Insect Myosuppressins and Sulfakinins Stimulate Release of the Digestive Enzyme ?-Amylase in Two Invertebrates: The Scallop Pecten maximus and Insect Rhynchophorus ferrugineus

Differential expression of neuropeptide F in the digestive organs of female freshwater prawn, Macrobrachium rosenbergii, during the ovarian cycle

Neuropeptide F is a key hormone that controls feeding in invertebrates, including decapod crustaceans. We investigated the differential expression of Macrobrachium rosenbergii neuropeptide F (MrNPF) in the digestive organs of female prawns, M. rosenbergii, during the ovarian cycle. By using RT-qPCR, the expression of MrNPF mRNA in the esophagus (ESO), cardia (CD), and pylorus (PY) of the foregut (FG) gradually increased from stage II and peaked at stage III. In the midgut (MG), hindgut (HG), and hepatopancreas (HP), MrNPF mRNA increased from stage I, reaching a maximal level at stage II, and declined by about half at stages III and IV (P < 0.05). In the ESO, CD, and PY, strong MrNPF-immunoreactivities were seen in the epithelium, muscle, and lamina propria. Intense MrNPF-ir was found in the MG cells and the muscular layer. In the HG, MrNPF-ir was detected in the epithelium of the villi and gland regions, while MrNPF-ir was also more intense in the F-, R-, and B-cells in the HP. However, we found little colocalization between the MrNPF and PGP9.5/ChAT in digestive tissues, implying that most of the positive cells might not be neurons but could be digestive tract-associated endocrine cells that produce and secrete MrNPF to control digestive organ functions in feeding and utilizing feed. Taken together, our first findings indicated that MrNPF was differentially expressed in digestive organs in correlation with the ovarian cycle, suggesting an important link between MrNPF, the physiology of various digestive organs in feeding, and possibly ovarian maturation in female M. rosenbergii.

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.

Starvation-Induced Changes to the Midgut Proteome and Neuropeptides in Manduca sexta

Starvation is a complex physiological state that induces changes in protein expression to ensure survival. The insect midgut is sensitive to changes in dietary content as it is at the forefront of communicating information about incoming nutrients to the body via hormones. Therefore, a DIA proteomics approach was used to examine starvation physiology and, specifically, the role of midgut neuropeptide hormones in a representative lepidopteran, Manduca sexta. Proteomes were generated from midguts of M. sexta fourth-instar caterpillars, starved for 24 h and 48 h, and compared to fed controls. A total of 3047 proteins were identified, and 854 of these were significantly different in abundance. KEGG analysis revealed that metabolism pathways were less abundant in starved caterpillars, but oxidative phosphorylation proteins were more abundant. In addition, six neuropeptides or related signaling cascade proteins were detected. Particularly, neuropeptide F1 (NPF1) was significantly higher in abundance in starved larvae. A change in juvenile hormone-degrading enzymes was also detected during starvation. Overall, our results provide an exploration of the midgut response to starvation in M. sexta and validate DIA proteomics as a useful tool for quantifying insect midgut neuropeptide hormones.

Evolutionary conserved peptide and glycoprotein hormone-like neuroendocrine systems in C. elegans

Peptides and protein hormones form the largest group of secreted signals that mediate intercellular communication and are central regulators of physiology and behavior in all animals. Phylogenetic analyses and biochemical identifications of peptide-receptor systems reveal a broad evolutionary conservation of these signaling systems at the molecular level. Substantial progress has been made in recent years on characterizing the physiological and putative ancestral roles of many peptide systems through comparative studies in invertebrate models. Several peptides and protein hormones are not only molecularly conserved but also have conserved roles across animal phyla. Here, we focus on functional insights gained in the nematode Caenorhabditis elegans that, with its compact and well-described nervous system, provides a powerful model to dissect neuroendocrine signaling networks involved in the control of physiology and behavior. We summarize recent discoveries on the evolutionary conservation and knowledge on the functions of peptide and protein hormone systems in C. elegans.

Hologenome analysis reveals independent evolution to chemosymbiosis by deep-sea bivalves

BACKGROUND

Bivalves have independently evolved a variety of symbiotic relationships with chemosynthetic bacteria. These relationships range from endo- to extracellular interactions, making them ideal for studies on symbiosis-related evolution. It is still unclear whether there are universal patterns to symbiosis across bivalves. Here, we investigate the hologenome of an extracellular symbiotic thyasirid clam that represents the early stages of symbiosis evolution.

RESULTS

We present a hologenome of Conchocele bisecta (Bivalvia: Thyasiridae) collected from deep-sea hydrothermal vents with extracellular symbionts, along with related ultrastructural evidence and expression data. Based on ultrastructural and sequencing evidence, only one dominant Thioglobaceae bacteria was densely aggregated in the large bacterial chambers of C. bisecta, and the bacterial genome shows nutritional complementarity and immune interactions with the host. Overall, gene family expansions may contribute to the symbiosis-related phenotypic variations in different bivalves. For instance, convergent expansions of gaseous substrate transport families in the endosymbiotic bivalves are absent in C. bisecta. Compared to endosymbiotic relatives, the thyasirid genome exhibits large-scale expansion in phagocytosis, which may facilitate symbiont digestion and account for extracellular symbiotic phenotypes. We also reveal that distinct immune system evolution, including expansion in lipopolysaccharide scavenging and contraction of IAP (inhibitor of apoptosis protein), may contribute to the different manners of bacterial virulence resistance in C. bisecta.

CONCLUSIONS

Thus, bivalves employ different pathways to adapt to the long-term co-existence with their bacterial symbionts, further highlighting the contribution of stochastic evolution to the independent gain of a symbiotic lifestyle in the lineage.

Expression analysis of peptidergic enteroendocrine cells in the silkworm Bombyx mori

Enteroendocrine cells (ECs) in the insect midgut respond to physiological changes in the intestine by releasing multiple peptides to control food intake, gastrointestinal activity and systemic metabolism. Here, we performed a comprehensive mapping of ECs producing different regulatory peptides in the larval midgut of Bombyx mori. In total, we identified 20 peptide genes expressed in different ECs in specific regions of the midgut. Transcript-specific in situ hybridisation combined with antibody staining revealed approximately 30 subsets of ECs, each producing a unique peptide or a combination of several different peptides. Functional significance of this diversity and specific roles of different enteroendocrine peptides are largely unknown. Results of this study highlight the importance of the midgut as a major endocrine/paracrine source of regulatory molecules in insects and provide important information to clarify functions of ECs during larval feeding and development.

Analysis of rhodopsin G protein-coupled receptor orthologs reveals semiochemical peptides for parasite (Schistosoma mansoni) and host (Biomphalaria glabrata) interplay

Schistosomiasis is a medically significant disease caused by helminth parasites of the genus Schistosoma. The schistosome life cycle requires chemically mediated interactions with an intermediate (aquatic snail) and definitive (human) host. Blocking parasite development within the snail stage requires improved understanding of the interactions between the snail host and the Schistosoma water-borne free-living form (miracidium). Innovations in snail genomics and aquatic chemical communication provide an ideal opportunity to explore snail-parasite coevolution at the molecular level. Rhodopsin G protein-coupled receptors (GPCRs) are of particular interest in studying how trematode parasites navigate towards their snail hosts. The potential role of GPCRs in parasites makes them candidate targets for new antihelminthics that disrupt the intermediate host life-cycle stages, thus preventing subsequent human infections. A genomic-bioinformatic approach was used to identify GPCR orthologs between the snail Biomphalaria glabrata and miracidia of its obligate parasite Schistosoma mansoni. We show that 8 S. mansoni rhodopsin GPCRs expressed within the miracidial stage share overall amino acid similarity with 8 different B. glabrata rhodopsin GPCRs, particularly within transmembrane domains, suggesting conserved structural features. These GPCRs include an orphan peptide receptor as well as several with strong sequence homologies with rhabdomeric opsin receptors, a serotonin receptor, a sulfakinin (SK) receptor, an allatostatin-A (buccalin) receptor and an FMRFamide receptor. Buccalin and FMRFa peptides were identified in water conditioned by B. glabrata, and we show synthetic buccalin and FMRFa can stimulate significant rates of change of direction and turn-back responses in S. mansoni miracidia. Ortholog GPCRs were identified in S. mansoni miracidia and B. glabrata. These GPCRs may detect similar ligands, including snail-derived odorants that could facilitate miracidial host finding. These results lay the foundation for future research elucidating the mechanisms by which GPCRs mediate host finding which can lead to the potential development of novel anti-schistosome interventions.

Cholecystokinin/sulfakinin peptide signaling: conserved roles at the intersection between feeding, mating and aggression

Neuropeptides are the most diverse messenger molecules in metazoans and are involved in regulation of daily physiology and a wide array of behaviors. Some neuropeptides and their cognate receptors are structurally and functionally well conserved over evolution in bilaterian animals. Among these are peptides related to gastrin and cholecystokinin (CCK). In mammals, CCK is produced by intestinal endocrine cells and brain neurons, and regulates gall bladder contractions, pancreatic enzyme secretion, gut functions, satiety and food intake. Additionally, CCK plays important roles in neuromodulation in several brain circuits that regulate reward, anxiety, aggression and sexual behavior. In invertebrates, CCK-type peptides (sulfakinins, SKs) are, with a few exceptions, produced by brain neurons only. Common among invertebrates is that SKs mediate satiety and regulate food ingestion by a variety of mechanisms. Also regulation of secretion of digestive enzymes has been reported. Studies of the genetically tractable fly Drosophila have advanced our understanding of SK signaling mechanisms in regulation of satiety and feeding, but also in gustatory sensitivity, locomotor activity, aggression and reproductive behavior. A set of eight SK-expressing brain neurons plays important roles in regulation of these competing behaviors. In males, they integrate internal state and external stimuli to diminish sex drive and increase aggression. The same neurons also diminish sugar gustation, induce satiety and reduce feeding. Although several functional roles of CCK/SK signaling appear conserved between Drosophila and mammals, available data suggest that the underlying mechanisms differ.

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.

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.

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

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

RNAi mediated myosuppressin deficiency affects muscle development and survival in the salmon louse (Lepeophtheirus salmonis)

Muscle activity is regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. In Arthropods, one of the important myoinhibitors is Myosuppressin, belonging to FMRFamide-like peptides, that was shown to have inhibitory effects on visceral muscle contraction and to regulate vital physiological processes including reproduction or feeding. We have identified myosuppressin in salmon louse Lepeophtheirus salmonis (LsalMS) and systematically characterised its function and complex abnormalities emerging after LsalMS knockdown by RNAi in all developmental stages in this species. Immunohistochemistry analysis localized the LsalMS mainly to the central nervous system, but also to the vital organs within the alimentary tract and the reproductive system. The most striking feature of LsalMS deficiency during lice development was severe reduction of the muscle content, with abnormalities detected in both the visceral and skeletal muscles. Moreover, down-regulation of LsalMS affects moulting, spermatophore deposition and feeding by affecting development of the intestinal wall and increasing its contraction frequency.

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.

Neuropeptides predicted from the transcriptome analysis of the gray garden slug Deroceras reticulatum

The gray garden slug, Deroceras reticulatum (Gastropoda: Pulmonata), is one of the most common terrestrial molluscs. Research for this slug has focused mainly on its ecology, biology, and management due to the severe damage it causes on a wide range of vegetables and field crops. However, little is known about neuropeptides and hormonal signalings. This study, therefore, aimed to establish the transcriptome of D. reticulatum and to identify a comprehensive repertoire of neuropeptides in this slug. Illumina high-throughput sequencing of the whole body transcriptome of D. reticulatum generated a total of 5.9 billion raw paired-end reads. De novo assembly by Trinity resulted in 143,575 transcripts and further filtration selected 120,553 unigenes. Gene Ontology (GO) terms were assigned to 30,588 unigenes, composed of biological processes (36.9%), cellular components (30.2%) and molecular functions (32.9%). Functional annotation by BLASTx revealed 39,987 unigenes with hits, which were further categorized into important functional groups based on sequence abundance. Neuropeptides, ion channels, ribosomal proteins, G protein-coupled receptors, detoxification, immunity and cytoskeleton-related sequences were dominant among the transcripts. BLAST searches and PCR amplification were used to identify 65 putative neuropeptide precursor genes from the D. reticulatum transcriptome, which include achatin, AKH, allatostatin A, B and C, allatotropin, APGWamide, CCAP, cerebrin, conopressin, cysteine-knot protein hormones (bursicon alpha/beta and GPA2/GPB5), elevenin, FCAP, FFamide, FVamide (enterin, fulicin, MIP and PRQFVamide), GGNG, GnRH, insulin, NdWFamide, NKY, PKYMDT, PRXamide (myomodulin, pleurin and sCAP), RFamide (CCK/SK, FMRFamide, FxRIamide, LFRFamide, luqin and NPF), and tachykinin. Over 330 putative peptides were encoded by these precursors. Comparative analysis among different molluscan species clearly revealed that, while D. reticulatum neuropeptide sequences are conserved in Mollusca, there are also some unique features distinct from other members of this species. This is the first transcriptome-wide report of neuropeptides in terrestrial slugs. Our results provide comprehensive transcriptome data of the gray garden slug, with a more detailed focus on the rich repertoire of putative neuropeptide sequences, laying the foundation for molecular studies in this terrestrial slug pest.

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.

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

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

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.

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.

Diversity of the RFamide Peptide Family in Mollusks

Since the initial characterization of the cardioexcitatory peptide FMRFamide in the bivalve mollusk Macrocallista nimbosa, a great number of FMRFamide-like peptides (FLPs) have been identified in mollusks. FLPs were initially isolated and molecularly characterized in model mollusks using biochemical methods. The development of recombinant technologies and, more recently, of genomics has boosted knowledge on their diversity in various mollusk classes. Today, mollusk FLPs represent approximately 75 distinct RFamide peptides that appear to result from the expression of only five genes: the FMRFamide-related peptide gene, the LFRFamide gene, the luqin gene, the neuropeptide F gene, and the cholecystokinin/sulfakinin gene. FLPs display a complex spatiotemporal pattern of expression in the central and peripheral nervous system. Working as neurotransmitters, neuromodulators, or neurohormones, FLPs are involved in the control of a great variety of biological and physiological processes including cardiovascular regulation, osmoregulation, reproduction, digestion, and feeding behavior. From an evolutionary viewpoint, the major challenge will then logically concern the elucidation of the FLP repertoire of orphan mollusk classes and the way they are functionally related. In this respect, deciphering FLP signaling pathways by characterizing the specific receptors these peptides bind remains another exciting objective.

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.

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.

Characterisation and tissue distribution of the PISCF allatostatin receptor in the red flour beetle, Tribolium castaneum

The insect PISCF/allatostatins (ASTs) are pleiotropic peptides that are involved in the regulation of juvenile hormone biosynthesis, are myoinhibitory on the gut and the heart, and suppress feeding in various insects, but their roles in beetles are poorly understood. To provide further insight into the significance of PISCF/ASTs in beetles, the PISCF/AST receptor from Tribolium castaneum has been characterised and its tissue distribution determined. The biological activity of the T. castaneum PISCF/AST (Trica-AS) was also investigated. The Trica-AS receptor shows high sequence homology to other insect PISCF/AST receptors, which are related to the mammalian somatostatin/opioid receptors, a family of G protein-coupled receptors. The Trica-AS receptor was activated in a dose-dependent manner by both Trica-AS and T. castaneum allatostatin double C (Trica-ASTCC) as well as Manduca sexta-allatostatin (Manse-AS). Other allatoregulatory peptides (a FLG/AST, a MIP/AST and an allatotropin) and somatostatin(14) were inactive on this receptor. Receptor transcript levels in tissues, determined by qRT-PCR, were highest in the head and the gut, with variable amounts in the fat body and reproductive organs. There were measurable differences in receptor levels of the head, fat body and reproductive organs between males and females. There was also a widespread distribution of Trica-AS in various tissues of T. castaneum. The Trica-AS peptide precursor was most abundant in the head and there was a significant difference between levels in the heads and reproductive organs of males and females. Whole mount immunocytochemistry localised Trica-AS in the median and lateral neurosecretory cells of the brain, in the corpus cardiacum and throughout the ventral nerve cord. The peptide was also present in midgut neurosecretory cells, but no immunostaining was detected in the reproductive organs or Malpighian tubules. The widespread distribution of both Trica-AS and its receptor suggest this peptide may have multiple roles in beetles. However, Trica-AS had no effect on the spontaneous contractions of the gut or ovaries of T. castaneum but this peptide did stimulate the release of proteases from the anterior midgut of another beetle, Tenebrio molitor. The activation of the Trica-AS receptor by Trica-ASTCC implies a physiological role for this peptide in beetles, which remains to be identified.

An unusual myosuppressin from the blood-feeding bug Rhodnius prolixus

The myosuppressin (MS) gene was cloned from a central nervous system (CNS) cDNA library of the hematophagous insect Rhodnius prolixus and is predicted to contain two introns and three exons. The mRNA transcribed from the myosuppressin gene encodes an 88 amino acid prepropeptide, which results in a mature decapeptide after post-translational modification. When compared with the myosuppressins isolated from other insects, the R. prolixus myosuppressin has a unique amino acid sequence (pQDIDHVFMRFamide), with isoleucine (I) in position 3 and methionine (M) in position 8. Reverse transcriptase (RT)-PCR shows that Rhopr-MS is expressed in the CNS and posterior midgut in R. prolixus and immunohistochemistry suggests that an RFamide-like peptide is present in endocrine-like cells in the midgut. Physiological assays using Rhopr-MS indicate that, despite the unusual M at position 8, it still retains myoinhibitory activity, inhibiting the frequency and reducing the amplitude of contractions in the anterior midgut and hindgut, and decreasing heart rate.

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.

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.

New physiological activities of myosuppressin, sulfakinin and NVP-like peptide in Zophobas atratus beetle

Three neuropeptides Zopat-MS-2 (pEDVDHVFLRFa), Zopat-SK-1 (pETSDDYGHLRFa) and Zopat-NVPL-4trunc. (GRWGGFA), recently isolated from the neuroendocrine system of the Zophobas atratus beetle, were tested for their myotropic and hyperglycaemic activities in this species. These peptides exerted differentiated dose-dependent and tissue specific physiological effects. Zopat-MS-2 inhibited contractions of the isolated heart, ejaculatory duct, oviduct and hindgut of adult beetles and induced bimodal effects in the heart contractile activity of pupae in vivo. It also increased the haemolymph free sugar level in larvae of this species, apart from myotropic activity. Zopat-SK-1 showed myostimulatory action on the isolated hindgut of the adult beetles, but it decreased contractions of the heart, ejaculatory duct and oviduct. Injections of this peptide at a dose of 2 μg also caused delayed cardioinhibitory effects on the heartbeat of the pupae. Together with the ability to increase free sugar level in the haemolymph of larvae these were new physiological activities of sulfakinins in insects. Zopat-NVPL-4trunc. inhibited the muscle contractions of the two organs: hindgut and ejaculatory duct but it was inactive on the oviduct and the heart of the adult beetles. This peptide also increased free sugar level concentration in the haemolymph of Z. atratus larvae. These physiological actions are the first biological activities discovered for this group of the insect peptides. The present work showed pleiotropic activity of three neuropeptides and indicates that the visceral muscle contractions and the haemolymph sugar homeostasis in Z. atratus are regulated by complex mechanisms.

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.

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.

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.

Isolation and sequencing of two FMRFamide-related peptides from the gut of Locusta migratoria L

Two FMRFamide-related peptides (FaRPs) have been isolated and sequenced from the whole gut of Locusta migratoria L. Peptides were extracted from 500 locust whole guts and separated using reversed-phase high performance liquid chromatography (RP-HPLC). Fractions containing FMRFamide-like immunoreactive (FLI) material were identified using radioimmunoassay (RIA). Sequencing of fractions, using tandem mass spectrometry (MALDI-TOF MS/MS), revealed the myosuppressin previously isolated from the locust CNS, SchistoFLRFamide (PDVDHVFLRFamide), and a novel extended RFamide (LWENLRFamide). The isolation of SchistoFLRFamide from midgut tissue supports the hypothesis that this myosuppressin is released locally from FLI processes over the gut and/or from endocrine-like midgut cells to play a role in the regulation of digestion.

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 anterior stomach of larval mosquitoes (Aedes aegypti): effects of neuropeptides on transepithelial ion transport and muscular motility

The present investigation studied the influence of a number of neuropeptides on semi-open preparations of the isolated and perfused anterior stomach of larval Aedes aegypti. Effects of peptides were observed on the lumen negative transepithelial voltage (Vte) that is present with serotonin in the bath; this voltage most likely reflects active HCO3- secretion involved in alkalization of the larval anterior stomach. The five different A. aegypti allatostatins (allatostatin A 1-5) all affected Vte in almost identical ways, causing a 10-15% reduction of the voltage at 10(-7) mol l(-1). A. aegypti neuropeptide F and proctolin reduced Vte at submicromolar concentrations. At 10(-6) mol l(-1), neuropeptide F reduced Vte by 30% and proctolin reduced Vte by 50%. In contrast, A. aegypti allatotropin, A. aegypti head peptides I and III and A. aegypti short neuropeptide F were without effect on Vte. During the investigation it was observed that the peristaltic contractions of the preparations caused a dynamic component of Vte. Peristaltic contractions and the correlated voltage fluctuations depended on the presence of serotonin. Peristaltic activity and Vte deflections were progressively inhibited by A. aegypti head peptides I and III by A. aegypti short neuropeptide F and by A. aegypti neuropeptide F when the peptide concentrations were increased from 10(-8) to 10(-6) mol l(-1). These observations show that physiological concentrations of some of the tested neuropeptides affect two processes that require coordination: ion transport and motility of the larval anterior stomach.

Aliphatic amino diacid Asu functions as an effective mimic of Tyr(SO3H) in sulfakinins for myotropic and food intake-inhibition activity in insects

The aliphatic amino diacid alpha-aminosuberic acid can function as an effective, stable mimic of the hydrolysis-susceptible Tyr(SO3H) group in sulfakinin neuropeptide analogs for both hindgut contractile activity in cockroach and food intake-inhibition activity in the desert locust. In the analog, the acidic sulfate group is replaced with an acidic carboxyl group. The degree of activity of sulfakinin analogs is correlated with the carboxyl/alpha-carbon distance in the cockroach hindgut contractile assay. The results represent an important step in the design and synthesis of biostable, sulfakinin analogs that could potentially suppress the feeding behavior of destructive insect pests of agricultural importance.

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.

The cDNA for leucomyosuppressin in Blattella germanica and molecular evolution of insect myosuppressins

Myosuppressins are a group of 10-residues FMRFamide-related peptides reported in Dictyoptera, Orthoptera, Lepidoptera and Diptera. Myosuppressins inhibit visceral muscle contractions and, in the cockroach Blattella germanica, inhibit food intake. In B. germanica, the cDNA of leucomyosuppressin (LMS) has been cloned and sequenced. The deduced precursor is 96 amino acids long and contains a single copy of LMS. Brain mRNA levels remain constant during the first reproductive cycle of adult females, whereas those in the gut show a slight decline during the time of maximal food intake. Comparison of myosuppressin precursors of different species reveals that all have the same organization. Phylogenetic analysis suggests that the precursor experienced an accelerated evolution in Lepidoptera and Diptera with respect to Dictyoptera, whereas only Lepidoptera has radical changes in the bioactive peptide.

Identification of leucomyosuppressin in the German cockroach, Blattella germanica, as an inhibitor of food intake

The feeding pattern of the adult female of Blattella germanica peaks in the middle of the vitellogenic cycle. Following the hypothesis that a factor inhibiting gut peristalsis also inhibits food intake and is involved in the regulation of feeding, we searched for the most powerful myoinhibitory peptide in brain extracts from B. germanica females collected after the peak within the feeding cycle. Through HPLC purification and sequence analysis, we obtained the peptide leucomyosuppressin (LMS): pQDVDHVFLRFamide. LMS elicited a powerful myoinhibitory effect on B. germanica foregut and hindgut, with ED(50) values around 10(-10) M. In addition, it inhibited food intake in vivo in a dose-dependent manner at doses between 5 and 50 microg. The study of the distribution of ingested food in the foregut, midgut and hindgut of B. germanica females treated with LMS showed that food accumulates in the foregut, which may be due to the myoinhibitory effects of the peptide. We propose that this accumulation inhibits food intake because of the persistence of the signals from gut stretch receptors.

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.

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first-fifth instar larvae, 1-3- and 14-17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.

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.