Characterization of two myotrophic neuropeptides in the FMRFamide family from the segmental ganglia of the moth Manduca sexta: candidate neurohormones and neuromodulators

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

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

RNAi mediated myosuppressin deficiency affects muscle development and survival in the salmon louse (Lepeophtheirus salmonis)

Muscle activity is regulated by stimulatory and inhibitory neuropeptides allowing for contraction and relaxation. In Arthropods, one of the important myoinhibitors is Myosuppressin, belonging to FMRFamide-like peptides, that was shown to have inhibitory effects on visceral muscle contraction and to regulate vital physiological processes including reproduction or feeding. We have identified myosuppressin in salmon louse Lepeophtheirus salmonis (LsalMS) and systematically characterised its function and complex abnormalities emerging after LsalMS knockdown by RNAi in all developmental stages in this species. Immunohistochemistry analysis localized the LsalMS mainly to the central nervous system, but also to the vital organs within the alimentary tract and the reproductive system. The most striking feature of LsalMS deficiency during lice development was severe reduction of the muscle content, with abnormalities detected in both the visceral and skeletal muscles. Moreover, down-regulation of LsalMS affects moulting, spermatophore deposition and feeding by affecting development of the intestinal wall and increasing its contraction frequency.

Neuropeptides in insect mushroom bodies

Owing to their experimental amenability, insect nervous systems continue to be in the foreground of investigations into information processing in - ostensibly - simple neuronal networks. Among the cerebral neuropil regions that hold a particular fascination for neurobiologists are the paired mushroom bodies, which, despite their function in other behavioral contexts, are most renowned for their role in learning and memory. The quest to understand the processes that underlie these capacities has been furthered by research focusing on unraveling neuroanatomical connections of the mushroom bodies and identifying key players that characterize the molecular machinery of mushroom body neurons. However, on a cellular level, communication between intrinsic and extrinsic mushroom body neurons still remains elusive. The present account aims to provide an overview on the repertoire of neuropeptides expressed in and utilized by mushroom body neurons. Existing data for a number of insect representatives is compiled and some open gaps in the record are filled by presenting additional original data.

Isolation and functional characterization of an allatotropin receptor from Manduca sexta

Manduca sexta allatotropin (Manse-AT) is a multifunctional neuropeptide whose actions include the stimulation of juvenile hormone biosynthesis, myotropic stimulation, cardioacceleratory functions, and inhibition of active ion transport. Manse-AT is a member of a structurally related peptide family that is widely found in insects and also in other invertebrates. Its precise role depends on the insect species and developmental stage. In some lepidopteran insects including M. sexta, structurally-related AT-like (ATL) peptides can be derived from alternatively spliced mRNAs transcribed from the AT gene. We have isolated a cDNA for an AT receptor (ATR) from M. sexta by a PCR-based approach using the sequence of the ATR from Bombyx mori. The sequence of the M. sexta ATR is similar to several G protein-coupled receptors from other insect species and to the mammalian orexin receptor. We demonstrate that the M. sexta ATR expressed in vertebrate cell lines is activated in a dose-responsive manner by Manse-AT and each Manse-ATL peptide in the rank order ATL-I > ATL-II > ATL-III > AT, and functional analysis in multiple cell lines suggest that the receptor is coupled through elevated levels of Ca(2+) and cAMP. In feeding larvae, Manse-ATR mRNA is present at highest levels in the Malpighian tubules, followed by the midgut, hindgut, testes, and corpora allata, consistent with its action on multiple target tissues. In the adult corpora cardiaca--corpora allata complex, Manse-ATR mRNA is present at relatively low levels in both sexes.

Brain organization in Collembola (springtails)

Arthropoda is comprised of four major taxa: Hexapoda, Crustacea, Myriapoda and Chelicerata. Although this classification is widely accepted, there is still some debate about the internal relationships of these groups. In particular, the phylogenetic position of Collembola remains enigmatic. Some molecular studies place Collembola into a close relationship to Protura and Diplura within the monophyletic Hexapoda, but this placement is not universally accepted, as Collembola is also regarded as either the sister group to Branchiopoda (a crustacean taxon) or to Pancrustacea (crustaceans + hexapods). To contribute to the current debate on the phylogenetic position of Collembola, we examined the brains in three collembolan species: Folsomia candida, Protaphorura armata and Tetrodontophora bielanensis, using antennal backfills, series of semi-thin sections, and immunostaining technique with several antisera, in conjunction with confocal laser scanning microscopy and three-dimensional reconstructions. We identified several neuroanatomical structures in the collembolan brain, including a fan-shaped central body showing a columnar organization, a protocerebral bridge, one pair of antennal lobes with 20-30 spheroidal glomeruli each, and a structure, which we interpret as a simply organized mushroom body. The results of our neuroanatomical study are consistent with the phylogenetic position of Collembola within the Hexapoda and do not contradict the hypothesis of a close relationship of Collembola, Protura and Diplura.

Oral activity of FMRFamide-related peptides on the pea aphid Acyrthosiphon pisum (Hemiptera: Aphididae) and degradation by enzymes from the aphid gut

Insect myosuppressins and myosuppressin analogues were tested for oral toxicity against the pea aphid Acyrthosiphon pisum (Harris) by incorporation into an artificial diet. Acyrthosiphon pisum myosuppressin (Acypi-MS) and leucomyosuppressin (LMS) had significant dose-dependent effects (0.1-0.5μg peptide/μl diet) on feeding suppression, mortality, reduced growth and fecundity compared with control insects, but Acypi-MS was more potent than LMS. One hundred percent of aphids had died after 10days of feeding on 0.5μg Acypi-MS/μl diet whereas 40% of aphids feeding on 0.5μg LMS/μl diet were still alive after 13days. Myosuppressins were degraded by aphid gut enzymes; degradation was most likely due to a carboxypeptidase-like protease, an aminopeptidase and a cathepsin L cysteine protease. The estimated half-life of Acypi-MS in a gut extract was 30min, whereas LMS was degraded more slowly (t½=54min). No toxicity was observed when the analogues δR(9) LMS and citrolline(9) Acypi-MS or FMRFamide were fed to the pea aphid. These findings not only help to better understand the biological effects of myosuppressins in aphids but also demonstrate the potential use of myosuppressins in a strategy to control aphid pests.

A review of FMRFamide- and RFamide-like peptides in metazoa

Neuropeptides are a diverse class of signalling molecules that are widely employed as neurotransmitters and neuromodulators in animals, both invertebrate and vertebrate. However, despite their fundamental importance to animal physiology and behaviour, they are much less well understood than the small molecule neurotransmitters. The neuropeptides are classified into families according to similarities in their peptide sequence; and on this basis, the FMRFamide and RFamide-like peptides, first discovered in molluscs, are an example of a family that is conserved throughout the animal phyla. In this review, the literature on these neuropeptides has been consolidated with a particular emphasis on allowing a comparison between data sets in phyla as diverse as coelenterates and mammals. The intention is that this focus on the structure and functional aspects of FMRFamide and RFamide-like neuropeptides will inform understanding of conserved principles and distinct properties of signalling across the animal phyla.

Neuropeptides associated with the regulation of feeding in insects

The stomatogastric nervous system plays a pivotal role in feeding behaviour. Central to this system is the frontal ganglion, which is responsible for foregut motor activity, and hence the passage of food through the gut. Many insect peptides, which exhibit myoactivity on the visceral muscles of the gut in vitro, have been detected in the stomatogastric nervous system by immunochemical or mass spectrometric techniques. This localisation of myoactive peptides, particularly in the frontal ganglion, implies roles for these peptides in the neural control and modulation of feeding in insects. Insect sulfakinins, tachykinins, allatotropin and proctolin have all been shown to stimulate the foregut muscles, whereas myosuppressins, myoinhibitory peptides and allatostatins all inhibited spontaneous contractions of the foregut in a variety of insects. Some of these peptides, when injected, inhibited feeding in vivo. Both the A-type and B-type allatostatins suppressed feeding activity when injected into the cockroach, Blattella germanica and the Manduca sexta C-type allatostatin and allatotropin inhibited feeding when injected into the larvae of two noctuid moths, Lacanobia oleracea and Spodoptera frugiperda, respectively. Injection of sulfakinins into the fly Phormia regina, the locust Schistocera gregaria and the cockroach B. germanica also suppressed feeding, whereas silencing the sulfakinin gene through the injection of double stranded RNA resulted in an increase in food consumption in the cricket Gryllus bimaculatus. The regulation of feeding in insects is clearly very complex, and involves the interaction of a number of mechanisms, one of which is the release, either centrally or locally, of neuropeptides. However, the role of neuropeptides, their mechanisms of action, interactions with each other, and their release are still poorly understood. It is also unclear why insects possess such a number of different peptides, some with multiples copies or homologues, which stimulate or inhibit gut motility, and how their release, sometimes from the same neurone, is regulated. These neuropeptides may also act at sites other than visceral muscles, such as centrally through the brain or on gut stretch receptors.

Degradation of leucomyosuppressin by enzymes in the hemolymph and midgut of Lacanobia oleracea and Spodoptera littoralis (Lepidoptera: Noctuidae) larvae

The degradation of 2 nmol synthetic leucomyosuppressin (LMS) by enzymes of the hemolymph, midgut lumen and midgut tissues of both Lacanobia oleracea and Spodoptera littoralis was investigated using reversed-phase high-performance liquid chromatography together with matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Degradation of LMS in diluted hemolymph of L. oleracea and S. littoralis was not rapid, t(1/2)=65.4 and 13.1 min, respectively, due to carboxypeptidase(s) and endopeptidase(s) present in the hemolymph. There was also some aminopeptidase activity in the hemolymph of both species. However, LMS was rapidly degraded by the diluted contents of the midgut lumen of L. oleracea and S. littoralis, t(1/2)=0.5 and 2.2 min, respectively. The enzymes most likely responsible were trypsin-like serine protease(s) and carboxypeptidase(s). Degradation of LMS by midgut tissues containing 5 microg protein was not rapid in L. oleracea or S. littoralis, t(1/2)=40.7 and 69.8 min, respectively. The most abundant degradation products probably resulted from carboxypeptidase activity, but some aminopeptidase activity was also detected.

Isolation and sequencing of two FMRFamide-related peptides from the gut of Locusta migratoria L

Two FMRFamide-related peptides (FaRPs) have been isolated and sequenced from the whole gut of Locusta migratoria L. Peptides were extracted from 500 locust whole guts and separated using reversed-phase high performance liquid chromatography (RP-HPLC). Fractions containing FMRFamide-like immunoreactive (FLI) material were identified using radioimmunoassay (RIA). Sequencing of fractions, using tandem mass spectrometry (MALDI-TOF MS/MS), revealed the myosuppressin previously isolated from the locust CNS, SchistoFLRFamide (PDVDHVFLRFamide), and a novel extended RFamide (LWENLRFamide). The isolation of SchistoFLRFamide from midgut tissue supports the hypothesis that this myosuppressin is released locally from FLI processes over the gut and/or from endocrine-like midgut cells to play a role in the regulation of digestion.

Inter-phyla studies on neuropeptides: the potential for broad-spectrum anthelmintic and/or endectocide discovery

Flatworm, nematode and arthropod parasites have proven their ability to develop resistance to currently available chemotherapeutics. The heavy reliance on chemotherapy and the ability of target species to develop resistance has prompted the search for novel drug targets. In view of its importance to parasite/pest survival, the neuromusculature of parasitic helminths and pest arthropod species remains an attractive target for the discovery of novel endectocide targets. Exploitation of the neuropeptidergic system in helminths and arthropods has been hampered by a limited understanding of the functional roles of individual peptides and the structure of endogenous targets, such as receptors. Basic research into these systems has the potential to facilitate target characterization and its offshoots (screen development and drug identification). Of particular interest to parasitologists is the fact that selected neuropeptide families are common to metazoan pest species (nematodes, platyhelminths and arthropods) and fulfil specific roles in the modulation of muscle function in each of the three phyla. This article reviews the inter-phyla activity of two peptide families, the FMRFamide-like peptides and allatostatins, on motor function in helminths and arthropods and discusses the potential of neuropeptide signalling as a target system that could uncover novel endectocidal agents.

Direct peptide profiling of lateral cell groups of the antennal lobes ofManduca sextareveals specific composition and changes in neuropeptide expression during development

The paired antennal lobes are the first integration centers for odor information in the insect brain. In the sphinx moth Manduca sexta, like in other holometabolous insects, they are formed during metamorphosis. To further understand mechanisms involved in the formation of this particularly well investigated brain area, we performed a direct peptide profiling of a well defined cell group (the lateral cell group) of the antennal lobe throughout development by MALDI-TOF mass spectrometry. Although the majority of the about 100 obtained ion signals represent still unknown substances, this first peptidomic characterization of this cell group indicated the occurrence of 12 structurally known neuropeptides. Among these peptides are helicostatin 1, cydiastatins 2, 3, and 4, M. sexta-allatotropin (Mas-AT), M. sexta-FLRFamide (Mas-FLRFamide) I, II, and III, nonblocked Mas-FLRFamide I, and M. sexta-myoinhibitory peptides (Mas-MIPs) III, V, and VI. The identity of two of the allatostatins (cydiastatins 3 and 4) and Mas-AT were confirmed by tandem mass spectrometry (MALDI-TOF/TOF). During development of the antennal lobe, number and frequency of ion signals including those representing known peptides generally increased at the onset of glomeruli formation at pupal Stage P7/8, with cydiastatin 2, helicostatin 1, and Mas-MIP V being the exceptions. Cydiastatin 2 showed transient occurrence mainly during the period of glomerulus formation, helicostatin 1 was restricted to late pupae and adults, while Mas-MIP V occurred exclusively in adult antennal lobes. The power of the applied direct mass spectrometric profiling lies in the possibility of chemically identifying neuropeptides of a given cell population in a fast and reliable manner, at any developmental stage in single specimens. The identification of neuropeptides in the antennal lobes now allows to specifically address the function of these signaling molecules during the formation of the antennal lobe network.

A simple purification protocol for the detection of peptide hormones in the hemolymph of individual insects by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The endocrine system of insects is largely based on peptide hormones. Nevertheless, an unequivocal chemical demonstration of the occurence in the hemolymph (the 'insect blood') is still lacking for most if not all insect peptide hormones, although this is the only way to prove their hormonal status. Focusing on peptides released during ecdysis behavior of the tobacco hornworm Manduca sexta, we developed a purification protocol based on ultrafiltration and a single reversed-phase high-performance liquid chromatography (RP-HPLC) step that for the first time allowed the mass spectrometric and chemical identification of a peptide hormone in the hemolymph of single specimens. Since this method is simple, relatively cheap and fast, it should be useful for routine endocrinological analyses and for monitoring peptide release during different physiological conditions and behaviors in insects.

The role of neuropeptides in caterpillar nutritional ecology

Plant diet strongly impacts the fitness of insect herbivores. Immediately, we think of plant defensive compounds that may act as feeding deterrents or toxins. We are, probably, less aware that plants also influence insect growth and fecundity through their nutritional quality. However, most herbivores respond to their environment and select the diet which optimizes their growth and development. This regulation of nutritional balance may occur on many levels: through selecting and ingesting appropriate plant tissue and nutrient digestion, absorption and utilization. Here, we review evidence of how nutritional requirements, particularly leaf protein to digestible carbohydrate ratios, affect caterpillar herbivores. We propose a model where midgut endocrine cells assess and integrate hemolymph nutritional status and gut content and release peptides which influence digestive processes. Understanding the effects of diet on the insect herbivore is essential for the rational design and implementation of sustainable pest management practices.

Mass spectrometric analysis of head ganglia and neuroendocrine tissue of larval Galleria mellonella (Arthropoda, Insecta)

A brain-retrocerebral complex-subesophageal ganglion acidified methanolic extract of 100 larval Galleria mellonella (greater wax moth) was prepared for the isolation and identification of (neuro)peptides. To reduce sample complexity, the isolated peptides were roughly separated using a single, conventional chromatographic separation step. Subsequently, screening of these fractions with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry in combination with nanoflow electrospray ionization quadrupole time-of-flight tandem mass spectrometry resulted in the identification of 12 lepidopteran peptides. None of these had been previously isolated or characterized within this species. VIFTPKLamide encoded by the diapause hormone-pheromone biosynthesis activating neuropeptide precursor was for the first time isolated and biochemically identified in a tissue extract, providing irrefutable evidence of its expression in larval nervous tissue. Another pentapeptide, AMVRFamide, with no resemblance to other lepidopteran peptides, was de novo sequenced and is most related to the neuropeptide F peptide family.

Development and steroid regulation of RFamide immunoreactivity in antennal-lobe neurons of the sphinx moth Manduca sexta

During metamorphosis, the insect nervous system undergoes considerable remodeling: new neurons are integrated while larval neurons are remodeled or eliminated. To understand further the mechanisms involved in transforming larval to adult tissue we have mapped the metamorphic changes in a particularly well established brain area, the antennal lobe of the sphinx moth Manduca sexta, using an antiserum recognizing RFamide-related neuropeptides. Five types of RFamide-immunoreactive (ir) neurons could be distinguished in the antennal lobe, based on morphology and developmental appearance. Four cell types (types II-V, each consisting of one or two cells) showed RFamide immunostaining in the larva that persisted into metamorphosis. By contrast, the most prominent group (type I), a mixed population of local and projection neurons consisting of about 60 neurons in the adult antennal lobe, acquired immunostaining in a two-step process during metamorphosis. In a first step, from 5 to 7 days after pupal ecdysis, the number of labeled neurons reached about 25. In a second step, starting about 4 days later, the number of RFamide-ir neurons increased within 6 days to about 60. This two-step process parallels the rise and fall of the developmental hormone 20-hydroxyecdysone (20E) in the hemolymph. Artificially shifting the 20E peak to an earlier developmental time point resulted in the precocious appearance of RFamide immunostaining and led to premature formation of glomeruli. Prolonging high 20E concentrations to stages when the hormone titer starts to decline had no effect on the second increase of immunostained cell numbers. These results support the idea that the rise in 20E, which occurs after pupal ecdysis, plays a role in the first phase of RFamide expression and in glomeruli formation in the developing antennal lobes. The role of 20E in the second phase of RFamide expression is less clear, but increased cell numbers showing RFamide-ir do not appear to be a consequence of the declining levels in 20E that occur during adult development.

A comparison of the neuropeptides from the retrocerebral complex of adult male and female Manduca sexta using MALDI-TOF mass spectrometry

The occurrence of neuropeptides in the retrocerebral complexes of adult male and females of the tobacco hawkmoth, Manduca sexta, was investigated using matrix-assisted laser desorption time of flight (MALDI-TOF) mass spectrometry (MS), post source decay (PSD) and collision-induced dissociation (CID) MS/MS. From fractions of methanol extracts of corpora cardiaca (CC)/corpora allata (CA), separated by reversed-phase high performance liquid chromatography (RP-HPLC), a total of 11 mass ions were assigned to known peptides from M. sexta. These peptides were adipokinetic hormone (AKH), FLRFamides I, II and III, crustacean cardioactive peptide (CCAP), cardioactive peptide 2b (CAP(2b)), three myoinhibitory peptides, corazonin, and M. sexta allatostatin (Manse-AS). A further six masses were in agreement with Y/FXFGLamide allatostatins identified from other Lepidoptera. The sequence identities of FLRFamide I and AKH were confirmed using post source decay analysis. Fragmentation by collision-induced dissociation MS/MS identified an extended AKH peptide. The apparent differences in the peptides present in male and female retrocerebral complexes are most likely quantitative rather than sex specific.

Neuropeptides in perisympathetic organs of Manduca sexta: specific composition and changes during the development

We used a combination of matrix-assisted laser desorption-ionization time-of-flight mass spectrometry and immunocytochemistry to investigate the peptides from abdominal perisympathetic organs of Manduca sexta. Altogether three mass peaks, detected in mass spectra from single abdominal perisympathetic organs were identical with already known neuropeptides, namely CAP(2b), CCAP, and Manduca-allatotropin. Only CAP(2b) was found throughout the postembryonic development. In larvae, perisympathetic organs of the abdominal ganglia 1 and 7 do not accumulate neuropeptides. During the metamorphosis, the number of putative hormones stored in the abdominal perisympathetic organs, increases dramatically. Not a single substance, however, obtained in mass spectra of larval perisympathetic organs disappeared in the respective adult neurohemal organs. Peptides from abdominal perisympathetic organs are different from those of thoracic perisympathetic organs and the retrocerebral complex. Manduca-FLRFa-2 and -3 are enriched in thoracic perisympathetic organs; FLRFa-1, corazonin and adipokinetic hormone are abundant peptides of the retrocerebral complex. The majority of ion signals, however, represent unknown substances. An antiserum which recognized CAP(2b) allowed the morphological characterization of a median neurosecretory system in the abdominal ventral nerve cord of M. sexta, which resembles that of cockroach embryos. Double stainings confirmed that crustacean cardioactive peptide (CCAP) becomes colocalized with CAP(2b) in median neurosecretory cells during the last larval instar. This colocalization continues in adult insects.

FMRFamide-related peptides in the gut of Locusta migratoria L.: a comprehensive map and developmental profile

The gut tissues and associated nervous system of the African migratory locust, Locusta migratoria, were found to contain FMRFamide-like immunoreactive (FLI) material throughout the five larval instars and 2 weeks into the adult stage in both males and females. FMRFamide-like immunoreactivity associated with the locust gut was described using camera lucida techniques. FMRFamide-like immunoreactivity is observed in the frontal connectives, recurrent nerve, and oesophageal nerves; projections from the ingluvial ganglion onto the anterior midgut, and from the proctodeal nerve onto the hindgut and posterior midgut; in the neuropils of the frontal ganglion, hypocerebral ganglion and ingluvial ganglia; 30 cell bodies in the frontal ganglion; multipolar sensory cells on the foregut; and endocrine-like cells in the gastric caecae and midgut. Radioimmunoassay (RIA) was used to determine the quantities of FLI material in foreguts, gastric caecae, anterior and posterior midguts, and hindgut of first-fifth instar larvae, 1-3- and 14-17-day male and female adult locusts. As expected, as the tissue size (assessed by total protein content) increases, so does the amount of FLI material in each tissue. Normalizing for tissue size reveals significant differences in FLI content among the stages for each tissue tested. Reversed phase-high pressure liquid chromatography (RP-HPLC) followed by RIA has identified four groups of FLI fractions present in the gut, and different members of these groups are present in the various gut tissues.

Identification of neuropeptides from brains of larval Manduca sexta and Lacanobia oleracea using MALDI-TOF mass spectrometry and post-source decay

The occurrence of neuropeptides in the brain of larvae of the tobacco hawkmoth, Manduca sexta, and tomato moth, Lacanobia oleracea, was investigated using matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF) mass spectrometry (MS) and post-source decay (PSD). Methanolic extracts of 100 brains separated by reversed-phase high performance liquid chromatography yielded numerous ion peaks, some of which were common to both species. In M. sexta six [M+H](+) ions were in agreement with peptides previously structurally characterised from M. sexta (FLRF-amides I, II and III, M. sexta allatostatin, CAP(2b) and myoinhibitory peptide VI), whereas a further five corresponded to other known lepidopteran peptides (cydiastatins 3 and 4, helicostatins 1 and 6 and helicokinin II). Of these the identities of FLRF-amide I, cydiastatins 3 and 4 and CAP(2b) were confirmed by PSD analysis. Fourteen [M+H](+) ions corresponding to known lepidopteran peptides (FLRF-amide I, cydiastatins 2, 3 and 4, helicostatins 1, 5, 6, 7 and 9, CCAP, CAP(2b), M. sexta allatostatin and myoinhibitory peptide VI) were measured in L. oleracea brain extracts. From this insect, cydiastatins 3 and 4, helicostatin 5 and FLRF-amide I were identified by PSD. These peptides had not previously been structurally characterised from L. oleracea.

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

A Drosophila melanogaster dFMRFamide gene product, TPAEDFMRFamide, decreased crop contractions. However, DPKQDFMRFamide and SDNFMRFamide, also encoded in dFMRFamide, did not affect crop motility, which suggests these peptides are not functionally redundant in the crop and their unique N-terminal structures are important for activity. TPAEDFMRFamide-specific antisera did not stain the crop, which suggests it acts as a hormone. TDVDHVFLRFamide (DMS), encoded in D. melanogaster myosuppressin, stops crop contractions. TPAEDFMRFamide and DMS each contains a RFamide C-terminus; however, their effects on crop contractions differ, which suggests that unique receptors or different ligand:receptor binding requirements exist for these structurally related peptides.

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

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

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

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

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

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

Drosophila melanogaster FMRFamide-containing peptides: redundant or diverse functions?

FMRFamide-related peptides (FaRPs) are expressed throughout the animal kingdom and regulate a multitude of physiological activities. FaRPs have an RFamide C-terminal consensus structure that is important for interaction with the receptor. The ease of genetic manipulation and availability of genomic sequences makes Drosophila melanogaster an important experimental organism. Multiple classes of FaRPs encoded by different genes have been identified within this species. Here, we review FMRFamide-containing peptides encoded by the D. melanogaster FMRFamide gene in order to review the data on the expression, regulation, and activity of these peptides as well as acknowledge further endeavors required to elucidate FaRP signaling.

Innervation of the heart and aorta of Manduca sexta

Innervation of the heart and aorta of Manduca sexta was studied by using anatomic, neuronal tracing and immunocytochemical techniques. The study was undertaken to provide a foundation for investigating the neural mechanisms controlling cardiac reversal in adults. Lateral cardiac nerves were not found in the larval or adult heart. The larval heart and aorta seem to lack innervation, but a neurohemal system for the release of a cardioactive peptide is associated with the larval alary muscles. At adult metamorphosis, this neurohemal system regresses, and, at the same time, processes grow onto the anterior aorta. These processes seem to be neurohemal and originate from two pairs of neurosecretory cells located in the subesophageal ganglion. This system is immunoreactive to cardioactive peptides and may function, therefore, in hormonal modulation of the activity of the adult heart. Also during metamorphosis, synaptic innervation develops on the terminal heart chamber, and this innervation is from axons extending through the seventh and eighth dorsal nerves of the terminal abdominal ganglion. These axons originate from cells that have been identified as serial homologs of motor neuron-1 of other abdominal ganglia. These neurons are immunoreactive to a cardioactive peptide, and this peptide probably modulates the synaptic innervation of the terminal heart chamber. During metamorphosis, the target of the motor neurons-1 of the seventh and eighth segments becomes respecified from larval skeletal muscles to the terminal chamber of the adult heart.

Tagma-specific distribution of FXPRLamides in the nervous system of the American cockroach

FXPRLamide (pyrokinin) distribution in the central nervous system and major neurohaemal organs of the American cockroach and related cockroach species was investigated using immunocytochemistry and MALDI-TOF mass spectrometry. Six isoforms (Pea-PK-1 through -6) were found in different neurohaemal release sites. Pea-PK-1-4 and Pea-PK-6 are all stored in the retrocerebral complex and are all produced in cells located in both the suboesophageal ganglion (SOG) and the tritocerebrum. These pyrokinins were found to be concentrated in and around the corpora allata. No other known peptides were detectable in such high concentrations in this neurohaemal organ. They reach the corpora cardiaca/allata via the nervi corporis cardiaci-1 (NCC-1), NCC-3, and nervi corporis allati-2 (NCA-2). Abdominal perisympathetic organs contained only Pea-PK-5 and low quantities of the sequence-related Pea-PK-6. Neither Pea-PK-5 nor -PK-6 was detected in thoracic perisympathetic organs. It is likely that the expression of pyrokinins in the central nervous system is tagma (body region)-specific. Pea-PK-6 was identified during this study as follows: Ser-Glu-Ser-Glu-Val-Pro-Gly-Met-Trp-Phe-Gly-Pro-Arg-Leu-NH(2).

Identification of neuropeptides in the midgut of parasitized insects: FLRFamides as candidate paracrines

Parasitism of Manduca sexta (Lepidoptera: Sphingidae) larvae by the braconid wasp Cotesia congregata (Hymenoptera: Braconidae) leads to accumulation of peptides in host neurons and neurosecretory cells of the central nervous system (CNS) and neurons and endocrine/paracrine cells of the midgut. This accumulation has now facilitated the characterization of two new members of the FLRFamide family from midguts of parasitized larvae. The peptides, given the names F24 and F39, are 24 and 39 amino acids in length with the sequences VRDYPQLLDSGMKRQDVVHSFLRFamide and YAEAAGEQVPEYQALVRDYPQLLDSGMKRQDVVHSFLRFamide. The sequence of F24 is identical to the C-terminal 24 amino acids of F39. The C-terminal 10-mer of each is identical to a previously characterized decapeptide neurohormone (F10). This sequence is preceded by a potential processing site. In nonparasitized insects F39 was present at several-fold the amount of F24. In parasitized insects F24 and F39 accumulate in the middle and posterior regions of the midgut, which are enriched in endocrine/paracrine cells reacting with FLRFamide antisera. In the combined brain and subesophageal ganglion F39 was not detected and the amount of F24 never exceeded 2 fmol per Br/SEG. Of the three peptides, only F10 was found in the hemolymph. Thus, F24 and F39 may be intermediates in the biosynthesis of F10 and may themselves be released locally from endocrine/paracrine cells in the midgut epithelium.

Allatostatin-like-immunoreactive neurons of the tobacco hornworm, Manduca sexta, and isolation and identification of a new neuropeptide related to cockroach allatostatins

The YXFGLamide C-terminus serves to define most members of a family of structurally related neuropeptides, the YXFGLamides. These peptides have been identified from the nervous system of various insects and include the allatostatins of cockroaches and crickets, the schistostatins of locusts, and the callatostatins of blowflies. The YXFGLamides have been shown to have various functions, including inhibition of juvenile hormone biosynthesis in cockroaches and crickets and inhibition of contraction of certain insect visceral muscles. We wanted to know if these peptides occur in Manduca sexta and what functions they might have. A new peptide, AKSYNFGLamide, was isolated and identified from M. sexta and has been named "lepidostatin-1"; this is the first YXFGLamide to be found in a lepidopteran, and there are indications that additional YXFGLamides occur in M. sexta. An antiserum to cockroach allatostatins (YXFGLamides) was shown to recognize lepidostatin-1 of M. sexta and was used to map YXFGLamide-immunoreactive neurons in larvae. Because immunoreactive interneurons were found to form an extensive neuropil, YXFGLamides probably function as neuromodulators in M. sexta. Neuroendocrine cells in the brain, abdominal ganglia, and their respective neurohemal organs were YXFGLamide immunoreactive and appear to release YXFGLamides as neurohormones. Immunoreactivity to YXFGLamides and M. sexta diuretic hormone were found to be colocalized and appear to be coreleased in these neuroendocrine cells, indicating that YXFGLamides may be involved in regulation of fluid transport. Innervation of the corpora allata by YXFGLamide-immunoreactive processes was very sparse, suggesting that this innervation does not play an important role in allatostasis. Many thoracic motor neurons were YXFGLamide immunoreactive, suggesting that YXFGLamides may have a myomodulatory or myotrophic function in larvae. However, this immunoreactivity disappeared early in metamorphosis and did not reappear in the adult. The YXFGLamide-immunoreactive neurons in the terminal abdominal ganglion were found to innervate the hindgut, indicating that YXFGLamides may be involved in the control of the rate of myogenic contractions of the larval hindgut.

Neuroanatomy and immunocytochemistry of the median neuroendocrine cells of the subesophageal ganglion of the tobacco hawkmoth, Manduca sexta: immunoreactivities to PBAN and other neuropeptides

The median neuroendocrine cells of the subesophageal ganglion, important components of the neuroendocrine system of the tobacco hawkmoth, Manduca sexta, have not been well investigated. Therefore, we studied the anatomy of these cells by axonal backfills and characterized their peptide immunoreactivities. Both larvae and adults were examined, and developmental changes in these neuroendocrine cells were followed. Processes of the median neuroendocrine cells project to terminations in the corpora cardiaca via the third and the ventral nerves of this neurohemal organ, but the ventral nerve of the corpus cardiacum is the principal neurohemal surface for this system. Cobalt backfills of the third cardiacal nerves revealed lateral cells in the maxillary neuromere and a ventro-median pair in the labial neuromere. Backfills of the ventral cardiacal nerves revealed two ventro-median pairs of cells in the mandibular neuromere and two ventro-median triplets in the maxillary neuromere. The efferent projections of these cells are contralateral. The anatomy of the system is basically the same in larvae and adults. The three sets of median neuroendocrine cells are PBAN- and FMRFamide-immunoreactive, but only the mandibular and maxillary cells are proctolin-immunoreactive. During metamorphosis, the mandibular and maxillary cells also acquire CCK-like immunoreactivity and the labial cells become SCP- and sulfakinin-immunoreactive. Characteristics of FMRFamide-like immunostaining suggest that the median neuroendocrine cells may contain one or more of the FLRFamides that have been identified in M. sexta. The mandibular and maxillary neuroendocrine cells appear to produce the same set of hormones, and a somewhat different set of hormones is produced by the labial neuroendocrine cells. Two pairs of interneurons immunologically related to the neurosecretory cells are associated with the median maxillary neuroendocrine cells. These cells are PBAN-, FMRFamide-, SCP-, and sulfakinin-immunoreactive and project to arborizations in the brain and all ventral ganglia. These interneurons appear to have extensive modulatory functions in the CNS.