Malaria Biology and Genetics  


  HEADDr Robert Ménard / rmenard@pasteur.fr
  MEMBERSDr Patricia Baldacci, Dr Pascale Morisse-Gueirard, Sara Brega, Samantha Blazquez, Bertrand Boisson, Tomoko Ishino, Sabine Thiberge, Céline Lacroix, Audrey Combe, Donatella Giovannini, Stephan Spath, Armelle Dupiat


  Annual Report

Our laboratory focuses on the pre-erythrocytic phase of malaria, i.e., the parasite’s (Plasmodium) journey from the site of the mosquito bite to the liver and its development in the liver. 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 vivoimaging approaches, and P. berghei, a parasite species that infects rodents.

Imaging parasite pre-erythrocytic stages

So far, the view of the pre-erythrocytic phase of malaria is that sporozoites, which are injected in the host’s skin by a mosquito, invade the bloodstream and eventually hepatocytes in the liver, where they generate merozoites, the erythrocyte-infective form. In collaboration with the Imaging platform at the Institut Pasteur, we have investigated by intravital imaging the behavior of P. berghei sporozoites in rodents, and the results suggest a more complex view. In the past years, we described (i) a lymph node step, with 20% of the parasites ending their life in the proximal draining lymph node ; (ii) a skin step, with about half of the inoculated parasites staying at the site of bite ; (iii) a complex process of release of merozoites, which occurs through specialized structures (we called merosomes) that both transport the parasites from hepatocytes into the sinusoids and protect them from phagocytosis by Kupffer cells, the resident macrophages in the liver ; and (iv) the role of the cell traversal activity of the sporozoites, previously thought to be important for activating the sporozoites for entry into hepatocytes, which appears to confer parasite resistance to destruction by phagocytic leukocytes both in the skin and in the liver sinusoids.

Last year, we characterized the fate of sporozoites that are inoculated by mosquitoes and eventually stay in the skin. Strikingly, we found that these skin parasites can undergo complete development (see illustration), that is exo-erythrocytic schizogony in the skin, and can also persist in the skin as growth-arrested or slowly-growing parasites. We identified dermal fibroblasts and keratinocytes as host cells allowing production of infectious merozoites.

Characterizing the important molecular players of parasite infection

In previous years, we have established new molecular genetics tools and approaches to study gene/protein function in pre-erythrocytic stages of P. berghei, including a new conditional mutagenesis procedure that allows for modifying any gene of interest specifically at the sporozoite stage (only erythrocytic stages of the parasite can be transfected), as well as a systematic mutagenesis (knock-out) technique. We have also identified new genes of interest by an extensive SAGE analysis of salivary gland sporozoites. Our primary goal is to better understand the molecular basis of sporozoite motility and invasion into host cells, and more generally the function of parasite proteins that act at the host-parasite interface.

In the past year, we have investigated the role of various proteins during the pre-erythrocytic phase of parasite infection, including (i) MSP1, a protein known to be essential for merozoite adhesion to erythrocytes, (ii) AMA1 and RON4, two proteins that are important for merozoite invasion into erythrocytes, (iii) P36 ansd P36p, which are thought to be involved in the sporozoite switch from cell traversal to cell entry, as well as (iv) other genes that were selected from our SAGE analysis and whose corresponding inactivation in the parasite genome causes striking phenotypes.

Keywords: Plasmodium, pre-erythrocytic phase, sporozoite, skin, liver, in vivo imaging, conditional mutagenesis, SAGE

Biogenpal.jpg

P. berghei dermal schizont



  Publications

Gil Carvalho T, Thiberge S, Sakamoto H, Ménard R. 2004. Conditional mutagenesis using site-specific recombination in Plasmodium berghei. Proceedings of National Academy of Sciences USA101, 14931-14936.

Amino R, Thiberge S, Martin B, Celli S, Shorte S, Frischknecht F, Ménard R. 2006. Quantitative imaging of Plasmodium transmission from mosquito to mammal. Nature Medicine 12, 220-224.

Sturm A, Amino R, van de Sand C, Regen T, Retzlaff S, Rennenberg A, Krueger A, Pollok JM, Ménard R, and 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, and Amino R. 2007. In vivoimaging of malaria parasites in the murine liver. Nature Protocols 2, 1705-1712.





Activity Reports 2007 - Institut Pasteur
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