Involvement of the cytokine MIF in the snail host immune response to the parasite Schistosoma mansoni

p63 gene structure in the phylum mollusca

Roles of p53 family ancestor (p63) in the organisms' response to stressful environmental conditions (mainly pollution) have been studied among molluscs, especially in the genus Mytilus, within the last 15 years. Nevertheless, information about gene structure of this regulatory gene in molluscs is scarce. Here we report the first complete genomic structure of the p53 family orthologue in the mollusc Mediterranean mussel Mytilus galloprovincialis and confirm its similarity to vertebrate p63 gene. Our searches within the available molluscan genomes (Aplysia californica, Lottia gigantea, Crassostrea gigas and Biomphalaria glabrata), found only one p53 family member present in a single copy per haploid genome. Comparative analysis of those orthologues, additionally confirmed the conserved p63 gene structure. Conserved p63 gene structure can be a helpful tool to complement or/and revise gene annotations of any future p63 genomic sequence records in molluscs, but also in other animal phyla. Knowledge of the correct gene structure will enable better prediction of possible protein isoforms and their functions. Our analyses also pointed out possible mis-annotations of the p63 gene in sequenced molluscan genomes and stressed the value of manual inspection (based on alignments of cDNA and protein onto the genome sequence) for a reliable and complete gene annotation.

Hyperdiverse gene cluster in snail host conveys resistance to human schistosome parasites

Schistosomiasis, a neglected global pandemic, may be curtailed by blocking transmission of the parasite via its intermediate hosts, aquatic snails. Elucidating the genetic basis of snail-schistosome interaction is a key to this strategy. Here we map a natural parasite-resistance polymorphism from a Caribbean population of the snail Biomphalaria glabrata. In independent experimental evolution lines, RAD genotyping shows that the same genomic region responds to selection for resistance to the parasite Schistosoma mansoni. A dominant allele in this region conveys an 8-fold decrease in the odds of infection. Fine-mapping and RNA-Seq characterization reveal a <1Mb region, the Guadeloupe Resistance Complex (GRC), with 15 coding genes. Seven genes are single-pass transmembrane proteins with putative immunological roles, most of which show strikingly high nonsynonymous divergence (5-10%) among alleles. High linkage disequilibrium among three intermediate-frequency (>25%) haplotypes across the GRC, a significantly non-neutral pattern, suggests that balancing selection maintains diversity at the GRC. Thus, the GRC resembles immune gene complexes seen in other taxa and is likely involved in parasite recognition. The GRC is a potential target for controlling transmission of schistosomiasis, including via genetic manipulation of snails.

Schistosomes are water-borne blood-flukes that are transmitted by snail vectors. They infect over 200 million people in more than 70 countries and cause severe and chronic disability. Snails naturally vary in resistance to this parasite even within species, so bolstering snail resistance in the wild would block transmission. We artificially selected snails for resistance and observed a rapid evolutionary response, with the greatest change occurring in the same genomic region in two independent trials. We subsequently confirmed that the selected haplotype conveys resistance to infection by schistosomes. The extraordinarily high sequence divergence among haplotypes in this region appears to be elevated due to ongoing natural selection, likely via host-parasite co-evolution. We observed the highest variation in genes encoding putative parasite recognition proteins, suggesting that these control the resistance phenotype in a manner reminiscent of immune gene complexes in other taxa. Thus, this gene cluster presents a potential new target to interfere with parasite transmission at the vector stage.

Digenean-gastropod host associations inform on aspects of specific immunity in snails

Gastropod immunology is informed importantly by the study of the frequent encounters snails endure with digeneans (digenetic trematodes). One of the hallmarks of gastropod-digenean associations is their specificity: any particular digenean parasite species is transmitted by a limited subset of snail taxa. We discuss the nature of this specificity, including its immunological basis. We then review studies of the model gastropod Biomphalaria glabrata indicating that the baseline responses of snails to digeneans can be elevated in a specific manner. Studies incorporating molecular and functional approaches are then highlighted, and are further suggestive of the capacity for specific gastropod immune responses. These studies have led to the compatibility polymorphism hypothesis: the interactions between diversified fibrinogen-related proteins (FREPs) and diverse carbohydrate-decorated polymorphic parasite antigens determine recognition and trigger specific immunity. Complex glycan structures are also likely to play a role in the host specificity typifying snail-digenean interactions. We conclude by noting the dynamic and consequential interactions between snails and digeneans can be considered as drivers of diversification of digenean parasites and in the development and maintenance of specific immunity in gastropods.

Evolution of Innate Immunity: Clues from Invertebrates via Fish to Mammals

Host responses against invading pathogens are basic physiological reactions of all living organisms. Since the appearance of the first eukaryotic cells, a series of defense mechanisms have evolved in order to secure cellular integrity, homeostasis, and survival of the host. Invertebrates, ranging from protozoans to metazoans, possess cellular receptors, which bind to foreign elements and differentiate self from non-self. This ability is in multicellular animals associated with presence of phagocytes, bearing different names (amebocytes, hemocytes, coelomocytes) in various groups including animal sponges, worms, cnidarians, mollusks, crustaceans, chelicerates, insects, and echinoderms (sea stars and urchins). Basically, these cells have a macrophage-like appearance and function and the repair and/or fight functions associated with these cells are prominent even at the earliest evolutionary stage. The cells possess pathogen recognition receptors recognizing pathogen-associated molecular patterns, which are well-conserved molecular structures expressed by various pathogens (virus, bacteria, fungi, protozoans, helminths). Scavenger receptors, Toll-like receptors, and Nod-like receptors (NLRs) are prominent representatives within this group of host receptors. Following receptor-ligand binding, signal transduction initiates a complex cascade of cellular reactions, which lead to production of one or more of a wide array of effector molecules. Cytokines take part in this orchestration of responses even in lower invertebrates, which eventually may result in elimination or inactivation of the intruder. Important innate effector molecules are oxygen and nitrogen species, antimicrobial peptides, lectins, fibrinogen-related peptides, leucine rich repeats (LRRs), pentraxins, and complement-related proteins. Echinoderms represent the most developed invertebrates and the bridge leading to the primitive chordates, cephalochordates, and urochordates, in which many autologous genes and functions from their ancestors can be found. They exhibit numerous variants of innate recognition and effector molecules, which allow fast and innate responses toward diverse pathogens despite lack of adaptive responses. The primitive vertebrates (agnathans also termed jawless fish) were the first to supplement innate responses with adaptive elements. Thus hagfish and lampreys use LRRs as variable lymphocyte receptors, whereas higher vertebrates [cartilaginous and bony fishes (jawed fish), amphibians, reptiles, birds, and mammals] developed the major histocompatibility complex, T-cell receptors, and B-cell receptors (immunoglobulins) as additional adaptive weaponry to assist innate responses. Extensive cytokine networks are recognized in fish, but related signal molecules can be traced among invertebrates. The high specificity, antibody maturation, immunological memory, and secondary responses of adaptive immunity were so successful that it allowed higher vertebrates to reduce the number of variants of the innate molecules originating from both invertebrates and lower vertebrates. Nonetheless, vertebrates combine the two arms in an intricate inter-dependent network. Organisms at all developmental stages have, in order to survive, applied available genes and functions of which some may have been lost or may have changed function through evolution. The molecular mechanisms involved in evolution of immune molecules, might apart from simple base substitutions be as diverse as gene duplication, deletions, alternative splicing, gene recombination, domain shuffling, retrotransposition, and gene conversion. Further, variable regulation of gene expression may have played a role.

Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions

BACKGROUND

The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions.

RESULTS

In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria.

CONCLUSIONS

This work provides evidence that while aphid's antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions.

Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions

Background

The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions.

Results

In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria.

Conclusions

This work provides evidence that while aphid’s antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-762) contains supplementary material, which is available to authorized users.

Resistance of Biomphalaria glabrata 13-16-R1 snails to Schistosoma mansoni PR1 is a function of haemocyte abundance and constitutive levels of specific transcripts in haemocytes

Continuing transmission of human intestinal schistosomiasis depends on the parasite's access to susceptible snail intermediate hosts (often Biomphalaria glabrata). Transmission fails when parasite larvae enter resistant individuals in wild snail populations. The genetic basis for differences in snail susceptibility/resistance is being intensively investigated as a means to devise novel control strategies based on resistance genes. Reactive oxygen species produced by the snail's defence cells (haemocytes) are effectors of resistance. We hypothesised that genes relevant to production and consumption of reactive oxygen species would be expressed differentially in the haemocytes of snail hosts with different susceptibility/resistance phenotypes. By restricting the genetic diversity of snails, we sought to facilitate identification of resistance genes. By inbreeding, we procured from a 13-16-R1 snail population with both susceptible and resistant individuals 52 lines of B. glabrata (expected homozygosity ~87.5%), and determined the phenotype of each in regard to susceptibility/resistance to Schistosoma mansoni. The inbred lines were found to have line-specific differences in numbers of spreading haemocytes; these were enumerated in both juvenile and adult snails. Lines with high cell numbers were invariably resistant to S. mansoni, whereas lines with lower cell numbers could be resistant or susceptible. Transcript levels in haemocytes were quantified for 18 potentially defence-related genes. Among snails with low cell numbers, the different susceptibility/resistance phenotypes correlated with differences in transcript levels for two redox-relevant genes: an inferred phagocyte oxidase component and a peroxiredoxin. Allograft inflammatory factor (potentially a regulator of leucocyte activation) was expressed at higher levels in resistant snails regardless of spread cell number. Having abundant spreading haemocytes is inferred to enable a snail to kill parasite sporocysts. In contrast, snails with fewer spreading haemocytes seem to achieve resistance only if specific genes are expressed constitutively at levels that are high for the species.

RNA-Seq reveals infection-induced gene expression changes in the snail intermediate host of the carcinogenic liver fluke, Opisthorchis viverrini

Background

Bithynia siamensis goniomphalos is the snail intermediate host of the liver fluke, Opisthorchis viverrini, the leading cause of cholangiocarcinoma (CCA) in the Greater Mekong sub-region of Thailand. Despite the severe public health impact of Opisthorchis-induced CCA, knowledge of the molecular interactions occurring between the parasite and its snail intermediate host is scant. The examination of differences in gene expression profiling between uninfected and O. viverrini-infected B. siamensis goniomphalos could provide clues on fundamental pathways involved in the regulation of snail-parasite interplay.

Methodology/Principal Findings

Using high-throughput (Illumina) sequencing and extensive bioinformatic analyses, we characterized the transcriptomes of uninfected and O. viverrini-infected B. siamensis goniomphalos. Comparative analyses of gene expression profiling allowed the identification of 7,655 differentially expressed genes (DEGs), associated to 43 distinct biological pathways, including pathways associated with immune defense mechanisms against parasites. Amongst the DEGs with immune functions, transcripts encoding distinct proteases displayed the highest down-regulation in Bithynia specimens infected by O. viverrini; conversely, transcription of genes encoding heat-shock proteins and actins was significantly up-regulated in parasite-infected snails when compared to the uninfected counterparts.

Conclusions/Significance

The present study lays the foundation for functional studies of genes and gene products potentially involved in immune-molecular mechanisms implicated in the ability of the parasite to successfully colonize its snail intermediate host. The annotated dataset provided herein represents a ready-to-use molecular resource for the discovery of molecular pathways underlying susceptibility and resistance mechanisms of B. siamensis goniomphalos to O. viverrini and for comparative analyses with pulmonate snail intermediate hosts of other platyhelminths including schistosomes.

Despite recent significant advances in knowledge of the fundamental biology of the carcinogenic liver fluke Opisthorchis viverrini, little is known of the complement of molecular interactions occurring between this parasite and its prosobranch snail intermediate host, Bithynia siamensis goniomphalos. The determination of such interactions is a key, necessary component of the development of future integrated control strategies for liver fluke infection and associated bile duct cancer. Here, we use cutting-edge high-throughput sequencing technologies and advanced bioinformatic analyses to characterize, for the first time, qualitative and quantitative differences in gene expression between uninfected and O. viverrini-infected B. siamensis goniomphalos collected from an endemic region of Northeast Thailand. The analyses led to the identification of a number of molecules putatively involved in immune defense pathways against invading O. viverrini, and of key biological mechanisms potentially implicated in the ability of the parasite to successfully colonize its snail intermediate host. We believe that this ready-to-use molecular resource will provide the scientific community with new tools for the development of strategies to control the spread of liver fluke infection and the resulting bile duct cancer.

Parental transfer of the antimicrobial protein LBP/BPI protects Biomphalaria glabrata eggs against oomycete infections

Vertebrate females transfer antibodies via the placenta, colostrum and milk or via the egg yolk to protect their immunologically immature offspring against pathogens. This evolutionarily important transfer of immunity is poorly documented in invertebrates and basic questions remain regarding the nature and extent of parental protection of offspring. In this study, we show that a lipopolysaccharide binding protein/bactericidal permeability increasing protein family member from the invertebrate Biomphalaria glabrata (BgLBP/BPI1) is massively loaded into the eggs of this freshwater snail. Native and recombinant proteins displayed conserved LPS-binding, antibacterial and membrane permeabilizing activities. A broad screening of various pathogens revealed a previously unknown biocidal activity of the protein against pathogenic water molds (oomycetes), which is conserved in human BPI. RNAi-dependent silencing of LBP/BPI in the parent snails resulted in a significant reduction of reproductive success and extensive death of eggs through oomycete infections. This work provides the first functional evidence that a LBP/BPI is involved in the parental immune protection of invertebrate offspring and reveals a novel and conserved biocidal activity for LBP/BPI family members.

Vertebrate immune systems not only protect adult organisms against infections but also increase survival of offspring through parental transfer of innate and adaptive immune factors via the placenta, colostrum and milk or via the egg yolk. This maternal transfer of immunity is critical for species survival as embryos and neonates are immunologically immature and unable to fight off infections at early life stages. Parental immune protection is poorly documented in invertebrates and how the estimated 1.3 million of invertebrate species protect their eggs against pathogens remains an intriguing question. Here, we show that a fresh-water snail, Biomphalaria glabrata massively loads its eggs with a lipopolysaccharide binding protein/bactericidal permeability increasing protein (LBP/BPI) displaying expected antibacterial activities. Remarkably, this snail LBP/BPI also displayed a strong biocidal activity against water molds (oomycetes). This yet unsuspected activity is conserved in human BPI. Gene expression knock-down resulted in the reduction of snail reproductive success and massive death of eggs after water mold infections. This work reveals a novel and conserved biocidal activity for LBP/BPI family members and demonstrates that the snail LBP/BPI represents a major fitness-related protein transferred from parents to their clutches and protecting them from widespread and lethal oomycete infections.

Molluscan cells in culture: primary cell cultures and cell lines

In vitro cell culture systems from molluscs have significantly contributed to our basic understanding of complex physiological processes occurring within or between tissue-specific cells, yielding information unattainable using intact animal models. In vitro cultures of neuronal cells from gastropods show how simplified cell models can inform our understanding of complex networks in intact organisms. Primary cell cultures from marine and freshwater bivalve and gastropod species are used as biomonitors for environmental contaminants, as models for gene transfer technologies, and for studies of innate immunity and neoplastic disease. Despite efforts to isolate proliferative cell lines from molluscs, the snail Biomphalaria glabrata Say, 1818 embryonic (Bge) cell line is the only existing cell line originating from any molluscan species. Taking an organ systems approach, this review summarizes efforts to establish molluscan cell cultures and describes the varied applications of primary cell cultures in research. Because of the unique status of the Bge cell line, an account is presented of the establishment of this cell line, and of how these cells have contributed to our understanding of snail host-parasite interactions. Finally, we detail the difficulties commonly encountered in efforts to establish cell lines from molluscs and discuss how these difficulties might be overcome.

Molluscan cells in culture: primary cell cultures and cell lines

In vitro cell culture systems from molluscs have significantly contributed to our basic understanding of complex physiological processes occurring within or between tissue-specific cells, yielding information unattainable using intact animal models. In vitro cultures of neuronal cells from gastropods show how simplified cell models can inform our understanding of complex networks in intact organisms. Primary cell cultures from marine and freshwater bivalve and gastropod species are used as biomonitors for environmental contaminants, as models for gene transfer technologies, and for studies of innate immunity and neoplastic disease. Despite efforts to isolate proliferative cell lines from molluscs, the snail Biomphalaria glabrata Say, 1818 embryonic (Bge) cell line is the only existing cell line originating from any molluscan species. Taking an organ systems approach, this review summarizes efforts to establish molluscan cell cultures and describes the varied applications of primary cell cultures in research. Because of the unique status of the Bge cell line, an account is presented of the establishment of this cell line, and of how these cells have contributed to our understanding of snail host-parasite interactions. Finally, we detail the difficulties commonly encountered in efforts to establish cell lines from molluscs and discuss how these difficulties might be overcome.

Biomphalysin, a new β pore-forming toxin involved in Biomphalaria glabrata immune defense against Schistosoma mansoni

Aerolysins are virulence factors belonging to the β pore-forming toxin (β-PFT) superfamily that are abundantly distributed in bacteria. More rarely, β-PFTs have been described in eukaryotic organisms. Recently, we identified a putative cytolytic protein in the snail, Biomphalaria glabrata, whose primary structural features suggest that it could belong to this β-PFT superfamily. In the present paper, we report the molecular cloning and functional characterization of this protein, which we call Biomphalysin, and demonstrate that it is indeed a new eukaryotic β-PFT. We show that, despite weak sequence similarities with aerolysins, Biomphalysin shares a common architecture with proteins belonging to this superfamily. A phylogenetic approach revealed that the gene encoding Biomphalysin could have resulted from horizontal transfer. Its expression is restricted to immune-competent cells and is not induced by parasite challenge. Recombinant Biomphalysin showed hemolytic activity that was greatly enhanced by the plasma compartment of B. glabrata. We further demonstrated that Biomphalysin with plasma is highly toxic toward Schistosoma mansoni sporocysts. Using in vitro binding assays in conjunction with Western blot and immunocytochemistry analyses, we also showed that Biomphalysin binds to parasite membranes. Finally, we showed that, in contrast to what has been reported for most other members of the family, lytic activity of Biomphalysin is not dependent on proteolytic processing. These results provide the first functional description of a mollusk immune effector protein involved in killing S. mansoni.

Schistosomiasis is the second most widespread tropical parasitic disease after malaria. It is caused by flatworms of the genus Schistosoma. Its life cycle is complex and requires certain freshwater snail species as intermediate host. Given the limited options for treating S. mansoni infections, much research has focused on a better understanding of the immunobiological interactions between the invertebrate host Biomphalaria glabrata and its parasite S. mansoni. A number of studies published over the last two decades have contributed greatly to our understanding of B. glabrata innate immune mechanisms involved in the defense against parasite. However, most studies have focused on the identification of recognition molecules or immune receptors involved in the host/parasite interplay. In the present study, we report the first functional description of a mollusk immune effector protein involved in killing S. mansoni, a protein related to the β pore forming toxin that we named Biomphalysin.

Evidence for specific genotype-dependent immune priming in the lophotrochozoan Biomphalaria glabrata snail

Historically, the prevailing view in the field of invertebrate immunity was that invertebrates that do not possess acquired adaptive immunity rely on innate mechanisms with low specificity and no memory. Several recent studies have shaken this paradigm and suggested that the immune defenses of invertebrates are more complex and specific than previously thought. Mounting evidence has shown that at least some invertebrates (mainly Ecdysozoa) show high levels of specificity in their immune responses to different pathogens, and that subsequent reexposure may result in enhanced protection (recently called 'immune priming'). Here, we investigated immune priming in the Lophotrochozoan snail species Biomphalaria glabrata, following infection by the trematode pathogen Schistosoma mansoni. We confirmed that snails were protected against a secondary homologous infection whatever the host strain. We then investigated how immune priming occurs and the level of specificity of B. glabrata immune priming. In this report we confirmed that immune priming exists and we identified a genotype-dependent immune priming in the fresh-water snail B. glabrata.

Compatibility polymorphism in snail/schistosome interactions: From field to theory to molecular mechanisms

Coevolutionary dynamics in host-parasite interactions potentially lead to an arms race that results in compatibility polymorphism. The mechanisms underlying compatibility have remained largely unknown in the interactions between the snail Biomphalaria glabrata and Schistosoma mansoni, one of the agents of human schistosomiasis. This review presents a combination of data obtained from field and laboratory studies arguing in favor of a matching phenotype model to explain compatibility polymorphism. Investigations focused on the molecular determinants of compatibility have revealed two repertoires of polymorphic and/or diversified molecules that have been shown to interact: the parasite antigens S. mansoni polymorphic mucins and the B. glabrata fibrinogen-related proteins immune receptors. We hypothesize their interactions define the compatible/incompatible status of a specific snail/schistosome combination. This line of thought suggests concrete approaches amenable to testing in field-oriented studies attempting to control schistosomiasis by disrupting schistosome-snail compatibility.

Reversing the resistance phenotype of the Biomphalaria glabrata snail host Schistosoma mansoni infection by temperature modulation

Biomphalaria glabrata snails that display either resistant or susceptible phenotypes to the parasitic trematode, Schistosoma mansoni provide an invaluable resource towards elucidating the molecular basis of the snail-host/schistosome relationship. Previously, we showed that induction of stress genes either after heat-shock or parasite infection was a major feature distinguishing juvenile susceptible snails from their resistant counterparts. In order to examine this apparent association between heat stress and snail susceptibility, we investigated the effect of temperature modulation in the resistant snail stock, BS-90. Here, we show that, incubated for up to 4 hrs at 32°C prior to infection, these resistant snails became susceptible to infection, i.e. shedding cercariae at 5 weeks post exposure (PE) while unstressed resistant snails, as expected, remained resistant. This suggests that susceptibility to infection by this resistant snail phenotype is temperature-sensitive (ts). Additionally, resistant snails treated with the Hsp 90 specific inhibitor, geldanamycin (GA) after heat stress, were no longer susceptible to infection, retaining their resistant phenotype. Consistently, susceptible snail phenotypes treated with 100 mM GA before parasite exposure also remained uninfected. These results provide direct evidence for the induction of stress genes (heat shock proteins; Hsp 70, Hsp 90 and the reverse transcriptase [RT] domain of the nimbus non-LTR retrotransposon) in B. glabrata susceptibility to S. mansoni infection and characterize the resistant BS-90 snails as a temperature-sensitive phenotype. This study of reversing snail susceptibility phenotypes to S. mansoni provides an opportunity to directly track molecular pathway(s) that underlie the B. glabrata snail's ability to either sustain or destroy the S. mansoni parasite.

Biomphalaria glabrata snails that are either resistant or susceptible to the parasite, Schistosoma mansoni, have been an invaluable resource in studies aimed at understanding the molecular basis of the snail/schistosome interaction. Schistosomes cause the chronic debilitating disease schistosomiasis. Thus, it is hoped that dissecting pathways that underlie the snail/schistosome relationship might translate into alternative control strategies that will include blocking transmission of the parasite at the snail-stage of its development. Induction of stress genes is a feature distinguishing early exposed juvenile susceptible NMRI snails from resistant BS-90 snail stocks. To further analyze this apparent involvement of stress induction and snail susceptibility, here we applied heat stress to the resistant BS-90 snail, enhancing induction of stress genes (Hsp 70, Hsp 90 and RT) prior to infection. Results showed these resistant snails became susceptible, indicating resistance as being a temperature sensitive phenotype in these snails. Stressed resistant snails treated with the Hsp 90 specific inhibitor, geldanamycin, prior to exposure, were, however, shown to maintain their refractory phenotype. Interestingly, inhibitor treated susceptible snails also became non-susceptible. Collectively, these data point to stress induction as an important early step in the ability of S. mansoni to infect juvenile B. glabrata snails.

MIF from mussel: coding sequence, phylogeny, polymorphism, 3D model and regulation of expression

Three macrophage migration inhibitory factor (MIF)-related sequences were identified from a Mytilus galloprovincialis EST library. The consensus sequence included a 5'-UTR of 32 nucleotides, the complete ORF of 345 nucleotides, and a 3'-UTR of 349 nucleotides. As for other MIFs, M. galloprovincialis ORF does not include any signal or C-terminus extensions. The translated sequence of 115 amino acids possesses a molecular mass of 12,681.4, a pI of 6.27 and a stability index of 21.48. Its 3D structure resembles human MIF except for one shorter α-helix. Although evolutionary separated from ticks and vertebrates, Mg-MIF appeared to be closely related to Pinctada fucata and Haliotis, but not to Chlamys farreri and Biomphalaria glabrata. Numerous mutation points were observed within the Mg-MIF ORF, defining 11 amino acid variants within the mussels from Palavas-France and 14 amino acid variants within the mussels from Palermo-Italy. The 2 major variants from Palavas were identical to 2 of the 4 major variants from Palermo. In all the 18 Mg-MIF variants, residues involved in tautomerase and in oxidoreductase activities were conserved. Generally, one mussel expressed 2 Mg-MIF amino acid sequences but with different frequencies of occurrence. Mg-MIF is constitutively expressed principally in hemocytes and in the mantle. In contrast to other animal models, Mg-MIF expression was always down regulated following challenge by bacteria and fungi, confirming previous data obtained with microarray. Down regulation started as soon as 1 h and Mg-MIF expression returned to background 9-48 h after the challenge. Exception was regarding the yeast, Candidaalbicans, down-regulation between 9 and 72 h, suggesting yeast and bacteria-filamentous fungi trigger different mechanisms of elimination.

A somatically diversified defense factor, FREP3, is a determinant of snail resistance to schistosome infection

Schistosomiasis, a neglected tropical disease, owes its continued success to freshwater snails that support production of prolific numbers of human-infective cercariae. Encounters between schistosomes and snails do not always result in the snail becoming infected, in part because snails can mount immune responses that prevent schistosome development. Fibrinogen-related protein 3 (FREP3) has been previously associated with snail defense against digenetic trematode infection. It is a member of a large family of immune molecules with a unique structure consisting of one or two immunoglobulin superfamily domains connected to a fibrinogen domain; to date fibrinogen containing proteins with this arrangement are found only in gastropod molluscs. Furthermore, specific gastropod FREPs have been shown to undergo somatic diversification. Here we demonstrate that siRNA mediated knockdown of FREP3 results in a phenotypic loss of resistance to Schistosoma mansoni infection in 15 of 70 (21.4%) snails of the resistant BS-90 strain of Biomphalaria glabrata. In contrast, none of the 64 control BS-90 snails receiving a GFP siRNA construct and then exposed to S. mansoni became infected. Furthermore, resistance to S. mansoni was overcome in 22 of 48 snails (46%) by pre-exposure to another digenetic trematode, Echinostoma paraensei. Loss of resistance in this case was shown by microarray analysis to be associated with strong down-regulation of FREP3, and other candidate immune molecules. Although many factors are certainly involved in snail defense from trematode infection, this study identifies for the first time the involvement of a specific snail gene, FREP3, in the phenotype of resistance to the medically important parasite, S. mansoni. The results have implications for revealing the underlying mechanisms involved in dictating the range of snail strains used by S. mansoni, and, more generally, for better understanding the phenomena of host specificity and host switching. It also highlights the role of a diversified invertebrate immune molecule in defense against a human pathogen. It suggests new lines of investigation for understanding how susceptibility of snails in areas endemic for S. mansoni could be manipulated and diminished.

Schistosomiasis, a neglected tropical disease, owes its continued success to freshwater snails that support production of prolific numbers of human-infective cercariae. Encounters between schistosomes and snails do not always result in the snail becoming infected, in part because snails can mount immune responses that prevent schistosome development. Understanding the factors important for snail resistance to schistosome infection will facilitate new lines of investigation to 1) understand the underlying basis of compatibility between schistosomes and snails in endemic areas and how this affects transmission dynamics and control efforts; and 2) to reveal ways to manipulate natural snail populations to enhance their resistance to schistosome infections. Here, we present the first evidence that a snail immune molecule, fibrinogen related protein 3 (FREP3), is important for successful defense against schistosome infections in Biomphalaria snails. In addition, we demonstrate that FREP3 is a target suppressed by trematode parasites to facilitate their establishment within the snail.

Specific versus non-specific immune responses in an invertebrate species evidenced by a comparative de novo sequencing study

Our present understanding of the functioning and evolutionary history of invertebrate innate immunity derives mostly from studies on a few model species belonging to ecdysozoa. In particular, the characterization of signaling pathways dedicated to specific responses towards fungi and Gram-positive or Gram-negative bacteria in Drosophila melanogaster challenged our original view of a non-specific immunity in invertebrates. However, much remains to be elucidated from lophotrochozoan species. To investigate the global specificity of the immune response in the fresh-water snail Biomphalaria glabrata, we used massive Illumina sequencing of 5′-end cDNAs to compare expression profiles after challenge by Gram-positive or Gram-negative bacteria or after a yeast challenge. 5′-end cDNA sequencing of the libraries yielded over 12 millions high quality reads. To link these short reads to expressed genes, we prepared a reference transcriptomic database through automatic assembly and annotation of the 758,510 redundant sequences (ESTs, mRNAs) of B. glabrata available in public databases. Computational analysis of Illumina reads followed by multivariate analyses allowed identification of 1685 candidate transcripts differentially expressed after an immune challenge, with a two fold ratio between transcripts showing a challenge-specific expression versus a lower or non-specific differential expression. Differential expression has been validated using quantitative PCR for a subset of randomly selected candidates. Predicted functions of annotated candidates (approx. 700 unisequences) belonged to a large extend to similar functional categories or protein types. This work significantly expands upon previous gene discovery and expression studies on B. glabrata and suggests that responses to various pathogens may involve similar immune processes or signaling pathways but different genes belonging to multigenic families. These results raise the question of the importance of gene duplication and acquisition of paralog functional diversity in the evolution of specific invertebrate immune responses.

Symptoms of behavioural anapyrexia--reverse fever as a defence response of snails to fluke invasion

The subject of the research was the thermal preferences of Planorbarius corneus individuals infected by larvae of digenetic trematodes. Snails were obtained over two consecutive years, 2009 and 2010, from 10 water bodies located in central Poland. The relationship between the seasons and the occurrence of patent invasions in hosts found in the shore-zone of lakes was observed. Behavioural experiments conducted on P. corneus individuals placed in a thermal gradient demonstrated that parasite infection had an impact on the thermal preferences of the snails. Individuals that shed cercariae of Bilharziella polonica, Cotylurus sp., Notocotylus ephemera, Rubenstrema exasperatum/Neoglyphe locellus, Rubenstrema opisthovitellinum, or Tylodelphys excavata displayed symptoms of behavioural anapyrexia, similarly to experimentally injured snails. This response increased the survival of infected individuals while simultaneously prolonging the period of shedding of dispersive forms of parasites. This point of view was upheld by the observation that infected snails bred at 19°C lived longer than at 26°C and the shedding rate of cercariae at a lower temperature was lower than at a higher one.

A macrophage migration inhibitory factor like oxidoreductase from pearl oyster Pinctada fucata involved in innate immune responses

Macrophage migration inhibitory factor (MIF) is an important cytokine and plays a crucial role as a pivotal regulator of innate immunity. In this study, a MIF cDNA was identified and characterized from the pearl oyster Pinctada fucata (designated as PoMIF). The full-length of PoMIF was 1544 bp and consisted of a 5'-untranslated region (UTR) of 45 bp, a 3'-UTR of 1139 bp with a polyadenylation signal (AATAAA) at 12 nucleotides upstream of the poly (A) tail. The open reading frame (ORF) of PoMIF was 360 bp which encoded a polypeptide of 120 amino acids with an estimated molecular mass of 13.3 kDa and a predicted pI of 6.1. SMART analysis showed that PoMIF contained the catalytic-sites P² and K³³ for tautomerase activity, a motif C⁵⁷GSV⁶⁰ for oxidoreductase activity and a MIF family signature D⁵⁵PCGSVEVYSIGALG⁶⁹. Homology analysis revealed that the PoMIF shared 40.3-65.5% similarity and 26.9-45.0% identity to other known MIF sequences. PoMIF mRNA was constitutively expressed in seven selected tissues of healthy pearl oysters, with the highest expression level in digestive gland. Eight hours after P. fucata was injected with Vibrio alginolyticus, the expression of PoMIF mRNA was significantly up-regulated in digestive gland, gills, hemocytes and intestine. The cDNA fragment encoding mature protein of PoMIF was subcloned to expression vector pRSET and transformed into Escherichia coli BL21 (DE3). The recombinant PoMIF (rPoMIF) was expressed and purified under optimized conditions. Function analysis showed that rPoMIF had oxidoreductase activity and could utilize dithiothreitol (DTT) as reductant to reduce insulin.

Polyethyleneimine (PEI) mediated siRNA gene silencing in the Schistosoma mansoni snail host, Biomphalaria glabrata

An in vivo, non-invasive technique for gene silencing by RNA interference (RNAi) in the snail, Biomphalaria glabrata, has been developed using cationic polymer polyethyleneimine (PEI) mediated delivery of long double-stranded (ds) and small interfering (si) RNA. Cellular delivery was evaluated and optimized by using a ‘mock’ fluorescent siRNA. Subsequently, we used the method to suppress expression of Cathepsin B (CathB) with either the corresponding siRNA or dsRNA of this transcript. In addition, the knockdown of peroxiredoxin (Prx) at both RNA and protein levels was achieved with the PEI-mediated soaking method. B. glabrata is an important snail host for the transmission of the parasitic digenean platyhelminth, Schistosoma mansoni that causes schistosomiasis in the neotropics. Progress is being made to realize the genome sequence of the snail and to uncover gene expression profiles and cellular pathways that enable the snail to either prevent or sustain an infection. Using PEI complexes, a convenient soaking method has been developed, enabling functional gene knockdown studies with either dsRNA or siRNA. The protocol developed offers a first whole organism method for host-parasite gene function studies needed to identify key mechanisms required for parasite development in the snail host, which ultimately are needed as points for disrupting this parasite mediated disease.

Freshwater snails are important in the transmission of schistosomiasis. As part of an integral control effort to combat the spread of schistosomiasis new intervention tools are being sought. One method is to interrupt the transmission of the causative schistosome parasite during the intra-molluscan phase of its development. Gene-silencing technology involving the use of dsRNA have used an injection route to disrupt gene translation in the Schistosoma mansoni snail host, Biomphalaria glabrata in an effort to investigate how inhibition of various transcripts can affect the dynamics of the snail/parasite interaction. These studies have been helpful in showing us that a gene-silencing pathway that uses dsRNA indeed exists in snails but the injection method previously utilized is impractical, especially when working with juvenile snails. To make the use of gene silencing technology more widely applicable to functional gene studies in snails, we have developed a more convenient soaking method that uses a cationic carrier polyethylene amine (PEI) to deliver dsRNA or siRNA into juvenile snails. Using this method we show the successful knockdown at both RNA and protein levels of the B. glabrata peroxiredoxin (Prx) gene. The method was also evaluated for silencing the Cathepsin B (CathB) gene in the snail.

Recovery of primary sporocysts in vivo in the Schistosoma mansoni/Biomphalaria glabrata model using a simple fixation method suitable for extraction of genomic DNA and RNA

Detailed studies of host/parasite interactions are currently limited because in situ gene sequencing or monitoring of parasite gene expression is so far limited to genes presenting a high loci copy number in the Schistosome genome or a high level of expression. Indeed, how to investigate the host parasite molecular interplay when parasites are not directly accessible in vivo? Here we describe a method to circumvent this problem and to analyze DNA and RNA of Schistosoma mansoni during the interaction with its intermediate snail host Biomphalaria glabrata. We propose a technique for improved DNA and RNA extraction from the intra-molluscan stage of the parasite recovered after fixation of infected snails in Raillet-Henry solution. The extractions can be used for genetic analysis, transcription studies and microsatellite genotyping.

Identification and characterization of five transcription factors that are associated with evolutionarily conserved immune signaling pathways in the schistosome-transmitting snail Biomphalaria glabrata

Innate immunity consists of humoral and cellular components that play a vital role in regulation of defense responses to various pathogens in vertebrates and invertebrates. Recent studies have shown that Rel/DIF (dorsal-related immunity factor), Relish, STAT (signal transducer and activator of transcription) and CREB (cAMP response element-binding protein) transcription factor associated pathways are evolutionarily conserved across the animal kingdom. Although the primary role and general structure of the pathways in immunity have been revealed in many invertebrates, particularly arthropods, almost nothing is known about these pathways in the freshwater snail Biomphalaria glabrata, the intermediate host of the human blood fluke Schistosoma mansoni, which is a causative agent of human schistosomiasis. Given the central role of transcription factors (TF) in controlling expression of effector genes, understanding the role of a given TF is essential to obtaining insight into the general function of the corresponding signaling pathway. To better understand the immunity of B. glabrata, we investigated five homologues of TFs that have been shown to be associated with multiple prominent immune signaling pathways based on the considerable data reported from a wide phylogenetic range of animals. In this study we identified and characterized cDNAs of five TFs from B. glabrata, designated BgRelish, BgRel, BgSTAT1, BgSTAT2 and BgCREB, for the first time. Among the five TFs, Relish is first reported in Lophotrochozoa, one of three superphyla in Metazoa. Our identification of class I (BgRelish) and II (BgRel) NF-κB in B. glabrata suggests the two pathways, Toll-like receptor (TLR) and immune deficiency (IMD)-like pathways, are present in the superphylum Lophotrochozoa. Preliminarily expression studies indicate these TF-associated pathways may be involved in the snail's anti-schistosome response. This study not only advances our understanding of the snail's defenses, but also provides new perspectives about the evolution of animal immunity.

Controlling and coordinating development in vector-transmitted parasites

Vector-borne parasites cause major human diseases of the developing world, including malaria, human African trypanosomiasis, Chagas disease, leishmaniasis, filariasis, and schistosomiasis. Although the life cycles of these parasites were defined over 100 years ago, the strategies they use to optimize their successful transmission are only now being understood in molecular terms. Parasites are now known to monitor their environment in both their host and vector and in response to other parasites. This allows them to adapt their developmental cycles and to counteract any unfavorable conditions they encounter. Here, I review the interactions that parasites engage in with their hosts and vectors to maximize their survival and spread.

Role of macrophage migration inhibitory factor in primary glioblastoma multiforme cells

Macrophage migration inhibitory factor (MIF) is a protein that is overexpressed in many tumors, such as colon and prostate cancer, melanoma, and glioblastoma multiforme (GBM). In its function as a cytokine, MIF induces angiogenesis, promotes cell cycle progression, and inhibits apoptosis. Recently, the molecular signal transduction has been specified: MIF has been found to be a ligand to the CD74/CD44-receptor complex and to activate the ERK1/2 MAPK cascade. In addition MIF binds to the chemokine receptors CXCR2 and CXCR4. This effects an integrin-dependent leukocyte arrest and mediates leukocyte chemotaxis. Recent work has described a clearer role of MIF in GBM tumor cell lines. The current study used human primary GBM cells. We show that inhibition of MIF with ISO-1, an inhibitor of the D-dopachrome tautomerase site of MIF, reduced the growth rate of primary GBM cells in a dose-dependent manner, and in addition ISO-1 increased protein expression of MIF and its receptors CD74, CXCR2, and CXCR4 in vitro but decreased expression of CD44. Furthermore, hypoxia as cell stressor increases the protein expression of MIF in primary GBM cells. These results underscore the importance of MIF in GBM and show that MIF and its receptors may be a promising target for the treatment of malignant gliomas.