Toxoplasma as a Model Apicomplexan Parasite: Biochemistry, Cell Biology, Molecular Genetics, Genomics and Beyond

More than twenty years ago, virologist Elmer Pfefferkorn recognised that the plaques formed following infection of mammalian host cell monolayers with the protozoan parasite Toxoplasma gondii should permit clonal isolation. Seeking to develop a genetic system suitable for the analysis of this intracellular pathogen, Pfefferkorn and his colleagues produced various mutant parasite lines. Carrying out classical genetic crosses (in cats, the definitive host for T. gondii), they demonstrated that tachyzoites are haploid, and that Mendelian segregation occurs through meiotic production of sporozoites within the oocyst (Pfefferkorn and Pfefferkorn, 1980). These investigators also exploited the ability of T. gondii to infect virtually any nucleated cell to develop somatic cell genetic approaches, infecting defined mammalian cell mutants to determine what wild-type and mutant parasites can do for themselves, and what they require from their host (Pfefferkorn et al., 1983).

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