Tracking maternal proteins uncovers a central role for the residual body in organelle recycling during Toxoplasma gondii replication

Toxoplasma gondii replicates through endodyogeny, an unconventional form of internal budding in which two daughter cells are assembled within a single mother cell. During this process, daughter cells must acquire a full complement of organelles, which may be inherited from the mother, formed de novo , or assembled through a combination of both mechanisms. To date, the fate of maternal components during replication remains poorly understood. We previously showed that F-actin–driven dynamics generate an intravacuolar network, associated with the residual body (RB) and facilitates the recycling of microneme proteins. However, the inheritance and recycling of other organelles have not been systematically analysed.

To address this, we employed a dual HaloTag-based pulse-chase fluorescence labelling strategy to distinguish between de novo-synthesized and maternally inherited proteins in replicating tachyzoites. This approach reveals three distinct modes of organelle inheritance: (1) inheritance of intact maternal organelles (e.g., rhoptries and micronemes), (2) expansion and division of pre-existing maternal organelles with incorporation of newly synthesized components (e.g., Golgi apparatus and apicoplast), and (3) degradation of maternal structures followed by de novo assembly (e.g., inner membrane complex). Furthermore, we identify Myosin F (MyoF) as an important factor in the redistribution of maternal micronemes and rhoptries. In the absence of MyoF, these organelles accumulate in the RB, while restoration of MyoF permits accumulated maternal micronemes to redistribute to daughter parasites. Together, these findings support a role for the RB as a dynamic compartment in the recycling and redistribution of maternal organelles.