UMSBP2 is chromatin remodeler that functions in regulation of gene expression and suppression of antigenic variation in trypanosomes.

Universal Minicircle Sequence binding proteins (UMSBPs) are CCHC-type zinc-finger proteins that bind the single-stranded G-rich UMS sequence, conserved at the replication origins of minicircles in the kinetoplast DNA, the mitochondrial genome of kinetoplastids. Trypanosoma brucei UMSBP2 has been recently shown to colocalize with telomeres and to play an essential role in chromosome end protection. Here we report that TbUMSBP2 decondenses in vitro DNA molecules, which were condensed by core histones H2B, H4 or linker histone H1. DNA decondensation is mediated via protein-protein interactions between TbUMSBP2 and these histones, independently of its previously described DNA binding activity. Silencing of the TbUMSBP2 gene resulted in a significant decrease in the disassembly of nucleosomes in T. brucei chromatin, a phenotype that could be reverted, by supplementing the knockdown cells with TbUMSBP2. Transcriptome analysis revealed that silencing of TbUMSBP2 affects the expression of multiple genes in T. brucei, with a most significant effect on the upregulation of the subtelomeric variant surface glycoproteins (VSG) genes, which mediate the antigenic variation in African trypanosomes. These observations suggest that UMSBP2 is a chromatin remodeling protein that functions in the regulation of gene expression and plays a role in the control of antigenic variation in T. brucei.

A nuclear redox sensor modulates gene activation and var switching in Plasmodium falciparum.

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 PfEMP1 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 (PfTPx-1), as one of the proteins associated with the var antisense lncRNA. We show that PfTPx-1 localizes to a nuclear subcompartment associated with active transcription on the nuclear periphery, in ring-stage parasite, when var transcription occurs. In addition, PfTPx-1 colocalizes with S-adenosylmethionine synthetase (PfSAMS) in the nucleus, and its overexpression leads to activation of var2csa, similar to overexpression of PfSAMS. Furthermore, we show that PfTPx-1 knockdown alters the var switch rate as well as activation of additional gene subsets. Taken together, our data indicate that nuclear PfTPx-1 plays a role in gene activation possibly by providing a redox-controlled nuclear microenvironment ideal for active transcription.

Gene knockdown in malaria parasites via non-canonical RNAi.

The lack of endogenous RNAi machinery in the malaria parasite Plasmodium hampers gene annotation and hence antimalarial drug and vaccine development. Here, we engineered rodent Plasmodium berghei to express a minimal, non-canonical RNAi machinery that solely requires Argonaute 2 (Ago2) and a modified short hairpin RNA, so-called AgoshRNA. Using this strategy, we achieved robust and specific gene knockdown throughout the entire parasite life cycle. We also successfully silenced the endogenous gene perforin-like protein 2, phenocopying a full gene knockout. Transcriptionally restricting Ago2 expression to the liver stage further enabled us to perform a stage-specific gene knockout. The RNAi-competent Plasmodium lines reported here will be a valuable resource for loss-of-function phenotyping of the many uncharacterized genes of Plasmodium in low or high throughput, without the need to engineer the target gene locus. Thereby, our new strategy and transgenic Plasmodium lines will ultimately benefit the discovery of urgently needed antimalarial drug and vaccine candidates. Generally, the ability to render RNAi-negative organisms RNAi-competent by mere introduction of two components, Ago2 and AgoshRNA, is a unique paradigm that should find broad applicability in other species.

Time to switch gears: how long noncoding RNAs function as epigenetic regulators in Apicomplexan parasites.

Long noncoding RNAs (lncRNA) are emerging as important regulators of gene expression in eukaryotes. In recent years, a large repertoire of lncRNA were discovered in Apicomplexan parasites and were implicated in several mechanisms of gene expression, including marking genes for activation, contributing to the formation of subnuclear compartments and organization, regulating the deposition of epigenetic modifications, influencing chromatin and chromosomal structure and manipulating host gene expression. Here, we aim to update recent knowledge on the role of lncRNAs as regulators in Apicomplexan parasites and highlight the possible molecular mechanisms by which they function. We hope that some of the hypotheses raised here will contribute to further investigation and lead to new mechanistic insight and better understanding of the role of lncRNA in parasite's biology.

Building genomic capacity for precision health in Africa.

The African continent is poised to have a pivotal role in the global population landscape, with the United Nations projecting a population of 2.5 billion (more than 25% of the global population) by 2050. Amid this demographic shift, Africa faces a unique healthcare challenge-navigating a complex landscape of infectious and non-communicable diseases. This necessitates a departure from the conventional 'one-size-fits-all' medical model toward precision approaches that are efficient and sustainable. Genomic capacity is a pillar of precision health; however, access to up-to-date genetic testing in African countries is limited, compounded by a startling lack of representation of data from populations of African descent in gene discovery studies. In this Review, we delve into the challenges impeding the development of genomic capacity in Africa, such as the lack of electronic clinical and epidemiological records, infrastructural challenges, high supply chain costs and the 'dependency trap' that jeopardizes long-term sustainability. We emphasize the need for strategies hinged on true partnerships, robust infrastructure, workforce development and well-crafted policies. Finally, we outline recent progress and existing initiatives that should be considered as role models for future capacity-building initiatives.

Resetting var Gene Transcription in Plasmodium falciparum.

One of the key mechanisms contributing to the virulence of Plasmodium falciparum is its ability to undergo antigenic switching among antigenically distinct variants of the PfEMP1 adhesive proteins, encoded by the var gene family. To avoid premature exposure of its antigenic repertoire, the parasite transcribes its var genes in a mutually exclusive manner, and switch expression at a very slow rate. This process is epigenetically regulated and it relies on "epigenetic memory," which imprints the single active var gene to remain active for multiple replication cycles. Erasing this epigenetic memory in parasites grown in culture resembles parasites, which egress from the liver. It could therefore be of interest for investigating var switching patterns at the onset of malaria infections. In addition, this procedure could be used for creating heterogeneity of var expression among parasite populations. The methodology described here for resetting of var gene expression is based on promoter titration, also known as molecular sponging.

FIT-PNAs as RNA-Sensing Probes for Drug-Resistant Plasmodium falciparum.

Detecting RNA at single-nucleotide resolution is a formidable task. Plasmodium falciparum is the deadliest form of malaria in humans and has shown to gain resistance to essentially all antimalarial drugs including artemisinin and chloroquine. Some of these drug resistances are associated with single-nucleotide polymorphisms (SNPs). Forced-intercalation peptide nucleic acids (FIT-PNAs) are DNA mimics that are designed as RNA-sensing molecules that fluoresce upon hybridization to their complementary (RNA) targets. We have previously designed and synthesized FIT-PNAs that target the C580Y SNP in the K13 gene of P. falciparum. In addition, we have now prepared FIT-PNAs that target the K76T SNP in the CRT gene of P. falciparum. Both SNPs are common ones associated with artemisinin and chloroquine drug resistance, respectively. Our FIT-PNAs are conjugated to a simple cell-penetrating peptide (CPP) that consists of eight d-lysines (dK8), which renders these FIT-PNAs cell-permeable to infected red blood cells (iRBCs). Herein, we demonstrate that FIT-PNAs clearly discriminate between wild-type (WT) strains (NF54-WT: artemisinin-sensitive or chloroquine-sensitive) and mutant strains (NF54-C580Y: artemisinin-resistant or Dd2: chloroquine-resistant) of P. falciparum parasites. Simple incubation of FIT-PNAs with live blood-stage parasites results in a substantial difference in fluorescence as corroborated by FACS analysis and confocal microscopy. We foresee FIT-PNAs as molecular probes that will provide a fast, simple, and cheap means for the assessment of drug resistance in malaria─a tool that would be highly desirable for the optimal choice of antimalarial treatment in endemic countries.

Targeted nanoparticles modify neutrophil function in vivo.

Neutrophils play critical roles in a broad spectrum of clinical conditions. Accordingly, manipulation of neutrophil function may provide a powerful immunotherapeutic approach. However, due to neutrophils characteristic short half-life and their large population number, this possibility was considered impractical. Here we describe the identification of peptides which specifically bind either murine or human neutrophils. Although the murine and human neutrophil-specific peptides are not cross-reactive, we identified CD177 as the neutrophil-expressed binding partner in both species. Decorating nanoparticles with a neutrophil-specific peptide confers neutrophil specificity and these neutrophil-specific nanoparticles accumulate in sites of inflammation. Significantly, we demonstrate that encapsulating neutrophil modifying small molecules within these nanoparticles yields specific modulation of neutrophil function (ROS production, degranulation, polarization), intracellular signaling and longevity both in vitro and in vivo. Collectively, our findings demonstrate that neutrophil specific targeting may serve as a novel mode of immunotherapy in disease.

Phosphorylation of the Canonical Histone H2A Marks Foci of Damaged DNA in Malaria Parasites.

Plasmodium falciparum parasites proliferate within circulating red blood cells and are responsible for the deadliest form of human malaria. These parasites are exposed to numerous intrinsic and external sources that could cause DNA damage; therefore, they have evolved efficient mechanisms to protect their genome integrity and allow them to proliferate under such conditions. In higher eukaryotes, double-strand breaks rapidly lead to phosphorylation of the core histone variant H2A.X, which marks the site of damaged DNA. We show that in P. falciparum that lacks the H2A.X variant, the canonical P. falciparum H2A (PfH2A) is phosphorylated on serine 121 upon exposure to sources of DNA damage. We further demonstrate that phosphorylated PfH2A is recruited to foci of damaged chromatin shortly after exposure to sources of damage, while the nonphosphorylated PfH2A remains spread throughout the nucleoplasm. In addition, we found that PfH2A phosphorylation is dynamic and that over time, as the parasite activates the repair machinery, this phosphorylation is removed. Finally, we demonstrate that these phosphorylation dynamics could be used to establish a novel and direct DNA repair assay in P. falciparumIMPORTANCEPlasmodium falciparum is the deadliest human parasite that causes malaria when it reaches the bloodstream and begins proliferating inside red blood cells, where the parasites are particularly prone to DNA damage. The molecular mechanisms that allow these pathogens to maintain their genome integrity under such conditions are also the driving force for acquiring genome plasticity that enables them to create antigenic variation and become resistant to essentially all available drugs. However, mechanisms of DNA damage response and repair have not been extensively studied for these parasites. The paper addresses our recent discovery that P. falciparum that lacks the histone variant H2A.X phosphorylates its canonical core histone PfH2A in response to exposure to DNA damage. The process of DNA repair in Plasmodium was mostly studied indirectly. Our findings enabled us to establish a direct DNA repair assay for P. falciparum similar to assays that are widely used in model organisms.

Comparative Genome Sequencing Reveals Within-Host Genetic Changes in Neisseria meningitidis during Invasive Disease.

Some members of the physiological human microbiome occasionally cause life-threatening disease even in immunocompetent individuals. A prime example of such a commensal pathogen is Neisseria meningitidis, which normally resides in the human nasopharynx but is also a leading cause of sepsis and epidemic meningitis. Using N. meningitidis as model organism, we tested the hypothesis that virulence of commensal pathogens is a consequence of within host evolution and selection of invasive variants due to mutations at contingency genes, a mechanism called phase variation. In line with the hypothesis that phase variation evolved as an adaptation to colonize diverse hosts, computational comparisons of all 27 to date completely sequenced and annotated meningococcal genomes retrieved from public databases showed that contingency genes are indeed enriched for genes involved in host interactions. To assess within-host genetic changes in meningococci, we further used ultra-deep whole-genome sequencing of throat-blood strain pairs isolated from four patients suffering from invasive meningococcal disease. We detected up to three mutations per strain pair, affecting predominantly contingency genes involved in type IV pilus biogenesis. However, there was not a single (set) of mutation(s) that could invariably be found in all four pairs of strains. Phenotypic assays further showed that these genetic changes were generally not associated with increased serum resistance, higher fitness in human blood ex vivo or differences in the interaction with human epithelial and endothelial cells in vitro. In conclusion, we hypothesize that virulence of meningococci results from accidental emergence of invasive variants during carriage and without within host evolution of invasive phenotypes during disease progression in vivo.