Potential epigenetic regulatory proteins localise to distinct nuclear sub-compartments in Plasmodium falciparum

The life cycle of the malaria parasite Plasmodium falciparum involves dramatic morphological and molecular changes required for infection of insect and mammalian hosts. Stage-specific gene expression is crucial, yet few nuclear factors, including potential epigenetic regulators, have been identified. Epigenetic mechanisms play an important role in the switched expression of members of species-specific gene families, which encode proteins exported into the cytoplasm and onto the surface of infected erythrocytes. This includes the large virulence-associated var gene family, in which monoallelic transcription of a single member and switching to other var genes leads to a display of different surface ligands with distinct antigenic and adhesive properties. Using a bio-informatic approach we identified 24 putative nuclear proteins. Tagging with sequences encoding GFP or haemagglutinin (HA) epitopes allowed for identification and localisation analysis of 12 nuclear proteins that are potential regulators of P. falciparum gene expression. These proteins specifically localise to distinct areas of the nucleus, reaching from the centre towards the nuclear envelope, giving new insights into the apicomplexan nuclear architecture. Proteins presenting a punctate distribution in the perinuclear sub-compartments are potential virulence gene regulators as silenced and active var genes reside at the nuclear periphery either clustered or in small expression sites, respectively. These analyses demonstrated an ordered compartmentalisation, indicating a complex sub-nuclear organisation that contributes to the complexity of transcriptional regulation in P. falciparum.

Graphical abstractThe life cycle of the malaria parasite Plasmodium falciparum involves dramatic morphological and molecular changes required for infection of insect and mammalian hosts. Stage-specific gene expression is crucial, yet few nuclear factors, including potential epigenetic regulators, have been identified. Epigenetic mechanisms play an important role in the switched expression of members of species-specific gene families, which encode proteins exported into the cytoplasm and onto the surface of infected erythrocytes. Using a bio-informatic approach we identified 24 putative nuclear proteins. Tagging with sequences encoding GFP or HA epitopes allowed for identification and localisation analysis of 12 nuclear proteins that are potential regulators of P. falciparum gene expression. These proteins specifically localise to distinct areas of the nucleus, reaching from the centre towards the nuclear envelope, giving new insights into the apicomplexan nuclear architecture. These analyses demonstrated an ordered compartmentalisation, indicating a complex sub-nuclear organisation that contributes to the complexity of transcriptional regulation in P. falciparum. A schematic representation of an infected red blood cell (RBC) and an enlargement of the P. falciparum nucleus are shown. From the centre towards the periphery we have defined three distinct areas (1–3) in which nuclear proteins specifically distribute. Proteins, previously predicted to functionally interact are shown in red. Proteins previously predicted for their histone target sites are indicated by grey boxes. A, apicoplast; M, mitochondria; No, nucleolus.Figure optionsDownload full-size imageDownload high-quality image (140 K)Download as PowerPoint slide