Neuropeptide discovery in Eucyclops serrulatus (Crustacea, Copepoda): in silico prediction of the first peptidome for a member of the Cyclopoida

The Crustacean Hyperglycemic Hormone Superfamily: Progress Made in the Past Decade

Early studies recognizing the importance of the decapod eyestalk in the endocrine regulation of crustacean physiology-molting, metabolism, reproduction, osmotic balance, etc.-helped found the field of crustacean endocrinology. Characterization of putative factors in the eyestalk using distinct functional bioassays ultimately led to the discovery of a group of structurally related and functionally diverse neuropeptides, crustacean hyperglycemic hormone (CHH), molt-inhibiting hormone (MIH), gonad-inhibiting hormone (GIH) or vitellogenesis-inhibiting hormone (VIH), and mandibular organ-inhibiting hormone (MOIH). These peptides, along with the first insect member (ion transport peptide, ITP), constitute the original arthropod members of the crustacean hyperglycemic hormone (CHH) superfamily. The presence of genes encoding the CHH-superfamily peptides across representative ecdysozoan taxa has been established. The objective of this review is to, aside from providing a general framework, highlight the progress made during the past decade or so. The progress includes the widespread identification of the CHH-superfamily peptides, in particular in non-crustaceans, which has reshaped the phylogenetic profile of the superfamily. Novel functions have been attributed to some of the newly identified members, providing exceptional opportunities for understanding the structure-function relationships of these peptides. Functional studies are challenging, especially for the peptides of crustacean and insect species, where they are widely expressed in various tissues and usually pleiotropic. Progress has been made in deciphering the roles of CHH, ITP, and their alternatively spliced counterparts (CHH-L, ITP-L) in the regulation of metabolism and ionic/osmotic hemostasis under (eco)physiological, developmental, or pathological contexts, and of MIH in the stimulation of ovarian maturation, which implicates it as a regulator for coordinating growth (molt) and reproduction. In addition, experimental elucidation of the steric structure and structure-function relationships have given better understanding of the structural basis of the functional diversification and overlapping among these peptides. Finally, an important finding was the first-ever identification of the receptors for this superfamily of peptides, specifically the receptors for ITPs of the silkworm, which will surely give great impetus to the functional study of these peptides for years to come. Studies regarding recent progress are presented and synthesized, and prospective developments remarked upon.

Transcriptomic characterisation of neuropeptides and their putative cognate G protein-coupled receptors during late embryo and stage-1 juvenile development of the Aotearoa-New Zealand crayfish, Paranephrops zealandicus

We de novo assembled a transcriptome for early life-stages of the Aotearoa-New Zealand crayfish, Paranephrops zealandicus, establishing the first genetic resource for this under-developed aquaculture species and for the Paranephrops genus. Mining of this transcriptome for neuropeptides and their putative cognate G protein-coupled receptors (GPCRs) yielded a comprehensive catalogue of neuropeptides, but few putative neuropeptide GPCRs. Of the neuropeptides commonly identified from decapod transcriptomes, only crustacean female sex hormone and insulin-like peptide were absent from our trinity de novo transcriptome assembly, and also RNA-sequence reads. We identified 63 putative neuropeptide precursors from 43 families, predicted to yield 122 active peptides. Transcripts encoding 26 putative neuropeptide GPCRs were identified but were often incomplete. Putative GPCRs for 15 of the neuropeptides identified here were absent from our transcriptome and RNAseq reads. These data highlight the diverse neuropeptide systems already present at the early development life stages sampled here for P. zealandicus.

AMGSEFLamide, a member of a broadly conserved peptide family, modulates multiple neural networks in Homarus americanus

Recent genomic/transcriptomic studies have identified a novel peptide family whose members share the carboxyl terminal sequence -GSEFLamide. However, the presence/identity of the predicted isoforms of this peptide group have yet to be confirmed biochemically, and no physiological function has yet been ascribed to any member of this peptide family. To determine the extent to which GSEFLamides are conserved within the Arthropoda, we searched publicly accessible databases for genomic/transcriptomic evidence of their presence. GSEFLamides appear to be highly conserved within the Arthropoda, with the possible exception of the Insecta, in which sequence evidence was limited to the more basal orders. One crustacean in which GSEFLamides have been predicted using transcriptomics is the lobster, Homarus americanus Expression of the previously published transcriptome-derived sequences was confirmed by reverse transcription (RT)-PCR of brain and eyestalk ganglia cDNAs; mass spectral analyses confirmed the presence of all six of the predicted GSEFLamide isoforms - IGSEFLamide, MGSEFLamide, AMGSEFLamide, VMGSEFLamide, ALGSEFLamide and AVGSEFLamide - in H. americanus brain extracts. AMGSEFLamide, of which there are multiple copies in the cloned transcripts, was the most abundant isoform detected in the brain. Because the GSEFLamides are present in the lobster nervous system, we hypothesized that they might function as neuromodulators, as is common for neuropeptides. We thus asked whether AMGSEFLamide modulates the rhythmic outputs of the cardiac ganglion and the stomatogastric ganglion. Physiological recordings showed that AMGSEFLamide potently modulates the motor patterns produced by both ganglia, suggesting that the GSEFLamides may serve as important and conserved modulators of rhythmic motor activity in arthropods.

Prediction of a peptidome for the ecotoxicological model Hyalella azteca (Crustacea; Amphipoda) using a de novo assembled transcriptome

Due to its sensitivity to many environmental and anthropogenic stressors, including a wide range of chemical compounds, Hyalella azteca, a freshwater amphipod, has emerged as one of the most commonly used invertebrates for ecotoxicological assessment.Peptidergic signaling systems are key components in the control of organism-environment interactions, and there is a growing literature suggesting that they are targets of a number of aquatic toxicants.Interestingly, and despite its model species status in the field of ecotoxicology, little is known about the peptide hormones of H. azteca.Here, a transcriptome was produced for this species using the de novo assembler Trinity and mined for sequences encoding putative peptide precursors; the transcriptome was assembled from 460,291,636 raw reads and consists of 133,486 unique transcripts.Seventy-six sequences encoding peptide pre/preprohormones were identified from this transcriptome, allowing for the prediction of 202 distinct peptides, which included members of the allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, ecdysis-triggering hormone, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone, GSEFLamide, inotocin, leucokinin, myosuppressin, 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.These peptides expand the known peptidome for H. azteca approximately nine-fold, forming a strong foundation for future studies of peptidergic control, including disruption by aquatic toxicants, in this important ecotoxicological model.

Non-amidated and amidated members of the C-type allatostatin (AST-C) family are differentially distributed in the stomatogastric nervous system of the American lobster, Homarus americanus

The crustacean stomatogastric nervous system (STNS) is a well-known model for investigating neuropeptidergic control of rhythmic behavior. Among the peptides known to modulate the STNS are the C-type allatostatins (AST-Cs). In the lobster, Homarus americanus, three AST-Cs are known. Two of these, pQIRYHQCYFNPISCF (AST-C I) and GNGDGRLYWRCYFNAVSCF (AST-C III), have non-amidated C-termini, while the third, SYWKQCAFNAVSCFamide (AST-C II), is C-terminally amidated. Here, antibodies were generated against one of the non-amidated peptides (AST-C I) and against the amidated isoform (AST-C II). Specificity tests show that the AST-C I antibody cross-reacts with both AST-C I and AST-C III, but not AST-C II; the AST-C II antibody does not cross-react with either non-amidated peptide. Wholemount immunohistochemistry shows that both subclasses (non-amidated and amidated) of AST-C are distributed throughout the lobster STNS. Specifically, the antibody that cross-reacts with the two non-amidated peptides labels neuropil in the CoGs and the stomatogastric ganglion (STG), axons in the superior esophageal (son) and stomatogastric (stn) nerves, and ~ 14 somata in each commissural ganglion (CoG). The AST-C II-specific antibody labels neuropil in the CoGs, STG and at the junction of the sons and stn, axons in the sons and stn, ~ 42 somata in each CoG, and two somata in the STG. Double immunolabeling shows that, except for one soma in each CoG, the non-amidated and amidated peptides are present in distinct sets of neuronal profiles. The differential distributions of the two AST-C subclasses suggest that the two peptide groups are likely to serve different modulatory roles in the lobster STNS.

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.

A deep transcriptomic resource for the copepod crustacean Labidocera madurae: A potential indicator species for assessing near shore ecosystem health

Coral reef ecosystems of many sub-tropical and tropical marine coastal environments have suffered significant degradation from anthropogenic sources. Research to inform management strategies that mitigate stressors and promote a healthy ecosystem has focused on the ecology and physiology of coral reefs and associated organisms. Few studies focus on the surrounding pelagic communities, which are equally important to ecosystem function. Zooplankton, often dominated by small crustaceans such as copepods, is an important food source for invertebrates and fishes, especially larval fishes. The reef-associated zooplankton includes a sub-neustonic copepod family that could serve as an indicator species for the community. Here, we describe the generation of a de novo transcriptome for one such copepod, Labidocera madurae, a pontellid from an intensively-studied coral reef ecosystem, Kāne'ohe Bay, Oahu, Hawai'i. The transcriptome was assembled using high-throughput sequence data obtained from whole organisms. It comprised 211,002 unique transcripts, including 72,391 with coding regions. It was assessed for quality and completeness using multiple workflows. Bench-marking-universal-single-copy-orthologs (BUSCO) analysis identified transcripts for 88% of expected eukaryotic core proteins. Targeted gene-discovery analyses included searches for transcripts coding full-length "giant" proteins (>4,000 amino acids), proteins and splice variants of voltage-gated sodium channels, and proteins involved in the circadian signaling pathway. Four different reference transcriptomes were generated and compared for the detection of differential gene expression between copepodites and adult females; 6,229 genes were consistently identified as differentially expressed between the two regardless of reference. Automated bioinformatics analyses and targeted manual gene curation suggest that the de novo assembled L. madurae transcriptome is of high quality and completeness. This transcriptome provides a new resource for assessing the global physiological status of a planktonic species inhabiting a coral reef ecosystem that is subjected to multiple anthropogenic stressors. The workflows provide a template for generating and assessing transcriptomes in other non-model species.

Circadian signaling in the Northern krill Meganyctiphanes norvegica: In silico prediction of the protein components of a putative clock system using a publicly accessible transcriptome

The Northern krill Meganyctiphanes norvegica is a significant component of the zooplankton community in many regions of the North Atlantic Ocean. In the areas it inhabits, M. norvegica is of great importance ecologically, as it is both a major consumer of phytoplankton/small zooplankton and is a primary food source for higher-level consumers. One behavior of significance for both feeding and predator avoidance in Meganyctiphanes is diel vertical migration (DVM), i.e., a rising from depth at dusk and a return to depth at dawn. In this and other euphausiids, an endogenous circadian pacemaker is thought, at least in part, to control DVM. Currently, there is no information concerning the identity of the genes/proteins that comprise the M. norvegica circadian system. In fact, there is little information concerning the molecular underpinnings of circadian rhythmicity in crustaceans generally. Here, a publicly accessible transcriptome was used to identify the molecular components of a putative Meganyctiphanes circadian system. A complete set of core clock proteins was deduced from the M. norvegica transcriptome (clock, cryptochrome 2, cycle, period and timeless), as was a large suite of proteins that likely function as modulators of the core clock (e.g., doubletime), or serves as inputs to it (cryptochrome 1) or outputs from it (pigment dispersing hormone). This is the first description of a "complete" (core clock through putative output pathway signals) euphausiid clock system, and as such, provides a foundation for initiating molecular investigations of circadian signaling in M. norvegica and other krill species, including how clock systems may regulate DVM and other behaviors.

Molecular Characterization of Copepod Photoreception

Copepod crustaceans are an abundant and ecologically significant group whose basic biology is guided by numerous visually guided behaviors. These behaviors are driven by copepod eyes, including naupliar eyes and Gicklhorn's organs, which vary widely in structure and function among species. Yet little is known about the molecular aspects of copepod vision. In this study we present a general overview of the molecular aspects of copepod vision by identifying phototransduction genes from newly generated and publicly available RNA-sequencing data and assemblies from 12 taxonomically diverse copepod species. We identify a set of 10 expressed transcripts that serve as a set of target genes for future studies of copepod phototransduction. Our more detailed evolutionary analyses of the opsin gene responsible for forming visual pigments found that all of the copepod species investigated express two main groups of opsins: middle-wavelength-sensitive (MWS) opsins and pteropsins. Additionally, there is evidence from a few species (e.g., Calanus finmarchicus, Eurytemora affinis, Paracyclopina nana, and Lernaea cyprinacea) for the expression of two additional groups of opsins-the peropsins and rhodopsin 7 (Rh7) opsins-at low levels or distinct developmental stages. An ontogenetic analysis of opsin expression in Calanus finmarchicus found the expression of a single dominant MWS opsin, as well as evidence for differences in expression across development in some MWS, pteropsin, and Rh7 opsins, with expression peaking in early naupliar through early copepodite stages.

Ecdysone Receptor Agonism Leading to Lethal Molting Disruption in Arthropods: Review and Adverse Outcome Pathway Development

Molting is critical for growth, development, reproduction, and survival in arthropods. Complex neuroendocrine pathways are involved in the regulation of molting and may potentially become targets of environmental endocrine disrupting chemicals (EDCs). Based on several known ED mechanisms, a wide range of pesticides has been developed to combat unwanted organisms in food production activities such as agriculture and aquaculture. Meanwhile, these chemicals may also pose hazards to nontarget species by causing molting defects, and thus potentially affecting the health of the ecosystems. The present review summarizes the available knowledge on molting-related endocrine regulation and chemically mediated disruption in arthropods (with special focus on insects and crustaceans), to identify research gaps and develop a mechanistic model for assessing environmental hazards of these compounds. Based on the review, multiple targets of EDCs in the molting processes were identified and the link between mode of action (MoA) and adverse effects characterized to inform future studies. An adverse outcome pathway (AOP) describing ecdysone receptor agonism leading to incomplete ecdysis associated mortality was developed according to the OECD guideline and subjected to weight of evidence considerations by evolved Bradford Hill Criteria. This review proposes the first invertebrate ED AOP and may serve as a knowledge foundation for future environmental studies and AOP development.

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.

Prediction of a peptidome for the western tarnished plant bug Lygus hesperus

Many strategies for controlling insect pests require an understanding of their hormonal signaling agents, peptides being the largest and most diverse single class of these molecules. Lygus hesperus is a pest species of particular concern, as it is responsible for significant damage to a wide variety of commercially important plant crops. At present, little is known about the peptide hormones of L. hesperus. Here, transcriptomic data were used to predict a peptidome for L. hesperus. Fifty-three L. hesperus transcripts encoding peptide precursors were identified, with a subset amplified by PCR for sequence verification. The proteins deduced from these transcripts allowed for the prediction of a 119-sequence peptidome for L. hesperus. The predicted peptides include isoforms of allatostatin A, allatostatin B (AST-B), allatostatin C, allatotropin, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, GSEFLamide, insulin-like peptide, myosuppressin, neuroparsin, neuropeptide F, orcokinin, orcomyotropin, pyrokinin, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide. Of note were several isoforms of AST-B that possess -WX₇Wamide carboxyl-termini rather than the stereotypical -WX₆Wamide (e.g., KWQDMQNPGWamide), an allatotropin ending in -SARGFamide rather than -TARGFamide (GLKNGPLNSARGFamide), a GSEFLamide ending in -GTEFLamide (TVGTEFLamide), several orcokinins with PMDEIDR- rather than NFDEIDR- amino-termini (e.g., PMDEIDRAGFTHFV), and an eight rather than 12 amino acid long isoform of SIFamide (PPFNGSIFamide). Collectively, the L. hesperus peptidome predicted here provides a resource for initiating physiological investigations of peptidergic signaling in this species, including studies directed at the biological control of this agricultural pest.

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.

Neuropeptide modulation of pattern-generating systems in crustaceans: comparative studies and approaches

Central pattern generators are subject to modulation by peptides, allowing for flexibility in patterned output. Current techniques used to characterize peptides include mass spectrometry and transcriptomics. In recent years, hundreds of neuropeptides have been sequenced from crustaceans; mass spectrometry has been used to identify peptides and to determine their levels and locations, setting the stage for comparative studies investigating the physiological roles of peptides. Such studies suggest that there is some evolutionary conservation of function, but also divergence of function even within a species. With current baseline data, it should be possible to begin using comparative approaches to ask fundamental questions about why peptides are encoded the way that they are and how this affects nervous system function.

Diversity of insulin-like peptide signaling system proteins in Calanus finmarchicus (Crustacea; Copepoda) - Possible contributors to seasonal pre-adult diapause

Calanus finmarchicus, an abundant calanoid copepod in the North Atlantic Ocean, is both a major grazer on phytoplankton and an important forage species for invertebrate and vertebrate predators. One component of the life history of C. finmarchicus is the overwintering dormancy of sub-adults, a feature key for the annual recruitment of this species in early spring. While little is known about the control of dormancy in C. finmarchicus, one hypothesis is that it is an insect-like diapause, where the endocrine system is a key regulator. One group of hormones implicated in the control of insect diapause is the insulin-like peptides (ILPs). Here, C. finmarchicus transcriptomic data were used to predict ILP signaling pathway proteins. Four ILP precursors were identified, each possessing a distinct A- and B-chain peptide; these peptides are predicted to form bioactive heterodimers via inter-chain disulfide bridging. Two ILP receptors, which likely represent splice variants of a common gene, were identified. Three insulin-degrading enzymes were also discovered, as were proteins encoding the transcription factor FOXO, a downstream target of ILP that has been implicated in the regulation of insect diapause, and insulin receptor substrate, a protein putatively linking the ILP receptor and FOXO. RNA-Seq data suggest that some C. finmarchicus insulin pathway transcripts are differentially expressed across development. As in insects, the ILP signaling system may be involved in controlling C. finmarchicus' organism-environment interactions (e.g., regulation of seasonal sub-adult diapause), a hypothesis that can now be investigated using these data.

Gonadotropin-releasing hormone and adipokinetic hormone/corazonin-related peptide in the female prawn

Crustacean neuropeptides (NPs) play important roles in the regulation of most physiological activities, including growth, molting and reproduction. In this study, we have performed an in silico analysis of female prawn (Macrobrachium rosenbergii) neural transcriptomes to identify NPs not previously identified. We predict that approximately 1309 proteins are destined for the secretory pathway, many of which are likely post-translationally processed to generate active peptides. Within this neural secretome, we identified a gene transcript that encoded a precursor protein with striking similarity to a gonadotropin-releasing hormone (GnRH). We additionally identified another GnRH NP superfamily member, the adipokinetic hormone/corazonin-related peptide (ACP). M. rosenbergii GnRH and ACP were widespread throughout the nervous tissues, implicating them as potential neuromodulators. Furthermore, GnRH was found in non-neural tissues, including the stomach, gut, heart, testis and ovary, in the latter most prominently within secondary oocytes. The GnRH/corazonin receptor-like gene is specific to the ovary, whereas the receptor-like gene expression is more widespread. Administration of GnRH had no effect on ovarian development and maturation, nor any effect on total hemolymph lipid levels, while ACP administration decreased oocyte proliferation (at high dose) and stimulated a significant increase in total hemolymph lipids. In conclusion, our targeted analysis of the M. rosenbergii neural secretome has revealed the decapod GnRH and ACP genes. We propose that ACP in crustaceans plays a role in the lipid metabolism and the inhibition of oocyte proliferation, while the role of the GnRH remains to be clearly defined, possibly through experiments involving gene silencing.

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.

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.

Identification of the first neuropeptides from the enigmatic hexapod order Protura

The Hexapoda consists of two classes, the Entognatha and the Insecta, with the former group considered basal to the latter. The Protura is a basal order within the Entognatha, the members of which are minute soil dwellers first identified in the early 20th century. Recently, a transcriptome shotgun assembly (TSA) was generated for the proturan Acerentomon sp., providing the first significant molecular resource for this enigmatic hexapod order. As part of an ongoing effort to predict peptidomes for little studied members of the Arthropoda, we have mined this TSA dataset for transcripts encoding putative neuropeptide precursors and predicted the structures of mature peptides from the deduced proteins. Forty-seven peptide-encoding transcripts were mined from the Acerentomon TSA dataset, with 202 distinct peptides predicted from them. The peptides identified included isoforms of adipokinetic hormone, adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, diuretic hormone 44, ecdysis-triggering hormone, eclosion hormone, FMRFamide-like peptide, GSEFLamide, insulin-like peptide, intocin, leucokinin, myosuppressin, neuropeptide F, orcokinin, proctolin, pyrokinin, RYamide, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide; these are the first neuropeptides described from any proturan. Comparison of the Acerentomon precursors and mature peptides with those from other arthropods revealed features characteristic of both the insects and the crustaceans, which is consistent with the hypothesized phylogenetic position of the Protura within the Pancrustacea, i.e. at or near the point of divergence of the hexapods from the crustaceans.

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.

In silico prediction of a neuropeptidome for the eusocial insect Mastotermes darwiniensis

Mastotermes darwiniensis is the most basal living member of the Isoptera (termites), yet it exhibits an extremely advanced level of eusocial organization. Given the interest in, and the high levels of differential developmental and behavioral control needed for, eusociality, it is surprising that essentially nothing is known about the native peptides of M. darwiniensis, which undoubtedly represent the largest and most diverse class of hormones present in this species. The recent public deposition of a 100,000(+)-sequence transcriptome for M. darwiniensis provides a means for peptide discovery in this termite. Here, this resource was mined for putative peptide-encoding transcripts via the BLAST algorithm tblastn and known arthropod neuropeptide precursor queries; mature peptide structures were predicted from the deduced pre/preprohormones using a well-vetted bioinformatics workflow. Thirty-four M. darwiniensis peptide-encoding transcripts were identified, with 163 distinct mature peptides predicted from these sequences. These peptides included members of the adipokinetic hormone, adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin C, allatotropin, bursicon β, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, diuretic hormone 44, FMRFamide-like peptide, insulin-like peptide, leucokinin, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone, pyrokinin, RYamide, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide families. This peptidome is the largest thus far predicted for any member of the Isoptera, and provides a foundation for initiating studies of peptidergic signaling in this and other termites, including ones directed at understanding the roles peptide hormones play in the developmental and behavioral control required for eusociality.

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.

Neuropeptide discovery in the Araneae (Arthropoda, Chelicerata, Arachnida): elucidation of true spider peptidomes using that of the Western black widow as a reference

The public deposition of large transcriptome shotgun assembly (TSA) datasets for the Araneae (true spiders) provides a resource for determining the structures of the native neuropeptides present in members of this chelicerate order. Here, the Araneae TSA data were mined for putative peptide-encoding transcripts using the recently deduced neuropeptide precursors from the Western black widow Latrodectus hesperus as query templates. Neuropeptide-encoding transcripts from five spiders, Latrodectus tredecimguttatus, Stegodyphus mimosarum, Stegodyphus lineatus, Stegodyphus tentoriicola and Acanthoscurria geniculata, were identified, including ones encoding members of the allatostatin A, allatostatin B, allatostatin C, allatotropin, CAPA/periviscerokinin/pyrokinin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, diuretic hormone 44, eclosion hormone, FMRFamide-like peptide (FLP), GSEFLamide, insulin-like peptide, orcokinin, proctolin, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide (TRP) families. A total of 156 distinct peptides were predicted from the precursor proteins deduced from the S. mimosarum transcripts, with 65, 26, 21 and 12 peptides predicted from those deduced from the A. geniculata, L. tredecimguttatus, S. lineatus and S. tentoriicola sequences, respectively. Among the peptides identified were variant isoforms of FLP, orcokinin and TRP, peptides whose structures are similar to ones previously identified from L. hesperus. The prediction of these atypical peptides from multiple spiders suggests that they may be broadly conserved within the Araneae rather than being species-specific variants. Taken collectively, the data described here greatly expand the number of known Araneae neuropeptides, providing a foundation for future functional studies of peptidergic signaling in this important Chelicerate order.