Functional analysis of the constrictome in the apicomplexan parasite Toxoplasma gondii: deciphering final events in parasite division.

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Cell division in apicomplexan parasites is defined by an interwoven relationship of mitosis and cytokinesis. This process occurs in parasites that either form daughter cells by peripheral (e.g. schizogony in Plasmodium ssp.) or by internal budding (e.g. endodyogeny in Toxoplasma gondii). Toxoplasma tachyzoites divide by the simplest division mode (endodyogeny) that produces two daughter cells per division round and therefore leads to their establishment as an accessible model for apicomplexan cell division. An essential linchpin for this division mode is the basal complex, a contractile cytoskeletal assemblage formed early in nascent daughter cells and acting critically in the final constriction/abscission events to complete cytokinesis. Recently, several basal complex proteins have been identified in Toxoplasma, but the identity of the contractile force is unknown so far. Interestingly, all known key contractile proteins involved in cytokinesis related constriction in other organisms are absent from the apicomplexan genomes, raising the question how this essential step is executed in the parasite?The goal of this project is the identification and characterization of the constrictive force in Toxoplasma gondii and revelation of its control by the parasite. To accomplish this, I will use a sub-set of established basal complex proteins as a starting point to analyze the complete composition and architecture of this compartment, the Toxoplasma constrictome. Hereto I will apply BioID screening, a novel technique based on in vivo biotin labeling of closely associated proteins in a complex of interest. I will use reverse genetics to characterize the identified candidates, focusing on proteins that can execute and/or control the constrictive force. Taken together, my work will highlight the molecular basis for an evolutionary distinct mode of cytokinesis thus contributing to fundamental new insights into the cell biology of cytokinesis.