Insect neuropeptides: Structures, chemical modifications and potential for insect control

Effects of alloferon and its analogues on reproduction and development of the Tenebrio molitor beetle

As the most numerous group of animals on Earth, insects are found in almost every ecosystem. Their useful role in the environment is priceless; however, for humans, their presence may be considered negative or even harmful. For years, people have been trying to control the number of pests by using synthetic insecticides, which eventually causes an increased level of resistance to applied compounds. The effects of synthetic insecticides have encouraged researchers to search for alternatives and thus develop safe compounds with high specificity. Using knowledge about the physiology of insects and the functionality of compounds of insect origin, a new class of bioinsecticides called peptidomimetics, which are appropriately modified insect analogues, was created. One promising compound that might be successfully modified is the thirteen amino acid peptide alloferon (HGVSGHGQHGVHG), which is obtained from the hemolymph of the blue blowfly Calliphora vicinia. Our research aimed to understand the physiological properties of alloferon and the activity of its peptidomimetics, which will provide the possibility of using alloferon or its analogues in the pharmaceutical industry, as a drug or adjuvant, or in agriculture as a bioinsecticide. We used alloferon and its three peptidomimetics, which are conjugates of the native peptide with three unsaturated fatty acids with various chain lengths: caprylic, myristic, and palmitic. We tested their effects on the morphology and activity of the reproductive system and the embryogenesis of the Tenebrio molitor beetle. We found that the tested compounds influenced the growth and maturation of ovaries and the expression level of the vitellogenin gene. The tested compounds also influenced the process of egg laying, embryogenesis, and offspring hatching, showing that alloferon might be a good peptide for the synthesis of effective bioinsecticides or biopharmaceuticals.

Identification and characterisation of PRXamide peptides in the western flower thrips, Frankliniella occidentalis

Insect CAPA-PVK (periviscerokinin) and pyrokinin (PK) neuropeptides belong to the PRX family peptides and are produced from capa and pyrokinin genes. We identified and characterised the two genes from the western flower thrips, Frankliniella occidentalis. The capa gene transcribes three splice variants, capa-a, -b, and -c, encoding two CAPA-PVKs (EVQGLFPFPRVamide; QGLIPFPRVamide) and two PKs (ASWMPSSSPRLamide; DSASFTPRLamide). The pyrokinin mRNA encodes three PKs: DLVTQVLQPGQTGMWFGPRLamide, SEGNLVNFTPRLamide, and ESGEQPEDLEGSMGGAATSRQLRTDSEPTWGFSPRLamide, the most extended pheromone biosynthesis activating neuropeptide (PBAN) ortholog in insects. Multiple potential endoproteolytic cleavage sites were presented in the prepropeptides from the pyrokinin gene, creating ambiguity to predict mature peptides. To solve this difficulty, we used three G protein-coupled receptors (GPCRs) for CAPA-PVK, tryptophan PK (trpPK), and PK peptides, and evaluated the binding affinities of the peptides. The binding activities revealed each subfamily of peptides exclusively bind to their corresponding receptors, and were significant for determining the CAPA-PVK and PK peptides. Our biological method using specific GPCRs would be a valuable tool for determining mature peptides, particularly with multiple and ambiguous cleavage sites in those prepropeptides. Both capa and pyrokinin mRNAs were strongly expressed in the head/thorax, but minimally expressed in the abdomen. The two genes also were clearly expressed during most of the life stages. Whole-mounting immunocytochemistry revealed that neurons contained PRXamide peptides throughout the whole-body: four to six neurosecretory cells in the head, and three and seven pairs of immunostained cells in the thorax and abdomen, respectively. Notably, the unusual PRXamide profiles of Thysanoptera are different from the other insect groups.

Insect kinin mimics act as potential control agents for aphids: Structural modifications of Trp4

Insect kinins are endogenous, biologically active peptides with various physiological functions. The use of insect kinins in plant protection is being evaluated by many groups. Some kinins have been chosen as lead compounds for pest control. We previously reported an insect kinin mimic IV-3 that had insecticidal activity. And by introducing a strong electron withdrawing group (-CF₃ ) on the benzene ring (Phe² ), we discovered a compound, L₇ , with better activity than lead IV-3. In this work, taking L₇ as the lead compound, we designed and synthesized 13 compounds to evaluate the influence of position 4 (Trp⁴ ) of insect kinin on insecticidal activity, by replacing the H atom on tryptophan with -CH₃ and -Cl or substituting the indole ring of tryptophan with the benzene, naphthalene, pyridine, imidazole, cyclohexane, and alkyl carboxamides. The aphid bioassay results showed that the compounds M₁ , M₃ , and M₅ were more active than the positive control, pymetrozine. Especially, replacing the side chain by an indole ring with 4-Cl substitution (M₁ , LC₅₀  = 0.0029 mmol/L) increased the aphicidal activity. The structure-activity relationships (SARs) indicated that the side chain benzene ring at this position may be important to the aphicidal activity. In addition, the toxicity prediction by Toxtree, and the toxicity experiments on Apis mellifera suggested that M₁ was no toxicity risk on a non-target organism. It could be used as a selective and bee-friendly insecticide to control aphids.

The effect of B-type allatostatin neuropeptides on crosstalk between the insect immune response and cold tolerance

Insects are the largest group of arthropod phyla and are capable of surviving in a variety of environments. One of the most important factors in enabling them to do so is their resistance to temperature stress, i.e., cold tolerance. The neuroendocrine system, together with the immune system, cooperates to regulate a number of physiological processes that are essential for the stability of the organism in stressful conditions. However, to date, no one has studied the effect of insect myoinhibitory peptides (MIPs) on cold stress tolerance and immune system activity. Here, we investigated the effect of Tenmo-MIP 5 (10^-6 M), cold stress (- 5 °C) and a combination of both on the immune response of Tenebrio molitor. All three treatments caused upregulation of immune-related genes (antimicrobial peptides and Toll) and increased phagocytosis activity (by approximately 10%). However, phenoloxidase activity and mortality were increased only after peptide injection and the combination of both treatments. The peptide injection combined with cold stress caused 40% higher mortality than that in the control. Together, our results show the links between cold stress, MIPs activity and the immune response, and to our knowledge, this is the first report showing the effect of MIP on the insect immune system.

Periviscerokinin (Cap2b; CAPA) receptor silencing in females of Rhipicephalus microplus reduces survival, weight and reproductive output

BACKGROUND

The cattle fever tick, Rhipicephalus (Boophilus) microplus, is a vector of pathogens causative of babesiosis and anaplasmosis, both highly lethal bovine diseases that affect cattle worldwide. In Ecdysozoa, neuropeptides and their G-protein-coupled receptors play a critical integrative role in the regulation of all physiological processes. However, the physiological activity of many neuropeptides is still unknown in ticks. Periviscerokinins (CAP2b/PVKs) are neuropeptides associated with myotropic and diuretic activities in insects. These peptides have been identified only in a few tick species, such as Ixodes ricinus, Ixodes scapularis and R. microplus, and their cognate receptor only characterized for the last two.

METHODS

Expression of the periviscerokinin receptor (Rhimi-CAP2bR) was investigated throughout the developmental stages of R. microplus and silenced by RNA interference (RNAi) in the females. In a first experiment, three double-stranded (ds) RNAs, named ds680-805, ds956-1109 and ds1102-1200, respectively, were tested in vivo. All three caused phenotypic effects, but only the last one was chosen for subsequent experiments. Resulting RNAi phenotypic variables were compared to those of negative controls, both non-injected and dsRNA beta-lactamase-injected ticks, and to positive controls injected with beta-actin dsRNA. Rhimi-CAP2bR silencing was verified by quantitative reverse-transcriptase PCR in whole females and dissected tissues.

RESULTS

Rhimi-CAP2bR transcript expression was detected throughout all developmental stages. Rhimi-CAP2bR silencing was associated with increased female mortality, decreased weight of surviving females and of egg masses, a delayed egg incubation period and decreased egg hatching (P < 0.05).

CONCLUSIONS

CAP2b/PVKs appear to be associated with the regulation of female feeding, reproduction and survival. Since the Rhimi-CAP2bR loss of function was detrimental to females, the discovery of antagonistic molecules of the CAP2b/PVK signaling system should cause similar effects. Our results point to this signaling system as a promising target for tick control.

Novel mechanisms of epithelial ion transport: insights from the cryptonephridial system of lepidopteran larvae

Lepidopterans are among the most widespread and easily recognized insects. Whereas adult lepidopterans are known for their beauty and ecological importance as pollinators and sources of food for other animals, larvae are economically important pests of forests and agricultural crops. In the larval body, rapid growth while feeding on plant-based diet is associated with extreme alkalinity (up to pH = 11) of the midgut lumen that helps digest plant proteins. Additionally, the presence of plant secondary metabolites which serve as anti-herbivory agents requires uninterrupted excretory function, accomplished primarily by the Malpighian tubules (MTs). The so-called cryptonephridial condition, along with extreme regional heterogeneity of the MTs, and the ability to rapidly and reversibly alter the direction of epithelial ion transport are features that allow uninterrupted MT functioning and recycling of base equivalents. Studies of MTs in lepidopteran larvae have revealed that rapid adjustments in epithelial ion transport include unexpected roles for voltage-gated, ligand-gated and mechanosensitive ion channels, as well as gap junctions. These molecular components are present in epithelia of a variety of vertebrates and invertebrates and thus are likely to constitute a universal epithelial toolkit for rapid autonomous regulation of epithelial function.

FMRF-related peptides in Aedes aegypti midgut: neuromuscular connections and enteric nervous system

FMRFamide-related peptides (FaRPs) are a class of neuropeptides that participate in a variety of physiological processes in invertebrates. They occur in nerves of stomatogastric ganglia and enteroendocrine cells of the insect digestive tract, where they may control muscle functions. However, their direct involvement in muscle function has never been shown in situ. We studied the relationship between FaRPs and midgut muscle during larval-pupal transition of the mosquito Aedes aegypti. In late L4, FaRP-positive neuronal extensions attach to the bundles of the external circular muscle layer, and muscle stem cells start to undergo mitosis in the internal circular layer. Thereafter, the external muscle layer degenerates, disappearing during early pupal development, and is completely absent in the adult mosquito. Our results indicate that FaRP-based neural signals are involved in the reorganization of the muscle fibers of the mosquito midgut during the larval-pupal transition. In addition to confirming FaRP involvement in muscle function, we show that the mosquito midgut muscles are largely innervated, and that circular and longitudinal muscle have specific neuron bodies associated with them.

Disruption of insect immunity using analogs of the pleiotropic insect peptide hormone Neb-colloostatin: a nanotech approach for pest control II

This work continues our studies on the pleiotropic activity of the insect peptide Neb-colloostatin in insects. In vivo immunological bioassays demonstrated that hemocytotoxic analogs of Neb-colloostatin injected into Tenebrio molitor significantly reduced the number of hemocytes in the hemolymph and impaired phagocytosis, nodulation and phenoloxidase activities in the insects. Among the analogs tested, [Ala¹]-,[Val¹]-, [Hyp⁴]- and [Ach⁴]-colloostatin were particularly potent in disrupting cellular immunity in larvae, pupae and adult insects. This result suggests that the most effective analogs showed increases in the bioactivity period in the hemolymph of insects when compared to Neb-colloostatin. Recently, we demonstrated that it is possible to introduce Neb-colloostatin through the cuticle of an insect into the hemolymph when the peptide is coupled with nanodiamonds. In this study, we showed that [Ala¹]-, [Val¹]-, [Hyp⁴]- and [Ach⁴]-colloostatin, when complexed with nanodiamonds, may also pass through the cuticle into the hemolymph and induce long-term impairments of immunity in T. molitor at all developmental stages. Studies on the tissue selectivity and effectiveness of Neb-colloostatin analogs and efficient methods for their introduction into insects may contribute to the development of eco-friendly pest control methods based on bioactive peptidomimetics.

Filling in the gaps: A reevaluation of the Lygus hesperus peptidome using an expanded de novo assembled transcriptome and molecular cloning

Peptides are the largest and most diverse class of molecules modulating physiology and behavior. Previously, we predicted a peptidome for the western tarnished plant bug, Lygus hesperus, using transcriptomic data produced from whole individuals. A potential limitation of that analysis was the masking of underrepresented genes, in particular tissue-specific transcripts. Here, we reassessed the L. hesperus peptidome using a more comprehensive dataset comprised of the previous transcriptomic data as well as tissue-specific reads produced from heads and accessory glands. This augmented assembly significantly improves coverage depth providing confirmatory transcripts for essentially all of the previously identified families and new transcripts encoding a number of new peptide precursors corresponding to 14 peptide families. Several families not targeted in our initial study were identified in the expanded assembly, including agatoxin-like peptide, CNMamide, neuropeptide-like precursor 1, and periviscerokinin. To increase confidence in the in silico data, open reading frames of a subset of the newly identified transcripts were amplified using RT-PCR and sequence validated. Further PCR-based profiling of the putative L. hesperus agatoxin-like peptide precursor revealed evidence of alternative splicing with near ubiquitous expression across L. hesperus development, suggesting the peptide serves functional roles beyond that of a toxin. The peptides predicted here, in combination with those identified in our earlier study, expand the L. hesperus peptidome to 42 family members and provide an improved platform for initiating molecular and physiological investigations into peptidergic functionality in this non-model agricultural pest.

Identification, Localization in the Central Nervous System and Novel Myostimulatory Effect of Allatostatins in Tenebrio molitor Beetle

Allatostatins (ASTs) are pleiotropic insect neuropeptides that are potent myoinhibitors of muscle contractions. In this study, we identified and immunolocalized peptides from the MIP/AST and PISCF/AST families in the nervous system of a model beetle, Tenebrio molitor. Neurons containing MIPs were immunolocalized in the brains of adults and the ventral nerve cords of larvae, pupae and imagines of this species as well as in the retrocerebral complex. PISCFs were immunolocalized in the ventral nerve cord of all stages as well as the brain of the adult beetle. Faint signals were also observed in the corpus allatum but not in the corpus cardiacum. The results allowed us to deduce the sequences of three neuropeptides belonging to MIP/ASTs, Tenmo-MIP4—NWGQFGXWa, Tenmo-MIP5—SKWDNFRGSWa and Tenmo-MIP6—EPAWSNLKGIWa, and one peptide from the PISCF/AST family, QSRYXQCYFNPISCX. Furthermore, we showed for the first time myostimulatory action of endogenous MIP/ASTs. Tenmo-MIP5 caused dose-dependent stimulation of the contractile activity of the beetle oviduct muscles, showing a sigmoidal curve up to 81.20% at the 10⁻⁸ M concentration, and the EC₅₀ value for the myostimulatory effect of this peptide was 8.50 × 10⁻¹² M. This is the first report of myostimulatory action of an endogenous myoinhibitory peptide in insect muscles.

The neuropeptidome of Carabus (Coleoptera, Adephaga: Carabidae)

Neuropeptides are signaling molecules involved in the regulation of virtually all physiological functions of Metazoa. In insects, more than 50 neuropeptide genes can be present in a single species, and thus neuropeptidergic systems are attractive targets for the development of environmentally friendly pesticides. Such approaches require not only knowledge of the neuropeptidomes of pests, but also detailed knowledge of the corresponding systems in beneficial insects. In Coleoptera, there is no profound knowledge of the neuropeptides in the adephagan lineage, which contains many of the ecologically important predators of caterpillars. We analyzed by transcriptomics, mass spectrometry and immunohistochemistry the neuropeptidomes of the two Carabus species C. violaceus and C. problematicus. This information, which contains detailed data on the differential processing of CAPA peptides, allows for the recognition of features typical only of the polyphagan lineage with its many pests. The neuropeptidomics data, which also confirmed the processing of a number of protein hormones, represent the highest number of neuropeptides that have been identified so far from Coleoptera. The sequences of the mature neuropeptides of the two Carabus species, whose ancestors separated about 13 Mya, are highly similar and no sequence substitutions were found in single-copy neuropeptides.

Neuropeptides and peptide hormones identified in codling moth, Cydia pomonella (Lepidoptera: Tortricidae)

The codling moth, Cydia pomonella, is a worldwide pest of pome fruits. Neuropeptides regulate most physiological functions in insects and represent new targets for the development of control agents. The only neuropeptides reported from the codling moth to date are the allatostatin A family peptides. To identify other neuropeptides and peptide hormones from codling moth, we analyzed head transcriptomes, identified 50 transcripts, and predicted 120 prepropeptides for the codling moth neuropeptides and peptide hormones. All transcripts were amplified, and these sequences were verified. One of the notable findings in this study is that diapause hormones (DHs) reported from Tortricid moths, including the codling moth, do not have the WFGPRL sequence in C-terminal ends in the pban genes. The C-terminal motif is critical to characterize insect DH peptides, and always conserved in pban/dh genes in Lepidoptera and many insect orders. Interestingly, the WFGPRL sequence was produced only from the capa gene in the codling moth. The allatostatin A-family encoding transcript predicted nine peptides, seven of which, as expected, are identical to those previously isolated from the moth. We also identified new codling moth orthologs of insect neuropeptides including CCHamides, allatostatin CC, RYamides, and natalisins. The information provided in this study will benefit future codling moth investigations using peptidoproteomics to determine peptide presence and functions.

Helicokinin alters ion transport in the secondary cell-containing region of the Malpighian tubule of the larval cabbage looper Trichoplusia ni

Excretion in insects is accomplished by the combined actions of the Malpighian tubules (MTs) and hindgut, which together form the functional kidney. MTs of many insect groups consist of principal cells (PC) and secondary cells (SC). In most insect groups SCs are reported to secrete ions from haemolymph into the tubule lumen. Paradoxically, SCs in the MTs of the lepidopteran cabbage looper T. ni are used to reabsorb Na⁺ and K⁺ back into haemolymph. The current study was designed to investigate the effects and mode of action of the lepidopteran kinin, Helicokinin (HK), on ion transport in the SC-containing region of MT of T. ni. We identified a HK receptor (HK-R) homologue in T. ni and detected its expression in the SC-containing region of the MTs. The mRNA abundance of hk-r altered in response to changes in dietary K⁺ and Na⁺ content. HK-R immunolocalized to both PCs and SCs. Ramsay assays of preparations of the isolated distal ileac plexus (DIP) indicated that [HK] = 10^-8 M: (i) decreased fluid secretion rate in unstimulated and serotonin-stimulated preparations, and (ii) increased [Na⁺]/[K⁺] ratio in the secreted fluid. Scanning ion-selective electrode technique measurements revealed that HK reduced: (i) K⁺ secretion by the PCs, and (ii) Na⁺ reabsorption by the SCs in intact tubules. In vitro incubation of the DIP with HK resulted in reduced mRNA abundance of hk-r as well as Na⁺/K⁺-ATPase subunit α (NKAα), Na⁺/K⁺/Cl^- co-transporter (nkcc), Na⁺/H⁺ exchangers (nhe) 7 and 8, and aquaporin (aqp) 1. Taken together, results of the current study suggest that HK is capable of altering fluid secretion rate and [Na⁺]/[K⁺] ratio of the fluid, and that HK targets both PCs and SCs in the DIP of T. ni.

Peptidergic control of the crop of the cabbage root fly, Delia radicum (L.) Diptera: Anthomyiidae): A role for myosuppressin

There is much interest in targeting neuropeptide signaling for the development of new and environmentally friendly insect control chemicals. In this study we have focused attention on the peptidergic control of the adult crop of Delia radicum (cabbage root fly), an important pest of brassicas in European agriculture. The dipteran crop is a muscular organ formed from the foregut of the digestive tract and plays a vital role in the processing of food in adult flies. We have shown using direct tissue profiling by MALDI-TOF mass spectrometry that the decapeptide myosuppressin (TDVDHVFLRFamide) is present in the crop nerve bundle and that application of this peptide to the crop potently inhibits the spontaneous contractions of the muscular lobes with an IC₅₀ of 4.4 × 10^-8 M. The delivery of myosuppressin either by oral administration or by injection had no significant detrimental effect on the adult fly. This failure to elicit a response is possibly due to the susceptibility of the peptide to degradative peptidases that cleave the parent peptide to inactive fragments. Indeed, we show that the crop of D. radicum is a source of neuropeptide-degrading endo- and amino-peptidases. In contrast, feeding benzethonium chloride, a non-peptide agonist of myosuppressin, reduced feeding rate and increased the rate of mortality of adult D. radicum. Current results are indicative of a key role for myosuppressin in the regulation of crop physiology and the results achieved during this project provide the basis for subsequent studies aimed at developing insecticidal molecules targeting the peptidergic control of feeding and food digestion in this pest species.

NeuroPIpred: a tool to predict, design and scan insect neuropeptides

Insect neuropeptides and their associated receptors have been one of the potential targets for the pest control. The present study describes in silico models developed using natural and modified insect neuropeptides for predicting and designing new neuropeptides. Amino acid composition analysis revealed the preference of residues C, D, E, F, G, N, S, and Y in insect neuropeptides The positional residue preference analysis show that in natural neuropeptides residues like A, N, F, D, P, S, and I are preferred at N terminus and residues like L, R, P, F, N, and G are preferred at C terminus. Prediction models were developed using input features like amino acid and dipeptide composition, binary profiles and implementing different machine learning techniques. Dipeptide composition based SVM model performed best among all the models. In case of NeuroPIpred_DS1, model achieved an accuracy of 86.50% accuracy and 0.73 MCC on training dataset and 83.71% accuracy and 0.67 MCC on validation dataset whereas in case of NeuroPIpred_DS2, model achieved 97.47% accuracy and 0.95 MCC on training dataset and 97.93% accuracy and 0.96 MCC on validation dataset. In order to assist researchers, we created standalone and user friendly web server NeuroPIpred, available at (https://webs.iiitd.edu.in/raghava/neuropipred.)

Sex-specific spatial and temporal gene expressions of Pheromone biosynthesis activating neuropeptide (PBAN) and binding proteins (PBP/OBP) in Spoladea recurvalis

Spoladea recurvalis is one of the most destructive insect pests of amaranth, a leafy vegetable in both Asia and Africa. The present study characterized the pheromone biosynthesis-activating neuropeptide (DH-PBAN) and pheromone/odorant binding proteins in S. recurvalis. The open reading frame of 600 base pairs encodes a 200-amino acid protein possessing five neuropeptide motifs (DH, PBAN, α-, β-, and γ- subesophageal ganglion neuropeptides) and shares a characteristic conserved C-terminal pentapeptide fragment FXPRL. The full-length genome of Spre-DH-PBAN was 4,295 bp in length and comprised of six exons interspersed by five introns. Sequence homology and phylogenetic analysis of Spre-DH-PBAN have high similarity to its homologs in Crambidae of Lepidopteran order. We quantitatively measured the relative expression level (qRT_PCR) of Spre-DH-PBAN gene, the binding proteins such as odorant binding proteins (OBPs) and pheromone binding protein (PBPs) at different developmental stages. The results confirmed their role in recognition and chemoreception of sex pheromone components, and they were distinct, tissue- and sex-specific. This is the first report on the molecular analysis of PBAN gene and binding proteins, which can improve the understanding of molecular mechanisms of growth, development, and reproductive behavior of S. recurvalis, and may become effective targets for controlling this insect.

Transcriptomic analysis of the Malpighian tubules of Trichoplusia ni: Clues to mechanisms for switching from ion secretion to ion reabsorption in the distal ileac plexus

Excretion of metabolic wastes and toxins in insect Malpighian tubules (MTs) is coupled to secretion of ions and fluid. Larval lepidopterans demonstrate a complex and regionalized MT morphology, and recent studies of larvae of the cabbage looper, Trichoplusia ni, have revealed several unusual aspects of ion transport in the MTs. Firstly, cations are reabsorbed via secondary cells (SCs) in T. ni, whereas in most insects SCs secrete ions. Secondly, SCs are coupled to neighbouring principal cells (PCs) via gap junctions to enable such ion reabsorption. Thirdly, PCs in the SC-containing distal ileac plexus (DIP) region of the tubule reverse from cation secretion to reabsorption in response to dietary ion loading. Lastly, antidiuresis is observed in response to a kinin neuropeptide, which targets both PCs and SCs, whereas in most insects kinins are diuretics that act exclusively via SCs. Recent studies have generated a basic model of ion transport in the DIP of the larval T. ni. RNAseq was used to elucidate previously uncharacterised aspects of ion transport and endocrine regulation in the DIP, with the aim of painting a composite picture of ion transport and identifying putative regulatory mechanisms of ion transport reversal in this tissue. Results indicated an overall expression of 9103 transcripts in the DIP, 993 and 382 of which were differentially expressed in the DIP of larvae fed high-K⁺ and high-Na⁺ diets respectively. Differentially expressed transcripts include ion-motive ATPases, ion channels and co-transporters, aquaporins, nutrient and xenobiotic transporters, cell adhesion and junction components, and endocrine receptors. Notably, several transcripts for voltage-gated ion channels and cell volume regulation-associated products were detected in the DIP and differentially expressed in larvae fed ion-rich diet. The study provides insights into the transport of solutes (sugars, amino acids, xenobiotics, phosphate and inorganic ions) by the DIP of lepidopterans. Our data suggest that this region of the MT in lepidopterans (as previously reported) transports cations, fluid, and xenobiotics/toxic metals. Besides this, the DIP expresses genes coding for the machinery involved in Na⁺- and H⁺-dependent reabsorption of solutes, chloride transport, and base recovery. Additionally, many of the transcripts expressed by the DIP a capacity of this region to respond to, process, and sometimes produce, neuropeptides, steroid hormones and neurotransmitters. Lastly, the DIP appears to possess an arsenal of septate junction components, differential expression of which may indicate junctional restructuring in the DIP of ion-loaded larvae.

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.

Members of the neuropeptide transcriptional network in Helicoverpa armigera and their expression in response to light stress

Neuropeptides and peptide hormones play central roles in the regulation of various types of insect physiology and behavior. Artificial light at night, a form of environmental stress, has recently been regarded as a source of light stress on nocturnal insects. Because related genomic information is not available, molecular biological studies on the response of neuropeptides in nocturnal insects to light stress are limited. Based on the de novo sequencing of the Helicoverpa armigera head transcriptome, we obtained 124,960 unigenes. Of these, the number of unigenes annotated as neuropeptides and peptide hormones, neurotransmitter precursor processing enzymes, and neurotransmitter receptors were 34, 17, and 58, respectively. Under light stress, there were sex-specific differences in gene expression measured by qRT-PCR. The IMFamide, leucokinin and sNPF genes were differentially expressed at the mRNA level in males but not in females in response to light stress. The results provide new insights on the diversity of the neuropeptide transcriptional network of H. armigera. In addition, some neuropeptides exhibited sex-specific differential expression in response to light stress. Taken collectively, these results not only expand the catalog of known insect neuropeptides but also provide a framework for future functional studies on the physiological roles they play in the light stress response behavior of nocturnal moths.

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

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

Neuropeptidomics of the Bed Bug Cimex lectularius

The bed bug Cimex lectularius is a globally distributed human ectoparasite with fascinating biology. It has recently acquired resistance against a broad range of insecticides, causing a worldwide increase in bed bug infestations. The recent annotation of the bed bug genome revealed a full complement of neuropeptide and neuropeptide receptor genes in this species. With regard to the biology of C. lectularius, neuropeptide signaling is especially interesting because it regulates feeding, diuresis, digestion, as well as reproduction and also provides potential new targets for chemical control. To identify which neuropeptides are translated from the genome-predicted genes, we performed a comprehensive peptidomic analysis of the central nervous system of the bed bug. We identified in total 144 different peptides from 29 precursors, of which at least 67 likely present bioactive mature neuropeptides. C. lectularius corazonin and myosuppressin are unique and deviate considerably from the canonical insect consensus sequences. Several identified neuropeptides likely act as hormones, as evidenced by the occurrence of respective mass signals and immunoreactivity in neurohemal structures. Our data provide the most comprehensive peptidome of a Heteropteran species so far and in comparison suggest that a hematophageous life style does not require qualitative adaptations of the insect peptidome.

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

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

Identification and expression profiling of pheromone biosynthesis activating neuropeptide in Chlumetia transversa (Walker)

Insect neuropeptides (NPs) in the pyrokinin/pheromone biosynthesis-activating neuropeptide (PBAN) family are actively involved in many essential endocrine functions. These peptides are potential targets in the search for novel insect control agents. This is the first report on the cloning and sequence determination of Chlumetia transversa (Walker) PBAN (Ct-PBAN) using rapid amplification of cDNA ends. The open reading frame of Ct-PBAN was 588bp in length and encoded 195 amino acids, which were assembled into five putative neuropeptides (diapause hormone homolog, α-neuropeptide, β-neuropeptide, PBAN, and γ-neuropeptide). These peptides were amidated at C-terminus and shared the conserved pentapeptide motif FXPR (or K) L. Moreover, Ct-PBAN had high homology to PBANs in Helicoverpa zea (84.1%), Helicoverpa armigera (83.5%), Helicoverpa assulta (83%), and Heliothis virescens (82.6%). Phylogenetic analysis showed that Ct-PBAN was closely related to its orthologs in the family Noctuidae. In addition, real-time quantitative polymerase chain reaction assays showed that the expression of Ct-PBAN peaked in the female head and was also detected at high levels in 1-d-old adults. These results suggested that Ct-PBAN is associated with sex pheromone biosynthesis in female C. transversa and could be used for developing C. transversa control systems based on molecular techniques.

Characterization of a neuropeptide F receptor in the tsetse fly, Glossina morsitans morsitans

Neuropeptides related to mammalian neuropeptide Y (NPY) and insect neuropeptide F (NPF) are conserved throughout Metazoa and intimately involved in a wide range of biological processes. In insects NPF is involved in regulating feeding, learning, stress and reproductive behavior. Here we identified and characterized an NPF receptor of the tsetse fly, Glossina morsitans morsitans, the sole transmitter of Trypanosoma parasites causing sleeping sickness. We isolated cDNA sequences encoding tsetse NPF (Glomo-NPF) and its receptor (Glomo-NPFR), and examined their spatial and temporal expression patterns using quantitative PCR. In tsetse flies, npfr transcripts are expressed throughout development and most abundantly in the central nervous system, whereas low expression is found in the flight muscles and posterior midgut. Expression of npf, by contrast, shows low transcript levels during development but is strongly expressed in the posterior midgut and brain of adult flies. Expression of Glomo-npf and its receptor in the brain and digestive system suggests that NPF may have conserved neuromodulatory or hormonal functions in tsetse flies, such as in the regulation of feeding behavior. Cell-based activity studies of the Glomo-NPFR showed that Glomo-NPF activates the receptor up to nanomolar concentrations. The molecular data of Glomo-NPF and Glomo-NPFR paves the way for further investigation of its functions in tsetse flies.

Draft Genome of the Scarab Beetle Oryctes borbonicus on La Réunion Island

Beetles represent the largest insect order and they display extreme morphological, ecological and behavioral diversity, which makes them ideal models for evolutionary studies. Here, we present the draft genome of the scarab beetle Oryctes borbonicus, which has a more basal phylogenetic position than the two previously sequenced pest species Tribolium castaneum and Dendroctonus ponderosae providing the potential for sequence polarization. Oryctes borbonicus is endemic to La Réunion, an island located in the Indian Ocean, and is the host of the nematode Pristionchus pacificus, a well-established model organism for integrative evolutionary biology. At 518 Mb, the O. borbonicus genome is substantially larger and encodes more genes than T. castaneum and D. ponderosae. We found that only 25% of the predicted genes of O. borbonicus are conserved as single copy genes across the nine investigated insect genomes, suggesting substantial gene turnover within insects. Even within beetles, up to 21% of genes are restricted to only one species, whereas most other genes have undergone lineage-specific duplications and losses. We illustrate lineage-specific duplications using detailed phylogenetic analysis of two gene families. This study serves as a reference point for insect/coleopteran genomics, although its original motivation was to find evidence for potential horizontal gene transfer (HGT) between O. borbonicus and P. pacificus. The latter was previously shown to be the recipient of multiple horizontally transferred genes including some genes from insect donors. However, our study failed to provide any clear evidence for additional HGTs between the two species.

Identification and expression profiles of neuropeptides and their G protein-coupled receptors in the rice stem borer Chilo suppressalis

In insects, neuropeptides play important roles in the regulation of multiple physiological processes by binding to their corresponding receptors, which are primarily G protein-coupled receptors (GPCRs). The genes encoding neuropeptides and their associated GPCRs in the rice stem borer Chilo suppressalis were identified by a transcriptomic analysis and were used to identify potential targets for the disruption of physiological processes and the protection of crops. Forty-three candidate genes were found to encode the neuropeptide precursors for all known insect neuropeptides except for arginine-vasopressin-like peptide (AVLP), CNMamide, neuropeptide-like precursors 2-4 (NPLP2-4), and proctolin. In addition, novel alternative splicing variants of three neuropeptide genes (allatostatin CC, CCHamide 1, and short neuropeptide F) are reported for the first time, and 51 putative neuropeptide GPCRs were identified. Phylogenetic analyses demonstrated that 44 of these GPCRs belong to the A-family (or rhodopsin-like), 5 belong to the B-family (or secretin-like), and 2 are leucine-rich repeat-containing GPCRs. These GPCRs and their likely ligands were also described. qRT-PCR analyses revealed the expression profiles of the neuropeptide precursors and GPCR genes in various tissues of C. suppressalis. Our study provides fundamental information that may further our understanding of neuropeptidergic signaling systems in Lepidoptera and aid in the design of peptidomimetics, pseudopeptides or small molecules capable of disrupting the physiological processes regulated by these signaling molecules and their receptors.

[des-Arg(1)]-Proctolin: A novel NEP-like enzyme inhibitor identified in Tityus serrulatus venom

The scorpion Tityus serrulatus venom comprises a complex mixture of molecules that paralyzes and kills preys, especially insects. However, venom components also interact with molecules in humans, causing clinic envenomation. This cross-interaction may result from homologous molecular targets in mammalians and insects, such as (NEP)-like enzymes. In face of these similarities, we searched for peptides in Tityus serrulatus venom using human NEP as a screening tool. We found a NEP-inhibiting peptide with the primary sequence YLPT, which is very similar to that of the insect neuropeptide proctolin (RYLPT). Thus, we named the new peptide [des-Arg(1)]-proctolin. Comparative NEP activity assays using natural substrates demonstrated that [des-Arg(1)]-proctolin has high specificity for NEP and better inhibitory activity than proctolin. To test the initial hypothesis that molecular homologies allow Tityus serrulatus venom to act on both mammal and insect targets, we investigated the presence of a NEP-like in cockroaches, the main scorpion prey, that could be likewise inhibited by [des-Arg(1)]-proctolin. Indeed, we detected a possible NEP-like in a homogenate of cockroach heads whose activity was blocked by thiorphan and also by [des-Arg(1)]-proctolin. Western blot analysis using a human NEP monoclonal antibody suggested a NEP-like enzyme in the homogenate of cockroach heads. Our study describes for the first time a proctolin-like peptide, named [des-Arg(1)]-proctolin, isolated from Tityus serrulatus venom. The tetrapeptide inhibits human NEP activity and a NEP-like activity in a cockroach head homogenate, thus it may play a role in human envenomation as well as in the paralysis and death of scorpion preys.

Characterization and pharmacological analysis of two adipokinetic hormone receptor variants of the tsetse fly, Glossina morsitans morsitans

Adipokinetic hormones (AKH) are well known regulators of energy metabolism in insects. These neuropeptides are produced in the corpora cardiaca and perform their hormonal function by interacting with specific G protein-coupled receptors (GPCRs) at the cell membranes of target tissues, mainly the fat body. Here, we investigated the sequences, spatial and temporal distributions, and pharmacology of AKH neuropeptides and receptors in the tsetse fly, Glossina morsitans morsitans. The open reading frames of two splice variants of the Glomo-akh receptor (Glomo-akhr) gene and of the AKH neuropeptide encoding genes, gmmhrth and gmmakh, were cloned. Both tsetse AKHR isoforms show strong sequence conservation when compared to other insect AKHRs. Glomo-AKH prepropeptides also have the typical architecture of AKH precursors. In an in vitro Ca(2+) mobilization assay, Glomo-AKH neuropeptides activated each receptor isoform up to nanomolar concentrations. We identified structural features of tsetse AKH neuropeptides essential for receptor activation in vitro. Gene expression profiles suggest a function for AKH signaling in regulating Glossina energy metabolism, where AKH peptides are released from the corpora cardiaca and activate receptors mainly expressed in the fat body. This analysis of the ligand-receptor coupling, expression, and pharmacology of the two Glomo-AKHR variants facilitates further elucidation of the function of AKH in G. m. morsitans.

Molecular and pharmacological characterization of the Chelicerata pyrokinin receptor from the southern cattle tick, Rhipicephalus (Boophilus) microplus

We identified the first pyrokinin receptor (Rhimi-PKR) in Chelicerata and analyzed structure-activity relationships of cognate ligand neuropeptides and their analogs. Based on comparative and phylogenetic analyses, this receptor, which we cloned from larvae of the cattle tick Rhipicephalus microplus (Acari: Ixodidae), is the ortholog of the insect pyrokinin (PK)/pheromone biosynthesis activating neuropeptide (PBAN)/diapause hormone (DH) neuropeptide family receptor. Rhimi-PKR functional analyses using calcium bioluminescence were performed with a developed stable recombinant CHO-K1 cell line. Rhimi-PKR was activated by four endogenous PKs from the Lyme disease vector, the tick Ixodes scapularis (EC50s range: 85.4 nM-546 nM), and weakly by another tick PRX-amide peptide, periviscerokinin (PVK) (EC50 = 24.5 μM). PK analogs with substitutions of leucine, isoleucine or valine at the C-terminus for three tick PK peptides, Ixosc-PK1, Ixosc-PK2, and Ixosc-PK3, retained their potency on Rhimi-PKR. Therefore, Rhimi-PKR is less selective and substantially more tolerant than insect PK receptors of C-terminal substitutions of leucine to isoleucine or valine, a key structural feature that serves to distinguish insect PK from PVK/CAP2b receptors. In females, ovary and synganglion had the highest Rhimi-PKR relative transcript abundance followed by the rectal sac, salivary glands, Malpighian tubules, and midgut. This is the first pharmacological analysis of a PK/PBAN/DH-like receptor from the Chelicerata, which will now permit the discovery of the endocrinological roles of this neuropeptide family in vectors of vertebrate pathogens.

Activation of BNGR-A24 by direct interaction with tachykinin-related peptides from the silkworm Bombyx mori leads to the Gq- and Gs-coupled signaling cascades

Tachykinins constitute one of the largest peptide families in the animal kingdom and exert their diverse actions via G protein-coupled receptors (GPCRs). In this study, the Bombyx tachykinin-related peptides (TKRPs) were identified as specific endogenous ligands for the Bombyx neuropeptide GPCR A24 (BNGR-A24) and thus designated BNGR-A24 as BmTKRPR. Using both mammalian cell line HEK293 and insect cell line Sf21, further characterization demonstrated that BmTKRPR was activated, thus resulting in intracellular accumulation of cAMP, Ca(2+) mobilization, and ERK1/2 phosphorylation in a Gs and Gq inhibitor-sensitive manner. Moreover, quantitative reverse transcriptase polymerase chain reaction analysis and dsRNA-mediated knockdown experiments suggested a possible role for BmTKRPR in the regulation of feeding and growth. Our findings enhance the understanding of the Bombyx TKRP system in the regulation of fundamental physiological processes.

In silico characterization of the peptidome of the sea louse Caligus rogercresseyi (Crustacea, Copepoda)

Copepods of the order Siphonostomatoida are a major concern for commercial aquaculture as many farmed fish serve as hosts for these parasitic crustaceans. Caligus rogercresseyi, a member of the Siphonostomatoida, is a significant problem for salmonid aquaculture in the Southern Hemisphere, and as such, a search for methods for controlling infestations of it is ongoing. One possibility for biological control of this and other copepod ectoparasites is endocrine manipulation. However, little is known about the native endocrine signaling systems in these animals. As part of an ongoing effort to characterize crustacean ectoparasite peptidergic systems, the publicly accessible C. rogercresseyi transcriptome shotgun assembly (TSA) was mined for peptide-encoding transcripts. Using the identified TSA sequences, precursor proteins were deduced and their mature peptides predicted. Thirty-three peptide-encoding transcripts were identified within the Caligus TSA dataset, with the structures of 131 distinct peptides characterized from the deduced pre/preprohormones. The predicted peptides included isoforms of allatostatin A, allatostatin B, bursicon α, bursicon β, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone, diuretic hormone 31, DXXRLamide, FLRFamide, FXGGXamide, GSEFLamide, insulin-like peptide (ILP), intocin, leucokinin, molt-inhibiting hormone, myosuppressin, neuroparsin, neuropeptide F (NPF), orcokinin and tachykinin-related peptide. The predicted ILPs are of particular note as they are the first members of this peptide family identified from a copepod. Similarly, the predicted complement of four distinct NPFs is larger than that known from other crustaceans. Taken collectively, these data greatly expand the known C. rogercresseyi peptidome and provide a foundation for initiating studies of peptidergic control in this species.

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.

Prediction of the first neuropeptides from a member of the Remipedia (Arthropoda, Crustacea)

The Remipedia is a small, recently described crustacean class that inhabits submerged marine/anchialine cave systems. Phylogenetic and morphological investigations support a sister group relationship between these animals and the hexapods. The recent deposition of numerous (>100,000) transcriptome shotgun assembly sequences for Speleonectes cf. tulumensis provides a unique resource to identify proteins of interest from a member of the Remipedia. Here, this dataset was mined for sequences encoding putative neuropeptide pre/preprohormones, with the mature peptides predicted from the deduced precursors using an established workflow. The structures of 40 mature peptides were obtained via this strategy, including members of 11 well-known arthropod peptide families (adipokinetic hormone/corazonin-like peptide [ACP], allatostatin A, allatostatin C, diuretic hormone 31, eclosion hormone, ion transport peptide/crustacean hyperglycemic hormone, neuropeptide F, proctolin, SIFamide, sulfakinin and tachykinin-related peptide); these are the only peptides thus far described from any member of the Remipedia. Comparison of the Speleonectes isoforms with those from other crustaceans and hexapods revealed the peptidome of this species to have characteristics of both subphyla (e.g. it possesses the stereotypical decapod crustacean SIFamide and tachykinin-related peptide isoforms, while simultaneously being the only crustacean with an insect AKC). Moreover, BLAST searches in which the deduced Speleonectes precursors were compared to the pancrustacean protein database most frequently returned insect homologs as the closest matches. The peptidomic analyses presented here are consistent with the hypothesized phylogenetic position of the Remipedia within the Pancrustacea, and serve as a foundation from which to launch future investigations of peptidergic signaling in remipedes.

Prediction of the peptidomes of Tigriopus californicus and Lepeophtheirus salmonis (Copepoda, Crustacea)

Transcriptome mining is a powerful method for crustacean peptide discovery, especially when large sequence datasets are available and an appropriate reference is extant. Recently, a 206,041-sequence transcriptome for the copepod Calanus finmarchicus was mined for peptide-encoding transcripts, with ones for 17 families/subfamilies identified. Here, the deduced Calanus pre/preprohormones were used as templates for peptide discovery in the copepods Tigriopus californicus and Lepeophtheirus salmonis; large transcriptome shotgun assembly datasets are publicly accessible for both species. Sixty-five Tigriopus and 17 Lepeophtheirus transcripts, encompassing 22 and 13 distinct peptide families/subfamilies, respectively, were identified, with the structures of 161 and 70 unique mature peptides predicted from the deduced precursors. The identified peptides included members of the allatostatin A, allatostatin C, bursicon α, bursicon β, CAPA/periviscerokinin/pyrokinin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, FLRFamide, leucokinin, myosuppressin, neuroparsin, neuropeptide F, orcokinin, and tachykinin-related peptide families, most of which possess novel structures, though isoforms from other copepods are known. Of particular note was the discovery of novel isoforms of adipokinetic hormone-corazonin-like peptide, allatotropin, corazonin, eclosion hormone and intocin, peptide families previously unidentified in copepods. In addition, Tigriopus precursors for two previously unknown peptide groups were discovered, one encoding GSEFLamides and the other DXXRLamides; precursors for the novel FXGGXamide family were identified from both Tigriopus and Lepeophtheirus. These data not only greatly expand the catalog of known copepod peptides, but also provide strong foundations for future functional studies of peptidergic signaling in members of this ecologically important crustacean subclass.

Neuropeptidergic regulation of reproduction in insects

Successful animal reproduction depends on multiple physiological and behavioral processes that take place in a timely and orderly manner in both mating partners. It is not only necessary that all relevant processes are well coordinated, they also need to be adjusted to external factors of abiotic and biotic nature (e.g. population density, mating partner availability). Therefore, it is not surprising that several hormonal factors play a crucial role in the regulation of animal reproductive physiology. In insects (the largest class of animals on planet Earth), lipophilic hormones, such as ecdysteroids and juvenile hormones, as well as several neuropeptides take part in this complex regulation. While some peptides can affect reproduction via an indirect action (e.g. by influencing secretion of juvenile hormone), others exert their regulatory activity by directly targeting the reproductive system. In addition to insect peptides with proven activities, several others were suggested to also play a role in the regulation of reproductive physiology. Because of the long evolutionary history of many insect orders, it is not always clear to what extent functional data obtained in a given species can be extrapolated to other insect taxa. In this paper, we will review the current knowledge concerning the neuropeptidergic regulation of insect reproduction and situate it in a more general physiological context.

Novel adipokinetic hormones in the kissing bugs Rhodnius prolixus, Triatoma infestans, Dipetalogaster maxima and Panstrongylus megistus

Peptides of the adipokinetic hormone (AKH)/red pigment-concentrating hormone (RPCH) family were isolated and sequenced from the retrocerebral corpora cardiaca of four kissing bugs which are all vectors of the protozoan Trypanosoma cruzi responsible for Chagas' disease. The sequence of three novel AKHs were deduced from the multiple MS(N) electrospray mass data: the octapeptide pGlu-Leu-Thr-Phe-Ser-Thr-Asp-Trp amide (denoted Rhopr-AKH) in Rhodnius prolixus and Panstrongylus megistus, the nonapeptide pGlu-Leu-Thr-Phe-Thr-Pro-Asn-Trp-Gly amide (denoted Triin-AKH) in Triatoma infestans and the decapeptide pGlu-Leu-Thr-Phe-Ser-Asp-Gly-Trp-Gly-Asn amide (denoted Dipma-AKH) in Dipetalogaster maxima. The sequences were confirmed by identical behavior of natural and synthetic forms in reversed-phase HPLC and by CID-MS mass spectra. Conspecific injections of a dose of 10 pmol of the respective synthetic peptides resulted in a small but significant increase of the lipid concentration in the hemolymph. These experiments suggest that AKHs in kissing bugs act to regulate lipid metabolism, possibly during dispersal flights which is one of the mechanisms whereby the insects reach new outbreak areas.

Identification, spatial expression analysis and functional characterization of a pyrokinin-1 receptor in the Chagas' disease vector, Rhodnius prolixus

The capability or capa gene, encodes a pyrokinin-related peptide (known as pyrokinin-1, PK1) that contains the consensus carboxy-terminal sequence of WFGPRL-NH(2). Although the CAPA precursor polypeptide in Rhodnius prolixus yields the anti-diuretic hormone, RhoprCAPA-α2, no function has yet been elucidated for the pyrokinin-1 peptide, RhoprCAPA-αPK1. In order to elucidate the possible physiological roles of the PK1-related peptides in R. prolixus, we have isolated and functionally characterized the PK1 receptor, RhoprPK1-R. Additionally, we have determined a set of three optimal reference genes to utilize for normalization of data obtained when carrying out spatial expression analyses via quantitative reverse transcriptase PCR (RT-qPCR) in various tissues of fifth instar R. prolixus. The RhoprPK1-R expression profile differs strikingly from the receptor for the anti-diuretic hormone RhoprCAPA-α2, which is localized mainly to gut epithelial tissues. Instead, RhoprPK1-R expression in fifth instar stage insects was identified in tissues that are not involved in osmotic and ionic balance, including the prothoracic glands, male reproductive tissues and a pooled sample composed of fat body, dorsal vessel, abdominal nerves and female reproductive tissues. Thus, this research establishes novel possibilities for the physiological roles of the pyrokinin-related peptides in this medically relevant disease vector.

Peptidomics of the agriculturally damaging larval stage of the cabbage root fly Delia radicum (Diptera: Anthomyiidae)

The larvae of the cabbage root fly induce serious damage to cultivated crops of the family Brassicaceae. We here report the biochemical characterisation of neuropeptides from the central nervous system and neurohemal organs, as well as regulatory peptides from enteroendocrine midgut cells of the cabbage maggot. By LC-MALDI-TOF/TOF and chemical labelling with 4-sulfophenyl isothiocyanate, 38 peptides could be identified, representing major insect peptide families: allatostatin A, allatostatin C, FMRFamide-like peptides, kinin, CAPA peptides, pyrokinins, sNPF, myosuppressin, corazonin, SIFamide, sulfakinins, tachykinins, NPLP1-peptides, adipokinetic hormone and CCHamide 1. We also report a new peptide (Yamide) which appears to be homolog to an amidated eclosion hormone-associated peptide in several Drosophila species. Immunocytochemical characterisation of the distribution of several classes of peptide-immunoreactive neurons and enteroendocrine cells shows a very similar but not identical peptide distribution to Drosophila. Since peptides regulate many vital physiological and behavioural processes such as moulting or feeding, our data may initiate the pharmacological testing and development of new specific peptide-based protection methods against the cabbage root fly and its larva.

OKB, a novel family of brain-gut neuropeptides from insects

In insects, neuropeptides play a central role in the control of most physiological processes. The knowledge and characterization of new neuropeptide families, is of interest on the fields of Genetics, Genomics, Neurobiology, Endocrinology and Evolution. This knowledge also provides the tools for the design of peptidomimetics, pseudopeptides or small molecules, capable of disrupting the physiological processes regulated by the signaling molecules and their receptors. This is a promising target for a novel generation of insecticides. Using database searches, mass spectrometry and RACE-PCR, we identified a neuropeptide precursor transcript encoding a new family of insect neuropeptides in the hemipteran Rhodnius prolixus. We named this precursor Orcokinin B, because is originated by the alternative splicing of the Orcokinin gen. EST and genomic data suggests that Orcokinin B is expressed in the nervous system and gut from several insect species, with the exception of Drosophila sp. (Diptera) and Acyirthosiphon pisum (Hemiptera). Mass spectrometry and RT-PCR confirmed the expression of Orcokinin B in brain and anterior midgut of R. prolixus. Furthermore, we identified orthologues of this new family of peptides in genomic and EST databases from Arachnids and Crustaceans.

Structure-activity studies of Drosophila adipokinetic hormone (AKH) by a cellular expression system of dipteran AKH receptors

Structure-activity studies for the adipokinetic hormone receptor of insects were for the first time performed in a cellular expression system. A series of single amino acid replacement analogues for the endogenous adipokinetic hormone of Drosophila melanogaster (pGlu-Leu-Thr-Phe-Ser-Pro-Asp-Trp-NH(2)) were screened for activity with a bioluminescence cellular assay, expressing the G-protein coupled receptor. For this series of peptide analogues, one amino acid of the N-terminal tetrapeptide was successively replaced by alanine, while those of the C-terminal tetrapeptide were successively substituted by glycine; other modifications included the blocked N- and C-termini that were replaced by an acetylated alanine and a hydroxyl group, respectively. The analogue series was tested on the AKH receptors of two dipteran species, D. melanogaster and Anopheles gambiae. The blocked termini of the AKH peptide probably play a minor role in receptor interaction and activation, but are considered functionally important elements to protect the peptide against exopeptidases. In contrast, the amino acids at positions 2, 3, 4 and 5 from the N-terminus all seem to be crucial for receptor activation. This can be explained by the potential presence of a β-strand in this part of the peptide that interacts with the receptor. The inferred β-strand is probably followed by a β-turn in which the amino acids at positions 5-8 are involved. In this β-turn, the residues at positions 6 and 8 seem to be essential, as their substitutions induce only a very low degree of receptor activation. Replacement of Asp(7), by contrast, does not influence receptor activation at all. This implies that its side chain is folded inside the β-turn so that no interaction with the receptor occurs.

Investigation of the potential involvement of eicosanoid metabolites in anti-diuretic hormone signaling in Rhodnius prolixus

The use of naturally occurring plant-derived compounds for controlling insect pests remains an attractive alternative to potentially dangerous synthetic chemical compounds. One prospective plant-based compound, isoforms of the so-called jack bean urease (JBU) from the jack bean, Canavalia ensiformis, as well a derived peptide, Jaburetox-2Ec, have insecticidal effects on an array of insect species. In the Chagas' disease vector, Rhodnius prolixus, some of the physiological effects attributed to these urease isoforms include inhibition of serotonin (5-HT)-stimulated fluid secretion by the Malpighian tubules (MTs). Here, we investigated whether the effects of these exogenous urease isoforms were targeting the neuroendocrine network involved in the anti-diuretic hormone (RhoprCAPA-2) signaling cascade. We show that pharmacological agents known to interfere with eicosanoid metabolite biosynthesis do not affect RhoprCAPA-2 inhibition of 5-HT-stimulated fluid secretion by MTs. In addition, we demonstrate that RhoprCAPA-2 inhibition of MTs is independent of extracellular or intracellular calcium. Using a heterologous system for analysis of receptor activation, we show that neither JBU nor Jaburetox-2Ec are agonists of the anti-diuretic hormone receptor, RhoprCAPAr1. Finally, activation of the receptor using sub-maximal doses of the natural ligand, RhoprCAPA-2, was not influenced by the presence of either JBU or Jaburetox-2Ec indicating that the urease isoforms do not compete with RhoprCAPA-2 for binding and activation of RhoprCAPAr1. Taken together, these results suggest that at least two distinct mechanisms leading to inhibition of fluid secretion by MTs exist in R. prolixus and, unlike the urease-related effects, the eicosanoid metabolite pathway is not involved in RhoprCAPA-2 mediated anti-diuresis.

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.

Dispersion of peptides in vegetable oil as a simple slow release formula for both injection and oral uptake in insects: a case study with [His7]-corazonin in an albino Locusta migratoria deficient in corazonin

Upon realizing that for drug delivery in the body, lipidization is a technique used in the pharmaceutical industry, we took in consideration that corazonin melanizes the cuticle of albino Locusta migratoria only when injected in an emulsion in oil, not when applied in a watery solution. In this study, we investigate the possibility for oral uptake of corazonin dispersed in oil, and validated the activity by a melanization assay. Not only was it active, it also induced red cuticular coloration in some animals, and it was also unexpectedly lethal for nymphs, but not for adults. These results necessitate the revision of the potential of (some) peptides for insect control. Also, they suggest practical recommendations for the application of other peptides in physiological assays where oil could be used as a simple slow release formula.

Oral activity of FMRFamide-related peptides on the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) and degradation by enzymes from the aphid gut

Insect myosuppressins and myosuppressin analogues were tested for oral toxicity against the pea aphid Acyrthosiphon pisum (Harris) by incorporation into an artificial diet. Acyrthosiphon pisum myosuppressin (Acypi-MS) and leucomyosuppressin (LMS) had significant dose-dependent effects (0.1-0.5μg peptide/μl diet) on feeding suppression, mortality, reduced growth and fecundity compared with control insects, but Acypi-MS was more potent than LMS. One hundred percent of aphids had died after 10days of feeding on 0.5μg Acypi-MS/μl diet whereas 40% of aphids feeding on 0.5μg LMS/μl diet were still alive after 13days. Myosuppressins were degraded by aphid gut enzymes; degradation was most likely due to a carboxypeptidase-like protease, an aminopeptidase and a cathepsin L cysteine protease. The estimated half-life of Acypi-MS in a gut extract was 30min, whereas LMS was degraded more slowly (t½=54min). No toxicity was observed when the analogues δR(9) LMS and citrolline(9) Acypi-MS or FMRFamide were fed to the pea aphid. These findings not only help to better understand the biological effects of myosuppressins in aphids but also demonstrate the potential use of myosuppressins in a strategy to control aphid pests.