Authors

A Pain¹;  ¹ KAUST, Saudi Arabia

Discussion

Apicomplexans are a diverse group of obligate parasites of humans and animals, with a high impact on human health, food security and economics. Several studies on apicomplexan evolution have revealed that before the switch to parasitic life, the ancestor contained a broad repertoire of genes many of which were subsequently repurposed towards parasitism, such as extracellular proteins, components of a motility apparatus, and DNA- and RNA-binding protein families. Proteins with DNA-binding domains (DBD) or RNA-binding domains (RBD) regulate various molecular processes of apicomplexan parasites. Indeed, during apicomplexan evolution, we have seen major lineage-specific expansions of proteins with AP2 (apiAP2) DBD – many of which have been shown to act as genetic control switches for diverse apicomplexan processes including pathogenesis. Several studies that focused on understanding gene regulation suggest that malaria parasites have evolved multilayered gene regulatory mechanisms to fine-tune the expression of genes that include genes encoding pathogenicity factors crucial for its growth and development inside the host. Recently, our group, in collaboration with several international partners, have characterized an essential Plasmodium-specific Apicomplexan AP2 (ApiAP2) transcription factor in Plasmodium falciparum (PfAP2-P; Pathogenesis) during the intraerythrocytic developmental cycle (IDC). An inducible gene knockout approach showed that PfAP2-P is essential for development during the trophozoite stage, and critical for var gene regulation, merozoite development and parasite egress. ChIP-seq experiments were performed at 16 hours post-invasion (h.p.i.) and 40 h.p.i. matching the two peaks of PfAP2-P expression, demonstrating the binding of PfAP2-P to the promoters of genes controlling antigenic variation, host cell remodelling and trophozoite development at 16 h.p.i. and antigenic variation and pathogenicity at 40 h.p.i. Using single-cell RNA-seq and fluorescence-activated cell sorting, we show the de-repression of var gene expression in Δpfap2-p parasites that express multiple PfEMP1 proteins on the surface of infected RBCs. In addition, the Δpfap2-p parasites overexpress several early gametocyte marker genes at both 16 and 40 h.p.i., indicating a putative regulatory role in the sexual stage conversion. Using the Chromosome Conformation Capture (Hi-C) experiment, we demonstrate that deletion of PfAP2-P results in a significant reduction of both intra-chromosomal and inter-chromosomal interactions in heterochromatin clusters. We conclude that PfAP2-P is a vital upstream transcriptional regulator controlling essential pathogenic processes in two distinct developmental stages during the IDC that include parasite growth, egress and invasion, chromatin structure and var gene expression.