afp-1: a gene encoding multiple transcripts of a new class of FMRFamide-like neuropeptides in the nematode Ascaris suum

My life with Sydney, 1961-1971

During the 1961-1971 decade, Sydney Brenner made several significant contributions to molecular biology-showing that the genetic code is a triplet code; discovery of messenger RNA; colinearity of gene and protein; decoding of chain terminating codons; and then an important transition: the development of the nematode Caenorhabditis elegans into the model eucaryote genetic system that has permeated the whole of recent biology.

Different neuropeptides are expressed in different functional subsets of cholinergic excitatory motorneurons in the nematode Ascaris suum

Neuropeptides are known to have dramatic effects on neurons and synapses; however, despite extensive studies of the motorneurons in the parasitic nematode Ascaris suum, their peptide content had not yet been described. We determined the peptide content of single excitatory motorneurons by mass spectrometry and tandem mass spectrometry. There are two subsets of ventral cord excitatory motorneurons, each with neuromuscular output either anterior or posterior to their cell body, mediating forward or backward locomotion, respectively. Strikingly, the two sets of neurons contain different neuropeptides, with AF9 and six novel peptides (As-NLP-21.1-6) in anterior projectors, and the six afp-1 peptides in addition to AF2 in posterior projectors. In situ hybridization confirmed the expression of these peptides, validating the integrity of the dissection technique. This work identifies new components of the functional behavioral circuit, as well as potential targets for antiparasitic drug development.

The FMRFamide-Like Peptide Family in Nematodes

In the three decades since the FMRFamide peptide was isolated from the mollusk Macrocallista nimbosa, structurally similar peptides sharing a C-terminal RFamide motif have been identified across the animal kingdom. FMRFamide-like peptides (FLPs) represent the largest known family of neuropeptides in invertebrates. In the phylum Nematoda, at least 32 flp-genes are classified, making the FLP system of nematodes unusually complex. The diversity of the nematode FLP complement is most extensively mapped in Caenorhabditis elegans, where over 70 FLPs have been predicted. FLPs have shown to be expressed in the majority of the 302 C. elegans neurons including interneurons, sensory neurons, and motor neurons. The vast expression of FLPs is reflected in the broad functional repertoire of nematode FLP signaling, including neuroendocrine and neuromodulatory effects on locomotory activity, reproduction, feeding, and behavior. In contrast to the many identified nematode FLPs, only few peptides have been assigned a receptor and there is the need to clarify the pathway components and working mechanisms of the FLP signaling network. Here, we review the diversity, distribution, and functions of FLPs in nematodes.

Changes in cyclic nucleotides, locomotory behavior, and body length produced by novel endogenous neuropeptides in the parasitic nematode Ascaris suum

Recent technical advances have rapidly advanced the discovery of novel peptides, as well as the transcripts that encode them, in the parasitic nematode Ascaris suum. Here we report that many of these novel peptides produce profound and varied effects on locomotory behavior and levels of cyclic nucleotides in A. suum. We investigated the effects of 31 endogenous neuropeptides encoded by transcripts afp-1, afp-2, afp-4, afp-6, afp-7, and afp-9-14 (afp: Ascaris FMRFamide-like Precursor protein) on cyclic nucleotide levels, body length and locomotory behavior. Worms were induced to generate anteriorly propagating waveforms, peptides were injected into the pseudocoelomic cavity, and changes in the specific activity (nmol/mg protein) of second messengers cAMP (3'5' cyclic adenosine monophosphate) and cGMP (3'5' cyclic guanosine monophosphate) were determined. Many of these neuropeptides changed the levels of cAMP (both increases and decreases were found), whereas few neuropeptides changed the level of cGMP. A subset of the peptides that lowered cAMP was investigated for effects on the locomotory waveform and on body length. Injection of AF19, or AF34 (afp-13), AF9 (afp-14), AF26 or AF41 (afp-11) caused immediate paralysis and cessation of propagating body waveforms. These neuropeptides also significantly increased body length. In contrast, injection of AF15 (afp-9) reduced the body length, and decreased the amplitude of waves in the body waveform. AF30 (afp-10) produced worms with tight ventral coils. Although injection of neuropeptides encoded by afp-1 (AF3, AF4, AF10 or AF13) produced an increased number of exaggerated body waves, there were no effects on either cAMP or cGMP. By injecting peptides into behaving A. suum, we have provided an initial screen of the effects of novel peptides on several behavioral and biochemical parameters.

Discovery of neuropeptides in the nematode Ascaris suum by database mining and tandem mass spectrometry

Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used to discover peptides in extracts of the large parasitic nematode Ascaris suum. This required the assembly of a new database of known and predicted peptides. In addition to those already sequenced, peptides were either previously predicted to be processed from precursor proteins identified in an A. suum library of expressed sequence tags (ESTs) or newly predicted from a library of A. suum genome survey sequences (GSSs). The predicted MS/MS fragmentation patterns of this collection of real and putative peptides were compared with the actual fragmentation patterns found in the MS/MS spectra of peptides fractionated by MS; this enabled individual peptides to be sequenced. Many previously identified peptides were found, and 21 novel peptides were discovered. Thus, this approach is very useful, despite the fact that the available GSS database is still preliminary, having only 1× coverage.

In situ hybridization of neuropeptide-encoding transcripts afp-1, afp-3, and afp-4 in neurons of the nematode Ascaris suum

The gene transcripts encoding both the AF8 and AF2 neuropeptides of the nematode Ascaris suum have been identified, cloned, and sequenced. The AF8 transcript (afp-3) encodes five identical copies of AF8; each peptide-encoding region is flanked by the appropriate dibasic or monobasic cleavage processing sites. The AF2 transcript (afp-4) encodes three identical copies of AF2 along with the appropriate cleavage sites. In contrast, the afp-1 transcript (Edison et al. [1997] Peptides 18:929-935) encodes six different AF peptides (AF3, 4, 10, 13, 14, 20) which all share a -PGVLRFamide C-terminus but have different N-terminal sequences. By using in situ hybridization, gene transcript expression patterns of afp-1, afp-3, and afp-4 (As-flp-18, As-flp-6, and As-flp-14, respectively, in the naming convention proposed by Blaxter et al. [1997] Parasitol Today 13:416-417) were determined in the adult A. suum anterior nervous system. Each gene transcript can be localized to a different subset of neurons. These subsets of neurons are different from the subsets of Caenorhabditis elegans neurons that were shown to express identical or similar peptides by the use of promoter GFP constructs (Kim and Li [2004] J Comp Neurol 475:540-550).

A review of FMRFamide- and RFamide-like peptides in metazoa

Neuropeptides are a diverse class of signalling molecules that are widely employed as neurotransmitters and neuromodulators in animals, both invertebrate and vertebrate. However, despite their fundamental importance to animal physiology and behaviour, they are much less well understood than the small molecule neurotransmitters. The neuropeptides are classified into families according to similarities in their peptide sequence; and on this basis, the FMRFamide and RFamide-like peptides, first discovered in molluscs, are an example of a family that is conserved throughout the animal phyla. In this review, the literature on these neuropeptides has been consolidated with a particular emphasis on allowing a comparison between data sets in phyla as diverse as coelenterates and mammals. The intention is that this focus on the structure and functional aspects of FMRFamide and RFamide-like neuropeptides will inform understanding of conserved principles and distinct properties of signalling across the animal phyla.

Neuropeptides

The role of neuropeptides in modulating behavior is slowly being elucidated. With the sequencing of the C. elegans genome, the extent of the neuropeptide genes in C. elegans can be determined. To date, 113 neuropeptide genes encoding over 250 distinct neuropeptides have been identified. Of these, 40 genes encode insulin-like peptides, 31 genes encode FMRFamide-related peptides, and 42 genes encode non-insulin, non-FMRFamide-related neuropeptides. As in other systems, C. elegans neuropeptides are derived from precursor molecules that must be post-translationally processed to yield the active peptides. These precursor molecules contain a single peptide, multiple copies of a single peptide, multiple distinct peptides, or any combination thereof. The neuropeptide genes are expressed extensively throughout the nervous system, including in sensory, motor, and interneurons. In addition, some of the genes are also expressed in non-neuronal tissues, such as the somatic gonad, intestine, and vulval hypodermis. To address the effects of neuropeptides on C. elegans behavior, animals in which the different neuropeptide genes are inactivated or overexpressed are being isolated. In a complementary approach the receptors to which the neuropeptides bind are also being identified and examined. Among the knockout animals analyzed thus far, defects in locomotion, dauer formation, egg laying, ethanol response, and social behavior have been reported. These data suggest that neuropeptides have a modulatory role in many, if not all, behaviors in C. elegans.

Inter-phyla studies on neuropeptides: the potential for broad-spectrum anthelmintic and/or endectocide discovery

Flatworm, nematode and arthropod parasites have proven their ability to develop resistance to currently available chemotherapeutics. The heavy reliance on chemotherapy and the ability of target species to develop resistance has prompted the search for novel drug targets. In view of its importance to parasite/pest survival, the neuromusculature of parasitic helminths and pest arthropod species remains an attractive target for the discovery of novel endectocide targets. Exploitation of the neuropeptidergic system in helminths and arthropods has been hampered by a limited understanding of the functional roles of individual peptides and the structure of endogenous targets, such as receptors. Basic research into these systems has the potential to facilitate target characterization and its offshoots (screen development and drug identification). Of particular interest to parasitologists is the fact that selected neuropeptide families are common to metazoan pest species (nematodes, platyhelminths and arthropods) and fulfil specific roles in the modulation of muscle function in each of the three phyla. This article reviews the inter-phyla activity of two peptide families, the FMRFamide-like peptides and allatostatins, on motor function in helminths and arthropods and discusses the potential of neuropeptide signalling as a target system that could uncover novel endectocidal agents.

NMR analysis of Caenorhabditis elegans FLP-18 neuropeptides: implications for NPR-1 activation

Phe-Met-Arg-Phe-NH2 (FMRFamide)-like peptides (FLPs) are the largest neuropeptide family in animals, particularly invertebrates. FLPs are characterized by a C-N-terminal gradient of decreasing amino acid conservation. Neuropeptide receptor 1 (NPR-1) is a G-protein coupled receptor (GPCR), which has been shown to be a strong regulator of foraging behavior and aggregation responses in Caenorhabditis elegans. Recently, ligands for NPR-1 were identified as neuropeptides coded by the precursor genes flp-18 and flp-21 in C. elegans. The flp-18 gene encodes eight FLPs including DFDGAMPGVLRF-NH2 and EMPGVLRF-NH2. These peptides exhibit considerably different activities on NPR-1, with the longer one showing a lower potency. We have used nuclear magnetic resonance and biological activity to investigate structural features that may explain these activity differences. Our data demonstrate that long-range electrostatic interactions exist between N-terminal aspartates and the C-terminal penultimate arginine as well as N-terminal hydrogen-bonding interactions that form transient loops within DFDGAMPGVLRF-NH2. We hypothesize that these loops, along with peptide charge, diminish the activity of this peptide on NPR-1 relative to that of EMPGVLRF-NH2. These results provide some insight into the large amino acid diversity in FLPs.

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.

Analysis of FMRFamide-like peptide (FLP) diversity in phylum Nematoda

This study reports a series of systematic BLAST searches of nematode ESTs on the Genbank database, using search strings derived from known nematode FLPs (those encoded by Caenorhabditis elegans flp genes as well as those isolated from other nematodes including Ascaris suum), as well as query sequences representative of theoretical FLPs. Over 1000 putative FLP-encoding ESTs were identified from multiple nematode species. A total of 969 ESTs representing sequelogs of the 23 known C. elegans flp genes were identified in 32 species, from clades I, III, IV and V. Numerical analysis of EST numbers suggests that flp-1, flp-11 and flp-14 are amongst the most highly expressed flp genes. Speculative BLAST searches were performed using theoretical FLP C-termini as queries, in an attempt to identify putative novel FLP sequences in the EST database. These searches yielded eight multi-species sequelogs encoding FLPs with novel signatures that are believed to identify distinct flp genes. These novel genes encode 25 distinct previously unidentified FLPs, and raise the current total of known nematode flp genes to 31. Additionally, software-based analyses of the presence of signal peptides were performed, with signal peptides being identified on at least one member of each group of flp ESTs, further confirming their status as secreted peptides. The data reveal that nematode FLPs encompass the most complex neuropeptide family known within the metazoa. Moreover, individual FLPs and FLP motifs are highly conserved across the nematodes with little evidence for inter-clade or inter-lifestyle variation, supporting their fundamental role in free-living and parasitic species.

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.

Changes in FaRP-like peptide levels during development of eggs from the plant-parasitic cyst nematode, Heterodera glycines

The plant-parasitic cyst nematode Heterodera glycines requires a host plant to complete its life cycle, which involves hatching of infective juveniles that parasitize through root entry. A laboratory population of H. glycines grown on soybean, Glycine max, undergoes a sharp increase in maturity between 5 and 6 weeks in culture, as measured by the proportion of eggs containing well developed pre-hatch juveniles (late development eggs) versus eggs without visible juveniles (early development eggs). The median percent of eggs classified as late development, representing all samples taken from 4 to 7 weeks in culture, was 61%. For all samples taken up to 5 weeks, 80% scored below the median. In samples taken after 5 weeks, 15% scored below the median. This shift in population maturity was accompanied by a significant increase (P < 0.01) in the number of hatched juveniles present in each sample. There was also a significant increase (P < 0.02) in amount of FaRP-like peptide detected by specific ELISA. Total FaRP levels increased from 0.18 +/- 0.07 fMol FLRFamide equivalents per ng protein in early development eggs to 0.40 +/- 0.17 in late development eggs. The level remained high in hatched juveniles. HPLC/ELISA detected as many as nine potential FaRPs in H. glycines, two of which were specifically increased (P < 0.005) in hatched juveniles. The association of FaRPs with maturing eggs and the possible involvement of these neuropeptides with juvenile hatching and motility are discussed.

Mass spectrometric map of neuropeptide expression in Ascaris suum

A mass spectrometric method was used for the localization and sequence characterization of peptides in the nervous system of the parasitic nematode Ascaris suum. Mass spectrometric techniques utilizing MALDI-TOF, MALDI-TOF/TOF, and MALDI-FT instruments were combined with in situ chemical derivatization to examine the expression of known and putative neuropeptides in the A. suum nervous system. This first attempt at peptidomic characterization in A. suum mapped the expression of 39 neuropeptides, 17 of which are considered to be novel and whose expression has not been previously reported. These analyses also revealed that the peptide expression profile is unique to each nervous structure and that the majority of peptides observed belong to the RFamide family of neuropeptides. In addition, four new peptide sequences with a shared C-terminal PNFLRFamide motif are proposed based on in situ sequencing with mass spectrometry.

Inhibition of Caenorhabditis elegans social feeding by FMRFamide-related peptide activation of NPR-1

Social and solitary feeding in natural Caenorhabditis elegans isolates are associated with two alleles of the orphan G-protein-coupled receptor (GPCR) NPR-1: social feeders contain NPR-1 215F, whereas solitary feeders contain NPR-1 215V. Here we identify FMRFamide-related neuropeptides (FaRPs) encoded by the flp-18 and flp-21 genes as NPR-1 ligands and show that these peptides can differentially activate the NPR-1 215F and NPR-1 215V receptors. Multicopy overexpression of flp-21 transformed wild social animals into solitary feeders. Conversely, a flp-21 deletion partially phenocopied the npr-1(null) phenotype, which is consistent with NPR-1 activation by FLP-21 in vivo but also implicates other ligands for NPR-1. Phylogenetic studies indicate that the dominant npr-1 215V allele likely arose from an ancestral npr-1 215F gene in C. elegans. Our data suggest a model in which solitary feeding evolved in an ancestral social strain of C. elegans by a gain-of-function mutation that modified the response of NPR-1 to FLP-18 and FLP-21 ligands.

The ovijector of Ascaris suum: multiple response types revealed by Caenorhabditis elegans FMRFamide-related peptides

Caenorhabditis elegans possesses 22 FMRFamide-like peptide (flp) genes predicted to encode 60 different FMRFamide-related peptides with a range of C-terminal signatures. Peptides from five flp genes (1, 6, 8, 9 and 14) are known to modulate the ovijector of Ascaris suum in vitro. This study examines the physiological effects of peptides from the remaining 17 flp genes such that the variety of FMRFamide-related peptide-induced ovijector response types can be delineated. Five categories of response were identified according to the pattern of changes in contractile behaviour and baseline tension. Peptides encoded on 16 flp genes (1, 2, 3, 4, 6, 7, 9, 10, 11, 12, 13, 14, 15, 16, 17 and 20) had qualitatively similar inhibitory (response type 1) actions, with the lowest activity thresholds (1 nM) recorded for peptides with FIRFamide or FLRFamide C-terminal signatures. Peptides encoded on four flp genes (2, 18, 19 and 21), and on the A. suum afp-1 gene, had excitatory actions on the ovijector (response type 2), with PGVLRFamides having the lowest activity threshold (1 nM). An flp-2 peptide (LRGEPIRFamide) induced a transient contraction of the ovijector (activity threshold, 10nM) that was designated response type 3. Response type 4 comprised a transient contraction followed by an extended period of inactivity and was observed with peptides encoded on flp-5 (AGAKFIRFamide, APKPKFIRFamide), flp-8 (KNEFIRFamide) and flp-22 (SPSAKWMRFamide). SPSAKWMRFamide was the most potent peptide tested with an activity threshold of 0.1 nM. A single peptide (AMRNALVRFamide; activity threshold 0.1 microM), encoded on flp-11, induced response type 5, a shortening of the ovijector coupled with an increase in contraction frequency. Although most flp genes encode structurally related peptides that trigger one of the five ovijector response types, flp-2 and flp-11 co-encode FMRFamide-related peptides that induce distinct responses. Within the ovijector of A. suum FaRPs play a complex role involving at least five receptor subtypes or signalling pathways.

Four novel PYFs: members of NPY/PP peptide superfamily from the eyestalk of the giant tiger prawn Penaeus monodon

An immunocytochemical method was used for localization of pancreatic polypeptide (PP) immunoreactive substances in the eyestalk of Penaeus monodon using anti-C-terminal hexapeptide of PP (anti-PP6) antiserum. Approximately 200 neuronal cell bodies were recognized in the ganglia between the medulla interna (MI) and medulla terminalis (MT) and surrounding MT in conjunction with the neuronal processes in medulla externa (ME), MI, MT and sinus gland. About half of the PP immunoreactive neurons were also recognized by a combination of three monoclonal antibodies raised against FMRFamide-like peptides. Isolation of the PP immunoreactive substances from the eyestalk was performed using 7500 eyestalks extracted in methanol/acetic acid/water (90/1/9) followed by five to six steps of RP-HPLC separation. Dot-ELISA with anti-PP6 antiserum was used to monitor PP-like substances in various fractions during the purification processes. Four new sequences of one hexapeptide; RARPRFamide, and three nonapeptides; YSQVSRPRFamide, YAIAGRPRFamide and YSLRARPRFamide were identified, and named as Pem-PYF1-4 due to their structural similarity to the PYF found in squid Loligo vulgaris. Each of the new peptides shares four to seven common residues with the C-terminus of the squid PYF and with the NPFs found in other invertebrates. The NPY/PP superfamily as well as the FMRFamide peptide family may be present throughout vertebrates and invertebrates.

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.

Seven novel FMRFamide-like neuropeptide sequences from the eyestalk of the giant tiger prawn Penaeus monodon

FMRFamide-like immunoreactivity (FLI) was localized in the eyestalk of Penaeus monodon by immunohistochemistry using a combination of three anti-FMRFamide-like peptide (FLPs) monoclonal antibodies. Approximately 3000 small neuronal cell bodies in the lamina ganglionalis; 100 medium to large size at the ganglion between the medulla interna and the medulla terminalis; and 250 medium size around the medulla terminalis were stained intensely. The neuronal processes in neuropils of the medulla externa, medulla interna, medulla terminalis, sinus gland and some nerve fibers in the optic nerve were also recognized. The small cell bodies, approximately 1500 cells, anterior to the medulla externa were stained inconsistently and the neuronal processes were not observed from these cells. Isolation of FLPs from 9000 eyestalks was performed using methanol/acetic/water (90:1:9) extraction. After the extract was partially purified using C18 cartridges, it was further purified by five to seven steps of RP-HPLC using three kinds of columns: C18; C8; and cyano, and three solvent systems: acetonitrile/trifluoro acetic acid; aceonitrile/heptafluoro butyric acid; and acetonitrile/triethyl ammonium acetate. Dot-ELISA using the combination of the same antibodies was used to monitor FLPs in the fractions during purification processes. Seven new sequences of FLPs were identified which can be divided into four subgroups according to the primary structure of the C-terminus: (1) GDRNFLRFamide; (2) AYSNLNYLRFamide; (3) AQPSMRLRFamide, SQPSMRLRFamide, SMPSLRLRFamide and DGRTPALRLRFamide; and (4) GYRKPPFNGSIFamide. These data indicate the high complexity of this peptide family in which multiple forms are usually exist.

Caenorhabditis elegans: how good a model for veterinary parasites?

The organism about which most is known on a molecular level is a nematode, the free-living organism Caenorhabditis elegans. This organism has served as a reasonable model for the discovery of anthelmintic drugs and for research on the mechanism of action of anthelmintics. Useful information on mechanisms of anthelmintic resistance has also been obtained from studies on C. elegans. Unfortunately, there has not been a large-scale extension of genetic techniques developed in C. elegans to research on parasitic species of veterinary (or human) parasites. Much can be learned about the essentials of nematode biology by studying C. elegans, but discovering the basic biology of nematode parasitism can only be gained through comparative studies on multiple parasitic species.

Regulation of the pharynx of Caenorhabditis elegans by 5-HT, octopamine, and FMRFamide-like neuropeptides

More than fifty FMRFamide-like neuropeptides have been identified in nematodes. We addressed the role of a subset of these in the control of nematode feeding by electrophysiological recording of the activity of C. elegans pharynx. AF1 (KNEFIRFamide), AF2 (KHEYLRFamide), AF8 (KSAYMRFamide), and GAKFIRFamide (encoded by the C. elegans genes flp-8, flp-14, flp-6, and flp-5, respectively) increased pharyngeal action potential frequency, in a manner similar to 5-HT. In contrast, SDPNFLRFamide, SADPNFLRFamide, SAEPFGTMRFamide, KPSVRFamide, APEASPFIRFamide, and AQTVRFamide (encoded by the C. elegans genes flp-1; flp-1; flp-3; flp-9; flp-13, and flp-16, respectively) inhibited the pharynx in a manner similar to octopamine. Only three of the neuropeptides had potent effects at low nanomolar concentrations, consistent with a physiological role in pharyngeal regulation. Therefore, we assessed whether these three peptides mediated their actions either directly on the pharynx or indirectly via the neural circuit controlling its activity by comparing actions between wild-type and mutants with deficits in synaptic signaling. Our data support the conclusion that AF1 and SAEPFGTMRFamide regulate the activity of the pharynx indirectly, whereas APEASPFIRFamide exerts its action directly. These results are in agreement with the expression pattern for the genes encoding the neuropeptides (Kim and Li, 1999) as both flp-8 and flp-3 are expressed in extrapharyngeal neurons, whereas flp-13 is expressed in I5, a neuron with synaptic output to the pharyngeal muscle. These results provide the first, direct, functional information on the action of neuropeptides in C. elegans. Furthermore, we provide evidence for a putative inhibitory peptidergic synapse, which is likely to have a role in the control of feeding.

Isolation and preliminary biological assessment of AADGAPLIRFamide and SVPGVLRFamide from Caenorhabditis elegans

To date, 9 FMRFamide-related peptides (FaRPs) have been structurally characterised from Caenorhabditis elegans. Radioimmunometrical screening of an ethanolic extract of C. elegans revealed the presence of two additional FaRPs that were purified by reverse-phase HPLC and subjected to Edman degradation analysis and gas-phase sequencing. Unequivocal primary structures for the two FaRPs were determined as Ala-Ala-Asp-Gly-Ala-Pro-Leu-Ile-Arg-Phe-NH(2) and Ser-Val-Pro-Gly-Val-Leu-Arg-Phe-NH(2). Using MALDI-TOF mass spectrometry, the molecular masses of the peptides were found to be 1032 Da (MH) and 875 Da (MH)(+), respectively. Two copies of AADGAPLIRFamide are predicted to be encoded on the precursor gene termed flp-13, while one copy of SVPGVLRFamide is located on flp-18. Synthetic replicates of the peptides were tested on Ascaris suum somatic muscle to assess bioactivity. ADDGAPLIRFamide had inhibitory effects on A. suum muscle strips, which occurred over a range of concentrations from a threshold for activity of 10 nM to 10 microM. SVPGVLRFamide was excitatory on A. suum somatic musculature from a threshold concentration for activity of 1 nM to 10 microM. The inhibitory and excitatory effects of AADGAPLIRFamide and SVPGVLRFamide, respectively, were the same for dorsal and ventral muscle strips as well as innervated and denervated preparations, suggesting that these physiological effects are not nerve cord dependent. Addition of ADDGAPLIRFamide (10 microM) to muscle strips preincubated in high-K(+) and -Ca(2+)-free medium resulted in a normal inhibitory response. Peptide addition to muscle strips preincubated in Cl(-)-free medium showed no inhibitory response, suggesting that the inhibitory response of the peptide may be chloride mediated. A normal excitatory response was noted following the addition of 10 microM SVPGVLRFamide to muscle strips preincubated in high-K(+), Ca(2+)- and Cl(-)-free media.

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.

Structure-activity relationships of 18 endogenous neuropeptides on the motor nervous system of the nematode Ascaris suum

Neuropeptides play an important role in all nervous systems and structure-activity studies of related peptides is one approach to understanding this role. This study of the motor nervous system of the parasitic nematode Ascaris suum describes the physiological effects of a family of 18 endogenous Ascaris FMRFamide-like peptides (AF peptides) on the membrane potential and input resistance of the dorsal excitatory type 2 (DE2) and dorsal inhibitory (DI) motor neurons. These motor neurons are part of the final common output pathway from the motor nervous system to the somatic muscle cells responsible for locomotion. AF peptide effects on the frequency of excitatory postsynaptic potentials (EPSPs) in DE2 motor neurons were also measured to infer peptide effects on central presynaptic spiking neurons. AF peptide injections into intact worms were made to assess their qualitative effects on behavior, providing a context for interpreting motor neuron data. One category of AF peptides, N-terminally extended -FIRFa peptides (AF5, AF7 and AF1), has pronounced behavioral effects and qualitatively similar, but quantitatively different effects on DE2 and DI motor neurons. A second category of AF peptides (AF2, AF9, and AF8) also produces dramatic behavioral effects and strong electrophysiological effects on DE2 and/or DI motor neurons. A third category of AF peptides, consisting of six members of the -PGVLRFa group (which are encoded by the same gene and have closely related sequences) and peptide AF11, have pronounced behavioral effects, but relatively weak or negligible effects on DE2 and DI motor neurons. A fourth category of AF peptides, also consisting of structurally unrelated members, has pronounced behavioral effects and, as individual peptides, similar effects on both DE2 and DI motor neurons; AF15 is excitatory, while AF17 and AF19 are inhibitory, on both motor neuron types. Finally, two AF peptides (AF6, AF16) are relatively weak or inactive in producing behavioral or motor neuronal effects. Based on comparisons of the effects of AF peptides on DE2 and DI motor neurons, a tentative list of 5 major response-types is proposed as a working hypothesis to guide the search for AF peptide receptors. The findings attest to the potential complexity of neurosignaling in this comparatively simple nervous system.

Changes in locomotory behavior and cAMP produced in Ascaris suum by neuropeptides from Ascaris suum or Caenorhabditis elegans

Injection of Ascaris FMRFamide-like (AF) peptides and peptides encoded by genes in Caenorhabditis elegans were analyzed for effects on locomotion, body waveforms, and cAMP concentrations in adult female Ascaris suum. Injection of AF1 (KNEFIRFamide) or AF2 (KHEYLRFamide) inhibited the propagation of locomotory waves and reduced the number of waveforms, decreased the body length, and caused a large, long-lasting increase in cAMP. Muscle tissue was identified as a major source of the cAMP response induced by AF1. The AF1 analog AF1R6A did not affect cAMP levels by itself, but inhibited the cAMP response produced by AF1. AF8 (KSAYMRFamide) produced ventral coiling in the behavioral assay, and AF10 (GFGDEMSMPGVLRFamide) decreased the body length and increased the number of body waveforms. In dorsal muscle strips, AF10 produced a long-lasting contraction. Neither AF8 nor AF10 changed cAMP concentrations. AF17 (FDRDFMHFamide) increased body length and decreased cAMP. The neuropeptides encoded by C. elegans genes flp-4, flp-7, flp-9, and flp-13 produced paralysis and loss of waveforms, increased body length and, like AF17, decreased cAMP. Three new predicted peptides from C. elegans genome sequences were synthesized and tested. One produced ventral coiling but no change in cAMP; the other two gave no detectable responses. The fact that C. elegans neuropeptides produce behavioral and physiological effects in A. suum suggests that structurally related peptides may exist in A. suum. The profound changes in cAMP produced by some neuropeptides has important implications for understanding cAMP signaling and shows that neuropeptide-mediated signal transduction pathways are potential targets for anthelmintic drug development.

Computational analysis of two similar neuropeptides yields distinct conformational ensembles

Conformational states and thermodynamic properties for two similar neuropeptides, GDPFLRF-NH(2) and GYPFLRF-NH(2), have been computed by Monte Carlo simulated annealing (MCSA) conformational searches and Metropolis Monte Carlo (MMC) calculations. These peptides were recently shown to have dramatically different conformations in solution by NMR [Edison et al., J Neuroscience 1999;19:6318-6326]. Final conformations of multiple independent MCSA runs were the starting points for MMC calculations, and conformations saved at intervals during MMC runs were characterized in terms of total energy, configuration entropy, side-chain fraction population, and ensemble average inter-nuclear distances. Without the use of any NMR data-generated pseudo-potentials, the present calculations were in excellent qualitative agreement with all previous NMR experimental data and provided a foundation by which to more quantitatively interpret the experimental NMR results. Proteins 2000;40:367-377.

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.

Gene expression and function of FMRFamide-related neuropeptides in the snail Lymnaea

FMRFamide and a large family of related peptides (FaRPs) have been identified in every major metazoan phylum examined, including chordates. In the pulmonate snail Lymnaea this family of neuropeptides is encoded by a five-exon locus that is subject to alternative splicing. The two alternative mRNA transcripts are expressed in the CNS in a mutually exclusive manner at the single cell level, resulting in the differential distribution of the distinct sets of FaRPs that they encode in defined neuronal networks. Biochemical peptide purification, single-cell analysis by mass spectroscopy, and immunocytochemistry have led to an understanding of the post-translational processing patterns of the two alternative precursor proteins and identified at least 12 known and novel peptides contained in neuronal networks involved in cardiorespiration, penial control and withdrawal response. The pharmacological actions of single or co-expressed peptides are beginning to emerge for the cardiorespiratory network and its central and peripheral targets. Peptides derived from protein precursor 1 and contained in the heart excitatory central motoneurons E(he) have distinct functions and also act in concert in cardiac regulation, based on their unique effects on heartbeat and their differential stimulatory effects on second messenger pathways. Precursor-2 derived peptides, contained in the Visceral White Interneuron, a key neuron of the cardiorespiratory network, have mostly inhibitory effects on the VWI's central postsynaptic target neurons but with some of the peptides also exhibiting excitatory effects on the same cells.

Pharmacology of FMRFamide-related peptides in helminths

Nervous systems of helminths are highly peptidergic. Species in the phylum Nematoda (roundworms) possess at least 50 FMRFamide-related peptides (FaRPs), with more yet to be identified. To date, few non-FaRP neuropeptides have been identified in these organisms, though evidence suggests that other families are present. FaRPergic systems have important functions in nematode neuromuscular control. In contrast, species in the phylum Platyhelminthes (flatworms) apparently utilize fewer FaRPs than do nematodes; those species examined possess one or two FaRPs. Other neuropeptides, such as neuropeptide F (NPF), play key roles in flatworm physiology. Although progress has been made in the characterization of FaRP pharmacology in helminths, much remains to be learned. Most studies on nematodes have been done with Ascaris suum because of its large size. However, thanks to the Caenorhabditis elegans genome project, we know most about the FaRP complement of this free-living animal. That essentially all C. elegans FaRPs are active on at least one A. suum neuromuscular system argues for conservation of ligand-receptor recognition features among the Nematoda. Structure-activity studies on nematode FaRPs have revealed that structure-activity relationship (SAR) "rules" differ considerably among the FaRPs. Second messenger studies, along with experiments on ionic dependence and anatomical requirements for activity, reveal that FaRPs act through many different mechanisms. Platyhelminth FaRPs are myoexcitatory, and no evidence exists of multiple FaRP receptors in flatworms. Interestingly, there are examples of cross-phylum activity, with some nematode FaRPs being active on flatworm muscle. The extent to which other invertebrate FaRPs show cross-phylum activity remains to be determined. How FaRPergic nerves contribute to the control of behavior in helminths, and are integrated with non-neuropeptidergic systems, also remains to be elucidated.

Actions of nematode FMRFamide-related peptides on the pharyngeal muscle of the parasitic nematode, Ascaris suum

The endogenous nematode peptides known as FMRFamide-related peptides (FaRPs) and various "classical" transmitters have a range of effects on nematodes that result in changes in behavior, particularly locomotion, including paralysis and inhibition of feeding. This study describes the application of an in vitro pharmacological approach to further delineate the action of a number of FaRP neurotransmitters on feeding behavior. Contraction of Ascaris suum pharyngeal muscle was monitored using a modified pressure transducer system that detects changes in intrapharyngeal pressure and therefore contraction of the radial muscle of the pharynx. The pharynx did not contract spontaneously. However, serotonin (5-HT, 100 microM) stimulated rhythmic contractions and relaxations (pumping) at a frequency of 0.5 Hz. The native nematode peptide, KNEFIRFamide (AF1), inhibited the pumping elicited by 5-HT. The duration of inhibition was concentration-dependent (1-1000 nM) with a threshold of 1 nM (n = 7). KSAYMRFamide (AF8/PF3) also inhibited pharyngeal pumping. There was no observable effect of any of the following nematode peptides on pharyngeal pumping behavior (1-1000 nM; n = 8): AF2, AF3, AF4, AF6, AF16, PF1/CF1, PF2/CF2, or PF4. Thus, interruption of pharyngeal processes, such as feeding, regulation of hydrostatic pressure, and secretion, may provide a new site of anthelmintic action.

Neuropeptide gene families in the nematode Caenorhabditis elegans

Neuropeptides have diverse roles in the function and development of the nervous system. With the completion of the sequencing of the C. elegans genome, rapid identification of nematode neuropeptide genes is possible. To date, 41 C. elegans neuropeptide genes have been identified. Of these genes, 20 genes, named flp (FMRFamide-like peptide) genes, encode FMRFamide-related proteins (FaRPs). Deletion of one of the flp genes, flp-1, results in several behavioral defects, suggesting that at least one flp gene is not functionally redundant with other flp genes. Twenty-one genes, named neuropeptide-like protein (nlp) genes, encode peptides distinct from the FaRP family. The predicted nlp-1 and nlp-2 neuropeptides have modest similarity to buccalin and myomodulin, respectively. Cellular expression patterns and genetic analysis of flp and nlp genes suggest that neuropeptides in nematodes also have widespread and varied roles in nervous system function.

Conformational ensembles: the role of neuropeptide structures in receptor binding

Conformational properties of several similar FMRFamide-like neuropeptides from mollusks were investigated by nuclear magnetic resonance (NMR) spectroscopy. It was found that amino acid substitutions in the N-terminal variable regions of the peptides had dramatic effects on the populations of reverse turns in solution. The populations of turns, as measured by two independent NMR parameters, were found to be highly correlated (r(2) = 0.93 and 0. 82) with IC(50) values using receptor membrane preparations from Helix aspersa (Payza, 1987; Payza et al., 1989). These results suggest that the amount of turn in the free peptide can influence the receptor binding affinities of that peptide. On the basis of these observations, a model was developed in which only a single species from a conformational ensemble of an unbound peptide will bind to a particular receptor. Thus, the conformational ensemble reduces the effective concentration of a particular peptide with respect to a particular receptor.

Differential processing of neuropeptides influences Drosophila heart rate

Peptides that play critical physiological roles are often encoded in precursors that contain several structurally-related gene products. Differential processing of a precursor by cell-specific processing enzymes can yield multiple messengers with diverse distributions and activities. We have reported the isolation of SDNFMRFamide, DPKQDFMRFamide, and TPAEDFMRFamide from adult Drosophila melanogaster. The peptides are encoded in the FMRFamide gene and have a common C-terminal FMRFamide but different N-terminal extensions. In order to investigate the processing of the FMRFamide polypeptide protein precursor, we generated antisera to distinguish among the structurally-related neuropeptides. Utilizing a triple-label immunofluorescent protocol, we mapped the distribution of the peptides. Each peptide has a unique, non-overlapping cellular expression pattern in neural tissue suggesting that the precursor is differentially processed. In order to identify a biological activity of the peptides, we established an in vivo heart rate assay. SDNFMRFamide decreases heart rate but DPKQDFMRFamide and TPAEDFMRFamide do not, indicating that the N-terminal residues are critical for this activity. SDNFMRFamide immunoreactivity is present in the aorta, implying that SDNFMRFamide acts locally to affect heart rate; DPKQDFMRFamide and TPAEDFMRFamide antisera do not stain cardiac tissue. Our data support the conclusion that Drosophila contains cell-specific proteolytic enzymes to differentially process a polypeptide protein precursor resulting in unique expression patterns of structurally-related, yet functionally distinct neuropeptides.

Exploring the neurotransmitter labyrinth in nematodes

Nematodes include both free-living species such as Caenorhabditis elegans and major parasites of humans, livestock and plants. The apparent simplicity and uniformity of their nervous system belies a rich diversity of putative signalling molecules, particularly neuropeptides. This new appreciation stems largely from the genome-sequencing project with C. elegans, which is due to be completed by the end of 1998. The project has provided additional insights into other aspects of nematode neurobiology, as have studies on the mechanism of action of anthelmintics. Here, progress on the identification, localization, synthesis and physiological actions of transmitters identified in nematodes is explored.

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.

FMRFamide-related gene family in the nematode, Caenorhabditis elegans

Many organisms, including mammals, use short peptides as neurotransmitters. The family of FMRFamide (Phe-Met-Arg-Phe-NH2)-like neuropeptides, which all share an -RFamide sequence at their C-termini, has been shown to have diverse functions, including neuromodulation and stimulation or inhibition of muscle contraction. In the nematode, Caenorhabditis elegans, FMRFamide-like peptides (FaRPs) are expressed in approximately 10% of the neurons, including motor, sensory, and interneurons that are involved in movement, feeding, defecation, and reproduction. At least 14 genes, designated flp-1 through flp-14, encode FaRPs in C. elegans. Here, we present data that all 14 flp genes are transcribed in C. elegans, and several of these genes are alternatively spliced. Each flp gene encodes a different set of FaRPs, yielding a predicted total of 44 distinct FaRPs. Using staged RNA for reverse-transcription/polymerase chain reactions (RT/PCR), we determined that most flp genes are expressed throughout development. These results suggest that a complex family of FaRPs have varied roles through all stages of development and in adulthood in C. elegans.

The role of cAMP in the actions of the peptide AF3 in the parasitic nematodes Ascaris suum and Ascaridia galli

AF3 (AVPGVLRFamide) is an endogenous RFamide-like peptide isolated from the parasitic nematode Ascaris suum. It has a potent and long lasting excitatory effect in A. suum and Ascaridia galli. This is mediated by a mechanism independent of the nicotinic-like acetylcholine (ACh) receptor, which mediates excitatory transmission at the neuromuscular junction of both nematodes. In addition, AF3 has been found to sensitise A. suum muscle to the contractile effect of ACh. In this study, the involvement of the second messenger cAMP in mediating the action of AF3 on the somatic musculature of A. suum and A. galli has been investigated. Two approaches have been used; the effects of drugs which raise intracellular cAMP levels on the contractile responses to AF3 have been examined and biochemical assays have been used to measure the effects of AF3 on cAMP levels. AF3 contractions were inhibited in A. suum by 10 microM forskolin (by 22% of control; P < 0.05; n = 9) and by 500 microM isobutylmethylxanthine (IBMX, by 27% of control; P < 0.001; n = 6). AF3 decreased cAMP concentrations in A. suum somatic muscle (basal, 1721 +/- 134 pmol mg-1 protein; with 1 microM AF3, 1148 +/- 133 pmol mg-1 protein; P < 0.05, n = 5). AF3 (1 microM) also reduced the 10 microM forskolin induced potentiation of cAMP concentrations in A. suum (forskolin 3242 +/- 471 pmol mg-1 protein; forskolin and AF3, 1524 +/- 143 pmol mg-1 protein; P < 0.001, n = 6) and A. galli (forskolin 291 +/- 32 pmol mg-1 protein, forskolin +AF3, 185 +/- 12 pmol mg-1 protein; P < 0.005, n = 5). These data suggest that in both nematodes the contractile effect of AF3 is, at least in part, regulated by cAMP.