Peptide-induced Ca(2+) movements in a tonic insect muscle: effects of proctolin and periviscerokinin-2

Molecular physiology of manganese in insects

Manganese is an essential element for maintaining life. Overexposure to the metal, however, can be toxic to organisms. Given the significant function of manganese in insects, agriculture, and human disease, as well as in the healthy ecology of the planet, the biological activities of manganese in insects needs consideration. Because of the role of manganese as a cofactor for essential enzymes present in different organelles, both over and underexposure to manganese has a multifaceted effect on organisms. At the physiological level, the effects of insect exposure to the metal on enzymatic activities and consequent alteration of insect behaviors are best explained through the metal's role in modulating the dopaminergic system. Despite numerous examples that alterations in manganese homeostasis have profound effects on insects, the cellular mechanisms that ensure homeostasis of this essential metal remain presently unknown, calling for further research in this area.

A nutrient-responsive hormonal circuit mediates an inter-tissue program regulating metabolic homeostasis in adult Drosophila

Animals maintain metabolic homeostasis by modulating the activity of specialized organs that adjust internal metabolism to external conditions. However, the hormonal signals coordinating these functions are incompletely characterized. Here we show that six neurosecretory cells in the Drosophila central nervous system respond to circulating nutrient levels by releasing Capa hormones, homologs of mammalian neuromedin U, which activate the Capa receptor (CapaR) in peripheral tissues to control energy homeostasis. Loss of Capa/CapaR signaling causes intestinal hypomotility and impaired nutrient absorption, which gradually deplete internal nutrient stores and reduce organismal lifespan. Conversely, increased Capa/CapaR activity increases fluid and waste excretion. Furthermore, Capa/CapaR inhibits the release of glucagon-like adipokinetic hormone from the corpora cardiaca, which restricts energy mobilization from adipose tissue to avoid harmful hyperglycemia. Our results suggest that the Capa/CapaR circuit occupies a central node in a homeostatic program that facilitates the digestion and absorption of nutrients and regulates systemic energy balance.

A Comparative Perspective on Functionally-Related, Intracellular Calcium Channels: The Insect Ryanodine and Inositol 1,4,5-Trisphosphate Receptors

Calcium (Ca²⁺) homeostasis is vital for insect development and metabolism, and the endoplasmic reticulum (ER) is a major intracellular reservoir for Ca²⁺. The inositol 1,4,5- triphosphate receptor (IP₃R) and ryanodine receptor (RyR) are large homotetrameric channels associated with the ER and serve as two major actors in ER-derived Ca²⁺ supply. Most of the knowledge on these receptors derives from mammalian systems that possess three genes for each receptor. These studies have inspired work on synonymous receptors in insects, which encode a single IP₃R and RyR. In the current review, we focus on a fundamental, common question: “why do insect cells possess two Ca²⁺ channel receptors in the ER?”. Through a comparative approach, this review covers the discovery of RyRs and IP₃Rs, examines their structures/functions, the pathways that they interact with, and their potential as target sites in pest control. Although insects RyRs and IP₃Rs share structural similarities, they are phylogenetically distinct, have their own structural organization, regulatory mechanisms, and expression patterns, which explains their functional distinction. Nevertheless, both have great potential as target sites in pest control, with RyRs currently being targeted by commercial insecticide, the diamides.

Modulation of neuromuscular synapses and contraction in Drosophila 3rd instar larvae

Over the past four decades, Drosophila melanogaster has become an increasingly important model system for studying the modulation of chemical synapses and muscle contraction by cotransmitters and neurohormones. This review describes how advantages provided by Drosophila have been utilized to investigate synaptic modulation, and it discusses key findings from investigations of cotransmitters and neurohormones that act on body wall muscles of 3rd instar Drosophila larvae. These studies have contributed much to our understanding of how neuromuscular systems are modulated by neuropeptides and biogenic amines, but there are still gaps in relating these peripheral modulatory effects to behavior.

CAPA periviscerokinin-mediated activation of MAPK/ERK signaling through Gq-PLC-PKC-dependent cascade and reciprocal ERK activation-dependent internalized kinetics of Bom-CAPA-PVK receptor 2

Bombyx mori neuropeptide G protein-coupled receptor (BNGR)-A27 is a specific receptor for B. mori capability (CAPA) periviscerokinin (PVK), that is, Bom-CAPA-PVK receptor 2. Upon stimulation of Bom-CAPA-PVK-1 or -PVK-2, Bom-CAPA-PVK receptor 2 significantly increases cAMP-response element-controlled luciferase activity and Ca²⁺ mobilization in a Gq inhibitor-sensitive manner. However, the underlying mechanism(s) for CAPA/CAPA receptor system mediation of extracellular signal-regulated kinases1/2 (ERK1/2) activation remains to be explained further. Here, we discovered that Bom-CAPA-PVK receptor 2 stimulated ERK1/2 phosphorylation in a dose- and time-dependent manner in response to Bom-CAPA-PVK-1 or -PVK-2 with similar potencies. Furthermore, ERK1/2 phosphorylation can be inhibited by Gq inhibitor UBO-QIC, PLC inhibitor U73122, protein kinase C (PKC) inhibitor Go 6983, phospholipase D (PLD) inhibitor FIPI and Ca²⁺ chelators EGTA and BAPTA-AM. Moreover, Bom-CAPA-PVK-R2-induced activation of ERK1/2 was significantly attenuated by treatment with the Gβγ-specific inhibitors, phosphatidylinositol 3-kinase (PI3K)-specific inhibitor Wortmannin and Src-specific inhibitor PP2. Our data also demonstrate that receptor tyrosine kinase (RTK) transactivation pathways are involved in the mechanisms of Bom-CAPA-PVK receptor to ERK1/2 phosphorylation. In addition, β-arrestin1/2 is not involved in Bom-CAPA-PVK-R2-mediated ERK1/2 activation but required for the agonist-independent, ERK1/2 activation-dependent internalization of the G protein-coupled receptor (GPCR).

BNGR-A25L and -A27 are two functional G protein-coupled receptors for CAPA periviscerokinin neuropeptides in the silkworm Bombyx mori

CAPA peptides, such as periviscerokinin (PVK), are insect neuropeptides involved in many signaling pathways controlling, for example, metabolism, behavior, and reproduction. They are present in a large number of insects and, together with their cognate receptors, are important for research into approaches for improving insect control. However, the CAPA receptors in the silkworm (Bombyx mori) insect model are unknown. Here, we cloned cDNAs of two putative CAPA peptide receptor genes, BNGR-A27 and -A25, from the brain of B. mori larvae. We found that the predicted BNGR-A27 ORF encodes 450 amino acids and that one BNGR-A25 splice variant encodes a full-length isoform (BNGR-A25L) of 418 amino acid residues and another a short isoform (BNGR-A25S) of 341 amino acids with a truncated C-terminal tail. Functional assays indicated that both BNGR-A25L and -A27 are activated by the PVK neuropeptides Bom-CAPA-PVK-1 and -PVK-2, leading to a significant increase in cAMP-response element-controlled luciferase activity and Ca²⁺ mobilization in a G_q inhibitor-sensitive manner. In contrast, BNGR-A25S was not significantly activated in response to the PVK peptides. Moreover, Bom-CAPA-PVK-1 directly bound to BNGR-A25L and -A27, but not BNGR-A25S. Of note, CAPA-PVK-mediated ERK1/2 phosphorylation and receptor internalization confirmed that BNGR-A25L and -A27 are two canonical receptors for Bombyx CAPA-PVKs. However, BNGR-A25S alone is a nonfunctional receptor but serves as a dominant-negative protein for BNGR-A25L. These results provide evidence that BNGR-A25L and -A27 are two functional G_q-coupled receptors for Bombyx CAPA-PVKs, enabling the further elucidation of the endocrinological roles of Bom-CAPA-PVKs and their receptors in insect biology.

Identification of mature peptides from pban and capa genes of the moths Heliothis peltigera and Spodoptera littoralis

By transcriptome analysis, we identified PBAN and CAPA precursors in the moths Spodoptera littoralis and Heliothis peltigera which are among the most damaging pests of agriculture in tropical and subtropical Africa as well as in Mediterranean countries. A combination of mass spectrometry and immunocytochemistry was used to identify mature peptides processed from these precursors and to reveal their spatial distribution in the CNS. We found that the sites of expression of pban genes, the structure of PBAN precursors and the processed neuropeptides are very similar in noctuid moths. The sequence of the diapause hormone (DH; tryptopyrokinin following the signal peptide), however, contains two N-terminal amino acids more than expected from comparison with already published sequences of related species. Capa genes of S. littoralis and H. peltigera encode, in addition to periviscerokinins, a tryptopyrokinin showing sequence similarity with DH, which is the tryptopyrokinin of the pban gene. CAPA peptides, which were not known from any noctuid moth so far, are produced in cells of abdominal ganglia. The shape of the release sites of these hormones in H. peltigera represents an exceptionally derived trait state and does not resemble the well-structured abdominal perisympathetic organs which are known from many other insects. Instead, axons of CAPA cells extensively ramify within the ventral diaphragm. The novel information regarding the sequences of all mature peptides derived from pban and capa genes of H. peltigera and S. littoralis now enables a detailed analysis of the bioactivity and species-specificity of the native peptides, especially those from the hitherto unknown capa genes, and to explore their interactions with PBAN/DH receptors.

Characterizing the physiological and behavioral roles of proctolin in Drosophila melanogaster

The neuropeptide proctolin (RYLPT) plays important roles as both a neurohormone and a cotransmitter in arthropod neuromuscular systems. We used third-instar Drosophila larvae as a model system to differentiate synaptic effects of this peptide from its direct effects on muscle contractility and to determine whether proctolin can work in a cell-selective manner on muscle fibers. Proctolin did not appear to alter the amplitude of excitatory junctional potentials but did induce sustained muscle contractions in preparations where the CNS had been removed and no stimuli were applied to the remaining nerves. Proctolin-induced contractions were dose-dependent, were reduced by knocking down expression of the Drosophila proctolin receptor in muscle tissue, and were larger in some muscle cells than others (i.e., larger in fibers 4, 12, and 13 than in 6 and 7). Proctolin also increased the amplitude of nerve-evoked contractions in a dose-dependent manner, and the magnitude of this effect was also larger in some muscle cells than others (again, larger in fibers 4, 12, and 13 than in 6 and 7). Increasing the intraburst impulse frequency and number of impulses per burst increased the magnitude of proctolin's enhancement of nerve-evoked contractions and decreased the threshold and EC50 concentrations for proctolin to enhance nerve-evoked contractions. Reducing proctolin receptor expression decreased the velocity of larval crawling at higher temperatures, and thermal preference in these larvae. Our results suggest that proctolin acts directly on body-wall muscles to elicit slow, sustained contractions and to enhance nerve-evoked contractions, and that proctolin affects muscle fibers in a cell-selective manner.

Serine phosphorylation of CAPA pyrokinin in cockroaches-a taxon-specific posttranslational modification

In insects, posttranslational modifications of neuropeptides are largely restricted to C- and N-terminal amino acids. The most common modifications, N-terminal pyroglutamate formation and C-terminal α-amidation, may prevent a fast degradation of these messenger molecules. This is particularly important for peptide hormones. Other common posttranslational modifications of proteins such as glycosylation and phosphorylation seem to be very rare in insect neuropeptides. To check this assumption, we used a computer algorithm to search an extensive data set of MALDI-TOF mass spectra from cockroach tissues for ion signal patterns indicating peptide phosphorylation. The results verify that phosphorylation is indeed very rare. However, a candidate was found and experimentally verified as phosphorylated CAPA pyrokinin (GGGGpSGETSGMWFGPRL-NH2) in the cockroach Lamproblatta albipalpus (Blattidae, Lamproblattinae). Tandem mass spectrometry revealed the phosphorylation site as Ser(5). Phosphorylated CAPA pyrokinin was then also detected in most other cockroach lineages (e.g. Blaberidae, Polyphagidae) but not in closely related blattid species such as Periplaneta americana. This is remarkable since the sequence of CAPA pyrokinin is identical in Lamproblatta and Periplaneta. A consensus sequence of CAPA pyrokinins of cockroaches revealed a conserved motif that suggests phosphorylation by a Four-jointed/FAM20C related kinase.

Peptide neuromodulation of synaptic dynamics in an oscillatory network

Although neuromodulation of synapses is extensively documented, its consequences in the context of network oscillations are not well known. We examine the modulation of synaptic strength and short-term dynamics in the crab pyloric network by the neuropeptide proctolin. Pyloric oscillations are driven by a pacemaker group which receives feedback through the inhibitory synapse from the lateral pyloric (LP) to pyloric dilator (PD) neurons. We show that proctolin modulates the spike-mediated and graded components of the LP to PD synapse. Proctolin enhances the graded component and unmasks a surprising heterogeneity in its dynamics where there is depression or facilitation depending on the amplitude of the voltage waveform of the presynaptic LP neuron. The spike-mediated component is influenced by the baseline membrane potential and is also enhanced by proctolin at all baseline potentials. In addition to direct modulation of this synapse, proctolin also changes the shape and amplitude of the presynaptic voltage waveform which additionally enhances synaptic output during ongoing activity. During ongoing oscillations, proctolin reduces the variability of cycle period but only when the LP to PD synapse is functionally intact. Using the dynamic clamp technique we find that the reduction in variability is a direct consequence of modulation of the LP to PD synapse. These results demonstrate that neuromodulation of synapses involves complex and interacting influences that target different synaptic components and dynamics as well as the presynaptic voltage waveform. At the network level, modulation of feedback inhibition can result in reduction of variability and enhancement of stable oscillatory output.

Two capa-genes are expressed in the neuroendocrine system of Rhodnius prolixus

CAPA-peptides have been isolated from a broad range of insect species and are typical of the neurosecretory system of the abdominal ventral nerve cord. In Rhodnius prolixus, which is known to transmit Chagas' disease, CAPA-peptides have potent antidiuretic effects. Recently, two capa-genes were isolated from this hemipteran insect; it was the first description of the occurrence of multiple capa-genes from a single insect species. The expression of peptides from one of these capa-genes was confirmed by mass spectrometry Paluzzi (2008) [10]. In this study, the abdominal neuroendocrine system of R. prolixus was screened for the occurrence of products of the second annotated capa-gene. Single nerve preparations of abdominal segmental nerves 1-3 of R. prolixus were analyzed by MALDI-TOF mass spectrometry and the products of both capa-genes were identified by tandem mass spectrometry. The co-occurrence of the different CAPA-peptides, including CAPA-precursor peptides, in all spectra from abdominal segmental nerves 1 to 3 suggests a common expression of both capa-genes in the same neuroendocrine cells. A comparison of mass spectra obtained from abdominal segmental nerves with those of the subesophageal ganglion (SEG) revealed an obvious differential processing of the CAPA-precursors within the CNS.

From molecule to sexual behavior: the role of the neuropentapeptide proctolin in acoustic communication in the male grasshopper Chorthippus biguttulus

Acoustic communication in male Chorthippus biguttulus is a suitable behavioral model to explore the physiological effects and underlying molecular mechanisms of identified neuropeptides. Proctolin plays a modulatory role in a neuronal circuit controlling sexual behavior in these insects. Activation of proctolin receptors triggers courtship singing (the second level of excitation in sexual behavior) that is preceded by call singing triggered by muscarinic acetylcholine receptor activation. The pharmacological studies presented here revealed that the Phospholipase C pathway was involved in courtship singing since neomycin and Li(+) strongly inhibited proctolin-stimulated singing. In addition, injecting phorbol ester into proctolin-sensitive neural sites only elicited stridulation. This confirms that proteinkinase C can mediate the effects of Phospholipase C activation in this model. These results partially clarify the molecular mechanisms in the decision making brain center that controls sexual behavior in these insects.

Identification of novel neuropeptides in the ventral nerve cord ganglia and their targets in an annelid worm, Eisenia fetida

Periviscerokinins (PVKs) and pyrokinins (PKs) are neuropeptides known in several arthropod species. Sequence homology of these peptides with the molluscan small cardioactive peptides reveals that the occurrence of PVKs and PKs is not restricted to arthropods. Our study focuses on the biochemical and immunocytochemical identification of neuropeptides with sequence homology to PVKs and PKs in the central and peripheral nervous system of the earthworm Eisenia fetida. By means of affinity chromatography, nanoflow liquid chromatography, and high accuracy mass spectrometry, six peptides, SPFPR(L/I)amide, APFPR(L/I)amide, SPLPR(L/I)amide, SFVR(L/I)amide, AFVR(L/I)amide, and SPAFVR(L/I)amide, were identified in the central nervous system with the common -XR(L/I)amide C-terminal sequence. The exact anatomical position of 13 labeled XR(I/L)amide expressing neuron groups and numerous peptide-containing fibers were determined by means of immunocytochemistry and confocal laser scanning microscopy in whole-mount preparations of ventral nerve cord ganglia. The majority of the stained neurons were interneurons with processes joining the distinct fine-fibered polysegmental tracts in the central neuropil. Some stained fibers were seen running in each segmental nerve that innervated metanephridia and body wall. Distinct groups of neurosecretory cells characterized by small round soma and short processes were also identified. Based on immunoelectron microscopy six different types of labeled cells were described showing morphological heterogeneity of earthworm peptides containing elements. Our findings confirm that the sequence of the identified earthworm neuropeptides homologous to the insect PVKs and PKs suggesting that these peptides are phylogenetically conservative molecules and are expressed in sister-groups of animals such as annelids, mollusks, and insects.

Nox regulation of smooth muscle contraction

The catalytic subunit gp91phox (Nox2) of the NADPH oxidase of mammalian phagocytes is activated by microbes and immune mediators to produce large amounts of reactive oxygen species (ROS) which participate in microbial killing. Homologs of gp91phox, the Nox and Duox enzymes, were recently described in a range of organisms, including plants, vertebrates, and invertebrates such as Drosophila melanogaster. While their enzymology and cell biology are being extensively studied in many laboratories, little is known about in vivo functions of Noxes. Here, we establish and use an inducible system for RNAi to discover functions of dNox, an ortholog of human Nox5 in Drosophila. We report here that depletion of dNox in musculature causes retention of mature eggs within ovaries, leading to female sterility. In dNox-depleted ovaries and ovaries treated with a Nox inhibitor, muscular contractions induced by the neuropeptide proctolin are markedly inhibited. This functional defect results from a requirement for dNox-for the proctolin-induced calcium flux in Drosophila ovaries. Thus, these studies demonstrate a novel biological role for Nox-generated ROS in mediating agonist-induced calcium flux and smooth muscle contraction.

The neuropeptide proctolin potentiates contractions and reduces cGMP concentration via a PKC-dependent pathway

As in many other arthropods, the neuropeptide proctolin enhances contractures of muscles in the crustacean isopod Idotea emarginata. The enhancement of high K+-induced contractures by proctolin (1 micromol l-1) was mimicked upon application of the protein kinase C (PKC) activator phorbol-12-myristate 1-acetate (PMA) and was inhibited by the PKC inhibitor bisindolylmaleimide (BIM-1). The potentiation was not inhibited by H89, a protein kinase A (PKA) inhibitor. Proctolin did not change the intracellular concentration of 3',5'-cyclic adenosine monophosphate (cAMP) whereas it significantly reduced the intracellular concentration of 3',5'-cyclic guanosine monophosphate (cGMP). The reduction of cGMP was not observed in the presence of the PKC inhibitor BIM-1. 8-Bromo-cGMP, a membrane-permeable cGMP analogue, reduced the potentiating effect of proctolin on muscle contracture. We thus conclude that proctolin in the studied crustacean muscle fibres induces an activation of PKC, which leads to a reduction of the cGMP concentration and, consequently, to the potentiation of muscle contracture.

Sites and modes of action of proctolin and the FLP F2 on lobster cardiac muscle

At the threshold concentration (1-10 pmol l-1), the neuropeptide hormones proctolin (PR) and the FLRFamide-like peptide (FLP) F2cause an increase in amplitude of electrically evoked contractions (each contraction is a brief tetanus) of lobster heart ostial muscle. At higher concentrations each peptide also induces an increase in tonus (contracture). The PR-induced contracture and augmentation of tetani are proportional to increases in [Ca2+]i. The rate of onset and recovery of peptide-induced effects on both tetani and contracture appeared to reduced by Ca2+ storage by the sarcoplasmic reticulum (SR). Enhanced tetani following a contracture may be due to enhanced voltage-gated Ca2+current and sarcoplasmic reticular (SR) Ca2+ loading. The SR Ca2+ loading appears to be specific for PR and F2, since glutamic-acid-induced contractures are not followed by increased tetani. The prolonged elevation of [Ca2+]i during contracture causes a right-ward shift in the force-pCa curve indicating a decrease in myofibrillar sensitivity to Ca2+. Blocking voltage-gated Ca2+ channels with Cd2+, nifedipine or verapamil, while reducing tetani, does not prevent peptide-induced contracture and enhanced tetani. Opening SR Ca2+ channels and depleting SR Ca2+with either caffeine or ryanodine blocked tetani but permitted accelerated peptide-induced contractures. We conclude that PR and F2 at low concentration enhance voltage-dependent Ca2+ induced Ca2+ release from the SR, while higher hormone levels directly gate Ca2+ entry across the sarcolemma.

Identification of a proctolin preprohormone gene (Proct) ofDrosophila melanogaster: Expression and predicted prohormone processing

Proctolin was the first insect neuropeptide to be sequenced and has been the subject of many physiological and pharmacological studies in insects and crustaceans. We have identified a Drosophila gene (CG7105, Proct) encoding a precursor protein containing the neuropeptide proctolin (RYLPT). In situ hybridization with a riboprobe to the Proct gene revealed a distribution of transcript in neurons of the larval central nervous system (CNS) matching that seen with antiserum to proctolin. An antiserum raised to a sequence in the precursor downstream of proctolin labeled the same neurons as those seen with the antiproctolin antisera. The predicted protein encoded by Proct has a single copy of the RYLPT sequence that directly follows the predicted signal peptidase cleavage point and precedes a consensus recognition site for a furinlike processing endoprotease. Ectopic expression of Proct in the CNS and midgut via the GAL4-UAS system, using an Actin5C-GAL4 driver, confirmed that the predicted preproproctolin can be processed to generate immunoreactive proctolin peptide. Pupae over-expressing Proct displayed a 14% increase in heart rate, providing evidence in support of a cardioacceleratory endocrine function for proctolin in Drosophila. The distribution of proctolin suggests roles as a neuromodulator in motoneurons and interneurons, and as a neurohormone that could be released from brain neurosecretory cells with terminations in the ring gland.

Corazonin promotes tegumentary pigment migration in the crayfish Procambarus clarkii

The undecapeptide corazonin (pGlu-Thr-Phe-Gln-Tyr-Ser-His-Gly-Trp-Thr-AsnNH(2)) elicits a retraction of erythrophore pigment granules and dispersion of leucophore pigment granules in the crayfish Procambarus clarkii. The effects are dose-dependent from 10(-10) to 10(-5)M. Influence on erythrophores is lower than that of Red Pigment Concentrating Hormone (RPCH), which is inactive on leucophores. Corazonin effects are partly blocked by an anti-corazonin antibody, and even less by an anti-RPCH antibody. Corazonin effects are completely suppressed by the calcium chelator BAPTA. Immunoreactive somata and fibers were identified in various regions of the eyestalk (medulla terminalis, medulla interna and medulla externa) with the anti-corazonin antibody. These results suggest the possible existence of a corazonin-like peptide in crustaceans.

Identification and characterization of a G protein-coupled receptor for the neuropeptide proctolin in Drosophilamelanogaster

Proctolin is a bioactive neuropeptide that modulates interneuronal and neuromuscular synaptic transmission in a wide variety of arthropods. We present several lines of evidence to propose that the orphan G protein-coupled receptor CG6986 of Drosophila is a proctolin receptor. When expressed in mammalian cells, CG6986 confers second messenger activation after proctolin application, with an EC(50) of 0.3 nM. In competition-based studies, the CG6986 receptor binds proctolin with high affinity (IC(50) = 4 nM). By microarray analysis, CG6986 transcript is consistently detected in head mRNA of different genotypes, and under different environmental conditions. By blot analysis, anti-CG6986 antibodies detect a band in tissue homogenates similar to the predicted size of the protein. Proctolin receptor immunosignals are found in the hindgut, heart, and in distinct neuronal populations of the CNS; such patterns correlate with previous demonstrations of proctolin biological activity, and in several instances, with areas of proctolin peptide immunosignals. The identification of a bona fide proctolin receptor provides the basis for a mechanistic analysis of this critical synaptic modulator.

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

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

The effects of crustacean cardioactive peptide on locust oviducts are calcium-dependent

The role of calcium as a second messenger in the crustacean cardioactive peptide (CCAP)-induced contractions of the locust oviducts was investigated. Incubation of the oviducts in a calcium-free saline containing, a preferential calcium cation chelator, or an extracellular calcium channel blocker, abolished CCAP-induced contractions, indicating that the effects of CCAP on the oviducts are calcium-dependent. In contrast, sodium free saline did not affect CCAP-induced contractions. Co-application of CCAP to the oviducts with preferential L-type voltage-dependent calcium channel blockers reduced CCAP-induced contractions by 32-54%. Two preferential T-type voltage-dependent calcium channel blockers both inhibited CCAP-induced oviduct contractions although affecting different components of the contractions. Amiloride decreased the tonic component of CCAP-induced contractions by 40-55% and flunarizine dihydrochloride decreased the frequency of CCAP-induced phasic contractions by as much as 65%, without affecting tonus. Flunarizine dihydrochloride did not alter the proctolin-induced contractions of the oviducts. Results suggest that the actions of CCAP are partially mediated by voltage-dependent calcium channels similar to vertebrate L-type and T-type channels. High-potassium saline does not abolish CCAP-induced contractions indicating the presence of receptor-operated calcium channels that mediate the actions of CCAP on the oviducts. The involvement of calcium from intracellular stores in CCAP-induced contractions of the oviducts is likely since, an intracellular calcium antagonist decreased CCAP-induced contractions by 30-35%.

The periviscerokinin (PVK) peptide family in insects: evidence for the inclusion of CAP(2b) as a PVK family member

Periviscerokinins (PVKs) are a distinct insect peptide family with unusual distribution in the central nervous system and neurohemal release sites. PVKs were first isolated from the abdominal perisympathetic organs of Periplaneta americana, but can be found in other insect species. Peptides with structural similarity to PVKs have been identified through searches of the Drosophila genome. The cardioacceleratory peptide CAP(2b) of the hawkmoth Manduca sexta shares close amino acid identity with the PVKs and may thus be included as a structural member of the PVK peptide family. In this review, we provide support for grouping CAP(2b) as a PVK family member based on published sequences, and new immunocytochemical findings and mass spectrometric data.

Characterization of transepithelial potential oscillations in theDrosophilaMalpighian tubule

The Malpighian tubule of Drosophila melanogaster is a useful model system for studying the regulation of epithelial ion transport. In acutely isolated tubules, the transepithelial potential (TEP) undergoes large oscillations in amplitude with a period of approximately 30s. The TEP oscillations are diminished by reductions in the peritubular chloride concentration in a manner consistent with their being caused by fluctuations in chloride conductance. The oscillations are eliminated by pretreating tubules with the calcium chelator BAPTA-AM, although removal of peritubular calcium has no effect, suggesting that the oscillations are a result of either the release of calcium from intracellular stores or the entry of calcium from the tubule lumen. Transcripts encoding two calcium-release channels, the ryanodine receptor and the inositol trisphosphate receptor, are detectable in the tubule by reverse transcription–polymerase chain reaction. To identify the cell type responsible for the oscillations, tubules were treated with diuretic hormones known to alter calcium levels in each of the two cell types. Leucokinin-IV, which increases calcium levels in the stellate cells, suppressed the oscillations, whereas cardioacceleratory peptide 2b (CAP2b), which increases calcium levels in the principal cells, had no effect. These data are consistent with a model in which rhythmic changes in transepithelial chloride conductance, regulated by intracellular calcium levels in the stellate cells, cause the TEP oscillations.

The neuropeptide proctolin induces phosphorylation of a 30 kDa protein associated with the thin filament in crustacean muscle

In the isopod Idotea emarginata, the neuropeptide proctolin is contained in a single pair of motoneurones located in pereion ganglion 4. The two neurones supply dorsal extensor muscle fibres of all segments. Proctolin (1μmoll−1) potentiates the amplitude of contractures of single extensor muscle fibres elicited by 10mmoll−1 caffeine. In western blots of myofibrillar proteins isolated from single muscle fibres and treated with an anti-phosphoserine antibody, a protein with an apparent molecular mass of 30kDa was consistently found. The phosphorylation of this protein was significantly increased by treating the fibres with proctolin. After separation of myofibrillar filaments, a 30kDa protein was found only in the thin filament fraction. This protein is phosphorylated and detected by an antiserum against crustacean troponin I.

Myostimulatory neuropeptides in cockroaches: structures, distribution, pharmacological activities, and mimetic analogs

In this brief overview we give the historical background on the discovery of myostimulatory neuropeptides in cockroaches. Related peptides were later found in other insect groups as well. We summarize the current knowledge on primary structures, localization, physiological and pharmacological effects of the different cockroach neuropeptides, including kinins, sulfakinins, pyrokinins, tachykinin-related peptides, periviscerokinins, corazonin, and proctolin. In addition, we briefly comment on the development of mimetic pseudopeptide analogs in the context of their possible use in insect pest management.