Developmental and immune regulation of gene expression in Hymenolepis diminuta

Introduction to neuropeptides: perspectives for the parasitologist

At the cellular and molecular levels, the small and simpler nervous systems of invertebrates do not differ fundamentally from the larger more complex ones of vertebrates. It seems therefore that the special properties of the human brain arise more from the fact that it has ten trillion cellular components than from any unusual properties of the components themselves. By studying invertebrates we can gain insight into what basic functions are performed by the cells and molecules of the nervous system and this will contribute to a more fundamental understanding of what goes on in a system in which the same functions are performed by uncountable numbers of neurones. Invertebrate studies are also important for an entirely different reason; they are interesting and important in their own right. Moreover, a relatively small number of invertebrates are pests; either parasites, vectors of serious parasitic diseases or pests of our agricultural production. It is no accident that most of the methods that are used to control such organisms act on their nervous system. That is because the nervous system is a complex chemical machine which works through a great variety of chemical interactions between a wide diversity of receptors and ligands. Many currently used control methods work because they disrupt these interactions. For this reason I would imagine that the new generation of compounds developed to control invertebrates will depend for their activity on interactions with the nervous system. Since most of the chemical effectors (transmitters, modulators and hormones) in the nervous system are peptides, a number of these newly developed approaches will depend upon a fundamental knowledge of peptidergic systems in parasites. This essay is about peptidergic systems and indicates how we might exploit their vulner-ability to interference.

Regulation of gene expression in parasitic flatworms

Transcriptional regulation and the role of transcription factors are widely regarded to be the major contributors controlling gene expression in eucaryotes. Translational control is less well understood due to the complexity of the components involved in regulation of protein synthesis at this level. Nevertheless, considerable advances have been made recently in elucidating the major controlling factors within the messenger RNA (mRNA) sequence and the translation machinery. In this article, Ron Podesta and Afzal Siddiqui suggest that protein synthesis in flatworm parasites is controlled post-transcriptionally and that these intracellular regulatory mechanisms are activated/suppressed by effectors of the host's immune response.

Characterization of Ca(2+)-dependent neutral protease (calpain) from human blood flukes, Schistosoma mansoni

Calcium-dependent, neutral cysteine-proteases (calpain) were purified from human blood flukes, Schistosoma mansoni. The electrophoretic mobilities, Western blot analyses and high specificity to peptide inhibitors confirmed the presence of both calpain I and II in the purified preparation. The schistosome calpains were localized in the surface syncytial epithelium and underlying musculature. Using peptide inhibitors, calpain was shown to function as a mediator of the surface membrane synthetic process. Since there was also no immunological cross-reactivity between vertebrate and schistosome calpains using antibodies affinity-purified from native and recombinant schistosome calpains, this protease may be usefully investigated as forming the basis of a molecular vaccine against schistosomiasis.

Comparison of in vitro translation products of Sarcocystis gigantea and Sarcocystis tenella

Poly(A)+ RNA was purified from cystozoites of Sarcocystis gigantea and Sarcocystis tenella and used to in vitro translate polypeptides in a wheat germ and a rabbit reticulocyte translation system. The in vitro translated polypeptides were compared by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The S. tenella mRNA translated at least two polypeptides (mol. wt about 80,000 and 21,500) in both translation systems that were not translated by the S. gigantea mRNA. To study co-translational and initial post-translational processing in Sarcocystis, the poly(A)+ RNA preparations were in vitro translated in the rabbit reticulocyte translation system in the presence or absence of canine microsomal membranes. Based on electrophoresis, there appeared to be modification of at least some Sarcocystis polypeptides in the mol. wt range 17,000-30,000. In addition, the translation products were immunoprecipitated with a homologous and a heterologous antiserum. The immunoprecipitated polypeptides were compared by electrophoresis and the S. tenella translation products contained at least one unique antigenic polypeptide with a mol. wt of about 34,700 that was not processed by the microsomal membranes. These results suggest that there is at least one polypeptide that is a candidate for use as an antigen for the differentiation of S. gigantea and S. tenella infections in sheep.

Developmental changes of Echinococcus multilocularis metacestodes revealed by tegumental ultrastructure and lectin-binding sites

Ultrastructural investigations (SEM, TEM) combined with lectin-binding analysis, have revealed concurrent modifications in tegumentary structure and surface glycoconjugates during the establishment and differentiation of Echinococcus multilocularis metacestodes in jirds. The laminated layer, which is amorphous and rich in polysaccharides when initially secreted by the young cyst, takes on a different appearance and has a different glycoconjugate composition according to whether the cyst becomes fertile or sterile. The laminated layer of fertile cysts transforms into a microfibrillar matrix, the protein content of which may increase while sugar content decreases during protoscolex differentiation. Independently of this structure, brood capsules, from which arise protoscoleces, are formed by invagination of the cyst tegument. The intense secretion of glycoconjugates from the brood capsule wall during invagination may serve to interact with host factors passing through the laminated layer. The combined use of ultrastructural study and lectin labelling has allowed the demonstration of an ultrastructural and biochemical gradient of differentiation of the protoscolex. Seven stages of differentiation have been described. The possibility that the excreted-secreted tegumentary glycoconjugates, revealed by lectin labelling during protoscolex differentiation, might be the gradual biochemical expression of one or several stimuli implicated in the phenomenon of protoscolex maturation, is discussed.

The role of the host in the regulation of end-product formation in two strains of the rat tapeworm, Hymenolepis diminuta

Individual worms from rats infected with different strains of Hymenolepis diminuta were incubated in vitro and the products lactate, succinate, acetate and ammonia assayed. Variability in excretion was not confined to differences between strains. Two metabolic types were identified. Where succinate was above 20 mumol g-1 h-1, lactate excretion was low. Where succinate was not detected, lactate excretion was high. Acetate excretion was variable. Lactate and ammonia excretion were positively correlated. All worms from one rat were of the same type but could be of either type from different rats. The host strain had no effect. A relationship was shown between lactate excretion and the number of worms from a standard inoculum present at 21 days of infection. The incidence of high lactate excretion was increased in worms from secondary infections. Components of the host immune response may thus exert effects on the metabolism of H. diminuta, manifest as shifts in emphasis on cytosolic and mitochondrial metabolism.

Comparison of the in vitro translation capacity of Taenia crassiceps metacestode mRNA prepared by the phenol and cesium chloride method

Total RNA of T. crassiceps metacestodes harvested from male and female NMRI mice was prepared by both the phenol extraction technique and cesium chloride (CsCl) gradient centrifugation. mRNA was selected by oligo (dT)-cellulose affinity chromatography and used as the template for the in vitro translation of parasite polypeptides in a cell-free rabbit reticulocyte lysate. The template activity of the mRNA obtained after CsCl preparation was clearly higher, as shown by the amount of 35S-methionine incorporated into the translation products and by fluorographed SDS-PAGE of the synthesized labelled polypeptides. SDS-PAGE fluorographs of antigens encoded by the mRNA prepared by CsCl centrifugation and selected by immunoprecipitation using purified IgG antibodies of T. crassiceps-infected mice (day 80 postinfection) exhibited seven labelled polypeptides of about 65, 46, 45, 42, 34, 29 kDa and a predominant 20-kDa antigen. The latter polypeptide was the only one recognized by the antibodies amongst the in vitro translation products directed by mRNA prepared by the phenol method.