Plasmodium liver stage developmental arrest by depletion of a protein at the parasite-host interface

Plasmodium parasites of mammals, including the species that cause malaria in humans, infect the liver first and develop there into clinically silent liver stages. Liver stages grow and ultimately produce thousands of first-generation merozoites, which initiate the erythrocytic cycles causing malaria pathology. Here, we present a Plasmodium protein with a critical function for complete liver stage development. UIS4 (up-regulated in infective sporozoites gene 4) is expressed exclusively in infective sporozoites and developing liver stages, where it localizes to the parasitophorous vacuole membrane. Targeted gene disruption of UIS4 in the rodent model malaria parasite Plasmodium berghei generated knockout parasites that progress through the malaria life cycle until after hepatocyte invasion but are severely impaired in further liver stage development. Immunization with UIS4 knockout sporozoites completely protects mice against subsequent infectious WT sporozoite challenge. Genetically attenuated liver stages may thus induce immune responses, which inhibit subsequent infection of the liver with WT parasites.

Simultaneous identification of the four human Plasmodium species and quantification of Plasmodium DNA load in human blood by real-time polymerase chain reaction

The incidence of imported malaria cases in travellers returning from endemic areas has considerably increased over the last few years. The microscopical examination of stained blood films is the gold standard method to confirm clinical suspicion of malaria but diagnosis is difficult in the case of mixed infections, low-grade parasitaemia, or forms altered by uncompleted treatment. We have developed a real-time polymerase chain reaction (PCR) for the simultaneous identification of the 4 human Plasmodium spp. and quantification of Plasmodium DNA in human blood. The rapid turnaround and reduction in the risk of PCR product carryover are major advantages compared with conventional PCR. In combination with conventional tests, this method could be a powerful tool for the diagnosis of malaria infections among travellers from endemic areas and during the follow-up of patients in reference centres involved in travel and tropical medicine. Quantitative real-time PCR could also be used for the follow-up of patients during drug resistance studies managed by national malaria programmes, the testing of new drugs, and vaccine trials.

Virus inactivation and protein recovery in a novel ultraviolet-C reactor

BACKGROUND AND OBJECTIVES

Ultraviolet-C (UVC) irradiation is a viral-inactivation method that was dismissed by many plasma fractionators as a result of the potential for protein damage and the difficulty in delivering uniform doses. A reactor with novel spiral flow hydraulic mixing was recently designed for uniform and controlled UVC treatment. The objective of this study was to investigate virus inactivation and protein recovery after treatment through the new reactor.

MATERIALS AND METHODS

Virus- and mock-spiked Alpha1-proteinase inhibitor (Alpha1-PI) solutions were treated with UVC. The virus samples were assayed for residual infectivity and amplified by the polymerase chain reaction (PCR). The mock-spiked samples were assayed for protein integrity.

RESULTS

Greater than 4 log10 of all test viruses were inactivated, regardless of the type of nucleic acid or presence of an envelope. Unlike previous studies, viruses with the smallest genomes were found to be those most sensitive to UVC irradiation, and detection of PCR amplicons > or = 2.0 kb was correlated to viral infectivity. Doses that achieved significant virus inactivation yielded recovery of > 90% protein activity, even in the absence of quenchers.

CONCLUSIONS

The results demonstrate the effectiveness of UVC treatment, in the novel reactor, to inactivate viruses without causing significant protein damage, and confirm the utility of large PCR amplicons as markers for infectious virus.

Differential transcriptome profiling identifies Plasmodium genes encoding pre-erythrocytic stage-specific proteins

Invasive sporozoite and merozoite stages of malaria parasites that infect mammals enter and subsequently reside in hepatocytes and red blood cells respectively. Each invasive stage may exhibit unique adaptations that allow it to interact with and survive in its distinct host cell environment, and these adaptations are likely to be controlled by differential gene expression. We used suppression subtractive hybridization (SSH) of Plasmodium yoelii salivary gland sporozoites versus merozoites to identify stage-specific pre-erythrocytic transcripts. Sequencing of the SSH library and matching the cDNA sequences to the P. yoelii genome yielded 25 redundantly tagged genes including the only two previously characterized sporozoite-specific genes encoding the circumsporozoite protein (CSP) and thrombospondin-related anonymous protein (TRAP). Twelve novel genes encode predicted proteins with signal peptides, indicating that they enter the secretory pathway of the sporozoite. We show that one novel protein bearing a thrombospondin type 1 repeat (TSR) exhibits an expression pattern that suggests localization in the sporozoite secretory rhoptry organelles. In addition, we identified a group of four genes encoding putative low-molecular-mass proteins. Two proteins in this group exhibit an expression pattern similar to TRAP, and thus possibly localize in the sporozoite secretory micronemes. Proteins encoded by the differentially expressed genes identified here probably mediate specific interactions of the sporozoite with the mosquito vector salivary glands or the mammalian host hepatocyte and are not used during merozoite-red blood cell interactions.

A member of a conserved Plasmodium protein family with membrane-attack complex/perforin (MACPF)-like domains localizes to the micronemes of sporozoites

Pore-forming proteins are employed by many pathogens to achieve successful host colonization. Intracellular pathogens use pore-forming proteins to invade host cells, survive within and productively interact with host cells, and finally egress from host cells to infect new ones. The malaria-causing parasites of the genus Plasmodium evolved a number of life cycle stages that enter and replicate in distinct cell types within the mosquito vector and vertebrate host. Despite the fact that interaction with host-cell membranes is a central theme in the Plasmodium life cycle, little is known about parasite proteins that mediate such interactions. We identified a family of five related genes in the genome of the rodent malaria parasite Plasmodium yoelii encoding secreted proteins all bearing a single membrane-attack complex/perforin (MACPF)-like domain. Each protein is highly conserved among Plasmodium species. Gene expression analysis in P. yoelii and the human malaria parasite Plasmodium falciparum indicated that the family is not expressed in the parasites blood stages. However, one of the genes was significantly expressed in P. yoelii sporozoites, the stage transmitted by mosquito bite. The protein localized to the micronemes of sporozoites, organelles of the secretory invasion apparatus intimately involved in host-cell infection. MACPF-like proteins may play important roles in parasite interactions with the mosquito vector and transmission to the vertebrate host.

Usefulness of quantitative polymerase chain reaction in amniotic fluid as early prognostic marker of fetal infection with Toxoplasma gondii

OBJECTIVE

Our purpose was to evaluate Toxoplasma gondii concentration in amniotic fluid (AF) samples as a prognostic marker of congenital toxoplasmosis.

STUDY DESIGN

A retrospective study was carried out in 88 consecutive AF samples from 86 pregnant women, which were found positive by prospective polymerase chain reaction (PCR) testing. Parasite AF concentrations were estimated by real-time quantitative PCR and analyzed in relation to the clinical outcome of infected fetuses during pregnancy and at birth, taking into account the gestational age at maternal infection.

RESULTS

A significant negative linear regression was observed between gestational age at maternal infection and T gondii DNA loads in AF. After adjusting for time at maternal seroconversion by multivariate analysis, higher parasite concentrations were significantly associated with a severe outcome of congenital infection (odds ratio [OR]=15.38/log (parasites/mL AF) [95% CI=2.45-97.7]).

CONCLUSION

PCR quantification of T gondii in AF can be highly contributive for early prognosis of congenital toxoplasmosis. Maternal infections acquired before 20 weeks with a parasite load greater than 100/mL of AF have the highest risk of severe fetal outcome.

[Real-time PCR for detection of molecular markers of resistance in Plasmodium falciparum]

Plasmodium falciparum drug resistance is a major problem in malaria endemic areas. Molecular markers and in vitro tests have been developed to study and monitor drug resistance. However, none used alone, can provide sufficient data concerning the level of drug resistance and to issue precise guideline for drug use policies in endemic areas. We propose real-time PCR for the simultaneous detection of pfcrt and pfmdr1 genes mutations. The aim of this study was not to provide definitive data concerning the rate of mutations in an endemic area, but to describe a powerful method allowing the detection of major pfmdr1 and pfcrt mutations.

Real-time PCR for chloroquine sensitivity assay and for pfmdr1-pfcrt single nucleotide polymorphisms in Plasmodium falciparum

Plasmodium falciparum drug resistance is a major problem in malaria endemic areas. Molecular markers and in vitro tests have been developed to study and monitor drug resistance. However, none, used alone, can provide sufficient data concerning the level of drug resistance and to issue precise guidelines for drug use policies in endemic areas. We propose real-time PCR for the simultaneous detection of pfcrt and pfmdr1 genes mutations and to determine the half-maximal inhibitory response (IC(50)) of antimalarial drug. Using hybridization probes and SybrGreen technology on LightCycler instrument, point mutations of pfcrt and pfmdr1 genes have been successfully detected in 161 human blood samples and determination of IC values was applied to chloroquine-sensitive and chloroquine-resistant strains. Moreover, mixed infections caused by P. falciparum clones with wild-type or mutant alleles could be efficiency separated. The aim of this study was not to provide definitive data concerning the rate of mutations in an endemic area, but to describe a powerful method allowing the quantification of DNA for IC(50) determination and the detection of major pfmdr1 and pfcrt mutations.

Transformation of sporozoites into early exoerythrocytic malaria parasites does not require host cells

Malaria parasite species that infect mammals, including humans, must first take up residence in hepatic host cells as exoerythrocytic forms (EEF) before initiating infection of red blood cells that leads to malaria disease. Despite the importance of hepatic stages for immunity against malaria, little is known about their biology and antigenic composition. Here, we show that sporozoites, the parasites' transmission stage that resides in the mosquito vector salivary glands, can transform into early EEF without intracellular residence in host hepatocytes. The morphological sequence of transformation and the expression of proteins in the EEF appear indistinguishable from parasites that develop within host cells. Transformation depends on temperature elevation to 37 degrees C and serum. Our findings demonstrate that residence in a host hepatocyte or specific host cell-derived factors are not necessary to bring about the profound morphological and biochemical changes of the parasite that occur after its transmission from vector to mammalian host.

The Plasmodium sporozoite journey: a rite of passage

Sporozoites are the most versatile of the invasive stages of the Plasmodium life cycle. During their passage within the mosquito vector and the vertebrate host, sporozoites display diverse behaviors, including gliding locomotion and invasion of, migration through and egress from target cells. At the end of the journey, sporozoites invade hepatocytes and transform into exoerythrocytic stages, marking the transition from the pre-erythrocytic to the erythrocytic part of the life cycle. This article discusses recent work, mostly done with rodent malaria parasites, that has contributed to a better understanding of the sporozoites' complex biology and which has opened up new avenues for future sporozoite research.

Myosin A tail domain interacting protein (MTIP) localizes to the inner membrane complex of Plasmodium sporozoites

Apicomplexan host cell invasion and gliding motility depend on the parasite's actomyosin system located beneath the plasma membrane of invasive stages. Myosin A (MyoA), a class XIV unconventional myosin, is the motor protein. A model has been proposed to explain how the actomyosin motor operates but little is known about the components, topology and connectivity of the motor complex. Using the MyoA neck and tail domain as bait in a yeast two-hybrid screen we identified MTIP, a novel 24 kDa protein that interacts with MyoA. Deletion analysis shows that the 15 amino-acid C-terminal tail domain of MyoA, rather than the neck domain, specifically interacts with MTIP. In Plasmodium sporozoites MTIP localizes to the inner membrane complex (IMC), where it is found clustered with MyoA. The data support a model for apicomplexan motility and invasion in which the MyoA motor protein is associated via its tail domain with MTIP, immobilizing it at the outer IMC membrane. The head domain of the immobilized MyoA moves actin filaments that, directly or via a bridging protein, connect to the cytoplasmic domain of a transmembrane protein of the TRAP family. The actin/TRAP complex is then redistributed by the stationary MyoA from the anterior to the posterior end of the zoite, leading to its forward movement on a substrate or to penetration of a host cell.

Infectivity-associated changes in the transcriptional repertoire of the malaria parasite sporozoite stage

Injection of Plasmodium salivary gland sporozoites into the vertebrate host by Anopheles mosquitoes initiates malaria infection. Sporozoites develop within oocysts in the mosquito midgut and then enter and mature in the salivary glands. Although morphologically similar, oocyst sporozoites and salivary gland sporozoites differ strikingly in their infectivity to the mammalian host, ability to elicit protective immune responses, and cell motility. Here, we show that differential gene expression coincides with these dramatic phenotypic differences. Using suppression subtractive cDNA hybridization we identified highly up-regulated mRNAs transcribed from 30 distinct genes in salivary gland sporozoites. Of those genes, 29 are not significantly expressed in the parasite's blood stages. The most frequently recovered transcript encodes a protein kinase. Developmental up-regulation of specific mRNAs in the infectious transmission stage of Plasmodium indicates that their translation products may have unique roles in hepatocyte infection and/or development of liver stages.

Real time quantitative PCR and RT--PCR for analysis of Pneumocystis carinii hominis

Pneumocystis carinii hominis is a common cause of pneumonia in immunocompromised patients and particularly in those infected by HIV. Giemsa- and Gomori--Grocott-stained smears are widely used for detection and quantification of this opportunistic fungus obtained from biological samples or from in vitro culture. But these methods are fastidious and time-consuming. Thus, instead of performing a count of organisms, we focused our attention on the level of specific DNA by a quantitative PCR technique. This procedure has the advantage of greater precision and more objectivity. To verify the presence of organisms, quantitative RT--PCR based on DHFR and a cell cycle mRNA have been developed. In this current study, we present a detailed description of these methods and their applications for analysis of P. carinii hominis.

Synchronized neural activity in the Drosophila memory centers and its modulation by amnesiac

The mushroom bodies are key features of the brain circuitry for insect associative learning, especially when evoked by olfactory cues. Mushroom bodies are also notable for the close-packed parallel architecture of their many intrinsic neuronal elements, known as Kenyon cells. Here, we report that Kenyon cells of adult Drosophila exhibit synchronous oscillation of intracellular calcium concentration, with a mean period of approximately 4 min. Robust oscillation within a dissected brain persists for hours in insect saline and is strongly modulated in amplitude by the product(s) of the memory consolidation gene, amnesiac. It is also sensitive to pharmacological agents specific for several classes of ion channel and for acetylcholine and GABA receptors. A role in memory consolidation involving transcriptionally mediated synaptic strengthening is proposed.

Production of refractory dissolved organic matter by bacteria

Most of the oceanic reservoir of dissolved organic matter (DOM) is of marine origin and is resistant to microbial oxidation, but little is known about the mechanisms of its formation. In a laboratory study, natural assemblages of marine bacteria rapidly (in <48 hours) utilized labile compounds (glucose, glutamate) and produced refractory DOM that persisted for more than a year. Only 10 to 15% of the bacterially derived DOM was identified as hydrolyzable amino acids and sugars, a feature consistent with marine DOM. These results suggest that microbial processes alter the molecular structure of DOM, making it resistant to further degradation and thereby preserving fixed carbon in the ocean.

The effects of ectopic white and transformer expression on Drosophila courtship behavior

The sex determining genes of Drosophila males and females function to establish the potential for sex-specific behaviors. Previous studies suggest that ectopic GAL4-directed misexpression of the female-specific isoform of the sex-determining gene transformer (tra) in specific sub-domains of an otherwise male brain can lead to bisexual courtship behavior, thus identifying brain domains that may mediate sex-specific behavior. However, expression of mini-white, the marker gene used in both P[GAL4] and P[UAS(G)] constructs, also induces males to court other males, questioning whether GAL4-mediated tra expression alone can induce bisexual behavior. Here we demonstrate the consequences of inducing mutations in the mini-white genes within P[GAL4] and P[UAS(G)] constructs to generate flies in which a white mutant phenotype is revealed. In these mini-white mutant strains, P[GAL4]-mediated transformer expression alone is both sufficient and necessary to generate bisexual behavior. In addition, using RT-PCR, we reveal the presence of female transcripts of doublesex and fruitless in the brains of otherwise male (XY) flies exhibiting P[GAL4]-directed tra-expression, demonstrating that P[GAL4]-directed tra is functional at the molecular level. We conclude that P[GAL4]-directed misexpression of tra is responsible for the bisexual behavior previously described and that this is mediated via sex-specific splicing of dsx and fru. Our results support the validity of such strategies for identifying regions of the fly brain that underlie sex-specific behaviors.

The amnesiac gene product is expressed in two neurons in the Drosophila brain that are critical for memory

Mutations in the amnesiac gene in Drosophila affect both memory retention and ethanol sensitivity. The predicted amnesiac gene product, AMN, is an apparent preproneuropeptide, and previous studies suggest that it stimulates cAMP synthesis. Here we show that, unlike other learning-related Drosophila proteins, AMN is not preferentially expressed in mushroom bodies. Instead, it is strongly expressed in two large neurons that project over all the lobes of the mushroom bodies, a finding that suggests a modulatory role for AMN in memory formation. Genetically engineered blockade of vesicle recycling in these cells abbreviates memory as in the amnesiac mutant. Moreover, restoration of amn gene expression to these cells reestablishes normal olfactory memory in an amn deletion background. These results indicate that AMN neuropeptide release onto the mushroom bodies is critical for normal olfactory memory.

Determination of amino sugars in environmental samples with high salt content by high-performance anion-exchange chromatography and pulsed amperometric detection

Amino sugars were determined in natural samples, including seawater, using high-performance anion-exchange chromatography with pulsed amperometric detection and a new-off-line sample cleanup procedure. Samples were hydrolyzed with 3 M HCl for 5 h (100 degrees C) and neutralized with anion retardation resin. Before injection, salts and organic contaminants were removed with a strong cation exchanger in the Na+ form. Detection limits for amino sugars were between 1 and 4 nM (signal-to-noise ratio 3), allowing for the first time quantification of amino sugars in seawater without preconcentration. Precision was 2-11% at the 20 nM level. The relatively simple and rapid sample preparation makes it suitable for routine analyses.