Organization of the musculature of schistosome cercariae

Neuromuscular organization and haptoral armament of Polyclithrum ponticum (Monogenea: Gyrodactylidae)

Most gyrodactylids have a haptor armed with a pair of hamuli, two connecting bars and 16 marginal hooks. In some gyrodactylids, however, the haptor is disc-shaped and reinforced by additional sclerites. The genus Polyclithrum has arguably the most elaborate haptor in this group. This study aimed to gain better understanding of the anatomy of Polyclithrum by examining neuromusculature and haptoral armament of Polyclithrum ponticum, a species parasitizing Mugil cephalus in the Black Sea, with emphasis on haptoral sclerites and musculature in connection with host-attachment mechanisms. Musculature was stained by phalloidin, the nervous system by anti-serotonin and anti-FMRFamide antibodies, and haptoral sclerites were visualized in reflected light. The study provided new information on sclerites: in addition to previously described supplementary sclerites (A1-6), ear-shaped sclerites (ESSs) and two paired groups of ribs, reflected light revealed a rod-shaped process on the ESSs and a pair of small posterior sclerites. The sclerites were shown to be operated by 16 muscles, the most prominent of which were two transverse muscles connecting the hamular roots, three muscles attached to sclerite A2, the muscle fibres of anterior ribs and a set of extrinsic muscles. The nervous system consists of a pair of cerebral ganglia connected by a commissure and three pairs of nerve cords that unite in the haptor to form a loop between the opposite cords. The arrangement of sclerites and muscles suggests that Polyclithrum initiates the attachment by clamping a host's surface with longitudinally folded haptor and then secures its position with marginal hooks.

Proteomics Investigations of Potential Protein Biomarkers in Sera of Rabbits Infected With Schistosoma japonicum

Schistosomiasis is a chronic parasitic disease that continues to be a pressing public health problem in many developing countries. The primary pathological damage from the disease is granuloma and fibrosis caused by egg aggregation, and early treatment can effectively prevent the occurrence of liver fibrosis. Therefore, it is very important to identify biomarkers that can be used for early diagnosis of Schistosoma japonicum infection. In this study, a label-free proteomics method was performed to observe the alteration of proteins before infection, 1 and 6 weeks after infection, and 5 and 7 weeks after treatment. A total of 10 proteins derived from S. japonicum and 242 host-derived proteins were identified and quantified as significantly changed. Temporal analysis was carried out to further analyze potential biomarkers with coherent changes during infection and treatment. The results revealed biological process changes in serum proteins compared to infection and treatment groups, which implicated receptor-mediated endocytosis, inflammatory response, and acute-phase response such as mannan-binding lectin serine peptidase 1, immunoglobulin, and collagen. These findings offer guidance for the in-depth analysis of potential biomarkers of schistosomiasis, host protein, and early diagnosis of S. japonicum and its pathogenesis. Data are available via ProteomeXchange with identifier PXD029635.

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.

Morphological framework for attachment and locomotion in several Digenea of the families Microphallidae and Heterophyidae

Digenea usually use ventral sucker for sustainable attachment within intestine of their definitive vertebrate host. However, if the ventral sucker is absent or poorly developed, the means of attachment are unclear. We investigated attachment and locomotion in such digeneans: three species of the family Microphallidae (Microphallus piriformes, M. pygmaeus, and Levinseniella brachysoma) and two species of the family Heterophyidae (Cryptocotyle concava and C. lingua). Their tegumental spines and musculature were described with use of fluorescent actin staining, confocal microscopy, and scanning electron microscopy. Locomotion of living worms was observed and recorded. Wide serrated tegumental spines probably play the main role in attachment. Their firm contact with the host mucosa may be provided by the action of the ventral concavity-when the entire body or its part acts as a sucker. Dorsoventral muscle bundles act like radial musculature of the sucker generating negative pressure in the ventral concavity. The solid layer of longitudinal muscle fibers on the ventral body surface provides support for the bottom of the ventral concavity. In all microphallids, a U-shaped arrangement of body wall musculature (mostly originating from longitudinal fibers) outlines posterior part of the ventral concavity ridge. In all the studied species, tegumental spines, body wall musculature, and dorsoventral muscle bundles are better developed in the forebody which moves more actively than the hindbody.

iTRAQ-Based Comparative Proteomic Analysis of Adult Schistosoma japonicum from Water Buffalo and Yellow Cattle

Schistosomiasis japonicum is one of the most severe zoonotic diseases in China. Water buffalo and yellow cattle are important reservoir hosts and the main transmission sources of Schistosoma japonicum in endemic areas. The susceptibility of these two hosts to schistosome infection is different, as water buffaloes are less susceptible to S. japonicum than yellow cattle. In this study, iTRAQ-coupled LC-MS/MS was applied to compare the protein expression profiles of adult schistosomes recovered from water buffalo with those of yellow cattle. A total of 131 differentially expressed proteins (DEPs) were identified, including 46 upregulated proteins and 85 downregulated proteins. The iTRAQ results were confirmed by Western blotting and quantitative real-time PCR. Further analysis indicated that these DEPs were primarily involved in protein synthesis, transcriptional regulation, protein proteolysis, cytoskeletal structure and oxidative stress response processes. The results revealed that some of the differential expression molecules may affect the development and survival of schistosomes in these two natural hosts. Of note, this study provides useful information for understanding the interplay between schistosomes and their final hosts.

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.

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.

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.

Proteomics analysis of differentially expressed proteins in schistosomula and adult worms of Schistosoma japonicum

Schistosoma japonicum has a complex lifecycle and exhibits dramatic changes in its biology and morphology at different developmental stages. The schistosomulum and adult worm are two stages of this complex lifecycle and differentially expressed proteins in these two stages should be important for survival, development, and reproduction of the parasites. In this study, soluble and hydrophobic proteins were extracted from eggs, cercariae, schistosomula (8d and 19d), and male and female adult worms (42d) of Schistosoma japonicum, and separated by two-dimensional (2D) gel electrophoresis. A total of 1376±52, 928±61, 1465±41, 1230±30, 904±34, and 1080±26 soluble proteins and 1437±44, 845±53, 986±22, 1145±35, 1066±39, and 1123±45 hydrophobic proteins were separated from eggs, cercariae, schistosomula (8d and 19d), and male and female adult worms (42d), respectively. There were 65±14, 27±7, 37±17 and 48±9 soluble protein spots only present in schistosomula (8d and/or 19d) and adult schistosomes (male and/or female). We successfully identified 22 spots from schistosomula and 11 spots from adult schistosomes by mass spectrometry. Quantitative real-time RT-PCR was used to examine six differentially expressed proteins at the transcription level. These proteins only found in schistosomula or adults stage by the proteomics analysis were highly expressed in the corresponding stage at mRNA level. Bioinformatics analysis showed that the differentially expressed proteins from schistosomula were mainly involved in cellular metabolic processes, stress response and developmental process. Differentially expressed proteins from adult schistosomes were involved with gene expression and protein metabolism processes. The results of this study might provide new insights to stimulate further exploration of the mechanism of growth and development in schistosomes and help identify candidate molecules for developing new vaccines or drugs.

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.

Identification and characterization of a Mef2 transcriptional activator in schistosome parasites

Myocyte enhancer factor 2 protein (Mef2) is an evolutionarily conserved activator of transcription that is critical to induce and control complex processes in myogenesis and neurogenesis in vertebrates and insects, and osteogenesis in vertebrates. In Drosophila, Mef2 null mutants are unable to produce differentiated muscle cells, and in vertebrates, Mef2 mutants are embryonic lethal. Schistosome worms are responsible for over 200 million cases of schistosomiasis globally, but little is known about early development of schistosome parasites after infecting a vertebrate host. Understanding basic schistosome development could be crucial to delineating potential drug targets. Here, we identify and characterize Mef2 from the schistosome worm Schistosoma mansoni (SmMef2). We initially identified SmMef2 as a homolog to the yeast Mef2 homolog, Resistance to Lethality of MKK1P386 overexpression (Rlm1), and we show that SmMef2 is homologous to conserved Mef2 family proteins. Using a genetics approach, we demonstrate that SmMef2 is a transactivator that can induce transcription of four separate heterologous reporter genes by yeast one-hybrid analysis. We also show that Mef2 is expressed during several stages of schistosome development by quantitative PCR and that it can bind to conserved Mef2 DNA consensus binding sequences.

Schistosome parasites infect more than 200 million people worldwide and cause human schistosomiasis. Free-swimming schistosome larvae are highly mobile and invade and penetrate the host's skin to perpetuate their lifecycle in their human host, growing from 90–215 micrometers in length as a schistosomulum to a 7–20 millimeter long adult worm. Few molecular pathways have been identified in schistosome worms that are important for parasite early development. The myocyte enhancer factor protein 2 is a major regulator of muscle and nerve development in mammals and insects and is highly conserved from bread yeast to vertebrates. Here we identify and characterize the Mef2 activator from parasitic schistosome worms, the first described in any parasitic worm, and delineation of its function may be important to further understanding the basic biology of schistosome early development. Additionally, since schistosomes developed early evolutionarily, an investigation of schistosome Mef2 regulatory mechanisms could lead to a greater understanding of the development of early muscle and neurogenic development in animals.

Proteomic analysis of human skin treated with larval schistosome peptidases reveals distinct invasion strategies among species of blood flukes

Background

Skin invasion is the initial step in infection of the human host by schistosome blood flukes. Schistosome larvae have the remarkable ability to overcome the physical and biochemical barriers present in skin in the absence of any mechanical trauma. While a serine peptidase with activity against insoluble elastin appears to be essential for this process in one species of schistosomes, Schistosoma mansoni, it is unknown whether other schistosome species use the same peptidase to facilitate entry into their hosts.

Methods

Recent genome sequencing projects, together with a number of biochemical studies, identified alternative peptidases that Schistosoma japonicum or Trichobilharzia regenti could use to facilitate migration through skin. In this study, we used comparative proteomic analysis of human skin treated with purified cercarial elastase, the known invasive peptidase of S. mansoni, or S. mansoni cathespin B2, a close homolog of the putative invasive peptidase of S. japonicum, to identify substrates of either peptidase. Select skin proteins were then confirmed as substrates by in vitro digestion assays.

Conclusions

This study demonstrates that an S. mansoni ortholog of the candidate invasive peptidase of S. japonicum and T. regenti, cathepsin B2, is capable of efficiently cleaving many of the same host skin substrates as the invasive serine peptidase of S. mansoni, cercarial elastase. At the same time, identification of unique substrates and the broader species specificity of cathepsin B2 suggest that the cercarial elastase gene family amplified as an adaptation of schistosomes to human hosts.

Schistosome parasites are a major cause of disease in the developing world, but the mechanism by which these parasites first infect their host has been studied at the molecular level only for S. mansoni. In this paper, we have mined recent genome annotations of S. mansoni and S. japonicum, a zoonotic schistosome species, to identify differential expansion of peptidase gene families that may be involved in parasite invasion and subsequent migration through skin. Having identified a serine peptidase gene family in S. mansoni and a cysteine peptidase gene family in S. japonicum, we then used a comparative proteomic approach to identify potential substrates of representative members of both classes of enzymes from S. mansoni in human skin. The results of this study suggest that while these species evolved to use different classes of peptidases in host invasion, both are capable of cleaving components of the epidermis and dermal extracellular matrix, as well as proteins involved in the host immune response against the migrating parasite.

Proteomic analysis of schistosoma japonicum schistosomulum proteins that are differentially expressed among hosts differing in their susceptibility to the infection

Schistosomiasis is a tropical, parasitic disease affecting humans and several animal species. The aim of this study was to identify proteins involved in the growth and survival of the parasitic forms inside a host. Schistosomula of Schistosoma japonicum were isolated from three different hosts: the susceptible BALB/c mice; the Wistar rats, which have a considerably lower susceptibility; and the resistant reed vole, Microtus fortis. Soluble proteins of the schistosomula collected from the above three hosts 10 days postinfection were subjected to two-dimensional difference gel electrophoresis. Comparative proteomic analyses revealed that 39, 21, and 25 protein spots were significantly differentially expressed between schistosomula from mice and rats, mice and reed voles, or rats and reed voles, respectively (ANCOVA, p < 0.05). Further, the protein spots were identified by liquid chromatography-tandem MS. Bioinformatics analysis showed that the differentially expressed proteins were essentially those involved in the metabolism of proteins, ribonucleotides, or carbohydrates, or in stress response or cellular movement. This study represents the first attempt at profiling S. japonicum living in different states and provides a basis for a better understanding of the molecular mechanisms in the development and survival of S. japonicum in different host environments.

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.

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.

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 japonicum: proteomics analysis of differentially expressed proteins from ultraviolet-attenuated cercariae compared to normal cercariae

Schistosomiasis is considered the most important human helminthiasis in terms of morbidity and mortality. In this study, comparative soluble proteomic analysis of normal cercariae and ultraviolet-irradiated attenuated cercariae (UVAC) from Schistosoma japonicum were carried out in view of the high efficiency of irradiation-attenuated cercariae vaccine. The results revealed that some proteins showed significant differential expression in the parasite after treatment with ultraviolet light. Total 20 protein spots were identified by mass spectrometry, corresponded to five groups according to their functions in the main that were structural and motor proteins (actin, et al.), energy metabolism associated enzymes (glyceraldehydes-3-phosphage dehydrogenase, et al.), signaling transduction pathway-associated molecules (14-3-3 protein, et al.), heat shock protein families (HSP 70 family, et al.), and other functional proteins (20S proteasome). Furthermore, our results indicated that the differential expression of the proteins by ultraviolet irradiation may be, at least partially, acquired by regulating the mRNA levels of corresponding proteins. These results may provide new clues for further exploring the mechanism of protective immunity induced by UVAC and may shed some light on the development of vaccines against schistosomiasis.

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.

The distribution of motor proteins in the muscles and flame cells of the Schistosoma mansoni miracidium and primary sporocyst

Schistosoma mansoni eggs, miracidia and primary sporocysts were labelled with phalloidin-rhodamine to visualize filamentous actin structures. Analysis of these forms by confocal fluorescence microscopy revealed the presence of previously well-defined circular and longitudinal muscle layers. Besides these muscular layers that sustain and provide motility to these parasite forms, we found in these 3 consecutive developmental stages of the parasite previously unidentified actin-rich tubular structures. In the 3 forms, 4 actin-rich tubules could be observed by optical sectioning underneath the well-developed muscle layers. The tubules appear in pairs, transversal to the length of the parasite, and located towards the extremities. By using an anti-flame cell specific antibody we confirmed that the tubules co-localize with flame cells and also determined that the tubule core is filled with microtubules. The additional presence of myosin in these tubules strongly suggests that they are contractile structures.

The musculature and associated innervation of adult and intramolluscan stages of Echinostoma caproni (Trematoda) visualised by confocal microscopy

Gross anatomy of muscle and sensory/motor innervation of adult and intramolluscan developmental stages of Echinostoma caproni have been investigated to ascertain the organisation and the functional correlates of any stage-specific patterns of staining. Using indirect immunocytochemistry to demonstrate neuroactive substances and the phalloidin-fluorescence technique for staining myofibril F-actin, the muscle systems and aminergic and peptidergic innervation of daughter rediae, cercariae, metacercariae, and pre- and post-ovigerous adults were examined and compared using confocal scanning laser microscopy. A complex arrangement of specific muscle fibre systems occurs within the body wall (composed of circular, longitudinal and diagonal fibres), suckers (radial, equatorial, meridional), pharynx (radial, circular), gut caeca (mainly circular), cercarial tail (circular, pseudo-striated longitudinal), and ducts of the reproductive system (circular, longitudinal), presumed to serve locomotor, adhesive, alimentary and reproductive functions. Immunostaining for serotonin (5-HT) and FMRFamide-related peptides (FaRPs) was evident throughout the central (CNS) and peripheral (PNS) nervous systems of all stages, and use of dual-labelling techniques demonstrated separate neuronal pathways for 5-HT and FaRP in both CNS and PNS. FaRP expression in the innervation of the ootype wall was demonstrated only in post-ovigerous worms and not in pre-ovigerous worms, suggesting an involvement of FaRP neuropeptides in the process of egg assembly. Comparison of the present findings with those recorded for other digeneans suggests that muscle organisation and innervation patterns in trematodes are highly conserved.

Flatworm nerve–muscle: structural and functional analysis

Platyhelminthes occupy a unique position in nerve–muscle evolution, being the most primitive of metazoan phyla. Essentially, their nervous system consists of an archaic brain and associated pairs of longitudinal nerve cords cross-linked as an orthogon by transverse commissures. Confocal imaging reveals that these central nervous system elements are in continuity with an array of peripheral nerve plexuses which innervate a well-differentiated grid work of somatic muscle as well as a complexity of myofibres associated with organs of attachment, feeding, and reproduction. Electrophysiological studies of flatworm muscles have exposed a diversity of voltage-activated ion channels that influence muscle contractile events. Neuronal cell types are mainly multi- and bi-polar and highly secretory in nature, producing a heterogeneity of vesicular inclusions whose contents have been identified cytochemically to include all three major types of cholinergic, aminergic, and peptidergic messenger molecules. A landmark discovery in flatworm neuro biology was the biochemical isolation and amino acid sequencing of two groups of native neuropeptides: neuro peptide F and FMRFamide-related peptides (FaRPs). Both families of neuropeptide are abundant and broadly distributed in platyhelminths, occurring in neuronal vesicles in representatives of all major flatworm taxa. Dual localization studies have revealed that peptidergic and cholinergic substances occupy neuronal sets separate from those of serotoninergic components. The physiological actions of neuronal messengers in flatworms are beginning to be established, and where examined, FaRPs and 5-HT are myoexcitatory, while cholinomimetic substances are generally inhibitory. There is immunocytochemical evidence that FaRPs and 5-HT have a regulatory role in the mechanism of egg assembly. Use of muscle strips and (or) muscle fibres from free-living and parasitic flatworms has provided baseline information to indicate that muscle responses to FaRPs are mediated by a G-protein-coupled receptor, and that the signal transduction pathway for contraction involves the second messengers cAMP and protein kinase C.

Comparative morphology of the body wall in flatworms (Platyhelminthes)

The soft-bodied nature of the platyhelminths is due largely to the structure of the body wall and its lack of sclerotic elements such as cuticle. Free-living members, i.e., most turbellarians, show considerable variety, but the basic form of the body wall comprises a simple ciliated epithelium overlying a network of muscles. We illustrate this body wall structure in a representative typhloplanoid rhabditophoran and discuss variations in representatives of the Acoela, Catenulida, and other free-living rhabditophorans. The major parasitic groups of platyhelminths, the rhabditophoran Neodermata, follow a developmental pattern that replaces a similar ciliated epidermis in a larval stage with a specialized epidermis called a neodermis, which is assumed to be key to their success as parasites. This neodermis consists of a syncytium that covers the body in a continuous sheet connected to perikarya that lie below the body wall musculature. The neodermis can be seen as a special adaptation of a developmental mechanism common to all platyhelminths, in which epidermal growth and renewal are accomplished by replacement cells originating beneath the body wall. The cell type responsible for all cell renewal, including body wall renewal, in platyhelminths is the neoblast, and its presence may be the one autapomorphic character that unites all taxonomic groups of platyhelminths.