Malaria Biology and Genetics  


  HEADDr Robert Ménard / robert.menard@pasteur.fr
  MEMBERSDr Patricia Baldacci, Dr Pascale Morisse-Gueirard, Dr Rogerio Amino, Technicians: Sabine Thiberge, Céline Lacroix, Students: Audrey Combe, Donatella Giovannini, Stephan Späth, Post-docs: Nicholas Malmquist, Samantha Blazquez, Bertrand Boisson, Tomoko Ishino, Tejram Sahu
Secretary: Armelle Dupiat


  Annual Report

Our laboratory focuses on the pre-erythrocytic phase of malaria. This phase extends from injection of the parasite in the skin by the mosquito to the onset of red blood cell infection, which causes the clinical symptoms of the disease. Our major aim is a functional understanding of the important host-parasite interactions that occur during the parasite journey as well as inside the hepatocyte. For this, we use a combination of molecular genetics, cell biology and in vivo imaging approaches, and parasite species that infect rodents.

Imaging Plasmodiumpre-erythrocytic stages

The clinically silent pre-erythrocytic phase of malaria is considered to amount to the journey of the sporozoites, the parasite form injected by the mosquito, from the skin to the liver. Inside hepatocytes, sporozoites transform into the red blood cell-infecting forms of the parasite. In recent years, our intra-vital imaging studies in rodents have revealed a more complex picture of the pre-erythrocytic phase. We have shown that (i) 20% of the inoculated sporozoites, which are motile, actively reach the lymph node draining the site of mosquito bite, (ii) while about half of the sporozoites stay at the site of bite. The latter can either fully develop into red blood cell-infecting forms in the dermis (inside fibroblasts) or the epidermis (inside keratinocytes), or persist as growth-arrested or slowly-growing parasites in association with the hair follicles, an immuno-privileged site of the mammalian body. We have also described how the red blood cell-infecting forms are released from hepatocytes; this process occurs via the formation of hepatocyte-derived structures (merosomes) that both transport the parasites into the sinusoids and protect them from phagocytosis by the resident macrophages (Kupffer cells). We have also documented the role of the cell traversal activity of the sporozoite; thought to be important for activating its capacity to enter hepatocytes inside a vacuole, it appears instead to confer sporozoite resistance to destruction by phagocytic leukocytes both in the skin and in the liver sinusoids. These findings have implications for vaccination strategies against the parasite.

Characterizing the important molecular players of parasite infection

We have recently established new molecular genetics tools and approaches for studying gene/protein function in pre-erythrocytic stages of the parasite, including a new conditional, Flp/FRT-based mutagenesis procedure that allows for modifying any gene of interest specifically at the sporozoite stage (only erythrocytic stages of the parasite can be transfected). We have also recently identified new genes of interest by an extensive SAGE analysis of sporozoites. Our primary goal is to better understand the function of parasite proteins, from both the extracellular sporozoite and the intracellular (intravacuolar) liver stage, which act at the interface with the host.

At the sporozoite stage, recent findings include the identification of a new protein involved in sporozoite motility, called TREP, and the characterization of the role of two proteins thought to be involved in sporozoite entry inside hepatocytes, called AMA1 and RON4. At the intracellular liver stage, we have established that MSP1, a protein known to be essential for parasite entry inside red blood cells and currently a major vaccine candidate against the erythrocytic phase of infection, is also essential for parasite development inside hepatocytes. We have also identified the first protein of Plasmodium that is involved in the lysis of the vacuolar membrane that surrounds the liver stage, called LISP1.

Keywords: Plasmodium, pre-erythrocytic phase, sporozoite, skin, liver, intravital imaging, molecular genetics

Biogenpalu.jpg

Figure legend: P. berghei sporozoites gliding in the dermis or inside blood vessels in the skin of a mouse



  Publications

Amino R, Thiberge S, Martin B, Celli S, Shorte S, Frischknecht F, Ménard R. 2006. Quantitative imaging of Plasmodiumtransmission from mosquito to mammal. Nature Medicine12, 220-224.

Sturm A, Amino R, van de Sand C, Regen T, Retzlaff S, Rennenberg A, Krueger A, Pollok JM, Ménard R, Heussler V. 2006. Manipulation of host hepatocytes by the malaria parasite for delivery into liver sinusoids. Science 313, 1287-1290.

Thiberge S, Blazquez S, Baldacci P, Renaud O, Shorte S, Ménard R, Amino R. 2007. in vivo imaging of malaria parasites in the murine liver.Nature Protocols2, 1705-1712.

Amino R, Giovannini D, Thiberge S, Gueirard P, Dubremetz JF, Prévost MC, Ishino T, Yuda M, Ménard R. 2008. Host cell traversal is important for progression of the malaria parasite from the dermis to the liver.Cell Host and Microbes 3, 88-96.

Ménard R, Heussler V, Yuda M, Nussenzweig V. 2008. Plasmodium pre-erythrocytic stages: what's new? Trends Parasitol. 24, 564-569.





Activity Reports 2009 - Institut Pasteur
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