Updated knowledge and a proposed nomenclature for nuclear receptors with two DNA binding domains (2DBD-NRs)

Nuclear receptors (NRs) are important transcriptional modulators in metazoans. Typical NRs possess a conserved DNA binding domain (DBD) and a ligand binding domain (LBD). Since we discovered a type of novel NRs each of them has two DBDs and single LBD (2DBD-NRs) more than decade ago, there has been very few studies about 2DBD-NRs. Recently, 2DBD-NRs have been only reported in Platyhelminths and Mollusca and are thought to be specific NRs to lophotrochozoan. In this study, we searched different databases and identified 2DBD-NRs in different animals from both protostomes and deuterostomes. Phylogenetic analysis shows that at least two ancient 2DBD-NR genes were present in the urbilaterian, a common ancestor of protostomes and deuterostomes. 2DBD-NRs underwent gene duplication and loss after the split of different animal phyla, most of them in a certain animal phylum are paralogues, rather than orthologues, like in other animal phyla. Amino acid sequence analysis shows that the conserved motifs in typical NRs are also present in 2DBD-NRs and they are gene specific. From our phylogenetic analysis of 2DBD-NRs and following the rule of Nomenclature System for the Nuclear Receptors, a nomenclature for 2DBD-NRs is proposed.

Oxamniquine derivatives overcome Praziquantel treatment limitations for Schistosomiasis

Human schistosomiasis is a neglected tropical disease caused by Schistosoma mansoni, S. haematobium, and S. japonicum. Praziquantel (PZQ) is the method of choice for treatment. Due to constant selection pressure, there is an urgent need for new therapies for schistosomiasis. Previous treatment of S. mansoni included the use of oxamniquine (OXA), a drug that is activated by a schistosome sulfotransferase (SULT). Guided by data from X-ray crystallography and Schistosoma killing assays more than 350 OXA derivatives were designed, synthesized, and tested. We were able to identify CIDD-0150610 and CIDD-0150303 as potent derivatives in vitro that kill (100%) of all three Schistosoma species at a final concentration of 71.5 μM. We evaluated the efficacy of the best OXA derivates in an in vivo model after treatment with a single dose of 100 mg/kg by oral gavage. The highest rate of worm burden reduction was achieved by CIDD -150303 (81.8%) against S. mansoni, CIDD-0149830 (80.2%) against S. haematobium and CIDD-066790 (86.7%) against S. japonicum. We have also evaluated the ability of the derivatives to kill immature stages since PZQ does not kill immature schistosomes. CIDD-0150303 demonstrated (100%) killing for all life stages at a final concentration of 143 μM in vitro and effective reduction in worm burden in vivo against S. mansoni. To understand how OXA derivatives fit in the SULT binding pocket, X-ray crystal structures of CIDD-0150303 and CIDD-0150610 demonstrate that the SULT active site will accommodate further modifications to our most active compounds as we fine tune them to increase favorable pharmacokinetic properties. Treatment with a single dose of 100 mg/kg by oral gavage with co-dose of PZQ + CIDD-0150303 reduced the worm burden of PZQ resistant parasites in an animal model by 90.8%. Therefore, we conclude that CIDD-0150303, CIDD-0149830 and CIDD-066790 are novel drugs that overcome some of PZQ limitations, and CIDD-0150303 can be used with PZQ in combination therapy.

Addressing the oxamniquine in vitro-in vivo paradox to facilitate a new generation of anti-schistosome treatments

The antischistosomal drug oxamniquine, OXA, requires activation by a sulfotransferase within the parasitic worm to enable killing. Examination of the pharmacokinetic/pharmacodynamic (PK/PD) relationship for OXA identified an in vitro-in vivo paradox with the maximal clinical plasma concentrations five-to ten-times lower than the efficacious concentration for in vitro schistosomal killing. The parasite resides in the vasculature between the intestine and the liver, and modeling the PK data to determine portal concentrations fits with in vitro studies and explains the required human dose. In silico models were used to predict murine dosing to recapitulate human conditions for OXA portal concentration and time course. Follow-up PK studies verified in mice that a 50-100 mg/kg oral gavage dose of OXA formulated in acetate buffer recapitulates the 20-40 mg/kg dose common in patients. OXA was rapidly cleared through a combination of metabolism and excretion into bile. OXA absorbance and tissue distribution were similar in wild-type and P-gp efflux transporter knockout mice. The incorporation of in vitro efficacy data and portal concentration was demonstrated for an improved OXA-inspired analog that has been shown to kill S. mansoni, S. haematobium, and S. japonicum, whereas OXA is only effective against S. mansoni. Second-generation OXA analogs should optimize both in vitro killing and physiochemical properties to achieve high portal concentration via rapid oral absorption, facilitated by favorable solubility, permeability, and minimal intestinal metabolism.

Schistosome Sulfotransferases: Mode of Action, Expression and Localization

Oxamniquine (OXA) is a prodrug activated by a sulfotransferase (SULT) that was only active against Schistosoma mansoni. We have reengineered OXA to be effective against S. haematobium and S. japonicum. Three derivatives stand out, CIDD-0066790, CIDD-0072229, and CIDD-0149830 as they kill all three major human schistosome species. However, questions remain. Is the OXA mode of action conserved in derivatives? RNA-interference experiments demonstrate that knockdown of the SmSULT, ShSULT, and SjSULT results in resistance to CIDD-0066790. Confirming that the OXA-derivative mode of action is conserved. Next is the level of expression of the schistosome SULTs in each species, as well as changes in SULT expression throughout development in S. mansoni. Using multiple tools, our data show that SmSULT has higher expression compared to ShSULT and SjSULT. Third, is the localization of SULT in the adult, multicellular eucaryotic schistosome species. We utilized fluorescence in situ hybridization and uptake of radiolabeled OXA to determine that multiple cell types throughout the adult schistosome worm express SULT. Thus, we hypothesize the ability of many cells to express the sulfotransferase accounts for the ability of the OXA derivatives to kill adult worms. Our studies demonstrate that the OXA derivatives are able to kill all three human schistosome species and thus will be a useful complement to PZQ.

Genomic analysis of a parasite invasion: Colonization of the Americas by the blood fluke Schistosoma mansoni

Schistosoma mansoni, a snail-borne, blood fluke that infects humans, was introduced into the Americas from Africa during the Trans-Atlantic slave trade. As this parasite shows strong specificity to the snail intermediate host, we expected that adaptation to South American Biomphalaria spp. snails would result in population bottlenecks and strong signatures of selection. We scored 475,081 single nucleotide variants in 143 S. mansoni from the Americas (Brazil, Guadeloupe and Puerto Rico) and Africa (Cameroon, Niger, Senegal, Tanzania, and Uganda), and used these data to ask: (i) Was there a population bottleneck during colonization? (ii) Can we identify signatures of selection associated with colonization? (iii) What were the source populations for colonizing parasites? We found a 2.4- to 2.9-fold reduction in diversity and much slower decay in linkage disequilibrium (LD) in parasites from East to West Africa. However, we observed similar nuclear diversity and LD in West Africa and Brazil, suggesting no strong bottlenecks and limited barriers to colonization. We identified five genome regions showing selection in the Americas, compared with three in West Africa and none in East Africa, which we speculate may reflect adaptation during colonization. Finally, we infer that unsampled populations from central African regions between Benin and Angola, with contributions from Niger, are probably the major source(s) for Brazilian S. mansoni. The absence of a bottleneck suggests that this is a rare case of a serendipitous invasion, where S. mansoni parasites were pre-adapted to the Americas and able to establish with relative ease.

The effect of fs800 on female egg production in Schistosoma mansoni

During schistosomiasis, the paired Schistosoma mansoni female produces about 300 eggs each day. These eggs are responsible for the clinical picture and the transmission of the disease. During female development and egg production, fs800 is expressed only in female vitelline cells. Blast search of fs800 did not show similarities with any published sequences by NCBI. We hypothesize that the product of this gene plays a role in S. mansoni egg production. By using RNA interference to knockdown fs800 and quantitative PCR to measure the gene expression in the female schistosomes, we were able to demonstrate that fs800 product is crucial for viable egg production, it has no effect on worm health or male-female pairing. Our data suggest fs800 inhibition as a potential target to prevent transmission and pathology of schistosomiasis.

Identification and evolution of nuclear receptors in Platyhelminths

Since the first complete set of Platyhelminth nuclear receptors (NRs) from Schistosoma mansoni were identified a decade ago, more flatworm genome data is available to identify their NR complement and to analyze the evolutionary relationship of Platyhelminth NRs. NRs are important transcriptional modulators that regulate development, differentiation and reproduction of animals. In this study, NRs are identified in genome databases of thirty-three species including in all Platyhelminth classes (Rhabditophora, Monogenea, Cestoda and Trematoda). Phylogenetic analysis shows that NRs in Platyhelminths follow two different evolutionary lineages: 1) NRs in a free-living freshwater flatworm (Schmidtea mediterranea) and all parasitic flatworms share the same evolutionary lineage with extensive gene loss. 2) NRs in a free-living intertidal zone flatworm (Macrostomum lignano) follow a different evolutionary lineage with a feature of multiple gene duplication and gene divergence. The DNA binding domain (DBD) is the most conserved region in NRs which contains two C4-type zinc finger motifs. A novel zinc finger motif is identified in parasitic flatworm NRs: the second zinc finger of parasitic Platyhelminth HR96b possesses a CHC2 motif which is not found in NRs of all other animals studied to date. In this study, novel NRs (members of NR subfamily 3 and 6) are identified in flatworms, this result demonstrates that members of all six classical NR subfamilies are present in the Platyhelminth phylum. NR gene duplication, loss and divergence in Platyhelminths are analyzed along with the evolutionary relationship of Platyhelminth NRs.

Rational approach to drug discovery for human schistosomiasis

Human schistosomiasis is a debilitating, life-threatening disease affecting more than 229 million people in as many as 78 countries. There is only one drug of choice effective against all three major species of Schistosoma, praziquantel (PZQ). However, as with many monotherapies, evidence for resistance is emerging in the field and can be selected for in the laboratory. Previously used therapies include oxamniquine (OXA), but shortcomings such as drug resistance and affordability resulted in discontinuation. Employing a genetic, biochemical and molecular approach, a sulfotransferase (SULT-OR) was identified as responsible for OXA drug resistance. By crystallizing SmSULT- OR with OXA, the mode of action of OXA was determined. This information allowed a rational approach to novel drug design. Our team approach with schistosome biologists, medicinal chemists, structural biologists and geneticists has enabled us to develop and test novel drug derivatives of OXA to treat this disease. Using an iterative process for drug development, we have successfully identified derivatives that are effective against all three species of the parasite. One derivative CIDD-0149830 kills 100% of all three human schistosome species within 5 days. The goal is to generate a second therapeutic with a different mode of action that can be used in conjunction with praziquantel to overcome the ever-growing threat of resistance and improve efficacy. The ability and need to design, screen, and develop future, affordable therapeutics to treat human schistosomiasis is critical for successful control program outcomes.

An iterative process produces oxamniquine derivatives that kill the major species of schistosomes infecting humans

Currently there is only one method of treatment for human schistosomiasis, the drug praziquantel. Strong selective pressure has caused a serious concern for a rise in resistance to praziquantel leading to the necessity for additional pharmaceuticals, with a distinctly different mechanism of action, to be used in combination therapy with praziquantel. Previous treatment of Schistosoma mansoni included the use of oxamniquine (OXA), a prodrug that is enzymatically activated in S. mansoni but is ineffective against S. haematobium and S. japonicum. The oxamniquine activating enzyme was identified as a S. mansoni sulfotransferase (SmSULT-OR). Structural data have allowed for directed drug development in reengineering oxamniquine to be effective against S. haematobium and S. japonicum. Guided by data from X-ray crystallographic studies and Schistosoma worm killing assays on oxamniquine, our structure-based drug design approach produced a robust SAR program that tested over 300 derivatives and identified several new lead compounds with effective worm killing in vitro. Previous studies resulted in the discovery of compound CIDD-0066790, which demonstrated broad-species activity in killing of schistosome species. As these compounds are racemic mixtures, we tested and demonstrate that the R enantiomer CIDD-007229 kills S. mansoni, S. haematobium and S. japonicum better than the parent drug (CIDD-0066790). The search for derivatives that kill better than CIDD-0066790 has resulted in a derivative (CIDD- 149830) that kills 100% of S. mansoni, S. haematobium and S. japonicum adult worms within 7 days. We hypothesize that the difference in activation and thus killing by the derivatives is due to the ability of the derivative to fit in the binding pocket of each sulfotransferase (SmSULT-OR, ShSULT-OR, SjSULT-OR) and to be efficiently sulfated. The purpose of this research is to develop a second drug to be used in conjunction with praziquantel to treat the major human species of Schistosoma. Collectively, our findings show that CIDD-00149830 and CIDD-0072229 are promising novel drugs for the treatment of human schistosomiasis and strongly support further development and in vivo testing.

Why does oxamniquine kill Schistosoma mansoni and not S. haematobium and S. japonicum?

Human schistosomiasis is a disease which globally affects over 229 million people. Three major species affecting humans are Schistosoma mansoni, S. haematobium and S. japonicum. Previous treatment of S. mansoni includes the use of oxamniquine (OXA), a prodrug that is enzymatically activated in S. mansoni but is ineffective against S. haematobium and S. japonicum. The OXA activating enzyme was identified and crystallized, as being a S. mansoni sulfotransferase (SmSULT). S. haematobium and S. japonicum possess homologs of SmSULT (ShSULT and SjSULT) begging the question; why does oxamniquine fail to kill S. haematobium and S. japonicum adult worms? Investigation of the molecular structures of the sulfotransferases indicates that structural differences, specifically in OXA contact residues, do not abrogate OXA binding in the active sites as previously hypothesized. Data presented argue that the ability of SULTs to sulfate and thus activate OXA and its derivatives is linked to the ability of OXA to fit in the binding pocket to allow the transfer of a sulfur group.

Oxamniquine resistance alleles are widespread in Old World Schistosoma mansoni and predate drug deployment

Do mutations required for adaptation occur de novo, or are they segregating within populations as standing genetic variation? This question is key to understanding adaptive change in nature, and has important practical consequences for the evolution of drug resistance. We provide evidence that alleles conferring resistance to oxamniquine (OXA), an antischistosomal drug, are widespread in natural parasite populations under minimal drug pressure and predate OXA deployment. OXA has been used since the 1970s to treat Schistosoma mansoni infections in the New World where S. mansoni established during the slave trade. Recessive loss-of-function mutations within a parasite sulfotransferase (SmSULT-OR) underlie resistance, and several verified resistance mutations, including a deletion (p.E142del), have been identified in the New World. Here we investigate sequence variation in SmSULT-OR in S. mansoni from the Old World, where OXA has seen minimal usage. We sequenced exomes of 204 S. mansoni parasites from West Africa, East Africa and the Middle East, and scored variants in SmSULT-OR and flanking regions. We identified 39 non-synonymous SNPs, 4 deletions, 1 duplication and 1 premature stop codon in the SmSULT-OR coding sequence, including one confirmed resistance deletion (p.E142del). We expressed recombinant proteins and used an in vitro OXA activation assay to functionally validate the OXA-resistance phenotype for four predicted OXA-resistance mutations. Three aspects of the data are of particular interest: (i) segregating OXA-resistance alleles are widespread in Old World populations (4.29–14.91% frequency), despite minimal OXA usage, (ii) two OXA-resistance mutations (p.W120R, p.N171IfsX28) are particularly common (>5%) in East African and Middle-Eastern populations, (iii) the p.E142del allele has identical flanking SNPs in both West Africa and Puerto Rico, suggesting that parasites bearing this allele colonized the New World during the slave trade and therefore predate OXA deployment. We conclude that standing variation for OXA resistance is widespread in S. mansoni.

It has been argued that drug resistance is unlikely to spread rapidly in helminth parasites infecting humans. This is based, at least in part, on the premise that resistance mutations are rare or absent within populations prior to treatment, and take a long time to reach appreciable frequencies because helminth parasite generation time is long. This argument is critically dependent on the starting frequency of resistance alleles–if high levels of “standing variation” for resistance are present prior to deployment of treatment, resistance may spread rapidly. We examined frequencies of oxamniquine resistance alleles present in Schistosoma mansoni from Africa and the Middle East where oxamniquine has seen minimal use. We found that oxamniquine resistance alleles are widespread in the Old World, ranging from 4.29% in the Middle East to 14.91% in East African parasite populations. Furthermore, we show that resistance alleles from West African and the Caribbean schistosomes share a common origin, suggesting that these alleles travelled to the New World with S. mansoni during the transatlantic slave trade. Together, these results demonstrate extensive standing variation for oxamniquine resistance. Our results have important implications for both drug treatment policies and drug development efforts, and demonstrate the power of molecular surveillance approaches for guiding helminth control.

Nuclear hormone receptors in parasitic Platyhelminths

Nuclear receptors (NRs) belong to a large protein superfamily which includes intracellular receptors for secreted hydrophobic signal molecules, such as steroid hormones and thyroid hormones. They regulate development and reproduction in metazoans by binding to the promoter region of their target gene to activate or repress mRNA synthesis. Isolation and characterization of NRs in the parasitic trematode Schistosoma mansoni identified two homologues of mammalian thyroid receptor (TR). This was the first known protostome exhibiting TR homologues. Three novel NRs each possess a novel set of two DNA binding domains (DBD) in tandem with a ligand binding domain (LBD) (2DBD-NRs) isolated in Schistosoma mansoni revealed a novel NR modular structure: A/B-DBD-DBD-hinge-LBD. Full length cDNA of several NRs have been isolated and studied in the parasitic trematodes S. mansoni, S. japonicum and in the cestode Echinococcus multilocularis. The genome of the blood flukes S. mansoni, S. japonicum and S. haematobium, the liver fluke Clonorchis sinensis and the cestode Echinococcus multilocularis have been sequenced. Study of the NR complement in parasitic Platyhelminths will help us to understand the role of NRs in regulation of their development and understand the evolution of NR in animals.

Design, Synthesis, and Characterization of Novel Small Molecules as Broad Range Antischistosomal Agents

Schistosomiasis is a major human parasitic disease afflicting more than 250 million people, historically treated with chemotherapies praziquantel or oxamniquine. Since oxamniquine is species-specific, killing Schistosoma mansoni but not other schistosome species (S. haematobium or S. japonicum) and evidence for drug resistant strains is growing, research efforts have focused on identifying novel approaches. Guided by data from X-ray crystallographic studies and Schistosoma worm killing assays on oxamniquine, our structure-based drug design approach produced a robust structure-activity relationship (SAR) program that identified several new lead compounds with effective worm killing. These studies culminated in the discovery of compound 12a, which demonstrated broad-species activity in killing S. mansoni (75%), S. haematobium (40%), and S. japonicum (83%).

Genetic Crosses and Linkage Mapping in Schistosome Parasites

Linkage mapping - utilizing experimental genetic crosses to examine cosegregation of phenotypic traits with genetic markers - is now 100 years old. Schistosome parasites are exquisitely well suited to linkage mapping approaches because genetic crosses can be conducted in the laboratory, thousands of progeny are produced, and elegant experimental work over the last 75 years has revealed heritable genetic variation in multiple biomedically important traits such as drug resistance, host specificity, and virulence. Application of this approach is timely because the improved genome assembly for Schistosoma mansoni and developing molecular toolkit for schistosomes increase our ability to link phenotype with genotype. We describe current progress and potential future directions of linkage mapping in schistosomes.

Structural and enzymatic insights into species-specific resistance to schistosome parasite drug therapy

The antischistosomal prodrug oxamniquine is activated by a sulfotransferase (SULT) in the parasitic flatworm Schistosoma mansoni. Of the three main human schistosome species, only S. mansoni is sensitive to oxamniquine therapy despite the presence of SULT orthologs in Schistosoma hematobium and Schistosoma japonicum The reason for this species-specific drug action has remained a mystery for decades. Here we present the crystal structures of S. hematobium and S. japonicum SULTs, including S. hematobium SULT in complex with oxamniquine. We also examined the activity of the three enzymes in vitro; surprisingly, all three are active toward oxamniquine, yet we observed differences in catalytic efficiency that implicate kinetics as the determinant for species-specific toxicity. These results provide guidance for designing oxamniquine derivatives to treat infection caused by all species of schistosome to combat emerging resistance to current therapy.

Building a global schistosomiasis alliance: an opportunity to join forces to fight inequality and rural poverty

Schistosomiasis, one of the 17 neglected tropical diseases listed by the World Health Organization, presents a substantial public health and economic burden. Of the 261 million people requiring preventive chemotherapy for schistosomiasis in 2013, 92% of them lived in sub-Saharan Africa and only 12.7% received preventive chemotherapy. Moreover, in 2010, the WHO reported that schistosomiasis mortality could be as high as 280 000 per year in Africa alone.In May 2012 delegates to the sixty-fifth World Health Assembly adopted resolution WHA65.21 that called for the elimination of schistosomiasis, and foresees the regular treatment of at least 75% of school age children in at-risk areas. The resolution urged member states to intensify schistosomiasis control programmes and to initiate elimination campaigns where possible.Despite this, in June 2015, schistosomiasis was indicated to have the lowest level of preventive chemotherapy implementation in the spectrum of neglected tropical diseases. It was also highlighted as the disease most lacking in progress. This is perhaps unsurprising, given that it was also the only NTD with access to drug donations but without a coalition of stakeholders that collaborates to boost commitment and implementation.As a consequence, and to ensure that the WHO NTDs Roadmap Targets of 2012 and World Health Assembly Resolution WHA65.21 are met, the Global Schistosomiasis Alliance (GSA) has been set up. Diverse and representative, the GSA aims to be a partnership of endemic countries, academic and research institutions, international development agencies and foundations, international organizations, non-governmental development organizations, private sector companies and advocacy and resource mobilisation partners. Ultimately, the GSA calls for a partnership to work for the benefit of endemic countries by addressing health inequity and rural poverty.

A next-generation proteome array for Schistosoma mansoni

A proteome microarray consisting of 992 Schistosoma mansoni proteins was produced and screened with sera to determine antibody signatures indicative of the clinical stages of schistosomiasis and the identification of subunit vaccine candidates. Herein, we describe the methods used to derive the gene list for this array (representing approximately 10% of the predicted S. mansoni proteome). We also probed a pilot version of the microarray with sera from individuals either acutely or chronically infected with S. mansoni from endemic areas in Brazil and sera from individuals resident outside the endemic area (USA) to determine if the array is functional and informative.

Independent origins of loss-of-function mutations conferring oxamniquine resistance in a Brazilian schistosome population

Molecular surveillance provides a powerful approach to monitoring the resistance status of parasite populations in the field and for understanding resistance evolution. Oxamniquine was used to treat Brazilian schistosomiasis patients (mid-1970s to mid-2000s) and several cases of parasite infections resistant to treatment were recorded. The gene underlying resistance (SmSULT-OR) encodes a sulfotransferase required for intracellular drug activation. Resistance has a recessive basis and occurs when both SmSULT-OR alleles encode for defective proteins. Here we examine SmSULT-OR sequence variation in a natural schistosome population in Brazil ∼40years after the first use of this drug. We sequenced SmSULT-OR from 189 individual miracidia (1-11 per patient) recovered from 49 patients, and tested proteins expressed from putative resistance alleles for their ability to activate oxamniquine. We found nine mutations (four non-synonymous single nucleotide polymorphisms, three non-coding single nucleotide polymorphisms and two indels). Both mutations (p.E142del and p.C35R) identified previously were recovered in this field population. We also found two additional mutations (a splice site variant and 1bp coding insertion) predicted to encode non-functional truncated proteins. Two additional substitutions (p.G206V, p.N215Y) tested had no impact on oxamniquine activation. Three results are of particular interest: (i) we recovered the p.E142del mutation from the field: this same deletion is responsible for resistance in an oxamniquine selected laboratory parasite population; (ii) frequencies of resistance alleles are extremely low (0.27-0.8%), perhaps due to fitness costs associated with carriage of these alleles; (iii) that four independent resistant alleles were found is consistent with the idea that multiple mutations can generate loss-of-function alleles.

Real-time PCR for sexing Schistosoma mansoni cercariae

The gender of cercarial larvae can only be determined using molecular methods. End point PCR methods that amplify repetitive markers on the W chromosome of the female (ZW) parasites have been developed, but sometimes results are ambiguous or incorrect. To more effectively distinguish sexes, and to determine why end point PCR can be incorrect, we quantified the W6 repeat sequence and a specific Z chromosome gene using real-time PCR. The ratio between copy number of W6 and a Z chromosome marker unambiguously identifies gender: females have higher ratios (421-4371) than males (0-21). However, some males have low numbers of W6 elements in their genome, and qPCR demonstrated significantly higher W6/Z marker ratios for male genotypes giving ambiguous end point PCR results compared with males giving clear end point results. The quantitative PCR sexing method developed will be particularly useful where reliable sexing of cercariae is critical, for example when staging genetic crosses.

Structural and Functional Characterization of the Enantiomers of the Antischistosomal Drug Oxamniquine

Background

For over two decades, a racemic mixture of oxamniquine (OXA) was administered to patients infected by Schistosoma mansoni, but whether one or both enantiomers exert antischistosomal activity was unknown. Recently, a ~30 kDa S. mansonisulfotransferase (SmSULT) was identified as the target of OXA action.

Methodology/Principal Findings

Here, we separate the OXA enantiomers using chromatographic methods and assign their optical activities as dextrorotary [(+)-OXA] or levorotary [(-)-OXA]. Crystal structures of the parasite enzyme in complex with optically pure (+)-OXA and (-)-OXA) reveal their absolute configurations as S- and R-, respectively. When tested in vitro, S-OXA demonstrated the bulk of schistosomicidal activity, while R-OXA had antischistosomal effects when present at relatively high concentrations. Crystal structures R-OXA•SmSULT and S-OXA•SmSULT complexes reveal similarities in the modes of OXA binding, but only the S-OXA enantiomer is observed in the structure of the enzyme exposed to racemic OXA.

Conclusions/Significance

Together the data suggest the higher schistosomicidal activity of S-OXA is correlated with its ability to outcompete R-OXA binding the sulfotransferase active site. These findings have important implications for the design, syntheses, and dosing of new OXA-based antischistosomal compounds.

Schistosomes, parasites that cause the disease schistosomiasis in humans, are blood flukes that infect an estimated 200 million people in 76 countries. Control of schistosomiasis is currently based on repeated doses of the drug praziquantel (PZQ). Parasites showing reduced susceptibility to PZQ have been recovered from patients that failed PZQ treatment and have been obtained by experimental selection. New anti-schistosomal drugs are therefore needed that can be used with PZQ to minimize the probability of resistance. The older anti-schistosomal drug oxamniquine (OXA) has an excellent efficacy and safety record but is only active against one of the three species infecting humans. Recently, a combination of genetic and structural analyses resulted in the determination of the structure of OXA in complex with its target enzyme in the parasite, providing opportunity for structure-guided modifications of OXA to make it more effective against all three schistosome species. Synthesis of OXA results in a racemic mixture. Here, we isolate OXA enantiomers and find that one is more effective than the other at killing schistosomes. Crystal structures of both OXA enantiomers bound to the target enzyme suggest a molecular basis for this observation that should be considered in ongoing and future OXA-based drug design efforts.

Monitoring the efficacy of drugs for neglected tropical diseases controlled by preventive chemotherapy

In the last decade, pharmaceutical companies, governments and global health organisations under the leadership of the World Health Organization (WHO) have pledged large-scale donations of anthelmintic drugs, including ivermectin (IVM), praziquantel (PZQ), albendazole (ALB) and mebendazole (MEB). This worldwide scale-up in drug donations calls for strong monitoring systems to detect any changes in anthelmintic drug efficacy. This review reports on the outcome of the WHO Global Working Group on Monitoring of Neglected Tropical Diseases Drug Efficacy, which consists of three subgroups: (i) soil-transmitted helminthiases (ALB and MEB); (ii) onchocerciasis and lymphatic filariasis (IVM); and (iii) schistosomiasis (PZQ). Progress of ongoing work, challenges and research needs for each of the four main drugs used in helminthic preventive chemotherapy (PC) are reported, laying the ground for appropriate implementation of drug efficacy monitoring programmes under the co-ordination and guidelines of the WHO. Best practices for monitoring drug efficacy should be made available and capacity built as an integral part of neglected tropical disease (NTD) programme monitoring. Development of a disease-specific model to predict the impact of PC programmes, to detect outliers and to solicit responses is essential. Research studies on genetic polymorphisms in relation to low-efficacy phenotypes should be carried out to identify markers of putative resistance against all NTD drugs and ultimately to develop diagnostic assays. Development of combination and co-administration of NTD drugs as well as of new drug entities to boost the armamentarium of the few drugs available for NTD control and elimination should be pursued in parallel.

Protective Potential of Antioxidant Enzymes as Vaccines for Schistosomiasis in a Non-Human Primate Model

Schistosomiasis remains a major cause of morbidity in the world. The challenge today is not so much in the clinical management of individual patients, but rather in population-based control of transmission in endemic areas. Despite recent large-scale efforts, such as integrated control programs aimed at limiting schistosomiasis by improving education and sanitation, molluscicide treatment programs and chemotherapy with praziquantel, there has only been limited success. There is an urgent need for complementary approaches, such as vaccines. We demonstrated previously that anti-oxidant enzymes, such as Cu-Zn superoxide dismutase (SOD) and glutathione S peroxidase (GPX), when administered as DNA-based vaccines induced significant levels of protection in inbred mice, greater than the target 40% reduction in worm burden compared to controls set as a minimum by the WHO. These results led us to investigate if immunization of non-human primates with antioxidants would stimulate an immune response that could confer protection as a prelude study for human trials. Issues of vaccine toxicity and safety that were difficult to address in mice were also investigated. All baboons in the study were examined clinically throughout the study and no adverse reactions occurred to the immunization. When our outbred baboons were vaccinated with two different formulations of SOD (SmCT-SOD and SmEC-SOD) or one of GPX (SmGPX), they showed a reduction in worm number to varying degrees, when compared with the control group. More pronounced, vaccinated animals showed decreased bloody diarrhea, days of diarrhea, and egg excretion (transmission), as well as reduction of eggs in the liver tissue and in the large intestine (pathology) compared to controls. Specific IgG antibodies were present in sera after immunizations and 10 weeks after challenge infection compared to controls. Peripheral blood mononuclear cells, mesenteric, and inguinal node cells from vaccinated animals proliferated and produced high levels of cytokines and chemokines in response to crude and recombinant antigens compared with controls. All together, these data demonstrate the potential of antioxidants as a vaccine in a non-human primate model.

Efficient linkage mapping using exome capture and extreme QTL in schistosome parasites

Background

Identification of parasite genes that underlie traits such as drug resistance and host specificity is challenging using classical linkage mapping approaches. Extreme QTL (X-QTL) methods, originally developed by rodent malaria and yeast researchers, promise to increase the power and simplify logistics of linkage mapping in experimental crosses of schistosomes (or other helminth parasites), because many 1000s of progeny can be analysed, phenotyping is not required, and progeny pools rather than individuals are genotyped. We explored the utility of this method for mapping a drug resistance gene in the human parasitic fluke Schistosoma mansoni.

Results

We staged a genetic cross between oxamniquine sensitive and resistant parasites, then between two F1 progeny, to generate multiple F2 progeny. One group of F2s infecting hamsters was treated with oxamniquine, while a second group was left untreated. We used exome capture to reduce the size of the genome (from 363 Mb to 15 Mb) and exomes from pooled F2 progeny (treated males, untreated males, treated females, untreated females) and the two parent parasites were sequenced to high read depth (mean = 95-366×) and allele frequencies at 14,489 variants compared. We observed dramatic enrichment of alleles from the resistant parent in a small region of chromosome 6 in drug-treated male and female pools (combined analysis: = 11.07, p = 8.74 × 10^-29). This region contains Smp_089320 a gene encoding a sulfotransferase recently implicated in oxamniquine resistance using classical linkage mapping methods.

Conclusions

These results (a) demonstrate the utility of exome capture for generating reduced representation libraries in Schistosoma mansoni, and (b) provide proof-of-principle that X-QTL methods can be successfully applied to an important human helminth. The combination of these methods will simplify linkage analysis of biomedically or biologically important traits in this parasite.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-617) contains supplementary material, which is available to authorized users.

Genetic and molecular basis of drug resistance and species-specific drug action in schistosome parasites

Oxamniquine resistance evolved in the human blood fluke (Schistosoma mansoni) in Brazil in the 1970s. We crossed parental parasites differing ~500-fold in drug response, determined drug sensitivity and marker segregation in clonally derived second-generation progeny, and identified a single quantitative trait locus (logarithm of odds = 31) on chromosome 6. A sulfotransferase was identified as the causative gene by using RNA interference knockdown and biochemical complementation assays, and we subsequently demonstrated independent origins of loss-of-function mutations in field-derived and laboratory-selected resistant parasites. These results demonstrate the utility of linkage mapping in a human helminth parasite, while crystallographic analyses of protein-drug interactions illuminate the mode of drug action and provide a framework for rational design of oxamniquine derivatives that kill both S. mansoni and S. haematobium, the two species responsible for >99% of schistosomiasis cases worldwide.

Evolution of sex chromosomes ZW of Schistosoma mansoni inferred from chromosome paint and BAC mapping analyses

Chromosomes of schistosome parasites among digenetic flukes have a unique evolution because they exhibit the sex chromosomes ZW, which are not found in the other groups of flukes that are hermaphrodites. We conducted molecular cytogenetic analyses for investigating the sex chromosome evolution using chromosome paint analysis and BAC clones mapping. To carry this out, we developed a technique for making paint probes of genomic DNA from a single scraped chromosome segment using a chromosome microdissection system, and a FISH mapping technique for BAC clones. Paint probes clearly identified each of the 8 pairs of chromosomes by a different fluorochrome color. Combination analysis of chromosome paint analysis with Z/W probes and chromosome mapping with 93 BAC clones revealed that the W chromosome of Schistosoma mansoni has evolved by at least four inversion events and heterochromatinization. Nine of 93 BAC clones hybridized with both the Z and W chromosomes, but the locations were different between Z and W chromosomes. The homologous regions were estimated to have moved from the original Z chromosome to the differentiated W chromosome by three inversions events that occurred before W heterohcromatinization. An inversion that was observed in the heterochromatic region of the W chromosome likely occurred after W heterochromatinization. These inversions and heterochromatinization are hypothesized to be the key factors that promoted the evolution of the W chromosome of S. mansoni.

Recent advances in Schistosoma genomics

Schistosome research has entered the genomic era with the publications reporting the Schistosoma mansoni and Schistosoma japonicum genomes. Schistosome genomics is motivated by the need for new control tools. However, much can also be learned about the biology of Schistosoma, which is a tractable experimental model. In this article, we review the recent achievements in the field of schistosome research and discuss future perspectives on genomics and how it can be integrated in a usable format, on the genetic mapping and how it has improved the genome assembly and provided new research approaches, on how epigenetics provides interesting insights into the biology of the species and on new functional genomics tools that will contribute to the understanding of the function of genes, many of which are parasite- or taxon specific.

Effect of human TGF-β on the gene expression profile of Schistosoma mansoni adult worms

Schistosoma mansoni is responsible for schistosomiasis, a parasitic disease that affects 200 million people worldwide. Molecular mechanisms of host-parasite interaction are complex and involve a crosstalk between host signals and parasite receptors. TGF-β signaling pathway has been shown to play an important role in S. mansoni development and embryogenesis. In particular human (h) TGF-β has been shown to bind to a S. mansoni receptor, transduce a signal that regulates the expression of a schistosome target gene. Here we describe 381 parasite genes whose expression levels are affected by in vitro treatment with hTGF-β. Among these differentially expressed genes we highlight genes related to morphology, development and cell cycle that could be players of cytokine effects on the parasite. We confirm by qPCR the expression changes detected with microarrays for 5 out of 7 selected genes. We also highlight a set of non-coding RNAs transcribed from the same loci of protein-coding genes that are differentially expressed upon hTGF-β treatment. These datasets offer potential targets to be explored in order to understand the molecular mechanisms behind the possible role of hTGF-β effects on parasite biology.

A systematically improved high quality genome and transcriptome of the human blood fluke Schistosoma mansoni

Schistosomiasis is one of the most prevalent parasitic diseases, affecting millions of people in developing countries. Amongst the human-infective species, Schistosoma mansoni is also the most commonly used in the laboratory and here we present the systematic improvement of its draft genome. We used Sanger capillary and deep-coverage Illumina sequencing from clonal worms to upgrade the highly fragmented draft 380 Mb genome to one with only 885 scaffolds and more than 81% of the bases organised into chromosomes. We have also used transcriptome sequencing (RNA-seq) from four time points in the parasite's life cycle to refine gene predictions and profile their expression. More than 45% of predicted genes have been extensively modified and the total number has been reduced from 11,807 to 10,852. Using the new version of the genome, we identified trans-splicing events occurring in at least 11% of genes and identified clear cases where it is used to resolve polycistronic transcripts. We have produced a high-resolution map of temporal changes in expression for 9,535 genes, covering an unprecedented dynamic range for this organism. All of these data have been consolidated into a searchable format within the GeneDB (www.genedb.org) and SchistoDB (www.schistodb.net) databases. With further transcriptional profiling and genome sequencing increasingly accessible, the upgraded genome will form a fundamental dataset to underpin further advances in schistosome research.

Schistosomiasis is a disease caused by parasitic blood flukes of the genus Schistosoma. Human-infective species are prevalent in developing countries, where they represent a major disease burden as well as an impediment to socioeconomic development. In addition to its clinical relevance, Schistosoma mansoni is the species most widely used for laboratory experimentation. In 2009, the first draft of the S. mansoni and S. japonicum genomes were published. Both genome sequences represented a great step forward for schistosome research, but their highly fragmented nature compromised the quality of potential downstream analyses. In this study, we have substantially improved both the genome and the transcriptome resources for S. mansoni. We collated existing data and added deep DNA sequence data from clonal worms and RNA sequence data from four key time points in the life cycle of the parasite. We were able to identify transcribed regions to single-base resolution and have profiled gene expression from the free-living larvae to the early human parasitic stage. We uncovered extensive use of single transcripts from multiple genes, which the organism subsequently resolves by trans-splicing. All data from this study comprise a major new release of the genome, which is publicly and easily accessible.

Nuclear hormone receptors in parasitic helminths

Nuclear receptors (NRs) belong to a large protein superfamily that are important transcriptional modulators in metazoans. Parasitic helminths include parasitic worms from the Lophotrochozoa (Platyhelminths) and Ecdysozoa (Nematoda). NRs in parasitic helminths diverged into two different evolutionary lineages. NRs in parasitic Platyhelminths have orthologues in Deuterostomes, in arthropods or both with a feature of extensive gene loss and gene duplication within different gene groups. NRs in parasitic Nematoda follow the nematode evolutionary lineage with a feature of multiple duplication of SupNRs and gene loss.

The genome of the blood fluke Schistosoma mansoni

Schistosoma mansoni is responsible for the neglected tropical disease schistosomiasis that affects 210 million people in 76 countries. We report here analysis of the 363 megabase nuclear genome of the blood fluke. It encodes at least 11,809 genes, with an unusual intron size distribution, and novel families of micro-exon genes that undergo frequent alternate splicing. As the first sequenced flatworm, and a representative of the lophotrochozoa, it offers insights into early events in the evolution of the animals, including the development of a body pattern with bilateral symmetry, and the development of tissues into organs. Our analysis has been informed by the need to find new drug targets. The deficits in lipid metabolism that make schistosomes dependent on the host are revealed, while the identification of membrane receptors, ion channels and more than 300 proteases, provide new insights into the biology of the life cycle and novel targets. Bioinformatics approaches have identified metabolic chokepoints while a chemogenomic screen has pinpointed schistosome proteins for which existing drugs may be active. The information generated provides an invaluable resource for the research community to develop much needed new control tools for the treatment and eradication of this important and neglected disease.

Signal transduction regulates schistosome reproductive biology

Schistosome parasites exhibit separate sexes and with the evolution of sex they have developed an intricate relationship between the male and female worms such that signals between the male and female that are initiated at the time of mating, regulate female reproductive development and subsequent egg production. As the egg stage is responsible for pathogenesis and transmission, understanding the molecular mechanisms of female reproductive development may identify novel targets for the control of transmission and morbidity of this major world public health problem. Recent data have demonstrated that the pairing process, proliferation, and differentiation of vitelline cells, expression of female-specific genes and egg embryogenesis are regulated by the TGFbeta pathway and protein tyrosine kinases.

Efficient genotyping of Schistosoma mansoni miracidia following whole genome amplification

Small parasites and larval stages pose a problem for molecular analyses because limited amounts of DNA template are available. Isothermal methods for faithfully copying DNA have the potential to revolutionize studies of such organisms. We evaluated the fidelity of multiple displacement amplification (MDA) for amplifying DNA extracted from a single miracidium of Schistosoma mansoni. To do this we genotyped DNA extracted from 28 F1 miracidia following MDA using 56 microsatellite markers. Because these miracidia were obtained from a cross between a male and female worm of known genotypes, we were able to predict the alleles present in the progeny and quantify the genotyping error rate. We found just 8/1568 genotypes deviated from Mendelian expectations. Furthermore, because 1 of these resulted from a genuine mutation, the error rate due to MDA is 7/1568 (0.45%). We conclude that many hundreds of microsatellites or other genetic markers can be accurately genotyped from a single miracidium using this method, greatly expanding the scope of population genetic, epidemiological and evolutionary studies on this parasite.

Genomic linkage map of the human blood fluke Schistosoma mansoni

BACKGROUND

Schistosoma mansoni is a blood fluke that infects approximately 90 million people. The complete life cycle of this parasite can be maintained in the laboratory, making this one of the few experimentally tractable human helminth infections, and a rich literature reveals heritable variation in important biomedical traits such as virulence, host-specificity, transmission and drug resistance. However, there is a current lack of tools needed to study S. mansoni's molecular, quantitative, and population genetics. Our goal was to construct a genetic linkage map for S. mansoni, and thus provide a new resource that will help stimulate research on this neglected pathogen.

RESULTS

We genotyped grandparents, parents and 88 progeny to construct a 5.6 cM linkage map containing 243 microsatellites positioned on 203 of the largest scaffolds in the genome sequence. The map allows 70% of the estimated 300 Mb genome to be ordered on chromosomes, and highlights where scaffolds have been incorrectly assembled. The markers fall into eight main linkage groups, consistent with seven pairs of autosomes and one pair of sex chromosomes, and we were able to anchor linkage groups to chromosomes using fluorescent in situ hybridization. The genome measures 1,228.6 cM. Marker segregation reveals higher female recombination, confirms ZW inheritance patterns, and identifies recombination hotspots and regions of segregation distortion.

CONCLUSIONS

The genetic linkage map presented here is the first for S. mansoni and the first for a species in the phylum Platyhelminthes. The map provides the critical tool necessary for quantitative genetic analysis, aids genome assembly, and furnishes a framework for comparative flatworm genomics and field-based molecular epidemiological studies.

Cloning and characterization of a cDNA fragment encoding a Schistosoma mansoni actin-binding protein (Smfilamin)

To identify vaccine candidates for Schistosoma mansoni, the IgG fraction of rabbit antiserum raised against immature female worms affinity purified over a NP-40 extract of 3-h schistosomula was used to immunoscreen a cercarial lambdagt11 cDNA library. One clone with a 1.5-kb cDNA insert revealed an encoded peptide of 479 amino acids, which bears homology to human actin-binding protein (ABP-280=filamin). Northern blot analysis revealed a transcript of about 8.6 kb, indicating that the complete gene was not cloned. Overlapping clones, which encode a composite sequence of 983 amino acids (45% identity with filamin), were subsequently isolated from the cDNA library. The 1.5-kb insert was cloned into pGEX, overexpressed, and the 479 amino acid peptide purified. Western blot analysis using polyclonal antisera specific to the peptide identified a 280-kDa molecule in adult worm extracts. RT-PCR demonstrated that Smfilaimin is expressed in various stages. Immunofluorescence studies with specific antisera revealed a tegument-associated fluorescence in adult worms. IgG specific to the Smfilamin fragment showed 36.6% killing of schistosomules in an in vitro killing assay.

The spatial distribution of Schistosoma mansoni infection before and after chemotherapy in the Jequitinhonha Valley in Brazil

Schistosomiasis prevalence and egg counts remained low one year after chemotherapy in most households in a hyperendemic rural area in northern Minas Gerais but several distinct spatial patterns could be observed in relation to IgE levels and to a lesser extent to exposure risk (TBM) and type of water supply. An inverse relationship between pre-treatment household prevalence and egg counts on the one hand and post-treatment IgE levels on the other were noted in two of the five communities. Low exposure risk was associated with the low pre-treatment infection rates in the central village but did not contribute to the decline of infection rates after chemotherapy in the study area, as indicated by the significant increase in water contact during the posttreatment period (p < 0.0001). Distance between households and the streams and socioeconomic factors were also unimportant in predicting the spatial distribution of infection. These results are consistent with the production and antiparasitic effect of high levels of IgE in Schistosoma mansoni infection.

Thyroid hormone receptor orthologues from invertebrate species with emphasis on Schistosoma mansoni

BACKGROUND

Thyroid hormone receptors (TRs) function as molecular switches in response to thyroid hormone to regulate gene transcription. TRs were previously believed to be present only in chordates.

RESULTS

We isolated two TR genes from the Schistosoma mansoni and identified TR orthologues from other invertebrates: the platyhelminths, S. japonium and Schmidtea mediterranea, the mollusc, Lottia gigantean and the arthropod Daphnia pulex. Phylogenetic analysis of the DNA binding domain and/or ligand binding domain shows that invertebrate and vertebrate TRs cluster together, TRs from the vertebrates and from the jawless vertebrate (lamprey) clustered within separate subgroups, Platyhelminth TRs cluster outside of the vertebrate TR subgroups and that the schistosome TRs and S. mediterranea TRs clustered within separate subgroups. Alignment of the C-terminus of the A/B domain revealed a conserved TR-specific motif, termed TR 'N-terminus signature sequence', with a consensus sequence of (G/P)YIPSY(M/L)XXXGPE(D/E)X. Heterodimer formation between S. mansoni TRs and SmRXR1 suggests that the invertebrate TR protein gained the ability to form a heterodimer with RXR. ESMA analysis showed that SmTR alpha could bind to a conserved DNA core motif as a monomer or homodimer.

CONCLUSION

Vertebrate TR genes originated from a common ancestor of the Bilateria. TR genes underwent duplication independently in the Protostomia and Deuterostomia. The duplication of TRs in deuterostomes occurred after the split of jawless and jawed vertebrates. In protostomes, TR genes underwent duplication in Platyhelminths, occurring independently in trematode and turbellarian lineages. Using S. mansoni TRs as an example, invertebrate TRs exhibited the ability to form a dimer with RXR prior to the emergence of the vertebrate TRs and were able to bind to vertebrate TR core DNA elements as a monomer or homodimer.

Molecular cloning and characterization of WD40-repeat protein from Clonorchis sinensis

WD40-repeat proteins have four to eight repeating units flanked by Gly-His (GH) and Trp-Asp (WD) at both termini and folds into a beta-propeller. A polypeptide deduced from a Clonorchis sinensis cDNA clone analyzed to have seven WD40-repeats and predicted to form a beta-propeller (CsWD1). The CsWD1 protein was expressed stage-specifically in the metacercariae and localized in the tegumental syncytium. The CsWD1 protein is suggested to serve as a platform for interacting partner proteins in the tegumental syncytium of C. sinensis metacercariae.

Schistosoma mansoni: Heterologous complementation of a yeast null mutant by SmRbx, a protein similar to a RING box protein involved in ubiquitination

The SCF (Skp1-Cul1-F-box) complex is one of the several E3 ligase enzymes and it catalyzes protein ubiquitination and degradation by the 26S proteasome. Rbx1 is a member of the SCF complex in humans and HRT1 is its yeast orthologue. A cDNA encoding a Schistosoma mansoni Rbx1 homolog was cloned and functionally characterized. Heterologous functional complementation in yeast showed that the worm SmRbx gene was able to complement the HRT1yeast null mutation. Gene deletion constructs for N- and C-termini truncated proteins were used to transform hrt1(-) yeast mutant strains, allowing us to observe that regions reported to be involved in the interaction with cullin1 (Cul1) were essential for SmRbx function. Yeast two-hybrid assays using SmRbx and yeast Cul1 confirmed that SmRbx, but not the mutant SmRbxDelta24N, lacking the N-terminus of the protein, was capable of interacting with Cul1. These results suggest that SmRbx protein is involved in the SCF complex formation.

DNA probes for identifying chromosomes 5, 6, and 7 of Schistosoma mansoni

Schistosoma mansoni has a genome of 270 Mb contained on 8 pairs of chromosomes. C-banding has been a useful technique in identifying the 7 autosomal and sex chromosomes. However, even with C-banding, S. mansoni chromosomes 5, 6, and 7 are difficult to discriminate from each other, because of their small sizes, morphological similarity, and poor banding patterns. We have identified probes that specifically paint chromosomes 5, 6, and 7 of S. mansoni with the use of chromosome microdissection and the degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). Exact chromosome identification is required for accurate chromosome mapping of genomic clones and genetic elements, which is an essential component of the schistosome genome project.

Identification and characterization of an R-Smad ortholog (SmSmad1B) fromSchistosoma mansoni

Smad proteins are the cellular mediators of the transforming growth factor-beta superfamily signals. Herein, we describe the isolation of a fourth Smad gene from the helminth Schistosoma mansoni, a receptor-regulated Smad (R-Smad) gene termed SmSmad1B. The SmSmad1B protein is composed of 380 amino acids, and contains conserved MH1 and MH2 domains separated by a short 42 amino acid linker region. The SmSmad1B gene (> 10.7 kb) is composed of five exons separated by four introns. On the basis of phylogenetic analysis, SmSmad1B demonstrates homology to Smad proteins involved in the bone morphogenetic protein pathway. SmSmad1B transcript is expressed in all stages of schistosome development, and exhibits the highest expression level in the cercariae stage. By immunolocalization experiments, the SmSmad1B protein was detected in the cells of the parenchyma of adult schistosomes as well as in female reproductive tissues. Yeast two-hybrid experiments revealed an interaction between SmSmad1B and the common Smad, SmSmad4. As determined by yeast three-hybrid assays and pull-down assays, the presence of the wild-type or mutated SmTbetaRI receptor resulted in a decreased interaction between SmSmad1B and SmSmad4. These results suggest the presence of a nonfunctional interaction between SmSmad1B and SmTbetaRI that does not give rise to the phosphorylation and the release of SmSmad1B to form a heterodimer with SmSmad4. SmSmad1B, as well as the schistosome bone morphogenetic protein-related Smad SmSmad1 and the transforming growth factor-beta-related SmSmad2, interacted with the schistosome coactivator proteins SmGCN5 and SmCBP1 in pull-down assays. In all, these data suggest the involvement of SmSmad1B in critical biological processes such as schistosome reproductive development.

Identification and characterization of a nuclear receptor subfamily I member in the Platyhelminth Schistosoma mansoni (SmNR1)

A cDNA encoding a nuclear receptor subfamily I member in the platyhelminth Schistosoma mansoni (SmNR1) was identified and characterized. SmNR1 cDNA is 2406 bp long and contains an open reading frame encoding a 715 residue protein. Phylogenetic analysis demonstrates that SmNR1 is a divergent member of nuclear receptor subfamily I with no known orthologue. SmNR1 was localized to S. mansoni chromosome 1 by fluorescent in situ hybridization. Gene structure of SmNR1 was determined showing it to consist of eight exons spanning more than 14 kb. Quantitative real-time RT-PCR showed that SmNR1 was expressed throughout schistosome development with a higher expression in eggs, sporocysts and 21-day worms. SmNR1 contains an autonomous transactivation function (AF1) in the A/B domain as demonstrated in a yeast one-hybrid assay; it interacts with SmRXR1 in a yeast two-hybrid assay and in a glutathione S-transferase pull-down assay. Electrophoretic mobility shift assay showed that SmNR1 could form a heterodimer with SmRXR1 to bind to DNA elements containing the half-site AGGTCA, a direct repeat of the half-site separated by 0-5 nucleotides (DR1-DR5) and a palindrome repeat of the half-site not separated by nucleic acids (Pal0). Transient transfection in mammalian COS-7 cells showed that SmNR1/SmRXR1 could enhance the transcriptional activation of a DR2-dependent reporter gene. Our results demonstrate that SmNR1 is a partner of SmRXR1.

Identification and characterization of a novel fushi tarazu factor 1 (FTZ-F1) nuclear receptor in Schistosoma mansoni

Fushi-tarazu factor-1 (FTZ-F1) is an orphan nuclear receptor involved in gene regulation of various developmental processes and physiological activities. We identified a new member of ftz-f1 gene in Schistosoma mansoni, termed Smftz-f1alpha. The Smftz-f1alpha gene has a complex structure with 15 exons interrupted by 14 introns. It encodes an unusually long SmFTZ-F1alpha protein of 1892 amino acids containing all the modular domains found in nuclear receptors. The DNA-binding domain (DBD) of SmFTZ-F1alpha is conserved and most similar to those of human and mouse FTZ-F1 orthologues, exhibiting a 76% identity. The ligand-binding domain (LBD) is less conserved than the DBD; it shares more diverse identity scores in different regions ranging from 23% to 42% in region II and 28% to 72% in region III. A conserved activation function-2 (AF-2) sequence is present in the SmFTZ-F1alpha LBD. This protein also contains a long hinge region (1027 aa) and an F region (220 aa) at the carboxyl end. Phylogenetic analysis suggests that SmFTZ-F1alpha is the orthologue of Drosophila FTZ-F1alpha and vertebrate NR5 members. Western blot analysis of a schistosome extract identified two proteins, one with a size (206 kDa) predicted by the SmFTZ-F1alpha cDNA sequence and a smaller component of 120 kDa. Smftz-f1alpha is expressed throughout the schistosome life cycle with the highest expression in the egg stage. SmFTZ-F1alpha mRNA is widely distributed in adult worms but does not appear in vitelline cells of female worms. SmFTZ-F1alpha localizes to a variety of tissues but is most abundant in the testis of the male and the ovary of female worms. Our results suggest that SmFTZ-F1alpha plays a role in regulating schistosome development and sexual differentiation similar to other FTZ-F1 family members.

Mapping of the complement C9 binding domain in paramyosin of the blood fluke Schistosoma mansoni

Schistosomes are believed to evade complement-mediated damage by expression of complement inhibitory proteins. Our previous results [Deng, J., Gold, D., LoVerde, P.T., Fishelson, Z., 2003. Inhibition of the complement membrane attack complex by Schistosoma mansoni paramyosin. Infect. Immun. 71, 6402-6410.] have demonstrated that paramyosin (Pmy) of the blood fluke S. mansoni binds to the human complement proteins C8 and C9, inhibits complement activation at the terminal stage and protects the parasite from complement-mediated damage. In order to locate the Pmy binding site to C8 and C9, various fragments of Pmy cDNA were PCR-cloned into a pET28a bacterial expression vector. Recombinant His-tagged Pmy fragments were expressed in BL21 Escherichia coli and purified over a nickel-nitrilotriacetic acid column. Binding assays by Western blotting with monoclonal anti-His antibody demonstrated that PmyCC (Pmy amino acids (744)Asp-(866)Met) was the only Pmy fragment that bound to human C8 and C9. Functional analyses demonstrated that PmyCC inhibited hemolysis of rabbit erythrocytes and of antibody-sensitized sheep erythrocytes by human complement. Importantly, PmyCC inhibited in vitro killing of trypsin-sensitized schistosomula of S. mansoni by human complement. In the presence of PmyCC, Zn(2+)-induced C9 polymerization was inhibited. Most of the immunodominant B-cell antigenic epitopes of Pmy are present in the PmyCC region, as antibodies collected from mice immunized with recombinant Pmy bound primarily to PmyCC. Taken together, this study has mapped the complement regulatory domain in Pmy, capable of binding to C8 and C9 and preventing polyC9 formation, to its C-terminal region.

Socioeconomic determinants of schistosomiasis in a poor rural area in Brazil

The objective of this paper is to identify and quantify socioeconomic determinants of Schistosoma mansoni infection in the rural area of Virgem das Graças in Minas Gerais State of Brazil. A cross-sectional study was carried out to examine the prevalence and intensity of schistosomiasis in relation to socioeconomic characteristics of the households. Log-binomial regression analysis was used to examine the data on both the household and individual levels, analyzing the prevalence ratios for the association of schistosomiasis and socioeconomic variables related to the head of the household. Multiple comparisons through mixed effect modeling were used to examine the relationship between intensity of infection (geometric mean egg counts) and different levels of socioeconomic variables, respectively. In the univariate analysis, place of residence, number of persons per room, and lack of motorized transport were associated with schistosomiasis at the household level and age and unsafe water contact at the individual level. Age, unsafe water contact, number of persons per room, household possessions and lack of education of head of household remained significant predictors of schistosomiasis in the multivariable analysis. Only age was significantly associated with intensity of infection of individuals. It is concluded that widespread poverty, the rural environment, and weak socioeconomic differentiation that result in intense contact with infective water appear to minimize the protective effect of piped water supply and other socioeconomic parameters on schistosomiasis found in other studies. The potential role of socioeconomic development in conjunction with schistosomiasis control is described and areas for further studies are identified.

SmTR2/4, a Schistosoma mansoni homologue of TR2/TR4 orphan nuclear receptor

cDNA clones encoding a Schistosoma mansoni homologue of the TR2/TR4 group of nuclear receptors, SmTR2/4, were identified by screening an adult female worm cDNA library. SmTR2/4 is a 1,943 amino acid protein, the largest member of the TR2/TR4 group of nuclear receptors and also the largest nuclear receptor reported to date. SmTR2/4 retains a typical domain organisation of nuclear receptors exhibiting 69-77% sequence identity in the DNA binding domain and 16-22% sequence identity in the ligand binding domain compared with its orthologues. SmTR2/4 contains a large A/B domain and hinge region. SmTR2/4 also contains a 100 amino acid F domain, which is absent from its orthologues. SmTR2/4 mRNA is expressed in every stage of the S. mansoni life cycle, exhibiting an elevated expression level in cercariae. Western blot analysis identified two forms of SmTR2/4 protein in adult worms. Our in vitro DNA binding assay showed that SmTR2/4 binds to the DR-3 consensus hormone response element, suggesting a functional conservation among the TR2/TR4 group members in terms of DNA binding specificity. A yeast-based transactivation assay demonstrated that the A/B domain, F domain and N-terminal part of the hinge region in SmTR2/4, when tethered to a GAL4 DNA binding domain, exhibited an autonomous transcription activation function.

DNA binding and transactivation properties of the Schistosoma mansoni constitutive androstane receptor homologue

SmCAR (Schistosoma mansoni constitutive androstane receptor) is a schistosome homologue of the CAR/PXR/VDR group of nuclear receptors. The P box sequence in the DNA binding domain (DBD) of SmCAR, which is essential in determining the DNA binding specificity of nuclear receptors, is different from its vertebrate homologues. Previous data demonstrates that SmCAR binds to a hormone response element containing a single half site AGTGCA as a monomer. SmRXR1 and SmRXR2 are two S. mansoni homologues of vertebrate retinoid X receptors (RXRs). RXRs usually heterodimerize with various nuclear receptors. Yeast-two hybrid analyses, in vitro pull-down and co-immunoprecipitation assays demonstrated that SmCAR interacts with SmRXR1 but not SmRXR2. Using chimeras consisting of the DBD of SmCAR and the ligand binding domain (LBD) of mouse (m) CAR, we show that despite a different P box, SmCAR DBD shares DNA binding specificity with mCAR. However, the SmCAR DBD does exhibit some of the DNA binding properties specific to SmCAR. Studies of the chimeras also demonstrated that the SmCAR DBD is able to heterodimerize with the DBD of human RXR, allowing high affinity DNA binding. Based on this study and previous results, we conclude that SmCAR may recognize its cognate hormone response element via two mechanisms: binding to DNA monomerically or heterodimerizing with SmRXR1. We also demonstrate that a transcription activation function-1 (AF-1) is located in the SmCAR A/B domain.

Characterization of the DNA-binding properties and the transactivation activity of Schistosoma mansoni nuclear receptor fushi tarazu-factor 1alpha (SmFTZ-F1alpha)

A FTZ-F1-related orphan nuclear receptor SmFTZ-F1alpha was previously identified from Schistosoma mansoni. The deduced SmFTZ-F1alpha protein contains a highly conserved DNA binding domain (DBD, C domain), a less conserved ligand binding domain (LBD, E domain) and three highly variable regions, the N-terminal A/B domain (108 aa), a large hinge region (D domain, 1027 aa) and an F domain (220 aa). Herein, we characterize the DNA binding properties and the transactivation activity of SmFTZ-F1alpha. In in vitro assays, SmFTZ-F1alpha bound as a monomer to a response element (FF1RE: TCAAGGTCA) recognized by mammalian steroidogenic factor 1 (SF-1), and to related sequences (p14: TTAAGGTCA and SmFF1a-2: CGAAGGTCA) derived from known schistosome gene promoters. Competition assays with p14 oligonucleotides containing a single mutation at each nucleotide position defined the optimum DNA sequence required for SmFTZ-F1alpha binding. The optimal consensus sequence for SmFTZ-F1alpha binding is TN(A/G)AGGTC(A/G) (N: any base). This sequence is similar but not identical to the SF-1 response element (SFRE) consensus sequence [(T/C)CAAGG(T/C)C(A/G)]. By performing yeast one-hybrid assays, the ability of SmFTZ-F1alpha to bind productively to a p14-derived 9-base pair sequence was demonstrated in vivo. The ability of the full-length SmFTZ-F1alpha to transactivate reporter gene expression was shown to be A/B domain-dependent in a yeast system. In addition, the hinge region contained an unexpected activation function (AF) domain, termed AF-3, while no transactivation activity was detected within the E/F domain. This AF-3 region (from aa 982 to aa 1110) revealed a strong autonomous transactivation activity, which was masked when it was present in the full-length SmFTZ-F1alpha. Taken together, our results suggest that SmFTZ-F1alpha possesses the characteristic DNA binding specificity of FTZ-F1 subfamily members and the capacity to transactivate a reporter gene.

Schistosoma mansoni TGF-beta receptor II: role in host ligand-induced regulation of a schistosome target gene

Members of transforming growth factor-beta (TGF-β) superfamily play pivotal roles in development in multicellular organisms. We report the functional characterization of the Schistosoma mansoni type II receptor (SmTβRII). Mining of the S. mansoni expressed sequence tag (EST) database identified an EST clone that shows homology to the kinase domain of type II receptors from different species. The amplified EST sequence was used as a probe to isolate a cDNA clone spanning the entire coding region of a type II serine/threonine kinase receptor. The interaction of SmTβRII with SmTβRI was elucidated and shown to be dependent on TGF-β ligand binding. Furthermore, in the presence of human TGF-β1, SmTβRII was able to activate SmTβRI, which in turn activated SmSmad2 and promoted its interaction with SmSmad4, proving the transfer of the signal from the receptor complex to the Smad proteins. Gynaecophoral canal protein (GCP), whose expression in male worms is limited to the gynaecophoric canal, was identified as a potential TGF-β target gene in schistosomes. Knocking down the expression of SmTβRII using short interfering RNA molecules (siRNA) resulted in a concomitant reduction in the expression of GCP. These data provide evidence for the direct involvement of SmTβRII in mediating TGF-β–induced activation of the TGF-β target gene, SmGCP, within schistosome parasites. The results also provide additional evidence for a role for the TGF-β signaling pathway in male-induced female reproductive development.

Schistosomes are multicellular parasites that infect 200 million people worldwide. Schistosome development in the human host likely involves host molecules that regulate biological processes of the parasite. Members of transforming growth factor-beta (TGF-β) superfamily play pivotal roles in development in multicellular organisms. TGF-β signaling requires ligand binding to a specific surface receptor, TGF-β type II receptor. The authors isolated the schistosome TGF-β type II receptor (SmTβRII), which was found to be biologically active and responded to stimulation by host TGF-β. The gynaecophoric canal is a ventral groove in the male worm in which the female must reside for sexual maturity. Gynaecophoral canal protein (GCP) is a protein whose expression in male worms is limited to the gynaecophoric canal and is implicated in female reproductive maturation. GCP expression was found to be regulated by human TGF-β. Knocking down the expression of SmTβRII resulted in a concomitant reduction in the expression of GCP, providing evidence for the direct involvement of SmTβRII-mediated, host TGF-β–induced regulation of schistosome gene expression. This study implicates the TGF-β signaling pathway in worm pairing, a prerequisite for female egg production. Because the eggs produced by the worm pairs are responsible for pathogenesis, the authors' research identifies potential targets for intervention.