Identification of a calcitonin-like diuretic hormone that functions as an intrinsic modulator of the American lobster, Homarus americanus, cardiac neuromuscular system

Diversity of neuropeptidergic modulation in decapod crustacean cardiac and feeding systems

All nervous systems are multiply modulated by polypeptides. However, a bulk of transmitter and modulation research has historically focused on small molecule transmitters released at synaptic sites. The stomatogastric nervous system (controls digestive movements of the foregut) and cardiac nervous system of decapod crustaceans have long been used to understand the processes that underlie neuromodulation. The circuits governing the rhythmic output from these nervous systems are comprised of a relatively small number of identified neurons, and the details of these nervous systems are well-defined. Here we discuss recent research highlighting advances in our understanding of peptidergic modulation in these systems. In particular, we focus on our ability to identify specific signaling peptide sequences and relate their expression patterns to their physiological effects, as well as on the multiple sites within a pattern generator-effector system at which modulation takes place. Recent efforts have enabled us to understand how co-modulation by two or more peptides can generate surprising effects on circuit physiology and that modulation at different receptor sites can produce supra-additive effects. Finally, we examine the protective role modulation plays in making circuits robust to perturbations, in this case, changes in temperature.

Isoforms of the neuropeptide myosuppressin differentially modulate the cardiac neuromuscular system of the American lobster, Homarus americanus

Post-translational modifications (PTMs) diversify peptide structure and allow for greater flexibility within signaling networks. The cardiac neuromuscular system of the American lobster, Homarus americanus, consists of a central pattern generator, the cardiac ganglion (CG), and peripheral cardiac muscle. Together, these components produce flexible output in response to peptidergic modulation. Here, we examined the role of PTMs in determining the effects of a cardioactive neuropeptide, myosuppressin (pQDLDHVFLRFamide), on the whole heart, the neuromuscular junction/muscle, the isolated CG, and the neurons of the CG. Mature myosuppressin and non-cyclized myosuppressin (QDLDHVFLRFamide) elicited similar and significant changes in whole heart contraction amplitude and frequency, stimulated muscle contraction amplitude, and the bursting pattern of the intact and ligatured neurons of the ganglion. In the whole heart, non-amidated myosuppressin (pQDLDHVFLRFG) elicited only a small decrease in frequency and amplitude. In the absence of motor neuron input, non-amidated myosuppressin did not cause any significant changes in the amplitude of stimulated contractions. In the intact CG, non-amidated myosuppressin elicited a small but significant decrease in burst duration. Further analysis revealed a correlation between the extent of modulation elicited by non-amidated myosuppressin in the whole heart and the isolated, intact CG. When the neurons of the CG were physically decoupled, non-amidated myosuppressin elicited highly variable responses. Taken together, these data suggest that amidation, but not cyclization, is critical in enabling this peptide to exert its effects on the cardiac neuromuscular system.

Identification and characterization of expression profiles of neuropeptides and their GPCRs in the swimming crab, Portunus trituberculatus

Neuropeptides and their G protein-coupled receptors (GPCRs) regulate multiple physiological processes. Currently, little is known about the identity of native neuropeptides and their receptors in Portunus trituberculatus. This study employed RNA-sequencing and reverse transcription-polymerase chain reaction (RT-PCR) techniques to identify neuropeptides and their receptors that might be involved in regulation of reproductive processes of P. trituberculatus. In the central nervous system transcriptome data, 47 neuropeptide transcripts were identified. In further analyses, the tissue expression profile of 32 putative neuropeptide-encoding transcripts was estimated. Results showed that the 32 transcripts were expressed in the central nervous system and 23 of them were expressed in the ovary. A total of 47 GPCR-encoding transcripts belonging to two classes were identified, including 39 encoding GPCR-A family and eight encoding GPCR-B family. In addition, we assessed the tissue expression profile of 33 GPCRs (27 GPCR-As and six GPCR-Bs) transcripts. These GPCRs were found to be widely expressed in different tissues. Similar to the expression profiles of neuropeptides, 20 of these putative GPCR-encoding transcripts were also detected in the ovary. This is the first study to establish the identify of neuropeptides and their GPCRs in P. trituberculatus, and provide information for further investigations into the effect of neuropeptides on the physiology and behavior of decapod crustaceans.

Mass spectrometry profiling and quantitation of changes in circulating hormones secreted over time in Cancer borealis hemolymph due to feeding behavior

The crustacean stomatogastric ganglion (STG) is a valuable model for understanding circuit dynamics in neuroscience as it contains a small number of neurons, all easily distinguishable and most of which contribute to two complementary feeding-related neural circuits. These circuits are modulated by numerous neuropeptides, with many gaining access to the STG as hemolymph-transported hormones. Previous work characterized neuropeptides in the hemolymph of the crab Cancer borealis but was limited by low peptide abundance in the presence of a complex biological matrix and the propensity for rapid peptide degradation. To improve their detection, a data-independent acquisition (DIA) mass spectrometry (MS) method was implemented. This approach improved the number of neuropeptides detected by approximately twofold and showed greater reproducibility between experimental and biological replicates. This method was then used to profile neuropeptides at different stages of the feeding process, including hemolymph from crabs that were unfed, or 0 min, 15 min, 1 h, and 2 h post-feeding. The results show differences both in the presence and relative abundance of neuropeptides at the various time points. Additionally, 96 putative neuropeptide sequences were identified with de novo sequencing, indicating there may be more key modulators within this system than is currently known. These results suggest that a distinct cohort of neuropeptides provides modulation to the STG at different times in the feeding process, providing groundwork for targeted follow-up electrophysiological studies to better understand the functional role of circulating hormones in the neural basis of feeding behavior.

Differential neuropeptide modulation of premotor and motor neurons in the lobster cardiac ganglion

The American lobster, Homarus americanus, cardiac neuromuscular system is controlled by the cardiac ganglion (CG), a central pattern generator consisting of four premotor and five motor neurons. Here, we show that the premotor and motor neurons can establish independent bursting patterns when decoupled by a physical ligature. We also show that mRNA encoding myosuppressin, a cardioactive neuropeptide, is produced within the CG. We thus asked whether myosuppressin modulates the decoupled premotor and motor neurons, and if so, how this modulation might underlie the role(s) that these neurons play in myosuppressin's effects on ganglionic output. Although myosuppressin exerted dose-dependent effects on burst frequency and duration in both premotor and motor neurons in the intact CG, its effects on the ligatured ganglion were more complex, with different effects and thresholds on the two types of neurons. These data suggest that the motor neurons are more important in determining the changes in frequency of the CG elicited by low concentrations of myosuppressin, whereas the premotor neurons have a greater impact on changes elicited in burst duration. A single putative myosuppressin receptor (MSR-I) was previously described from the Homarus nervous system. We identified four additional putative MSRs (MSR-II-V) and investigated their individual distributions in the CG premotor and motor neurons using RT-PCR. Transcripts for only three receptors (MSR-II-IV) were amplified from the CG. Potential differential distributions of the receptors were observed between the premotor and motor neurons; these differences may contribute to the distinct physiological responses of the two neuron types to myosuppressin.NEW & NOTEWORTHY Premotor and motor neurons of the Homarus americanus cardiac ganglion (CG) are normally electrically and chemically coupled, and generate rhythmic bursting that drives cardiac contractions; we show that they can establish independent bursting patterns when physically decoupled by a ligature. The neuropeptide myosuppressin modulates different aspects of the bursting pattern in these neuron types to determine the overall modulation of the intact CG. Differential distribution of myosuppressin receptors may underlie the observed responses to myosuppressin.

Characterization of an evolutionarily conserved calcitonin signaling system in a lophotrochozoan, the Pacific oyster (Crassostrea gigas)

In Protostoma, the diuretic hormone 31 (DH31) signaling system was long considered as the orthologue of the chordate calcitonin (CT) signaling system. Using the Pacific oyster (Crassostrea gigas) transcriptomic database GigaTON (http://ngspipelines-sigenae.toulouse.inra.fr/), we characterized seven G-protein-coupled receptors (GPCRs) named Cragi-CTR1/7 and phylogenetically related to chordate CT receptors (CTRs) and to protostome DH31 receptors. Two CT Precursors (Cragi-CTP1 and Cragi-CTP2) containing two CT-type peptides and encoded by two distinct genes with a similar organization were also characterized. These oyster neuropeptides (Cragi-CT1/2) exhibit the two N-terminal paired cysteine residues and except CTP2 derived peptide (Cragi-CTP2dp) the C-terminal proline-amide motif typical of deuterostome CT-type peptides. All mature Cragi-CTs but Cragi-CTP2dp were detected in visceral ganglion (VG) extracts using mass spectrometry. Cell-based assays revealed that the formerly characterized oyster receptors Cg-CTR and Cragi-CTR2 were specifically activated by Cragi-CT1b and Cragi-CT2, respectively. This activation does not require the co-expression of receptor activity-modifying proteins (RAMPs). Thus, the oyster CT signaling appears functionally more closely related to the vertebrate CT/CTR signaling than to the (Calcitonin Gene Related Peptide) CGRP/CLR signaling. Gene expression profiles in different adult tissues and in oysters acclimated to brackish water suggest the potential implication of both Cg-CT-R/Cragi-CT1b and Cragi-CTR2/Cragi-CT2 in water and ionic regulations, though with apparently opposite effects. The present study represents the first comprehensive characterization of a functional CT-type signaling system in a protostome and provides evidence for its evolutionarily ancient origin and its early role in osmotic homeostasis.

Functional Identification and Characterization of the Diuretic Hormone 31 (DH31) Signaling System in the Green Shore Crab, Carcinus maenas

The functional characterization of crustacean neuropeptides and their cognate receptors has not kept pace with the recent advances in sequence determination and, therefore, our understanding of the physiological roles of neuropeptides in this important arthropod sub-phylum is rather limited. We identified a candidate receptor-ligand pairing for diuretic hormone 31 (DH31) in a neural transcriptome of the crab, Carcinus maenas. In insects, DH31 plays species -specific but central roles in many facets of physiology, including fluid secretion, myoactivity, and gut peristalsis but little is known concerning its functions in crustaceans. The C. maenas DH31 transcript codes for a 147 amino acid prepropeptide, and a single receptor transcript translates to a secretin-like (Class B1) G protein-coupled receptor (GPCR). We used an in vitro aequorin luminescence Ca2+ mobilization assay to demonstrate that this candidate DH31R is activated byCarcinus and insect DH31s in a dose-dependent manner (EC50 15-30 nM). Whole mount immunohistochemical and in situ hybridization localization revealed extensive DH31 expressing neurons throughout the central nervous system, most notably in the abdominal ganglion where large, unpaired cells give rise to medial nerves, which terminate in extensive DH31 immunopositive dendritic fields intimately associated with oesophageal musculature. This system constitutes a large and hitherto undescribed neurohemal area adjacent to key muscle groups associated with the gastric system. DH31 expressing neurons were also seen in the cardiac, commissural, oesophageal, and stomatogastric ganglia and intense labeling was seen in dendrites innervating fore- and hindgut musculature but not with limb muscles. These labeling patterns, together with measurement of DH31R mRNA in the heart and hindgut, prompted us test the effects of DH31 on semi-isolated heart preparations. Cardiac superfusion with peptide evoked increased heart rates (10-100 nM). The neuroanatomical distribution of DH31 and its receptor transcripts, particularly that associated with gastric and cardiac musculature, coupled with the cardio- acceleratory effects of the peptide implicate this peptide in key myoactive roles, likely related to rhythmic coordination.

Neuropeptide discovery in Proasellus cavaticus: Prediction of the first large-scale peptidome for a member of the Isopoda using a publicly accessible transcriptome

In silico transcriptome mining is one of the most effective methods for neuropeptide discovery in crustaceans, particularly for species that are small, rare or from geographically inaccessible habitats that make obtaining the large pools of tissue needed for other peptide discovery platforms impractical. Via this approach, large peptidomes have recently been described for members of many of the higher crustacean taxa, one notable exception being the Isopoda; no peptidome has been predicted for any member of this malacostracan order. Using a publicly accessible transcriptome for the isopod Proasellus cavaticus, a subcentimeter subterranean ground water dweller, the first in silico-predicted peptidome for a member of the Isopoda is presented here. BLAST searches employing known arthropod neuropeptide pre/preprohormone queries identified 49 transcripts as encoding putative homologs within the P. cavaticus transcriptome. The proteins deduced from these transcripts allowed for the prediction of 171 distinct mature neuropeptides. The P. cavaticus peptidome includes members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, diuretic hormone 31, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone α2, leucokinin, myosuppressin, neuroparsin, neuropeptide F, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, sulfakinin, tachykinin-related peptide and trissin families, as well as many linker/precursor-related sequences that may or may not represent additional bioactive molecules. Interestingly, many of the predicted P. cavaticus neuropeptides possess structures identical (or nearly so) to those previously described from members of several other malacostracan orders, i.e., the Decapoda, Amphipoda and Euphausiacea, a finding that suggests broad phylogenetic conservation of bioactive peptide structures, and possibly functions, may exist within the Malacostraca.

Prediction of a neuropeptidome for the eyestalk ganglia of the lobster Homarus americanus using a tissue-specific de novo assembled transcriptome

In silico transcriptome mining is a powerful tool for crustacean peptidome prediction. Using homology-based BLAST searches and a simple bioinformatics workflow, large peptidomes have recently been predicted for a variety of crustaceans, including the lobster, Homarus americanus. Interestingly, no in silico studies have been conducted on the eyestalk ganglia (lamina ganglionaris, medulla externa, medulla interna and medulla terminalis) of the lobster, although the eyestalk is the location of a major neuroendocrine complex, i.e., the X-organ-sinus gland system. Here, an H. americanus eyestalk ganglia-specific transcriptome was produced using the de novo assembler Trinity. This transcriptome was generated from 130,973,220 Illumina reads and consists of 147,542 unique contigs. Eighty-nine neuropeptide-encoding transcripts were identified from this dataset, allowing for the deduction of 62 distinct pre/preprohormones. Two hundred sixty-two neuropeptides were predicted from this set of precursors; the peptides include members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, bursicon α, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone (CHH), CHH precursor-related peptide, diuretic hormone 31, diuretic hormone 44, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone α2, glycoprotein hormone β5, GSEFLamide, intocin, leucokinin, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, orcomyotropin, pigment dispersing hormone, proctolin, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, SIFamide, sulfakinin, tachykinin-related peptide and trissin families. The predicted peptides expand the H. americanus eyestalk ganglia neuropeptidome approximately 7-fold, and include 78 peptides new to the lobster. The transcriptome and predicted neuropeptidome described here provide new resources for investigating peptidergic signaling within/from the lobster eyestalk ganglia.

Peptidergic signaling in the crab Cancer borealis: Tapping the power of transcriptomics for neuropeptidome expansion

The crab Cancer borealis has long been used as a model for understanding neural control of rhythmic behavior. One significant discovery made through its use is that even numerically simple neural circuits are capable of producing an essentially infinite array of distinct motor outputs via the actions of locally released and circulating neuromodulators, the largest class being peptides. While much work has focused on elucidating the peptidome of C. borealis, no investigation has used in silico transcriptome mining for peptide discovery in this species, a strategy proven highly effective for identifying neuropeptides in other crustaceans. Here, we mined a C. borealis neural transcriptome for putative peptide-encoding transcripts, and predicted 200 distinct mature neuropeptides from the proteins deduced from these sequences. The identified peptides include isoforms of allatostatin A, allatostatin B, allatostatin C, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31 (DH31), diuretic hormone 44 (DH44), FMRFamide-like peptide, GSEFLamide, HIGSLYRamide, insulin-like peptide (ILP), intocin, leucokinin, neuroparsin, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, short neuropeptide F and SIFamide. While some of the predicted peptides were known previously from C. borealis, most (159) are new discoveries for the species, e.g., the isoforms of CCHamide, DH31, DH44, GSEFLamide, ILP, intocin and neuroparsin, which are the first members of these peptide families identified from C. borealis. Collectively, the peptides predicted here approximately double the peptidome known for C. borealis, and in so doing provide an expanded platform from which to launch new investigations of peptidergic neuromodulation in this species.

Expansion of the neuropeptidome of the globally invasive marine crab Carcinus maenas

Carcinus maenas is widely recognized as one of the world's most successful marine invasive species; its success as an invader is due largely to its ability to thrive under varied environmental conditions. The physiological/behavioral control systems that allow C. maenas to adapt to new environments are undoubtedly under hormonal control, the largest single class of hormones being peptides. While numerous studies have focused on identifying native C. maenas peptides, none has taken advantage of mining transcriptome shotgun assembly (TSA) sequence data, a strategy proven highly successful for peptide discovery in other crustaceans. Here, a C. maenas peptidome was predicted via in silico transcriptome mining. Thirty-seven peptide families were searched for in the extant TSA database, with transcripts encoding precursors for 29 groups identified. The pre/preprohormones deduced from the identified sequences allowed for the prediction of 263 distinct mature peptides, 193 of which are new discoveries for C. maenas. The predicted peptides include isoforms of adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31, diuretic hormone 44, eclosion hormone, FMRFamide-like peptide, HIGSLYRamide, intocin, leucokinin, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone, proctolin, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, SIFamide, and tachykinin-related peptide. This peptidome is the largest predicted from any single crustacean using the in silico approach, and provides a platform for investigating peptidergic signaling in C. maenas, including control of the processes that allow for its success as a global marine invader.

Prediction of Scylla olivacea (Crustacea; Brachyura) peptide hormones using publicly accessible transcriptome shotgun assembly (TSA) sequences

The aquaculture of crabs from the genus Scylla is of increasing economic importance for many Southeast Asian countries. Expansion of Scylla farming has led to increased efforts to understand the physiology and behavior of these crabs, and as such, there are growing molecular resources for them. Here, publicly accessible Scylla olivacea transcriptomic data were mined for putative peptide-encoding transcripts; the proteins deduced from the identified sequences were then used to predict the structures of mature peptide hormones. Forty-nine pre/preprohormone-encoding transcripts were identified, allowing for the prediction of 187 distinct mature peptides. The identified peptides included isoforms of adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, bursicon β, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, diuretic hormone 31, eclosion hormone, FMRFamide-like peptide, HIGSLYRamide, insulin-like peptide, intocin, leucokinin, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, SIFamide and tachykinin-related peptide, all well-known neuropeptide families. Surprisingly, the tissue used to generate the transcriptome mined here is reported to be testis. Whether or not the testis samples had neural contamination is unknown. However, if the peptides are truly produced by this reproductive organ, it could have far reaching consequences for the study of crustacean endocrinology, particularly in the area of reproductive control. Regardless, this peptidome is the largest thus far predicted for any brachyuran (true crab) species, and will serve as a foundation for future studies of peptidergic control in members of the commercially important genus Scylla.

Forces generated during stretch in the heart of the lobster Homarus americanus are anisotropic and are altered by neuromodulators

Mechanical and neurophysiological anisotropies mediate three-dimensional responses of the heart of ITALIC! Homarus americanus Although hearts ITALIC! in vivoare loaded multi-axially by pressure, studies of invertebrate cardiac function typically use uniaxial tests. To generate whole-heart length-tension curves, stretch pyramids at constant lengthening and shortening rates were imposed uniaxially and biaxially along longitudinal and transverse axes of the beating whole heart. To determine whether neuropeptides that are known to modulate cardiac activity in ITALIC! H. americanusaffect the active or passive components of these length-tension curves, we also performed these tests in the presence of SGRNFLRFamide (SGRN) and GYSNRNYLRFamide (GYS). In uniaxial and biaxial tests, both passive and active forces increased with stretch along both measurement axes. The increase in passive forces was anisotropic, with greater increases along the longitudinal axis. Passive forces showed hysteresis and active forces were higher during lengthening than shortening phases of the stretch pyramid. Active forces at a given length were increased by both neuropeptides. To exert these effects, neuropeptides might have acted indirectly on the muscle via their effects on the cardiac ganglion, directly on the neuromuscular junction, or directly on the muscles. Because increases in response to stretch were also seen in stimulated motor nerve-muscle preparations, at least some of the effects of the peptides are likely peripheral. Taken together, these findings suggest that flexibility in rhythmic cardiac contractions results from the amplified effects of neuropeptides interacting with the length-tension characteristics of the heart.

Neuropeptidergic Signaling in the American Lobster Homarus americanus: New Insights from High-Throughput Nucleotide Sequencing

Peptides are the largest and most diverse class of molecules used for neurochemical communication, playing key roles in the control of essentially all aspects of physiology and behavior. The American lobster, Homarus americanus, is a crustacean of commercial and biomedical importance; lobster growth and reproduction are under neuropeptidergic control, and portions of the lobster nervous system serve as models for understanding the general principles underlying rhythmic motor behavior (including peptidergic neuromodulation). While a number of neuropeptides have been identified from H. americanus, and the effects of some have been investigated at the cellular/systems levels, little is currently known about the molecular components of neuropeptidergic signaling in the lobster. Here, a H. americanus neural transcriptome was generated and mined for sequences encoding putative peptide precursors and receptors; 35 precursor- and 41 receptor-encoding transcripts were identified. We predicted 194 distinct neuropeptides from the deduced precursor proteins, including members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin C, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone (CHH), CHH precursor-related peptide, diuretic hormone 31, diuretic hormone 44, eclosion hormone, FLRFamide, GSEFLamide, insulin-like peptide, intocin, leucokinin, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone, proctolin, pyrokinin, SIFamide, sulfakinin and tachykinin-related peptide families. While some of the predicted peptides are known H. americanus isoforms, most are novel identifications, more than doubling the extant lobster neuropeptidome. The deduced receptor proteins are the first descriptions of H. americanus neuropeptide receptors, and include ones for most of the peptide groups mentioned earlier, as well as those for ecdysis-triggering hormone, red pigment concentrating hormone and short neuropeptide F. Multiple receptors were identified for most peptide families. These data represent the most complete description of the molecular underpinnings of peptidergic signaling in H. americanus, and will serve as a foundation for future gene-based studies of neuropeptidergic control in the lobster.

Prediction of the neuropeptidomes of members of the Astacidea (Crustacea, Decapoda) using publicly accessible transcriptome shotgun assembly (TSA) sequence data

The decapod infraorder Astacidea is comprised of clawed lobsters and freshwater crayfish. Due to their economic importance and their use as models for investigating neurochemical signaling, much work has focused on elucidating their neurochemistry, particularly their peptidergic systems. Interestingly, no astacidean has been the subject of large-scale peptidomic analysis via in silico transcriptome mining, this despite growing transcriptomic resources for members of this taxon. Here, the publicly accessible astacidean transcriptome shotgun assembly data were mined for putative peptide-encoding transcripts; these sequences were used to predict the structures of mature neuropeptides. One hundred seventy-six distinct peptides were predicted for Procambarus clarkii, including isoforms of adipokinetic hormone-corazonin-like peptide (ACP), allatostatin A (AST-A), allatostatin B, allatostatin C (AST-C) bursicon α, bursicon β, CCHamide, crustacean hyperglycemic hormone (CHH)/ion transport peptide (ITP), diuretic hormone 31 (DH31), eclosion hormone (EH), FMRFamide-like peptide, GSEFLamide, intocin, leucokinin, neuroparsin, neuropeptide F, pigment dispersing hormone, pyrokinin, RYamide, short neuropeptide F (sNPF), SIFamide, sulfakinin and tachykinin-related peptide (TRP). Forty-six distinct peptides, including isoforms of AST-A, AST-C, bursicon α, CCHamide, CHH/ITP, DH31, EH, intocin, myosuppressin, neuroparsin, red pigment concentrating hormone, sNPF and TRP, were predicted for Pontastacus leptodactylus, with a bursicon β and a neuroparsin predicted for Cherax quadricarinatus. The identification of ACP is the first from a decapod, while the predictions of CCHamide, EH, GSEFLamide, intocin, neuroparsin and RYamide are firsts for the Astacidea. Collectively, these data greatly expand the catalog of known astacidean neuropeptides and provide a foundation for functional studies of peptidergic signaling in members of this decapod infraorder.

Neuropeptide discovery in Symphylella vulgaris (Myriapoda, Symphyla): In silico prediction of the first myriapod peptidome

Arthropods have contributed greatly to our understanding of peptidergic control of physiology and behavior, and being the largest and most diverse animal phylum, represent a model for investigating peptide hormone evolution. Surprisingly, one arthropod subphylum, the Myriapoda, is uninvestigated in terms of its peptide hormones. The public deposition of a transcriptome for Symphylella vulgaris, a pseudocentipede, provides a means for peptide discovery in myriapods. Here, in silico transcriptome mining was used to identify 47 S. vulgaris neuropeptide-encoding transcripts within this dataset. The identified transcripts allowed for the deduction of 31 unique pre/preprohormone sequences, with 97 distinct mature peptides predicted from the deduced proteins. The predicted S. vulgaris peptidome includes members of the adipokinetic hormone/red pigment concentrating hormone, adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin C (AST-C), allatotropin, CCHamide, crustacean cardioactive peptide, GSEFLamide, insulin-like peptide, intocin, proctolin, pyrokinin, short neuropeptide F, SIFamide and sulfakinin families. This is the first, and thus far only, peptidome predicted for a myriapod. Of particular note were a modified AST-C, TYWKQCAFNAVSRFamide, that lacks one of two cysteine residues (i.e. one at position 13) stereotypically present in members of this peptide family (and hence is missing the disulfide bridge that spans these residues) and a SIFamide, PPFNGSIFamide, that is truncated due to a lysine for arginine substitution in the dibasic residue pair commonly located at positions 3 and 4 of stereotypical full-length isoforms (e.g. the crustacean peptide GYRKPPFNGSIFamide). The peptides predicted here represent the only extant resource for initiating investigations of native peptidergic signaling in the Myriapoda.

Defining the Neuropeptidome of the Spiny Lobster Panulirus interruptus Brain Using a Multidimensional Mass Spectrometry-Based Platform

Decapod crustaceans are important animal models for neurobiologists due to their relatively simple nervous systems with well-defined neural circuits and extensive neuromodulation by a diverse set of signaling peptides. However, biochemical characterization of these endogenous neuropeptides is often challenging due to limited sequence information about these neuropeptide genes and the encoded preprohormones. By taking advantage of sequence homology in neuropeptides observed in related species using a home-built crustacean neuropeptide database, we developed a semi-automated sequencing strategy to characterize the neuropeptidome of Panulirus interruptus, an important aquaculture species, with few known neuropeptide preprohormone sequences. Our streamlined process searched the high mass accuracy and high-resolution data acquired on a LTQ-Orbitrap with a flexible algorithm in ProSight that allows for sequence discrepancy from reported sequences in our database, resulting in the detection of 32 neuropeptides, including 19 novel ones. We further improved the overall coverage to 51 neuropeptides with our multidimensional platform that employed multiple analytical techniques including dimethylation-assisted fragmentation, de novo sequencing using nanoliquid chromatography-electrospray ionization-quadrupole-time-of-flight (nanoLC-ESI-Q-TOF), direct tissue analysis, and mass spectrometry imaging on matrix-assisted laser desorption/ionization (MALDI)-TOF/TOF. The high discovery rate from this unsequenced model organism demonstrated the utility of our neuropeptide discovery pipeline and highlighted the advantage of utilizing multiple sequencing strategies. Collectively, our study expands the catalog of crustacean neuropeptides and more importantly presents an approach that can be adapted to exploring neuropeptidome from species that possess limited sequence information.

Distinct or shared actions of peptide family isoforms: I. Peptide-specific actions of pyrokinins in the lobster cardiac neuromuscular system

Although the crustacean heart is modulated by a large number of peptides and amines, few of these molecules have been localized to the cardiac ganglion itself; most appear to reach the cardiac ganglion only by hormonal routes. Immunohistochemistry in the American lobster Homarus americanus indicates that pyrokinins are present not only in neuroendocrine organs (pericardial organ and sinus gland), but also in the cardiac ganglion itself, where pyrokinin-positive terminals were found in the pacemaker cell region, as well as surrounding the motor neurons. Surprisingly, the single pyrokinin peptide identified from H. americanus, FSPRLamide, which consists solely of the conserved FXPRLamide residues that characterize pyrokinins, did not alter the activity of the cardiac neuromuscular system. However, a pyrokinin from the shrimp Litopenaeus vannamei [ADFAFNPRLamide, also known as Penaeus vannamei pyrokinin 2 (PevPK2)] increased both the frequency and amplitude of heart contractions when perfused through the isolated whole heart. None of the other crustacean pyrokinins tested (another from L. vannamei and two from the crab Cancer borealis) had any effect on the lobster heart. Similarly, altering the PevPK2 sequence either by truncation or by the substitution of single amino acids resulted in much lower or no activity in all cases; only the conservative substitution of serine for alanine at position 1 resulted in any activity on the heart. Thus, in contrast to other systems (cockroach and crab) in which all tested pyrokinins elicit similar bioactivities, activation of the pyrokinin receptor in the lobster heart appears to be highly isoform specific.

Expansion of the Litopenaeus vannamei and Penaeus monodon peptidomes using transcriptome shotgun assembly sequence data

The shrimp Litopenaeus vannamei and Penaeus monodon are arguably the most important commercially farmed crustaceans. While expansion of their aquaculture has classically relied on improvements to rearing facilities, these options have largely been exhausted, and today a shift in focus is occurring, with increased investment in manipulating the shrimp themselves. Hormonal control is one strategy for increasing aquaculture output. However, to use it, one must first understand an animal's native hormonal systems. Here, transcriptome shotgun assembly (TSA) data were used to expand the peptidomes for L. vannamei and P. monodon. Via an established bioinformatics workflow, 41 L. vannamei and 25 P. monodon pre/preprohormone-encoding transcripts were identified, allowing for the prediction of 158 and 106 distinct peptide structures for these species, respectively. The identified peptides included isoforms of allatostatin A, B and C, as well as members the bursicon, CAPA, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31, eclosion hormone, FLRFamide, GSEFLamide, intocin, leucokinin, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, orcomyotropin, pigment dispersing hormone, proctolin, red pigment concentrating hormone, RYamide, SIFamide, short neuropeptide F and tachykinin-related peptide families. While some of the predicted peptides are known L. vannamei and/or P. monodon isoforms (which vet the structures of many peptides identified previously via mass spectrometry and other means), most are described here for the first time. These data more than double the extant catalogs of L. vannamei and P. monodon peptides and provide platforms from which to launch future physiological studies of peptidergic signaling in these two commercially important species.

Peptide discovery in the ectoparasitic crustacean Argulus siamensis: identification of the first neuropeptides from a member of the Branchiura

Recent advances in high-throughput sequencing have facilitated the generation of large transcriptomic datasets for an ever-growing number of crustaceans, one being the carp louse Argulus siamensis. This and other members of the subclass Branchiura are obligate fish ectoparasites, and as such, are a major concern for commercial aquaculture. Using the extant transcriptome shotgun assembly (TSA) sequences for A. siamensis, 27 transcripts encoding putative neuropeptide precursors were identified, and their pre/preprohormones deduced and characterized using a well-established bioinformatics workflow. The structures of 105 distinct peptides were predicted from the deduced proteins, including isoforms of adipokinetic hormone (AKH), allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, crustacean cardioactive peptide (CCAP), diuretic hormone 31, diuretic hormone 44, eclosion hormone, myosuppressin, neuroparsin, neuropeptide Y, orcokinin, pigment dispersing hormone, proctolin, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide. While several of the predicted peptides are known from other crustacean and/or insect species, e.g. RYLPT, a broadly conserved arthropod proctolin isoform, and PFCNAFTGCamide (disulfide bridging between the two cysteines), the stereotypical crustacean CCAP, the vast majority of them are described here for the first time, e.g. pQVNFSTKWamide, a new AKH/red pigment concentrating hormone superfamily member, pQEGLDHMFMRFamide, a novel myosuppressin, and SYKSKPPFNGSIFamide, a new member of the SIFamide family. As the peptides presented here are the only ones thus far described from A. siamensis, or for that matter, any branchiuran, they represent a new resource to begin investigations of peptidergic control of physiology and behavior in this and other related aquacultural pests.

Molecular evolution of GPCRs: CRH/CRH receptors

Corticotrophin-releasing hormone (CRH) is the pivotal neuroendocrine peptide hormone associated with the regulation of the stress response in vertebrates. However, CRH-like peptides are also found in a number of invertebrate species. The origin of this peptide can be traced to a common ancestor of lineages leading to chordates and to arthropods, postulated to occur some 500 million years ago. Evidence indicates the presence of a single CRH-like receptor and a soluble binding protein system that acted to transduce and regulate the actions of the early CRH peptide. In vertebrates, genome duplications led to the divergence of CRH receptors into CRH1 and CRH2 forms in tandem with the development of four paralogous ligand lineages that included CRH; urotensin I/urocortin (Ucn), Ucn2 and Ucn3. In addition, taxon-specific genome duplications led to further local divergences in CRH ligands and receptors. Functionally, the CRH ligand-receptor system evolved initially as a molecular system to integrate early diuresis and nutrient acquisition. As multicellular organisms evolved into more complex forms, this ligand-receptor system became integrated with the organismal stress response to coordinate homoeostatic challenges with internal energy usage. In vertebrates, CRH and the CRH1 receptor became associated with the hypothalamo-pituitary-adrenal/interrenal axis and the initial stress response, whereas the CRH2 receptor was selected to play a greater role in diuresis, nutrient acquisition and the latter aspects of the stress response.

Prediction of the first neuropeptides from a member of the Remipedia (Arthropoda, Crustacea)

The Remipedia is a small, recently described crustacean class that inhabits submerged marine/anchialine cave systems. Phylogenetic and morphological investigations support a sister group relationship between these animals and the hexapods. The recent deposition of numerous (>100,000) transcriptome shotgun assembly sequences for Speleonectes cf. tulumensis provides a unique resource to identify proteins of interest from a member of the Remipedia. Here, this dataset was mined for sequences encoding putative neuropeptide pre/preprohormones, with the mature peptides predicted from the deduced precursors using an established workflow. The structures of 40 mature peptides were obtained via this strategy, including members of 11 well-known arthropod peptide families (adipokinetic hormone/corazonin-like peptide [ACP], allatostatin A, allatostatin C, diuretic hormone 31, eclosion hormone, ion transport peptide/crustacean hyperglycemic hormone, neuropeptide F, proctolin, SIFamide, sulfakinin and tachykinin-related peptide); these are the only peptides thus far described from any member of the Remipedia. Comparison of the Speleonectes isoforms with those from other crustaceans and hexapods revealed the peptidome of this species to have characteristics of both subphyla (e.g. it possesses the stereotypical decapod crustacean SIFamide and tachykinin-related peptide isoforms, while simultaneously being the only crustacean with an insect AKC). Moreover, BLAST searches in which the deduced Speleonectes precursors were compared to the pancrustacean protein database most frequently returned insect homologs as the closest matches. The peptidomic analyses presented here are consistent with the hypothesized phylogenetic position of the Remipedia within the Pancrustacea, and serve as a foundation from which to launch future investigations of peptidergic signaling in remipedes.

Analysis of the central nervous system transcriptome of the eastern rock lobster Sagmariasus verreauxi reveals its putative neuropeptidome

Neuropeptides have been discovered in many arthropod species including crustaceans. The nature of their biological function is well studied and varies from behavior modulation to physiological regulation of complex biochemical processes such as metabolism, molt and reproduction. Due to their key role in these fundamental processes, neuropeptides are often targeted for modulating these processes to align with market demands in commercially important species. We generated a comprehensive transcriptome of the eyestalk and brain of one of the few commercially important spiny lobster species in the southern Hemisphere, the Eastern rock lobster Sagmariasus verreauxi and mined it for novel neuropeptide and protein hormone-encoding transcripts. We then characterized the predicted mature hormones to verify their validity based on conserved motifs and features known from previously reported hormones. Overall, 37 transcripts which are predicted to encode mature full-length/partial peptides/proteins were identified, representing 21 peptide/protein families/subfamilies. All transcripts had high similarity to hormones that were previously characterized in other decapod crustacean species or, where absent in crustaceans, in other arthropod species. These included, in addition to other proteins previously described in crustaceans, prohormone-3 and prohormone-4 which were previously identified only in insects. A homolog of the crustacean female sex hormone (CFSH), recently found to be female-specific in brachyuran crabs was found to have the same levels of expression in both male and female eyestalks, suggesting that the CFSH female specificity is not conserved throughout decapod crustaceans. Digital gene expression showed that 24 out of the 37 transcripts presented in this study have significant changes in expression between eyestalk and brain. In some cases a trend of difference between males and females could be seen. Taken together, this study provides a comprehensive neuropeptidome of a commercially important crustacean species with novel peptides and protein hormones identified for the first time in decapods.

Transcriptome and peptidome characterisation of the main neuropeptides and peptidic hormones of a euphausiid: the Ice Krill, Euphausia crystallorophias

Background

The Ice krill, Euphausia crystallorophias is one of the species at the base of the Southern Ocean food chain. Given their significant contribution to the biomass of the Southern Ocean, it is vitally important to gain a better understanding of their physiology and, in particular, anticipate their responses to climate change effects in the warming seas around Antarctica.

Methodology/Principal Findings

Illumina sequencing was used to produce a transcriptome of the ice krill. Analysis of the assembled contigs via two different methods, produced 36 new pre-pro-peptides, coding for 61 neuropeptides or peptide hormones belonging to the following families: Allatostatins (A, B et C), Bursicon (α and β), Crustacean Hyperglycemic Hormones (CHH and MIH/VIHs), Crustacean Cardioactive Peptide (CCAP), Corazonin, Diuretic Hormones (DH), the Eclosion Hormone (EH), Neuroparsin, Neuropeptide F (NPF), small Neuropeptide F (sNPF), Pigment Dispersing Hormone (PDH), Red Pigment Concentrating Hormone (RPCH) and finally Tachykinin. LC/MS/MS proteomics was also carried out on eyestalk extracts, which are the major site of neuropeptide synthesis in decapod crustaceans. Results confirmed the presence of six neuropeptides and six precursor-related peptides previously identified in the transcriptome analyses.

Conclusions

This study represents the first comprehensive analysis of neuropeptide hormones in a Eucarida non-decapod Malacostraca, several of which are described for the first time in a non-decapod crustacean. Additionally, there is a potential expansion of PDH and Neuropeptide F family members, which may reflect certain life history traits such as circadian rhythms associated with diurnal migrations and also the confirmation via mass spectrometry of several novel pre-pro-peptides, of unknown function. Knowledge of these essential hormones provides a vital framework for understanding the physiological response of this key Southern Ocean species to climate change and provides a valuable resource for studies into the molecular phylogeny of these organisms and the evolution of neuropeptide hormones.

Peptidergic signaling in Calanus finmarchicus (Crustacea, Copepoda): in silico identification of putative peptide hormones and their receptors using a de novo assembled transcriptome

The copepod Calanus finmarchicus is the most abundant zooplankton species in the North Atlantic. While the life history of this crustacean is well studied, little is known about its peptidergic signaling systems despite the fact that these pathways are undoubtedly important components of its physiological/behavioral control systems. Here we have generated and used a de novo assembled transcriptome for C. finmarchicus (206,041 sequences in total) to identify peptide precursor proteins and receptors. Using known protein queries, 34 transcripts encoding peptide preprohormones and 18 encoding peptide receptors were identified. Using a combination of online software programs and homology to known arthropod isoforms, 148 mature peptides were predicted from the deduced precursors, including members of the allatostatin-A, allatostatin-B, allatostatin-C, bursicon, crustacean cardioactive peptide (CCAP), crustacean hyperglycemic hormone, diuretic hormone 31 (DH31), diuretic hormone 44 (DH44), FMRFamide-like peptide (myosuppressin, neuropeptide F [NPF] and extended FL/IRFamide subfamilies), leucokinin, neuroparsin, orcokinin, orcomyotropin, periviscerokinin, RYamide and tachykinin-related peptide (TRP) families. The identified receptors included ones for allatostatin-A, allatostatin-C, bursicon, CCAP, DH31, DH44, ecdysis-triggering hormone, NPF, short NPF, FMRFamide, insulin-like peptide, leucokinin, periviscerokinin, pigment dispersing hormone, and TRP. Developmental profiling of the identified transcripts in embryos, early nauplii, late nauplii, early copepodites, late copepodites, and adult females was also undertaken, with all showing the highest expression levels in the naupliar and copepodite stages. Collectively, these data radically expand the catalog of known C. finmarchicus peptidergic signaling proteins and provide a foundation for experiments directed at understanding the physiological roles served by them in this species.

The neuropeptide transcriptome of a model echinoderm, the sea urchin Strongylocentrotus purpuratus

Neuronal secretion of peptide signaling molecules (neuropeptides) is an evolutionarily ancient feature of nervous systems. Here we report the identification of 20 cDNAs encoding putative neuropeptide precursors in the sea urchin Strongylocentrotus purpuratus (Phylum Echinodermata), providing new insights on the evolution and diversity of neuropeptides. Identification of a gonadotropin-releasing hormone-like peptide precursor (SpGnRHP) is consistent with the widespread phylogenetic distribution of GnRH-type neuropeptides in the bilateria. A protein (SpTRHLP) comprising multiple copies of peptides that share structural similarity with thyrotropin-releasing hormone (TRH) is the first TRH-like precursor to be identified in an invertebrate. SpCTLP is the first calcitonin-like peptide with two N-terminally located cysteine residues to be found in a non-chordate species. Discovery of two proteins (SpPPLNP1, SpPPLNP2) comprising homologs of molluscan pedal peptides and arthropod orcokinins indicates the existence of a bilaterian family of pedal peptide/orcokinin-type neuropeptides. Other proteins identified contain peptides that do not share apparent sequence similarity with known neuropeptides. These include Spnp5, which comprises multiple copies of C-terminally amidated peptides that have an N-terminal Ala-Asn motif (AN peptides), and Spnp9, Spnp10 and Spnp12, which contain putative neuropeptides with a C-terminal Phe-amide, Ser-amide or Pro-amide, respectively. Several proteins (Spnp11, 14, 15, 16, 17, 18, 19 and 20) contain putative neuropeptides with multiple cysteine residues (2, 6 or 8), which may mediate formation of intramolecular or intermolecular disulphide bridges. Looking ahead, the identification of these neuropeptide precursors in S. purpuratus has provided a strong basis for a comprehensive analysis of neuropeptide function in this model echinoderm species.

Transcriptomic analysis of neuropeptides and peptide hormones in the barnacle Balanus amphitrite: evidence of roles in larval settlement

The barnacle Balanus amphitrite is a globally distributed marine crustacean and has been used as a model species for intertidal ecology and biofouling studies. Its life cycle consists of seven planktonic larval stages followed by a sessile juvenile/adult stage. The transitional processes between larval stages and juveniles are crucial for barnacle development and recruitment. Although some studies have been conducted on the neuroanatomy and neuroactive substances of the barnacle, a comprehensive understanding of neuropeptides and peptide hormones remains lacking. To better characterize barnacle neuropeptidome and its potential roles in larval settlement, an in silico identification of putative transcripts encoding neuropeptides/peptide hormones was performed, based on transcriptome of the barnacle B. amphitrite that has been recently sequenced. Potential cleavage sites andstructure of mature peptides were predicted through homology search of known arthropod peptides. In total, 16 neuropeptide families/subfamilies were predicted from the barnacle transcriptome, and 14 of them were confirmed as genuine neuropeptides by Rapid Amplification of cDNA Ends. Analysis of peptide precursor structures and mature sequences showed that some neuropeptides of B. amphitrite are novel isoforms and shared similar characteristics with their homologs from insects. The expression profiling of predicted neuropeptide genes revealed that pigment dispersing hormone, SIFamide, calcitonin, and B-type allatostatin had the highest expression level in cypris stage, while tachykinin-related peptide was down regulated in both cyprids and juveniles. Furthermore, an inhibitor of proprotein convertase related to peptide maturation effectively delayed larval metamorphosis. Combination of real-time PCR results and bioassay indicated that certain neuropeptides may play an important role in cypris settlement. Overall, new insight into neuropeptides/peptide hormones characterized in this study shall provide a platform for unraveling peptidergic control of barnacle larval behavior and settlement process.

Calcitonin-like diuretic hormones in insects

Insect neuropeptides control various biological processes including growth, development, homeostasis and reproduction. The calcitonin-like diuretic hormone (CT/DH) is one such neuropeptide that has been shown to affect salt and water transport by Malpighian tubules of several insects. With an increase in the number of sequenced insect genomes, CT/DHs have been predicted in several insect species, making it easier to characterize the gene encoding this hormone and determine its function in the species in question. This mini review summarizes the current knowledge on insect CT/DHs, focusing on mRNA and peptide structures, distribution patterns, physiological roles, and receptors in insects.

Inter-animal variability in the effects of C-type allatostatin on the cardiac neuromuscular system in the lobster Homarus americanus

Although the global effects of many modulators on pattern generators are relatively consistent among preparations, modulators can induce different alterations in different preparations. We examined the mechanisms that underlie such variability in the modulatory effects of the peptide C-type allatostatin (C-AST; pQIRYHQCYFNPISCF) on the cardiac neuromuscular system of the lobster Homarus americanus. Perfusion of C-AST through the semi-intact heart consistently decreased the frequency of ongoing contractions. However, the effect of C-AST on contraction amplitude varied between preparations, decreasing in some preparations and increasing in others. To investigate this variable effect, we examined the effects of C-AST both peripherally and centrally. When contractions of the myocardium were elicited by controlled stimuli, C-AST did not alter heart contraction at the periphery (myocardium or neuromuscular junction) in any hearts. However, when applied either to the semi-intact heart or to the cardiac ganglion (CG) isolated from hearts that responded to C-AST with increased contraction force, C-AST increased both motor neuron burst duration and the number of spikes per burst by about 25%. In contrast, CG output was increased only marginally in hearts that responded to C-AST with a decrease in contraction amplitude, suggesting that the decrease in amplitude in those preparations resulted from decreased peripheral facilitation. Our data suggest that the differential effects of a single peptide on the cardiac neuromuscular system are due solely to differential effects of the peptide on the pattern generator; the extent to which the peptide induces increased burst duration is crucial in determining its overall effect on the system.

Genomics, transcriptomics, and peptidomics of Daphnia pulex neuropeptides and protein hormones

We report 43 novel genes in the water flea Daphnia pulex encoding 73 predicted neuropeptide and protein hormones as partly confirmed by RT-PCR. MALDI-TOF mass spectrometry identified 40 neuropeptides by mass matches and 30 neuropeptides by fragmentation sequencing. Single genes encode adipokinetic hormone, allatostatin-A, allatostatin-B, allatotropin, Ala(7)-CCAP, CCHamide, Arg(7)-corazonin, DENamides, CRF-like (DH52) and calcitonin-like (DH31) diuretic hormones, two ecdysis-triggering hormones, two FIRFamides, one insulin, two alternative splice forms of ion transport peptide (ITP), myosuppressin, neuroparsin, two neuropeptide-F splice forms, three periviscerokinins (but no pyrokinins), pigment dispersing hormone, proctolin, Met(4)-proctolin, short neuropeptide-F, three RYamides, SIFamide, two sulfakinins, and three tachykinins. There are two genes for a preprohormone containing orcomyotropin-like peptides and orcokinins, two genes for N-terminally elongated ITPs, two genes (clustered) for eclosion hormones, two genes (clustered) for bursicons alpha, beta, and two genes (clustered) for glycoproteins GPA2, GPB5, three genes for different allatostatins-C (two of them clustered) and three genes for IGF-related peptides. Detailed comparisons of genes or their products with those from insects and decapod crustaceans revealed that the D. pulex peptides are often closer related to their insect than to their decapod crustacean homologues, confirming that branchiopods, to which Daphnia belongs, are the ancestor group of insects.

Identification, tissue distribution and orexigenic activity of neuropeptide F (NPF) in penaeid shrimp

The neuropeptide Fs (NPFs) are an invertebrate subgroup of the FMRFamide-like peptides, and are proposed by some to be the homologs of vertebrate neuropeptide Y. Although there is some information about the identity, tissue distribution and function of NPFs in insects, essentially nothing is known about them in crustaceans. We have identified and characterized NPF-encoding transcripts from the penaeid shrimp Litopenaeus vannamei and Melicertus marginatus. Two transcripts were identified from each species. For each shrimp species, the two transcripts differed from one another by the presence or absence of an insert in the portion of the open reading frame that encodes the NPF peptide. The two NPF isoforms are identical in L. vannamei and M. marginatus, with their predicted structures being KPDPSQLANMAEALKYLQELDKYYSQVSRPRFamide and KPDPSQLANMAEALKYLQELDKYYSQVSRPSPRSAPGPASQIQALENTLKFLQLQELGKLYSLRARPRFamide. RT-PCR tissue profiling showed both transcripts are broadly distributed within the nervous system of each species. The transcript encoding the shorter NPF was detected in some, but not all, midgut samples. The transcript encoding the longer NPF was absent in the midgut of both species, and neither transcript was detected in their skeletal muscle. Juvenile L. vannamei fed on a diet supplemented with the shorter NPF exhibited a marked increase in food intake relative to control individuals that did not receive the supplement; the NPF-fed shrimp also showed a significant increase in growth relative to the control group. Our data suggest that NPF is present in both the nervous system and midgut of penaeid shrimp, functioning, at least in part, as a powerful orexigenic agent.

Bioinformatic prediction of arthropod/nematode-like peptides in non-arthropod, non-nematode members of the Ecdysozoa

The Onychophora, Priapulida and Tardigrada, along with the Arthropoda, Nematoda and several other small phyla, form the superphylum Ecdysozoa. Numerous peptidomic studies have been undertaken for both the arthropods and nematodes, resulting in the identification of many peptides from each group. In contrast, little is known about the peptides used as paracrines/hormones by species from the other ecdysozoan taxa. Here, transcriptome mining and bioinformatic peptide prediction were used to identify peptides in members of the Onychophora, Priapulida and Tardigrada, the only non-arthropod, non-nematode members of the Ecdysozoa for which there are publicly accessible expressed sequence tags (ESTs). The extant ESTs for each phylum were queried using 106 arthropod/nematode peptide precursors. Transcripts encoding calcitonin-like diuretic hormone and pigment-dispersing hormone (PDH) were identified for the onychophoran Peripatopsis sedgwicki, with transcripts encoding C-type allatostatin (C-AST) and FMRFamide-like peptide identified for the priapulid Priapulus caudatus. For the Tardigrada, transcripts encoding members of the A-type allatostatin, C-AST, insect kinin, orcokinin, PDH and tachykinin-related peptide families were identified, all but one from Hypsibius dujardini (the exception being a Milnesium tardigradum orcokinin-encoding transcript). The proteins deduced from these ESTs resulted in the prediction of 48 novel peptides, six onychophoran, eight priapulid and 34 tardigrade, which are the first described from these phyla.

Identification of chelicerate neuropeptides using bioinformatics of publicly accessible expressed sequence tags

While numerous investigations have focused on the identification of neuropeptides in arthropods, most have been conducted on members of the Hexapoda or Crustacea, and little is currently known about those in the Chelicerata. Here, publicly accessible expressed sequence tags (ESTs) were mined for putative chelicerate neuropeptide-encoding transcripts; the peptides encoded by the ESTs were deduced using on-line peptide prediction programs and homology to known isoforms. Fifty-eight ESTs representing eight peptide families/subfamilies were identified using this strategy. Of note was the prediction of the first authentic chelicerate C-type allatostatin, pQIRYHQCYFNPISCF, from the mite Tetranychus urticae, as well as the prediction a novel allatostatin CC peptide, GEGKMFWRCYFNAVSCF, from both the tick Amblyomma variegatum and the scorpion Mesobuthus gibbosus. Also identified from T. urticae were authentic crustacean cardioactive peptide (CCAP), several peptides belonging to the crustacean hyperglycemic hormone/ion transport peptide superfamily, members of the calcitonin-like diuretic hormone/diuretic hormone 31 family, and several FMRFamide-like peptides, specifically members of the neuropeptide F (NPF) and short neuropeptide F subfamilies. To the best of our knowledge the identifications of CCAP and NPF in T. urticae are the first for the Chelicerata. In addition, several novel orcokinins were identified from the scorpion Scorpiops jendeki and the spider Loxosceles laeta; in S. jendeki previously unknown isoforms of SIFamide, ESRNPPLNGSMFamide and ESKNPPLNGSMFamide, were also predicted. Taken collectively, the data presented in our study expand the catalog of known chelicerate neuropeptides and provide a foundation for future physiological studies of them in these animals.

Crustacean neuropeptides

Crustaceans have long been used for peptide research. For example, the process of neurosecretion was first formally demonstrated in the crustacean X-organ-sinus gland system, and the first fully characterized invertebrate neuropeptide was from a shrimp. Moreover, the crustacean stomatogastric and cardiac nervous systems have long served as models for understanding the general principles governing neural circuit functioning, including modulation by peptides. Here, we review the basic biology of crustacean neuropeptides, discuss methodologies currently driving their discovery, provide an overview of the known families, and summarize recent data on their control of physiology and behavior.

Distribution of C-type allatostatin (C-AST)-like immunoreactivity in the central nervous system of the copepod Calanus finmarchicus

The C-type allatostatins (C-ASTs) are a family of highly pleiotropic arthropod neuropeptides. In crustaceans, transcriptomic/mass spectral studies have identified C-ASTs in the nervous systems of many species; the cellular distributions of these peptides remain unknown. Here, the distribution of C-AST was mapped in the nervous system of the copepod Calanus finmarchicus, the major contributor to the North Atlantic's zooplanktonic biomass; C-AST-immunopositive neurons were identified in the protocerebrum, in several peripheral ganglia associated with feeding appendages, and in the ganglia controlling the swimming legs, with immunopositive axons present throughout the ventral nerve cord. In addition, axons innervating the dorsal longitudinal and ventral longitudinal muscles of the body wall of the metasome were labeled by the C-AST antibody. While the distribution of C-AST-like immunoreactivity was similar between sexes, several differences were noted, i.e., two pair of somata located at the deutocerebral/tritocerebral border in males and immunopositive fibers that surround the genital opening in females. To place the C-AST-like labeling into context with those of several previously mapped peptides, i.e., A-type allatostatin (A-AST) and tachykinin-related peptide (TRP), we conducted double-labeling studies; the C-AST-like immunopositive neurons appear distinct from those expressing either A-AST or TRP (and through extrapolation, pigment dispersing hormone). Collectively, our data represent the first mapping of C-AST in crustacean neural tissue, show that sex-specific differences in the distribution of C-AST exist in the C. finmarchicus CNS, and suggest that the peptide may be involved in the modulation of both feeding and postural control/locomotion.

Bioinformatic analyses of the publicly accessible crustacean expressed sequence tags (ESTs) reveal numerous novel neuropeptide-encoding precursor proteins, including ones from members of several little studied taxa

ESTs have been generated for many crustacean species, providing an invaluable resource for peptide discovery in members of this arthropod subphylum. Here, these data were mined for novel peptide-encoding transcripts, with the mature peptides encoded by them predicted using a combination of online peptide prediction programs and homology to known arthropod sequences. In total, 70 mature full-length/partial peptides representing members of 16 families/subfamilies were predicted, the vast majority being novel; the species from which the peptides were identified included members of the Branchiopoda (Daphnia carinata and Triops cancriformis), Maxillopoda (Caligus clemensi, Caligus rogercresseyi, Lepeophtheirus salmonis and Lernaeocera branchialis) and Malacostraca (Euphausia superba, Marsupenaeus japonicus, Penaeus monodon, Homarus americanus, Petrolisthes cinctipes, Callinectes sapidus and Portunus trituberculatus). Of particular note were the identifications of an intermediate between the insect adipokinetic hormones and crustacean red pigment concentrating hormone and a modified crustacean cardioactive peptide from the daphnid D. carinata; Arg(7)-corazonin was also deduced from this species, the first identification of a corazonin from a non-decapod crustacean. Our data also include the first reports of members of the calcitonin-like diuretic hormone, FMRFamide-related peptide (neuropeptide F subfamily) and orcokinin families from members of the Copepoda. Moreover, the prediction of a bursicon alpha from the euphausid E. superba represents the first peptide identified from any member of the basal eucaridean order Euphausiacea. In addition, large collections of insect eclosion hormone- and neuroparsin-like peptides were identified from a variety of species, greatly expanding the number of known members of these families in crustaceans.

The peptide hormone pQDLDHVFLRFamide (crustacean myosuppressin) modulates the Homarus americanus cardiac neuromuscular system at multiple sites

pQDLDHVFLRFamide is a highly conserved crustacean neuropeptide with a structure that places it within the myosuppressin subfamily of the FMRFamide-like peptides. Despite its apparent ubiquitous conservation in decapod crustaceans, the paracrine and/or endocrine roles played by pQDLDHVFLRFamide remain largely unknown. We have examined the actions of this peptide on the cardiac neuromuscular system of the American lobster Homarus americanus using four preparations: the intact animal, the heart in vitro, the isolated cardiac ganglion (CG), and a stimulated heart muscle preparation. In the intact animal, injection of myosuppressin caused a decrease in heartbeat frequency. Perfusion of the in vitro heart with pQDLDHVFLRFamide elicited a decrease in the frequency and an increase in the amplitude of heart contractions. In the isolated CG, myosuppressin induced a hyperpolarization of the resting membrane potential of cardiac motor neurons and a decrease in the cycle frequency of their bursting. In the stimulated heart muscle preparation, pQDLDHVFLRFamide increased the amplitude of the induced contractions, suggesting that myosuppressin modulates not only the CG, but also peripheral sites. For at least the in vitro heart and the isolated CG, the effects of myosuppressin were dose-dependent (10(-9) to 10(-6) mol l(-1) tested), with threshold concentrations (10(-8)-10(-7) mol l(-1)) consistent with the peptide serving as a circulating hormone. Although cycle frequency, a parameter directly determined by the CG, consistently decreased when pQDLDHVFLRFamide was applied to all preparation types, the magnitudes of this decrease differed, suggesting the possibility that, because myosuppressin modulates the CG and the periphery, it also alters peripheral feedback to the CG.