Spatial and temporal expression identify dromyosuppressin as a brain-gut peptide in Drosophila melanogaster

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.

Nutrient Sensing via Gut in Drosophila melanogaster

Nutrient-sensing mechanisms in animals' sense available nutrients to generate a physiological regulatory response involving absorption, digestion, and regulation of food intake and to maintain glucose and energy homeostasis. During nutrient sensing via the gastrointestinal tract, nutrients interact with receptors on the enteroendocrine cells in the gut, which in return respond by secreting various hormones. Sensing of nutrients by the gut plays a critical role in transmitting food-related signals to the brain and other tissues informing the composition of ingested food to digestive processes. These signals modulate feeding behaviors, food intake, metabolism, insulin secretion, and energy balance. The increasing significance of fly genetics with the availability of a vast toolbox for studying physiological function, expression of chemosensory receptors, and monitoring the gene expression in specific cells of the intestine makes the fly gut the most useful tissue for studying the nutrient-sensing mechanisms. In this review, we emphasize on the role of Drosophila gut in nutrient-sensing to maintain metabolic homeostasis and gut-brain cross talk using endocrine and neuronal signaling pathways stimulated by internal state or the consumption of various dietary nutrients. Overall, this review will be useful in understanding the post-ingestive nutrient-sensing mechanisms having a physiological and pathological impact on health and diseases.

Enteric neurons increase maternal food intake during reproduction

Reproduction induces increased food intake across females of many animal species1-4, providing a physiologically relevant paradigm for the exploration of appetite regulation. Here, by examining the diversity of enteric neurons in Drosophila melanogaster, we identify a key role for gut-innervating neurons with sex- and reproductive state-specific activity in sustaining the increased food intake of mothers during reproduction. Steroid and enteroendocrine hormones functionally remodel these neurons, which leads to the release of their neuropeptide onto the muscles of the crop-a stomach-like organ-after mating. Neuropeptide release changes the dynamics of crop enlargement, resulting in increased food intake, and preventing the post-mating remodelling of enteric neurons reduces both reproductive hyperphagia and reproductive fitness. The plasticity of enteric neurons is therefore key to reproductive success. Our findings provide a mechanism to attain the positive energy balance that sustains gestation, dysregulation of which could contribute to infertility or weight gain.

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.

Anatomy and Physiology of the Digestive Tract of Drosophila melanogaster

The gastrointestinal tract has recently come to the forefront of multiple research fields. It is now recognized as a major source of signals modulating food intake, insulin secretion and energy balance. It is also a key player in immunity and, through its interaction with microbiota, can shape our physiology and behavior in complex and sometimes unexpected ways. The insect intestine had remained, by comparison, relatively unexplored until the identification of adult somatic stem cells in the Drosophila intestine over a decade ago. Since then, a growing scientific community has exploited the genetic amenability of this insect organ in powerful and creative ways. By doing so, we have shed light on a broad range of biological questions revolving around stem cells and their niches, interorgan signaling and immunity. Despite their relatively recent discovery, some of the mechanisms active in the intestine of flies have already been shown to be more widely applicable to other gastrointestinal systems, and may therefore become relevant in the context of human pathologies such as gastrointestinal cancers, aging, or obesity. This review summarizes our current knowledge of both the formation and function of the Drosophila melanogaster digestive tract, with a major focus on its main digestive/absorptive portion: the strikingly adaptable adult midgut.

Neuropeptide Mapping of Dimmed Cells of Adult Drosophila Brain

Neuropeptides are structurally highly diverse messenger molecules that act as regulators of many physiological processes such as development, metabolism, reproduction or behavior in general. Differentiation of neuropeptidergic cells often corresponds with the presence of the transcription factor DIMMED. In the central nervous system of the fruit fly Drosophila melanogaster, DIMMED commonly occurs in neuroendocrine neurons that release peptides as neurohormones but also in interneurons with complex branching patterns. Fly strains with green fluorescence protein (GFP)-expressing dimmed cells make it possible to systematically analyze the processed neuropeptides in these cells. In this study, we mapped individual GFP-expressing neurons of adult D. melanogaster from the dimmed (c929)>GFP line. Using single cell mass spectrometry, we analyzed 10 types of dimmed neurons from the brain/gnathal ganglion. These cells included neuroendocrine cells with projection into the retrocerebral complex but also a number of large interneurons. Resulting mass spectra not only provided comprehensive data regarding mature products from 13 neuropeptide precursors but also evidence for the cellular co-localization of neuropeptides from different neuropeptide genes. The results can be implemented in a neuroanatomical map of the D. melanogaster brain. Graphical Abstract ᅟ.

Peptidergic control in a fruit crop pest: The spotted-wing drosophila, Drosophila suzukii

Neuropeptides play an important role in the regulation of feeding in insects and offer potential targets for the development of new chemicals to control insect pests. A pest that has attracted much recent attention is the highly invasive Drosophila suzukii, a polyphagous pest that can cause serious economic damage to soft fruits. Previously we showed by mass spectrometry the presence of the neuropeptide myosuppressin (TDVDHVFLRFamide) in the nerve bundle suggesting that this peptide is involved in regulating the function of the crop, which in adult dipteran insects has important roles in the processing of food, the storage of carbohydrates and the movement of food into the midgut for digestion. In the present study antibodies that recognise the C-terminal RFamide epitope of myosuppressin stain axons in the crop nerve bundle and reveal peptidergic fibres covering the surface of the crop. We also show using an in vitro bioassay that the neuropeptide is a potent inhibitor (EC₅₀ of 2.3 nM) of crop contractions and that this inhibition is mimicked by the non-peptide myosuppressin agonist, benzethonium chloride (Bztc). Myosuppressin also inhibited the peristaltic contractions of the adult midgut, but was a much weaker agonist (EC₅₀ = 5.7 μM). The oral administration of Bztc (5 mM) in a sucrose diet to adult female D. suzukii over 4 hours resulted in less feeding and longer exposure to dietary Bztc led to early mortality. We therefore suggest that myosuppressin and its cognate receptors are potential targets for disrupting feeding behaviour of adult D. suzukii.

Physiological characterization and regulation of the contractile properties of the mosquito ventral diverticulum (crop)

In adult dipteran insects (flies), the crop is a diverticulum of the esophagus that serves as a food storage organ. The crop pumps stored contents into the alimentary canal for digestion and absorption. The pumping is mediated by peristaltic contractions of the crop musculature. In adult female mosquitoes, the crop (ventral diverticulum) selectively stores sugar solutions (e.g., nectar); proteinaceous blood meals by-pass the crop and are transferred directly to the midgut for digestion. The mechanisms that regulate crop contractions have never been investigated in mosquitoes. Here we provide the first physiological characterization of the contractile properties of the mosquito crop and explore the mechanisms that regulate crop contractions. Using an in vitro bioassay we found that the isolated crop spontaneously contracts in Ringer solution for at least 1 h and its contractions are dependent on extracellular Ca2+. Adding serotonin (5-hydroxytryptamine, 5-HT) or a membrane-permeable analog of cyclic adenosine monophosphate (cAMP) to the extracellular bath increased the frequency of crop contractions. On the other hand, adding benzethonium chloride (BzCl; a chemical that mimics the effects of myosuppressins), H-89 or Rp-cAMPS (inhibitors of protein kinase A, PKA), or carbenoxolone (an inhibitor of gap junctions) reduced the frequency of the unstimulated, spontaneous and/or 5-HT-stimulated crop contractions. Adding aedeskinin III did not detectably alter crop contraction rates. In addition to pharmacological evidence of gap junctions, we demonstrated that the crop expressed several mRNAs encoding gap junctional proteins (i.e. innexins). Furthermore, we localized immunoreactivity for innexin 2 and innexin 3 to muscle and epithelial cells of the crop, respectively. Our results 1) suggest that 5-HT and myosupressins oppositely regulate contractile activity of the mosquito crop, and 2) provide the first evidence for putative roles of cAMP, PKA, and gap junctions in modulating contractile activity of the dipteran crop.

From mouth to anus: Functional and structural relevance of enteric neurons in the Drosophila melanogaster gut

The intestinal tract is the main organ involved in host nutritional homeostasis. Intestinal function in both vertebrates and invertebrates is partly controlled by enteric neurons that innervate the gut. Though anatomical and functional aspects of enteric neurons are relatively less characterized in Drosophila than in large insects, analyses of the role of the enteric neurons in flies have remarkably progressed in the last few years. In this review, we first provide a summary of the structure and function of the Drosophila intestine. We then discuss recent studies of the structure and function of enteric neurons in Drosophila melanogaster.

Role of Phote-HrTH (Phormia terraenovae hypertrehalosemic hormone) in modulating the supercontractile muscles of the crop of adult Phormia regina Meigen

Phote-HrTH (Phormia terraenovae hypertrehalosemic hormone) has been demonstrated in the Diptera to be involved in flight metabolism, reproduction, and diapause. Each of these events needs the hormone's action and requirement for carbohydrates is the common denominator. In Diptera, carbohydrates are taken up during feeding by action of the cibarial pump and are then stored in the crop. Using adult Phormia regina, both a bioassay and electrophysiological recordings show that Phote-HrTH slows down or inhibits the crop lobe muscles (P5) and, at the same time, stimulates the muscles of the pump 4 (P4) involved in pushing fluids out of the crop and up into the midgut for digestion. The EC50 for P4 was in the nanomolar range while the IC50 for P5 was 1.4-75.1 pM. The effect of Phote-HrTH on P4/5 suggests that the peptide is important in coordinating the two pumps, which are involved in moving carbohydrates up into the midgut for digestion. The adult crop organ is an essential storage organ for carbohydrates and now should be considered an important structure capable of delivering nutrients to the midgut for digestion.

The digestive tract of Drosophila melanogaster

The digestive tract plays a central role in the digestion and absorption of nutrients. Far from being a passive tube, it provides the first line of defense against pathogens and maintains energy homeostasis by exchanging neuronal and endocrine signals with other organs. Historically neglected, the gut of the fruit fly Drosophila melanogaster has recently come to the forefront of Drosophila research. Areas as diverse as stem cell biology, neurobiology, metabolism, and immunity are benefitting from the ability to study the genetics of development, growth regulation, and physiology in the same organ. In this review, we summarize our knowledge of the Drosophila digestive tract, with an emphasis on the adult midgut and its functional underpinnings.

Selective elimination/RNAi silencing of FMRF-related peptides and their receptors decreases the locomotor activity in Drosophila melanogaster

Five neuropeptide genes are classified in the FMRF-related (FaRP) group: the Fmrf, dromyosuppressin (Dms), drosulfakinin (Dsk), neuropeptide F (npf) and short neuropeptide F (sNPF) genes coding for 8, 1, 2, 1 and 4 peptides, respectively. In order to compare their effects on the locomotor activity of Drosophila adults, we made RNAi knockdown of the peptides and their specific receptor genes. In addition, we constructed Gal4 drivers with three distinct parts of the Fmrf gene's 5' regulatory sequence (RS8-Gal4, RS11-Gal4, RS17-Gal4), and used them to ablate FMRF-positive neurons inducing apoptosis by expressing the reaper (rpr) gene. We examined the locomotor activity of flies by measuring the mean velocity of movement (MVM) following repeated air-puffs. Locomotor activity was decreased by RNAi knockdown induced in the CNS by the elav-Gal4 driver. According to the MVM curve profiles, RNAi knockdown most effectively decreased the velocity when the DmsR-1 and DmsR-2 genes were silenced together (DmsR-1-RNAi/elav-Gal4; DmsR-2-RNAi/+). Similar effect was observed in Dsk-RNAi/ elav-Gal4; DskR-2-RNAi/+, while moderate effects were found in three other combinations (Fmrf-RNAi/elav-Gal4; FR-RNAi/+, Dms-RNAi/ elav-Gal4;DmsR-2-RNAi/+, CCKLR-17D1-RNAi/elav-Gal4; CCKLR-17D3-RNAi/+), and weak effect in DmsR-2-RNAi/elav-Gal4; DmsR-1-RNAi/+. Male and female flies were not different in this respect. In the cell ablation experiment, the MVM profiles of the female flies were different from the controls when the UAS-rpr transgene was driven by RS8-Gal4 or RS17-Gal4. The RS11-Gal4 and Fmrf-Gal4 drivers were ineffective. In the males only the RS17-Gal4 showed a weak effect. RNAi silencing of the FaRP and FaRP-receptor genes effectively decreased the startle-induced locomotor activity of flies. Ablation of FMRF-positive neurons by the RS8-Gal4 and/or RS17-Gal4 drivers also decreased the flies' activity.

Structure-activity and immunochemical data provide evidence of developmental- and tissue-specific myosuppressin signaling

Myosuppressin peptides dramatically diminish contractions of the gut and heart. Thus, delineating mechanisms involved in myosuppressin signaling may provide insight into peptidergic control of muscle contractility. Drosophila myosuppressin (DMS, TDVDHVFLRFamide) structure-activity relationship (SAR) was investigated to identify an antagonist and explore signaling. Alanyl-substituted, N-terminal truncated, and modified amino acid analogs identified residues and peptide length required for activity. Immunochemistry independently provided insight into myosuppressin mechanisms. DMS decreased gut motility and cardiac contractility dose dependently; the different effective concentrations at half maximal-response were indicative of tissue-specific mechanisms. Replacement of aspartic acid 2 (D2) generated an analog with different developmental- and tissue-specific effects; [A2] DMS mimicked DMS in adult gut (100% inhibition), yet decreased larval gut contractions by only 32% with increased potency in pupal heart (126% inhibition). The DMS active core differed across development and in tissues; adult (DHVFLRFamide) and larval gut (TDVDHVFLRFamide), and adult (VFLRFamide) and pupal heart (VFLRFamide). Substitution of D2 and D4 with a modified amino acid, p-benzoyl-phenylalanine, produced developmental- and tissue-specific antagonists. In the presence of protease inhibitors, DMS and VFLRFamide were more effective in adult gut, but lower or unchanged in pupal heart compared to peptide or analog alone, respectively. DMS-specific antisera stained neurons that innervated the gut or heart. This study describes novel antagonists and data to identify developmental- and tissue-specific mechanisms underlying the pleotropic effects of myosuppressin in muscle physiology.

Effects of neuropeptides on feeding initiation in larvae of the silkworm, Bombyx mori

In insects, especially phytophagous insects, feeding behavior occurs at a regular frequency. Although a number of physiological studies have revealed various causal factors leading to feeding behavior in insects, little has been demonstrated regarding the regulatory mechanisms underlying insect feeding behavior. To confirm the presence of an endocrinological regulatory mechanism in feeding behavior, we tested the effects of several biologically active peptides on silkworm, Bombyx mori larvae feeding behaviors. To evaluate the effects of the biologically active peptides, we measured the period of latency to the first bite following sample injection into starved Bombyx larvae. Of the chemically synthesized peptides tested, myosuppressin exhibited a prolonged latency, indicating that myosuppressin is a possible inhibitory peptide in Bombyx larvae. In contrast, injections of tachykinin and short neuropeptide F, which are members of the structurally related RF-amide peptide family, had a shorter latency period, indicating that these two peptides are possible stimulatory peptides. In addition, the present study suggests that this bioassay will be advantageous for screening for peptides that regulate insect feeding behavior.

The diverticulated crop of adult Phormia regina

The crop of adult Phormia regina consists of a duct that diverges from the esophagus, just in front of the cardia, and extends ventrally and posteriorly into the thorax and abdomen where it forms a bilobed sac. Flattened epithelial cells produce the cuticular lining of the crop. When empty, or partially full, the epithelial cells and cuticular lining form folds extending into the lumen, thus providing for expansion as the crop sac fills. Covering the sac on the hemolymph side is a layer of anastomosed, intrinsic muscles connected to one another by intercellular cytoplasmic bridges. Mitochondria are located at the periphery of the sarcomere. Also inside the sarcomere are glycogen, sarcoplasmic reticula, and transverse tubular systems (T-system). I, A, and Z-bands are present and the Z-bands are not in register making the muscle-type supercontractile. Important structures, not previously researched and associated with the crop muscles, are the crop nerves. Coming off the corpora cardiaca, and running down each side of the crop duct, is a pair of nerves, each housing several axons. These nerves extend to and branch over the crop sac. Here they penetrate the muscle mass and form neuromuscular junctions where electron-dense droplets of neurosecretion are released. Based on the literature, and research in our laboratory, it has now been shown that these nerves carry adipokinetic hormone, Drosophila insulin-like peptide, and a dromyosuppressin-like neuropeptide.

Analysis of neuropeptide expression and localization in adult drosophila melanogaster central nervous system by affinity cell-capture mass spectrometry

A combined approach using mass spectrometry, a novel neuron affinity capture technique, and Drosophila melanogaster genetic manipulation has been developed to characterize the expression and localization of neuropeptides in the adult D. melanogaster brain. In extract from the whole adult brain, 42 neuropeptides from 18 peptide families were sequenced. Neuropeptide profiling also was performed on targeted populations of cells which were enriched with immunoaffinity purification using a genetically expressed marker.

Regulatory peptides in fruit fly midgut

Regulatory peptides were immunolocalized in the midgut of the fruit fly Drosophila melanogaster. Endocrine cells were found to produce six different peptides: allatostatins A, B and C, neuropeptide F, diuretic hormone 31, and the tachykinins. Small neuropeptide-F (sNPF) was found in neurons in the hypocerebral ganglion innervating the anterior midgut, whereas pigment-dispersing factor was found in nerves on the most posterior part of the posterior midgut. Neuropeptide-F (NPF)-producing endocrine cells were located in the anterior and middle midgut and in the very first part of the posterior midgut. All NPF endocrine cells also produced tachykinins. Endocrine cells containing diuretic hormone 31 were found in the caudal half of the posterior midgut; these cells also produced tachykinins. Other endocrine cells produced exclusively tachykinins in the anterior and posterior extemities of the midgut. Allatostatin-immunoreactive endocrine cells were present throughout the midgut. Those in the caudal half of the posterior midgut produced allatostatins A, whereas those in the anterior, middle, and first half of the posterior midgut produced allatostatin C. In the middle of the posterior midgut, some endocrine cells produced both allatostatins A and C. Allatostatin-C-immunoreactive endocrine cells were particularly prominent in the first half of the posterior midgut. Allatostatin B/MIP-immunoreactive cells were not consistently found and, when present, were only weakly immunoreactive, forming a subgroup of the allatostatin-C-immunoreactive cells in the posterior midgut. Previous work on Drosophila and other insect species suggested that (FM)RFamide-immunoreactive endocrine cells in the insect midgut could produce NPF, sNPF, myosuppressin, and/or sulfakinins. Using a combination of specific antisera to these peptides and transgenic fly models, we showed that the endocrine cells in the adult Drosophila midgut produced exclusively NPF. Although the Drosophila insulin gene Ilp3 was abundantly expressed in the midgut, Ilp3 was not expressed in endocrine cells, but in midgut muscle.

How to innervate a simple gut: familiar themes and unique aspects in the formation of the insect enteric nervous system

Like the vertebrate enteric nervous system (ENS), the insect ENS consists of interconnected ganglia and nerve plexuses that control gut motility. However, the insect ENS lies superficially on the gut musculature, and its component cells can be individually imaged and manipulated within cultured embryos. Enteric neurons and glial precursors arise via epithelial-to-mesenchymal transitions that resemble the generation of neural crest cells and sensory placodes in vertebrates; most cells then migrate extensive distances before differentiating. A balance of proneural and neurogenic genes regulates the morphogenetic programs that produce distinct structures within the insect ENS. In vivo studies have also begun to decipher the mechanisms by which enteric neurons integrate multiple guidance cues to select their pathways. Despite important differences between the ENS of vertebrates and invertebrates, common features in their programs of neurogenesis, migration, and differentiation suggest that these relatively simple preparations may provide insights into similar developmental processes in more complex systems.

Peptide immunocytochemistry of neurons projecting to the retrocerebral complex in the blow fly, Protophormia terraenovae

Antisera against a variety of vertebrate and invertebrate neuropeptides were used to characterize neurons with somata in the pars intercerebralis (PI), pars lateralis (PL), and subesophageal ganglion (SEG), designated as PI neurons, PL neurons, and SEG neurons, respectively, all of which project to the retrocerebral complex in the blow fly, Protophormia terraenovae. Immunocytochemistry combined with backfills through the cardiac-recurrent nerve revealed that at least two pairs of PI and SEG neurons for each were FMRFamide-immunoreactive. Immunoreactivity against [Arg7]-corazonin, beta-pigment-dispersing hormone (beta-PDH), cholecystokinin8, or FMRFamide was observed in PL neurons. Immunoreactive colocalization of [Arg7]-corazonin with beta-PDH, [Arg7]-corazonin with cholecystokinin8, or beta-PDH with FMRFamide was found in two to three somata in the PL of a hemisphere. Based on their anatomical and immunocytochemical characteristics, PI neurons were classified into two types, PL neurons into six types, and SEG neurons into two types. Fibers in the retrocerebral complex showed [Arg7]-corazonin, beta-PDH, cholecystokinin8, and FMRFamide immunoreactivity. Cholecystokinin8 immunoreactivity was also detected in intrinsic cells of the corpus cardiacum. The corpus allatum was densely innervated by FMRFamide-immunoreactive varicose fibers. These results suggest that PI, PL, and SEG neurons release [Arg7]-corazonin, beta-PDH, cholecystokinin8, or FMRFamide-like peptides from the corpus cardiacum or corpus allatum into the hemolymph, and that some PL neurons may simultaneously release several neuropeptides.

Molecular characterization and cell-specific expression of an ion transport peptide in the tobacco hornworm, Manduca sexta

The crustacean hyperglycemic hormone (CHH) peptides regulate diverse physiological processes from reproduction to metabolism and molting in arthropods. In insects, the ion transport peptides (ITP), also members of the CHH family, have only been implicated in ion transport. In this study, we sequenced a nucleotide fragment spanning the conserved A1/A2 region of the putative CHH/ITP gene. This fragment was amplified from larval cDNA of the tobacco hornworm, Manduca sexta and showed a high degree of sequence conservation with the same region from other insects and, to a lesser degree, with that of crustacean species, suggesting the presence of a Manduca-specific CHH/ITP mRNA (MasITP mRNA). CHH-like immunocytochemical analyses with two crustacean antisera (from Carcinus maenas and Cancer pagurus) identified the presence of CHH-like immunoreactivity in nervous tissue of all developmental stages, but not in the gut of M. sexta. Specifically, CHH-like peptides localized to paired type IA(2) neurosecretory cells of the pars lateralis of the brain (projecting ipsilaterallly to the corpora cardiaca-allata complex) and to neurosecretory cells and transverse nerves of the ventral nerve cord in larvae, pupae, and adults. The distribution of the putative MasITP peptide shifted during development in a manner consistent with metamorphic reorganization. A comparison of hemolymph equivalents of CHH detected by enzyme-linked immunosorbent assay with CHH-like immunoreactivity in transverse nerves provided evidence for the release of MasITP from the transverse nerves into the hemolymph at insect ecdysis. These data suggest the presence of an insect ITP in M. sexta and a role for this hormone during ecdysis.

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

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

Evidence dromyosuppressin acts at posterior and anterior pacemakers to decrease the fast and the slow cardiac activity in the blowfly Protophormia terraenovae

The molecular complexity of the simple blowfly heart makes it an attractive preparation to delineate cardiovascular mechanisms. Blowfly cardiac activity consists of a fast, high-frequency signal phase alternating with a slow, low-frequency signal phase triggered by pacemakers located in the posterior abdominal heart and anterior thoracocephalic aorta, respectively. Mechanisms underlying FMRFamide-related peptides (FaRPs) effects on heart contractions are not well understood. Here, we report antisera generated to a FaRP, dromyosuppressin (DMS, TDVDHVFLRFamide), recognized neuronal processes that innervated the blowfly Protophormia terraenovae heart and aorta. Dromyosuppressin caused a reversible cardiac arrest. High- and low-frequency signals were abolished after which they resumed; however, the concentration-dependent resumption of the fast phase differed from the slow phase. Dromyosuppressin decreased the frequency of cardiac activity in a dose-dependent manner with threshold values between 5 fM and 0.5 fM (fast phase), and 0.5 fM and 0.1 fM (slow phase). Dromyosuppressin structure-activity relationship (SAR) for the decrease of the fast-phase frequency was not the same as the SAR for the decrease of the slow-phase frequency. The alanyl-substituted analog TDVDHVFLAFamide ([Ala9] DMS) was inactive on the fast phase, but active on the slow phase, a novel finding. FaRPs including myosuppressins are reported to require the C-terminal RFamide for activity. Our data are consistent with the conclusions DMS acts on posterior and anterior cardiac tissue to play a role in regulating the fast and slow phases of cardiac activity, respectively, and ligand-receptor binding requirements of the abdominal and thoracocephalic pacemakers are different.

Localization of leucomyosuppressin in the brain and circadian clock of the cockroach Leucophaea maderae

The myosuppressins (X1DVX2HX3FLRFamide), which reduce the frequency of insect muscle contractions, constitute a subgroup of the FMRFamide-related peptides. In the cockroach Leucophaea maderae, we have examined whether leucomyosuppressin (pQDVDHVFLRFamide) is present in the accessory medulla, viz., the circadian clock, which governs circadian locomotor activity rhythms. Antisera that specifically recognize leucomyosuppressin stain one to three neurons near the accessory medulla. MALDI-TOF mass spectrometry has confirmed the presence of leucomyosuppressin in the isolated accessory medulla. Injections of 1.15 pmol leucomyosuppressin into the vicinity of the accessory medulla at various circadian times have revealed no statistically significant effects on the phase of circadian locomotor activity rhythms. This is consistent with the morphology of the myosuppressin-immunoreactive neurons, which restrict their arborizations to the circadian clock and other optic lobe neuropils. Thus, leucomyosuppressin might play a role in the circadian system other than in the control of locomotor activity rhythms.

Neuropeptides in interneurons of the insect brain

A large number of neuropeptides has been identified in the brain of insects. At least 35 neuropeptide precursor genes have been characterized in Drosophila melanogaster, some of which encode multiple peptides. Additional neuropeptides have been found in other insect species. With a few notable exceptions, most of the neuropeptides have been demonstrated in brain interneurons of various types. The products of each neuropeptide precursor seem to be co-expressed, and each precursor displays a unique neuronal distribution pattern. Commonly, each type of neuropeptide is localized to a relatively small number of neurons. We describe the distribution of neuropeptides in brain interneurons of a few well-studied insect species. Emphasis has been placed upon interneurons innervating specific brain areas, such as the optic lobes, accessory medulla, antennal lobes, central body, and mushroom bodies. The functional roles of some neuropeptides and their receptors have been investigated in D. melanogaster by molecular genetics techniques. In addition, behavioral and electrophysiological assays have addressed neuropeptide functions in the cockroach Leucophaea maderae. Thus, the involvement of brain neuropeptides in circadian clock function, olfactory processing, various aspects of feeding behavior, and learning and memory are highlighted in this review. Studies so far indicate that neuropeptides can play a multitude of functional roles in the brain and that even single neuropeptides are likely to be multifunctional.

The effects of Calliphora vomitoria Tachykinin-I and the FMRFamide-related peptide Perisulfakinin on female Phormia regina crop contractions, in vitro

The dipteran crop is an elaborate diverticulation of the foregut that serves as an important food reservoir and feeding regulator. Peptidergic innervation has been associated with the crop of the blow fly Phormia regina and myotropic neuropeptides have been previously demonstrated to affect crop contraction rates, in vitro. The blow fly peptide, callitachykinin-1 was found to increase the rate of contractions and alter the contractile morphology of the P. regina crop, in vitro. The cockroach peptide perisulfakinin, however, had no measurable affect on crop contractions.

FMRFamide-related peptides and serotonin regulate Drosophila melanogaster heart rate: mechanisms and structure requirements

Drosophila melanogaster FMRFamide-related peptides (FaRPs) include SDNFMRFamide, PDNFMRFamide, and TDVDHVFLRFamide (dromyosuppressin, DMS); each peptide contains a C-terminal FMRFamide but a different N-terminal extension. FaRPs and serotonin (5-HT) each affect the frequency of D. melanogaster heart contractions in vivo. We examined the cellular expression of FaRPs and 5-HT, and the activities of FMRFamide, SDNFMRFamide, PDNFMRFamide, or DMS and 5-HT on heart rate. FaRPs and 5-HT were not co-localized; FaRP-and 5-HT-immunoreactive fibers extended from different brain cells and innervated the anterior D. melanogaster dorsal vessel. However, no neuron expressed both a FaRP and 5-HT. The effect of FMRFamide and 5-HT was not different from the effect of 5-HT alone on heart rate. The effect of PDNFMRFamide and 5-HT showed an additive effect on heart rate. SDNFMRFamide and 5-HT or DMS and 5-HT resulted in non-additive effects on heart rate. Our data provide evidence for the complexity of FaRP and 5-HT interactions to regulate frequency of heart contractions in vivo. Our results also confirm the biological importance of FaRP N-terminal amino acid extensions.

Direct mass spectrometric peptide profiling and fragmentation of larval peptide hormone release sites in Drosophila melanogaster reveals tagma-specific peptide expression and differential processing

Regulatory peptides represent a diverse group of messenger molecules. In insects, they are produced by endocrine cells as well as secretory neurones within the CNS. Many regulatory peptides are released as hormones into the haemolymph to regulate, for example, diuresis, heartbeat or ecdysis behaviour. Hormonal release of neuropeptides takes place at specialized organs, so-called neurohaemal organs. We have performed a mass spectrometric characterization of the peptide complement of the main neurohaemal organs and endocrine cells of the Drosophila melanogaster larva to gain insight into the hormonal communication possibilities of the fruit fly. Using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and MALDI-TOF-TOF tandem mass spectrometry, we detected 23 different peptides of which five were unpredicted by previous genome screenings. We also found a hitherto unknown peptide product of the capa gene in the ring gland and transverse nerves, suggesting that it might be released as hormone. Our results show that the peptidome of the neurohaemal organs is tagma-specific and does not change during metamorphosis. We also provide evidence for the first case of differential prohormone processing in Drosophila.

Peptidomic analysis of the larval Drosophila melanogaster central nervous system by two-dimensional capillary liquid chromatography quadrupole time-of-flight mass spectrometry

Peptides are the largest class of signalling molecules found in animals. Nevertheless, in most proteomic studies peptides are overlooked since they literally fall through the mazes of the net. In analogy with proteomics technology, where all proteins expressed in a cell or tissue are analyzed, the peptidomic approach aims at the simultaneous visualization and identification of the whole peptidome of a cell or tissue, i.e. all expressed peptides with their post-translational modifications. In this paper we describe the analysis of the larval fruit fly central nervous system using two-dimensional capillary liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (LC/Q-TOF-MS/MS. Using the central nervous systems of only 50 larval Drosophila as starting material, we identified 38 peptides in a single analysis, 20 of which were not detected in a previous study that reported on the one-dimensional capillary LC/MS/MS analysis of the same tissue. Among the 38 sequenced peptides, some originate from precursors, such as the tachykinin and the IFamide precursor that were entirely missed in the first study. This clearly demonstrates that the two-dimensional capillary LC approach enhances the coverage of the peptidomic analysis.

Peptidergic innervation of the crop and the effects of an ingested nonpeptidal agonist on longevity in female Musca domestica (Diptera: Muscidae)

Dromyosuppressin (DMS) immunoreactive neurons were discovered running along the crop duct and on the surface of the crop in the house fly, Musca domestica L. DMS is a myoinhibitory neuropeptide that has been shown to inhibit crop contractions, in vitro, in the blow fly, Phormia regina (Meigen), and in Drosophila melanogaster Meigen. Various concentrations of benzethonium chloride (Bztc), an agonist of DMS with shown inhibitory effects on blow fly crop contractions, were fed to adult female M. domestica. Flies exhibited a dose-dependent mortality; avoidance and subsequent dehydration are probably the cause of the low survivorship at higher Bztc concentrations.

Abdominal pericardial sinus: a neurohemal site in the tsetse and other cyclorraphan flies

An ultrastructural study of the heart of the tsetse fly, Glossina morsitans, and of several other species of cyclorraphan flies revealed that the ventral region of the heart of adult flies is supported by a muscular septum not present in the larval stage. The pericardial septum of the adult heart is composed laterally of alary muscles and a central longitudinal muscle that extends the length of the abdominal aorta, whereas the larval heart is supported ventrally only by alary muscles and strands of connective tissue. Thus, unlike the larval stage, and the heart of other insects, the pericardial septum of adult cyclorraphan flies contains a central band of longitudinal muscle, that along with the alary muscle, forms a large pericardial sinus lying between the septum and the heart. Neurosecretory nerves arising from the lateral nerves of the thoracicoabdominal ganglion extend dorsad to the pericardial septum, where they form neuromuscular junctions on the muscle fibers of the pericardial septum or traverse the septum terminating in the pericardial sinus, thereby creating one of the largest neurohemal organs in these flies. In the tsetse fly, some of the neurosecretory fibers also extend between the muscle fibers of the myocardium, and release their material into the lumen of the heart.

The regulation of circadian rhythms in the fly's visual system: involvement of FMRFamide-like neuropeptides and their relationship to pigment dispersing factor in Musca domestica and Drosophila melanogaster

The cross-sectional area of axon profiles in two classes of interneuron, L1 and L2, in the fly's lamina, exhibits a circadian rhythm of swelling and shrinking; axon caliber also changes after microinjecting putative lamina neurotransmitters. Among these, the neuropeptide pigment-dispersing factor, PDF, is proposed to transmit circadian information from the housefly's (Musca domestica) clock to L1 and L2, increasing axon caliber during the day. Testing whether other neurotransmitters may modulate this effect we have: (1) examined optic lobe cell immunoreactivity to FMRFamide peptides and its co-immunolocalization to PDF in M. domestica and Drosophila melanogaster, and to the product of the circadian clock gene PER in D. melanogaster; and (2) made microinjections of FMRFamide and related neuropeptides into the second neuropil, or medulla. In M. domestica, nine groups of optic lobe cells, several cells in the lateral and dorsal protocerebrum, and in the subesophageal ganglion, together contribute dense FMRFamide immunoreactive arborizations in almost all central brain and optic lobe neuropils. In D. melanogaster a similar pattern of labeling arises from fewer cells. Daytime microinjections show that another neuropeptide, similar to molluscan FMRFamide, shrinks M. domestica's L1 and L2 axons, thus opposing the action of PDF. We discuss evidence for a medulla site of action for a released FMRFamide-like peptide, either from: MeRF2 cells, acting directly on L1 and L2's medulla terminals; or MeRF1 cells, acting indirectly via medulla centrifugal cells C2 and C3.

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.

Anatomy and functions of brain neurosecretory cells in diptera

In the larval brain of dipteran insects, there are two medial and three lateral groups of neurons innervating the ring gland. One lateral group extends fibers to the corpus allatum. After metamorphosis, a large cluster of the medial group in the pars intercerebralis and two lateral groups in the pars lateralis innervate the retrocerebral complex and some neurons from the lateral group and a few from the medial group extend fibers to the corpus allatum in the adults. Neuropeptides such as insulin-like peptides, FMRFamide related peptides, Locusta-diuretic hormone, beta-pigment dispersing hormone, Manduca sexta-allatostatin, ovary ecdysteroidogenic hormone, and proctolin have been immunocytochemically revealed in medial groups in the pars intercerebralis, and FMRFamide related peptides, beta-pigment dispersing hormone, corazonin, and M. sexta-allatostatin in lateral groups in the pars lateralis of dipteran brains. In mosquitoes after the blood meal, ovary ecdysteroidogenic hormone from 2-3 pairs of medial neurosecretory cells is released at the corpus cardiacum to stimulate the ovaries to secrete ecdysteroid to cause ovarian development. In addition to ovarian development, removal and implantation experiments have shown that neurosecretory cells in the pars intercerebralis and pars lateralis are involved in control of reproductive diapause, cuticular tanning, sugar metabolism, and diures.

A nonpeptide provides insight into mechanisms that regulate Drosophila melanogaster heart contractions

Here we report the effect of a nonpeptide, benzethonium chloride (bztc), on Drosophila melanogaster larval, pupal, and adult heart rates in vivo. Benzethonium chloride reduced the frequency of spontaneous contractions in the D. melanogaster pupal heart, but not in the larval heart or the adult heart as measured in noninvasive whole animal preparations. When applied directly to the D. melanogaster heart, in the absence of hemolymph, bztc reduced the frequency of spontaneous contractions in larval, pupal, and adult hearts. These findings are consistent with the conclusion that bztc acts through or is regulated by different mechanisms in these three developmental stages. An alternative explanation is that larval hemolymph and adult hemolymph contain a material that interferes with the effect of the nonpeptide on heart contractions. Bztc mimicked the effect of the peptide dromyosuppressin (DMS) on the heart at an equivalent concentration; in contrast, 103-fold more nonpeptide is required to mimic the effect of DMS on fly gut. These findings are consistent with the presence of tissue-specific myosuppressin receptors or mechanisms.

Molecular cloning and functional expression of the first two specific insect myosuppressin receptors

The Drosophila Genome Project database contains the sequences of two genes, CG8985 and CG13803, which are predicted to code for G protein-coupled receptors. We cloned the cDNAs corresponding to these genes and found that their gene structures had not been correctly annotated. We subsequently expressed the coding regions of the two corrected receptor genes in Chinese hamster ovary cells and found that each of them coded for a receptor that could be activated by low concentrations of Drosophila myosuppressin (EC50,4 x 10(-8) M). The insect myosuppressins are decapeptides that generally inhibit insect visceral muscles. Other tested Drosophila neuropeptides did not activate the two receptors. In addition to the two Drosophila myosuppressin receptors, we identified a sequence in the genomic database from the malaria mosquito Anopheles gambiae that also very likely codes for a myosuppressin receptor. To our knowledge, this paper is the first report on the molecular identification of specific insect myosuppressin receptors.

The structure of the FMRFamide receptor and activity of the cardioexcitatory neuropeptide are conserved in mosquito

Numerous peptides are structurally related to the cardioexcitatory tetrapeptide FMRFamide. One subgroup of FMRFamide-related peptides (FaRPs) contains an FMRFamide C terminus. Searches of the Drosophila melanogaster genome database identified the first invertebrate FMRFamide G-protein coupled receptor (GPCR), DrmFMRFa-R (Cazzamali and Grimmelikhuijzen, Meeusen et al., 2002). In order to explore molecular mechanisms involved in FMRFamide signal transduction we identified a receptor from the malaria mosquito Anopheles gambiae genome (Holt et al., 2002), AngFMRFa-R, and compared its structure to DrmFMRFa-R. The cytoplasmic loops, extracellular loops, and transmembrane regions are highly conserved between these two FMRFamide receptors. Another subgroup of FaRPs is the sulfakinins which are represented by the consensus structure -XDYGHMRFamide, where X is D or E (Nichols, 2003). We compared AngFMRFa-R and DrmFMRFa-R to the A. gambiae sulfakinin receptors, ASK-R1 and ASK-R2 ( Duttlinger et al., 2003), and the D. melanogaster sulfakinin receptors, DSK-R1 and DSK-R2 Brody and Cravchik, 2000; Hewes and Taghert, 2001 ). The cytoplasmic loops, extracellular loops, and the transmembrane regions are not highly conserved between the FMRFamide and sulfakinin receptors. In order to explore the role of FMRFamide in mosquito biology we measured the effect of the tetrapeptide on in vivo heart rate. The tetrapeptide increased the frequency of spontaneous contractions of the larval mosquito heart and, thus, increased heart rate. These data support the conclusion that the structure of the FMRFamide receptor and activity of the cardioexcitatory FMRFamide neuropeptide are conserved in mosquito.

Neuropeptides in the nervous system of Drosophila and other insects: multiple roles as neuromodulators and neurohormones

Neuropeptides in insects act as neuromodulators in the central and peripheral nervous system and as regulatory hormones released into the circulation. The functional roles of insect neuropeptides encompass regulation of homeostasis, organization of behaviors, initiation and coordination of developmental processes and modulation of neuronal and muscular activity. With the completion of the sequencing of the Drosophila genome we have obtained a fairly good estimate of the total number of genes encoding neuropeptide precursors and thus the total number of neuropeptides in an insect. At present there are 23 identified genes that encode predicted neuropeptides and an additional seven encoding insulin-like peptides in Drosophila. Since the number of G-protein-coupled neuropeptide receptors in Drosophila is estimated to be around 40, the total number of neuropeptide genes in this insect will probably not exceed three dozen. The neuropeptides can be grouped into families, and it is suggested here that related peptides encoded on a Drosophila gene constitute a family and that peptides from related genes (orthologs) in other species belong to the same family. Some peptides are encoded as multiple related isoforms on a precursor and it is possible that many of these isoforms are functionally redundant. The distribution and possible functions of members of the 23 neuropeptide families and the insulin-like peptides are discussed. It is clear that each of the distinct neuropeptides are present in specific small sets of neurons and/or neurosecretory cells and in some cases in cells of the intestine or certain peripheral sites. The distribution patterns vary extensively between types of neuropeptides. Another feature emerging for many insect neuropeptides is that they appear to be multifunctional. One and the same peptide may act both in the CNS and as a circulating hormone and play different functional roles at different central and peripheral targets. A neuropeptide can, for instance, act as a coreleased signal that modulates the action of a classical transmitter and the peptide action depends on the cotransmitter and the specific circuit where it is released. Some peptides, however, may work as molecular switches and trigger specific global responses at a given time. Drosophila, in spite of its small size, is now emerging as a very favorable organism for the studies of neuropeptide function due to the arsenal of molecular genetics methods available.

Signaling pathways and physiological functions of Drosophila melanogaster FMRFamide-related peptides

FMRFamide-related peptides (FaRPs) contain a C-terminal RFamide but unique N-terminal extensions. They are expressed throughout the animal kingdom and affect numerous biological activities. Like other animal species, Drosophila melanogaster contains multiple genes that encode different FaRPs. The ease of genetic manipulations, the availability of genomic sequence data, the existence of established bioassays, and its short lifespan make D. melanogaster a versatile experimental organism in which to investigate peptide processing, functions, and signal transduction pathways. Here, the structures, precursor organizations, distributions, and activities of FaRPs encoded by D. melanogaster FMRFamide (dFMRFamide), myosuppressin (Dms), and sulfakinin (Dsk) genes are reviewed, and predictions are made on their signaling pathways and biological functions.

Molecular characterization and cell-specific expression of a Manduca sexta FLRFamide gene

FMRFamide-related peptides (FaRPs) are a large group of neuropeptides containing a common RFamide C-terminus; they have been identified in vertebrates and invertebrates. We have isolated the cDNA that encodes three FaRPs in the tobacco hornworm, Manduca sexta, including the amidated decapeptide F10. The larger FaRPs are the partially processed precursors of F10, a neuropeptide belonging to the myosuppressin family of peptides. The presence of all three FaRPs in different tissues suggests differential utilization of typical dibasic processing sites and atypical processing sites C-terminal to leucine residues. F10 mRNA was detected in the brain, nerve cord, and midgut, and the mRNA levels in the nervous system are dynamically regulated during development. In situ hybridization analysis localized the F10 mRNA to a variety of cell types within the central nervous system (CNS), a peripheral neurosecretory cell (L1), and midgut endocrine cells, which suggests diverse functions. Distribution of the F10-containing neurons within the central nervous system is segment-specific, and the developmental profile suggests that the F10 gene products may have stage-specific functions. Molecular characterization of the F10 gene has provided insights into its regulation and cell-specific distribution that will enhance our understanding of how these FaRPs modulate different physiological systems and ultimately behavior.

Drosophila melanogaster myotropins have unique functions and signaling pathways

Drosophila melanogaster TDVDHVFLRFamide (DMS), SDNFMRFamide, and pEVRFRQCYFNPISCF (FLT) represent three structurally distinct peptide families. Each peptide decreases heart rate albeit with different magnitudes and time-dependent responses. DMS and FLT are expressed in the crop and decrease crop motility; however, SDNFMRFamide expression and effect on the crop has not been reported. These data suggest the peptides have different physiological roles. The peptides have non-overlapping expression patterns in neural tissue, which suggests different mechanisms regulate their synthesis and release. The structures, expression patterns, and activities of the myotropins suggest they have important but different roles in biology and different signaling pathways.

Characterization and baculovirus-directed expression of a myosuppressin encoding cDNA from the true armyworm, Pseudaletia unipuncta

Insect myosuppressins are a highly conserved sub-family of peptides which are primarily characterized by the ability to suppress contraction of visceral muscles in a variety of insect species. We have isolated a cDNA from the true armyworm, Pseudaletia unipuncta, that encodes a prohormone containing a peptide identical to ManducaFLRFamide. We have shown that this myosuppressin gene appears to be expressed in late larval and adult insects. In Manduca sexta, a number of extended-FLRFamide peptides have previously been purified including ManducaFLRFamide, F7D (DPSFLRFamide), F7G (GNSFLRFamide) and two larger peptides F24 and F39 that contain the shorter ManducaFLRFamide sequence at their C-terminus. Comparison with the true armyworm prepropeptide characterized here identifies F24 and F39 as partially processed products from the same precursor. Expression in the true armyworm was shown by in situ hybridization to occur in over 150 cells throughout the adult brain and nerve cord, and also to occur in both open and closed endocrine type cells of the gut. Overexpression of the P. unipuncta FLRFamide cDNA from a baculovirus vector in cabbage looper caterpillars was used to assess the potential for myosuppressin expression as a means of enhancing virus efficacy. Viral expression of the armyworm prohormone cDNA resulted in raised levels of RFamide-like products in the hemolymph of infected insects, but the products were found to be chemically distinguishable from authentic mature peptide and probably represent partially processed hormone.

Neuropeptides and their precursors in the fruitfly, Drosophila melanogaster

Neuropeptides form the most diverse class of chemical messenger molecules in metazoan nervous systems. They are usually generated from biosynthetic precursor polypeptides by enzymatic processing and modification. Many different peptides belonging to a number of distinct neuropeptide families have already been characterized from various insect species. The Drosophila Genome Sequencing Project has important implications for the future of neurobiological research. This paper describes the discovery of several new fruitfly neuropeptides by an in silico data mining approach. In addition, the state-of-the-art of Drosophila peptide research is reviewed.

DPKQDFMRFamide expression is similar in two distantly related Drosophila species

Drosophila melanogaster DPKQDFMRFamide was isolated and its expression reported. Distribution of DPKQDFMRFamide immunoreactivity is now described in Drosophila virilis. DPKQDFMRFamide antibody stained a cell in the subesophageal ganglion in embryo. DPKQDFMRFamide antibody stained cells in the superior protocerebrum, subesophageal ganglion, thoracic ganglia, and an abdominal ganglion in larva, pupa, and adult. DPKQDFMRFamide antibody stained an additional pair of cells in the optic lobe and a cell in the lateral protocerebrum in adult. Structure identity and similar distribution of DPKQDFMRFamide in D. virilis and D. melanogaster, two distantly related Drosophila species, suggests an important and conserved activity for the peptide.

Native and heterologous neuropeptides are cardioactive in Drosophila melanogaster

Nine neuropeptides isolated from Drosophila melanogaster and five neuropeptides, previously isolated from the CNS of Limulus with antisera to FMRFamide-related peptides, were tested for their effects on the myogenic heart of Drosophila melanogaster. Of the native peptides, TDVDHVFLRF-NH(2) (Dromyosuppressin), DPKQDFMRFamide, and PDNFMRFamide significantly slowed the heart. Of the Limulus peptides, DEGHKMLYFamide (LP1) increased heart rate significantly, GHSLLHFamide (LP2) and PDHHMMYFamide (LP3) decreased the heart's rate, while DHGNMLYFamide (LP4) and GGRSPSLRLRFamide (LP5) had no effect at the concentrations we employed. Dromyosuppressin, DPKQDFMRFamide, and PDNFMRFamide from Drosophila, and LP2 and LP3 from Limulus, which belong to a novel group of peptides structurally unrelated to FMRFamide, are among only a very few substances from within the general group of neuropeptides and neurohormones known to slow the heart of Drosophila, and as such offer an important tool for investigating the molecular mechanisms underlying the control of the pacemaker.

Interaction of Drosophila melanogaster prohormone convertase 2 and 7B2. Insect cell-specific processing and secretion

The prohormone convertases (PCs) are an evolutionarily ancient group of proteases required for the maturation of neuropeptide and peptide hormone precursors. In Drosophila melanogaster, the homolog of prohormone convertase 2, dPC2 (amontillado), is required for normal hatching behavior, and immunoblotting data indicate that flies express 80- and 75-kDa forms of this protein. Because mouse PC2 (mPC2) requires 7B2, a helper protein for productive maturation, we searched the fly data base for the 7B2 signature motif PPNPCP and identified an expressed sequence tag clone encoding the entire open reading frame for this protein. dPC2 and d7B2 cDNAs were subcloned into expression vectors for transfection into HEK-293 cells; mPC2 and rat 7B2 were used as controls. Although active mPC2 was detected in medium in the presence of either d7B2 or r7B2, dPC2 showed no proteolytic activity upon coexpression of either d7B2 or r7B2. Labeling experiments showed that dPC2 was synthesized but not secreted from HEK-293 cells. However, when dPC2 and either d7B2 or r7B2 were coexpressed in Drosophila S2 cells, abundant immunoreactive dPC2 was secreted into the medium, coincident with the appearance of PC2 activity. Expression and secretion of dPC2 enzyme activity thus appears to require insect cell-specific posttranslational processing events. The significant differences in the cell biology of the insect and mammalian enzymes, with 7B2 absolutely required for secretion of dPC2 and zymogen conversion occurring intracellularly in the case of dPC2 but not mPC2, support the idea that the Drosophila enzyme has specific requirements for maturation and secretion that can be met only in insect cells.