Last Updated: 18/03/2025
The role of RecQ1 Helicase in the epigenetic memory of transcription of variant genes in Plasmodium falciparum, the parasite that causes malaria
Objectives
*Original in Portuguese: O papel da Helicase RecQ1 na memória epigenética da transcrição de genes variantes em Plasmodium falciparum, o parasita causador da malária
This proposal sets to evaluate what happens to epigenetic memory when PfRQ01, which was the Helicase recently identified as essential for the activation of active var loci and the knockout of PfRQ01 led to the complete silencing of all var genes is reduced or removed from its place of action for just one or two cycles of reinvasion.
During the intraerythrocytic phase, the human malaria parasite Plasmodium falciparum exports several proteins to the surface of infected red blood cells. Among these proteins are members of the 45-90 alleles of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family of proteins. These are important virulence factors because they cause cytoadherence and sequestration of infected red blood cells in deep vessels, which can eventually develop into severe malaria. Due to its exposure to the immune system, the expression of PfEMP1 antigens is strictly regulated by epigenetic events such as chromatin modification. This leads to the transcription of only one var gene encoding a PfEMP1 variant at a time on the surface of the infected red blood cell. After subsequent cycles of reinvasion into new red blood cells, the expression pattern of PfEMP1 (activation and silencing of var promoters) is normally maintained (epigenetic memory). Which components and in what sequence of events they act to inherit the var transcription pattern during subsequent cycles is not yet completely understood. Recently, the Helicase PfRQ01 was identified as essential for the activation of active var loci and the knockout of PfRQ01 led to the complete silencing of all var genes. However, it is unclear what recruits PfRQ01 to loci var to be activated. This may inform the interaction/feedback of PfRQ01 with factors that determine its recruitment to an initially active var locus. For this, two strains of modified parasites have already been prepared. In one lineage, the PfRQ01 gene was tagged with sequences encoding the hemagglutinin (HA) tag followed by the self-cleaving peptide 2A, the neomycin/G418 resistance gene and a glmS ribozyme that allows subsequent selective degradation of the PfRQ01-HA transcript. In the other strain, PfRQ01 was tagged with 2xFKBP, GFP, 2A, neomycin resistance/G418, and glmS domains. The second configuration allows conditional displacement of the tagged protein in the knock sideways system (after supertransfection of plasmid encoding the FRB ligand plus secretion signal). This included as a positive control a strain where the heterochromatin protein 1 (HP1) was labeled in the same way. The study of factors that influence var transcription may reveal potential targets for intervention, as disruption of cytoadherence patterns in a natural infection situation (decreasing the specific pathogenic adhesive phenotype) can potentially alleviate symptoms of severe malaria and facilitate elimination of infected red blood cells.
Apr 2024 — Jan 2026
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