The ultrastructural architecture of the adult Schistosoma japonicum tegument

Characterizing genetic variation on the Z chromosome in Schistosoma japonicum reveals host-parasite co-evolution

BACKGROUND

Schistosomiasis is a neglected tropical disease that afflicts millions of people worldwide; it is caused by Schistosoma, the only dioecious flukes with ZW systems. Schistosoma japonicum is endemic to Asia; the Z chromosome of S. japonicum comprises one-quarter of the entire genome. Detection of positive selection using resequencing data to understand adaptive evolution has been applied to a variety of pathogens, including S. japonicum. However, the contribution of the Z chromosome to evolution and adaptation is often neglected.

METHODS

We obtained 1,077,526 high-quality SNPs on the Z chromosome in 72 S. japonicum using re-sequencing data publicly. To examine the faster Z effect, we compared the sequence divergence of S. japonicum with two closely related species, Schistosoma haematobium and S. mansoni. Genetic diversity was compared between the Z chromosome and autosomes in S. japonicum by calculating the nucleotide diversity (π) and Dxy values. Population structure was also assessed based on PCA and structure analysis. Besides, we employed multiple methods including Tajima's D, FST, iHS, XP-EHH, and CMS to detect positive selection signals on the Z chromosome. Further RNAi knockdown experiments were performed to investigate the potential biological functions of the candidate genes.

RESULTS

Our study found that the Z chromosome of S. japonicum showed faster evolution and more pronounced genetic divergence than autosomes, although the effect may be smaller than the variation among genes. Compared with autosomes, the Z chromosome in S. japonicum had a more pronounced genetic divergence of sub-populations. Notably, we identified a set of candidate genes associated with host-parasite co-evolution. In particular, LCAT exhibited significant selection signals within the Taiwan population. Further RNA interference experiments suggested that LCAT is necessary for S. japonicum survival and propagation in the definitive host. In addition, we identified several genes related to the specificity of the intermediate host in the C-M population, including Rab6 and VCP, which are involved in adaptive immune evasion to the host.

CONCLUSIONS

Our study provides valuable insights into the adaptive evolution of the Z chromosome in S. japonicum and further advances our understanding of the co-evolution of this medically important parasite and its hosts.

What about the Cytoskeletal and Related Proteins of Tapeworms in the Host's Immune Response? An Integrative Overview

Recent advances have increased our understanding of the molecular machinery in the cytoskeleton of mammalian cells, in contrast to the case of tapeworm parasites, where cytoskeleton remains poorly characterized. The pertinence of a better knowledge of the tapeworm cytoskeleton is linked to the medical importance of these parasitic diseases in humans and animal stock. Moreover, its study could offer new possibilities for the development of more effective anti-parasitic drugs, as well as better strategies for their surveillance, prevention, and control. In the present review, we compile the results of recent experiments on the cytoskeleton of these parasites and analyze how these novel findings might trigger the development of new drugs or the redesign of those currently used in addition to supporting their use as biomarkers in cutting-edge diagnostic tests.

Characterization of aspartyl aminopeptidase from Schistosoma japonicum

The tegument of schistosomes is the interface between the worm and the host environment. Some molecules distributed on the tegument participate in host-parasite interactions. Aspartyl aminopeptidase (AAP), identified on the tegument of Schistosoma japonicum (S. japonicum), facilitate protein turnover by acting in concert with other aminopeptidases. In this study, the gene encoding S. japonicum aspartyl aminopeptidase (SjAAP) was cloned, expressed and characterized. Quantitative real-time PCR analysis showed that SjAAP was expressed in all studied developmental stages. The transcript level was higher in 8, 14, 21, and 28 days old worms than the other detected stages. Moreover, the level of expression in 42-day-old male worms was significantly higher than that in females. The recombinant SjAAP (rSjAAP) was expressed as both supernatant and inclusion bodies in Escherichia coli BL21 cells. The enzymatic activity of rSjAAP was 4.45 U/mg. The Km and Vmax values for H-Asp-pNA hydrolysis were discovered to be 5.93 mM and 0.018 mM·min^-1. Immunofluorescence analysis revealed that SjAAP is primarily distributed on the tegument and parenchyma of schistosomes. Western blot showed that rSjAAP possessed good immunogenicity. Although specific antibodies were produced in BALB/c mice vaccinated with rSjAAP emulsified with ISA 206 adjuvant, no significant reduction of worm burden and number of eggs in the liver was observed. Therefore, rSjAAP may not be suitable to act as a potential vaccine candidate against schistosomiasis japonica in mice. However, this study provides some foundation for further exploration of the biological function of this molecule.

Adult schistosomes have an epithelial bacterial population distinct from the surrounding mammalian host blood

Background

Schistosomiasis is a neglected tropical parasitic and chronic disease affecting hundreds of millions of people. Adult schistosomes reside in the blood stream of the definitive mammalian host. These helminth parasites possess two epithelial surfaces, the tegument and the gastrodermis, both of which interact with the host during immune evasion and in nutrient uptake.

Methods

Female ARC Swiss mice (4–6 weeks old) were infected percutaneously with Schistosoma japonicum cercariae freshly shed from Oncomelania hupensis quadrasi snails (Philippines strain). Fluorescent in situ hybridisation (FISH) was performed by using fresh adult S. japonicum perfused from those infected mice. Adult S. japonicum worms were processed to isolate the tegument from the carcass containing the gastrodermis; blood and bile were collected individually from infected and uninfected mice. Total DNA extracted from all those samples were used for microbiome profiling.

Results

FISH and microbiome profiling showed the presence of bacterial populations on two epithelial surfaces of adult worms, suggesting they were distinct not only from the host blood but also from each other. Whereas microbial diversity was reduced overall in the parasite epithelial tissues when compared with that of host blood, specific bacterial taxa, including Anoxybacillus and Escherichia, were elevated on the tegument. Minimal differences were evident in the microbiome of host blood during an active infection, compared with that of control uninfected blood. However, sampling of bile from infected animals identified some differences compared with controls, including elevated levels of Limnohabitans, Clostridium and Curvibacter.

Conclusions

Using FISH and microbial profiling, we were able to demonstrate, for the first time, that bacteria are presented on the epithelial surfaces of adult schistosomes. These schistosome surface-associated bacteria, which are distinct from the host blood microenvironment, should be considered as a new and important component of the host-schistosome interaction. The importance of individual bacterial species in relation to schistosome parasitism needs further elucidation.

Fifty years of the schistosome tegument: discoveries, controversies, and outstanding questions

The unique multilaminate appearance of the tegument surface of schistosomes was first described in 1973, in one of the earliest volumes of the International Journal for Parasitology. The present review, published almost 50 years later, traces the development of our knowledge of the tegument, starting with those earliest cytological advances, particularly the surface plasma membrane-membranocalyx complex, through an era of protein discovery to the modern age of protein characterization, aided by proteomics. More recently, analysis of single cell transcriptomes of schistosomes is providing insight into the organisation of the cell bodies that support the surface syncytium. Our understanding of the tegument, notably the nature of the proteins present within the plasma membrane and membranocalyx, has provided insights into how the schistosomes interact with their hosts but many aspects of how the tegument functions remain unanswered. Among the unresolved aspects are those concerned with maintenance and renewal of the surface membrane complex, and whether surface proteins and membrane components are recycled. Current controversies arising from investigations about whether the tegument is a source of extracellular vesicles during parasitism, and if it is covered with glycolytic enzymes, are evaluated in the light of cytological and proteomic knowledge of the layer.

Synergistic effect of combination chemotherapy with praziquantel and DW-3-15 for Schistosoma japonicum in vitro and in vivo

BACKGROUND

Schistosomiasis is a debilitating and neglected tropical disease for which praziquantel (PZQ) remains the first-choice drug for treatment and control of the disease. In our previous studies, we found that the patented compound DW-3-15 (patent no. ZL201110142538.2) displayed significant and stabilized antiparasitic activity through a mechanism that might be distinct from PZQ. Here, we investigated the antischistosomal efficacy of PZQ combined with DW-3-15 against schistosomula and adult worms of Schistosoma japonicum in vitro and in vivo, to verify whether there was a synergistic effect of the two compounds.

METHODS

The antischistosomal efficacy of PZQ combined with DW-3-15 in comparison with an untreated control and monotherapy group against schistosomula and adult worms was assessed both in vitro and in vivo. Parasitological studies, scanning electron microscopy, combination index, and histopathological analysis were used for the assessment.

RESULTS

The results showed significantly reduced viability of schistosomes, achieving 100% viability reduction for juveniles and males by combination chemotherapy using PZQ together with DW-3-15 in vitro. The combination index was 0.28, 0.27, and 0.53 at the higher concentration of PZQ combined with DW-3-15 against juveniles, males, and females, respectively, indicating that the two compounds display strong synergism. Scanning electron microscopy observations also demonstrated that the compound combination induced more severe and extensive alterations to the tegument and subtegument of S. japonicum than those with each compound alone. In vivo, compared with the single-compound-treated group, the group treated with the higher-dose combination demonstrated the best schistosomicidal efficacy, with significantly reduced worm burden, egg burden, and granuloma count and area, which was evident against schistosomula and adult worms.

CONCLUSIONS

Our study provides a potential novel chemotherapy for schistosomiasis caused by S. japonicum. It would improve the antischistosomal effect on schistosomula and adult worms of S. japonicum, and decrease individual dosages.

Revisiting the Schistosoma japonicum life cycle transcriptome for new insights into lung schistosomula development

Schistosome parasites are complex trematode blood flukes responsible for the disease schistosomiasis; a global health concern prevalent in many tropical and sub-tropical countries. While established transcriptomic databases are accessed ad hoc to facilitate studies characterising specific genes or gene families, a more comprehensive systematic updating of gene annotation and survey of the literature to aid in annotation and context is rarely addressed. We have reanalysed an online transcriptomic dataset originally published in 2009, where seven life cycle stages of Schistosoma japonicum were examined. Using the online pathway analysis tool Reactome, we have revisited key data from the original study. A key focus of this study was to improve the interpretation of the gene expression profile of the developmental lung-stage schistosomula, since it is one of the principle targets for worm elimination. Highly enriched transcripts, associated with lung schistosomula, were related to a number of important biological pathways including host immune evasion, energy metabolism and parasitic development. Revisiting large transcriptomic databases should be considered in the context of substantial new literature. This approach could aid in the improved understanding of the molecular basis of parasite biology. This may lead to the identification of new targets for diagnosis and therapies for schistosomes, and other helminths.

Lipid profile of Trichinella papuae muscle-stage larvae

Outbreaks of trichinellosis caused by Trichinella papuae have been reported in South-East Asia. Mebendazole and thiabendazole are the treatments of choice for trichinellosis; however, both drugs result in significant side effects and are less effective for muscle-stage larvae (L1). An alternative therapeutic agent is needed to improve treatment. Information on lipid composition and metabolic pathways may bridge gaps in our knowledge and lead to new antiparasitics. The T. papuae L1 lipidome was analysed using a mass spectrometry-based approach, and 403 lipid components were identified. Eight lipid classes were found and glycerophospholipids were dominant, corresponding to 63% of total lipids, of which the glycerolipid DG (20:1[11Z]/22:4[7Z,10Z,13Z,16Z]/0:0) (iso2) was the most abundant. Overall, 57% of T. papuae lipids were absent in humans; therefore, lipid metabolism may be dissimilar in the two species. Proteins involved T. papuae lipid metabolism were explored using bioinformatics. We found that 4-hydroxybutyrate coenzyme A transferase, uncharacterized protein (A0A0V1MCB5) and ML-domain-containing protein are not present in humans. T. papuae glycerophospholipid metabolic and phosphatidylinositol dephosphorylation processes contain several proteins that are dissimilar to those in humans. These findings provide insights into T. papuae lipid composition and metabolism, which may facilitate the development of novel trichinellosis treatments.

Behind Enemy Lines: Immunomodulatory Armamentarium of the Schistosome Parasite

The deeply rooted, intricate relationship between the Schistosoma parasite and the human host has enabled the parasite to successfully survive within the host and surreptitiously evade the host's immune attacks. The parasite has developed a variety of strategies in its immunomodulatory armamentarium to promote infection without getting harmed or killed in the battlefield of immune responses. These include the production of immunomodulatory molecules, alteration of membranes, and the promotion of granuloma formation. Schistosomiasis thus serves as a paradigm for understanding the Th2 immune responses seen in various helminthiases. This review therefore aims to summarize the immunomodulatory mechanisms of the schistosome parasites to survive inside the host. Understanding these immunomodulatory strategies not only provides information on parasite-host interactions, but also forms the basis in the development of novel drugs and vaccines against the schistosome infection, as well as various types of autoimmune and inflammatory conditions.

Insights into the origin of metazoan multicellularity from predatory unicellular relatives of animals

BACKGROUND

The origin of animals from their unicellular ancestor was one of the most important events in evolutionary history, but the nature and the order of events leading up to the emergence of multicellular animals are still highly uncertain. The diversity and biology of unicellular relatives of animals have strongly informed our understanding of the transition from single-celled organisms to the multicellular Metazoa. Here, we analyze the cellular structures and complex life cycles of the novel unicellular holozoans Pigoraptor and Syssomonas (Opisthokonta), and their implications for the origin of animals.

RESULTS

Syssomonas and Pigoraptor are characterized by complex life cycles with a variety of cell types including flagellates, amoeboflagellates, amoeboid non-flagellar cells, and spherical cysts. The life cycles also include the formation of multicellular aggregations and syncytium-like structures, and an unusual diet for single-celled opisthokonts (partial cell fusion and joint sucking of a large eukaryotic prey), all of which provide new insights into the origin of multicellularity in Metazoa. Several existing models explaining the origin of multicellular animals have been put forward, but these data are interestingly consistent with one, the "synzoospore hypothesis."

CONCLUSIONS

The feeding modes of the ancestral metazoan may have been more complex than previously thought, including not only bacterial prey, but also larger eukaryotic cells and organic structures. The ability to feed on large eukaryotic prey could have been a powerful trigger in the formation and development of both aggregative (e.g., joint feeding, which also implies signaling) and clonal (e.g., hypertrophic growth followed by palintomy) multicellular stages that played important roles in the emergence of multicellular animals.

Unique ultrastructural characteristics of the tegument of the digenean blood fluke Aporocotyle simplex Odhner, 1900 (Digenea: Aporocotylidae), a parasite of flatfishes

This paper includes the first transmission electron microscopical (TEM) study of the tegument of a member of the basal digenean family Aporocotylidae. Scanning electron microscopical investigations of the fish blood fluke Aporocotyle simplex show that each boss on the lateral body surface bears 12-15 simple, uniform spines which extend from 0.5-2.7 μm above the surface of the boss. TEM observations revealed that these spines reach deep beneath the distal cytoplasm of the tegument for much of their length (9-12 μm) and are surrounded by a complex of diagonal muscles in each boss. This is the first record of any digenean with so-called 'sunken' spines. The results suggest that aporocotylid spines arise from within the sarcoplasm of the boss diagonal muscles. The sunken cell bodies (perikarya) of the tegument are connected to the distal cytoplasm via ducts (specialised processes lined by microtubules); this in contrast to other digeneans studied, where they are connected via non-specialised cytoplasmic processes. Within the distal cytoplasm, the tegumental ducts of A. simplex are surrounded by invaginations of the basal membrane and release their cytoplasmic inclusions into the distal cytoplasm. These apparently unique morphological features of the tegument, especially the deep origin of the spines, may represent useful characteristics for understanding aporocotylid relationships, especially in view of the known variation in the spine patterns of aporocotylids.

Phosphoproteomics analysis of male and female Schistosoma mekongi adult worms

Schistosoma mekongi is one of the major causative agents of human schistosomiasis in Southeast Asia. Praziquantel is now the only drug available for treatment and there are serious concerns about parasite resistance to it. Therefore, a dataset of schistosome targets is necessary for drug development. Phosphorylation regulates signalling pathways to control cellular processes that are important for the parasite's growth and reproduction. Inhibition of key phosphoproteins may reduce the severity of schistosomiasis. In this research, we studied the phosphoproteomes of S. mekongi male and female adult worms by using computational and experimental approaches. Using a phosphoproteomics approach, we determined that 88 and 44 phosphoproteins were male- and female-biased, respectively. Immunohistochemistry using anti-phosphoserine antibodies demonstrated phosphorylation on the tegument and muscle of male S. mekongi worms and on the vitelline gland and gastrointestinal tract of female worms. This research revealed S. mekongi sex-dependent phosphoproteins. Our findings provide a better understanding of the role of phosphorylation in S. mekongi and could be integrated with information from other Schistosoma species to facilitate drug and vaccine development.

14-3-3 protein and ubiquitin C acting as SjIAP interaction partners facilitate tegumental integrity in Schistosoma japonicum

Schistosomiasis, caused by trematodes of the genus Schistosoma, remains an important public health issue. Adult schistosomes can survive in the definitive host for several decades, although they are subject to the host immune response. Consequently, understanding the mechanism underlying worm survival in the definitive hosts could aid in developing novel strategies against schistosomiasis. We previously found that an inhibitor of apoptosis in Schistosoma japonicum (SjIAP) could negatively regulate apoptosis by inhibiting caspase activity, which plays a critical role in maintaining tegument integrity. The current study aimed to further analyze the mechanism related to SjIAP governing worm tegument integrity; therefore, we used a yeast two-hybrid screen and identified a series of putative interacting partners of SjIAP, including 14-3-3 (Sj14-3-3) and ubiquitin C (SjUBC). Quantitative real time PCR (qRT-PCR) analysis indicated that transcript profiles of Sj14-3-3 and SjUBC increased together with worm development in definitive hosts, which corresponds to those of SjIAP in S. japonicum. Immunohistochemical analysis showed Sj14-3-3 and SjUBC were located in the tegument of adult parasites while they were also ubiquitously distributed in the bodies of worms. Silencing of Sj14-3-3/SjUBC expression led to increased caspase activity and induced worm death. Inhibition of Sj14-3-3 or SjUBC resulted in significant morphological alterations in the schistosome tegument. Overall, our findings indicated that Sj14-3-3 and SjUBC interacting with SjIAP may belong to another strategy of S. japonicum to maintain the tegument integrity.

Schistosoma japonicum IAP and Teg20 safeguard tegumental integrity by inhibiting cellular apoptosis

Schistosomes are causative agents of human schistosomiasis, which is endemic in tropical and subtropical areas of the world. Adult schistosomes can survive in their final hosts for several decades, and they have evolved various strategies to overcome the host immune response. Consequently, understanding the mechanisms that regulate parasitic cell survival will open avenues for developing novel strategies against schistosomiasis. Our previous study suggested that an inhibitor of apoptosis protein in Schistosoma japonicum (SjIAP) may play important roles in parasitic survival and development. Here, we demonstrated that SjIAP can negatively regulate cellular apoptosis in S. japonicum by suppressing caspase activity. Immunohistochemistry analysis indicated that SjIAP ubiquitously expressed within the worm body including the tegument. Silencing of SjIAP expression via small interfering RNA led to destruction of the tegument integrity in schistosomes. We further used co-immunoprecipitation to identify interaction partners of SjIAP and revealed the tegument protein SjTeg-20 as a putative interacting partner of SjIAP. The interaction between SjIAP and SjTeg-20 was confirmed by a yeast two-hybrid (Y2H) assay. Moreover, results of a TUNEL assay, RNA interference, scanning and transmission electron microscopy, caspase assays, transcript profiling, and protein localization of both interacting molecules provided first evidence for an essential role of SjIAP and SjTeg-20 to maintain the structural integrity of the tegument by negatively regulating apoptosis. Taken together, our findings suggest that the cooperative activities of SjIAP and SjTeg-20 belong to the strategic inventory of S. japonicum ensuring survival in the hostile environment within the vasculature of the final host.

Schistosomiasis is a worldwide public health concern particularly in developing countries. The causative agents, schistosomes, can survive within the vascular system of their final hosts for several decades despite facing the host’s immune response. Therefore, elucidating the mechanism of cell survival will contribute to the understanding of host-parasite interaction and may lead to the identification of suitable targets for developing novel strategies against schistosomiasis. Inhibitor of apoptosis proteins are highly conserved proteins functioning as endogenous inhibitors of apoptotic cell death. Here, we demonstrated that an inhibitor of apoptosis protein of Schistosoma japonicum (SjIAP) governs the integrity of the tegument of schistosomes by inhibiting cellular apoptosis of the parasite. Further studies revealed that SjTeg-20, an S. japonicum tegumental protein, cooperates with SjIAP to inhibit apoptosis in schistosomes. Our findings provide new insights into the role of SjIAP and SjTeg-20 in maintaining the integrity of the worm tegument by negatively regulating apoptosis.

Suppression of VAMP2 Alters Morphology of the Tegument and Affects Glucose uptake, Development and Reproduction of Schistosoma japonicum

Schistosomiasis caused by schsitosomes is a serious global public health concern. The tegument that surrounds the worm is critical to the schistosomes survival. The tegument apical membrane undergoes a continuous process of rupture and repair owing to membranous vacuoles fusing with the plasma membrane. Vesicle-associated membrane protein 2 (VAMP2), a member of soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNAREs) is required for membrane fusion. Here, we used RNA interference (RNAi) to knock down the expression of VAMP2 of Schistosoma japonicum (SjVAMP2), and both real-time PCR and western blot analysis confirmed the suppression of this molecule, as well as the suppression of the transcript levels of schistosome glucose transporters (SGTP1 and SGTP4), and insulin receptors (SjIR1 and SjIR2). SjVAMP2-suppressed worms exhibited a lower viability, and phenotypic alterations were also observed in the tegument. Moreover, the glucose consumption of SjVAMP2-suppressed worms decreased significantly in 4 and 6 days, respectively, as well as a significant reduction in egg production. We also observed a significant reduction in worm burden and hepatic eggs burden in two independent RNAi experiment in vivo, and minor pathological changes in mice treated with SjVAMP2 specific small interfering (si)RNA. These findings reveal that SjVAMP2 may play important roles in the maintenance of tegument, glucose uptake, worm development and egg production in schistosomes.

HIV-1 Integrates Widely throughout the Genome of the Human Blood Fluke Schistosoma mansoni

Schistosomiasis is the most important helminthic disease of humanity in terms of morbidity and mortality. Facile manipulation of schistosomes using lentiviruses would enable advances in functional genomics in these and related neglected tropical diseases pathogens including tapeworms, and including their non-dividing cells. Such approaches have hitherto been unavailable. Blood stream forms of the human blood fluke, Schistosoma mansoni, the causative agent of the hepatointestinal schistosomiasis, were infected with the human HIV-1 isolate NL4-3 pseudotyped with vesicular stomatitis virus glycoprotein. The appearance of strong stop and positive strand cDNAs indicated that virions fused to schistosome cells, the nucleocapsid internalized and the RNA genome reverse transcribed. Anchored PCR analysis, sequencing HIV-1-specific anchored Illumina libraries and Whole Genome Sequencing (WGS) of schistosomes confirmed chromosomal integration; >8,000 integrations were mapped, distributed throughout the eight pairs of chromosomes including the sex chromosomes. The rate of integrations in the genome exceeded five per 1,000 kb and HIV-1 integrated into protein-encoding loci and elsewhere with integration bias dissimilar to that of human T cells. We estimated ~ 2,100 integrations per schistosomulum based on WGS, i.e. about two or three events per cell, comparable to integration rates in human cells. Accomplishment in schistosomes of post-entry processes essential for HIV-1replication, including integrase-catalyzed integration, was remarkable given the phylogenetic distance between schistosomes and primates, the natural hosts of the genus Lentivirus. These enigmatic findings revealed that HIV-1 was active within cells of S. mansoni, and provided the first demonstration that HIV-1 can integrate into the genome of an invertebrate.

Functional characterisation of Schistosoma japonicum acetylcholinesterase

BACKGROUND

Acetylcholinesterase (AChE) is an important metabolic enzyme of schistosomes present in the musculature and on the surface of the blood stage where it has been implicated in the modulation of glucose scavenging from mammalian host blood. As both a target for the antischistosomal drug metrifonate and as a potential vaccine candidate, AChE has been characterised in the schistosome species Schistosoma mansoni, S. haematobium and S. bovis, but not in S. japonicum. Recently, using a schistosome protein microarray, a predicted S. japonicum acetylcholinesterase precursor was significantly targeted by protective IgG1 immune responses in S. haematobium-exposed individuals that had acquired drug-induced resistance to schistosomiasis after praziquantel treatment.

RESULTS

We report the full-length cDNA sequence and describe phylogenetic and molecular structural analysis to facilitate understanding of the biological function of AChE (SjAChE) in S. japonicum. The protein has high sequence identity (88 %) with the AChEs in S. mansoni, S. haematobium and S. bovis and has 25 % sequence similarity with human AChE, suggestive of a highly specialised role for the enzyme in both parasite and host. We immunolocalized SjAChE and demonstrated its presence on the surface of adult worms and schistosomula, as well as its lower expression in parenchymal regions. The relatively abundance of AChE activity (90 %) present on the surface of adult S. japonicum when compared with that reported in other schistosomes suggests SjAChE may be a more effective drug or immunological target against this species. We also demonstrate that the classical inhibitor of AChE, BW285c51, inhibited AChE activity in tegumental extracts of paired worms, single males and single females by 59, 22 and 50 %, respectively, after 24 h incubation with 200 μM BW284c51.

CONCLUSIONS

These results build on previous studies in other schistosome species indicating major differences in the enzyme between parasite and mammalian host, and provide further support for the design of an anti-schistosome intervention targeting AChE.

Characterization of VAMP2 in Schistosoma japonicum and the Evaluation of Protective Efficacy Induced by Recombinant SjVAMP2 in Mice

Background

The outer-tegument membrane covering the schistosome is believed to maintain via the fusion of membranous vesicles. Fusion of biological membranes is a fundamental process in all eukaryotic cells driven by formation of trans-SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes through pairing of vesicle associated v-SNAREs (VAMP) with complementary t-SNAREs on target membranes. The purpose of this study was to characterize Schistosoma japonicum vesicle-associated membrane protein 2 (SjVAMP2) and to investigate its potential as a candidate vaccine against schistosomiasis.

Methodology/Principal Findings

The sequence of SjVAMP2 was analyzed, cloned, expressed and characterized. SjVAMP2 is a member of the synaptobrevin superfamily harboring the v-SNARE coiled-coil homology domain. RT–PCR analysis revealed that significantly higher SjVAMP2 levels were observed in 14-, 28- and 42-day-old worms, and SjVAMP2 expression was much higher in 42-day-old female worms than in those male worms. Additionally, the expression of SjVAMP2 was associated with membrane recovery in PZQ-treated worms. Immunostaining assay showed that SjVAMP2 was mainly distributed in the sub-tegument of the worms. Western blotting revealed that rSjVAMP2 showed strong immunogenicity. Purified rSjVAMP2 emulsified with ISA206 adjuvant induced 41.5% and 27.3% reductions in worm burden, and 36.8% and 23.3% reductions in hepatic eggs in two independent trials. Besides, significantly higher rSjVAMP2-specific IgG, IgG1, IgG2a levels were detected in rSjVAMP2-vaccinated mice.

Conclusion

Our study indicated that SjVAMP2 is a potential vaccine candidate against S. japonicum and provided the basis for further investigations into the biological function of SjVAMP2.

Clinical implications of recent findings in schistosome proteomics

Schistosomiasis is a neglected tropical disease of clinical significance that, despite years of research, still requires an effective vaccine and improved diagnostics for surveillance, control and potential elimination. Furthermore, the causes of host pathology during schistosomiasis are still not completely understood. The recent sequencing of the genomes of the three key schistosome species has enabled the discovery of many new possible vaccine and drug targets, as well as diagnostic biomarkers, using high-throughput and sensitive proteomics methods. This review focuses on the literature of the last 5 years that has reported on the use of proteomics to both better understand the biology of the schistosome parasites and the disease they cause in definitive mammalian hosts.

Excretory/secretory proteome of 14-day schistosomula, Schistosoma japonicum

Schistosomiasis remains a serious public health problem, with 200 million people infected and 779 million people at risk worldwide. The schistosomulum is the early stage of the complex lifecycle of Schistosoma japonicum in their vertebrate hosts, and is the main target of vaccine-induced protective immunity. Excretory/secretory (ES) proteins play a major role in host-parasite interactions and ES protein compositions of schistosomula of S. japonicum have not been characterized to date. In the present study, the proteome of ES proteins from 14 day schistosomula of S. japonicum was analyzed by liquid chromatography/tandem mass spectrometry and 713 unique proteins were finally identified. Gene ontology and pathway analysis revealed that identified proteins were mainly involved in carbohydrate metabolism, degradation, response to stimulus, oxidation-reduction, biological regulation and binding. Flow cytometry analysis demonstrated that thioredoxin peroxidase identified in this study had the effect on inhibiting MHCII and CD86 expression on LPS-activated macrophages. The present study provides insight into the growth and development of the schistosome in the final host and valuable information for screening vaccine candidates for schistosomiasis.

Structure-function analysis of apical membrane-associated molecules of the tegument of schistosome parasites of humans: prospects for identification of novel targets for parasite control

Neglected tropical diseases are a group of some 17 diseases that afflict poor and predominantly rural people in developing nations. One significant disease that contributes to substantial morbidity in endemic areas is schistosomiasis, caused by infection with one of five species of blood fluke belonging to the trematode genus Schistosoma. Although there is one drug available for treatment of affected individuals in clinics, or for mass administration in endemic regions, there is a need for new therapies. A prominent target organ of schistosomes, either for drug or vaccine development, is the peculiar epithelial syncytium that forms the body wall (tegument) of this parasite. This dynamic layer is maintained and organized by concerted activity of a range of proteins, among which are the abundant tegumentary annexins. In this review, we will outline advances in structure-function analyses of these annexins, as a means to understanding tegument cell biology in host-parasite interaction and their potential exploitation as targets for anti-schistosomiasis therapies.

Transmission electron microscopic observations on ultrastructural alterations in Schistosoma mansoni adult worms recovered from C57BL/6 mice treated with radiation-attenuated vaccine and/or praziquantel in addition to passive immunization with normal and vaccinated rabbit sera against infection

Although the current treatment of schistosomiasis relies largely on praziquantel (PZQ), it has not been successful in significantly reducing the overall rate of disease cases, one of the suggested reasons being the inevitable resistance to PZQ. Previous studies showed that radiation-attenuated vaccine provides protection against Schistosoma mansoni in a host of various species. In the present study, we evaluated the effect of various vaccination strategies in C57BL/6 mice, including single or multiple vaccination strategy, subcurative dose (20 mg/kg) of PZQ, and a combination of single vaccination with subcurative dose of PZQ. Treatment either with subcurative dose of PZQ or with a single vaccination of attenuated cercariae (500 per mouse), caused significant reduction in total worm burden, hepatic, and intestinal ova counts of 43.03, 73.2, and 59.5 and 37.97, 52.02, and 26.3%, respectively. Furthermore, tegumental changes were observed. In multiple vaccinated group, there was an extensive lysis in tegumental layers. High deformations in gastrodermis, testis cells, vitelline cells, and oocytes were recorded. Also, this study is to explore the role of humoral immunity using highly resistant rabbits that had been exposed to three immunizations with ultraviolet (UV)-irradiated cercariae (8000 per rabbit in each immunization), and their sera were tested for their ability to transfer protection. The reduction in challenge worm burden had reached 32.76-43.64% when compared with recipients of normal serum or no serum. The reduction in hepatic and intestinal ova counts reached to 74.4 and 71.08% in group immunized with vaccinated rabbit sera. Swelling and extensive lysis of tegumental layers, gastrodermis lumen, spermatocytes, and deformation of oocytes were recorded with more severity than that recorded in normal rabbit sera group. Our findings recorded that multiple vaccination strategy is the most effective strategy then passive transfer of vaccinated rabbit. This gives guiding in the design the appropriate therapeutic strategy.

Extracellular Onchocerca-derived small RNAs in host nodules and blood

Background

microRNAs (miRNAs), a class of short, non-coding RNA can be found in a highly stable, cell-free form in mammalian body fluids. Specific miRNAs are secreted by parasitic nematodes in exosomes and have been detected in the serum of murine and dog hosts infected with the filarial nematodes Litomosoides sigmodontis and Dirofilaria immitis, respectively. Here we identify extracellular, parasite-derived small RNAs associated with Onchocerca species infecting cattle and humans.

Methods

Small RNA libraries were prepared from total RNA extracted from the nodule fluid of cattle infected with Onchocerca ochengi as well as serum and plasma from humans infected with Onchocerca volvulus in Cameroon and Ghana. Parasite-derived miRNAs were identified based on the criteria that sequences unambiguously map to hairpin structures in Onchocerca genomes, do not align to the human genome and are not present in European control serum.

Results

A total of 62 mature miRNAs from 52 distinct pre-miRNA candidates were identified in nodule fluid from cattle infected with O. ochengi of which 59 are identical in the genome of the human parasite O. volvulus. Six of the extracellular miRNAs were also identified in sequencing analyses of serum and plasma from humans infected with O. volvulus. Based on sequencing analysis the abundance levels of the parasite miRNAs in serum or plasma range from 5 to 127 reads/per million total host miRNA reads identified, comparable to our previous analyses of Schistosoma mansoni and L. sigmodontis miRNAs in serum. All six of the O. volvulus miRNAs identified have orthologs in other filarial nematodes and four were identified in the serum of mice infected with L. sigmodontis.

Conclusions

We have identified parasite-derived miRNAs associated with onchocerciasis in cattle and humans. Our results confirm the conserved nature of RNA secretion by diverse nematodes. Additional species-specific small RNAs from O. volvulus may be present in serum based on the novel miRNA sequences identified in the nodule fluid. In our analyses comparison to European control serum illuminates the scope for false-positives, warranting caution in criteria that should be applied to identification of biomarkers of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0656-1) contains supplementary material, which is available to authorized users.

The anterior esophageal region of Schistosoma japonicum is a secretory organ

Background

The esophagus of blood-feeding schistosomes has been largely neglected although its posterior portion was designated as a gland decades ago. However, we recently showed it plays a pivotal role in blood processing. It is clearly demarcated into anterior and posterior compartments, both surrounded by a mass of cell bodies. Feeding movies revealed that erythrocytes accumulate in the anterior compartment before entering the posterior, indicating that a distinct process is executed there. We therefore investigated ultrastructural aspects and possible functions of the anterior region.

Methods

The heads of adult Schistosoma japonicum were detached and prepared for both transmission and scanning electron microscopy to define the detailed ultrastructure of the anterior esophagus. Cryosections of heads were also prepared for immunocytochemistry and confocal microscopy to define the pattern of intrinsic host antibody binding in the anterior esophageal lining.

Results

The anterior syncytial lining of the esophagus is highly extended by long, thin corrugations of cytoplasm projecting towards the lumen. Strikingly in the male worm, the tips of the corrugations are further expanded by numerous threads of cytoplasm, producing a spaghetti-like appearance in the central lumen. Flattened, pitted cytoplasmic plates are interspersed in the tangled mass of threads. Abundant, morphologically distinct light vesicles of varied size and contents are manufactured in the cell bodies, from where they traffic through cytoplasmic connections to the corrugations and out to the tips. Clusters of vesicles accumulate in expanded tips in males, together with occasional mitochondria whilst females have more mitochondria but fewer vesicles. The membranous contents of light vesicles are secreted mainly from the tips, but also from the sides of the corrugations. They coat the surfaces and then form organised self-adherent membrane figures when shed into the lumen. Host antibody binds strongly in a characteristic pattern to the anterior esophageal lining indicating that the secretions are highly immunogenic.

Conclusions

We suggest that the anterior esophageal region is an independent secretory organ. The contents of light vesicles are released into the esophageal lumen via the tips of corrugation to interact with incoming blood. Our immediate task is to establish their composition and role in blood processing.

Gaining biological perspectives from schistosome genomes

Characterization of the genomic basis underlying schistosome biology is an important strategy for the development of future treatments and interventions. Genomic sequence is now available for the three major clinically relevant schistosome species, Schistosoma mansoni, S. japonicum and S. haematobium, and this information represents an invaluable resource for the future control of human schistosomiasis. The identification of a biologically important, but distinct from the host, schistosome gene product is the ultimate goal for many research groups. While the initial elucidation of the genome of an organism is critical for most biological research, continued improvement or curation of the genome construction should be an ongoing priority. In this review we will discuss prominent recent findings utilizing a systems approach to schistosome biology, as well as the increased use of interference RNA (RNAi). Both of these research strategies are aiming to place parasite genes into a more meaningful biological perspective.

Revisiting glucose uptake and metabolism in schistosomes: new molecular insights for improved schistosomiasis therapies

A better understanding of the molecular mechanisms required for schistosomes to take up glucose, the major nutritional source exploited by these blood flukes from their mammalian hosts and the subsequent metabolism required to fuel growth and fecundity, can provide new avenues for developing novel interventions for the control of schistosomiasis. This aspect of parasitism is particularly important to paired adult schistosomes, due to their considerable requirements for the energy needed to produce the extensive numbers of eggs laid daily by the female worm. This review describes recent advances in characterizing glucose metabolism in adult schistosomes. Potential intervention targets are discussed within the insulin signaling and glycolysis pathways, both of which play critical roles in the carbohydrate and energy requirements of schistosomes.

Crystal structure and immunological properties of the first annexin from Schistosoma mansoni: insights into the structural integrity of the schistosomal tegument

Schistosomiasis is a major parasitic disease of humans, second only to malaria in its global impact. The disease is caused by digenean trematodes that infest the vasculature of their human hosts. These flukes are limited externally by a body wall composed of a syncytial epithelium, the apical surface membrane of which is a parasitism-adapted dual membrane complex. Annexins are thought to be of integral importance for the stability of this apical membrane system. Here, we present the first structural and immunobiochemical characterization of an annexin from Schistosoma mansoni. The crystal structure of annexin B22 confirms the presence of the previously predicted α-helical segment in the II/III linker and reveals a covalently linked head-to-head dimer. From the calcium-bound crystal structure of this protein, canonical type II, type III and B site positions are occupied, and a novel binding site has been identified. The dimer arrangement observed in the crystal structure suggests the presence of two prominent features, a potential non-canonical membrane binding site and a potential binding groove opposite to the former. Results from transcriptional profiling during development show that annexin B22 expression is correlated with life stages of the parasite that possess the syncytial tegument layer, and ultrastructural localization by immuno-electron microscopy confirms the occurrence of annexins in the tegument of S. mansoni. Data from membrane binding and aggregation assays indicate the presence of differential molecular mechanisms and support the hypothesis of annexin B22 providing structural integrity in the tegument.

Proteomic analysis of tegument-exposed proteins of female and male Schistosoma japonicum worms

The interplay between sexes is a prerequisite for female growth, reproductive maturation, and egg production, and the basis of schistosome pathopoiesis and propagation. The tegument is in direct contact with the host environment and its surface membranes are particularly crucial for schistosome survival in the definitive host. In this study, a streptavidin-biotin affinity purification technique combined with LC-MS/MS was used to analyze putative tegument-exposed proteins in female and male adult Schistosoma japonicum worms. In total, 179 proteins were identified in females and 300 in males, including 119 proteins common to both sexes, and 60 female biased and 181 male biased proteins. Some (e.g., serpin and CD36-like class B scavenger receptor) were involved in host-schistosome interactions, while some (e.g., gynecophoral canal protein) were important in the interplay between sexes. Gene Ontology analysis revealed that proteins involved in protein glycosylation and lysosome were highly expressed in females, while proteins involved in intracellular signal transduction, regulation of actin filament polymerization, and proteasome core complex were highly expressed in males. These results might elucidate physiological differences between the sexes. Our study provides new insights into schistosome growth and sexual maturity in the final host and permits the screening of vaccine candidates or drug targets for schistosomiasis.

Cloning, expression, and preliminary characterization of the dysferlin tegument protein in Schistosoma japonicum

The schistosomal tegument is a dynamic host-interactive layer. Proteins exposed to the host on the tegumental surface are important for completion of the parasitic lifecycle. Dysferlin is a member of the ferlin family and is involved in plasma membrane repair. Based on the results of a proteomics study of tegument surface proteins of Schistosoma japonicum in our laboratory, dysferlin was identified as a tegumental protein of S. japonicum. The gene encoding S. japonicum dysferlin (SjDF), which codes for several Ca(2+) binding sites, was cloned, expressed in Escherichia coli, and characterized. Western blot analysis revealed that recombinant SjDF had good immunogenicity. Real-time RT-PCR analysis showed that SjDF was upregulated mainly in adult worms and the transcription level in 42-day-old female worms was significantly higher than that in males. Immunofluorescence analysis revealed that SjDF was mainly distributed in the tegument at various developmental stages. Experimental mice were treated with praziquantel and at 35days post-infection, we noted that damage to the tegument and subtegument worsened and did not recover at 36h post-treatment in the high-dose group and was accompanied by downregulation of SjDF mRNA, while the damage was less severe and recovered by this time in the low-dose group, and accompanied by upregulation of SjDF. Our results suggested that SjDF is a tegumental protein that may be important in schistosomal development and may participate in the repair process in muscle and tegument, and could present a viable vaccine candidate for schistosomiasis.

Proteomics analysis of differentially expressed proteins in schistosomula and adult worms of Schistosoma japonicum

Schistosoma japonicum has a complex lifecycle and exhibits dramatic changes in its biology and morphology at different developmental stages. The schistosomulum and adult worm are two stages of this complex lifecycle and differentially expressed proteins in these two stages should be important for survival, development, and reproduction of the parasites. In this study, soluble and hydrophobic proteins were extracted from eggs, cercariae, schistosomula (8d and 19d), and male and female adult worms (42d) of Schistosoma japonicum, and separated by two-dimensional (2D) gel electrophoresis. A total of 1376±52, 928±61, 1465±41, 1230±30, 904±34, and 1080±26 soluble proteins and 1437±44, 845±53, 986±22, 1145±35, 1066±39, and 1123±45 hydrophobic proteins were separated from eggs, cercariae, schistosomula (8d and 19d), and male and female adult worms (42d), respectively. There were 65±14, 27±7, 37±17 and 48±9 soluble protein spots only present in schistosomula (8d and/or 19d) and adult schistosomes (male and/or female). We successfully identified 22 spots from schistosomula and 11 spots from adult schistosomes by mass spectrometry. Quantitative real-time RT-PCR was used to examine six differentially expressed proteins at the transcription level. These proteins only found in schistosomula or adults stage by the proteomics analysis were highly expressed in the corresponding stage at mRNA level. Bioinformatics analysis showed that the differentially expressed proteins from schistosomula were mainly involved in cellular metabolic processes, stress response and developmental process. Differentially expressed proteins from adult schistosomes were involved with gene expression and protein metabolism processes. The results of this study might provide new insights to stimulate further exploration of the mechanism of growth and development in schistosomes and help identify candidate molecules for developing new vaccines or drugs.

Transcriptional responses of in vivo praziquantel exposure in schistosomes identifies a functional role for calcium signalling pathway member CamKII

Treatment for clinical schistosomiasis has relied centrally on the broad spectrum anthelmintic praziquantel; however, there is limited information on its mode of action or the molecular response of the parasite. This paper presents a transcriptional and functional approach to defining the molecular responses of schistosomes to praziquantel. Differential gene expression in Schistosoma japonicum was investigated by transcriptome-wide microarray analysis of adult worms perfused from infected mice after 0.5 to 24 hours after oral administration of sub-lethal doses of praziquantel. Genes up-regulated initially in male parasites were associated with "Tegument/Muscle Repair" and "Lipid/Ion Regulation" functions and were followed by "Drug Resistance" and "Ion Regulation" associated genes. Prominent responses induced in female worms included up-regulation of "Ca(2+) Regulation" and "Drug Resistance" genes and later by transcripts of "Detoxification" and "Pathogen Defense" mechanisms. A subset of highly over-expressed genes, with putative drug resistance/detoxification roles or Ca(2+)-dependant/modulatory functions, were validated by qPCR. The leading candidate among these was CamKII, a putative calcium/calmodulin-dependent protein kinase type II delta chain. RNA interference was employed to knockdown CamKII in S. japonicum to determine the role of CamKII in the response to praziquantel. After partial-knockdown, schistosomes were analysed using IC50 concentrations (50% worm motility) and quantitative monitoring of parasite movement. When CamKII transcription was reduced by 50-69% in S. japonicum, the subsequent effect of an IC50 dosage of praziquantel was exacerbated, reducing motility from 47% to 27% in female worms and from 61% to 23% in males. These observations indicated that CamKII mitigates the effects of praziquantel, probably through stabilising Ca(2+) fluxes within parasite muscles and tegument. Together, these studies comprehensively charted transcriptional changes upon exposure to praziquantel and, notably, identified CamKII as potentially central to the, as yet undefined, mode of action of praziquantel.

Morphological and morphometric study of cercariae and adult worms of Schistosoma mansoni (SLM strain) isolated from infected mice

In northeastern Brazil, the schistosomiasis is historically endemic and considered as a public health problem. The Schistosoma mansoni São Lourenço da Mata (SLM-PE, Brazil) strain was used in several paper already published; however, morphological and morphometric studies about this strain was never done. In this work, scanning electron microscopy (SEM) was used in morphological and morphometric analysis of cercariae and adult worms. Cercariae were obtained from Biomphalaria glabrata snails and adult worms from mice, both infected by the S. mansoni SLM strain, fixed and prepared for SEM. The results showed that cercariae of S. mansoni measures 254.9 μm of length. The bodies are covered by spines, with a ventral sucker, an oral sucker with sensory receivers, and a pair of penetration glands in the head. The area of tail and body and the distance between suckers were 3,011.77, 1,530.32, and 42.9 μm, respectively. Adult worms of S. mansoni were divided into three main regions: the anterior, medial, and posterior, besides the gynecophoral canal in males. The measure of adult worms of S. mansoni was 4 mm males and 5 mm females. The anterior region length of the male was 470 μm and of the female 271 μm. All the parameters were assayed in ten samples. The morphometric values found in the SLM strain were smaller than other S. mansoni strains described in the literature as well as other helminths. This is the first morphological and morphometric study with the SLM strain of S. mansoni being extremely important for improving control strategies and life quality of the local population.

Differences in genomic architecture between two distinct geographical strains of the blood fluke Schistosoma japonicum reveal potential phenotype basis

The Chinese (SjC) and Philippine (SjP) strains of the blood fluke Schistosoma japonicum have been shown to present clearly different phenotypes in fecundity, pathology, drug sensitivity and immunology. We used microarray based comparative genomic hybridisation (aCGH) to investigate structural differences in the genomes of the two strains and identified seven distinct regions of the S. japonicum genome that present differential aCGH representing either deletion or duplication regions in SjP. Within these regions, genes predicted to be associated with the recognised phenotypic differences were identified and that may provide new insights into the biology and evolution of the two strains, with implications for the epidemiology and control of schistosomiasis japonica in China and the Philippines.

Antischistosomal activity of trioxaquines: in vivo efficacy and mechanism of action on Schistosoma mansoni

Schistosomiasis is among the most neglected tropical diseases, since its mode of spreading tends to limit the contamination to people who are in contact with contaminated waters in endemic countries. Here we report the in vitro and in vivo anti-schistosomal activities of trioxaquines. These hybrid molecules are highly active on the larval forms of the worms and exhibit different modes of action, not only the alkylation of heme. The synergy observed with praziquantel on infected mice is in favor of the development of these trioxaquines as potential anti-schistosomal agents.

Schistosomiasis is a tropical disease affecting more than 200 million people throughout the sub-tropical and tropical world. The treatment and control of schistosomiasis rely on the use of a single drug, the praziquantel and no vaccine is available. However, schistosome species with low sensitivity or resistance to praziquantel have been identified in several countries. It is an urgent need to develop new drugs against this parasite. In this context, our study reports the activity the trioxaquine PA1259. PA1259 is an hybrid drug containing two pharmacophores within a single molecule: a trioxane and an aminoquinoline. Initially developed against malaria, the trioxaquines target the heme a disposal product resulting from the digestion of the hemoglobin. The first action of the trioxaquine is an alkylation of the heme with the trioxane entity, and the second action is stacking with the heme due to the aminoquinoline moiety. In this study we show that this new drug is active in vitro against all schistosome stages (cercariae, schistosomule and adult). The PA1259 is also active in vivo and shows synergistic action in association with praziquantel. This opens the route to an efficient bitherapy of a highly neglected disease.

An antibiotic selection marker for schistosome transgenesis

Drug selection is widely used in transgene studies of microbial pathogens, mammalian cell and plant cell lines. Drug selection of transgenic schistosomes would be desirable to provide a means to enrich for populations of transgenic worms. We adapted murine leukaemia retrovirus vectors - widely used in human gene therapy research - to transduce schistosomes, leading to integration of transgenes into the genome of the blood fluke. A dose-response kill curve and lethal G418 (geneticin) concentrations were established: 125-1,000μg/ml G418 were progressively more toxic for schistosomules of Schistosoma mansoni with toxicity increasing with antibiotic concentration and with duration of exposure. By day 6 of exposure to ⩾500μg/ml, significantly fewer worms survived compared with non-exposed controls and by day 8, significantly fewer worms survived than controls at ⩾250μg/ml G418. When schistosomules were transduced with murine leukaemia retrovirus encoding the neomycin resistance (neoR) transgene and cultured in media containing G418, the neoR transgene rescued transgenic schistosomules from the antibiotic; by day 4 in 1,000μg/ml and by day 8 in 500μg/ml G418, significantly more transgenic worms survived the toxic effects of the antibiotic. More copies of neoR were detected per nanogram of genomic DNA from populations of transgenic schistosomes cultured in G418 than from transgenic schistosomes cultured without G418. This trend was G418 dose-dependent, demonstrating enrichment of transgenic worms from among the schistosomules exposed to virions. Furthermore, higher expression of neoR was detected in transgenic schistosomes cultured in the presence of G418 than in transgenic worms cultured without antibiotic. The availability of antibiotic selection can be expected to enhance progress with functional genomics research on the helminth parasites responsible for major neglected tropical diseases.

Molecular analysis of zinc transporters in Schistosoma japonicum

Members of the zinc-regulated transporter/iron-regulated transporter-like protein (ZIP) family of proteins transport metal ions across cell membranes. Genes encoding ZIPs are present in the genomes of schistosomes. Here, we describe molecular characterisation of six ZIPs (SjZIPA-F) from Schistosoma japonicum. Quantitative PCR analyses of these ZIPs through the lifecycle showed that each is expressed predominantly during the intramammalian stage and are particularly enriched in adult females. Using laser microdissected tissue as template, SjZIPA-D were transcriptionally enriched in female reproductive tissues, SjZIPE was not expressed in specific tissues and SjZIPF was expressed similarly in each tissue. Whole mount in situ hybridization revealed that SjZIPA and SjZIPB were localised to the oesophageal gland of adults and the vitellaria. We have shown that multiple ZIPs are expressed by schistosomes during the intramammalian parasitic phases and propose that the encoded products perform diverse cellular functions related to metal transport in different cells of S. japonicum.

A cytochrome b561 with ferric reductase activity from the parasitic blood fluke, Schistosoma japonicum

BACKGROUND

Iron has an integral role in numerous cellular reactions and is required by virtually all organisms. In physiological conditions, iron is abundant in a largely insoluble ferric state. Ferric reductases are an essential component of iron uptake by cells, reducing iron to the soluble ferrous form. Cytochromes b561 (cyts-b561) are a family of ascorbate reducing transmembrane proteins found in most eukaryotic cells. The identification of the ferric reductase duodenal cytochrome b (dcytb) and recent observations that other cyts-b561 may be involved in iron metabolism have opened novel perspectives for elucidating their physiological function.

METHODOLOGY/PRINCIPAL FINDINGS

Here we have identified a new member of the cytochrome b561 (Sjcytb561) family in the pathogenic blood fluke Schistosoma japonicum that localises to the outer surface of this parasitic trematode. Heterologous expression of recombinant Sjcyt-b561 in a Saccharomyces cerevisiae mutant strain that lacks plasma membrane ferrireductase activity demonstrated that the molecule could rescue ferric reductase activity in the yeast.

SIGNIFICANCE/CONCLUSIONS

This finding of a new member of the cytochrome b561 family further supports the notion that a ferric reductase function is likely for other members of this protein family. Additionally, the localisation of Sjcytb561 in the surface epithelium of these blood-dwelling schistosomes contributes further to our knowledge concerning nutrient acquisition in these parasites and may provide novel targets for therapeutic intervention.

The secreted and surface proteomes of the adult stage of the carcinogenic human liver fluke Opisthorchis viverrini

Infection with the human liver fluke, Opisthorchis viverrini, is a serious public health problem in Thailand, Laos and nearby locations in Southeast Asia. Both experimental and epidemiological evidence strongly implicate liver fluke infection in the etiology of one of the liver cancer subtypes, cholangiocarcinoma (CCA). To identify parasite proteins critical for liver fluke survival and the etiology of CCA, OFFGEL electrophoresis and multiple reaction monitoring were employed to characterize 300 parasite proteins from the O. viverrini excretory/secretory products and, utilizing selective labeling and sequential solubilization, from the host-exposed tegument. The excretory/secretory included a complex mixture of proteins that have been associated with cancers, including proteases of different mechanistic classes and orthologues of mammalian growth factors and anti-apoptotic proteins. Also identified was a cysteine protease inhibitor which, in other helminth pathogens, induces nitric oxide production by macrophages, and, hence may contribute to malignant transformation of inflamed cells. More than 160 tegumental proteins were identified using sequential solubilization of isolated teguments, and a subset of these was localized to the surface membrane of the tegument by labeling living flukes with biotin and confirming surface localization with fluorescence microscopy. These included annexins, which are potential immuno-modulators, and orthologues of the schistosomiasis vaccine antigens Sm29 and tetraspanin-2. Novel roles in pathogenesis were suggested for the tegument-host interface since more than ten surface proteins had no homologues in the public databases. The O. viverrini proteins identified here provide an extensive catalogue of novel leads for research on the pathogenesis of opisthorchiasis and the development of novel interventions for this disease and CCA, as well as providing a scaffold for sequencing the genome of this fluke.

Transcriptional changes in Schistosoma mansoni during early schistosomula development and in the presence of erythrocytes

Background

Schistosomes cause more mortality and morbidity than any other human helminth, but control primarily relies on a single drug that kills adult worms. The newly transformed schistosomulum stage is susceptible to the immune response and is a target for vaccine development and rational drug design.

Methodology/Principal Findings

To identify genes which are up-regulated during the maturation of Schistosoma mansoni schistosomula in vitro, we cultured newly transformed parasites for 3 h or 5 days with and without erythrocytes and compared their transcriptional profiles using cDNA microarrays. The most apparent changes were in the up-regulation of genes between 3 h and 5 day schistosomula involved in blood feeding, tegument and cytoskeletal development, cell adhesion, and stress responses. The most highly up-regulated genes included a tegument tetraspanin Sm-tsp-3 (1,600-fold up-regulation), a protein kinase, a novel serine protease and serine protease inhibitor, and intestinal proteases belonging to distinct mechanistic classes. The inclusion of erythrocytes in the culture medium resulted in a general but less pronounced increase in transcriptional activity, with the highest up-regulation of genes involved in iron metabolism, proteolysis, and transport of fatty acids and sugars.

Conclusions

We have identified the genes that are up-regulated during the first 5 days of schistosomula development in vitro. Using a combination of gene silencing techniques and murine protection studies, some of these highly up-regulated transcripts can be targeted for future development of new vaccines and drugs.

Schistosome blood flukes cause more mortality and morbidity than any other human worm infection, but current control methods primarily rely on a single drug. There is a desperate need for new approaches to control this parasite, including vaccines. People become infected when the free-swimming larva, the cercaria, enters through the skin and becomes the schistosomulum. Schistosomula are susceptible to immune responses during their first few days in the host before they become adult parasites. We characterised the genes that these newly transformed parasites switch on when they enter the host to identify molecules that are critical for survival in the human host. Some of these highly up-regulated genes can be targeted for future development of new vaccines and drugs.

Exposed proteins of the Schistosoma japonicum tegument

The ability of the mammalian blood fluke Schistosoma japonicum to survive in the inhospitable environment of the mammalian bloodstream can be attributed, at least in part, to its host-exposed outer surface, called the tegument. The tegument is a dynamic organ and is involved in nutrition, immune evasion and modulation, excretion, osmoregulation and signal transduction. Given its importance for parasite survival, proteins exposed to the host at the surface of the tegument are ideal targets for the development of vaccines and drugs. By biotinylating live adult worms and using a combination of OFFGEL electrophoresis and tandem mass spectrometry 54 proteins were identified as putatively host-exposed in S. japonicum. These included glucose transport proteins, an amino permease, a leucine aminopeptidase and a range of transporters, heat shock proteins and novel immune-active proteins. Members of the tetraspanin protein family and a homologue of Sm 29, a tegument membrane protein from Schistosoma mansoni, both effective vaccine antigens in S. mansoni, were also identified. The fate of labelled surface proteins was monitored over time using electron microscopy and revealed that biotinylated proteins were rapidly internalised from the surface of the tegument and trafficked into the cytoplasmic bridges that connect the distal cytoplasm of the tegument to the underlying cell bodies. The results reported herein dramatically increase the number of S. japonicum proteins known to be exposed to the host and, hence, those of interest as therapeutic targets. The ability of the parasite to rapidly internalise proteins at its surface has implications for the development of vaccines and may explain how these parasites are able to avoid the host immune system for long periods of time.

Transcriptional profiles of adult male and female Schistosoma japonicum in response to insulin reveal increased expression of genes involved in growth and development

Microarray analysis was used to investigate differential gene regulation in adult male and female Schistosoma japonicum cultured in the presence or absence of insulin in vitro. A total of 1,101 genes were up- or down-regulated in response to insulin, the majority of differential expression occurring 24h after the addition of insulin to the cultures. Genes differentially expressed in male or female worms were predominantly involved in growth and development, with significant sex-specific differences in transcriptional profiles evident. Insulin appeared to promote protein synthesis and control protein degradation more prominently in male parasites. The study also indicated that insulin plays a more pronounced role in the uptake of glucose in unpaired female parasites, as reflected in the increased stimulation of gene expression of the phosphatidylinositol 3-kinase sub-pathway of insulin signalling. Insulin may also impact on the sexual differentiation and fecundity of female schistosomes by activation of the mitogenic-activated protein kinase sub-pathway.

Developmental gene expression profiles of the human pathogen Schistosoma japonicum

BACKGROUND

The schistosome blood flukes are complex trematodes and cause a chronic parasitic disease of significant public health importance worldwide, schistosomiasis. Their life cycle is characterised by distinct parasitic and free-living phases involving mammalian and snail hosts and freshwater. Microarray analysis was used to profile developmental gene expression in the Asian species, Schistosoma japonicum. Total RNAs were isolated from the three distinct environmental phases of the lifecycle -- aquatic/snail (eggs, miracidia, sporocysts, cercariae), juvenile (lung schistosomula and paired but pre-egg laying adults) and adult (paired, mature males and egg-producing females, both examined separately). Advanced analyses including ANOVA, principal component analysis, and hierarchal clustering provided a global synopsis of gene expression relationships among the different developmental stages of the schistosome parasite.

RESULTS

Gene expression profiles were linked to the major environmental settings through which the developmental stages of the fluke have to adapt during the course of its life cycle. Gene ontologies of the differentially expressed genes revealed a wide range of functions and processes. In addition, stage-specific, differentially expressed genes were identified that were involved in numerous biological pathways and functions including calcium signalling, sphingolipid metabolism and parasite defence.

CONCLUSION

The findings provide a comprehensive database of gene expression in an important human pathogen, including transcriptional changes in genes involved in evasion of the host immune response, nutrient acquisition, energy production, calcium signalling, sphingolipid metabolism, egg production and tegumental function during development. This resource should help facilitate the identification and prioritization of new anti-schistosome drug and vaccine targets for the control of schistosomiasis.

Analysis of early hepatic stage schistosomula gene expression by subtractive expressed sequence tags library

Schistosome parasites require a complex lifecycle requiring two hosts and aquatic phases of development. The schistosomula is a key phase of parasite development within the mammalian host, however relatively little is understood about the molecular processes underlying this stage. In this study 5723 subtractive expressed sequence tags (ESTs) were randomly selected from a 7 day hepatic schistosomula enriched library constructed using suppression subtractive hybridization method. Sequence analysis of these ESTs identified 1762 unique genes (contigs). Among them, 989 contigs were annotated with known genes, 311 contigs were homologous to established genes, 101 contigs were similar to established genes, 72 contigs were weakly similar to established genes and 289 sequences did not match any published sequences. Genes identified related to metabolism, cellular development, immune evasion and host-parasite interactions were identified as enriched in the hepatic schistosomula stage. The future identification of poorly annotated but stage-specific genes may potentially represent new drugs or vaccine targets, applicable for the future controlling of schistosomiasis.

SjTPdb: integrated transcriptome and proteome database and analysis platform for Schistosoma japonicum

Background

Schistosoma japonicum is one of the three major blood fluke species, the etiological agents of schistosomiasis which remains a serious public health problem with an estimated 200 million people infected in 76 countries. In recent years, enormous amounts of both transcriptomic and proteomic data of schistosomes have become available, providing information on gene expression profiles for developmental stages and tissues of S. japonicum. Here, we establish a public searchable database, termed SjTPdb, with integrated transcriptomic and proteomic data of S. japonicum, to enable more efficient access and utility of these data and to facilitate the study of schistosome biology, physiology and evolution.

Description

All the available ESTs, EST clusters, and the proteomic dataset of S. japonicum are deposited in SjTPdb. The core of the database is the 8,420 S. japonicum proteins translated from the EST clusters, which are well annotated for sequence similarity, structural features, functional ontology, genomic variations and expression patterns across developmental stages and tissues including the tegument and eggshell of this flatworm. The data can be queried by simple text search, BLAST search, search based on developmental stage of the life cycle, and an integrated search for more specific information. A PHP-based web interface allows users to browse and query SjTPdb, and moreover to switch to external databases by the following embedded links.

Conclusion

SjTPdb is the first schistosome database with detailed annotations for schistosome proteins. It is also the first integrated database of both transcriptome and proteome of S. japonicum, providing a comprehensive data resource and research platform to facilitate functional genomics of schistosome. SjTPdb is available from URL: .