In vitro segmentation induction of Mesocestoides corti (Cestoda) tetrathyridia

microRNA silencing in a whole worm cestode model provides insight into miR-71 function

Parasites belonging to the class Cestoda include zoonotic species such as Echinococcus spp. and Taenia spp. that cause morbidity and mortality in endemic areas, mainly affecting pastoral and rural communities in low income countries but also upper middle income countries. Cestodes show remarkable developmental plasticity, implying tight regulation of gene expression throughout their complex life cycles. Despite the recent availability of genomic data for cestodes, little progress was made on postgenomic functional studies. MicroRNAs (miRNAs) are key components of gene regulatory systems that guide diverse developmental processes in multicellular organisms. miR-71 is a highly expressed miRNA in cestodes, which is absent in vertebrates and targets essential parasite genes, representing a potential key player in understanding the role of miRNAs in cestodes biology. Here we used transfection with antisense oligonucleotides to perform whole worm miRNA knockdown in tetrathyridia of Mesocestoides vogae (syn. Mesocestoides corti), a laboratory model of cestodes. We believe this is the first report of miRNA knockdown at the organism level in these parasites. Our results showed that M. vogae miR-71 is involved in the control of strobilation in vitro and in the establishment of murine infection. In addition, we identified miR-71 targets in M. vogae, several of them being de-repressed upon miR-71 knockdown. This study provides new knowledge on gene expression regulation in cestodes and suggests that miRNAs could be evaluated as new selective therapeutic targets for treating Neglected Tropical Diseases prioritised by the World Health Organization.

The Tapeworm Hymenolepis diminuta as an Important Model Organism in the Experimental Parasitology of the 21st Century

The tapeworm Hymenolepis diminuta is a common parasite of the small intestine in rodents but it can also infect humans. Due to its characteristics and ease of maintenance in the laboratory, H. diminuta is also an important model species in studies of cestodiasis, including the search for new drugs, treatments, diagnostics and biochemical processes, as well as its host-parasite interrelationships. A great deal of attention has been devoted to the immune response caused by H. diminuta in the host, and several studies indicate that infection with H. diminuta can reduce the severity of concomitant disease. Here, we present a critical review of the experimental research conducted with the use of H. diminuta as a model organism for over more than two decades (in the 21st century). The present review evaluates the tapeworm H. diminuta as a model organism for studying the molecular biology, biochemistry and immunology aspects of parasitology, as well as certain clinical applications. It also systematizes the latest research on this species. Its findings may contribute to a better understanding of the biology of tapeworms and their adaptation to parasitism, including complex correlations between H. diminuta and invertebrate and vertebrate hosts. It places particular emphasis on its value for the further development of modern experimental parasitology.

Identification and characterization of sirtuin enzymes in cestodes and evaluation of sirtuin inhibitors as new cestocidal molecules

Anti-parasitic treatment of neglected tropical diseases (NTDs) caused by cestodes such as echinococcosis and cysticercosis relies on a small number of approved anthelmintic drugs. Furthermore, the treatment is usually prolonged and often partially effective and not well tolerated by some patients. Therefore, the identification of novel drug targets and their associated compounds is critical. In this study, we identified and characterized sirtuin (SIRT) enzymes in cestodes and evaluated the cestocidal potential of SIRT inhibitors. SIRTs are a highly conserved family of nicotinamide-adenine dinucleotide (NAD⁺)-lysine deacylases involved in multiple cellular functions. Here, we described the full repertoire of SIRT-encoding genes in several cestode species. We identified six SIRT-encoding genes that were classified into SIRTs Class I (SIRT1, SIRT2, and SIRT3), Class III (SIRT5), and Class IV (SIRT6 and SIRT7). In Echinococcus spp., SIRT genes showed transcriptional expression throughout several developmental stages, SIRT2 being the most expressed. To evaluate the potential of SIRT inhibitors as new cestocidal molecules, we determined the in vitro effect of several Class I SIRT inhibitors by motility assay. Of those, the selective SIRT2 inhibitor Mz25 showed a strong cestocidal activity in Mesocestoides vogae (syn. Mesocestoides corti) tetrathyridia at various concentrations. The Mz25 cestocidal activity was time- and dose-dependent with a half-maximal inhibitory concentration (IC₅₀) value significantly lower than that of albendazole. Additionally, Mz25 induced extensive damage in the general morphology with marked alterations in the tegument and ultrastructural features. By homology modeling, we found that cestode SIRT2s showed a high conservation of the canonical SIRT structure as well as in the residues related to Mz25 binding. Interestingly, some non-conservative mutations were found on the selectivity pocket (an Mz25-induced structural rearrangement on the active site), which represent a promising lead for developing selective cestode SIRT2 inhibitors derived from Mz25. Nevertheless, the Mz25 molecular target in M. vogae is unknown and remains to be determined. This report provides the basis for further studies of SIRTs to understand their roles in cestode biology and to develop selective SIRT inhibitors to treat these parasitic NTDs.

Characterization of a new type of neuronal 5-HT G- protein coupled receptor in the cestode nervous system

Cestodes are platyhelminth parasites with a wide range of hosts that cause neglected diseases. Neurotransmitter signaling is of critical importance for these parasites which lack circulatory, respiratory and digestive systems. For example, serotonin (5-HT) and serotonergic G-protein coupled receptors (5-HT GPCRs) play major roles in cestode motility, development and reproduction. In previous work, we deorphanized a group of 5-HT7 type GPCRs from cestodes. However, little is known about another type of 5-HT GPCR, the 5-HT1 clade, which has been studied in several invertebrate phyla but not in platyhelminthes. Three putative 5-HT GPCRs from Echinococcus canadensis, Mesocestoides vogae (syn. M. corti) and Hymenolepis microstoma were cloned, sequenced and bioinformatically analyzed. Evidence grouped these new sequences within the 5-HT1 clade of GPCRs but differences in highly conserved GPCR motifs were observed. Transcriptomic analysis, heterologous expression and immunolocalization studies were performed to characterize the E. canadensis receptor, called Eca-5-HT_1a. Functional heterologous expression studies showed that Eca-5-HT_1a is highly specific for serotonin. 5-Methoxytryptamine and α-methylserotonin, both known 5-HT GPCR agonists, give stimulatory responses whereas methysergide, a known 5-HT GPCR ligand, give an antagonist response in Eca-5-HT_1a. Mutants obtained by the substitution of key predicted residues resulted in severe impairment of receptor activity, confirming that indeed, these residues have important roles in receptor function. Immunolocalization studies on the protoscolex stage from E. canadensis, showed that Eca-5-HT_1a is localized in branched fibers which correspond to the nervous system of the parasite. The patterns of immunoreactive fibers for Eca-5-HT_1a and for serotonin were intimately intertwined but not identical, suggesting that they are two separate groups of fibers. These data provide the first functional, pharmacological and localization report of a serotonergic receptor that putatively belongs to the 5-HT1 type of GPCRs in cestodes. The serotonergic GPCR characterized here may represent a new target for antiparasitic intervention.

The potential for histone deacetylase (HDAC) inhibitors as cestocidal drugs

Background

Echinococcosis and cysticercosis are neglected tropical diseases caused by cestode parasites (family Taeniidae). Not only there is a small number of approved anthelmintics for the treatment of these cestodiases, but also some of them are not highly effective against larval stages, such that identifying novel drug targets and their associated compounds is critical. Histone deacetylase (HDAC) enzymes are validated drug targets in cancers and other diseases, and have been gaining relevance for developing new potential anti-parasitic treatments in the last years. Here, we present the anthelmintic profile for a panel of recently developed HDAC inhibitors against the model cestode Mesocestoides vogae (syn. M. corti).

Methodology/Principal findings

Phenotypic screening was performed on M. vogae by motility measurements and optical microscopic observations. Some HDAC inhibitors showed potent anthelmintic activities; three of them -entinostat, TH65, and TH92- had pronounced anthelmintic effects, reducing parasite viability by ~100% at concentrations of ≤ 20 μM. These compounds were selected for further characterization and showed anthelmintic effects in the micromolar range and in a time- and dose-dependent manner. Moreover, these compounds induced major alterations on the morphology and ultrastructural features of M. vogae. The potencies of these compounds were higher than albendazole and the anthelmintic effects were irreversible. Additionally, we evaluated pairwise drug combinations of these HDAC inhibitors and albendazole. The results suggested a positive interaction in the anthelmintic effect for individual pairs of compounds. Due to the maximum dose approved for entinostat, adjustments in the dose regime and/or combinations with currently-used anthelmintic drugs are needed, and the selectivity of TH65 and TH92 towards parasite targets should be assessed.

Conclusion, significance

The results presented here suggest that HDAC inhibitors represent novel and potent drug candidates against cestodes and pave the way to understanding the roles of HDACs in these parasites.

Neglected tropical diseases, such as echinococcosis and cysticercosis, which are caused by taeniid cestodes (tapeworms), represent serious public health problems in many countries around the world. Given that there is only a small number of approved anthelmintics for the treatment of cestodiases, and that most of them are not highly effective against larval stages, identifying novel drug targets and their associated compounds is critical. Histone deacetylases (HDACs) are enzymes that produce epigenetic modifications of chromatin, thus modifying cellular gene expression. In this study, we evaluate and characterize a number of HDAC inhibitors on the model cestode Mesocestoides vogae and report the anthelmintic profile of these compounds. Some of the HDAC inhibitors tested showed potent anthelmintic effects, particularly entinostat, TH65 and TH92. These compounds were selected as the most promising candidates due to their high potencies, which were superior to the commercially-available anthelmintic drug albendazole. We also evaluated pairwise drug combinations of HDAC inhibitors and albendazole. The findings of this study provide a starting point for the development of new HDAC-based cestocidal compounds.

Dynamics of protein synthesis in the initial steps of strobilation in the model cestode parasite Mesocestoides corti (syn. vogae)

Mesocestoides corti (syn. vogae) is a useful model for developmental studies of platyhelminth parasites of the Cestoda class, such as Taenia spp. or Echinococcus spp. It has been used in studies to characterize cestode strobilation, i.e. the development of larvae into adult worms. So far, little is known about the initial molecular events involved in cestode strobilation and, therefore, we carried out a study to characterize newly synthesized (NS) proteins upon strobilation induction. An approach based on bioorthogonal noncanonical amino acid tagging and mass spectrometry was used to label, isolate, identify, and quantify NS proteins in the initial steps of M. corti strobilation. Overall, 121 NS proteins were detected exclusively after induction of strobilation, including proteins related to development pathways, such as insulin and notch signaling. Metabolic changes that take place in the transition from the larval stage to adult worm were noted in special NS protein subsets related to developmental processes, such as focal adhesion, cell leading edge, and maintenance of location. The data shed light on mechanisms underlying early steps of cestode strobilation and enabled identification of possible developmental markers. We also consider the use of developmental responsive proteins as potential drug targets for developing novel anthelmintics. BIOLOGICAL SIGNIFICANCE: Larval cestodiases are life-threatening parasitic diseases that affect both man and domestic animals worldwide. Cestode parasites present complex life cycles, in which they undergo major morphological and physiological changes in the transition from one life-stage to the next. One of these transitions occurs during cestode strobilation, when the mostly undifferentiated and non-segmented larval or pre-adult form develops into a fully segmented and sexually differentiated (strobilated) adult worm. Although the proteomes of bona fide larvae and strobialted adults have been previously characterized for a few cestode species, little is still known about the dynamic of protein synthesis during the early steps of cestode strobilation. Now, the assessment of newly synthesized (NS) proteins within the first 48 h of strobilation the model cestode M. corti allowed to shed light on molecular mechanisms that are triggered by strobilation induction. The functional analyses of this repertoire of over a hundred NS proteins pointed out to changes in metabolism and activation of classical developmental signaling pathways in early strobilation. Many of the identified NS proteins may become valuable cestode developmental markers and their involvement in vital processes make them also good candidate targets for novel anthelmintic drugs.

Histone deacetylase enzymes as potential drug targets of Neglected Tropical Diseases caused by cestodes

Cestode parasites cause neglected diseases, such as echinococcosis and cysticercosis, which represent a significant problem in human and animal health. Benzimidazoles and praziquantel are the only available drugs for chemotherapy and it is therefore important to identify new alternative drugs against cestode parasites. Histone deacetylases (HDACs) are validated drug targets for the treatment of cancer and other diseases, including neglected diseases. However, knowledge of HDACs in cestodes is very scarce. In this work, we investigated cestode HDACs as potential drug targets to develop new therapies against neglected diseases caused by cestodes. Here we showed the full repertoire of HDAC coding genes in several members of the class Cestoda. Between 6 and 7 zinc-dependent HDAC coding genes were identified in the genomes of species from Echinococcus, Taenia, Mesocestoides and Hymenolepis genera. We classified them as Class I and II HDACs and analyzed their transcriptional expression levels throughout developmental stages of Echinococcus spp. We confirmed for the first time the complete HDAC8 nucleotide sequences from Echinococcus canadensis G7 and Mesocestoides corti. Homology models for these proteins showed particular structural features which differentiate them from HDAC8 from Homo sapiens. Furthermore, we showed that Trichostatin A (TSA), a pan-HDAC inhibitor, decreases the viability of M. corti, alters its tegument and morphology and produces an increment of the total amount of acetylated proteins, including acetylated histone H4. These results suggest that HDAC from cestodes are functional and might play important roles on survival and development. The particular structural features observed in cestode HDAC8 proteins suggest that these enzymes could be selectively targeted. This report provides the basis for further studies on cestode HDAC enzymes and for discovery of new HDAC inhibitors for the treatment of neglected diseases caused by cestode parasites.

Transcriptomic profile of two developmental stages of the cestode parasite Mesocestoides corti

Cestode development involves complex morphological and physiological changes. Here, we performed a differential expression analysis of gene transcripts between two developmental stages of the model cestode Mesocestoides corti. A RNA-seq-based approach was used to compare the transcriptomes of the tetrathyridium (larval, TT) and strobilated worm (ST) stages of the parasite. We found 19,053 transcripts, from which ∼45% were complete matches to genes previously annotated in the available M. corti draft genome sequence, ∼24% were considered novel isoforms, and ∼24% were considered potential novel transcripts. Stage-specific transcripts were found for both TTs (66) and STs (136), along with shared transcripts significantly overrepresented in one stage (342 in TTs, and 559 in STs). Differential expression and Gene Ontology term enrichment analyzes provided evidence of upregulation of different sets of transcripts associated with 'cytoskeleton', 'metabolism' and 'oxidation-reduction' processes in each stage, suggesting functional involvement of the corresponding genes with stage-specific features. Transcripts and processes enriched in the TT reflect typical larval processes that occur with the parasite in the intermediate host, such as asexual reproduction and budding, as well as active migration from the peritoneum to the liver and vice versa. In STs, transcripts associated with 'development', 'cell growth', and 'morphogenesis' were enriched, along with processes related to sexual reproduction, represented by the upregulation of numerous transcription factors, protein kinases, and histones. Overall, our results contributed to significantly increase the knowledge on the M. corti gene repertoire and expression profile in two developmental stages. Functional implications for the biology of larval and adult cestode parasites and for host-parasite interactions are discussed.

Comparison of different staining methods for determination of viability on Mesocestoides vogae tetrathyridia

Mesocestoides vogae is widely employed as a model for studying the biology, differentiation, and experimental chemotherapy of cestodes. Currently, there are few techniques to measure the viability of M. vogae metacestodes during pharmacological experiments. The aim of the present work was to evaluate and compare different staining techniques to determine objectively the viability of M. vogae tetrathyridia. Eosin (0.05% w/v), methylene blue (0.01% w/v), propidium iodide (PI, 2 μg/ml), and fluorescein diacetate (FDA, 0.5 μg/ml) solutions were tested against live, heat-killed (cultivated at 65 °C for 2 h) and thymol-treated tetrathyridia (50 and 250 μg/ml). Parasites were counted under a dissecting microscope or a fluorescence compound microscope, as appropriate. Studies by scanning electron microscope were performed to compare the ultrastructural damage with the viability of parasites. After comparing the performance of different dyes, we chose the eosin staining technique because its simplicity, rapidity, sensitivity, low cost and fidelity.

Experimental murine model of neurocysticercosis: first report of cerebellum as a location for Mesocestoides corti tetrathyridia

Neurocysticercosis is a parasitic disease caused by encysted larvae of Taenia solium in the human central nervous system. Cysts mainly affect the cerebral hemispheres, although they can also be found in ventricles, basal cisterns, and subarachnoid spaces, and rarely in the cerebellum. Given the impossibility of studying the disease in human patients, Cardona et al. (1999) developed a mouse model of neurocysticercosis, using Mesocestoides corti, a closely related cestode. This allows us to study the parasite-host relationship and the mechanisms involved in the disease, in order to improve the therapy. In this murine model of neurocysticercosis, the location of tetrathyridia in parenchyma, ventricles and meninges has already been reported. The aim of this work is to report the cerebellum as a new location for M. corti tetrathyridia in the murine model of neurocysticercosis. A murine model that reproduces the human pathology is essential to evaluate the symptomatology and response to drug treatment in experimentally infected mice.

Endoparasites of Crotalus tzabcan (Serpentes: Viperidae), with a checklist in rattlesnakes

The helminth and pentastomid fauna of 50 specimens of Crotalus tzabcan from the Yucatán Peninsula, Mexico is documented. The examination revealed the presence of three nematode species (Hastospiculum onchocercum, Hexametra boddaertii, and Travassosascaris araujoi), and one pentastomid (Porocephalus crotali). The threee nematode species had the same prevalence (2%), while the pentastomid had a higher prevalence (8%). The pentastomid P. crotali was the most abundant and intense parasite, although it was only found in four snake hosts. Crotalus tzabcan acts as definitive host for the adult helminths and pentastomids, with rodents as the probable intermediate hosts. This work represents the first systematic survey on the parasitic helminth and pentastomid fauna of C. tzabcan, and includes four new geographical records. Additionally, a checklist of helminths and pentastomids reported for Crotalus and Sistrurus is provided. To date, a total of 32 helminth and 7 pentastomid species have been recorded as parasites of rattlesnakes. Nematoda possessed the highest species richness. The genera with the highest number of host species were Mesocestoides and Hexametra, followed by Kalicephalus. The rattlesnake species with the highest number of reported parasites was C. durissus (18 nematodes and 2 pentastomids).

Comparative proteomics of the larval and adult stages of the model cestode parasite Mesocestoides corti

Mesocestoides corti is a widely used model for the study of cestode biology, and its transition from the larval tetrathyridium (TT) stage to the strobilated, adult worm (ST) stage can be induced and followed in vitro. Here, a proteomic approach was used to describe and compare M. corti TT and ST protein repertories. Overall, 571 proteins were identified, 238 proteins in TT samples and 333 proteins in ST samples. Among the identified proteins, 207 proteins were shared by TTs and STs, while 157 were stage-specific, being 31 exclusive from TTs, and 126 from STs. Functional annotation revealed fundamental metabolic differences between the TT and the ST stages. TTs perform functions related mainly to basic metabolism, responsible for growth and vegetative development by asexual reproduction. STs, in contrast, perform a wider range of functions, including macromolecule biosynthetic processes, gene expression and control pathways, which may be associated to its proglottization/segmentation, sexual differentiation and more complex physiology. Furthermore, the generated results provided an extensive list of cestode proteins of interest for functional studies in M. corti. Many of these proteins are novel candidate diagnostic antigens, and/or potential targets for the development of new and more effective antihelminthic drugs.

BIOLOGICAL SIGNIFICANCE

Cestodiases are parasitic diseases with serious impact on human and animal health. Efforts to develop more effective strategies for diagnosis, treatment or control of cestodiases are impaired by the still limited knowledge on many aspects of cestode biology, including the complex developmental processes that occur in the life cycles of these parasites. Mesocestoides corti is a good experimental model to study the transition from the larval to the adult stage, called strobilation, which occur in typical cestode life-cycles. The performed proteomics approach provided large-scale identification and quantification of M. corti proteins. Many stage-specific or differentially expressed proteins were detected in the larval tetrathyridium (TT) stage and in the strobilated, adult worm (ST) stage. Functional comparative analyses of the described protein repertoires shed light on function and processes associated to specific features of both stages, such as less differentiation and asexual reproduction in TTs, and proglottization/segmentation and sexual differentiation in ST. Moreover, many of the identified stage-specific proteins are useful as cestode developmental markers, and are potential targets for development of novel diagnostic methods and therapeutic drugs for cestodiases.

In vitro culture of Mesocestoides corti metacestodes and isolation of immunomodulatory excretory-secretory products

Cestode-mediated diseases hold the interesting feature of persisting metacestode larvae dwelling within the host tissues, in the midst of the immune response. Excretory-secretory (ES) products of the metacestode larval stage modulate the host immune response and modify the outcome of the disease. Therefore, isolation and analysis of axenic metacestode ES products are crucial to study their properties. Here, we report the development of a system for long-term in vitro cultivation of the metacestode of the parasitic cestode Mesocestoides corti (syn. Mesocestoides vogae). Although feeder cells and host serum supported the early growth of the parasite, long-term survival was not dependent on host serum or host-derived factors enabling the collection of parasite released products in serum-free medium. Functionally, these axenic ES products recapitulated M. corti tetrathyridia's ability to inhibit LPS-driven IL-12p70 secretion by dendritic cells. Thus, our new axenic culture system will simplify the identification and characterization of M. corti-derived immunomodulatory factors that will indirectly enable the identification and characterization of corresponding factors in the metacestode larvae of medically relevant cestodes such as Echinococcus multilocularis that are not yet amenable to serum-free cultivation.

Evolutionary developmental biology (evo-devo) of cestodes

Cestodes (tapeworms) have complex adaptations to their obligatory parasitic life-style. Among these adaptations, they show many evolutionary innovations in their development, including complex life-cycles with multiple hosts and life-stages, several independent origins of asexual reproduction, and the evolution of segmentation as a mean to generate massive reproductive output. Therefore, cestodes offer many opportunities for the investigation of the evolutionary origins of developmental novelties (evo-devo). However, cestodes have not been exploited as major models for evo-devo research due to the considerable technical difficulties involved in their study. In this review, a panoramic view is given of classical aspects, methods and hypothesis of cestode development, together with recent advances in phylogenetics, genomics, culture methods, and comparative analysis of cestode gene expression. Together with the availability of powerful models for related free-living flatworms, these developments should encourage the incorporation of these fascinating parasites into the first-line of evo-devo research.

Expression of the histone chaperone SET/TAF-Iβ during the strobilation process of Mesocestoides corti (Platyhelminthes, Cestoda)

The histone chaperone SET/TAF-Iβ is implicated in processes of chromatin remodelling and gene expression regulation. It has been associated with the control of developmental processes, but little is known about its function in helminth parasites. In Mesocestoides corti, a partial cDNA sequence related to SET/TAF-Iβ was isolated in a screening for genes differentially expressed in larvae (tetrathyridia) and adult worms. Here, the full-length coding sequence of the M. corti SET/TAF-Iβ gene was analysed and the encoded protein (McSET/TAF) was compared with orthologous sequences, showing that McSET/TAF can be regarded as a SET/TAF-Iβ family member, with a typical nucleosome-assembly protein (NAP) domain and an acidic tail. The expression patterns of the McSET/TAF gene and protein were investigated during the strobilation process by RT-qPCR, using a set of five reference genes, and by immunoblot and immunofluorescence, using monospecific polyclonal antibodies. A gradual increase in McSET/TAF transcripts and McSET/TAF protein was observed upon development induction by trypsin, demonstrating McSET/TAF differential expression during strobilation. These results provided the first evidence for the involvement of a protein from the NAP family of epigenetic effectors in the regulation of cestode development.

In Vitro Cestocidal Activity of Thymol on Mesocestoides corti Tetrathyridia and Adult Worms

Nothing is known about the possible effect of thymol or other compounds of essential oils against the adult worms of cestodes. The aim of the present work was to determine in vitro cestodicidal activity of thymol against Mesocestoides corti adult worms. Moreover, the in vitro effect on tetrathyridia was also demonstrated. Tetrathyridia exposed to different concentrations of thymol showed a concentration and time-dependent effect. At lower concentrations, the main change observed was mainly in morphology, with larvae exhibiting an elongation of the body. When tetrathyridia were exposed to higher concentrations, increased surface alterations and damage were detected. The body appeared elongated and flattened, and a complete loss of morphology and microtriches was observed. Thymol was able to kill M. corti tetrathyridia, since following inoculation of treated parasites in mice no parasites could be recovered. The effect on M. corti adult worms was dose and time-dependent. Changes in motility coincide with the tissue damage were observed at the structural and ultrastructural level. Thymol caused severe damages to both developmental stages analyzed. Damages were more significant in fully segmented worms. The data reported in this paper demonstrate a clear in vitro effect of thymol against M. corti tetrathyridia and adult worms.

A new approach for the characterization of proliferative cells in cestodes

Cestodes show a remarkable proliferative capability that sustains the constant growth and differentiation of proglottids essential for their lifestyle. It is believed that a separate population of undifferentiated stem cells (the so-called germinative cells) are the only cells capable of proliferation during growth and development. The study of this particular cell subpopulation is hampered by the current lack of methods to isolate it. In this work, we developed a reproducible flow cytometry and cell sorting method to quantify and isolate the proliferating cells in the tetrathyridia larvae of the model cestode Mesocestoides corti, based on the DNA content of the cells. The isolated cells display the typical germinative cell morphology, and can be used for RNA isolation with a yield in the ng to μg range. We expect that this approach may facilitate the characterization of the germinative cells in M. corti and other model tapeworms.

RNA-mediated gene suppression and in vitro culture in Hymenolepis microstoma

Hymenolepis microstoma, the mouse bile-duct tapeworm, is a classical rodent-hosted model that provides easy laboratory access to all stages of the life cycle. Recent characterisation of its genome has greatly advanced its utility for molecular research, albeit contemporary techniques such as those for assaying gene function have yet to be developed in the system. Here we present research on the development of RNA-mediated gene suppression via RNA interference (RNAi), and on in vitro culture of the enteric, adult phase of the life cycle to support this work. We demonstrate up to 80% quantitative suppression of a Hox transcript via soaking activated juvenile worms with double-stranded RNAs. However, we were unable to achieve segmentation of the worms in culture despite extensive manipulations of the culture media and supplements, preventing functional interpretation. An alternative, in vivo approach to RNAi was also tested by exposing cysticercoids prior to inoculation in mice, but fluorescent labelling showed that the RNAs did not sufficiently penetrate the cyst body and no difference in expression was found between exposed and control groups grown in vivo. Genomic and transcriptomic data revealed that H. microstoma has two orthologs each of Dicer, Drosha and Ago-1-like genes and that expression of one of the Ago-1 genes appears exclusive to germline development, suggesting that two or more independent RNA-mediated pathways are in operation. These studies demonstrate the viability of RNAi in H. microstoma and extend the utility of the model for research in the genomic era.

First report of a gryporhynchid tapeworm (Cestoda: Cyclophyllidea) from New Zealand and from an eleotrid fish, described from metacestodes and in vitro-grown worms

Metacestodes are often found in the body cavity of the common bully (Gobiomorphus cotidianus McDowall), from freshwater habitats in Otago, New Zealand. Identification of metacestodes relies only on the number, size and shape of the rostellar hooks. To attempt species determination, we cultivated metacestodes in vitro for up to 23 days, during which they matured to at least the male stage of development, although female organs were not discernable. Identified as members of the genus Paradilepis Hsü, 1935 (family Gryporhynchidae), these specimens are compared to previously described species, in particular P. minima (Goss, 1940), from Australia, the closest species, both geographically and morphologically. Although the size of scolex, suckers and proglottids differ significantly from those of P. minima, we are cautious about interpreting ‘adults’ grown in vitro, because we are unsure whether the artificial conditions alter development. For this reason, and because of the lack of female organs, we refrain from erecting a new species, and refer to the specimens as Paradilepis cf. minima until such time as the adults are found in the definitive host. With this proviso we present here a description of the in vitro-grown worms and the metacestodes as a preliminary study of this cestode. A molecular analysis of small subunit (SSU) rDNA sequences, shows the position of P. cf. minima and another gryporhynchid, Neogryporhynchus cheilancristrotus (Wedl, 1855), to be equivocal, but confirms their exclusion from the Dilepididae and Hymenolepididae. This is the first record of a gryporhynchid from New Zealand, and the first from the fish family Eleotridae.

Description of Hymenolepis microstoma (Nottingham strain): a classical tapeworm model for research in the genomic era

BACKGROUND

Hymenolepis microstoma (Dujardin, 1845) Blanchard, 1891, the mouse bile duct tapeworm, is a rodent/beetle-hosted laboratory model that has been used in research and teaching since its domestication in the 1950s. Recent characterization of its genome has prompted us to describe the specific strain that underpins these data, anchoring its identity and bringing the 150+ year-old original description up-to-date.

RESULTS

Morphometric and ultrastructural analyses were carried out on laboratory-reared specimens of the 'Nottingham' strain of Hymenolepis microstoma used for genome characterization. A contemporary description of the species is provided including detailed illustration of adult anatomy and elucidation of its taxonomy and the history of the specific laboratory isolate.

CONCLUSIONS

Our work acts to anchor the specific strain from which the H. microstoma genome has been characterized and provides an anatomical reference for researchers needing to employ a model tapeworm system that enables easy access to all stages of the life cycle. We review its classification, life history and development, and briefly discuss the genome and other model systems being employed at the beginning of a genomic era in cestodology.

Proteomic survey of the cestode Mesocestoides corti during the first 24 hours of strobilar development

Despite the fact that cestodes represent major etiological agents of both human and domestic animal diseases, little is known about the molecular aspects of cestode development. In this work, Mesocestoides corti, a model cestode species, was studied from the early development of its larval form (tetrathyridium) into adult worms (strobilation) using different proteomic approaches. The protein profiles of M. corti tetrathyridia induced or not induced to undergo strobilation were compared. Proteomic mapping by two-dimensional gel electrophoresis showed the resolution of 248 and 154 spots from tetrathyridia that were subjected or not subjected to strobilation induction, respectively, allowing for the detection of at least nine spots exclusive to each group. Spot analysis by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) or MALDI-TOF MS/MS identified four reference proteins (six spots). LC-MS/MS analyses of protein extracts identified 66 proteins, eight of which were found exclusively in non-induced tetrathyridia, while 13 were found exclusively in strobilation-induced tetrathyridia. Among the proteins exclusively identified in strobilation-induced worms, there was a predominance of proteins with functions relating to chaperone activity and protein synthesis and turnover. Quantitative differential expression analysis between M. corti tetrathyridia prior to and after strobilation induction revealed six proteins upregulated in strobilation-induced worms; these proteins were involved in metabolic pathways, cell proliferation, and cytoskeletal rearrangement. Overall, despite the absence of a sequenced M. corti genome, using sequences from other platyhelminthes, we were able to establish comprehensive protein profiles for tetrathyridia prior to and after strobilation induction and identify several proteins potentially involved in the early events leading to strobilation.

Stem cell proliferation during in vitro development of the model cestode Mesocestoides corti from larva to adult worm

Background

In free-living flatworms somatic differentiated cells do not divide, and a separate population of stem cells (called neoblasts) is responsible for cell proliferation and renewal. In cestodes, there is evidence that similar mechanisms of cell renewal exist.

Results

In this work, we have characterized proliferative cells during the development of the model cestode Mesocestoides corti from larva (tetrathyridium) to young segmented worm. This was done by two complementary strategies with congruent results: characterizing cells in S phase and their progeny by incorporation of 5-bromo-2'-deoxyuridine, and characterizing cells in M phase by arresting mitotic cells with colchicine and studying their morphology and distribution. Proliferative cells are localized only in the inner parenchyma, particularly in close proximity to the inner muscle layer, but not in the cortical parenchyma nor in the sub-tegumental tissue. After proliferation some of these cells migrate to the outer regions were they differentiate. In the larvae, proliferative cells are more abundant in the anterior regions (scolex and neck), and their number diminishes in an antero-posterior way. During the development of adult segments periodic accumulation of proliferative cells are observed, including a central mass of cells that constitutes the genital primordium, which grows at least in part due to in situ proliferation. In later segments, the inner cells of genital primordia cease to proliferate and adopt a compact distribution, and proliferative cells are also found in the testes primordia.

Conclusions

Proliferative cells have a characteristic localization and morphology throughout development from larva to adult of Mesocestoides corti, which is similar, and probably evolutionary conserved, to that described in other model cestodes. The characteristics of proliferative cells suggest that these consist of undifferentiated stem cells.

Mesocestoides corti: morphological features and glycogen mobilization during in vitro differentiation from larva to adult worm

Mesocestodes corti has the capacity to develop from the tetrathyridium (larva) stage to adult worm in vitro by trypsin and serum stimulation. Consequently, it has been used as an experimental model system for studying cestode development, host-parasite relationships and anthelmintic drugs. We describe morphological features in 5 different developmental stages of M. corti obtained in vitro, including larvae from the peritoneal cavity of infected mice, trypsin- and serum-stimulated larvae, elongated parasites as well as segmented and mature worms. It is unambiguously confirmed that sexually mature worms are obtained as a result of this in vitro process of differentiation. Defined cellular regions are present in all stages of development studied, some of them surrounded by a basal lamina. Glycogen is present in the larvae obtained from the mouse peritoneal cavity and in parasites encapsulated in the mouse host liver. Glycogen distribution in the parasite changes on trypsin and serum stimulation to differentiate. We propose that changes in the distribution of neutral polysaccharides in the parenchyma of the parasite at different stages of development and degradation of polysaccharides in the transition from segmented to adult worm are related to energy needs necessary for the cellular processes leading to the mature specimen.

Mucin-type O-glycosylation in Mesocestoides vogae (syn. corti)

Protein glycosylation is an important post-translational modification underlying host-parasite interactions, which may determine the outcome of infection. Although Mesocestoides vogae represents an important model for investigating the various aspects of cestode biology, virtually no information is available about the structure and synthesis of glycans in this parasite. In this work, focused on the initiation pathway of mucin-type O-glycosylation in M. vogae, we characterized O-glycoproteins bearing the simple mucin-type cancer-associated Tn and sialyl-Tn antigens, and the expression and activity of ppGalNAc-T, the key enzyme responsible for the first step of mucin-type O-glycosylation. Using immunohistochemistry, Tn and sialyl-Tn antigens were detected mainly in the tegument (microtriches) and in parenchymal cells. Tn expression was also observed in lateral nerve cords. Both Tn and sialyl-Tn antigens were detected in in vitro cultured parasites. Based on their electrophoretic mobility, Tn- and sialyl-Tn-bearing glycoproteins from M. vogae were separated into several components of 22 to 60 kDa. The observation that Tn and sialyl-Tn glycoproteins remained in the 0.6N perchloric acid-soluble fraction suggested that they could be good candidates for characterizing mucin-type glycosylation in this parasite. O-glycoproteins were purified and initially characterized using a proteomic approach. Immunohistochemical analysis of the tissue distribution of ppGalNAc-T revealed that this enzyme is expressed in the sub-tegumental region and in the parenchyma of the parasite. In M. vogae cultured in vitro, ppGalNAc-T was mainly detected in the suckers. Using a panel of 8 acceptor substrate synthetic peptides, we found that M. vogae ppGalNAc-T preferentially glycosylate threonine residues, the best substrates being peptides derived from human mucin MUC1 and from Trypanosoma cruzi mucin. These results suggest that M. vogae might represent a useful model to study O-glycosylation, and provide new research avenues for future studies on the glycopathobiology of helminth parasites.

Mesocestoides corti (syn. vogae, cestoda): Characterization of genes encoding cysteine-rich secreted proteins (CRISP)

With the aim of identifying genes involved in development and parasite adaptation in cestodes, four coding sequences were isolated from the cyclophyllidean Mesocestoides corti larval stage (tetrathyridium). Genes showed significant similarity to the cysteine-rich secreted protein (CRISP) encoding genes, a large family that includes stage and tissue-specific genes from diverse organisms, many associated with crucial biological processes. The full-length McCrisp2 cDNA encodes a predicted protein of 202 residues in length, containing 10 cysteines and a putative signal peptide. The expression level of McCrisp2 was estimated by Real-time PCR, relative to GAPDH, showing an increase of 75% in segmented worms compared to tetrathyridia. By in situ hybridization, McCrisp2 expression was localized mainly at the larvae apical region of tetrathyridia and in the proglottids of segmented worms. Taken together our results suggest a possible role for M. corti CRISP proteins as ES products, potentially involved in differentiation processes as proposed for homologs in other organisms.

Developmental expression pattern of histone H4 gene associated to DNA synthesis in the endoparasitic platyhelminth Mesocestoides corti

In higher eukaryotes, histone gene expression is coupled to DNA replication during the S-phase of the cell cycle. This coupling is primarily controlled at the transcriptional level. Considering the basal phylogenic position of platyhelminthes in the bilateria phylum, we have cloned a partial sequence of the histone H4 gene of Mesocestoides corti and studied its expression during the post larval development of this endoparasitic platyhelminth. In in vitro trypsin-induced tetrathyridia development to segmented adult worm, we found that histone H4 is expressed concomitantly with DNA synthesis throughout all stages of development. DNA synthesis and histone H4 mRNA levels were sharply increased at 24 h after inducing development. Afterwards, tetrathyridia grew in length from days 4 to 12 of development as proliferative cells gradually increased in number. Consequently, during this period of development histone H4 mRNA levels were upregulated. Taken together these results suggest that a replication-dependent expression pattern of histone H4 occurs in ancient bilateria, such as platyhelminthes, as previously observed in higher eukaryotes.

Localization, specific activity, and molecular forms of acetylcholinesterase in developmental stages of the cestode Mesocestoides corti

The nervous system of flatworms is quite simple although there is increasing evidence indicating that it is chemically complex. Studies of the nervous system in these animals have only been performed in the larval stage or in the adult worms, which are easy to obtain in nature, while the description of the nervous system in developing stages of these organisms is missing. Mesocestoides corti is a parasitic platyhelminth whose larvae can be induced in vitro to develop to adult, sexually mature worms, opening the possibility of studying the nervous system of a flatworm in different stages of development. Here, we describe the presence, activity, location, and molecular forms of acetylcholinesterase (AChE) in different stages of development of M. corti, from the larvae to adult forms of this endoparasite, obtained in in vitro cultures after induction of the larval stage with trypsin. Our results point to AChE as a molecular marker of the nervous system in platyhelminthes. The change in molecular forms of this enzyme and the increase in its activity during development from larvae to adult worm may reflect the presence of a more complex nervous system, necessary to adjust and coordinate the movement of a much bigger structure. A relationship between the development of the reproductive apparatus in segmented and adult worms with a more complex nervous system in these stages is also apparent. Finally, our study opens the possibility of applying anti-AChE as more effective therapeutic strategies against cestode parasites.

Early post-larval development of the endoparasitic platyhelminth Mesocestoides corti: trypsin provokes reversible tegumental damage leading to serum-induced cell proliferation and growth

Mesocestoides corti is a suitable in vitro model for studying the development of human endoparasitic platyhelminthes. Treatment with trypsin, supplemented with fetal bovine serum (FBS), induces M. corti development from larvae (tetrathyridia) to segmented adult worm; however, the role of this protease and of FBS in post-larval development induction remains unknown. To characterize the participation of trypsin enzymatic activity and of FBS in the induction of tetrathyridia growth and development, both stimuli were added to the larvae either together or sequentially. Additionally, specific inhibition of trypsin activity was also monitored. Finally, the effect of the enzyme on the parasite tegument as well as the proliferative activity and location of proliferating cells after induction of tetrathyridia development were also studied. We conclude that trypsin-induced tetrathyridia development to adult worm is FBS-dependent and that the effect of serum factors is dependent upon a previous trypsin-induced reversible damage to the larva tegument. In dividing and non-dividing tetrathyridia, proliferative activity of cells is mainly located within the apical massif in the anterior region and nerve cords of larvae, respectively. In tetrathyridia stimulated to develop to adult worms, an intense proliferative activity is evident along the nerve cords. Our results suggest that in natural infections the tetrathyridia tegument is temporally made permeable to growth factors by proteolytic enzyme activity in the intestine juice of the definitive host, thus leading to development to adult worms.

Praziquantel and albendazole damaging action on in vitro developing Mesocestoides corti (Platyhelminthes: Cestoda)

Parasitic flatworms present several steps of body architecture rearrangement during their fast transition from one developmental stage to another, which are, at least in part, responsible for their evasion from host immune response. Besides, different developmental stages present different degrees of susceptibility to drug action, and the identification of more susceptible stages is of importance for the definition of therapeutical approaches. Mesocestoides corti (syn. Mesocestoides vogae) is considered a good model to study cestode biology because it can be easily manipulated both in vivo and in vitro and due to its relatively close relationship to cestodes of medical relevance, such as those from genera Echinococcus or Taenia. We have analyzed the damaging action of two broad spectrum anthelmintic drugs (praziquantel and albendazole) throughout the in vitro strobilization process of M. corti in order to identify developmental stages or body structures more susceptible to these drugs. Tetrathyridia (larval stage) and segmented-induced worms were cultivated and treated with praziquantel and albendazole. Whole mounted samples, taken from different developmental stages, were fixed and stained with fluorophore-labeled WGA lectin and phalloidin for the analysis of tegument and muscles, respectively. Confocal laser scanning microscopy was used to identify anatomical changes and lesions caused by each anthelmintic drug in a 3D view. We demonstrated that both praziquantel and albendazole cause extensive tissue damage, especially on tegument, and that adult forms were the most susceptible to drug exposure.