87 research outputs found
Plasmodium sexual differentiation: how to make a female
Sexual development is integral to the transmission of Plasmodium parasites between vertebrates and mosquitos. Recent years have seen great advances in understanding the gene expression that underlies commitment of asexual parasites to differentiate into sexual gametocyte stages, then how they mature and form gametes once inside a mosquito. Less well understood is how parasites differentially control development to become males or females. Plasmodium parasites are haploid at the time of sexual differentiation, but a clonal haploid line can produce both male and female gametocytes, so they presumably lack the sex‐determining alleles present in some other eukaryotes. Though the molecular switch to initiate male or female development remains hidden, recent studies reveal regulatory proteins needed for the sex‐specific maturation of male and female gametocytes. In this issue, Yuda and collaborators report the characterization of a transcription factor necessary for female gametocyte maturation. With renewed attention on malaria elimination, sex has been an increasing focus because transmission‐blocking strategies are likely to be an important component of elimination efforts
Plasmodium sexual differentiation: how to make a female
Sexual development is integral to the transmission of Plasmodium parasites between vertebrates and mosquitos. Recent years have seen great advances in understanding the gene expression that underlies commitment of asexual parasites to differentiate into sexual gametocyte stages, then how they mature and form gametes once inside a mosquito. Less well understood is how parasites differentially control development to become males or females. Plasmodium parasites are haploid at the time of sexual differentiation, but a clonal haploid line can produce both male and female gametocytes, so they presumably lack the sex‐determining alleles present in some other eukaryotes. Though the molecular switch to initiate male or female development remains hidden, recent studies reveal regulatory proteins needed for the sex‐specific maturation of male and female gametocytes. In this issue, Yuda and collaborators report the characterization of a transcription factor necessary for female gametocyte maturation. With renewed attention on malaria elimination, sex has been an increasing focus because transmission‐blocking strategies are likely to be an important component of elimination efforts
Virulence of malaria is associated with differential expression of Plasmodium falciparum var gene subgroups in a case-control study
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a major pathogenicity factor in falciparum malaria that mediates cytoadherence. PfEMP1 is encoded by approximately 60 var genes per haploid genome. Most var genes are grouped into 3 subgroups: A, B, and C. Evidence is emerging that the specific expression of these subgroups has clinical significance. Using field samples from children from Papua New Guinea with severe, mild, and asymptomatic malaria, we compared proportions of transcripts of var groups, as determined by quantitative polymerase chain reaction. We found a significantly higher proportion of var group B transcripts in children with clinical malaria (mild and severe), whereas a large proportion of var group C transcripts was found in asymptomatic children. These data from naturally infected children clearly show that major differences exist in var gene expression between parasites causing clinical disease and those causing asymptomatic infections. Furthermore, parasites forming rosettes showed a significant up-regulation of var group A transcripts
Transcriptional variation in malaria parasites: why and how
Transcriptional differences enable the generation of
alternative phenotypes from the same genome. In malaria
parasites, transcriptional plasticity plays a major role in the
process of adaptation to fluctuations in the environment.
Multiple studies with culture-adapted parasites and field
isolates are starting to unravel the different transcriptional
alternatives available to Plasmodium falciparum and the
underlying molecular mechanisms. Here we discuss how epigenetic
variation, directed transcriptional responses and also genetic
changes that affect transcript levels can all contribute to
transcriptional variation and, ultimately, parasite survival.
Some transcriptional changes are driven by stochastic events.
These changes can occur spontaneously, resulting in
heterogeneity within parasite populations that provides the
grounds for adaptation by dynamic natural selection. However,
transcriptional changes can also occur in response to external
cues. A better understanding of the mechanisms that the parasite
has evolved to alter its transcriptome may ultimately contribute
to the design of strategies to combat malaria to which the
parasite cannot adapt
New Assays to Characterise Growth-Related Phenotypes of Plasmodium falciparum Reveal Variation in Density-Dependent Growth Inhibition between Parasite Lines
The growth phenotype of asexual blood stage malaria parasites
can influence their virulence and also their ability to survive
and achieve transmission to the next host, but there are few
methods available to characterise parasite growth parameters in
detail. We developed a new assay to measure growth rates at
different starting parasitaemias in a 96-well format and applied
it to characterise the growth of Plasmodium falciparum lines
3D7-A and 3D7-B, previously shown to have different invasion
rates and to use different invasion pathways. Using this simple
and accurate assay we found that 3D7-B is more sensitive to high
initial parasitaemia than 3D7-A. This result indicates that
different parasite lines show variation in their levels of
density-dependent growth inhibition. We also developed a new
assay to compare the duration of the asexual blood cycle between
different parasite lines. The assay is based on the tight
synchronisation of cultures to a 1 h parasite age window and the
subsequent monitoring of schizont bursting and formation of new
rings by flow cytometry. Using this assay we observed
differences in the duration of the asexual blood cycle between
parasite lines 3D7 and HB3. These two new assays will be useful
to characterise variation in growth-related parameters and to
identify growth phenotypes associated with the targeted deletion
of specific genes or with particular genomic, transcriptomic or
proteomic patterns. Furthermore, the identification of
density-dependent growth inhibition as an intrinsic parasite
property that varies between parasite lines expands the
repertoire of measurable growth-related phenotypic traits that
have the potential to influence the outcome of a malarial blood
infection
Malaria Epigenetics
Organisms with identical genome sequences can show substantial
differences in their phenotypes owing to epigenetic changes that
result in different use of their genes. Epigenetic regulation of
gene expression plays a key role in the control of several
fundamental processes in the biology of malaria parasites,
including antigenic variation and sexual differentiation. Some
of the histone modifications and chromatin-modifying enzymes
that control the epigenetic states of malaria genes have been
characterized, and their functions are beginning to be
unraveled. The fundamental principles of epigenetic regulation
of gene expression appear to be conserved between malaria
parasites and model eukaryotes, but important peculiarities
exist. Here, we review the current knowledge of malaria
epigenetics and discuss how it can be exploited for the
development of new molecular markers and new types of drugs that
may contribute to malaria eradication efforts
Virulence of Malaria Is Associated with Differential Expression of Plasmodium falciparum var Gene Subgroups in a Case-Control Study
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a major pathogenicity factor in falciparum malaria that mediates cytoadherence. PfEMP1 is encoded by ∼60 var genes per haploid genome. Most var genes are grouped into 3 subgroups: A, B, and C. Evidence is emerging that the specific expression of these subgroups has clinical significance. Using field samples from children from Papua New Guinea with severe, mild, and asymptomatic malaria, we compared proportions of transcripts of var groups, as determined by quantitative polymerase chain reaction. We found a significantly higher proportion of var group B transcripts in children with clinical malaria (mild and severe), whereas a large proportion of var group C transcripts was found in asymptomatic children. These data from naturally infected children clearly show that major differences exist in var gene expression between parasites causing clinical disease and those causing asymptomatic infections. Furthermore, parasites forming rosettes showed a significant up-regulation of var group A transcript
Conditional expression of PfAP2-G for controlled massive sexual conversion in Plasmodium falciparum
--- - i: - Plasmodium falciparum content: - "Malaria transmission requires that some asexual parasites convert into sexual forms termed gametocytes. The initial stages of sexual development, including sexually committed schizonts and sexual rings, remain poorly haracterized, mainly because they are morphologically identical to their sexual counterparts and only a small subset of parasites undergo sexual development. Here, we describe a system for controlled sexual conversion in the human
malaria parasite " - ", based on conditional expression of the
PfAP2-G transcription factor. Using this system, ~90 percent of
the parasites converted into sexual forms upon induction,
enabling the characterization of committed and early sexual
stages without further purification. We characterized sexually
committed schizonts and sexual rings at the transcriptomic and
phenotypic levels, which revealed down-regulation of genes
involved in solute transport upon sexual commitment, among other
findings. The new inducible lines will facilitate the study of
early sexual stages at additional levels, including multiomic
characterization and drug susceptibility assays.
Characterization of the accessible genome in the human malaria parasite Plasmodium falciparum
Human malaria is a devastating disease and a major cause of poverty in resource-limited countries. To develop and adapt
within hosts Plasmodium falciparum undergoes drastic switches in
gene expression. To identify regulatory regions in the parasite
genome, we performed genome-wide profiling of chromatin
accessibility in two culture-adapted isogenic subclones at four
developmental stages during the intraerythrocytic cycle by using
the Assay for Transposase-Accessible Chromatin by sequencing
(ATAC-seq). Tn5 transposase hypersensitivity sites (THSSs)
localize preferentially at transcriptional start sites (TSSs).
Chromatin accessibility by ATAC-seq is predictive of active
transcription and of the levels of histone marks H3K9ac and
H3K4me3. Our assay allows the identification of novel regulatory
regions including TSS and enhancer-like elements. We show that
the dynamics in the accessible chromatin profile matches
temporal transcription during development. Motif analysis of
stage-specific ATAC-seq sites predicts the in vivo binding sites
and function of multiple ApiAP2 transcription factors. At last,
the alternative expression states of some clonally variant genes
(CVGs), including eba, phist, var and clag genes, associate with
a differential ATAC-seq signal at their promoters. Altogether,
this study identifies genome-wide regulatory regions likely to
play an essential function in the developmental transitions and
in CVG expression in P. falciparum
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Conditional expression of PfAP2-G for controlled massive sexual conversion in Plasmodium falciparum.
Malaria transmission requires that some asexual parasites convert into sexual forms termed gametocytes. The initial stages of sexual development, including sexually committed schizonts and sexual rings, remain poorly characterized, mainly because they are morphologically identical to their asexual counterparts and only a small subset of parasites undergo sexual development. Here, we describe a system for controlled sexual conversion in the human malaria parasite Plasmodium falciparum, based on conditional expression of the PfAP2-G transcription factor. Using this system, ~90 percent of the parasites converted into sexual forms upon induction, enabling the characterization of committed and early sexual stages without further purification. We characterized sexually committed schizonts and sexual rings at the transcriptomic and phenotypic levels, which revealed down-regulation of genes involved in solute transport upon sexual commitment, among other findings. The new inducible lines will facilitate the study of early sexual stages at additional levels, including multiomic characterization and drug susceptibility assays
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