Structure and bioactivity of neuropeptide F from the human parasites Schistosoma mansoni and Schistosoma japonicum

The blood flukes Schistosoma mansoni and Schistosoma japonicum inflict immense suffering as agents of human schistosomiasis. Previous investigations have found the nervous systems of these worms contain abundant immunoreactivity to antisera targeting invertebrate neuropeptide Fs (NPFs) as well as structurally similar neuropeptides of the mammalian neuropeptide Y (NPY) family. Here, cDNAs encoding NPF in these worms were identified, and the mature neuropeptides from the two species differed by only a single amino acid. Both neuropeptides feature the characteristics common among NPFs; they are 36 amino acids long with a carboxyl-terminal Gly-Arg-X-Arg-Phe-amide and Tyr residues at positions 10 and 17 from the carboxyl terminus. Synthetic S. mansoni NPF potently inhibits the forskolin-stimulated accumulation of cAMP in worm homogenates, with significant effects at 10(-11) M. This is the first demonstration of an endogenous inhibition of cAMP by an NPF, and because this is the predominant pathway associated with vertebrate NPY family peptides, it demonstrates a conservation of downstream signaling pathways used by NPFs and NPY peptides.

How parasites affect interactions between competitors and predators

We present a synthesis of empirical and theoretical work investigating how parasites influence competitive and predatory interactions between other species. We examine the direct and indirect effects of parasitism and discuss examples of density and parasite-induced trait-mediated effects. Recent work reveals previously unrecognized complexity in parasite-mediated interactions. In addition to parasite-modified and apparent competition leading to species exclusion or enabling coexistence, parasites and predators interact in different ways to regulate or destablize the population dynamics of their joint prey. An emerging area is the impact of parasites on intraguild predation (IGP). Parasites can increase vulnerability of infected individuals to cannibalism or predation resulting in reversed species dominance in IGP hierarchies. We discuss the potential significance of parasites for community structure and biodiversity, in particular their role in promoting species exclusion or coexistence and the impact of emerging diseases. Ongoing invasions provide examples where parasites mediate native/invader interactions and play a key role in determining the outcome of invasions. We highlight the need for more quantitative data to assess the impact of parasites on communities, and the combination of theoretical and empirical studies to examine how the effects of parasitism scale up to community-level processes.

Satellite flies (Leucophora personata, Diptera : Anthomyiidae) and other dipteran parasites of the communal bee Andrena agilissima (Hymenoptera : Andrenidae) on the island of Elba, Italy

Solitary and presocial aculueate Hymenoptera are parasitized by a range of dipteran species in the families Axithomyiidae, Bombyliidae, Conopidae, Phoridae, and Sarcophagidae that are likely to impact on their hosts. We undertook a study over several years of a univoltine and communal bee, Andrena agilissima, and its main dipteran parasites, in particular the satellite fly Leucophora personata (Diptera: Anthomyiidae). Behavioural and ecological data were collected from one nesting aggregation of the host bee on the island of Elba, Italy, from 1993 to 2003, and from a foraging site of the bee, ca 5 km from the nesting aggregation. Other Diptera associated with A. agilissmia at the field site were the bee fly Bombylius fimbriatus (Bombyliidae), the conopid fly Zodion cinereum (Conopidae), and the scuttle fly Megaselia andrenae (Phoridae). The phenology of the Diptera broadly overlapped with that of their host across the season of activity (end of April and all of May). Diurnal activity patterns differed slightly; L. personata in particular was active at the host's nesting site before A. agilissima. Female satellite flies also showed a range of behaviours in gaining entry to a host nest. We summarize published data on this and other Leucophora species that parasitize Andrena host bees. Host bees returning to their nests occasionally undertook zig-zag flight manoeuvres if followed by a satellite fly that were generally successful in evading the fly. Satellite flies that entered a nest, presumably to oviposit, were less likely to remain therein if another host bee entered the same nest, suggesting that one advantage to communal nesting for this host is a reduction in brood cell parasitism by L. personata. We provide the first clear evidence for parasitism by a Zodion of any Andrena host. Both L. personata and M. andrenae concentrated their parasitic activities in the zone of the host nesting aggregation with highest nest densities. Three of the Diptera, L. personata, B. fimbriatus, and Z. cinereum, seemed to have extremely low rates of parasitism whilst that of M. andrenae appeared low. Though they have refined parasitic behaviour that allows them to gain entry into host nests (L. personata, B. fimbriatus, and M. andrenae) or to parasitize adults (Z. cinercum), these parasites seem not to impact upon the dynamics of the host A. agilissima at the nesting aggregation, and the host possesses traits to reduce parasitism.

A keystone effect for parasites in intraguild predation?

Intraguild predation (IGP) is common in communities, yet theory suggests it should not often persist and coexistence of participating species should be rare. As parasitism can play keystone roles in interactions between competitors, and between predators and prey, here we examine the role of parasites in maintaining IGP. We used numerical exploration of population dynamic equations to determine coexistence and exclusion zones for two species engaged in IGP with shared parasitism. We demonstrate that parasitism increases the range of conditions leading to coexistence when the parasite exerts a greater deleterious effect on the 'stronger' species in terms of the combined effects of competition and predation. Such a parasite can enable an inferior competitor that is also the less predatory to persist, and may actually lead to numerical dominance of this species.

An eye on RNAi in nematode parasites

RNA interference (RNAi) has revolutionised approaches to gene function determination. From a parasitology perspective, gene function studies have the added dimension of providing validation data, increasingly deemed essential to the initial phases of drug target selection, pre-screen development. Notionally advantageous to those working on nematode parasites is the fact that Caenorhabditis elegans research spawned RNAi discovery and continues to seed our understanding of its fundamentals. Unfortunately, RNAi data for nematode parasites illustrate variable and inconsistent susceptibilities which undermine confidence and exploitation. Now well-ensconced in an era of nematode parasite genomics, we can begin to unscramble this variation.

FMRFamide-related peptides (FaRPs) in helminth parasites

Neuropeptides are ubiquitous intercellular signalling molecules in all Metazoa with nervous systems. Research over the past 10 years has confirmed through immunocytochemistry that neuropeptides are widespread and abundant in the nervous systems of helminth parasites. Biochemical isolation and characterisation studies have indentified the primary structures of numerous structurally-related peptides in helminths, the best studied being the FMRFamide-related peptides (FaRPs). While to date only four FaRPs have been identified from platyhelminths, some 60 FaRPs or FaRP-like peptides have been isolated or predicted for nematodes. Preliminary physiological studies have shown that FaRPs are strongly myoactive, but with quire different actions in the two groups of helminth parasite. The absence of FaRPs from vertebrates suggests compounds with a high affinity for FaRP receptors are likely to have selective effects against helminths and, if protected from degradation, could have therapeutic potential.

SEROTONIN AND NEUROPEPTIDE IMMUNOREACTIVITIES IN THE INTRAMOLLUSCAN STAGES OF 3 MARINE TREMATODE PARASITES

Using an indirect immunofluorescence technique interfaced with confocal scanning laser microscopy, whole-mount preparations of three genera of marine trematode larvae, Cryntocotyle lingua, Cercaria emasculans and Himasthla leptosoma, were screened for 5-hydroxytryptamine (5-HT) and selected neuropeptide immunoreactivities (IRs). IRs for pancreatic polypeptide (PP), peptide YY (PYY) and FMRFamide were found in the central nervous systems of the three species of cercariae, immunostaining the paired ganglia and central commissure and the longitudinal nerve cords, with slight differences in both distribution and intensity of IRs being observed for the different antisera used. PP, PYY and FMRFamide IRs were evident in both central and peripheral components of the nervous system in the rediae of C. lingua. 5-HT IR was confined to the peripheral nervous systems of the cercariae of C. emasculans and the rediae of C. lingua, appearing in the form of a network of immunoreactive fibres and associated large cell bodies. A moderate substance P IR was observed in the nervous system of the cercariae of C. lingua. The patterns of immunostaining described were compared with those obtained using antiserum directed to the C-terminal decapeptide amide of neuropeptide F (NPF), a native parasitic peptide from the cestode Moniezia expansa. Results demonstrated that serotoninergic and peptidergic components were present in the nervous systems of all of the trematode larvae studied and that some, if not all, of the IR for PP. PYY and FMRFamide was due to the presence of a trematode NPF homologue.