Microtubule stability and dynamics in Plasmodium sporozoites

• Applicant: Professor Dr. Friedrich Frischknecht
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens ; Cell Biology
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423870657

Microtubules are long filamentous cytoskeletal structures that are formed from dimers of α- and β-tubulin. Microtubules form and disassemble dynamically and these dynamics are essential for many cellular processes. Post-translational modifications, temperature and microtubule binding proteins play key roles in modulating microtubule dynamics. Malaria causing Plasmodium parasites belong to the apicomplexa within the chromalveolata and are divergent life forms with a cellular biology distinct to opisthokont model organisms such as yeast. Like in other organisms, microtubules in Plasmodium spp are important for cell division, vesicular transport, motility and parasite morphogenesis. In the last funding period, we showed that deletion of a microtubule binding protein, SPM3 affects the infectivity of Plasmodium sporozoites, the forms transmitted by the Anopheles mosquito. Sporozoites are formed in oocysts, invade the salivary glands prior to transmission, migrate in the skin and enter into hepatocytes to differentiate into blood cell infecting forms. Parasites lacking SPM3 can still form sporozoites but these do not invade into salivary glands efficiently. Electron and light microscopy revealed that microtubules in these mutants detach from the inner membrane complex and that sporozoites cannot migrate. Additionally, we investigated the two microtubule inner proteins SPM1 and TrxL1, which were thought to stabilize microtubules. Strikingly, deletion of both genes revealed no defect at any stage of the parasite under optimal conditions. Interestingly, it was found by collaborators that SPM1 and TrxL1 protect microtubules from depolymerizing on ice in vitro. This suggests that the role of these proteins is to stabilize microtubules when mosquitoes are facing cold periods. We now want to investigate this phenomenon in detail in vivo. To do so we will establish a new set of assays, where mosquitoes are kept at distinct temperatures for different times to examine the consequences these changes have on the microtubules in parasites expressing none, some or all of the different microtubule stabilizing proteins. This will advance our understanding of how Plasmodium ensures microtubule integrity and thus function at different environmental conditions.

• DFG Programme: Research Grants