Identification of multiple peptides homologous to cockroach and cricket allatostatins in the stick insect Carausius morosus

Functional Characterization of Allatostatin C (PISCF/AST) and Juvenile Hormone Acid O-Methyltransferase in Dendroctonus armandi

Allatostatin C (PISCF/AST) is a neuropeptide gene that affects juvenile hormone (JH) synthesis in the corpora allata. Juvenile hormone acid O-methyltransferase (JHAMT) is a key gene in the JH biosynthetic pathway. In this study, two genes encoding DaAST and DaJHAMT were cloned. Both DaAST and DaJHAMT were expressed in the larvae, pupae and adults of Chinese white pine beetle (Dendroctonus armandi), and highly expressed in the head and the gut. The expression of the two genes was induced by JH analog (JHA) methoprene and the functions of the two genes were then investigated by RNAi. Considering the role of hormones in metamorphosis, JHA significantly induced DaAST and DaJHAMT in the larval stage. DaAST knockdown in larvae, pupae and adults significantly increased the DaJHAMT mRNA levels. Moreover, knockdown of DaAST instead of DaJHAMT increased pupae mortality and the abnormal rate of emergence morphology and reduced emergence rates. However, knockdown of DaJHAMT instead of DaAST significantly reduced frontalin biosynthesis in adult males. The results showed that DaAST acts as an allatostatin and inhibits JH biosynthesis, and that JHAMT is a key regulatory enzyme for JH synthesis in the D. armandi.

Pharmacological Characterization of the Stick Insect Carausius morosus Allatostatin-C Receptor with Its Endogenous Agonist

G protein-coupled receptors (GPCRs) play a pivotal role in regulating key physiological events in all animal species. Recent advances in collective analysis of genes and proteins revealed numerous potential neuropeptides and GPCRs from insect species, allowing for the characterization of peptide-receptor pairs. In this work, we used fluorescence resonance energy transfer (FRET)-based genetically encoded biosensors in intact mammalian cells to study the pharmacological features of the cognate GPCR of the type-C allatostatin (AST-C) peptide from the stick insect, Carausius morosus. Analysis of multiple downstream pathways revealed that AST-C can activate the human Gi2 protein, and not Gs or Gq, through AST-C receptor (AlstRC). Activated AlstRC recruits β-arrestin2 independent of the Gi protein but stimulates ERK phosphorylation in a Gi protein-dependent manner. Identification of Gαi-, arrestin-, and GRK-like transcripts from C. morosus revealed high evolutionary conservation at the G protein level, while β-arrestins and GRKs displayed less conservation. In conclusion, our study provides experimental and homology-based evidence on the functionality of vertebrate G proteins and downstream signaling biosensors to characterize early signaling steps of an insect GPCR. These results may serve as a scaffold for developing assays to characterize pharmacological and structural aspects of other insect GPCRs and can be used in deorphanization and pesticide studies.

Structure-Activity Studies on the Hypertrehalosemic Hormone II of the Stick Insect Carausius morosus (Phasmatodea): Carbohydrate-Mobilization and Cardio-Stimulatory Activities

The corpora cardiaca of the Indian stick insect, Carausius morosus, synthesize two decapeptide neuropeptides of the adipokinetic hormone (AKH) family, both of which can increase the trehalose levels in the hemolymph when the stick insect is ligated between the head and the thorax. Here, we use two biological assays to assess the potencies of 19 AKH analogs in ligated C. morosus: the carbohydrate-mobilizing assay measures the change in the levels of circulating carbohydrates following injection of a substance, while the semi-exposed heart assay measures a change in heart beat rate after the peptide is applied onto the heart. With the endogenous AKH (Carmo-HrTH-II) as lead peptide, we report here on seven naturally-occurring AKH peptides (bioanalogs) selected for testing because of a single or double amino acid replacement, or for being octapeptides. Single amino acid substitutions by an alanine residue at all positions of Carmo-HrTH-II, as well as analogs modified at the termini were also investigated to give a comprehensive view of ligand-receptor interaction at the physiological level in a hemimetabolous insect that practices thanatosis (feigning death). Only small changes are elicited in the bioassays, but the results from the two tests are comparable bar one or two anomalies. Results show that analogs modified at the termini have no or reduced activity. Regarding structural requirements of a ligand, the C. morosus AKH receptor appears to be strict: octapeptides are not preferred and many of the decapeptide analogs failed to reach 50% activity relative to Carmo-HrTH-II. The data implies that the AKH receptor in C. morosus mostly does not tolerate shorter peptides and single amino acid replacements in most places of the native AKH peptide. This information is important if environmentally friendly insect-specific pesticides are made based on an insect AKH as lead peptide: stick insects that are normally not viewed as pest insects may not be easily targeted by cross-reactive AKH mimetics directed at harmful insects, due to the very specific amino acid requirements to activate the C. morosus AKH receptor.

Expression profile of genes encoding allatoregulatory neuropeptides in females of the spider Parasteatoda tepidariorum (Araneae, Theridiidae)

Allatoregulatory neuropeptides are multifunctional proteins that take part in the synthesis and secretion of juvenile hormones. In insects, allatostatins are inhibitors of juvenile hormone biosynthesis in the corpora allata while allatotropins, act as stimulators. By quantitative real-time PCR, we analyzed the gene expression of allatostatin A (PtASTA), allatostatin B (PtASTB), allatostatin C (PtASTC), allatotropin (PtAT) and their receptors (PtASTA-R, PtASTB-R, PtASTC-R, PtAT-R) in various tissues in different age groups of female spiders. In the presented manuscript, the presence of allatostatin A, allatostatin C, and allatotropin are reported in females of the spider P. tepidariorum. The obtained results indicated substantial differences in gene expression levels for allatoregulatory neuropeptides and their receptors in the different tissues. Additionally, the gene expression levels also varied depending on the female age. Strong expression was observed coinciding with sexual maturation in the neuroendocrine and nervous system, and to a lower extent in the digestive tissues and ovaries. Reverse trends were observed for the expression of genes encoding the receptors of these neuropeptides. In conclusion, our study is the first hint that the site of synthesis and secretion is fulfilled by similar structures as observed in other arthropods. In addition, the results of the analysis of spider physiology give evidence that the general functions like regulation of the juvenile hormone synthesis, regulation of the digestive tract and ovaries action, control of vitellogenesis process by the neuropeptides seem to be conserved among arthropods and are the milestone to future functional studies.

Myotropic activity of allatostatins in tenebrionid beetles

Neuropeptides control the functioning of the nervous system of insects, and they are the most diverse signalling molecules in terms of structure and function. Allatostatins are pleiotropic neuropeptides that are considered potent myoinhibitors of muscle contractions in insects. We investigated the effects caused by three distinct allatostatins, Dippu-AST1 (LYDFGL-NH₂ from Diploptera punctata), Grybi-MIP1 (GWQDLNGGW-NH₂ from Gryllus bimaculatus) and Trica-ASTC (pESRYRQCYFNPISCF-OH from Tribolium castaneum) on contractile activity of the myocardium, oviduct and hindgut of two tenebrionid beetles, Tenebrio molitor and Zophobas atratus. Studies showed that all three peptides exerted myostimulatory effects on the oviduct and hindgut of the beetles, however they did not cause any effect on myocardium. The effects of Dippu-AST1, Grybi-MIP1 and Trica-ASTC were dose-dependent and tissue and species specific. The highest stimulatory effect was caused by Trica-ASTC, showing stimulation of approximately 82% at a 10^-12 M concentration and 76% at a 10^-11 M concentration for T. molitor and Z. atratus, respectively. The oviduct of T. molitor was more susceptible to allatostatins than that of Z. atratus. Dippu-AST1 showed the maximum stimulating effect at 10^-11 M (57%), whereas Grybi-MIP 1 at 10^-10 M caused a 41% stimulation. Trica-ASTC, in both species, showed a myostimulatory effect over the whole range of tested concentrations but was most potent at a 10^-12 M concentration and caused a 54% and 31.9% increase in the frequency of contractions in the oviduct of T. molitor and Z. atratus, respectively. The results suggest that allatostatins may affect the regulation of egg movement within the oviducts and movement of food in the digestive tract of beetles and do not regulate directly the activity of heart, thus being good candidate compounds in neuropeptides based pest control agents in future research.

Newly identified allatostatin Bs and their receptor in the two-spotted cricket, Gryllus bimaculatus

A cDNA encoding allatostatin Bs (ASTBs) containing the W(X)6W motif was identified using a database generated by a next generation sequencer (NGS) in the two-spotted cricket, Gryllus bimaculatus. The contig sequence revealed the presence of five novel putative ASTBs (GbASTBs) in addition to GbASTBs previously identified in G. bimaculatus. MALDI-TOF MS analyses revealed the presence of these novel and previously identified GbASTBs with three missing GbASTBs. We also identified a cDNA encoding G. bimaculatus GbASTB receptor (GbASTBR) in the NGS data. Phylogenetic analysis demonstrated that this receptor was highly conserved with other insect ASTBRs, including the sex peptide receptor of Drosophila melanogaster. Calcium imaging analyses indicated that the GbASTBR heterologously expressed in HEK293 cells exhibited responses to all identified GbASTBs at a concentration range of 10(-10)-10(-5)M.

Functional characterization and expression analysis of the myoinhibiting peptide receptor in the Chagas disease vector, Rhodnius prolixus

Myoinhibiting peptides (MIPs), which are also known as B-type allatostatins, are a family of neuropeptides found in protostomes. Their primary structure is characterized by an amidated carboxyl-terminal motif consisting of a conserved pair of tryptophan residues normally separated by six non-conserved amino acids (W(X6)Wamide). In the fruit fly Drosophila melanogaster, MIPs are likely the ancestral ligands of the sex peptide receptor, which plays an important role in courtship and reproduction. Recently, several endogenous MIPs were discovered in the Chagas disease vector, Rhodnius prolixus, having both conserved (W(X6)Wamide) and atypical (W(X7)Wamide) carboxyl-terminal motifs. Physiological functions of MIPs are plentiful and include inhibition of visceral muscle activity; a role that has been illustrated on hindgut in R. prolixus. In order to identify novel physiological targets and elucidate biological actions for the MIPs in R. prolixus, we have isolated and examined the spatial expression profile of the MIP receptor transcript in various fifth instar tissues and have additionally determined the expression profile in reproductive tissues of fifth instar as well as adult insects. The most abundant MIP receptor transcript expression was found in the salivary glands and central nervous system, which corroborates roles previously determined for MIPs in other insects. We functionally-characterized the endogenous MIP receptor and examined its activation by R. prolixus MIPs containing the typical W(X6)Wamide and atypical W(X7)Wamide carboxyl-terminal motifs. These peptides dose-dependently activated the MIP receptor (RhoprMIPr1) with EC50 values in the mid-nanomolar range. We also examined the activity of these RhoprMIPs on spontaneous muscle contractions of oviducts from female adult R. prolixus. Our findings confirm the myoinhibitory nature of the MIP peptides, which dose-dependently reduced spontaneous oviduct contractions by nearly 70%, again having mid-nanomolar EC50 values. Finally, we utilized a heterologous receptor assay and oviduct bioassay to examine the activity of several MIP structural analogs, which independently confirmed the requirement of the highly conserved tryptophan residues as well as the amidated C-terminus for retaining full biological activity.

The distribution and physiological effects of the myoinhibiting peptides in the kissing bug, rhodnius prolixus

The myoinhibiting peptides (MIPs), also designated as allatostatin-Bs or prothoracicostatic peptides in some insects, are neuropeptides that are characterized by two tryptophan (W) residues at the C-terminal, denoted as the W(X₆)Wamide motif. They are believed to be the ancestral ligands for the Drosophila sex peptide (SP) receptor. Physiological functions of MIPs include the inhibition of contraction of insect visceral muscles, in addition to allatostatic and prothoracicostatic activities. The MIP precursor in Rhodnius prolixus encodes MIPs that have an unusual W(X₇)Wamide motif. In the present study, MIP-like immunoreactivity was detected within neurons in the central nervous system and within the innervation to the salivary glands, hindgut, and female and male reproductive systems of adult R. prolixus. The effects of peptides with the unusual W(X₇)Wamide motif (Rhopr-MIP-4) and with the typical W(X₆)Wamide motif (Rhopr-MIP-7) were tested for physiological activity on R. prolixus hindgut contractions. Both peptides reduce the frequency and amplitude of hindgut contractions in a dose-dependent manner. In addition, both peptides activate the Drosophila SP receptor. The MIP/SP receptors are therefore activated by peptides with the unusual W(X₇)Wamide motif.

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.

MIPs are ancestral ligands for the sex peptide receptor

Upon mating, females of many animal species undergo dramatic changes in their behavior. In Drosophila melanogaster, postmating behaviors are triggered by sex peptide (SP), which is produced in the male seminal fluid and transferred to female during copulation. SP modulates female behaviors via sex peptide receptor (SPR) located in a small subset of internal sensory neurons that innervate the female uterus and project to the CNS. Although required for postmating responses only in these female sensory neurons, SPR is expressed broadly in the CNS of both sexes. Moreover, SPR is also encoded in the genomes of insects that lack obvious SP orthologs. These observations suggest that SPR may have additional ligands and functions. Here, we identify myoinhibitory peptides (MIPs) as a second family of SPR ligands that is conserved across a wide range of invertebrate species. MIPs are potent agonists for Drosophila, Aedes, and Aplysia SPRs in vitro, yet are unable to trigger postmating responses in vivo. In contrast to SP, MIPs are not produced in male reproductive organs, and are not required for postmating behaviors in Drosophila females. We conclude that MIPs are evolutionarily conserved ligands for SPR, which are likely to mediate functions other than the regulation of female reproductive behaviors.

Bombyx prothoracicostatic peptides activate the sex peptide receptor to regulate ecdysteroid biosynthesis

Insect molting and metamorphosis are induced by steroid hormones named ecdysteroids, whose production is regulated by various neuropeptides. We cloned the gene and analyzed the expression of the prothoracicostatic peptide, a unique neuropeptide shown to suppress the production of ecdysteroids in the prothoracic gland of the silkworm, Bombyx mori. We also characterized a Bombyx G protein-coupled receptor, which has previously been identified as an ortholog of the Drosophila sex peptide receptor, as a functional prothoracicostatic peptide receptor. This receptor responded specifically to the prothoracicostatic peptides when examined using a heterologous expression system. The receptor was highly expressed in the prothoracic gland on the day before each larval and pupal ecdysis, when prothoracicostatic peptides are synthesized at a high level in the epiproctodeal glands. These results suggest that the sex peptide receptor functions as a prothoracicostatic peptide receptor in Bombyx and that the peripheral neurosecretory cells as well as the central neuroendocrine system play stage-specific roles in regulating ecdysteroidogenesis.

Role of allatostatin-like factors from the brain of Tenebrio molitor females

The effect of brain extract from females of freshly emerged Tenebrio molitor on ovary, oocyte development, total protein content of hemolymph, and ovary was studied in 4-day-old adult mealworm females. Injections of extracts of 2-brain equivalents into intact (unligatured) Tenebrio females did not affect ovarian and oocyte development. Injections of ligated females, however, with 2-brain equivalents on day 1 and 2 after adult emergence strongly inhibited ovarian growth and oocyte development. At day 4, ligated and injected females did not develop their ovaries and pre-vitellogenic oocytes were not found. The changes in ovarian development correlated with an increase in the concentration of soluble proteins in the hemolymph as compared with the saline-injected controls. Additionally, a strong reduction of total protein content in ovarian tissue was observed. Reverse phase HPLC separation of a methanolic brain extract of T. molitor females showed that fraction 5 has a similar retention time to synthetic cockroach allatostatin. Fraction 5 was eluted at 12.88 min, which was closest to the internal standard Dippu-AST I, which eluted at 12.77 min. An ELISA of fraction 5 from the methanolic brain extract using antibodies against allatostatins Grybi-AST A1 and Grybi-AST B1 from cricket Gryllus bimaculatus showed that fraction 5 cross-reacted with Grybi-AST A1 antibodies. The cross-reactivity was similar to the synthetic allatostatin from D. punctata, which was used as a positive control. These observations demonstrate a possible role for allatostatin-like brain factor(s) in regulating the reproductive cycle of Tenebrio molitor.

Comparative peptidomics of Caenorhabditis elegans versus C. briggsae by LC-MALDI-TOF MS

Neuropeptides are important signaling molecules that function in cell-cell communication as neurotransmitters or hormones to orchestrate a wide variety of physiological conditions and behaviors. These endogenous peptides can be monitored by high throughput peptidomics technologies from virtually any tissue or organism. The neuropeptide complement of the soil nematode Caenorhabditis elegans has been characterized by on-line two-dimensional liquid chromatography and quadrupole time-of-flight tandem mass spectrometry (2D-nanoLC Q-TOF MS/MS). Here, we use an alternative peptidomics approach combining liquid chromatography (LC) with matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry to map the peptide content of C. elegans and another Caenorhabditis species, Caenorhabditis briggsae. This study allows a better annotation of neuropeptide-encoding genes from the C. briggsae genome and provides a promising basis for further evolutionary comparisons.

Identification of putative crustacean neuropeptides using in silico analyses of publicly accessible expressed sequence tags

The development of expressed sequence tags (ESTs) for crustacean cDNA libraries and their deposition in publicly accessible databases has generated a rich resource for peptide discovery in this commercially and ecologically important arthropod subphylum. Here, we have conducted in silico searches of these databases for unannotated ESTs encoding putative neuropeptide precursors using the BLAST program tblastn, and have predicted the mature forms of the peptides encoded by them. The primary strategy used was to query the database with known decapod prepro-hormone sequences or, in some instances, insect precursor protein sequences. For neuropeptides for which no prepro-hormones are known, the peptides themselves were used as queries. For those peptides expected to originate from a common precursor, the individual sequences were combined, with each peptide flanked by a dibasic processing site and, if amidated, a glycine residue. Using these approaches, 13 unannotated ESTs encoding putative neuropeptide precursors were found. For example, using the first strategy, putative Marsupenaeus japonicus prepro-hormones encoding B-type allatostatins, neuropeptide F (NPF), and orcokinins were identified. Similarly, several Homarus americanus ESTs encoding putative orcokinin precursors were found. In addition to the decapod prepro-hormones, ESTs putatively encoding a NPF isoform and a red pigment concentrating hormone-like peptide were identified from the cladoceran Daphnia magna, as was one EST putatively encoding multiple tachykinin-related peptides from the isopod Eurydice pulchra. Using the second strategy, we identified a Carcinus maenas EST encoding HIGSLYRamide, a peptide recently discovered via mass spectrometry from Cancer productus. Using mass spectral methods we confirmed that this peptide is also present in Carcinus maenas. Collectively over 50 novel crustacean peptides were predicted from the identified ESTs, providing a strong foundation for future investigations of the evolution, regulation and function of these and related molecules in this arthropod taxon.

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

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

Neuropeptidergic signaling in the nematode Caenorhabditis elegans

The nematode Caenorhabditis elegans joins the menagerie of behavioral model systems next to the fruit fly Drosophila melanogaster, the marine snail Aplysia californica and the mouse. In contrast to Aplysia, which contains 20,000 neurons having cell bodies of hundreds of microns in diameter, C. elegans harbors only 302 tiny neurons from which the cell lineage is completely described, as is the case for all the other somatic cells. As such, this nervous system appears at first sight incommensurable with those of higher organisms, although genome-wide comparison of predicted C. elegans genes with their counterparts in vertebrates revealed many parallels. Together with its short lifespan and ease of cultivation, suitability for high-throughput genetic screenings and genome-wide RNA interference approaches, access to an advanced genetic toolkit and cell-ablation techniques, it seems that this tiny transparent organism of only 1mm in length has nothing to hide. Recently, highly exciting developments have occurred within the field of neuropeptidergic signaling in C. elegans, not only because of the availability of a sequenced genome since 1998, but especially because of state of the art post genomic technologies, that allow for molecular characterization of the signaling molecules. Here, we will focus on endogenous, bioactive (neuro)peptides and mainly discuss biosynthesis, peptide sequence information, localization and G-protein coupled receptors of the three major peptide families in C. elegans.

Mass spectrometric characterization and physiological actions of VPNDWAHFRGSWamide, a novel B type allatostatin in the crab, Cancer borealis

The neural networks in the crustacean stomatogastric ganglion are modulated by neuroactive substances released locally into the neuropil of the stomatogastric ganglion and by circulating hormones released by neuroendocrine structures including the pericardial organs. Using nanoscale liquid chromatography coupled to electrospray ionization quadrupole-time-of-flight mass spectrometry, we have identified and sequenced a novel B type allatostatin (CbAST-B1), VPNDWAHFRGSWamide, present in the pericardial organs of the crabs, Cancer borealis, and Cancer productus. We describe the physiological actions of CbAST-B1 on the pyloric rhythm of the stomatogastric ganglion of the crab, Cancer borealis. CbAST-B1 reduces the pyloric network frequency in a dose-dependent manner. The effect of bath-applied CbAST-B1 depends on the preceding physiological state of the preparation. Surprisingly, despite marked amino-acid sequence dissimilarity between the novel CbAST-B1 and the A type allatostatin family of peptides (AST-A), the physiological effects of CbAST-B1 are similar to those of AST-A.

The role of allatostatins in juvenile hormone synthesis in insects and crustaceans

Allatostatins are pleiotropic neuropeptides for which one function in insects is the inhibition of juvenile hormone synthesis. Juvenile hormone, an important regulator of development and reproduction in insects, is produced by the corpora allata. Mandibular organs, the crustacean homologs of insect corpora allata, produce precursors of juvenile hormone with putatively similar functions. Three types of allatostatins in insects have been isolated: FGLamides, W(X)(6)Wamides, and PISCFs. All act rapidly and reversibly; however, although these types occur in all groups of insects studied, they act as inhibitors of juvenile hormone production in only some groups. Only the FGLamide-type peptides have been isolated in crustaceans, in which they may function to stimulate production of hormone by the mandibular glands, as occurs in early cockroach embryos. Much remains to be learned in order to understand the role of allatostatins in the modulation of hormone production.

Silencing allatostatin expression using double-stranded RNA targeted to preproallatostatin mRNA in the German cockroach

YXFGL-NH(2) family allatostatins (ASTs) were isolated from cockroach brain extracts based on their capacity to inhibit juvenile hormone (JH) biosynthesis in corpora allata (CA) incubated in vitro. Subsequently, the inhibitory activity of synthetic ASTs was demonstrated experimentally, although these peptides were shown to be active as JH inhibitors only in cockroaches, crickets, and termites. Here, we sought to examine whether ASTs are true physiological regulators of JH synthesis. To this end, we used RNA interference methodologies and the cockroach Blattella germanica as a model. Treatments with double-stranded RNA targeting the allatostatin gene in females of B. germanica produced a rapid and long-lasting reduction in mRNA and peptide levels in both brain and midgut during the reproductive cycle. Nevertheless, while brain AST levels were reduced approximately 70-80%, JH synthesis did not increase in any of the age groups tested.

Discovering new invertebrate neuropeptides using mass spectrometry

Neuropeptides are a complex set of messenger molecules controlling a wide array of regulatory functions and behaviors within an organism. These neuromodulators are cleaved from longer protein molecules and often experience numerous post-translational modifications to achieve their bioactive form. As a result of this complexity, sensitive and versatile analysis schemes are needed to characterize neuropeptides. Mass spectrometry (MS) through a variety of approaches has fueled the discovery of hundreds of neuropeptides in invertebrate species in the last decade. Particularly successful are direct tissue and single neuron analyses by matrix-assisted laser desorption/ionization (MALDI) MS, which has been used to elucidate approximately 440 neuropeptides, and examination of neuronal homogenates by electrospray ionization techniques (ESI), also leading to the characterization of over 450 peptides. Additional MS methods with great promise for the discovery of neuropeptides are MS imaging and large-scale peptidomics studies in combination with a sequenced genome.

Expression and bioactivity of allatostatin-like neuropeptides in helminths

Allatostatins are the largest family of known arthropod neuropeptides. To date more than 150 different arthropod type-A allatostatins have been identified and are characterized by the C-terminal signature, (Y/F)XFG(L/I)amide. Using specific allatostatin antisera, positive immunoreactivity has been identified within the central and peripheral nervous systems of the flatworm (platyhelminth) Procerodes littoralis and the roundworm (nematode) Panagrellus redivivus. Comparative analyses of the allatostatin-like immunoreactivity and that of other known helminth neuropeptides (FMRFamide-like peptides [FLPs]) indicate differences in the distribution of these peptide families. Specific differences in neuropeptide distribution have been noted within the pharyngeal innervation of flatworms and in the cephalic papillary neurons of nematodes. In arthropods, type-A allatostatins have functions that include potent myoactivity. In this study, seven members of the allatostatin superfamily induced concentration-dependent contractions of flatworm muscle fibres. Pharmacological studies indicate that these peptides do not interact with muscle-based FLP receptors. The type-A allatostatins, therefore, represent the second family of neuropeptides that induce muscle contraction in flatworms. Although the majority of arthropod type-A allatostatins examined did not affect the somatic body wall muscle or the ovijector of the pig nematode, Ascaris suum, two type-A allatostatins (GDGRLYAFGLamide and DRLYSFGLamide) exhibited significant inhibitory effects on the A. suum ovijector at 10 microM. These data suggest that allatostatin-like peptides and receptors occur in helminths. Further, although arthropod type-A allatostatins display inter-phyla activities, their receptors are less compelling as potential targets for broad-spectrum parasiticides (endectocides) than FLP receptors.

Discovering neuropeptides in Caenorhabditis elegans by two dimensional liquid chromatography and mass spectrometry

Completion of the Caenorhabditis elegans genome sequencing project in 1998 has provided more insight into the complexity of nematode neuropeptide signaling. Several C. elegans neuropeptide precursor genes, coding for approximately 250 peptides, have been predicted from the genomic database. One can, however, not deduce whether all these peptides are actually expressed, nor is it possible to predict all post-translational modifications. Using two dimensional nanoscale liquid chromatography combined with tandem mass spectrometry and database mining, we analyzed a mixed stage C. elegans extract. This peptidomic setup yielded 21 peptides derived from formerly predicted neuropeptide-like protein (NLP) precursors and 28 predicted FMRFamide-related peptides. In addition, we were able to sequence 11 entirely novel peptides derived from nine peptide precursors that were not predicted or identified in any way previously. Some of the identified peptides display profound sequence similarities with neuropeptides from other invertebrates, indicating that these peptides have a long evolutionary history.

Hormone complement of theCancer productus sinus gland and pericardial organ: An anatomical and mass spectrometric investigation

In crustaceans, circulating hormones influence many physiological processes. Two neuroendocrine organs, the sinus gland (SG) and the pericardial organ (PO), are the sources of many of these compounds. As a first step in determining the roles played by hemolymph-borne agents in the crab Cancer productus, we characterized the hormone complement of its SG and PO. We show via transmission electron microscopy that the nerve terminals making up each site possess dense-core and/or electron-lucent vesicles, suggesting diverse complements of bioactive molecules for both structures. By using immunohistochemistry, we show that small molecule transmitters, amines and peptides, are among the hormones present in these tissues, with many differentially distributed between the two sites (e.g., serotonin in the PO but not the SG). With several mass spectrometric (MS) methods, we identified many of the peptides responsible for the immunolabeling and surveyed the SG and PO for peptides for which no antibodies exist. By using MS, we characterized 39 known peptides [e.g., beta-pigment-dispersing hormone (beta-PDH), crustacean cardioactive peptide, and red pigment-concentrating hormone] and de novo sequenced 23 novel ones (e.g., a new beta-PDH isoform and the first B-type allatostatins identified from a non-insect species). Collectively, our results show that diverse and unique complements of hormones, including many previously unknown peptides, are present in the SG and PO of C. productus. Moreover, our study sets the stage for future biochemical and physiological studies of these molecules and ultimately the elucidation of the role(s) they play in hormonal control in C. productus.

Cloning and tissue-specific localization of cricket-type allatostatins from Gryllus bimaculatus

Cricket- or B-type allatostatins [W(X(6))W-amides] inhibit the biosynthesis of juvenile hormones in vitro in crickets. Peptides of this family are present also in other insects where they may bare different functions. Here we report the identification of a partial sequence of the B-type preproallatostatin from Gryllus bimaculatus. By PCR screening of a random primer cDNA library and by RACE, a 535bp 3'cDNA sequence was obtained which encodes a putative translation product of 85 amino acids, containing three copies of Grybi-AST B1 and one copy each of Grybi-AST B2, Grybi-AST B3, and Grybi-AST B6. The last represents a novel member of this peptide family. By means of one-step RT-PCR, RNA dot blot, and RT in situ PCR analyses the mRNA expression of the gene in the central nervous system and the digestive tract of female adult crickets was demonstrated. The results confirm that the B-type allatostatins of G. bimaculatus are brain-gut peptides.

The distribution and effects of Dippu-allatostatin-like peptides in the blood-feeding bug, Rhodnius prolixus

Using a polyclonal antiserum to Dippu-allatostatin 7 (Dippu-AST 7; formerly AST 1) of the cockroach Diploptera punctata, we have demonstrated the presence of AST-like immunoreactivity (ALI) in cells and processes throughout the nervous system, gut, and peripheral tissues of unfed fifth instar and adult Rhodnius prolixus. ALI in apparent neurosecretory cells of the brain, suboesophageal ganglion, and mesothoracic ganglionic mass, as well as in midgut endocrine cells, suggests that Rhodnius allatostatins may act as neurohormones/hormones. The presence of ALI in possible interneurons and areas of neuropile throughout the CNS also suggests roles as neuromodulators and/or neurotransmitters. Dippu-AST 7 inhibits spontaneous and leucokinin 1 (LK 1)-induced contractions of the Rhodnius hindgut in a dose-dependent manner. The low concentrations capable of inhibiting both spontaneous (10(-12)M) and LK 1-induced contractions (10(-10) to 10(-9)M) suggest that ASTs may be acting as neurohormones/hormones on the hindgut. We have also shown that Dippu-AST 7 influences the muscle activity of the Rhodnius dorsal vessel at concentrations as low as 10(-11)M.

Localization of myoinhibitory peptide immunoreactivity in Manduca sexta and Bombyx mori, with indications that the peptide has a role in molting and ecdysis

For normal development of Manduca sexta larvae, the ecdysteroid titer must drop following its sudden rise at the start of the molting cycle; this sudden decline in titer may be due to myoinhibitory peptide I (MIP I), which has an inhibitory effect on the release of ecdysone by the prothoracic glands of Bombyx mori in vitro. Using an antiserum to MIP, we have demonstrated secretion of an MIP-like peptide by the epiproctodeal glands of Manduca sexta, which are located on each proctodeal nerve, just anterior to the rectum. These MIP-immunoreactive glands are also present in B. mori. In fourth-instar larvae of M. sexta, the epiproctodeal glands show a distinct cycle of synthesis and sudden release of MIP that coincides with the time of the rapid decline in ecdysteroid titer. The function of the epiproctodeal glands appears to be the timely release of MIP during the molting cycle, so as to inhibit the prothoracic glands and thus to facilitate the sudden decline in ecdysteroid titer. In addition, we have found that MIP immunoreactivity is co-localized with that of crustacean cardioactive peptide (CCAP) in the 704 interneurons; these peptides appear to be co-released at the time of ecdysis. It is known that CCAP can initiate the ecdysis motor program; our results suggest that MIP may also be involved in activating ecdysis behavior.

Inhibition of cAMP signalling cascade-mediated Ca2+ influx by a prothoracicostatic peptide (Mas-MIP I) via dihydropyridine-sensitive Ca2+ channels in the prothoracic glands of the silkworm, Bombyx mori

Measurements of Ca(2+) influx in Fura-2/AM loaded prothoracic glands (PGs) of the silkworm, Bombyx mori, after application of forskolin or the cAMP analogue, 8-bromo-cAMP, showed a steady increase in [Ca(2+)](i), which was of extracellular origin and was inhibited, in both cases, by the dihydropyridine (DHP) derivative, nitrendipine. Nitrendipine also inhibited the abrupt S(-).Bay K 8644-mediated increase in [Ca(2+)](i) and its effects were mimicked by a myoinhibitory/prothoracicostatic peptide (Mas-MIP I/PTSP), which was isolated from Manduca sexta and was found to possess ecdysteroidostatic activity in Bombyx mori PGs. This peptide blocked both the forskolin and S(-).Bay K 8644-mediated increase in [Ca(2+)](i) of PG cells. It was ineffective, however, in blocking the recombinant prothoracicotropic hormone (rPTTH)-stimulated high increase in [Ca(2+)](i) of PG cells suggesting that distinct and independently regulated Ca(2+) influx mechanisms operate in the PG cells of Bombyx mori. The dependence of DHP-sensitive Ca(2+) channels on the cAMP-signalling cascade was further corroborated by the inabilitity of nitrendipine to block the thapsigargin-stimulated high increase in [Ca(2+)](i) after depletion of Ca(2+) from the intracellular stores. This, together with the inability of thapsigargin to stimulate the cAMP levels of PG cells suggest that there is a tightly regulated cross-talk mechanism between the two signalling cascades of Ca(2+) and cAMP. The combined results suggest a cAMP-mediated regulation of the opening-state of DHP-sensitive Ca(2+) channels and stimulation of [Ca(2+)](i) increases and ecdysteroid secretion by a positive feedback mechanism. Mas-MIP I/PTSP interferes with this mechanism by blocking DHP-sensitive Ca(2+) channels. This regulatory mechanism appears to be autonomously stimulating ecdysteroidogenesis by the PGs, it is regulated by Mas-MIP I/PTSPS, and it is not involved in other Ca(2+) influx mechanisms that operate within the PG cells of Bombyx mori.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

Molecular cloning of a functional allatostatin gut/brain receptor and an allatostatin preprohormone from the silkworm Bombyx mori

The cockroach-type or A-type allatostatins are inhibitory insect neuropeptides with the C-terminal sequence Tyr/Phe-X-Phe-Gly-Leu-NH(2). Here, we have cloned an A-type allatostatin receptor from the silkworm Bombyx mori (BAR). BAR is 361 amino acid residues long, has seven transmembrane domains, shows 60% amino acid residue identity with the first Drosophila allatostatin receptor (DAR-1), and 48% identity with the second Drosophila allatostatin receptor (DAR-2). The BAR gene has two introns and three exons. These two introns coincide with and have the same intron phasing as two introns in the DAR-1 and DAR-2 genes, showing that the three receptors are not only structurally but also evolutionarily related. Furthermore, we have cloned a Bombyx allatostatin preprohormone that contains eight different A-type allatostatins. Chinese hamster ovary cells permanently transfected with BAR DNA react on the addition of 4 x 10(-9)M Bombyx A-type allatostatins with a second messenger cascade (measured as bioluminescence), showing that BAR is a functional A-type allatostatin receptor. Southern blots suggest that Bombyx has at least one other BAR-related gene in addition to the BAR gene described in this paper. Northern blots and quantitative reverse transcriptase-polymerase chain reaction of different larval tissues show that BAR mRNA is mainly expressed in the gut and to a much lesser extent in the brain. To our knowledge, this is the first report on the molecular cloning and functional expression of an insect gut/brain peptide hormone receptor.

Identification of four Drosophila allatostatins as the cognate ligands for the Drosophila orphan receptor DAR-2

The allatostatins are generally inhibitory insect neuropeptides. The Drosophila orphan receptor DAR-2 is a G-protein-coupled receptor, having 47% amino acid residue identity with another Drosophila receptor, DAR-1 (which is also called dros. GPCR, or DGR) that was previously shown to be the receptor for an intrinsic Drosophila A-type (cockroach-type) allatostatin. Here, we have permanently expressed DAR-2 in CHO cells and found that it is the cognate receptor for four Drosophila A-type allatostatins, the drostatins-A1 to -A4. Of all the drostatins, drostatin-A4 (Thr-Thr-Arg-Pro-Gln-Pro-Phe-Asn-Phe-Gly-Leu-NH(2)) is the most effective in causing a second messenger cascade (measured as bioluminescence; threshold, 10(-9) M; EC(50), 10(-8) M), whereas the others are less effective and about equally potent (EC(50), 8 x 10(-8) M). Northern blots showed that the DAR-2 gene is expressed in embryos, larvae, pupae, and adult flies. In adult flies, the receptor is more strongly expressed in the thorax/abdomen than in the head parts, suggesting that DAR-2 is a gut receptor. This is confirmed by Northern blots from 3rd instar larvae, showing that the DAR-2 gene is mainly expressed in the gut and only very weakly in the brain. The Drosophila larval gut also contains about 20-30 endocrine cells, expressing the gene for the drostatins-A1 to -A4. We suggest, therefore, that DAR-2 mediates an allatostatin (drostatin)-induced inhibition of gut motility. This is the first report on the permanent and functional expression of a Drosophila gut neurohormone receptor.

Action kinetics of a prothoracicostatic peptide from Bombyx mori and its possible signaling pathway

A prothoracicostatic peptide (PTSP), purified from the brains of Bombyx mori, was found to inhibit ecdysteroidogenesis in the prothoracic glands (PGs) of this insect. This peptide was active at inhibiting ecdysteroidogenesis in the PGs at concentrations higher than 23 nM and glands incubated in 230 nM PTSP in vitro exhibited maximum inhibition of ecdysteroid production. By incubating PGs in vitro at different incubation periods it was observed that the first statistically significant inhibitory effect occurred after 30 min incubation in the presence of PTSP. Transferral of PGs from a medium with PTSP to a medium without PTSP resulted in the resumption of ecdysteroid production. Statistically significant inhibition of ecdysteroid production by PTSP was observed only in day 6 and in day 3 PGs of the 5th instar. The extracts of day 6 glands incubated in the presence of PTSP did not contain elevated amounts of ecdysteroid relative to controls after the incubations, indicating that PTSP does not inhibit the secretion, rather the synthesis, of ecdysteroid in the PGs. The presence of PTSP completely blocked the increased ecdysteroid production via L-type Ca(2+) channel activation by S(-)*Bay K 8644. There was no inhibition of ecdysteroid production by PTSP with glands incubated in Ca(2+)-free medium. The combined results suggest that PTSP regulates ecdysteroid synthesis only during specific stages of the 5th instar through a mechanism that likely involves the blocking of Ca(2+) influx through voltage-sensitive Ca(2+) channels in the PG cells of B. mori.

Molecular cloning, genomic organization, and expression of a C-type (Manduca sexta-type) allatostatin preprohormone from Drosophila melanogaster

The insect allatostatins are a diverse group of neuropeptides that obtained their names by their inhibitory actions on the corpora allata (two endocrine glands near the insect brain), where they block the biosynthesis of juvenile hormone (a terpenoid important for development and reproduction). Chemically, the allatostatins can be subdivided into three different peptide groups: the large group of A-type (cockroach-type) allatostatins, which have the common C-terminal sequence Y/FXFGLamide; the B-type (cricket-type) allatostatins, which have the C-terminal sequence W(X(6))Wamide in common; and a single allatostatin that we now call C-type allatostatin that was first discovered in the moth Manduca sexta, and which has a nonamidated C terminus, and a structure unrelated to the A- and B-type allatostatins. We have previously cloned the preprohormones for the A- and B-type allatostatins from Drosophila melanogaster. Here we report on the cloning of a Drosophila C-type allatostatin preprohormone (DAP-C). DAP-C is 121 amino acid residues long and contains one copy of a peptide sequence that in its processed form has the sequence <EVRYRQCYFNPISCF (drostatin-C). This drostatin-C sequence is only one amino acid residue different (F --> Y in position 4) from the Manduca sexta C-type allatostatin. The DAP-C gene has three introns and four exons and is located at position 32D2-3 on the left arm of the second chromosome. Northern blots show that the gene is strongly expressed in larvae and adult flies, but less in pupae and embryos. In situ hybridizations of larvae show that the gene is expressed in various neurons of the brain and abdominal ganglia and in endocrine cells of the midgut. This is the first publication on the structure of a C-type allatostatin from insects other than moths and the first report on the presence of all three types of allatostatins in a representative of the insect order Diptera (flies).

Molecular cloning, genomic organization, and expression of a B-type (cricket-type) allatostatin preprohormone from Drosophila melanogaster

The insect allatostatins obtained their names because they block the biosynthesis of juvenile hormone (a terpenoid) in the corpora allata (two endocrine organs near the insect brain). Chemically, the allatostatins can be subdivided into three different peptide groups: the A-type allatostatins, first discovered in cockroaches, which have the C-terminal sequence Y/FXFGLamide in common; the B-type allatostatins, first discovered in crickets, which all have the C-terminal sequence W(X)(6)Wamide; and the C-type allatostatins, first discovered in the moth Manduca sexta, which have an unrelated and nonamidated C terminus. We have previously reported the structure of an A-type allatostatin preprohormone from the fruitfly Drosophila melanogaster. Here we describe the molecular cloning of a B-type prepro-allatostatin from Drosophila (DAP-B). DAP-B is 211 amino acid residues long and contains one copy each of the following putative allatostatins: AWQSLQSSWamide (drostatin-B1), AWKSMNVAWamide (drostatin-B2), <EAQGWNKFRGAWamide (drostatin-B3), EPTWNNLKGMWamide (drostatin-B4), and DQWQKLHGGWamide (drostatin-B5). All five drostatins are novel peptide structures. The DAP-B gene has one intron and two exons and is located at position 74B1 on the left arm of the third chromosome. The gene is expressed in all developmental stages, but weakly in embryos and strongly in larvae. In situ hybridizations of larvae showed that neurons in the brain and abdominal ganglia and endocrine cells in the gut expressed DAP-B. This is the first published report of a B-type allatostatin preprohormone in insects, and the first paper describing the presence of B-type allatostatins in a representative of the insect order Diptera (flies).

A review of the role of neurosecretion in the control of juvenile hormone synthesis: a tribute to Berta Scharrer

In the 1950s, Berta Scharrer predicted that neurosecretions from the brain regulated corpus allatum activity based upon the observation of the change in localization of neurosecretory material in the brain and change in gland activity after severance of nerves between the brain and corpus allatum. Isolation and characterization of neuropeptide regulators of juvenile hormone production by the corpora allata in the late 1980s has confirmed this prediction. Both a stimulatory allatotropin and an inhibitory allatostatin have been isolated from moth brains. Two families of allatostatins, both quite different from each other and that of moths, have been isolated from cockroaches and crickets. The wide distribution of these peptides in the nervous system, in nerves to visceral muscle, in endocrine cells of the midgut and in blood cells, indicate multifunctions in the insects in which they are allatoregulatory. Some of these other functions have been demonstrated in these insects and in insects in which these neuropeptides occur but do not act as corpus allatum regulators. For the latter group, the neuropeptide regulators of the corpora allata have yet to be isolated. The families of neurosecretory regulators will continue to grow.