The role of actin as a determinant of cell shape and virulence of the sexual blood stage of the malaria parasite, Plasmodium falciparum
Cell Biology
Final Report Abstract
"Plasmodium falciparum" is an obligate intracellular parasite that causes severe malaria. A major bottleneck in the parasite life-cycle is the transmission of sexual blood stage gametocytes from humans to the mosquito host. During this process P. falciparum gametocytes undergo remarkable morphological transformation into elongated falciforme cells that distort the host red blood cell and adhere in the human vasculature. Our research aims to understand the molecular mechanisms that underlie this morphological transformation. We describe a novel and highly stable F-actin based cytoskeleton present in all stages of maturing gametocytes. Super-resolution microscopy revealed that F-actin concentrates at the poles of the parasite cell, from where actin bundles align along the microtubule cytoskeleton. Immuno-electron microscopy confirmed its unusual position at the cytosolic side of the inner membrane complex. In mature non-adherent stage V gametocytes, the actin and tubulin cytoskeleton are reorganized in a coordinated fashion. Pharmacological interference with actin dynamics prevents gametocyte maturation and disrupts mitochondrial morphology leading to decreased viability. We further investigated potential actin- and tubulin-binding proteins that facilitate cytoskeletal cross-talk by proteome analysis and bio-informatic screens. Two protein candidates, the microtubule plus-end binding protein EB1 and the inner membrane complex (IMC) associated PhiL1 protein were characterized in detail during the funding period. Genetic modifications such as gene deletion and tagging were applied to investigate the function and localization of both proteins during gametocyte development. The EB1 protein was additionally studied in the rodent infective "Plasmodium berghe" parasite, providing access to extra-erythrocytic parasite stages. Our results show that EB1 associates with sub-pellicular microtubules and plays an essential role during the parasitic life cycle. The genetic disruption of the IMC associated PhIL1 protein ablates cellular elongation of gametocytes into their characteristic falciforme shape and disrupts the maturation process. In summary, our research highlights the presence and role of a novel F-actin cytoskeleton in P. falciparum gametocytes as well as the role of a microtubule and an IMC associated protein providing desired understanding of cellular mechanisms underlying shape shifting abilities, transmission and viability of malaria parasites. Parts of this work have been published, are under revision and are in preparation for publication.
Publications
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Organization and function of an actin cytoskeleton in Plasmodium falciparum gametocytes. Cellular Microbiology, Vol. 17.2015, Issue 2, pp. 207–225.
Marion Hliscs, Coralie Millet, Matthew W. Dixon, Inga Siden-Kiamos, Paul McMillan and Leann Tilley
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“Comparative Plasmodium gene overexpression reveals distinct perturbation of sporozoite transmission by profilin”. Molecular Biology of the Cell, Vol 27 No 14, July 15, 2016, 2145-2340
Yuko Sato, Marion Hliscs, Josefine Dunst, Christian Goosmann, Volker Brinkmann, Georgina N. Montagna and Kai Matuschewski
