Structural studies of Drosophila short neuropeptide F: Occurrence and receptor binding activity

Short neuropeptide F enhances the immune response in the hepatopancreas of mud crab (Scylla paramamosain)

Short neuropeptide F (sNPF), a highly conserved neuropeptide, displays pleiotropic functions on multiple aspects of physiological processes, such as feeding, metabolic stress, locomotion, circadian clock and reproduction. However, to date there has no any report on the possible immunoregulation of sNPF in crustaceans. In the present study, we found that the Sp-sNPF was mainly expressed in the nervous tissue in the mud crab Scylla paramamosain, while the sNPF receptor gene (Sp-sNPF-R) was expressed in a wide variety of tissues, including the hepatopancreas. In situ hybridization further showed that the Sp-sNPF-R positive signal mainly localized in the F-cells of the hepatopancreas. Moreover, the Sp-sNPF-R transcription could be significantly up-regulated after the challenge of bacteria-analog LPS or virus-analog Poly (I:C). Both in vitro and in vivo experiments showed that the synthetic sNPF peptide significantly increased the gene expressions of sNPF-R, nuclear factor-κB (NF-κB) signaling genes and antimicrobial peptides (AMPs) in the hepatopancreas. Simultaneously, the administration of sNPF peptide in vitro also increased the concentration of nitric oxide (NO) and the bacteriostasis of the culture medium of hepatopancreas. These results indicated that sNPF up-regulated hepatopancreas immune responses, which may bring new insight into the neuroendocrine-immune regulatory system in crustacean species, and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.

Optogenetic activation of short neuropeptide F (sNPF) neurons induces sleep in Drosophila melanogaster

Sleep abnormalities have widespread and costly public health consequences, yet we have only a rudimentary understanding of the events occurring at the cellular level in the brain that regulate sleep. Several key signaling molecules that regulate sleep across taxa come from the family of neuropeptide transmitters. For example, in Drosophila melanogaster, the neuropeptide Y (NPY)-related transmitter short neuropeptide F (sNPF) appears to promote sleep. In this study, we utilized optogenetic activation of neuronal populations expressing sNPF to determine the causal effects of precisely timed activity in these cells on sleep behavior. Combining sNPF-GAL4 and UAS-Chrimson transgenes allowed us to activate sNPF neurons using red light. We found that activating sNPF neurons for as little as 3 s at a time of day when most flies were awake caused a rapid transition to sleep that persisted for another 2+ hours following the stimulation. Changing the timing of red light stimulation to times of day when flies were already asleep caused the control flies to wake up (due to the pulse of light), but the flies in which sNPF neurons were activated stayed asleep through the light pulse, and then showed further increases in sleep at later points when they would have normally been waking up. Video recording of individual fly responses to short-term (0.5-20 s) activation of sNPF neurons demonstrated a clear light duration-dependent decrease in movement during the subsequent 4-min period. These results provide supportive evidence that sNPF-producing neurons promote long-lasting increases in sleep, and show for the first time that even brief periods of activation of these neurons can cause changes in behavior that persist after cessation of activation. We have also presented evidence that sNPF neuron activation produces a homeostatic sleep drive that can be dissipated at times long after the neurons were stimulated. Future studies will determine the specific roles of sub-populations of sNPF-producing neurons, and will also assess how sNPF neurons act in concert with other neuronal circuits to control sleep.

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

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

Regulation of Feeding and Metabolism by Neuropeptide F and Short Neuropeptide F in Invertebrates

Numerous neuropeptide systems have been implicated to coordinately control energy homeostasis, both centrally and peripherally. However, the vertebrate neuropeptide Y (NPY) system has emerged as the best described one regarding this biological process. The protostomian ortholog of NPY is neuropeptide F, characterized by an RXRF(Y)amide carboxyterminal motif. A second neuropeptide system is short NPF, characterized by an M/T/L/FRF(W)amide carboxyterminal motif. Although both short and long NPF neuropeptide systems display carboxyterminal sequence similarities, they are evolutionary distant and likely already arose as separate signaling systems in the common ancestor of deuterostomes and protostomes, indicating the functional importance of both. Both NPF and short-NPF systems seem to have roles in the coordination of feeding across bilaterian species, but during chordate evolution, the short NPF system appears to have been lost or evolved into the prolactin releasing peptide signaling system, which regulates feeding and has been suggested to be orthologous to sNPF. Here we review the roles of both NPF and sNPF systems in the regulation of feeding and metabolism in invertebrates.

Functional characterization of mosquito short neuropeptide F receptors

Mosquito blood feeding transiently inhibits sugar- and host seeking through neuropeptide signaling. Short neuropeptide F (sNPF) is one of the neuromodulators involved in this regulation. Here, we identified the genes for the sNPF precursor and the sNPF receptor in the southern house mosquito, Culex quinquefasciatus. Comparative analyses are made with the genes of the sNPF precursor and receptor from two other important vectors, Aedes aegypti and Anopheles coluzzii. We functionally characterized the receptors in all three species using endogenous neuropeptides, and quantified their transcript expression following a blood meal and a sugar meal. Our analysis reveals several Cx. quinquefasciatus-specific duplications of the sNPF-3 isoform on the sNPF precursor, which are not reflected in the precursors of the other two species. In contrast, the structure of the sNPF receptors is highly conserved within mosquitoes, and a putative ligand binding region is proposed and discussed. Reflecting the high structural conservation, the sNPF receptor sensitivity to endogenous sNPF isoforms is conserved across mosquito species. Using quantitative real time PCR, we demonstrate that transcript abundance of the sNPF receptor and precursor is regulated following feeding, only in Cx. quinquefasciatus. We discuss our findings in relation to previous work on sNPF signaling and its role in feeding regulation.

Bombyx neuropeptide G protein-coupled receptor A7 is the third cognate receptor for short neuropeptide F from silkworm

The short neuropeptide F (sNPF) neuropeptides, closely related to vertebrate neuropeptide Y (NPY), have been suggested to exert pleiotropic effects on many physiological processes in insects. In the silkworm (Bombyx mori) two orphan G protein-coupled receptors, Bombyx neuropeptide G protein-coupled receptor (BNGR) A10 and A11, have been identified as cognate receptors for sNPFs, but other sNPF receptors and their signaling mechanisms in B. mori remain unknown. Here, we cloned the full-length cDNA of the orphan receptor BNGR-A7 from the brain of B. mori larvae and identified it as a receptor for Bombyx sNPFs. Further characterization of signaling and internalization indicated that BNGR-A7, -A10, and -A11 are activated by direct interaction with synthetic Bombyx sNPF-1 and -3 peptides. This activation inhibited forskolin or adipokinetic hormone-induced adenylyl cyclase activity and intracellular Ca²⁺ mobilization via a G_i/o-dependent pathway. Upon activation by sNPFs, BNGR-A7, -A10, and -A11 evoked ERK1/2 phosphorylation and underwent internalization. On the basis of these findings, we designated the receptors BNGR-A7, -A10, and -A11 as Bommo-sNPFR-1, -2, and -3, respectively. Moreover, the results obtained with quantitative RT-PCR analysis revealed that the three Bombyx sNPF receptor subtypes exhibit differential spatial and temporal expression patterns, suggesting possible roles of sNPF signaling in the regulation of a wide range of biological processes. Our findings provide the first in-depth information on sNPF signaling for further elucidation of the roles of the Bombyx sNPF/sNPFR system in the regulation of physiological activities.

Drosophila neprilysins control insulin signaling and food intake via cleavage of regulatory peptides

Insulin and IGF signaling are critical to numerous developmental and physiological processes, with perturbations being pathognomonic of various diseases, including diabetes. Although the functional roles of the respective signaling pathways have been extensively studied, the control of insulin production and release is only partially understood. Herein, we show that in Drosophila expression of insulin-like peptides is regulated by neprilysin activity. Concomitant phenotypes of altered neprilysin expression included impaired food intake, reduced body size, and characteristic changes in the metabolite composition. Ectopic expression of a catalytically inactive mutant did not elicit any of the phenotypes, which confirms abnormal peptide hydrolysis as a causative factor. A screen for corresponding substrates of the neprilysin identified distinct peptides that regulate insulin-like peptide expression, feeding behavior, or both. The high functional conservation of neprilysins and their substrates renders the characterized principles applicable to numerous species, including higher eukaryotes and humans.

DOI:http://dx.doi.org/10.7554/eLife.19430.001

The hormone insulin and similar molecules called insulin-like peptides act as signals to control many processes in the body, including growth, stress responses and aging. Disrupting these signaling pathways can cause many diseases, with diabetes being the most common of these. Although the roles of the signaling pathways have been well studied, it is less clear how the body controls the production of insulin and insulin-like peptides.

Neprilysins are enzymes that can cut other proteins and peptides by a process known as hydrolysis. Their targets (known as “substrates”) include peptides that regulate a range of cell processes, and neprilysins have therefore been linked with many diseases. Fruit flies have at least five different neprilysin enzymes, but their substrates have not yet been identified. One of these, known as Nep4A, is produced in muscle tissue and appears to be important for muscles to work properly.

Hallier, Schiemann et al. reveal that Nep4A regulates the production of insulin-like peptides. The experiments used fruit fly larvae that had been genetically engineered so that the level of Nep4A could be altered in muscle tissue. Larvae with very high or very low levels of Nep4A eat less food, have smaller bodies and produce different amounts of insulin-like peptides compared to normal larvae.

Further experiments show that Nep4A can hydrolyze a number of peptides that regulate the production and the release of insulin-like peptides. This suggests that the enzymatic activity of neprilysins plays a direct role in controlling the production of insulin. The next challenge is to find out whether these findings apply to humans and other animals that also have neprilysins.

DOI:http://dx.doi.org/10.7554/eLife.19430.002

The red imported fire ant (Solenopsis invicta Buren) kept Y not F: predicted sNPY endogenous ligands deorphanize the short NPF (sNPF) receptor

Neuropeptides and their receptors play vital roles in controlling the physiology and behavior of animals. Short neuropeptide F (sNPF) signaling regulates several physiological processes in insects such as feeding, locomotion, circadian rhythm and reproduction, among others. Previously, the red imported fire ant (Solenopsis invicta) sNPF receptor (S. invicta sNPFR), a G protein-coupled receptor, was immunolocalized in queen and worker brain and queen ovaries. Differential distribution patterns of S. invicta sNPFR protein in fire ant worker brain were associated both with worker subcastes and with presence or absence of brood in the colony. However, the cognate ligand for this sNPFR has not been characterized and attempts to deorphanize the receptor with sNPF peptides from other insect species which ended in the canonical sequence LRLRFamide, failed. Receptor deorphanization is an important step to understand the neuropeptide receptor downstream signaling cascade. We cloned the full length cDNA of the putative S. invicta sNPF prepropeptide and identified the putative “sNPF” ligand within its sequence. The peptide ends with an amidated Tyr residue whereas in other insect species sNPFs have an amidated Phe or Trp residue at the C-terminus. We stably expressed the HA-tagged S. invicta sNPFR in CHO-K1 cells. Two S. invicta sNPFs differing at their N-terminus were synthesized that equally activated the sNPFR, SLRSALAAGHLRYa (EC₅₀ = 3.2 nM) and SALAAGHLRYa (EC₅₀ = 8.6 nM). Both peptides decreased the intracellular cAMP concentration, indicating signaling through the G_αi-subunit. The receptor was not activated by sNPF peptides from other insect species, honey bee long NPF (NPY) or mammalian PYY. Further, a synthesized peptide otherwise identical to the fire ant sequence but in which the C-terminal amidated amino acid residue ‘Y’ was switched to ‘F’, failed to activate the sNPFR. This discovery will now allow us to investigate the function of sNPY and its cognate receptor in fire ant biology.

The Drosophila neuropeptides PDF and sNPF have opposing electrophysiological and molecular effects on central neurons

Neuropeptides have widespread effects on behavior, but how these molecules alter the activity of their target cells is poorly understood. We employed a new model system in Drosophila melanogaster to assess the electrophysiological and molecular effects of neuropeptides, recording in situ from larval motor neurons, which transgenically express a receptor of choice. We focused on two neuropeptides, pigment-dispersing factor (PDF) and small neuropeptide F (sNPF), which play important roles in sleep/rhythms and feeding/metabolism. PDF treatment depolarized motor neurons expressing the PDF receptor (PDFR), increasing excitability. sNPF treatment had the opposite effect, hyperpolarizing neurons expressing the sNPF receptor (sNPFR). Live optical imaging using a genetically encoded fluorescence resonance energy transfer (FRET)-based sensor for cyclic AMP (cAMP) showed that PDF induced a large increase in cAMP, whereas sNPF caused a small but significant decrease in cAMP. Coexpression of pertussis toxin or RNAi interference to disrupt the G-protein Gαo blocked the electrophysiological responses to sNPF, showing that sNPFR acts via Gαo signaling. Using a fluorescent sensor for intracellular calcium, we observed that sNPF-induced hyperpolarization blocked spontaneous waves of activity propagating along the ventral nerve cord, demonstrating that the electrical effects of sNPF can cause profound changes in natural network activity in the brain. This new model system provides a platform for mechanistic analysis of how neuropeptides can affect target cells at the electrical and molecular level, allowing for predictions of how they regulate brain circuits that control behaviors such as sleep and feeding.

Differences in sNPF receptor-expressing neurons in brains of fire ant (Solenopsis invicta Buren) worker subcastes: indicators for division of labor and nutritional status?

In the red imported fire ant, Solenopsis invicta Buren, the neuronal and molecular mechanisms related to worker division of labor are poorly understood. Workers from different subcastes (major, medium and minors) perform different tasks, which are loosely associated with their size. We hypothesized that the short neuropeptide F (sNPF) signaling system (NPY-like) could be involved in mechanisms of worker division of labor and sensing or responding to colony nutritional requirements. Thus, we investigated the expression of the short neuropeptide F receptor (sNPFR) in the brain and subesophageal ganglion (SEG) of workers from colonies with and without brood. Across worker subcastes a total of 9 clusters of immunoreactive sNPFR cells were localized in the brain and the subesophageal ganglion (SEG); some of these cells were similar to those observed previously in the queen. Worker brain sNPFR cell clusters were found in the protocerebrum near mushroom bodies, in the central complex and in the lateral horn. Other sNPFR immunoreactive cells were found at the edge of the antennal lobes. Across subcastes, we observed both a constant and a differential pattern of sNPFR clusters, with a higher number of sNPFR cells found in minor than in major workers. Those sNPFR cells detected in all worker subcastes appear to be involved in olfaction or SEG functions. The differential expression of clusters in subcastes suggests that sNPFR signaling is involved in regulating behaviors associated with specific subcastes and thus, division of labor. Some sNPFR cells appear to be involved in nutrient sensing and/or brood care, feeding behavior and locomotion. In colonies without brood, workers showed a lower cluster number, and an overall reduced sNPFR signal. Our results suggest the sNPF signaling system is a candidate for the neurobiological control of worker division of labor and sensing brood presence, perhaps correlating with protein requirements and availability.

Functional and genetic characterization of neuropeptide Y-like receptors in Aedes aegypti

Background

Female Aedes aegypti mosquitoes are the principal vector for dengue fever, causing 50–100 million infections per year, transmitted between human and mosquito by blood feeding. Ae. aegypti host-seeking behavior is known to be inhibited for three days following a blood meal by a hemolymph-borne humoral factor. Head Peptide-I is a candidate peptide mediating this suppression, but the mechanism by which this peptide alters mosquito behavior and the receptor through which it signals are unknown.

Methodology/Principal Findings

Head Peptide-I shows sequence similarity to short Neuropeptide-F peptides (sNPFs) that have been implicated in feeding behaviors and are known to signal through Neuropeptide Y (NPY)-Like Receptors (NPYLRs). We identified eight NPYLRs in the Ae. aegypti genome and screened each in a cell-based calcium imaging assay for sensitivity against a panel of peptides. Four of the Ae. aegypti NPYLRs responded to one or more peptide ligands, but only NYPLR1 responded to Head Peptide-I as well as sNPFs. Two NPYLR1 homologues identified in the genome of the Lyme disease vector, Ixodes scapularis, were also sensitive to Head Peptide-I. Injection of synthetic Head Peptide-I and sNPF-3 inhibited host-seeking behavior in non-blood-fed female mosquitoes, whereas control injections of buffer or inactive Head Peptide-I [Cys10] had no effect. To ask if NPYLR1 is necessary for blood-feeding-induced host-seeking inhibition, we used zinc-finger nucleases to generate five independent npylr1 null mutant strains and tested them for behavioral abnormalities. npylr1 mutants displayed normal behavior in locomotion, egg laying, sugar feeding, blood feeding, host seeking, and inhibition of host seeking after a blood meal.

Conclusions

In this work we deorphanized four Ae. aegypti NPYLRs and identified NPYLR1 as a candidate sNPF receptor that is also sensitive to Head Peptide-I. Yet npylr1 alone is not required for host-seeking inhibition and we conclude that other receptors, additional peptides, or both, regulate this important behavior.

Female mosquitoes are responsible for spreading many deadly infectious diseases including malaria, dengue fever, and yellow fever. These mosquitoes require a blood meal to produce eggs and preferentially feed on humans, thereby spreading disease as they feed. Females of the dengue vector mosquito Aedes aegypti undergo a natural change in behavior after a blood meal in which they lose attraction to humans for over three days. We are interested in understanding this natural behavioral inhibition because it may provide an opportunity to control mosquito blood-feeding behavior. Previous work showed that a small protein called Head Peptide-I could mimic this behavioral inhibition when injected into non-blood-fed females, which normally show very high attraction to humans. In this work, we set out to find the Head Peptide-I receptor and ask if it causes this behavioral inhibition. By testing eight different candidate receptors, we found one called NPYLR1 that responds to Head-Peptide I but is much more sensitive to another peptide called sNPF-3. We made mutant mosquitoes that lack the npylr1 gene and found that the mutants showed normal sugar- and blood-feeding behavior. We conclude that there must be additional receptors and/or peptides that together cause this long-lasting inhibition of female mosquito attraction to humans.

Regulation of sleep by the short neuropeptide F (sNPF) in Drosophila melanogaster

The short neuropeptide F (sNPF), a neuropeptide in the central nervous system (CNS) of Drosophila melanogaster, is expressed in a large population of diverse neurons of brain. Most of these neurons are intrinsic interneurons of the mushroom bodies, which are the most prominent insect bilateral CNS structures that regulate memory and sleep. However, its role in sleep regulation still remains elusive. Here, we showed that sNPF-deficient female and male flies exhibit sleep enhancement with an increase of sleep bout duration. Loss of function of sNPF and sNPFR1 also elevated sleep. Moreover, the homeostatic regulation of flies after sleep deprivation was disrupted by aberrant sNPF signaling, since sleep deprivation increased transcription of sNPF and wakefulness at night in control flies but not in the sNPF mutant flies, suggesting that sNPF autoregulation plays an important role in sleep homeostasis. We further verified that sNPF signal elevated cAMP levels, and subsequently activated the downstream CREB transcription factor. The duration of sleep was found to be inversely related to cAMP signaling and CREB activity in the mushroom bodies. Thus, we concluded that sleep might be regulated by sNPF through modulating the cAMP-PKA-CREB signal pathway in vivo.

Neuropeptide F regulates male reproductive processes in the desert locust, Schistocerca gregaria

Although Neuropeptide F (NPF) has been identified in different insect species, its function has mainly been studied in the fruit fly, Drosophila melanogaster, where it regulates diverse physiological processes, such as learning, stress responses and male courtship behavior. In locusts, only a truncated form of the "full-length" NPF (the biologically active "trNPF") has been isolated. This 9 AA peptide stimulates oocyte maturation, food intake and weight increase in adult desert locusts (Schistocerca gregaria [Forskål]). In this study, we investigated whether this peptide is also involved in the regulation of male reproductive physiology in this orthopteran species. Daily injections of trNPF in adult males resulted in proportionally heavier testes and seminal vesicles, while RNAi-mediated knockdown of the Schgr-NPF precursor transcript gave rise to proportionally lighter testes and seminal vesicles. Furthermore, adult males precociously displayed courtship behavior when injected daily with trNPF, while this behavior was inhibited or delayed by RNAi knockdown of the Schgr-NPF precursor transcript. In order to further analyze these effects of trNPF on male reproductive physiology, fertility of males was tested by analyzing progeny numbers following copulation with untreated females. In this way, we showed that daily trNPF injection in adult males resulted in a larger egg pod size and a higher percentage of hatched eggs per egg pod after copulation, while RNAi knockdown caused the opposite effects. Taken together, we provide clear evidence for a role of trNPF in the regulation of reproductive physiology in adult males of the desert locust, S. gregaria. Possible modes of action of trNPF in influencing these reproductive processes in male locusts are discussed.

Neuropeptide F peptides act through unique signaling pathways to affect cardiac activity

Elucidating how neuropeptides affect physiology may result in delineating peptidergic mechanisms and identifying antagonists for application in basic and translational science. Human neuropeptide Y (NPY) regulates cardiac activity; frequently invertebrates contain orthologs of vertebrate peptides. We report invertebrate NPY-like neuropeptide F (NPF) arrested the signal frequency of the slow phase of the cardiac cycle (EC50 = 1 pM); however, signal frequency of the fast phase was affected only minimally. Neuropeptide F decreased the duration of the slow phase by ~70% (EC50 = 0.6 pM), but increased the duration of the fast phase by ~57% (EC50 = 10nM). Short NPF-1 (sNPF-1) decreased the signal frequency of the slow phase by ~70% (EC50 = 9 nM); yet, signal frequency of the fast phase was unaffected. Short NPF-1 decreased the duration of the slow phase ~55% (EC50 ~50 nM), but increased the duration of the fast phase ~20% without dose dependency. Neuropeptide F and sNPF-1 increased isoelectric period duration. This novel report demonstrated NPY-like peptides are cardioactive but functionally unique. These data contribute to understanding how invertebrate orthologs affect cardiovascular activity. Dipteran fast and slow phases may be generated from separate pacemakers in the abdominal heart and in the anterior thoracocephalic aorta, respectively. Thus, our research suggests NPF and sNPF-1 act through different mechanisms to regulate cardiac activity. Invertebrate NPY-like peptides act in olfaction and feeding yet mechanisms which are associated with their cardioactive effects remain unknown; our work may provide evidence linking their roles in sensory response and cardiac activity.

Immunolocalization of the short neuropeptide F receptor in queen brains and ovaries of the red imported fire ant (Solenopsis invicta Buren)

Background

Insect neuropeptides are involved in diverse physiological functions and can be released as neurotransmitters or neuromodulators acting within the central nervous system, and as circulating neurohormones in insect hemolymph. The insect short neuropeptide F (sNPF) peptides, related to the vertebrate neuropeptide Y (NPY) peptides, have been implicated in the regulation of food intake and body size, and play a gonadotropic role in the ovaries of some insect species. Recently the sNPF peptides were localized in the brain of larval and adult Drosophila. However, the location of the sNPF receptor, a G protein-coupled receptor (GPCR), has not yet been investigated in brains of any adult insect. To elucidate the sites of action of the sNPF peptide(s), the sNPF receptor tissue expression and cellular localization were analyzed in queens of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera), an invasive social insect.

Results

In the queen brains and subesophageal ganglion about 164 cells distributed in distinctive cell clusters (C1-C9 and C12) or as individual cells (C10, C11) were immuno-positive for the sNPF receptor. Most of these neurons are located in or near important sensory neuropils including the mushroom bodies, the antennal lobes, the central complex, and in different parts of the protocerebrum, as well as in the subesophageal ganglion. The localization of the sNPF receptor broadly links the receptor signaling pathway with circuits regulating learning and feeding behaviors. In ovaries from mated queens, the detection of sNPF receptor signal at the posterior end of oocytes in mid-oogenesis stage suggests that the sNPF signaling pathway may regulate processes at the oocyte pole.

Conclusions

The analysis of sNPF receptor immunolocalization shows that the sNPF signaling cascade may be involved in diverse functions, and the sNPF peptide(s) may act in the brain as neurotransmitter(s) or neuromodulator(s), and in the ovaries as neurohormone(s). To our knowledge, this is the first report of the cellular localization of a sNPF receptor on the brain and ovaries of adult insects.

A comparative review of short and long neuropeptide F signaling in invertebrates: Any similarities to vertebrate neuropeptide Y signaling?

Neuropeptides referred to as neuropeptide F (NPF) and short neuropeptide F (sNPF) have been identified in numerous invertebrate species. Sequence information has expanded tremendously due to recent genome sequencing and EST projects. Analysis of sequences of the peptides and prepropeptides strongly suggest that NPFs and sNPFs are not closely related. However, the NPFs are likely to be ancestrally related to the vertebrate family of neuropeptide Y (NPY) peptides. Peptide diversification may have been accomplished by different mechanisms in NPFs and sNPFs; in the former by gene duplications followed by diversification and in the sNPFs by internal duplications resulting in paracopies of peptides. We discuss the distribution and functions of NPFs and their receptors in several model invertebrates. Signaling with sNPF, however, has been investigated mainly in insects, especially in Drosophila. Both in invertebrates and in mammals NPF/NPY play roles in feeding, metabolism, reproduction and stress responses. Several other NPF functions have been studied in Drosophila that may be shared with mammals. In Drosophila sNPFs are widely distributed in numerous neurons of the CNS and some gut endocrines and their functions may be truly pleiotropic. Peptide distribution and experiments suggest roles of sNPF in feeding and growth, stress responses, modulation of locomotion and olfactory inputs, hormone release, as well as learning and memory. Available data indicate that NPF and sNPF signaling systems are distinct and not likely to play redundant roles.

Neuropeptide physiology in insects

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

The G protein-coupled receptors in the silkworm, Bombyx mori

G protein-coupled receptors (GPCRs) are the largest and most versatile family of transmembrane receptors in the cell, occupying the highest hierarchical positions in the regulation of many physiological processes. Although they have been extensively studied in a number of model insects, there have been few investigations of GPCRs in large Lepidopterans, such as Bombyx mori, an organism that provides a means to perform detailed tissue expression analyses, which may help to characterize GPCRs and their ligands. In addition, B. mori, also known as the silkworm, is an insect of substantial economic importance, due to its use in silk production and traditional medicines. In this work, we computationally identified 90 putative GPCRs in B. mori, 33 of which represent novel proteins. These GPCRs were annotated and compared with their homologs in Drosophila melanogaster and Anopheles gambiae. Phylogenetics analyses of the GPCRs from these three insects showed that GPCRs may easily duplicate or disappear during insect evolution, especially in the neuropeptide and protein hormone receptor subfamily. Interestingly, we observed a decrease in the quantity and diversity of the stress-tolerance gene, Methuselah, in B. mori, which may be related to its long history of domestication. Moreover, the presence of many Bombyx-specific GPCRs suggests that neither Drosophila nor Anopheles is good representatives for the GPCRs in the Class Insecta.

Mass spectral analysis of neuropeptide expression and distribution in the nervous system of the lobster Homarus americanus

The lobster Homarus americanus has long served as an important animal model for electrophysiological and behavioral studies. Using this model, we performed a comprehensive investigation of the neuropeptide expression and their localization in the nervous system, which provides useful insights for further understanding of their biological functions. Using nanoLC ESI Q-TOF MS/MS and three types of MALDI instruments, we analyzed the neuropeptide complements in a major neuroendocrine structure, pericardial organ. A total of 57 putative neuropeptides were identified and 18 of them were de novo sequenced. Using direct tissue/extract analysis and bioinformatics software SpecPlot, we charted the global distribution of neuropeptides throughout the nervous system in H. americanus. Furthermore, we also mapped the localization of several neuropeptide families in the brain by high mass resolution and high mass accuracy mass spectrometric imaging (MSI) using a MALDI LTQ Orbitrap mass spectrometer. We have also compared the utility and instrument performance of multiple mass spectrometers for neuropeptide analysis in terms of peptidome coverage, sensitivity, mass spectral resolution and capability for de novo sequencing.

Combining in silico transcriptome mining and biological mass spectrometry for neuropeptide discovery in the Pacific white shrimp Litopenaeus vannamei

The shrimp Litopenaeus vannamei is arguably the most important aquacultured crustacean, being the subject of a multi-billion dollar industry worldwide. To extend our knowledge of peptidergic control in this species, we conducted an investigation combining transcriptomics and mass spectrometry to identify its neuropeptides. Specifically, in silico searches of the L. vannamei EST database were conducted to identify putative prepro-hormone-encoding transcripts, with the mature peptides contained within the deduced precursors predicted via online software programs and homology to known isoforms. MALDI-FT mass spectrometry was used to screen tissue fragments and extracts via accurate mass measurements for the predicted peptides, as well as for known ones from other species. ESI-Q-TOF tandem mass spectrometry was used to de novo sequence peptides from tissue extracts. In total 120 peptides were characterized using this combined approach, including 5 identified both by transcriptomics and by mass spectrometry (e.g. pQTFQYSRGWTNamide, Arg(7)-corazonin, and pQDLDHVFLRFamide, a myosuppressin), 49 predicted via transcriptomics only (e.g. pQIRYHQCYFNPISCF and pQIRYHQCYFIPVSCF, two C-type allatostatins, and RYLPT, authentic proctolin), and 66 identified solely by mass spectrometry (e.g. the orcokinin NFDEIDRAGMGFA). While some of the characterized peptides were known L. vannamei isoforms (e.g. the pyrokinins DFAFSPRLamide and ADFAFNPRLamide), most were novel, either for this species (e.g. pEGFYSQRYamide, an RYamide) or in general (e.g. the tachykinin-related peptides APAGFLGMRamide, APSGFNGMRamide and APSGFLDMRamide). Collectively, our data not only expand greatly the number of known L. vannamei neuropeptides, but also provide a foundation for future investigations of the physiological roles played by them in this commercially important species.

Processed short neuropeptide F peptides regulate growth through the ERK-insulin pathway in Drosophila melanogaster

The Drosophila sNPF gene regulates growth through the ERK-insulin pathway. sNPF encodes a precursor protein that is processed and produces biologically active sNPF peptides. However, the functions of these peptides are not known. In Drosophila neuronal cells in culture and in flies in vivo, sNPF1 and sNPF2 activated the ERK-insulin pathway and regulated body growth. In addition, the sNPF precursor and the processed sNPF peptide were co-localized in the neurons of the central nervous system. These results indicate that sNPF1 and sNPF2 peptides processed from the sNPF precursor are sufficient for regulating body growth through the ERK-insulin pathway in Drosophila.

Expanding the Crustacean neuropeptidome using a multifaceted mass spectrometric approach

Jonah crab Cancer borealis is an excellent, long-served model organism for many areas of physiology, including the study of endocrinology and neurobiology. Characterizing the neuropeptides present in its nervous system provides the first critical step toward understanding the physiological roles of these complex molecules. Multiple mass spectral techniques were used to comprehensively characterize the neuropeptidome in C. borealis, including matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), MALDI time-of-flight (TOF)/TOF MS and nanoflow liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nanoLC-ESI-Q-TOF MS/MS). To enhance the detection signals and expand the dynamic range, direct tissue analysis, tissue extraction, capillary electrophoresis (CE) and off-line HPLC separation have also been employed. In total, 142 peptides were identified, including 85 previously known C. borealis peptides, 22 peptides characterized previously from other decapods, but new to this species, and 35 new peptides de novo sequenced for the first time in this study. Seventeen neuropeptide families were revealed including FMRFamide-related peptide (FaRP), allatostatin (A and B type), RYamide, orcokinin, orcomyotropin, proctolin, crustacean cardioactive peptide (CCAP), crustacean hyperglycemic hormone precursor-related peptide (CPRP), crustacean hyperglycemic hormone (CHH), corazonin, pigment-dispersing hormone (PDH), tachykinin, pyrokinin, SIFamide, red pigment concentrating hormone (RPCH) and HISGLYRamide. Collectively, our results greatly increase the number and expand the coverage of known C. borealis neuropeptides, and thus provide a stronger framework for future studies on the physiological roles played by these molecules in this important model organism.

Identification of new members of the (short) neuropeptide F family in locusts and Caenorhabditis elegans

Both the long and short neuropeptides F (NPF) represent important families of invertebrate neuropeptides that have been implicated in the regulation of reproduction and feeding behavior. In the present study, two short NPFs (SNRSPS(L/I)R(L/I)RFamide and SPS(L/I)R(L/I)RFamide) were de novo sequenced by mass spectrometry in two major pest insects, the desert locust Schistocerca gregaria and the African migratory locust Locusta migratoria. They are two of the most widespread peptides in the locust neuroendocrine system. A peptide that was previously reported to accelerate egg development in S. gregaria is shown to represent a truncated form of long NPF. This peptide is most likely derived by a novel processing mechanism involving cleavage at RY. In addition, an NPF peptide from the nematode Caenorhabditis elegans was isolated and sequenced by tandem mass spectrometry.

Neuropeptides associated with the regulation of feeding in insects

The stomatogastric nervous system plays a pivotal role in feeding behaviour. Central to this system is the frontal ganglion, which is responsible for foregut motor activity, and hence the passage of food through the gut. Many insect peptides, which exhibit myoactivity on the visceral muscles of the gut in vitro, have been detected in the stomatogastric nervous system by immunochemical or mass spectrometric techniques. This localisation of myoactive peptides, particularly in the frontal ganglion, implies roles for these peptides in the neural control and modulation of feeding in insects. Insect sulfakinins, tachykinins, allatotropin and proctolin have all been shown to stimulate the foregut muscles, whereas myosuppressins, myoinhibitory peptides and allatostatins all inhibited spontaneous contractions of the foregut in a variety of insects. Some of these peptides, when injected, inhibited feeding in vivo. Both the A-type and B-type allatostatins suppressed feeding activity when injected into the cockroach, Blattella germanica and the Manduca sexta C-type allatostatin and allatotropin inhibited feeding when injected into the larvae of two noctuid moths, Lacanobia oleracea and Spodoptera frugiperda, respectively. Injection of sulfakinins into the fly Phormia regina, the locust Schistocera gregaria and the cockroach B. germanica also suppressed feeding, whereas silencing the sulfakinin gene through the injection of double stranded RNA resulted in an increase in food consumption in the cricket Gryllus bimaculatus. The regulation of feeding in insects is clearly very complex, and involves the interaction of a number of mechanisms, one of which is the release, either centrally or locally, of neuropeptides. However, the role of neuropeptides, their mechanisms of action, interactions with each other, and their release are still poorly understood. It is also unclear why insects possess such a number of different peptides, some with multiples copies or homologues, which stimulate or inhibit gut motility, and how their release, sometimes from the same neurone, is regulated. These neuropeptides may also act at sites other than visceral muscles, such as centrally through the brain or on gut stretch receptors.

Characterization of the Carcinus maenas neuropeptidome by mass spectrometry and functional genomics

Carcinus maenas, commonly known as the European green crab, is one of the best-known and most successful marine invasive species. While a variety of natural and anthropogenic mechanisms are responsible for the geographic spread of this crab, its ability to adapt physiologically to a broad range of salinities, temperatures and other environmental factors has enabled its successful establishment in new habitats. To extend our understanding of hormonal control in C. maenas, including factors that allow for its extreme adaptability, we have undertaken a mass spectral/functional genomics investigation of the neuropeptides used by this organism. Via a strategy combining MALDI-based high resolution mass profiling, biochemical derivatization, and nanoscale separation coupled to tandem mass spectrometric sequencing, 122 peptide paracrines/hormones were identified from the C. maenas central nervous system and neuroendocrine organs. These peptides include 31 previously described Carcinus neuropeptides (e.g. NSELINSILGLPKVMNDAamide [beta-pigment dispersing hormone] and PFCNAFTGCamide [crustacean cardioactive peptide]), 49 peptides only described in species other than the green crab (e.g. pQTFQYSRGWTNamide [Arg(7)-corazonin]), and 42 new peptides de novo sequenced here for the first time (e.g. the pyrokinins TSFAFSPRLamide and DTGFAFSPRLamide). Of particular note are large collections of FMRFamide-like peptides (25, including nine new isoforms sequenced de novo) and A-type allatostatin peptides (25, including 10 new sequences reported here for the first time) in this study. Also of interest is the identification of two SIFamide isoforms, GYRKPPFNGSIFamide and VYRKPPFNGSIFamide, the latter peptide known previously only from members of the astacidean genus Homarus. Using transcriptome analyses, 15 additional peptides were characterized, including an isoform of bursicon beta and a neuroparsin-like peptide. Collectively, the data presented in this study not only greatly expand the number of identified C. maenas neuropeptides, but also provide a framework for future investigations of the physiological roles played by these molecules in this highly adaptable species.

A large population of diverse neurons in the Drosophila central nervous system expresses short neuropeptide F, suggesting multiple distributed peptide functions

Background

Insect neuropeptides are distributed in stereotypic sets of neurons that commonly constitute a small fraction of the total number of neurons. However, some neuropeptide genes are expressed in larger numbers of neurons of diverse types suggesting that they are involved in a greater diversity of functions. One of these widely expressed genes, snpf, encodes the precursor of short neuropeptide F (sNPF). To unravel possible functional diversity we have mapped the distribution of transcript of the snpf gene and its peptide products in the central nervous system (CNS) of Drosophila in relation to other neuronal markers.

Results

There are several hundreds of neurons in the larval CNS and several thousands in the adult Drosophila brain expressing snpf transcript and sNPF peptide. Most of these neurons are intrinsic interneurons of the mushroom bodies. Additionally, sNPF is expressed in numerous small interneurons of the CNS, olfactory receptor neurons (ORNs) of the antennae, and in a small set of possibly neurosecretory cells innervating the corpora cardiaca and aorta. A sNPF-Gal4 line confirms most of the expression pattern. None of the sNPF immunoreactive neurons co-express a marker for the transcription factor DIMMED, suggesting that the majority are not neurosecretory cells or large interneurons involved in episodic bulk transmission. Instead a portion of the sNPF producing neurons co-express markers for classical neurotransmitters such as acetylcholine, GABA and glutamate, suggesting that sNPF is a co-transmitter or local neuromodulator in ORNs and many interneurons. Interestingly, sNPF is coexpressed both with presumed excitatory and inhibitory neurotransmitters. A few sNPF expressing neurons in the brain colocalize the peptide corazonin and a pair of dorsal neurons in the first abdominal neuromere coexpresses sNPF and insulin-like peptide 7 (ILP7).

Conclusion

It is likely that sNPF has multiple functions as neurohormone as well as local neuromodulator/co-transmitter in various CNS circuits, including olfactory circuits both at the level of the first synapse and at the mushroom body output level. Some of the sNPF immunoreactive axons terminate in close proximity to neurosecretory cells producing ILPs and adipokinetic hormone, indicating that sNPF also might regulate hormone production or release.

Mass spectral characterization of peptide transmitters/hormones in the nervous system and neuroendocrine organs of the American lobster Homarus americanus

The American lobster Homarus americanus is a decapod crustacean with both high economic and scientific importance. To facilitate physiological investigations of peptide transmitter/hormone function in this species, we have used matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and nanoscale liquid chromatography coupled to electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nanoLC-ESI-Q-TOF MS/MS) to elucidate the peptidome present in its nervous system and neuroendocrine organs. In total, 84 peptides were identified, including 27 previously known H. americanus peptides (e.g., VYRKPPFNGSIFamide [Val(1)-SIFamide]), 23 peptides characterized previously from other decapods, but new to the American lobster (e.g., pQTFQYSRGWTNamide [Arg(7)-corazonin]), and 34 new peptides de novo sequenced/detected for the first time in this study. Of particular note are a novel B-type allatostatin (TNWNKFQGSWamide) and several novel FMRFamide-related peptides, including an unsulfated analog of sulfakinin (GGGEYDDYGHLRFamide), two myosuppressins (QDLDHVFLRFamide and pQDLDHVFLRFamide), and a collection of short neuropeptide F isoforms (e.g., DTSTPALRLRFamide and FEPSLRLRFamide). Our data also include the first detection of multiple tachykinin-related peptides in a non-brachyuran decapod, as well as the identification of potential individual-specific variants of orcokinin and orcomyotropin-related peptide. Taken collectively, our results not only expand greatly the number of known H. americanus neuropeptides, but also provide a framework for future studies on the physiological roles played by these molecules in this commercially and scientifically important species.

Intrinsic neurons of Drosophila mushroom bodies express short neuropeptide F: relations to extrinsic neurons expressing different neurotransmitters

Mushroom bodies constitute prominent paired neuropils in the brain of insects, known to be involved in higher olfactory processing and learning and memory. In Drosophila there are about 2,500 intrinsic mushroom body neurons, Kenyon cells, and a large number of different extrinsic neurons connecting the calyx, peduncle, and lobes to other portions of the brain. The neurotransmitter of the Kenyon cells has not been identified in any insect. Here we show expression of the gene snpf and its neuropeptide products (short neuropeptide F; sNPFs) in larval and adult Drosophila Kenyon cells by means of in situ hybridization and antisera against sequences of the precursor and two of the encoded peptides. Immunocytochemistry displays peptide in intrinsic neuronal processes in most parts of the mushroom body structures, except for a small core in the center of the peduncle and lobes and in the alpha'- and beta'-lobes. Weaker immunolabeling is seen in Kenyon cell bodies and processes in the calyx and initial peduncle and is strongest in the more distal portions of the lobes. We used different antisera and Gal4-driven green fluorescent protein to identify Kenyon cells and different populations of extrinsic neurons defined by their signal substances. Thus, we display neurotransmitter systems converging on Kenyon cells: neurons likely to utilize dopamine, tyramine/octopamine, glutamate, and acetylcholine. Attempts to identify other neurotransmitter components (including vesicular glutamate transporter) in Kenyon cells failed. However, it is likely that the Kenyon cells utilize an additional neurotransmitter, yet to be identified, and that the neuropeptides described here may represent cotransmitters.

Prediction of neuropeptide cleavage sites in insects

MOTIVATION

The production of neuropeptides from their precursor proteins is the result of a complex series of enzymatic processing steps. Often, the annotation of new neuropeptide genes from sequence information outstrips biochemical assays and so bioinformatics tools can provide rapid information on the most likely peptides produced by a gene. Predicting the final bioactive neuropeptides from precursor proteins requires accurate algorithms to determine which locations in the protein are cleaved.

RESULTS

Predictive models were trained on Apis mellifera and Drosophila melanogaster precursors using binary logistic regression, multi-layer perceptron and k-nearest neighbor models. The final predictive models included specific amino acids at locations relative to the cleavage sites. Correct classification rates ranged from 78 to 100% indicating that the models adequately predicted cleaved and non-cleaved positions across a wide range of neuropeptide families and insect species. The model trained on D.melanogaster data had better generalization properties than the model trained on A. mellifera for the data sets considered. The reliable and consistent performance of the models in the test data sets suggests that the bioinformatics strategies proposed here can accurately predict neuropeptides in insects with sequence information based on neuropeptides with biochemical and sequence information in well-studied species.

The first nonsulfated sulfakinin activity reported suggests nsDSK acts in gut biology

Invertebrate sulfakinins are structurally and functionally homologous to vertebrate cholecystokinin (CCK) and gastrin. To date, sulfakinins are reported to require a sulfated tyrosine for activity; sulfated and nonsulfated CCK and gastrin are active. This is the first nonsulfated sulfakinin activity reported. Nonsulfated Drosophila melanogaster sulfakinins or drosulfakinins (nsDSK I; PheAspAspTyrGlyHisMetArgPheNH2) and (nsDSK II; GlyGlyAspAspGlnPheAspAspTyrGlyHisMetArgPheNH2) decreased the frequency of contractions of adult D. melanogaster foregut (crop) in vivo. The EC50's for nsDSK I and nsDSK II were approximately 2 x 10(-9)M and approximately 3 x 10(-8)M, respectively. Nonsulfated DSK peptides also decreased the frequency of larval anterior midgut contractions. Sulfated DSK peptides decreased both adult and larval gut contractions. Whether sulfation is required for sulfakinin activity may depend on where the peptide is applied, what tissue is analyzed, or what preparation is used. D. melanogaster contains two sulfakinin receptors, DSK-R1 and DSK-R2; vertebrates contain two CCK receptors, CCK-1 and CCK-2. A sulfated DSK I analog, [Leu7] sDSK I, binds to expressed DSK-R1; the corresponding nonsulfated analog does not bind to DSK-R1. No DSK-R2 binding data are reported. Sulfated and nonsulfated CCK peptides preferentially bind to CCK-1 or CCK-2, respectively. Sulfated and nonsulfated sulfakinins may bind to DSK-R1 or DSK-R2, respectively. Sulfakinin activities, spatial and temporal distribution, and homology to CCK and gastrin suggest sulfated and nonsulfated DSK peptides act in diverse roles in the neural and gastrointestinal systems including gut emptying and satiety.

Characterization and expression of the short neuropeptide F receptor in the African malaria mosquito, Anopheles gambiae

A short neuropeptide F (sNPF) precursor and a sNPF receptor (sNPFR) were characterized for the mosquito, Anopheles gambiae. The sNPFR was expressed in CHO-K1 cells, and it exhibited high affinity binding, IC(50) approximately 3-5 nM, for specific sNPFs. sNPF1 potently inhibited forskolin-stimulated cAMP production by transfected cells, suggesting sNPFR acts via G(i/o). Transcripts for sNPF and sNPFR were present in all body regions of larvae, pupae, and adults, and immunoblots for sNPFR confirmed this distribution in females. Membranes from female heads and thoraces exhibited prototypical high affinity binding for radiolabeled sNPF, indicating sNPFR is a bona fide endogenous receptor.