Biology subjects

Deitsch, K. W.

Publications and source records attributed to Deitsch, K. W..

5 recordsLinked to original sources

bioRxiv2025

The molecular basis of coordinated antigen switching enabling chronic infection by human malaria parasites

The exceptional virulence of the human malaria parasite, Plasmodium falciparum, is in large part attributed to the adhesive properties of infected red blood cells and the parasites ability to avoid antibody recognition through antigenic variation. Both properties are derived from a hypervariable protein placed on the infected cell surface called PfEMP1, different versions of which are encoded by members of the multi-copy var gene family. Over the course of an infection, rising and falling waves of parasitemia correspond to transcriptional switching between var genes, with parasites expressing alternative PfEMP1 isoforms replacing those eliminated by antibodies targeting the previously expressed PfEMP1. var gene expression is controlled epigenetically, however what triggers transcriptional switching and determines which genes are activated is largely unknown. Previous work implicated a unique, universally conserved gene called var2csa as a central component in transcriptional switching, however the molecular basis for its role was obscure. Here we describe how noncoding RNAs, an upstream open reading frame and the nonsense mediated mRNA decay pathway interact to enable var2csa to function as a transiently activated "switching hub" that unifies the var gene family into a single coordinated network, thereby perpetuating chronic infections.

microbiology↗

bioRxiv2025

Plasmodium falciparum DNA repair dynamics reveal unique roles for TLS polymerases and PfRad51 in genome diversification

The haploid malaria parasite, Plasmodium falciparum, evolved a unique cohort of DNA repair pathways enabling the parasite to survive in a vertebrate host red blood cell and the mosquito vector. P. falciparum chromosomes are partitioned into a highly conserved core genome and remarkably diverse, largely subtelomeric regions that contain genes encoding important parasite virulence factors. The molecular mechanisms that maintain this chromosomal structure have not been identified. Here, we describe specific DNA repair pathways that differentiate between hypervariable subtelomeric and conserved core regions of the genome. Based on our previous work, we hypothesized that there are potentially important interactions between translesion (TLS) and homologous recombination (HR) pathways for the diversification of multicopy gene families in P. falciparum. Thus, we created knockout parasite lines of the DNA repair enzymes: PfRad51 and the TLS polymerases PfPol{zeta} and PfRev1. We identified that irradiation hypersensitivity varied across the cell cycle for TLS{Delta} parasites and was uniform across the erythrocytic cycle for PfRad51{Delta} parasites, highlighting the variable roles of these pathways. However, important interactions between these pathways were found when we studied directed double strand break (DSB) repair, which revealed a difference in the DNA damage response according to chromosomal location. PfRad51 was essential for HR-mediated repair in the core genome. In contrast, we identified a Rad51 independent homology-directed repair in all three of our knockout lines when a DSB was made in the subtelomeric region of the chromosome. We propose that this differential DNA damage response maintains the distinction in diversification across the chromosome.

microbiology↗

bioRxiv2024

Transcriptional plasticity of virulence genes provides malaria parasites with greateradaptive capacity for avoiding host immunity

Chronic, asymptomatic malaria infections contribute substantially to disease transmission and likely represent the most significant impediment preventing malaria elimination and eradication. Plasmodium falciparum parasites evade antibody recognition through transcriptional switching between members of the var gene family, which encodes the major virulence factor and surface antigen on infected red blood cells. This process can extend infections for up to a year; however, infections have been documented to last for over a decade, constituting an unseen reservoir of parasites that undermine eradication and control efforts. How parasites remain immunologically "invisible" for such lengthy periods is entirely unknown. Here we show that in addition to the accepted paradigm of mono-allelic var gene expression, individual parasites can simultaneously express multiple var genes or enter a state in which little or no var gene expression is detectable. This unappreciated flexibility provides parasites with greater adaptive capacity than previously understood and challenges the dogma of mutually exclusive var gene expression. It also provides an explanation for the antigenically "invisible" parasites observed in chronic asymptomatic infections.

microbiology↗

bioRxiv2022

A coordinated transcriptional switching network mediates antigenic variation of human malaria parasites

Malaria parasites avoid immune clearance through their ability to systematically alter antigens exposed on the surface of infected red blood cells. This is accomplished by tightly regulated transcriptional control of individual members of a large, multicopy gene family called var and is the key to both the virulence and chronic nature of malaria infections. Expression of var genes is mutually exclusive and controlled epigenetically, however how large populations of parasites coordinate var gene switching to avoid premature exposure of the antigenic repertoire is unknown. Here we provide evidence for a transcriptional network anchored by a universally conserved gene called var2csa that coordinates the switching process. We describe a structured switching bias that shifts overtime and could shape the pattern of var expression over the course of a lengthy infection. Our results provide an explanation for a previously mysterious aspect of malaria infections and shed light on how parasites possessing a relatively small repertoire of variant antigen encoding genes can coordinate switching events to limit antigen exposure, thereby maintaining chronic infections.

microbiology↗

bioRxiv2022

Metabolic competition between lipid metabolism and histone methylation regulates sexual differentiation in human malaria parasites.

For Plasmodium falciparum, the most widespread and virulent malaria parasite that infects humans, persistence depends on continuous asexual replication in red blood cells, while transmission to their mosquito vector requires asexual blood-stage parasites to differentiate into non-replicating gametocytes. This decision is controlled by stochastic de-repression of a heterochromatin-silenced locus encoding PfAP2-G, the master transcription factor of sexual differentiation. The frequency of pfap2-g de-repression was shown to be responsive to extracellular phospholipid precursors but the mechanism linking these metabolites to epigenetic regulation of pfap2-g was unknown. Here we show that this response is mediated by metabolic competition for the methyl donor S-adenosylmethionine between histone methyltransferases and phosphoethanolamine methyltransferase, a critical enzyme in the parasites pathway for de novo phosphatidylcholine synthesis. When phosphatidylcholine precursors are scarce, increased consumption of SAM for de novo phosphatidylcholine synthesis impairs maintenance of the histone methylation responsible for silencing pfap2-g, increasing the frequency of derepression and sexual differentiation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/476397v3_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@5e2c69org.highwire.dtl.DTLVardef@b5a7d6org.highwire.dtl.DTLVardef@1e118aorg.highwire.dtl.DTLVardef@1191a6_HPS_FORMAT_FIGEXP M_FIG C_FIG

systems biology↗