A confocal microscopical study of the musculature of adult Schistosoma mansoni

Serotonergic elements in the nervous system of parasite of acipenserid fishes, Acrolichanus auriculatus (Digenea: Allocreadiidae)

The trematode Acrolichanus auriculatus is a widely distributed intestine parasite of acipenserid fishes. For the first time the localization and distribution of the serotonergic nerve elements in A. auriculatus was studied using immunocytochemical method and confocal laser scanning microscopy. The study revealed the presence of biogenic amine, serotonin, in the central and peripheral nervous systems of A. auriculatus, that is in the neurons and neurites of the brain ganglia, brain commissure, the longitudinal nerve cords, and the connective nerve commissures. The innervation of the attachment organs, pharynx, oesophagus and distal regions of the reproductive system by the serotonergic nerve elements is observed. The distribution of serotonergic neurons in A. auriculatus is schematically marked. The comparative analysis of findings obtained in A. auriculatus with those recorded for other digeneans reveals the presence of both conservative and distinctive features in the organization of the serotonergic nervous system in various representatives of trematodes.

Biomechanics of parasite migration within hosts

The dissemination of protozoan and metazoan parasites through host tissues is hindered by cellular barriers, dense extracellular matrices, and fluid forces in the bloodstream. To overcome these diverse biophysical impediments, parasites implement versatile migratory strategies. Parasite-exerted mechanical forces and upregulation of the host's cellular contractile machinery are the motors for these strategies, and these are comparably better characterized for protozoa than for helminths. Using the examples of the protozoans, Toxoplasma gondii and Plasmodium, and the metazoan, Schistosoma mansoni, we highlight how quantitative tools such as traction force and reflection interference contrast microscopies have improved our understanding of how parasites alter host mechanobiology to promote their migration.

Neuromuscular system of the causative agent of dicrocoeliosis, Dicrocoelium lanceatum. II. Neuropeptide FMRFamide immunoreactivity in nervous system

The parasitic flatworm, trematoda Dicrocoelium lanceatum or lancet fluke is the causative agent of a widespread parasite disease of grazing ruminants, dicrocoeliosis. The aim of this work is the study of the presence and localization of neuropeptide FMRFamide immunoreactive elements in the nervous system of D. lanceatum using immunocytochemical technique and confocal scanning laser microscopy. For the first time the data on the presence and distribution of the FMRFamide-immunopositive components in the central and peripheral departments of the nervous system of D. lanceatum has been obtained. FMRFamidergic neurons and neurites were identified in paired brain ganglia, in the brain commissure, longitudinal nerve cords and connective nerve commissures. The innervation of the oral and ventral suckers by peptidergic nerve structures was revealed. The distal part of the reproductive system is innervated by FMRFamide immunopositive neurites. The data obtained suggest that the neuropeptides of FMRFamide family can be involved in the regulation of functions of the attachment organs and the reproductive system in D. lanceatum. The study of neurotransmitters and their functions in flatworms expand our knowledge on the structure and function of the nervous system of trematodes of various taxonomic groups. The results obtained on the morphological organization of D. lanceatum nervous system support the exploitation of the FMRFamidergic components as an anthelmintic target.

Neuromuscular system of the causative agent of dicrocoeliosis, Dicrocoelium lanceatum. I. 5-Hydroxytryptamine in the nervous system

The trematode Dicrocoelium lanceatum known as lancet fluke, is a causative agent of dicrocoeliosis, a widespread parasitic disease of the grazing ruminants. The investigation of the major neurotransmitters and their functions are an important step in the development of a new pharmacological strategy of the struggle against the dicrocoeliosis affecting the neuronal signal substances and the functions of its nervous system. The aim of this work was to study the presence and localization of the neurotransmitter serotonin (5-HT, 5-Hydroxytryptamine) in the nervous system of D. lanceatum using immunocytochemical technique and confocal laser scanning microscopy. For the first time the data on the presence and distribution of serotonin-immunopositive components in the central and peripheral compartments of the nervous system of D. lanceatum has been obtained. Serotonin-immunopositive neurons and neurites were identified in paired brain ganglia, in the brain commissure, longitudinal nerve cords and connective nerve commissures. The innervation of the oral and ventral suckers by serotonergic nerve structures was revealed. The distal part of the reproductive system and the region of the reproductive pore were intensively innervated by serotonergic neurites. Serotonin-immunopositive neurons and neurites were also revealed in the proximal region of the reproductive system. The data obtained suggest that the serotonergic nervous system is involved in the regulation of the attachment organs and the reproductive system functions in D. lanceatum. The new results on the morphological and functional organization of the D. lanceatum nervous system increase our knowledge of the structure and function of nervous system of trematodes of various taxonomic groups and support the possibility of the exploitation of the serotonergic system of the parasite as a target for anthelmintic drugs.

An atlas of the germ ball-cercaria-schistosomulum transition in Schistosoma mansoni, using confocal microscopy and in situ hybridisation

Schistosomes are complex platyhelminth parasites with a genome comprising ∼12,000 protein-coding genes, three distinct generations, and at least seven distinct phenotypes. We chart here cellular and gene expression changes associated with development of the cercaria, in the intramolluscan daughter sporocyst, and its transformation into the skin stage schistosomulum upon infection of the mammalian host. We describe the morphology of the early daughter sporocyst and the increasing complexity of cellular organisation in germ balls as they rapidly develop into cercariae. We show how individual myocytes differentiate and combine to create the complex musculature of the head capsule and body wall. In situ hybridisation reveals that some transcripts encoding the secretory proteins, released during skin penetration, are expressed in gland-cell precursors very early in germ ball development. However, those for the projected anti-inflammatory protein Sm16-stathmin are widely expressed in germ ball tissues, suggesting the protein has intracellular functions. Transcripts for smkk7 are expressed in six cells of the larval body, while the KK7 protein is present throughout the peripheral nerve net, including sensory nerve bulbs, providing a marker for the nerve net in adult worms. We also note that the cercaria-schistosomulum transformation is accompanied by tissue remodelling without growth.

Musculature and neurotransmitters of internal organs of trematodes (the digestive, reproductive and excretory systems)

The article analyzes the results on the presence and organization of the muscle elements in the visceral organs of parasitic flatworms, trematodes, as well as their innervations. The different regions of the digestive, reproductive and excretory systems of trematodes contain circular, longitudinal and diagonal muscle fibers. The results of immunocytochemical investigations and confocal scanning laser microscopy show the presence of serotonin and FMRFamide-like immunoreactivity in the nervous system elements in various parts of the digestive, reproductive and excretory systems of trematodes. The data suggest that serotonergic and FMRFamide-immunopositive components of parasite's nervous system are involved in the regulation of the muscle activity of the digestive, reproductive and excretory systems. Comparative analysis of the results presented for trematodes from different taxonomic groups indicates that the organization of muscle elements in the visceral organs in trematodes and their innervation by serotonergic and peptidergic components are highly conserved.

The neuromuscular system of the sheep tapeworm Moniezia expansa

Cestodes are common gastrointestinal parasites of humans and livestock. They attach to the host gut and, without a mouth or intestinal system, absorb nutrients through their epidermis. Here we show that despite this simplified anatomy and sessile lifestyle, they maintain a complex neuromuscular system. We used fluorescently labelled phalloidin as a specific probe for filamentous actin to define the overall organisation of several distinct muscle systems in the cyclophyllidean Moniezia expansa. Like all flatworms, the body wall musculature below the neodermis of this intestinal parasite of sheep is characterised by outer circular and inner longitudinal muscle fibres. Diagonal fibres, typically found in free-living and trematode platyhelminths, on the other hand, are notably absent. Prominent longitudinal sheaths dominate the parenchyma and provide retractor muscles to the four acetabula in the scolex; they attach at the bottom of each cup-shaped holdfast. Within sexually mature proglottids, circular fibres dominate the duct walls of the male and female reproductive systems. Nerve cells and fibres that express serotonin or neuropeptide F supply well-developed innervation to several of the described muscle systems: emanating from the central nervous system, fibres in the periphery develop pervasive nerve nets that anastomose within body wall musculature as well as the parenchymal longitudinal and oblique muscle fibres, and innervate the sexual organs and gonopore in mature proglottids. Using homology searches, we provide evidence for 20 neuropeptide precursors together with four prepropeptide processing enzymes as well as several 5-HT signalling components to be represented in the Moniezia transcriptome.

Pharmacological inhibition of lysine-specific demethylase 1 (LSD1) induces global transcriptional deregulation and ultrastructural alterations that impair viability in Schistosoma mansoni

Treatment and control of schistosomiasis still rely on only one effective drug, praziquantel (PZQ) and, due to mass treatment, the increasing risk of selecting for schistosome strains that are resistant to PZQ has alerted investigators to the urgent need to develop novel therapeutic strategies. The histone-modifying enzymes (HMEs) represent promising targets for the development of epigenetic drugs against Schistosoma mansoni. In the present study, we targeted the S. mansoni lysine-specific demethylase 1 (SmLSD1), a transcriptional corepressor, using a novel and selective synthetic inhibitor, MC3935, which was used to treat schistosomula and adult worms in vitro. By using cell viability assays and optical and electron microscopy, we showed that treatment with MC3935 affected parasite motility, egg-laying, tegument, and cellular organelle structures, culminating in the death of schistosomula and adult worms. In silico molecular modeling and docking analysis suggested that MC3935 binds to the catalytic pocket of SmLSD1. Western blot analysis revealed that MC3935 inhibited SmLSD1 demethylation activity of H3K4me1/2. Knockdown of SmLSD1 by RNAi recapitulated MC3935 phenotypes in adult worms. RNA-Seq analysis of MC3935-treated parasites revealed significant differences in gene expression related to critical biological processes. Collectively, our findings show that SmLSD1 is a promising drug target for the treatment of schistosomiasis and strongly support the further development and in vivo testing of selective schistosome LSD1 inhibitors.

The neuroactive substances and associated muscle system in Rhipidocotyle campanula (Digenea, Bucephalidae) from the intestine of the pike Esox lucius

We report about the muscular system and the serotonergic and FMRFamidergic components of the nervous system of the Bucephalidae trematode, Rhipidocotyle campanula, an intestinal parasite of the pike. We use immunocytochemical methods and confocal scanning laser microscopy (CLSM). The musculature is identified by histochemical staining with fluorescently labeled phalloidin. The body wall musculature of R. campanula contains three layers of muscle fibres - the outer thin circular, intermediate longitudinal and inner diagonal muscle fibres running in two opposite directions. The digestive system of R. campanula possess of a well-developed musculature: radial, longitudinal and circular muscle elements are detected in the pharynx, circular and longitudinal muscle filaments seen in the oesophagus, and longitudinal and the circular muscle fibres were found in the intestinal wall. Specific staining indicating the presence of actin muscle filaments occurs in the cirrus sac localized in the posterior body region. The frontal region of anterior attachment organ, the rhynchus, in R. campanula is represented by radial muscle fibres. The posterior part of the rhynchus comprise of radial muscles forming the organ's wall, and several strong longitudinal muscle bundles. Serotonergic and FMRFamidergic structures are detected in the central and peripheral compartments of the nervous system of R. campanula, that is, in the paired brain ganglia, the brain commissure, the longitudinal nerve cords, and connective nerve commissures. The innervations of the rhynchus, pharynx, oesophagus and distal regions of the reproductive system by the serotonergic and FMRFamidergic nervous elements are revealed. We compare our findings obtained on R. campanula with related data for other trematodes.

The New Data on the Serotonin and FMRFamide Localization in the Nervous System of Opisthorchis felineus Metacercaria

BACKGROUND

Trematoda Opisthorchis felineus Rivolta, 1884 is the causative agent of dangerous parasite disease-opisthorchiasis, widespread in the Russian Federation. The details of the neuroanatomical localization of the serotoninergic and FMRFamidergic neurotransmitter elements as well as their functional roles remain not studied enough in both adult and larval forms of O. felineus. The studies in this area are important in term of the development of a new pharmacological strategy of the struggle with the causative agent of opisthorchiasis affecting the neuronal signal substances and the function of its nervous system.

PURPOSE

The aim of this work was the immunocytochemical study of the neurotransmitters serotonin (5-HT, 5-Hydroxitryptamine) and neuropeptide FMRFamide localization in the nervous system of the opisthorchiasis causative agent-O. felineus metacercaria. To study the relationship between the detected neurotransmitters and the muscular elements of the parasite, the muscle staining was carried out simultaneously using fluorophore-conjugated phalloidin.

METHODS

The localization of 5-HTergic and FMRFamidergic nerve structures was determined by immunocytochemical method. The staining samples were analyzed using a fluorescent and confocal laser scanning microscopies.

RESULTS

The new data on the presence and distribution of the serotonin-immunopositive (IP)- and FMRFa-IP components in the central and peripheral departments of the nervous system of  O. felineus metacercaria has been obtained. Besides that a number of the new anatomical details of the nervous system organization and of the innervation of the organs and tissues in the investigated parasite have been revealed.

CONCLUSION

The data obtained on the presence and localization of the 5-HTergic and peptidergic (FMRFamide) components in central and peripheral departments of the nervous system of O. felineus metacercaria elaborated and expanded the existing information about the nervous system as well as the innervations of the tissues and organs in the causative agent of opistchorchiasis.

Eurytrema coelomaticum: updated morphology of adult worms using advanced microscopy experiments

Eurytrema coelomaticum is a digenean flatworm of ruminants that is the causative agent of eurytrematosis, a disease of veterinary health concern. Although modern techniques of morphological analysis have provided new insights about the morphology and anatomy of parasitic helminths, most studies on E. coelomaticum adults are based on conventional light microscopy. In the present study, a combined approach using brightfield, fluorescence, confocal and scanning electron microscopies (SEMs), together with the cryofracture technique, have updated morphological data on E. coelomaticum recovered from cattle in Rio de Janeiro State, Brazil. Light microscopy confirmed the presence of several structures present in the current description, such as suckers, pharynx, oesophagus, intestinal bifurcation and the cirrus-sac. Fluorescence stereomicroscopy revealed for the first time the cubic crystal protein inclusions in the forebody, which were further detailed by confocal and SEMs. Confocal microscopy provided detailed information of the muscular architecture associated with the attachment structures (suckers), digestive system (pharynx and oesophagus), egg-forming complex (ovary, Mehlis' gland and Laurer's canal) and male reproductive system, which are similar to those found in other digenean flukes. SEM images of cryofractured parasites showed mucus and developing eggs within uterine loops. It was demonstrated that the combination of advanced tools generated complementary information, confirming the importance of experimental morphology in parasitology. Therefore, the knowledge of the adult structural organization of E. coelomaticum was improved and this work has contributed to propose new morphological criteria to evaluate the effects of antiparasitic drugs on flukes of medical and veterinary importance.

Insects in anthelminthics research: Lady beetle-derived harmonine affects survival, reproduction and stem cell proliferation of Schistosoma mansoni

Natural products have moved into the spotlight as possible sources for new drugs in the treatment of helminth infections including schistosomiasis. Surprisingly, insect-derived compounds have largely been neglected so far in the search for novel anthelminthics, despite the generally recognized high potential of insect biotechnology for drug discovery. This motivated us to assess the antischistosomal capacity of harmonine, an antimicrobial alkaloid from the harlequin ladybird Harmonia axyridis that raised high interest in insect biotechnology in recent years. We observed remarkably pleiotropic effects of harmonine on physiological, cellular, and molecular processes in adult male and female Schistosoma mansoni at concentrations as low as 5 μM in vitro. This included tegumental damage, gut dilatation, dysplasia of gonads, a complete stop of egg production at 10 μM, and increased production of abnormally shaped eggs at 5 μM. Motility was reduced with an EC50 of 8.8 μM and lethal effects occurred at 10–20 μM within 3 days of culture. Enzyme inhibition assays revealed acetylcholinesterase (AChE) as one potential target of harmonine. To assess possible effects on stem cells, which represent attractive anthelminthic targets, we developed a novel in silico 3D reconstruction of gonads based on confocal laser scanning microscopy of worms after EdU incorporation to allow for quantification of proliferating stem cells per organ. Harmonine significantly reduced the number of proliferating stem cells in testes, ovaries, and also the number of proliferating parenchymal neoblasts. This was further supported by a downregulated expression of the stem cell markers nanos-1 and nanos-2 in harmonine-treated worms revealed by quantitative real-time PCR. Our data demonstrate a multifaceted antischistosomal activity of the lady beetle-derived compound harmonine, and suggest AChE and stem cell genes as possible targets. Harmonine is the first animal-derived alkaloid detected to have antischistosomal capacity. This study highlights the potential of exploiting insects as a source for the discovery of anthelminthics.

Natural compounds represent one of the richest sources for the discovery of new active compounds against diseases such as cancer or infections, including helminth infections that cause the highest disease burden in tropical countries. Surprisingly, insects have been almost completely neglected with respect to anthelminthics discovery although they represent the most species-rich class of animals known on earth, producing a wide spectrum of compounds with biological activities. In insect biotechnology, the harlequin ladybird Harmonia axyridis raised high interest being a rich source of antimicrobial compounds such as the alkaloid harmonine. Harmonine is thought to act as a chemical weapon keeping otherwise detrimental microsporidia in the beetle under control. Testing the antiparasitic potential of harmonine against adult Schistosoma mansoni, one of the most harmful helminths worldwide, resulted in multifaceted negative effects. The compound damaged tissues essential for survival and reproduction of schistosomes (tegument, intestine, gonads) and also affected stem-cell proliferation. Furthermore, we obtained first evidence for acetylcholinesterase as one potential molecular target, which was partially inhibited by harmonine. This is the first time to proof a direct effect of a defined insect-derived compound on a helminth parasite, a finding that will encourage further studies to explore insects as sources of novel anthelminthics.

Octopamine signaling in the metazoan pathogen Schistosoma mansoni: localization, small-molecule screening and opportunities for drug development

Schistosomiasis is a tropical disease caused by a flatworm trematode parasite that infects over 200 million people worldwide. Treatment and control of the disease rely on just one drug, praziquantel. The possibility of drug resistance coupled with praziquantel's variable efficacy encourages the identification of new drugs and drug targets. Disruption of neuromuscular homeostasis in parasitic worms is a validated strategy for drug development. In schistosomes, however, much remains to be understood about the organization of the nervous system, its component neurotransmitters and potential for drug discovery. Using synapsin as a neuronal marker, we map the central and peripheral nervous systems in the Schistosoma mansoni adult and schistosomulum (post-infective larva). We discover the widespread presence of octopamine (OA), a tyrosine-derived and invertebrate-specific neurotransmitter involved in neuromuscular coordination. OA labeling facilitated the discovery of two pairs of ganglia in the brain of the adult schistosome, rather than the one pair thus far reported for this and other trematodes. In quantitative phenotypic assays, OA and the structurally related tyrosine-derived phenolamine and catecholamine neurotransmitters differentially modulated schistosomulum motility and length. Similarly, from a screen of 28 drug agonists and antagonists of tyrosine-derivative signaling, certain drugs that act on OA and dopamine receptors induced robust and sometimes complex concentration-dependent effects on schistosome motility and length; in some cases, these effects occurred at concentrations achievable in vivo The present data advance our knowledge of the organization of the nervous system in this globally important pathogen and identify a number of drugs that interfere with tyrosine-derivative signaling, one or more of which might provide the basis for a new chemotherapeutic approach to treat schistosomiasis.This article has an associated First Person interview with the first author of the paper.

Serotonin and Neuropeptide FMRFamide in the Attachment Organs of Trematodes

The serotoninergic and FMRFamidergic nervous system of the attachment organs of trematodes were examined using immunocytochemical techniques and confocal scanning laser microscopy. Adult trematodes from eight families as well as cercariae and metacercariae from ten families were studied. TRITC-conjugated phalloidin was used to stain the muscle fibres. The serotonin- and FMRFamide-immunoreactive (IR) nerve cells and fibres were revealed to be near the muscle fibres of the oral and ventral suckers of the trematodes and their larvae. The results indicate the important role of neurotransmitters, serotonin and neuropeptide FMRFamide in the regulation of muscle activity in the attachment organs of trematodes and can be considered in perspective for the development of new anthelmintic drugs, which can interrupt the function of the attachment organs of the parasites.

Molecular characterization and confocal laser scanning microscopic study of Pygidiopsis macrostomum (Trematoda: Heterophyidae) parasites of guppies Poecilia vivipara

Pygidiopsis macrostomum and Ascocotyle (Phagicola) pindoramensis (Digenea: Heterophyidae) parasitize guppies as intermediate hosts and, respectively, fish-eating mammals or birds as definitive hosts. Heterophyids have zoonotic potential, and molecular studies associated with morphological and ecological aspects have helped to clarify their taxonomy and phylogeny. Poecilia vivipara naturally parasitized by metacercariae of both species (100% prevalence) exhibit no external signs of parasitism. In this work, four new sequences of P. macrostomum (18S rDNA, 28S rDNA and ITS2 rDNA) and one new sequence of A. (P.) pindoramensis (mtDNA cox-1) are presented. Phylogeny reconstructions linked P. macrostomum to other heterophyids, but the separation of the Heterophyidae and Opisthorchiidae remains unclear. Additionally, we used indirect immunocytochemistry and the phalloidin-fluorescence techniques allied with confocal laser scanning microscopy to describe muscular and neuronal structures of P. macrostomum. A complex arrangement of muscular fibres is associated with the tegument, suckers, gut and reproductive system. Radial fibres around the ventral sucker are thick, branched and extend to the body wall. High-resolution confocal imaging revealed a typical digenean muscular arrangement and important heterophyid morphological traits. These data will support future control measures to reduce the parasitism in guppies reared in fish farming systems, especially for aquarium and experimental purposes.

An invertebrate smooth muscle with striated muscle myosin filaments

Muscle tissues are classically divided into two major types, depending on the presence or absence of striations. In striated muscles, the actin filaments are anchored at Z-lines and the myosin and actin filaments are in register, whereas in smooth muscles, the actin filaments are attached to dense bodies and the myosin and actin filaments are out of register. The structure of the filaments in smooth muscles is also different from that in striated muscles. Here we have studied the structure of myosin filaments from the smooth muscles of the human parasite Schistosoma mansoni. We find, surprisingly, that they are indistinguishable from those in an arthropod striated muscle. This structural similarity is supported by sequence comparison between the schistosome myosin II heavy chain and known striated muscle myosins. In contrast, the actin filaments of schistosomes are similar to those of smooth muscles, lacking troponin-dependent regulation. We conclude that schistosome muscles are hybrids, containing striated muscle-like myosin filaments and smooth muscle-like actin filaments in a smooth muscle architecture. This surprising finding has broad significance for understanding how muscles are built and how they evolved, and challenges the paradigm that smooth and striated muscles always have distinctly different components.

Somatic musculature in trematode hermaphroditic generation

BACKGROUND

The somatic musculature in trematode hermaphroditic generation (cercariae, metacercariae and adult) is presumed to comprise uniform layers of circular, longitudinal and diagonal muscle fibers of the body wall, and internal dorsoventral muscle fibers. Meanwhile, specific data are few, and there has been no analysis taking the trunk axial differentiation and regionalization into account. Yet presence of the ventral sucker (= acetabulum) morphologically divides the digenean trunk into two regions: preacetabular and postacetabular. The functional differentiation of these two regions is already evident in the nervous system organization, and the goal of our research was to investigate the somatic musculature from the same point of view.

RESULTS

Somatic musculature of ten trematode species was studied with use of fluorescent-labelled phalloidin and confocal microscopy. The body wall of examined species included three main muscle layers (of circular, longitudinal and diagonal fibers), and most of the species had them distinctly better developed in the preacetabuler region. In majority of the species several (up to seven) additional groups of muscle fibers were found within the body wall. Among them the anterioradial, posterioradial, anteriolateral muscle fibers, and U-shaped muscle sets were most abundant. These groups were located on the ventral surface, and associated with the ventral sucker. The additional internal musculature was quite diverse as well, and included up to twelve separate groups of muscle fibers or bundles in one species. The most dense additional bundles were found in the preacetabular region and were connected with the suckers.

CONCLUSIONS

Previously unknown additional somatic musculature probably provides the diverse movements of the preacetabular region, ventral sucker, and oral sucker (or anterior organ). Several additional muscle groups of the body wall (anterioradial, posterioradial, anteriolateral fibers and U-shaped sets) are proposed to be included into the musculature ground pattern of trematode hermaphroditic generation. This pattern is thought to be determined by the primary trunk morphofunctional differentiation into the preacetabular and the postacetabular regions.

Evidence That Rhesus Macaques Self-Cure from a Schistosoma japonicum Infection by Disrupting Worm Esophageal Function: A New Route to an Effective Vaccine?

Background

Rhesus macaques are unusual among schistosome hosts, self-curing from an established infection and thereafter manifesting solid immunity against a challenge, an ideal model for vaccine development. Previously, the immunological basis of self-cure was confirmed; surviving worms had ceased feeding but how immunological pressure achieved this was unclear. The schistosome esophagus is not simply a conduit for blood but plays a central role in its processing. Secretions from the anterior and posterior esophageal glands mix with incoming blood causing erythrocyte lysis and tethering and killing of leucocytes.

Methodology/Principal Findings

We have analysed the self-cure process in rhesus macaques infected with Schistosoma japonicum. Faecal egg output and circulating antigen levels were used to chart the establishment of a mature worm population and its subsequent demise. The physiological stress of surviving females at perfusion was especially evident from their pale, shrunken appearance, while changes in the structure and function of the esophagus were observed in both sexes. In the anterior region electron microscopy revealed that the vesicle secretory process was disrupted, the tips of lining corrugations being swollen by greatly enlarged vesicles and the putative sites of vesicle release obscured by intense deposits of IgG. The lumen of the posterior esophagus in starving worms was occluded by cellular debris and the lining cytoplasmic plates were closely adherent, also potentially preventing secretion. Seven proteins secreted by the posterior gland were identified and IgG responses were detected to some or all of them. Intrinsic rhesus IgG colocalized with secreted SjMEGs 4.1, 8.2, 9, 11 and VAL-7 on cryosections, suggesting they are potential targets for disruption of function.

Conclusions/Significance

Our data suggest that rhesus macaques self-cure by blocking esophagus function with antibody; the protein products of the glands provide a new class of potential vaccine targets.

Rhesus macaques can self-cure from a schistosome infection. Antibody is crucial to drive this process and adult worm elimination is preceded by cessation of blood feeding. Recently we have shown that the schistosome esophagus plays a central role in blood processing. We first confirm the self-cure process in rhesus macaques infected with Schistosoma japonicum and provide evidence that the self-cure mechanism involves blocking the worm esophagus function with antibody. In the anterior region, secretion of light vesicles is disrupted hence their contents are not released into the lumen to interact with blood components to fulfil their tasks. The plates in the posterior lining stick together whilst the lumen is occluded, hampering blood processing. Furthermore, rhesus IgG binds strongly to the worm esophageal lumen and co-localizes completely with five esophageal secreted proteins, SjMEGs 4.1, 8.2, 9, 11 and VAL-7. Our results indicate that rhesus macaques eliminate their adult worms by disrupting esophageal function making blood difficult to ingest; feeding stops eventually causing their demise because nutrient uptake across the body surface cannot fully compensate.

Muscle architecture during the course of development of Diplostomum pseudospathaceum Niewiadomska, 1984 (Trematoda, Diplostomidae) from cercariae to metacercariae

Recent confocal microscopy studies have greatly expanded our knowledge of muscle systems in cercariae and adult digeneans, but the gross anatomy and development of metacercarial musculature remain relatively little known. To further our understanding of metacercarial development, this study used phalloidin staining and confocal microscopy to examine changes in muscle architecture over the course of development from cercariae to infective metacercariae in Diplostomum pseudospathaceum Niewiadomska, 1984. The paper describes muscle development in the body wall, anterior organ (oral sucker), acetabulum, pharynx and midgut and in the musculo-glandular organs that first appear in metacercariae (lappets and holdfast). The muscle architecture of the cercarial tail is also described. The results of the study support previously reported observations that diplostomid musculature undergoes substantial transformation during metacercarial development. The most profound changes, involving extensive remodelling and replacement of cercarial muscles, were seen in the body-wall musculature and in the anterior organ as it developed into the oral sucker. Muscle systems of other cercarial organs showed more gradual changes. The adaptive importance of developmental changes in musculature is discussed.

Kicking in the Guts: Schistosoma mansoni Digestive Tract Proteins are Potential Candidates for Vaccine Development

Schistosomiasis is a debilitating disease that represents a major health problem in at least 74 tropical and subtropical countries. Current disease control strategies consist mainly of chemotherapy, which cannot prevent recurrent re-infection of people living in endemic area. In the last decades, many researchers made a remarkable effort in the search for an effective vaccine to provide long-term protection. Parasitic platyhelminthes of Schistosoma genus, which cause the disease, live in the blood vessels of definitive hosts where they are bathed in host blood for many years. Among the most promising molecules as vaccine candidates are the proteins present in the host–parasite interface, so numerous tegument antigens have been assessed and the achieved protection never got even close to 100%. Besides the tegument, the digestive tract is the other major site of host–parasite interface. Since parasites feed on blood, they need to swallow a considerable amount of blood for nutrient acquisition. Host blood ingested by schistosomes passes through the esophagus and reaches the gut where many peptidases catalyze the proteolysis of blood cells. Recent studies show the emergence of antigens related to the parasite blood feeding, such as esophageal gland proteins, proteases, and other proteins related to nutrient uptake. Herein, we review what is known about Schistosoma mansoni digestive tract proteins, emphasizing the ones described as potential vaccine candidates.

Functional characterization of a novel family of acetylcholine-gated chloride channels in Schistosoma mansoni

Acetylcholine is the canonical excitatory neurotransmitter of the mammalian neuromuscular system. However, in the trematode parasite Schistosoma mansoni, cholinergic stimulation leads to muscle relaxation and a flaccid paralysis, suggesting an inhibitory mode of action. Information about the pharmacological mechanism of this inhibition is lacking. Here, we used a combination of techniques to assess the role of cholinergic receptors in schistosome motor function. The neuromuscular effects of acetylcholine are typically mediated by gated cation channels of the nicotinic receptor (nAChR) family. Bioinformatics analyses identified numerous nAChR subunits in the S. mansoni genome but, interestingly, nearly half of these subunits carried a motif normally associated with chloride-selectivity. These putative schistosome acetylcholine-gated chloride channels (SmACCs) are evolutionarily divergent from those of nematodes and form a unique clade within the larger family of nAChRs. Pharmacological and RNA interference (RNAi) behavioral screens were used to assess the role of the SmACCs in larval motor function. Treatment with antagonists produced the same effect as RNAi suppression of SmACCs; both led to a hypermotile phenotype consistent with abrogation of an inhibitory neuromuscular mediator. Antibodies were then generated against two of the SmACCs for use in immunolocalization studies. SmACC-1 and SmACC-2 localize to regions of the peripheral nervous system that innervate the body wall muscles, yet neither appears to be expressed directly on the musculature. One gene, SmACC-1, was expressed in HEK-293 cells and characterized using an iodide flux assay. The results indicate that SmACC-1 formed a functional homomeric chloride channel and was activated selectively by a panel of cholinergic agonists. The results described in this study identify a novel clade of nicotinic chloride channels that act as inhibitory modulators of schistosome neuromuscular function. Additionally, the iodide flux assay used to characterize SmACC-1 represents a new high-throughput tool for drug screening against these unique parasite ion channels.

Serotonin signaling in Schistosoma mansoni: a serotonin-activated G protein-coupled receptor controls parasite movement

Serotonin is an important neuroactive substance in all the parasitic helminths. In Schistosoma mansoni, serotonin is strongly myoexcitatory; it potentiates contraction of the body wall muscles and stimulates motor activity. This is considered to be a critical mechanism of motor control in the parasite, but the mode of action of serotonin is poorly understood. Here we provide the first molecular evidence of a functional serotonin receptor (Sm5HTR) in S. mansoni. The schistosome receptor belongs to the G protein-coupled receptor (GPCR) superfamily and is distantly related to serotonergic type 7 (5HT7) receptors from other species. Functional expression studies in transfected HEK 293 cells showed that Sm5HTR is a specific serotonin receptor and it signals through an increase in intracellular cAMP, consistent with a 5HT7 signaling mechanism. Immunolocalization studies with a specific anti-Sm5HTR antibody revealed that the receptor is abundantly distributed in the worm's nervous system, including the cerebral ganglia and main nerve cords of the central nervous system and the peripheral innervation of the body wall muscles and tegument. RNA interference (RNAi) was performed both in schistosomulae and adult worms to test whether the receptor is required for parasite motility. The RNAi-suppressed adults and larvae were markedly hypoactive compared to the corresponding controls and they were also resistant to exogenous serotonin treatment. These results show that Sm5HTR is at least one of the receptors responsible for the motor effects of serotonin in S. mansoni. The fact that Sm5HTR is expressed in nerve tissue further suggests that serotonin stimulates movement via this receptor by modulating neuronal output to the musculature. Together, the evidence identifies Sm5HTR as an important neuronal protein and a key component of the motor control apparatus in S. mansoni.

On the three-finger protein domain fold and CD59-like proteins in Schistosoma mansoni

Background

It is believed that schistosomes evade complement-mediated killing by expressing regulatory proteins on their surface. Recently, six homologues of human CD59, an important inhibitor of the complement system membrane attack complex, were identified in the schistosome genome. Therefore, it is important to investigate whether these molecules could act as CD59-like complement inhibitors in schistosomes as part of an immune evasion strategy.

Methodology/Principal Findings

Herein, we describe the molecular characterization of seven putative SmCD59-like genes and attempt to address the putative biological function of two isoforms. Superimposition analysis of the 3D structure of hCD59 and schistosome sequences revealed that they contain the three-fingered protein domain (TFPD). However, the conserved amino acid residues involved in complement recognition in mammals could not be identified. Real-time RT-PCR and Western blot analysis determined that most of these genes are up-regulated in the transition from free-living cercaria to adult worm stage. Immunolocalization experiments and tegument preparations confirm that at least some of the SmCD59-like proteins are surface-localized; however, significant expression was also detected in internal tissues of adult worms. Finally, the involvement of two SmCD59 proteins in complement inhibition was evaluated by three different approaches: (i) a hemolytic assay using recombinant soluble forms expressed in Pichia pastoris and E. coli; (ii) complement-resistance of CHO cells expressing the respective membrane-anchored proteins; and (iii) the complement killing of schistosomula after gene suppression by RNAi. Our data indicated that these proteins are not involved in the regulation of complement activation.

Conclusions

Our results suggest that this group of proteins belongs to the TFPD superfamily. Their expression is associated to intra-host stages, present in the tegument surface, and also in intra-parasite tissues. Three distinct approaches using SmCD59 proteins to inhibit complement strongly suggested that these proteins are not complement inhibitors and their function in schistosomes remains to be determined.

Schistosomes are parasites that reside for many years in the blood stream, demanding efficient mechanisms of evading immune response effectors such as complement deposition. A group of genes similar to human CD59, an important complement inhibitor in mammals, were identified in the schistosome genome. Computer predictions of protein structure indicated substantial similarity of the schistosome proteins and the mammalian CD59 family of proteins, which due to their three-finger-shaped spatial conformation are members of the Three-Finger Protein Domain fold superfamily (TFPD). Members of this family of schistosome proteins were also shown to be expressed predominantly during the mammalian stages when worms are exposed to complement and found to be present at the host-interactive surface of schistosomes. Three different methods were employed to test the possible involvement of these proteins in complement inhibition. Our results strongly suggest that these proteins are not involved in the inhibition of complement and that further studies are needed to establish their functional role(s) in schistosomes.

The schistosome oesophageal gland: initiator of blood processing

BACKGROUND

Although the ultrastructure of the schistosome esophageal gland was described >35 years ago, its role in the processing of ingested blood has never been established. The current study was prompted by our identification of MEG-4.1 expression in the gland and the observation of erythrocyte uncoating in the posterior esophagus.

METHODOLOGY/PRINCIPAL FINDINGS

The salient feature of the posterior esophagus, characterized by confocal and electron microscopy, is the enormous increase in membrane surface area provided by the plate-like extensions and basal invaginations of the lining syncytium, with unique crystalloid vesicles releasing their contents between the plates. The feeding process was shown by video microscopy to be divided into two phases, blood first accumulating in the anterior lumen before passing as a bolus to the posterior. There it streamed around a plug of material revealed by confocal microscopy as tethered leucocytes. These were present in far larger numbers than predicted from the volume of the lumen, and in varying states of damage and destruction. Intact erythrocytes were detected in the anterior esophagus but not observed thereafter, implying that their lysis occurred rapidly as they enter the posterior. Two further genes, MEGs 4.2 and 14, were shown to be expressed exclusively in the esophageal gland. Bioinformatics predicted that MEGs 4.1 and 4.2 possessed a common hydrophobic region with a shared motif, while antibodies to SjMEG-4.1 showed it was bound to leucocytes in the esophageal lumen. It was also predicted that MEGs 4.1 and 14 were heavily O-glycosylated and this was confirmed for the former by 2D-electrophoresis and Western blotting.

CONCLUSIONS/SIGNIFICANCE

The esophageal gland and its products play a central role in the processing of ingested blood. The binding of host antibodies in the esophageal lumen shows that some constituents are antibody targets and could provide a new source of vaccine candidates.

Functional mapping of protein kinase A reveals its importance in adult Schistosoma mansoni motor activity

Cyclic AMP (cAMP)-dependent protein kinase/protein kinase A (PKA) is the major transducer of cAMP signalling in eukaryotic cells. Here, using laser scanning confocal microscopy and 'smart' anti-phospho PKA antibodies that exclusively detect activated PKA, we provide a detailed in situ analysis of PKA signalling in intact adult Schistosoma mansoni, a causative agent of debilitating human intestinal schistosomiasis. In both adult male and female worms, activated PKA was consistently found associated with the tegument, oral and ventral suckers, oesophagus and somatic musculature. In addition, the seminal vesicle and gynaecophoric canal muscles of the male displayed activated PKA whereas in female worms activated PKA localized to the ootype wall, the ovary, and the uterus particularly around eggs during expulsion. Exposure of live worms to the PKA activator forskolin (50 µM) resulted in striking PKA activation in the central and peripheral nervous system including at nerve endings at/near the tegument surface. Such neuronal PKA activation was also observed without forskolin treatment, but only in a single batch of worms. In addition, PKA activation within the central and peripheral nervous systems visibly increased within 15 min of worm-pair separation when compared to that observed in closely coupled worm pairs. Finally, exposure of adult worms to forskolin induced hyperkinesias in a time and dose dependent manner with 100 µM forskolin significantly increasing the frequency of gross worm movements to 5.3 times that of control worms (P≤0.001). Collectively these data are consistent with PKA playing a central part in motor activity and neuronal communication, and possibly interplay between these two systems in S. mansoni. This study, the first to localize a protein kinase when exclusively in an activated state in adult S. mansoni, provides valuable insight into the intricacies of functional protein kinase signalling in the context of whole schistosome physiology.

The functional role of a serotonin transporter in Schistosoma mansoni elucidated through immunolocalization and RNA interference (RNAi)

Serotonin is an important neurotransmitter in both vertebrates and invertebrates. In the parasitic flatworm, Schistosoma mansoni, serotonin stimulates worm movement and potentiates muscle contraction. A specific serotonin transporter (SmSERT) was previously cloned from S. mansoni and characterized in vitro. Here we conduct a first investigation of the native protein in the worm so as to elucidate the biological role of SmSERT and to assess its drug targeting potential. Confocal immunofluorescence studies using specific antibodies determined that SmSERT is expressed predominantly in the nervous system both in adult worms and larvae (schistosomula). SmSERT immunoreactivity was detected in the main nerve cords of the central nervous system and the peripheral nerve plexus of the body wall in adult males and females, in apparent nerve endings of the male tubercles and possibly the male tegument. In the larvae, SmSERT localized mainly to the peripheral nerve plexus of the body wall. Co-localization experiments showed that the pattern of SmSERT expression coincides with that of serotonin itself, suggesting that SmSERT is present in serotonergic neurons. To test whether SmSERT is involved in the motor effects of serotonin, we treated S. mansoni schistosomula with SmSERT blockers or SmSERT-specific short-interfering RNAs (siRNAs) and then recorded larval motility, using a quantitative imaging assay. In both cases, the treatment produced a strongly hyperactive phenotype, corresponding to a ~3-fold increase in larval motility, roughly the same effect as treatment with an excess of exogenous serotonin. The siRNA effect correlated with a ≈50% decrease in expression of the SmSERT when tested by real-time qPCR. To test if SmSERT mediates transport of exogenous serotonin across the tegument, uptake assays were also performed in intact schistosomula treated with SmSERT siRNAs or an irrelevant siRNA. We found a significant but modest decrease (~25%) in serotonin uptake in the siRNA-suppressed larvae when compared to the negative controls. These results suggest that the SmSERT's function is primarily neuromuscular and may also play a secondary role in the uptake of exogenous (host-derived) serotonin.

F-actin accumulates in the vulva of female Strongyloides venezuelensis

Little is known about the actin cytoskeleton architecture in female Strongyloides venezuelensis and thus to investigate the distribution and concentration of actin, female worms were labelled with phalloidin-rhodamine and visualized under confocal microscopy. Our results demonstrate that filamentous actin accumulates in the vulva and the concentration of F-actin at this site suggests its important role, especially during oviposition, in the life cycle of S. venezuelensis.

The cell biology of schistosomes: a window on the evolution of the early metazoa

This review of schistosome cell biology has a dual purpose; its intent is to alert two separate research communities to the activities of the other. Schistosomes are by far and away the best-characterised platyhelminths, due to their medical and economic importance, but seem to be almost totally ignored by researchers on the free-living lower metazoans. Equally, in their enthusiasm for the parasitic way of life, schistosome researchers seldom pay attention to the work on free-living animals that could inform their molecular investigations. The publication of transcriptomes and/or genomes for Schistosoma mansoni and Schistosoma japonicum, the sponge Archimedon, the cnidarians Nematostella and Hydra and the planarian Schmidtea provide the raw material for comparisons. Apart from interrogation of the databases for molecular similarities, there have been differences in technical approach to these lower metazoans; widespread application of whole mount in situ hybridisation to Schmidtea contrasts with the application of targeted proteomics to schistosomes. Using schistosome cell biology as the template, the key topics of cell adhesion, development, signalling pathways, nerve and muscle, and epithelia, are reviewed, where possible interspersing comparisons with the sponge, cnidarian and planarian data. The biggest jump in the evolution of cellular capabilities appears to be in the transition from a diploblast to triploblast level of organisation associated with development of a mobile and plastic body form.

A novel G protein-coupled receptor of Schistosoma mansoni (SmGPR-3) is activated by dopamine and is widely expressed in the nervous system

Schistosomes have a well developed nervous system that coordinates virtually every activity of the parasite and therefore is considered to be a promising target for chemotherapeutic intervention. Neurotransmitter receptors, in particular those involved in neuromuscular control, are proven drug targets in other helminths but very few of these receptors have been identified in schistosomes and little is known about their roles in the biology of the worm. Here we describe a novel Schistosoma mansoni G protein-coupled receptor (named SmGPR-3) that was cloned, expressed heterologously and shown to be activated by dopamine, a well established neurotransmitter of the schistosome nervous system. SmGPR-3 belongs to a new clade of "orphan" amine-like receptors that exist in schistosomes but not the mammalian host. Further analysis of the recombinant protein showed that SmGPR-3 can also be activated by other catecholamines, including the dopamine metabolite, epinine, and it has an unusual antagonist profile when compared to mammalian receptors. Confocal immunofluorescence experiments using a specific peptide antibody showed that SmGPR-3 is abundantly expressed in the nervous system of schistosomes, particularly in the main nerve cords and the peripheral innervation of the body wall muscles. In addition, we show that dopamine, epinine and other dopaminergic agents have strong effects on the motility of larval schistosomes in culture. Together, the results suggest that SmGPR-3 is an important neuronal receptor and is probably involved in the control of motor activity in schistosomes. We have conducted a first analysis of the structure of SmGPR-3 by means of homology modeling and virtual ligand-docking simulations. This investigation has identified potentially important differences between SmGPR-3 and host dopamine receptors that could be exploited to develop new, parasite-selective anti-schistosomal drugs.

Organization of the nervous system in Opisthorchis viverrini investigated by histochemical and immunohistochemical study

The structure and organization of the nervous system has been documented for various helminth parasites. However, the neuroanatomy of the carcinogenic liver fluke, Opisthorchis viverrini has not been described. This study therefore investigated the organization of the nervous system of this fluke using cholinesterase activity, aminergic and peptidergic (FMRFamide-like peptides) immunostaining to tag major neural elements. The nervous system, as detected by acetylcholinesterase (AchE) reaction, was similar in newly excysted metacercariae, migrating juveniles and adult parasites. In these stages, there were three pairs (dorsal, ventral and lateral) of bilaterally symmetrical longitudinal nerve cords and two cerebral ganglia. The ventral nerve cords and the cerebral ganglia were well-developed and exhibited strong AchE reactivity, as well as aminergic and FMRFamide-like immunoreactivity. Numerous immunoreactive nerve cell bodies were observed around the inner surface of the ventral sucker. Fine FMRFamide-like peptides immunopositive nerve fiber was rarely observed. Overall, the organization of the nervous system of O. viverrini is similar to other trematodes.

Schistosoma mansoni specimens first described by Pirajá da Silva in Brazil (1908) re-examined by confocal laser scanning microscopy

INTRODUCTION

Pirajá da Silva made a seminal contribution to helminthology by demonstrating both schistosome eggs in feces of patients from the State of Bahia and the morphology of Schistosoma mansoni adult worms.

METHODS

In this study, a microscopic investigation of the whole-mounts deposited at the Helminthological Collection of the Oswaldo Cruz Institute is presented. Confocal laser scanning microscopy was used as the main investigation technique.

RESULTS

At the anterior end of the adult male, suckers with well-developed musculature and germinative cells inside the testicular lobes were observed, as well as spines located in the mid region of the male gynecophoric canal. Tegumental tubercles and transversal and longitudinal muscular bundles were observed at the dorsal surface. The female reproductive system presented a uterus lacking eggs and an elongated ovary with germinative cells. The vitellaria were restricted to the extreme posterior end of each female connected to a short vitelline duct.

CONCLUSIONS

The results reported in this study demonstrate that the characteristic studied here are similar to those previously reported, using fresh worms. Moreover, this study also highlights the importance of deposits of specimens in helminthological collections, which further permit revisiting whole-mounts in such institutions.

An atlas for Schistosoma mansoni organs and life-cycle stages using cell type-specific markers and confocal microscopy

Schistosomiasis (bilharzia) is a tropical disease caused by trematode parasites (Schistosoma) that affects hundreds of millions of people in the developing world. Currently only a single drug (praziquantel) is available to treat this disease, highlighting the importance of developing new techniques to study Schistosoma. While molecular advances, including RNA interference and the availability of complete genome sequences for two Schistosoma species, will help to revolutionize studies of these animals, an array of tools for visualizing the consequences of experimental perturbations on tissue integrity and development needs to be made widely available. To this end, we screened a battery of commercially available stains, antibodies and fluorescently labeled lectins, many of which have not been described previously for analyzing schistosomes, for their ability to label various cell and tissue types in the cercarial stage of S. mansoni. This analysis uncovered more than 20 new markers that label most cercarial tissues, including the tegument, the musculature, the protonephridia, the secretory system and the nervous system. Using these markers we present a high-resolution visual depiction of cercarial anatomy. Examining the effectiveness of a subset of these markers in S. mansoni adults and miracidia, we demonstrate the value of these tools for labeling tissues in a variety of life-cycle stages. The methodologies described here will facilitate functional analyses aimed at understanding fundamental biological processes in these parasites.

Schistosomes are parasitic flatworms that infect hundreds of millions of people worldwide. The development of genomic resources and recent application of functional genomic tools (e.g., global gene expression studies, inhibition of gene expression by RNA interference, and transgenesis) hold the promise of revolutionizing the study of schistosome biology. These advances necessitate the introduction of molecular markers for examining the consequences of manipulating schistosome genes. In this manuscript we report the use of several cell type-specific markers and confocal microscopy for visualizing various schistosome tissues in a variety of life-cycle stages. Our analysis provides an atlas of the major organ systems in three different life-cycle stages in these important parasites. The tools and methodologies reported here are widely available and can be readily adopted by researchers interested in more detailed studies of these organisms. We anticipate that these resources will be particularly useful for detailed phenotypic characterization following gene inhibition or over-expression studies.

Glutamate-mediated signaling in Schistosoma mansoni: a novel glutamate receptor is expressed in neurons and the female reproductive tract

l-Glutamate is a major neurotransmitter of both vertebrates and invertebrates. Earlier studies have shown that glutamate stimulates neuromuscular activity in the bloodfluke, Schistosoma mansoni, but its mode of action is unknown. Here we describe a novel glutamate receptor in S. mansoni (SmGluR), the first of its kind to be identified in a parasitic flatworm. SmGluR belongs to the G protein-coupled receptor (GPCR) superfamily and is distantly related to metabotropic glutamate receptors from other species. The full-length receptor cDNA was cloned, stably expressed in HEK-293 cells and shown to be activated by glutamate, whereas aspartate and the glutamate derivative, gamma-aminobutyric acid (GABA) had no significant effect. Among the classical (mammalian) agonists and antagonists tested, only LY341495 was able to interact with the schistosome receptor, suggesting that the pharmacological profile of SmGluR is substantially different from that of receptors in the host. The presence of SmGluR in the parasite was verified by immunoprecipitation and Western blot analyses, using a specific peptide antibody. Confocal immunolocalization studies revealed that SmGluR is strongly expressed in the nervous system of adult worms and larvae. In the adults, the receptor was detected in the longitudinal nerve cords and cerebral commissures, as well as the peripheral nerve fibers and plexuses innervating the acetabulum and the somatic musculature. Outside the nervous system, SmGluR was detected along the length of the female reproductive system, including the oviduct, ootype and the uterus. A comparative expression analysis at the RNA level revealed that SmGluR is expressed at about the same level in cercaria and adult stages, as determined by quantitative reverse-transcription PCR. The results identify SmGluR as an important neuronal receptor and provide the first molecular evidence for a glutamate signaling system in schistosomes.

Trichobilharzia regenti (Digenea: Schistosomatidae): changes of body wall musculature during the development from miracidium to adult worm

Trichobilharzia regenti (Schistosomatidae, Digenea), a parasite of birds, exhibits a unique strategy among schistosomes, having affinity to the nervous system of vertebrate hosts. Migration of parasitic stages within hosts and/or swimming of non-parasitic larvae in water environment depend on the action of body wall muscles which were studied with confocal and electron microscopy. In all stages, body wall musculature is comprised of differently organized circular and longitudinal muscles. During the development, an extensive change of musculature characteristics and/or formation of new muscle structures were recorded; cercariae, schistosomula and adult worms produce additional underlying diagonal muscle fibers and inner plexus of radial musculature. Substantial changes of the outer environment during penetration of a host (osmotic values of water vs. host tissues) are accompanied by surface transformation of miracidia/mother sporocysts and cercariae/schistosomula. Contrary to that, changes of body musculature in these stages are characterized only by growth and re-organization of existing structures, and never by formation of new components of body musculature. Future studies in this field may contribute to a better knowledge of morphology and function of trematode muscles, including those of schistosomes that are important pathogens of humans and animals.

Myogenesis in two polyclad platyhelminths with indirect development, Pseudoceros canadensis and Stylostomum sanjuania

Myogenesis of two representatives of Platyhelminthes, Stylostomum sanjuania and Pseudoceros canadensis, was followed from egg deposition until well-differentiated free-swimming larval stages, using F-actin staining and confocal laserscanning microscopy. Zonulae adhaerentes are the only structures to stain before 50% of development between egg deposition and hatching in S. sanjuania, and before 67% of development in P. canadenis. Subsequently, irregular fibers appear in the embryo, followed by a helicoid muscle close to the apical pole. Three longitudinal muscle pairs form, of which the dorsal pair remains more pronounced than the others. Gradually, new muscles form by branching or from double-stranded muscle zones adjacent to existing muscles. This results in an elaborate muscular bodywall that consists of a single helicoid muscle as well as multiple circular and longitudinal muscles. Diverse retractor muscles insert at the sphincter muscles around the stomodeum. The overall arrangement and formation mode of the larval musculature appears very similar in both species, although only P. canadensis has a primary circular muscle posterior to the helicoid muscle. Muscle formation in the apical region of the embryo precedes that at the abapical pole and the primary longitudinal muscles form slightly later than the primary circular muscles. Myogenesis and larval myoanatomy appears highly conserved among polyclad flatworms, but differs significantly from that of other trochozoan clades. Our data suggest that the larval muscular ground pattern of polyclad larvae comprises a bodywall consisting of a helicoid muscle, circular and longitudinal muscles, several retractor muscles, and sphincter muscles around the stomodeum.

Protein variation in blood-dwelling schistosome worms generated by differential splicing of micro-exon gene transcripts

Schistosoma mansoni is a well-adapted blood-dwelling parasitic helminth, persisting for decades in its human host despite being continually exposed to potential immune attack. Here, we describe in detail micro-exon genes (MEG) in S. mansoni, some present in multiple copies, which represent a novel molecular system for creating protein variation through the alternate splicing of short (< or =36 bp) symmetric exons organized in tandem. Analysis of three closely related copies of one MEG family allowed us to trace several evolutionary events and propose a mechanism for micro-exon generation and diversification. Microarray experiments show that the majority of MEGs are up-regulated in life cycle stages associated with establishment in the mammalian host after skin penetration. Sequencing of RT-PCR products allowed the description of several alternate splice forms of micro-exon genes, highlighting the potential use of these transcripts to generate a complex pool of protein variants. We obtained direct evidence for the existence of such pools by proteomic analysis of secretions from migrating schistosomula and mature eggs. Whole-mount in situ hybridization and immunolocalization showed that MEG transcripts and proteins were restricted to glands or epithelia exposed to the external environment. The ability of schistosomes to produce a complex pool of variant proteins aligns them with the other major groups of blood parasites, but using a completely different mechanism. We believe that our data open a new chapter in the study of immune evasion by schistosomes, and their ability to generate variant proteins could represent a significant obstacle to vaccine development.

Investigation of a dopamine receptor in Schistosoma mansoni: functional studies and immunolocalization

A dopamine receptor (SmD2) was cloned from adult Schistosoma mansoni. The receptor has the classical heptahelical topology of class A (rhodopsin-like) G protein-coupled receptors (GPCR) and shares sequence homology with D2-like receptors from other species. The full length SmD2 cDNA was expressed in the yeast Saccharomyces cerevisiae and mammalian HEK293 cells. Functional assays in both expression systems revealed that SmD2 was responsive to dopamine in a dose-dependent manner, whereas other structurally related amines had no effect. Activation of SmD2 in mammalian cells caused an elevation in intracellular cAMP but not calcium, suggesting that the receptor coupled to Gs and the stimulation of adenylate cyclase. Pharmacological studies showed that the S. mansoni dopamine receptor was inhibited by apomorphine, a classical dopamine agonist, as well as known dopaminergic antagonists, including chlorpromazine, spiperone and haloperidol. SmD2 immunoreactivity was detected in membrane protein fractions of S. mansoni cercaria, in vitro transformed schistosomula and adult parasites, using a specific peptide antibody. When tested by confocal immunofluorescence, SmD2 was detected in the subtegumental somatic musculature and acetabulum of all larval stages tested. In the adults, SmD2 was enriched in the somatic muscles and, to a lesser extent, the muscular lining of the caecum. The results suggest that SmD2 is an important component of the neuromuscular system in schistosomes.

Schistosoma mansoni P-glycoprotein levels increase in response to praziquantel exposure and correlate with reduced praziquantel susceptibility

One potential physiological target for new antischistosomals is the parasite's system for excretion of wastes and xenobiotics. P-glycoprotein (Pgp), a member of the ATP-binding-cassette superfamily of proteins, is an ATP-dependent efflux pump involved in transport of toxins and xenobiotics from cells. In vertebrates, increased expression of Pgp is associated with multidrug resistance in tumor cells. Pgp may also play a role in drug resistance in helminths. In this report, we examine the relationship between praziquantel (PZQ), the current drug of choice against schistosomiasis, and Pgp expression in Schistosoma mansoni. We show that levels of RNA for SMDR2, a Pgp homolog from S. mansoni, increase transiently in adult male worms following exposure to sub-lethal concentrations (100-500 nM) of PZQ. A corresponding, though delayed, increase in anti-Pgp immunoreactive protein expression occurs in adult males following exposure to PZQ. The level of anti-Pgp immunoreactivity in particular regions of adult worms also increases in response to PZQ. Adult worms from an Egyptian S. mansoni isolate with reduced sensitivity to PZQ express increased levels of SMDR2 RNA and anti-Pgp-immunoreactive protein, perhaps indicating a role for multidrug resistance proteins in development or maintenance of PZQ resistance.

Developmental expression analysis and immunolocalization of a biogenic amine receptor in Schistosoma mansoni

A Schistosoma mansoni G-protein coupled receptor (SmGPCR) was previously cloned and shown to be activated by the biogenic amine, histamine. Here we report a first investigation of the receptor's subunit organization, tissue distribution and expression levels in different stages of the parasite. A polyclonal antibody was produced in rabbits against the recombinant third intracellular loop (il3) of SmGPCR. Western blot studies of the native receptor and recombinant protein expressed in HEK293 cells showed that SmGPCR exists both as a monomer (65 kDa) and an apparent dimer of approximately 130 kDa These species were verified by immunoprecipitation of SmGPCR from S. mansoni extracts, using antibody that was covalently attached to agarose beads. Further investigation determined that the SmGPCR dimer was resistant to treatment with various detergents, 4 M urea and 0.1 M DTT but could be made to dissociate at acidic pH, suggesting the dimer is non-covalent in nature. Confocal immunofluorescence studies revealed significant SmGPCR immunoreactivity in sporocysts, schistosomula and adult worms but not miracidia. SmGPCR was found to be most widely expressed in the schistosomula, particularly the tegument, the subtegumental musculature and the acetabulum. In the adult stage we detected SmGPCR immunofluorescence mainly in the tubercles of male worms and, to a lesser extent, the body wall musculature. Localization in sporocysts was mainly confined to the tegument and cells within parenchymal matrices. A real-time quantitative reverse-transcription PCR analysis revealed that SmGPCR is upregulated at the mRNA level in the parasitic stages compared to the free-living miracidium and cercariae, and it is particularly elevated during early sporocyst and schistosomula development. The results identify SmGPCR as an important parasite receptor with potential functions in muscle and the tegument of S. mansoni.

Neuropeptide signalling systems in flatworms

Two distinct families of neuropeptides are known to endow platyhelminth nervous systems - the FMRFamide-like peptides (FLPs) and the neuropeptide Fs (NPFs). Flatworm FLPs are structurally simple, each 4-6 amino acids in length with a carboxy terminal aromatic-hydrophobic-Arg-Phe-amide motif. Thus far, four distinct flatworm FLPs have been characterized, with only one of these from a parasite. They have a widespread distribution within the central and peripheral nervous system of every flatworm examined, including neurones serving the attachment organs, the somatic musculature and the reproductive system. The only physiological role that has been identified for flatworm FLPs is myoexcitation. Flatworm NPFs are believed to be invertebrate homologues of the vertebrate neuropeptide Y (NPY) family of peptides. Flatworm NPFs are 36-39 amino acids in length and are characterized by a caboxy terminal GRPRFamide signature and conserved tyrosine residues at positions 10 and 17 from the carboxy terminal. Like FLPs, NPF occurs throughout flatworm nervous systems, although less is known about its biological role. While there is some evidence for a myoexcitatory action in cestodes and flukes, more compelling physiological data indicate that flatworm NPF inhibits cAMP levels in a manner that is characteristic of NPY action in vertebrates. The widespread expression of these neuropeptides in flatworm parasites highlights the potential of these signalling systems to yield new targets for novel anthelmintics. Although platyhelminth FLP and NPF receptors await identification, other molecules that play pivotal roles in neuropeptide signalling have been uncovered. These enzymes, involved in the biosynthesis and processing of flatworm neuropeptides, have recently been described and offer other distinct and attractive targets for therapeutic interference.

Towards tissue specific transcriptomics and expression pattern analysis in schistosomes using laser microdissection microscopy

One difficulty facing post-genomic analyses of schistosomes is the limited data on sites of expression of many gene products expressed by the parasites in their hosts. The potential for use of laser microdissection microscopy as a preparative technique for transcriptional and proteomic profiling is reviewed. This technique allows tissues to be dissected for subsequent molecular and protein analysis. The method is reviewed in the light of the acoelomate triploblastic nature of tissue organisation in the parasite.