Biology subjects

Niederwieser, I.

Publications and source records attributed to Niederwieser, I..

3 recordsLinked to original sources

bioRxiv2025

The regulation of virulence gene expression is controlled by phase separation of heterochromatin protein 1 (HP1) in Plasmodium falciparum

Malaria caused by Plasmodium falciparum involves antigenic variation on the infected red blood cell surface by a mutually exclusive expression of virulence (var) genes. The repressed var genes have a distinct genome organization where they localize as a cluster near the nuclear periphery and are bound by PfHP1 (P. falciparum Heterochromatin Protein 1). However, the mode of regulation of var genes by PfHP1 remains unclear. In this study, we show that PfHP1 undergoes phase separation in vitro in an RNA and DNA-dependent manner. Single-molecule DNA tethering experiments further revealed that AT-rich DNA sequences act as nucleation sites for the assembly and compaction of PfHP1-mediated heterochromatinization. We have also identified point mutations in the IDRs (intrinsically disordered regions) of PfHP1 that disrupt its phase separation as well as DNA compaction in vitro. To assess the dynamic properties of PfHP1 condensates in vivo, we performed fluorescence recovery after photobleaching (FRAP) in GFP tagged PfHP1 parasites, which revealed rapid fluorescence recovery, supporting their fluidity and phase separation behaviour. Ectopic expression of PfHP1 phase separation and DNA compaction mutants led to dispersed nuclear localization of PfHP1, in contrast to the punctate appearance of the wild-type protein and altered chromatin binding at var genes. These results were corroborated with DiCre/loxP-based conditional expression of the same PfHP1 mutants, which also led to the de-repression of multiple var genes (as many as 54 out of 60 var genes), mimicking the phenotype of PfHP1 depletion mutants. Hi-C sequencing of PfHP1 mutants revealed loss of interactions in the heterochromatic regions, indicating that PfHP1 phase separation is an essential mechanism for repressive cluster formation. In conclusion, our study demonstrates the role of PfHP1-mediated phase separation in heterochromatin formation and var gene silencing; unveiling a fundamental mechanism that drives antigenic variation in P. falciparum.

molecular biology↗

bioRxiv2024

The Plasmodium falciparum histone methyltransferase PfSET10 is dispensable for the regulation of antigenic variation and gene expression in blood stage parasites

The malaria parasite Plasmodium falciparum employs antigenic variation of the virulence factor P. falciparum erythrocyte membrane protein 1 (PfEMP1) to escape adaptive immune responses during blood infection. Antigenic variation of PfEMP1 occurs through epigenetic switches in the mutually exclusive expression of individual members of the multi-copy var gene family. var genes are located in perinuclear clusters of transcriptionally inactive heterochromatin. Singular var gene activation is linked to locus repositioning into a dedicated zone at the nuclear periphery and deposition of histone 3 lysine 4 di-/trimethylation (H3K4me2/3) and H3K9 acetylation marks in the promoter region. While previous work identified the putative H3K4-specific methyltransferase PfSET10 as an essential enzyme and positive regulator of var gene expression, a recent study reported conflicting data. Here, we used iterative genome editing to engineer a conditional PfSET10 knockout line tailored to study the function of PfSET10 in var gene regulation. We demonstrate that PfSET10 is not required for mutually exclusive var gene expression and switching. We also show that PfSET10 is dispensable not only for asexual parasite proliferation but also for sexual conversion and gametocyte differentiation. Furthermore, comparative RNA-seq experiments revealed that PfSET10 plays no obvious role in regulating gene expression during asexual parasite development and gametocytogenesis. Interestingly, however, PfSET10 shows different subnuclear localization patterns in asexual and sexual stage parasites and female-specific expression in mature gametocytes. In summary, our work confirms in detail that PfSET10 is not involved in regulating var gene expression and not required for blood stage parasite viability, indicating PfSET10 may be important for life cycle progression in the mosquito vector or during liver stage development.

microbiology↗

bioRxiv2020

GDV1 C-terminal truncation of 39 amino acids disrupts sexual commitment in Plasmodium falciparum

Malaria is a mosquito-borne disease caused by apicomplexan parasites of the genus Plasmodium. Completion of the parasites life cycle depends on the transmission of sexual stages, the gametocytes, from an infected human host to the mosquito vector. Sexual commitment occurs in only a small fraction of asexual blood stage parasites and is initiated by external cues. The gametocyte development protein 1 (GDV1) has been described as a key facilitator to trigger sexual commitment. GDV1 interacts with the silencing factor heterochromatin protein 1 (HP1), leading to its dissociation from heterochromatic DNA at the genomic locus encoding AP2-G, the master transcription factor of gametocytogenesis. How this process is regulated is not known. In this study we have addressed the role of protein kinases implicated in gametocyte development. From a pool of available protein kinase KO lines, we identified two kinase knockout lines which fail to produce gametocytes. However, independent genetic verification revealed that both kinases are not required for gametocytogenesis but both lines harbour the same mutation that leads to a truncation in the extreme C-terminus of GDV1. Introduction of the identified nonsense mutation into the genome of wild type parasite lines replicates the observed phenotype. Using a GDV1 overexpression line we show that the truncation in the GDV1 C-terminus does neither interfere with the nuclear import of GDV1 nor its interaction with HP1 in vitro, but appears important to sustain GDV1 protein levels and thereby sexual commitment. ImportanceTransmission of malaria causing Plasmodium species by mosquitos requires the parasite to change from a continuously growing asexual parasite form growing in the blood, to a sexually differentiated form, the gametocyte. Only a small subset of asexual parasites differentiates into gametocytes that are taken up by the mosquito. Transmission represents a bottleneck in the lifecycle of the parasite, so a molecular understanding of the events that lead to stage conversion may identify novel intervention points. Here we screened a subset of kinases we hypothesized to play a role in this process. While we did not identify kinases required for sexual conversion, we identified a mutation in the C-terminus of the Gametocyte Development 1 protein (GDV1), which abrogates sexual development. The mutation destabilises the protein but not its interaction with its cognate binding partner HP1. This suggest an important role for the GDV1 C-terminus beyond trafficking and protein stability.

microbiology↗