Orcokinins in insects and other invertebrates

Orcokinin neuropeptides regulate reproduction in the fruit fly, Drosophila melanogaster

In animals, neuropeptidergic signaling is essential for the regulation of survival and reproduction. In insects, Orcokinins are poorly studied, despite their high level of conservation among different orders. In particular, there are currently no reports on the role of Orcokinins in the experimental insect model, the fruit fly, Drosophila melanogaster. In the present work, we made use of the genetic tools available in this species to investigate the role of Orcokinins in the regulation of different innate behaviors including ecdysis, sleep, locomotor activity, oviposition, and courtship. We found that RNAi-mediated knockdown of the orcokinin gene caused a disinhibition of male courtship behavior, including the occurrence of male to male courtship, which is rarely seen in wildtype flies. In addition, orcokinin gene silencing caused a reduction in egg production. Orcokinin is emerging as an important neuropeptide family in the regulation of the physiology of insects from different orders. In the case of the fruit fly, our results suggest an important role in reproductive success.

Mass spectrometry-based top-down and bottom-up approaches for proteomic analysis of the Moroccan Buthus occitanus scorpion venom

Buthus occitanus (B. occitanus) is one of the most dangerous scorpions in the world. Despite the involvement of B. occitanus scorpion in severe cases of envenomation in Morocco, no study has focused yet on the proteomic composition of the Moroccan B. occitanus scorpion venom. Mass spectrometry‐based proteomic techniques are commonly used in the study of scorpion venoms. The implementation of top‐down and bottom‐up approaches for proteomic analyses facilitates screening by allowing a global view of the structural aspects of such complex matrices. Here, we provide a partial overview of the venom of B. occitanus scorpion, in order to explore the diversity of its toxins and hereafter understand their effects. To this end, a combination of top‐down and bottom‐up approaches was applied using nano‐high liquid chromatography coupled to nano‐electrospray tandem mass spectrometry (nano‐LC‐ESI MS/MS). The LC‐MS results showed that B. occitanus venom contains around 200 molecular masses ranging from 1868 to 16 720 Da, the most representative of which are those between 5000 and 8000 Da. Interestingly, combined top‐down and bottom‐up LC‐MS/MS results allowed the identification of several toxins, which were mainly those acting on ion channels, including those targeting sodium (NaScTxs), potassium (KScTxs), chloride (ClScTxs), and calcium channels (CaScTx), as well as antimicrobial peptides (AMPs), amphipathic peptides, myotropic neuropeptides, and hypothetical secreted proteins. This study reveals the molecular diversity of B. occitanus scorpion venom and identifies components that may have useful pharmacological activities.

A Review of Pedal Peptide/Orcokinin-type Neuropeptides

Neuropeptides are endogenous active substances that play important roles in a number of physiological processes and are ubiquitous in the nervous tissue in vivo. The gene encoding pedal peptide/orcokinin-type (PP/OK-type) neuropeptide is an important member of the neuropeptide gene family and is ubiquitous in invertebrates of Bilateria; orcokinin (OK) is mainly found in Arthropoda, while pedal peptide (PP) is mainly found in Mollusca. OK and PP are also present in other animals. PP/OK-type neuropeptides are a kind of multifunctional neuropeptides predominantly expressed in the nervous tissue and play important roles in the nerve regulation of movement. Moreover, OK has a number of other physiological functions. This review describes the distribution, expression, function and maturation of PP/OK-type neuropeptides to facilitate investigations of new functions and receptors of PP/OK-type neuropeptides, providing the theoretical foundation for the potential use of PP/OK-type neuropeptides in the prevention and control of agricultural and forestry pests, as an additive for skin care products and in the screening of drugs for the treatment of diabetes.

Evolutionary trends of neuropeptide signaling in beetles - A comparative analysis of Coleopteran transcriptomic and genomic data

Insects employ neuropeptides to regulate their growth & development, behaviour, metabolism and their internal milieu. At least 50 neuropeptides are known to date, with some ancestral to the insects and others more specific to particular taxa. In order to understand the evolution and essentiality of neuropeptides, we data mined publicly available high quality genomic or transcriptomic data for 31 species of the largest insect Order, the Coleoptera, chosen to represent the superfamilies' of the Adephaga and Polyphaga. The resulting neuropeptide distributions were compared against the habitats, lifestyle and other parameters. Around half of the neuropeptide families were represented across the Coleoptera, suggesting essentiality or at least continuing utility. However, the remaining families showed patterns of loss that did not correlate with any obvious life history parameter, suggesting that these neuropeptides are no longer required for the Coleopteran lifestyle. This may perhaps indicate a decreasing reliance on neuropeptide signaling in insects.

The silkworm (Bombyx mori) neuropeptide orcokinin is involved in the regulation of pigmentation

The natural colorful cuticles of insects play important roles in many physiological processes. Pigmentation is a physiological process with a complex regulatory network whose regulatory mechanism remains unclear. Bombyx mori pigmentation mutants are ideal materials for research on pigmentation mechanisms. The purple quail-like (q-l^p) and brown quail-like (q-l^b) mutants originated from plain silkworm breeds 932VR and 0223JH respectively exhibit similar cuticle pigmentation to that of the quail mutant. The q-l^p mutant also presents a developmental abnormality. In this study, genes controlling q-l^p and q-l^b mutants were located on chromosome 8 by positional cloning. Then the neuropeptide gene orcokinin (OK) was identified to be the major gene responsible for two quail-like mutants. The B. mori orcokinin gene (BommoOK) produces two transcripts, BommoOKA and BommoOKB, by alternative splicing. The CRISPR/Cas9 system and orcokinin peptides injection were used for further functional verification. We show a novel function of BommoOKA in inhibiting pigmentation, and one mature peptide of orcokinin A, OKA_type2, is the key factor in pigmentation inhibition. These results provide a reference for studying the function of orcokinin and are of theoretical importance for studying the regulatory mechanism of pigmentation.

Recent advances in neuropeptide signaling in Drosophila, from genes to physiology and behavior

This review focuses on neuropeptides and peptide hormones, the largest and most diverse class of neuroactive substances, known in Drosophila and other animals to play roles in almost all aspects of daily life, as w;1;ell as in developmental processes. We provide an update on novel neuropeptides and receptors identified in the last decade, and highlight progress in analysis of neuropeptide signaling in Drosophila. Especially exciting is the huge amount of work published on novel functions of neuropeptides and peptide hormones in Drosophila, largely due to the rapid developments of powerful genetic methods, imaging techniques and innovative assays. We critically discuss the roles of peptides in olfaction, taste, foraging, feeding, clock function/sleep, aggression, mating/reproduction, learning and other behaviors, as well as in regulation of development, growth, metabolic and water homeostasis, stress responses, fecundity, and lifespan. We furthermore provide novel information on neuropeptide distribution and organization of peptidergic systems, as well as the phylogenetic relations between Drosophila neuropeptides and those of other phyla, including mammals. As will be shown, neuropeptide signaling is phylogenetically ancient, and not only are the structures of the peptides, precursors and receptors conserved over evolution, but also many functions of neuropeptide signaling in physiology and behavior.

Malpighian tubules of caterpillars: blending RNAseq and physiology to reveal regional functional diversity and novel epithelial ion transport control mechanisms

Malpighian tubules (MTs) and hindgut constitute the functional kidney of insects. MTs are outpouches of the gut and in most insects demonstrate proximodistal heterogeneity in function. In most insects, such heterogeneity is confined to ion/fluid secretion in the distal portion and ion/fluid reabsorption in the proximal portion. In contrast, MTs of larval Lepidoptera (caterpillars of butterflies and moths), are comprised of five regions that differ in their association with the gut, their structure, and ion/fluid transport function. Recent studies have shown that several regions can rapidly and reversibly switch between ion secretion and reabsorption. The current study employed RNAseq, pharmacology and electrophysiology to characterize four distinct regions of the MT in larval Trichoplusia ni. Luminal microelectrode measurements indicate changes in [K+], [Na+] and pH as fluid passes through different regions of the tubule. In addition, the regions examined differ in gene ontology enrichment, and demonstrate robust gradients in expression of ion transporters and endocrine ligand receptors. Lastly, the study provides evidence for direct involvement of voltage-gated and ligand-gated ion channels in epithelial ion transport of insect MTs.

Identification of evolutionarily conserved residues required for the bioactivity of a pedal peptide/orcokinin-type neuropeptide

Pedal peptides and orcokinins are structurally related neuropeptides that were first discovered in protostomian invertebrates - mollusks and arthropods, respectively. Recently, pedal peptide/ocokinin (PP/OK)-type neuropeptides were discovered in a deuterostomian phylum, the echinoderms, indicating that the evolutionary origin of this neuropeptide family can be traced back to the common ancestor of bilaterian animals. Sequences comparison of PP/OK-type neuropeptides reveals several conserved residues, including N- and C-terminally located hydrophobic residues that are important for the bioactivity of orcokinin. Here we report the first comprehensive analysis of the structure-activity relationships of a PP/OK-type neuropeptide - starfish myorelaxant peptide (SMP; FGKGGAYDPLSAGFTD) from the starfish Patiria pectinifera (Phylum Echinodermata). Comparison of the bioactivity of SMP with N-terminally and/or C-terminally truncated and alanine-substituted SMP analogs revealed a core peptide (GAYDPLSAGF; SMP(5-14)) that retains the muscle-relaxing activity of SMP, albeit with reduced potency and efficacy. Within this core peptide, alanine-substitution of several residues resulted in complete or partial loss of bioactivity, whilst loss or substitution of the N-terminal phenylalanine residue of SMP also caused a substantial reduction in bioactivity. Furthermore, analysis of the bioactivity of other SMP-like peptides derived from the same precursor as SMP revealed that none of these were more potent/effective than SMP as muscle relaxants. In conclusion, we have identified key residues required for the bioactivity of a PP/OK-type neuropeptide (SMP), including hydrophobic residues located in the N- and C-terminal regions that are conserved in PP/OK-type peptides from other phyla as well as core residues that are conserved in echinoderm PP/OK-type peptides.

A Multifaceted Mass Spectrometric Method to Probe Feeding Related Neuropeptide Changes in Callinectes sapidus and Carcinus maenas

Food intake is regulated by various neuromodulators, including numerous neuropeptides. However, it remains elusive at the molecular and cellular level as to how these important chemicals regulate internal processes and which regions of the neuronal organs are responsible for regulating the behavior. Here we report a comparative neuropeptidomic analysis of the brain and pericardial organ (PO) in response to feeding in two well-studied crustacean physiology model organisms, Callinectes sapidus and Carcinus maenas, using mass spectrometry (MS) techniques. A multifaceted MS-based approach has been developed to obtain complementary information on the expression changes of a large array of neuropeptides in the brain and PO. The method employs stable isotope labeling of brain and PO extracts for relative MS quantitation, capillary electrophoresis (CE)-MS for fractionation and high-specificity analysis, and mass spectrometric imaging (MSI) for in-situ molecular mapping of peptides. A number of neuropeptides, including RFamides, B-type allatostatins (AST-B), RYamides, and orcokinins exhibit significant changes in abundance after feeding in this investigation. Peptides from the AST-B family found in PO tissue were shown to have both altered expression and localization changes after feeding, indicating that they may be a class of vital neuropeptide regulators involved in feeding behavior. Graphical Abstract ᅟ.

Pedal peptide/orcokinin-type neuropeptide signaling in a deuterostome: The anatomy and pharmacology of starfish myorelaxant peptide in Asterias rubens

Pedal peptide (PP) and orcokinin (OK) are related neuropeptides that were discovered in protostomian invertebrates (mollusks, arthropods). However, analysis of genome/transcriptome sequence data has revealed that PP/OK‐type neuropeptides also occur in a deuterostomian phylum—the echinoderms. Furthermore, a PP/OK‐type neuropeptide (starfish myorelaxant peptide, SMP) was recently identified as a muscle relaxant in the starfish Patiria pectinifera. Here mass spectrometry was used to identify five neuropeptides (ArPPLN1a‐e) derived from the SMP precursor (PP‐like neuropeptide precursor 1; ArPPLNP1) in the starfish Asterias rubens. Analysis of the expression of ArPPLNP1 and neuropeptides derived from this precursor in A. rubens using mRNA in situ hybridization and immunohistochemistry revealed a widespread pattern of expression, with labeled cells and/or processes present in the radial nerve cords, circumoral nerve ring, digestive system (e.g., cardiac stomach) and body wall‐associated muscles (e.g., apical muscle) and appendages (e.g., tube feet and papulae). Furthermore, our data provide the first evidence that neuropeptides are present in the lateral motor nerves and in nerve processes innervating interossicular muscles. In vitro pharmacological tests with SMP (ArPPLN1b) revealed that it causes dose‐dependent relaxation of apical muscle, tube foot and cardiac stomach preparations from A. rubens. Collectively, these anatomical and pharmacological data indicate that neuropeptides derived from ArPPLNP1 act as inhibitory neuromuscular transmitters in starfish, which contrasts with the myoexcitatory actions of PP/OK‐type neuropeptides in protostomian invertebrates. Thus, the divergence of deuterostomes and protostomes may have been accompanied by an inhibitory–excitatory transition in the roles of PP/OK‐type neuropeptides as regulators of muscle activity.

Neuropeptide Evolution: Chelicerate Neurohormone and Neuropeptide Genes may reflect one or more whole genome duplications

Four genomes and two transcriptomes from six Chelicerate species were analyzed for the presence of neuropeptide and neurohormone precursors and their GPCRs. The genome from the spider Stegodyphus mimosarum yielded 87 neuropeptide precursors and 101 neuropeptide GPCRs. High neuropeptide transcripts were also found in the trancriptomes of three other spiders, Latrodectus hesperus, Parasteatoda tepidariorum and Acanthoscurria geniculata. For the scorpion Mesobuthus martensii the numbers are 79 and 74 respectively. The very small genome of the house dust mite, Dermatophagoides farinae, on the other hand contains a much smaller number of such genes. A few new putative Arthropod neuropeptide genes were discovered. Thus, both spiders and the scorpion have an achatin gene and in spiders there are two different genes encoding myosuppressin-like peptides while spiders also have two genes encoding novel LGamides. Another finding is the presence of trissin in spiders and scorpions, while neuropeptide genes that seem to be orthologs of Lottia LFRYamide and Platynereis CCRFamide were also found. Such genes were also found in various insect species, but seem to be lacking from the Holometabola. The Chelicerate neuropeptide and neuropeptide GPCR genes often have paralogs. As the large majority of these are probably not due to local gene duplications, is not impossible that they reflect the effects of one or more ancient whole genome duplications.

Neuropeptide evolution: Chelicerate neurohormone and neuropeptide genes may reflect one or more whole genome duplications

Four genomes and two transcriptomes from six Chelicerate species were analyzed for the presence of neuropeptide and neurohormone precursors and their GPCRs. The genome from the spider Stegodyphus mimosarum yielded 87 neuropeptide precursors and 120 neuropeptide GPCRs. Many neuropeptide transcripts were also found in the transcriptomes of three other spiders, Latrodectus hesperus, Parasteatoda tepidariorum and Acanthoscurria geniculata. For the scorpion Mesobuthus martensii the numbers are 79 and 93 respectively. The very small genome of the house dust mite, Dermatophagoides farinae, on the other hand contains a much smaller number of such genes. A few new putative Arthropod neuropeptide genes were discovered. Thus, both spiders and the scorpion have an achatin gene and in spiders there are two different genes encoding myosuppressin-like peptides while spiders also have two genes encoding novel LGamides. Another finding is the presence of trissin in spiders and scorpions, while neuropeptide genes that seem to be orthologs of Lottia LFRYamide and Platynereis CCRFamide were also found. Such genes were also found in various insect species, but seem to be lacking from the Holometabola. The Chelicerate neuropeptide and neuropeptide GPCR genes often have paralogs. As the large majority of these are probably not due to local gene duplications, is plausible that they reflect the effects of one or more ancient whole genome duplications.

Orcokinins contribute to the regulation of vitellogenin transcription in the cockroach Blattella germanica

Orcokinins (OKs) are neuropeptides that were first identified in crustacean through their myotropic activity. In insects, the OK gene gives rise to two mRNAs coding for two different families of conserved mature neuropeptides: OKA and OKB. Although OKs are conserved in many insect species, its physiological role in this animal class is not fully understood. Until now prothoracicotropic, regulatory of light entrainment to the circadian clock and "awakening" activities have been reported for these peptides in different insect species. Here we report the identification of OKA and OKB precursors in the cockroach Blattella germanica. OKA mRNA was detected in brain, whereas OKB mRNA was detected both in brain and midgut. In vivo silencing of OK precursors suggests the involvement of OK gene products in the regulation of vitellogenin expression in the fat body, an action that appears to be independent of juvenile hormone. This is the first time that a function of this kind has been reported for OKs.

Alternatively spliced orcokinin isoforms and their functions in Tribolium castaneum

Orcokinin and orcomyotropin were originally described as neuropeptides in crustaceans but have now been uncovered in many species of insects in which they are called orcokinin-A (OK-A) and orcokinin-B (OK-B), respectively. The two groups of mature peptides are products of alternatively spliced transcripts of the single copy gene orcokinin in insects. We investigated the expression patterns and the functions of OK-A and OK-B in the red flour beetle Tribolium castaneum. In situ hybridization and immunohistochemistry using isoform-specific probes and antibodies for each OK-A and OK-B suggests that both peptides are co-expressed in 5-7 pairs of brain cells and in the midgut enteroendocrine cells, which contrasts to expression patterns in other insects in which the two peptides are expressed in different cells. We developed a novel behavioral assay to assess the phenotypes of orcokinin RNA interference (RNAi) in T. castaneum. RNAi of ok-a and ok-b alone or in combination resulted in higher frequencies and longer durations of death feigning in response to mechanical stimulation in the adult assay. In the larval behavioral assays, we observed longer recovery times from knockout induced by water submergence in the insects treated with RNAi for ok-a and ok-b alone or in combination. We conclude that both OK-A and OK-B have "awakening" activities and are potentially involved in the control of circadian rhythms.

Molecular characterization and expression profiles of neuropeptide precursors in the migratory locust

Neuropeptides serve as the most important regulatory signals in insects. Many neuropeptides and their precursors have been identified in terms of the contig sequences of whole genome information of the migratory locust (Locusta migratoria), which exhibits a typical phenotypic plasticity in morphology, behavior and physiology. However, functions of these locust neuropeptides are largely unknown. In this study, we first revised the 23 reported neuropeptide precursor genes and identified almost all the neuropeptide precursors and corresponding products in L. migratoria. We further revealed the significant expansion profiles (such as AKH) and alternative splicing of neuropeptide genes (Lom-ITP, Lom-OK and Lom-NPF1). Transcriptomic analysis indicated that several neuropeptides, such as Lom-ACP and Lom-OK, displayed development-specific expression patterns. qRT-PCR data confirmed that most neuropeptide precursors were strongly expressed in the central nervous system. Fifteen neuropeptide genes displayed different expression levels between solitarious and gregarious locusts. These findings provide valuable clues to understand neuropeptide evolution and their functional roles in basic biology and phase transition in locusts.

Isoform-specific expression of the neuropeptide orcokinin in Drosophila melanogaster

Orcokinins are neuropeptides that have been identified in diverse arthropods. In some species, an orcokinin gene encodes two isoforms of mature orcokinin peptide through alternative mRNA splicing. The existence of two orcokinin isoforms was predicted in Drosophila melanogaster as well, but the expression pattern of both isoforms has not been characterized. Here, we use in situ hybridization, antibody staining, and enhancer fusion GAL4 transgenic flies to examine the expression patterns of the A and B forms of orcokinin, and provide evidence that they are expressed differentially in the central nervous system (CNS) and the intestinal enteroendocrine system. The orcokinin A isoform is mainly expressed in the CNS of both larvae and adults. The A form is expressed in 5 pairs of neurons in abdominal neuromeres 1-5 of the larval CNS. In the adult brain, the A form is expressed in one pair of neurons in the posteriorlateral protocerebrum, and an additional four pairs of neurons located near the basement of the accessory medulla. Orcokinin A expression is also observed in two pairs of neurons in the ventral nerve cord (VNC). The orcokinin B form is mainly expressed in intestinal enteroendocrine cells in the larva and adult, with additional expression in one unpaired neuron in the adult abdominal ganglion. Together, our results provide elucidation of the existence and differential expression of the two orcokinin isoforms in the Drosophila brain and gut, setting the stage for future functional studies of orcokinins utilizing the genetically amenable fly model.

Orcokinin-like immunoreactivity in central neurons innervating the salivary glands and hindgut of ixodid ticks

Orcokinins are conserved neuropeptides within the Arthropoda but their cellular distribution and functions in ticks are unknown. We use an antibody against the highly conserved N-terminal (NFDEIDR) of mature orcokinin peptides to examine their distribution in six ixodid species: Amblyomma variegatum, Dermacentor reticulatus, Hyalomma anatolicum, Ixodes scapularis, Ixodes ricinus and Rhipicephalus appendiculatus. Numerous immunoreactive neurons (~100) were detected in various regions of the synganglion (central nervous system) in all examined tick species. Immunoreactive projections of two prominent groups of efferent neurons in the post-oesophageal region were examined in detail: (1) neurons innervating the salivary glands; (2) neurons innervating the hindgut. Using matrix-assisted laser desorption/ionisation-time-of-flight (MALDI-TOF), we detected orcokinin peaks in extracts of the synganglia and hindguts but not in the salivary glands of I. scapularis females. Our data provide further evidence of the presence of orcokinin in ixodid ticks and establish a morphological basis for functional studies of identified peptidergic neuronal networks.

The contribution of the genomes of a termite and a locust to our understanding of insect neuropeptides and neurohormones

The genomes of the migratory locust Locusta migratoria and the termite Zootermopsis nevadensis were mined for the presence of genes encoding neuropeptides, neurohormones, and their G-protein coupled receptors (GPCRs). Both species have retained a larger number of neuropeptide and neuropeptide GPCRs than the better known holometabolous insect species, while other genes that in holometabolous species appear to have a single transcript produce two different precursors in the locust, the termite or both. Thus, the recently discovered CNMa neuropeptide gene has two transcripts predicted to produce two structurally different CNMa peptides in the termite, while the locust produces two different myosuppressin peptides in the same fashion. Both these species also have a calcitonin gene, which is different from the gene encoding the calcitonin-like insect diuretic hormone. This gene produces two types of calcitonins, calcitonins A and B. It is also present in Lepidoptera and Coleoptera and some Diptera, but absent from mosquitoes and Drosophila. However, in holometabolous insect species, only the B transcript is produced. Their putative receptors were also identified. In contrast, Locusta has a highly unusual gene that codes for a salivation stimulatory peptide. The Locusta genes for neuroparsin and vasopressin are particularly interesting. The neuroparsin gene produces five different transcripts, of which only one codes for the neurohormone identified from the corpora cardiaca. The other four transcripts code for neuroparsin-like proteins, which lack four amino acid residues, and that for that reason we called neoneuroparsins. The number of transcripts for the neoneuroparsins is about 200 times larger than the number of neuroparsin transcripts. The first exon and the putative promoter of the vasopressin genes, of which there are about seven copies in the genome, is very well-conserved, but the remainder of these genes is not. The relevance of these findings is discussed.

More Drosophila enteroendocrine peptides: Orcokinin B and the CCHamides 1 and 2

Antisera to orcokinin B, CCHamide 1, and CCHamide 2 recognize enteroendocrine cells in the midgut of the fruitfly Drosophila melanogaster and its larvae. Although the antisera to CCHamide 1 and 2 are mutually cross-reactive, polyclonal mouse antisera raised to the C-terminals of their respective precursors allowed the identification of the two different peptides. In both larva and adult, CCHamide 2 immunoreactive endocrine cells are large and abundant in the anterior midgut and are also present in the anterior part of the posterior midgut. The CCHamide 2 immunoreactive endocrine cells in the posterior midgut are also immunoreactive with antiserum to allatostatin C. CCHamide 1 immunoreactivity is localized in endocrine cells in different regions of the midgut; those in the caudal part of the posterior midgut are identical with the allatostatin A cells. In the larva, CCHamide 1 enteroendocrine cells are also present in the endocrine junction and in the anterior part of the posterior midgut. Like in other insect species, the Drosophila orcokinin gene produces two different transcripts, A and B. Antiserum to the predicted biologically active peptide from the B-transcript recognizes enteroendocrine cells in both larva and adult. These are the same cells as those expressing β-galactosidase in transgenic flies in which the promoter of the orcokinin gene drives expression of this enzyme. In the larva, a variable number of orcokinin-expressing enteroendocrine cells are found at the end of the middle midgut, while in the adult, those cells are most abundant in the middle midgut, while smaller numbers are present in the anterior midgut. In both larva and adult, these cells also express allatostatin C. We also made a specific polyclonal antiserum to the NPF precursor in order to determine more precisely the expression of this peptide in the midgut. Using this antiserum, we find expression in the midgut to be the same as described previously using transgenic flies, while in the adult, midgut expression appears to be concentrated in the middle midgut, thus suggesting that in the anterior midgut only minor quantities of NPF are produced.

Neuropeptides in insect mushroom bodies

Owing to their experimental amenability, insect nervous systems continue to be in the foreground of investigations into information processing in - ostensibly - simple neuronal networks. Among the cerebral neuropil regions that hold a particular fascination for neurobiologists are the paired mushroom bodies, which, despite their function in other behavioral contexts, are most renowned for their role in learning and memory. The quest to understand the processes that underlie these capacities has been furthered by research focusing on unraveling neuroanatomical connections of the mushroom bodies and identifying key players that characterize the molecular machinery of mushroom body neurons. However, on a cellular level, communication between intrinsic and extrinsic mushroom body neurons still remains elusive. The present account aims to provide an overview on the repertoire of neuropeptides expressed in and utilized by mushroom body neurons. Existing data for a number of insect representatives is compiled and some open gaps in the record are filled by presenting additional original data.

More than two decades of research on insect neuropeptide GPCRs: an overview

This review focuses on the state of the art on neuropeptide receptors in insects. Most of these receptors are G protein-coupled receptors (GPCRs) and are involved in the regulation of virtually all physiological processes during an insect's life. More than 20 years ago a milestone in invertebrate endocrinology was achieved with the characterization of the first insect neuropeptide receptor, i.e., the Drosophila tachykinin-like receptor. However, it took until the release of the Drosophila genome in 2000 that research on neuropeptide receptors boosted. In the last decade a plethora of genomic information of other insect species also became available, leading to a better insight in the functions and evolution of the neuropeptide signaling systems and their intracellular pathways. It became clear that some of these systems are conserved among all insect species, indicating that they fulfill crucial roles in their physiological processes. Meanwhile, other signaling systems seem to be lost in several insect orders or species, suggesting that their actions were superfluous in those insects, or that other neuropeptides have taken over their functions. It is striking that the deorphanization of neuropeptide GPCRs gets much attention, but the subsequent unraveling of the intracellular pathways they elicit, or their physiological functions are often hardly examined. Especially in insects besides Drosophila this information is scarce if not absent. And although great progress made in characterizing neuropeptide signaling systems, even in Drosophila several predicted neuropeptide receptors remain orphan, awaiting for their endogenous ligand to be determined. The present review gives a précis of the insect neuropeptide receptor research of the last two decades. But it has to be emphasized that the work done so far is only the tip of the iceberg and our comprehensive understanding of these important signaling systems will still increase substantially in the coming years.

Recent topics on the regulatory mechanism of ecdysteroidogenesis by the prothoracic glands in insects

Molting and metamorphosis are strictly regulated by steroid hormones known as ecdysteroids. It is now widely recognized that ecdysteroid biosynthesis (ecdysteroidogenesis) in the prothoracic gland (PG) is regulated by the tropic factor prothoracicotropic hormone (PTTH). However, the importance of PTTH in the induction of molting and metamorphosis remains unclear, and other mechanisms are thought to be involved in the regulation of ecdysteroidogenesis by the PG. Recently, new regulatory mechanisms, prothoracicostatic factors, and neural regulation have been explored using the silkworm, Bombyx mori, and two circulating prothoracicostatic factors, prothoracicostatic peptide (PTSP) and Bommo-myosuppressin (BMS), have been identified. Whereas PTTH and BMS are secreted from the brain, PTSP is secreted from the peripheral neurosecretory system - the epiproctodeal gland - during the molting stage. The molecular basis of neural regulation of ecdysteroidogenesis has been revealed for the first time in B. mori. The innervating neurons supply both Bommo-FMRF related peptide (BRFa) and orcokinin to maintain low levels of ecdysteroids during the feeding stage. These complex regulatory mechanisms - involving tropic and static factors, peripheral neurosecretory cells as well as the central neuroendocrine system, and neural regulation in addition to circulating factors collaborate to regulate ecdysteroidogenesis. Thus, together they create the finely tuned fluctuations in ecdysteroid titers needed in the hemolymph during insect development.

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.

Discovery and characterization of the Crustacean hyperglycemic hormone precursor related peptides (CPRP) and orcokinin neuropeptides in the sinus glands of the blue crab Callinectes sapidus using multiple tandem mass spectrometry techniques

The crustacean sinus gland (SG) is a well-defined neuroendocrine site that produces numerous hemolymph-borne agents including the most complex class of endocrine signaling molecules-neuropeptides. Via a multifaceted mass spectrometry (MS) approach, 70 neuropeptides were identified including orcokinins, orcomyotropin, crustacean hyperglycemic hormone (CHH) precursor-related peptides (CPRPs), red pigment concentrating hormone (RPCH), pigment dispersing hormone (PDH), proctolin, RFamides, RYamides, and HL/IGSL/IYRamide. Among them, 15 novel orcokinins, 9 novel CPRPs, 1 novel orcomyotropin, 1 novel Ork/Orcomyotropin-related peptide, and 1 novel PDH were de novo sequenced via collision induced dissociation (CID) from the SG of a model organism Callinectes sapidus. Electron transfer dissociation (ETD) was used for sequencing of intact CPRPs due to their large size and higher charge state. Capillary isoelectric focusing (CIEF) was employed for separation of members of the orcokinin family, which is one of the most abundant neuropeptide families observed in the SG. Collectively, our study represents the most complete characterization of neuropeptides in the SG and provides a foundation for future investigation of the physiological function of neuropeptides in the SG of C. sapidus.

Bombyx orcokinins are brain-gut peptides involved in the neuronal regulation of ecdysteroidogenesis

Biosynthesis of ecdysteroids, the insect steroid hormones controlling gene expression during molting and metamorphosis, takes place primarily in the prothoracic gland (PG). The activity of the PG is regulated by various neuropeptides. In the silkworm Bombyx mori, these neuropeptides utilize both hormonal and neuronal pathways to regulate the activity of the PG, making the insect an excellent model system to investigate the complex signaling network controlling ecdysteroid biosynthesis. Here we report another group of neuropeptides, orcokinins, as neuronal prothoracicotropic factors. Using direct mass spectrometric profiling of the axons associated with the PG, we detected several peptide peaks which correspond to orcokinin gene products in addition to the previously described Bommo-FMRFamides (BRFas). In situ hybridization and immunohistochemistry revealed that orcokinins are produced in the prominent neurosecretory cells in the ventral ganglia, as well as in numerous small neurons throughout the central nervous system and in midgut endocrine cells. One of the two pairs of BRFa-expressing neurosecretory cells in the prothoracic ganglion coexpresses orcokinin, and these neurons project axons through the transverse nerve and terminate on the surface of the PG. Using an in vitro PG bioassay, we show that orcokinins have a clear prothoracicotropic activity and are able to cancel the static effect of BRFas on ecdysteroid biosynthesis, whereas the suppressive effect of BRFas on cAMP production remained unchanged in the presence of orcokinins. The discovery of a second regulator of PG activity in these neurons further illustrates the potential importance of the PG innervation in the regulation of insect development.

Toward a consensus nomenclature for insect neuropeptides and peptide hormones

The nomenclature currently in use for insect neuropeptide and peptide hormone families is reviewed and suggestions are made as to how it can be rationalized. Based upon this review, a number of conventions are advanced as a guide to a more rationale nomenclature. The scheme that is put forward builds upon the binomial nomenclature scheme proposed by Raina and Gäde in 1988, when just over 20 insect neuropeptides had been identified. Known neuropeptides and peptide hormones are assigned to 32 structurally distinct families, frequently with overlapping functions. The names given to these families are those that are currently in use, and describe a biological function, homology to known invertebrate/vertebrate peptides, or a conserved structural motif. Interspecific isoforms are identified using a five-letter code to indicate genus and species names, and intraspecific isoforms are identified by Roman or Arabic numerals, with the latter used to signify the order in which sequences are encoded on a prepropeptide. The proposed scheme is sufficiently flexible to allow the incorporation of novel peptides, and could be extended to other arthropods and non-arthropod invertebrates.

Neuropeptide precursor gene discovery in the Chagas disease vector Rhodnius prolixus

We show a straightforward workflow combining homology search in Rhodnius prolixus genome sequence with cloning by rapid amplification of cDNA ends and mass spectrometry. We have identified 32 genes and their transcripts that encode a number of neuropeptide precursors leading to 194 putative peptides. We validated by mass spectrometry 82 of those predicted neuropeptides in the brain of R. prolixus to achieve the first comprehensive genomic, transcriptomic and neuropeptidomic analysis of an insect disease vector. Comparisons of available insect neuropeptide sequences revealed that the R. prolixus genome contains most of the conserved neuropeptides in insects, many of them displaying specific features at the sequence level. Some gene families reported here are identified for the first time in the order Hemiptera, a highly biodiverse group of insects that includes many human, animal and plant disease agents.

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.

Circadian pacemaker coupling by multi-peptidergic neurons in the cockroach Leucophaea maderae

Lesion and transplantation studies in the cockroach, Leucophaea maderae, have located its bilaterally symmetric circadian pacemakers necessary for driving circadian locomotor activity rhythms to the accessory medulla of the optic lobes. The accessory medulla comprises a network of peptidergic neurons, including pigment-dispersing factor (PDF)-expressing presumptive circadian pacemaker cells. At least three of the PDF-expressing neurons directly connect the two accessory medullae, apparently as a circadian coupling pathway. Here, the PDF-expressing circadian coupling pathways were examined for peptide colocalization by tracer experiments and double-label immunohistochemistry with antisera against PDF, FMRFamide, and Asn¹³-orcokinin. A fourth group of contralaterally projecting medulla neurons was identified, additional to the three known groups. Group one of the contralaterally projecting medulla neurons contained up to four PDF-expressing cells. Of these, three medium-sized PDF-immunoreactive neurons coexpressed FMRFamide and Asn¹³-orcokinin immunoreactivity. However, the contralaterally projecting largest PDF neuron showed no further peptide colocalization, as was also the case for the other large PDF-expressing medulla cells, allowing the easy identification of this cell group. Although two-thirds of all PDF-expressing medulla neurons coexpressed FMRFamide and orcokinin immunoreactivity in their somata, colocalization of PDF and FMRFamide immunoreactivity was observed in only a few termination sites. Colocalization of PDF and orcokinin immunoreactivity was never observed in any of the terminals or optic commissures. We suggest that circadian pacemaker cells employ axonal peptide sorting to phase-control physiological processes at specific times of the day.

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.

N,N-dimethyl leucines as novel isobaric tandem mass tags for quantitative proteomics and peptidomics

Herein, we describe the development and application of a set of novel N,N-dimethyl leucine (DiLeu) 4-plex isobaric tandem mass (MS(2)) tagging reagents with high quantitation efficacy and greatly reduced cost for neuropeptide and protein analysis. DiLeu reagents serve as attractive alternatives for isobaric tags for relative and absolute quantitation (iTRAQ) and tandem mass tags (TMTs) due to their synthetic simplicity, labeling efficiency, and improved fragmentation efficiency. DiLeu reagent resembles the general structure of a tandem mass tag in that it contains an amine reactive group (triazine ester) targeting the N-terminus and epsilon-amino group of the lysine side chain of a peptide, a balance group, and a reporter group. A mass shift of 145.1 Da is observed for each incorporated label. Intense a(1) reporter ions at m/z 115.1, 116.1, 117.1, and 118.1 are observed for all pooled samples upon MS(2). All labeling reagents are readily synthesized from commercially available chemicals with greatly reduced cost. Labels 117 and 118 can be synthesized in one step and labels 115 and 116 can be synthesized in two steps. Both DiLeu and iTRAQ reagents show comparable protein sequence coverage (approximately 43%) and quantitation accuracy (<15%) for tryptically digested protein samples. Furthermore, enhanced fragmentation of DiLeu labeling reagents offers greater confidence in protein identification and neuropeptide sequencing from complex neuroendocrine tissue extracts from a marine model organism, Callinectes sapidus.

Molecular, mass spectral, and physiological analyses of orcokinins and orcokinin precursor-related peptides in the lobster Homarus americanus and the crayfish Procambarus clarkii

Recently, cDNAs encoding prepro-orcokinins were cloned from the crayfish Procambarus clarkii; these cDNAs encode multiple copies of four orcokinin isoforms as well as several other peptides. Using the translated open reading frames of the P. clarkii transcripts as queries, five ESTs encoding American lobster Homarus americanus orthologs were identified via BLAST analysis. From these clones, three cDNAs, each encoding one of two distinct prepro-hormones, were characterized. Predicted processing of the deduced prepro-hormones would generate 13 peptides, 12 of which are conserved between the 2 precursors: the orcokinins NFDEIDRSGFGFN (3 copies), NFDEIDRSGFGFH (2 copies) and NFDEIDRSGFGFV (2 copies), FDAFTTGFGHN (an orcomyotropin-related peptide), SSEDMDRLGFGFN, GDY((SO3))DVYPE, VYGPRDIANLY and SAE. Additionally, one of two longer peptides (GPIKVRFLSAIFIPIAAPARSSPQQDAAAGYTDGAPV or APARSSPQQDAAAGYTDGAPV) is predicted from each prepro-hormone. MALDI-FTMS analyses confirmed the presence of all predicted orcokinins, the orcomyotropin-related peptide, and three precursor-related peptides, SSEDMDRLGFGFN, GDYDVYPE (unsulfated) and VYGPRDIANLY, in H. americanus neural tissues. SAE and the longer, unshared peptides were not detected. Similar complements of peptides are predicted from P. clarkii transcripts; the majority of these were detected in its neural tissues with mass spectrometry. Truncated orcokinins not predicted from any precursor were also detected in both species. Consistent with previous studies in the crayfish Orconectes limosus, NFDEIDRSGFGFN increased mid-/hindgut motility in P. clarkii. Surprisingly, the same peptide, although native to H. americanus, did not affect gut motility in this species. Together, our results provide the framework for future investigations of the regulation and physiological function of orcokinins/orcokinin precursor-related peptides in astacideans.

In silico analyses of peptide paracrines/hormones in Aphidoidea

The Aphidoidea is an insect superfamily comprising most of the known aphid species. While small in size, these animals are of considerable economic importance as many members of this taxon are serious agricultural pests, inflicting physical damage upon crop plants and serving as vectors in the transmission of viral plant diseases. In terms of identifying the paracrines/hormones used to modulate behavior, particularly peptides, members of the Aphidoidea have largely been ignored, as it is not tractable to isolate the large pools of tissue needed for standard biochemical investigations. Here, a bioinformatics approach to peptide discovery has been used to overcome this limitation of scale. Specifically, in silico searches of publicly accessible aphidoidean ESTs were conducted to identify transcripts encoding putative peptides precursors, with the mature peptides contained within them deduced using peptide processing software and homology to known arthropod sequences. In total, 39 ESTs encoding putative peptides precursors were identified from four aphid species: Acyrthosiphon pisum (14 ESTs), Aphis gossypii (four ESTs), Myzus persicae (20 ESTs) and Toxoptera citricida (one EST). These precursors included ones predicted to encode isoforms of B-type allatostatin, crustacean cardioactive peptide, FMRFamide-related peptide (both myosuppressin and short neuropeptide F subfamilies), insect kinin, orcokinin, proctolin, pyrokinin/periviscerokinin/pheromone biosynthesis activating neuropeptide, SIFamide and tachykinin-related peptide. In total, 83 peptides were characterized from the identified precursors, most novel, including two B-type allatostatins possessing the variant -WX(7)Wamide motif, two N-terminally extended proctolin isoforms and an N-terminally truncated and substituted SIFamide. Collectively, these results expand greatly the number of known/predicted aphid peptide paracrines/hormones, and provide a strong foundation for future molecular and physiological investigations of peptidergic control in this insect group.

Neuropeptide discovery in Ixodoidea: an in silico investigation using publicly accessible expressed sequence tags

The Ixodoidea (ticks) are important vectors in the transmission of many human diseases; for example, the blacklegged tick Ixodes scapularis is the major vector in the transmission of Lyme disease, the most frequently reported vector-borne illness in the United States. The development of expressed sequence tags (ESTs) for ixodoidean cDNA libraries, and their public deposition, has generated a rich resource for protein discovery in members of this taxon, thereby providing an opportunity for better understanding the physiology and behavior of these disease vectors. Here, in silico searches of publicly accessible ESTs were conducted to identify transcripts encoding putative ixodoidean neuropeptide precursors, with the mature peptides contained within them predicted using online peptide processing programs and homology to known arthropod sequences. In total, 37 putative neuropeptide-encoding ESTs were identified from three ixodoidean species: I. scapularis (29 ESTs), Rhipicephalus microplus (seven ESTs) and Amblyomma americanum (one EST). Among those identified from I. scapularis were ones predicted to encode isoforms of corazonin, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone (both calcitonin- and corticotropin-releasing factor-like), FMRFamide-related peptide (both short neuropeptide F and sulfakinin subfamilies) orcokinin, proctolin, pyrokinin/periviscerokinin/pheromone biosynthesis activating neuropeptide, SIFamide, and tachykinin-related peptide. Collectively, 80 distinct ixodoidean neuropeptides were characterized from the identified precursors. These results not only expand greatly the number of known/predicted ixodoidean neuropeptides, but also provide a strong foundation for future molecular and physiological investigations of peptidergic control in this important group of disease-transmitting arthropods.

Methyl esterification assisted MALDI FTMS characterization of the orcokinin neuropeptide family

Methyl esterification of a peptide converts carboxylic acids, such as those present on the side chains of aspartic (D) and glutamic acid (E) as well as the free carboxyl terminus, to their corresponding methyl esters. This method has been applied to peptide and protein quantitation, de novo sequencing, and reduction of nonspecific binding in immobilized metal affinity chromatography for enrichment of phosphorylated peptides. In this study, we investigate the application of this derivatization reaction to the identification and characterization of the orcokinin neuropeptide family by screening and localizing the acidic side chains in peptides. The methyl esterification reaction drastically improves the fragmentation efficiency of modified orcokinins due to blockage of the aspartate selective cleavage pathway of the native orcokinin peptides. With the improved sustained off-resonance irradiation-collisional-induced dissociation spectra, the number and the locations of D and E residues are easily deduced. In addition, a side reaction that occurs at the carboxamide group of asparagine (N) is studied. The deamidation followed by subsequent methyl esterification reaction mechanism is proposed based on the study of an isotope-labeled standard N*FDEIDR. Reaction kinetics is studied by elevating the temperature from room temperature to 37 degrees C. The deamidation-methyl esterification products are greatly enhanced with elevated reaction temperature. Furthermore, we also explore the utility of this side reaction for rapid screening and characterization of C-terminally amidated neuropeptides. This derivatization reaction is applied to both in situ direct tissue neuropeptide analysis and the analysis of HPLC fractions from the separation of complex neuronal tissue extracts. Overall, this study reports a simple and effective method for profiling and localizing acidic amino acid residues (D/E), amide-containing residues (N/Q), and the C-terminal amide group in a peptide.

Evidence for a role of orcokinin-related peptides in the circadian clock controlling locomotor activity of the cockroach Leucophaea maderae

The accessory medulla (AMe), a small neuropil in the optic lobe, houses the master circadian clock in the brain of the cockroach Leucophaea maderae and controls circadian rhythms in locomotor activity. Recently, members of the orcokinin family of crustacean neuropeptides were identified in a cockroach and a locust and were shown by immunocytochemistry to be prominently present in the AMe. In the cockroach L. maderae, about 30 neurons in five of six established cell groups of the AMe showed orcokinin immunostaining. By means of tracer injections into one AMe and immunostaining with anti-orcokinin antiserum, we show here that one orcokinin-immunoreactive ventral neuron and three ventromedian neurons directly connect both AMae. To determine a possible circadian function of orcokinin in the cockroach, we injected 150 fmol Asn(13)-orcokinin into the vicinity of the AMe at different circadian times. These experiments resulted in stable phase-dependent phase shifts of circadian locomotor activity of the cockroach. The shape of the resulting phase-response curve closely matched the phase-shifting effects of light pulses, and its amplitude was dependent on the amount of the injected peptide. Together with the anatomical data, the results suggest that orcokinin-related peptides play an important role in light entrainment pathways to the circadian clock via the contralateral compound eye. This study, furthermore, provides the first evidence for a physiological role of an orcokinin-related peptide in insects.

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

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

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

The olfactory system plays important roles in various crustacean behaviors. Despite numerous studies on different aspects of the olfactory neural pathway, only the decapod-tachykinin-related peptide (decapod-TRP) has been identified as a neuromodulator in this processing to date. To establish the functions of other related neuropeptides, we initially performed cDNA cloning of FMRFamide-related peptide (FaRP) and allatostatin (AST)-like peptide from the crayfish Procambarus clarkii, followed by in situ hybridization (ISH) analysis of these peptides, along with decapod-TRP, orcokinin, and crustacean-SIFamide. Cloned FaRP cDNA encodes seven copies of C-terminal RN(F/Y)LRFamide-containing peptide, whereas AST-like peptide cDNA comprises 29 copies of AST-like peptide (-YXFGLamide) and three additional putative peptides. ISH analysis of the brain revealed specific expression of crustacean-SIFamide mRNA in most projection neurons (cell cluster 10), and predominant localization of other mRNAs to interneurons. The data suggest that the crustacean-SIFamide neuropeptide is involved in output of the deutocerebrum to the protocerebrum. Double-fluorescence ISH data further disclose that, in cluster 9, orcokinin is coexpressed in decapod-TRP-specific interneurons, whereas AST-like peptide-containing cells do not overlap with orcokinin-expressing cells. On the other hand, FaRP-expressing cells overlap with both orcokinin- and AST-like peptide-specific cells. In cluster 11, where signals for AST-like peptide are absent, a number of interneurons express both decapod-TRP and orcokinin, emphasizing a close relationship between these two factors with regard to olfactory processing, and possibly tactile and/or visual sensory systems. These characteristic expression patterns of neuropeptides support their distinct involvement in the modulation of olfactory processing.

Orcokinin immunoreactivity in the accessory medulla of the cockroach Leucophaea maderae

The accessory medulla is the master circadian clock in the brain of the cockroach Leucophaea maderae and controls circadian locomotor activity. Previous studies have demonstrated that a variety of neuropeptides are prominent neuromediators in this brain area. Recently, members of the orcokinin family of crustacean neuropeptides have been identified in several insect species and shown to be widely distributed in the brain, including the accessory medulla. To investigate the possible involvement of orcokinins in circadian clock function, we have analyzed the distribution of orcokinin immunostaining in the accessory medulla of L. maderae in detail. The accessory medulla is densely innervated by approximately 30 orcokinin-immunoreactive neurons with cell bodies distributed in five of six established cell groups in the accessory medulla. Immunostaining is particularly prominent in three ventromedian neurons. These neurons have processes in a median layer of the medulla and in the internodular neuropil of the accessory medulla and send axonal fibers via the posterior optic commissure to their contralateral counterparts. Double-labeling experiments have revealed the colocalization of orcokinin immunostaining with immunoreactivity for pigment-dispersing hormone, FMRFamide, Mas-allatotropin, and gamma-aminobutyric acid in two cell groups of the accessory medulla, but not in the ventromedian neurons or in the anterior and posterior optic commissure. Immunostaining in the ventromedian neurons suggests that orcokinin-related peptides play a role in the heterolateral transmission of photic input to the pacemaker and/or in the coupling of the bilateral pacemakers of the cockroach.

In Silico Identification of New Secretory Peptide Genes in Drosophila melanogaster

Bioactive peptides play critical roles in regulating most biological processes in animals. The elucidation of the amino acid sequence of these regulatory peptides is crucial for our understanding of animal physiology. Most of the (neuro)peptides currently known were identified by purification and subsequent amino acid sequencing. With the entire genome sequence of some animals now available, it has become possible to predict novel putative peptides. In this way, BLAST (Basic Local Alignment Searching Tool) analysis of the Drosophila melanogaster genome has allowed annotation of 36 secretory peptide genes so far. Peptide precursor genes are, however, poorly predicted by this algorithm, thus prompting an alternative approach described here. With the described searching program we scanned the Drosophila genome for predicted proteins with the structural hallmarks of neuropeptide precursors. As a result, 76 additional putative secretory peptide genes were predicted in addition to the 43 annotated ones. These putative (neuro)peptide genes contain conserved motifs reminiscent of known neuropeptides from other animal species. Peptides that display sequence similarities to the mammalian vasopressin, atrial natriuretic peptide, and prolactin precursors and the invertebrate peptides orcokinin, prothoracicotropic hormones, trypsin modulating oostatic factor, and Drosophila immune induced peptides (DIMs) among others were discovered. Our data hence provide further evidence that many neuropeptide genes were already present in the ancestor of Protostomia and Deuterostomia prior to their divergence. This bioinformatic study opens perspectives for the genome-wide analysis of peptide genes in other eukaryotic model organisms.

Novel insect orcokinins: characterization and neuronal distribution in the brains of selected dicondylian insects

Orcokinins are a family of myotropic neuropeptides identified in various decapod crustaceans and recently in a cockroach. Their presence in the crustacean nervous system and hemolymph suggests that they act as hormones and as locally acting neuromodulators. To provide further evidence for the existence of orcokinins in insects, we identified a novel orcokinin-related peptide in the locust Schistocerca gregaria and used an antiserum against Asn13-orcokinin for immunostaining in the brains of selected dicondylian insects, including a silverfish, three polyneopteran species (a cockroach and two locusts), and three endopterygote species (a moth, a bee, and a fly). As analyzed by MALDI-TOF spectrometry and nanoelectrospray Q-TOF, the locust orcokinin is a novel tetradecapeptide with striking sequence similarity to crustacean orcokinins. Orcokinin immunostaining was widespread and occurred in similar patterns in the brain of the silverfish and the polyneopteran species. Prominent immunostaining was detected in the optic lobe, especially in the medulla and in the accessory medulla, in local interneurons of the antennal lobe, and in extrinsic and intrinsic mushroom-body neurons. All parts of the central complex and many other areas of the brains were densely stained. In the silverfish, the cockroach, and the locusts, processes in the corpora cardiaca showed orcokinin immunoreactivity, suggesting that orcokinins also serve a hormonal role. In contrast to the case in polyneopteran species, immunostaining was completely lacking in the brains of the honeybee, fruitfly, and sphinx moth. This indicates that orcokinins either are modified considerably or may be completely absent in the brains of endopterygote insects.

Identification of neuropeptides from the decapod crustacean sinus glands using nanoscale liquid chromatography tandem mass spectrometry

Neurosecretory systems are known to synthesize and secrete a diverse class of peptide hormones which regulate many physiological processes. The crustacean sinus gland (SG) is a well-defined neuroendocrine site that produces numerous hemolymph-borne agents including the most complex class of endocrine signaling molecules--neuropeptides. As an ongoing effort to define the peptidome of the crustacean SG, we determine the neuropeptide complements of the SG of the Jonah crab, Cancer borealis, and the Maine lobster, Homarus americanus, using nanoflow liquid chromatography electrospray ionization quadrupole time-of-flight (ESI-QTOF) MS/MS. Numerous neuropeptides were identified, including orcokinins, orcomyotropin, crustacean hyperglycemic hormone (CHH), CHH precursor-related peptides (CPRPs), red pigment concentrating hormone (RPCH), beta-pigment dispersing hormone (beta-PDH), proctolin and HL/IGSL/IYRamide. Among them, two novel orcokinins were de novo sequenced from the SG of H. americanus. Three CPRPs including a novel isoform were sequenced in H. americanus. Four new CPRPs were sequenced from the SG of C. borealis. Our results show that structural polymorphisms in CPRPs (and thus the CHH precursors) are common in Dendrobranchiata as well as in Pleocyemata. The evolutionary relationship between the CPRPs is also discussed.

Matrix-Assisted Laser Desorption/Ionization Fourier Transform Mass Spectrometry for the Identification of Orcokinin Neuropeptides in Crustaceans Using Metastable Decay and Sustained Off-Resonance Irradiation

Vacuum UV matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been applied to the direct analysis of crustacean neuronal tissues using in-cell accumulation techniques to improve sensitivity. In an extension of previous work by Li and co-workers (Kutz, K. K.; Schmidt, J. J.; Li, L. Anal. Chem. 2004, 76, 5630-5640), and with a focus on the Maine lobster, Homarus americanus, we report that many peaks appearing in direct tissue spectra from crustaceans result from the metastable decay of aspartate-containing neuropeptides with localized protonation sites. We report on mass spectral characteristics of crustacean neuropeptides under MALDI-FTMS conditions and show how fragments formed by Asp-Xxx cleavages can be used to advantage for the identification of orcokinin peptides, a ubiquitous family of crustacean neuropeptides with a highly conserved N-terminus sequence. We show that predicted fragment ion fingerprints (FIFs) can be used to screen internally calibrated direct tissue spectra to provide high-confidence identification of previously identified orcokinin peptides. We use FIFs, identified based upon characteristic neutral losses, to screen for new members of the orcokinin family. Sustained off-resonance irradiation of y-series fragment ions is used to sequence the variable C-terminus. We apply these techniques to the analysis of CoG tissues from Cancer borealis and Panulirus interruptus and show that orcokinins in P. interruptus were misidentified in a previous MALDI-TOF study.