From the Genome to the Proteome: Uncovering Peptides in the Apis Brain

Serine phosphorylation of CAPA pyrokinin in cockroaches-a taxon-specific posttranslational modification

In insects, posttranslational modifications of neuropeptides are largely restricted to C- and N-terminal amino acids. The most common modifications, N-terminal pyroglutamate formation and C-terminal α-amidation, may prevent a fast degradation of these messenger molecules. This is particularly important for peptide hormones. Other common posttranslational modifications of proteins such as glycosylation and phosphorylation seem to be very rare in insect neuropeptides. To check this assumption, we used a computer algorithm to search an extensive data set of MALDI-TOF mass spectra from cockroach tissues for ion signal patterns indicating peptide phosphorylation. The results verify that phosphorylation is indeed very rare. However, a candidate was found and experimentally verified as phosphorylated CAPA pyrokinin (GGGGpSGETSGMWFGPRL-NH2) in the cockroach Lamproblatta albipalpus (Blattidae, Lamproblattinae). Tandem mass spectrometry revealed the phosphorylation site as Ser(5). Phosphorylated CAPA pyrokinin was then also detected in most other cockroach lineages (e.g. Blaberidae, Polyphagidae) but not in closely related blattid species such as Periplaneta americana. This is remarkable since the sequence of CAPA pyrokinin is identical in Lamproblatta and Periplaneta. A consensus sequence of CAPA pyrokinins of cockroaches revealed a conserved motif that suggests phosphorylation by a Four-jointed/FAM20C related kinase.

Brain proteomics of Anopheles gambiae

Anopheles gambiae has a well-adapted system for host localization, feeding, and mating behavior, which are all governed by neuronal processes in the brain. However, there are no published reports characterizing the brain proteome to elucidate neuronal signaling mechanisms in the vector. To this end, a large-scale mapping of the brain proteome of An. gambiae was carried out using high resolution tandem mass spectrometry, revealing a repertoire of >1800 proteins, of which 15% could not be assigned any function. A large proportion of the identified proteins were predicted to be involved in diverse biological processes including metabolism, transport, protein synthesis, and olfaction. This study also led to the identification of 10 GPCR classes of proteins, which could govern sensory pathways in mosquitoes. Proteins involved in metabolic and neural processes, chromatin modeling, and synaptic vesicle transport associated with neuronal transmission were predominantly expressed in the brain. Proteogenomic analysis expanded our findings with the identification of 15 novel genes and 71 cases of gene refinements, a subset of which were validated by RT-PCR and sequencing. Overall, our study offers valuable insights into the brain physiology of the vector that could possibly open avenues for intervention strategies for malaria in the future.

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

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

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.

Analysis of the central nervous system transcriptome of the eastern rock lobster Sagmariasus verreauxi reveals its putative neuropeptidome

Neuropeptides have been discovered in many arthropod species including crustaceans. The nature of their biological function is well studied and varies from behavior modulation to physiological regulation of complex biochemical processes such as metabolism, molt and reproduction. Due to their key role in these fundamental processes, neuropeptides are often targeted for modulating these processes to align with market demands in commercially important species. We generated a comprehensive transcriptome of the eyestalk and brain of one of the few commercially important spiny lobster species in the southern Hemisphere, the Eastern rock lobster Sagmariasus verreauxi and mined it for novel neuropeptide and protein hormone-encoding transcripts. We then characterized the predicted mature hormones to verify their validity based on conserved motifs and features known from previously reported hormones. Overall, 37 transcripts which are predicted to encode mature full-length/partial peptides/proteins were identified, representing 21 peptide/protein families/subfamilies. All transcripts had high similarity to hormones that were previously characterized in other decapod crustacean species or, where absent in crustaceans, in other arthropod species. These included, in addition to other proteins previously described in crustaceans, prohormone-3 and prohormone-4 which were previously identified only in insects. A homolog of the crustacean female sex hormone (CFSH), recently found to be female-specific in brachyuran crabs was found to have the same levels of expression in both male and female eyestalks, suggesting that the CFSH female specificity is not conserved throughout decapod crustaceans. Digital gene expression showed that 24 out of the 37 transcripts presented in this study have significant changes in expression between eyestalk and brain. In some cases a trend of difference between males and females could be seen. Taken together, this study provides a comprehensive neuropeptidome of a commercially important crustacean species with novel peptides and protein hormones identified for the first time in decapods.

NeuroPID: a classifier of neuropeptide precursors

Neuropeptides (NPs) are short secreted peptides produced in neurons. NPs act by activating signaling cascades governing broad functions such as metabolism, sensation and behavior throughout the animal kingdom. NPs are the products of multistep processing of longer proteins, the NP precursors (NPPs). We present NeuroPID (Neuropeptide Precursor Identifier), an online machine-learning tool that identifies metazoan NPPs. NeuroPID was trained on 1418 NPPs annotated as such by UniProtKB. A large number of sequence-based features were extracted for each sequence with the goal of capturing the biophysical and informational-statistical properties that distinguish NPPs from other proteins. Training several machine-learning models, including support vector machines and ensemble decision trees, led to high accuracy (89–94%) and precision (90–93%) in cross-validation tests. For inputs of thousands of unseen sequences, the tool provides a ranked list of high quality predictions based on the results of four machine-learning classifiers. The output reveals many uncharacterized NPPs and secreted cell modulators that are rich in potential cleavage sites. NeuroPID is a discovery and a prediction tool that can be used to identify NPPs from unannotated transcriptomes and mass spectrometry experiments. NeuroPID predicted sequences are attractive targets for investigating behavior, physiology and cell modulation. The NeuroPID web tool is available at http:// neuropid.cs.huji.ac.il.

Identification and expression of capa gene in the fire ant, Solenopsis invicta

Recent genome analyses suggested the absence of a number of neuropeptide genes in ants. One of the apparently missing genes was the capa gene. Capa gene expression in insects is typically associated with the neuroendocrine system of abdominal ganglia; mature CAPA peptides are known to regulate diuresis and visceral muscle contraction. The apparent absence of the capa gene raised questions about possible compensation of these functions. In this study, we re-examined this controversial issue and searched for a potentially unrecognized capa gene in the fire ant, Solenopsis invicta. We employed a combination of data mining and a traditional PCR-based strategy using degenerate primers designed from conserved amino acid sequences of insect capa genes. Our findings demonstrate that ants possess and express a capa gene. As shown by MALDI-TOF mass spectrometry, processed products of the S. invicta capa gene include three CAPA periviscerokinins and low amounts of a pyrokinin which does not have the C-terminal WFGPRLa motif typical of CAPA pyrokinins in other insects. The capa gene was found with two alternative transcripts in the CNS. Within the ventral nerve cord, two capa neurons were immunostained in abdominal neuromeres 2–5, respectively, and projected into ventrally located abdominal perisympathetic organs (PSOs), which are the major hormone release sites of abdominal ganglia. The ventral location of these PSOs is a characteristic feature and was also found in another ant, Atta sexdens.

Molecular cloning and functional characterization of the diapause hormone receptor in the corn earworm Helicoverpa zea

The diapause hormone (DH) in the heliothine moth has shown its activity in termination of pupal diapause, while the orthology in the silkworm is known to induce embryonic diapause. In the current study, we cloned the diapause hormone receptor from the corn earworm Helicoverpa zea (HzDHr) and tested its ligand specificities in a heterologous reporter system. HzDHr was expressed in Chinese Hamster Ovary (CHO) cells, which were co-transfected with the aequorin reporter, and was used to measure the ligand activities. A total of 68 chemicals, including natural DH analogs and structurally similar peptide mimetics, were tested for agonistic and antagonistic activities. Several peptide mimetics with a 2-amino-7-bromofluorene-succinoyl (2Abf-Suc) N-terminal modification showed strong agonistic activities; these mimetics included 2Abf-Suc-F[dA]PRLamide, 2Abf-Suc-F[dR]PRLamide, 2Abf-Suc-FKPRLamide and 2Abf-Suc-FGPRLamide. Antagonistic activity was found in the ecdysis triggering hormone in Drosophila melanogaster (FFLKITKNVPRLamide). Interestingly, HzDHr does not discriminate between DH (WFGPRLamide C-terminal motif) and another closely related endogenous peptide, pyrokinin 1 (FXPRXamide; a C-terminal motif that is separate from WFGPRLamide). We provide large-scale in vitro data that serve as a reference for the development of agonists and antagonists to disrupt the DH signaling pathway.

Transcriptome analysis of neuropeptides and G-protein coupled receptors (GPCRs) for neuropeptides in the brown planthopper Nilaparvata lugens

The genes encoding neuropeptides, neurohormones and their putative G-protein coupled receptors were identified in the brown planthopper (BPH), Nilaparvata lugens (Stål) by transcriptome analysis (RNA-seq). Forty-eight candidate genes were found to encode neuropeptides or peptide hormones. These include all known insect neuropeptides and neurohormones, with the exception of neuropeptide-like precursor 2 (NPLP2) and trissin. The gene coding for prothoracicotropic hormone (PTTH) was first identified from hemimetabolous insect. A total of 57 putative neuropeptide GPCR genes were identified and phylogenetic analysis showed most of them to be closely related to insect GPCRs. A notable finding was the occurrence of vertebrate hormone receptors, thyrotropin-releasing hormone receptor (TRHR)-like GPCR and parathyroid hormone receptor (PTHR)-like GPCRs. These results suggest that N. lugens possesses the most comprehensive neuropeptide system yet found in insects. Moreover, our findings demonstrate the power of RNA-seq as a tool for analyzing the neuropeptide-related genes in the absence of whole genome sequence information.

Identification of the short neuropeptide F precursor in the desert locust: evidence for an inhibitory role of sNPF in the control of feeding

Peptides of the short neuropeptide F (sNPF) family have been shown to modulate feeding behavior in a wide variety of insect species. While these peptides stimulate feeding and food-searching behavior in Drosophila melanogaster and Apis mellifera, an opposite effect has recently been demonstrated in the desert locust, Schistocerca gregaria. In this study, we elaborate on these observations with the identification of the nucleotide sequence encoding the Schgr-sNPF precursor and the study of its role in the regulation of locust feeding behavior. We confirm that both Schgr-sNPF-like peptides, previously identified in mass spectrometric studies, are genuine precursor-encoded peptides. RNA interference mediated silencing of the Schgr-sNPF precursor transcript generates novel evidence for an inhibitory role of Schgr-sNPF in the regulation of feeding in S. gregaria. Furthermore, we show that starvation reduces the Schgr-sNPF precursor transcript level in the optic lobes, the primary visual centers of the locust brain. Our data indicate that Schgr-sNPF exerts an inhibitory effect on food uptake in the desert locust, which contrasts with effects of sNPF reported for several other insect species.

Activation of Bombyx neuropeptide G protein-coupled receptor A4 via a Gαi-dependent signaling pathway by direct interaction with neuropeptide F from silkworm, Bombyx mori

Members of the mammalian neuropeptide Y (NPY) family serve as neurotransmitters and contribute to a diversity of physiological functions. Although neuropeptide F (NPF), the NPY-like orthologs from insects, have been identified, the NPF receptors and their signaling and physiological functions remain largely unknown. In this study, we established the stable and transient functional expression of a Bombyx orphan G protein-coupled receptor, BNGR-A4, in both mammalian HEK293 and insect SF21 cells. We identified Bombyx mori NPFs as specific endogenous ligands for the Bombyx Neuropeptide GPCR A4 (BNGR-A4) and, accordingly, named the receptor BomNPFR. Our results demonstrated that BomNPFR was activated by synthetic BomNPF1a and BomNPF1b at a high efficacy and by BomNPF2 at a low efficacy. This activation led to a decrease of forskolin or adipokinetic hormone peptide-stimulated adenylyl cyclase activity, an increase of intracellular Ca(2+), the activation of ERK1/2 signaling and receptor internalization. Moreover, a Rhodamine-labeled BomNPF1a peptide was found to bind specifically to BomNPFR. The results derived from quantitative RT-PCR analysis and dsRNA-mediated knockdown experiments demonstrated the possible role of BomNPFR in the regulation of food intake and growth. Our results provide the first in-depth information on BomNPFR-mediated signaling for the further elucidation of the BomNPF/BomNPFR system in the regulation of fundamental physiological processes.

Deorphanizing the human transmembrane genome: A landscape of uncharacterized membrane proteins

The sequencing of the human genome has fueled the last decade of work to functionally characterize genome content. An important subset of genes encodes membrane proteins, which are the targets of many drugs. They reside in lipid bilayers, restricting their endogenous activity to a relatively specialized biochemical environment. Without a reference phenotype, the application of systematic screens to profile candidate membrane proteins is not immediately possible. Bioinformatics has begun to show its effectiveness in focusing the functional characterization of orphan proteins of a particular functional class, such as channels or receptors. Here we discuss integration of experimental and bioinformatics approaches for characterizing the orphan membrane proteome. By analyzing the human genome, a landscape reference for the human transmembrane genome is provided.

A rapid MALDI-TOF mass spectrometry workflow for Drosophila melanogaster differential neuropeptidomics

BACKGROUND

Neuropeptides are a diverse category of signaling molecules in the nervous system regulating a variety of processes including food intake, social behavior, circadian rhythms, learning, and memory. Both the identification and functional characterization of specific neuropeptides are ongoing fields of research. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis of nervous tissues from a variety of organisms allows direct detection and identification of neuropeptides. Here, we demonstrate an analysis workflow that allows for the detection of differences in specific neuropeptides amongst a variety of neuropeptides being simultaneously measured. For sample preparation, we describe a straight-forward and rapid (minutes) method where individual adult Drosophila melanogaster brains are analyzed. Using a MATLAB-based data analysis workflow, also compatible with MALDI-TOF mass spectra obtained from other sample preparations and instrumentation, we demonstrate how changes in neuropeptides levels can be detected with this method.

RESULTS

Over fifty isotopically resolved ion signals in the peptide mass range are reproducibly observed across experiments. MALDI-TOF MS profile spectra were used to statistically identify distinct relative differences in organ-wide endogenous levels of detected neuropeptides between biological conditions. In particular, three distinct levels of a particular neuropeptide, pigment dispersing factor, were detected by comparing groups of preprocessed spectra obtained from individual brains across three different D. melanogaster strains, each of which express different amounts of this neuropeptide. Using the same sample preparation, MALDI-TOF/TOF tandem mass spectrometry confirmed that at least 14 ion signals observed across experiments are indeed neuropeptides. Among the identified neuropeptides were three products of the neuropeptide-like precursor 1 gene previously not identified in the literature.

CONCLUSIONS

Using MALDI-TOF MS and preprocessing/statistical analysis, changes in relative levels of a particular neuropeptide in D. melanogaster tissue can be statistically detected amongst a variety of neuropeptides. While the data analysis methods should be compatible with other sample preparations, the presented sample preparation method was sufficient to identify previously unconfirmed D. melanogaster neuropeptides.

NeuroPID: a predictor for identifying neuropeptide precursors from metazoan proteomes

MOTIVATION

The evolution of multicellular organisms is associated with increasing variability of molecules governing behavioral and physiological states. This is often achieved by neuropeptides (NPs) that are produced in neurons from a longer protein, named neuropeptide precursor (NPP). The maturation of NPs occurs through a sequence of proteolytic cleavages. The difficulty in identifying NPPs is a consequence of their diversity and the lack of applicable sequence similarity among the short functionally related NPs.

RESULTS

Herein, we describe Neuropeptide Precursor Identifier (NeuroPID), a machine learning scheme that predicts metazoan NPPs. NeuroPID was trained on hundreds of identified NPPs from the UniProtKB database. Some 600 features were extracted from the primary sequences and processed using support vector machines (SVM) and ensemble decision tree classifiers. These features combined biophysical, chemical and informational-statistical properties of NPs and NPPs. Other features were guided by the defining characteristics of the dibasic cleavage sites motif. NeuroPID reached 89-94% accuracy and 90-93% precision in cross-validation blind tests against known NPPs (with an emphasis on Chordata and Arthropoda). NeuroPID also identified NPP-like proteins from extensively studied model organisms as well as from poorly annotated proteomes. We then focused on the most significant sets of features that contribute to the success of the classifiers. We propose that NPPs are attractive targets for investigating and modulating behavior, metabolism and homeostasis and that a rich repertoire of NPs remains to be identified.

AVAILABILITY

NeuroPID source code is freely available at http://www.protonet.cs.huji.ac.il/neuropid

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.

Improving the identification rate of endogenous peptides using electron transfer dissociation and collision-induced dissociation

Tandem mass spectrometry (MS/MS) combined with bioinformatics tools have enabled fast and systematic protein identification based on peptide-to-spectrum matches. However, it remains challenging to obtain accurate identification of endogenous peptides, such as neuropeptides, peptide hormones, peptide pheromones, venom peptides, and antimicrobial peptides. Since these peptides are processed at sites that are difficult to predict reliably, the search of their MS/MS spectra in sequence databases needs to be done without any protease setting. In addition, many endogenous peptides carry various post-translational modifications, making it essential to take these into account in the database search. These characteristics of endogenous peptides result in a huge search space, frequently leading to poor confidence of the peptide characterizations in peptidomics studies. We have developed a new MS/MS spectrum search tool for highly accurate and confident identification of endogenous peptides by combining two different fragmentation methods. Our approach takes advantage of the combination of two independent fragmentation methods (collision-induced dissociation and electron transfer dissociation). Their peptide spectral matching is carried out separately in both methods, and the final score is built as a combination of the two separate scores. We demonstrate that this approach is very effective in discriminating correct peptide identifications from false hits. We applied this approach to a spectral data set of neuropeptides extracted from mouse pituitary tumor cells. Compared to conventional MS-based identification, i.e., using a single fragmentation method, our approach significantly increased the peptide identification rate. It proved also highly effective for scanning spectra against a very large search space, enabling more accurate genome-wide searches and searches including multiple potential post-translational modifications.

A multi-scale strategy for discovery of novel endogenous neuropeptides in the crustacean nervous system

The conventional mass spectrometry (MS)-based strategy is often inadequate for the comprehensive characterization of various size neuropeptides without the assistance of genomic information. This study evaluated sequence coverage of different size neuropeptides in two crustacean species, blue crab Callinectes sapidus and Jonah crab Cancer borealis using conventional MS methodologies and revealed limitations to mid- and large-size peptide analysis. Herein we attempt to establish a multi-scale strategy for simultaneous and confident sequence elucidation of various sizes of peptides in the crustacean nervous system. Nine novel neuropeptides spanning a wide range of molecular weights (0.9-8.2kDa) were fully sequenced from a major neuroendocrine organ, the sinus gland of the spiny lobster Panulirus interruptus. These novel neuropeptides included seven allatostatin (A- and B-type) peptides, one crustacean hyperglycemic hormone precursor-related peptide, and one crustacean hyperglycemic hormone. Highly accurate multi-scale characterization of a collection of varied size neuropeptides was achieved by integrating traditional data-dependent tandem MS, improved bottom-up sequencing, multiple fragmentation technique-enabled top-down sequencing, chemical derivatization, and in silico homology search. Collectively, the ability to characterize a neuropeptidome with vastly differing molecule sizes from a neural tissue extract could find great utility in unraveling complex signaling peptide mixtures employed by other biological systems.

BIOLOGICAL SIGNIFICANCE

Mass spectrometry (MS)-based neuropeptidomics aims to completely characterize the neuropeptides in a target organism as an important first step toward a better understanding of the structure and function of these complex signaling molecules. Although liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) with data-dependent acquisition is a powerful tool in peptidomic research, it often lacks the capability for de novo sequencing of mid-size and large peptides due to inefficient fragmentation of peptides larger than 4kDa. This study describes a multi-scale strategy for complete and confident sequence elucidation of various sizes of neuropeptides in the crustacean nervous system. The aim is to fill a technical gap where the conventional strategy is inefficient for comprehensive characterization of a complex neuropeptidome without assistance of genomic information. Nine novel neuropeptides in a wide range of molecular weights (0.9-8.2kDa) were fully sequenced from a major neuroendocrine organ of the spiny lobster, P. interruptus. The resulting molecular information extracted from such multi-scale peptidomic analysis will greatly accelerate functional studies of these novel neuropeptides.

Global view of the evolution and diversity of metazoan neuropeptide signaling

Neuropeptides are signaling molecules that commonly act via G protein-coupled receptors (GPCRs) and are generated in neurons by proneuropeptide (pNP) cleavage. Present in both cnidarians and bilaterians, neuropeptides represent an ancient and widespread mode of neuronal communication. Due to the inherent difficulties of analyzing highly diverse and repetitive pNPs, the relationships among different families are often elusive. Using similarity-based clustering and sensitive similarity searches, I obtained a global view of metazoan pNP diversity and evolution. Clustering revealed a large and diffuse network of sequences connected by significant sequence similarity encompassing one-quarter of all families. pNPs belonging to this cluster were also identified in the early-branching neuronless animal Trichoplax adhaerens. Clustering of neuropeptide GPCRs identified several orthology groups and allowed the reconstruction of the phyletic distribution of receptor families. GPCR phyletic distribution closely paralleled that of pNPs, indicating extensive conservation and long-term coevolution of receptor-ligand pairs. Receptor orthology and intermediate sequences also revealed the homology of pNPs so far considered unrelated, including allatotropin and orexin. These findings, together with the identification of deuterostome achatin and luqin and protostome opioid pNPs, extended the neuropeptide complement of the urbilaterian. Several pNPs were also identified from the hemichordate Saccoglossus kowalevskii and the cephalochordate Branchiostoma floridae, elucidating pNP evolution in deuterostomes. Receptor-ligand conservation also allowed ligand predictions for many uncharacterized GPCRs from nonmodel species. The reconstruction of the neuropeptide-signaling repertoire at deep nodes of the animal phylogeny allowed the formulation of a testable scenario of the evolution of animal neuroendocrine systems.

Profiling of diet-induced neuropeptide changes in rat brain by quantitative mass spectrometry

Neuropeptides are intercellular signal transmitters that play key roles in modulation of many behavioral and physiological processes. Neuropeptide signaling in several nuclei in the hypothalamus contributes to the control of food intake. Additionally, food intake regulation involves neuropeptide signaling in the reward circuitry in the striatum. Here, we analyze neuropeptides extracted from hypothalamus and striatum from rats in four differentially treated dietary groups including a high-fat/high-sucrose diet, mimicking diet-induced obesity. We employ high-resolution tandem mass spectrometry using higher-energy collision dissociation and electron transfer dissociation fragmentation for sensitive identification of more than 1700 unique endogenous peptides, including virtually all key neuropeptides known to be involved in food intake regulation. Label-free quantification of differential neuropeptide expression revealed comparable upregulation of orexigenic and anorexigenic neuropeptides in rats that were fed on a high-fat/high-sucrose diet.

Extending the honey bee venome with the antimicrobial peptide apidaecin and a protein resembling wasp antigen 5

Honey bee venom is a complex mixture of toxic proteins and peptides. In the present study we tried to extend our knowledge of the venom composition using two different approaches. First, worker venom was analysed by liquid chromatography-mass spectrometry and this revealed the antimicrobial peptide apidaecin for the first time in such samples. Its expression in the venom gland was confirmed by reverse transcription PCR and by a peptidomic analysis of the venom apparatus tissue. Second, genome mining revealed a list of proteins with resemblance to known insect allergens or venom toxins, one of which showed homology to proteins of the antigen 5 (Ag5)/Sol i 3 cluster. It was demonstrated that the honey bee Ag5-like gene is expressed by venom gland tissue of winter bees but not of summer bees. Besides this seasonal variation, it shows an interesting spatial expression pattern with additional production in the hypopharyngeal glands, the brains and the midgut. Finally, our immunoblot study revealed that both synthetic apidaecin and the Ag5-like recombinant from bacteria evoke no humoral activity in beekeepers. Also, no IgG4-based cross-reactivity was detected between the honey bee Ag5-like protein and its yellow jacket paralogue Ves v 5.

Functional characterization of the short neuropeptide F receptor in the desert locust, Schistocerca gregaria

Whereas short neuropeptide F (sNPF) has already been reported to stimulate feeding behaviour in a variety of insect species, the opposite effect was observed in the desert locust. In the present study, we cloned a G protein-coupled receptor (GPCR) cDNA from the desert locust, Schistocerca gregaria. Cell-based functional analysis of this receptor indicated that it is activated by both known isoforms of Schgr-sNPF in a concentration dependent manner, with EC₅₀ values in the nanomolar range. This Schgr-sNPF receptor constitutes the first functionally characterized peptide GPCR in locusts. The in vivo effects of the sNPF signalling pathway on the regulation of feeding in locusts were further studied by knocking down the newly identified Schgr-sNPF receptor by means of RNA interference, as well as by means of peptide injection studies. While injection of sNPF caused an inhibitory effect on food uptake in the desert locust, knocking down the corresponding peptide receptor resulted in an increase of total food uptake when compared to control animals. This is the first comprehensive study in which a clearly negative correlation is described between the sNPF signalling pathway and feeding, prompting a reconsideration of the diverse roles of sNPFs in the physiology of insects.

Phylogenetic investigation of Peptide hormone and growth factor receptors in five dipteran genomes

Peptide hormones and growth factors bind to membrane receptors and regulate a myriad of processes in insects and other metazoans. The evolutionary relationships among characterized and uncharacterized ("orphan") receptors can provide insights into receptor-ligand biology and narrow target choices in deorphanization studies. However, the large number and low sequence conservation of these receptors make evolutionary analysis difficult. Here, we characterized the G-protein-coupled receptors (GPCRs), receptor guanylyl cyclases (RGCs), and protein kinase receptors (PKRs) of mosquitoes and select other flies by interrogating the genomes of Aedes aegypti, Anopheles gambiae, Culex quinquefasciatus, Drosophila melanogaster, and D. mojavensis. Sequences were grouped by receptor type, clustered using the program CLANS, aligned using HMMR, and phylogenetic trees built using PhyML. Our results indicated that PKRs had relatively few orphan clades whereas GPCRs and RGCs had several. In addition, more than half of the Class B secretin-like GPCRs and RGCs remained uncharacterized. Additional studies revealed that Class B GPCRs exhibited more gain and loss events than other receptor types. Finally, using the neuropeptide F family of insect receptors and the neuropeptide Y family of vertebrate receptors, we also show that functional sites considered critical for ligand binding are conserved among distinct family members and between distantly related taxa. Overall, our results provide the first comprehensive analysis of peptide hormone and growth factor receptors for a major insect group.

Regulation of feeding by Neuropeptide F in the desert locust, Schistocerca gregaria

Our knowledge on the physiological function of the insect Neuropeptide F (NPF) mostly comes from studies in the fruit fly, Drosophila melanogaster, where NPF was shown to regulate diverse processes, such as feeding, learning and responding to stress. In the desert locust, Schistocerca gregaria, only a truncated form of the "full-length" NPF (the biologically active "trNPF") has been isolated. In this study, we investigated whether this peptide is involved in the regulation of feeding in this orthopteran species. In the S. gregaria EST-database, an NPF-precursor encoding transcript was found. Alignment with other insect NPF-precursors showed relatively highest sequence conservation within the trNPF region (and the flanking dibasic cleavage site), as compared to other regions of the NPF-precursor. Quantitative real-time RT-PCR revealed that the Schgr-NPF-precursor encoding transcript occurs throughout the central nervous system with relatively high transcript levels in the brain, optic lobes and suboesophageal ganglion. It was also detected at relatively high levels in the midgut, which suggests that the encoded peptide also functions in the digestive system. Moreover, Schgr-NPF-transcript levels were notably higher in starved animals than in animals fed ad libitum, while transcript levels were also shown to be regulated after the consumption of a meal. Injection of locust trNPF in adults stimulated food intake, while RNAi knockdown reduced food intake. Furthermore, injection of trNPF in adults stimulated weight increase, while RNAi knockdown reduced weight gain. This effect of trNPF on body weight gain may result from its stimulatory effect on food intake. Taken together, we provide clear evidence for an important role of trNPF in the regulation of feeding in the desert locust, S. gregaria.

First survey and functional annotation of prohormone and convertase genes in the pig

Background

The pig is a biomedical model to study human and livestock traits. Many of these traits are controlled by neuropeptides that result from the cleavage of prohormones by prohormone convertases. Only 45 prohormones have been confirmed in the pig. Sequence homology can be ineffective to annotate prohormone genes in sequenced species like the pig due to the multifactorial nature of the prohormone processing. The goal of this study is to undertake the first complete survey of prohormone and prohormone convertases genes in the pig genome. These genes were functionally annotated based on 35 gene expression microarray experiments. The cleavage sites of prohormone sequences into potentially active neuropeptides were predicted.

Results

We identified 95 unique prohormone genes, 2 alternative calcitonin-related sequences, 8 prohormone convertases and 1 cleavage facilitator in the pig genome 10.2 assembly and trace archives. Of these, 11 pig prohormone genes have not been reported in the UniProt, UniGene or Gene databases. These genes are intermedin, cortistatin, insulin-like 5, orexigenic neuropeptide QRFP, prokineticin 2, prolactin-releasing peptide, parathyroid hormone 2, urocortin, urocortin 2, urocortin 3, and urotensin 2-related peptide. In addition, a novel neuropeptide S was identified in the pig genome correcting the previously reported pig sequence that is identical to the rabbit sequence. Most differentially expressed prohormone genes were under-expressed in pigs experiencing immune challenge relative to the un-challenged controls, in non-pregnant relative to pregnant sows, in old relative to young embryos, and in non-neural relative to neural tissues. The cleavage prediction based on human sequences had the best performance with a correct classification rate of cleaved and non-cleaved sites of 92% suggesting that the processing of prohormones in pigs is similar to humans. The cleavage prediction models did not find conclusive evidence supporting the production of the bioactive neuropeptides urocortin 2, urocortin 3, torsin family 2 member A, tachykinin 4, islet amyloid polypeptide, and calcitonin receptor-stimulating peptide 2 in the pig.

Conclusions

The present genomic and functional characterization supports the use of the pig as an effective animal model to gain a deeper understanding of prohormones, prohormone convertases and neuropeptides in biomedical and agricultural research.

Urotensin II in invertebrates: from structure to function in Aplysia californica

Neuropeptides are ancient signaling molecules that are involved in many aspects of organism homeostasis and function. Urotensin II (UII), a peptide with a range of hormonal functions, previously has been reported exclusively in vertebrates. Here, we provide the first direct evidence that UII-like peptides are also present in an invertebrate, specifically, the marine mollusk Aplysia californica. The presence of UII in the central nervous system (CNS) of Aplysia implies a more ancient gene lineage than vertebrates. Using representational difference analysis, we identified an mRNA of a protein precursor that encodes a predicted neuropeptide, we named Aplysia urotensin II (apUII), with a sequence and structural similarity to vertebrate UII. With in-situ hybridization and immunohistochemistry, we mapped the expression of apUII mRNA and its prohormone in the CNS and localized apUII-like immunoreactivity to buccal sensory neurons and cerebral A-cluster neurons. Mass spectrometry performed on individual isolated neurons, and tandem mass spectrometry on fractionated peptide extracts, allowed us to define the posttranslational processing of the apUII neuropeptide precursor and confirm the highly conserved cyclic nature of the mature neuropeptide apUII. Electrophysiological analysis of the central effects of a synthetic apUII suggests it plays a role in satiety and/or aversive signaling in feeding behaviors. Finding the homologue of vertebrate UII in the numerically small CNS of an invertebrate animal model is important for gaining insights into the molecular mechanisms and pathways mediating the bioactivity of UII in the higher metazoan.

From genes to behavior: investigations of neurochemical signaling come of age for the model crustacean Daphnia pulex

The cladoceran crustacean Daphnia pulex has served as a standard organism for aquatic toxicity testing for decades. The model organism status of D. pulex rests largely on its remarkable ability to rapidly adapt morphologically, physiologically and behaviorally to a wide range of environmental challenges, as well as on its parthenogenetic reproduction and ease of laboratory culture. As in all multicellular organisms, neurochemical control systems are undoubtedly major contributors to the functional flexibility of Daphnia. Surprisingly, little work has focused on understanding its neurochemistry at any level. Recently, D. pulex has been the subject of extensive genome and transcriptome sequencing, and it is currently the only crustacean with a fully sequenced, publicly accessible genome. Although the molecular work was initiated for gene-based investigations of ecotoxicology and toxicogenomics, the data generated have allowed for investigations into numerous aspects of Daphnia biology, including its neurochemical signaling. This Commentary summarizes our knowledge of D. pulex neurochemistry obtained from recent genomic and transcriptomic studies, and places these data in context with other anatomical, biochemical and physiological experiments using D. pulex and its sister species Daphnia magna. Suggestions as to how the Daphnia molecular data may be useful for future investigations of crustacean neurochemical signaling are also provided.

Identification of Peptide lv, a novel putative neuropeptide that regulates the expression of L-type voltage-gated calcium channels in photoreceptors

Neuropeptides are small protein-like signaling molecules with diverse roles in regulating neural functions such as sleep/wake cycles, pain modulation, synaptic plasticity, and learning and memory. Numerous drugs designed to target neuropeptides, their receptors, or relevant pathways have been developed in the past few decades. Hence, the discovery and characterization of new neuropeptides and their functions have received considerable attention from scientific research. Computational bioinformatics coupled with functional assays are powerful tools to address the difficulties in discovering new bioactive peptides. In this study, a new bioinformatic strategy was designed to screen full length human and mouse cDNA databases to search for novel peptides. One was discovered and named peptide Lv because of its ability to enhance L-type voltage-gated calcium channel (L-VGCC) currents in retinal photoreceptors. Using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), peptide Lv was detected in the culture media, which indicated that it was secreted from 661W cells transfected with the gene. In vitro treatments with either glutathione S-transferase (GST) fusion peptide Lv or synthesized peptide Lv enhanced L-VGCC channel activities in cone photoreceptors. At the molecular level, peptide Lv stimulated cAMP production, enhanced phosphorylation of extracellular signal-regulated kinase (ERK), and increased the protein expression of L-VGCCα1 subunits in cone photoreceptors. Therefore, the biological activities of peptide Lv may be very important in the modulation of L-VGCC dependent neural plasticity.

Mathematical modelling of the MAP kinase pathway using proteomic datasets

The advances in proteomics technologies offer an unprecedented opportunity and valuable resources to understand how living organisms execute necessary functions at systems levels. However, little work has been done up to date to utilize the highly accurate spatio-temporal dynamic proteome data generated by phosphoprotemics for mathematical modeling of complex cell signaling pathways. This work proposed a novel computational framework to develop mathematical models based on proteomic datasets. Using the MAP kinase pathway as the test system, we developed a mathematical model including the cytosolic and nuclear subsystems; and applied the genetic algorithm to infer unknown model parameters. Robustness property of the mathematical model was used as a criterion to select the appropriate rate constants from the estimated candidates. Quantitative information regarding the absolute protein concentrations was used to refine the mathematical model. We have demonstrated that the incorporation of more experimental data could significantly enhance both the simulation accuracy and robustness property of the proposed model. In addition, we used the MAP kinase pathway inhibited by phosphatases with different concentrations to predict the signal output influenced by different cellular conditions. Our predictions are in good agreement with the experimental observations when the MAP kinase pathway was inhibited by phosphatase PP2A and MKP3. The successful application of the proposed modeling framework to the MAP kinase pathway suggests that our method is very promising for developing accurate mathematical models and yielding insights into the regulatory mechanisms of complex cell signaling pathways.

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.

Gustatory perception and fat body energy metabolism are jointly affected by vitellogenin and juvenile hormone in honey bees

Honey bees (Apis mellifera) provide a system for studying social and food-related behavior. A caste of workers performs age-related tasks: young bees (nurses) usually feed the brood and other adult bees inside the nest, while older bees (foragers) forage outside for pollen, a protein/lipid source, or nectar, a carbohydrate source. The workers' transition from nursing to foraging and their foraging preferences correlate with differences in gustatory perception, metabolic gene expression, and endocrine physiology including the endocrine factors vitellogenin (Vg) and juvenile hormone (JH). However, the understanding of connections among social behavior, energy metabolism, and endocrine factors is incomplete. We used RNA interference (RNAi) to perturb the gene network of Vg and JH to learn more about these connections through effects on gustation, gene transcripts, and physiology. The RNAi perturbation was achieved by single and double knockdown of the genes ultraspiracle (usp) and vg, which encode a putative JH receptor and Vg, respectively. The double knockdown enhanced gustatory perception and elevated hemolymph glucose, trehalose, and JH. We also observed transcriptional responses in insulin like peptide 1 (ilp1), the adipokinetic hormone receptor (AKHR), and cGMP-dependent protein kinase (PKG, or "foraging gene" Amfor). Our study demonstrates that the Vg-JH regulatory module controls changes in carbohydrate metabolism, but not lipid metabolism, when worker bees shift from nursing to foraging. The module is also placed upstream of ilp1, AKHR, and PKG for the first time. As insulin, adipokinetic hormone (AKH), and PKG pathways influence metabolism and gustation in many animals, we propose that honey bees have conserved pathways in carbohydrate metabolism and conserved connections between energy metabolism and gustatory perception. Thus, perhaps the bee can make general contributions to the understanding of food-related behavior and metabolic disorders.

Allatotropin, leucokinin and AKH in honey bees and other Hymenoptera

In the honey bee no allatotropin gene has been found, even though allatotropin stimulates the synthesis of juvenile hormone in this species. We report here that honey bees and other Hymenoptera do have a typical allatotropin gene, although the peptides predicted have a somewhat different structure from that of other insect allatotropins. Polyclonal antisera to honey bee allatotropin reacted with material in the neurohemal organs of the segmental nerves of abdominal ganglia. We were unable to find the allatotropin peptide using mass spectrometry in extracts from these tissues. Thus the expression of this gene in honey bees is less important than in other insect species. We also characterized the leucokinin gene which similarly appears to be very weakly expressed in worker honey bees. Unlike the allatotropin gene, which is conserved within Hymenoptera, the leucokinin gene is much more variable in structure and was not found in ants nor the parasitic wasp Nasonia vitripennis. The absence of significant expression of adipokinetic hormone (AKH) in the honey bee may be due to the existence of a second TATA box in the promotor region of the gene, which explains the production of an mRNA encoding a putative peptide precursor from which no AKH should be released. Such a second TATA box was not found in other Hymenoptera, and may therefore be specific for the two Apis species. It is suggested that functional disintegration of this important metabolic gene became possible in Apis because of the highly evolved social nature of the species.

Neuropeptides in insect mushroom bodies

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

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.

Insect omics research coming of age1This 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

As more and more insect genomes are fully sequenced and annotated, omics technologies, including transcriptomic, proteomic, peptidomics, and metobolomic profiling, as well as bioinformatics, can be used to exploit this huge amount of sequence information for the study of different biological aspects of insect model organisms. Omics experiments are an elegant way to deliver candidate genes, the function of which can be further explored by genetic tools for functional inactivation or overexpression of the genes of interest. Such tools include mainly RNA interference and are currently being developed in diverse insect species. In this manuscript, we have reviewed how omics technologies were integrated and applied in insect biology.

The Arginine Residue within the C-Terminal Active Core of Bombyx mori Pheromone Biosynthesis-Activating Neuropeptide is Essential for Receptor Binding and Activation

In most lepidopteran insects, the biosynthesis of sex pheromones is regulated by pheromone biosynthesis-activating neuropeptide (PBAN). Bombyx mori PBAN (BomPBAN) consists of 33 amino acid residues and contains a C-terminus FSPRLamide motif as the active core. Among neuropeptides containing the FXPRLamide motif, the arginine (Arg, R) residue at the second position from the C-terminus is highly conserved across several neuropeptides, which can be designated as RXamide peptides. The purpose of this study was to clarify the role of the Arg residue in the BomPBAN active core. We synthesized 10-residue peptides corresponding to the C-terminal part of BomPBAN with a series of replacements at the second position from the C-terminus, termed the C2 position, and measured their efficacy in stimulating Ca(2+) influx in insect cells expressing a fluorescent PBAN receptor chimera (PBANR-EGFP) using the fluorescent Ca(2+) indicator, Fura Red-AM. The PBAN analogs with the C2 position replaced with alanine (Ala, A), aspartic acid (Asp, D), serine (Ser, S), or l-2-aminooctanoic acid (Aoc) decreased PBAN-like activity. R(C2)A (SKTRYFSPALamide) and R(C2)D (SKTRYFSPDLamide) had the lowest activity and could not inhibit the activity of PBAN C10 (SKTRYFSPRLamide). We also prepared Rhodamine Red-labeled peptides of the PBAN analogs and examined their ability to bind PBANR. In contrast to Rhodamine Red-PBAN C10 at 100 nM, none of the synthetic analogs exhibited PBANR binding at the same concentration. Taken together, our results demonstrate that the C2 Arg residue in BomPBAN is essential for PBANR binding and activation.

Neuropeptides of the cotton fleahopper, Pseudatomoscelis seriatus (Reuter)

The cotton fleahopper, Pseudatomoscelis seriatus (Reuter), is an economically important pest of cotton, and increasing concerns over resistance, detrimental effects on beneficial insects and safety issues associated with traditional insecticide applications have led to an interest in research on novel, alternative strategies for control. One such approach requires a more basic understanding of the neurohormonal system that regulates important physiological properties of the fleahopper; e.g. the expression of specific messenger molecules such as neuropeptides. Therefore we performed a peptidomic study of neural tissues from the fleahopper which led to the first identification of the sequences of native peptide hormones. These peptide hormones include the following neuropeptides: corazonin, short neuropeptide F (sNPF), myosuppressin, CAPA-pyrokinin and CAPA-PVK peptides. The CAPA-pyrokinin, sNPF, and CAPA-PVK peptides represent novel sequences. A comparison of fleahopper neuropeptides with those of related heteropteran species indicates that they are quite different. The sNPF of P. seriatus shows, among others, a novel substitution of Leu with Phe within the C-terminal region; a modification that sets it apart from the known sNPFs of not only other Heteroptera but of other arthropod species as well. The identity of the neuropeptides native to the fleahopper can aid in the potential development of biostable, bioavailable mimetic agonists and antagonists capable of disrupting the physiological functions that these neuropeptides regulate.

The receptor guanylate cyclase Gyc76C and a peptide ligand, NPLP1-VQQ, modulate the innate immune IMD pathway in response to salt stress

Receptorguanylate cyclases (rGCs) modulate diverse physiological processes including mammalian cardiovascular function and insect eclosion. The Drosophila genome encodes several receptor and receptor-like GCs, but no ligand for any Drosophila rGC has yet been identified. By screening peptide libraries in Drosophila S2 cells, the Drosophila peptide NPLP1-VQQ (NLGALKSSPVHGVQQ) was shown to be a ligand for the rGC, Gyc76C (CG42636, previously CG8742, l(3)76BDl, DrGC-1). In the adult fly, expression of Gyc76C is highest in immune and stress-sensing epithelial tissues, including Malpighian tubules and midgut; and NPLP1-VQQ stimulates fluid transport and increases cGMP content in tubules. cGMP signaling is known to modulate the activity of the IMD innate immune pathway in tubules via activation and nuclear translocation of the NF-kB orthologue, Relish, resulting in increased anti-microbial peptide (AMP) gene expression; and so NPLP1-VQQ might act in immune/stress responses. Indeed, NPLP1-VQQ induces nuclear translocation of Relish in intact tubules and increases expression of the anti-microbial peptide gene, diptericin. Targeted Gyc76C RNAi to tubule principal cells inhibited both NPLP1-VQQ-induced Relish translocation and diptericin expression. Relish translocation and increased AMP gene expression also occurs in tubules in response to dietary salt stress. Gyc76C also modulates organismal survival to salt stress - ablation of Gyc76C expression in only tubule principal cells prevents Relish translocation, reduces diptericin expression, and reduces organismal survival in response to salt stress. Thus, the principal-cell localized NPLP1-VQQ/Gyc76C cGMP pathway acts to signal environmental (salt) stress to the whole organism.

CRF-like diuretic hormone negatively affects both feeding and reproduction in the desert locust, Schistocerca gregaria

Diuretic hormones (DH) related to the vertebrate Corticotropin Releasing Factor (CRF) have been identified in diverse insect species. In the migratory locust, Locusta migratoria, the CRF-like DH (CRF/DH) is localized in the same neurosecretory cells as the Ovary Maturating Parsin (OMP), a neurohormone that stimulates oocyte growth, vitellogenesis and hemolymph ecdysteroid levels in adult female locusts. In this study, we investigated whether CRF-like DH can influence feeding and reproduction in the desert locust, Schistocerca gregaria. We identified two highly similar S. gregaria CRF-like DH precursor cDNAs, each of which also encodes an OMP isoform. Alignment with other insect CRF-like DH precursors shows relatively high conservation of the CRF/DH sequence while the precursor region corresponding to OMP is not well conserved. Quantitative real-time RT-PCR revealed that the precursor transcripts mainly occur in the central nervous system and their highest expression level was observed in the brain. Injection of locust CRF/DH caused a significantly reduced food intake, while RNAi knockdown stimulated food intake. Therefore, our data indicate that CRF-like DH induces satiety. Furthermore, injection of CRF/DH in adult females retarded oocyte growth and caused lower ecdysteroid titers in hemolymph and ovaries, while RNAi knockdown resulted in opposite effects. The observed effects of CRF/DH may be part of a wider repertoire of neurohormonal activities, constituting an integrating control system that affects food intake and excretion, as well as anabolic processes like oocyte growth and ecdysteroidogenesis, following a meal. Our discussion about the functional relationship between CRF/DH and OMP led to the hypothesis that OMP may possibly act as a monitoring peptide that can elicit negative feedback effects.

A circadian neuropeptide PDF in the honeybee, Apis mellifera: cDNA cloning and expression of mRNA

Pigment-dispersing factor (PDF) is a pacemaker hormone regulating the locomotor rhythm in insects. In the present study, we cloned the cDNAs encoding the Apis PDF precursor protein, and found that there are at least seven different pdf mRNAs yielded by an alternative splicing site and five alternative polyadenylation sites in the 5'UTR and 3'UTR regions. The amino acid sequence of Apis PDF peptide has a characteristic novel amino acid residue, aspargine (Asn), at position 17. Quantitative real-time PCR of total and 5'UTR insertion-type pdf mRNAs revealed, for the first time, that the expression levels change in a circadian manner with a distinct trough at the beginning of night in LD conditions, and at the subjective night under DD conditions. In contrast, the expression level of 5'UTR deletion-type pdf mRNAs was about half of that of the insertion type, and the expression profile failed to show a circadian rhythm. As the expression profile of the total pdf mRNA exhibited a circadian rhythm, transcription regulated at the promoter region was supposed to be controlled by some of the clock components. Whole mount in situ hybridization revealed that 14 lateral neurons at the frontal margin of the optic lobe express these mRNA isoforms. PDF expressing cells examined with a newly produced antibody raised against Apis PDF were also found to have a dense supply of axon terminals in the optic lobes and the central brain.

Worker honeybee brain proteome

A large-scale mapping of the worker honeybee brain proteome was achieved by MudPIT. We identified 2742 proteins from forager and nurse honeybee brain samples; 17% of the total proteins were found to be differentially expressed by spectral count sampling statistics and a G-test. Sequences were compared with the EuKaryotic Orthologous Groups (KOG) catalog set using BLASTX and then categorized into the major KOG categories of most similar sequences. According to this categorization, nurse brain showed increased expression of proteins implicated in translation, ribosomal structure, and biogenesis (14.5%) compared with forager (1.8%). Experienced foragers overexpressed proteins involved in energy production and conversion, showing an extensive difference in this set of proteins (17%) in relation to the nurse subcaste (0.6%). Examples of proteins selectively expressed in each subcaste were analyzed. A comparison between these MudPIT experiments and previous 2-DE experiments revealed nine coincident proteins differentially expressed in both methodologies.

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.