Plasmodium male gametocyte development and transmission are critically regulated by the two putative deadenylases of the CAF1/CCR4/NOT complex

An axonemal intron splicing program sustains Plasmodium male development

Differentiation of male gametocytes into flagellated fertile male gametes relies on the assembly of axoneme, a major component of male development for mosquito transmission of the malaria parasite. RNA-binding protein (RBP)-mediated post-transcriptional regulation of mRNA plays important roles in eukaryotic sexual development, including the development of female Plasmodium. However, the role of RBP in defining the Plasmodium male transcriptome and its function in male gametogenesis remains incompletely understood. Here, we performed genome-wide screening for gender-specific RBPs and identified an undescribed male-specific RBP gene Rbpm1 in the Plasmodium. RBPm1 is localized in the nucleus of male gametocytes. RBPm1-deficient parasites fail to assemble the axoneme for male gametogenesis and thus mosquito transmission. RBPm1 interacts with the spliceosome E complex and regulates the splicing initiation of certain introns in a group of 26 axonemal genes. RBPm1 deficiency results in intron retention and protein loss of these axonemal genes. Intron deletion restores axonemal protein expression and partially rectifies axonemal defects in RBPm1-null gametocytes. Further splicing assays in both reporter and endogenous genes exhibit stringent recognition of the axonemal introns by RBPm1. The splicing activator RBPm1 and its target introns constitute an axonemal intron splicing program in the post-transcriptional regulation essential for Plasmodium male development.

Ready for renascence in mosquito: The regulation of gene expression in Plasmodium sexual development

Malaria remains one of the most perilous vector-borne infectious diseases for humans globally. Sexual gametocyte represents the exclusive stage at which malaria parasites are transmitted from the vertebrate to the Anopheles host. The feasible and effective approach to prevent malaria transmission is by addressing the sexual developmental processes, that is, gametocytogenesis and gametogenesis. Thus, this review will comprehensively cover advances in the regulation of gene expression surrounding the transmissible stages, including epigenetic, transcriptional, and post-transcriptional control.

Global Release of Translational Repression Across Plasmodium's Host-to-Vector Transmission Event

Malaria parasites must be able to respond quickly to changes in their environment, including during their transmission between mammalian hosts and mosquito vectors. Therefore, before transmission, female gametocytes proactively produce and translationally repress mRNAs that encode essential proteins that the zygote requires to establish a new infection. This essential regulatory control requires the orthologues of DDX6 (DOZI), LSM14a (CITH), and ALBA proteins to form a translationally repressive complex in female gametocytes that associates with many of the affected mRNAs. However, while the release of translational repression of individual mRNAs has been documented, the details of the global release of translational repression have not. Moreover, the changes in spatial arrangement and composition of the DOZI/CITH/ALBA complex that contribute to translational control are also not known. Therefore, we have conducted the first quantitative, comparative transcriptomics and DIA-MS proteomics of Plasmodium parasites across the host-to-vector transmission event to document the global release of translational repression. Using female gametocytes and zygotes of P. yoelii, we found that nearly 200 transcripts are released for translation soon after fertilization, including those with essential functions for the zygote. However, we also observed that some transcripts remain repressed beyond this point. In addition, we have used TurboID-based proximity proteomics to interrogate the spatial and compositional changes in the DOZI/CITH/ALBA complex across this transmission event. Consistent with recent models of translational control, proteins that associate with either the 5' or 3' end of mRNAs are in close proximity to one another during translational repression in female gametocytes and then dissociate upon release of repression in zygotes. This observation is cross-validated for several protein colocalizations in female gametocytes via ultrastructure expansion microscopy and structured illumination microscopy. Moreover, DOZI exchanges its interaction from NOT1-G in female gametocytes to the canonical NOT1 in zygotes, providing a model for a trigger for the release of mRNAs from DOZI. Finally, unenriched phosphoproteomics revealed the modification of key translational control proteins in the zygote. Together, these data provide a model for the essential translational control mechanisms used by malaria parasites to promote their efficient transmission from their mammalian host to their mosquito vector.

Mast cell-derived IL-10 protects intestinal barrier integrity during malaria in mice and regulates parasite transmission to Anopheles stephensi with a female-biased immune response

Malaria is strongly predisposed to bacteremia, which is associated with increased gastrointestinal permeability and a poor clinical prognosis. We previously identified mast cells (MCs) as mediators of intestinal permeability in malaria and described multiple cytokines that rise with parasitemia, including interleukin (IL)-10, which could protect the host from an inflammatory response and alter parasite transmission to Anopheles mosquitoes. Here, we used the Cre-loxP system and non-lethal Plasmodium yoelii yoelii 17XNL to study the roles of MC-derived IL-10 in malaria immunity and transmission. Our data suggest a sex-biased and local inflammatory response mediated by MC-derived IL-10, supported by early increased number and activation of MCs in females relative to males. Increased parasitemia in female MC IL-10 (-) mice was associated with increased ileal levels of chemokines and plasma myeloperoxidase (MPO). We also observed increased intestinal permeability in female and male MC IL-10 (-) mice relative to MC IL-10 (+) mice but no differences in blood bacterial 16S DNA levels. Transmission success of P. yoelii to A. stephensi was higher in female relative to male mice and from female and male MC IL-10 (-) mice relative to MC IL-10 (+) mice. These patterns were associated with increased plasma levels of pro-inflammatory cytokines in female MC IL-10 (-) mice and increased plasma levels of chemokines and markers of neutrophil activation in male MC IL-10 (-) mice. Overall, these data suggest that MC-derived IL-10 protects intestinal barrier integrity, regulates parasite transmission, and controls local and systemic host immune responses during malaria, with a female bias.

The Plasmodium falciparum CCCH zinc finger protein MD3 regulates male gametocytogenesis through its interaction with RNA-binding proteins

The transmission of malaria parasites to mosquitoes is dependent on the formation of gametocytes. Once fully matured, gametocytes are able to transform into gametes in the mosquito's midgut, a process accompanied with their egress from the enveloping erythrocyte. Gametocyte maturation and gametogenesis require a well-coordinated gene expression program that involves a wide spectrum of regulatory proteins, ranging from histone modifiers to transcription factors to RNA-binding proteins. Here, we investigated the role of the CCCH zinc finger protein MD3 in Plasmodium falciparum gametocytogenesis. MD3 was originally identified as an epigenetically regulated protein of immature gametocytes and recently shown to be involved in male development in a barcode-based screen in P. berghei. We report that MD3 is mainly present in the cytoplasm of immature male P. falciparum gametocytes. Parasites deficient of MD3 are impaired in gametocyte maturation and male gametocytogenesis. BioID analysis in combination with co-immunoprecipitation assays unveiled an interaction network of MD3 with RNA-binding proteins like PABP1 and ALBA3, with translational initiators, regulators and repressors like elF4G, PUF1, NOT1 and CITH, and with further regulators of gametocytogenesis, including ZNF4, MD1 and GD1. We conclude that MD3 is part of a regulator complex crucial for post-transcriptional fine-tuning of male gametocytogenesis.

Roles of the CCR4-Not complex in translation and dynamics of co-translation events

The Ccr4-Not complex is a global regulator of mRNA metabolism in eukaryotic cells that is most well-known to repress gene expression. Delivery of the complex to mRNAs through a multitude of distinct mechanisms accelerates their decay, yet Ccr4-Not also plays an important role in co-translational processes, such as co-translational association of proteins and delivery of translating mRNAs to organelles. The recent structure of Not5 interacting with the translated ribosome has brought to light that embedded information within the codon sequence can be monitored by recruitment of the Ccr4-Not complex to elongating ribosomes. Thereby, the Ccr4-Not complex is empowered with regulatory decisions determining the fate of proteins being synthesized and their encoding mRNAs. This review will focus on the roles of the complex in translation and dynamics of co-translation events. This article is categorized under: Translation > Mechanisms Translation > Regulation.

Phenotypic Screens Identify Genetic Factors Associated with Gametocyte Development in the Human Malaria Parasite Plasmodium falciparum

Transmission of the deadly malaria parasite Plasmodium falciparum from humans to mosquitoes is achieved by specialized intraerythrocytic sexual forms called gametocytes. Though the crucial regulatory mechanisms leading to gametocyte commitment have recently come to light, networks of genes that control sexual development remain to be elucidated. Here, we report a pooled-mutant screen to identify genes associated with gametocyte development in P. falciparum. Our results categorized genes that modulate gametocyte progression as hypoproducers or hyperproducers of gametocytes, and the in-depth analysis of individual clones confirmed phenotypes in sexual commitment rates and putative functions in gametocyte development. We present a new set of genes that have not been implicated in gametocytogenesis before and demonstrate the potential of forward genetic screens in isolating genes impacting parasite sexual biology, an exciting step toward the discovery of new antimalarials for a globally significant pathogen. IMPORTANCE Blocking human-to-vector transmission is an essential step toward malaria elimination. Gametocytes are solely responsible for achieving this transmission and represent an opportunity for therapeutic intervention. While these falciform-shaped parasite stages were first discovered in the 1880s, our understanding of the genetic determinants responsible for their formation and molecular mechanisms that drive their development is limited. In this work, we developed a scalable screening methodology with piggyBac mutants to identify genes that influence the development of gametocytes in the most lethal human malaria parasite, P. falciparum. By doing so, we lay the foundation for large-scale functional genomic studies specifically designed to address remaining questions about sexual commitment, maturation, and mosquito infection in P. falciparum. Such functional genetic screens will serve to expedite the identification of essential pathways and processes for the development of novel transmission-blocking agents.

The troubled puberty of malaria parasites

Sexual differentiation of malaria parasites is essential for transmission, yet the underlying mechanisms are poorly understood. Russell et al. elegantly combined a loss-of-function screen with single-cell RNA-sequencing to identify key factors in this process. Gomes et al. further characterized one of them, MD1, as a regulator contributing to male fate determination.

Identification of basal complex protein that is essential for maturation of transmission-stage malaria parasites

Malaria remains a global driver of morbidity and mortality. To generate new antimalarials, one must elucidate the fundamental cell biology of Plasmodium falciparum, the parasite responsible for the deadliest cases of malaria. A membranous and proteinaceous scaffold called the inner membrane complex (IMC) supports the parasite during morphological changes, including segmentation of daughter cells during asexual replication and formation of transmission-stage gametocytes. The basal complex lines the edge of the IMC during segmentation and likely facilitates IMC expansion. It is unknown, however, what drives IMC expansion during gametocytogenesis. We describe the discovery of a basal complex protein, PfBLEB, which we find to be essential for gametocytogenesis. Parasites lacking PfBLEB harbor defects in IMC expansion and are unable to form mature gametocytes. This article demonstrates a role for a basal complex protein outside of asexual division, and, importantly, highlights a potential molecular target for the ablation of malaria transmission.

Adapt or Die: Targeting Unique Transmission-Stage Biology for Malaria Elimination

Plasmodium parasites have a complex life cycle that includes development in the human host as well as the Anopheles vector. Successful transmission of the parasite between its host and vector therefore requires the parasite to balance its investments in asexual replication and sexual reproduction, varying the frequency of sexual commitment to persist within the human host and generate future opportunities for transmission. The transmission window is extended further by the ability of stage V gametocytes to circulate in peripheral blood for weeks, whereas immature stage I to IV gametocytes sequester in the bone marrow and spleen until final maturation. Due to the low gametocyte numbers in blood circulation and with the ease of targeting such life cycle bottlenecks, transmission represents an efficient target for therapeutic intervention. The biological process of Plasmodium transmission is a multistage, multifaceted process and the past decade has seen a much deeper understanding of the molecular mechanisms and regulators involved. Clearly, specific and divergent processes are used during transmission compared to asexual proliferation, which both poses challenges but also opportunities for discovery of transmission-blocking antimalarials. This review therefore presents an update of our molecular understanding of gametocyte and gamete biology as well as the status of transmission-blocking activities of current antimalarials and lead development compounds. By defining the biological components associated with transmission, considerations for the development of new transmission-blocking drugs to target such untapped but unique biology is suggested as an important, main driver for transmission-blocking drug discovery.

Standard Selection Treatments with Sulfadiazine Limit Plasmodium yoelii Host-to-Vector Transmission

Some antimalarial drugs that have lost clinical usefulness have been repurposed for experimental applications. One example is sulfadiazine, an analog of p-aminobenzoic acid (pABA), which inhibits the parasite's folate synthesis pathway to block DNA synthesis. Sulfadiazine treatment of mice infected with Plasmodium yoelii and P. berghei is routinely used to enrich for gametocytes by killing asexual blood-stage parasites, but it is not well known if there are downstream effects on transmission. To determine if there was a significant effect of sulfadiazine exposure upon transmission, we transmitted Plasmodium yoelii (17XNL strain) parasites to Anopheles stephensi mosquitoes and evaluated the prevalence and intensity of infection under different sulfadiazine treatment conditions. We observed that there was a reduction in both the number of mosquitoes that became infected and in the intensity of infection if parasites were exposed to sulfadiazine in the mouse host or mosquito vector. Sulfadiazine treatment could be marginally overcome if mosquitoes were provided fresh pABA. In contrast, we determined that gametocytes exposed to sulfadiazine could develop into morphologically mature ookinetes in vitro, thus sulfadiazine exposure in the host may be reversible if the drug is washed out and the parasites are supplemented with pABA in the culture media. Overall, this indicates that sulfadiazine dampens host-to-vector transmission and that this inhibition can only be partially overcome by exposure to fresh pABA in vivo and in vitro. Because gametocytes are of great interest for developing transmission-blocking interventions, we recommend the use of less disruptive approaches for gametocyte enrichment. IMPORTANCE In this work, we have uncovered a substantial problem with how many studies of the sexual stages of rodent malaria parasites are conducted. Briefly, the isolation of sexual blood-stage Plasmodium parasites, or gametocytes, is essential to study pretransmission and transmission-stage biology of malaria. A routine method for the isolation of this specific stage in rodent-infectious malaria models is drug treatment with sulfadiazine, an antifolate that selectively kills actively replicating asexual blood-stage parasites but not gametocytes. Thus, researchers use this as a convenient way to produce highly enriched gametocyte samples. However, in this work, we describe how this standard drug selection with sulfadiazine not only kills asexual blood-stage parasites but also substantially impacts host-to-vector transmission.

New insights into the evolution of CAF1 family and utilization of TaCAF1Ia1 specificity to reveal the origin of the maternal progenitor for common wheat

INTRODUCTION

Until now, the most likely direct maternal progenitor (AABB) for common wheat (AABBDD) has yet to be identified. Here, we try to solve this particular problem with the specificity of a novel gene family in wheat and by using large population of rare germplasm resources.

OBJECTIVES

Dissect the novelty of TaCAF1Ia subfamily in wheat. Exploit the conservative and specific characteristics of TaCAF1Ia1 to reveal the origin of the maternal progenitor for common wheat.

METHODS

Phylogenetic and collinear analysis of TaCAF1 genes were performed to identify the evolutionary specificity of TaCAF1Ia subfamily. The large-scale expression patterns and interaction patterns analysis of CCR4-NOT complex were used to clarify the expressed and structural specificity of TaCAF1Ia subfamily in wheat. The population resequencing and phylogeny analysis of the TaCAF1Ia1 were utilized for the traceability analysis to understand gene-pool exchanges during the transferring and subsequent development from tetraploid to hexaploidy wheat.

RESULTS

TaCAF1Ia is a novel non-typical CAF1 subfamily without DEDD (Asp-Glu-Asp-Asp) domain, whose members were extensively duplicated in wheat genome. The replication events had started and constantly evolved from ancestor species. Specifically, it was found that a key member CAF1Ia1 was highly specialized and only existed in the subB genome and S genome. Unlike CAF1s reported in other plants, TaCAF1Ia genes may be new factors for anther development. These atypical TaCAF1s could also form CCR4-NOT complex in wheat but with new interaction sites. Utilizing the particular but conserved characteristics of the TaCAF1Ia1 gene, the comparative analysis of haplotypes composition for TaCAF1Ia1 were identified among wheat populations with different ploidy levels. Based on this, the dual-lineages origin model of maternal progenitor for common wheat and potential three-lineages domestication model for cultivated tetraploid wheat were proposed.

CONCLUSION

This study brings fresh insights for revealing the origin of wheat and the function of CAF1 in plants.

A transcriptional switch controls sex determination in Plasmodium falciparum

Sexual reproduction and meiotic sex are deeply rooted in the eukaryotic tree of life, but mechanisms determining sex or mating types are extremely varied and are only well characterized in a few model organisms¹. In malaria parasites, sexual reproduction coincides with transmission to the vector host. Sex determination is non-genetic, with each haploid parasite capable of producing either a male or a female gametocyte in the human host². The hierarchy of events and molecular mechanisms that trigger sex determination and maintenance of sexual identity are yet to be elucidated. Here we show that the male development 1 (md1) gene is both necessary and sufficient for male fate determination in the human malaria parasite Plasmodium falciparum. We show that Md1 has a dual function stemming from two separate domains: in sex determination through its N terminus and in male development from its conserved C-terminal LOTUS/OST-HTH domain. We further identify a bistable switch at the md1 locus, which is coupled with sex determination and ensures that the male-determining gene is not expressed in the female lineage. We describe one of only a few known non-genetic mechanisms of sex determination in a eukaryote and highlight Md1 as a potential target for interventions that block malaria transmission.

Analysis of pir gene expression across the Plasmodium life cycle

Background

Plasmodium interspersed repeat (pir) is the largest multigene family in the genomes of most Plasmodium species. A variety of functions for the PIR proteins which they encode have been proposed, including antigenic variation, immune evasion, sequestration and rosetting. However, direct evidence for these is lacking. The repetitive nature of the family has made it difficult to determine function experimentally. However, there has been some success in using gene expression studies to suggest roles for some members in virulence and chronic infection.

Methods

Here pir gene expression was examined across the life cycle of Plasmodium berghei using publicly available RNAseq data-sets, and at high resolution in the intraerythrocytic development cycle using new data from Plasmodium chabaudi.

Results

Expression of pir genes is greatest in stages of the parasite which invade and reside in red blood cells. The marked exception is that liver merozoites and male gametocytes produce a very large number of pir gene transcripts, notably compared to female gametocytes, which produce relatively few. Within the asexual blood stages different subfamilies peak at different times, suggesting further functional distinctions. Representing a subfamily of its own, the highly conserved ancestral pir gene warrants further investigation due to its potential tractability for functional investigation. It is highly transcribed in multiple life cycle stages and across most studied Plasmodium species and thus is likely to play an important role in parasite biology.

Conclusions

The identification of distinct expression patterns for different pir genes and subfamilies is likely to provide a basis for the design of future experiments to uncover their function.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03979-6.

The Plasmodium NOT1-G paralogue is an essential regulator of sexual stage maturation and parasite transmission

Productive transmission of malaria parasites hinges upon the execution of key transcriptional and posttranscriptional regulatory events. While much is now known about how specific transcription factors activate or repress sexual commitment programs, far less is known about the production of a preferred mRNA homeostasis following commitment and through the host-to-vector transmission event. Here, we show that in Plasmodium parasites, the NOT1 scaffold protein of the CAF1/CCR4/Not complex is duplicated, and one paralogue is dedicated for essential transmission functions. Moreover, this NOT1-G paralogue is central to the sex-specific functions previously associated with its interacting partners, as deletion of not1-g in Plasmodium yoelii leads to a comparable or complete arrest phenotype for both male and female parasites. We show that, consistent with its role in other eukaryotes, PyNOT1-G localizes to cytosolic puncta throughout much of the Plasmodium life cycle. PyNOT1-G is essential to both the complete maturation of male gametes and to the continued development of the fertilized zygote originating from female parasites. Comparative transcriptomics of wild-type and pynot1-g⁻ parasites shows that loss of PyNOT1-G leads to transcript dysregulation preceding and during gametocytogenesis and shows that PyNOT1-G acts to preserve mRNAs that are critical to sexual and early mosquito stage development. Finally, we demonstrate that the tristetraprolin (TTP)-binding domain, which acts as the typical organization platform for RNA decay (TTP) and RNA preservation (ELAV/HuR) factors is dispensable for PyNOT1-G’s essential blood stage functions but impacts host-to-vector transmission. Together, we conclude that a NOT1-G paralogue in Plasmodium fulfills the complex transmission requirements of both male and female parasites.

Malaria parasites face two bottlenecks in their life cycle: their two transmission events. This study shows that Plasmodium has taken the unorthodox approach of duplicating the gene for the NOT1 RNA regulatory scaffold protein, allowing it to dedicate one paralog to functions that are essential for transmission from mammalian hosts to the mosquito vector.

Mechanisms of triggering malaria gametocytogenesis by AP2-G

The transcription factor (TF) AP2-G is essential for gametocytogenesis in the malaria parasite; however, it remains unclear if AP2-G determines commitment to sexual stage development fate in the schizont stage, or whether AP2-G directly initiates sexual stage differentiation and development beginning in the late-trophozoite stage. In this study, we addressed this issue by investigating the expression profile of AP2-G and determining genome-wide target genes in Plasmodium berghei. Fluorescence microscopy showed that AP2-G expression was first observed in the parasite 12 h after erythrocyte invasion and peaked at 18 h when sexual features were first manifested in early gametocytes. Expression of AP2-G decreased with manifestation of sex-specific features. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) was performed at peak AP2-G expression and identified over 1000 binding sites in the genome. The main binding motif of the TF predicted from the binding sites was GTACNY. Predicted targets contained a number of genes related to protein biogenesis, suggesting that AP2-G plays a role in establishing a cellular basis required for sexual differentiation. AP2-G binding sites also existed upstream of gametocyte-specific TFs, namely AP2-G2, AP2-FG, and AP2-G itself. Furthermore, the target contained two AP2 TF-related genes. Disruption of these genes resulted in the arrest of ookinete development. These results suggest another role of AP2-G: activating a transcriptional cascade to promote conversion into early gametocytes. Taken together, AP2-G is involved not in establishing sexual commitment of schizonts, but rather in triggering the initiation of differentiation and the early development of gametocytes in the late trophozoite stage.

Genome-Wide and Comprehensive Analysis of the Multiple Stress-Related CAF1 (CCR4-Associated Factor 1) Family and Its Expression in Poplar

Poplar is one of the most widely used tree in afforestation projects. However, it is susceptible to abiotic and biotic stress. CCR4-associated factor 1 (CAF1) is a major member of CCR4-NOT, and it is mainly involved in transcriptional regulation and mRNA degradation in eukaryotes. However, there are no studies on the molecular phylogeny and expression of the CAF1 gene in poplar. In this study, a total of 19 PtCAF1 genes were identified in the Populus trichocarpa genome. Phylogenetic analysis of the PtCAF1 gene family was performed with two closely related species (Arabidopsis thaliana and Oryza sativa) to investigate the evolution of the PtCAF1 gene. The tissue expression of the PtCAF1 gene showed that 19 PtCAF1 genes were present in different tissues of poplar. Additionally, the analysis of the expression of the PtCAF1 gene showed that the CAF1 family was up-regulated to various degrees under biotic and abiotic stresses and participated in the poplar stress response. The results of our study provide a deeper understanding of the structure and function of the PtCAF1 gene and may contribute to our understanding of the molecular basis of stress tolerance in poplar.

Metabolic Survival Adaptations of Plasmodium falciparum Exposed to Sublethal Doses of Fosmidomycin

The malaria parasite Plasmodium falciparum contains the apicoplast organelle that synthesizes isoprenoids, which are metabolites necessary for posttranslational modification of Plasmodium proteins. We used fosmidomycin, an antibiotic that inhibits isoprenoid biosynthesis, to identify mechanisms that underlie the development of the parasite's adaptation to the drug at sublethal concentrations. We first determined a concentration of fosmidomycin that reduced parasite growth by ∼50% over one intraerythrocytic developmental cycle (IDC). At this dose, we maintained synchronous parasite cultures for one full IDC and collected metabolomic and transcriptomic data at multiple time points to capture global and stage-specific alterations. We integrated the data with a genome-scale metabolic model of P. falciparum to characterize the metabolic adaptations of the parasite in response to fosmidomycin treatment. Our simulations showed that, in treated parasites, the synthesis of purine-based nucleotides increased, whereas the synthesis of phosphatidylcholine during the trophozoite and schizont stages decreased. Specifically, the increased polyamine synthesis led to increased nucleotide synthesis, while the reduced methyl-group cycling led to reduced phospholipid synthesis and methyltransferase activities. These results indicate that fosmidomycin-treated parasites compensate for the loss of prenylation modifications by directly altering processes that affect nucleotide synthesis and ribosomal biogenesis to control the rate of RNA translation during the IDC. This also suggests that combination therapies with antibiotics that target the compensatory response of the parasite, such as nucleotide synthesis or ribosomal biogenesis, may be more effective than treating the parasite with fosmidomycin alone.

Definition of constitutive and stage-enriched promoters in the rodent malaria parasite, Plasmodium yoelii

Background

Well-defined promoters are essential elements for genetic studies in all organisms, and enable controlled expression of endogenous genes, transgene expression, and gene editing. Despite this, there is a paucity of defined promoters for the rodent-infectious malaria parasites. This is especially true for Plasmodium yoelii, which is often used to study the mosquito and liver stages of malarial infection, as well as host immune responses to infection.

Methods

Here six promoters were selected from across the parasite’s life cycle (clag-a, dynein heavy chain delta, lap4, trap, uis4, lisp2) that have been invoked in the literature as controlling their genes in a stage-specific manner. A minimal promoter length for the constitutive pybip promoter that confers strong expression levels was also determined, which is useful for expression of reporters and gene editing enzymes.

Results

Instead, it was observed that these promoters confer stage-enriched gene control, as some parasites also effectively use these promoters in other stages. Thus, when used alone, these promoters could complicate the interpretation of results obtained from promoter swaps, stage-targeted recombination, or gene editing experiments.

Conclusions

Together these data indicate that achieving stage-specific effects, such as gene editing, is likely best done using a two-component system with independent promoter activities overlapping only in the intended life cycle stage.

The molecular machinery of translational control in malaria parasites

Translational control regulates the levels of protein synthesized from its transcript and is key for the rapid adjustment of gene expression in response to environmental stimuli. The regulation of translation is of special importance for malaria parasites, which pass through a complex life cycle that includes various replication phases in the different organs of the human and mosquito hosts and a sexual reproduction phase in the mosquito midgut. In particular, the quiescent transmission stages rely on translational control to rapidly adapt to the new environment, once they switch over from the human to the mosquito and vice versa. Three control mechanisms are currently proposed in Plasmodium, (1) global regulation that acts on the translation initiation complex; (2) mRNA-specific regulation, involving cis control elements, mRNA-binding proteins and translational repressors; and (3) induced mRNA decay by the Ccr4-Not and the RNA exosome complex. The main molecules controlling translation are highly conserved in malaria parasites and an increasing number of studies shed light on the interwoven pathways leading to the up or downregulation of protein synthesis in the diverse plasmodial stages. We here highlight recent findings on translational control during life cycle progression of Plasmodium and discuss the molecules involved in regulating protein synthesis.

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. 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.