Altered Gene Expression in the Schistosome-Transmitting Snail Biomphalaria glabrata following Exposure to Niclosamide, the Active Ingredient in the Widely Used Molluscicide Bayluscide

Immuno-molecular profile for Biomphalaria glabrata/Schistosoma mansoni interaction

The complex innate immune defense of Biomphalaria glabrata, the intermediate host of Schistosoma mansoni, governs the successful development of the intramolluscan stages of the parasite. The interaction between the snail and the parasite involves a complex immune molecular crosstalk between several parasite antigens and the snail immune recognition receptors, evoking different signals and effector molecules. This work seeks to discuss the immune-related molecules that influence compatibility in Biomphalaria glabrata/Schistosoma mansoni interaction and the differential expression of these molecules between resistant and susceptible snails. It also includes the current understanding of the immune molecular determinants that govern the compatibility in sympatric and allopatric interactions, and the expression of these molecules after immune priming and the secondary immune response. Herein, the differences in the immune-related molecules in the interaction of other Biomphalaria species with Schistosoma mansoni compared to the Biomphalaria glabrata model snail are highlighted. Understanding the diverse immune molecular determinants in the snail/schistosome interaction can lead to alternative control strategies for schistosomiasis.

Sublethal effects of niclosamide on the aquatic snail Pomacea canaliculata

Pomacea canaliculata is a malignant invasive aquatic snail found worldwide, and niclosamide (NS) is one of the primary agents used for its control. NS applied to water will exist in non-lethal concentrations for some time due to degradation or water exchange, thus resulting in sublethal effects on environmental organisms. To identify sublethal effects of NS on Pomacea canaliculata, we studied the aspects of histopathology, oxygen-nitrogen ratio (R_O∶N), enzyme activity determination, and gene expression. After LC₃₀ NS treatment (0.310 g/L), many muscle fibers of the feet degenerated and some acinar vesicles of the hepatopancreas collapsed and dissolved. The oxygen-nitrogen ratio (R_O∶N) decreased significantly from 15.0494 to 11.5183, indicating that NS had changed the metabolic mode of Pomacea canaliculata and shifted it primarily to protein catabolism. Transcriptome analysis identified the sublethal effects of LC₃₀ NS on the snails at the transcriptional level. 386, 322, and 583 differentially expressed genes (DEGs) were identified in the hepatopancreas, gills, and feet, respectively. GO (Gene Ontology) functional analysis and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway annotations showed that DEGs in the hepatopancreas were mainly enriched for sugar metabolism, protein biosynthesis, immune response, and amino acid metabolism functional categories; DEGs in the gills were mainly enriched for ion transport and amino acid metabolism; DEGs in the feet were mainly enriched for transmembrane transport and inositol biosynthesis. In the future, we will perform functional validation of key genes to further explain the molecular mechanism of sublethal effects.

Evaluation of the developmental toxicity of solvents, metals, drugs, and industrial chemicals using a freshwater snail (Biomphalaria glabrata) assay

A freshwater snail assay was employed to assess the embryotoxicity of solvents including acetone, methanol, ethanol, isopropanol, dimethyl-sulfoxide, glycerin, metals/metalloids including mercuric chloride (HgCl₂), cadmium chloride (CdCl₂,), antimony salts Sb⁺³ and Sb⁺⁵, drugs including colchicine, hydroxyurea, cyclophosphamide, an industrial chemical sodium azide (SA), an anionic surfactant dodecyl sodium sulfate-(DSS), H₂O₂ and sodium chloride (NaCl). The assay consists of exposing Biomphalaria glabrata egg masses (EM) to the substances for 96-hr and following up embryo/snail development for lethality, abnormal morphology (teratogenicity), and day of hatching up to day 10 or 14 after spawning. Based upon concentration-response relationships, LC_50%s (embryolethality), EC_50%s (teratogenicity) and IC_50%s (hatching retardation) and 95%CIs were determined for tested chemicals. The LOECs indicated that HgCl₂ (37 nM) and CdCl₂ (140 nM) are potent embryotoxic agents in snails. Teratogenic indices (TI = LC₅₀/EC₅₀) for almost all tested chemicals were lower than or close to unity suggesting that these compounds were not teratogenic in this assay. The snail assay may be adequately performed in a cost-effective standardized protocol which enables testing a number of environmental chemicals over a broad concentration range. The snail assay needs to undergo further validation to be recognized for an internationally harmonized hazard identification in ecotoxicity risk assessment.

Compatibility between snails and schistosomes: insights from new genetic resources, comparative genomics, and genetic mapping

The freshwater snail Biomphalaria glabrata is an important intermediate host of the parasite Schistosoma mansoni that causes human intestinal schistosomiasis. To better understand vector snail biology and help advance innovative snail control strategies, we have developed a new snail model consisting of two homozygous B. glabrata lines (iM line and iBS90) with sharply contrasting schistosome-resistance phenotypes. We produced and compared high-quality genome sequences for iM line and iBS90 which were assembled from 255 (N50 = 22.7 Mb) and 346 (N50 = 19.4 Mb) scaffolds, respectively. Using F2 offspring bred from the two lines and the newly generated iM line genome, we constructed 18 linkage groups (representing the 18 haploid chromosomes) covering 96% of the genome and identified three new QTLs (quantitative trait loci), two involved in snail resistance/susceptibility and one relating to body pigmentation. This study provides excellent genomic resources for unveiling complex vector snail biology, reveals genomic difference between resistant and susceptible lines, and offers novel insights into genetic mechanism of the compatibility between snail and schistosome.

An Overview of Transcriptional Responses of Schistosome-Susceptible (M line) or -Resistant (BS-90) Biomphalaria glabrata Exposed or Not to Schistosoma mansoni Infection

Background

We seek to provide a comprehensive overview of transcriptomics responses of immune-related features of the gastropod Biomphalaria glabrata (Bg) following exposure to Schistosoma mansoni (Sm), a trematode causing human schistosomiasis. Responses of schistosome-susceptible (M line, or SUS) and -resistant (BS-90, or RES) Bg strains were characterized following exposure to Sm for 0.5, 2, 8 or 40 days post-exposure (dpe).

Methods

RNA-Seq and differential expression analysis were undertaken on 56 snails from 14 groups. We considered 7 response categories: 1) constitutive resistance factors; 2) constitutive susceptibility factors; 3) generalized stress responses; 4) induced resistance factors; 5) resistance factors suppressed in SUS snails; 6) suppressed/manipulated factors in SUS snails; and 7) tolerance responses in SUS snails. We also undertook a gene co-expression network analysis. Results from prior studies identifying schistosome resistance/susceptibility factors were examined relative to our findings.

Results

A total of 792 million paired-end reads representing 91.2% of the estimated 31,985 genes in the Bg genome were detected and results for the 7 categories compiled and highlighted. For both RES and SUS snails, a single most supported network of genes with highly correlated expression was found.

Conclusions

1) Several constitutive differences in gene expression between SUS and RES snails were noted, the majority over-represented in RES; 2) There was little indication of a generalized stress response shared by SUS and RES snails at 0.5 or 2 dpe; 3) RES snails mounted a strong, multi-faceted response by 0.5 dpe that carried over to 2 dpe; 4) The most notable SUS responses were at 40 dpe, in snails shedding cercariae, when numerous features were either strongly down-regulated indicative of physiological distress or parasite manipulation, or up-regulated, suggestive of tolerance or survival-promoting effects; 5) Of 55 genes previously identified in genome wide mapping studies, 29 (52.7%) were responsive to Sm, as were many familiar resistance-associated genes (41.0%) identified by other means; 6) Both network analysis and remarkably specific patterns of expression of lectins and G protein-coupled receptors in categories 4, 6 and 7 were indicative of orchestrated responses of different suites of genes in SUS or RES snails following exposure to Sm.

Metabolic profiles of Oncomelania hupensis after molluscicidal treatment: Carbohydrate metabolism targeted and energy deficiency

Oncomelania hupensis is the intermediate host of Schistosoma japonicum, one of the Schistosoma species that can cause human schistosomiasis. Molluscicidal treatment remains the primary means to control snail. Niclosamide is the only molluscicide recommended by the World Health Organization, and it has been used throughout schistosomiasis-endemic areas in China for almost 30 years. In our previous studies on transcriptomics, morphology, and enzymology of snails after molluscicidal treatment, two effective molluscicides were used, 50% wettable powder of niclosamide ethanolamine salt (WPN) and a new molluscicide derived from niclosamide, the salt of quinoid-2', 5-dichloro-4'-nitro-salicylanilide (LDS, simplified for Liu Dai Shui Yang An). Genes involved in cell structure mintenance, inhibition of neurohumoral transmission, and energy metabolism showed significant differential expression after molluscicide treatments. Damages in the structure of liver and muscle cells were accompanied by inhibited activities of enzymes related to carbohydrate metabolism and energy supply. This study was designed to clarify the dynamic metabolic process by metabonomics, together with the previous transcriptomic and enzymological profiles, to identify potential metabolite markers and metabolism pathways that related to the toxic mechanism of the molluscicide. In total, 56 metabolites were identified for O. hupensis, and 75% of these metabolites consisted of amino acids and derivatives, organic acids, and nucleic acid components. The concentration of glucose, maltose, succinate, choline, and alanine changed significantly after molluscicide treatments. These changes in metabolites mainly occurred in the process of carbohydrate metabolism, energy metabolism, and amino acid metabolism, primarily related to glycolysis/gluconeogenesis, oxidative phosphorylation, and transamination by KEGG pathway identification. Most of the identified pathways were also related to those differentially expressed unigenes and observed enzymes from our previous studies. Inhibited aerobic respiration and oxidative phosphorylation, and energy deficiency were implied further to be the leading causes of the final death of snails after molluscicide treatments. The hypothesised mathematical model in this study identified the rational hysteresis to explain the inconsistency of responses of unigenes, enzymes, and metabolites to molluscicide treatments. This study contributes to the comprehensive understanding of the molluscicidal mechanism in the metabolic process and this could assist in improving existing molluscicide formulations or development of new molluscicides.

Molluscicidal and parasiticidal activities of Eryngium triquetrum essential oil on Schistosoma mansoni and its intermediate snail host Biomphalaria glabrata, a double impact

Background

Freshwater snails are the intermediate hosts of a large variety of trematode flukes such as Schistosoma mansoni responsible for one of the most important parasitic diseases caused by helminths, affecting 67 million people worldwide. Recently, the WHO Global Vector Control Response 2017–2030 (GVCR) programme reinforced its message for safer molluscicides as part of required strategies to strengthen vector control worldwide. Here, we present the essential oil from Eryngium triquetrum as a powerful product with molluscicide and parasiticide effect against S. mansoni and the snail intermediate host Biomphalaria glabrata.

Methods

In the present study, we describe using several experimental approaches, the chemical composition of E. triquetrum essential oil extract and its biological effects against the snail B. glabrata and its parasite S. mansoni. Vector and the free-swimming larval stages of the parasite were exposed to different oil concentrations to determine the lethal concentration required to produce a mortality of 50% (LC₅₀) and 90% (LC₉₀). In addition, toxic activity of this essential oil was analyzed against embryos of B. glabrata snails by monitoring egg hatching and snail development. Also, short-time exposure to sublethal molluscicide concentrations on S. mansoni miracidia was performed to test a potential effect on parasite infectivity on snails. Mortality of miracidia and cercariae of S. mansoni is complete for 5, 1 and 0.5 ppm of oil extract after 1 and 4 h exposure.

Results

The major chemical component found in E. triquetrum oil determined by GC-FID and GC/MS analyses is an aliphatic polyacetylene molecule, the falcarinol with 86.9–93.1% of the total composition. The LC₅₀ and LC₉₀ values for uninfected snails were 0.61 and 1.02 ppm respectively for 24 h exposure. At 0.5 ppm, the essential oil was two times more toxic to parasitized snails with a mortality rate of 88.8 ± 4.8%. Moderate embryonic lethal effects were observed at the concentration of 1 ppm. Severe surface damage in miracidia was observed with a general loss of cilia that probably cause their immobility. Miracidia exposed 30 min to low concentration of plant extract (0.1 ppm) were less infective with 3.3% of prevalence compare to untreated with a prevalence of 44%.

Conclusions

Essential oil extracted from E. triquetrum and falcarinol must be considered as a promising product for the development of new interventions for schistosomiasis control and could proceed to be tested on Phase II according to the WHO requirements.

The golden mussel proteome and its response to niclosamide: Uncovering rational targets for control or elimination

The Asian invasive species Limnoperna fortunei (Dunker, 1857), known as the golden mussel, causes great economic and environmental damage due to its fixative capacity and accelerated proliferation. Molecular studies for the control of larval and adult forms are of great economic, scientific and technological interest. Here, we first report on the compositional analysis of the L. fortunei proteome obtained through shotgun analysis using LC-MS/MS. Among those 2790 proteins identified, many of them related to secretory processes and membrane receptors. Our second approach consisted in exposing the mollusc to the molluscicide niclosamide to evaluate the induced proteomic alterations. Exposure to niclosamide at 0.25 mg/L for 24 h resulted in a pronounced differential abundance of proteins when compared to those obtained when exposure was reduced to 4 h at 2.3 mg/L. In total, 342 proteins were found differentially expressed in the responsive individuals as revealed by label-free quantitative proteomics. Regarding the affected cell processes were: cell division and differentiation, cytoskeletal organization and compartment acidification (upregulated), and energy metabolism (downregulated). Our findings constitute the first inventory of the expressed proteome of the golden mussel and have the potential to contribute with a more rational proposition of molecular targets for control and monitoring of this species. SIGNIFICANCE: With the recent availability of transcriptomic and genomic data applied to L. fortunei the timing is right to interrogate its putative gene repertoire using proteomic techniques. These have the potential to validate the existence of the predicted genes, infer their relative abundance and quantify their levels as a response to environmental stressors or various agents. Here we provided an inventory of the golden mussel proteome and evaluated its response to the molluscicide niclosamide. The obtained results open new avenues for intervention aimed at its control or elimination, particularly by targeting the various cellular processes that were uncovered.

High-throughput transcriptome sequencing reveals the developmental toxicity mechanisms of niclosamide in zebrafish embryo

Niclosamide (NIC) is the most widely used molluscicides for preventing the occurrence of schistosomiasis disease, and its residues can be found in various environmental samples. However, the toxicity mechanism of NIC during early developmental stage remains largely unknown. In the present study, zebrafish embryos were acutely exposed to NIC at an environmentally realistic concentration (0 and 40 μg/L) until 120 h post-fertilization. Transcriptomic sequencing was performed to provide mechanistic insight into developmental impairment. Pathway enrichment analyses found that biological processes related to lipid metabolism were significantly affected in exposed zebrafish larvae. Consistently, biochemical measurements showed that NIC developmental exposure depleted lipid storage, elevated lipid utilization, but inhibited lipid synthesis. Furthermore, as characterized by pathway enrichment and hormonal levels, steroid hormone biosynthesis was also significantly disrupted by NIC exposure in zebrafish larvae, indicating the endocrine disrupting potential of NIC. Detoxifying phase I and II processes (e.g., metabolism, conjugation and elimination) were significantly activated by NIC exposure. Overall, our findings suggest that NIC developmental exposure at an environmentally realistic concentration disturbs the lipid metabolism, induces endocrine disruption and initiates detoxifying capacity in zebrafish larvae, which will provide preliminary clues for developmental toxicity mechanisms of NIC.

Public health concerns over gene-drive mosquitoes: will future use of gene-drive snails for schistosomiasis control gain increased level of community acceptance?

With the advent of CRISPR (clustered regularly interspaced short palindromic repeat)-based gene drive, present genetic research in schistosomiasis vector control envisages the breeding and release of transgenic schistosome-resistant (TSR) snail vectors to curb the spread of the disease. Although this approach is still in its infancy, studies focussing on production of genetically modified (GM) mosquitoes (including gene-drive mosquitoes) are well advanced and set the pace for other transgenic vector research. Unfortunately, as with other GM mosquitoes, open field release of gene-drive mosquitoes is currently challenged in part by some concerns such as gene drive failure and increased transmission potential for other mosquito-borne diseases among others, which might have adverse effects on human well-being. Therefore, not only should we learn from the GM mosquito protocols, frameworks and guidelines but also appraise the applicability of its current hurdles to other transgenic vector systems, such as the TSR snail approach. Placing these issues in a coherent comparative perspective, I argue that although the use of TSR snails may face similar technical, democratic and diplomatic challenges, some of the concerns over gene-drive mosquitoes may not apply to gene-drive snails, proposing a theory that community consent will be no harder and possibly easier to obtain for TSR snails than the experience with GM mosquitoes. In the future, these observations may help public health practitioners and policy makers in effective communication with communities on issues regarding the use of TSR snails to interrupt schistosomiasis transmission, especially in sub-Saharan Africa.

The Stakeholders' Views on Planting Trees to Control Schistosomiasis in China

China has initiated a tree planting program in epidemic regions of schistosomiasis as a part of efforts to eliminate schistosomiasis. More than 518,900 ha of tree plantations have been planted through the program between 2006 and 2015. However, whether the planting program has fulfilled its mission or not is an open question. In this study, we intended to get the answer from the main stakeholders of the planting program through a large-scale survey. Based on interviews with 80 administrators of the planting program and 1440 farmers in 24 counties and districts in four provinces, we found that most stakeholders viewed the planting program positively. Nearly 92% of farmers and all administrators believed that the planting program had reduced snail densities, while 94.3% of farmers and all administrators believed that the program had lowered the incidences of schistosomiasis. In addition, they reported that the impacts on farmers’ living and local environments by the tree planting program were mainly positive. Based on the stakeholders’ responses, we conclude that the tree planting program has been perceived by the main stakeholders as an effective environmental control measure of schistosomiasis. However, certain places and people that may be impacted negatively by the program should be given more attention when implementing the program.

Transcriptional responses of Biomphalaria pfeifferi and Schistosoma mansoni following exposure to niclosamide, with evidence for a synergistic effect on snails following exposure to both stressors

BACKGROUND

Schistosomiasis is one of the world's most common NTDs. Successful control operations often target snail vectors with the molluscicide niclosamide. Little is known about how niclosamide affects snails, including for Biomphalaria pfeifferi, the most important vector for Schistosoma mansoni in Africa. We used Illumina technology to explore how field-derived B. pfeifferi, either uninfected or harboring cercariae-producing S. mansoni sporocysts, respond to a sublethal treatment of niclosamide. This study afforded the opportunity to determine if snails respond differently to biotic or abiotic stressors, and if they reserve unique responses for when presented with both stressors in combination. We also examined how sporocysts respond when their snail host is treated with niclosamide.

PRINCIPAL FINDINGS

Cercariae-producing sporocysts within snails treated with niclosamide express ~68% of the genes in the S. mansoni genome, as compared to 66% expressed by intramolluscan stages of S. mansoni in snails not treated with niclosamide. Niclosamide does not disable sporocysts nor does it seem to provoke from them distinctive responses associated with detoxifying a xenobiotic. For uninfected B. pfeifferi, niclosamide treatment alone increases expression of several features not up-regulated in infected snails including particular cytochrome p450s and heat shock proteins, glutathione-S-transferases, antimicrobial factors like LBP/BPI and protease inhibitors, and also provokes strong down regulation of proteases. Exposure of infected snails to niclosamide resulted in numerous up-regulated responses associated with apoptosis along with down-regulated ribosomal and defense functions, indicative of a distinctive, compromised state not achieved with either stimulus alone.

CONCLUSIONS/SIGNIFICANCE

This study helps define the transcriptomic responses of an important and under-studied schistosome vector to S. mansoni sporocysts, to niclosamide, and to both in combination. It suggests the response of S. mansoni sporocysts to niclosamide is minimal and not reflective of a distinct repertoire of genes to handle xenobiotics while in the snail host. It also offers new insights for how niclosamide affects snails.

Proteomic, metabolic and immunological changes in Biomphalaria glabrata infected with Schistosoma mansoni

Mansonic schistosomiasis is a neglected disease transmitted by Biomphalaria spp. snails. Understanding what happens inside the intermediate host is important to develop more efficient ways of reducing schistosomiasis prevalence. Our purpose was to characterize metabolic and immunological changes in Biomphalaria glabrata 24 h after exposure to Schistosoma mansoni. For this purpose, proteins were extracted from snails' whole tissue with Tris-Urea buffer and digested with tripsin. Mass spectrometry was performed and analyzed with MaxQuant and Perseus software. Also, the hemolymph of five snails 24 h post exposure was collected, and the numbers of hemocytes, levels of urea, uric acid, nitric oxide, calcium, glycogen and alanine and aspartate aminotransferases activities were assessed. Snails were also dissected for measurement of glycogen content in the cephalopodal region and gonoda-digestive gland complex. Globin domain proteins were found to be up-regulated; also the number of circulating hemocytes was significantly higher after 24 h of exposure to the parasite. NO levels were higher 24 h post exposure. Several proteins associated with energy metabolism were found to be up-regulated. Glycogen analysis showed a significant decrease in the gonad-digestive gland complex glycogen content. We found several proteins which seem to be associated with the host immune response, most of which were up-regulated, however some were down-regulated, which may represent an important clue in understanding B. glabrata - S. mansoni compatibility.

Comparative study of excretory-secretory proteins released by Schistosoma mansoni-resistant, susceptible and naïve Biomphalaria glabrata

BACKGROUND

Schistosomiasis is a harmful neglected tropical disease caused by infection with Schistosoma spp., such as Schistosoma mansoni. Schistosoma must transition within a molluscan host to survive. Chemical analyses of schistosome-molluscan interactions indicate that host identification involves chemosensation, including naïve host preference. Proteomic technique advances enable sophisticated comparative analyses between infected and naïve snail host proteins. This study aimed to compare resistant, susceptible and naïve Biomphalaria glabrata snail-conditioned water (SCW) to identify potential attractants and deterrents.

METHODS

Behavioural bioassays were performed on S. mansoni miracidia to compare the effects of susceptible, F1 resistant and naïve B. glabrata SCW. The F1 resistant and susceptible B. glabrata SCW excretory-secretory proteins (ESPs) were fractionated using SDS-PAGE, identified with LC-MS/MS and compared to naïve snail ESPs. Protein-protein interaction (PPI) analyses based on published studies (including experiments, co-expression, text-mining and gene fusion) identified S. mansoni and B. glabrata protein interaction. Data are available via ProteomeXchange with identifier PXD015129.

RESULTS

A total of 291, 410 and 597 ESPs were detected in the susceptible, F1 resistant and naïve SCW, respectively. Less overlap in ESPs was identified between susceptible and naïve snails than F1 resistant and naïve snails. F1 resistant B. glabrata ESPs were predominately associated with anti-pathogen activity and detoxification, such as leukocyte elastase and peroxiredoxin. Susceptible B. glabrata several proteins correlated with immunity and anti-inflammation, such as glutathione S-transferase and zinc metalloproteinase, and S. mansoni sporocyst presence. PPI analyses found that uncharacterised S. mansoni protein Smp_142140.1 potentially interacts with numerous B. glabrata proteins.

CONCLUSIONS

This study identified ESPs released by F1 resistant, susceptible and naïve B. glabrata to explain S. mansoni miracidia interplay. Susceptible B. glabrata ESPs shed light on potential S. mansoni miracidia deterrents. Further targeted research on specific ESPs identified in this study could help inhibit B. glabrata and S. mansoni interactions and stop human schistosomiasis.

Effects of the Environment on Developmental Plasticity and Infection Success of Schistosoma Parasites - An Epigenetic Perspective

Evidence of how environmental cues affect the phenotypes of, and compatibility between Schistosoma mansoni and their hosts come from studies in environmental parasitology and research on host diet and chemotherapeutic treatment. Schistosomes deal with a multitude of signals from the water environment as well as cues that come from their hosts, particularly in response to molecules that serve to recognize and destroy them, i.e., those molecules that arise from their hosts' immune systems. These interactions shape, not only the parasite's morphology, metabolism and behavior in the short-term, but also their infection success and development into different stage-specific phenotypes later in their life cycle, through the modification of the parasite's inheritance system. Developmental phenotypic plasticity of S. mansoni is based on epigenetic mechanisms which are also sensitive to environmental cues, but are poorly understood. Here, we argue that specific cues from the environment could lead to changes in parasite development and infectivity, and consequently, environmental signals that come from environmental control measures could be used to influence S. mansoni dynamics and transmission. This approach poses a challenge since epigenetic modification can lead to unexpected and undesired outcomes. However, we suggest that a better understanding of how environmental cues are interpreted by epigenome during schistosome development and host interactions could potentially be applied to control parasite's virulence. We review evidence about the role of environmental cues on the phenotype of S. mansoni and the compatibility between this parasite and its intermediate and definitive hosts.

Proteomic Analysis of Biomphalaria glabrata Hemocytes During in vitro Encapsulation of Schistosoma mansoni Sporocysts

Circulating hemocytes of the snail Biomphalaria glabrata, a major intermediate host for the blood fluke Schistosoma mansoni, represent the primary immune effector cells comprising the host's internal defense system. Within hours of miracidial entry into resistant B. glabrata strains, hemocytes infiltrate around developing sporocysts forming multi-layered cellular capsules that results in larval death, typically within 24–48 h post-infection. Using an in vitro model of hemocyte-sporocyst encapsulation that recapitulates in vivo events, we conducted a comparative proteomic analysis on the responses of hemocytes from inbred B. glabrata strains during the encapsulation of S. mansoni primary sporocysts. This was accomplished by a combination of Laser-capture microdissection (LCM) to isolate sections of hemocyte capsules both in the presence and absence of sporocysts, in conjunction with mass spectrometric analyses to establish protein expression profiles. Comparison of susceptible NMRI snail hemocytes in the presence and absence of sporocysts revealed a dramatic downregulation of proteins in during larval encapsulation, especially those involved in protein/CHO metabolism, immune-related, redox and signaling pathways. One of 4 upregulated proteins was arginase, competitor of nitric oxide synthetase and inhibitor of larval-killing NO production. By contrast, when compared to control capsules, sporocyst-encapsulating hemocytes of resistant BS-90 B. glabrata exhibited a more balanced profile with enhanced expression of shared proteins involved in protein synthesis/processing, immunity, and redox, and unique expression of anti-microbial/anti-parasite proteins. A final comparison of NMRI and BS-90 host hemocyte responses to co-cultured sporocysts demonstrated a decrease or downregulation of 77% of shared proteins by NMRI cells during encapsulation compared to those of the BS-90 strain, including lipopolysaccharide-binding protein, thioredoxin reductase 1 and hemoglobins 1 and 2. Overall, using this in vitro model, results of our proteomic analyses demonstrate striking differences in proteins expressed by susceptible NMRI and resistant BS-90 snail hemocytes to S. mansoni sporocysts during active encapsulation, with NMRI hemocytes exhibiting extensive downregulation of protein expression and a lower level of constitutively expressed immune-relevant proteins (e.g., FREP2) compared to BS-90. Our data suggest that snail strain differences in hemocyte protein expression during the encapsulation process account for observed differences in their cytotoxic capacity to interact with and kill sporocysts.

Transcriptomic responses of Biomphalaria pfeifferi to Schistosoma mansoni: Investigation of a neglected African snail that supports more S. mansoni transmission than any other snail species

BACKGROUND

Biomphalaria pfeifferi is highly compatible with the widespread human-infecting blood fluke Schistosoma mansoni and transmits more cases of this parasite to people than any other snail species. For these reasons, B. pfeifferi is the world's most important vector snail for S. mansoni, yet we know relatively little at the molecular level regarding the interactions between B. pfeifferi and S. mansoni from early-stage sporocyst transformation to the development of cercariae.

METHODOLOGY/PRINCIPAL FINDINGS

We sought to capture a portrait of the response of B. pfeifferi to S. mansoni as it occurs in nature by undertaking Illumina dual RNA-Seq on uninfected control B. pfeifferi and three intramolluscan developmental stages (1- and 3-days post infection and patent, cercariae-producing infections) using field-derived west Kenyan specimens. A high-quality, well-annotated de novo B. pfeifferi transcriptome was assembled from over a half billion non-S. mansoni paired-end reads. Reads associated with potential symbionts were noted. Some infected snails yielded fewer normalized S. mansoni reads and showed different patterns of transcriptional response than others, an indication that the ability of field-derived snails to support and respond to infection is variable. Alterations in transcripts associated with reproduction were noted, including for the oviposition-related hormone ovipostatin and enzymes involved in metabolism of bioactive amines like dopamine or serotonin. Shedding snails exhibited responses consistent with the need for tissue repair. Both generalized stress and immune factors immune factors (VIgLs, PGRPs, BGBPs, complement C1q-like, chitinases) exhibited complex transcriptional responses in this compatible host-parasite system.

SIGNIFICANCE

This study provides for the first time a large sequence data set to help in interpreting the important vector role of the neglected snail B. pfeifferi in transmission of S. mansoni, including with an emphasis on more natural, field-derived specimens. We have identified B. pfeifferi targets particularly responsive during infection that enable further dissection of the functional role of these candidate molecules.

Do terrestrial gastropods use olfactory cues to locate and select food actively?

Having been investigated for over 40 years, some aspects of the biology of terrestrial gastropod's olfactory system have been challenging and highly contentious, while others still remain unresolved. For example, a number of terrestrial gastropod species can track the odor of food, while others have no strong preferences toward food odor; rather they find it by random encounter. Here, while assessing the most recent findings and comparing them with earlier studies, the aspects of the food selection based on olfactory cues are examined critically to highlight the speculations and controversies that have arisen. We analyzed and compared the potential role of airborne odors in the feeding behavior of several terrestrial gastropod species. The available results indicate that in the foraging of most of the terrestrial gastropod species odor cues contribute substantially to food finding and selection. The results also suggest, however, that what they will actually consume largely depends on where they live and the species of gastropod that they are. Due to the voluminous literature relevant to this object, this review is not intended to be exhaustive. Instead, I selected what I consider to be the most important or critical in studies regarding the role of the olfaction in feeding of terrestrial gastropods.

Pathogen-associated molecular patterns activate expression of genes involved in cell proliferation, immunity and detoxification in the amebocyte-producing organ of the snail Biomphalaria glabrata

The anterior pericardial wall of the snail Biomphalaria glabrata has been identified as a site of hemocyte production, hence has been named the amebocyte-producing organ (APO). A number of studies have shown that exogenous abiotic and biotic substances, including pathogen associated molecular patterns (PAMPs), are able to stimulate APO mitotic activity and/or enlarge its size, implying a role for the APO in innate immunity. The molecular mechanisms underlying such responses have not yet been explored, in part due to the difficulty in obtaining sufficient APO tissue for gene expression studies. By using a modified RNA extraction technique and microarray technology, we investigated transcriptomic responses of APOs dissected from snails at 24 h post-injection with two bacterial PAMPs, lipopolysaccharide (LPS) and peptidoglycan (PGN), or with fucoidan (FCN), which may mimic fucosyl-rich glycan PAMPs on sporocysts of Schistosoma mansoni. Based upon the number of genes differentially expressed, LPS exhibited the strongest activity, relative to saline-injected controls. A concurrent activation of genes involved in cell proliferation, immune response and detoxification metabolism was observed. A gene encoding checkpoint 1 kinase, a key regulator of mitosis, was highly expressed after stimulation by LPS. Also, seven different aminoacyl-tRNA synthetases that play an essential role in protein synthesis were found to be highly expressed. In addition to stimulating genes involved in cell proliferation, the injected substances, especially LPS, also induced expression of a number of immune-related genes including arginase, peptidoglycan recognition protein short form, tumor necrosis factor receptor, ficolin, calmodulin, bacterial permeability increasing proteins and E3 ubiquitin-protein ligase. Importantly, significant up-regulation was observed in four GiMAP (GTPase of immunity-associated protein) genes, a result which provides the first evidence suggesting an immune role of GiMAP in protostome animals. Moreover, altered expression of genes encoding cytochrome P450, glutathione-S-transferase, multiple drug resistance protein as well as a large number of genes encoding enzymes associated with degradation and detoxification metabolism was elicited in response to the injected substances.