3-D FINE STRUCTURE OF THE APICAL POLAR RING IN TOXOPLASM GONDII

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Toxoplasma gondii is an obligate intracellular parasite that is related to Plasmodium, the agent of malaria. Toxoplasma is disseminated by cats, which harbor infectious spores and pass them in their feces. Toxoplasma in pregnant women can cause birth defects or miscarriage; in immunocompromised individuals it can cause life- threatening infection. Toxoplasma, Plasmodium and other Apicomplexan parasites all have morphologically similar microtubule cytoskeletons. We are interested in the structural arrangement of the apical polar ring, a microtubule organizing center that nucleates 22 subpellicular microtubules. This year we have produced tomograms of this cytoplasmic region from wild type cells, using chemically-fixed preparations. To improve the structural preservation of the cells, Morrissette has been using the Balzers high pressure freezer at the Danforth Center in St. Louis and has produced some promising samples. In addition, the Morrissette lab is currently developing molecular genetic techniques to complement cellular and biochemical studies that are going on elsewhere. They are constructing genetic tools for Toxoplasma including a genomic map, vectors for DNA transformation and protein expression, and large-scale sequencing of cDNAs for gene discovery. These approaches are being applied to identify the molecular basis of virulence and to generate mutants with altered phenotypes in adhesion, invasion, and intracellular survival. The 3-D lab will characterize the phenotypes of these mutants, as they become available.