The intracellular parasite Toxoplasma gondii is a leading cause of congenital neurological defects. To cause disease, it must reiterate its lytic cycle through host cell invasion, replication,and parasite egress. This requires the parasite to sense changes in its environment and switch between the non-motile (for replication) and motile (for invasion and egress) states appropriately. Recently, we discovered a previously unknown mechanism of motility regulation in T. gondii, mediated by a lysine methyltransferase, AKMT (for Apical complex lysine (K) methyltransferase). When AKMT is absent, activation of motility is inhibited, which compromises parasite invasion and egress, and thus severely impairs the lytic cycle. Although the methyltransferase activity of AKMT has been established, the phylogenetic relationship of AKMT with other better studied lysine methyltransferases (KMTs) was not known. Also unknown was the functional relationships between different domains of AKMT. In this work we carried out phylogenetic analyses, which show that AKMT orthologs form a new subfamily of KMTs. We systematically generated truncation mutants of AKMT, and discovered that the predicted enzymatic domain alone is a very poor enzyme and cannot complement the function of AKMT in vivo. Interestingly, the N- and C-terminal domains of the AKMT have drastically different impacts on its enzyme activity, localization as well as in vivo function. Our results thus reveal that AKMT is an unusual, parasite-specific enzyme and identified regions and interactions within this novel lysine methyltransferase that can be used as drug targets.
lysine methyltransferase; AKMT; motility; Toxoplasma gondii; Plasmodium; KMT phylogeny
Malaria, most commonly caused by the parasite Plasmodium falciparum, is a devastating disease that remains a large global health burden. Lack of vaccines and drug resistance necessitate the continual development of new drugs and exploration of new drug targets. Due to their essential role in protein synthesis, aminoacyl-tRNA synthetases are potential anti-malaria drug targets. Here we report the crystal structures of P. falciparum cytosolic tryptophanyl-tRNA synthetase (Pf-cTrpRS) in its ligand-free state and tryptophanyl-adenylate (WAMP)-bound state at 2.34 Å and 2.40 Å resolutions, respectively. Large conformational changes are observed when the ligand-free protein is bound to WAMP. Multiple residues, completely surrounding the active site pocket, collapsed onto WAMP. Comparison of the structures to those of human cytosolic TrpRS (Hs-cTrpRS) provides information about the possibility of targeting Pf-cTrpRS for inhibitor development. There is a high degree of similarity between Pf-cTrpRS and Hs-cTrpRS within the active site. However, the large motion that Pf-cTrpRS undergoes during transitions between different functional states avails an opportunity to arrive at compounds which selectively perturb the motion, and may provide a starting point for the development of new anti-malaria therapeutics.
Plasmodium falciparum; malaria; tryptophanyl-tRNA synthetase; crystal structure; conformational changes; drug design
In the mosquito, Plasmodium sporozoites rupture from oocysts found on the midgut wall, circulate in the hemolymph and invade salivary glands where they wait to be injected into a vertebrate host during a bloodmeal. The mechanisms by which sporozoites specifically attach to and invade salivary glands are not known but evidence suggests that it is a receptor-mediated process. Here we show that the major surface protein of sporozoites, the circumsporozoite protein (CS), binds preferentially to salivary glands when compared to other organs exposed to the circulating hemolymph. In addition, we show that a peptide encompassing region I, a highly conserved sequence found in all rodent and primate Plasmodium CS proteins, inhibits binding of CS to mosquito salivary glands.
Plasmodium; Malaria; Salivary glands; Circumsporozoite protein; Mosquito; Sporozoite
Steinernema carpocapsae is an insect parasitic nematode widely used in pest control programs. The efficacy of this nematode in controlling insects has been found to be related to the pathogenicity of the infective stage. In order to study the parasitic mechanisms exhibited by this parasite, a cDNA library of the induced S. carpocapsae parasitic phase was generated. A total of 2500 clones were sequenced and 2180 high-quality ESTs were obtained from this library. Cluster analysis generated a total of 1592 unique sequences including 1393 singletons. About 63% of the unique sequences had significant hits (e≤1e-05) to the non-redundant protein database. The remaining sequences most likely represent putative novel protein coding genes. Comparative analysis identified 377 homologs in C. elegans, 431 in C. briggsae and 75 in other nematodes. Classification of the predicted proteins revealed involvement in diverse cellular, metabolic and extracellular functions. One hundred and nineteen clusters were predicted to encode putative secreted proteins such as proteases, proteases inhibitors, lectins, saposin-like proteins, acetyl-cholinesterase, anti-oxidants, and heat-shock proteins, which can possibly have host interactions. This dataset provides a basis for genomic studies towards a better understanding of the events that occur in the parasitic process of this entomopathogenic nematode, including invasion of the insect haemocoelium, adaptations to insect innate immunity and stress responses, and production of virulence factors. The identification of key genes in the parasitic process provides useful tools for the improvement of S. carpocapsae as a biological agent.
Entomopathogenic nematode; Steinernema carpocapsae; EST; Nematode transcripts; Secreted proteins; Virulence factors
PA28γ is a proteasome activator involved in the regulation of the cellular proliferation, differentiation and growth. In the present study, we identified and characterized a cDNA from Schistosoma mansoni exhibiting significant homology to PA28γ of diverse taxa ranging from mammals (including humans) to simple invertebrates. Designated SmPA28γ, this transcript has a 753 bp predicted ORF encoding a protein of 250 amino acid residues. Alignment of SmPA28γ with multiple PA28γ orthologues revealed an average similarity of ~40% among the investigated organisms, and 90% similarity with PA28γ from Schistosoma japonicum. In addition, phylogenetic analysis demonstrated a close linkage between SmPA28γ to its sister group that contains well-characterized PA28γ sequences from Drosophila spp., as well as sharing the same branch with PA28γ from S. japonicum. Gene expression profiling of SmPA28γ using real-time quantitative PCR revealed elevated steady-state transcript levels in the eggs, miracidia and paired adult worms compared to other stages. In parallel with gene expression profiles, an affinity-purified anti-SmPA28γ antibody produced against recombinant protein exhibited strongest reactivity in Western blot analyses to endogenous SmPA28γ from miracidia, sporocysts and paired adult worms. Given its known regulatory function in other organisms, we hypothesized that the high level of SmPA28γ transcript and protein in these stages may be correlated with an important role of the PA28γ in the cellular growth and/or development of this parasite. To address this hypothesis, miracidia were transformed in vitro to sporocysts in the presence of SmPA28γ double-stranded RNAs (dsRNAs) and cultivated for 4 days, after which time steady-state transcript and protein levels, and phenotypic changes were evaluated. SmPA28γ dsRNA treatment resulted in gene and protein knockdown of ~60% and ~80%, respectively, which were correlated with a significant decrease in larval length compared to its controls. These findings are consistent with a putative role of SmPA28γ in larval growth/development of the S. mansoni.
Schistosoma mansoni; proteasome activator; PA28γ subunit; protease; stage-specific expression; molecular phylogeny; RNAi
African trypanosomes differentiate between various developmental stages both in mammalian hosts and their tsetse vector to adapt to and survive in the different environments they encounter. In the bloodstream, trypanosomes naturally exist as either proliferative slender-forms or non-proliferative stumpy-forms, the latter being responsible for both prolonged infection and transmission. However, most trypanosome studies are carried out on laboratory-adapted monomorphic cell lines, incapable of differentiating to stumpy-forms or completing the life cycle through the tsetse fly. Partly, this has been due to the inefficiency of transfection of pleomorphic strains which have retained the ability to generate stumpy-forms. Recently, Amaxa Nucleofector® technology was shown to increase transfection efficiency for monomorphic bloodstream forms. Using this technology we have optimised a similar method for pleomorphic bloodstream form transfection, generating transfection efficiencies of 10−7–10−6. This permits routine genetic manipulation of pleomorphic lines, which have the most biological relevance for trypanosomes in the field.
Trypanosome; Transfection; Pleomorphic; Stumpy; Trypanosoma brucei
StartectR is a novel anthelmintic combination of derquantel and abamectin. It is hypothesized that derquantel and abamectin interact pharmacologically. We investigated the effects of derquantel, abamectin and their combination on somatic muscle nicotinic acetylcholine receptors and pharyngeal muscle glutamate gated chloride receptor channels of Ascaris suum. We used muscle-strips to test the effects of abamectin, derquantel, and abamectin + derquantel together on the contraction responses to different concentrations of acetylcholine. We found that abamectin reduced the response to acetylcholine, as did derquantel. In combination (abamectin + derquantel), inhibition of the higher acetylcholine concentration responses was statistically greater than the predicted additive effect. A two-micropipette current-clamp technique was used to study electrophysiological effects of the anthelmintics on: 1) acetylcholine responses in somatic muscle and; 2) on L-glutamate responses in pharyngeal preparations. On somatic muscle, derquantel (0.1 - 30 μM) produced a potent (IC50 0.22, CI 0.18-0.28 μM) reversible antagonism of acetylcholine depolarizations. Abamectin (0.3 μM) produced a slow onset inhibition of acetylcholine depolarizations. We compared effects of abamectin and derquantel on muscle preparations pretreated for 30 minutes with these drugs. The effect of the combination was significantly greater than the predicted additive effect of both drugs at higher acetylcholine concentrations. On the pharynx, application of derquantel produced no significant effect by itself or on responses to abamectin and L-glutamate. Abamectin increased the input conductance of the pharynx (EC50 0.42, CI 0.13-1.36 μM). Our study demonstrates that abamectin and derquantel interact at nicotinic acetylcholine receptors on the somatic muscle and suggested synergism can occur.
abamectin; derquantel; combination; interaction; nAChRs; GluCls
Current antimalarial drug treatment does not effectively kill mature Plasmodium falciparum gametocytes, the parasite stage responsible for malaria transmission from human to human via a mosquito. Consequently, following standard therapy malaria can still be transmitted for over a week after the clearance of asexual parasites. A new generation of malaria drugs with gametocytocidal properties, or a gametocytocidal drug that could be used in combinational therapy with currently available antimalarials, is needed to control the spread of the disease and facilitate eradication efforts. We have developed a 1,536-well gametocyte viability assay for the high throughput screening of large compound collections to identify novel compounds with gametocytocidal activity. The signal-to-basal ratio and Z′-factor for this assay were 3.2-fold and 0.68, respectively. The IC50 value of epoxomicin, the positive control compound, was 1.42 ± 0.09 nM that is comparable to previously reported values. This miniaturized assay significantly reduces the number of gametocytes required for the alamarBlue viability assay, and enables high throughput screening for lead discovery efforts. Additionally, the screen does not require a specialized parasite line, gametocytes from any strain, including field isolates, can be tested. A pilot screen utilizing the commercially available LOPAC library, consisting of 1,280 known compounds, revealed two selective gametocytocidal compounds having 54 and 7.8-fold gametocytocidal selectivity in comparison to their cell cytotoxicity effect against the mammalian SH-SY5Y cell line.
Malaria; gametocytes; alamarBlue; high throughput screening; malaria drug discovery
Aotus nancymaae, the owl monkey, provides a useful laboratory model for research to develop drugs and vaccines against human falciparum malaria; however, many Plasmodium falciparum parasites are unable to invade A. nancymaae erythrocytes, rendering the parasites noninfective to the monkeys. In previous work, we identified a key polymorphism that determined the inheritance of erythrocyte invasion in a genetic cross of two P. falciparum clones that were virulent (GB4) or noninfective (7G8) to A. nancymaae. This polymorphism, an isoleucine-to-lysine polymorphism at position 204 (I204K) of the GB4 erythrocyte binding protein PfRH5, was nevertheless not found in several other P. falciparum lines that could also invade A. nancymaae erythrocytes. Alternative PfRH5 polymorphisms occur at different positions in these virulent parasites, and additional polymorphisms are found in P. falciparum parasites that cannot infect A. nancymaae. By allelic replacement methods, we have introduced the polymorphisms of these A. nancymaae-virulent or noninfective parasites at codons 204, 347, 358, 362, 410, and 429 of the endogenous PfRH5 gene in the noninfective 7G8 line. 7G8 transformants expressing the polymorphisms of the A. nancymaae-virulent parasites show neuraminidase-sensitive (sialic acid-dependent) invasion into the monkey erythrocytes, whereas 7G8 transformants expressing the PfRH5 alleles of noninfective parasites show little or no invasion of these erythrocytes. Parasites harboring PfRH5 polymorphisms 204K or 204R are also able to invade rat erythrocytes and are differentially sensitive to the removal of surface sialic acids by neuraminidase. These studies offer insights into the PfRH5 receptor-binding domain and interactions that support the invasion of various primate and rodent erythrocytes by P. falciparum.
Malaria; Virulence; Aotus nancymaae; Sialic acid; Rattus norvegicus; Mus musculus
Trypanosomes; RNA interference; TbAGO1; VSG; Life-cycle
Manipulation of gene expression has been used to elucidate gene function, explore fundamental biological processes and to identify potential drug targets in Trypanosoma brucei. We show in bloodstream forms that CDC2-related kinase CRK12 (Tb11.01.4130) is essential since transcriptional inactivation in conditional null mutants is lethal but 19 other protein kinases are not essential since null mutants are viable. We did so using efficient methods for the generation of null and conditional null cell lines of T. brucei by approaches that generate transfection constructs with large targeting sequences and which use reliable transfection and selection conditions. These methods, which are described in detail in the supplementary material, employ multiple oligonucleotides and PCR reactions and several transfections but are cost effective and can simultaneously generate 24 transfectants thus shifting the rate limiting experimental steps from the production of cell lines to their analysis.
Trypanosoma brucei; Protein kinases; Gene knockout; Conditional expression; Fusion PCR Method
In natural populations of the human parasite Schistosoma mansoni, parasite distribution among snail intermediate hosts is generally overdispersed, such that a small proportion of hosts harbor the majority of parasite genotypes. Within these few infected snails, researchers have found that it can be common for hosts to harbor multiple parasite genotypes, creating circumstances in which co-infecting parasites are faced with potential competition over limited host resources. Much theoretical modeling has focused on parasite competition, especially regarding the influence of co-infection on parasite exploitation strategy evolution. However, particularly in the case of intra-molluscan intermediate stages, empirical investigations of parasite-parasite competition have often hinged on the untested assumption that co-exposure produces co-infection. That is, infected hosts exposed to multiple strains have been assumed to harbor multiple strains, regardless of the true nature of the infection outcome. Here we describe a real-time quantitative PCR method to distinguish the conditions of multiple- versus single-strain infection, as well as quantify the relative larval output of co-infecting strains. We applied the method to an empirical investigation of intraspecific parasite competition between S. mansoni strains within the intermediate snail host Biomphalaria glabrata, assessing co-exposure's effects on parasite infectivity and productivity and the concomitant effects on host fitness. Overall, there was no effect of parasite co-infection on snail life history traits relative to single-strain infection. Parasite infectivity significantly increased as a result of increasing overall miracidial dose, rather than co-exposure, though strain-specific productivity was significantly reduced in co-infections in manner consistent with resource competition. Moreover, we show that less than half of infected, co-exposed hosts had patent co-infections and demonstrate the utility of this molecular tool for the study of trematode life history variation in molluscan hosts.
parasite competition; trematodes; snails; real-time quantitative PCR; molecular detection
Clones isolated from a single benznidazole-resistant Trypanosoma cruzi population contain a stop-codon-generating mutation in the nitroreductase gene TcNTR. Clonal variation in resistance suggests that additional mechanisms must also operate.
•Drug-resistance in T. cruzi can arise independently within a single population.•Distinct mechanisms can contribute to benznidazole-resistance in T. cruzi.•Stop-codon generating mutations in the TcNTR gene linked to benznidazole-resistance.
Benznidazole is the main drug used to treat Trypanosoma cruzi infections. However, frequent instances of treatment failure have been reported. To better understand potential resistance mechanisms, we analysed three clones isolated from a single parasite population that had undergone benznidazole-selection. These clones exhibited differing levels of benznidazole-resistance (varying between 9 and 26-fold), and displayed cross-resistance to nifurtimox (2 to 4-fold). Each clone had acquired a stop-codon-generating mutation in the gene which encodes the nitroreductase (TcNTR) that is responsible for activating nitroheterocyclic pro-drugs. In addition, one clone had lost a copy of the chromosome containing TcNTR. However, these processes alone are insufficient to account for the extent and diversity of benznidazole-resistance. It is implicit from our results that additional mechanisms must also operate and that T. cruzi has an intrinsic ability to develop drug-resistance by independent sequential steps, even within a single population. This has important implications for drug development strategies.
Trypanosoma cruzi; Drug-resistance; Benznidazole; Nitroreductase
The pyrimidine biosynthesis pathway in the protozoan pathogen Toxoplasma gondii is essential for parasite growth during infection. To investigate the properties of dihydroorotate dehydrogenase (TgDHOD), the fourth enzyme in the T. gondii pyrimidine pathway, we expressed and purified recombinant TgDHOD. TgDHOD exhibited a specific activity of 84 U/mg, a kcat of 89 sec−1, a Km = 60 μM for L-dihydroorotate, and a Km = 29 μM for decylubiquinone (QD). Quinones lacking or having short isoprenoid side chains yielded lower kcats than QD. As expected, fumarate was a poor electron acceptor for this family 2 DHOD. The The IC50s determined for A77-1726, the active derivative of the human DHOD inhibitor leflunomide, and related compounds MD249 and MD209 were, 91 μM, 96 μM, and 60 μM, respectively. The enzyme was not significantly affected by brequinar or TTFA, known inhibitors of human DHOD, or by atovaquone. DSM190, a known inhibitor of Plasmodium falciparum DHOD, was a poor inhibitor of TgDHOD. TgDHOD exhibits a lengthy 157-residue N-terminal extension, consistent with a potential organellar targeting signal. We constructed C-terminally c-myc tagged TgDHODs to examine subcellular localization of TgDHOD in transgenic parasites expressing the tagged protein. Using both exogenous and endogenous expression strategies, anti-myc fluorescence signal colocalized with antibodies against the mitochondrial marker ATPase. These findings demonstrate that TgDHOD is associated with the parasite’s mitochondrion, revealing this organelle as the site of orotate production in T gondii. The TgDHOD gene appears to be essential because while gene tagging was successful at the TgDHOD gene locus, attempts to delete the TgDHOD gene were not successful in the KU80 background. Collectively, our study suggests that TgDHOD is an excellent target for the development of anti-Toxoplasma drugs.
Dihydroorotate dehydrogenase; pyrimidine biosynthesis; Toxoplasma gondii; mitochondria; oxidative phosphorylation
RNA polymerase II (RNAP-II) synthesizes the m7G-capped Spliced Leader (SL) RNA and most protein-coding mRNAs in trypanosomes. RNAP-II recruitment to DNA usually requires a set of transcription factors that make sequence-specific contacts near transcriptional start sites within chromosomes. In trypanosomes, the transcription factor TFIIB is necessary for RNAP-II-dependent SL RNA transcription. However, the trypanosomal TFIIB (tTFIIB) lacks the highly basic DNA binding region normally found in the C-terminal region of TFIIB proteins. To assess the precise pattern of tTFIIB binding within the SL RNA gene locus, as well as within several other loci, we performed chromatin immunoprecipitation/microarray analysis using a tiled gene array with a probe spacing of 10 nucleotides. We found that tTFIIB binds non-randomly within the SL RNA gene locus mainly within a 220-nt long region that straddles the transcription start site. tTFIIB does not bind within the small subunit (SSU) rRNA locus, indicating that trypanosomal TFIIB is not a component of an RNAP-I transcriptional complex. Interestingly, discrete binding sites were observed within the putative promoter regions of two loci on different chromosomes. These data suggest that although trypanosomal TFIIB lacks a highly basic DNA binding region, it nevertheless localizes to discrete regions of chromatin that include the SL RNA gene promoter.
Trypanosoma brucei; trypanosomes; RNA synthesis; transcription; SL RNA genes; chromatin immunoprecipitation; TFIIB
Schistosomiasis is one of the foremost health problems in developing countries and has been estimated to account for the loss of up to 56 million annual disability-adjusted life years. Control of the disease relies almost exclusively on praziquantel (PZQ) but this drug does not kill juvenile worms during the early stages of infection or prevent post-treatment reinfection. As the use of PZQ continues to grow, there are fears that drug resistance may become problematic thus there is a need to develop a new generation of more broadly effective anti-schistosomal drugs, a task that will be made easier by having an understanding of why PZQ kills sexually mature worms but fails to kill juveniles. Here, we describe the exposure of mixed-sex juvenile and sexually mature male and female Schistosoma mansoni to 1 μg/mL PZQ in vitro and the use of microarrays to observe changes to the transcriptome associated with drug treatment. Although there was no significant difference in the total number of genes expressed by adult and juvenile schistosomes after treatment, juveniles differentially regulated a greater proportion of their genes. These included genes encoding multiple drug transporter as well as calcium regulatory, stress and apoptosis-related proteins. We propose that it is the greater transcriptomic flexibility of juvenile schistosomes that allows them to respond to and survive exposure to PZQ in vivo.
Schistosomiasis; schistosoma; praziquantel; microarray; drug resistance; apoptosis
Although draft genome sequences of two of the major human schistosomes, Schistosoma japonicum and S. mansoni are available, the structures and characteristics of most genes and the influence of exogenous genes on the metabolism of schistosomes remain uncharacterized. Furthermore, which functional genomics approaches will be tractable for schistosomes are not yet apparent. Here, the vesicular stomatitis virus glycoprotein (VSVG)-pseudotyped pantropic retroviral vector pBABE-puro was modified to incorporate the human telomerase reverse transcriptase gene (hTERT) as a reporter, under the control of the retroviral long terminal repeat (LTR). Pseudotyped virions were employed to transduce S. japonicum to investigate the utility of retrovirus-mediated transgenesis of S. japonicum and the activity of human telomerase reverse transcriptase as a reporter transgene in schistosomes. Schistosomules perfused from experimentally infected rabbits were cultured for six days after exposure to the virions after which genomic DNAs from virus-exposed and control worms were extracted. Analysis of RNA from transduced parasites and immunohistochemistry of thin parasite sections revealed expression of hTERT in the transduced worms. Expression of hTERT was also confirmed by immunoblot analysis. These findings indicated that S. japonicum could be effectively transduced by VSVG pseudotyped retrovirus carrying the hTERT gene. Given the potential of hTERT to aid in derivation of immortalized cells, these findings suggest that this pantropic retroviral approach can be employed to transduce cells from specific tissues and organs of schistosomes to investigate the influence of transgene hTERT on growth and proliferation of schistosome cells.
Schistosoma japonicum; glycoprotein of vesicular stomatitis virus (VSVG); pantropic retrovirus; murine leukemia virus; transgene; telomerase
In Trypanosoma brucei, RNA interference (RNAi) and recombinant protein expression are established as powerful approaches for functional genomics, particularly when combined with inducible expression. The favoured methods involve exploiting homologous recombination to target expression cassettes to a chromosome sub-set to establish stable cell-lines. Unfortunately, bloodstream-form cells, those that cause disease in mammals, exhibit low efficiency stable transfection. Current expression systems can also exhibit other undesirable features, including variable position effects and leaky, inducible expression. We have developed systems in bloodstream-form cells that alleviate these problems. Using constructs for RNAi and expression of (GFP) tagged proteins, we target a (hyg) tagged ribosomal RNA (RRNA) locus which circumvents position effects and allows increased targeting efficiency. We also report a compatible double-inducible system for tight regulation of highly toxic products. This system exploits a new inducible RRNA promoter to drive T7 RNA polymerase (T7RNAP) transcription which then drives expression from inducible T7 promoters. The developments described should facilitate functional analysis and increased throughput.
bloodstream-form; functional genomics; GFP; leaky; position effect; RNAi; transfection; T7 RNA polymerase
A major obstacle to reproducible expression of recombinant transcripts lies in the epigenetic effects of the flanking chromatin following integration. We previously presented a strategy to overcome this problem in bloodstream form Trypanosoma brucei, using a reporter to identify a ribosomal-spacer locus that supports optimal expression and then marking that locus for subsequent targeting. Advantages include elimination of variable-expression position-effects and the easy confirmation of correct integration. We now report a set of validated constructs that exploit this system for expression of dsRNA or recombinant protein. The current construct-set allows expression of intramolecular dsRNA for RNA interference knockdown or expression of proteins that can incorporate c-Myc epitope(s) or a fluorescent-tag for subcellular localisation, interaction and/or other functional analysis. The constructs are integrated at a single, marked locus and deliver reliable and reproducible expression.
functional genomics; RNAi barcode screen; ornithine decarboxylase
We have developed cross-genotype and genotype-specific quantitative reverse-transcription PCR (qRT-PCR) assays to detect and quantify the number of parasites, transmission stages (gametocytes) and male gametocytes in blood stage Plasmodium chabaudi infections. Our cross-genotype assays are reliable, repeatable and generate counts that correlate strongly (R2s > 90%) with counts expected from blood smears. Our genotype-specific assays can distinguish and quantify different stages of genetically distinct parasite clones (genotypes) in mixed infections and are as sensitive as our cross-genotype assays. Using these assays we show that gametocyte density and gametocyte sex ratios vary during infections for two genetically distinct parasite lines (genotypes) and present the first data to reveal how sex ratio is affected when each genotype experiences competition in mixed-genotype infections. Successful infection of mosquito vectors depends on both gametocyte density and their sex ratio and we discuss the implications of competition in genetically diverse infections for transmission success.
Plasmodium chabaudi; Gametocyte; Sex ratio; qRT-PCR
Leishmania parasites are intracellular protozoans capable of salvaging and remodeling lipids from the host. To understand the role of lipid metabolism in Leishmania virulence, it is necessary to characterize the enzymes involved in the uptake and turnover of phospholipids. This study focuses on a putative phospholipase A2 (PLA2)/platelet-activating factor acetylhydrolase (PAF-AH) in L. major. In mammals, PAF-AH is a subgroup of PLA2 catalyzing the hydrolysis/inactivation of platelet-activating factor (PAF), a potent mediator of many leukocyte functions. By immunofluorescence microscopy, L. major PLA2/PAF-AH is predominantly localized in the ER. While wild type L. major parasites are able to hydrolyze PAF, this activity is completely absent in the PLA2/PAF-AH-null mutants. Meanwhile, deletion of PLA2/PAF-AH had no significant effect on the turnover of common glycerophospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylglycerol. PLA2/PAF-AH is not required for the growth of L. major parasites in culture, or the production of GPI-anchored virulence factors. Nonetheless, it does play a key role in the mammalian host as the PLA2/PAF-AH null mutants exhibit attenuated virulence in BALB/c mice. In conclusion, these data suggest that Leishmania parasites possess a functional PAF-AH and the degradation of PAF or PAF-like lipids is an important step in infection.
Phospholipase; virulence; Leishmania; platelet-activating factor; PAF-AH; macrophage
Recent studies have demonstrated that filarial parasites contain a functional homologue of the insect ecdysone receptor (EcR). As a first step in deciphering the physiological role that ecdysteroids play in filarial parasites, adult female parasites cultured in the presence and absence of 20-OH ecdysone were metabolically labeled. Gel electrophoretic analysis of proteins extracted from the cultured parasites revealed changes in the level of expression of several proteins, indicating that adult female parasites contained an ecdysone-responsive gene network. A bioinformatic analysis was then conducted to identify putative ecdysone response elements (EcREs) in the B. malayi genome. A total of 18 genes were identified that contained putative EcREs located in the 4 kbp upstream from the start of their open reading frames. The most common functional classifications of the encoded proteins were factors involved in transcription and metabolism. These genes revealed a number of different developmental patterns of transcription. The promoter of one EcRE-containing gene was cloned into a luciferase reporter vector and transfected into B. malayi embryos. Reporter gene expression from embryos transfected with this construct was up-regulated by 20-OH ecdysone. Deletion and substitution mutations in the canonical EcRE resulted in a loss of the ecdysone response. These results demonstrate the presence of functional EcREs in the B. malayi genome.
filariasis; ecdysone; transfection; promoter
In Leishmania major, the core of the abundant surface lipophosphoglycan (LPG) is structurally related to that of the smaller glycosylinositolphospholipids (GIPLs) in containing galactosylfuranose (Galf ) residues in a Galf (β1, 3)Man motif. However, deletion of the putative Galf-transferase (Galf T) LPG1 affected Galf incorporation in LPG but not GIPLs. We hypothesized that the presumptive GIPL Galf-transferases could be homologous to LPG1, and identified three related genes in the L. major genome. These were termed LPG1L, LPG1R, and LPG1G, the latter of which was found in three identical copies located at the telomeres of chromosomes 5, 19, and 32 based on Leishmania genome project data. Neither LPG1 nor its homologues LPG1L and LPG1R were involved in the biosynthesis of GIPLs, as an lpg1−/lpg1l−/lpg1r− triple knockout (the first such in Leishmania) grew normally and made wild-type levels of Galf-containing GIPLs. In contrast, overexpression of these three led to elevated galactose incorporation in glycoproteins. Galf-containing glycoproteins had not been described in Leishmania but occur at high levels in other closely related trypanosomatids including Trypanosoma cruzi, Crithidia, Leptomonas, and Endotrypanum, and LPG1L and LPG1R homologs were detected in these species. These data suggest that the glyco-synthetic capabilities of Leishmania and perhaps other trypanosomatids may be larger than previously thought, with some activities being ‘cryptic’ in different lineages and potentially serving as reservoirs for glycoconjugate variation during evolution. Future tests will address whether the LPG1G family encodes the hypothesized GIPL-specific Galf T.
Glycosylinositolphospholipids; Lipophosphoglycan; Galactosylfuranose; Galactosylfuranose transferase