Immunocytochemical demonstration of a SALMFamide-like neuropeptide in the nervous system of adult and larval stages of the human blood fluke, Schistosoma mansoni

Drug-induced exposure of Schistosoma mansoni antigens SmCD59a and SmKK7

Background

Schistosomiasis is a serious health problem especially in developing countries and affects more than 243 million people. Only few anthelmintic drugs are available up to now. A major obstacle for drug treatment is the different developmental stages and the varying host compartments during worm development. Anthelmintic drugs have been tested mainly on adult schistosomes or freshly transformed cercariae. Knowledge concerning the larval stages is lacking.

Methodology/Principal Findings

In this study, we used in vitro-grown schistosomula (aged between 2 to 14 days) to investigate drug effects of the three anthelmintics praziquantel, artemether, and oxamniquine. Further, we analyzed the antibody accessibility of two exemplary schistosome antigens SmCD59a and SmKK7, before and after drug treatment. Our results demonstrated that praziquantel applied at a concentration of 1 μM inhibited development of all life stages. Application of 10 μM praziquantel led to dramatic morphological changes of all schistosomula. Artemether at 1 and 10 μM had differential effects depending on whether it was applied to 2-day as compared to 7- and 14-day schistosomula. While 2-day schistosomula were not killed but inhibited from further development, severe morphological damage was seen in 7- and 14-day schistosomula. Oxamniquine (1 and 10 μM) led to severe morphological impairment in all life stages. Analyzing the accessibility of the antigens SmCD59a and SmKK7 before drug treatment showed no antibody binding on living intact schistosomula. However, when schistosomula were treated with anthelmintics, both antigens became exposed on the larvae. Oxamniquine turned out to be most effective in promoting antibody binding to all schistosomula stages.

Conclusion

This study has revealed marked differences in anthelmintic drug effects against larvae. Drug treatment increases surface antigen presentation and renders larvae accessible to antibody attack.

Schistosomiasis is one of the major parasitic diseases in developing countries and still causes 200,000 deaths per year. Mass drug administration programs with praziquantel, the drug of choice against schistosomiasis, are currently undertaken in Sub-Saharan Africa. Praziquantel, although efficient against adult worms, fails to cure early infection. The complex developmental stages of schistosomes and migration through varying host compartments with different local drug concentration are a challenge for drug treatment. After infecting their mammalian host, schistosomula traverse through skin and the vasculature of lung, liver and intestines. During their migration, they develop from larvae to paired adults in approximately 4 to 5 weeks. So far, drug effects have been analyzed on adult worms or freshly transformed schistosomula only. Information about the effects on the larval stages is lacking. We were able to transfer the larval development of the first three weeks into the culture dish. This tool can be used for the analysis of drug effects against schistosomula and for investigation of the accessibility, expression and localization of antigens. Rendering the parasite’s larvae vulnerable to the host’s immune system by increasing antigen presentation is an important aspect of drug activity. We demonstrate on in vitro-cultured Schistosoma mansoni larvae, that SmCD59a and SmKK7, as examples for hidden antigens, become accessible to antibodies following drug treatment.

Transcriptome analyses of inhibitor-treated schistosome females provide evidence for cooperating Src-kinase and TGFβ receptor pathways controlling mitosis and eggshell formation

Schistosome parasites cause schistosomiasis, one of the most prevalent parasitemias worldwide affecting humans and animals. Constant pairing of schistosomes is essential for female sexual maturation and egg production, which causes pathogenesis. Female maturation involves signaling pathways controlling mitosis and differentiation within the gonads. In vitro studies had shown before that a Src-specific inhibitor, Herbimycin A (Herb A), and a TGFβ receptor (TβR) inhibitor (TRIKI) have physiological effects such as suppressed mitoses and egg production in paired females. As one Herb A target, the gonad-specifically expressed Src kinase SmTK3 was identified. Here, we comparatively analyzed the transcriptome profiles of Herb A- and TRIKI-treated females identifying transcriptional targets of Src-kinase and TβRI pathways. After demonstrating that TRIKI inhibits the schistosome TGFβreceptor SmTβRI by kinase assays in Xenopus oocytes, couples were treated with Herb A, TRIKI, or both inhibitors simultaneously in vitro. RNA was isolated from females for microarray hybridizations and transcription analyses. The obtained data were evaluated by Gene Ontology (GO) and Ingenuity Pathway Analysis (IPA), but also by manual classification and intersection analyses. Finally, extensive qPCR experiments were done to verify differential transcription of candidate genes under inhibitor influence but also to functionally reinforce specific physiological effects. A number of genes found to be differentially regulated are associated with mitosis and differentiation. Among these were calcium-associated genes and eggshell-forming genes. In situ hybridization confirmed transcription of genes coding for the calcium sensor hippocalcin, the calcium transporter ORAI-1, and the calcium-binding protein calmodulin-4 in the reproductive system pointing to a role of calcium in parasite reproduction. Functional qPCR results confirmed an inhibitor-influenced, varying dependence of the transcriptional activities of Smp14, Smp48, fs800, a predicted eggshell precursor protein and SmTYR1. The results show that eggshell-formation is regulated by at least two pathways cooperatively operating in a balanced manner to control egg production.

As one of the most prevalent parasitic infections worldwide, schistosomiasis is caused by blood-flukes of the genus Schistosoma. Pathology coincides with egg production, which is started upon pairing of the dioeciously living adults. A constant pairing contact is required to induce mitoses and differentiation processes in the female leading to the development of the gonads. Although long known, the molecular processes controlling gonad development or egg-production in schistosomes or other platyhelminths are largely unknown. Using an established in vitro-culture system and specific, chemical inhibitors we have obtained first evidence in previous studies for the participation of signal transduction processes playing essential roles in controlling mitoses, differentiation and egg production. In the present study we applied combinatory inhibitor treatments combined with subsequent microarray and qPCR analyses and demonstrate for the first time that cooperating Src-Kinase- und TGFβ-signaling pathways control mitoses and egg formation processes. Besides direct evidence for managing transcription of eggshell-forming genes, new target molecules of these pathways were identified. Among these are calcium-associated genes providing a first hint towards a role of this ion for reproduction. Our finding shed first light on the signaling mechanisms controlling egg formation, which is important for life-cycling and pathology.

The distribution of neuroactive substances within the cercaria ofSanguinicola inermis

The serotoninergic and peptidergic components of the nervous system of the cercaria ofSanguinicola inermis(Digenea: Sanguinicolidae) were examined using whole-mount immunocytochemistry and a plan of the nervous system has been described. Antibodies to serotonin (5-hydroxytryptamine, 5-HT) and the neuropeptides, FMRFamide, GFNSALMFamide (S1) and SGPYSFNSGLTFamide (S2) were used in the study. Immunoreactivity (IR) was demonstrated to all but the S2 antisera and showed a similar fundamental distribution. IR was found in paired cerebral ganglia located anteriorly within the body and connected by a cerebral commissure. From the ganglia paired ventral and dorsal longitudinal nerve cords extend anteriorly into the cephalic organ and into the body. There is no apparent connection with the tail. Several transverse commissures connect the longitudinal nerve cords throughout the body and several associated cell bodies have been located. A double-stranded dorsal and ventral longitudinal nerve cord extends the length of the tail and six cell bodies are associated with these cords, uniquely demonstrating either FMRFamide and S1, or 5-HT-like IR. Only 5-HT-like IR was found to extend into the posterior tail furcae and there appears to be a lack of any peripheral tegumental innervation. Double-labelling experiments suggest that the serotoninergic and peptidergic components of the cercarial nervous system are distinct.

Innervation of cercarial tegumentary receptors investigated by the Sevier-Munger method

The investigation of the sensory nature of tegumentary receptors in platyhelminths remains a challenge due to technical difficulties related to nerve tissue exposure and its experimental handling. Neuromorphological studies have been carried out but few demonstrated the association of these receptors with the nervous system. This paper introduces the Sevier-Munger method as an alternative approach to study the innervation of tegumentary receptors in larval flatworms. Twenty heterophyid cercariae were fixed in hot 5% formalin, with all washes performed in tap and distilled water. They were developed in a solution of ammoniacal silver and 2% formalin under the microscope for 10 min, with preparations shaken gently throughout the procedure. In all specimens, nerve cells stained black against a pale gold background. Fine nerve fibers of the subsurface nerve plexus were observed. These fibers sent distal branches from the plexus to the cercarial tegument. The branches became fine nerve endings, projecting as receptors in the cephalic (5CIV(5), 2CV(2), and 2CV(4)), anterior (4AIL, 3AIIL, 2AIIIL), midbody (1ML, 3MV), posterior (1PIL, 1PIIL, and 1PIIIL), and caudal (2UD) regions of the cercaria. These results indicate that the Sevier-Munger method is useful to demonstrate the association of cercarial tegumentary receptors with the subsurface nerve plexus. They also recommend the use of alternative methods to further investigate flatworm nervous systems. Moreover, there is a pressing urge for a standardized protocol, combining a plethora of methods and techniques. Interdisciplinary collaboration aiming at a better understanding of the function of flatworm nervous systems is particularly encouraged.

Trematode behaviours and the perceptual worlds of parasites

There is a great deal of empirical data and theoretical predictions on the patterns and processes of trematode behaviour, particularly in relation to host-finding activities by the free-living stages and site-finding migrations by the parasitic stages within their hosts. Ecological and evolutionary models of trematode life histories often make explicit assumptions about how these organisms must perceive and respond to signals in their worlds as they move from host to host and as they parasitize each host. Nevertheless, it is unclear how natural selection shapes the parasites' behavioural strategies. In addition, at each stage in their life cycle, trematodes are adorned with elaborate sensory organs and possess sophisticated neuromuscular systems, but it is not clear how they use these complex machinery to perceive their worlds. The purpose of this review is to address this question through insights gathered from a century of research on trematode behaviour. Core theoretical assumptions from modern animal behaviour are used to provide the context for this analysis; a key concept is that all animals have unique perceptual worlds that may be inferred from their behaviours. A critical idea is that all animals possess complex patterns of innate behaviour which can be released by extremely specific signals from the environment. The evidence suggests that trematode parasites live in ecologically predictable aquatic and internal host environments where they perceive only small subsets of the total information available from the environment. A general conclusion is that host finding in miracidia and cercaria, and site-finding by trematodes migrating within their definitive hosts, is accomplished through the release of innate patterns of behaviours which are adaptive within the context of conditions in the worm's environment. Examples from empirical studies are used to support the contention that, despite the apparent complexity of their free-living and parasitic environments, the perceptual worlds of trematodes are impoverished, and complex patterns of behaviour may be released by only a few signals in their environment.

A divergent member of the transforming growth factor beta receptor family from Schistosoma mansoni is expressed on the parasite surface membrane

To optimize reproductive success under the limitations determined by conditions within an individual host, parasitic helminths have evolved mechanisms that allow them to detect and respond to host factors such as species, age, sex, reproductive condition, and immune status. Using the model helminth Schistosoma mansoni, we have explored the possibility that parasitic helminths express signal-transducing receptor molecules on their surfaces. Here, we present the identification of a schistosome member of the transforming growth factor beta receptor family of cell-surface receptors, the first member of this family to be identified in a platyhelminth. The putative protein kinase domain of the schistosome receptor displays up to 58% amino acid identity to kinase domains of other type I receptor serine-threonine kinases, and contains a potential "GS domain," suggesting it is a divergent member of the type I receptor subfamily. This receptor is expressed on the surface of the parasite's syncytial tegument and expression of receptor messenger RNA and protein is up-regulated following infection of the mammalian host. The receptor protein can be isolated in a phosphorylated form from adult parasites, which together with its surface location, suggests that it functions in transducing signals across the parasite surface membrane.

Characterisation of a novel Kunitz-type molecule from the trematode Fasciola hepatica

A low molecular mass monomeric protein termed Fh-KTM (Fasciola hepatica Kunitz-type molecule) was isolated from the trematode Fasciola hepatica. Fh-KTM is a single polypeptide of 58 amino acids and a Mr of 6751. The complete amino acid sequence of Fh-KTM was determined and revealed significant similarity to the Kunitz-type (BPTI) family of proteinase inhibitors. Several polymorphisms were observed suggesting that more than one Fh-KTM molecule may be expressed by this parasite. Modified proline residues were shown to occur at all four positions in this protein as 3-hydroxy derivatives. This is the first report of 3-hydroxyproline residues in a Kunitz-type molecule. Indirect immunofluorescence and immunogold labelling revealed that Fh-KTM is an abundant molecule within the parasite localised to the gut, the parenchymal tissue and the tegument of adult F. hepatica. Serine protease inhibition assays revealed that Fh-KTM exhibited little or no inhibition against chymotrypsin, kallikrein, urokinase or key serine proteases of the blood coagulation pathways. However, Fh-KTM was able to inhibit trypsin even though the P1 reactive amino acid of Fh-KTM was a leucine residue.