Diuretic action of the peptide locustatachykinin I: cellular localisation and effects on fluid secretion in Malpighian tubules of locusts

Another fly diuretic hormone: tachykinins increase fluid and ion transport by adult Drosophila melanogaster Malpighian 'renal' tubules

Insects such as the model organism Drosophila melanogaster must modulate their internal physiology to withstand changes in temperature and availability of water and food. Regulation of the excretory system by peptidergic hormones is one mechanism by which insects maintain their internal homeostasis. Tachykinins are a family of neuropeptides that have been shown to stimulate fluid secretion from the Malpighian 'renal' tubules (MTs) in some insect species, but it is unclear if that is the case in the fruit fly, D. melanogaster. A central objective of the current study was to examine the physiological role of tachykinin signaling in the MTs of adult D. melanogaster. Using the genetic toolbox available in this model organism along with in vitro and whole-animal bioassays, our results indicate that Drosophila tachykinins (DTKs) function as diuretic hormones by binding to the DTK receptor (DTKR) localized in stellate cells of the MTs. Specifically, DTK activates cation and anion transport across the stimulated MTs, which impairs their survival in response to desiccation because of their inability to conserve water. Thus, besides their previously described roles in neuromodulation of pathways controlling locomotion and food search, olfactory processing, aggression, lipid metabolism and metabolic stress, processing of noxious stimuli and hormone release, DTKs also appear to function as bona fide endocrine factors regulating the excretory system and appear essential for the maintenance of hydromineral balance.

Insecticidal efficacy and risk assessment of different neuropeptide analog combinations against the peach-potato aphid following topical exposure

BACKGROUND

Insect neuropeptides control essential physiological metabolic activities. In our previous studies, Capability/CAP2b (PK/CAPA) analog 1895 applied alone or as a combination of CAPA analogs (1895 + 2315) was reported to decrease aphid fitness. While this was obtained with the combination of two peptide analogs of the same neuropeptide class, the effect of combining peptide analogs of different neuropeptide classes has not been explored so far.

RESULTS

In this study, we assessed the effect of combinations of the PK/CAPA analog 1895 with neuropeptide analogs of four different classes [adipokinetic hormone (AKH) analog: 2271; myosuppressin analog: 2434; kinin analog: 2460; tachykinin-related peptide analog: 2463] on the fitness of aphids. We found that the combination of 1895 and AKH analog 2271 was the most effective one to control Myzus persicae. The triple combination 1895 + 2271 + 2315 provided a synergistic effect by further increasing aphid mortality and reducing reproduction relative to 1895 + 2315. Additionally, a biosafety assessment of the combination 1895 + 2271 + 2315 showed no significant lethal nor sub-lethal effects on survival rates and food intake for the pollinator (Bombus terrestris) and the two representative natural enemies (Harmonia axyridis and Nasonia vitripennis).

CONCLUSION

These results could facilitate establishment of the triple combination 1895 + 2271 + 2315, and/or inclusion of second generation analogs, as alternatives to broad spectrum and less friendly insecticides. © 2022 Society of Chemical Industry.

Multiple tachykinins and their receptors characterized in the gastropod mollusk Pacific abalone: Expression, signaling cascades, and potential role in regulating lipid metabolism

Tachykinin (TK) families, including the first neuropeptide substance P, have been intensively explored in bilaterians. Knowledge of signaling of TK receptors (TKRs) has enabled the comprehension of diverse physiological processes. However, TK signaling systems are largely unknown in Lophotrochozoa. This study identified two TK precursors and two TKR isoforms in the Pacific abalone Haliotis discus hannai (Hdh), and characterized Hdh-TK signaling. Hdh-TK peptides harbored protostomian TK-specific FXGXRamide or unique YXGXRamide motifs at the C-termini. A phylogenetic analysis showed that lophotrochozoan TKRs, including Hdh-TKRs, form a monophyletic group distinct from arthropod TKRs and natalisin receptor groups. Although reporter assays demonstrated that all examined Hdh-TK peptides activate intracellular cAMP accumulation and Ca²⁺ mobilization in Hdh-TKR-expressing mammalian cells, Hdh-TK peptides with N-terminal aromatic residues and C-terminal FXGXRamide motifs were more active than shorter or less aromatic Hdh-TK peptides with a C-terminal YXGXRamide. In addition, we showed that ligand-stimulated Hdh-TKRs mediate ERK1/2 phosphorylation in HEK293 cells and that ERK1/2 phosphorylation is inhibited by PKA and PKC inhibitors. In three-dimensional in silico Hdh-TKR binding modeling, higher docking scores of Hdh-TK peptides were consistent with the lower EC50 values in the reporter assays. The transcripts for Hdh-TK precursors and Hdh-TKR were highly expressed in the neural ganglia, with lower expression levels in peripheral tissues. When abalone were starved for 3 weeks, Hdh-TK1 transcript levels, but not Hdh-TK2, were increased in the cerebral ganglia (CG), intestine, and hepatopancreas, contrasting with the decreased lipid content and transcript levels of sterol regulatory element-binding protein (SREBP). At 24 h post-injection in vivo, the lower dose of Hdh-TK1 mixture increased SREBP transcript levels in the CG and hepatopancreas and accumulative food consumption of abalone. Higher doses of Hdh-TK1 and Hdh-TK2 mixtures decreased the SREBP levels in the CG. When Hdh-TK2-specific siRNA was injected into abalone, intestinal SREBP levels were significantly increased, whereas administration of both Hdh-TK1 and Hdh-TK2 siRNA led to decreased SREBP expression in the CG. Collectively, our results demonstrate the first TK signaling system in gastropod mollusks and suggest a possible role for TK peptides in regulating lipid metabolism in the neural and peripheral tissues of abalone.

Identification of cells expressing Calcitonins A and B, PDF and ACP in Locusta migratoria using cross-reacting antisera and in situ hybridization

This work was initiated because an old publication suggested that electrocoagulation of four paraldehyde fuchsin positive cells in the brain of Locusta migratoria might produce a diuretic hormone, the identity of which remains unknown, since none of the antisera to the various putative Locusta diuretic hormones recognizes these cells. The paraldehyde fuchsin positive staining suggests a peptide with a disulfide bridge and the recently identified Locusta calcitonins have both a disulfide bridge and are structurally similar to calcitonin-like diuretic hormone. In situ hybridization and antisera raised to calcitonin-A and -B were used to show where these peptides are expressed in Locusta. Calcitonin-A is produced by neurons and neuroendocrine cells that were previously shown to be immunoreactive to an antiserum to pigment dispersing factor (PDF). The apparent PDF-immunoreactivity in these neurons and neuroendocrine cells is due to crossreactivity with the calcitonin-A precursor. As confirmed by both an PDF-precursor specific antiserum and in situ hybridisation, those calcitonin-A expressing cells do not express PDF. Calcitonin B is expressed by numerous enteroendocrine cells in the midgut as well as the midgut caeca. A guinea pig antiserum to calcitonin A seemed quite specific as it recognized only the calcitonin A expressing cells. However, rabbit antisera to calcitonin-A and-B both crossreacted with neuroendocrine cells in the brain that produce ACP (AKH/corazonin-related peptide), this is almost certainly due to the common C-terminal dipeptide SPamide that is shared between Locusta calcitonin-A, calcitonin-B and ACP.

Bacterial-mediated RNAi and functional analysis of Natalisin in a moth

The neuropeptide natalisin (NTL) has been determined to play essential roles in reproduction in two Diptera and one Coleoptera species. Whether NTL has similar or even different functions in Lepidoptera remains to be determined. Here, we cloned the NTL transcript in the common cutworm moth Spodoptera litura. This transcript encodes a 438-amino acid protein. Twelve putative Sl-NTL neuropeptides were defined by cleavage sites. These NTL peptides share a DDPFWxxRamide C-terminal motif. The expressions of Sl-NTL is low during the egg and larval stages, which increased to a higher level during the pupal stage, and then reached the maximum during the adult stage. Moreover, the expression pattern during the pupal stage is similar between sexes while during the adult stage, it is dimorphic. To explore the function of Sl-NTL and assess its potential as a target for pest control, we knocked down the expression of Sl-NTL in both sexes by using bacteria-mediated RNAi. This technique significantly down regulated (reduced up to 83%) the expression of Sl-NTL in both sexes. Knocking down Sl-NTL expression did not significantly affect its development, survival and morphology but significantly reduced adults' reproductive behavior (including female calling, male courtship, mating and remating patterns and rates) and reproductive output (offspring gain reduced more than 70%).

Tachykinins: Neuropeptides That Are Ancient, Diverse, Widespread and Functionally Pleiotropic

Tachykinins (TKs) are ancient neuropeptides present throughout the bilaterians and are, with some exceptions, characterized by a conserved FX1GX2Ramide carboxy terminus among protostomes and FXGLMamide in deuterostomes. The best-known TK is the vertebrate substance P, which in mammals, together with other TKs, has been implicated in health and disease with important roles in pain, inflammation, cancer, depressive disorder, immune system, gut function, hematopoiesis, sensory processing, and hormone regulation. The invertebrate TKs are also known to have multiple functions in the central nervous system and intestine and these have been investigated in more detail in the fly Drosophila and some other arthropods. Here, we review the protostome and deuterostome organization and evolution of TK precursors, peptides and their receptors, as well as their functions, which appear to be partly conserved across Bilateria. We also outline the distribution of TKs in the brains of representative organisms. In Drosophila, recent studies have revealed roles of TKs in early olfactory processing, neuromodulation in circuits controlling locomotion and food search, nociception, aggression, metabolic stress, and hormone release. TK signaling also regulates lipid metabolism in the Drosophila intestine. In crustaceans, TK is an important neuromodulator in rhythm-generating motor circuits in the stomatogastric nervous system and a presynaptic modulator of photoreceptor cells. Several additional functional roles of invertebrate TKs can be inferred from their distribution in various brain circuits. In addition, there are a few interesting cases where invertebrate TKs are injected into prey animals as vasodilators from salivary glands or paralyzing agents from venom glands. In these cases, the peptides are produced in the glands of the predator with sequences mimicking the prey TKs. Lastly, the TK-signaling system appears to have duplicated in Panarthropoda (comprising arthropods, onychophores, and tardigrades) to give rise to a novel type of peptides, natalisins, with a distinct receptor. The distribution and functions of natalisins are distinct from the TKs. In general, it appears that TKs are widely distributed and act in circuits at short range as neuromodulators or cotransmitters.

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

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

A de novo transcriptome of the Malpighian tubules in non-blood-fed and blood-fed Asian tiger mosquitoes Aedes albopictus: insights into diuresis, detoxification, and blood meal processing

Background. In adult female mosquitoes, the renal (Malpighian) tubules play an important role in the post-prandial diuresis, which removes excess ions and water from the hemolymph of mosquitoes following a blood meal. After the post-prandial diuresis, the roles that Malpighian tubules play in the processing of blood meals are not well described.

Methods. We used a combination of next-generation sequencing (paired-end RNA sequencing) and physiological/biochemical assays in adult female Asian tiger mosquitoes (Aedes albopictus) to generate molecular and functional insights into the Malpighian tubules and how they may contribute to blood meal processing (3–24 h after blood ingestion).

Results/Discussion. Using RNA sequencing, we sequenced and assembled the first de novo transcriptome of Malpighian tubules from non-blood-fed (NBF) and blood-fed (BF) mosquitoes. We identified a total of 8,232 non-redundant transcripts. The Malpighian tubules of NBF mosquitoes were characterized by the expression of transcripts associated with active transepithelial fluid secretion/diuresis (e.g., ion transporters, water channels, V-type H⁺-ATPase subunits), xenobiotic detoxification (e.g., cytochrome P450 monoxygenases, glutathione S-transferases, ATP-binding cassette transporters), and purine metabolism (e.g., xanthine dehydrogenase). We also detected the expression of transcripts encoding sodium calcium exchangers, G protein coupled-receptors, and septate junctional proteins not previously described in mosquito Malpighian tubules. Within 24 h after a blood meal, transcripts associated with active transepithelial fluid secretion/diuresis exhibited a general downregulation, whereas those associated with xenobiotic detoxification and purine catabolism exhibited a general upregulation, suggesting a reinvestment of the Malpighian tubules’ molecular resources from diuresis to detoxification. Physiological and biochemical assays were conducted in mosquitoes and isolated Malpighian tubules, respectively, to confirm that the transcriptomic changes were associated with functional consequences. In particular, in vivo diuresis assays demonstrated that adult female mosquitoes have a reduced diuretic capacity within 24 h after a blood meal. Moreover, biochemical assays in isolated Malpighian tubules showed an increase in glutathione S-transferase activity and the accumulation of uric acid (an end product of purine catabolism) within 24 h after a blood meal. Our data provide new insights into the molecular physiology of Malpighian tubules in culicine mosquitoes and reveal potentially important molecular targets for the development of chemical and/or gene-silencing insecticides that would disrupt renal function in mosquitoes.

Ligand selectivity in tachykinin and natalisin neuropeptidergic systems of the honey bee parasitic mite Varroa destructor

The varroa mite, Varroa destructor, is a devastating ectoparasite of the honey bees Apis mellifera and A. cerana. Control of these mites in beehives is a challenge in part due to the lack of toxic agents that are specific to mites and not to the host honey bee. In searching for a specific toxic target of varroa mites, we investigated two closely related neuropeptidergic systems, tachykinin-related peptide (TRP) and natalisin (NTL), and their respective receptors. Honey bees lack both NTL and the NTL receptor in their genome sequences, providing the rationale for investigating these receptors to understand their specificities to various ligands. We characterized the receptors for NTL and TRP of V. destructor (VdNTL-R and VdTRP-R, respectively) and for TRP of A. mellifera (AmTRP-R) in a heterologous reporter assay system to determine the activities of various ligands including TRP/NTL peptides and peptidomimetics. Although we found that AmTRP-R is highly promiscuous, activated by various ligands including two VdNTL peptides when a total of 36 ligands were tested, we serendipitously found that peptides carrying the C-terminal motif -FWxxRamide are highly specific to VdTRP-R. This motif can serve as a seed sequence for designing a VdTRP-R-specific agonist.

G protein coupled receptors as targets for next generation pesticides

There is an on-going need for the discovery and development of new pesticides due to the loss of existing products through the continuing development of resistance, the desire for products with more favourable environmental and toxicological profiles and the need to implement the principles of integrated pest management. Insect G protein coupled receptors (GPCRs) have important roles in modulating biology, physiology and behaviour, including reproduction, osmoregulation, growth and development. Modifying normal receptor function by blocking or over stimulating its actions may either result in the death of a pest or disrupt its normal fitness or reproductive capacity to reduce pest populations. Hence GPCRs offer potential targets for the development of next generation pesticides providing opportunities to discover new chemistries for invertebrate pest control. Such receptors are important targets for pharmaceutical drugs, but are under-exploited by the agro-chemical industry. The octopamine receptor agonists are the only pesticides with a recognized mode of action, as described in the classification scheme developed by the Insecticide Resistance Action Committee, that act via a GPCR. The availability of sequenced insect genomes has facilitated the characterization of insect GPCRs, but the development and utilization of screening assays to identify lead compounds has been slow. Various studies using knock-down technologies or applying the native ligands and/or neuropeptide analogues to pest insects in vivo, have however demonstrated that modifying normal receptor function can have an insecticidal effect. This review presents examples of potential insect neuropeptide receptors that are potential targets for lead compound development, using case studies from three representative pest species, Tribolium castaneum, Acyrthosiphon pisum, and Drosophila suzukii. Functional analysis studies on T. castaneum suggest that GPCRs involved in growth and development (eclosion hormone, ecdysis triggering hormone and crustacean cardioacceleratory peptide receptors) as well as the dopamine-2 like, latrophilin-like, starry night, frizzled-like, methuselah-like and the smoothened receptors may be suitable pesticide targets. From in vivo studies using native ligands and peptide analogues, receptors which appear to have a role in the regulation of feeding in the pea aphid, such as the PISCF-allatostatin and the various "kinin" receptors, are also potential targets. In Drosophila melanogaster various neuropeptides and their signalling pathways have been studied extensively. This may provide insights into potential pesticide targets that could be exploited in D. suzukii. Examples include the sex peptide receptor, which is involved in reproduction and host seeking behaviours, and those responsible for osmoregulation such as the diuretic hormone receptors. However the neuropeptides and their receptors in insects are often poorly characterized, especially in pest species. Although data from closely related species may be transferable (e.g. D. melanogaster to D. suzukii), peptides and receptors may have different roles in different insects, and hence a target in one insect may not be appropriate in another. Hence fundamental knowledge of the roles and functions of receptors is vital for development to proceed.

Serotonin and insulin-like peptides modulate leucokinin-producing neurons that affect feeding and water homeostasis in Drosophila

Metabolic homeostasis and water balance is maintained by tight hormonal and neuronal regulation. In Drosophila, insulin-like peptides (DILPs) are key regulators of metabolism, and the neuropeptide leucokinin (LK) is a diuretic hormone that also modulates feeding. However, it is not known whether LK and DILPs act together to regulate feeding and water homeostasis. Because LK neurons express the insulin receptor (dInR), we tested functional links between DILP and LK signaling in feeding and water balance. Thus, we performed constitutive and conditional manipulations of activity in LK neurons and insulin-producing cells (IPCs) in adult flies and monitored food intake, responses to desiccation, and peptide expression levels. We also measured in vivo changes in LK and DILP levels in neurons in response to desiccation and drinking. Our data show that activated LK cells stimulate diuresis in vivo, and that LK and IPC signaling affect food intake in opposite directions. Overexpression of the dInR in LK neurons decreases the LK peptide levels, but only caused a subtle decrease in feeding, and had no effect on water balance. Next we demonstrated that LK neurons express the serotonin receptor 5-HT1B . Knockdown of this receptor in LK neurons diminished LK expression, increased desiccation resistance, and diminished food intake. Live calcium imaging indicates that serotonin inhibits spontaneous activity in abdominal LK neurons. Our results suggest that serotonin via 5-HT1B diminishes activity in the LK neurons and thereby modulates functions regulated by LK peptide, but the action of the dInR in these neurons remains less clear.

Activation of BNGR-A24 by direct interaction with tachykinin-related peptides from the silkworm Bombyx mori leads to the Gq- and Gs-coupled signaling cascades

Tachykinins constitute one of the largest peptide families in the animal kingdom and exert their diverse actions via G protein-coupled receptors (GPCRs). In this study, the Bombyx tachykinin-related peptides (TKRPs) were identified as specific endogenous ligands for the Bombyx neuropeptide GPCR A24 (BNGR-A24) and thus designated BNGR-A24 as BmTKRPR. Using both mammalian cell line HEK293 and insect cell line Sf21, further characterization demonstrated that BmTKRPR was activated, thus resulting in intracellular accumulation of cAMP, Ca(2+) mobilization, and ERK1/2 phosphorylation in a Gs and Gq inhibitor-sensitive manner. Moreover, quantitative reverse transcriptase polymerase chain reaction analysis and dsRNA-mediated knockdown experiments suggested a possible role for BmTKRPR in the regulation of feeding and growth. Our findings enhance the understanding of the Bombyx TKRP system in the regulation of fundamental physiological processes.

The role of serotonin in feeding and gut contractions in the honeybee

Serotonin (5-hydroxytryptamine, 5-HT) is involved in the regulation of feeding and digestion in many animals from worms to mammals. In insects, 5-HT functions both as a neurotransmitter and as a systemic hormone. Here we tested its role as a neurotransmitter in feeding and crop contractions and its role as a systemic hormone that affected feeding in adult foraging honeybees. We found 5-HT immunoreactive processes throughout the gut, including on the surface of the oesophagus, crop, proventriculus, and the midgut, as well as in the ventral nerve cord. mRNA transcripts for all four of the known bee 5-HT receptors (Am5-ht1A,2α,2β,7) were expressed in the crop and the midgut suggesting a functional role for 5-HT in these locations. Application of a cocktail of antagonists with activity against these known receptors to the entire gut in vivo reduced the rate of spontaneous contraction in the crop and proventriculus. Although feeding with sucrose caused a small elevation of endogenous 5-HT levels in the haemolymph, injection of exogenous 5-HT directly into the abdomen of the bee to elevate 5-HT in the haemolymph did not alter food intake. However, when 5-HT was injected into directly into the brain there was a reduction in intake of carbohydrate, amino acid, or toxin-laced food solutions. Our data demonstrate that 5-HT inhibits feeding in the brain and excites muscle contractions in the gut, but general elevation of 5-HT in the bee's haemolymph does not affect food intake.

K+ absorption by locust gut and inhibition of ileal K+ and water transport by FGLamide allatostatins

The Scanning Ion-Selective Electrode Technique (SIET) was utilized for the first time in Locusta migratoria to characterize K+ transport along the digestive tract and to determine the effect of two locust FGLamide allatostatins (FGLa/ASTs) on K+ transport: a previously sequenced FGLa/AST from Schistocerca gregaria (Scg-AST-6; ARPYSFGL-NH2) and a newly sequenced FGLa/AST from L. migratoria (Locmi-FGLa/AST-2; LPVYNFGL-NH2). Regional differences in K+ fluxes along the gut were evident, where K+ efflux in vitro (or absorption into the hemolymph in vivo) was greatest at the anterior ileum, and lowest at the colon. Ileal K+ efflux was inhibited by both Scg-AST-6 and Locmi-FGLa/AST-2, with maximal inhibition at 10-10 and 10-11 M, respectively. Both FGLa/ASTs also inhibited cAMP-stimulated K+ efflux from the ileum. Locmi-FGLa/AST-2 also inhibited efflux of water across the ileum. Locusts are terrestrial insects living in dry climates, risking desiccation and making water conservation a necessity. The results suggest that FGLa/ASTs may be acting as diuretics by increasing K+ excretion and therefore increasing water excretion. Thus, it is likely that FGLa/ASTs are involved in the control of hemolymph water and ion levels during feeding and digestion, to help the locust deal with the excess K+ load (and subsequently fluid) when the meal is processed.

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.

Endocrine regulation of insect diuresis in the early postgenomic era1This 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

Diuresis, the removal of excess metabolic waste through production of primary urine while maintaining homeostasis, is an important biological process that is tightly regulated by endocrine factors. Several hormonal components that act as diuretic or antidiuretic factors in insects have been identified in the last few decades. Physiological mechanisms responsible for ion and water transport across biological membranes have been intensively studied. The large amount of data rapidly accumulating in the genomics era has led to an increased dependence on reverse genetic and physiological approaches, first identifying candidate genes and subsequently deriving functions. In many cases, the reverse approaches have been highly successful, especially in studies of the receptors for diuretic factors, which are mainly G-protein-coupled receptors. This review summarizes research on insect diuretic and antidiuretic endocrine factors, and their receptors. Emphases of the review are given to the genomics of ligands and their receptors, as well as to their implications for evolution and function.

Insulin-producing cells and their regulation in physiology and behavior ofDrosophila1This 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

Insulin-like peptide signaling regulates development, growth, reproduction, metabolism, stress resistance, and life span in a wide spectrum of animals. Not only the peptides, but also their tyrosine kinase receptors and the downstream signaling pathways are conserved over evolution. This review summarizes roles of insulin-like peptides (DILPs) in physiology and behavior of Drosophila melanogaster Meigen, 1830. Seven DILPs (DILP1–7) and one receptor (dInR) have been identified in Drosophila. These DILPs display cell and stage specific expression patterns. In the adult, DILP2, 3, and 5 are expressed in insulin-producing cells (IPCs) among the median neurosecretory cells of the brain, DILP7 in 20 neurons of the abdominal ganglion, and DILP6 in the fat body. The DILPs of the IPCs regulate starvation resistance, responses to oxidative and temperature stress, and carbohydrate and lipid metabolism. Furthermore, the IPCs seem to regulate feeding, locomotor activity, sleep and ethanol sensitivity, but the mechanisms are not elucidated. Insulin also alters the sensitivity in the olfactory system that affects food search behavior, and regulates peptidergic neurons that control aspects of feeding behavior. Finally, the control of insulin production and release by humoral and neuronal factors is discussed. This includes a fat body derived factor and the neurotransmitters GABA, serotonin, octopamine, and two neuropeptides.

Blockade of the release of the neuropeptide leucokinin to determine its possible functions in fly behavior: chemoreception assays

Previous studies have revealed leucokinin (LK) expression in the brain and ventral ganglion of Drosophila CNS. One pair of protocerebrum neurons located in the lateral horn area (LHLK) surrounds the peduncles of the mushroom bodies while two pairs of subesophageal neurons (SELKs) project extended processes to the tritocerebrum and through a cervical connection to the ventral ganglion. There, axons of eight or nine pairs of abdominal (ABLK) neurons leave the CNS through the abdominal nerves and processes connecting each other ipsilaterally and contralaterally. The neural functions of LK remain largely unknown, especially those related to Drosophila behavior. Here, we have studied the role of LK in olfactory and gustatory perception by keeping the LK neurons electrically silent through targeted expression of inward rectifier K(+) channels. In order to examine the effects of LK failure, we first analyzed the dehydration response, comparing the leucokinin-silent individuals with their parents as a control. Our results showed significant differences that demonstrate the effectiveness of the method. We then tested the olfactory behavioral response to a set of odorants over a range of concentrations in a T-maze paradigm in which flies were allowed to choose between the odorant and solvent compartments. The feeding preference assays were carried out on microplates in which flies were allowed to choose between two colored tastes. Our results show that the blockade of LK release alters both olfactory and gustatory responses, and are therefore evidence that this neuropeptide also modulates chemosensory responses through LHLK and SELK neurons.

Biostable multi-Aib analogs of tachykinin-related peptides demonstrate potent oral aphicidal activity in the pea aphid Acyrthosiphon pisum (Hemiptera: Aphidae)

The tachykinin-related peptides (TRPs) are multifunctional neuropeptides found in a variety of arthropod species, including the pea aphid Acyrthosiphon pisum (Hemiptera: Aphidae). Two new biostable TRP analogs containing multiple, sterically hindered Aib residues were synthesized and found to exhibit significantly enhanced resistance to hydrolysis by angiotensin converting enzyme and neprilysin, membrane-bound enzymes that degrade and inactivate natural TRPs. The two biostable analogs were also found to retain significant myostimulatory activity in an isolated cockroach hindgut preparation, the bioassay used to isolate and identify the first members of the TRP family. Indeed one of the analogs (Leuma-TRP-Aib-1) matched the potency and efficacy of the natural, parent TRP peptide in this myotropic bioassay. The two biostable TRP analogs were further fed in solutions of artificial diet to the pea aphid over a period of 3 days and evaluated for antifeedant and aphicidal activity and compared with the effect of treatment with three natural, unmodified TRPs. The two biostable multi-Aib TRP analogs were observed to elicit aphicidal effects within the first 24 h. In contrast natural, unmodified TRPs, including two that are native to the pea aphid, demonstrated little or no activity. The most active analog, double-Aib analog Leuma-TRP-Aib-1 (pEA[Aib]SGFL[Aib]VR-NH(2)), featured aphicidal activity calculated at an LC(50) of 0.0083 nmol/μl (0.0087 μg/μl) and an LT(50) of 1.4 days, matching or exceeding the potency of commercially available aphicides. The mechanism of this activity has yet to be established. The aphicidal activity of the biostable TRP analogs may result from disruption of digestive processes by interfering with gut motility patterns and/or with fluid cycling in the gut; processes shown to be regulated by the TRPs in other insects. These active TRP analogs and/or second generation analogs offer potential as environmentally friendly pest aphid control agents.

The control of Malpighian tubule secretion in a predacious hemipteran insect, the spined soldier bug Podisus maculiventris (Heteroptera, Pentatomidae)

Spined soldier bugs, Podisus maculiventris, are heteropteran insects that feed voraciously on other insects, particular the soft bodied larval forms of Lepidoptera and Coleoptera. The response of P. maculiventris Malpighian tubules (MTs) to serotonin and known diuretic and antidiuretic peptides has been investigated, and is compared with that of MT from the hematophagous and phytophagous heteropteran bugs Rhodnius prolixus and Acrosternum hilare, respectively. A CRF-related peptide diuretic hormone (DH) from the termite Zootermopsis nevadensis (Zoone-DH) stimulated MT secretion, which was reversed by a member of the CAP(2b) family of peptides from A. hilare (Acrhi-CAP(2b)-2), an antidiuretic effect. Serotonin had no effect on secretion, neither did a representative calcitonin-like DH, kinin, tachykinin-related peptide, and an antidiuretic factor from the mealworm Tenebrio molitor (Tenmo-ADFb) in both P. maculiventris or A. hilare. Serotonin is a DH in R. prolixus, and its lack of effect on MT from P. maculiventris and A. hilare suggests this is an adaptation to hematophagy. On the other hand, the antidiuretic activity of members of the CAP(2b) family in all three bugs is consistent with this being a heteropteran feature rather than a specialism for hematophagy.

Metabolic stress responses in Drosophila are modulated by brain neurosecretory cells that produce multiple neuropeptides

In Drosophila, neurosecretory cells that release peptide hormones play a prominent role in the regulation of development, growth, metabolism, and reproduction. Several types of peptidergic neurosecretory cells have been identified in the brain of Drosophila with release sites in the corpora cardiaca and anterior aorta. We show here that in adult flies the products of three neuropeptide precursors are colocalized in five pairs of large protocerebral neurosecretory cells in two clusters (designated ipc-1 and ipc-2a): Drosophila tachykinin (DTK), short neuropeptide F (sNPF) and ion transport peptide (ITP). These peptides were detected by immunocytochemistry in combination with GFP expression driven by the enhancer trap Gal4 lines c929 and Kurs-6, both of which are expressed in ipc-1 and 2a cells. This mix of colocalized peptides with seemingly unrelated functions is intriguing and prompted us to initiate analysis of the function of the ten neurosecretory cells. We investigated the role of peptide signaling from large ipc-1 and 2a cells in stress responses by monitoring the effect of starvation and desiccation in flies with levels of DTK or sNPF diminished by RNA interference. Using the Gal4-UAS system we targeted the peptide knockdown specifically to ipc-1 and 2a cells with the c929 and Kurs-6 drivers. Flies with reduced DTK or sNPF levels in these cells displayed decreased survival time at desiccation and starvation, as well as increased water loss at desiccation. Our data suggest that homeostasis during metabolic stress requires intact peptide signaling by ipc-1 and 2a neurosecretory cells.

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.

Identification, physiological actions, and distribution of TPSGFLGMRamide: a novel tachykinin-related peptide from the midgut and stomatogastric nervous system of Cancer crabs

In most invertebrates, multiple species-specific isoforms of tachykinin-related peptide (TRP) are common. In contrast, only a single conserved TRP isoform, APSGFLGMRamide, has been documented in decapod crustaceans, leading to the hypothesis that it is the sole TRP present in this arthropod order. Previous studies of crustacean TRPs have focused on neuronal tissue, but the recent demonstration of TRPs in midgut epithelial cells in Cancer species led us to question whether other TRPs are present in the gut, as is the case in insects. Using direct tissue matrix assisted laser desorption/ionization Fourier transform mass spectrometry, in combination with sustained off-resonance irradiation collision-induced dissociation, we found that at least one additional TRP is present in Cancer irroratus, Cancer borealis, Cancer magister, and Cancer productus. The novel TRP isoform, TPSGFLGMRamide, was present not only in the midgut, but also in the stomatogastric nervous system (STNS). In addition, we identified an unprocessed TRP precursor APSGFLGMRG, which was detected in midgut tissues only. TRP immunohistochemistry, in combination with preadsorption studies, suggests that APSGFLGMRamide and TPSGFLGMRamide are co-localized in the stomatogastric ganglion (STG), which is contained within the STNS. Exogenous application of TPSGFLGMRamide to the STG elicited a pyloric motor pattern that was identical to that elicited by APSGFLGMRamide, whereas APSGFLGMRG did not alter the pyloric motor pattern.

Neuropeptide Control of Fluid Balance in Insects

This minireview considers various aspects of the control of hydromineral balance in insects with particular reference to the control of diuresis and natriuresis in mosquitoes, with new information on the diuretic peptides of Anopheles gambiae.

Drosophila melanogaster NEP2 is a new soluble member of the neprilysin family of endopeptidases with implications for reproduction and renal function

The mammalian neprilysin (NEP) family members are typically type II membrane endopeptidases responsible for the activation/inactivation of neuropeptides and peptide hormones. Differences in substrate specificity and subcellular localization of the seven mammalian NEPs contribute to their functional diversity. The sequencing of the Drosophila melanogaster genome has revealed a large expansion of this gene family, resulting in over 20 fly NEP-like genes, suggesting even greater diversity in structure and function than seen in mammals. We now report that one of these genes (Nep2) codes for a secreted endopeptidase with a highly restricted pattern of expression. D. melanogaster NEP2 is expressed in the specialized stellate cells of the renal tubules and in the cyst cells that surround the elongating spermatid bundles in adult testis, suggesting roles for the peptidase in renal function and in spermatogenesis. D. melanogaster NEP2 was found in vesicle-like structures in the syncytial cytoplasm of the spermatid bundles, suggesting that the protein was acquired by endocytosis of protein secreted from the cyst cells. Expression of NEP2 cDNA in D. melanogaster S2 cells confirmed that the peptidase is secreted and is only weakly inhibited by thiorphan, a potent inhibitor of human NEP. D. melanogaster NEP2 also differs from human NEP in the manner in which the peptidase cleaves the tachykinin, GPSGFYGVR-amide. Molecular modelling suggests that there are important structural differences between D. melanogaster NEP2 and human NEP in the S1' and S2' ligand-binding subsites, which might explain the observed differences in inhibitor and substrate specificities. A soluble isoform of a mouse NEP-like peptidase is strongly expressed in spermatids, suggesting an evolutionarily conserved role for a soluble endopeptidase in spermatogenesis.

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.