RSB Directors Seminar: Defining the Apical Complex in Toxoplasma

Presented by ANU College of Health & Medicine

The phylum Apicomplexa is named for its specialized apical features, which include a novel microtubule-organizing center, and dedicated secretory organelles that are discharged during cell invasion. Similar to other coccidian members of this phylum, Toxoplasma gondii contains a microtubule-rich conoid as part of the apical complex. During motility and invasion, the conoid is extruded in a calcium-dependent fashion by a process that also requires the actin cytoskeleton. Although previous proteomic studies have estimated there are more than 60 core proteins in the conoid, very few have been characterized functionally. Among the core set of conoidal proteins are many hypothetical unknowns, making it difficult to assign putative functions by orthology. We are examining the core conoidal proteome using genomic editing by CRISPR/Cas9, to identify essential genes, combined with regulated degradation using an auxin-induced degron, to explore function. We have also implemented permissive biotin ligase labeling to develop an interactome of key components of the conoid. Collectively, these studies are elucidating the key structural and functional components of the conoid, and defining its role in controlling microneme secretion, motility, and cell invasion.