Characteristic expression patterns of allatostatin-like peptide, FMRFamide-related peptide, orcokinin, tachykinin-related peptide, and SIFamide in the olfactory system of crayfish Procambarus clarkii

Switching neuron contributions to second network activity

Network flexibility is important for adaptable behaviors. This includes neuronal switching, where neurons alter their network participation, including changing from single- to dual-network activity. Understanding the implications of neuronal switching requires determining how a switching neuron interacts with each of its networks. Here, we tested 1) whether "home" and second networks, operating via divergent rhythm generation mechanisms, regulate a switching neuron and 2) if a switching neuron, recruited via modulation of intrinsic properties, contributes to rhythm or pattern generation in a new network. Small, well-characterized feeding-related networks (pyloric, ∼1 Hz; gastric mill, ∼0.1 Hz) and identified modulatory inputs make the isolated crab (Cancer borealis) stomatogastric nervous system (STNS) a useful model to study neuronal switching. In particular, the neuropeptide Gly1-SIFamide switches the lateral posterior gastric (LPG) neuron (2 copies) from pyloric-only to dual-frequency pyloric/gastric mill (fast/slow) activity via modulation of LPG-intrinsic properties. Using current injections to manipulate neuronal activity, we found that gastric mill, but not pyloric, network neurons regulated the intrinsically generated LPG slow bursting. Conversely, selective elimination of LPG from both networks using photoinactivation revealed that LPG regulated gastric mill neuron-firing frequencies but was not necessary for gastric mill rhythm generation or coordination. However, LPG alone was sufficient to produce a distinct pattern of network coordination. Thus, modulated intrinsic properties underlying dual-network participation may constrain which networks can regulate switching neuron activity. Furthermore, recruitment via intrinsic properties may occur in modulatory states where it is important for the switching neuron to actively contribute to network output.NEW & NOTEWORTHY We used small, well-characterized networks to investigate interactions between rhythmic networks and neurons that switch their network participation. For a neuron switching into dual-network activity, only the second network regulated its activity in that network. In addition, the switching neuron was sufficient but not necessary to coordinate second network neurons and regulated their activity levels. Thus, regulation of switching neurons may be selective, and a switching neuron is not necessarily simply a follower in additional networks.

Immunolocalization of SIFamide-like neuropeptides in the adult and developing central nervous system of the amphipod Parhyale hawaiensis (Malacostraca, Peracarida, Amphipoda)

Immunohistochemical analyses on the distribution of neuropeptides in the pancrustacean brain in the past have focussed mostly on representatives of the decapod ("ten-legged") pancrustaceans whereas other taxa are understudied in this respect. The current report examines the post-embryogenic and adult brain and ventral nerve cord of the amphipod pancrustacean Parhyale hawaiensis (Dana. 1853; Peracarida, Amphipoda, Hyalide), a subtropical species with a body size of 1.5 cm and a direct post-embryonic development using immunohistochemistry to label the neuropeptide SIFamide and synaptic proteins (synapsins). We found strong SIFamide-like labelling in proto-, deuto- and tritocerebrum, especially in the lamina, the lateral protocerebrum, lateral assessory lobe, the central body, olfactory lobe, medial antenna 1 neuropil and antenna 2 neuropil. Out of a total of 28 ± 5 (N = 12) SIFamide-positive neurons in the central brain of adult P. hawaiensis, we found three individually identifiable somata which were consistently present within the brain of adult and subadult animals. Additionally, the subesophageal and two adjacent thoracic ganglia were analysed in only adult animals and also showed a strong SIFamide-like immunoreactivity. We compare our findings to other pancrustaceans including hexapods and discuss them in an evolutionary context.

Unravelling the neuropeptidome of the ornate spiny lobster Panulirus ornatus: A focus on peptide hormones and their processing enzymes expressed in the reproductive tissues

Neuropeptides are commonly produced in the neural tissues yet can have effects on far-reaching targets, with varied biological responses. We describe here the neuropeptidome of the ornate spiny lobster, Panulirus ornatus, a species of emerging importance to closed-system aquaculture, with a focus on peptide hormones produced by the reproductive tissues. Transcripts for a precursor to one neuropeptide, adipokinetic hormone/corazonin-related peptide (ACP) were identified in high numbers in the sperm duct of adult spiny lobsters suggesting a role for ACP in the reproduction of this species. Neuropeptide production in the sperm duct may be linked with physiological control of spermatophore production in the male, or alternatively may function in signalling to the female. The enzymes which process nascent neuropeptide precursors into their mature, active forms have seldom been studied in decapods, and never before at the multi-tissue level. We have identified transcripts for multiple members of the proprotein convertase subtisilin/kexin family in the ornate spiny lobster, with some enzymes showing specificity to certain tissues. In addition, other enzyme transcripts involved with neuropeptide processing are identified along with their tissue and life stage expression patterns.

Local olfactory interneurons provide the basis for neurochemical regionalization of olfactory glomeruli in crustaceans

The primary olfactory centers of metazoans as diverse as arthropods and mammals consist of an array of fields of dense synaptic neuropil, the olfactory glomeruli. However, the neurochemical structure of crustacean olfactory glomeruli is largely understudied when compared to the insects. We analyzed the glomerular architecture in selected species of hermit crabs using immunohistochemistry against presynaptic proteins, the neuropeptides orcokinin, RFamide and allatostatin, and the biogenic amine serotonin. Our study reveals an unexpected level of structural complexity, unmatched by what is found in the insect olfactory glomeruli. Peptidergic and aminergic interneurons provide the structural basis for a regionalization of the crustacean glomeruli into longitudinal and concentric compartments. Our data suggest that local olfactory interneurons take a central computational role in modulating the information transfer from olfactory sensory neurons to projection neurons within the glomeruli. Furthermore, we found yet unknown neuronal elements mediating lateral inhibitory interactions across the glomerular array that may play a central role in modulating the transfer of sensory input to the output neurons through presynaptic inhibition. Our study is another step in understanding the function of crustacean olfactory glomeruli as highly complex units of local olfactory processing.

Intrinsic sources of tachykinin-related peptide in the thoracic ganglion mass of the crab, Cancer borealis

Neuropeptides comprise the largest class of neural and neuroendocrine signaling molecules. Vertebrate tachykinins (TKs) and the structurally-related invertebrate tachykinin-related peptides (TRPs) together form the largest neuropeptide superfamily, with a number of conserved neural and neuroendocrine functions across species. Arthropods, including crustaceans, have provided many insights into neuropeptide signaling and function. Crustacean tachykinin-related peptide occurs in endocrine organs and cells and in two of the major crustacean CNS components, the supraoesophageal ganglion ("brain") and the stomatogastric nervous system. However, little is known about TRP sources in the remaining major CNS component, the thoracic ganglion mass (TGM). To gain further insight into the function of this peptide, we aimed to identify intrinsic TRP sources in the TGM of the Jonah crab, Cancer borealis. We first adapted a clearing protocol to improve TRP immunoreactivity specifically in the TGM, which is a dense, fused mass of multiple ganglia in short-bodied crustaceans such as Cancer species of crabs. We verified that the clearing protocol avoided distortion of cell body morphology yet increased visibility of TRP immunoreactivity. Using confocal microscopy, we found TRP-immunoreactive (TRP-IR) axon tracts running the length of the TGM, TRP-IR neuropil in all ganglia, and approximately 110 TRP-IR somata distributed throughout the TGM, within and between ganglia. These somata likely represent both neural and neuroendocrine sources of TRP. Thus, there are many potential intrinsic sources of TRP in the TGM that are positioned to regulate behaviors such as food intake, locomotion, respiration, and reproduction.

Localization of neurons expressing choline acetyltransferase, serotonin and/or FMRFamide in the central nervous system of the decapod shore crab Hemigrapsus sanguineus

Although it is now established that neurons in crustacea contain multiple transmitter substances, little is know about patterns of expression and co-expression or about the functional effects of such co-transmission. The present study was designed to characterize the distributions and potential colocalization of choline acetyltransferase (ChAT), serotonin (5-HT) and neuropeptide H-Phe-Met-Arg-Phe-NH2 (FMRFamide) in the central nervous system (CNS) of the Asian shore crab, Hemigrapsus sanguineus using immunohistochemical analyses in combination with laser scanning confocal microscopy. ChAT was found to be expressed by small, medium-sized, and large neurons in all regions of the brain and ventral nerve cord (VNC). For the most part, ChAT, FMRFamide, and 5-HT are expressed in different neurons, although some colocalization of ChAT- with FMRFamide- or 5-HT-LIR is observed in small and medium-sized cells, mostly neurons that immunostain only weakly. In the brain, such double immunolabeling is observed primarily in neurons of the protocerebrum and, to a particularly great extent, in local olfactory interneurons of the deutocerebrum. The clusters of neurons in the VNC that stain most intensely for ChAT, FMRFamide, and 5-HT, with colocalization in some cases, are located in the subesophageal ganglia. This colocalization appears to be related to function, since it is present in regions of the CNS characterized by multiple afferent projections and outputs to a variety of functionally related centers involved in various physiological and behavioral processes. Further elucidation of the functional significance of these neurons and of the widespread process of co-transmission in the crustaceans should provide fascinating new insights.

Functional morphology of the primary olfactory centers in the brain of the hermit crab Coenobita clypeatus (Anomala, Coenobitidae)

Terrestrial hermit crabs of the genus Coenobita display strong behavioral responses to volatile odors and are attracted by chemical cues of various potential food sources. Several aspects of their sense of aerial olfaction have been explored in recent years including behavioral aspects and structure of their peripheral and central olfactory pathway. Here, we use classical histological methods and immunohistochemistry against the neuropeptides orcokinin and allatostatin as well as synaptic proteins and serotonin to provide insights into the functional organization of their primary olfactory centers in the brain, the paired olfactory lobes. Our results show that orcokinin is present in the axons of olfactory sensory neurons, which target the olfactory lobe. Orcokinin is also present in a population of local olfactory interneurons, which may relay lateral inhibition across the array of olfactory glomeruli within the lobes. Extensive lateral connections of the glomeruli were also visualized using the histological silver impregnation method according to Holmes-Blest. This technique also revealed the structural organization of the output pathway of the olfactory system, the olfactory projection neurons, the axons of which target the lateral protocerebrum. Within the lobes, the course of their axons seems to be reorganized in an axon-sorting zone before they exit the system. Together with previous results, we combine our findings into a model on the functional organization of the olfactory system in these animals.

Similarities and differences in circuit responses to applied Gly1-SIFamide and peptidergic (Gly1-SIFamide) neuron stimulation

Microcircuit modulation by peptides is well established, but the cellular/synaptic mechanisms whereby identified neurons with identified peptide transmitters modulate microcircuits remain unknown for most systems. Here, we describe the distribution of GYRKPPFNGSIFamide (Gly1-SIFamide) immunoreactivity (Gly1-SIFamide-IR) in the stomatogastric nervous system (STNS) of the crab Cancer borealis and the Gly1-SIFamide actions on the two feeding-related circuits in the stomatogastric ganglion (STG). Gly1-SIFamide-IR localized to somata in the paired commissural ganglia (CoGs), two axons in the nerves connecting each CoG with the STG, and the CoG and STG neuropil. We identified one Gly1-SIFamide-IR projection neuron innervating the STG as the previously identified modulatory commissural neuron 5 (MCN5). Brief (~10 s) MCN5 stimulation excites some pyloric circuit neurons. We now find that bath applying Gly1-SIFamide to the isolated STG also enhanced pyloric rhythm activity and activated an imperfectly coordinated gastric mill rhythm that included unusually prolonged bursts in two circuit neurons [inferior cardiac (IC), lateral posterior gastric (LPG)]. Furthermore, longer duration (>30 s) MCN5 stimulation activated a Gly1-SIFamide-like gastric mill rhythm, including prolonged IC and LPG bursting. The prolonged LPG bursting decreased the coincidence of its activity with neurons to which it is electrically coupled. We also identified local circuit feedback onto the MCN5 axon terminals, which may contribute to some distinctions between the responses to MCN5 stimulation and Gly1-SIFamide application. Thus, MCN5 adds to the few identified projection neurons that modulate a well-defined circuit at least partly via an identified neuropeptide transmitter and provides an opportunity to study peptide regulation of electrical coupled neurons in a functional context. NEW & NOTEWORTHY Limited insight exists regarding how identified peptidergic neurons modulate microcircuits. We show that the modulatory projection neuron modulatory commissural neuron 5 (MCN5) is peptidergic, containing Gly1-SIFamide. MCN5 and Gly1-SIFamide elicit similar output from two well-defined motor circuits. Their distinct actions may result partly from circuit feedback onto the MCN5 axon terminals. Their similar actions include eliciting divergent activity patterns in normally coactive, electrically coupled neurons, providing an opportunity to examine peptide modulation of electrically coupled neurons in a functional context.

Molecular cloning and characterization of the SIFamide precursor and receptor in a hymenopteran insect, Bombus terrestris

SIFamides (SIFa) are a family of neuropeptides that are highly conserved among arthropods. In insects, this peptide is mainly expressed in four medial interneurons in the pars intercerebralis and affects sexual behavior, sleep regulation and pupal mortality. Furthermore, an influence on the hatching rate has been observed. The first SIFa receptor (SIFR) was pharmacologically characterized in Drosophila melanogaster and is homologous to the vertebrate gonadotropin-inhibitory hormone (GnIH) receptor (NPFFR). In this study, we pharmacologically characterized the SIFR of the buff-tailed bumblebee Bombus terrestris. We demonstrated an intracellular increase in calcium ions and cyclic AMP (cAMP) upon ligand binding with an EC₅₀ value in the picomolar and nanomolar range, respectively. In addition, we studied the agonistic properties of a range of related and modified peptides. By means of quantitative real time PCR (qPCR), we examined the relative transcript levels of Bomte-SIFa and Bomte-SIFR in a variety of tissues.

Characterization of the neuropeptidome of a Southern Ocean decapod, the Antarctic shrimp Chorismus antarcticus: Focusing on a new decapod ITP-like peptide belonging to the CHH peptide family

As part of the study of the resilience of Antarctic crustaceans to global warming, the shrimp Chorismus antarcticus was subjected to an analysis of global approach using the Next Generation Sequencing Illumina Hi-Seq platform. With this data a detailed study into the principal neuropeptides and neurohormones of this species have been undertaken. Total RNAs from whole animals were enriched with eyestalk extracts to ensure maximum sequencing depth of the different neurohormones and neuropeptides mainly expressed into the X organ-sinus gland complex, which is a major endocrine organ of their synthesis. Apart from the information that can provide the availability of the transcriptome of a polar crustacean, the study of neuropeptides of a caridean shrimp will partially fill the limited data available for this taxon. Illumina sequencing was used to produce a transcriptome of the polar shrimp. Analysis of the Trinity assembled contigs produced 55 pre-pro-peptides, coding for 111 neuropeptides belonging to the following families: adipokinetic-corazonin-like peptide, Allatostatins (A, B et C), Bursicon (α), CCHamide, Crustacean Hyperglycemic Hormones (CHH), Crustacean Cardioactive Peptide (CCAP), Corazonin, Crustacean Female Sex Hormone (CSFH), Diuretic Hormones 31 and 45 (DH), Eclosion Hormone (EH), FLRFamide, GSEFLamide, Intocin, Ion Transport Peptide-like (ITP-like), Leucokinin, Molt-inhibiting Hormone, Myosuppresin, Neuroparsin, Neuropeptide F (NPF), Orcokinin, Orcomyotropin, Pigment Dispersing Hormone (PDH), Pyrokinin, Red Pigment Concentrating Hormone (RPCH), SIFamide, small Neuropeptide F (sNPF), Sulfakinin and finally Tachykinin Related peptides. Among the new peptides highlighted in this study, the focus was placed on the peptides of the CHH family and more particularly on a new ITP-like in order to confirm its belonging to a new group of peptides of the family. A phylogeny made from more than 200 sequences of peptides, included new sequences from new species besides Chorismus antarcticus, confirms the peculiarity of this new set of peptides gathered under the name ITP-like.

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.

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.

Comparative analyses of olfactory systems in terrestrial crabs (Brachyura): evidence for aerial olfaction?

Adaptations to a terrestrial lifestyle occurred convergently multiple times during the evolution of the arthropods. This holds also true for the "true crabs" (Brachyura), a taxon that includes several lineages that invaded land independently. During an evolutionary transition from sea to land, animals have to develop a variety of physiological and anatomical adaptations to a terrestrial life style related to respiration, reproduction, development, circulation, ion and water balance. In addition, sensory systems that function in air instead of in water are essential for an animal's life on land. Besides vision and mechanosensory systems, on land, the chemical senses have to be modified substantially in comparison to their function in water. Among arthropods, insects are the most successful ones to evolve aerial olfaction. Various aspects of terrestrial adaptation have also been analyzed in those crustacean lineages that evolved terrestrial representatives including the taxa Anomala, Brachyura, Amphipoda, and Isopoda. We are interested in how the chemical senses of terrestrial crustaceans are modified to function in air. Therefore, in this study, we analyzed the brains and more specifically the structure of the olfactory system of representatives of brachyuran crabs that display different degrees of terrestriality, from exclusively marine to mainly terrestrial. The methods we used included immunohistochemistry, detection of autofluorescence- and confocal microscopy, as well as three-dimensional reconstruction and morphometry. Our comparative approach shows that both the peripheral and central olfactory pathways are reduced in terrestrial members in comparison to their marine relatives, suggesting a limited function of their olfactory system on land. We conclude that for arthropod lineages that invaded land, evolving aerial olfaction is no trivial task.

SIFamide acts on fruitless neurons to modulate sexual behavior in Drosophila melanogaster

The Drosophila gene fruitless expresses male and female specific transcription factors which are responsible for the generation of male specific neuronal circuitry for courtship behavior. Mutations in this gene may lead to bisexual behavior in males. Bisexual behavior in males also occurs in the absence of the neuropeptide SIFamide. We show here that the SIFamide neurons do not express fruitless. However, when fruitless neurons are made to express RNAi specific for the SIFamide receptor, male flies engage in bisexual behavior, showing that SIFamide acts on fruitless neurons. If neurons expressing a SIFaR-gal4 transgene are killed by the apoptotic protein reaper or when these neurons express SIFamide receptor RNAi, males also show male-male courtship behavior. We next used this transgene to localize neurons that express the SIFamide receptor. Such neurons are ubiquitously present in the central nervous and we also found two neurons in the uterus that project into the central nervous system.

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.

The power of next-generation sequencing as illustrated by the neuropeptidome of the crayfish Procambarus clarkii

Transcriptomes of the crayfish Procambarus clarkii were analyzed for the presence of transcripts encoding neurohormones, neuropeptides and their receptors. A total of 58 different transcripts were found to encode such ligands and another 82 for their receptors. A very large number of the neuropeptide transcripts appeared to be complete and for those that were not only small parts seemed to be lacking. Transcripts for the neuropeptide GPCRs as well as for the putative receptors for insulin, neuroparsin and eclosion hormone were often also complete or almost so. Of particular interest is the presence of three different neuroparsin genes and two putative neuroparsin receptors. There are also three pigment dispersing hormones as well three likely receptors for these neuropeptides. CNMamide, calcitonin, CCRFamide, natalisin, trissin and relaxin appear to be new crustacean neuropeptides. The recently identified crustacean female sex hormone was also found and in the crayfish appears to be not only expressed in the eyestalk, but in the ovary as well (though not in the testis). Interestingly, there are two other proteins in the crayfish with a structure similar to crustacean female sex hormone, that could be precursors of neurohormones, but these are not expressed by the ovary. The ovary also appears to contain significant numbers of transcripts encoding pigment dispersing hormones, CNMamide as well as glycoprotein B5, but not glycoprotein A2.

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.

Identification and distribution of SIFamide in the nervous system of the desert locust Schistocerca gregaria

SIFamides are a family of highly conserved arthropod neuropeptides. To date, nine orthocopies from different arthropods, most of them insects, have been identified, all consisting of 11-12 amino acid residues. The striking conservation in sequence is mirrored by highly similar morphologies of SIFamide-immunoreactive neurons: immunolabeling in various insect species revealed four immunopositive neurons with somata in the pars intercerebralis and arborizations extending throughout the brain and ventral nervous system. In contrast, the functional role of these neurons and their neuropeptide SIFamide is largely obscure. To provide an additional basis for functional analysis, we identified, by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry, a SIFamide peptide in the desert locust Schistocerca gregaria and studied its distribution throughout the nervous system. Identification was supported by analysis of transcriptomic data obtained from another grasshopper, Stenobothrus lineatus. Scg-SIFamide, unlike all SIFamides identified so far, is a pentadecapeptide with an extended and highly modified N-terminus (AAATFRRPPFNGSIFamide). As in other insects, pairs of descending neurons with somata in the pars intercerebralis and ramifications in most areas of the nervous system are SIFamide-immunoreactive. In addition, a small number of local interneurons in the brain and ventral ganglia were immunostained. Double-label experiments showed that the SIFamide-immunoreactive descending neurons are identical to previously characterized primary commissure pioneer (PNP) neurons of the locust brain that pioneer the first commissure in the brain. The data suggest that the descending SIFamide-immunoreactive neurons play a developmental role in organizing the insect central nervous system. J. Comp. Neurol. 523:108-125, 2015. © 2014 Wiley Periodicals, Inc.

Identification of putative ecdysteroid and juvenile hormone pathway genes in the shrimp Neocaridina denticulata

Although the sesquiterpenoid juvenile hormone (JH) and the steroidal ecdysteroids are of vital importance to the development and reproduction of insects, our understanding of the evolution of these crucial hormonal regulators in other arthropods is limited. To better understand arthropod hormone evolution and regulation, here we describe the hormonal pathway genes (e.g. those involved in hormone biosynthesis, degradation, regulation and signal transduction) of a new decapod model, the shrimp Neocaridina denticulata. The majority of known insect sesquiterpenoid and ecdysteroid pathway genes and their regulators are contained in the N. denticulata genome. In the sesquiterpenoid pathway, these include biosynthetic pathway components: juvenile hormone acid methyltransferase (JHAMT); hormone binding protein: juvenile hormone binding protein (JHBP); and degradation pathway components: juvenile hormone esterase (JHE), juvenile hormone esterase binding protein (JHEBP) and juvenile hormone epoxide hydrolase (JHEH), with the JHBP, JHEBP and JHEH genes being discovered in a crustacean for the first time here. Ecdysteroid biosynthetic pathway genes identified include spook, phantom, disembodied, shadow and CYP18. Potential hormonal regulators and signal transducers such as allatostatins (ASTs), Methoprene-tolerant (Met), Retinoid X receptor (RXR), Ecdysone receptor (EcR), calponin-like protein Chd64, FK509-binding protein (FKBP39), Broad-complex (Br-c), and crustacean hyperglycemic hormone/molt-inhibiting hormone/gonad-inhibiting hormone (CHH/MIH/GIH) genes are all present in the shrimp N. denticulata. To our knowledge, this is the first report of these hormonal pathways and their regulatory genes together in a single decapod, providing a vital resource for further research into development, reproduction, endocrinology and evolution of crustaceans, and arthropods in general.

In silico characterization of the neuropeptidome of the Western black widow spider Latrodectus hesperus

Technological advancements in high-throughput sequencing have resulted in the production/public deposition of an ever-growing number of arthropod transcriptomes. While most sequencing projects have focused on hexapods, transcriptomes have also been generated for members of the Chelicerata. One chelicerate for which a large transcriptome has recently been released is the Western black widow Latrodectus hesperus, a member of the Araneae (true spiders). Here, a neuropeptidome for L. hesperus was predicted using this resource. Thirty-eight peptide-encoding transcripts were mined from the L. hesperus transcriptome, with 216 distinct peptides predicted from the deduced pre/preprohormones. The identified peptides included members of the allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CAPA/periviscerokinin/pyrokinin, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, diuretic hormone 44, FMRFamide-like peptide (FLP), GSEFLamide, insulin-like peptide, neuropeptide F (NPF), orcokinin, proctolin, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide (TRP) families. Of particular note were the identifications of a carboxyl (C)-terminally extended corazonin, FLPs possessing -IMRFamide, -MMYFamide, and -MIHFamide C-termini, a NPF and a sulfakinin each ending in -RYamide rather than -RFamide, a precursor whose orcokinins include C-terminally amidated isoforms, and a collection of TRPs possessing -FXPXLamide rather than the stereotypical -FXGXLamide C-termini. The L. hesperus peptidome is by far the largest thus far published for any member of the Chelicerata. Taken collectively, these data serve as a reference for future neuropeptide discovery in the Araneae and provide a foundation for future studies of peptidergic control in L. hesperus and other spiders.

Cells from the immune system generate adult-born neurons in crayfish

Neurogenesis is an ongoing process in the brains of adult decapod crustaceans. However, the first-generation precursors that produce adult-born neurons, which reside in a neurogenic niche, are not self-renewing in crayfish and must be replenished. The source of these neuronal precursors is unknown. Here, we report that adult-born neurons in crayfish can be derived from hemocytes. Following adoptive transfer of 5-ethynyl-2'-deoxyuridine (EdU)-labeled hemocytes, labeled cells populate the neurogenic niche containing the first-generation neuronal precursors. Seven weeks after adoptive transfer, EdU-labeled cells are located in brain clusters 9 and 10 (where adult-born neurons differentiate) and express appropriate neurotransmitters. Moreover, the number of cells composing the neurogenic niche in crayfish is tightly correlated with total hemocyte counts (THCs) and can be manipulated by raising or lowering THC. These studies identify hemocytes as a source of adult-born neurons in crayfish and demonstrate that the immune system is a key contributor to adult neurogenesis.

Identification of the first neuropeptides from the Amphipoda (Arthropoda, Crustacea)

Despite being used as models in the field of ecotoxicology, including use in studies of endocrine disruption, little is known about the hormonal systems of amphipods, particularly their peptidergic signaling systems. Here, transcriptome shotgun assembly (TSA) sequences were used to predict the structures of the first neuropeptides from members of this crustacean order. Using a well-established workflow, BLAST searches of the extant amphipod TSA data were conducted for putative peptide-encoding transcripts. The pre/preprohormones deduced from the identified TSA sequences were then used to predict the mature structures of amphipod neuropeptides. In total, 43 putative peptide-encoding transcripts were identified from three amphipods, Echinogammarus veneris, Hyalella azteca and Melita plumulosa. Collectively, 139 distinct mature peptides (110 from E. veneris alone) were predicted from these TSA sequences. The identified peptides included members of the adipokinetic hormone/red pigment concentrating hormone, allatostatin A, allatostatin B, allatostatin C, bursicon α, bursicon β, crustacean hyperglycemic hormone, diuretic hormone 31, FLRFamide, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F, orcokinin, pigment dispersing hormone (PDH), proctolin, RYamide, SIFamide, sulfakinin and tachykinin-related peptide families. Of particular note were the identifications of orcokinins possessing SFDEIDR- rather than the typical NFDEIDR- amino-termini, e.g. SFDEINRSNFGFN, a carboxyl-terminally amidated orcokinin, i.e. SFDEINRSNFGFSamide, PDHs longer than the stereotypical 18 amino acids, e.g. NSELLNTLLGSKSLAALRAAamide, and a 13 rather than 12 amino acid long SIFamide, i.e. GPYRKPPFNGSIFamide. These data not only provide the first descriptions of native amphipod neuropeptides, but also represent a new resource for initiating investigations of peptidergic signaling in the Amphipoda.

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.

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.

First-generation neuronal precursors in the crayfish brain are not self-renewing

Adult-born neurons in crayfish (Procambarus clarkii) are the progeny of 1st-generation precursor cells (functionally analogous to neuronal stem cells in vertebrates) that are located in a neurogenic niche on the ventral surface of the brain. The daughters of these precursor cells migrate along the processes of bipolar niche cells to proliferation zones in the cell clusters where the somata of the olfactory interneurons reside. Here they divide again, producing offspring that differentiate into olfactory local and projection neurons. The features of this neuronal assembly line, and the fact that it continues to function when the brain is isolated and perfused or maintained in organotypic culture, provide opportunities unavailable in other organisms to explore the sequence of cellular and molecular events leading to the production of new neurons in adult brains. Further, we have determined that the 1st-generation precursor cells are not a self-renewing population, and that the niche is, nevertheless, not depleted as the animals grow and age. We conclude, therefore, that the niche is not a closed system and that there must be an extrinsic source of neuronal stem cells. Based on in vitro studies demonstrating that cells extracted from the hemolymph are attracted to the niche, as well as the intimate relationship between the niche and vasculature, we hypothesize that the hematopoietic system is a likely source of these cells.

Neuropeptide complexity in the crustacean central olfactory pathway: immunolocalization of A-type allatostatins and RFamide-like peptides in the brain of a terrestrial hermit crab

BACKGROUND

In the olfactory system of malacostracan crustaceans, axonal input from olfactory receptor neurons associated with aesthetascs on the animal's first pair of antennae target primary processing centers in the median brain, the olfactory lobes. The olfactory lobes are divided into cone-shaped synaptic areas, the olfactory glomeruli where afferents interact with local olfactory interneurons and olfactory projection neurons. The local olfactory interneurons display a large diversity of neurotransmitter phenotypes including biogenic amines and neuropeptides. Furthermore, the malacostracan olfactory glomeruli are regionalized into cap, subcap, and base regions and these compartments are defined by the projection patterns of the afferent olfactory receptor neurons, the local olfactory interneurons, and the olfactory projection neurons. We wanted to know how neurons expressing A-type allatostatins (A-ASTs; synonym dip-allatostatins) integrate into this system, a large family of neuropeptides that share the C-terminal motif -YXFGLamide.

RESULTS

We used an antiserum that was raised against the A-type Diploptera punctata (Dip)-allatostatin I to analyse the distribution of this peptide in the brain of a terrestrial hermit crab, Coenobita clypeatus (Anomura, Coenobitidae). Allatostatin A-like immunoreactivity (ASTir) was widely distributed in the animal's brain, including the visual system, central complex and olfactory system. We focussed our analysis on the central olfactory pathway in which ASTir was abundant in the primary processing centers, the olfactory lobes, and also in the secondary centers, the hemiellipsoid bodies. In the olfactory lobes, we further explored the spatial relationship of olfactory interneurons with ASTir to interneurons that synthesize RFamide-like peptides. We found that these two peptides are present in distinct populations of local olfactory interneurons and that their synaptic fields within the olfactory glomeruli are also mostly distinct.

CONCLUSIONS

We discuss our findings against the background of the known neurotransmitter complexity in the crustacean olfactory pathway and summarize what is now about the neuronal connectivity in the olfactory glomeruli. A-type allatostatins, in addition to their localization in protocerebral brain areas, seem to be involved in modulating the olfactory signal at the level of the deutocerebrum. They contribute to the complex local circuits within the crustacean olfactory glomeruli the connectivity within which as yet is completely unclear. Because the glomeruli of C. clypeatus display a distinct pattern of regionalization, their olfactory systems form an ideal model to explore the functional relevance of glomerular compartments and diversity of local olfactory interneurons for olfactory processing in crustaceans.

Families of allatoregulator sequences: a 2011 perspective1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Three different peptide families have been named “allatostatins” (ASTs), based on their initial purifications which were based on their ability to inhibit juvenile hormone (JH) biosynthesis. These include (i) a family of peptides that have a consensus C-terminal sequence Y/FXFGL-NH2; (ii) a family of peptides with a conserved C-terminal sequence W(X)6W-NH2; and(iii) a family of peptides with C-terminal sequence PISCF, some of which are C-terminally-amidated. Each allatostatin family has functions distinct and apart from the inhibition of JH biosynthesis. A peptide family known as the “allatotropins” serve to stimulate JH biosynthesis. This family of peptides also has been proven to exert multiple effects dependent on the species in question. Genome and peptidome projects are uncovering new members of these families and it is clear that these structures are not just confined to Insecta but are found in a range of invertebrates. The receptors for these neuropeptides have been identified and tested experimentally for specific ligand binding. The Y/FXFGLa-ASTs exert their action through galanin-like receptors, W(X)6Wa-ASTs through a sex peptide-binding receptor, and PISCF-ASTs through somatostatin-like receptors. These receptors are conserved through evolutionary time and are being identified in numerous invertebrates by way of genome projects.

Adult neurogenesis in the decapod crustacean brain: a hematopoietic connection?

New neurons are produced and integrated into circuits in the adult brains of many organisms, including crustaceans. In some crustacean species, the first-generation neuronal precursors reside in a niche exhibiting characteristics analogous to mammalian neurogenic niches. However, unlike mammalian niches where several generations of neuronal precursors co-exist, the lineage of precursor cells in crayfish is spatially separated allowing the influence of environmental and endogenous regulators on specific generations in the neuronal precursor lineage to be defined. Experiments also demonstrate that the first-generation neuronal precursors in the crayfish Procambarus clarkii are not self-renewing. A source external to the neurogenic niche must therefore provide cells that replenish the first-generation precursor pool, because although these cells divide and produce a continuous efflux of second-generation cells from the niche, the population of first-generation niche precursors is not diminished with growth and aging. In vitro studies show that cells extracted from the hemolymph, but not other tissues, are attracted to and incorporated into the neurogenic niche, a phenomenon that appears to involve serotonergic mechanisms. We propose that, in crayfish, the hematopoietic system may be a source of cells that replenish the niche cell pool. These and other studies reviewed here establish decapod crustaceans as model systems in which the processes underlying adult neurogenesis, such as stem cell origins and transformation, can be readily explored. Studies in diverse species where adult neurogenesis occurs will result in a broader understanding of fundamental mechanisms and how evolutionary processes may have shaped the vertebrate/mammalian condition.

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.

Adult neurogenesis: examples from the decapod crustaceans and comparisons with mammals

Defining evolutionary origins is a means of understanding an organism's position within the integrated web of living beings, and not only to trace characteristics back in time, but also to project forward in an attempt to reveal relationships with more recently evolved forms. Both the vertebrates and arthropods possess condensed nervous systems, but this is dorsal in the vertebrates and ventral in the arthropods. Also, whereas the nervous system in the vertebrates develops from a neural tube in the embryo, that of the arthropods comes from an ectodermal plate. Despite these apparently fundamental differences, it is now generally accepted that life-long neurogenesis, the generation of functionally integrated neurons from progenitor cells, is a common feature of the adult brains of a variety of organisms, ranging from insects and crustaceans to birds and mammals. Among decapod crustaceans, there is evidence for adult neurogenesis in basal species of the Dendrobranchiata, as well as in more recent terrestrial, marine and fresh-water species. The widespread nature of this phenomenon in decapod species may relate to the importance of the adult-born neurons, although their functional contribution is not yet known. The many similarities between the systems generating neurons in the adult brains of decapod crustaceans and mammals, reviewed in this paper, suggest that adult neurogenesis is governed by common ancestral mechanisms that have been retained in a phylogenetically broad group of species.

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.

Brain architecture of the largest living land arthropod, the Giant Robber Crab Birgus latro (Crustacea, Anomura, Coenobitidae): evidence for a prominent central olfactory pathway?

BACKGROUND

Several lineages within the Crustacea conquered land independently during evolution, thereby requiring physiological adaptations for a semi-terrestrial or even a fully terrestrial lifestyle. Birgus latro Linnaeus, 1767, the giant robber crab or coconut crab (Anomura, Coenobitidae), is the largest land-living arthropod and inhabits Indo-Pacific islands such as Christmas Island. B. latro has served as a model in numerous studies of physiological aspects related to the conquest of land by crustaceans. From an olfactory point of view, a transition from sea to land means that molecules need to be detected in gas phase instead of in water solution. Previous studies have provided physiological evidence that terrestrial hermit crabs (Coenobitidae) such as B. latro have a sensitive and well differentiated sense of smell. Here we analyze the brain, in particular the olfactory processing areas of B. latro, by morphological analysis followed by 3 D reconstruction and immunocytochemical studies of synaptic proteins and a neuropeptide.

RESULTS

The primary and secondary olfactory centers dominate the brain of B. latro and together account for ca. 40% of the neuropil volume in its brain. The paired olfactory neuropils are tripartite and composed of more than 1,000 columnar olfactory glomeruli, which are radially arranged around the periphery of the olfactory neuropils. The glomeruli are innervated ca. 90,000 local interneurons and ca. 160,000 projection neurons per side. The secondary olfactory centers, the paired hemiellipsoid neuropils, are targeted by the axons of these olfactory projection neurons. The projection neuron axonal branches make contact to ca. 250.000 interneurons (per side) associated with the hemiellipsoid neuropils. The hemiellipsoid body neuropil is organized into parallel neuropil lamellae, a design that is quite unusual for decapod crustaceans. The architecture of the optic neuropils and areas associated with antenna two suggest that B. latro has visual and mechanosensory skills that are comparable to those of marine Crustacea.

CONCLUSIONS

In parallel to previous behavioral findings that B. latro has aerial olfaction, our results indicate that their central olfactory pathway is indeed most prominent. Similar findings from the closely related terrestrial hermit crab Coenobita clypeatus suggest that in Coenobitidae, olfaction is a major sensory modality processed by the brain, and that for these animals, exploring the olfactory landscape is vital for survival in their terrestrial habitat. Future studies on terrestrial members of other crustacean taxa such as Isopoda, Amphipoda, Astacida, and Brachyura will shed light on how frequently the establishment of an aerial sense of olfaction evolved in Crustacea during the transition from sea to land. Amounting to ca. 1,000,000, the numbers of interneurons that analyse the olfactory input in B. latro brains surpasses that in other terrestrial arthropods, as e.g. the honeybee Apis mellifera or the moth Manduca sexta, by two orders of magnitude suggesting that B. latro in fact is a land-living arthropod that has devoted a substantial amount of nervous tissue to the sense of smell.

Two novel neuropeptides in innervation of the salivary glands of the black-legged tick, Ixodes scapularis: myoinhibitory peptide and SIFamide

The peptidergic signaling system is an ancient cell-cell communication mechanism that is involved in numerous behavioral and physiological events in multicellular organisms. We identified two novel neuropeptides in the neuronal projections innervating the salivary glands of the black-legged tick, Ixodes scapularis (Say, 1821). Myoinhibitory peptide (MIP) and SIFamide immunoreactivities were colocalized in the protocerebral cells and their projections terminating on specific cells of salivary gland acini (types II and III). Immunoreactive substances were identified by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis: a 1,321.6-Da peptide with the sequence typical for MIP (ASDWNRLSGMWamide) and a 1,395.7-Da SIFamide (AYRKPPFNGSIFamide), which are highly conserved among arthropods. Genes encoding these peptides were identified in the available Ixodes genome and expressed sequence tag (EST) database. In addition, the cDNA encoding the MIP prepropeptide was isolated by rapid amplification of cDNA ends (RACE). In this report, we describe the anatomical structure of specific central neurons innervating salivary gland acini and identify different neuropeptides and their precursors expressed by these neurons. Our data provide evidence for neural control of salivary gland by MIP and SIFamide from the synganglion, thus leading a basis for functional studies of these two distinct classes of neuropeptides.

Molecular and mass spectral identification of the broadly conserved decapod crustacean neuropeptide pQIRYHQCYFNPISCF: the first PISCF-allatostatin (Manduca sexta- or C-type allatostatin) from a non-insect

The PISCF-allatostatins (Manduca sexta- or C-type allatostatins) are a family of pentadecapeptides characterized by a pyroglutamine blocked N-terminus, an unamidated-PISCF C-terminus, and a disulfide bridge between two internal Cys residues. Several isoforms of PISCF-AST are known, all from holometabolous insects. Using a combination of transcriptomics and mass spectrometry, we have identified the first PISCF-type peptides from a non-insect species. In silico analysis of crustacean ESTs identified several Litopenaeus vannamei (infraorder Penaeidea) transcripts encoding putative PISCF-AST precursors. Translation of these ESTs, with subsequent prediction of their putative post-translational processing, revealed the existence of as many as three PISCF-type peptides, including pQIRYHQCYFNPISCF (disulfide bridging between Cys(7) and Cys(14)). Although none of the predicted isoforms was detected by mass spectrometry in L. vannamei, MALDI-FTMS mass profiling identified an m/z signal corresponding to pQIRYHQCYFNPISCF (disulfide bridge present) in neural tissue from 28 other decapods, which included members of six infraorders (Stenopodidea, Astacidea, Thalassinidea, Achelata, Anomura and Brachyura). Further characterization of the peptide using SORI-CID and chemical derivatization/enzymatic digestion supported the theorized structure. In both the crab Cancer borealis and the lobster Homarus americanus, MALDI-based tissue surveys suggest that pQIRYHQCYFNPISCF is broadly distributed in the nervous system; it was also detected in the posterior midgut caecum. Collectively, our data show that members of the PISCF-AST family are not restricted to the holometabolous insects, but instead may be broadly conserved within the Pancrustacea. Moreover, our data suggest that one highly conserved PISCF-type peptide, pQIRYHQCYFN-PISCF, is present in decapod crustaceans, functioning as a brain-gut paracrine/hormone.

Combining in silico transcriptome mining and biological mass spectrometry for neuropeptide discovery in the Pacific white shrimp Litopenaeus vannamei

The shrimp Litopenaeus vannamei is arguably the most important aquacultured crustacean, being the subject of a multi-billion dollar industry worldwide. To extend our knowledge of peptidergic control in this species, we conducted an investigation combining transcriptomics and mass spectrometry to identify its neuropeptides. Specifically, in silico searches of the L. vannamei EST database were conducted to identify putative prepro-hormone-encoding transcripts, with the mature peptides contained within the deduced precursors predicted via online software programs and homology to known isoforms. MALDI-FT mass spectrometry was used to screen tissue fragments and extracts via accurate mass measurements for the predicted peptides, as well as for known ones from other species. ESI-Q-TOF tandem mass spectrometry was used to de novo sequence peptides from tissue extracts. In total 120 peptides were characterized using this combined approach, including 5 identified both by transcriptomics and by mass spectrometry (e.g. pQTFQYSRGWTNamide, Arg(7)-corazonin, and pQDLDHVFLRFamide, a myosuppressin), 49 predicted via transcriptomics only (e.g. pQIRYHQCYFNPISCF and pQIRYHQCYFIPVSCF, two C-type allatostatins, and RYLPT, authentic proctolin), and 66 identified solely by mass spectrometry (e.g. the orcokinin NFDEIDRAGMGFA). While some of the characterized peptides were known L. vannamei isoforms (e.g. the pyrokinins DFAFSPRLamide and ADFAFNPRLamide), most were novel, either for this species (e.g. pEGFYSQRYamide, an RYamide) or in general (e.g. the tachykinin-related peptides APAGFLGMRamide, APSGFNGMRamide and APSGFLDMRamide). Collectively, our data not only expand greatly the number of known L. vannamei neuropeptides, but also provide a foundation for future investigations of the physiological roles played by them in this commercially important species.

Neuroanatomical tracing combined with in situ hybridization: analysis of gene expression patterns within brain circuits of interest

Most of our current understanding of brain circuits is based on hodological studies carried out using neuroanatomical tract-tracing. Our aim is to advance one step further by visualizing the functional correlate in a given circuit. In this regard, we believe it is feasible to combine retrograde tracing with fluorescence, non-radioactive in situ hybridization (ISH) protocols. The subsequent detection at the single-cell level of the expression of a given mRNA within retrograde-labeled neurons provides information regarding cellular function. This may be of particular interest when trying to elucidate the performance of brain circuits of interest in animal models of brain diseases. Several combinations of retrograde tracing with either single- and double-ISH are presented here, together with some criteria that influence the selection of the tracer to be used in conjunction with the strong demands of the ISH.

GYRKPPFNGSIFamide (Gly-SIFamide) modulates aggression in the freshwater prawn Macrobrachium rosenbergii

The freshwater prawn Macrobrachium rosenbergii is a tropical crustacean with characteristics similar to those of lobsters and crayfish. Adult males develop through three morphological types-small (SC), yellow (YC), and blue claws (BC)-with each representing a level in the dominance hierarchy of a group, BC males being the most dominant. We are interested in understanding the role played by neuropeptides in the mechanisms underlying aggressive behavior and the establishment of dominance hierarchies in this type of prawn. SIFamides are a family of arthropod peptides recently identified in the central nervous system of insects and crustaceans, where it has been linked to olfaction, sexual behavior, and gut endocrine functions. One of the six SIFamide isoforms, GYRKPPFNGSIFamide (Gly-SIFamide), is highly conserved among decapod crustaceans such as crabs and crayfish. We wanted to determine whether Gly-SIFamide plays a role in modulating aggression and dominant behavior in the prawn. To do this, we performed behavioral experiments in which interactions between BC/YC pairs were recorded and quantified before and after injecting Gly-SIFamide directly into the circulating hemolymph of the living animal. Behavioral data showed that aggression among interacting BC/YC prawns was enhanced by injection of Gly-SIFamide, suggesting that this neuropeptide does have a modulatory role for this type of behavior in the prawn.

Inhibitory effect of molt-inhibiting hormone on phantom expression in the Y-organ of the kuruma prawn, Marsupenaeus japonicus

Molting in crustaceans is induced by ecdysteroids as in insects. The ecdysteroid titre in hemolymph is negatively regulated by molt-inhibiting hormone (MIH) that inhibits the secretion of ecdysteroids from the Y-organ, an ecdysteroid-producing gland of crustaceans, whereas little is known about the molecular mechanism of inhibition by MIH. Recently, the Halloween genes encoding cytochrome P450 monooxygenases were characterized as the steroidogenic enzymes in insects. To elucidate whether the ecdysteroidogenesis in the Y-organ is regulated by molt-inhibiting hormone (MIH), we analyzed the expression level of an orthologue of a member of the Halloween genes, phantom (Cyp306a1, phm), in the Y-organ of a decapod crustacean, Marsupenaeus japonicus. A cDNA encoding phm (Mj-phm) was cloned by degenerate PCR and 5'- and 3'-RACEs. The deduced amino acid sequence of Mj-phm showed about 40% identity to those of insect phm. The six motif sequences and the four substrate recognition sites were well conserved between Mj-PHM and other PHM. RT-PCR showed the specific expression of Mj-phm mRNA in the Y-organ. In addition, quantitative real-time PCR verified that the expression level of Mj-phm was significantly increased at the pre-molt stage and decreased after ecdysis. Furthermore, exposure of the Y-organ to MIH significantly decreased the Mj-phm expression level in vitro. These results indicate that the transcription of Mj-phm in the Y-organ may be regulated by the inhibitory mechanism of MIH of M. japonicus, which involves the consequent negative regulation of ecdysteroidogenesis at the transcriptional level.

Identification of SYWKQCAFNAVSCFamide: a broadly conserved crustacean C-type allatostatin-like peptide with both neuromodulatory and cardioactive properties

The allatostatins comprise three structurally distinct peptide families that regulate juvenile hormone production by the insect corpora allata. A-type family members contain the C-terminal motif -YXFGLamide and have been found in species from numerous arthropod taxa. Members of the B-type family exhibit a -WX(6)Wamide C-terminus and, like the A-type peptides, appear to be broadly conserved within the Arthropoda. By contrast, members of the C-type family, typified by the unblocked C-terminus -PISCF, a pyroglutamine blocked N-terminus, and a disulfide bridge between two internal Cys residues, have only been found in holometabolous insects, i.e. lepidopterans and dipterans. Here, using transcriptomics, we have identified SYWKQCAFNAVSCFamide (disulfide bridging predicted between the two Cys residues), a known honeybee and water flea C-type-like peptide, from the American lobster Homarus americanus (infraorder Astacidea). Using matrix assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), a mass corresponding to that of SYWKQCAFNAVSCFamide was detected in the H. americanus brain, supporting the existence of this peptide and its theorized structure. Furthermore, SYWKQCAFNAVSCFamide was detected by MALDI-FTMS in neural tissues from five additional astacideans as well as 19 members of four other decapod infraorders (i.e. Achelata, Anomura, Brachyura and Thalassinidea), suggesting that it is a broadly conserved decapod peptide. In H. americanus, SYWKQCAFNAVSCFamide is capable of modulating the output of both the pyloric circuit of the stomatogastric nervous system and the heart. This is the first demonstration of bioactivity for this peptide in any species.

SIFamide illustrates the rapid evolution in Arthropod neuropeptide research

This review is focussed on SIFamide. This neuropeptide was discovered as a result of an extensive purification process, typical for 20th century physiology, of an extract of 350,000 flesh flies. Our knowledge of SIFamide greatly expanded since the first publication in 1996. Describing the minor and major findings on this peptide is our lead to summarise a number of innovations that recently became common in research on Arthropods. Mass spectrometry, nanoLC, whole mount immunocytochemistry, genome sequencing, deorphanizing receptors and functional gene knock downs are aspects that dramatically improved and changed peptide research. Some of the techniques mentioned in this review were of course applied before 1996, but they were not widespread. Although the focus of the review is on insects we incorporated the data of SIFamide in Crustaceans as well. SIFamide illustrates that crustaceans and insects might have more in common than was previously anticipated. Today, six isoforms of SIFamide are discovered in many crustaceans, several insects and a tick. The sequence of SIFamide is extremely conserved among these species. Deorphanizing its receptor in Drosophila, learned that both the ligand and receptor are impressively conserved, pointing at a crucial function. Immunohistochemistry and mass spectrometry data reveal that SIFamide is present in the crustacean brain and gut, but restricted to four neurons in the insect pars intercerebralis. The immunoreactive patterns in the brain refer to a neuromodulatory role in combining visual, tactile and olfactory input. Eventually, targeted cell ablation and RNAi revealed that SIFamide modulates sexual behaviour in fruit flies.