Gene suppression in schistosomes using RNAi

Expression, Characterization and Selective Chemical Inhibition of Essential Schistosoma mansoni Tegumental Acetylcholinesterase (SmTAChE)

Schistosomiasis, a parasitic disease caused by worms of the genus Schistosoma, affects >250 million people worldwide. With no available vaccine, treatment relies solely on one drug-praziquantel-underscoring the urgent need for new therapies. We identified a tegumental, non-neuronal acetylcholinesterase (AChE) from Schistosoma mansoni-SmTAChE-as a promising drug target. RNA interference confirmed its essential role in parasite survival, as gene suppression significantly reduced parasite recovery from infected animals. Here, we produced functionally active recombinant SmTAChE by using a mammalian expression system. Biochemical characterization confirmed its identity as a true acetylcholinesterase, with the highest turnover rate (Kcat = 373 ± 39 s-1) and catalytic efficiency (Kcat/Km = 1.17 × 106 M-1·S-1) for acetylthiocholine. Additionally, rSmTAChE was inhibited by classical AChE-specific inhibitors but not by a butyrylcholinesterase-specific inhibitor. To identify novel SmTAChE inhibitors, we developed a high-throughput chemical screening protocol (Z' factor > 0.9) and screened a 1894-compound validation library. Twelve compounds reproducibly inhibited rSmTAChE by >30% at 7.5 µM, including known AChE inhibitors like physostigmine and new selective inhibitors. Notably, compound #2 preferentially inhibited rSmTAChE (IC50 = 0.74 µM) over human AChE (IC50 = 151 µM), thus providing a foundation for developing parasite-specific therapies targeting SmTAChE and potentially leading to new treatments for schistosomiasis.

Wnt/β-catenin signalling underpins juvenile Fasciola hepatica growth and development

Infection by the liver fluke, Fasciola hepatica, places a substantial burden on the global agri-food industry and poses a significant threat to human health in endemic regions. Widespread resistance to a limited arsenal of chemotherapeutics, including the frontline flukicide triclabendazole (TCBZ), renders F. hepatica control unsustainable and accentuates the need for novel therapeutic target discovery. A key facet of F. hepatica biology is a population of specialised stem cells which drive growth and development - their dysregulation is hypothesised to represent an appealing avenue for control. The exploitation of this system as a therapeutic target is impeded by a lack of understanding of the molecular mechanisms underpinning F. hepatica growth and development. Wnt signalling pathways govern a myriad of stem cell processes during embryogenesis and drive tumorigenesis in adult tissues in animals. Here, we identify five putative Wnt ligands and five Frizzled receptors in liver fluke transcriptomic datasets and find that Wnt/β-catenin signalling is most active in juveniles, the most pathogenic life stage. FISH-mediated transcript localisation revealed partitioning of the five Wnt ligands, with each displaying a distinct expression pattern, consistent with each Wnt regulating the development of different cell/tissue types. The silencing of each individual Wnt or Frizzled gene yielded significant reductions in juvenile worm growth and, in select cases, blunted the proliferation of neoblast-like cells. Notably, silencing FhCTNNB1, the key effector of the Wnt/β-catenin signal cascade led to aberrant development of the neuromuscular system which ultimately proved lethal - the first report of a lethal RNAi-induced phenotype in F. hepatica. The absence of any discernible phenotypes following the silencing of the inhibitory Wnt/β-catenin destruction complex components is consistent with low destruction complex activity in rapidly developing juvenile worms, corroborates transcriptomic expression profiles and underscores the importance of Wnt signalling as a key molecular driver of growth and development in early-stage juvenile fluke. The putative pharmacological inhibition of Wnt/β-catenin signalling using commercially available inhibitors phenocopied RNAi results and provides impetus for drug repurposing. Taken together, these data functionally and chemically validate the targeting of Wnt signalling as a novel strategy to undermine the pathogenicity of juvenile F. hepatica.

CRISPR-based functional genomics for schistosomes and related flatworms

CRISPR genome editing is actively used for schistosomes and other flukes. The ability to genetically manipulate these flatworms enables deeper investigation of their (patho)biological nature. CRISPR gene knockout (KO) demonstrated that a liver fluke growth mediator contributes to disease progression. Genome safe harbor sites have been predicted in Schistosoma mansoni and targeted for transgene insertion. CRISPR-based diagnosis has been demonstrated for infection with schistosomes and Opisthorchis viverrini. This review charts the progress, and the state of play, and posits salient questions for the field to address. Derivation of heritably transgenic loss-of-function or gain-of-function lines is the next milestone.

The riboflavin (vitamin B2) transporter protein (SmaRT) of the human intravascular parasitic trematode Schistosoma mansoni

Schistosomes are intravascular parasitic worms infecting >200 million people globally. Here we examine how the worms acquire an essential nutrient - vitamin B2 (riboflavin). We demonstrate that all intravascular life stages (schistosomula, adult males and females) take up radiolabeled riboflavin. This process is impeded in the presence of excess unlabeled riboflavin and at 4 °C. We have identified a transporter homolog in worms designated SmaRT (Schistosoma mansoni riboflavin transporter) that localizes to the tegument and internal tissues of adults. CHO-S cells transfected with plasmid encoding SmaRT import significantly more radiolabeled riboflavin compared to controls. Uptake of radiolabel is impeded when SmaRT-expressing cells are incubated in an excess of unlabeled riboflavin but not by an excess of an irrelevant metabolite. Uptake is mediated in a sodium-independent manner and over a wide range of pH values (pH 5.5-9). This is the first identification of a bone fide riboflavin transporter in any platyhelminth.

Schistosome Transgenesis: The Long Road to Success

As research on parasitic helminths has entered the post-genomic era, research efforts have turned to deciphering the function of genes in the public databases of genome sequences. It is hoped that, by understanding the role of parasite genes in maintaining their parasitic lifestyle, critical insights can be gained to develop new intervention and control strategies. Methods to manipulate and transform parasitic worms are now developed to a point where it has become possible to gain a comprehensive understanding of the molecular mechanisms underlying host-parasite interplay, and here, we summarise and discuss the advances that have been made in schistosome transgenesis over the past 25 years. The ability to genetically manipulate schistosomes holds promise in finding new ways to control schistosomiasis, which ultimately may lead to the eradication of this debilitating disease.

A novel, non-neuronal acetylcholinesterase of schistosome parasites is essential for definitive host infection

Schistosomes are long-lived parasitic worms that infect >200 million people globally. The intravascular life stages are known to display acetylcholinesterase (AChE) activity internally as well as, somewhat surprisingly, on external tegumental membranes. Originally it was hypothesized that a single gene (SmAChE1 in Schistosoma mansoni) encoded both forms of the enzyme. Here, we demonstrate that a second gene, designated "S. mansoni tegumental acetylcholinesterase, SmTAChE", is responsible for surface, non-neuronal AChE activity. The SmTAChE protein is GPI-anchored and contains all essential amino acids necessary for function. AChE surface activity is significantly diminished following SmTAChE gene suppression using RNAi, but not following SmAChE1 gene suppression. Suppressing SmTAChE significantly impairs the ability of parasites to establish infection in mice, showing that SmTAChE performs an essential function for the worms in vivo. Living S. haematobium and S. japonicum parasites also display strong surface AChE activity, and we have cloned SmTAChE homologs from these two species. This work helps to clarify longstanding confusion regarding schistosome AChEs and paves the way for novel therapeutics for schistosomiasis.

Schistosoma mansoni phosphoglycerate mutase: a glycolytic ectoenzyme with thrombolytic potential

Schistosomiasis is a debilitating parasitic disease caused by intravascular flatworms called schistosomes (blood flukes) that affects >200 million people worldwide. Proteomic analysis has revealed the surprising presence of classical glycolytic enzymes – typically cytosolic proteins – located on the extracellular surface of the parasite tegument (skin). Immunolocalization experiments show that phosphoglycerate mutase (PGM) is widely expressed in parasite tissues and is highly expressed in the tegument. We demonstrate that live Schistosoma mansoni parasites express enzymatically active PGM on their tegumental surface. Suppression of PGM using RNA interference (RNAi) diminishes S. mansoni PGM (SmPGM) gene expression, protein levels, and surface enzyme activity. Sequence comparisons place SmPGM in the cofactor (2,3-bisphosphoglycerate)-dependent PGM (dPGM) family. We have produced recombinant SmPGM (rSmPGM) in an enzymatically active form in Escherichia coli. The Michaelis-Menten constant (K_m) of rSmPGM for its glycolytic substrate (3-phosphoglycerate) is 0.85 mM ± 0.02. rSmPGM activity is inhibited by the dPGM-specific inhibitor vanadate. Here, we show that rSmPGM not only binds to plasminogen but also promotes its conversion to an active form (plasmin) in vitro. This supports the hypothesis that host-interactive tegumental proteins (such as SmPGM), by enhancing plasmin formation, may help degrade blood clots around the worms in the vascular microenvironment and thus promote parasite survival in vivo.

Vaccines for Human Schistosomiasis: Recent Progress, New Developments and Future Prospects

Schistosomiasis, caused by human trematode blood flukes (schistosomes), remains one of the most prevalent and serious of the neglected tropical parasitic diseases. Currently, treatment of schistosomiasis relies solely on a single drug, the anthelmintic praziquantel, and with increased usage in mass drug administration control programs for the disease, the specter of drug resistance developing is a constant threat. Vaccination is recognized as one of the most sustainable options for the control of any pathogen, but despite the discovery and reporting of numerous potentially promising schistosome vaccine antigens, to date, no schistosomiasis vaccine for human or animal deployment is available. This is despite the fact that Science ranked such an intervention as one of the top 10 vaccines that need to be urgently developed to improve public health globally. This review summarizes current progress of schistosomiasis vaccines under clinical development and advocates the urgent need for the establishment of a revolutionary and effective anti-schistosome vaccine pipeline utilizing cutting-edge technologies (including developing mRNA vaccines and exploiting CRISPR-based technologies) to provide novel insight into future vaccine discovery, design, manufacture and deployment.

Characterisation and preliminary functional analysis of N-acetyltransferase 13 from Schistosoma japonicum

Background

N-acetyltransferase 13 (NAT13) is a probable catalytic component of the ARD1A-NARG1 complex possessing alpha (N-terminal) acetyltransferase activity.

Results

In this study, a full-length complementary DNA (cDNA) encoding Schistosoma japonicum NAT13 (SjNAT13) was isolated from schistosome cDNAs. The 621 bp open reading frame of SjNAT13 encodes a polypeptide of 206 amino acids. Real-time PCR analysis revealed SjNAT13 expression in all tested developmental stages. Transcript levels were highest in cercariae and 21-day-old worms, and higher in male adult worms than female adult worms. The rSjNAT13 protein induced high levels of anti-rSjNAT13 IgG antibodies. In two independent immunoprotection trials, rSjNAT13 induced 24.23% and 24.47% reductions in the numbers of eggs in liver. RNA interference (RNAi) results showed that small interfering RNA (siRNA) Sj-514 significantly reduced SjNAT13 transcript levels in worms and decreased egg production in vitro.

Conclusions

Thus, rSjNAT13 might play an important role in the development and reproduction of schistosomes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03045-y.

Vitamin B6 Acquisition and Metabolism in Schistosoma mansoni

Schistosomes are parasitic platyhelminths that currently infect >200 million people globally. The adult worms can live within the vasculature of their hosts for many years where they acquire all nutrients necessary for their survival and growth. In this work we focus on how Schistosoma mansoni parasites acquire and metabolize vitamin B6, whose active form is pyridoxal phosphate (PLP). We show here that live intravascular stage parasites (schistosomula and adult males and females) can cleave exogenous PLP to liberate pyridoxal. Of the three characterized nucleotide-metabolizing ectoenzymes expressed at the schistosome surface (SmAP, SmNPP5, and SmATPDase1), only SmAP hydrolyzes PLP. Heat-inactivated recombinant SmAP can no longer cleave PLP. Further, parasites whose SmAP gene has been suppressed by RNAi are significantly impaired in their ability to cleave PLP compared to controls. When schistosomes are incubated in murine plasma, they alter its metabolomic profile-the levels of both pyridoxal and phosphate increase over time, a finding consistent with the action of host-exposed SmAP acting on PLP. We hypothesize that SmAP-mediated dephosphorylation of PLP generates a pool of pyridoxal around the worms that can be conveniently taken in by the parasites to participate in essential, vitamin B6-driven metabolism. In addition, since host PLP-dependent enzymes play active roles in inflammatory processes, parasite-mediated cleavage of this metabolite may serve to limit parasite-damaging inflammation. In this work we also identified schistosome homologs of enzymes that are involved in intracellular vitamin B6 metabolism. These are pyridoxal kinase (SmPK) as well as pyridoxal phosphate phosphatase (SmPLP-Ph) and pyridox(am)ine 5'-phosphate oxidase (SmPNPO) and cDNAs encoding these three enzymes were cloned and sequenced. The three genes encoding these enzymes all display high relative expression in schistosomula and adult worms suggestive of robust vitamin B6 metabolism in the intravascular life stages.

The essential schistosome tegumental ectoenzyme SmNPP5 can block NAD-induced T cell apoptosis

Infection with intravascular platyhelminths of the genus Schistosoma can result in the debilitating disease schistosomiasis. Schistosomes (blood flukes) can survive in the host for many years. We hypothesize that proteins on their host-interactive surface modify the worm's external environment to help insure worm survival. Previously, we have shown that a surface ectoenzyme of Schistosoma mansoni, SmNPP5 - a nucleotide pyrophosphatase/phosphodiesterase - can cleave ADP and block platelet aggregation in vitro. In this work, we show that both adult schistosomes and recombinant SmNPP5 can cleave the exogenous purinergic signaling molecule nicotinamide adenine dinucleotide (NAD). In doing so, worms and rSmNPP5 can prevent NAD-induced apoptosis of T cells in vitro. Since regulatory T cells (Tregs) are especially prone to such NAD-induced cell death (NICD), we hypothesize that schistosome cleavage of NAD promotes Treg survival which creates a more immunologically hospitable environment for the worms in vivo. In addition to SmNPP5, schistosomes express another host-interactive NAD-degrading enzyme, SmNACE. We successfully suppressed the expression of SmNPP5 and SmNACE (singly or together) using RNAi. Only SmNPP5-suppressed worms, and not SmNACE-suppressed worms, were significantly impaired in their ability to cleave exogenous NAD compared to controls. Therefore, we contend that ectoenzyme SmNPP5 on the surface of the worm is primarily responsible for extracellular NAD cleavage and that this helps modulate the host immune environment by preventing Treg cell death.

Post-genomic progress in helminth parasitology

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

The role of the adaptor molecule STING during Schistosoma mansoni infection

Schistosomiasis is a human parasitic disease responsible for serious consequences for public health, as well as severe socioeconomic impacts in developing countries. Here, we provide evidence that the adaptor molecule STING plays an important role in Schistosoma mansoni infection. S. mansoni DNA is sensed by cGAS leading to STING activation in murine embryonic fibroblasts (MEFs). Sting^-/- and C57BL/6 (WT) mice were infected with schistosome cercariae in order to assess parasite burden and liver pathology. Sting^-/- mice showed worm burden reduction but no change in the number of eggs or granuloma numbers and area when compared to WT animals. Immunologically, a significant increase in IFN-γ production by the spleen cells was observed in Sting^-/- animals. Surprisingly, Sting^-/- mice presented an elevated percentage of neutrophils in lungs, bronchoalveolar lavage, and spleens. Moreover, Sting^-/- neutrophils exhibited increased survival rate, but similar ability to kill schistosomula in vitro when stimulated with IFN-γ when compared to WT cells. Finally, microbiota composition was altered in Sting^-/- mice, revealing a more inflammatory profile when compared to WT animals. In conclusion, this study demonstrates that STING signaling pathway is important for S. mansoni DNA sensing and the lack of this adaptor molecule leads to enhanced resistance to infection.

Schistosoma mansoni glyceraldehyde-3-phosphate dehydrogenase enhances formation of the blood-clot lysis protein plasmin

Schistosomes are intravascular blood flukes that cause the parasitic disease schistosomiasis. In agreement with Schistosoma mansoni (Sm) proteomic analysis, we show here that the normally intracellular glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is also found at the parasite surface; live worms from all intravascular life stages display GAPDH activity. Suppressing GAPDH gene expression using RNA interference significantly lowers this live worm surface activity. Medium in which the worms are cultured overnight displays essentially no activity, showing that the enzyme is not shed or excreted but remains associated with the worm surface. Immunolocalization experiments confirm that the enzyme is highly expressed in the parasite tegument (skin). Surface activity in schistosomula amounts to ∼8% of that displayed by equivalent parasite lysates. To address the functional role of SmGAPDH, we purified the protein following its expression in Escherichiacoli strain DS113. The recombinant protein displays optimal enzymatic activity at pH 9.2, shows robust activity at the temperature of the parasite's hosts, and has a Michaelis-Menten constant for glyceraldehyde-3-phosphate (GAP) of 1.4 mM±0.24. We show that recombinant SmGAPDH binds plasminogen (PLMG) and promotes PLMG conversion to its active form (plasmin) in a dose response in the presence of tissue plasminogen activator. Since plasmin is a key mediator of thrombolysis, our results support the hypothesis that SmGAPDH, a host-interactive tegumental protein that can enhance PLMG activation, could help degrade blood clots around the worms in the vascular microenvironment and thus promote parasite survival in vivoThis article has an associated First Person interview with the first author of the paper.

Gene Silencing in the Liver Fluke Fasciola hepatica: RNA Interference

The chronic infection with the liver fluke of the genus Fasciola spp. is the most prevalent foodborne trematodiasis, affecting at least one-fourth of the world livestock grazing in areas where the parasite is present. Moreover, fascioliasis is considered a major zoonosis mainly in rural areas of central South America, Northern Africa, and Central Asia. Increasing evidences of resistance against triclabendazole may compromise its use as drug of choice; thus, novel control strategies are desperately needed. Functional genomic approaches play a key role in the validation and characterization of new targets for drug and vaccine development. So far, RNA interference has been the only gene silencing approach successfully employed in liver flukes of the genus Fasciola spp. Herein, we describe a detailed step-by-step protocol to perform gene silencing mediated by RNAi in Fasciola hepatica.

Differential gene expression, including Sjfs800, in Schistosoma japonicum females at pre-pairing, initial pairing and oviposition

Background

Schistosomiasis is a prevalent but neglected tropical disease caused by parasitic trematodes of the genus Schistosoma, with the primary disease-causing species being S. haematobium, S. mansoni and S. japonicum. Male–female pairing of schistosomes is necessary for sexual maturity and the production of a large number of eggs, which are primarily responsible for schistosomiasis dissemination and pathology.

Methods

Here, we used microarray hybridization, bioinformatics, quantitative PCR, in situ hybridization and gene silencing assays to identify genes that play critical roles in S. japonicum reproduction biology, particularly in vitellarium development, a process that affects male–female pairing, sexual maturation and subsequent egg production.

Results

Microarray hybridization analyses generated a comprehensive set of genes differentially transcribed before and after male–female pairing. Although the transcript profiles of females were similar 16 and 18 days after host infection, marked gene expression changes were observed at 24 days. The 30 most abundantly transcribed genes on day 24 included those associated with vitellarium development. Among these, the gene for female-specific 800 (fs800) was substantially upregulated. Our in situ hybridization results in female S. japonicum indicated that Sjfs800 mRNA was observed only in the vitellarium, localized in mature vitelline cells. Knocking down the Sjfs800 gene in female S. japonicum by approximately 60% reduced the number of mature vitelline cells, decreased rates of pairing and oviposition, and decreased the number of eggs produced in each male–female pairing by about 50%.

Conclusions

These results indicate that Sjfs800 may play a role in vitellarium development and egg production in S. japonicum and suggest that Sjfs800 regulation may provide a novel approach for the prevention or treatment of schistosomiasis.

Interactive online application for the prediction, ranking and prioritisation of drug targets in Schistosoma haematobium

BACKGROUND

Human schistosomiasis is a neglected tropical disease caused by parasitic worms of the genus Schistosoma that still affects some 200 million people. The mainstay of schistosomiasis control is a single drug, praziquantel. The reliance on this drug carries a risk of resistance emerging to this anthelmintic, such that research towards alternative anti-schistosomal drugs is warranted. In this context, a number of studies have employed computational approaches to prioritise proteins for investigation as drug targets, based on extensive genomic, transcriptomic and small-molecule data now available.

METHODS

Here, we established a customisable, online application for the prioritisation of drug targets and applied it, for the first time, to the entire inferred proteome of S. haematobium. This application enables selection of weighted and ranked proteins representing potential drug targets, and integrates transcriptional data, orthology and gene essentiality information as well as drug-drug target associations and chemical properties of predicted ligands.

RESULTS

Using this application, we defined 25 potential drug targets in S. haematobium that associated with approved drugs, and 3402 targets that (although they could not be linked to any compounds) are conserved among a range of socioeconomically important flatworm species and might represent targets for new trematocides.

CONCLUSIONS

The online application developed here represents an interactive, customisable, expandable and reproducible drug target ranking and prioritisation approach that should be useful for the prediction of drug targets in schistosomes and other species of parasitic worms in the future. We have demonstrated the utility of this online application by predicting potential drug targets in S. haematobium that can now be evaluated using functional genomics tools and/or small molecules, to establish whether they are indeed essential for parasite survival, and to assist in the discovery of novel anti-schistosomal compounds.

RNA Interference as an Approach to Functional Genomics Genetic Manipulation of Opisthorchis viverrini

The availability of genome and transcriptome data of the liver fluke Opisthorchis viverrini provides the foundation for exploration of gene function and its effect on host-parasite interactions and pathogenesis of O. viverrini-associated bile duct cancer. Functional genomics approaches address the function of DNA at levels of the gene, RNA transcript and protein product using informative manipulations of the genome, epigenome, transcriptome, proteome, microbiome and metabolome. Advances in functional genomics for O. viverrini have thus far focused on RNA interference. The flukes have been transfected with double-stranded RNAs aiming to silence target gene expression. In general, this approach for functional genomics investigation of this pathogen has been found to be tractable and efficient: suppression of messenger RNA expression in O. viverrini results in reduction of protein activity and phenotypic changes. Future perspectives for functional genomics of this liver fluke and close phylogenetic relatives are also discussed.

A metalloprotease produced by larval Schistosoma mansoni facilitates infection establishment and maintenance in the snail host by interfering with immune cell function

Metalloproteases (MPs) have demonstrated roles in immune modulation. In some cases, these enzymes are produced by parasites to influence host immune responses such that parasite infection is facilitated. One of the best examples of parasite-mediated immune modulation is the matrix metalloprotease (MMP) leishmanolysin (Gp63), which is produced by species of the genus Leishmania to evade killing by host macrophages. Leishmanolysin-like proteins appear to be quite common in many invertebrates, however our understanding of the functions of these non-leishmania enzymes is limited. Numerous proteomic and transcriptomic screens of schistosomes, at all life cycle stages of the parasite, have identified leishmanolysin-like MPs as being present in abundance; with the highest levels being found during the intramolluscan larval stages and being produced by cercaria. This study aims to functionally characterize a Schistosoma mansoni variant of leishmanolysin that most resembles the enzyme produced by Leishmania, termed SmLeish. We demonstrate that SmLeish is an important component of S. mansoni excretory/secretory (ES) products and is produced by the sporocyst during infection. The presence of SmLeish interferes with the migration of Biomphalaria glabrata haemocytes, and causes them to present a phenotype that is less capable of sporocyst encapsulation. Knockdown of SmLeish in S. mansoni miracidia prior to exposure to susceptible B. glabrata reduces miracidia penetration success, causes a delay in reaching patent infection, and lowers cercaria output from infected snails.

Parasitic flatworms, or digenetic trematodes, cause a wide range of diseases of both medical and agricultural importance. Nearly all species of digenea require specific species of snail for their larval development and transmission. The factors underpinning snail host specificity and how they dictate infection establishment and maintenance are interesting areas of research, both from the perspective of evolutionary immunology and potential application in the design of tools that aim to prevent trematode transmission. Currently, our understanding of snail-trematode associations is one-sided, being predominantly derived from studies that have focused on the snail immune response, with almost nothing known about how the parasite facilitates infection. Metalloproteases, such as leishmanolysin, are proteolytic enzymes; some of which are produced by parasites to influence host immune responses and facilitate parasite success upon encountering the host defense response. Here, we have functionally characterized a leishmanolysin-like metalloprotease (SmLeish) from Schistosoma mansoni, a causative agent of human schistosomiasis, which afflicts over 260 million people globally. We demonstrate that SmLeish is associated with developing sporocysts and is also located in S. mansoni excretory/secretory products and interferes with snail haemocyte morphology and migration. Knockdown of SmLeish in S. mansoni miracidia prior to exposure to Biomphalaria glabrata snails reduces miracidia penetration success, delays attainment of patent infections, and lowers cercaria output from infected snails.

Schistosoma mansoni SmKI-1 or Its C-Terminal Fragment Induces Partial Protection Against S. mansoni Infection in Mice

Current schistosomiasis control strategies are mainly based on chemotherapy, but the development of a vaccine against this parasitic disease would contribute to a long-lasting decrease in disease spectrum and transmission. When it comes to vaccine candidates, several genes encoding Schistosoma mansoni proteins expressed at the mammalian host-parasite interface have been tested. Among the most promising molecules are the proteins present on the tegument and digestive tract of the parasite. In this study, we evaluate the potential of SmKI-1, the first Kunitz-type protease inhibitor functionally characterized in S. mansoni, as a vaccine candidate. Bioinformatic analysis points to the C-terminal fragment as the main region of the molecule responsible for the development of a potential protective immune response induced by SmKI-1. Therefore, for the vaccine formulations, we produced the recombinant (r) SmKI-1 and two different fragments, its Kunitz (KI) domain and its C-terminal tail. First, we demonstrate that mice immunized with recombinant SmKI-1 (rSmKI-1) or its fragments, formulated with Freund's adjuvant, induced the production of IgG-specific antibodies. Further, all vaccine formulations tested here also induced a Th1-type of immune response, as suggested by the production of IFN-γ and TNF-α by protein-stimulated cultured splenocytes. However, the protective effect conferred by vaccination was only observed in groups which received rSmKI-1 or C-terminal domain vaccines. Mice administered with rSmKI-1 demonstrated reduction of 47% in worm burden, 36% in egg number in mouse livers, and 33% in area of liver granulomas. Additionally, mice injected with C-terminal domain showed reduction of 28% in worm burden, 38% in egg number in liver, and 25% in area of liver granulomas. In contrast, KI domain immunization was unable to reduce worm burden and ameliorate liver pathology after challenge infection. Taken together, our data demonstrated that SmKI-1 is a potential candidate for use in a vaccine to control schistosomiasis, and its C-terminal tail seems to be the main region of the molecule responsible for protection conferred by this antigen.

RNA interference in vivo in Schistosoma japonicum: Establishing and optimization of RNAi mediated suppression of gene expression by long dsRNA in the intra-mammalian life stages of worms

Schistosomes are parasitic platyhelminths that threaten over 600 million people globally. In recent years, RNA interference (RNAi) has been widely used as a molecular tool in research into the genomic function of parasites. We aim to develop effective protocols for application of RNAi technology in the intra-mammalian life stages of Schistosoma japonicum. In this work, the expression of the parasite gene encoding cathepsin B1 (SjCB1) was targeted by exposing the worms to 10 μg of long dsRNA dissolved in 0.1 ml of 0.7% NaCl injected into the tail vein of infected mice. This method was effective and specific for eliciting SjCB1 gene suppression in both male and female adult worms in vivo (>79.4% in male and >91.5% in female knockdown relative to control). In 60 cercaria infected mice, RNAi suppression of gene expression was best achieved by using 10 μg of target dsRNA for at least 4 days. The recommended procedure for interference producing long-term suppression was an injection of dsRNA on the first day of infection with booster injections administered every 4 days for up to 26 days. Long-term suppression of three published functional genes (peroxiredoxin-1, mago nashi, insulin receptor) in S. japonicum provided more information about the role of the expression of these genes in producing particular phenotypes. The protocols described here may be more convenient, economical and applicable, than currently available technology and have contributed to the observation of more phenotypes during worm development from schistosomula to adult. These approaches may promote and facilitate further studies into functional schistosome genomics.

Advances in kinome research of parasitic worms - implications for fundamental research and applied biotechnological outcomes

Protein kinases are enzymes that play essential roles in the regulation of many cellular processes. Despite expansions in the fields of genomics, transcriptomics and bioinformatics, there is limited information on the kinase complements (kinomes) of most eukaryotic organisms, including parasitic worms that cause serious diseases of humans and animals. The biological uniqueness of these worms and the draft status of their genomes pose challenges for the identification and classification of protein kinases using established tools. In this article, we provide an account of kinase biology, the roles of kinases in diseases and their importance as drug targets, and drug discovery efforts in key socioeconomically important parasitic worms. In this context, we summarise methods and resources commonly used for the curation, identification, classification and functional annotation of protein kinase sequences from draft genomes; review recent advances made in the characterisation of the worm kinomes; and discuss the implications of these advances for investigating kinase signalling and developing small-molecule inhibitors as new anti-parasitic drugs.

The blood fluke Schistosoma mansoni cleaves the coagulation protein high molecular weight kininogen (HK) but does not generate the vasodilator bradykinin

Background

Schistosomes are blood dwelling parasitic worms that cause the debilitating disease schistosomiasis. Here we examined the influence of the parasites on their external environment by monitoring the impact of adult Schistosoma mansoni worms on the murine plasma proteome in vitro and, in particular, on how the worms affect the blood coagulation protein high molecular weight kininogen (HK).

Methods

Following the incubation of adult schistosomes in murine plasma, two-dimensional differential in-gel electrophoresis (2D-DIGE) was conducted to look for changes in the plasma proteome compared with control plasma. A major change to the blood protein kininogen (HK) was observed, and the interaction of Schistosoma mansoni parasite with this protein alone was then investigated by western blot analysis and activity assays. Finally, the generation of bradykinin from HK was monitored using a bradykinin detection kit.

Results

The most striking change to the plasma proteome concerned HK; while the full-length protein was more abundant in control plasma, carboxyl-terminal truncated forms were more abundant in plasma that contained schistosomes. Incubating parasites in buffer with pure HK followed by Western blot analysis confirmed that human HK is degraded by the worms. The resulting digestion pattern differed from that brought about by kallikrein, a host serine protease that normally acts on HK to release the vasodilator bradykinin. We found that live schistosomes, while digesting HK, do not generate bradykinin nor do they cleave a chromogenic kallikrein substrate. Since the cleavage of HK by the worms is not impeded by the serine protease inhibitor PMSF but is blocked by the cysteine protease inhibitor E64c, we hypothesize that schistosome tegumental cysteine proteases are responsible for HK cleavage.

Conclusions

Since proteomic and biochemical studies have revealed that the schistosome tegument contains two cysteine proteases belonging to the calpain family (SmCalp1 and SmCalp2) we conclude that these are likely responsible for the HK cleavage reported here. Schistosome cleavage of HK should help impede blood clotting and inflammation around the worms in vivo and so promote their ease of movement within the vasculature of their hosts.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2704-0) contains supplementary material, which is available to authorized users.

Schistosoma mansoni SmKI-1 serine protease inhibitor binds to elastase and impairs neutrophil function and inflammation

Protease inhibitors have important function during homeostasis, inflammation and tissue injury. In this study, we described the role of Schistosoma mansoni SmKI-1 serine protease inhibitor in parasite development and as a molecule capable of regulating different models of inflammatory diseases. First, we determine that recombinant (r) SmKI-1 and its Kunitz domain but not the C-terminal region possess inhibitory activity against trypsin and neutrophil elastase (NE). To better understand the molecular basis of NE inhibition by SmKI-1, molecular docking studies were also conducted. Docking results suggest a complete blockage of NE active site by SmKI-1 Kunitz domain. Additionally, rSmKI-1 markedly inhibited the capacity of NE to kill schistosomes. In order to further investigate the role of SmKI-1 in the parasite, we designed specific siRNA to knockdown SmKI-1 in S. mansoni. SmKI-1 gene suppression in larval stage of S. mansoni robustly impact in parasite development in vitro and in vivo. To determine the ability of SmKI-1 to interfere with neutrophil migration and function, we tested SmKI-1 anti-inflammatory potential in different murine models of inflammatory diseases. Treatment with SmKI-1 rescued acetaminophen (APAP)-mediated liver damage, with a significant reduction in both neutrophil recruitment and elastase activity. In the model of gout arthritis, this protein reduced neutrophil accumulation, IL-1β secretion, hypernociception, and overall pathological score. Finally, we demonstrated the ability of SmKI-1 to inhibit early events that trigger neutrophil recruitment in pleural cavities of mice in response to carrageenan. In conclusion, SmKI-1 is a key protein in S. mansoni survival and it has the ability to inhibit neutrophil function as a promising therapeutic molecule against inflammatory diseases.

Schistosoma mansoni is one of the main agents of schistosomiasis, which is the most important human helminthic infection in terms of global morbidity and mortality. Although schistosomiasis represents a major public health problem in endemic countries, evidences show that S. mansoni downregulates inflammatory responses in many diseases. Fortunately, the control of inflammatory responses is extended to pathogen-derived antigens, leading us to study one S. mansoni Kunitz type protease inhibitor (SmKI-1), found in larval and adult phases of the parasite. We demonstrate that SmKI-1 inhibits trypsin and neutrophil elastase (NE). Additionally, live parasites that SmKI-1 gene has been suppressed using siRNA displayed an impaired schistosome development both in vitro and in vivo. Further, we demonstrate that SmKI-1 possesses an anti-inflammatory potential in three different murine models of inflammatory diseases: acetaminophen (APAP)-mediated liver damage, gout arthritis, and pleural inflammation in response to carrageenan. In these inflammatory disease models, we evaluated SmKI-1 effect on neutrophil and our results demonstrate this molecule is able to inhibit neutrophil migration and function, regulating inflammation. Thus, our data suggest that SmKI-1 is a promising therapeutic molecule against inflammatory diseases.

The human blood parasite Schistosoma mansoni expresses extracellular tegumental calpains that cleave the blood clotting protein fibronectin

Schistosomes are intravascular, parasitic flatworms that cause debilitating disease afflicting >200 million people. Proteins expressed at the host-parasite interface likely play key roles in modifying the worm's local environment to ensure parasite survival. Proteomic analysis reveals that two proteases belonging to the calpain family (SmCalp1 and SmCalp2) are expressed in the Schistosoma mansoni tegument. We have cloned both; while highly conserved in domain organization they display just 31% amino acid sequence identity. Both display high relative expression in the parasite's intravascular life forms. Immunolocalization and activity based protein profiling experiments confirm the presence of the enzymes at the host-parasite interface. Living parasites exhibit surface calpain activity that is blocked in the absence of calcium and in the presence of calpain inhibitors (E64c, PD 150606 and calpastatin). While calpains are invariably reported to be exclusively intracellular (except in diseased or injured tissues), our data show that schistosomes display unique, constitutive, functional extracellular calpain activity. Furthermore we show that the worms are capable of cleaving the host blood clotting protein fibronectin and that this activity can be inhibited by E64c. We hypothesize that SmCalp1 and/or SmCalp2 perform this cleavage function to impede blood clot formation around the worms in vivo.

Identification and validation of a Schistosoma japonicum U6 promoter

Background

RNA polymerase III promoters have been widely used to express short hairpin-RNA (shRNA), microRNA (miRNA), and small guide RNA (sgRNA) in gene functional analysis in a variety of organisms including Schistosoma mansoni. However, no endogenous RNA polymerase III promoters have been identified in Schistosoma japonicum. The lack of appropriate promoters in S. japonicum has hindered its gene functional analysis. Identification of functional promoters in S. japonicum is therefore in urgent need.

Results

Via sequence alignment, a 347 bp sequence upstream from the coding region of S. japonicum U6 small nuclear RNA (snRNA) was identified, cloned, and named as S. japonicum U6 (sjU6) promoter. A sgRNA sequence named as sgRNA970 was designed, and its Cas9 nuclease guiding activity was confirmed by in vitro cleavage assay. The sjU6 promoter was ligated with sgRNA970 coding sequence by overlap PCR to generate a sjU6-sgRNA970 expression cassette. The expression cassette was inserted into a lentiviral plasmid to construct the pHBLV-sgRNA970 plasmid. First, we tested the sjU6 promoter activity in HEK293 cells by transfecting HEK293 cells with the pHBLV-sgRNA970 plasmid. RT-PCR amplification of the total RNA from the transfected HEK293 cells confirmed the presence of sgRNA970 transcript and indicated sjU6 promoter was functional to initiate transcription in HEK293 cells. Then we transduced the lentivirus expressing Cas9-ZsGreen fusion protein into 14 dpi schistosomula to test whether lentivirus was capable to induce exogenous gene expression in S. japonicum. Fluorescence microscopy and western blot results confirmed the expression of Cas9-ZsGreen fusion protein in S. japonicum. Therefore, this lentiviral system was adapted to test promoter activity in S. japonicum. Finally, we transduced 14 dpi S. japonicum with lentivirus produced from the pHBLV-sgRNA970 plasmid. RT-PCR amplification of the total RNA from transduced schistosomula confirmed the presence of sgRNA970 transcript and therefore indicated sjU6 promoter was functional to initiate transcription in S. japonicum.

Conclusion

To our knowledge, sjU6 promoter would be the first identified and validated endogenous RNA polymerase III promoter in S. japonicum, which could be used for future CRISPR/Cas9 studies in S. japonicum.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2207-4) contains supplementary material, which is available to authorized users.

A RNAi-based therapeutic proof of concept targets salmonid whirling disease in vivo

Myxobolus cerebralis is a cnidarian-myxozoan parasite that causes salmonid whirling disease. M. cerebralis alternates between two hosts: (1) a vertebrate salmonid and (2) an invertebrate oligochaete, Tubifex tubifex. There is no successful treatment for salmonid whirling disease. MyxSP-1 is a M. cerebralis serine protease implicated in whirling disease pathogenesis. We hypothesized that short-interfering RNA (siRNA)-induced RNA interference (RNAi) can silence MyxSP-1 in the invertebrate host and abrogate the M. cerebralis life cycle. This would preclude whirling disease infection in the salmonid host. To test this hypothesis, we first developed a siRNA delivery protocol in T. tubifex. Second, we determined the effective dose for siRNA treatment of M. cerebralis-infected T. tubifex. M. cerebralis-infected T. tubifex were treated with different concentrations of MyxSP-1 or negative control siRNAs (1μM, 2μM, 5μM or 7μM) at 15°C for 24h, 48h, 72h and 96h, respectively. We monitored MyxSP-1 knockdown using real-time quantitative PCR (qPCR). siRNA treatment with MyxSP-1 siRNA at 2μM concentration for 24h at 15°C showed maximum significant MyxSP-1 knockdown in T. tubifex. Third, we determined the time points in the M. cerebralis life cycle in T. tubifex at which siRNA treatment was most effective. M. cerebralis-infected T. tubifex were treated with MyxSP-1 or negative control siRNAs (2μM concentration for 24h at 15°C) at 24 hours post-infection (24hpi), 48hpi, 72hpi, 96hpi, 1 month post-infection (1mpi), 2mpi and 3mpi, respectively. We observed that siRNA treatment of T. tubifex was most effective at 1mpi, 2mpi and 3mpi. Fourth, we immersed specific-pathogen-free rainbow trout fry in water inhabited by MyxSP-1 siRNA-treated T. tubifex (at 1mpi, 2mpi and 3mpi). The salmonids did not develop whirling disease and showed significant MyxSP-1 knockdown. We also observed long-term RNAi in T. tubifex. Together these results demonstrate a novel RNAi-based therapeutic proof of concept in vivo against salmonid whirling disease.

Schistosoma mansoni Infection of Mice, Rats and Humans Elicits a Strong Antibody Response to a Limited Number of Reduction-Sensitive Epitopes on Five Major Tegumental Membrane Proteins

Schistosomiasis is a major disease of the developing world for which no vaccine has been successfully commercialized. While numerous Schistosoma mansoni worm antigens have been identified that elicit antibody responses during natural infections, little is known as to the identities of the schistosome antigens that are most prominently recognized by antibodies generated through natural infection. Non-reducing western blots probed with serum from schistosome-infected mice, rats and humans on total extracts of larval or adult schistosomes revealed that a small number of antigen bands predominate in all cases. Recognition of each of these major bands was lost when the blots were run under reducing condition. We expressed a rationally selected group of schistosome tegumental membrane antigens in insect host cells, and used the membrane extracts of these cells to unambiguously identify the major antigens recognized by S. mansoni infected mouse, rat and human serum. These results revealed that a limited number of dominant, reduction-sensitive conformational epitopes on five major tegumental surface membrane proteins: SmTsp2, Sm23, Sm29, SmLy6B and SmLy6F, are primary targets of mouse, rat and human S. mansoni infection sera antibodies. We conclude that, Schistosoma mansoni infection of both permissive (mouse) and non-permissive (rat) rodent models, as well as humans, elicit a dominant antibody response recognizing a limited number of conformational epitopes on the same five tegumental membrane proteins. Thus it appears that neither infecting schistosomula nor mature adult schistosomes are substantively impacted by the robust circulating anti-tegumental antibody response they elicit to these antigens. Importantly, our data suggest a need to re-evaluate host immune responses to many schistosome antigens and has important implications regarding schistosome immune evasion mechanisms and schistosomiasis vaccine development.

Schistosomiasis is caused by blood flukes residing in the veins of infected individuals and afflicts millions of people in the developing world. The schistosome worms can remain healthy in the bloodstream for more than 10 years, implying an extraordinary ability to evade host immune damage. Scientists are seeking to understand immune evasion so as to find weaknesses in defenses that can be exploited in the development of effective vaccines. Here we investigate the normal antibody response to schistosomes during infection of mice, rats and humans, and show for the first time that this response is highly skewed to the recognition of a small number of proteins present at the worm surface. Surprisingly, these abundant antibodies recognize their targets only when the proteins retain their native conformations, stabilized by the presence of intramolecular disulfide bridges. Because of this conformational-dependence, these antibodies have remained undetected in prior studies in which antibody binding assays were routinely performed in a reducing environment that destroys disulfide bridges. The routine presence of these antibodies within the serum of schistosome infected patients and animals raises new and interesting questions as to their possible role in immune evasion, and has significant implications for schistosomiasis vaccine development.

Hsp70 May Be a Molecular Regulator of Schistosome Host Invasion

Schistosomiasis is a debilitating disease that affects over 240 million people worldwide and is considered the most important neglected tropical disease following malaria. Free-swimming freshwater cercariae, one of the six morphologically distinct schistosome life stages, infect humans by directly penetrating through the skin. Cercariae identify and seek the host by sensing chemicals released from human skin. When they reach the host, they burrow into the skin with the help of proteases and other contents released from their acetabular glands and transform into schistosomula, the subsequent larval worm stage upon skin infection. Relative to host invasion, studies have primarily focused on the nature of the acetabular gland secretions, immune response of the host upon exposure to cercariae, and cercaria-schistosomulum transformation methods. However, the molecular signaling pathways involved from host-seeking through the decision to penetrate skin are not well understood. We recently observed that heat shock factor 1 (Hsf1) is localized to the acetabular glands of infectious schistosome cercariae, prompting us to investigate a potential role for heat shock proteins (HSPs) in cercarial invasion. In this study, we report that cercarial invasion behavior, similar to the behavior of cercariae exposed to human skin lipid, is regulated through an Hsp70-dependent process, which we show by using chemical agents that target Hsp70. The observation that biologically active protein activity modulators can elicit a direct and clear behavioral change in parasitic schistosome larvae is itself interesting and has not been previously observed. This finding suggests a novel role for Hsp70 to act as a switch in the cercaria-schistosomulum transformation, and it allows us to begin elucidating the pathways associated with cercarial host invasion. In addition, because the Hsp70 protein and its structure/function is highly conserved, the model that Hsp70 acts as a behavior transitional switch could be relevant to other parasites that also undergo an invasion process and can apply more broadly to other organisms during morphological transitions. Finally, it points to a new function for HSPs in parasite/host interactions.

Parasitic schistosome worms cause morbid disease in over 240 million individuals worldwide. Acute infections with these worms can lead to Katayama fever, while chronic infections can lead to portal hypertension, enlarged abdomen, and liver damage. The infective larval stage, called cercariae, are free-swimming and can detect, seek, and penetrate human skin to enter the human host circulatory system, eventually developing into egg-laying adult worms that cause schistosomiasis. Molecular pathways associated with the initial cercarial invasion of the host, however, are largely unknown, especially with respect to the parasite-specific signals involved in host detection and subsequent decision to invade. Here, we describe a role for Hsp70 in cercarial invasion behavior. To date, only generic stimulation with skin lipid, linoleic acid or L-arginine are known to induce cercarial invasion behavior; thus, we can begin an initial investigation of molecular requirements for host invasion and environment transition for schistosomes and possibly other parasitic organisms.

Schistosomes Enhance Plasminogen Activation: The Role of Tegumental Enolase

Schistosoma mansoni is a blood fluke parasite that causes schistosomiasis, a debilitating disease of global public health importance. These relatively large parasites are able to survive prolonged periods in the human vasculature without inducing stable blood clots around them. We show here that the intravascular life stages (schistosomula and adult males and females) can all promote significant plasminogen (PLMG) activation in the presence of tissue plasminogen activator (tPA). This results in the generation of the potent fibrinolytic agent plasmin which could degrade blood clots forming around the worms in vivo. We demonstrate that S. mansoni enolase (SmEno) is a host-interactive tegumental enzyme that, in recombinant form, can bind PLMG and promote its activation. Like classical members of the enolase protein family, SmEno can catalyze the interconversion of 2-phospho-D-glycerate (2-PGA) and phosphoenolpyruvate (PEP). The enzyme has maximal activity at pH 7.5, requires Mg²⁺ for optimal activity and can be inhibited by NaF but not mefloquin. Suppressing expression of the SmEno gene significantly diminishes enolase mRNA levels, protein levels and surface enzyme activity but, surprisingly, does not affect the ability of the worms to promote PLMG activation. Thus, while SmEno can enhance PLMG activation, our analysis suggests that it is not the only contributor to the parasite’s ability to perform this function. We show that the worms possess several other PLMG-binding proteins in addition to SmEno and these may have a greater importance in schistosome-driven PLMG activation.

Schistosomiasis affects more than 200 million people worldwide and causes up to 280,000 deaths per year. In terms of global mortality and morbidity, this disease is the most important human helminth infection. Schistosoma mansoni parasites can live for years within human blood vessels and seem to be refractory to intravascular thrombus formation. We hypothesize that the parasites are able to promote fibrinolysis in order to avoid firm clot formation around them. In this work, we characterize S. mansoni enolase (SmEno), an enzyme that is found both inside and at the surface of the intravascular worms, and we evaluate its involvement in plasminogen (PLMG) activation. We demonstrate that SmEno is highly expressed in schistosomula, the larval intravascular stages of S. mansoni, as well as adult worms and eggs. We confirm the localization of SmEno within the parasites and at the host/parasite interface. We demonstrate that tegumental SmEno is enzymatically functional and it is able to bind to and enhance the activation of human PLMG. Live parasites whose SmEno gene has been suppressed using RNAi display lower surface enolase activity, but their ability to activate PLMG is unchanged compared to control parasites. Thus, our data show that SmEno can contribute to PLMG activation, although it is not the only schistosome molecule responsible for this activity.

Functional conservation of an ancestral Pellino protein in helminth species

The immune system of H. sapiens has innate signaling pathways that arose in ancestral species. This is exemplified by the discovery of the Toll-like receptor (TLR) pathway using free-living model organisms such as Drosophila melanogaster. The TLR pathway is ubiquitous and controls sensitivity to pathogen-associated molecular patterns (PAMPs) in eukaryotes. There is, however, a marked absence of this pathway from the plathyhelminthes, with the exception of the Pellino protein family, which is present in a number of species from this phylum. Helminth Pellino proteins are conserved having high similarity, both at the sequence and predicted structural protein level, with that of human Pellino proteins. Pellino from a model helminth, Schistosoma mansoni Pellino (SmPellino), was shown to bind and poly-ubiquitinate human IRAK-1, displaying E3 ligase activity consistent with its human counterparts. When transfected into human cells SmPellino is functional, interacting with signaling proteins and modulating mammalian signaling pathways. Strict conservation of a protein family in species lacking its niche signalling pathway is rare and provides a platform to examine the ancestral functions of Pellino proteins that may translate into novel mechanisms of immune regulation in humans.