We will probe the function of two potential formin-like actin nucleation factors in malaria parasite adhesion and motility using recently developed quantitative imaging tools

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The polymerization of actin and thus parasite motility is essential throughout the life cycle of the malaria parasite. We are mainly working on Plasmodium berghei sporozoites, the forms of a rodent malaria parasite transmitted by an infected mosquito to the mammalian host. During a mosquito bite sporozoites are injected into the skin wherein they migrate to find a blood vessel. After entering the blood stream, sporozoites continue their journey to the liver, where they actively invade liver cells to differentiate. Migration is driven by an actin-myosin motor. Curiously, polymerized actin filaments in parasites are very short and little is known about where actin filaments are formed and which molecules are essential for actin nucleation. Importantly, the sequenced genomes of several malaria parasites encode only a very limited number of actin binding proteins of which there are, depending on species, two to three formin like proteins containing formin homology domains. We have recently shown that actin polymerization is not just important for sporozoite motility, but also for distinct steps during sporozoite adhesion. This suggests that different spatially separated sets of actin filaments are formed. We now want to dissect the roles of the potential actin nucleating factors by expressing the functional domains as fluorescently labeled fusion proteins from stage-specific strong and weak promoters to localize them in the parasite and to interfere with the function of the endogenous proteins. We will test the effect of over-expression of wild type and mutant formin homology domains on parasite adhesion, motility and host cell invasion with a number of tools we recently adapted to the study of sporozoites or developed newly in the lab.