Actin dynamics, regulation and function during intracellular development of the apicomplexan parasite Toxoplasma gondii

• Applicant: Professor Dr. Markus Meißner
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology ; Cell Biology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426682790

During the last funding period, we identified and described the role of an intravacuolar F-actin network, generated by the coordinated action of Formin-2 and the actin depolymerisation factor (ADF) for recycling of maternal organelles, such as the micronemes during intracellular replication. See: Periz et al., Nature Communications 2019; Stortz et al., Elife 2019. The findings that maternal organelles can be recycled in an actin dependent transport process, led to novel interest in the multiple functions of apicomplexan actin during the intracellular development of the parasite, as evidenced by several publications, where our reagents have been used or where we actively collaborated. See for example: Carmeille et al., 2021; Hunt et al., 2019; Gras et al., 2019; Venugopal et al., 2020.Together these studies opened a myriad of novel questions. Now we will continue these important studies focusing on three major objectives.:1. Identification of cargo that requires F-actin dependent transport mechanisms. We hypothesised that the identified recycling pathway is not restricted to micronemes but is also in place for the recycling of other organelles.2. Identification of trafficking factors involved in F-actin dependent transport. We started to re-investigate the role of trafficking factors such as Rab-GTPases and dynamins in recycling.3. Characterisation and identification of factors involved in regulation of F-actin dynamics We reinvestigated the role of several regulatory proteins in recycling and regulation of the intravacuolar F-actin network and performed a phenotypic screen based on splitCas9 to identify novel proteins that are crucial in this process (see Li et al., BioRXiv2021; under revision in Nature Microbiology). Among others, we identified a Golgi-protein that appears to be required for Golgi-organisation, recycling and formation of the plant-like-vacuole (PLV/VAC), a lysosomal compartment.4. Coordination of actin and the microtubule network and the protein sorting pathway. Our observations lead to the hypothesis that the actin network can regulate protein trafficking by restricting or facilitating vesicle transport dependent on endomembrane sorting mechanism or microtubules.

• DFG Programme: Research Grants