Insect allatotropins belong to a family of structurally-related myoactive peptides present in several invertebrate phyla

Allatotropin (AT) related peptides L-ATRP and D2-ATRP diastereomers activate an endogenous receptor and suppress heart rate in the Pacific abalone Haliotis discus hannai

Allatotropin (AT) has been identified in many insects and plays important roles in the regulation of their intestinal contraction, heart rate, ion transport, and digestive enzyme secretion. However, information on AT-related bioinformatics in other animal phyla is scarce. In this study, we cloned a full-length cDNA encoding the AT-related peptide receptor (ATRPR) of the abalone Haliotis discus hannai (Hdh) and further characterized Hdh-ATRPR with its potential ligands, Hdh-ATRPs. In luciferase reporter and Ca2+ mobilization assays, Hdh-ATRPs, including a D-type Phe at the second amino acid position, Hdh-D2-ATRP, activated Hdh-ATRPR in a dose-dependent manner, whereas all-L-type Hdh-ATRP was a more potent ligand than Hdh-D2-ATRP. Furthermore, Hdh-ATRPs induced ERK1/2 phosphorylation in Hdh-ATRPR-expressing HEK293 cells, which was dose-dependently abolished by the PKC inhibitor Gö6983. The heart rate decreased significantly within 10min when Hdh-D2-ATRP was injected into the adduct muscle sinus of abalone (0.2 or 1.0µg/g body weight), while the abalone injected with a high concentration of Hdh-D2-ATRP (1.5μg/g body weight) were sublethal within 5h. Thus, Hdh-ATRP signaling is primarily linked to the Gαq/PKC and is possibly associated with heart rate regulation in abalone.

Transcriptome sequencing of the central nervous system to identify the neuropeptides and neuropeptide receptors of Antheraea pernyi

Neuropeptides and neuropeptide receptors are crucial regulators for the behavior, lifecycle, and physiology of insects and are mainly produced and released from the neurosecretory cells of the central nervous system (CNS). In this study, RNA-seq was employed to investigate the transcriptome profile of the CNS which is composed of the brain and ventral nerve cord (VNC) of Antheraea pernyi. From the data sets, a total of 18 and 42 genes were identified, which respectively encode the neuropeptides and neuropeptide receptors involved in regulating multiple behaviors including feeding, reproductive behavior, circadian locomotor, sleep, and stress response and physiological processes such as nutrient absorption, immunity, ecdysis, diapause, and excretion. Comparison of the patterns of expression of those genes between the brain and VNC showed that most had higher levels of expression in the brain than VNC. Besides, 2760 differently expressed genes (DEGs) (1362 up-regulated and 1398 down-regulated ones between the B and VNC group) were also screened and further analyzed via gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) enrichment analyses. The results of this study could provide comprehensive profiles of the neuropeptides and neuropeptide receptors of A. pernyi CNS and lay the foundation for further research into their functions.

Prevention of tick-borne diseases: challenge to recent medicine

Abstract

Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population.

Highlights

• Tick-borne diseases have an increasing incidence due to climate change and increased human migration

• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector

• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases

• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design

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

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

Coordinated transcriptomics and peptidomics of central nervous system identify neuropeptides and their G protein-coupled receptors in the oriental fruit moth Grapholita molesta

The oriental fruit moth Grapholita molesta is a cosmopolitan pest of orchard, which causes serious economic losses to the fruit production. Neuropeptides and their specific receptors (primarily G protein-coupled receptors, GPCRs) regulate multiple biological functions in insects and represent promising next-generation pest management strategy. Here, we generated a transcriptome of the central nervous system (CNS) of G. molesta. Overall, 57 neuropeptide precursor genes were identified and 128 various mature peptides were predicted from these precursors. Using peptidomic analysis of CNS of G. molesta, we identified total of 28 mature peptides and precursor-related peptides from 16 precursors. A total of 41 neuropeptide GPCR genes belonging to three classes were also identified. These GPCRs and their probable ligands were predicted. Additionally, expression patterns of these 98 genes in various larval tissues were evaluated using quantitative real-time PCR. Taken together, these results will benefit further investigations to determine physiological functions and pharmacological characterization of neuropeptides and their GPCRs in G. molesta; and to develop specific neuropeptide-based agents for this tortricid fruit pest control.

Fitness Costs of Chlorantraniliprole Resistance Related to the SeNPF Overexpression in the Spodoptera exigua (Lepidoptera: Noctuidae)

Spodopteraexigua, a multifeeding insect pest, has developed a high level of resistance to chlorantraniliprole, which is a benzoylurea insecticide that targets the ryanodine receptors (RyRs). Herein, the resistant strain (SE-Sel) and sensitive strain (SE-Sus) were obtained by bidirectional screening for six generations. The potential oviposited eggs and oviposition rate of the SE-Sel strain were dramatically lower than those of the SE-Sus strain; on the contrary, the weights of prepupae and preadult were significantly increased. As a post-mating response, the higher number of non-oviposited eggs in the SE-Sel strain was caused by a lower mating rate. In addition, the expression levels of vitellogenin (SeVg) and its receptor (SeVgR) in the SE-Sel strain were consistently lower than those in the SE-Sus strain. An RyR^I4743M mutation, contributing to the resistance to chlorantraniliprole, was located in the S3 transmembrane segments and might have affected the release of calcium ions; it led to the upregulated expression of the neuropeptide SeNPF and its receptor SeNPFR, and the mating and oviposition rate were significantly recovered when the SeNPF was knocked down though RNA interference (RNAi) in the male adult of the SE-Sel strain. Moreover, the expression of the juvenile hormone-binding proteins SeJHBWDS3 and SeJHBAN in the male adult of the SE-Sel strain was significantly decreased, which proved the existence of a fitness cost from another angle. Therefore, these results indicate that the fitness cost accompanied by chlorantraniliprole resistance in S. exigua may be related to the decrease in mating desire due to SeNPF overexpression.

G protein-coupled receptor signal transduction and Ca2+ signaling pathways of the allatotropin/orexin system in Hydra

Allatotropin is a pleiotropic peptide originally characterized in insects. The existence of AT neuropeptide signaling was proposed in other invertebrates. In fact, we previously proposed the presence of an AT-like system regulating feeding behavior in Hydra sp. Even in insects, the information about the AT signaling pathway is incomplete. The aim of this study is to analyze the signaling cascade activated by AT in Hydra plagiodesmica using a pharmacological approach. The results show the involvement of Ca²⁺ and IP₃ signaling in the transduction pathway of the peptide. Furthermore, we confirm the existence of a GPCR system involved in this pathway, that would be coupled to a G_q subfamily of Gα protein, which activates a PLC, inducing an increase in IP₃ and cytosolic Ca²⁺. To the best of our knowledge, this work represents the first in vivo approach to study the overall signaling pathway and intracellular events involved in the myoregulatory effect of AT in Hydra sp.

Isolation functional characterization of allatotropin receptor from the cotton bollworm, Helicoverpa armigera

Insect allatotropin (AT) plays multi-functions including regulation of juvenile hormone synthesis, growth, development and reproduction. In the present study, the full-length cDNA encoding the AT receptor was cloned from the brain of Helicoverpa armigera (Helar-ATR). The ORF of Helar-ATR exhibited the characteristic seven transmembrane domains of the G protein-coupled receptor (GPCR) and was close to the ATR of Manduca sexta in the phylogenetic tree. The Helar-ATR expressed in vertebrate cell lines can be activated by Helar-AT and each Helar-ATL in a dose-responsive manner, in the following order: Helar-ATLI > Helar-ATLII > Helar-AT > Helar-ATLIII. Helar-ATLI and Helar-ATLII represented the functional ligands to Helar-ATR in vitro, while Helar-AT and Helar-ATLIII behaved as partial agonists. The in vitro functional analysis suggested that the Helar-ATR signal was mainly coupled with elevated levels of Ca²⁺ and independent of cAMP levels. Helar-ATR mRNA in larvae showed the highest level in the brain, followed by the thorax ganglion, abdomen ganglion, fat body and midgut. Helar-ATR mRNA levels in the complex of the brain-thoracic-abdomen ganglion on the 2nd day of the larval stage and during later pupal stages were observed to be relatively higher than in the wandering and early pupal stages.

The Evolutionary History of The Orexin/Allatotropin GPCR Family: from Placozoa and Cnidaria to Vertebrata

Peptidic messengers constitute a highly diversified group of intercellular messengers widely distributed in nature that regulate a great number of physiological processes in Metazoa. Being crucial for life, it seem that they have appeared in the ancestral group from which Metazoa evolved, and were highly conserved along the evolutionary process. Peptides act mainly through G-protein coupled receptors (GPCRs), a family of transmembrane molecules. GPCRs are also widely distributed in nature being present in metazoan, but also in Choanoflagellata and Fungi. Among GPCRs, the Allatotropin/Orexin (AT/Ox) family is particularly characterized by the presence of the DRW motif in the second intracellular loop (IC Loop 2), and seems to be present in Cnidaria, Placozoa and in Bilateria, suggesting that it was present in the common ancestor of Metazoa. Looking for the evolutionary history of this GPCRs we searched for corresponding sequences in public databases. Our results suggest that AT/Ox receptors were highly conserved along evolutionary process, and that they are characterized by the presence of the E/DRWYAI motif at the IC Loop 2. Phylogenetic analyses show that AT/Ox family of receptors reflects evolutionary relationships that agree with current phylogenetic understanding in Actinopterygii and Sauropsida, including also the largely discussed position of Testudines.

Identification and expression analysis of the Spodoptera exigua neuropeptidome under different physiological conditions

Neuropeptides are small signalling molecules acting as neurohormones, neurotransmitters and neuromodulators. Being part of the chemical communication system between cells within an organism, they are involved in the regulation of different aspects of animal physiology and behaviour such as feeding, reproduction, development and locomotion. Transcriptomic data from larval and adult tissues have been obtained and mined to generate a comprehensive neuropeptidome for the polyphagous insect pest Spodoptera exigua. Sixty-three neuropeptides have been identified and described based on their tissue specificity and their regulation in response to different abiotic perturbations. Expression analyses have identified those neuropeptides involved in ingestive and digestive behaviour of S. exigua larvae and revealed a general pattern of upregulation in the midgut during larval starvation. Our results represent a comprehensive neuropeptidome of a lepidopteran species that will be highly relevant to future studies and provide novel information of the insect's perception of its environment.

Aplysia allatotropin-related peptide and its newly identified d-amino acid-containing epimer both activate a receptor and a neuronal target

l- to d-residue isomerization is a post-translational modification (PTM) present in neuropeptides, peptide hormones, and peptide toxins from several animals. In most cases, the d-residue is critical for the biological function of the resulting d-amino acid-containing peptide (DAACP). Here, we provide an example in native neuropeptides in which the DAACP and its all-l-amino acid epimer are both active at their newly identified receptor in vitro and at a neuronal target associated with feeding behavior. On the basis of sequence similarity to a known DAACP from cone snail venom, we hypothesized that allatotropin-related peptide (ATRP), a neuropeptide from the neuroscience model organism Aplysia californica, may form multiple diastereomers in the Aplysia central nervous system. We determined that ATRP exists as a d-amino acid-containing peptide (d2-ATRP) and identified a specific G protein-coupled receptor as an ATRP receptor. Interestingly, unlike many previously reported DAACPs and their all-l-residue analogs, both l-ATRP and d2-ATRP were potent agonists of this receptor and active in electrophysiological experiments. Finally, d2-ATRP was much more stable than its all-l-residue counterpart in Aplysia plasma, suggesting that in the case of ATRP, the primary role of the l- to d-residue isomerization may be to protect this peptide from aminopeptidase activity in the extracellular space. Our results indicate that l- to d-residue isomerization can occur even in an all-l-residue peptide with a known biological activity and that in some cases, this PTM may help modulate peptide signal lifetime in the extracellular space rather than activity at the cognate receptor.

Discovery of a Manduca sexta Allatotropin Antagonist from a Manduca sexta Allatotropin Receptor Homology Model

Insect G protein coupled receptors (GPCRs) have important roles in modulating biology, physiology and behavior. They have been identified as candidate targets for next-generation insecticides, yet these targets have been relatively poorly exploited for insect control. In this study, we present a pipeline of novel Manduca sexta allatotropin (Manse-AT) antagonist discovery with homology modeling, docking, molecular dynamics simulation and structure-activity relationship. A series of truncated and alanine-replacement analogs of Manse-AT were assayed for the stimulation of juvenile hormone biosynthesis. The minimum sequence required to retain potent biological activity is the C-terminal amidated octapeptide Manse-AT (6–13). We identified three residues essential for bioactivity (Thr⁴, Arg6 and Phe⁸) by assaying alanine-replacement analogs of Manse-AT (6–13). Alanine replacement of other residues resulted in reduced potency but bioactivity was retained. The 3D structure of the receptor (Manse-ATR) was built and the binding pocket was identified. The binding affinities of all the analogs were estimated by calculating the free energy of binding. The calculated binding affinities corresponded to the biological activities of the analogs, which supporting our localization of the binding pocket. Then, based on the docking and molecular dynamics studies of Manse-AT (10–13), we described it can act as a potent Manse-AT antagonist. The antagonistic effect on JH biosynthesis of Manse-AT (10–13) validated our hypothesis. The IC₅₀ value of antagonist Manse-AT (10–13) is 0.9 nM. The structure-activity relationship of antagonist Manse-AT (10–13) was also studied for the further purpose of investigating theoretically the structure factors influencing activity. These data will be useful for the design of new Manse-AT agonist and antagonist as potential pest control agents.

Allatoregulatory-like systems and changes in cytosolic Ca2+ modulate feeding behavior in Hydra

Allatotropin (AT) and allatostatin-C (AST-C) are neuropeptides originally characterized by their ability to modulate the secretion of juvenile hormones in insects. Beyond the allatoregulatory function, these neuropeptides are pleiotropic acting as myoregulators not only in insects, but also in other groups of invertebrates. We have previously proposed the existence of AT and AST-C like systems in Hydra sp., a member of the phylum Cnidaria, which is a basal group of Metazoa, sharing a common ancestor with Bilateria. In the present study we analyze the regulatory effects of both peptides on the activity of the hypostome during feeding in Hydra sp. Furthermore, the importance of changes in the cytosolic Ca²⁺ levels involved in the response of the hypostome were analyzed. Physiological assays showed that while the presence of food or treatment with AT stimulates the extrusion of the hypostome, AST-C has an inhibitory effect on the behavior induced by both, food and AT. These facts suggest that both systems participate in the regulatory mechanisms associated with feeding and, as in insects, AST-C and AT may exert opposite effects. The use of thapsigargin (TG) and nifedipine, two compounds that modify the levels of cytosolic Ca²⁺, showed that changes in the levels of this ion are involved in the regulation of the activity of the hypostome. Indeed, these results suggest that the two basic mechanisms operating to increase the cytosolic levels of Ca²⁺ (i.e. the influx from the extracellular space and the release from endoplasmic reticulum) are relevant for the extrusion of the hypostome. Like in insects, the treatment with TG counteracted the effect of AST-C, suggesting that this peptide acts by reducing cytosolic Ca²⁺ levels. Furthermore, nifedipine prevented the myostimulatory effect of AT, showing that the effect of this peptide depends on the influx of Ca²⁺ throughout voltage-gated calcium channels. Altogether, these results suggest that the Allatotropin/Orexin and Allatostatin/Somatostatin regulatory systems could represent an ancestral mechanisms regulating hypostome activity and feeding behavior in Cnidaria.

Allatotropin: A pleiotropic neuropeptide that elicits mosquito immune responses

Allatotropins (AT) are neuropeptides with pleotropic functions on a variety of insect tissues. They affect processes such as juvenile hormone biosynthesis, cardiac rhythm, oviduct and hindgut contractions, nutrient absorption and circadian cycle. The present work provides experimental evidence that AT elicits immune responses in two important mosquito disease vectors, Anopheles albimanus and Aedes aegypti. Hemocytes and an immune-competent mosquito cell line responded to AT by showing strong morphological changes and increasing bacterial phagocytic activity. Phenoloxidase activity in hemolymph was also increased in Ae. aegypti mosquitoes treated with AT but not in An. albimanus, suggesting differences in the AT-dependent immune activation in the two species. In addition, two important insect immune markers, nitric oxide levels and expression of antimicrobial peptide genes, were increased in An. albimanus guts after AT treatment. AT conjugated to quantum dot nanocrystals (QDots) specifically labeled hemocytes in vivo in both mosquito species, implying molecular interactions between AT and hemocytes. The results of our studies suggest a new role for AT in the modulation of the immune response in mosquitoes.

Developmental and sex-specific differences in expression of neuropeptides derived from allatotropin gene in the silkmoth Bombyx mori

Allatotropin (AT) and related neuropeptides are widespread bioactive molecules that regulate development, food intake and muscle contractions in insects and other invertebrates. In moths, alternative splicing of the at gene generates three mRNA precursors encoding AT with different combinations of three structurally similar AT-like peptides (ATLI-III). We used in situ hybridization and immunohistochemistry to map the differential expression of these transcripts during the postembryonic development of Bombyx mori. Transcript encoding AT alone was expressed in numerous neurons of the central nervous system and frontal ganglion, whereas transcripts encoding AT with ATLs were produced by smaller specific subgroups of neurons in larval stages. Metamorphosis was associated with considerable developmental changes and sex-specific differences in the expression of all transcripts. The most notable was the appearance of AT/ATL transcripts (1) in the brain lateral neurosecretory cells producing prothoracicotropic hormone; (2) in the male-specific cluster of about 20 neurons in the posterior region of the terminal abdominal ganglion; (3) in the female-specific medial neurons in the abdominal ganglia AG2-7. Immunohistochemical staining showed that these neurons produced a mixture of various neuropeptides and innervated diverse peripheral organs. Our data suggest that AT/ATL neuropeptides are involved in multiple stage- and sex-specific functions during the development of B. mori.

Transcriptomic identification of starfish neuropeptide precursors yields new insights into neuropeptide evolution

Neuropeptides are evolutionarily ancient mediators of neuronal signalling in nervous systems. With recent advances in genomics/transcriptomics, an increasingly wide range of species has become accessible for molecular analysis. The deuterostomian invertebrates are of particular interest in this regard because they occupy an ‘intermediate' position in animal phylogeny, bridging the gap between the well-studied model protostomian invertebrates (e.g. Drosophila melanogaster, Caenorhabditis elegans) and the vertebrates. Here we have identified 40 neuropeptide precursors in the starfish Asterias rubens, a deuterostomian invertebrate from the phylum Echinodermata. Importantly, these include kisspeptin-type and melanin-concentrating hormone-type precursors, which are the first to be discovered in a non-chordate species. Starfish tachykinin-type, somatostatin-type, pigment-dispersing factor-type and corticotropin-releasing hormone-type precursors are the first to be discovered in the echinoderm/ambulacrarian clade of the animal kingdom. Other precursors identified include vasopressin/oxytocin-type, gonadotropin-releasing hormone-type, thyrotropin-releasing hormone-type, calcitonin-type, cholecystokinin/gastrin-type, orexin-type, luqin-type, pedal peptide/orcokinin-type, glycoprotein hormone-type, bursicon-type, relaxin-type and insulin-like growth factor-type precursors. This is the most comprehensive identification of neuropeptide precursor proteins in an echinoderm to date, yielding new insights into the evolution of neuropeptide signalling systems. Furthermore, these data provide a basis for experimental analysis of neuropeptide function in the unique context of the decentralized, pentaradial echinoderm bauplan.

Somatostatin signaling system as an ancestral mechanism: Myoregulatory activity of an Allatostatin-C peptide in Hydra

The coordination of physiological processes requires precise communication between cells. Cellular interactions allow cells to be functionally related, facilitating the maintaining of homeostasis. Neuropeptides functioning as intercellular signals are widely distributed in Metazoa. It is assumed that neuropeptides were the first intercellular transmitters, appearing early during the evolution. In Cnidarians, neuropeptides are mainly involved in neurotransmission, acting directly or indirectly on epithelial muscle cells, and thereby controlling coordinated movements. Allatostatins are a group of chemically unrelated neuropeptides that were originally characterized based on their ability to inhibit juvenil hormone synthesis in insects. Allatostatin-C has pleiotropic functions, acting as myoregulator in several insects. In these studies, we analyzed the myoregulatory effect of Aedes aegypti Allatostatin-C in Hydra sp., a member of the phylum Cnidaria. Allatostatin-C peptide conjugated with Qdots revealed specifically distributed cell populations that respond to the peptide in different regions of hydroids. In vivo physiological assays using Allatostatin-C showed that the peptide induced changes in shape and length in tentacles, peduncle and gastrovascular cavity. The observed changes were dose and time dependent suggesting the physiological nature of the response. Furthermore, at highest doses, Allatostatin-C induced peristaltic movements of the gastrovascular cavity resembling those that occur during feeding. In silico search of putative Allatostatin-C receptors in Cnidaria showed that genomes predict the existence of proteins of the somatostatin/Allatostatin-C receptors family. Altogether, these results suggest that Allatostatin-C has myoregulatory activity in Hydra sp, playing a role in the control of coordinated movements during feeding, indicating that Allatostatin-C/Somatostatin based signaling might be an ancestral mechanism.

Identification of the first neuropeptides from the enigmatic hexapod order Protura

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

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

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

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

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

The pleiotropic allatoregulatory neuropeptides and their receptors: A mini-review

Juvenile hormones (JH) are highly pleiotropic insect hormones essential for post-embryonic development. The circulating JH titer in the hemolymph of insects is influenced by enzymatic degradation, binding to JH carrier proteins, uptake and storage in target organs, but evidently also by rates of production at its site of synthesis, the corpora allata (CA). The multiple processes in which JH is involved alongside the critical significance of JH in insect development emphasize the importance for elucidating the control of JH production. Production of JH in CA cells is regulated by different factors: by neurotransmitters, such as dopamine and glutamate, but also by allatoregulatory neuropeptides originating from the brain and axonally transported to the CA where they bind to their G protein-coupled receptors (GPCRs). Different classes of allatoregulatory peptides exist which have other functions aside from acting as influencers of JH production. These pleiotropic neuropeptides regulate different processes in different insect orders. In this mini-review, we will give an overview of allatotropins and allatostatins, and their recently characterized GPCRs with a view to better understand their modes of action and different action sites.

Molecular cloning and characterization of the allatotropin precursor and receptor in the desert locust, Schistocerca gregaria

Allatotropins (ATs) are pleiotropic neuropeptides initially isolated from the tobacco hornworm, Manduca sexta. In 2008, the first receptor for AT-like peptides (ATR) was characterized in Bombyx mori. Since then, ATRs have also been characterized in M. sexta, Tribolium castaneum, Aedes aegypti and Bombus terrestris. These receptors show sequence similarity to vertebrate orexin (ORX) receptors. When generating an EST-database of the desert locust (Schistocerca gregaria) central nervous system, we found cDNA sequences encoding the Schgr-AT precursor and a fragment of its putative receptor. This receptor cDNA has now been completed and functionally expressed in mammalian cell lines. Activation of this receptor, designated as Schgr-ATR, by Schgr-AT caused an increase in intracellular calcium ions, as well as cyclic AMP (cAMP), with an EC₅₀ value in the nanomolar range. In addition, the transcript distribution of both the Schgr-AT precursor and Schgr-ATR was investigated by means of quantitative real-time PCR. Moreover, we found more evidence for the myotropic and allatostimulatory actions of Schgr-AT in the desert locust. These data are discussed and situated in a broader context by comparison with literature data on AT and ATR in insects.

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

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

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

Crustaceans of the subclass Copepoda are key components of essentially all aquatic ecosystems as they serve both as the primary consumers of phytoplankton and/or as major food sources for a wide variety of higher-level consumers. The dominant group of copepods in most freshwater ecosystems is the Cyclopoida; members of this order are routinely used as environmental indicators, and some predatory species are used for the biological control of disease-causing mosquitoes. Given their ecological and disease control importance, it is surprising that little is known about endocrine control in cyclopoids. Here, as part of an ongoing effort to identify and characterize the neurochemical signaling systems of members of the Copepoda, the extant transcriptome shotgun assembly for Eucyclops serrulatus, a member of the Cyclopoida, was mined for transcripts encoding putative peptide hormone-encoding transcripts. Via queries using known arthropod pre/preprohormone sequences, primarily ones from other copepod species, 36 E. serrulatus peptide-encoding transcripts were identified. The proteins deduced from these sequences allowed for the prediction of 160 unique mature neuropeptides, including the first copepod isoform of pigment dispersing hormone, as well as isoforms of adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, allatotropin, crustacean hyperglycemic hormone, diuretic hormone 31, DXXRLamide, FLRFamide, FXGGXamide, GSEFLamide, insulin-like peptide, intocin, leucokinin, myosuppressin, neuroparsin, neuropeptide F and tachykinin-related peptide. These peptides are currently the only ones known from any member of the Cyclopoida, and as such, provide a new resource for investigating peptidergic signaling in this important copepod order.

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

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

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

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

Molecular characterization and possible biological roles of allatotropin in Rhodnius prolixus

Allatotropins (ATs) are a family of neuropeptides that have been shown to stimulate the biosynthesis of juvenile hormone in certain insect species, and to have stimulatory activity on some visceral muscles. Here, we have examined the AT in Rhodnius prolixus. Molecular analysis revealed a cDNA fragment of 973 bp encoding one mature amidated AT (Rhopr-AT) with transcript levels observed in the central nervous system (CNS) and pool of fat body, trachea and associated peripheral nerves. AT-like immunoreactive neurons were found throughout the CNS and AT-like immunoreactive processes were present on some peripheral tissues. Bioassays based upon changes in hindgut and dorsal vessel contractions failed to demonstrate any myotropic effects of Rhopr-AT on these tissues; however Rhopr-AT stimulated contractions of muscles surrounding the salivary glands and secretion of saliva, as judged by the reduction in content of the cherry red saliva from the salivary glands. Serotonin stimulated an increase in peristaltic contractions of the gland though no secretion was observed. Co-application of Rhopr-AT and serotonin resulted in a more rapid secretion than either chemical alone.

Characterisation of a functional allatotropin receptor in the bumblebee, Bombus terrestris (Hymenoptera, Apidae)

Allatotropins (ATs) are multifunctional neuropeptides initially isolated from the tobacco hornworm, Manduca sexta, where they were found to stimulate juvenile hormone synthesis and release from the corpora allata. ATs have been found in a wide range of insects, but appear to be absent in Drosophila. The first AT receptor (ATR) was characterised in 2008 in the lepidopteran Bombyx mori. Since then ATRs have been characterised in Coleoptera and Diptera and in 2012, an AT precursor gene was identified in hymenopteran species. ATRs show large sequence and structural similarity to vertebrate orexin receptors (OXR). Also, AT in insects and orexin in vertebrates show some overlap in functions, including modulation of feeding behaviour and reproduction. The goal of this study was to identify a functional ATR in a hymenopteran species. We used ATRs (insect sequences) and OXRs (vertebrate sequences) to search the genome of the bumblebee, Bombus terrestris. Two receptors (XP_003402490 and XP_003394933) with resemblance to ATRs and OXRs were found. Phylogenetic analysis provided the first indication that XP_003402490 was more closely related to ATRs than XP_003394933. We investigated the transcript level distribution of both receptors and the AT precursor gene by means of quantitative real-time reverse transcriptase PCR. XP_003402490 displayed a tissue distribution comparable with ATRs in other species, with high transcript levels in the male accessory glands. After pharmacological characterisation, it appeared that XP_003402490 is indeed a functional ATR. Activation of the receptor causes an increase in intracellular calcium and cyclic AMP levels with an EC50 value in the low nanomolar to picomolar range. XP_003394933 remains an orphan receptor.

Allatotropin: an ancestral myotropic neuropeptide involved in feeding

Background

Cell-cell interactions are a basic principle for the organization of tissues and organs allowing them to perform integrated functions and to organize themselves spatially and temporally. Peptidic molecules secreted by neurons and epithelial cells play fundamental roles in cell-cell interactions, acting as local neuromodulators, neurohormones, as well as endocrine and paracrine messengers. Allatotropin (AT) is a neuropeptide originally described as a regulator of Juvenile Hormone synthesis, which plays multiple neural, endocrine and myoactive roles in insects and other organisms.

Methods

A combination of immunohistochemistry using AT-antibodies and AT-Qdot nanocrystal conjugates was used to identify immunoreactive nerve cells containing the peptide and epithelial-muscular cells targeted by AT in Hydraplagiodesmica. Physiological assays using AT and AT- antibodies revealed that while AT stimulated the extrusion of the hypostome in a dose-response fashion in starved hydroids, the activity of hypostome in hydroids challenged with food was blocked by treatments with different doses of AT-antibodies.

Conclusions

AT antibodies immunolabeled nerve cells in the stalk, pedal disc, tentacles and hypostome. AT-Qdot conjugates recognized epithelial-muscular cell in the same tissues, suggesting the existence of anatomical and functional relationships between these two cell populations. Physiological assays indicated that the AT-like peptide is facilitating food ingestion.

Significance

Immunochemical, physiological and bioinformatics evidence advocates that AT is an ancestral neuropeptide involved in myoregulatory activities associated with meal ingestion and digestion.

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

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

Peptidergic control of food intake and digestion in insects 1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Like all heterotrophic organisms, insects require a strict control of food intake and efficient digestion of food into nutrients to maintain homeostasis and to fulfill physiological tasks. Feeding and digestion are steered by both external and internal signals that are transduced by a multitude of regulatory factors, delivered either by neurons innervating the gut or mouthparts, or by midgut endocrine cells. The present review gives an overview of peptide regulators known to control feeding and digestion in insects. We describe the discovery and functional role in these processes for insect allatoregulatory peptides, diuretic hormones, FMRFamide-related peptides, (short) neuropeptide F, proctolin, saliva production stimulating peptides, kinins, and tachykinins. These peptides control either gut myoactivity, food intake, and (or) release of digestive enzymes. Some peptides exert their action at multiple levels, possibly having a biological function that depends on their site of delivery. Many regulatory peptides have been physically extracted from different insect species. However, multiple peptidomics, proteomics, transcriptomics, and genome sequencing projects have led to increased discovery and prediction of peptide (precursor) and receptor sequences. In combination with physiological experiments, these large-scale projects have already led to important steps forward in unraveling the physiology of feeding and digestion in insects.

In silico cloning of genes encoding neuropeptides, neurohormones and their putative G-protein coupled receptors in a spider mite

The genome of the spider mite was prospected for the presence of genes coding neuropeptides, neurohormones and their putative G-protein coupled receptors. Fifty one candidate genes were found to encode neuropeptides or neurohormones. These include all known insect neuropeptides and neurohormones, with the exception of sulfakinin, corazonin, neuroparsin and PTTH. True orthologs of adipokinetic hormone (AKH) were neither found, but there are three genes encoding peptides similar in structure to both AKH and the AKH-corazonin-related peptide. We were also unable to identify the precursors for pigment dispersing factor (PDF) or the recently discovered trissin. However, the spider mite probably does have such genes, as we found their putative receptors. A novel arthropod neuropeptide gene was identified that shows similarity to previously described molluscan neuropeptide genes and was called EFLamide. A total of 65 putative neuropeptide GPCR genes were also identified, of these 58 belong to the A-family and 7 to the B-family. Phylogenetic analysis showed that 50 of them are closely related to insect GPCRs, which allowed the identification of their putative ligand in 39 cases with varying degrees of certainty. Other spider mite GPCRs however have no identifiable orthologs in the genomes of the four holometabolous insect species best analyzed. Whereas some of the latter have orthologs in hemimetabolous insect species, crustaceans or ticks, for others such arthropod homologs are currently unknown.

Functional characterization of an allatotropin receptor expressed in the corpora allata of mosquitoes

Allatotropin is an insect neuropeptide with pleiotropic actions on a variety of different tissues. In the present work we describe the identification, cloning and functional and molecular characterization of an Aedes aegypti allatotropin receptor (AeATr) and provide a detailed quantitative study of the expression of the AeATr gene in the adult mosquito. Analysis of the tissue distribution of AeATr mRNA in adult female revealed high transcript levels in the nervous system (brain, abdominal, thoracic and ventral ganglia), corpora allata-corpora cardiaca complex and ovary. The receptor is also expressed in heart, hindgut and male testis and accessory glands. Separation of the corpora allata (CA) and corpora cardiaca followed by analysis of gene expression in the isolated glands revealed expression of the AeATr primarily in the CA. In the female CA, the AeATr mRNA levels were low in the early pupae, started increasing 6h before adult eclosion and reached a maximum 24h after female emergence. Blood feeding resulted in a decrease in transcript levels. The pattern of changes of AeATr mRNA resembles the changes in JH biosynthesis. Fluorometric Imaging Plate Reader recordings of calcium transients in HEK293 cells expressing the AeATr showed a selective response to A. aegypti allatotropin stimulation in the low nanomolar concentration range. Our studies suggest that the AeATr play a role in the regulation of JH synthesis in mosquitoes.

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.

Characterization of an allatotropin-like peptide receptor in the red flour beetle, Tribolium castaneum

Following a reverse pharmacology approach, we identified an allatotropin-like peptide receptor in Tribolium castaneum. Allatotropins are multifunctional neuropeptides initially isolated from the tabacco hornworm, Manduca sexta. They have been shown to be myoactive, to be cardio-acceleratory, to inhibit active ion transport, to stimulate juvenile hormone production and release and to be involved in the photic entrainment of the circadian clock. A tissue distribution analysis of the T. castaneum allatotropin-like peptide receptor by means of qRT-PCR revealed a prominent sexual dimorphism, the transcript levels being significantly higher in the male fat body and reproductive system. The endogenous ligand of the receptor, Trica-ATL, is able to increase the frequency and tonus of contractions in the gut and in the reproductive tract of mature red flour beetles.

Isolation and functional characterization of an allatotropin receptor from Manduca sexta

Manduca sexta allatotropin (Manse-AT) is a multifunctional neuropeptide whose actions include the stimulation of juvenile hormone biosynthesis, myotropic stimulation, cardioacceleratory functions, and inhibition of active ion transport. Manse-AT is a member of a structurally related peptide family that is widely found in insects and also in other invertebrates. Its precise role depends on the insect species and developmental stage. In some lepidopteran insects including M. sexta, structurally-related AT-like (ATL) peptides can be derived from alternatively spliced mRNAs transcribed from the AT gene. We have isolated a cDNA for an AT receptor (ATR) from M. sexta by a PCR-based approach using the sequence of the ATR from Bombyx mori. The sequence of the M. sexta ATR is similar to several G protein-coupled receptors from other insect species and to the mammalian orexin receptor. We demonstrate that the M. sexta ATR expressed in vertebrate cell lines is activated in a dose-responsive manner by Manse-AT and each Manse-ATL peptide in the rank order ATL-I > ATL-II > ATL-III > AT, and functional analysis in multiple cell lines suggest that the receptor is coupled through elevated levels of Ca(2+) and cAMP. In feeding larvae, Manse-ATR mRNA is present at highest levels in the Malpighian tubules, followed by the midgut, hindgut, testes, and corpora allata, consistent with its action on multiple target tissues. In the adult corpora cardiaca--corpora allata complex, Manse-ATR mRNA is present at relatively low levels in both sexes.

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.

Genomic analyses of the Daphnia pulex peptidome

Genome mining has provided a valuable tool for peptide discovery in many species, yet no crustacean has undergone this analysis. Currently, the only crustacean with a sequenced genome is the cladoceran Daphnia pulex, a model organism in many fields of biology. Here, we have mined the D. pulex genome for peptide-encoding genes. For each gene identified, the encoded precursor protein was deduced, and its mature peptides predicted. Twenty-four peptide-encoding genes were identified, including ones predicted to produce members of the A-type allatostatin, B-type allatostatin, C-type allatostatin, allatotropin (ATR), bursicon α, bursicon β, calcitonin-like diuretic hormone, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone, ecdysis-triggering hormone, eclosion hormone (EH), insulin-like peptide (ILP), molt-inhibiting hormone, neuropeptide F, orcokinin (two genes), pigment-dispersing hormone, proctolin, red pigment concentrating hormone/adipokinetic hormone (RPCH/AKH), short neuropeptide F, SIFamide, sulfakinin, and tachykinin-related peptide (TRP) families/subfamilies. In total, 96 peptides were predicted from these genes. Our identification of isoforms of corazonin, EH, ILP, proctolin, RPCH/AKH, sulfakinin and TRP are the first for D. pulex, while our prediction of ATR from this species is the first from any crustacean. The number of peptides predicted in our study shows the power of genome mining for peptide discovery, and provides a model for future genomic analyses of the peptidomes of other crustaceans. In addition, the data presented in our study provide foundations for future molecular, biochemical, anatomical, and physiological investigation of peptidergic signaling in D. pulex and other cladoceran species.

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 physiology in insects

In a search for more environmentally benign alternatives to chemical pesticides, insect neuropeptides have been suggested as ideal candidates. Neuropeptides are neuromodulators and/or neurohormones that regulate most major physiological and behavioral processes in insects. The major neuropeptide structures have been identified through peptide purification in insects (peptidomics) and insect genome projects. Neuropeptide receptors have been identified and characterized in Drosophila and similar receptors are being targeted in other insects considered to be economically detrimental pests in agriculture and forestry. Defining neuropeptide action in different insect systems has been more challenging and as a consequence, identifying unique targets for potential pest control is also a challenge. In this chapter, neuropeptide biosynthesis as well as select physiological processes are examined with a view to pest control targets. The application of molecular techniques to transform insects with neuropeptide or neuropeptide receptor genes, or knockout genes to identify potential pest control targets, is a relatively new area that offers promise to insect control. Insect immune systems may also be manipulated through neuropeptides which may aid in compromising the insects ability to defend against foreign invasion.

Feedforward compensation mediated by the central and peripheral actions of a single neuropeptide discovered using representational difference analysis

Compensatory mechanisms are often used to achieve stability by reducing variance, which can be accomplished via negative feedback during homeostatic regulation. In principle, compensation can also be implemented through feedforward mechanisms where a regulator acts to offset the anticipated output variation; however, few such neural mechanisms have been demonstrated. We provide evidence that an Aplysia neuropeptide, identified using an enhanced representational difference analysis procedure, implements feedforward compensation within the feeding network. We named the novel peptide "allatotropin-related peptide" (ATRP) because of its similarity to insect allatotropin. Mass spectrometry confirmed the peptide's identity, and in situ hybridization and immunostaining mapped its distribution in the Aplysia CNS. ATRP is present in the higher-order cerebral-buccal interneuron (CBI) CBI-4, but not in CBI-2. Previous work showed that CBI-4-elicited motor programs have a shorter protraction duration than those elicited by CBI-2. Here we show that ATRP shortens protraction duration of CBI-2-elicited ingestive programs, suggesting a contribution of ATRP to the parametric differences between CBI-4-evoked and CBI-2-evoked programs. Importantly, because Aplysia muscle contractions are a graded function of motoneuronal activity, one consequence of the shortening of protraction is that it can weaken protraction movements. However, this potential weakening is offset by feedforward compensatory actions exerted by ATRP. Centrally, ATRP increases the activity of protraction motoneurons. Moreover, ATRP is present in peripheral varicosities of protraction motoneurons and enhances peripheral motoneuron-elicited protraction muscle contractions. Therefore, feedforward compensatory mechanisms mediated by ATRP make it possible to generate a faster movement with an amplitude that is not greatly reduced, thereby producing stability.

Neuropeptide regulators of the juvenile hormone biosynthesis (in vitro) in the beetle, Tenebrio molitor (Coleoptera, Tenebrionidae)

The genome of Tribolium castaneum encodes two allatostatin [AS type B; W(X)(6)Wamide and AS type C; PISCF-OH] and one allatotropin (AT) precursor, but no AS type A (FGLamide) (Tribolium Genome Sequencing Consortium, 2008: Nature 452:949-955). Here we studied the activity (in vitro) of peptides derived from these precursors on the synthesis/release of juvenile hormone (JH) III. The corpora cardiaca-corpora allata (CC-CA) complexes of adult females of another tenebrionid beetle, the mealworm Tenebrio molitor, were used. Incubating the gland complexes in a medium containing Trica-AS B3 peptide, we showed that the peptide has allatostatic function in T. molitor. The activity of the type C AS depended on the age of the test animals and their intrinsic rate of JH III biosynthesis. The Trica-AS C peptide inhibited the JH release from CA of 3-day-old females with a high intrinsic rate of JH synthesis, but activated JH release from the CA of 7-day-old females with a lower intrinsic rate of JH production. The allatotropin peptide (Trica-AT) also activated the JH release from the CA of 7-day-old females in a dose-dependent and reversible manner. Unexpectedly, a type A AS derived from the precursor of the American cockroach Periplaneta americana (Peram-AS A2b) inhibited the JH release from the CA of younger and older females in the concentration range of 10(-8) to 10(-4) M, and the effects were fully reversible in the absence of peptide. These data suggest a complex role of allatoactive neuropeptides in the regulation of JH III biosynthesis in beetles.

Neurohormones and neuropeptides encoded by the genome of Lottia gigantea, with reference to other mollusks and insects

The Lottia gigantea genome was prospected for the presence of genes coding neuropeptides and neurohormones. Four genes code insulin-related peptides: two genes code molluscan insulin-like growth hormones, one gene an insulin very similar to vertebrate insulin, and the fourth a peptide related to drosophila insulin-like peptide 7. Four other genes encode the cysteine-knot proteins GPA2/GPB5 and bursicon/parabursicon. Another 37 genes code for precursors of the following neuropeptides: achatin, APGWamide, allatostatin C, allatotropin, buccalin (perhaps an allatostatin A homolog), cerebrin, CCAP, conopressin, elevenin (the predicted neuropeptide made by abdominal neuron 11 in Aplysia), egg laying hormone (two genes), enterin, feeding circuit activating neuropeptide (FCAP), FFamide, FMRFamide, GGNG, a GnRH-like peptide, the newly discovered LASGLVamide, LFRFamide, LFRYamide, LRNFVamide, luqin, lymnokinin, myomodulin (two genes), the newly discovered NKY, NPY, pedal peptide (three genes), PKYMDT, pleurin, PXFVamide, small cardioactive peptides, tachykinins (two genes) and WWamide (an allatostatin B homolog). One gene was found to encode FWISamide, while about 20 closely related genes were found to encode WWFamide. These small neuropeptides appear homologous to the NdWFamide, which contains d-Trp; these genes are similar to the Aplysia gene encoding NWFamide. Some of these peptides had not been previously identified from mollusks, such as the predicted hormones similar to Drosophila and vertebrate insulins, bursicon, the putative proctolin homolog PKYMDT and allatostatin C. Together with neuropeptides which are likely homologs of other insect neuropeptides, such as cerebrin and WWamide, this shows that despite significant differences the molluscan and arthropod neuropeptidomes are more similar than generally recognized.

Spatial expression of the mevalonate enzymes involved in juvenile hormone biosynthesis in the corpora allata in Bombyx mori

The developmental expressions of the mRNA of JH synthetic enzymes have been studied using homogenates of the corpora cardiaca-corpora allata (CC-CA) complexes in Bombyx mori [Kinjoh, T., Kaneko, Y., Itoyama, K., Mita, K., Hiruma, K., Shinoda, T., 2007. Control of juvenile hormone biosynthesis in Bombyx mori: cloning of the enzymes in the mevalonate pathway and assessment of their developmental expression in the corpora allata. Insect Biochemistry and Molecular Biology 37, 808-818]. The in situ hybridization analyses in the CC-CA complex showed that the distribution of the mRNAs of all the mevalonate enzymes and juvenile hormone (JH) acid O-methyltransferase occurred only in the CA cells, indicating that the fluctuations of the enzyme mRNA amounts in the CC-CA complexes were derived solely from the CA. In addition, the size of the CA and their nuclei was not associated with the JH synthetic activity by the CA until the pharate adult. Only female adult CA synthesized JH in B. mori, and the CA and the nuclei were significantly larger than those of male CA which do not synthesize JH.