Characterisation and expression of a stage-regulated gene of Leishmania major

Proteomic Analysis of the Promastigote Secretome of Seven Leishmania Species

Leishmaniasis is one of the most impactful parasitic diseases worldwide, endangering the lives of 1 billion people every year. There are 20 different species of Leishmania able to infect humans, causing cutaneous (CL), visceral (VL), and/or mucocutaneous leishmaniasis (MCL). Leishmania parasites are known to secrete a plethora of proteins to establish infection and modulate the host's immune system. In this study, we analyzed using tandem mass spectrometry the total protein content of the secretomes produced by promastigote forms from seven Leishmania species grown in serum-free in vitro cultures. The core secretome shared by all seven Leishmania species corresponds to up to one-third of total secreted proteins, suggesting conserved mechanisms of adaptation to the vertebrate host. The relative abundance confirms the importance of known virulence factors and some proteins uniquely present in CL- or VL-causing species and may provide further insight regarding their pathogenesis. Bioinformatic analysis showed that most proteins were secreted via unconventional mechanisms, with an important role for vesicle-based secretion for all species. Gene Ontology annotation and enrichment analyses showed a high level of functional conservation among species. This study contributes to the current knowledge on the biological significance of differently secreted proteins and provides new information on the correlation of Leishmania secretome to clinical outcomes and species-specific pathogenesis.

Identification of positive and negative regulators in the stepwise developmental progression towards infectivity in Trypanosoma brucei

Trypanosoma brucei is a protozoan parasite that causes important human and livestock diseases in sub-Saharan Africa. By overexpressing a single RNA-binding protein, RBP6, in non-infectious procyclics trypanosomes, we previously recapitulated in vitro the events occurring in the tsetse fly vector, namely the development of epimastigotes and infectious, quiescent metacyclic parasites. To identify genes involved in this developmental progression, we individually targeted 86 transcripts by RNAi in the RBP6 overexpression cell line and assessed the loss-of-function phenotypes on repositioning the kinetoplast, an organelle that contains the mitochondrial genome, the expression of BARP or brucei alanine rich protein, a marker for epimastigotes, and metacyclic variant surface glycoprotein. This screen identified 22 genes that positively or negatively regulate the stepwise progression towards infectivity at different stages. Two previously uncharacterized putative nucleic acid binding proteins emerged as potent regulators, namely the cold shock domain-containing proteins CSD1 and CSD2. RNA-Seq data from a selected group of cell lines further revealed that the components of gene expression regulatory networks identified in this study affected the abundance of a subset of transcripts in very similar fashion. Finally, our data suggest a considerable overlap between the genes that regulate the formation of stumpy bloodstream form trypanosomes and the genes that govern the development of metacyclic form parasites.

Leishmania dual-specificity tyrosine-regulated kinase 1 (DYRK1) is required for sustaining Leishmania stationary phase phenotype

Although the multiplicative and growth-arrested states play key roles in Leishmania development, the regulators of these transitions are largely unknown. In an attempt to gain a better understanding of these processes, we characterised one member of a family of protein kinases with dual specificity, LinDYRK1, which acts as a stasis regulator in other organisms. LinDYRK1 overexpressing parasites displayed a decrease in proliferation and in cell cycle re-entry of arrested cells. Parasites lacking LinDYRK1 displayed distinct fitness phenotypes in logarithmic and stationary growth phases. In logarithmic growth phase, LinDYRK1-/- parasites proliferated better than control lines, supporting a role of this kinase in stasis, while in stationary growth phase, LinDYRK1-/- parasites had important defects as they rounded up, accumulated vacuoles and lipid bodies and displayed subtle but consistent differences in lipid composition. Moreover, they expressed less metacyclic-enriched transcripts, displayed increased sensitivity to complement lysis and a significant reduction in survival within peritoneal macrophages. The distinct LinDYRK1-/- growth phase phenotypes were mirrored by the distinct LinDYRK1 localisations in logarithmic (mainly in flagellar pocket area and endosomes) and late stationary phase (mitochondrion). Overall, this work provides first evidence for the role of a DYRK family member in sustaining promastigote stationary phase phenotype and infectivity.

A single-point mutation in the RNA-binding protein 6 generates Trypanosoma brucei metacyclics that are able to progress to bloodstream forms in vitro

We previously established an in vitro differentiation system based on the inducible expression of the RNA binding protein 6 (RBP6), which initiated differentiation of Trypanosoma brucei non-infectious procyclics to infectious metacyclics (MFs). However, further differentiation to bloodstream forms (BFs) required infection of mice. Here we report the serendipitous isolation of a single point mutation in RBP6 (Q109K), whose expression not only generated MFs, but purified MFs continued the developmental cycle in vitro to BFs expressing variant surface glycoprotein-2 (VSG-2), formerly known as VSG 221. This transition occurred over a period of 11 days and by RNA-Seq, VSG-2 was first measureable on day 1, whereas metacyclic VSGs were detected up to 8 days. We further showed that inducible expression of mutant RBP6 appeared to skip the intermediate epimastigote stage and we highlight the potential involvement of RBP33 in the establishment of metacyclics and in particular in the generation of metacyclics uncharacteristically arrested at the G2/M checkpoint.

The Transcriptome of Leishmania major Developmental Stages in Their Natural Sand Fly Vector

The life cycle of the Leishmania parasite in the sand fly vector involves differentiation into several distinctive forms, each thought to represent an adaptation to specific microenvironments in the midgut of the fly. Based on transcriptome sequencing (RNA-Seq) results, we describe the first high-resolution analysis of the transcriptome dynamics of four distinct stages of Leishmania major as they develop in a natural vector, Phlebotomus duboscqi. The early transformation from tissue amastigotes to procyclic promastigotes in the blood-fed midgut was accompanied by the greatest number of differentially expressed genes, including the downregulation of amastins, and upregulation of multiple cell surface proteins, sugar and amino acid transporters, and genes related to glucose metabolism and cell cycle progression. The global changes accompanying post-blood meal differentiation of procyclic promastigotes to the nectomonad and metacyclic stages were less extensive, though each displayed a unique signature. The transcriptome of nectomonads, which has not been studied previously, revealed changes consistent with cell cycle arrest and the upregulation of genes associated with starvation and stress, including autophagic pathways of protein recycling. Maturation to the infective, metacyclic stage was accompanied by changes suggesting preadaptation to the intracellular environment of the mammalian host, demonstrated by the amastigote-like profiles of surface proteins and metabolism-related genes. Finally, a direct comparison between sand fly-derived and culture-derived metacyclics revealed a reassuring similarity between the two forms, with the in vivo forms distinguished mainly by a stronger upregulation of transcripts associated with nutrient stress.

The life cycle of Leishmania parasites in the sand fly vector includes their growth and development as morphologically distinct forms of extracellular promastigotes found within the different microenvironments of the gut. Based on RNA-Seq, we provide here the first high-resolution, transcriptomic analysis of Leishmania insect stages during their cyclical development in vivo, from tissue amastigotes ingested with the blood meal to infective, metacyclic promastigotes that initiate infection in the mammalian host. The most extensive genetic reprogramming occurred during the early transformation of amastigotes to rapidly dividing procyclic promastigotes in the blood-fed midgut, with major changes in the abundance of mRNAs for surface proteins and metabolism. The post-blood meal-adapted nectomonad stage was characterized by the downregulation of cell cycle-related genes and the upregulation of stress- and starvation-related genes. Finally, the transcriptome of metacyclic promastigotes shifted to a more amastigote-like profile, suggesting their preadaptation to the intracellular host environment.

Dual Transcriptome Profiling of Leishmania-Infected Human Macrophages Reveals Distinct Reprogramming Signatures

Macrophages are mononuclear phagocytes that constitute a first line of defense against pathogens. While lethal to many microbes, they are the primary host cells of Leishmania spp. parasites, the obligate intracellular pathogens that cause leishmaniasis. We conducted transcriptomic profiling of two Leishmania species and the human macrophage over the course of intracellular infection by using high-throughput RNA sequencing to characterize the global gene expression changes and reprogramming events that underlie the interactions between the pathogen and its host. A systematic exclusion of the generic effects of large-particle phagocytosis revealed a vigorous, parasite-specific response of the human macrophage early in the infection that was greatly tempered at later time points. An analogous temporal expression pattern was observed with the parasite, suggesting that much of the reprogramming that occurs as parasites transform into intracellular forms generally stabilizes shortly after entry. Following that, the parasite establishes an intracellular niche within macrophages, with minimal communication between the parasite and the host cell later during the infection. No significant difference was observed between parasite species transcriptomes or in the transcriptional response of macrophages infected with each species. Our comparative analysis of gene expression changes that occur as mouse and human macrophages are infected by Leishmania spp. points toward a general signature of the Leishmania-macrophage infectome.

Little is known about the transcriptional changes that occur within mammalian cells harboring intracellular pathogens. This study characterizes the gene expression signatures of Leishmania spp. parasites and the coordinated response of infected human macrophages as the pathogen enters and persists within them. After accounting for the generic effects of large-particle phagocytosis, we observed a parasite-specific response of the human macrophages early in infection that was reduced at later time points. A similar expression pattern was observed in the parasites. Our analyses provide specific insights into the interplay between human macrophages and Leishmania parasites and constitute an important general resource for the study of how pathogens evade host defenses and modulate the functions of the cell to survive intracellularly.

Simultaneous transcriptional profiling of Leishmania major and its murine macrophage host cell reveals insights into host-pathogen interactions

BACKGROUND

Parasites of the genus Leishmania are the causative agents of leishmaniasis, a group of diseases that range in manifestations from skin lesions to fatal visceral disease. The life cycle of Leishmania parasites is split between its insect vector and its mammalian host, where it resides primarily inside of macrophages. Once intracellular, Leishmania parasites must evade or deactivate the host's innate and adaptive immune responses in order to survive and replicate.

RESULTS

We performed transcriptome profiling using RNA-seq to simultaneously identify global changes in murine macrophage and L. major gene expression as the parasite entered and persisted within murine macrophages during the first 72 h of an infection. Differential gene expression, pathway, and gene ontology analyses enabled us to identify modulations in host and parasite responses during an infection. The most substantial and dynamic gene expression responses by both macrophage and parasite were observed during early infection. Murine genes related to both pro- and anti-inflammatory immune responses and glycolysis were substantially upregulated and genes related to lipid metabolism, biogenesis, and Fc gamma receptor-mediated phagocytosis were downregulated. Upregulated parasite genes included those aimed at mitigating the effects of an oxidative response by the host immune system while downregulated genes were related to translation, cell signaling, fatty acid biosynthesis, and flagellum structure.

CONCLUSIONS

The gene expression patterns identified in this work yield signatures that characterize multiple developmental stages of L. major parasites and the coordinated response of Leishmania-infected macrophages in the real-time setting of a dual biological system. This comprehensive dataset offers a clearer and more sensitive picture of the interplay between host and parasite during intracellular infection, providing additional insights into how pathogens are able to evade host defenses and modulate the biological functions of the cell in order to survive in the mammalian environment.

Transcriptomic profiling of gene expression and RNA processing during Leishmania major differentiation

Protozoan parasites of the genus Leishmania are the etiological agents of leishmaniasis, a group of diseases with a worldwide incidence of 0.9–1.6 million cases per year. We used RNA-seq to conduct a high-resolution transcriptomic analysis of the global changes in gene expression and RNA processing events that occur as L. major transforms from non-infective procyclic promastigotes to infective metacyclic promastigotes. Careful statistical analysis across multiple biological replicates and the removal of batch effects provided a high quality framework for comprehensively analyzing differential gene expression and transcriptome remodeling in this pathogen as it acquires its infectivity. We also identified precise 5′ and 3′ UTR boundaries for a majority of Leishmania genes and detected widespread alternative trans-splicing and polyadenylation. An investigation of possible correlations between stage-specific preferential trans-splicing or polyadenylation sites and differentially expressed genes revealed a lack of systematic association, establishing that differences in expression levels cannot be attributed to stage-regulated alternative RNA processing. Our findings build on and improve existing expression datasets and provide a substantially more detailed view of L. major biology that will inform the field and potentially provide a stronger basis for drug discovery and vaccine development efforts.

Metabolic reprogramming during purine stress in the protozoan pathogen Leishmania donovani

The ability of Leishmania to survive in their insect or mammalian host is dependent upon an ability to sense and adapt to changes in the microenvironment. However, little is known about the molecular mechanisms underlying the parasite response to environmental changes, such as nutrient availability. To elucidate nutrient stress response pathways in Leishmania donovani, we have used purine starvation as the paradigm. The salvage of purines from the host milieu is obligatory for parasite replication; nevertheless, purine-starved parasites can persist in culture without supplementary purine for over three months, indicating that the response to purine starvation is robust and engenders parasite survival under conditions of extreme scarcity. To understand metabolic reprogramming during purine starvation we have employed global approaches. Whole proteome comparisons between purine-starved and purine-replete parasites over a 6–48 h span have revealed a temporal and coordinated response to purine starvation. Purine transporters and enzymes involved in acquisition at the cell surface are upregulated within a few hours of purine removal from the media, while other key purine salvage components are upregulated later in the time-course and more modestly. After 48 h, the proteome of purine-starved parasites is extensively remodeled and adaptations to purine stress appear tailored to deal with both purine deprivation and general stress. To probe the molecular mechanisms affecting proteome remodeling in response to purine starvation, comparative RNA-seq analyses, qRT-PCR, and luciferase reporter assays were performed on purine-starved versus purine-replete parasites. While the regulation of a minority of proteins tracked with changes at the mRNA level, for many regulated proteins it appears that proteome remodeling during purine stress occurs primarily via translational and/or post-translational mechanisms.

Leishmania, the cause of a deadly spectrum of diseases in humans, surmounts a number of environmental challenges, including changes in the availability of salvageable nutrients, to successfully colonize its host. Adaptation to environmental stress is clearly of significance in parasite biology, but the underlying mechanisms are not well understood. To simulate the response to periodic nutrient scarcity in vivo, we have induced purine starvation in vitro. Purines are essential for growth and viability, and serve as the major energy currency of cells. Leishmania cannot synthesize purines and must salvage them from the surroundings. Extracellular purine depletion in culture induces a robust survival response in Leishmania, whereby growth arrests, but parasites persist for months. To profile the events that enable endurance of purine starvation, we used shotgun proteomics. Our data suggest that purine starvation induces extensive proteome remodeling, tailored to enhance purine capture and recycling, reduce energy expenditures, and maintain viability of the metabolically active, non-dividing population. Through global and targeted approaches, we reveal that proteome remodeling is multifaceted, and occurs through an array of responses at the mRNA, translational, and post-translational level. Our data provide one of the most inclusive views of adaptation to microenvironmental stress in Leishmania.

Differential quantitative proteomic profiling of Leishmania infantum and Leishmania mexicana density gradient separated membranous fractions

Leishmaniasis, caused by infection with Leishmania, is a major public health concern affecting more than 20million people globally. Leishmania has a digenetic lifecycle consisting of an extracellular flagellated promastigote, adapted to live in the mid-gut of the sand fly host and an aflagellated intracellular amastigote that resides within the macrophage of the mammalian host. Leishmania mexicana and Leishmania infantum are causative agents of cutaneous and visceral leishmaniasis, respectively. Membrane proteins play a pivotal role in host-pathogen interactions and in regulatory pathways. As the genome of Leishmania is essentially constitutively expressed, regulation of protein expression during differentiation occurs post-transcriptionally and/or post-translationally. Quantitative mass spectrometry using iTRAQ labeling identified differences in the proteomes of density gradient separated membranous fractions of promastigote and amastigote life-stages. We identified 189 L. infantum and 107 L. mexicana non-redundant proteins of which 20-40% showed differential expression levels between promastigote and amastigote lifecycle stages. Differentially expressed proteins mapped to several pathways including cell motility, metabolism, and infectivity as well as virulence factors such as eEF-1α, amastin and leishmanolysin (GP63). Western blot analysis validated iTRAQ quantitation for leishmanolysin. Focusing on differentially expressed proteins essential for pathogenesis, may ultimately lead to the identification of novel potential therapeutic targets.

BIOLOGICAL SIGNIFICANCE

Leishmania, protozoan parasites of the Trypanosomatidae family, are the causative agents of leishmaniasis that represents a major public health concern affecting more than 20million people globally Membrane associated proteins play a pivotal role in host-pathogen interactions and in regulatory pathways. Quantitative proteomic analysis of the membranous fractions from L. mexicana and L. infantum (causative agents of cutaneous and visceral leishmaniasis, respectively) identified a number of proteins that may have important stage-specific functions in either the sand fly or mammalian host. The function of these proteins includes roles in virulence, as well as differences in metabolic process between life stages. Many of the proteins identified may act as virulence factors playing significant roles in parasite invasion, host-parasite interaction or parasite survival and thus may have therapeutic potential as drug target candidates.

Evolutionary and functional insights into Leishmania META1: evidence for lateral gene transfer and a role for META1 in secretion

Background

Leishmania META1 has for long been a candidate molecule for involvement in virulence: META1 transcript and protein are up-regulated in metacyclic Leishmania. Yet, how META1 contributes to virulence remains unclear. We sought insights into the possible functions of META1 by studying its evolutionary origins.

Results

Using multiple criteria including sequence similarity, nucleotide composition, phylogenetic analysis and selection pressure on gene sequence, we present evidence that META1 originated in trypanosomatids as a result of a lateral gene transfer of a bacterial heat-inducible protein, HslJ. Furthermore, within the Leishmania genome, META1 sequence is under negative selection pressure against change/substitution. Using homology modeling of Leishmania META1 based on solved NMR structure of HslJ, we show that META1 and HslJ share a similar structural fold. The best hit for other proteins with similar fold is MxiM, a protein involved in the type III secretion system in Shigella. The striking structural similarity shared by META1, HslJ and MxiM suggests a possibility of shared functions. Upon structural superposition with MxiM, we have observed a putative hydrophobic cavity in META1. Mutagenesis of select hydrophobic residues in this cavity affects the secretion of the secreted acid phosphatase (SAP), indicating META1's involvement in secretory processes in Leishmania.

Conclusions

Overall, this work uses an evolutionary biology approach, 3D-modeling and site-directed mutagenesis to arrive at new insights into functions of Leishmania META1.

Leishmania amazonensis META2 protein confers protection against heat shock and oxidative stress

The META cluster of Leishmania amazonensis contains both META1 and META2 genes, which are upregulated in metacyclic promastigotes and encode proteins containing the META domain. Previous studies defined META2 as a 48.0-kDa protein, which is conserved in other Leishmania species and in Trypanosoma brucei. In this work, we demonstrate that META2 protein expression is regulated during the Leishmania life cycle but constitutive in T. brucei. META2 protein is present in the cytoplasm and flagellum of L. amazonensis promastigotes. Leishmania META2-null replacement mutants are more sensitive to oxidative stress and, upon heat shock, assume rounded morphology with shortened flagella. The increased susceptibility of null parasites to heat shock is reversed by extra-chromosomal expression of the META2 gene. Defective Leishmania promastigotes exhibit decreased ability to survive in macrophages. By contrast, META2 expression is decreased by 80% in RNAi-induced T. brucei bloodstream forms with no measurable effect on survival or resistance to heat shock.

Phosphoproteomic analysis of Leishmania donovani pro- and amastigote stages

Following transmission to the vertebrate host, the protozoan parasite Leishmania donovani differentiates into the pathogenic amastigote stage that is adapted for intracellular survival. This developmental transition is induced by environmental factors including elevated temperature and acidic pH and is likely transduced by signaling cascades involving protein kinases and their downstream phosphoprotein substrates. These signaling networks are highly adapted to the specific nutritional and physiological requirements of the organism and thus studying Leishmania phosphorylation may allow important insight into the parasite-specific biology. We used a gel-based approach to investigate qualitative and quantitative changes of the phosphoproteome of the major L. donovani life cycle stages. Phosphoproteins were purified by immobilized metal affinity chromatography (IMAC), separated by IEF and SDS-PAGE using pH 4-7 IPG immobiline strips, revealed by fluorescent multiplex staining, and identified by MALDI-MS and MS/MS. Our analysis allowed us to establish a first repertoire of the Leishmania phosphoproteome and to identify phosphoproteins implicated in stress- and heat shock response, RNA/protein turnover, metabolism, and signaling.

Putative markers of infective life stages in Leishmania (Viannia) braziliensis

Gene expression is known to vary significantly during the Leishmania life-cycle. Its monitoring might allow identification of molecular changes associated with the infective stages (metacyclics and amastigotes) and contribute to the understanding of the complex host-parasite relationships. So far, very few studies have been done on Leishmania (Viannia) braziliensis, one of the most pathogenic species. Such studies require, first of all, reference molecular markers. In the present work, we applied differential display analysis (DD analysis) in order to identify transcripts that might be (i) candidate markers of metacyclics and intracellular amastigotes of L. (V.) braziliensis or (ii) potential controls, i.e. constitutively expressed. In total, 48 DNA fragments gave reliable sequencing data, 29 of them being potential markers of infective stages and 12 potential controls. Eight sequences could be identified with reported genes. Validation of the results of DD analysis was done for 4 genes (2 differentially expressed and 2 controls) by quantitative real-time PCR. The infective insect stage-specific protein (meta 1) was more expressed in metacyclic-enriched preparations. The oligopeptidase b showed a higher expression in amastigotes. Two genes, glucose-6-phosphate dehydrogenase and a serine/threonine protein kinase, were found to be similarly expressed in the different biological samples.

Leishmania spp.: proficiency of drug-resistant parasites

Leishmaniasis is a disease caused by at least 17 different species of protozoan Leishmania parasites and currently affects around 12 million people living mostly in tropical and subtropical areas. Failure to treat leishmaniasis successfully is often due to drug resistance. However, there are no cellular and molecular markers of chemoresistance against leishmanicidal drugs and the only reliable method for monitoring resistance of individual isolates is the in vitro amastigote/macrophage model. It is thus necessary to find cellular and molecular markers that can be used systematically to identify the drug-resistant phenotype of the infecting parasites. Until now, whether drug resistance in Leishmania compromises parasite proficiency, e.g. in terms of infectivity or metabolism, has not been systematically evaluated. Therefore, here we examine whether the physiological changes expressed by drug-resistant Leishmania reflect a modification of parasite vitality in drug-resistant compared with drug-sensitive parasites. Finally, the clinical implications of drug resistance in Leishmania are also discussed.

Analysis of genetic elements regulating the methionine adenosyltransferase gene in Leishmania infantum

Methionine adenosyltransferase (MAT) is an important enzyme for metabolic processes, inasmuch as its product, S-adenosylmethionine (AdoMet), plays a key role in trans-methylation, trans-sulphuration and polyamine synthesis. Our prior studies have shown that the Leishmania infantum genome contains two identical copies of the gene encoding MAT (MAT2 gene), arranged in head-to-tail configuration and alternating with another gene, called LORIEN that contains a zinc-finger motif. Both genes are constitutively expressed throughout the promastigote stage of the parasite cell cycle, and their flanking regions were detected by RT-PCR. Luciferase (luc) reporter assays indicated the presence of regulatory elements within the MAT2 3'UTR and intergenic region, and fragments responsible for such regulation were identified by deletional analysis. By site-directed mutagenesis of the wild-type -42 AG recognized in the trans-splicing of the MAT2 gene, the AG slightly downstream (position -36) was observed to be able to generate the same levels of luc expression, thus suggesting that potentially this gene has alternative spliced leader acceptor sites. The stability of MAT2 and LORIEN transcripts was very similar in both logarithmic and stationary phases. However, cycloheximide (CHX) inhibition of protein synthesis increased MAT2 and LORIEN mRNA levels in the logarithmic phase only, an indication that these genes are regulated in promastigotes at the post-transcriptional level by protein factors that targets both transcripts for degradation. However, during the stationary phase, another CHX-independent factor also led to MAT2 and LORIEN mRNAs degradation, indicating the existence of different mechanisms operating on the post-transcriptional regulation of these two genes.

Genomic and proteomic expression analysis of Leishmania promastigote and amastigote life stages: The Leishmania genome is constitutively expressed

Leishmania are protozoan parasites that cause a wide spectrum of clinical diseases in humans and are a major public health risk in several countries. Leishmania life cycle consists of an extracellular flagellated promastigote stage within the midgut of a sandfly vector, and a morphological distinct intracellular amastigote stage within macrophages of a mammalian host. This study reports the use of DNA oligonucleotide genome microarrays representing 8160 genes to analyze the mRNA expression profiles of L. major promastigotes and lesion derived amastigotes. Over 94% of the genes were expressed in both life stages. Advanced statistical analysis identified a surprisingly low degree of differential mRNA expression: 1.4% of the total genes in amastigotes and 1.5% in promastigotes. These microarray results demonstrate that the L. major genome is essentially constitutively expressed in both life stages and suggest that Leishmania is constitutively adapted for survival and replication in either the sandfly vector or macrophage host utilizing an appropriate set of genes for each vastly different environment. Quantitative proteomics, using the isotope coded affinity tag (ICAT) technology and mass spectrometry, was used to identify L. infantum promastigote and axenic amastigote differentially expressed proteins. Of the 91 distinct proteins identified, 8% were differentially expressed in the amastigote stage, 20% were differentially expressed in the promastigote stage, and the remaining 72% were considered constitutively expressed. The differential expression was validated by the identification of previously reported stage specific proteins and identified several amastigote and promastigote novel stage specific proteins.

Pathogenomics analysis of Leishmania spp.: flagellar gene families of putative virulence factors

The trypanosomatid flagellar apparatus contains conventional and unique features, whose roles in infectivity are still enigmatic. Although the flagellum and the flagellar pocket are critical organelles responsible for all vesicular trafficking between the cytoplasm and cell surface, still very little is known about their roles in pathogenesis and how molecules get to and from the flagellar pocket. The ongoing analysis of the genome sequences and proteome profiles of Leishmania major and L infantum, Trypanosoma cruzi, T. brucei, and T. gambiensi ( www.genedb.org ), coupled with our own work on L. chagasi (as part of the Brazilian Northeast Genome Program- www.progene.ufpe.br ), prompted us to scrutinize flagellar genes and proteins of Leishmania spp. promastigotes that could be virulence factors in leishmaniasis. We have identified some overlooked parasite factors such as the MNUDC-1 (a protein involved in nuclear development and genomic fusion) and SQS (an enzyme of sterol biosynthesis), among the described flagellar gene families. A database concerning the results of this work, as well as of other studies of Leishmania and its organelles, is available at http://nugen.lcc.uece.br/LPGate . It will serve as a convenient bioinformatics resource on genomics and pathology of the etiological agents of leishmaniasis.

Cell differentiation and infectivity ofLeishmania mexicanaare inhibited in a strain resistant to an ABC-transporter blocker

We analysed whether markers of cell differentiation and infectivity differed when compared to the parental sensitive strain [NR(Gs)] in anin vitroselectedLeishmaniastrain [NR(Gr)] resistant to Glibenclamide®, an ATP-binding-cassette (ABC)-transporter blocker. The data show that the cell body area was larger in NR(Gr) compared to NR(Gs) and that functional characters associated with an infective metacyclic phenotype, such as resistance to the lytic effect of the alternative complement pathway and expression of the Meta-1 protein, were reduced. The infectivity of NR(Gr) to J774.1 macrophages was also significantly reduced. These results suggest that resistance inLeishmaniaagainst Glibenclamide®, a general blocker of P-glycoproteins, could produce functional modifications that may be relevant forLeishmaniadifferentiation, infectivity and survival.

Evaluation of differential gene expression in Leishmania major Friedlin procyclics and metacyclics using DNA microarray analysis

The various Leishmania species are flagellated protozoans, responsible for a wide spectrum of human diseases. The sequence of the L. major genome is nearing completion and a large proportion of the identified genes have yet to be ascribed functions. DNA microarrays containing PCR-amplified DNA from a random amplified genomic library of L. major Friedlin (LmjF) [Mol. Biochem. Parasitol. 113 (2001) 337] were hybridized with fluorescent probes made from L. major Friedlin RNA from five time-points during differentiation from procyclics to metacyclics. The data were normalized for background and probe intensity and the relative abundance of RNA for each spot was calculated. Almost 15% (1387/9282) of the DNAs showed statistically significant (P<0.01) changes in expression (1.1-5-fold) during the transition, with 1.16% (108) showing up-regulation at two or more time-points and 0.14% (13) showing down-regulation. Northern blot analyses of selected genes confirmed these results. These studies confirmed the stage-specific expression of several known genes, as well as identifying a number of novel genes that are up-regulated in either procyclics or metacyclics.

Genetic characterization of glucose transporter function in Leishmania mexicana

Both insect and mammalian life cycle stages of Leishmania mexicana take up glucose and express all three isoforms encoded by the LmGT glucose transporter gene family. To evaluate glucose transporter function in intact parasites, a null mutant line has been created by targeted disruption of the LmGT locus that encompasses the LmGT1, LmGT2, and LmGT3 genes. This deltalmgt null mutant exhibited no detectable glucose transport activity. The growth rate of the deltalmgt knockout in the promastigote stage was reduced to a rate comparable with that of WT cells grown in the absence of glucose. deltalmgt cells also exhibited dramatically reduced infectivity to macrophages, demonstrating that expression of LmGT isoforms is essential for viability of amastigotes. Furthermore, WT L. mexicana were not able to grow as axenic culture form amastigotes if glucose was withdrawn from the medium, implying that glucose is an essential nutrient in this life cycle stage. Expression of either LmGT2 or LmGT3, but not of LmGT1, in deltalmgt null mutants significantly restored growth as promastigotes, but only LmGT3 expression substantially rescued amastigote growth in macrophages. Subcellular localization of the three isoforms was investigated in deltalmgt cells expressing individual LmGT isoforms. Using anti-LmGT antiserum and GFP-tagged LmGT fusion proteins, LmGT2 and LmGT3 were localized to the cell body, whereas LmGT1 was localized specifically to the flagellum. These results establish that each glucose transporter isoform has distinct biological functions in the parasite.

Evaluation of the murine immune response to Leishmania meta 1 antigen delivered as recombinant protein or DNA vaccine

The meta 1 gene of Leishmania is conserved across the genus and encodes a protein upregulated in metacyclic promastigotes. Meta 1 constitutive overexpressing mutants show increased virulence to mice. In this paper, both meta 1 recombinant protein and plasmids bearing the meta 1 gene were tested for their antigenicity and potential for inducing protective immunity in mice. Vaccination with the recombinant protein induced a predominant Th2-type of response and did not result in protection upon challenge with live parasites. Surprisingly, the expected reversal to a CD4(+) Th1-type of response upon genetic immunisation by the intramuscular route was not observed. Instead, vaccination with either the meta 1 gene alone or in fusion with the monocyte chemotactic protein (MCP)-3 cDNA induced a Th2-type of response that correlated with lack of protection against infection.

A common mechanism of stage-regulated gene expression in Leishmania mediated by a conserved 3'-untranslated region element

Developmental regulation of mRNA levels in trypanosomatid protozoa is determined post-transcriptionally and often involves sequences located in the 3'-untranslated regions (3'-UTR) of the mRNAs. We have previously identified a developmentally regulated gene family in Leishmania encoding the amastin surface proteins and showed that stage-specific accumulation of the amastin mRNA is mediated by sequences within the 3'-UTR. Here we identified a 450-nt region within the amastin 3'-UTR that can confer amastigote-specific gene expression by a novel mechanism that increases mRNA translation without an increase in mRNA stability. Remarkably, this 450-nt 3'-UTR element is highly conserved among a large number of Leishmania mRNAs in several Leishmania species. Here we show that several of these mRNAs are differentially expressed in the intracellular amastigote stage of the parasite and that the 450-nt conserved element in their 3'-UTRs is responsible for stage-specific gene regulation. We propose that the 450-nt conserved element, which is unlike any other regulatory element identified thus far, is part of a common mechanism of stage-regulated gene expression in Leishmania that regulates mRNA translation in response to intracellular stresses.

Characterization of a differentially expressed protein that shows an unusual localization to intracellular membranes in Leishmania major

The SHERP genes are found as a tandem pair within the differentially regulated LmcDNA16 locus of Leishmania major. The SHERP gene product (small hydrophilic endoplasmic reticulum-associated protein) is unusual in its small size (6.2 kDa), its acidic pI (4.6) and its exclusive, high-level expression ( approximately 100000 copies per cell) in infective non-replicative parasite stages. No homologues have been found to date. Secondary-structure predictions suggest that SHERP contains an amphiphilic alpha-helix that is presumably involved in protein-protein interactions. SHERP has been localized to the endoplasmic reticulum as well as to the outer mitochondrial membrane in both wild-type and over-expressing parasites. Given the absence of an N-terminal signal sequence, transmembrane-spanning domains or detectable post-translational modifications, it is likely that this hydrophilic molecule is a peripheral membrane protein on the cytosolic face of intracellular membranes. This weak membrane association has been confirmed in cell-fractionation assays, in which SHERP redistributes from the cytoplasmic to the membrane fraction after in vivo cross-linking. SHERP does not appear to be involved in rearrangements of the cytoskeleton or conservation of organelle morphology during parasite differentiation. The role of this novel protein, presumed to be part of a protein complex, in infective parasites that are nutrient-deficient and pre-adapted for intracellular survival in the mammalian host is under investigation.

Leishmania: overexpression and comparative structural analysis of the stage-regulated meta 1 gene

The meta 1 gene of Leishmania major is upregulated in metacyclic promastigotes and encodes an 11.5-kDa protein with no significant similarities to other proteins in the existing databases. In this paper, we characterize the homologous meta 1 genes in L. amazonensis and L. donovani. Proteins encoded by this gene in all three species present a high degree of identity. The meta 1 gene cannot be replaced by gene targeting in L. major, suggesting an essential role for the protein, at least in promastigotes. Overexpression of the meta 1 protein in L. amazonensis generates parasites that are more virulent than wild-type organisms in vivo.

Stage-specific gene expression in Angiostrongylus cantonensis: characterisation and expression of an adult-specific gene

We have previously used differential mRNA display to identify and clone a range of cDNAs derived from genes expressed in only one developmental stage of Angiostrongylus cantonensis. In this paper we report the characterisation of a gene designated Ac-fmp-1 and its product, expressed only in the adult stage. Full length cDNA of 1.5 kb terminates at the 5' end with the conserved nematode spliced leader (SL) sequence and contains one open reading frame coding for a putative protein of 417 amino-acids. The recombinant protein expressed from this open reading frame is antigenic in the infected host and polyclonal antibodies raised against the recombinant protein recognize a 66 kDa protein present only in adult female worms. This protein localises to the muscle cell membranes adjacent to the pseudocoelom. Nine kb of genomic DNA has been amplified by polymerase chain reaction and 7 kb has been cloned and sequenced. This sequence includes 1.5 kb of 5' flanking region and 5.5 kb of the Ac-fmp-1 gene sequence. In this sequence, corresponding to approximately 0.8 kb of the cDNA, the exon/intron pattern has been determined.