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 the intravacuolar network, which defines the residual body (RB) and facilitates 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 recycled proteins in replicating tachyzoites. This approach reveals three distinct organelle inheritance patterns: (1) direct transmission of intact maternal organelles (e.g., rhoptries, micronemes), (2) expansion and division of pre-existing maternal organelles with incorporation of newly synthesized components (e.g., Golgi apparatus, apicoplast), and (3) degradation of maternal structures without recycling (e.g., inner membrane complex). Furthermore, we identify Myosin F (MyoF) as the key motor protein that mediates the selective recycling of maternal organelles via the RB. These findings redefine the RB as an active trafficking hub and reveal a selective, regulated system of organelle inheritance and recycling that is critical for intracellular organization and parasite development.