The genomes of malaria parasites contain many genes of unknown function. To assist drug development through the identification of essential genes and pathways, we have measured competitive growth ...rates in mice of 2,578 barcoded Plasmodium berghei knockout mutants, representing >50% of the genome, and created a phenotype database. At a single stage of its complex life cycle, P. berghei requires two-thirds of genes for optimal growth, the highest proportion reported from any organism and a probable consequence of functional optimization necessitated by genomic reductions during the evolution of parasitism. In contrast, extreme functional redundancy has evolved among expanded gene families operating at the parasite-host interface. The level of genetic redundancy in a single-celled organism may thus reflect the degree of environmental variation it experiences. In the case of Plasmodium parasites, this helps rationalize both the relative successes of drugs and the greater difficulty of making an effective vaccine.
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•Two-thirds of Plasmodium berghei genes contribute to normal blood stage growth•The core genome of malaria parasites is highly optimized for rapid host colonization•Essential parasite genes and pathways are identified for drug target prioritization•Low functional redundancy reflects the constant environment encountered by a parasite
An in vivo genetic screen in a mouse model of malaria reveals the essential genes and pathways required by Plasmodium parasite, with a surprising two-thirds of the genome being required for normal parasite growth in the blood.
The packaging, expression, and maintenance of nuclear genomes using histone proteins is a ubiquitous and fundamental feature of eukaryotic cells, yet the phylum Dinoflagellata has apparently ...abandoned this model of nuclear organization. Their nuclei contain permanently condensed, liquid crystalline chromosomes that seemingly lack histone proteins, and contain remarkably large genomes. The molecular basis for this reorganization is poorly understood, as is the sequence of evolutionary events that led to such radical change. We have investigated nuclear organization in the closest relative to dinoflagellates, Perkinsus marinus, and an early-branching dinoflagellate, Hematodinium sp., to identify early changes that occurred during dinoflagellate nuclear evolution.
We show that P. marinus has a typical nuclear organization that is based on the four core histones. By the early divergence of Hematodinium sp., however, dinoflagellate genome size is dramatically enlarged, chromosomes are permanently condensed, and histones are scarcely detectable. In place of histones, we identify a novel, dominant family of nuclear proteins that is only found in dinoflagellates and, surprisingly, in a family of large algal viruses, the Phycodnaviridae. These new proteins, which we call DVNPs (dinoflagellate/viral nucleoproteins), are highly basic, bind DNA with similar affinity to histones, and occur in multiple posttranslationally modified forms. We find these proteins throughout all dinoflagellates, including early- and late-branching taxa, but not in P. marinus.
Gain of a major novel family of nucleoproteins, apparently from an algal virus, occurred early in dinoflagellate evolution and coincides with rapid and dramatic reorganization of the dinoflagellate nucleus.
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► Novel dominant DNA-binding protein DVNP was gained early in dinoflagellate evolution ► DVNP was likely gained by a lateral gene transfer from an algal virus ► Dinoflagellates containing DVNP have lost nucleosomal bulk packing of their DNA ► Histone proteins are highly divergent and very lowly expressed in dinoflagellates
In recent years, various intervention strategies have reduced malaria morbidity and mortality, but further improvements probably depend upon development of a broadly protective vaccine. To better ...understand immune requirement for protection, we examined liver-stage immunity after vaccination with irradiated sporozoites, an effective though logistically difficult vaccine. We identified a population of memory CD8+ T cells that expressed the gene signature of tissue-resident memory T (Trm) cells and remained permanently within the liver, where they patrolled the sinusoids. Exploring the requirements for liver Trm cell induction, we showed that by combining dendritic cell-targeted priming with liver inflammation and antigen recognition on hepatocytes, high frequencies of Trm cells could be induced and these cells were essential for protection against malaria sporozoite challenge. Our study highlights the immune potential of liver Trm cells and provides approaches for their selective transfer, expansion, or depletion, which may be harnessed to control liver infections or autoimmunity.
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•CD8+ tissue-resident memory T cells (Trm cells) can be found in the murine liver•These liver Trm cells survey the liver from within the sinusoids•A prime-and-trap vaccination strategy efficiently induces liver Trm cells•Liver Trm cells are essential for protection against liver-stage malaria after vaccination
While various intervention strategies have reduced morbidity and mortality from malaria, further improvement is likely to depend on an effective vaccine. Fernandez-Ruiz et al. identify liver-resident memory CD8+ T cells as vital for liver-stage immunity and describe a protective vaccination strategy that drives their formation.
The clinical symptoms of malaria are caused by the asexual replication of Plasmodium parasites in the blood of the vertebrate host. To spread to new hosts, however, the malaria parasite must ...differentiate into sexual forms, termed gametocytes, which are ingested by a mosquito vector. Sexual differentiation produces either female or male gametocytes, and involves significant morphological and biochemical changes. These transformations prepare gametocytes for the rapid progression to gamete formation and fertilisation, which occur within 20 min of ingestion. Here we present the transcriptomes of asexual, female, and male gametocytes in P. berghei, and a comprehensive statistically-based differential-expression analysis of the transcriptional changes that underpin this sexual differentiation.
RNA-seq analysis revealed numerous differences in the transcriptomes of female and male gametocytes compared to asexual stages. Overall, there is net downregulation of transcripts in gametocytes compared to asexual stages, with this trend more marked in female gametocytes. Our analysis identified transcriptional changes in previously-characterised gametocyte-specific pathways, which validated our approach. We also detected many previously-unreported female- and male-specific pathways and genes. Transcriptional biases in stage and gender were then used to investigate sex-specificity and sexual dimorphism of Plasmodium in an evolutionary context. Sex-related gene expression is well conserved between Plasmodium species, but relatively poorly conserved in related organisms outside this genus. This pattern of conservation is most evident in genes necessary for both male and female gametocyte formation. However, this trend is less pronounced for male-specific genes, which are more highly conserved outside the genus than genes specific to female development.
We characterised the transcriptional changes that are integral to the development of the female and male sexual forms of Plasmodium. These differential-expression patterns provide a vital insight into understanding the gender-specific characteristics of this essential stage that is the primary target for treatments that block parasite transmission. Our results also offer insight into the evolution of sex genes through Alveolata, and suggest that many Plasmodium sex genes evolved within the genus. We further hypothesise that male gametocytes co-opted pre-existing cellular machinery in their evolutionary history, whereas female gametocytes evolved more through the development of novel, parasite-specific pathways.
Plastid evolution Gould, Sven B; Waller, Ross F; McFadden, Geoffrey I
Annual review of plant biology,
01/2008, Letnik:
59
Journal Article
Recenzirano
The ancestors of modern cyanobacteria invented O(2)-generating photosynthesis some 3.6 billion years ago. The conversion of water and CO(2) into energy-rich sugars and O(2) slowly transformed the ...planet, eventually creating the biosphere as we know it today. Eukaryotes didn't invent photosynthesis; they co-opted it from prokaryotes by engulfing and stably integrating a photoautotrophic prokaryote in a process known as primary endosymbiosis. After approximately a billion of years of coevolution, the eukaryotic host and its endosymbiont have achieved an extraordinary level of integration and have spawned a bewildering array of primary producers that now underpin life on land and in the water. No partnership has been more important to life on earth. Secondary endosymbioses have created additional autotrophic eukaryotic lineages that include key organisms in the marine environment. Some of these organisms have subsequently reverted to heterotrophic lifestyles, becoming significant pathogens, microscopic predators, and consumers. We review the origins, integration, and functions of the different plastid types with special emphasis on their biochemical abilities, transfer of genes to the host, and the back supply of proteins to the endosymbiont.
Rapid emergence of resistance to atovaquone, which targets electron transport in the malaria parasite mitochondrion, relegated its use to prophylaxis and even cast a shadow over the development of ...drugs targeting other parasite mitochondrial pathways. Here we argue for a renewed focus on the mitochondrion as a drug target, focusing particularly on the issues of resistance. We posit a hypothesis for why atovaquone resistance emerges so quickly, and we explain how facile acquisition of resistance is apparently offset by an inability of parasites to spread this resistance. We also explore the utility and resistance issues for emerging new drugs targeting parasite mitochondria, concluding that the mitochondrion is indeed an excellent target.
Highlights • Toxoplasma and Plasmodium possess two organelles of endosymbiotic origin: the apicoplast, and the mitochondrion. • The mitochondrion hosts a complete TCA cycle and an electron transport ...chain lacking complex I. Glutamine catabolism contributes to the TCA cycle. • Haem biosynthesis is an extremely unusual chimerical pathway shared between the two organelles and the cytoplasm. • Isoprenoid precursor synthesis and fatty acid synthesis are essential roles of the apicoplast. Different life stages show differential dependencies on these pathways.
Mitochondrial ATP synthase is driven by chemiosmotic oxidation of pyruvate derived from glycolysis. Blood-stage malaria parasites eschew chemiosmosis, instead relying almost solely on glycolysis for ...their ATP generation, which begs the question of whether mitochondrial ATP synthase is necessary during the blood stage of the parasite life cycle. We knocked out the mitochondrial ATP synthase β subunit gene in the rodent malaria parasite, Plasmodium berghei , ablating the protein that converts ADP to ATP. Disruption of the β subunit gene of the ATP synthase only marginally reduced asexual blood-stage parasite growth but completely blocked mouse-to-mouse transmission via Anopheles stephensi mosquitoes. Parasites lacking the β subunit gene of the ATP synthase generated viable gametes that fuse and form ookinetes but cannot progress beyond this stage. Ookinetes lacking the β subunit gene of the ATP synthase had normal motility but were not viable in the mosquito midgut and never made oocysts or sporozoites, thereby abrogating transmission to naive mice via mosquito bite. We crossed the self-infertile ATP synthase β subunit knockout parasites with a male-deficient, self-infertile strain of P. berghei , which restored fertility and production of oocysts and sporozoites, which demonstrates that mitochondrial ATP synthase is essential for ongoing viability through the female, mitochondrion-carrying line of sexual reproduction in P. berghei malaria. Perturbation of ATP synthase completely blocks transmission to the mosquito vector and could potentially be targeted for disease control.
Recent progress in understanding the origins of plastids from endosymbiotic cyanobacteria is reviewed. Establishing when during geological time the endosymbiosis occurred remains elusive, but ...progress has been made in defining the cyanobacterial lineage most closely related to plastids, and some mechanistic insight into the possible existence of cryptic endosymbioses perhaps involving Chlamydia-like infections of the host have also been presented. The phylogenetic affinities of the host remain obscure. The existence of a second lineage of primary plastids in euglyphid amoebae has now been confirmed, but the quasipermanent acquisition of plastids by animals has been shown to be more ephemeral than initially suspected. A new understanding of how plastids have been integrated into their hosts by transfer of photosynthate, by endosymbiotic gene transfer and repatriation of gene products back to the endosymbiont, and by regulation of endosymbiont division is presented in context.
A highly protective vaccine will greatly facilitate achieving and sustaining malaria elimination. Understanding mechanisms of antibody-mediated immunity is crucial for developing vaccines with high ...efficacy. Here, we identify key roles in humoral immunity for Fcγ-receptor (FcγR) interactions and opsonic phagocytosis of sporozoites. We identify a major role for neutrophils in mediating phagocytic clearance of sporozoites in peripheral blood, whereas monocytes contribute a minor role. Antibodies also promote natural killer cell activity. Mechanistically, antibody interactions with FcγRIII appear essential, with FcγRIIa also required for maximum activity. All regions of the circumsporozoite protein are targets of functional antibodies against sporozoites, and N-terminal antibodies have more activity in some assays. Functional antibodies are slowly acquired following natural exposure to malaria, being present among some exposed adults, but uncommon among children. Our findings reveal targets and mechanisms of immunity that could be exploited in vaccine design to maximize efficacy.
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