Isolation, characterization and biological activity of a diuretic myokinin neuropeptide from the housefly, Musca domestica

A fluorescently-tagged tick kinin neuropeptide triggers peristalsis and labels tick midgut muscles

Ticks are blood-feeding arthropods that require heme for their successful reproduction. During feeding they also acquire pathogens that are subsequently transmitted to humans, wildlife and/or livestock. Understanding the regulation of tick midgut is important for blood meal digestion, heme and nutrient absorption processes and for aspects of pathogen biology in the host. We previously demonstrated the activity of tick kinins on the cognate G protein-coupled receptor. Herein we uncovered the physiological role of the kinin receptor in the tick midgut. A fluorescently-labeled kinin peptide with the endogenous kinin 8 sequence (TMR-RK8), identical in the ticks Rhipicephalus microplus and R. sanguineus, activated and labeled the recombinant R. microplus receptor expressed in CHO-K1 cells. When applied to the live midgut the TMR-RK8 labeled the kinin receptor in muscles while the labeled peptide with the scrambled-sequence of kinin 8 (TMR-Scrambled) did not. The unlabeled kinin 8 peptide competed TMR-RK8, decreasing confocal microscopy signal intensity, indicating TMR-RK8 specificity to muscles. TMR-RK8 was active, inducing significant midgut peristalsis that was video-recorded and evaluated with video tracking software. The TMR-Scrambled peptide used as a negative control did not elicit peristalsis. The myotropic function of kinins in eliciting tick midgut peristalsis was established.

Functional Identification and Characterization of Leucokinin and Its Receptor in the Fall Webworm, Hyphantria cunea

Neuropeptides function as central neuromodulators and circulating hormones that modulate insect behavior and physiology. Leucokinin (LK) is an intercellular signaling molecule that mediates many physiological and behavioral processes. However, the functions of LK associated with environmental stress and feeding behavior in the fall webworm, Hyphantria cunea, is little known. Our primary objective is to understand the function of LK and LK receptor (LKR) neuroendocrine system in H. cunea. In the present study, the results showed that LK/LKR are expressed at different developmental stages and in various tissues of H. cunea. A candidate receptor-ligand pairing for LK was identified in the larval transcriptome of H. cunea. In a heterologous expression system, the calcium assay was used to demonstrate that LKR is activated by HcLKs in a dose-dependent manner, with 50% effective concentration (EC50) values of 8.44-90.44nM. Knockdown of HcLK and HcLKR by microinjecting target-specific dsRNA leads to several effects in H. cunea, including feeding promotion, increase in resistance to desiccation and starvation stress, and regulation of water homeostasis. The transcript levels of HILP2 (except in the LK knockdown group), HILP5, and HILP8 increased, whereas those of HILP3, HILP4, and HILP6 decreased; HILP1, HILP2 (in the LK knockdown group), and HILP7 gene expression was not influenced after LK and LKR knockdown. Variations in mRNA expression levels in insulin-like peptide genes in the knockdown larvae suggest an essential role of these genes in survival in H. cunea. To our knowledge, the present study is the first comprehensive study of LK and LKR - from gene to behavior - in H. cunea.

Leucokinin and Associated Neuropeptides Regulate Multiple Aspects of Physiology and Behavior in Drosophila

Leucokinins (LKs) constitute a family of neuropeptides identified in numerous insects and many other invertebrates. LKs act on G-protein-coupled receptors that display only distant relations to other known receptors. In adult Drosophila, 26 neurons/neurosecretory cells of three main types express LK. The four brain interneurons are of two types, and these are implicated in several important functions in the fly's behavior and physiology, including feeding, sleep-metabolism interactions, state-dependent memory formation, as well as modulation of gustatory sensitivity and nociception. The 22 neurosecretory cells (abdominal LK neurons, ABLKs) of the abdominal neuromeres co-express LK and a diuretic hormone (DH44), and together, these regulate water and ion homeostasis and associated stress as well as food intake. In Drosophila larvae, LK neurons modulate locomotion, escape responses and aspects of ecdysis behavior. A set of lateral neurosecretory cells, ALKs (anterior LK neurons), in the brain express LK in larvae, but inconsistently so in adults. These ALKs co-express three other neuropeptides and regulate water and ion homeostasis, feeding, and drinking, but the specific role of LK is not yet known. This review summarizes Drosophila data on embryonic lineages of LK neurons, functional roles of individual LK neuron types, interactions with other peptidergic systems, and orchestrating functions of LK.

Leucokinins: Multifunctional Neuropeptides and Hormones in Insects and Other Invertebrates

Leucokinins (LKs) constitute a neuropeptide family first discovered in a cockroach and later identified in numerous insects and several other invertebrates. The LK receptors are only distantly related to other known receptors. Among insects, there are many examples of species where genes encoding LKs and their receptors are absent. Furthermore, genomics has revealed that LK signaling is lacking in several of the invertebrate phyla and in vertebrates. In insects, the number and complexity of LK-expressing neurons vary, from the simple pattern in the Drosophila larva where the entire CNS has 20 neurons of 3 main types, to cockroaches with about 250 neurons of many different types. Common to all studied insects is the presence or 1-3 pairs of LK-expressing neurosecretory cells in each abdominal neuromere of the ventral nerve cord, that, at least in some insects, regulate secretion in Malpighian tubules. This review summarizes the diverse functional roles of LK signaling in insects, as well as other arthropods and mollusks. These functions include regulation of ion and water homeostasis, feeding, sleep-metabolism interactions, state-dependent memory formation, as well as modulation of gustatory sensitivity and nociception. Other functions are implied by the neuronal distribution of LK, but remain to be investigated.

Activity of native tick kinins and peptidomimetics on the cognate target G protein-coupled receptor from the cattle fever tick, Rhipicephalus microplus (Acari: Ixodidae)

BACKGROUND

Kinins are multifunctional neuropeptides that regulate key insect physiological processes such as diuresis, feeding, and ecdysis. However, the physiological roles of kinins in ticks are unclear. Furthermore, ticks have an expanded number of kinin paracopies in the kinin gene. Silencing the kinin receptor (KR) in females of Rhipicephalus microplus reduces reproductive fitness. Thus, it appears the kinin signaling system is important for tick physiology and its disruption may have potential for tick control.

RESULTS

We determined the activities of endogenous kinins on the KR, a G protein-coupled receptor, and identified potent peptidomimetics. Fourteen predicted R. microplus kinins (Rhimi-K), and 11 kinin analogs containing aminoisobutyric acid (Aib) were tested. The latter incorporated tick kinin sequences and/or were modified for enhanced resistance to arthropod peptidases. A high-throughput screen using a calcium fluorescence assay in 384-well plates was performed. All tested kinins and Aib analogs were full agonists. The most potent kinin and two kinin analogs were equipotent. Analogs 2414 ([Aib]FS[Aib]WGa) and 2412 ([Aib]FG[Aib]WGa) were the most active with EC₅₀ values of 0.9 and 1.1 nM, respectively, matching the EC₅₀ of the most potent tick kinin, Rhimi-K-14 (QDSFNPWGa) (EC₅₀  = 1 nM). The potent analog 2415 ([Aib]FR[Aib]WGa, EC₅₀  = 6.8 nM) includes both Aib molecules for resistance to peptidases and a positively charged residue, R, for enhanced water solubility and amphiphilic character.

CONCLUSION

These tick kinins and pseudopeptides expand the repertoire of reagents for tick physiology and toxicology towards finding novel targets for tick management. © 2019 Society of Chemical Industry.

Synthesis, aphicidal activity and conformation of novel insect kinin analogues as potential eco-friendly insecticides

BACKGROUND

The discovery of ecofriendly insecticides through a new strategy for aphid control is important because of the substantial resistance and unexpected eco-toxicity to honeybees caused by traditional insecticides. The insect kinins, a class of multifunctional insect neuropeptides, are considered for potential application in pest control. In our previous work we developed several series of insect kinin analogues and found a promising lead II-1 with good aphicidal activity. To seek further eco-friendly aphicides, the optimization of II-1 is carried out in this study.

RESULTS

Fifteen novel Yaa³ modified analogues based on the lead II-1 were synthesized. The aphicidal tests indicated that IV-3, IV-5 and IV-10 exhibited significant activity against the soybean aphid Aphis glycines with LC₅₀ values of 0.0029, 0.0072 and 0.0086 mmol L^-1 , respectively, higher than that of lead II-1 and the commercial Pymetrozine. The molecular modeling results showed that analogues II-1, IV-3, IV-5, IV-7 and IV-10 formed a β-turn-like conformation, while the conformation of analogues IV-1, IV-2 and IV-9 seemed to be linear. Some structural elements favorable for the activity were proposed based on the conformation-activity relationship of the analogues.

CONCLUSION

Insect kinin analogues derived from lead II-1 by modifying the hydrolysis site Yaa³ with natural, sterically hindered α- and β-amino acids showed great potential as eco-friendly insecticides. Inspiringly, the most active analogue IV-3 can be a candidate for further development. The β-turn-like conformation and the orientation of the aromatic rings of the side chain of Phe² and Trp⁴ may be critical factors beneficial to activity. © 2019 Society of Chemical Industry.

Evaluation of Aib and PEG-polymer insect kinin analogs on mosquito and tick GPCRs identifies potent new pest management tools with potentially enhanced biostability and bioavailability

Insect kinins modulate aspects of diuresis, digestion, development, and sugar taste perception in tarsi and labellar sensilla in mosquitoes. They are, however, subject to rapid biological degradation by endogenous invertebrate peptidases. A series of α-aminoisobutyric (Aib) acid-containing insect kinin analogs incorporating sequences native to the Aedes aegypti mosquito aedeskinins were evaluated on two recombinant kinin invertebrate receptors stably expressed in cell lines, discovering a number of highly potent and biostable insect kinin mimics. On the Ae. aegypti mosquito kinin receptor, three highly potent, biostable Aib analogs matched the activity of the Aib-containing biostable insect kinin analog 1728, which previously showed disruptive and/or aversive activity in aphid, mosquito and kissing bug. These three analogs are IK-Aib-19 ([Aib]FY[Aib]WGa, EC₅₀ = 18 nM), IK-Aib-12 (pQKFY[Aib]WGa, EC₅₀ = 23 nM) and IK-Aib-20 ([Aib]FH[Aib]WGa, EC₅₀ = 28 nM). On the Rhipicephalus (Boophilus) microplus tick receptor, IK-Aib-20 ([Aib]FH[Aib]WGa, EC₅₀ = 2 nM) is more potent than 1728 by a factor of 3. Seven other potentially biostable analogs exhibited an EC₅₀ range of 5-10 nM, all of which match the potency of 1728. Among the multi-Aib hexapeptide kinin analogs tested the tick receptor has a preference for the positively-charged, aromatic H over the aromatic residues Y and F in the X¹ variable position ([Aib]FX¹[Aib]WGa), whereas the mosquito receptor does not distinguish between them. In contrast, in a mono-Aib pentapeptide analog framework (FX¹[Aib]WGa), both receptors exhibit a preference for Y over H in the variable position. Among analogs incorporating polyethylene glycol (PEG) polymer attachments at the N-terminus that can confer enhanced bioavailability and biostability, three matched or surpassed the potency of a positive control peptide. On the tick receptor IK-PEG-9 (P₈-R[Aib]FF[Aib]WGa) was the most potent. Two others, IK-PEG-8 (P₈-RFFPWGa) and IK-PEG-6 (P₄-RFFPWGa), were most potent on the mosquito receptor, with the first surpassing the activity of the positive control peptide. These analogs and others in the IK-Aib series expand the toolbox of potent analogs accessible to invertebrate endocrinologists studying the structural requirements for bioactivity and the as yet unknown role of the insect kinins in ticks. They may contribute to the development of selective, environmentally friendly pest arthropod control agents.

Assessment of neuropeptide binding sites and the impact of biostable kinin and CAP2b analogue treatment on aphid (Myzus persicae and Macrosiphum rosae) stress tolerance

BACKGROUND

Neuropeptides are regulators of critical life processes in insects and, due to their high specificity, represent potential targets in the development of greener insecticidal agents. Fundamental to this drive is understanding neuroendocrine pathways that control key physiological processes in pest insects and the screening of potential analogues. The current study investigated neuropeptide binding sites of kinin and CAPA (CAPA-1) in the aphids Myzus persicae and Macrosiphum rosae and the effect of biostable analogues on aphid fitness under conditions of desiccation, starvation and thermal (cold) stress.

RESULTS

M. persicae and M. rosae displayed identical patterns of neuropeptide receptor mapping along the gut, with the gut musculature representing the main target for kinin and CAPA-1 action. While kinin receptor binding was observed in the brain and VNC of M. persicae, this was not observed in M. rosae. Furthermore, no CAPA-1 receptor binding was observed in the brain and VNC of either species. CAP2b/PK analogues (with CAPA receptor cross-activity) were most effective in reducing aphid fitness under conditions of desiccation and starvation stress, particularly analogues 1895 (2Abf-Suc-FGPRLa) and 2129 (2Abf-Suc-ATPRIa), which expedited aphid mortality. All analogues, with the exception of 2139-Ac, were efficient at reducing aphid survival under cold stress, although were equivalent in the strength of their effect.

CONCLUSION

In demonstrating the effects of analogues belonging to the CAP2b neuropeptide family and key analogue structures that reduce aphid fitness under stress conditions, this research will feed into the development of second generation analogues and ultimately the development of neuropeptidomimetic-based insecticidal agents. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The leucokinin-like peptide receptor from the cattle fever tick, Rhipicephalus microplus, is localized in the midgut periphery and receptor silencing with validated double-stranded RNAs causes a reproductive fitness cost

The cattle fever tick, Rhipicephalus microplus (Canestrini) (Acari: Ixodidae), is a one-host tick that infests primarily cattle in tropical and sub-tropical regions of the world. This species transmits deadly cattle pathogens, especially Babesia spp., for which a recombinant vaccine is not available. Therefore, disease control depends on tick vector control. Although R. microplus was eradicated in the USA, tick populations in Mexico and South America have acquired resistance to many of the applied acaricides. Recent acaricide-resistant tick reintroductions detected in the U.S. underscore the need for novel tick control methods. The octopamine and tyramine/octopamine receptors, both G protein-coupled receptors (GPCR), are believed to be the main molecular targets of the acaricide amitraz. This provides the proof of principle that investigating tick GPCRs, especially those that are invertebrate-specific, may be a feasible strategy for discovering novel targets and subsequently new anti-tick compounds. The R. microplus leucokinin-like peptide receptor (LKR), also known as the myokinin- or kinin receptor, is such a GPCR. While the receptor was previously characterized in vitro, the function of the leucokinin signaling system in ticks remains unknown. In this work, the LKR was immunolocalized to the periphery of the female midgut and silenced through RNA interference (RNAi) in females. To optimize RNAi experiments, a dual-luciferase system was developed to determine the silencing efficiency of LKR-double stranded RNA (dsRNA) constructs prior to testing those in ticks placed on cattle. This assay identified two effective dsRNAs. Silencing of the LKR with these two validated dsRNA constructs was verified by quantitative real time PCR (qRT-PCR) of female tick dissected tissues. Silencing was significant in midguts and carcasses. Silencing caused decreases in weights of egg masses and in the percentages of eggs hatched per egg mass, as well as delays in time to oviposition and egg hatching. A role of the kinin receptor in tick reproduction is apparent.

Neuropeptidomics in Triatoma infestans. Comparative transcriptomic analysis among triatomines

Chagas' disease, affecting up to 6-7 million people worldwide, is transmitted to humans through the feces of triatomine kissing bugs. From these, Rhodnius prolixus, Triatoma dimidiata, Triatoma infestans and Triatoma pallidipennis are important vectors distributed throughout the Latin American subcontinent. Resistance to pyrethroids has been developed by some triatomine populations, especially T. infestans, obstructing their control. Given their role in the regulation of physiological processes, neuroendocrine-derived factors have been proposed as a source of molecular targets for new-generation insecticides. However, the involvement of neuropeptides in insecticide metabolism and resistance in insects has been poorly studied. In the present work, the sequences of 20 neuropeptide precursor genes in T. infestans, 16 in T. dimidiata, and 13 in T. pallidipennis detected in transcriptomic databases are reported, and a comparative analysis in triatomines is presented. A total of 59 neuropeptides were validated by liquid chromatography-tandem mass spectrometry in brain and nervous ganglia from T. infestans, revealing the existence of differential post-translational modifications, extended and truncated forms. The results suggest a high sequence conservation in some neuropeptide systems in triatomines, whereas remarkable differences occur in several others within the core domains. Comparisons of the basal expression levels for several neuropeptide precursor genes between pyrethroid sensitive and resistant population of T. infestans are also presented here, in order to introduce a proof of concept to test the involvement of neuropeptides in insecticide resistance. From the precursors tested, NVP and ITG peptides are significantly higher expressed in the resistant population. To our knowledge, this is the first report to associate differential neuropeptide expression with insecticide resistance. The information provided here contributes to creating conditions to widely extend functional and genetic studies involving neuropeptides in triatomines.

Biostable insect kinin analogs reduce blood meal and disrupt ecdysis in the blood-gorging Chagas' disease vector, Rhodnius prolixus

Rhodnius prolixus is a blood-gorging hemipteran that takes blood meals that are approximately 10 times its body weight. This blood meal is crucial for growth and development and is needed to ensure a successful molt into the next instar. Kinins are a multifunctional family of neuropeptides which have been shown to play a role in the control of feeding in a variety of insects. In this study, two biostable Aib-containing kinin analogs were tested to see if they interfere with blood-feeding and subsequent development into the next instar. One of the analogs, 1729 (Ac-R[Aib]FF[Aib]WGa), had no effect on the size of the blood meal or on the subsequent molting of the insect into the next instar. This analog also did not interfere with either short-term or long-term diuresis. The second analog, 1728 ([Aib]FF[Aib]WGa), appeared to be an antifeedant. Insects feeding on blood containing this analog (15μM) only consumed 60% of the blood meal taken by insects fed on blood without analog. Insects feeding on blood containing 1728 had a slower rate of rapid diuresis (diuresis in the first 3-5h after feeding) leading to less urine being excreted by 5days post feeding. The consequence of these effects was that insects fed on 1728 did not molt. This data indicates that the biostable Aib-containing analog 1728 disrupts normal growth and development in the blood-feeding insect, R. prolixus.

Design, synthesis and aphicidal activity of N-terminal modified insect kinin analogs

The insect kinins are a class of multifunctional insect neuropeptides present in a diverse variety of insects. Insect kinin analogs showed multiple bioactivities, especially, the aphicidal activity. To find a biostable and bioactive insecticide candidate with simplified structure, a series of N-terminal modified insect kinin analogs was designed and synthesized based on the lead compound [Aib]-Phe-Phe-[Aib]-Trp-Gly-NH2. Their aphicidal activity against the soybean aphid Aphis glycines was evaluated. The results showed that all the analogs maintained the aphicidal activity. In particular, the aphicidal activity of the pentapeptide analog X Phe-Phe-[Aib]-Trp-Gly-NH2 (LC50=0.045mmol/L) was similar to the lead compound (LC50=0.048mmol/L). This indicated that the N-terminal protective group may not play an important role in the activity and the analogs structure could be simplified to pentapeptide analogs while retaining good aphicidal activity. The core pentapeptide analog X can be used as the lead compound for further chemical modifications to discover potential insecticides.

Eco-Friendly Insecticide Discovery via Peptidomimetics: Design, Synthesis, and Aphicidal Activity of Novel Insect Kinin Analogues

Insect kinin neuropeptides are pleiotropic peptides that are involved in the regulation of hindgut contraction, diuresis, and digestive enzyme release. They share a common C-terminal pentapeptide sequence of Phe(1)-Xaa(2)-Yaa(3)-Trp(4)-Gly(5)-NH2 (where Xaa(2) = His, Asn, Phe, Ser, or Tyr; Yaa(3) = Pro, Ser, or Ala). Recently, the aphicidal activity of insect kinin analogues has attracted the attention of researchers. Our previous work demonstrated that the sequence-simplified insect kinin pentapeptide analogue Phe-Phe-[Aib]-Trp-Gly-NH2 could retain good aphicidal activity and be the lead compound for the further discovery of eco-friendly insecticides which encompassed a broad array of biochemicals derived from micro-organisms and other natural sources. Using the peptidomimetics strategy, we chose Phe-Phe-[Aib]-Trp-Gly-NH2 as the lead compound, and we designed and synthesized three series, including 31 novel insect kinin analogues. The aphicidal activity of the new analogues against soybean aphid was determined. The results showed that all of the analogues exhibited aphicidal activity. Of particular interest was the analogue II-1, which exhibited improved aphicidal activity with an LC50 of 0.019 mmol/L compared with the lead compound (LC50 = 0.045 mmol/L) or the commercial insecticide pymetrozine (LC50 = 0.034 mmol/L). This suggests that the analogue II-1 could be used as a new lead for the discovery of potential eco-friendly insecticides.

Relative contribution of biomolecules in bacterial extracellular polymeric substances to disinfection byproduct formation

In this study, detailed chemical compositions of the biomolecules in extracellular polymeric substances (EPS) from both pure cultures of bacteria and mixed species biofilm isolated from a water utility were analyzed. Then, based on detailed EPS analysis results, the DBP yield experiments were conducted with both extracted EPS and surrogate chemicals to indirectly identify the influence of biomolecules and their structures on DBP formation and speciation. DBP yield results of both extracted EPS and EPS surrogates indicated that proteins in EPS have a greater influence on DBP formation, especially on the formation of nitrogenous DBPs (N-DBPs), where amino acids containing unsaturated organic carbon or conjugated bonds in R-group produced higher amount of DBPs. For regulated DBPs, HAA yields were higher than THM yields, while haloacetonitriles were the dominant DBP species formed among unregulated DBPs. However, DBP yields of polysaccharide monomers were lower than those of tested amino acids groups and the DBP yields of polysaccharide monomers were not significantly influenced by their structures. Considering the results obtained in this study, biofilm needs to be considered an important precursor to DBP formation and biofilm eradication methods for water distribution systems need to be carefully selected to minimize subsequent DBP formation.

Evaluation of insect CAP2b analogs with either an (E)-alkene, trans- or a (Z)-alkene, cis-Pro isostere identifies the Pro orientation for antidiuretic activity in the stink bug

The CAP2b neuropeptide family plays an important role in the regulation of the processes of diuresis and/or antidiuresis in a variety of insects. While Manse-CAP2b (pELYAFPRV-NH2) and native CAP2bs elicit diuretic activity in a number of species of flies, native CAP2b sequences have been shown to elicit antidiuretic activity in the kissing bug Rhodnius prolixus and the green stink bug Acrosternum hilare, the latter being an important pest of cotton and soybean in the southern United States. Analogs of CAP2b containing either a (Z)-alkene, cis-Pro or an (E)-alkene, trans-Pro isosteric component were synthesized and evaluated in an in vitro stink bug diuretic assay, which involved measurement of fluid secretion by Malpighian tubules isolated from A. hilare. The conformationally constrained trans-Pro analog demonstrated statistically significant antidiuretic activity, whereas the cis-Pro analog failed to elicit activity. The results are consistent with the adoption of a trans orientation for the Pro in CAP2b neuropeptides during interaction with receptors associated with the antidiuretic process in the stink bug. In addition, the results are further consistent with a theory of ligand-receptor coevolution between the CAP2b and pyrokinin/PBAN neuropeptide classes, both members of the '-PRXamide' superfamily. This work further identifies a scaffold with which to design mimetic CAP2b analogs as potential leads in the development of environmentally favorable pest management agents capable of disrupting CAP2b-regulated diuretic/antidiuretic functions.

A dynamic paracellular pathway serves diuresis in mosquito Malpighian tubules

Female mosquitoes gorge on vertebrate blood, a rich nutrient source for developing eggs, but gorging meals increase the risk of predation. Mosquitoes are quick to reduce the flight payload with a potent diuresis. Diuretic peptides of the insect kinin family induce a tenfold reduction in the paracellular resistance of Malpighian tubules and increase the paracellular permeation of Cl(-), the counterion of the transepithelial secretion of Na(+) and K(+). As a result, the transepithelial secretion of NaCl and KCl and water increases. Insect kinins signal the opening of the paracellular pathway via G protein-coupled receptors and the elevation of intracellular [Ca(2+)], which leads to the reorganization of the cytoskeleton associated with the septate junction (SJ). The reorganization may affect the septate junctional proteins that control the barrier and permselectivity properties of the paracellular pathway. The proteins involved in the embryonic formation of the SJ and in epithelial polarization are largely known for ectodermal epithelia, but the proteins that form and mediate the dynamic functions of the SJ in Malpighian tubules remain to be determined.

Anti-diuretic factors in insects: the role of CAPA peptides

Insects have adapted to live in a wide variety of habitats and utilize an array of feeding strategies that present challenges to their ability to maintain osmotic balance. Regardless of the feeding strategy, water and ion levels within the haemolymph (insect blood) are maintained within a narrow range. This homeostasis involves the action of a variety of tissues, but is often chiefly regulated by the excretory system. Until recently, most research on the hormonal control of the excretory tissues has focused on factors known to have diuretic activities. In this mini-review, the current state of knowledge on anti-diuretic factors in insects will be discussed with a particular emphasis on the CAPA peptides in the blood-feeding Chagas' disease vector, Rhodnius prolixus.

Active diuretic peptidomimetic insect kinin analogs that contain β-turn mimetic motif 4-aminopyroglutamate and lack native peptide bonds

The multifunctional 'insect kinins' of arthropods share the evolutionarily conserved C-terminal pentapeptide core sequence Phe-X(1)-X(2)-Trp-Gly-NH(2), where X(1)=His, Asn, Ser, or Tyr and X(2)=Ser, Pro, or Ala. Insect kinins regulate diuresis in many species of insects, including the house cricket, Acheta domesticus. Insect kinins, however, are susceptible to fast enzymatic degradation by endogenous peptidases that severely limit their potential use as tools for pest control or for endocrinological studies. To enhance resistance to peptidases, the core insect kinin sequence was structurally modified in this study to replace native peptide bonds susceptible to proteolytic degradation. These modifications include incorporation of two stereochemical variants of the β-turn mimetic motif 4-aminogutamate in place of the X(1)-X(2) residues, insertion of a reduced peptide bond between residues Trp-Gly, and replacement of the Phe residue with a hydrocinnamyl group. The resulting biostable, peptidomimetic analogs contain no native peptide bonds and yet retain significant diuretic activity in an in vitro cricket Malpighian tubule fluid secretion assay, matching the efficacy of a native A. domesticus kinin (Achdo-KI). These novel analogs represent ideal new tools for endocrinologists studying arthropod kinin regulated processes in vivo, and provide leads in the development of novel, environmentally friendly pest insect management agents capable of disruption of the critical processes that kinins regulate.

Neuropeptide evolution: neurohormones and neuropeptides predicted from the genomes of Capitella teleta and Helobdella robusta

Genes encoding neurohormones and neuropeptide precursors were identified in the genomes of two annelids, the leech Helobdella robusta and the polychaete worm Capitella teleta. Although no neuropeptides have been identified from these two species and relatively few neuropeptides from annelids in general, 43 and 35 such genes were found in Capitella and Helobdella, respectively. The predicted peptidomes of these two species are similar to one another and also similar to those of mollusks, particular in the case of Capitella. Helobdella seems to have less neuropeptide genes than Capitella and it lacks the glycoprotein hormones bursicon and GPA2/GPB5; in both cases the genes coding the two subunits as well as the genes coding their receptors are absent from its genome. In Helobdella several neuropeptide genes are duplicated, thus it has five NPY genes, including one pseudogene, as well as four genes coding Wwamides (allatostatin B). Genes coding achatin, allatotropin, allatostatin C, conopressin, FFamide, FLamide, FMRFamide, GGRFamide, GnRH, myomodulin, NPY, pedal peptides, RGWamide (a likely APGWamide homolog), RXDLamide, VR(F/I)amide, WWamide were found in both species, while genes coding cerebrin, elevenin, GGNG, LFRWamide, LRFYamide, luqin, lymnokinin and tachykinin were only found in Capitella.

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.

The single kinin receptor signals to separate and independent physiological pathways in Malpighian tubules of the yellow fever mosquito

In the past, we have used the kinins of the cockroach Leucophaea (the leucokinins) to evaluate the mechanism of diuretic action of kinin peptides in Malpighian tubules of the yellow fever mosquito Aedes aegypti. Now using the kinins of Aedes (the aedeskinins), we have found that in isolated Aedes Malpighian tubules all three aedeskinins (1 microM) significantly 1) increased the rate of fluid secretion (V(S)), 2) hyperpolarized the basolateral membrane voltage (V(bl)), and 3) decreased the input resistance (R(in)) of principal cells, consistent with the known increase in the Cl(-) conductance of the paracellular pathway in Aedes Malpighian tubules. Aedeskinin-III, studied in further detail, significantly increased V(S) with an EC(50) of 1.5 x 10(-8) M. In parallel, the Na(+) concentration in secreted fluid significantly decreased, and the K(+) concentration significantly increased. The concentration of Cl(-) remained unchanged. While the three aedeskinins triggered effects on V(bl), R(in), and V(S), synthetic kinin analogs, which contain modifications of the COOH-terminal amide pentapeptide core sequence critical for biological activity, displayed variable effects. For example, kinin analog 1578 significantly stimulated V(S) but had no effect on V(bl) and R(in), whereas kinin analog 1708 had no effect on V(S) but significantly affected V(bl) and R(in). These observations suggest separate signaling pathways activated by kinins. One triggers the electrophysiological response, and the other triggers fluid secretion. It remains to be determined whether the two signaling pathways emanate from a single kinin receptor via agonist-directed signaling or from a differentially glycosylated receptor. Occasionally, Malpighian tubules did not exhibit a detectable response to natural and synthetic kinins. Hypothetically, the expression of the kinin receptor may depend on developmental, nutritional, and/or reproductive signals.

Antifeedant activity and high mortality in the pea aphid Acyrthosiphon pisum (Hemiptera: Aphidae) induced by biostable insect kinin analogs

The insect kinins are multifunctional neuropeptides found in a variety of arthropod species, including the pea aphid Acyrthosiphon pisum (Hemiptera: Aphidae). A series of biostable insect kinin analogs based on the shared C-terminal pentapeptide core region were fed in solutions of artificial diet to the pea aphid over a period of 3 days and evaluated for antifeedant and aphicidal activity. The analogs contained either alpha,alpha-disubstituted or beta-amino acids in key positions to enhance resistance to tissue-bound peptidases and retain activity in a number of insect kinin bioassays and/or on expressed receptors. Three of the biostable analogs demonstrated antifeedant activity, with a marked reduction in honeydew formation observed after 1 day, and very high mortality. In contrast, an unmodified, parent insect kinin and two other analogs containing some of the same structural components that promote biostability are inactive. The most active analog, double Aib analog K-Aib-1 ([Aib]FF[Aib]WGa), featured aphicidal activity calculated at an LC(50) of 0.063 nmol/microl (0.048 microg/microl) and an LT(50) of 1.68 days, matching the potency of some commercially available aphicides. The mechanism of this activity has yet to be established. The aphicidal activity of the biostable insect kinin analogs may result from different potential mechanisms as disruption of digestive processes by interfering with gut motility patterns, digestive enzyme release, and/or with fluid cycling in the gut, and also nutrient transport across the gut itself; all processes shown to be regulated by the insect kinins in other insects. However the mechanism(s) is(are) not yet known. The active insect kinin analogs represent potential leads in the development of selective, environmentally friendly pest aphid control agents.

Biostable agonists that match or exceed activity of native insect kinins on recombinant arthropod GPCRs

The multifunctional arthropod 'insect kinins' share the evolutionarily conserved C-terminal pentapeptide motif Phe-X(1)-X(2)-Trp-Gly-NH(2), where X(1)=His, Asn, Ser, or Tyr and X(2)=Ser, Pro, or Ala. Insect kinins regulate diuresis in many species of insects. Compounds with similar biological activity could be exploited for the control of arthropod pest populations such as the mosquito Aedes aegypti (L.) and the southern cattle tick Rhipicephalus (Boophilus) microplus (Canestrini), vectors of human and animal pathogens, respectively. Insect kinins, however, are susceptible to fast enzymatic degradation by endogenous peptidases that severely limit their use as tools for pest control or for endocrinological studies. To enhance resistance to peptidases, analogs of the insect kinins incorporating bulky alpha,alpha-disubstituted amino acids in positions adjacent to both primary and secondary peptidase hydrolysis sites were synthesized. In comparison with a control insect kinin, several of these analogs are highly stable to hydrolysis by degradative enzymes ANCE, neprilysin and Leucine aminopeptidase. Six analogs were evaluated by calcium bioluminescence assay on recombinant receptors from mosquito and tick. Four of these analogs either matched or exceeded the potency of the control kinin peptide agonist. One of these was about 5-fold more potent than the control agonist on the tick receptor. This analog was 8-fold more potent than the control agonist on the mosquito receptor, and twice more potent than the endogenous Aedes kinin-II. The analog also demonstrated potent activity in an in vitro Aedes Malpighian tubule fluid secretion assay. Similar comparisons of analog potency cannot be made to tick kinins because no endogenous kinin has yet been identified. These potent, biostable analogs represent ideal new tools for endocrinologists studying arthropod kinin-regulated processes in vivo, particularly for ticks in which their role remains to be established.

A photoswitchable thioxopeptide bond facilitates the conformation-activity correlation study of insect kinin

Thioxopeptide bond psi[CS-N], a nearly isosteric modification of the native peptide bond, was introduced into insect kinin active core pentapeptide to evaluate the impact of backbone cis/trans photoswitching on bioactivity. The thioxo analog Phe(1)-Tyr(2)-psi[CS-N]-Pro(3)-Trp(4)-Gly(5)-NH(2) (psi[CS-N](2)-kinin), was synthesized by Fmoc solid-phase peptide strategy. The reversible photoswitching property was characterized via spectroscopic methods and HPLC, which showed that the cis conformer increased from 15.7 to 47.7% after 254 nm UV irradiation. A slow thermal reisomerization (t(1/2) = 40 min) permitted us to determine the cockroach hindgut myotropic activity of the thioxopeptide in the photostationary state. The results indicated that the activity increased significantly after UV irradiation and recovered to the ground level after thermal re-equilibration. In the present study, by utilizing the phototriggered isomerization in a specific position of peptide backbone, we revealed that the cis psi[CS-N](2)-kinin conformer is the active conformation when interacting with kinin receptor on cockroach hindgut.

An antidiuretic peptide (Tenmo-ADFb) with kinin-like diuretic activity on Malpighian tubules of the house cricket, Acheta domesticus (L.)

Acheta domesticus is reported to have an antidiuretic hormone that reduces Malpighian tubule secretion. Identified peptides known to work in this way (Tenmo-ADFa and ADFb, and Manse-CAP(2b)) were tested as candidates for the unidentified hormone, along with their second messenger, cyclic GMP. Only Tenmo-ADFb was active, but was diuretic, as was 8-bromo cyclic GMP. The activity of Tenmo-ADFb is comparable to that of the cricket kinin neuropeptide, Achdo-KII, but it is much less potent. Its activity was unaffected by deleting either the six N-terminal residues or the C-terminal phenylalanine. At high concentrations, tubule secretion is doubled by Tenmo-ADFb and Achdo-KII, but their actions are non-additive, suggesting they have a similar mode of action. Both stimulate a non-selective KCl and NaCl diuresis, which is consistent with the opening of a transepithelial Cl(-) conductance. In support of this, the diuretic response to Tenmo-ADFb and Achdo-KII is prevented by a ten-fold reduction in bathing fluid chloride concentration, and both peptides cause the lumen-positive transepithelial voltage to collapse. The Cl(-) conductance pathway appears likely to be transcellular, because the Cl(-) channel blocker DPC reduces both basal and peptide-stimulated rates of secretion. The effects of 8-bromo cyclic GMP on transepithelial voltage and composition of the secreted fluid are markedly different from those of Tenmo-ADFb. This is the first report of the antidiuretic factor Tenmo-ADFb stimulating tubule secretion. Although the actions of Tenmo-ADFb are indistinguishable from those of Achdo-KII, it is unlikely to act at a kinin receptor, because the core sequence (residues 7-12) lacks the Phe and Trp residues that are critical for kinin activity.

Identification of selective and non-selective, biostable beta-amino acid agonists of recombinant insect kinin receptors from the southern cattle tick Boophilus microplus and mosquito Aedes aegypti

The multifunctional arthropod 'insect kinins' share the evolutionarily conserved C-terminal pentapeptide motif Phe-X1-X2-Trp-Gly-NH2, where X1=His, Asn, Ser, or Tyr and X2=Ser, Pro, or Ala. Eight different analogs of the insect kinin C-terminal pentapeptide active core in which the critical residues Phe 1, Pro3 and Trp 4 are replaced with beta 3-amino acid and/or their beta2-amino acid counterparts were evaluated on recombinant insect kinin receptors from the southern cattle tick, Boophilus microplus (Canestrini) and the dengue vector, the mosquito Aedes aegypti (L.). A number of these analogs previously demonstrated enhanced resistance to degradation by peptidases. Single-replacement analog beta 2 Trp 4 and double-replacement analog [beta 3 Phe 2, beta 3 Pro 3] of the insect kinins proved to be selective agonists for the tick receptor, whereas single-replacement analog beta 3 Pro 3 and double-replacement analog [beta 3 Phe, beta 3 Pro 3] were strong agonists on both mosquito and tick receptors. These biostable analogs represent new tools for arthropod endocrinologists and potential leads in the development of selective, environmentally friendly arthropod pest control agents capable of disrupting insect kinin-regulated processes.

Comparison of insect kinin analogs with cis-peptide bond, type VI-turn motifs identifies optimal stereochemistry for interaction with a recombinant arthropod kinin receptor from the southern cattle tick Boophilus microplus

The multifunctional 'insect kinins' share the evolutionarily conserved C-terminal pentapeptide motif Phe-X1-X2-Trp-Gly-NH2, where X1=His, Asn, Ser, or Tyr and X2=Ser, Pro, or Ala; and are associated with the regulation of diuresis in a variety of species of insects. We previously reported the functional expression of a southern cattle tick (Boophilus microplus) G protein-coupled receptor that is activated by insect kinins. Four different stereochemical variants of each of the 4-aminopyroglutamic acid (APy) and tetrazole moieties, mimics of a cis-peptide bond, type VI beta-turn in insect kinins were now evaluated on the expressed tick receptor using a calcium bioluminescence plate assay. This study represents the first investigation of the interaction of restricted-conformation analogs incorporating components that mimic specific conformations and/or peptide bond orientations in an expressed arthropod neuropeptide receptor. Analog Ac-RF[APy]WGa (2R,4S) was at least 10-fold more active than the other analogs, thus identifying the optimal stereochemistry for tick receptor interaction. The optimal stereochemistry for the tetrazole insect kinin analogs in the tick receptor assay was identified as (D,L). The APy is superior to the tetrazole as a scaffold for the design of mimetic insect kinin analogs. These biostable analogs provide new tools for arthropod endocrinologists and potential leads in the development of selective, environmentally friendly arthropod pest control agents capable of disrupting insect kinin regulated processes.

Beetle diuretic peptides: the response of mealworm (Tenebrio molitor) Malpighian tubules to synthetic peptides, and cross-reactivity studies with a dung beetle (Onthophagus gazella)

This paper reports the effects of different diuretic factors on the Malpighian tubules of beetles. Calcitonin (CT)-like peptides from silkmoth and mosquito increase fluid secretion in a dose-dependent manner in the tubules of Tenebrio molitor, but the cockroach CT-like peptide, Dippu-DH(31), has no effect. Thapsigargin induces a small but significant increase in tubule secretion rates. The interactions between different factors in mealworm tubules were explored by testing CT-like peptides, thapsigargin and the mealworm CRF-related diuretic factor Tenmo-DH(37) in various combinations, but no synergistic effects were observed. C-terminal fragments of the CRF-related diuretic peptides Locmi-DH(46) and Dippu-DH(46) fail to increase fluid secretion in mealworm tubules, unlike their corresponding whole peptides. Cross-reactivity of factors between beetle species was investigated using the scarabaeid Onthophagus gazella. Tenmo-DH(37) increases fluid secretion in isolated tubules of O. gazella in a dose-dependent manner, revealing a high degree of cross-reactivity in this distantly related beetle species. However, homogenates of O. gazella brains inhibited fluid secretion in mealworm tubules.

A C-terminal aldehyde analog of the insect kinins inhibits diuresis in the housefly

The insect kinins are present in a wide variety of insects and function as potent diuretic peptides in flies. A C-terminal aldehyde insect kinin analog, Fmoc-RFFPWG-H (R-LK-CHO), demonstrates stimulation of Malpighian tubule fluid secretion in crickets, but shows inhibition of both in vitro and in vivo diuresis in the housefly. R-LK-CHO reduced the total amount of urine voided over 3 h from flies injected with 1 microL of distilled water by almost 50%. The analog not only inhibits stimulation of housefly fluid secretion by the native kinin Musdo-K, but also by thapsigargin, a SERCA inhibitor, and by ionomycin, a calcium ionophore. The activity of R-LK-CHO is selective, however, as related C-terminal aldehyde analogs do not demonstrate an inhibitory response on housefly fluid secretion. The selective inhibitory activity of R-LK-CHO on housefly tubules represents an important lead in the development of environmentally friendly insect management agents based on the insect kinins.

Comparison of insect kinin analogs withcis-peptide bond motif 4-aminopyroglutamate identifies optimal stereochemistry for diuretic activity

The insect kinins are present in a wide variety of insects and function as potent diuretic peptides, though they are subject to rapid degradation by internal peptidases. Insect kinin analogs incorporating stereochemical variants of (2S,4S)-4-aminopyroglutamate (APy), a cis-peptide bond motif, demonstrate significant activity in a cricket diuretic assay. Insect kinin analogs containing (2R,4R)-APy, (2S,4R)-APy and (2S,4S)-APy are essentially equipotent on an insect diuretic assay, with EC(50) values of about 10(-7)M, whereas the (2R,4S)-APy analog is at least 10-fold more potent (EC(50) = 7 x 10(-9)M). Conformational studies in aqueous solution indicate that the (2R,4S)-APy analog is considerably more flexible than the other three variants, which may explain its greater potency. The work identifies the optimal stereochemistry for the APy scaffold with which to design biostable, peptidomimetic analogs with the potential to disrupt critical insect kinin-regulated processes in insects.

Structure-activity relationships for in vitro diuretic activity of CAP2b in the housefly

A series of truncated and Ala-replacement analogs of the peptide Manse-CAP2b (pELYAFPRV-NH(2)) were assayed for diuretic activity on Malpighian tubules of the housefly Musca domestica (M. domestica). The C-terminal hexapeptide proved to be the active core, the minimum sequence required to retain significant diuretic activity. However, full activity required the C-terminal heptapeptide, which was equipotent with the most active of the native housefly CAP2b peptides. Replacement of Arg(7) and Val(8) with Ala led to inactivity and a large 70-fold drop in potency, respectively, indicating that these were critical residues. The Leu(2) was semicritical, where a six-fold loss in potency was observed. Conversely, the replacement of all other residues with Ala led to much smaller effects on potency and these positions were considered to be noncritical. This structure-activity relationship data can aid in the design of mimetic agonist/antagonist analogs of this diuretic peptide family with enhanced biostability and bioavailability, as tools for arthropod endocrinologists and as potential pest management agents capable of disrupting the water balance in pest flies.

Serotonin: A coordinator of feeding-related physiological events in the blood-gorging bug, Rhodnius prolixus

Rhodnius prolixus is an obligatory blood-feeder that can ingest blood meals of up to 10 times its mass. Rapid production of urine commences within 2-3 min of the start of feeding in order to eliminate the load of water and salts, and so there is an increase of Malpighian tubule secretion greater than 1,000 fold in response to feeding. Feeding and post-prandial diuresis in Rhodnius are highly coordinated events, including for example, host recognition, probing, injection of saliva, cuticle plasticization, passage of blood through the digestive system, diuresis and excretion. This review illustrates that many of the known functions of serotonin in Rhodnius are feeding-related. Serotonin coordinates or 'orchestrates' feeding-related physiological events either as a neurotransmitter/neuromodulator, delivered to target tissues in the nerve supply, or as a neurohormone, delivered by the haemolymph. Thus, serotonin has physiological effects upon the salivary glands, cuticle, digestive tract, cardiac muscle, and Malpighian tubules. By discussing these aspects, the review illustrates that serotonin acts in a coordinated manner to prepare Rhodnius for this energy-demanding process of feeding and diuresis.

Comparative structure-activity analysis of insect kinin core analogs on recombinant kinin receptors from Southern cattle tick Boophilus microplus (Acari: Ixodidae) and mosquito Aedes aegypti (Diptera: Culicidae)

The systematic analysis of structure-activity relationships of insect kinins on two heterologous receptor-expressing systems is described. Previously, kinin receptors from the southern cattle tick, Boophilus microplus (Canestrini), and the dengue vector, the mosquito Aedes aegypti (L.), were functionally and stably expressed in CHO-K1 cells. In order to determine which kinin residues are critical for the peptide-receptor interaction, kinin core analogs were synthesized as an Ala-replacement series of the peptide FFSWGa and tested by a calcium bioluminescence plate assay. The amino acids Phe(1) and Trp(4) were essential for activity of the insect kinins in both receptors. It was confirmed that the pentapeptide kinin core is the minimum sequence required for activity and that the C-terminal amide is also essential. In contrast to the tick receptor, a large increase in efficacy is observed in the mosquito receptor when the C-terminal pentapeptide is N-terminally extended to a hexapeptide. The aminoisobutyric acid (Aib)-containing analog, FF[Aib]WGa, was as active as superagonist FFFSWGa on the mosquito receptor in contrast to the tick receptor where it was statistically more active than FFFSWGa by an order of magnitude. This restricted conformation Aib analog provides information on the conformation associated with the interaction of the insect kinins with these two receptors. Furthermore, the analog FF[Aib]WGa has been previously shown to resist degradation by the peptidases ACE and nephrilysin and represents an important lead in the development of biostable insect kinin analogs that ticks and mosquitoes cannot readily deactivate.

Identification of PVK/CAP2b neuropeptides from single neurohemal organs of the stable fly and horn fly via MALDI-TOF/TOF tandem mass spectrometry

MALDI-TOF/TOF tandem mass spectrometry has been applied to determine the complete sequences of the PVK/CAP2b neuropeptides in the stable fly Stomoxys calcitrans and horn fly Haematobia irritans, insect pests of livestock. This peptidomic analysis of single neurohemal organ preparations allows the unambiguous assignment of internal Leu/Ile positions not distinguishable by previous mass spectrometric techniques. The sequences are as follows: Stoca-PVK/CAP2b-1, AGGASGLYAFPRVa; Stoca-PVK/CAP2b-2, NAKLYPVPRVa; and Haeir-PVK/CAP2b-1, AGGASGLYAFPRVa; Haeir-PVK/CAP2b-1, NAKLYPMPRVa. Both Stoca-PVK/CAP2b-1 and -2 stimulate Malpighian tubule fluid secretion in the stable fly, with EC50 values between 3 and 11 nM. The identification of these novel neuropeptides adds to our knowledge of the peptidomes of flies, and can aid in the development of neuropeptide-based control strategies of these insect pests.

Mass spectrometric assignment of Leu/Ile in neuropeptides from single neurohemal organ preparations of insects

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF-TOF) tandem mass spectrometry has been applied for the first time on an insect/arthropod target, focusing on PVK/CAP2b neuropeptides in the housefly Musca domestica and flesh fly Neobellieria bullata. The peptidomic analysis of single neurohemal organ preparations allows the unambiguous assignment of internal Leu/Ile positions not distinguishable by previous mass spectrometric techniques. The confirmation of side-chain fragments which allows assignment of Leu/Ile even from samples as small as neurohemal organs will greatly accelerate the identification of novel neuropeptides that are implicated in the regulation of critical physiological processes in insects. The unnatural Ile analog is 4.5 times more active than the native Leu sequence in a housefly Malpighian tubule fluid secretion assay, which reinforces the caveat that potency values in a biological assay cannot be relied upon to predict the native sequence.

The presence and distribution of crustacean cardioactive peptide in the central and peripheral nervous system of the stick insect, Baculum extradentatum

Crustacean cardioactive peptide (CCAP)-like immunoreactivity was localized and quantified in the central and peripheral nervous system of the Vietnamese stick insect, Baculum extradentatum, using immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). The brain, frontal ganglion, suboesophageal ganglion and ventral nerve cord displayed neurons and processes with CCAP-like immunoreactivity. The brain, in comparison to the other parts of the central nervous system, contained the greatest amount of CCAP (167 +/- 18 fmol), and showed CCAP-like staining in neurons, neuropil regions and the central complex. There were also CCAP-like varicosities and processes associated with the corpus cardiacum. The alimentary canal of B. extradentatum contained CCAP with the largest amount localized in the midgut (1110 +/- 274 fmol CCAP equivalents). The midgut contained numerous endocrine-like cells which stained positively for CCAP, whereas the foregut and hindgut revealed an extensive network of CCAP-like immunoreactive axons and varicosities. Based on physiological assays, the hindgut of the stick insect was found to be sensitive to CCAP, showing dose-dependent increases in contractions with threshold at 10(-10) M CCAP and maximal response at 5 x 10(-7) M CCAP. There were negligible quantities of CCAP in the oviducts and no CCAP-like immunoreactivity was associated with the oviducts. CCAP had no effect on spontaneous contractions of the oviducts. The presence of CCAP in the central nervous system, the stomatogastric nervous system, the corpus cardiacum and the alimentary canal, suggest broad ranging roles for CCAP in B. extradentatum.

Functional characterisation of the Anopheles leucokinins and their cognate G-protein coupled receptor

Identification of the Anopheles gambiae leucokinin gene from the completed A. gambiae genome revealed that this insect species contains three leucokinin peptides, named Anopheles leucokinin I-III. These peptides are similar to those identified in two other mosquito species, Aedes aegypti and Culex salinarius. Additionally, Anopheles leucokinin I displays sequence similarity to Drosophila melanogaster leucokinin. Using a combination of computational and molecular approaches, a full-length cDNA for a candidate leucokinin-like receptor was isolated from A. stephensi, a close relative of A. gambiae. Alignment of the known leucokinin receptors--all G protein-coupled receptors (GPCRs)--with this receptor, identified some key conserved regions within the receptors, notably transmembrane (TM) domains I, II, III, VI and VII. The Anopheles leucokinins and receptor were shown to be a functional receptor-ligand pair. All three Anopheles leucokinins caused a dose-dependent rise in intracellular calcium ([Ca2+]i) when applied to S2 cells co-expressing the receptor and an aequorin transgene, with a potency order of I>II>III. Drosophila leucokinin was also found to activate the Anopheles receptor with a similar EC50 value to Anopheles leucokinin I. However, when the Anopheles peptides were applied to the Drosophila receptor, only Anopheles leucokinin I and II elicited a rise in [Ca2+]i. This suggests that the Anopheles receptor has a broader specificity for leucokinin ligands than the Drosophila receptor. Antisera raised against the Anopheles receptor identified a doublet of approx. 65 and 72 kDa on western blots, consistent with the presence of four N-glycosylation sites within the receptor sequence, and the known glycosylation of the receptor in Drosophila. In Anopheles tubules, as in Drosophila, the receptor was localised to the stellate cells. Thus we provide the first identification of Anopheles mosquito leucokinins (Anopheles leucokinins) and a cognate leucokinin receptor, characterise their interaction and show that Dipteran leucokinin signalling is closely conserved between Drosophila and Anopheles.

A study of signal transduction for the two diuretic peptides of Diploptera punctata

We investigated second messengers involved in the action of the CRF-related peptide Dippu-DH46 and the calcitonin-like peptide Dippu-DH31 in Diploptera punctata. Dippu-DH46 causes a dose-dependent increase in intracellular cAMP levels, its diuretic activity is mimicked by cAMP agonists, but is attenuated by Rp-cAMPS. Dippu-DH46 acts synergistically with kinins and thapsigargin; both mobilize intracellular Ca2+. Dippu-DH46 also acts synergistically with cAMP agonists, and its effect is inhibited by a PKC inhibitor, suggesting it also activates intracellular Ca2+. Dippu-DH31 has no effect on cAMP levels and its activity is not blocked by cAMP agonists. Neither peptide stimulated cGMP levels in a dose-dependent manner, nor does cGMP have any effect on fluid secretion.

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.

Continuous recording of excretory water loss from Musca domestica using a flow-through humidity meter: hormonal control of diuresis

Water loss from adult male houseflies was continuously recorded using a flow-through humidity meter, which enabled losses to be apportioned between the sum of cuticular and respiratory transpiration, salivation and excretion. Transpiration accounted for >95% of water lost from sham-injected flies, compared with excretion (3.0%) and salivation (2.4%). In contrast, excretion accounted for 40% of water lost from flies injected with > or =3 microl of saline, whereas salivary losses were unchanged. Saline injections (1-5 microl) expanded the abdomen in the dorsal-ventral plane, and this expansion was positively correlated with the magnitude of the ensuing diuresis, suggesting the signal for diuretic hormone release originates from stretch receptors in abdominal tergal-sternal muscles. The effects of decapitation, severing the ventral nerve cord within the neck or ligaturing the neck, showed the head was needed to initiate and maintain diuresis, but was neither the source of diuretic hormone nor did it control the discharge of urine from the anus. These findings indicate the head is part of the neural-endocrine pathway between abdominal stretch receptors and sites for diuretic hormone release from the thoracic-abdominal ganglion mass. Evidence is presented for Musdo-K having a hormonal role in the control of diuresis, although other neuropeptides may also be implicated.

An active insect kinin analog with 4-aminopyroglutamate, a novelcis-peptide bond, type VI ?-turn motif

The insect kinins are potent diuretic peptides that preferentially form a cis-Pro, type VI beta-turn. An insect kinin analog containing (2S,4S)-4-aminopyroglutamate, a novel cis-peptide bond, type VI beta-turn motif, demonstrates significant activity in the physiological range in a cricket diuretic assay. This is the first instance of a 4-aminopyroglutamate analog of a peptide with a preference for a type VI turn that demonstrates significant bioactivity. The results provide further confirmatory evidence for the active conformation of the insect kinins, and a new scaffold with which to design biostable, peptidomimetic analogs capable of disrupting critical insect kinin-regulated processes in insects.

Anatomy and functions of brain neurosecretory cells in diptera

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

A C-terminal aldehyde insect kinin analog enhances inhibition of weight gain and induces significant mortality in Helicoverpa zea larvae

The first reported examples of C-terminal aldehyde analogs of an insect neuropeptide are described. They are hexapeptide insect kinin analogs Boc-VFFPWG-H and Fmoc-RFFPWG-H. Activity observed for these modified analogs in an in vitro insect diuretic assay confirms that the C-terminal aldehyde group is tolerated by an insect kinin receptor. The two analogs demonstrate greatly enhanced activity over standard C-terminal amide insect kinins in a larval weight gain inhibition assay in the corn earworm Helicoverpa zea. Treatment with Boc-VFFPWG-H led to significant increases in larval mortality at doses of 500pm (45%) and 5nm (67%). Boc-VFFPWG-H represents a lead analog in the development of novel, environmentally friendly pest insect management agents based on the insect kinin class of neuropeptides.

Functional analysis of a G protein-coupled receptor from the southern cattle tick Boophilus microplus (Acari: Ixodidae) identifies it as the first arthropod myokinin receptor

The myokinins are invertebrate neuropeptides with myotropic and diuretic activity. The lymnokinin receptor from the snail Lymnaea stagnalis (Mollusca) has been the only previously identified myokinin receptor. We had cloned a G protein-coupled receptor (AF228521) from the tick Boophilus microplus (Arthropoda: Acari), 40% identical to the lymnokinin receptor, that we have now expressed in CHO-K1 cells. Myokinins at nanomolar concentrations induced intracellular calcium release, as measured by fluorescent cytometry and the receptor coupled to a pertussis toxin-insensitive G protein. Absence of extracellular calcium did not inhibit the fluorescence response, indicating that intracellular stores were sufficient for the initial response. Control cells only transfected with vector did not respond. We conclude that the tick receptor is the first myokinin receptor to be cloned from an arthropod.

Evidence for crustacean cardioactive peptide-like innervation of the gut in Locusta migratoria

Hindguts from female Vth instar larvae, young adults (1-2 days) and old adults (>10 days) are equally sensitive to the crustacean cardioactive peptide (CCAP), with changes in contraction occurring at a threshold concentration of 10(-9)M and maximal responses observed at concentrations ranging between 10(-7) and 5x10(-6)M. An immunohistochemical examination of the gut of Locusta migratoria with an antiserum raised against CCAP revealed an extensive network of CCAP-like immunoreactive processes on the hindgut and posterior midgut via the 11th sternal nerve arising from the terminal abdominal ganglion. Anterograde filling of the 11th sternal nerve with neurobiotin revealed extensive processes and terminals on the hindgut. Retrograde filling of the branch of the 11th sternal nerve which innervates the hindgut with neurobiotin revealed two bilaterally paired cells in the terminal abdominal ganglion which co-localized with CCAP-like immunoreactivity. Results suggest that a CCAP-like substance acts as a neurotransmitter/neuromodulator at the locust hindgut.

Occurrence of insect kinins in the flesh fly, stable fly and horn fly-mass spectrometric identification from single nerves and diuretic activity

MALDI-TOF mass spectrometric analysis of single lateral abdominal nerves (LANs) demonstrate the presence of the insect kinin Musdo-K in the housefly Musca domestica, and identify heretofore unknown insect kinins in two other Dipteran species as Musdo-K in the stable fly Stomoxys calcitrans and horn fly Haematobia irritans. The insect kinin native to the flesh fly Neobellieria bullata is identified as Drome-K. Musdo-K and Drome-K are identical save for the conservative substitution of Ser for Thr in position 2. The sequences of the insect kinins are, therefore, remarkably conserved throughout Dipterans. The in vitro Malpighian tubule fluid secretion activity of Musdo-K in the stable fly is similar to that in the housefly, whereas that of Drome-K is 30-fold more potent in the flesh fly than in the fruit fly. Given the structural identities of the kinins and CRF-like diuretic hormones of these Dipteran species, the housefly can serve as a model insect for the study of diuretic peptides and their functions in the stable fly and horn fly, both livestock pests.