotype observed for 76-E2.-Characterization of mutants from the screen performed in this study has furthered knowledge about the transition between the tachyzoite and bradyzoite development stages. Hopefully, continuing research of mutants identified from this screen, and their respective disrupted genes, will lead to better treatment therapies for chronic infection by the parasite or the development of a non-encysting strain of T. gondii for vaccine development.