68 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
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
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
Artemisinin exposure at the ring or trophozoite stage impacts <i>Plasmodium falciparum</i> sexual conversion differently.
--- - Malaria transmission is dependent on the formation of
gametocytes in the human blood. The sexual conversion rate, the
proportion of asexual parasites that convert into gametocytes at
each multiplication cycle, is variable and reflects the relative
parasite investment between transmission and maintaining the
infection. The impact of environmental factors such as drugs on
sexual conversion rates is not well understood. We developed a
robust assay using gametocyte-reporter parasite lines to
accurately measure the impact of drugs on sexual conversion
rates, independently from their gametocytocidal activity. We
found that exposure to subcurative doses of the frontline
antimalarial drug dihydroartemisinin (DHA) at the trophozoite
stage resulted in a ~ fourfold increase in sexual conversion. In
contrast, no increase was observed when ring stages were exposed
or in cultures in which sexual conversion was stimulated by
choline depletion. Our results reveal a complex relationship
between antimalarial drugs and sexual conversion, with potential
public health implications
Revisiting the initial steps of sexual development in the malaria parasite Plasmodium falciparum
Human to vector transmission of malaria requires that
some blood-stage parasites abandon asexual growth and convert
into non-replicating sexual forms called gametocytes. The
initial steps of gametocytogenesis remain largely
uncharacterized. Here, we study this part of the malaria life
cycle in Plasmodium falciparum using PfAP2-G, the master
regulator of sexual conversion, as a marker of commitment. We
demonstrate the existence of PfAP2-G-positive sexually committed
parasite stages that precede the previously known committed
schizont stage. We also found that sexual conversion can occur
by two different routes: the previously described route in which
PfAP2-G-expressing parasites complete a replicative cycle as
committed forms before converting into gametocytes upon
re-invasion, or a direct route with conversion within the same
cycle as initial PfAP2-G expression. The latter route is linked
to early PfAP2-G expression in ring stages. Reanalysis of
published single-cell RNA-sequencing (RNA-seq) data confirmed
the presence of both routes. Consistent with these results,
using plaque assays we observed that, in contrast to the
prevailing model, many schizonts produced mixed plaques
containing both asexual parasites and gametocytes. Altogether,
our results reveal unexpected features of the initial steps of
sexual development and extend the current view of this part of
the malaria life cycle
Reporter lines based on the gexp02 promoter enable early quantification of sexual conversion rates in the malaria parasite Plasmodium falciparum
Transmission of malaria parasites from humans to mosquito
vectors requires that some asexual parasites differentiate into
sexual forms termed gametocytes. The balance between
proliferation in the same host and conversion into transmission
forms can be altered by the conditions of the environment. The
ability to accurately measure the rate of sexual conversion
under different conditions is essential for research addressing
the mechanisms underlying sexual conversion, and to assess the
impact of environmental factors. Here we describe new Plasmodium
falciparum transgenic lines with genome-integrated constructs in
which a fluorescent reporter is expressed under the control of
the promoter of the gexp02 gene. Using these parasite lines, we
developed a sexual conversion assay that shortens considerably
the time needed for an accurate determination of sexual
conversion rates, and dispenses the need to add chemicals to
inhibit parasite replication. Furthermore, we demonstrate that
gexp02 is expressed specifically in sexual parasites, with
expression starting as early as the sexual ring stage, which
makes it a candidate marker for circulating sexual rings in
epidemiological studies
Computing discrete logarithms in cryptographically-interesting characteristic-three finite fields
Since 2013 there have been several developments in algorithms for
computing discrete logarithms in small-characteristic finite fields,
culminating in a quasi-polynomial algorithm. In this paper, we
report on our successful computation of discrete logarithms in the
cryptographically-interesting characteristic-three finite field
using these new algorithms; prior to 2013, it was believed that this field enjoyed a security level of 128 bits. We also show that a recent
idea of Guillevic can be used to compute discrete logarithms in
the cryptographically-interesting finite field using essentially
the same resources as we expended on the computation. Finally,
we argue that discrete logarithms in the finite field can
feasibly be computed today; this is significant because this
cryptographically-interesting field was previously believed to
enjoy a security level of 192 bits
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