TgCep250 is dynamically processed through the division cycle and essential for structural integrity of the Toxoplasma centrosome

Abstract

The Toxoplasma centrosome is a unique bipartite structure comprising an inner- and outer-core responsible for the nuclear cycle (mitosis) and budding cycles (cytokinesis), respectively. These two cores remain associated during the cell cycle but have been proposed to function independently. Here, we describe the function of a large coiled-coil protein, TgCep250, in connecting the two centrosomal cores and promoting their structural integrity. Throughout the cell cycle TgCep250 localizes to the centrosome inner-core but resides on both inner- and outer-cores during the onset of cell division. This dynamic localization pattern is associated with proteolysis: the processed version residing on the inner-core. In the absence of TgCep250, stray centrosome inner- and outer-core foci were observed; detachment of the inner-outer-core connection resulted in nuclear partitioning defects. The detachment between centrosome inner- and outer-core was found in only one of the centrosomes during cell division, indicating distinct states of mother and daughter centrosomes. We further dissected the hierarchical organization of centrosome and kinetochore complex through depletion of kinetochore component TgNuf2, which resulted in dissociation of the intact bipolar centrosome from the nuclear periphery. Together, these data suggest that TgCep250 bridges the interaction between the centrosome cores but not between the inner-core and kinetochore.\n\nShort SummaryThe opportunistic apicomplexan parasite Toxoplasma gondii uses a bipartite centrosome to independently regulate mitosis and cytokinesis. Here we report a large coiled-coil protein that functions to integrate the two centrosomal cores for faithful cell division. This study also reveals the layered structural organization of the centrosome/kinetochore complex.