Introduction: The laboratory focuses on strategies that enable the human protozoan pathogen Plasmodium falciparum to survive in the hostile environment of the human host and establish chronic blood stage infection.

Molecular mechanisms of antigenic variation. Antigenic Variation is a strategy employed by malaria species to outmanoeuvre the host defence mechanisms long enough for their progeny to spread. Mutually exclusive expression of a single member of a multigene family (called vargene family) leads to the successive expression of variant molecules on the surface of infected erythrocytes. Subtelomeric non-coding elements are critical DNA regions involved in cluster formation between chromosome ends and recruit a number of chromatin silencing factors such as PfSir2. These Perinuclear Repressive Centers are crucial for the control of the silent state of antigenic variation genes and we identified several histone modifications that are linked to epigenetic memory of active and silent vargenes. Spatial tethering of members of the gene family to the perinuclear region involves varintrons. Another epigenetic factor associated with vargene activation is the relocation of a silent var gene into a particular perinuclear region compatible with transcription. We showed recently that perinuclear actin polymerisation is involved in this process. We are now developing new methods to study the molecular mechanism that controls mutually exclusive expression.

Cytoadhesion and malaria pathogenesis. Parasite-encoded virulence factors are inserted into the erythrocyte membrane during intracellular blood stage development. We focus on host–parasite interactions during pregnancy-associated malaria (PAM) and investigate a member of the vargene family called var2CSA, which mediates the CSA adhesion to placenta syncytiotrophoblasts. Var2CSAgene disruptant mutants do not recover the CSA binding phenotype, demonstrating that no other parasite gene can compensate for the loss of function. Purified recombinant var2CSA domains are now being evaluated for the development of a vaccine. We have obtained potent adhesion-blocking antibodies from animals immunized with distinct var2CSA domains (DBL4 and DBL5-e). Recently, the expression of the full-length var2CSA ectodomain has given important structural insight, which may improve strategies for rational vaccine design being able to protect pregnant women from malaria disease.

Intracellular trafficking. We investigate mutant parasites that have a defect in infected erythrocyte (IE) adhesion to endothelial cells. The analysis of mutant parasite lines that have deleted a chromosome region including the clag9 gene, revealed that parasites express a member of the var gene family at the surface of IE but these IEs are unable to adhere to common adhesion receptors (CD36, ICAM-1, CSA etc.). Our data indicate that clag9 is not itself an adhesion molecule but is crucial for the correct assembly of the adhesive complex at the IE surface.

Expression and spatial organisation of rRNA genes. P. falciparumhas a low copy number of rRNAunits, which are, unlike other rDNAgenes, distributed on different chromosomes and are differentially expressed. We found that all rRNAgenes are clustered in the nucleolus independent of their transcriptional state. This rDNAnuclear confinement is DNA sequence dependent, as plasmids carrying rDNAfragments are targeted to the nucleolus. Likewise, insertion of an rDNAsequence into a subtelomere from a chromosome lacking rRNAgenes leads to repositioning in the nucleolus. Using Br-UTP incorporation, we observed two alpha-amanitin-resistant nucleolar transcription sites that disappeared when the rDNAcluster broke up in the replicative blood stages. We are now investigating the factors that determine their differential expression.

Pathogenesis of experimental cerebral malaria (CM). The group of S. Mecheri (E3 attached to BIHP since 2008) had previously identified a mechanism by which histamine, a vaso-active amine and an inflammatory mediator of the allergic response, plays an essential role in the pathogenesis of ECM (P. berghei/mouse system). This group has pursued his studies by exploring the upstream mechanisms that initiate this inflammatory cascade. Using genetic, pharmacologic and antibody-based cell depletion approaches, each component of the allergic cascade was explored, including IgE synthesis, FceRI expression, mast cells, basophils, neutrophils, and eosinophils in their capacity to participate to the disease pathogenesis. The original finding resides in the discovery of a new population of neutrophils expressing the FceRI/IgE complex which was found to be associated with brain lesions and was critical for disease expression and severity“.

P. falciparum Transfection Platform. It is specialized in the construction of P. falciparumtransfection plasmids for different research topics and the generation of new generic vectors to study the biology of this parasite.

Keywords: Malaria, Antigenic variation, Protein Trafficking, Cytoadhesion, Telomere

Scherf, A., Rivière, L., Lopez-Rubio, JJ. (2008) SnapShot: Var gene expression in the malaria parasite. Cell 11;134(1):190

Beghdadi W, Porcherie A, Schneider BS, Dubayle D, Peronet R, Huerre M, Watanabe T, Ohtsu H, Louis J, Mécheri S.(2008) Inhibition of histamine-mediated signaling confers significant protection against severe malaria in mouse models of disease.J Exp Med. Feb 18;205(2):395-408.

Lopez-Rubio JJ, Mancio-Silva L, Scherf A.(2009) Genome-wide analysis of heterochromatin associates clonally variant gene regulation with perinuclear repressive centers in malaria parasites.Cell Host Microbe. 19;5(2):179-90.

Srivastava A, Gangnard S, Round A, Dechavanne S, Juillerat A, Raynal B, Faure G, Baron B, Ramboarina S, Singh SK, Belrhali H, England P, Lewit-Bentley A, Scherf A, Bentley GA, Gamain B.(2010) Full-length extracellular region of the var2CSA variant of PfEMP1 is required for specific, high-affinity binding to CSA. Proc Natl Acad Sci U S A. Mar 16;107(11):4884-9.

Mancio-Silva L, Zhang Q, Scheidig-Benatar C, Scherf A. (2010) Clustering of dispersed ribosomal DNA and its role in gene regulation and chromosome-end associations in malaria parasites.Proc Natl Acad Sci U S A. 2010 Aug 9.