Research

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 var genes. Spatial tethering of members of the gene family to the perinuclear region involves var introns. Another epigenetic factor associated with var gene 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. A putative transcription factor (a member of AP2 family) binds to var introns. We will investigate the role of this protein in var gene expression. We are now developing new methods such as random mutagenesis to study the molecular mechanism that controls mutually exclusive expression.

Characterization of new chromatin factors that binds DNA and RNA: the Alba gene family. Perinuclear subtelomeric chromatin conveys monoallelic expression of virulence genes. However, proteins that directly bind to chromosome ends are poorly described. Recently, we identified a novel DNA/RNA-binding protein family that bears homology to the archaeal protein Alba (Acetylation lowers binding affinity). We isolated three of the four PfAlba paralogs as part of a molecular complex that is associated with the P. falciparum-specific TARE6 (Telomere-Associated Repetitive Elements 6) subtelomeric region and showed in electromobility shift assays (EMSAs) that the PfAlbas bind to TARE6 repeats. The perinuclear PfAlba location changed at the onset of parasite proliferation (trophozoite-schizont), where the PfAlba proteins were also detectable in the cytoplasm in a punctate pattern. Using single-stranded RNA (ssRNA) probes in EMSAs, we found that PfAlbas bind to ssRNA, albeit with different binding preferences. We demonstrate for the first time in eukaryotes that Alba-like proteins bind to both DNA and RNA and that their intracellular location is developmentally regulated. Discovery of the PfAlbas may provide a link between the previously described subtelomeric non-coding RNA and the regulation of antigenic variation.

Cytoadhesion and malaria pathogenesis. Parasite-encoded adhesion molecules are inserted into the erythrocyte membrane during intracellular blood stage development. 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 9 subtelomeric 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.). Gene knock out of clag9 demonstrates that this gene is not essential to assemble the adhesive complex at the IE surface. We are now complementing genes deleted on chromosome 9 to identify molecules that are able to restore the adhesion phenotype.

Pathogenesis of experimental cerebral malaria (ECM). The group of S. Mecheri (E3 attached to BIHP since 2008) had previously identified a mechanism by which histamine, an inflammatory mediator of the allergic response, plays an essential role in the pathogenesis of ECM (P. berghei/mouse system). Recently, they made the unprecedented finding that 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. The relevance of this inflammatory cascade was recently implemented by the finding that a Plasmodium gene product, the translationally controlled tumor protein, which is endowed with a histamine releasing activity, was found to be associated with disease severity. Our work highlights the fact that the allergic response during plasmodium infection is a hallmark of disease severity.

P. falciparum Transfection Vectors. We focus on construction of P. falciparum transfection plasmids for different research topics and the generation of new generic vectors to study the biology of this parasite.