Whole-organ isolation approach as a basis for tissue-specific analyses in Schistosoma mansoni

Identification and characterisation of the tegument-expressed aldehyde dehydrogenase SmALDH_312 of Schistosoma mansoni, a target of disulfiram

Schistosomiasis is an infectious disease caused by blood flukes of the genus Schistosoma and affects approximately 200 million people worldwide. Since Praziquantel (PZQ) is the only drug for schistosomiasis, alternatives are needed. By a biochemical approach, we identified a tegumentally expressed aldehyde dehydrogenase (ALDH) of S. mansoni, SmALDH_312. Molecular analyses of adult parasites showed Smaldh_312 transcripts in both genders and different tissues. Physiological and cell-biological experiments exhibited detrimental effects of the drug disulfiram (DSF), a known ALDH inhibitor, on larval and adult schistosomes in vitro. DSF also reduced stem-cell proliferation and caused severe tegument damage in treated worms. In silico-modelling of SmALDH_312 and docking analyses predicted DSF binding, which we finally confirmed by enzyme assays with recombinant SmALDH_312. Furthermore, we identified compounds of the Medicine for Malaria Venture (MMV) pathogen box inhibiting SmALDH_312 activity. Our findings represent a promising starting point for further development towards new drugs for schistosomiasis.

Dissection of schistosome tissues under LC-MS compatible preservative conditions for quantitative proteomics

Schistosomes are blood flukes with specialised tissues and organs, each one playing a pivotal role in perpetuating the parasite life cycle. Herein, we describe a detailed methodology for preserving the proteome of adult Schistosoma mansoni worms during manual dissection for enrichment of tissues associated with the parasite's alimentary tract. We provide step-by-step directions for specimen storage and dissection while in preservative solution, tissue homogenisation, protein extraction and digestion using a methodology fully compatible with downstream quantitative liquid chromatography-mass spectrometry analysis. Our methodology uses label-free and QconCAT-based absolute quantification for detection of S. mansoni oesophageal gland products proposed as vaccine candidates. Through stabilisation of the proteome and minimising sample degradation during dissection our approach has allowed us to access the hidden proteome of target tissues not readily available from total lysates because of their small volume. This protocol can be replicated or adapted to other Schistosoma species lacking quantitative proteomics characterisation of specialised tissues for discovery of proteins with potential diagnostic and therapeutic utility.

Schistosome proteomics: updates and clinical implications

INTRODUCTION

Schistosomes are long-lived blood dwelling helminth parasites using intricate mechanisms to invade, mature, and reproduce inside their vertebrate hosts, whilst simultaneously deploying immune evasion strategies. Their multi-tissue organization and solid body plan presents particular problems for the definition of sub-proteomes.

AREAS COVERED

Here, we focus on the two host-parasite interfaces of the adult worm accessible to the immune system, namely the tegument and the alimentary tract, but also on the secretions of the infective cercaria, the migrating schistosomulum and the mature egg. In parallel, we introduce the concepts of "leakyome' and 'disintegrome' to emphasize the importance of interpreting data in the context of schistosome biology so that misleading conclusions about the distinct proteome compositions are avoided. Lastly, we highlight the possible clinical implications of the reviewed proteomic findings for pathogenesis, vaccine design and diagnostics.

EXPERT OPINION

Proteomics has provided considerable insights into the biology of schistosomes, most importantly for rational selection of novel vaccine candidates that might confer protective immunity, but also into the pathogenesis of schistosomiasis. However, given the increasing sensitivity of mass spectrometric instrumentation, we stress the need for care in data interpretation since schistosomes do not deviate from the fundamental rules of eukaryotic cell biology.

First insights into the autophagy machinery of adult Schistosoma mansoni

Schistosomiasis is a disease of global importance caused by parasitic flatworms, schistosomes, which cause pathogenicity through eggs laid by the female worm inside the host's blood vessels. Maintenance of cellular homeostasis is crucial for parasites, as for other organisms, and is quite likely important for schistosome reproduction and vitality. We hypothesize a role for autophagy in these processes, an evolutionarily conserved and essential cellular degradation pathway. Here, for the first known time, we shed light on the autophagy machinery and its involvement in pairing-dependent processes, vitality and reproduction of Schistosoma mansoni. We identified autophagy genes by in silico analyses and determined the influence of in vitro culture on the transcriptional expression in male and female worms using quantitative real-time PCR. Among the identified autophagy genes were Beclin, Ambra1, Vps34, DRAM, DAP1, and LC3B, of which some showed a sex-dependent expression. Specifically, the death-associated protein DAP1 was significantly more highly expressed in females compared with males, while for the damage-regulated autophagy modulator DRAM it was the opposite. Furthermore, in-vitro culture significantly changed the transcript expression level of DAP1 in female worms. Next, worms were treated with an autophagy inducer (rapamycin) or inhibitors (bafilomycin A1, wortmannin and spautin-1) to evaluate effects on autophagy protein expression, worm vitality, and reproduction. The conversion of the key autophagy protein LC3B, a marker for autophagic activity, was increased by rapamycin and blocked by bafilomycin. All inhibitors affected worm fitness, egg production, and negatively affected the morphology of gonads and intestine. In summary, autophagy genes in S. mansoni show an interesting sex-dependent expression pattern and manipulation of autophagy in S. mansoni by inhibitors induced detrimental effects, which encourages subsequent studies to identify antischistosomal targets within the autophagy machinery.

Innovations and Advances in Schistosome Stem Cell Research

Schistosomes infect about 250 million people globally causing the devastating and persistent disease of schistosomiasis. These blood flukes have a complicated life cycle involving alternating infection of freshwater snail intermediate and definitive mammalian hosts. To survive and flourish in these diverse environments, schistosomes transition through a number of distinct life-cycle stages as a result of which they change their body plan in order to quickly adapt to each new environment. Current research suggests that stem cells, present in adults and larvae, are key in aiding schistosomes to facilitate these changes. Given the recent advances in our understanding of schistosome stem cell biology, we review the key roles that two major classes of cells play in the different life cycle stages during intramolluscan and intramammalian development; these include the germinal cells of sporocysts involved in asexual reproduction in molluscan hosts and the neoblasts of adult worms involved in sexual reproduction in human and other mammalian hosts. These studies shed considerable new light in revealing the stem cell heterogeneity driving the propagation of the schistosome life cycle. We also consider the possibility and value of establishing stem cell lines in schistosomes to advance schistosomiasis research. The availability of such self-renewable resources will provide new platforms to study stem cell behavior and regulation, and to address fundamental aspects of schistosome biology, reproductive development and survival. In turn, such studies will create new avenues to unravel individual gene function and to optimize genome-editing processes in blood flukes, which may lead to the design of novel intervention strategies for schistosomiasis.

Post-genomic progress in helminth parasitology

Helminth parasitology is an important discipline, which poses often unique technical challenges. One challenge is that helminth parasites, particularly those in humans, are often difficult to obtain alive and in sufficient quantities for study; another is the challenge of studying these organisms in vitro – no helminth parasite life cycle has been fully recapitulated outside of a host. Arguably, the key issue retarding progress in helminth parasitology has been a lack of experimental tools and resources, certainly relative to the riches that have driven many parasitologists to adopt free-living model organisms as surrogate systems. In response to these needs, the past 10–12 years have seen the beginnings of helminth parasitology's journey into the ‘omics’ era, with the release of abundant sequencing resources, and the functional genomics tools with which to test biological hypotheses. To reflect this progress, the 2019 Autumn Symposium of the British Society for Parasitology was held in Queen's University Belfast on the topic of ‘post-genomic progress in helminth parasitology’. This issue presents examples of the current state of play in the field, while this editorial summarizes how genomic datasets and functional genomic tools have stimulated impressive recent progress in our understanding of parasite biology.

Insects in anthelminthics research: Lady beetle-derived harmonine affects survival, reproduction and stem cell proliferation of Schistosoma mansoni

Natural products have moved into the spotlight as possible sources for new drugs in the treatment of helminth infections including schistosomiasis. Surprisingly, insect-derived compounds have largely been neglected so far in the search for novel anthelminthics, despite the generally recognized high potential of insect biotechnology for drug discovery. This motivated us to assess the antischistosomal capacity of harmonine, an antimicrobial alkaloid from the harlequin ladybird Harmonia axyridis that raised high interest in insect biotechnology in recent years. We observed remarkably pleiotropic effects of harmonine on physiological, cellular, and molecular processes in adult male and female Schistosoma mansoni at concentrations as low as 5 μM in vitro. This included tegumental damage, gut dilatation, dysplasia of gonads, a complete stop of egg production at 10 μM, and increased production of abnormally shaped eggs at 5 μM. Motility was reduced with an EC50 of 8.8 μM and lethal effects occurred at 10–20 μM within 3 days of culture. Enzyme inhibition assays revealed acetylcholinesterase (AChE) as one potential target of harmonine. To assess possible effects on stem cells, which represent attractive anthelminthic targets, we developed a novel in silico 3D reconstruction of gonads based on confocal laser scanning microscopy of worms after EdU incorporation to allow for quantification of proliferating stem cells per organ. Harmonine significantly reduced the number of proliferating stem cells in testes, ovaries, and also the number of proliferating parenchymal neoblasts. This was further supported by a downregulated expression of the stem cell markers nanos-1 and nanos-2 in harmonine-treated worms revealed by quantitative real-time PCR. Our data demonstrate a multifaceted antischistosomal activity of the lady beetle-derived compound harmonine, and suggest AChE and stem cell genes as possible targets. Harmonine is the first animal-derived alkaloid detected to have antischistosomal capacity. This study highlights the potential of exploiting insects as a source for the discovery of anthelminthics.

Natural compounds represent one of the richest sources for the discovery of new active compounds against diseases such as cancer or infections, including helminth infections that cause the highest disease burden in tropical countries. Surprisingly, insects have been almost completely neglected with respect to anthelminthics discovery although they represent the most species-rich class of animals known on earth, producing a wide spectrum of compounds with biological activities. In insect biotechnology, the harlequin ladybird Harmonia axyridis raised high interest being a rich source of antimicrobial compounds such as the alkaloid harmonine. Harmonine is thought to act as a chemical weapon keeping otherwise detrimental microsporidia in the beetle under control. Testing the antiparasitic potential of harmonine against adult Schistosoma mansoni, one of the most harmful helminths worldwide, resulted in multifaceted negative effects. The compound damaged tissues essential for survival and reproduction of schistosomes (tegument, intestine, gonads) and also affected stem-cell proliferation. Furthermore, we obtained first evidence for acetylcholinesterase as one potential molecular target, which was partially inhibited by harmonine. This is the first time to proof a direct effect of a defined insect-derived compound on a helminth parasite, a finding that will encourage further studies to explore insects as sources of novel anthelminthics.

Preliminary evaluation of neoblast-like stem cell factor and transcript expression profiles in Schistosoma japonicum

Neoblast-like stem cell factors and transcripts are essential for cell proliferation, self-renewal, and differentiation. Recent studies have demonstrated that nanos, sox, and vasa-like transcription factors are associated with neoblast-like stem cells in Schistosoma mansoni and play crucial roles in the regulation of worm development. However, these neoblast-like stem cell factors and transcripts and their expression profiles remain unknown in Schistosoma japonicum. In this study, we identified orthologs of 11 neoblast-like stem cell factors and transcripts in S. japonicum using bioinformatics and confirmed them by PCR. The expression profiles of neoblast-like stem cell factors and transcripts revealed that some of them were highly expressed in certain stages. Sex-based expression analysis revealed that nanos, polo-like kinase, PCNA, cyclin B, and H2A showed significantly higher expression in female worms, whereas ago and bruli showed higher expression in male worms. In addition, we noted that ago, bruli, and pp32 exhibited higher expression in the testes, while nanos, polo-like kinase, cyclin B, H2A, and H2B showed notable higher expression in both isolated ovaries and testes. Our preliminary results are expected to provide important information about the regulatory roles of these stem cell factors in parasite development and sexual maturation.

Evolution of gene dosage on the Z-chromosome of schistosome parasites

XY systems usually show chromosome-wide compensation of X-linked genes, while in many ZW systems, compensation is restricted to a minority of dosage-sensitive genes. Why such differences arose is still unclear. Here, we combine comparative genomics, transcriptomics and proteomics to obtain a complete overview of the evolution of gene dosage on the Z-chromosome of Schistosoma parasites. We compare the Z-chromosome gene content of African (Schistosoma mansoni and S. haematobium) and Asian (S. japonicum) schistosomes and describe lineage-specific evolutionary strata. We use these to assess gene expression evolution following sex-linkage. The resulting patterns suggest a reduction in expression of Z-linked genes in females, combined with upregulation of the Z in both sexes, in line with the first step of Ohno's classic model of dosage compensation evolution. Quantitative proteomics suggest that post-transcriptional mechanisms do not play a major role in balancing the expression of Z-linked genes.

Stem cell heterogeneity drives the parasitic life cycle of Schistosoma mansoni

Schistosomes are parasitic flatworms infecting hundreds of millions of people. These parasites alternate between asexual reproduction in molluscan hosts and sexual reproduction in mammalian hosts; short-lived, water-borne stages infect each host. Thriving in such disparate environments requires remarkable developmental plasticity, manifested by five body plans deployed throughout the parasite’s life cycle. Stem cells in Schistosoma mansoni provide a potential source for such plasticity; however, the relationship between stem cells from different life-cycle stages remains unclear, as does the origin of the germline, required for sexual reproduction. Here, we show that subsets of larvally derived stem cells are likely sources of adult stem cells and the germline. We also identify a novel gene that serves as the earliest marker for the schistosome germline, which emerges inside the mammalian host and is ultimately responsible for disease pathology. This work reveals the stem cell heterogeneity driving the propagation of the schistosome life cycle.

Parasitic flatworms called schistosomes infect around 250 million people, causing the disease schistosomiasis. Schistosomes live complex lives, spending part of their life cycle inside snails and part of it inside mammals; short-lived, water-borne stages infect each of these hosts. To thrive in such different environments, schistosomes go through several life-cycle stages. At each stage the flatworms transition to a new body plan adapted to its new environment. Understanding how these transitions occur could help researchers devise new strategies for eliminating these parasites.

Previous research suggested that stem cells help schistosomes transition to new body plans. Stem cells have the ability to transform into many different cell types, and have been found in schistosome larvae and adults. However, the relationship between the larval and adult stem cells was not clear.

Wang et al. used transcriptional profiling, a technique that measures the genes currently in use in different cells, to study the stem cells in the schistosome species Schistosoma mansoni. This uncovered four types of stem cell, each of which uses a slightly different combination of genes. Examining the behaviour of these cells at different schistosome life-cycle stages revealed that certain larval stem cells produce adult stem cells. Other larval stem cells seem to be the source of the ‘germline’ cells that make gametes (egg and sperm) and allow the parasites to reproduce sexually.

Schistosomes only produce germline cells when they are inside mammals. Wang et al. found that as juvenile flatworms develop inside mouse blood vessels, a gene called eledh becomes active in some of their stem cells. Further investigation showed that this activity is the earliest indicator that germline cells are developing and is also required for proper development of the germline. This knowledge, along with future work to characterize the roles of the stem cell populations identified by Wang et al., could ultimately help researchers develop new ways to stop the spread of schistosomiasis.

Tissue-specific transcriptome analyses provide new insights into GPCR signalling in adult Schistosoma mansoni

Schistosomes are blood-dwelling trematodes with global impact on human and animal health. Because medical treatment is currently based on a single drug, praziquantel, there is urgent need for the development of alternative control strategies. The Schistosoma mansoni genome project provides a platform to study and connect the genetic repertoire of schistosomes to specific biological functions essential for successful parasitism. G protein-coupled receptors (GPCRs) form the largest superfamily of transmembrane receptors throughout the Eumetazoan phyla, including platyhelminths. Due to their involvement in diverse biological processes, their pharmacological importance, and proven druggability, GPCRs are promising targets for new anthelmintics. However, to identify candidate receptors, a more detailed understanding of the roles of GPCR signalling in schistosome biology is essential. An updated phylogenetic analysis of the S. mansoni GPCR genome (GPCRome) is presented, facilitated by updated genome data that allowed a more precise annotation of GPCRs. Additionally, we review the current knowledge on GPCR signalling in this parasite and provide new insights into the potential roles of GPCRs in schistosome reproduction based on the findings of a recent tissue-specific transcriptomic study in paired and unpaired S. mansoni. According to the current analysis, GPCRs contribute to gonad-specific functions but also to nongonad, pairing-dependent processes. The latter may regulate gonad-unrelated functions during the multifaceted male-female interaction. Finally, we compare the schistosome GPCRome to that of another parasitic trematode, Fasciola, and discuss the importance of GPCRs to basic and applied research. Phylogenetic analyses display GPCR diversity in free-living and parasitic platyhelminths and suggest diverse functions in schistosomes. Although their roles need to be substantiated by functional studies in the future, the data support the selection of GPCR candidates for basic and applied studies, invigorating the exploitation of this important receptor class for drug discovery against schistosomes but also other trematodes.

A gene expression atlas of adult Schistosoma mansoni and their gonads

RNA-Seq has proven excellence in providing information about the regulation and transcript levels of genes. We used this method for profiling genes in the flatworm Schistosoma mansoni. This parasite causes schistosomiasis, an infectious disease of global importance for human and animals. The pathology of schistosomiasis is associated with the eggs, which are synthesized as a final consequence of male and female adults pairing. The male induces processes in the female that lead to the full development of its gonads as a prerequisite for egg production. Unpaired females remain sexually immature. Based on an organ-isolation method we obtained gonad tissue for RNA extraction from paired and unpaired schistosomes, with whole adults included as controls. From a total of 23 samples, we used high-throughput cDNA sequencing (RNA-Seq) on the Illumina platform to profile gene expression between genders and tissues, with and without pairing influence. The data obtained provide a wealth of information on the reproduction biology of schistosomes and a rich resource for exploitation through basic and applied research activities.

Evidence for Integrin - Venus Kinase Receptor 1 Alliance in the Ovary of Schistosoma mansoni Females Controlling Cell Survival

In metazoan integrin signaling is an important process of mediating extracellular and intracellular communication processes. This can be achieved by cooperation of integrins with growth factor receptors (GFRs). Schistosoma mansoni is a helminth parasite inducing schistosomiasis, an infectious disease of worldwide significance for humans and animals. First studies on schistosome integrins revealed their role in reproductive processes, being involved in spermatogenesis and oogenesis. With respect to the roles of eggs for maintaining the parasite´s life cycle and for inducing the pathology of schistosomiasis, elucidating reproductive processes is of high importance. Here we studied the interaction of the integrin receptor Smβ-Int1 with the venus kinase receptor SmVKR1 in S. mansoni. To this end we cloned and characterized SmILK, SmPINCH, and SmNck2, three putative bridging molecules for their role in mediating Smβ-Int1/SmVKR1 cooperation. Phylogenetic analyses showed that these molecules form clusters that are specific for parasitic platyhelminths as it was shown for integrins before. Transcripts of all genes colocalized in the ovary. In Xenopus oocytes germinal vesicle breakdown (GVBD) was only induced if all members were simultaneously expressed. Coimmunoprecipitation results suggest that a Smβ-Int1-SmILK-SmPINCH-SmNck2-SmVKR1 complex can be formed leading to the phosphorylation and activation of SmVKR1. These results indicate that SmVKR1 can be activated in a ligand-independent manner by receptor-complex interaction. RNAi and inhibitor studies to knock-down SmILK as a representative complex member concurrently revealed effects on the extracellular matrix surrounding the ovary and oocyte localization within the ovary, oocyte survival, and egg production. By TUNEL assays, confocal laser scanning microscopy (CLSM), Caspase-3 assay, and transcript profiling of the pro-apoptotic BCL-2 family members BAK/BAX we obtained first evidence for roles of this signaling complex in mediating cell death in immature and primary oocytes. These results suggest that the Smβ-Int1/SmVKR1 signaling complex is important for differentiation and survival in oocytes of paired schistosomes.

Parasites of the genus Schistosoma cause schistosomiasis, a life-threatening infectious disease for humans and animals worldwide. Among the remarkable biological features of schistosomes is the differentiation of the female gonads which is controlled by pairing with the male and a prerequisite for egg production. Eggs, however, are not only important for the maintenance of the life-cycle; they also cause the pathological consequences of schistosomiasis. Part of the eggs gets trapped in host tissues such as liver and spleen and trigger inflammatory processes, finally leading to liver cirrhosis. Research activities of the last decade have indicated that different families of cellular and receptor-type kinases but also integrins contribute to the control of mitogenic activity and differentiation the female goands. In this context an unusual class of receptor tyrosine kinases (RTKs) has been identified, the venus kinase receptors (SmVKRs). By biochemical and molecular approaches we demonstrate that SmVKR1 activation can be achieved by cooperation with a signaling complex consisting of the beta integrin receptor Smβ-Int1 and the bridging molecules SmILK, SmPINCH, SmNck2. Besides unravelling a novel way of SmVKR1 activation, we provide evidence that this complex controls the differentiation status of oocytes by regulating cell death-associated processes.

Methods for Studying the Germline of the Human Parasite Schistosoma mansoni

Schistosomes are flatworm parasites that claim the lives of more than 200,000 people in poverty-stricken regions every year. Much of the pathology due to infection is the direct result of injury spurred by the parasite's eggs becoming lodged in host tissues. Thus, asking basic questions about germ cell biology may not only identify novel therapeutic approaches, but could also uncover conserved mechanisms that regulate the germline in diverse metazoa. Here, we detail useful methods for studying the schistosome germline including EdU labeling, whole-mount in situ hybridization, and RNA interference. These methods will hopefully lead to new insights about germline development in the schistosome and facilitate new investigators to begin asking questions about these important and fascinating parasites.

Schistosome sex matters: a deep view into gonad-specific and pairing-dependent transcriptomes reveals a complex gender interplay

As a key event for maintaining life cycles, reproduction is a central part of platyhelminth biology. In case of parasitic platyhelminths, reproductive processes can also contribute to pathology. One representative example is the trematode Schistosoma, which causes schistosomiasis, an infectious disease, whose pathology is associated with egg production. Among the outstanding features of schistosomes is their dioecious lifestyle and the pairing-dependent differentiation of the female gonads which finally leads to egg synthesis. To analyze the reproductive biology of Schistosoma mansoni in-depth we isolated complete ovaries and testes from paired and unpaired schistosomes for comparative RNA-seq analyses. Of >7,000 transcripts found in the gonads, 243 (testes) and 3,600 (ovaries) occurred pairing-dependently. Besides the detection of genes transcribed preferentially or specifically in the gonads of both genders, we uncovered pairing-induced processes within the gonads including stem cell-associated and neural functions. Comparisons to work on neuropeptidergic signaling in planarian showed interesting parallels but also remarkable differences and highlights the importance of the nervous system for flatworm gonad differentiation. Finally, we postulated first functional hints for 235 hypothetical genes. Together, these results elucidate key aspects of flatworm reproductive biology and will be relevant for basic as well as applied, exploitable research aspects.

Identification of new markers for the Schistosoma mansoni vitelline lineage

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Transcriptional profiling identifies candidate factors associated with the schistosome vitellarium.

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In situ hybridization confirms many new markers of this tissue.

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New cell type-specific markers for various stages of vitellocyte development are reported.

Schistosomes cause significant morbidity and mortality in millions of the world’s poorest people. While parasite egg-induced inflammation is the primary driver of host pathology, relatively little is known at the molecular level about the organ systems that participate in schistosome egg production (i.e., testes, ovaries and vitellaria). Here we use transcriptional profiling and in situ hybridization to characterise the vitellarium of Schistosoma mansoni. We uncovered several previously uncharacterised vitellaria-specific factors and defined molecular markers for various stages in the vitellocyte differentiation process. These data provide the framework for future in-depth molecular studies exploring the biology of this important parasite organ.

Human TNF-α induces differential protein phosphorylation in Schistosoma mansoni adult male worms

Schistosoma mansoni and its vertebrate host have a complex and intimate connection in which several molecular stimuli are exchanged and affect both organisms. Human tumor necrosis factor alpha (hTNF-α), a pro-inflammatory cytokine, is known to induce large-scale gene expression changes in the parasite and to affect several parasite biological processes such as metabolism, egg laying, and worm development. Until now, the molecular mechanisms for TNF-α activity in worms are not completely understood. Here, we aimed at exploring the effect of hTNF-α on S. mansoni protein phosphorylation by 2D gel electrophoresis followed by a quantitative analysis of phosphoprotein staining and protein identification by mass spectrometry. We analyzed three biological replicates of adult male worms exposed to hTNF-α and successfully identified 32 protein spots with a statistically significant increase in phosphorylation upon in vitro exposure to hTNF-α. Among the differentially phosphorylated proteins, we found proteins involved in metabolism, such as glycolysis, galactose metabolism, urea cycle, and aldehyde metabolism, as well as proteins related to muscle contraction and to cytoskeleton remodeling. The most differentially phosphorylated protein (30-fold increase in phosphorylation) was 14-3-3, whose function is known to be modulated by phosphorylation, belonging to a signal transduction protein family that regulates a variety of processes in all eukaryotic cells. Further, 75% of the identified proteins are known in mammals to be related to TNF-α signaling, thus suggesting that TNF-α response may be conserved in the parasite. We propose that this work opens new perspectives to be explored in the study of the molecular crosstalk between host and pathogen.

Inhibition of Schistosoma mansoni ether-a-go-go related gene-encoded potassium channels leads to hypermotility and impaired egg production

The purpose of this work was to investigate the effect of ether-a-go-go related gene (ERG) potassium channel inhibition on Schistosoma mansoni. Use of dofetilide to block the schistosome ERGs resulted in a striking 'corkscrew' effect. The worms were unable to control their motility; they were hypermotile. The treated worms produced abnormal eggs, some of which consisted of little more than a spine. One of the S. mansoni ERGs (SmERGs), Smp_161140, was chosen for further study by RNAi. The transcript was knocked down to 50% compared to the controls. These RNAi-treated worms demonstrated seizure-like movements. In S. mansoni, as in other organisms, ERG channels seem to play a role in regulating muscle excitability. This work shows that egg production can be greatly reduced by effectively targeting muscle coordination in these important parasites.

Isolation, enrichment and primary characterisation of vitelline cells from Schistosoma mansoni obtained by the organ isolation method

In the emerging era of post-genomic research on schistosomes, new methods are required to functionally analyse genes of interest in more detail. Among other tools, schistosome cell lines are needed to overcome present research constraints. Based on a recently established organ isolation protocol for adult Schistosoma mansoni, we report here on the successful enrichment of vitellarium tissue and isolation of vitelline cells. Morphological analyses performed by bright field, fluorescence, scanning and transmission electron microscopy showed typical features of S1 to S4 stage vitelline cells. In addition, molecular analyses using reverse transcription-PCR confirmed the identity of vitelline cells. Cytological and physiological studies included staining experiments with viability dyes and a neutral lipid stain, as well as calcium (Ca2+) imaging. Together they demonstrated cell viability, the possibility to define the differentiation stage of individual vitelline cells, and the suitability to investigate Ca(2+)-associated processes herein. Finally, fluorescence-activated cell sorting was shown to be a convenient way to separate and enrich S1 to S4 stage vitelline cells. In summary, these results demonstrate the expedience of the organ isolation protocol to obtain vitellarium tissue. Importantly, the protocol allows vitelline cells representing defined differentiation stages to be purified, which can be cultured in vitro and used to investigate diverse aspects of schistosome reproductive biology in the post-genomic era.

New research tools for urogenital schistosomiasis

Approximately 200,000,000 people have schistosomiasis (schistosome infection). Among the schistosomes, Schistosoma haematobium is responsible for the most infections, which are present in 110 million people globally, mostly in sub-Saharan Africa. This pathogen causes an astonishing breadth of sequelae: hematuria, anemia, dysuria, stunting, uremia, bladder cancer, urosepsis, and human immunodeficiency virus coinfection. Refined estimates of the impact of schistosomiasis on quality of life suggest that it rivals malaria. Despite S. haematobium's importance, relevant research has lagged. Here, we review advances that will deepen knowledge of S. haematobium. Three sets of breakthroughs will accelerate discoveries in the pathogenesis of urogenital schistosomiasis (UGS): (1) comparative genomics, (2) the development of functional genomic tools, and (3) the use of animal models to explore S. haematobium-host interactions. Comparative genomics for S. haematobium is feasible, given the sequencing of multiple schistosome genomes. Features of the S. haematobium genome that are conserved among platyhelminth species and others that are unique to S. haematobium may provide novel diagnostic and drug targets for UGS. Although there are technical hurdles, the integrated use of these approaches can elucidate host-pathogen interactions during this infection and can inform the development of techniques for investigating schistosomes in their human and snail hosts and the development of therapeutics and vaccines for the control of UGS.

Transcriptional profiling of the oesophageal gland region of male worms of Schistosoma mansoni

The intestinal tract of schistosomes opens at the mouth and leads into the foregut or oesophageal region that is lined with syncytium continuous with the apical cytoplasm of the tegument. The oesophagus is surrounded by a specialised gland, the oesophageal gland. This gland releases materials into the lumen of the oesophagus and the region is thought to initiate the lysis of erythrocytes and neutralisation of immune effectors of the host. The oesophageal region is present in the early invasive schistosomulum, a stage potentially targetable by anti-schistosome vaccines. We used a 44k oligonucleotide microarray to identify highly up-regulated genes in microdissected frozen sections of the oesophageal gland of male worms of S. mansoni. We show that 122 genes were up-regulated 2-fold or higher in the oesophageal gland compared with a whole male worm tissue control. The enriched genes included several associated with lipid metabolism and transmembrane transport as well as some micro-exon genes. Since the oesophageal gland is important in the initiation of digestion and the fact that it develops early after invasion of the mammalian host, further study of selected highly up-regulated functionally important genes in this tissue may reveal new anti-schistosome intervention targets for schistosomiasis control.

Receptor tyrosine kinases and schistosome reproduction: new targets for chemotherapy

Schistosome parasites still represent a serious public health concern and a major economic problem in developing countries. Pathology of schistosomiasis is mainly due to massive egg production by these parasites and to inflammatory responses raised against the eggs which are trapped in host tissues. Tyrosine kinases (TKs) are key molecules that control cell differentiation and proliferation and they already represent important targets in cancer therapy. During recent years, it has been shown that receptor tyrosine kinases (RTK) signaling was active in reproductive organs and that it could regulate sexual maturation of schistosomes and egg production. This opens interesting perspectives for the control of transmission and pathogenesis of schistosomiasis based on new therapies targeting schistosome RTKs. This review relates the numerous data showing the major roles of kinase signaling in schistosome reproduction. It describes the conserved and particular features of schistosome RTKs, their implication in gametogenesis and reproduction processes and summarizes recent works indicating that RTKs and their signaling partners are interesting chemotherapeutical targets in new programs of control.

Gonad RNA-specific qRT-PCR analyses identify genes with potential functions in schistosome reproduction such as SmFz1 and SmFGFRs

In the search for new strategies to fight schistosomiasis, the unique reproductive biology of Schistosoma mansoni has come into the focus of research. The development of the gonads and the ability of egg production are fundamental not only for continuing the life cycle but also for pathogenicity. Previous studies of schistosome biology demonstrated an influence of pairing on gonad development of the female and on gene expression profiles in both genders. Due to the limited access to specific tissues, however, most of these studies were done at the level of whole worms neglecting individual tissues that may be targets of pairing-dependent processes. Recently, we established a protocol allowing the isolation of testes and ovaries from adult S. mansoni. Here, we describe tissue-specific qRT-PCR analyses comparing transcript levels of selected genes on the basis of RNA from gonads and whole worms. Gene expression in ovary and testes was in some cases found to be significantly influenced by pairing, which was not traceable in whole worms. Among the candidate genes identified as regulated by pairing in gonads were the frizzled homolog SmFz1 and the two fibroblast growth factor receptor homologs SmFGFR-A and SmFGFR-B. First functional characterizations were done, including comparative qRT-PCR analyses, in situ-localization experiments, heterologous expression in Xenopus oocytes (SmFGFR-A/B), and inhibitor studies using the Fz/Dvl-pathway inhibitor 3289-8625, or BIBF1120 blocking FGFR-signaling. Besides confirming gonad localization and receptor functions, inhibitor-induced phenotypes were observed in vitro such as decreased egg production as well as drastic effects on gonad differentiation, morphology, embryogenesis, and survival of adult worms. In summary, these results emphasise the usefulness of tissue-specific qRT-PCRs for selection of candidate genes with important roles in reproduction, allowing subsequent studies to determine their suitability as drug targets.

Venus kinase receptors control reproduction in the platyhelminth parasite Schistosoma mansoni

The Venus Kinase Receptor (VKR) is a single transmembrane molecule composed of an intracellular tyrosine kinase domain close to that of insulin receptor and an extracellular Venus Flytrap (VFT) structure similar to the ligand binding domain of many class C G Protein Coupled Receptors. This receptor tyrosine kinase (RTK) was first discovered in the platyhelminth parasite Schistosoma mansoni, then in a large variety of invertebrates. A single vkr gene is found in most genomes, except in S. mansoni in which two genes Smvkr1 and Smvkr2 exist. VKRs form a unique family of RTKs present only in invertebrates and their biological functions are still to be discovered. In this work, we show that SmVKRs are expressed in the reproductive organs of S. mansoni, particularly in the ovaries of female worms. By transcriptional analyses evidence was obtained that both SmVKRs fulfill different roles during oocyte maturation. Suppression of Smvkr expression by RNA interference induced spectacular morphological changes in female worms with a strong disorganization of the ovary, which was dominated by the presence of primary oocytes, and a defect of egg formation. Following expression in Xenopus oocytes, SmVKR1 and SmVKR2 receptors were shown to be activated by distinct ligands which are L-Arginine and calcium ions, respectively. Signalling analysis in Xenopus oocytes revealed the capacity of SmVKRs to activate the PI3K/Akt/p70S6K and Erk MAPK pathways involved in cellular growth and proliferation. Additionally, SmVKR1 induced phosphorylation of JNK (c-Jun N-terminal kinase). Activation of JNK by SmVKR1 was supported by the results of yeast two-hybrid experiments identifying several components of the JNK pathway as specific interacting partners of SmVKR1. In conclusion, these results demonstrate the functions of SmVKR in gametogenesis, and particularly in oogenesis and egg formation. By eliciting signalling pathways potentially involved in oocyte proliferation, growth and migration, these receptors control parasite reproduction and can therefore be considered as potential targets for anti-schistosome therapies.

Schistosomiasis is a chronic, debilitating disease affecting more than 200 million people in the world caused by parasitic flatworms of the genus Schistosoma. Pathology is mainly due to massive egg production by parasites and formation of granulomas around the eggs trapped in liver and different organs. Therefore, targeting the molecular processes responsible for gonad development or egg production in schistosomes appears as a valuable strategy to reduce pathogenesis and dissemination of schistosomiasis. In the present study, we investigated the importance of Venus Kinase Receptors (VKRs) which are unusual receptor tyrosine kinases (RTKs) with an extracellular Venus Flytrap (VFT) ligand-binding domain in the control of reproduction of schistosomes. SmVKRs are expressed in female ovaries of Schistosoma mansoni and the knock-down of their expression provoked dramatic alterations of the oocyte content in ovaries and reduction of egg formation. SmVKRs were also shown to activate different signalling pathways potentially involved in oocyte proliferation, growth and migration. Therefore our results demonstrate that VKRs are essential actors of oogenesis and egg formation in S. mansoni. Moreover, their presence in a large variety of invertebrate species including other helminth parasites and insect parasite vectors can open new perspectives in the control of various vector-borne infectious diseases.

Venus kinase receptors: prospects in signaling and biological functions of these invertebrate kinases

Venus kinase receptors (VKRs) form a family of invertebrate receptor tyrosine kinases (RTKs) initially discovered in the parasitic platyhelminth Schistosoma mansoni. VKRs are single transmembrane receptors that contain an extracellular venus fly trap structure similar to the ligand-binding domain of G protein-coupled receptors of class C, and an intracellular tyrosine kinase domain close to that of insulin receptors. VKRs are found in a large variety of invertebrates from cnidarians to echinoderms and are highly expressed in larval stages and in gonads, suggesting a role of these proteins in embryonic and larval development as well as in reproduction. VKR gene silencing could demonstrate the function of these receptors in oogenesis as well as in spermatogenesis in S. mansoni. VKRs are activated by amino acids and are highly responsive to arginine. As many other RTKs, they form dimers when activated by ligands and induce intracellular pathways involved in protein synthesis and cellular growth, such as MAPK and PI3K/Akt/S6K pathways. VKRs are not present in vertebrates or in some invertebrate species. Questions remain open about the origin of this little-known RTK family in evolution and its role in emergence and specialization of Metazoa. What is the meaning of maintenance or loss of VKR in some phyla or species in terms of development and physiological functions? The presence of VKRs in invertebrates of economical and medical importance, such as pests, vectors of pathogens, and platyhelminth parasites, and the implication of these RTKs in gametogenesis and reproduction processes are valuable reasons to consider VKRs as interesting targets in new programs for eradication/control of pests and infectious diseases, with the main advantage in the case of parasite targeting that VKR counterparts are absent from the vertebrate host kinase panel.

Combinatory microarray and SuperSAGE analyses identify pairing-dependently transcribed genes in Schistosoma mansoni males, including follistatin

Background

Schistosomiasis is a disease of world-wide importance and is caused by parasitic flatworms of the genus Schistosoma. These parasites exhibit a unique reproduction biology as the female's sexual maturation depends on a constant pairing-contact to the male. Pairing leads to gonad differentiation in the female, and even gene expression of some gonad-associated genes is controlled by pairing. In contrast, no morphological changes have been observed in males, although first data indicated an effect of pairing also on gene transcription in males.

Methodology/Principal Findings

To investigate the influence of pairing on males, we performed a combinatory approach applying SuperSAGE and microarray hybridization, generating the most comprehensive data-set on differential transcription available to date. Of 6,326 sense transcripts detected by both analyses, 29 were significantly differentially transcribed. Besides mutual confirmation, the two methods complemented each other as shown by data comparison and real-time PCR, which revealed a number of genes with consistent regulation across all methods. One of the candidate genes, follistatin of S. mansoni (SmFst) was characterized in more detail by in situ hybridization and yeast two-hybrid (Y2H) interaction analyses with potential binding partners.

Conclusions/Significance

Beyond confirming previously hypothesized differences in metabolic processes between pairing-experienced (EM) and pairing-unexperienced males (UM), our data indicate that neuronal processes are involved in male-female interaction but also TGFβ-signaling. One candidate revealing significant down-regulation in EM was the TGFβ-pathway controlling molecule follistatin (SmFst). First functional analyses demonstrated SmFst interaction with the S. mansoni TGFβ-receptor agonists inhibin/activin (SmInAct) and bone morphogenic protein (SmBMP), and all molecules colocalized in the testes. This indicates a yet unknown role of the TGFβ-pathway for schistosome biology leading to male competence and a possible influence of pairing on the male gonad.

Schistosomiasis is an important infectious disease caused by worm parasites of the genus Schistosoma and directly affects more than 240 million people in 78 tropical and sub-tropical countries but also animals. Pathogenesis is triggered by eggs that are produced by paired females and get trapped in liver and gut causing severe inflammation. While studies have concentrated on the reproductive biology of schistosome females in the past, not much is known about males even though they are indispensable for female sexual development and egg production. Therefore, we studied pairing-dependent processes in S. mansoni males using two independent transcriptomics approaches providing a congruent and most comprehensive data-set on genes being differentially transcribed between pairing-experienced, competent males and pairing-unexperienced, naive males. Besides confirming former studies concerning changes in metabolic processes, our results give new insights into processes leading to male competence indicating among others a potential role of neurotransmitters and TGFβ signal-transduction processes. We especially highlight the follistatin gene SmFst, which codes for an inhibitor of the TGFβ-pathway. SmFst transcription was localized in the testes and found to be down-regulated in pairing-experienced males. This indicates a yet unknown function of pairing on the male gonad and a further role of TGFβ-signaling for schistosome biology.