Single-cell deconstruction of stem-cell-driven schistosome development.

Schistosomes cause one of the most devastating neglected tropical diseases, schistosomiasis. Their transmission is accomplished through a complex life cycle with two obligate hosts and requires multiple radically different body plans specialized for infecting and reproducing in each host. Recent single-cell transcriptomic studies on several schistosome body plans provide a comprehensive map of their cell types, which include stem cells and their differentiated progeny along an intricate developmental hierarchy. This progress not only extends our understanding of the basic biology of the schistosome life cycle but can also inform new therapeutic and preventive strategies against the disease, as blocking the development of specific cell types through genetic manipulations has shown promise in inhibiting parasite survival, growth, and reproduction.

Innovations and Advances in Schistosome Stem Cell Research.

Schistosomes infect about 250 million people globally causing the devastating and persistent disease of schistosomiasis. These blood flukes have a complicated life cycle involving alternating infection of freshwater snail intermediate and definitive mammalian hosts. To survive and flourish in these diverse environments, schistosomes transition through a number of distinct life-cycle stages as a result of which they change their body plan in order to quickly adapt to each new environment. Current research suggests that stem cells, present in adults and larvae, are key in aiding schistosomes to facilitate these changes. Given the recent advances in our understanding of schistosome stem cell biology, we review the key roles that two major classes of cells play in the different life cycle stages during intramolluscan and intramammalian development; these include the germinal cells of sporocysts involved in asexual reproduction in molluscan hosts and the neoblasts of adult worms involved in sexual reproduction in human and other mammalian hosts. These studies shed considerable new light in revealing the stem cell heterogeneity driving the propagation of the schistosome life cycle. We also consider the possibility and value of establishing stem cell lines in schistosomes to advance schistosomiasis research. The availability of such self-renewable resources will provide new platforms to study stem cell behavior and regulation, and to address fundamental aspects of schistosome biology, reproductive development and survival. In turn, such studies will create new avenues to unravel individual gene function and to optimize genome-editing processes in blood flukes, which may lead to the design of novel intervention strategies for schistosomiasis.

Detecting hybridization in African schistosome species: does egg morphology complement molecular species identification?

Hybrid parasites may have an increased transmission potential and higher virulence compared to their parental species. Consequently, hybrid detection is critical for disease control. Previous crossing experiments showed that hybrid schistosome eggs have distinct morphotypes. We therefore compared the performance of egg morphology with molecular markers with regard to detecting hybridization in schistosomes. We studied the morphology of 303 terminal-spined eggs, originating from 19 individuals inhabiting a hybrid zone with natural crosses between the human parasite Schistosoma haematobium and the livestock parasite Schistosoma bovis in Senegal. The egg sizes showed a high variability and ranged between 92·4 and 176·4 µm in length and between 35·7 and 93·0 µm in width. No distinct morphotypes were found and all eggs resembled, to varying extent, the typical S. haematobium egg type. However, molecular analyses on the same eggs clearly showed the presence of two distinct partial mitochondrial cox1 profiles, namely S. bovis and S. haematobium, and only a single nuclear ITS rDNA profile (S. haematobium). Therefore, in these particular crosses, egg morphology appears not a good indicator of hybrid ancestry. We conclude by discussing strengths and limitations of molecular methods to detect hybrids in the context of high-throughput screening of field samples.

The QDREC web server: determining dose-response characteristics of complex macroparasites in phenotypic drug screens.

SUMMARY: Neglected tropical diseases (NTDs) caused by helminths constitute some of the most common infections of the world's poorest people. The etiological agents are complex and recalcitrant to standard techniques of molecular biology. Drug screening against helminths has often been phenotypic and typically involves manual description of drug effect and efficacy. A key challenge is to develop automated, quantitative approaches to drug screening against helminth diseases. The quantal dose-response calculator (QDREC) constitutes a significant step in this direction. It can be used to automatically determine quantitative dose-response characteristics and half-maximal effective concentration (EC50) values using image-based readouts from phenotypic screens, thereby allowing rigorous comparisons of the efficacies of drug compounds. QDREC has been developed and validated in the context of drug screening for schistosomiasis, one of the most important NTDs. However, it is equally applicable to general phenotypic screening involving helminths and other complex parasites. AVAILABILITY AND IMPLEMENTATION: QDREC is publically available at: http://haddock4.sfsu.edu/qdrec2/. Source code and datasets are at: http://tintin.sfsu.edu/projects/phenotypicAssays.html. CONTACT: rahul@sfsu.edu. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

The use of imaging to detect schistosomes and diagnose schistosomiasis.

Several imaging modalities have been employed to examine schistosomes and monitor schistosome-induced pathology. Ultrasound is a noninvasive imaging method that has long been used in the laboratory and in the field to evaluate pathological changes, notably fibrosis, that arise as a consequence of the host response to schistosome eggs lodging in a variety of tissues. Ultrasonography has been widely used to monitor changes in the extent of fibrosis and in spleen/liver enlargement following chemotherapeutic treatment for schistosomiasis. Imaging methods to monitor schistosomes themselves in vivo (as opposed to detecting schistosome-induced pathology) include positron emission tomography and fluorescence molecular tomography. Both approaches rely on schistosome uptake of tracers that are introduced into infected animals and that can be detected externally. These methods have been used to successfully detect schistosomes in vivo and to monitor their elimination following chemotherapeutic treatment. Direct monitoring of live schistosomes in vivo has been achieved using intravital microscopy, when the infected tissues of anaesthetized animals are exposed. Finally, schistosome eggs have been visualized by confocal laser scanning microscopy in infected mice as well as in a human patient with schistosomiasis hematobium. Further advances in imaging technologies seem likely to provide greater insight into disease progression and into the biology of schistosomes in the most relevant setting-within a live animal.

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.

Applications for profiling the schistosome transcriptome.

Some of the most fruitful applications of gene expression studies of schistosome parasites have occurred in the last decade. Recent transcriptomics approaches to schistosome research from an expanding biological perspective will be reviewed, ranging from the whole organism tissue or cellular levels. The latest studies of transcription in relation to schistosome-host interactions are examined, including the impact of the environment or therapies on the parasite and the reciprocal impact the parasite has on the host. Finally, the relevance of transcriptomics for exploring and contrasting different parasite populations or species is discussed.

Cell cultures for schistosomes - Chances of success or wishful thinking?

Due to their worldwide importance for human and animal health, schistosomes are in the focus of national and international research activities. Their aims are to elucidate the genome, the transcriptome, the proteome and the glycome of schistosomes with the expectation to understand the biology of these blood flukes and to identify new candidate antigens for the development of a vaccine, or target molecules for the design of novel pharmaceutical compounds. All of these efforts have delivered a vast amount of information about the genetic equipment of schistosomes. In the emerging era of post-genomic research, however, methods and tools are necessary to interpret all available data and to characterise molecules of interest in more detail. In addition to transgenesis, it is generally accepted that cell lines for schistosomes are among the requirements to overcome present research limitations. In our commentary the prospect of establishing cell cultures for schistosomes is discussed. To this end we summarise the comprehensive endeavours made in the past regarding the establishment of invertebrate cell lines pointing to critical parameters that should be considered when making new attempts towards schistosome cell culturing. Furthermore, based on preliminary data with pilot-character, we discuss recent advances indicating the possibility of overcoming existing restrictions with respect to the 'immortalisation' of cells by oncogenes.

Activity of praziquantel on in vitro transformed Schistosoma mansoni sporocysts

Praziquantel (PZQ) is effective against all the evolutive phases of Schistosoma mansoni. Infected Biomphalaria glabrata snails have their cercarial shedding interrupted when exposed to PZQ. Using primary in vitro transformed sporocysts, labeled with the probe Hoechst 33258 (indicator of membrane integrity), and lectin of Glycine max (specific for carbohydrate of N-acetylgalactosamine membrane), we evaluated the presence of lysosomes at this evolutive phase of S. mansoni, as well as the influence of PZQ on these acidic organelles and on the tegument of the sporocyst. Although the sporocyst remained alive, it was observed that there was a marked contraction of its musculature, and there occurred a change in the parasite's structure. Also, the acidic vesicles found in the sporocysts showed a larger delimited area after contact of the parasites with PZQ. Damages to the tegument was also observed, as show a well-marked labeling either with Hoechst 33258 or with lectin of Glycine max after contact of sporocysts with the drug. These results could partially explain the interruption/reduction mechanism of cercarial shedding in snails exposed to PZQ.

Activity of praziquantel on in vitro transformed Schistosoma mansoni sporocysts.

Praziquantel (PZQ) is effective against all the evolutive phases of Schistosoma mansoni. Infected Biomphalaria glabrata snails have their cercarial shedding interrupted when exposed to PZQ. Using primary in vitro transformed sporocysts, labeled with the probe Hoechst 33258 (indicator of membrane integrity), and lectin of Glycine max (specific for carbohydrate of N-acetylgalactosamine membrane), we evaluated the presence of lysosomes at this evolutive phase of S. mansoni, as well as the influence of PZQ on these acidic organelles and on the tegument of the sporocyst. Although the sporocyst remained alive, it was observed that there was a marked contraction of its musculature, and there occurred a change in the parasite's structure. Also, the acidic vesicles found in the sporocysts showed a larger delimited area after contact of the parasites with PZQ. Damages to the tegument was also observed, as show a well-marked labeling either with Hoechst 33258 or with lectin of Glycine max after contact of sporocysts with the drug. These results could partially explain the interruption/reduction mechanism of cercarial shedding in snails exposed to PZQ.

The cytoskeleton and motor proteins of human schistosomes and their roles in surface maintenance and host-parasite interactions.

Schistosomes are parasitic blood flukes, responsible for significant human disease in tropical and developing nations. Here we review information on the organization of the cytoskeleton and associated motor proteins of schistosomes, with particular reference to the organization of the syncytial tegument, a unique cellular adaptation of these and other neodermatan flatworms. Extensive EST databases show that the molecular constituents of the cytoskeleton and associated molecular systems are likely to be similar to those of other eukaryotes, although there are potentially some molecules unique to schistosomes and platyhelminths. The biology of some components, particular those contributing to host-parasite interactions as well as chemotherapy and immunotherapy are discussed. Unresolved questions in relation to the structure and function of the tegument relate to dynamic organization of the syncytial layer.

Multiple strategies of schistosomes to meet their requirements in the intermediate snail host.

The results of the studies on our model combination Trichobilharzia ocellata-Lymnaea stagnalis, presented in this review, lead to the conclusion that schistosomes use multiple strategies to reach their goals, i.e. to propagate and to continue their life cycle. They have to escape from being attacked by the internal defence system (IDS) of the snail host and to profoundly affect the host's energy flow, of which reproduction and growth are the main determinants, for their own benefit. These physiological changes they establish mainly by interfering with the two regulatory systems in the snail host, the IDS and the neuroendocrine system (NES). Moreover, these two regulatory systems clearly interact with each other. Parasitic E/S products affect the host's IDS both in a direct and an indirect way. The neuropeptides or neuropeptide-like substances that are secreted by parasite glands into the host directly suppress haemocyte activity in the snail. The indirect effects include effects of (1) peptides from connective tissue cells and (2) neuropeptides from NES and/or IDS. Parasitic E/S products also induce the effects on energy flow in the host. These E/S products act either directly on a target, as shown for the inhibiting effect of the parasite on the development of the male copulation organ, or on the NES regulating reproductive activity, e.g. on gene expression. Indirect effects of E/S products on the NES (hormone-receptor interaction, electrical activity) are mediated by a factor from connective tissue cells, presumably belonging to the IDS. The physiological changes in the snail host are obviously of vital importance for the parasites, since they make use of different strategies to bring them about.

Physiologic oxygen tensions limit oxidant-mediated killing of schistosome eggs by inflammatory cells and isolated granulomas.

Explanted hepatic granulomas, eosinophils obtained from the peritoneal cavity of schistosome-infected mice, schistosome egg granuloma macrophages, alveolar macrophages, and activated peritoneal macrophages obtained from Listeria-infected mice were miracidicidal when cultured at 21% oxygen. This activity was markedly attenuated at physiologic oxygen concentrations (1-15%). Catalase and superoxide dismutase blocked the miracidicidal activity of inflammatory cells but did not prevent granuloma-mediated egg killing. However, the biomimetic superoxide dismutase, copper (II) [diisopropyl salicylate]2, inhibited granuloma-mediated egg killing in a dose-dependent, apparently nontoxic manner. Thioglycollate-elicited macrophages did not kill schistosome egg miracidia even when cultured in 21% oxygen, unless pretreated with lipopolysaccharide. Isolated schistosome eggs initiated an oxidative burst in macrophages, as measured by superoxide anion production. This burst was suppressed at reduced oxygen concentrations. Thus schistosome egg miracidia can be killed nonspecifically by macrophages through the release of cytotoxic reactive oxygen intermediates triggered by the egg. This activity is not supported by the oxygen concentrations found in most tissues, with the possible exception of the lung. Schistosoma mansoni eggs, injected intraveneously and lodged in the pulmonary vasculature of mice, were killed rapidly, with a half life of 3.5 days. Eggs, injected into the mesenteric veins and lodged in the liver, remained fully viable for several weeks. The data suggest that the high oxygen tension of the lung allows for the increased production of reactive oxygen intermediates (ROI) by local inflammatory cells, which in turn increases their miracidicidal efficiency. Conversely, the relatively hypoxic environment of the liver decreases ROI production by local inflammatory cells and decreases their miracidicidal efficiency.

A study of the biological characteristics of a hybrid line between male Schistosoma haematobium (Dar es Salaam, Tanzania) and female S. intercalatum (Edea, Cameroun).

The viability of a hybrid between male Schistosoma haematobium (Dar es Salaam, Tanzania) and female S. intercalatum (Edea, Cameroun) was studied for up to the F7 hybrid generation and the biological characteristics of the hybrid were compared with those of each of the parental species. Using the total cercarial production/100 exposed snails/5 weeks value (TCP) as an index the hybrid miracidial infectivity to Bulinus forskalii (Kinshasa, Zaire), the host snail for S. intercalatum, remained comparable to that of S. intercalatum for up to at least the F5 generation and the TCP values for the hybrid/B. wrighti combination remained for up to the F7 generation intermediate between those of the parental species in B. wrighti. The hybrid also retained the infectivity for up to at least the F5 generation to B. globosus (Mazeras, Kenya), the host snail for S. haematobium, but the TCP values for the hybrid/B. globosus combination remained consistently lower than that of the S. haematobium/B. globosus combination. The hybrid cercarial infectivity to hamsters was for up to the F7 generation comparable to that of both parental species and the egg production capacity/worm pair/day of production of the F1 hybrid generation exceeded in both hamsters and mice that of both parental species. However, the egg production capacity subsequently decreased with that of the F3 to F6 generations in hamsters and with that of the F2 and F5 generations in mice being comparable to that of S. intercalatum. The pattern of distribution of eggs in tissue of hamsters of the F1 and F2 generations resembled that of S. haematobium and S. intercalatum, respectively, but the distributional pattern of the F3 to F6 generations deviated markedly from that of both the parental species and the preceding hybrid generations. The hybrid cercarial infectivity to mice and the pattern of egg distribution corresponded to that of S. intercalatum. The egg morphology of the P1 generation corresponded to that of S. intercalatum while that of the F1, F2 and F3 hybrid generations exhibited great polymorphism with a range of shapes through those of the parental species but with most eggs being intermediate in shape. However, the eggs of the F4 to F7 hybrid generations exhibited less polymorphism and resembled those of S. bovis in both size and shape.

Pathology of Schistosoma curassoni infection in sheep.

The gross- and histopathology of natural and experimental Schistosoma curassoni infections in sheep were studied. The data obtained showed that S. curassoni infection in sheep causes only slight clinico-pathological manifestations with preferential involvement of the liver, the lower intestine and the urinary bladder. A variable spectrum of host reaction to the eggs within an individual animal was observed, reflecting the duration of presence of eggs in the organs. In the liver, egg granulomas were most numerous in the perilobular regions, while in the intestine, lesions were most pronounced in the mucosa of the rectum. The presence of eggs in 10% of the urinary bladders examined indicated some bladder involvement.