The different effects of three Drosophila melanogaster dFMRFamide-containing peptides on crop contractions suggest these structurally related peptides do not play redundant functions in gut

FMRF-related peptides in Aedes aegypti midgut: neuromuscular connections and enteric nervous system

FMRFamide-related peptides (FaRPs) are a class of neuropeptides that participate in a variety of physiological processes in invertebrates. They occur in nerves of stomatogastric ganglia and enteroendocrine cells of the insect digestive tract, where they may control muscle functions. However, their direct involvement in muscle function has never been shown in situ. We studied the relationship between FaRPs and midgut muscle during larval-pupal transition of the mosquito Aedes aegypti. In late L4, FaRP-positive neuronal extensions attach to the bundles of the external circular muscle layer, and muscle stem cells start to undergo mitosis in the internal circular layer. Thereafter, the external muscle layer degenerates, disappearing during early pupal development, and is completely absent in the adult mosquito. Our results indicate that FaRP-based neural signals are involved in the reorganization of the muscle fibers of the mosquito midgut during the larval-pupal transition. In addition to confirming FaRP involvement in muscle function, we show that the mosquito midgut muscles are largely innervated, and that circular and longitudinal muscle have specific neuron bodies associated with them.

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.

Characterization of G-protein coupled receptors from the blackback land crab Gecarcinus lateralis Y organ transcriptome over the molt cycle

BACKGROUND

G-protein coupled receptors (GPCRs) are ancient, ubiquitous, constitute the largest family of transducing cell surface proteins, and are integral to cell communication via an array of ligands/neuropeptides. Molt inhibiting hormone (MIH) is a key neuropeptide that controls growth and reproduction in crustaceans by regulating the molt cycle. It inhibits ecdysone biosynthesis by a pair of endocrine glands (Y-organs; YOs) through binding a yet uncharacterized GPCR, which triggers a signalling cascade, leading to inhibition of the ecdysis sequence. When MIH release stops, ecdysone is synthesized and released to the hemolymph. A peak in ecdysone titer is followed by a molting event. A transcriptome of the blackback land crab Gecarcinus lateralis YOs across molt was utilized in this study to curate the list of GPCRs and their expression in order to better assess which GPCRs are involved in the molt process.

RESULTS

Ninety-nine G. lateralis putative GPCRs were obtained by screening the YO transcriptome against the Pfam database. Phylogenetic analysis classified 49 as class A (Rhodopsin-like receptor), 35 as class B (Secretin receptor), and 9 as class C (metabotropic glutamate). Further phylogenetic analysis of class A GPCRs identified neuropeptide GPCRs, including those for Allatostatin A, Allatostatin B, Bursicon, CCHamide, FMRFamide, Proctolin, Corazonin, Relaxin, and the biogenic amine Serotonin. Three GPCRs clustered with recently identified putative CHH receptors (CHHRs), and differential expression over the molt cycle suggests that they are associated with ecdysteroidogenesis regulation. Two putative Corazonin receptors showed much higher expression in the YOs compared with all other GPCRs, suggesting an important role in molt regulation.

CONCLUSIONS

Molting requires an orchestrated regulation of YO ecdysteroid synthesis by multiple neuropeptides. In this study, we curated a comprehensive list of GPCRs expressed in the YO and followed their expression across the molt cycle. Three putative CHH receptors were identified and could include an MIH receptor whose activation negatively regulates molting. Orthologs of receptors that were found to be involved in molt regulation in insects were also identified, including LGR3 and Corazonin receptor, the latter of which was expressed at much higher level than all other receptors, suggesting a key role in YO regulation.

Gene expression in reproductive organs of tsetse females - initial data in an approach to reduce fecundity

BACKGROUND

Tsetse flies are vectors of African trypanosomes, and their vectorial capacity results in a major public health emergency and vast economic losses in sub-Saharan Africa. Given the limited ability of trypanosome prevention and eradication, tsetse vectors remain major targets of control efforts. Larvae of all three instars are developed in mothers' uteri, nourished through milk, and 'larviposited' shortly before pupation. The past few years have witnessed the emergence of approaches based on knockdown of genes involved in milk production, resulting in a significant reduction of fecundity.

RESULTS

In order to identify further genes applicable in the control of tsetse flies, we determined the expression of protein-coding genes in ovaries and uteri from both virgin and heavily pregnant Glossina morsitans morsitans females. Comparison of expression profiles allowed us to identify candidate genes with increased expression in pregnant individuals. Lists with the highest increases include genes involved in oocyte and embryonic development, or nourishment. Maximum ovarian fold change does not exceed 700, while the highest uterine fold change reaches to more than 4000. Relatively high fold changes of two neuropeptide receptors (for corazonin and myosuppressin) propose the corresponding genes alternative targets.

CONCLUSIONS

Given the higher fold changes in the uterus, targeting gene expression in this tissue may result in a more evident reduction of fecundity. However, ovaries should not be neglected, as manifested by several genes with top fold changes involved in early developmental stages. Apart from focusing on the highest fold changes, neuropeptide receptors with moderate increases in expression should be also verified as targets, given their roles in mediating the tissue control. However, this data needs to be considered initial, and the potential of these genes in affecting female fecundity needs to be verified experimentally.

Histochemistry, immunohistochemistry and cytochemistry of the anterior midgut region of the stingless bee Melipona quadrifasciata and honey bee Apis mellifera (Hymenoptera: Apidae)

The anterior midgut region of stingless bees is anatomically differentiated with tall and narrow cells, whereas in other social and solitary bees this anatomical gut region is lacking. The objective of the present study was to describe the histochemistry, immunohistochemistry and cytochemistry of the anterior midgut region of the stingless bee Melipona quadrifasciata in comparison with the honey bee Apis mellifera. The anterior midgut region of both species was evaluated for identification of the enzymes β- galactosidase, glucose-6-phosphatase, acid phosphatase, and alkaline phosphatase, the membrane transporter aquaporin, the hormone FMRF-amide, and lysosomes. Histology of the anterior midgut region showed that this region in M. quadrifasciata workers did not present external folds of the wall, whereas the following midgut wall presented many. In A. mellifera, folds in the midgut wall occur starting from the fore- midgut transition region. Despite these morphological differences, the tests evaluated were similar in both species. β-galactosidase was not found in the anterior midgut cells. Glucose-6-phosphatase and acid phosphatase occurred in the apical region of the gut epithelium. Alkaline phosphatase occurred in vesicles in apical cytoplasm and in the basal plasma membrane infoldings of the epithelial cells. Aquaporin was found in the basal region of the midgut epithelium and in the associated visceral muscles. FMRF-amide was found only in nerve endings in the anterior midgut region. All cells in the anterior midgut region were rich in lysosomes. These results suggest that in both bee species, although they have anatomically different anterior midgut regions, these regions present high metabolic activity and function in cellular homeostasis, lipid absorption and are under neurohormone control.

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.

Opposite effects of 5-HT/AKH and octopamine on the crop contractions in adult Drosophila melanogaster: Evidence of a double brain-gut serotonergic circuitry

This study showed that in adult Drosophila melanogaster, the type of sugar-either present within the crop lumen or in the bathing solution of the crop-had no effect on crop muscle contraction. What is important, however, is the volume within the crop lumen. Electrophysiological recordings demonstrated that exogenous applications of serotonin on crop muscles increases both the amplitude and the frequency of crop contraction rate, while adipokinetic hormone mainly enhances the crop contraction frequency. Conversely, octopamine virtually silenced the overall crop activity. The present study reports for the first time an analysis of serotonin effects along the gut-brain axis in adult D. melanogaster. Injection of serotonin into the brain between the interocellar area shows that brain applications of serotonin decrease the frequency of crop activity. Based on our results, we propose that there are two different, opposite pathways for crop motility control governed by serotonin: excitatory when added in the abdomen (i.e., directly bathing the crop) and inhibitory when supplied within the brain (i.e., by injection). Finally, our results point to a double brain-gut serotonergic circuitry suggesting that not only the brain can affect gut functions, but the gut can also affect the central nervous system. On the basis of our results, and data in the literature, a possible mechanism for these two discrete serotonergic functions is suggested.

Genomic and peptidomic analyses of the neuropeptides from the emerging pest, Drosophila suzukii

Drosophila suzukii is a highly polyphagous invasive pest which has been recently introduced into Europe and North America, where it is causing severe economic losses through larval infestations of stone and berry fruits. The peptidome of the selected nervous tissues of adult D. suzukii was investigated as a first step in identifying potential targets for the development of novel insecticides. Through in silico analyses of the D. suzukii genome databases 28 neuropeptide families, comprising more than 70 predicted peptides were identified. Using a combination of liquid chromatography and mass spectrometry of tissue extracts, 33 predicted peptides, representing 15 different peptide families were identified by their molecular masses and a total of 17 peptide sequences were confirmed by ion fragmentation. A comparison between the peptides and precursors of D. suzukii and D. melanogaster shows they are highly conserved, with differences only identified in the amino acid sequences of the peptides encoded in the FMRFamide, hugin and ecydysis triggering hormone precursors. All other peptides predicted and identified from D. suzukii appear to be identical to those previously characterized from D. melanogaster. Adipokinetic hormone was only identified in the corpus cardiacum, other peptides present included short neuropeptide F, a pyrokinin and myosuppressin, the latter of which was the only peptide identified from the crop nerve bundle. Peptides present in extracts of the brain and/or thoracico-abdominal ganglion included allatostatins, cardioacceleratory peptide 2b, corazonin, extended FMRFamides, pyrokinins, myoinihibitory peptides, neuropeptide-like precursor 1, SIFamide, short neuropeptide F, kinin, sulfakinins and tachykinin related peptides.

Drosophila C virus systemic infection leads to intestinal obstruction

Drosophila C virus (DCV) is a positive-sense RNA virus belonging to the Dicistroviridae family. This natural pathogen of the model organism Drosophila melanogaster is commonly used to investigate antiviral host defense in flies, which involves both RNA interference and inducible responses. Although lethality is used routinely as a readout for the efficiency of the antiviral immune response in these studies, virus-induced pathologies in flies still are poorly understood. Here, we characterize the pathogenesis associated with systemic DCV infection. Comparison of the transcriptome of flies infected with DCV or two other positive-sense RNA viruses, Flock House virus and Sindbis virus, reveals that DCV infection, unlike those of the other two viruses, represses the expression of a large number of genes. Several of these genes are expressed specifically in the midgut and also are repressed by starvation. We show that systemic DCV infection triggers a nutritional stress in Drosophila which results from intestinal obstruction with the accumulation of peritrophic matrix at the entry of the midgut and the accumulation of the food ingested in the crop, a blind muscular food storage organ. The related virus cricket paralysis virus (CrPV), which efficiently grows in Drosophila, does not trigger this pathology. We show that DCV, but not CrPV, infects the smooth muscles surrounding the crop, causing extensive cytopathology and strongly reducing the rate of contractions. We conclude that the pathogenesis associated with systemic DCV infection results from the tropism of the virus for an important organ within the foregut of dipteran insects, the crop.

IMPORTANCE

DCV is one of the few identified natural viral pathogens affecting the model organism Drosophila melanogaster. As such, it is an important virus for the deciphering of host-virus interactions in insects. We characterize here the pathogenesis associated with DCV infection in flies and show that it results from the tropism of the virus for an essential but poorly characterized organ in the digestive tract, the crop. Our results may have relevance for other members of the Dicistroviridae, some of which are pathogenic to beneficial or pest insect species.

Structure-activity relationships of FMRF-NH2 peptides demonstrate A role for the conserved C terminus and unique N-terminal extension in modulating cardiac contractility

FMRF-NH2 peptides which contain a conserved, identical C-terminal tetrapeptide but unique N terminus modulate cardiac contractility; yet, little is known about the mechanisms involved in signaling. Here, the structure-activity relationships (SARs) of the Drosophila melanogaster FMRF-NH2 peptides, PDNFMRF-NH2, SDNFMRF-NH2, DPKQDFMRF-NH2, SPKQDFMRF-NH2, and TPAEDFMRF-NH2, which bind FMRFa-R, were investigated. The hypothesis tested was the C-terminal tetrapeptide FMRF-NH2, particularly F1, makes extensive, strong ligand-receptor contacts, yet the unique N terminus influences docking and activity. To test this hypothesis, docking, binding, and bioactivity of the C-terminal tetrapeptide and analogs, and the FMRF-NH2 peptides were compared. Results for FMRF-NH2 and analogs were consistent with the hypothesis; F1 made extensive, strong ligand-receptor contacts with FMRFa-R; Y → F (YMRF-NH2) retained binding, yet A → F (AMRF-NH2) did not. These findings reflected amino acid physicochemical properties; the bulky, aromatic residues F and Y formed strong pi-stacking and hydrophobic contacts to anchor the ligand, interactions which could not be maintained in diversity or number by the small, aliphatic A. The FMRF-NH2 peptides modulated heart rate in larva, pupa, and adult distinctly, representative of the contact sites influenced by their unique N-terminal structures. Based on physicochemical properties, the peptides each docked to FMRFa-R with one best pose, except FMRF-NH2 which docked with two equally favorable poses, consistent with the N terminus influencing docking to define specific ligand-receptor contacts. Furthermore, SDNAMRF-NH2 was designed and, despite lacking the aromatic properties of one F, it binds FMRFa-R and demonstrated a unique SAR, consistent with the N terminus influencing docking and conferring binding and activity; thus, supporting our hypothesis.

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.

Peptidergic control of food intake and digestion in insects 1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Like all heterotrophic organisms, insects require a strict control of food intake and efficient digestion of food into nutrients to maintain homeostasis and to fulfill physiological tasks. Feeding and digestion are steered by both external and internal signals that are transduced by a multitude of regulatory factors, delivered either by neurons innervating the gut or mouthparts, or by midgut endocrine cells. The present review gives an overview of peptide regulators known to control feeding and digestion in insects. We describe the discovery and functional role in these processes for insect allatoregulatory peptides, diuretic hormones, FMRFamide-related peptides, (short) neuropeptide F, proctolin, saliva production stimulating peptides, kinins, and tachykinins. These peptides control either gut myoactivity, food intake, and (or) release of digestive enzymes. Some peptides exert their action at multiple levels, possibly having a biological function that depends on their site of delivery. Many regulatory peptides have been physically extracted from different insect species. However, multiple peptidomics, proteomics, transcriptomics, and genome sequencing projects have led to increased discovery and prediction of peptide (precursor) and receptor sequences. In combination with physiological experiments, these large-scale projects have already led to important steps forward in unraveling the physiology of feeding and digestion in insects.

More than two decades of research on insect neuropeptide GPCRs: an overview

This review focuses on the state of the art on neuropeptide receptors in insects. Most of these receptors are G protein-coupled receptors (GPCRs) and are involved in the regulation of virtually all physiological processes during an insect's life. More than 20 years ago a milestone in invertebrate endocrinology was achieved with the characterization of the first insect neuropeptide receptor, i.e., the Drosophila tachykinin-like receptor. However, it took until the release of the Drosophila genome in 2000 that research on neuropeptide receptors boosted. In the last decade a plethora of genomic information of other insect species also became available, leading to a better insight in the functions and evolution of the neuropeptide signaling systems and their intracellular pathways. It became clear that some of these systems are conserved among all insect species, indicating that they fulfill crucial roles in their physiological processes. Meanwhile, other signaling systems seem to be lost in several insect orders or species, suggesting that their actions were superfluous in those insects, or that other neuropeptides have taken over their functions. It is striking that the deorphanization of neuropeptide GPCRs gets much attention, but the subsequent unraveling of the intracellular pathways they elicit, or their physiological functions are often hardly examined. Especially in insects besides Drosophila this information is scarce if not absent. And although great progress made in characterizing neuropeptide signaling systems, even in Drosophila several predicted neuropeptide receptors remain orphan, awaiting for their endogenous ligand to be determined. The present review gives a précis of the insect neuropeptide receptor research of the last two decades. But it has to be emphasized that the work done so far is only the tip of the iceberg and our comprehensive understanding of these important signaling systems will still increase substantially in the coming years.

Insulin-Producing Cells in the Drosophila Brain also Express Satiety-Inducing Cholecystokinin-Like Peptide, Drosulfakinin

Regulation of meal size and assessing the nutritional value of food are two important aspects of feeding behavior. The mechanisms that regulate these two aspects have not been fully elucidated in Drosophila. Diminished signaling with insulin-like peptides Drosophila insulin-like peptides (DILPs) affects food intake in flies, but it is not clear what signal(s) mediates satiety. Here we investigate the role of DILPs and drosulfakinins (DSKs), cholecystokinin-like peptides, as satiety signals in Drosophila. We show that DSKs and DILPs are co-expressed in insulin-producing cells (IPCs) of the brain. Next we analyzed the effects of diminishing DSKs or DILPs employing the Gal4-UAS system by (1) diminishing DSK-levels without directly affecting DILP levels by targeted Dsk-RNAi, either in all DSK-producing cells (DPCs) or only in the IPCs or (2) expressing a hyperpolarizing potassium channel to inactivate either all the DPCs or only the IPCs, affecting release of both peptides. The transgenic flies were assayed for feeding and food choice, resistance to starvation, and for levels of Dilp and Dsk transcripts in brains of fed and starved animals. Diminishment of DSK in the IPCs alone is sufficient to cause defective regulation of food intake and food choice, indicating that DSK functions as a hormonal satiety signal in Drosophila. Quantification of Dsk and Dilp transcript levels reveals that knockdown of either peptide type affects the transcript levels of the other, suggesting a possible feedback regulation between the two signaling pathways. In summary, DSK and DILPs released from the IPCs regulate feeding, food choice and metabolic homeostasis in Drosophila in a coordinated fashion.

Defective gut function in drop-dead mutant Drosophila

Mutation of the gene drop-dead (drd) causes adult Drosophila to die within 2 weeks of eclosion and is associated with reduced rates of defecation and increased volumes of crop contents. In the current study, we demonstrate that flies carrying the strong allele drd(lwf) display a reduction in the transfer of ingested food from the crop to the midgut, as measured both as a change in the steady-state distribution of food within the gut and also in the rates of crop emptying and midgut filling following a single meal. Mutant flies have abnormal triglyceride (TG) and glycogen stores over the first 4 days post-eclosion, consistent with their inability to move food into the midgut for digestion and nutrient absorption. However, the lifespan of mutants was dependent upon food presence and quality, suggesting that at least some individual flies were able to digest some food. Finally, spontaneous motility of the crop was abnormal in drd(lwf) flies, with the crops of mutant flies contracting significantly more rapidly than those of heterozygous controls. We therefore hypothesize that mutation of drd causes a structural or regulatory defect that inhibits the entry of food into the midgut.

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.

Evidence for postsynaptic modulation of muscle contraction by a Drosophila neuropeptide

DPKQDFMRFamide, the most abundant FMRFamide-like peptide in Drosophila melanogaster, has been shown previously to enhance contractions of larval body wall muscles elicited by nerve stimulation and to increase excitatory junction potentials (EJPs). The present work investigated the possibility that this peptide can also stimulate muscle contraction by a direct action on muscle fibers. DPKQDFMRFamide induced slow contractions and increased tonus in body wall muscles of Drosophila larvae from which the central nervous system had been removed. The threshold for this effect was approximately 10(-8)M. The increase in tonus persisted in the presence of 7x10(-3)M glutamate, which desensitized postsynaptic glutamate receptors. Thus, the effect on tonus could not be explained by enhanced release of glutamate from synaptic terminals and, thus, may represent a postsynaptic effect. The effect on tonus was abolished in calcium-free saline and by treatment with L-type calcium channel blockers, nifedipine and nicardipine, but not by T-type blockers, amiloride and flunarizine. The present results provide evidence that this Drosophila peptide can act postsynaptically in addition to its apparent presynaptic effects, and that the postsynaptic effect requires influx through L-type calcium channels.

FMRFamide-like immunoreactivity in the central nervous system and alimentary tract of the non-hematophagous blow fly, Phormia regina, and the hematophagous horse fly, Tabanus nigrovittatus

FMRFamide-related peptides (FaRPs) are a diverse and physiologically important class of neuropepeptides in the metazoa. In insects, FaRPs function as brain-gut neuropeptides and have been immunolocalized throughout the nervous system and alimentary tract where they have been shown to affect feeding behavior. The occurrence of FMRFamide-like immunoreactivity (FLI) was examined in the central nervous system and alimentary tract of non-hematophagous blow fly, Phormia regina Meigen (Diptera: Calliphoridae), and the hematophagous horse fly, Tabanus nigrovittatus Macquart (Diptera:Tabanidae). Although the central nervous system and alimentary anatomy differ between these two dipteran species, many aspects of FLI remain similar. FLI was observed throughout the central and stomatogastric nervous systems, foregut, and midgut in both flies. In the central nervous system, cells and processes with FLI occurred in the brain, subesophageal ganglion, and ventral nerve cord. FLI was associated with neurohemal areas of the brain and ventral nerve cord. A neurohemal plexus of fibers with FLI was present on the dorsal region of the thoracic central nervous system in both species. In the gut, processes with FLI innervated the crop duct, crop and anterior midgut. Endocrine cells with FLI were present in the posterior midgut. The distribution of FLI in these two flies, in spite of their different feeding habits, further supports the role of FaRPs as important components of the braingut neurochemical axis in these insects and implicates FaRPs as regulators of insect feeding physiology among divergent insect taxa.

The drosulfakinin 0 (DSK 0) peptide encoded in the conserved Dsk gene affects adult Drosophila melanogaster crop contractions

We report that the drosulfakinin 0 (DSK 0; NQKTMSFNH2) structure and genomic organization are conserved. The DSK 0 C-terminus, SFNH2, is widely distributed in the animal kingdom suggesting it defines a novel peptide family. We also report the first description of DSK 0 activity. DSK 0, I (DSK I, FDDYGHMRFNH2), and II (DSK II, GGDDQFDDYGHMRFNH2) are encoded in sulfakinin (Dsk). Drosophila erecta, Drosophila sechellia, Drosophila simulans, and Drosophila yakuba shared 62.5-87.5% identity to Drosophila melanogaster DSK 0; Drosophila pseudoobscura shared 37.5% identity; numerous amino acids were one nucleotide different from a corresponding residue in D. melanogaster. DSK I and II were identical among the drosopholids. DSK 0 proteolytic processing sites were RR except D. yakuba contained KR and D. pseudoobscura contained HR, one nucleotide different from RR. DSK I and II processing sites were identical among the drosopholids. We established DSK 0 decreased adult (EC50=237nM and R(2)=0.941), but not larval gut contractions. DSK 0 exists in the central nervous system including the subesophageal ganglion and an abdominal ganglion. Peptide and genomic conservation, activity, and spatial and temporal distribution support the conclusion that DSK 0 plays diverse biological roles in drosopholids including regulating gut muscle contraction.

Distribution of FMRFamide-like immunoreactivity in the alimentary tract and hindgut ganglia of the barnacle Balanus amphitrite (Cirripedia, Crustacea)

In this study, the presence and distribution of FMRFamide-like immunoreactivity in the alimentary tract of barnacle Balanus amphitrite were investigated. A net of nerve fibers strongly immunoreactive to FMRFamide-like molecules was localized in the posterior midgut and hindgut. Positive varicose nerve terminals were also localized close to the circular muscle cells and, in the hindgut, close to the radial muscular fibers. Besides this nerve fibers network, one pair of contralateral ganglia was localized in the hindgut, each of them constituted by two strongly FMRFamide-labeled neurons and one nonlabeled neuron. Their immunoreactive axons directed toward the hindgut and posterior midgut suggest an involvement of FMRFamide-like substances in adult B. amphitrite gut motility. The hindgut associated ganglia of barnacles seem to correspond to the terminal abdominal ganglia of the other crustaceans. Since they are the only residual gut ganglia in the barnacle's reduced nervous system, we can hypothesize that gut motility needs a nervous system regulation partially independent of the central nervous system.

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.

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

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

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

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

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.

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.

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.

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.