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Abstract

Proliferation of the malaria-causing parasite Plasmodium falciparum in human erythrocytes is associated with all clinical symptoms of the disease. However, organization and dynamics of critical cell division structures are poorly studied. The parasite divides by an atypical division mode, called schizogony. It is characterized by several rounds of asynchronous nuclear divisions, which lead to formation of a multinucleated parasite stage before cytokinesis. Centriolar plaques, the centrosomes of Plasmodium, are key regulators of schizogony as they organize spindle microtubules. The detailed organization of centriolar plaques and microtubules, however, remains elusive and their dynamics have not yet been analyzed during schizogony. Detailed visualization of microtubules and centriolar plaques has been limited by the small size of the parasite and slow adaptation of advanced microscopy techniques. In my PhD project, I established RescueSTED nanoscopy as well as correlative light and electron microscopy for Plasmodium blood-stages. Combining these technologies with ultrastructure expansion microscopy, I revealed the bipartite organization of the centriolar plaque consisting of an amorphous extranuclear and a DNA-free intranuclear compartment. The compartments are connected through a neck-like structure within the nuclear membrane. My data demonstrates that hemispindle microtubules are nucleated from the intranuclear region, before the centriolar plaque is further assembled as indicated by centrin accumulation at the extranuclear compartment. Using co-immunoprecipitations, I identified a novel centrin-interacting protein essential for parasite growth. The highly dynamic hemispindles are rearranged into a short mitotic spindle, organized by two duplicated centriolar plaques prior to spindle extension. Segregated nuclei then undergo consecutive rounds of asynchronous nuclear divisions at an increased pace. By integrating state-of-the-art microscopy techniques, I provide a refined model of nuclear division and centriolar plaque organization during the highly divergent division of P. falciparum. Both the technological and biological progress made in this PhD project will bring forward the cell biological understanding of malaria parasite proliferation.