In vitro release of digestive enzymes by FMRF amide related neuropeptides and analogues in the lepidopteran insect Opisina arenosella (Walk.)

Activation of the G protein-coupled sulfakinin receptor inhibits blood meal intake in the mosquito Aedes aegypti

Little is known about the blood-feeding physiology of arbovirus vector Aedes aegypti although this type of mosquito is known to transmit infectious diseases dengue, Zika, yellow fever, and chikungunya. Blood feeding in the female A. aegypti mosquito is essential for egg maturation and for transmission of disease agents between human subjects. Here, we identify the A. aegypti sulfakinin receptor gene SKR from the A. aegypti genome and show that SKR is expressed at different developmental stages and in varied anatomical localizations in the adult mosquito (at three days after eclosion), with particularly high expression in the CNS. Knockingdown sulfakinin and sulfakinin receptor gene expression in the female A. aegypti results in increased blood meal intake, but microinjection in the thorax of the sulfakinin peptide 1 and 2 both inhibits dose dependently blood meal intake (and delays the time course of blood intake), which is reversible with receptor antagonist. Sulfakinin receptor expressed ectopically in mammalian cells CHO-K1 responds to sulfakinin stimulation with persistent calcium spikes, blockable with receptor antagonist. These data together suggest that activation of the Gq protein-coupled (i.e., calcium-mobilizing) sulfakinin receptor inhibits blood meal intake in female A. aegypti mosquitoes and could serve as a strategic node for the future control of A. aegypti mosquito reproduction/population and disease transmission.

Identification of sulfakinin receptor regulating feeding behavior and hemolymph trehalose homeostasis in the silkworm, Bombyx mori

Feeding behavior, the most fundamental physiological activity, is controlled by two opposing groups of factors, orexigenic and anorexigenic factors. The sulfakinin family, an insect analogue of the mammalian satiety factor cholecystokinin (CCK), has been shown to suppress food intake in various insects. Nevertheless, the mechanisms through which sulfakinin regulates feeding behavior remain a biological question. This study aimed to elucidate the signaling pathway mediated by the anorexigenic peptide sulfakinin in Bombyx mori. We identified the Bombyx mori neuropeptide G protein-coupled receptor A9 (BNGR-A9) as the receptor for sulfakinin through functional assays. Stimulation with sulfakinin triggered a swift increase in intracellular IP3, Ca2+, and a notable enhancement of ERK1/2 phosphorylation, in a manner sensitive to a Gαq-specific inhibitor. Treatment with synthetic sulfakinin resulted in decreased food consumption and average body weight. Additionally, administering synthetic sulfakinin to silkworms significantly elevated hemolymph trehalose levels, an effect markedly reduced by pre-treatment with BNGR-A9 dsRNA. Consequently, our findings establish the sulfakinin/BNGR-A9 signaling pathway as a critical regulator of feeding behavior and hemolymph trehalose homeostasis in Bombyx mori, highlighting its roles in the negative control of food intake and the positive regulation of energy balance.

Identification and functional characterization of the sulfakinin and sulfakinin receptor in the Chinese white pine beetle Dendroctonus armandi

The sulfakinin (SK) is an important signal molecule. As a neuromodulator, it mediates a variety of behavioral processes and physiological functions in invertebrates through the interaction with G-protein-coupled receptors (GPCRs). However, there is no report on the functional role of SK in the Chinese white pine beetle, Dendroctonus armandi. We have cloned and characterized SK and SKR genes in the D. armandi and carried out bioinformatics predictions on the basis of the deduced amino acid sequences, which are very similar to those from Dendroctonus ponderosa. The expression levels of the two genes were different between male and female adults, and there were significant changes in different developmental stages, tissues, and between starvation and following re-feeding states. Additionally, RNA-interference (RNAi) using double-stranded RNA to knock down SK and SKR reduced the transcription levels of the target genes and increased their body weight. In parallel, injection of SK caused a significant reduction in body weight and increase in mortality of D. armandi and also led to an increase in trehalose and a decrease in glycogen and free fatty acid. The results show that the SK signal pathway plays a positive and significant role in feeding regulation and provides a potential molecular target for the control of this pest.

Ancient role of sulfakinin/cholecystokinin-type signalling in inhibitory regulation of feeding processes revealed in an echinoderm

Sulfakinin (SK)/cholecystokinin (CCK)-type neuropeptides regulate feeding and digestion in protostomes (e.g. insects) and chordates. Here, we characterised SK/CCK-type signalling for the first time in a non-chordate deuterostome - the starfish Asterias rubens (phylum Echinodermata). In this species, two neuropeptides (ArSK/CCK1, ArSK/CCK2) derived from the precursor protein ArSK/CCKP act as ligands for an SK/CCK-type receptor (ArSK/CCKR) and these peptides/proteins are expressed in the nervous system, digestive system, tube feet, and body wall. Furthermore, ArSK/CCK1 and ArSK/CCK2 cause dose-dependent contraction of cardiac stomach, tube foot, and apical muscle preparations in vitro, and injection of these neuropeptides in vivo triggers cardiac stomach retraction and inhibition of the onset of feeding in A. rubens. Thus, an evolutionarily ancient role of SK/CCK-type neuropeptides as inhibitory regulators of feeding-related processes in the Bilateria has been conserved in the unusual and unique context of the extra-oral feeding behaviour and pentaradial body plan of an echinoderm.

Sulfakinins influence lipid composition and insulin-like peptides level in oenocytes of Zophobas atratus beetles

Insect sulfakinins are pleiotropic neuropeptides with the homology to vertebrate gastrin/cholecystokinin peptide family. They have been identified in many insect species and affect different metabolic processes. They have a strong influence on feeding and digestion as well as on carbohydrate and lipid processing. Our study reveals that sulfakinins influence fatty acids composition in Zophobas atratus oenocytes and regulate insulin-like peptides (ILPs) level in these cells. Oenocytes are cells responsible for maintenance of the body homeostasis and have an important role in the regulation of intermediary metabolism, especially of lipids. To analyze the lipid composition in oenocytes after sulfakinins injections we used gas chromatography combined with mass spectrometry and for ILPs level determination an immunoenzymatic test was used. Because sulfakinin peptides and their receptors are the main components of sulfakinin signaling, we also analyzed the presence of sulfakinin receptor transcript (SKR2) in insect tissues. We have identified for the first time the sulfakinin receptor transcript (SKR2) in insect oenocytes and found its distribution more widespread in the peripheral tissues (gut, fat body and haemolymph) as well as in the nervous and neuro-endocrine systems (brain, ventral nerve cord, corpora cardiaca/corpora allata CC/CA) of Z. atratus larvae. The presence of sulfakinin receptor transcript (SKR2) in oenocytes suggests that observed effects on oenocytes lipid and ILPs content may result from direction action of these peptides on oenocytes.

Cholecystokinin-like peptide mediates satiety by inhibiting sugar attraction

Feeding is essential for animal survival and reproduction and is regulated by both internal states and external stimuli. However, little is known about how internal states influence the perception of external sensory cues that regulate feeding behavior. Here, we investigated the neuronal and molecular mechanisms behind nutritional state-mediated regulation of gustatory perception in control of feeding behavior in the brown planthopper and Drosophila. We found that feeding increases the expression of the cholecystokinin-like peptide, sulfakinin (SK), and the activity of a set of SK-expressing neurons. Starvation elevates the transcription of the sugar receptor Gr64f and SK negatively regulates the expression of Gr64f in both insects. Interestingly, we found that one of the two known SK receptors, CCKLR-17D3, is expressed by some of Gr64f-expressing neurons in the proboscis and proleg tarsi. Thus, we have identified SK as a neuropeptide signal in a neuronal circuitry that responds to food intake, and regulates feeding behavior by diminishing gustatory receptor gene expression and activity of sweet sensing GRNs. Our findings demonstrate one nutritional state-dependent pathway that modulates sweet perception and thereby feeding behavior, but our experiments cannot exclude further parallel pathways. Importantly, we show that the underlying mechanisms are conserved in the two distantly related insect species.

Food intake is critical for animal survival and reproduction and is regulated both by internal states that signal appetite or satiety, and by external sensory stimuli. It is well known that the internal nutritional state influences the strength of the chemosensory perception of food signals. Thus, both gustatory and olfactory signals of preferred food are strengthened in hungry animals. However, the molecular mechanisms behind satiety-mediated modulation of taste are still not known. We show here that cholecystokinin-like (SK) peptide in brown planthopper and Drosophila signals satiety and inhibits sugar attraction by lowering the activity of sweet-sensing gustatory neurons and transcription of a sugar receptor gene, Gr64f. We show that SK peptide signaling reflects the nutritional state and inhibits feeding behavior. Re-feeding after starvation increases SK peptide expression and spontaneous activity of SK producing neurons. Interestingly, we found that SK peptide negatively regulates the expression of the sweet gustatory receptor and that activation of SK producing neurons inhibits the activity of sweet-sensing gustatory neurons (GRNs). Furthermore, we found that one of the two known SK peptide receptors is expressed in some sweet-sensing GRNs in the proboscis and proleg tarsi. In summary, our findings provide a mechanism that is conserved in distantly related insects and which explains how feeding state modulates sweet perception to regulate feeding behavior. Thus, we have identified a neuropeptide signal and its neuronal circuitry that respond to satiety, and that regulate feeding behavior by inhibiting gustatory receptor gene expression and activity of sweet sensing GRNs.

Identification of sulfakinin receptors (SKR) in Tenebrio molitor beetle and the influence of sulfakinins on carbohydrates metabolism

Sulfakinins (SKs) are pleiotropic neuropeptides commonly found in insects, structurally and functionally homologous to the mammalian gastrin/cholecystokinin (CCK) neuropeptides. SKs together with sulfakinin receptors (SKRs) are involved in sulfakinin signaling responsible for variety of biological functions, including food intake or fatty acid metabolism. In the present study, we determined the distribution of SKRs in Tenebrio molitor larvae and characterized the impact of nonsulfated and sulfated SKs on carbohydrates and insulin-like peptides (ILPs) level in beetle hemolymph. Our results indicate the presence of both sulfakinin receptors, SKR1 and SKR2, in the nervous system of T. molitor. The distribution of SKR2 in peripheral tissues was more widespread than SKR1, and their transcripts have been found in fat body, gut and hemolymph. This is also the first evidence for SKRs presence in insect hemocytes indicating immunotropic activity of SKs. Moreover, in the present study, we have demonstrated that SKs regulate ILPs and carbohydrates level in insect hemolymph, and that sulfation is not crucial for peptides activity. Our study confirms the role of SKs in maintaining energy homeostasis in beetles.

Identification, Functional Characterization, and Pharmacological Analysis of Two Sulfakinin Receptors in the Medically-Important Insect Rhodnius prolixus

The chordate gastrin/cholecystokinin and ecdysozoan sulfakinin (SK)-signaling systems are functionally and structurally homologous. In the present study, we isolated the cDNA sequences encoding the SK receptors in Rhodnius prolixus (Rhopr-SKR-1 and Rhopr-SKR-2). The Rhopr-SKRs have been functionally characterized and their intracellular signaling pathways analysed via a functional receptor assay. Both Rhopr-SKRs are exclusively activated via the two native R. prolixus sulfakinins, Rhopr-SK-1 and Rhopr-SK-2, but not via nonsulfated Rhopr-SK-1. The Rhopr-SKRs are each linked to the intracellular Ca²⁺ second messenger pathway, and not to the cyclic AMP pathway. Spatial transcript expression analyses revealed that each Rhopr-SKR is predominantly expressed in the central nervous system with lower expression throughout peripheral tissues. The critical importance of the SK-signaling pathway in the blood-feeding behaviour of R. prolixus was demonstrated by knockdown of the transcripts for Rhopr-SKs and Rhopr-SKRs, which results in an increase in the mass of blood meal taken. The parasite causing Chagas disease is transmitted to the host after R. prolixus has taken a blood meal, and characterization of the SKRs provides further understanding of the coordination of feeding and satiation, and ultimately the transmission of the parasite.

Sulfakinin Signalling Influences Fatty Acid Levels and Composition in Tenebrio Molitor Beetle

BACKGROUND

Sulfakinins are arthropod neuropeptides that are structurally and functionally similar to vertebrate gastrin-cholecystokinin. Sulfakinins with sulfated tyrosine (sSK) or nonsulfated tyrosine (nSK) in the C-terminated heptapeptide XY(SO3H)GHMRFamide display different biological functions, including myotropic activity, inhibition of food intake, stimulation of digestive enzymes and regulation of carbohydrate and lipid content.

OBJECTIVE

To reveal the mechanisms by which sulfakinin signalling modulates lipid homeostasis, we analysed the changes in the level and composition of fatty acids and organic compounds in the fat body and haemolymph of Tenebrio molitor larvae after nSK and sSK treatment.

METHODS

Fatty acids in fat body and haemolymph of insects were analysed using Gas Chromatography - Mass Spectrometry (GC-MS).

RESULTS

The direction of the changes observed for major fatty acids, 18:1 and 18:2, and the less abundant fatty acids, 16:0, 18:0, 16:1 and 14:0, was the same for unsaturated (UFAs) and saturated (SFAs) fatty acids, and elevated after nSK application in both analysed tissues. However, the action of sSK in fat body tissue evoked distinct effects and induced either significant decreases in individual fatty acids or UFAs and SFAs. Administration of nSK and sSK significantly increased the level of total organic compounds in the haemolymph, contrary to the effect of sSK in fat body, where the level of total organic compounds decreased, although changes differ between individual chemicals.

CONCLUSION

Sulfakinins are engaged in the precise modulation of fatty acid levels and composition, but their action depends on the presence of sulfate group on the tyrosyl residue of the peptide what determines the different roles of these peptides in insect physiology.

Emergence of a cholecystokinin/sulfakinin signalling system in Lophotrochozoa

Chordate gastrin/cholecystokinin (G/CCK) and ecdysozoan sulfakinin (SK) signalling systems represent divergent evolutionary scenarios of a common ancestral signalling system. The present article investigates for the first time the evolution of the CCK/SK signalling system in a member of the Lophotrochozoa, the second clade of protostome animals. We identified two G protein-coupled receptors (GPCR) in the oyster Crassostrea gigas (Mollusca), phylogenetically related to chordate CCK receptors (CCKR) and to ecdysozoan sulfakinin receptors (SKR). These receptors, Cragi-CCKR1 and Cragi-CCKR2, were characterised functionally using a cell-based assay. We identified di- and mono-sulphated forms of oyster Cragi-CCK1 (pEGAWDY(SO₃H)DY(SO₃H)GLGGGRF-NH₂) as the potent endogenous agonists for these receptors. The Cragi-CCK genes were expressed in the visceral ganglia of the nervous system. The Cragi-CCKR1 gene was expressed in a variety of tissues, while Cragi-CCKR2 gene expression was more restricted to nervous tissues. An in vitro bioassay revealed that different forms of Cragi-CCK1 decreased the frequency of the spontaneous contractions of oyster hindgut. Expression analyses in oysters with contrasted nutritional statuses or in the course of their reproductive cycle highlighted the plausible role of Cragi-CCK signalling in the regulation of feeding and its possible involvement in the coordination of nutrition and energy storage in the gonad. This study confirms the early origin of the CCK/SK signalling system from the common bilaterian ancestor and delivers new insights into its structural and functional evolution in the lophotrochozoan lineage.

Cloning, localization, and physiological effects of sulfakinin in the kissing bug, Rhodnius prolixus

Sulfakinins (SKs) are a family of multifunctional neuropeptides that have been shown to have myotropic activity on muscles of the digestive system and to function as feeding satiety factors. Here, we confirm via cloning the presence of two sulfakinins (Rhopr-SK-1 and Rhopr-SK-2) in Rhodnius prolixus. Reverse transcriptase quantitative PCR demonstrates that the Rhopr-SK transcript is highly expressed in the central nervous system (CNS) of unfed fifth-instar R. prolixus. Fluorescent in situ hybridization shows transcript expression only in neurons in the brain. Immunohistochemical staining of SK-like peptides was observed in the same neurons in the brain and in processes extending throughout the CNS, as well as over the posterior midgut and anterior hindgut. Rhopr-SK-1 (sulfated form) induces contractions of the hindgut in a dose-dependent manner. Injection Rhopr-SK-1 (sulfated form) significantly decreases the overall weight of the blood meal consumed, suggesting SK's role as a satiety factor in R. prolixus.

NONSULFATED SULFAKININ CHANGES METABOLIC PARAMETERS OF INSECT FAT BODY MITOCHONDRIA

We investigated the effect of neuropeptide, the nonsulfated sulfakinin (SK) Zopat-SK-1 (pETSDDYGHLRFa) on the mitochondrial oxidative metabolism in the Zophobas atratus larval fat body. Mitochondria were isolated from beetle fat bodies 2 and 24 h after hormone injection. The administration of 20 pmol of Zopat-SK-1 to feeding larvae led to decreased mitochondrial oxidative activities in larval fat body. Diminished activities of citrate synthase and the cytochrome pathway, that is, nonphosphorylating and phosphorylating respiration during succinate oxidation, were observed. However, the effect of Zopat-SK-1 was more pronounced in fat body of insects after 24 h since hormone application. In hormone-treated larval fat bodies, mitochondrial respiration was decreased at the level of respiratory chain and the TCA cycle as well as at the level of mitochondrial biogenesis, as indicated by decreased activities of mitochondrial marker enzymes in fat body homogenates. The inhibition of succinate oxidation may indicate the role of Zopat-SK-1 in the regulation of mitochondrial complex II activity. Moreover, decreased respiratory chain activity was accompanied by the reduced activity of mitochondrial energy-dissipating pathway, uncoupling protein 4. The observed decrease in mitochondrial oxidative metabolism may reflect the Zopat-SK-1-induced reduction in the metabolic rate of larval fat body linked to actual energetic demands of animal.

The activity of the nonsulfated sulfakinin Zopat-SK-1 in the neck-ligated larvae of the beetle Zophobas atratus

Insect sulfakinins (SKs) are multifunctional neuropeptides structurally and functionally homologous to the mammalian gastrin/cholecystokinin (CCK). It has been proposed that SKs play a role in modulating energy management in insects by interacting with adipokinetic hormone (AKH), the principle hormone controlling insect intermediary metabolism. To exclude head factors (including AKH) that influence the activity of the nonsulfated sulfakinin Zopat-SK-1 in the larvae of the beetle Zophobas atratus, ligature and in vitro bioassays were used. Our study showed that in the neck-ligated larvae, Zopat-SK-1 evoked a much more pronounced glycogenolytic effect in fat body tissue and a significantly higher hypertrahelosemic effect in hemolymph than in larvae without ligation. We found that the concentration of the sugar trehalose increased under hormonal treatment but no changes in glucose levels were observed. Under in vitro conditions, the maximal glycogenolytic effect of Zopat-SK-1 in fat body was observed at 10 pmol of hormone. Ligature and in vitro bioassays indicated that Zopat-SK-1 activity in the Z. atratus larvae is modulated by head signals and/or factors from the gastrointestinal tract. Our data indicate the existence of a brain-gastrointestinal axis that has a role in controlling of energy (carbohydrate) metabolism in the insect body. Moreover, these results, together with immunological evidence of a cholecystokinin-like (sulfakinin) receptor in the Z. atratus fat body, help us to better understand the SK signaling pathways and its physiological role in insect biology.

New metabolic activity of the nonsulfated sulfakinin Zopat-SK-1 in the insect fat body

Insect sulfakinins are multifunctional neuropeptides homologous to vertebrate gastrin/cholecystokin (CCK) neuropeptide hormones. We investigated the action of the nonsulfated sulfakinin Zopat-SK-1 (pETSDDYGHLRFa) on the levels of chosen metabolites in the Zophobas atratus beetle fat body. Samples of fat body were collected 2h and 24h after hormone injection. The administration of 20pmol of Zopat-SK-1 to feeding larvae significantly increased concentrations of lipids and proteins and decreased the content of glycogen in fat body tissue in the 24h experimental group. In contrast, the only increase in total lipid concentration in prepupal fat bodies was observed 24h after Zopat-SK-1 treatment. Simultaneously, changes in the quality and quantity of free sugars in the hemolymph were measured. In larval hemolymph, a marked increase in free sugar concentration and a decrease in glucose content were observed 24h and 2h after Zopat-SK-1 application, respectively. No changes in the prepupal stage were observed. For the first time we show potent metabolic activity of sulfakinin in the fat body tissue of an insect. Our findings imply a physiological function of the nonsulfated form of sulfakinin in energy storage and release processes in fat body tissue of larvae and prepupae was indicated. We suggest a role for sulfakinin signaling in the regulation of energy metabolism in insect tissues.

Sulfakinin is an important regulator of digestive processes in the migratory locust, Locusta migratoria

Sulfakinin (SK) is a sulfated insect neuropeptide that is best known for its function as a satiety factor. It displays structural and functional similarities with the vertebrate peptides gastrin and cholecystokinin. Peptidomic studies in multiple insects, crustaceans and arachnids have revealed the widespread occurrence of SK in the arthropod phylum. Multiple studies in hemi- and holometabolous insects revealed the pleiotropic nature of this neuropeptide: in addition to its activity as a satiety factor, SK was also reported to affect muscle contraction, digestive enzyme release, odor preference, aggression and metabolism. However, the main site of action seems to be the digestive system of insects. In this study, we have investigated whether SK can intervene in the control of nutrient uptake and digestion in the migratory locust (Locusta migratoria). We provide evidence that sulfakinin reduces food uptake in this species. Furthermore, we discovered that SK has very pronounced effects on the main digestive enzyme secreting parts of the locust gut. It effectively reduced digestive enzyme secretion from both the midgut and gastric caeca. SK injection also elicited a reduction in absorbance and proteolytic activity of the gastric caeca contents. The characteristic sulfation of the tyrosine residue is crucial for the observed effects on digestive enzyme secretion. In an attempt to provide potential leads for the development of peptidomimetic compounds based on SK, we also tested two mimetic analogs of the natural peptide ligand in the digestive enzyme secretion assay. These analogs were able to mimic the effect of the natural SK, but their effects were milder. The results of this study provide new insights into the action of SK on the digestive system in (hemimetabolous) insects.

In silico Neuropeptidome of Female Macrobrachium rosenbergii Based on Transcriptome and Peptide Mining of Eyestalk, Central Nervous System and Ovary

Macrobrachium rosenbergii is the most economically important of the cultured freshwater crustacean species, yet there is currently a deficiency in genomic and transcriptomic information for research requirements. In this study, we present an in silico analysis of neuropeptide genes within the female M. rosenbergii eyestalk, central nervous system, and ovary. We could confidently predict 37 preproneuropeptide transcripts, including those that encode bursicons, crustacean cardioactive peptide, crustacean hyperglycemic hormones, eclosion hormone, pigment-dispersing hormones, diuretic hormones, neuropeptide F, neuroparsins, SIFamide, and sulfakinin. These transcripts are most prominent within the eyestalk and central nervous system. Transcript tissue distribution as determined by reverse transcription-polymerase chain reaction revealed the presence of selected neuropeptide genes of interest mainly in the nervous tissues while others were additionally present in the non-nervous tissues. Liquid chromatography-mass spectrometry analysis of eyestalk peptides confirmed the presence of the crustacean hyperglycemic hormone precursor. This data set provides a strong foundation for further studies into the functional roles of neuropeptides in M. rosenbergii, and will be especially helpful for developing methods to improve crustacean aquaculture.

CCK(-like) and receptors: structure and phylogeny in a comparative perspective

Cholecystokinin (CCK) and gastrin are regulatory peptides in vertebrates. Their homologues are widely present in metazoan animals, in form of cionin in tunicates, neuropeptide-like protein 12 in nematodes and sulfakinin (SK) in arthropods. CCK(-like) peptides exert diverse physiological effects through binding their corresponding receptors, which are important members of the hormone-binding G-protein-coupled receptors. In this paper, CCK(-like) peptides and receptors are reviewed in a comparative way at levels of molecular structure, physiological functions and phylogeny. CCK signalling system is widely involved in the regulation of satiety, gastric acid secretion, pancreatic secretion, anxiety and memory processes in vertebrates. Its counterpart SK in arthropods is also found with similar functions on regulation of satiety and gastrointestinal motility. Co-evolution of peptide and receptor has been recognized through metazoans. The CCK(-like) receptors seem to be evolved from a common ancestor based on the phylogenetic analysis, with species-specific events in arthropods. In addition, tetraploidization has been brought up to study the evolution of receptors. There are 2 receptors in chordates and nematodes, whereas, the number of sulfakinin receptor varies in arthropods from 0 to 2. We discussed here that the presence or absence of the SK signalling system is likely to be related to feeding behaviour.

Signaling Properties and Pharmacological Analysis of Two Sulfakinin Receptors from the Red Flour Beetle, Tribolium castaneum

Sulfakinin is an insect neuropeptide that constitutes an important component of the complex network of hormonal and neural factors that regulate feeding and digestion. The key modulating functions of sulfakinin are mediated by binding and signaling via G-protein coupled receptors. Although a substantial amount of functional data have already been reported on sulfakinins in different insect species, only little information is known regarding the properties of their respective receptors. In this study, we report on the molecular cloning, functional expression and characterization of two sulfakinin receptors in the red flour beetle, Tribolium castaneum. Both receptor open reading frames show extensive sequence similarity with annotated sulfakinin receptors from other insects. Comparison of the sulfakinin receptor sequences with homologous vertebrate cholecystokinin receptors reveals crucial conserved regions for ligand binding and receptor activation. Quantitative reverse transcriptase PCR shows that transcripts of both receptors are primarily expressed in the central nervous system of the beetle. Pharmacological characterization using 29 different peptide ligands clarified the essential requirements for efficient activation of these sulfakinin receptors. Analysis of the signaling pathway in multiple cell lines disclosed that the sulfakinin receptors of T. castaneum can stimulate both the Ca²⁺ and cyclic AMP second messenger pathways. This in depth characterization of two insect sulfakinin receptors may provide useful leads for the further development of receptor ligands with a potential applicability in pest control and crop protection.

Characterization of sulfakinin receptor 2 and its role in food intake in the red flour beetle, Tribolium castaneum

Insects acquire essential nutrients from their food to support a diverse range of biological processes such as development and reproduction. An important role in the food intake regulation is attributed to the neurohormone sulfakinin signaling pathway. Sulfakinins (SKs) elicit satiety together with sulfakinin receptors (SKRs). In this project, the gene coding a second putative SKR, namely skr2, was cloned, characterized and functionally studied in the red flour beetle Tribolium castaneum, with the purpose to understand its role in food intake regulation. The gene skr2 encoded a seven-transmembrane SKR2 protein with 420 amino acids and is evolutionarily close to the two SKRs in Drosophila. A distribution analysis by means of quantitative real-time PCR revealed a tissue- and stage-specific expression pattern with skr2 being dominantly expressed in head, and in the pupal and adult stages. Besides, its expression in gut was notable. With use of dsRNA of skr2, larval food intake was stimulated in an injection RNAi assay. Based on the data obtained, skr2 is considered as an indispensable component in the regulation of food intake in T. castaneum.

Cholecystokinin-Like Peptide (DSK) in Drosophila, Not Only for Satiety Signaling

Cholecystokinin (CCK) signaling appears well conserved over evolution. In Drosophila, the CCK-like sulfakinins (DSKs) regulate aspects of gut function, satiety and food ingestion, hyperactivity and aggression, as well as escape-related locomotion and synaptic plasticity during neuromuscular junction development. Activity in the DSK-producing neurons is regulated by octopamine. We discuss mechanisms behind CCK function in satiety, aggression, and locomotion in some detail and highlight similarities to mammalian CCK signaling.

Characterization of sulfakinin and sulfakinin receptor and their roles in food intake in the red flour beetle Tribolium castaneum

Sulfakinins (SK) are multifunctional neuropeptides widely found in insects that are structurally and functionally homologous to the mammalian gastrin/cholecystokinin (CCK) neuropeptides. CCK is involved in various biological processes such as the feeding regulation where it induces satiety. In this project we characterized SK and SK receptor (SKR) of an important pest and model beetle insect, the red flour beetle Tribolium castaneum, with the aim to better understand the SK signaling pathway and its function in food intake. The sk gene encoded a SK precursor with 113 amino acids and the skr gene a seven-transmembrane SKR with 554 amino acids. Both genes were expressed in the larval, pupal and adult stages with different expression levels in tested tissues. By RNA interference, sk dsRNA and skr dsRNA reduced the expression of the corresponding target gene by 80-90% and 30-50%, respectively, and stimulated food intake in the larvae. In parallel, we injected insects with a SK analog reducing food intake. In conclusion, the data are discussed in relation to the SK signaling pathway and its physiological-endocrinological role in regulating food intake and potential usage in the control of important pest insects.

Differential protease activity augments polyphagy in Helicoverpa armigera

Helicoverpa armigera (Lepidoptera: Noctuidae) and other polyphagous agricultural pests are extending their plant host range and emerging as serious agents in restraining crop productivity. Dynamic regulation, coupled with a diversity of digestive and detoxifying enzymes, play a crucial role in the adaptation of polyphagous insects. To investigate the functional intricacy of serine proteases in the development and polyphagy of H. armigera, we profiled the expression of eight trypsin-like and four chymotrypsin-like phylogenetically diverse mRNAs from different life stages of H. armigera reared on nutritionally distinct host plants. These analyses revealed diet- and stage-specific protease expression patterns. The trypsins expressed showed structural variations, which might result in differential substrate specificity and interaction with inhibitors. Protease profiles in the presence of inhibitors and their mass spectrometric analyses revealed insight into their differential activity. These findings emphasize the differential expression of serine proteases and their consequences for digestive physiology in promoting polyphagy in H. armigera.

Analogs of sulfakinin-related peptides demonstrate reduction in food intake in the red flour beetle, Tribolium castaneum, while putative antagonists increase consumption

The insect sulfakinins (SKs) constitute a family of neuropeptides that display both structural and functional similarities to the mammalian hormones gastrin and cholecystokinin (CCK). As a multifunctional neuropeptide, SKs are involved in muscle contractions as well as food intake regulation in many insects. In the red flour beetle Tribolium castaneum, the action on food intake by a series of synthetic SK analogs and one putative antagonist was investigated by injection in beetle adults. The most remarkable result was that both sulfated and non-sulfated SKs [FDDY(SO3H)GHMRFamide] inhibited food intake by about 70%. Strong activity observed for SK analogs featuring a residue that mimics the acidic nature of Tyr(SO3H) but lack the phenyl ring of Tyr, indicate that aromaticity is not a critical characteristic for this position of the peptide. SK demonstrated considerable tolerance to Ser and Ala substitution in position 8 (basic Arg), as analogs featuring these uncharged substitutions retained almost all of the food intake inhibitory activity. Also, the Phe in position 1 could be replaced by Ser without complete loss of activity. Conversely, substitution of Met by Nle in position 7 led to inactive compounds. Finally, the Caenorhabditis elegans sulfated neuropeptide-like protein-12 (NLP-12), that shares some sequence similarities with the SKs but features a Gln-Phe-amide rather than an Arg-Phe-amide at the C-terminus, elicited increased food intake in T. castaneum, which may indicate an antagonist activity. Co-injection of NLP-12 with nsSK blocked the food intake inhibitory effects of nsSK.

The effect of adipokinetic hormone on midgut characteristics in Pyrrhocoris apterus L. (Heteroptera)

Digestive processes and the effect of adipokinetic hormone (Pyrap-AKH) on the amount of nutrients (lipids, proteins, and carbohydrates), and on the activity of digestive enzymes (lipases, peptidases, and carbohydrases) were studied in the midgut of the firebug, Pyrrhocoris apterus. The analyses were performed on samples of anterior (AM), middle (MM) and posterior (PM) midgut parts. The results revealed that the digestion of lipids, carbohydrates and proteins take place in the acidic milieu. The Pyrap-AKH treatment increased significantly the level of lipids and proteins in the midgut, and also the level of triacylglycerols (TGs) predominantly in the AM, and the level of diacylglycerols (DGs) in the MM. The increase was not uniform for all present TG and DG species - those containing the linoleic fatty acid were predominant. No hormonal effect on lipase activity was recorded, while peptidase and glucosidase activity was increased in the MM and PM. All these facts indicate that the Pyrap-AKH probably stimulates digestion by more intensive food ingestion or turnover, and perhaps by the stimulation of metabolite absorption; the activation of digestive enzymes seems to be secondary or controlled by other mechanisms.

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.

Mechanisms of pH control in the midgut of Lutzomyia longipalpis: roles for ingested molecules and hormones

Control of the midgut pH in Lutzomyia longipalpis enables the insect's digestive system to deal with different types of diet. Phlebotomines must be able to suddenly change from a condition adequate to process a sugar diet to one required to digest blood. Prior to blood ingestion, the pH in the midgut is maintained at ∼6 via an efficient mechanism. In the abdominal midgut, alkalization to a pH of ∼8 occurs as a consequence of the loss of CO(2) from blood (CO(2) volatilization) and by a second mechanism that is not yet characterized. The present study aimed to characterize the primary stimuli, present in the blood, that are responsible for shutting down the mechanism that maintains a pH of 6 and switching on that responsible for alkalization. Our results show that any ingested protein could induce alkalization. Free amino acids, at the concentrations found in blood, were ineffective at inducing alkalization, although higher concentrations of amino acids were able to induce alkalization. Aqueous extracts of midgut tissue containing putative hormones from intestinal endocrine cells slightly alkalized the midgut lumen when applied to dissected intestines, as did hemolymph collected from blood-fed females. Serotonin, a hormone that is possibly released in the hemolymph after hematophagy commences, was ineffective at promoting alkalization. The carbonic anhydrase (CA) enzyme seems to be involved in alkalizing the midgut, as co-ingestion of acetazolamide (a CA inhibitor) with proteins impaired alkalization efficiency. A general model of alkalization control is presented.

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

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

The CCK(-like) receptor in the animal kingdom: functions, evolution and structures

In this review, the cholecystokinin (CCK)(-like) receptors throughout the animal kingdom are compared on the level of physiological functions, evolutionary basis and molecular structure. In vertebrates, the CCK receptor is an important member of the G-protein coupled receptors as it is involved in the regulation of many physiological functions like satiety, gastrointestinal motility, gastric acid secretion, gall bladder contraction, pancreatic secretion, panic, anxiety and memory and learning processes. A homolog for this receptor is also found in nematodes and arthropods, called CK receptor and sulfakinin (SK) receptor, respectively. These receptors seem to have evolved from a common ancestor which is probably still closely related to the nematode CK receptor. The SK receptor is more closely related to the CCK receptor and seems to have similar functions. A molecular 3D-model for the CCK receptor type 1 has been built together with the docking of the natural ligands for the CCK and SK receptors in the CCK receptor type 1. These molecular models can help to study ligand-receptor interactions, that can in turn be useful in the development of new CCK(-like) receptor agonists and antagonists with beneficial health effects in humans or potential for pest control.

Effects of starvation and parasitism on foregut contraction in larval Manduca sexta

Larvae of Manduca sexta are parasitised by the braconid wasp, Cotesia congregata. In this study we examined whether contraction activity of the semi-isolated foregut was affected by parasitism. Parasitised larvae fed significantly less compared with unparasitised control larvae, therefore starved unparasitised animals were used as controls. Rate and force of foregut contraction in control caterpillars significantly increased with days of starvation. However, only contraction force in foreguts of parasitised larvae increased over time following infection. The presence of food in the foregut of caterpillars starved 7 days suggested that food moved anteriorly from the midgut and that contraction became antiperistaltic, but only normal peristalsis occurred in parasitised caterpillars. Rate and force of gut contractions may be controlled independently and starvation did not truly mimic the effects of the parasitoids. Dissection of caterpillars with emerged wasps indicated that 47% had a single wasp larva wedged between the brain and foregut. Removal of this wasp caused an increased rate of foregut contraction of the caterpillar. Brain removal resulted in an increased rate of foregut contraction only for unparasitised insects. Sectioning of the recurrent nerve temporarily eliminated foregut contraction, but the contraction began again in 250 s in parasitised caterpillars prior to wasp emergence, compared with over 500 s for unparasitised controls and parasitised caterpillars following wasp emergence.

Control of the release of digestive enzymes in the larvae of the fall armyworm, Spodoptera frugiperda

There is a basal level of enzyme activity for trypsin, aminopeptidase, amylase, and lipase in the gut of unfed larval (L6) Spodoptera frugiperda. Trypsin activity does not decrease with non-feeding, possibly because of the low protein levels in plants along with high amino acid requirements for growth and storage (for later reproduction in adults). Therefore, trypsin must always be present so that only a minimal protein loss via egestion occurs. Larvae, however, adjust amylase activity to carbohydrate ingestion, and indeed amylase activity is five-fold higher in fed larvae compared to unfed larvae. Gut lipase activity is low, typical of insects with a high carbohydrate diet. A flat-sheet preparation of the ventriculus was used to measure the release of enzymes in response to specific nutrients and known brain/gut hormones in S. frugiperda. Sugars greatly increase (>300%) amylase release, but starch has no effect. Proteins and amino acids have little or no effect on trypsin or aminopeptidase release. The control of enzyme release in response to food is likely mediated through neurohormones. Indeed, an allatostatin (Spofr-AS A5) inhibits amylase and trypsin, and allatotropin (Manse- AT) stimulates amylase and trypsin release. Spofr-AS A5 also inhibits ileum myoactivity and Manse-AT stimulates myoactivity. The epithelial secretion rate of amylase and trypsin was about 20% of the amount of enzyme present in the ventricular lumen, which, considering the efficient counter-current recycling of enzymes, suggests that the secretion rate is adequate to replace egested enzymes.

Structural and functional diversities in lepidopteran serine proteases

Primary protein-digestion in Lepidopteran larvae relies on serine proteases like trypsin and chymotrypsin. Efforts toward the classification and characterization of digestive proteases have unraveled a considerable diversity in the specificity and mechanistic classes of gut proteases. Though the evolutionary significance of mutations that lead to structural diversity in serine proteases has been well characterized, detailing the resultant functional diversity has continually posed a challenge to researchers. Functional diversity can be correlated to the adaptation of insects to various host-plants as well as to exposure of insects to naturally occurring antagonistic biomolecules such as plant-derived protease inhibitors (PIs) and lectins. Current research is focused on deciphering the changes in protease specificities and activities arising from altered amino acids at the active site, specificity-determining pockets and other regions, which influence activity. Some insight has been gained through in silico modeling and simulation experiments, aided by the limited availability of characterized proteases. We examine the structurally and functionally diverse Lepidopteran serine proteases, and assess their influence on larval digestive processes and on overall insect physiology.

Discovery of a cholecystokinin-gastrin-like signaling system in nematodes

Members of the cholecystokinin (CCK)/gastrin family of peptides, including the arthropod sulfakinins, and their cognate receptors, play an important role in the regulation of feeding behavior and energy homeostasis. Despite many efforts after the discovery of CCK/gastrin immunoreactivity in nematodes 23 yr ago, the identity of these nematode CCK/gastrin-related peptides has remained a mystery ever since. The Caenorhabditis elegans genome contains two genes with high identity to the mammalian CCK receptors and their invertebrate counterparts, the sulfakinin receptors. By using the potential C. elegans CCK receptors as a fishing hook, we have isolated and identified two CCK-like neuropeptides encoded by neuropeptide-like protein-12 (nlp-12) as the endogenous ligands of these receptors. The neuropeptide-like protein-12 peptides have a very limited neuronal expression pattern, seem to occur in vivo in the unsulfated form, and react specifically with a human CCK-8 antibody. Both receptors and ligands share a high degree of structural similarity with their vertebrate and arthropod counterparts, and also display similar biological activities with respect to digestive enzyme secretion and fat storage. Our data indicate that the gastrin-CCK signaling system was already well established before the divergence of protostomes and deuterostomes.

RNA interference suggests sulfakinins as satiety effectors in the cricket Gryllus bimaculatus

In the Mediterranean field cricket, Gryllus bimaculatus, the action of sulfakinin (SK) gene expression on food intake, food transport in the gut and carbohydrate digestion (alpha-amylase activity) was investigated by using the RNA interference (RNAi) method. Injection of SK double-stranded (ds) RNA into the abdomen of female adults and last instar larvae led to a systemic silencing of the SK gene, as was shown by RT-PCR studies. In adults, suppression of SK gene expression was effective from the first day after injection up to at least the third day. Treatment of the adult crickets by injection or feeding of dsRNA led to a stimulation of the food intake. Assuming that the gene silencing is followed by a depletion of the SK in tissues and/or haemolymph implies an inhibitiory role of the native SK peptides on food intake. The alpha-amylase activity in vitro in the midgut tissue and in the secretions of adult females was not affected by silencing the SK gene.

Structure of the sulfakinin cDNA and gene expression from the Mediterranean field cricket Gryllus bimaculatus

The sulfakinins are multifunctional insect neuropeptides displaying sequence similarities with the gastrin/ cholecystokinin (CCK) peptide family. In vertebrates, the peptides gastrin and CCK are involved in the regulation of digestion and food-intake. In this study sulfakinin cDNA was cloned and sequenced from the Mediterranean field cricket Gryllus bimaculatus. The cDNA encodes two peptides flanked by endoproteolytic processing sites, designated GrybiSKI (QSDDYGHMRFG) and GrybiSKII (EPFDDYGHMRFG). The peptides include the characteristic amino acid Tyr, which is potentially sulphated, and a Gly, as a recognition site for amidation yeilding the common C-terminal amino acid sequence of the sulfakinin peptide family. RT-PCR studies indicate an expression of the gene restricted to the brain, with a constant level of expression throughout the last larval stage, but showing an age-dependent decrease of expression in adult females.

Identification and cardiotropic actions of sulfakinin peptides in the American lobster Homarus americanus

In arthropods, a group of peptides possessing a–Y(SO3H)GHM/LRFamide carboxy-terminal motif have been collectively termed the sulfakinins. Sulfakinin isoforms have been identified from numerous insect species. In contrast, members of this peptide family have thus far been isolated from just two crustaceans, the penaeid shrimp Penaeus monodon and Litopenaeus vannamei. Here, we report the identification of a cDNA encoding prepro-sulfakinin from the American lobster Homarus americanus. Two sulfakinin-like sequences were identified within the open-reading frame of the cDNA. Based on modifications predicted by peptide modeling programs, and on homology to the known isoforms of sulfakinin, particularly those from shrimp, the mature H. americanus sulfakinins were hypothesized to be pEFDEY(SO3H)GHMRFamide (Hoa-SK I) and GGGEY(SO3H)DDY(SO3H)GHLRFamide (Hoa-SK II). Hoa-SK I is identical to one of the previously identified shrimp sulfakinins, while Hoa-SK II is a novel isoform. Exogenous application of either synthetic Hoa-SK I or Hoa-SK II to the isolated lobster heart increased both the frequency and amplitude of spontaneous heart contractions. In preparations in which spontaneous contractions were irregular, both peptides increased the regularity of the heartbeat. Our study provides the first molecular characterization of a sulfakinin-encoding cDNA from a crustacean, as well as the first demonstration of bioactivity for native sulfakinins in this group of arthropods.

The role of neuropeptides in caterpillar nutritional ecology

Plant diet strongly impacts the fitness of insect herbivores. Immediately, we think of plant defensive compounds that may act as feeding deterrents or toxins. We are, probably, less aware that plants also influence insect growth and fecundity through their nutritional quality. However, most herbivores respond to their environment and select the diet which optimizes their growth and development. This regulation of nutritional balance may occur on many levels: through selecting and ingesting appropriate plant tissue and nutrient digestion, absorption and utilization. Here, we review evidence of how nutritional requirements, particularly leaf protein to digestible carbohydrate ratios, affect caterpillar herbivores. We propose a model where midgut endocrine cells assess and integrate hemolymph nutritional status and gut content and release peptides which influence digestive processes. Understanding the effects of diet on the insect herbivore is essential for the rational design and implementation of sustainable pest management practices.

FMRFamide-like immunocytochemistry in the brain and subesophageal ganglion of Triatoma infestans (Insecta: Heteroptera). Coexpression with β-pigment-dispersing hormone and small cardioactive peptide B

The distribution of FMRFamide (FMRFa)-like immunoreactivity (LI) was studied in the brain and subesophageal ganglion of Triatoma infestans, the insect vector of Chagas' disease. The neuropeptide displayed a widespread distribution with immunostained somata in the optic lobe, in the anterior, lateral, and posterior soma rinds of the protocerebrum, and around the antennal sensory and mechanosensory and motor neuropils of the deutocerebrum. FMRFa-immunoreactive profiles of the subesophageal ganglion were seen in the mandibular, maxillary, and labial neuromeres. Immunostained neurites were detected in the medulla and lobula of the optic lobe, the lateral protocerebral neuropil, the median bundle, the calyces and the stalk of the mushroom bodies, and the central body. In the deutocerebrum, the sensory glomeruli showed a higher density of immunoreactive processes than the mechanosensory and motor neuropil, whereas the neuropils of each neuromere of the subesophageal ganglion displayed a moderate density of immunoreactive neurites. Colocalization of FMRFa-LI and crustacean pigment-dispersing hormone-LI was found in perikarya of the proximal optic lobe, the lobula, the sensory deutocerebrum, and the labial neuromere of the subesophageal ganglion. The distribution pattern of small cardioactive peptide B (SCP(B))-LI was also widespread, with immunolabeled somata surrounding every neuropil region of the brain and subesophageal ganglion, except for the optic lobe. FMRFa- and SCP(B)-LIs showed extensive colocalization in the brain of this triatomine species. The presence of immunolabeled perikarya displaying either FMRFa- or SCP(B)-LI confirmed that each antisera identified different peptide molecules. The distribution of FMRFa immunostaining in T. infestans raises the possibility that FMRFa plays a role in the regulation of circadian rhythmicity. The finding of immunolabeling in neurosecretory somata of the protocerebrum suggests that this neuropeptide may also act as a neurohormone.

In vitro analysis of the digestive enzymes amylase and alpha-glucosidase in the midguts of Locusta migratoria L. in response to the myosuppressin, SchistoFLRFamide

We have investigated the effect of the locust myosuppressin, SchistoFLRFamide, on the activity of amylase and alpha-glucosidase in the midgut of 2-week old male locusts. Total enzyme activity in the lumen contents and tissue extracts of midguts responds to SchistoFLRFamide in a dose-dependent manner that appears to vary with the feeding state of the locust and duration of exposure to the peptide. Starvation for 24h prior to assessment alters the distribution of enzyme activity between the midgut lumen contents and tissue extracts in response to SchistoFLRFamide when compared with fed locusts. Duration of exposure to SchistoFLRFamide also alters the distribution of total amylase and alpha-glucosidase activity; as duration of exposure increases, lower concentrations of SchistoFLRFamide increase total enzyme activity in the lumen contents while decreasing total enzyme activity in the tissue extracts. We suggest that the minimum amino acid sequence in SchistoFLRFamide necessary to increase both amylase and alpha-glucosidase activity is DHVFLRFamide. We have determined that two other peptides endogenous to the locust, AFIRFamide and GQERNFLRFamide, increase amylase and alpha-glucosidase activity in midgut lumen contents.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

The influence of diet and feeding state on FMRFamide-related peptides in the gut of Locusta migratoria L

Gut tissues of 2-week post-ecdysis female Locusta migratoria L. were assayed for FMRFamide-like immunoreactivity (FLI) during various feeding states using both radioimmunoassay and immunohistochemistry. The feeding states investigated were: (a) 48- and 24-h starved; (b) 5-, 30-, or 60-min post-feeding initiation; and (c) a diet of wheat grass, carrots, or apples. We determined: (1) the feeding state of a locust influences FLI in all gut tissues; (2) variations in diet appear to influence FLI in all gut tissues; (3) more than one FMRFamide-related peptide (FaRP) responds to differences in diet and state of starvation in the gut tissues; and (4) the protein poor diets (carrot and apple), in conjunction with the assertion that protein to carbohydrate ratio in the diet is the key component for nutrient balancing, suggests that FaRPs may play a role in maintaining balanced nutrient content in the locust.

A brain peptide stimulates release of amylase from the midgut tissue of larvae of Opisina arenosella Walk. (Lepidoptera: Cryptophasidae)

Brain extracts from 3 to 4 day old final (eighth) instar larvae of Opisina arenosella (Lepidoptera) stimulate amylase release from midgut preparations maintained in vitro. This effect of the brain extract was both time and dose dependent. The brain factor stimulating enzyme release may be a peptide as it is heat stable and susceptible to treatment with proteolytic enzymes. For purification of the brain factor, a head extract prepared in 2% NaCl was first precipitated in 80% aqueous acetone and then fractionated by DEAE cellulose ion exchange chromatography. The fraction OCF(2), from ion exchange chromatography was further purified on a Sephadex G25 column. The fraction designated as OCF(2.3) obtained by gel filtration showed maximum activity and it was selected for HPLC analysis. HPLC elution profiles of OCF(2.3) showed two major peaks separated by a time interval of 0.107 min. The two overlapping peaks of OCF(2.3) may represent either different forms of a peptide or different peptides of a family. The molecular weight OCF(2.3) was estimated to be 1070 Da.