Biology subjects

Kafsack, B. F. C.

Publications and source records attributed to Kafsack, B. F. C..

11 recordsLinked to original sources

bioRxiv2025

A single valine to leucine switch disrupts Plasmodium falciparum AP2-G DNA binding and reveals the role of GDV1 in ap2-g activation.

Sexual commitment in Plasmodium parasites is essential for malaria transmission, yet much remains unknown about the underlying signaling events initiating sexual conversion in a subpopulation of parasites. We discovered a single valine (V2163) to leucine (L2163) mutation in an Apetala 2 (AP2) transcription factor required for P. falciparum gametocytogenesis, ap2-g that abrogates sexual differentiation and confirmed this with forward and reverse mutation editing. Mutated AP2-G.L2163 does not bind the ap2-g consensus motif, GnGTAC, or stimulate AP2-G-dependent gene transcription including autoregulation. We then used AP2-G.L2163 parasite lines as tools to demonstrate the critical role of GDV1 in the initial activation of the silent ap2-g locus during the trophozoite to schizont transition in the absence of functional AP2-G and its autoregulation. Additionally, we show that AP2-G.V is required for MSRP1 expression, which can be used to distinguish early and late sexually committed schizonts. Together this work demonstrates that valine2163 in AP2-G plays a critical role in DNA binding, highlighting the functional importance of this specific region for malaria transmission as well as the critical role of GDV1 in the initial activation of ap2-g expression and induction of sexual differentiation. The reporter lines generated allow further study of signaling pathways or screening of factors regulating sexual commitment.

microbiology↗

bioRxiv2025

Toxoplasma induced cytokine release syndrome is critically dependent on the expression of pore-forming Perforin-Like Protein-1

Acute virulence in Toxoplasma gondii is linked to an excessive proinflammatory cytokine cascade during laboratory murine infection. Previous work showed that T. gondii secretes a pore forming protein, PLP1, that is required for efficient cytolytic egress from host cells. Deletion of the PLP1 gene results in defective egress from infected culture cells and a marked reduction in parasite virulence. The goal of the present study was to gain insight into the nature of the attenuated virulence observed in PLP1 knockout compared to wild type (WT) RH parasites. Using in vivo bioluminescence imaging, we show that parasites lacking PLP1 establish an acute infection and disseminate throughout the infected mice. Histological tissue analysis indicates that parasites cause severe pathology, even in the absence of PLP1. However, mice infected with{Delta} plp1 parasites evoke a protective inflammatory response, demonstrated by mouse survival and control of infection. Flow cytometric analysis was used to determine cellular changes occurring during both WT and {Delta}plp1 parasite infection. Parasite control in the{Delta} plp1 infection was associated with earlier activation of myeloid cells and a moderate neutrophil response that, by comparison, becomes the dominant infiltrating cell type of WT infection. Positive disease outcome during{Delta} plp1 parasite infection is also associated with regulated induction of proinflammatory cytokines, including IFN-{gamma} and TNF-, and an earlier IL-10 regulatory response that is dysregulated during WT infection. Together these findings suggest a key role for Toxoplasma PLP1 in promoting a lethal inflammatory immune response during acute infection with a virulent strain of the parasite. Author SummaryPore-forming proteins are virulence determinants expressed by multiple different pathogens, with varied roles including cellular invasion and escape, immune cell destruction, and the hijack of host cell defenses. The pathogen, Toxoplasma gondii, expresses a pore-forming protein PLP1, that is required for cell lysis and acute virulence in mice. Here, we investigate the potential mechanisms by which this pore-forming protein promotes parasite virulence; from parasite replication and dissemination to immunologic outcomes after infection. In vivo infections demonstrate that parasites replicate, disseminate, and stimulate a protective immune response when PLP1 is not expressed. We show that PLP1 expression induces a parasite driven dysregulation of cell populations and cytokine/chemokine responses, resulting in cytokine release syndrome. In a broader context, Toxoplasmas PLP1 is comparable to other pathogen pore-forming proteins that function as virulence determinants by their ability to alter host immune responses.

microbiology↗

bioRxiv2024

Suppression by RNA Polymerase I Inhibitors Varies Greatly Between Distinct RNA Polymerase I Transcribed Genes in Malaria Parasites.

Transcription of ribosomal RNA (rRNA) by RNA Polymerase I (Pol I) is the rate-limiting step in ribosome biogenesis and a major determinant of cellular growth rates. Unlike virtually every other eukaryote, which express identical rRNA from large tandem arrays of dozens to hundreds of identical rRNA genes in every cell, the genome of the human malaria parasite Plasmodium falciparum contains only a handful single-copy 47S rRNA loci that differ substantially from one another in length, sequence and expression in different cell-types. We found that growth of malaria parasite was acutely sensitive to the Pol I inhibitors 9-hydroxyellipticine and BMH-21 and demonstrate that they greatly reduce the transcription of 47S rRNAs as well as transcription of other non-coding RNA genes. Surprisingly, we found that the various types of Pol I-transcribed genes differed by more than two orders of magnitude in their susceptibility to these inhibitors and explore the implications of these findings for regulation of rRNA in P. falciparum.

molecular biology↗

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

Safe, effective, and inexpensive clearance of mycoplasma contamination from cultures of apicomplexan parasites with Sparfloxacin.

Most commercial products cannot be used for clearance of mycoplasma contamination from cultures of apicomplexan parasites due to the parasites dependence on the apicoplast, an essential organelle with DNA replication and translation machinery of cyanobacterial origin. The lone exception, Mycoplasma Removal Agent (MRA), is relatively expensive and some mycoplasma strains have shown resistance to clearance with MRA. Here, we report that the fluoroquinolone antibiotic Sparfloxacin is a safe, effective, and inexpensive alternative for treatment of mycoplasma contamination in cultures of apicomplexan parasites. Sparfloxacin cleared both MRA- sensitive and MRA-resistant mycoplasma species from P. falciparum cultures at 1 and 4 g/mL, respectively. We show that cultures of three different apicomplexan parasites can be maintained at concentrations of Sparfloxacin required to clear mycoplasma without resulting in substantial deleterious effects on parasite growth. We also describe an alternative low-cost, in-house PCR assay for detecting mycoplasma. These findings will be useful to laboratories maintaining apicomplexan parasites in vitro, especially in low-resource environments, where the high cost of commercial products creates an economic barrier for detecting and eliminating mycoplasma from culture.

microbiology↗

bioRxiv2022

Global Profiling of Histone Modifications in Plasmodium falciparum using CUT&RUN.

We recently adapted a CUT&RUN protocol for genome-wide profiling of chromatin modifications in the human malaria parasite Plasmodium. Using the step-by-step protocol described below, we were able to generate high quality profiles of multiple histone modifications using only a small fraction of the cells required for ChIPseq. Using antibodies against two commonly profiled histone modifications, H3K4me3 and H3K9me3, we show here that CUT&RUN profiling is highly reproducible and closely recapitulates previously published ChIPseq-based abundance profiles of histone marks. Finally, we show that CUT&RUN requires substantially lower sequencing coverage for accurate profiling compared to ChIPseq.

microbiology↗

bioRxiv2022

PfD123 modulates K13-mediated survival and recovery after artemisinin exposure.

Recent advances in curbing the deadly toll of malaria have been threatened by the emergence of parasites resistant to the front-line antimalarial artemisinin. Resistance is mediated by point-mutations in the parasite protein Kelch13, but the mechanism of resistance is multi-factorial and only partially understood. Resistance-conferring Kelch13 mutations have been shown to lead to low-level activation of the parasites integrated stress response (ISR) which has a protective effect against artemisinin through an unclear mechanism. Furthermore, only a subpopulation of resistant parasites ever survives drug exposure, implying an underlying heterogeneity. By applying scRNAseq to the resistance-relevant early ring stage, we found expansion of a subpopulation in Kelch13 mutant parasites that is chiefly characterized by transcription of the putative positive translational regulator D123, while we conversely observed reduced D123 protein levels at the same stage. Analogous inverse changes in D123 expression are produced by experimental activation of the ISR, and genetically manipulating D123 expression modulates sensitivity to artemisinin, establishing it as a stress-responsive gene that contributes to artemisinin resistance in Kelch13-mutant malaria parasites.

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↗

bioRxiv2020

Activity of epigenetic inhibitors against Babesia divergens.

Babesiosis in a tick-borne parasitic disease of humans and livestock, that has dramatically increased in frequency and geographical range over the past few decades. Infection of cattle often causes large economic losses, and human infection can be fatal in immunocompromised patients. Unlike for malaria, another disease caused by hemoprotozoan parasites, limited treatment options exist for Babesia infections. As epigenetic regulation is a promising target for new anti-parasitic drugs, we screened 324 epigenetic inhibitors against Babesia divergens blood stages and identified 75 (23%) and 17 (5%) compounds that displayed [≥]90% inhibition at 10 {micro}M and 1 {micro}M, respectively, including over a dozen compounds with activity in the low nanomolar range. We observed differential activity of some inhibitor classes against Babesia divergens and Plasmodium falciparum parasites and identified pairs of compounds with a high difference in activity, despite a high similarity in chemical structure, highlighting new insights into the development of epigenetic inhibitors as anti-parasitic drugs.

microbiology↗

bioRxiv2020

Homeodomain protein 1 is an essential regulator of gene expression during sexual differentiation of malaria parasites

Transmission of Plasmodium falciparum and other malaria parasites requires their differentiation from asexual blood stages into gametocytes, the non-replicative sexual stage necessary for transmission to the mosquito vector. This transition involves changes in gene expression and chromatin reorganization that result in the activation and silencing of stage-specific genes. However, the genomes of malaria parasites have been noted for their dearth of transcriptional and chromatin regulators and the molecular mediators of these changes remain largely unknown. We recently identified HomeoDomain Protein 1 (HDP1) as a DNA-binding protein that enhances the expression of key genes that are critical for early sexual differentiation. The discovery of a homeodomain-like DNA-binding protein marks a new class of transcriptional regulator in malaria parasites outside of the better-characterized ApiAP2 family. In this study, we show that HDP1 facilitates the necessary upregulation of inner membrane complex components during early gametocytogenesis that gives P. falciparum gametocytes they characteristic shape and is required for gametocyte maturation and parasite transmission.

microbiology↗

bioRxiv2019

Activity of epigenetic inhibitors against Plasmodium falciparum asexual and sexual blood stages.

Regulation of gene expression by epigenetic processes is critical for malaria parasite survival in multiple life stages. To evaluate the suitability of targeting these pathways we screened 350 epigenetic inhibitors against asexual blood stages and gametocytes of P. falciparum. We observed [≥]90% inhibition at 10 {micro}M for 28% of compounds, of which a third retained [≥]90% inhibition at 1 {micro}M. These results suggest epigenetic regulation as a promising target for the development of new multi-stage anti-malarials.

microbiology↗