Ultrastructural localization of pancreatic polypeptide- and FMRFamide immunoreactivities within the central nervous system of the nematode, Ascaris suum (Nematoda: Ascaroidea)

The trypsin inhibitor-like domain is required for a serine protease inhibitor of Haemonchus contortus to inhibit host coagulation

Haemonchus contortus, a blood-feeding nematode, inhibits blood coagulation at the site of infection to facilitate blood-sucking and digesting for successful parasitism. However, the mechanism underlying anti-coagulation at the host-parasite interface is largely unknown. In the current study, Hc-spi-i8, which has two greatly different transcripts named Hc-spi-i8a and Hc-spi-i8b, respectively, was described. Hc-SPI-I8A was a serine protease inhibitor containing a trypsin inhibitor-like cysteine rich (TIL) domain, while Hc-SPI-I8B was not. Hc-SPI-I8A/B were primarily expressed in the hypodermis, intestines and gonads in the parasitic stages of H. contortus. Hc-SPI-I8A interacted with Ovis aries TSP1-containing protein (OaTSP1CP), which was determined by yeast two-hybrid, co-immunoprecipitation (Co-IP), pull down and co-localization experiments. The blood clotting time contributed by the TIL domain was prolonged by Hc-SPI-I8A. Hc-SPI-I8A is most likely interfering in the extrinsic coagulation cascade by interacting with OaTSP1CP through its TIL domain and intrinsic coagulation cascade by an unknown mechanism. These findings depict a crucial point in the host-parasite interaction during H. contortus colonization, which should contribute to drug discovery and vaccine development in fighting against this important parasite worldwide.

Gene expression and pharmacology of nematode NLP-12 neuropeptides

This study examines the biology of NLP-12 neuropeptides in Caenorhabditis elegans, and in the parasitic nematodes Ascaris suum and Trichostrongylus colubriformis. DYRPLQFamide (1 nM-10 microM; n > or =6) produced contraction of innervated dorsal and ventral Ascaris body wall muscle preparations (10 microM, 6.8+/-1.9 g; 1 microM, 4.6+/-1.8 g; 0.1 microM, 4.1+/-2.0 g; 10 nM, 3.8+/-2.0 g; n > or =6), and also caused a qualitatively similar, but quantitatively lower contractile response (10 microM, 4.0+/-1.5 g, n=6) on denervated muscle strips. Ovijector muscle displayed no measurable response (10 microM, n=5). nlp-12 cDNAs were characterised from A. suum (As-nlp-12) and T. colubriformis (Tc-nlp-12), both of which show sequence similarity to C. elegans nlp-12, in that they encode multiple copies of -LQFamide peptides. In C. elegans, reverse transcriptase (RT)-PCR analysis showed that nlp-12 was transcribed throughout the life cycle, suggesting that DYRPLQFamide plays a constitutive role in the nervous system of this nematode. Transcription was also identified in both L3 and adult stages of T. colubriformis, in which Tc-nlp-12 is expressed in a single tail neurone. Conversely, As-nlp-12 is expressed in both head and tail tissue of adult female A. suum, suggesting species-specific differences in the transcription pattern of this gene.

Neuromuscular function in plant parasitic nematodes: a target for novel control strategies?

Over the last decade the need for new strategies and compounds to control parasitic helminths has become increasingly urgent. The neuromuscular systems of these worms have been espoused as potential sources of target molecules for new drugs which may address this need. One facet of helminth neuromuscular biology which has garnered considerable research interest is that of neuropeptidergic neurotransmission, particularly regarding parasites of humans and animals, as well as free-living nematode model species. This research interest has been piqued by the fact that neuropeptides have been demonstrated to be fundamentally important to nematode biology and thus may be of utility in this search for new drug targets. This review focuses on the neuropeptide biology of plant parasitic nematodes, a subject which has been comparatively neglected despite the fact that the search for alternative control measures also extends to these economically important parasites. We focus on the FMRFamide-like peptide (FLP) neuropeptides and the complexity and distribution of this peptide family in plant parasitic nematodes. Possible roles for FLPs in plant parasitic nematode behaviour, as elucidated by a combination of molecular imaging techniques and RNA interference (RNAi), are discussed. We propose that disruption of FLP neurosignalling in plant parasitic nematodes represents a novel form of pest control and speculate as to how this may be achieved.

Role of a FMRFamide-like family of neuropeptides in the pharyngeal nervous system of Caenorhabditis elegans

The nervous system of C. elegans has a remarkable abundance of flp genes encoding FMRFamide-like (FLP) neuropeptides. To provide insight into the physiological relevance of this neuropeptide diversity, we have tested more than 30 FLPs (encoded by 23 flps) for bioactivity on C. elegans pharynx. Eleven flp genes encode peptides that inhibit pharyngeal activity, while eight flp genes encode peptides that are excitatory. Three potent peptides (inhibitory, FLP-13A, APEASPFIRFamide; excitatory, FLP-17A, KSAFVRFamide; excitatory, FLP-17B, KSQYIRFamide) are encoded by flp genes, which, according to reporter gene constructs, are expressed in pharyngeal motoneurons. Thus, they may act through receptors localized on the pharyngeal muscle. The two other potent peptides, FLP-8 (excitatory AF1, KNEFIRFamide,) and FLP-11A (inhibitory, AMRNALVRFamide), appear to be expressed in extrapharyngeal neurons and are therefore likely to act either indirectly or as neurohormones. Intriguingly, a single neuron can express peptides that have potent but opposing biological activity in the pharynx. Only five flp genes encode neuropeptides that have no observable effect on the pharynx, but none of these have shown reporter gene expression in the pharyngeal nervous system. To examine the roles of multiple peptides produced from single precursors, a comparison was made between the bioactivity of different neuropeptides for five flp genes (flp-3, flp-13, flp-14, flp-17, and flp-18). For all but one gene (flp-14), the effects of peptides encoded by the same gene were similar. Overall, this study demonstrates the impressive neurochemical complexity of the simple circuit that regulates feeding in the nematode, C. elegans.

Nematode neuropeptides: Localization, isolation and functions

Historically, peptidergic substances (in the form of neurosecretions) were linked to moulting in nematodes. More recently, there has been a renewal of interest in nematode neurobiology, initially triggered by studies demonstrating the localization of peptide immunoreactivities to the nervous system. Here, David Brownlee, Ian Fairweather, Lindy Holden-Dye and Robert Walker will review progress on the isolation of nematode neuropeptides and efforts to unravel their physiological actions and inactivation mechanisms. Future avenues for research are suggested and the potential exploitation of peptidergic pathways in future therapeutic strategies highlighted.

Localisation of Globodera pallida FMRFamide-related peptide encoding genes using in situ hybridisation

The present study employed an in situ hybridisation technique to detect the expression of a number of FMRFamide-like peptide encoding (flp) genes, previously identified from Globodera pallida, in whole-mount preparations of the J(2) stage of this worm. gpflp-1, encoding the FMRFamide-related peptide (FaRP) KSAYMRFamide, was expressed in neurones associated with the circumpharyngeal nerve ring and specifically in a number of cell bodies in the lumbar ganglia of the perianal nerve ring. The lumbar ganglia and pre-anal ganglia along with the BDU neurones and a number of cells in the retrovesicular ganglion were observed to express gpflp-2, encoding KNKFEFIRFamide. gpflp-3 (encoding KHEYLRFamide) expression was localised to the anterior ganglion and a number of paired cells posterior to the circumpharyngeal nerve ring whilst expression of gpflp-4, encoding a number of -P(G/Q)VLRFamides, was localised to the retrovesicular ganglion. No expression of gpflp-5 was observed. Identification of the reactive cells has implicated distinct roles for the FaRPs encoded on these genes in regulation of both dorsal and ventral body wall muscles, the musculature of the vulva and in the function of a number of sensory structures in both the head and tail of G. pallida. Comparison with the expression patterns of analogous genes in Caenorhabditis elegans suggests that, whilst some of the encoded peptides are conserved between nematode species, their functions therein are distinct. Furthermore, the expression of some of these genes in a number of interneurones supports the idea that FaRPs fulfil neuromodulatory as well as neurotransmitter roles.

FMRFamide-related peptides in potato cyst nematodes

This study presents data demonstrating the presence of FMRFamide-related peptides (FaRPs) in potato cyst nematodes (PCN). Five transcripts of FaRP encoding genes, designated gpflp-1 to gpflp-5, were characterised using RACE. In terms of ORFs, gpflp-1 was 444 base pairs (bp) long and coded for four copies of the FaRP, PF3 (KSAYMRFamide) whilst gpflp-2 was 309 bp long and encoded one copy of the peptide, KNKFEFIRFamide. gpflp-3 (420 bp) Encoded two copies of KHEYLRFamide (AF2) and the genes gpflp-4 and gpflp-5 encoded a total of 11 FaRPs, most of which are novel to PCN. FMRFamide-related peptide (FaRP)-like immunoreactivity was observed in both PCN species, Globodera pallida and Globodera rostochiensis, using an antiserum raised against the invertebrate peptide, FMRFamide. Immunopositive neurones were found throughout the central nervous system in the ventral and dorsal nerve cords and the circumpharyngeal and perianal nerve rings. Reactive neurones were also present peripherally, innervating the highly muscular pharynx with a nerve net and ring-like structures. Positive immunostaining was also observed in neurones running toward the stylet protractor muscles and/or the anterior sensory apparatus. This study implicates a role for FaRPs in feeding, host penetration and sensory function of PCN. This is the first study to characterise FaRP encoding genes from a plant-parasitic nematode using a targeted PCR based RACE approach and further underlines the importance and diversity of this neuropeptide group in the phylum Nematoda.

The range and biological activity of FMRFamide-related peptides and classical neurotransmitters in nematodes

Nematodes include both major parasites of humans, livestock and plants in addition to free-living species such as Caenorhabditis elegans. The nematode nervous system (especially in C. elegans) is exceptionally well defined in terms of the number, location and projections of the small number of neurons in the nervous system and their integration into circuits involved in regulatory behaviours vital to their survival. This review will summarize what is known about the biological activity of neurotransmitters in nematodes: the biosynthetic pathways and genes involved, their receptors, inactivation mechanisms and secondary messenger signalling systems. It will cover the 'classical' transmitters, such as acetylcholine (ACh), GABA, glutamate, serotonin, dopamine, octopamine, noradrenaline and nitric oxide. The localization of peptides throughout the nematode nervous system is summarized, in addition to the isolation of nematode neuropeptides by both traditional biochemical techniques and more modern genetic means. The major contribution of the completion of the C. elegans genome-sequencing program is highlighted throughout. Efforts to unravel neurotransmitter action in various physiological actions such as locomotion, feeding and reproduction are detailed as well as the various inactivation mechanisms for the current complement of nematode transmitters.

Neuromusculature of the ovijector of ascaris suum (Ascaroidea, nematoda): an ultrastructural and immunocytochemical study

This study used electron microscopy and confocal scanning laser microscopy interfaced with cytochemistry to study neuromuscular interrelationships in the ovijector of Ascaris suum. An extensive nerve plexus with both FaRPergic and non-FaRPergic components extends over the outer surface of the ovijector. The non-FaRPergic component is derived from nerve branches of the ventral nerve cord, whereas the FaRPergic component emanates from two large FMRFamide-immunoreactive neurons. In the vagina vera, most myofibrils are circular in orientation and a number of them divide and run for short distances in longitudinal and diagonal directions, their myofilaments are also orientated in a variety of directions. Parallel nerve fibres run in tracts along the length of the vagina vera with branches that penetrate the muscle layers. The vagina uteri possesses a thicker hypodermis than that of the vagina vera. It appears rich in secretory and phagocytic vesicles and the luminal side is invested with an electron-dense substance. The musculature of the vagina uteri is less well developed than that of the vagina vera, being restricted to circular myofibrils, with an apparent diagonal arrangement of myofilaments. Also, the innervation is less extensive in the vagina uteri with many fibres returning to the vagina vera to rejoin the nerve net and others continuing into the uteri.

Parasitic peptides! The structure and function of neuropeptides in parasitic worms

Parasitic worms come from two very different phyla-Platyhelminthes (flatworms) and Nematoda (roundworms). Although both phyla possess nervous systems with highly developed peptidergic components, there are key differences in the structure and action of native neuropeptides in the two groups. For example, the most abundant neuropeptide known in platyhelminths is the pancreatic polypeptide-like neuropeptide F, whereas the most prevalent neuropeptides in nematodes are FMRFamide-related peptides (FaRPs), which are also present in platyhelminths. With respect to neuropeptide diversity, platyhelminth species possess only one or two distinct FaRPs, whereas nematodes have upwards of 50 unique FaRPs. FaRP bioactivity in platyhelminths appears to be restricted to myoexcitation, whereas both excitatory and inhibitory effects have been reported in nematodes. Recently interest has focused on the peptidergic signaling systems of both phyla because elucidation of these systems will do much to clarify the basic biology of the worms and because the peptidergic systems hold the promise of yielding novel targets for a new generation of antiparasitic drugs.

Natural variation in a neuropeptide Y receptor homolog modifies social behavior and food response in C. elegans

Natural isolates of C. elegans exhibit either solitary or social feeding behavior. Solitary foragers move slowly on a bacterial lawn and disperse across it, while social foragers move rapidly on bacteria and aggregate together. A loss-of-function mutation in the npr-1 gene, which encodes a predicted G protein-coupled receptor similar to neuropeptide Y receptors, causes a solitary strain to take on social behavior. Two isoforms of NPR-1 that differ at a single residue occur in the wild. One isoform, NPR-1 215F, is found exclusively in social strains, while the other isoform, NPR-1 215V, is found exclusively in solitary strains. An NPR-1 215V transgene can induce solitary feeding behavior in a wild social strain. Thus, isoforms of a putative neuropeptide receptor generate natural variation in C. elegans feeding behavior.

Nematode FMRFamide-related peptide (FaRP)-systems: occurrence, distribution and physiology

The application of rational (mechanism-based) approaches to anthelmintic discovery requires information about target proteins which are pharmacologically distinguishable from their vertebrate homologs. In helminths, several such targets (e.g., beta-tubulin, ATP-generating enzymes, cholinergic receptors, CI- channels) have been characterized only after the discovery, through empirical screening, of compounds that interfere with their function. From the perspective of anthelmintic discovery, the utility of these targets is diminishing due to the emergence of drug-resistant strains of parasites. This has motivated the search for compounds with novel modes-of-action. Recent basic research in helminth physiology and biochemistry has identified several potential targets for rational anthelmintic discovery, including receptors for FMRFamide-related peptides (FaRPs). To date, over 20 different nematode FaRPs have been identified and these peptides, which are broadly distributed in helminths, have been localized to all of the major neuronal subtypes in nematodes. The FaRPs that have been examined have been found profoundly to affect somatic muscle function in gastrointestinal nematodes. In this respect, complex inhibitory and excitatory actions have been identified for a number of these peptides. Although the transduction pathways for any of these peptides remain to be elucidated, the available evidence indicates that nematode FaRPs have numerous mechanisms of action. The employment of nematode neuropeptide receptors in mechanism-based screens has immense potential in the identification of novel anthelmintics.