A nuclear redox sensor modulates gene activation andvarswitching inPlasmodium falciparum

Abstract

The virulence of Plasmodium falciparum , which causes the deadliest form of human malaria, is attributed to its ability to evade the human immune response. These parasites “choose” to express a single variant from a repertoire of surface antigens called PfEMP1, which are placed on the surface of the infected red cell. Immune evasion is achieved by switches in expression between var genes, each encoding a different Pf EMP1 variant. While the mechanisms that regulate mutually exclusive expression of var genes are still elusive, antisense long-noncoding RNAs (lncRNAs) transcribed from the intron of the active var gene were implicated in the “choice” of the single active var gene. Here, we show that this lncRNA colocalizes with the site of var mRNA transcription and is anchored to the var locus via DNA:RNA interactions. We define the var lncRNA interactome and identify a redox sensor, P. falciparum thioredoxin peroxidase I ( Pf TPx-1), as one of the proteins associated with the var antisense lncRNA. We show that Pf TPx-1 localizes to a nuclear subcompartment associated with active transcription on the nuclear periphery, in ring-stage parasite, when var transcription occurs. In addition, Pf TPx-1 colocalizes with S-adenosylmethionine synthetase ( Pf SAMS) in the nucleus, and its overexpression leads to activation of var2csa, similar to overexpression of Pf SAMS. Furthermore, we show that Pf TPx-1 knockdown alters the var switch rate as well as activation of additional gene subsets. Taken together, our data indicate that nuclear Pf TPx-1 plays a role in gene activation possibly by providing a redox-controlled nuclear microenvironment ideal for active transcription.

Evolution of hierarchical switching pattern in antigenic variation ofPlasmodium falciparumunder variable host immunity

“…Thus, all the variants show maximum bias towards a variant like Var2csa (PF_120600) which is at the top of the hierarchy. In order to experimentally validate the outcome of the theoretical analysis, we explored the switching rate measurement form the recently performed experiment 27 . In this study, they utilized a transgenic strain of P. falciparum (DC-J line) where this line allows for activation of a specific var gene (PF3D7_0223500-BSD) by culturing the parasites in the presence of blasticidin-S-HCl (DC-J “ON”).…”

“…Parasites were collected 3, 6, or 12 wk following blasticidin removal. Synchronous ring-stage parasite (20 to 22 h postsynchronization) cultures were collected for RNA, and RT-qPCR for the var gene family was performed on cDNA at the times indicated 27 . The pie chart for the off switch rates per generration of the different var genes in absence of GlcN (B) Off switch rates per generation in presence of GlcN at the time point of 3 weeks.…”

“…Here, we construct a mathematical model by incorporating response of the immune system and subsequent clearing of the variants following similar method 18 . The biased switching pattern in the absence of immune system is initially calibrated using the single cell RNA-sequencing data sets providing in vitro expression of all the variants over a population of the Plasmodium falciparum parasites 23 in conjunction with recently measured switching pattern datasets 27 . Finally, the calibrated intrinsic switching pattern is utilized to construct a genetic algorithm based evolutionary simulation 18 in presence of immune response where are varied through generations.…”

SUN-domain proteins of the malaria parasitePlasmodium falciparumare essential for proper nuclear division and DNA repair

“…The PfSUN1-HA-glms and PfSUN2-HA-glms lines were created using the plasmid pSLI-HAx3glmS (70) as backbone. pSLI-HAx3glms was generated on the basis of the pSLI-2 X FKBP-GFP construct (25).…”

Host-parasite interactions during Plasmodium infection: Implications for immunotherapies

“…Recently, one group of researchers have identified an anti-sense lncRNA-associated protein, Pf TPx-1 which localizes to specific nuclear subcompartment and creates a redox-controlled microenvironment essential for the active transcription of var genes. Furthermore, alterations in Pf TPx-1 expression influence both gene switching as well as transcriptional activation of var genes ( 47 ). Although var genes are involved in Pf EMP1 expression which is a key to parasite survival in their host, the mechanism of mutually exclusive expression of var genes is not completely understood.…”