Microanalysis of the amino acid sequence of the eclosion hormone from the tobacco hornworm Manduca sexta

A Life's Journey Through Insect Metamorphosis

This autobiographical article describes the research career of Lynn M. Riddiford from its early beginnings in a summer program for high school students at Jackson Laboratory to the present "retirement" at the Friday Harbor Laboratories. The emphasis is on her forays into many areas of insect endocrinology, supported by her graduate students and postdoctoral associates. The main theme is the hormonal regulation of metamorphosis, especially the roles of juvenile hormone (JH). The article describes the work of her laboratory first in the elucidation of the endocrinology of the tobacco hornworm, Manduca sexta, and later in the molecular aspects of the regulation of cuticular and pigment proteins and of the ecdysone-induced transcription factor cascade during molting and metamorphosis. Later studies utilized Drosophila melanogaster to answer further questions about the actions of JH.

Neuromodulation and Strategic Action Choice in Drosophila Aggression

In this review, I discuss current knowledge and outstanding questions on the neuromodulators that influence aggressive behavior of the fruit fly Drosophila melanogaster. I first present evidence that Drosophila exchange information during an agonistic interaction and choose appropriate actions based on this information. I then discuss the influence of several biogenic amines and neuropeptides on aggressive behavior. One striking characteristic of neuromodulation is that it can configure a neural circuit dynamically, enabling one circuit to generate multiple outcomes. I suggest a consensus effect of each neuromodulatory molecule on Drosophila aggression, as well as effects of receptor proteins where relevant data are available. Lastly, I consider neuromodulation in the context of strategic action choices during agonistic interactions. Genetic components of neuromodulatory systems are highly conserved across animals, suggesting that molecular and cellular mechanisms controlling Drosophila aggression can shed light on neural principles governing action choice during social interactions.

Peptide neuromodulation in invertebrate model systems

Neuropeptides modulate neural circuits controlling adaptive animal behaviors and physiological processes, such as feeding/metabolism, reproductive behaviors, circadian rhythms, central pattern generation, and sensorimotor integration. Invertebrate model systems have enabled detailed experimental analysis using combined genetic, behavioral, and physiological approaches. Here we review selected examples of neuropeptide modulation in crustaceans, mollusks, insects, and nematodes, with a particular emphasis on the genetic model organisms Drosophila melanogaster and Caenorhabditis elegans, where remarkable progress has been made. On the basis of this survey, we provide several integrating conceptual principles for understanding how neuropeptides modulate circuit function, and also propose that continued progress in this area requires increased emphasis on the development of richer, more sophisticated behavioral paradigms.

Relationship between the expression of Rab family GTPases and neuropeptide hormones in the brain of Bombyx mori

Rab proteins are small GTPases that play essential roles in vesicle transport. In this study, we examined the expression of Rab proteins and neuropeptide hormones in the brain of the silkworm, Bombyx mori. We produced antibodies against B. mori Rab1 and Rab14 in rabbits. Immunoblotting of samples of brain tissue from B. mori revealed a single band for each antibody. Rab1 and Rab14 immunohistochemical labeling in the brain of B. mori was restricted to neurons of the pars intercerebralis and dorsolateral protocerebrum. Rab1, Rab7 and Rab14 co-localized with bombyxin. Rab1 and Rab7 co-localized with eclosion hormone. Rab1 co-localized with prothoracicotropic hormone. These results suggest that Rab1, Rab7 and Rab14 may be involved in neuropeptide transport in the brain of B. mori. This is the first report on the specificity of Rab proteins for the secretion of different neuropeptides in insects.

Bioinformatic analyses of the publicly accessible crustacean expressed sequence tags (ESTs) reveal numerous novel neuropeptide-encoding precursor proteins, including ones from members of several little studied taxa

ESTs have been generated for many crustacean species, providing an invaluable resource for peptide discovery in members of this arthropod subphylum. Here, these data were mined for novel peptide-encoding transcripts, with the mature peptides encoded by them predicted using a combination of online peptide prediction programs and homology to known arthropod sequences. In total, 70 mature full-length/partial peptides representing members of 16 families/subfamilies were predicted, the vast majority being novel; the species from which the peptides were identified included members of the Branchiopoda (Daphnia carinata and Triops cancriformis), Maxillopoda (Caligus clemensi, Caligus rogercresseyi, Lepeophtheirus salmonis and Lernaeocera branchialis) and Malacostraca (Euphausia superba, Marsupenaeus japonicus, Penaeus monodon, Homarus americanus, Petrolisthes cinctipes, Callinectes sapidus and Portunus trituberculatus). Of particular note were the identifications of an intermediate between the insect adipokinetic hormones and crustacean red pigment concentrating hormone and a modified crustacean cardioactive peptide from the daphnid D. carinata; Arg(7)-corazonin was also deduced from this species, the first identification of a corazonin from a non-decapod crustacean. Our data also include the first reports of members of the calcitonin-like diuretic hormone, FMRFamide-related peptide (neuropeptide F subfamily) and orcokinin families from members of the Copepoda. Moreover, the prediction of a bursicon alpha from the euphausid E. superba represents the first peptide identified from any member of the basal eucaridean order Euphausiacea. In addition, large collections of insect eclosion hormone- and neuroparsin-like peptides were identified from a variety of species, greatly expanding the number of known members of these families in crustaceans.

De novo molecular modeling and biophysical characterization of Manduca sexta eclosion hormone

Eclosion hormone (EH) is an integral component in the cascade regulating the behaviors culminating in emergence of an insect from its old exoskeleton. Little is known regarding the EH solution structure; consequently, we utilized a computational approach to generate a hypothetical structure for Manduca sexta EH. The de novo algorithm exploited the restricted conformational space of disulfide bonds (Cys14-Cys38, Cys18-Cys34, and Cys21-Cys49) and predicted secondary structure elements to generate a thermodynamically stable structure characterized by 55% helical content, an unstructured N-terminus, a helical C-terminus, and a solvent-exposed loop containing Trp28 and Phe29. Both the strain and pseudo energies of the predicted peptide compare favorably with those of known structures. The 62-amino acid peptide was synthesized, folded, assayed for activity, and structurally characterized to confirm the validity of the model. The helical content is supported by circular dichroism and hydrogen-deuterium exchange mass spectrometry. Fluorescence emission spectra and acrylamide quenching are consistent with the solvent exposure predicted for Trp28, which is shielded by Phe29. Furthermore, thermodynamically stable conformations that deviated only slightly from the predicted Manduca EH structure were generated in silico for the Bombyx mori and Drosophila melanogaster EHs, indicating that the conformation is not species-dependent. In addition, the biological activities of known mutants and deletion peptides were rationalized with the predicted Manduca EH structure, and we found that, on the basis of sequence conservation, functionally important residues map to two conserved hydrophobic clusters incorporating the C-terminus and the first loop.

Receptor guanylyl cyclases in Inka cells targeted by eclosion hormone

A signature of eclosion hormone (EH) action in insect ecdysis is elevation of cGMP in Inka cells, leading to massive release of ecdysis triggering hormone (ETH) and ecdysis initiation. Although this aspect of EH-induced signal transduction is well known, the receptor mediating this process has not been identified. Here, we describe a receptor guanylyl cyclase BdmGC-1 and its isoform BdmGC-1B in the Oriental fruit fly Bactrocera dorsalis that are activated by EH. The B form exhibits the conserved domains and putative N-glycosylation sites found in BdmGC-1, but possesses an additional 46-amino acid insertion in the extracellular domain and lacks the C-terminal tail of BdmGC-1. Combined immunolabeling and in situ hybridization reveal that BdmGC-1 is expressed in Inka cells. Heterologous expression of BdmGC-1 in HEK cells leads to robust increases in cGMP following exposure to low picomolar concentrations of EH. The B-isoform responds only to higher EH concentrations, suggesting different physiological roles of these cyclases. We propose that BdmGC-1 and BdmGC-1B are high- and low-affinity EH receptors, respectively.

Molecular characters and expression analysis of the gene encoding eclosion hormone from the Asian corn borer,Ostrinia furnacalis

Using rapid amplification of cDNA ends (RACE), the cDNA encoding eclosion hormone (EH) was cloned from the brain of Ostrinia furnacalis. The full Osf-EH cDNA is 986 bp and contains a 267 bp open reading frame encoding an 88 amino acid preprohormone, which including a hydrophobic 26 amino acid signal peptide and a 62 amino acid mature peptide. The mature Osf-EH shows high identity with Manduca sexta (95.2%), Helicoverpa armigera (91.9%) and Bombyx mori (85.5%), but low identify with Tribolium castaneum (63.6%), Drosophila melanogaster (56.5%) and Apis mellifera (54.8%). Using the HMMSTR Prediction Server, the 3D structure of Osf-EH was modeled. There are four beta-turns and three alpha-helixes predicted in Osf-EH, with the pattern of beta-beta-alpha-alpha-beta-beta-alpha. Northern blot analysis indicated a 1.0 kb transcript present only in the brain. The Osf-EH mRNA can not be detected in other neural tissues, such as the suboesophageal ganglion, thoracic ganglion, abdominal ganglion and other non-neural tissues, such as the midgut, fat body and epidermis. The Osf-EH mRNA content in the brain was measured using the combined method of quantitative RT-PCR and Southern blotting, which reached its highest level the day before the molt.

Insect peptide hormones, an overview of the present literature

A comprehensive overview of the recent state of the art of insect peptide hormones with chemical structures is presented. An increased interest in insect neuropeptides and dynamic development of that research area has been influenced by a rapid improvement of instrumentation necessary for isolation and structural characterization. Several research teams have studied the relationships between biological properties of insect and vertebrate peptide hormones. Thus hormones from the AKH family can be considered glucagon counterparts, whereas the myotropic hormones such as proctolin and Lem-PK (LPK) are a substance P equivalent. Insect melanization hormones Bom-MRCH in their structural characteristics and properties resemble those of mammal MSH, and leucosulfakinins Lem-SK-I and -II show some similarities with gastrin II and cholecystokinin. Bombyxin-II (Bom-PTTH-II) reveals a structural homology with human insulin and similar biological properties to adenocorticotropic mammal hormone. Allatostatin (Dip-JHS-I) may be compared to somatostatin as it can be inferred from the observations that this peptide modulates JH secretion in cockroach, Blattella germanica. Determination of the primary structure of eclosion hormones Mas-EH and Bom-EH-II as well as the amino acid sequence of allatotropin and allatostatin is a significant contribution to the understanding of the molecular mechanisms of metamorphosis and insect development.

Development of a heat shock inducible and inheritable RNAi system in silkworm

A heat shock inducible and inheritable RNA interference (RNAi) system was developed in the silkworm (Bombyx mori). RNAi transgenic silkworms were generated by injecting silkworm eggs with a piggyBac transposon plasmid carrying RNAi sequence against target gene driven by the Drosophila heat shock protein 70 (HSP70) promoter and the helper plasmid expressing piggyBac transposase. The transgenic EGFP gene and the endogenous eclosion hormone (EH) gene were chosen respectively as the target genes. In the RNAi transgenic silkworms, heat shock at 42 degrees C significantly and specifically reduced the expression of EGFP or EH gene in silkworms according to the corresponding RNAi targeting sequence but not in silkworms with the irrelevant RNAi sequence demonstrating the efficiency and specificity of the RNAi effect. Heat shock in the pupal stage hampered pupal-adult eclosion and reduced egg fertility in EH RNAi transgenic silkworms but not in the wild type or EGFP RNAi transgenic silkworms. The establishment of this heat inducible and inheritable conditional RNA interference system in silkworms provided an approach for the first time to dissect the functions of target genes in silkworms at different stages.

Complex steroid-peptide-receptor cascade controls insect ecdysis

Insect ecdysis sequence is composed of pre-ecdysis, ecdysis and post-ecdysis behaviors controlled by a complex cascade of peptide hormones from endocrine Inka cells and neuropeptides in the central nervous system (CNS). Inka cells produce pre-ecdysis and ecdysis triggering hormones (ETH) which activate the ecdysis sequence through receptor-mediated actions on specific neurons in the CNS. Multiple experimental approaches have been used to determine mechanisms of ETH expression and release from Inka cells and its action on the CNS of moths and flies. During the preparatory phase 1-2 days prior to ecdysis, high ecdysteroid levels induce expression of ETH receptors in the CNS and increased ETH production in Inka cells, which coincides with expression of nuclear ecdysone receptor (EcR) and transcription factor cryptocephal (CRC). However, high ecdysteroid levels prevent ETH release from Inka cells. Acquisition of Inka cell competence to release ETH requires decline of ecdysteroid levels and beta-FTZ-F1 expression few hours prior to ecdysis. The behavioral phase is initiated by ETH secretion into the hemolymph, which is controlled by two brain neuropeptides-corazonin and eclosion hormone (EH). Corazonin acts on its receptor in Inka cells to elicit low level ETH secretion and initiation of pre-ecdysis, while EH induces cGMP-mediated ETH depletion and consequent activation of ecdysis. The activation of both behaviors is accomplished by ETH action on central neurons expressing ETH receptors A and B (ETHR-A and B). These neurons produce numerous excitatory or inhibitory neuropeptides which initiate or terminate different phases of the ecdysis sequence. Our data indicate that insect ecdysis is a very complex process characterized by two principal steps: (1) ecdysteroid-induced expression of receptors and transcription factors in the CNS and Inka cells. (2) Release and interaction of Inka cell peptide hormones and multiple central neuropeptides to control consecutive phases of the ecdysis sequence.

Isolation of an eclosion hormone gene from the cotton bollworm, Helicoverpa armigera: Temporal and spatial distribution of transcripts

The cDNA encoding eclosion hormone (EH), which plays an integral role in triggering ecdysis behavior at the end of each molt, was cloned from the cotton bollworm, Helicoverpa armigera (Har) (Lepidoptera: Noctuidae). The EH polyprotein precursor contains a 26-amino acid signal peptide and a single 62-amino acid mature EH. Compared the mature Har-EH with other known EHs, it shows 94%, 84%, and 59% identities to Manduca sexta, Bombyx mori, and Drosophila melanogaster, respectively. Har-EH mRNA is expressed only in the brain by Northern blot and RT-PCR, but not in other tissues. By in situ hybridization and immunocytochemistry, both Har-EH mRNA and protein are localized in two pairs of neurosecretory cells of the brain. Prior to a molt, expression level of Har-EH gene reaches the highest point, and then drops after molt. EH release is detected both centrally, within the ganglia, and peripherally, into the hemolymph. A peak of the EH titer in hemolymph measured by ELISA presents at ecdysis. These results are consistent with the biological function of Har-EH associated with ecdysis. Furthermore, Har-EH gene is expressed throughout all of the developmental stages examined, implicating that the EH gene may possess other biological functions in post-embryonic development other than triggering ecdysis behavior.

The cycling and distribution of PER-like antigen in relation to neurons recognized by the antisera to PTTH and EH in Thermobia domestica

The cephalic nervous system of the firebrat contains antigens recognized by antisera to the clock protein period (PER), the prothoracicotropic hormone (PTTH) and the eclosion hormone (EH). The content of the 115 kDa PER-like antigen visualized on the western blots fluctuates in diurnal rhythm with a maximum in the night. The oscillations entrained in a 12:12 h light/dark (LD) cycle persist in the darkness and disappear in continuous light. They are detected by immunostaining in 14 pairs of the protocerebral neurons and are extreme in four suboesophageal neurons and two cells in each corpus cardiacum that contain PER only during the night phase. No circadian fluctuations occur in three lightly stained perikarya of the optic lobe. Five cell bodies located in each brain hemisphere between the deuto-and the tritocerebrum retain weak immunoreactivity under constant illumination. In all cells, the staining is confined to the cytoplasm and never occurs in the cell nuclei. The cells containing PER-like material do not react with the anti-PTTH and anti-EH antisera, which recognize antigens of about 50 and 20 kDa, respectively. The anti-PTTH antiserum stains in each brain hemisphere seven neurons in the protocerebrum, eight in the optic lobe, and 3-5 in the posterior region of the deutocerebrum. The antiserum to EH reacts in each hemisphere with just two cells located medially to the mushroom bodies. No cycling of the PTTH-like and EH-like antigens was detected.

Distribution of PER protein, pigment-dispersing hormone, prothoracicotropic hormone, and eclosion hormone in the cephalic nervous system of insects

Investigations performed on adult insects revealed that putative components of the central pacemaker, the protein Period (PER) and the pigment-dispersing hormone (PDH), are immunocytochemically detectable in discrete sets of brain neurons throughout the class of Insecta, represented by a bristletail, mayfly, damselfly, 2 locust species, stonefly, 2 bug species, goldsmith beetle, caddisfly, honeybee, and 2 blowfly species. The PER-positive cells are localized in the frontal protocerebrum and in most species also in the optic lobes, which are their only location in damselfly and goldsmith beetle. Additional PER-positive cells occur in a few species either in the deuto- and tritocerebrum or in the suboesophageal ganglion. The PER staining was always confined to the cytoplasm. The PDH immunoreactivity consistently occurs in a cluster of perikarya located frontoventrally at the proximal edge of the medulla. The mayfly and both locust species possess additional PDH neurons in 2 posterior cell clusters at the proximal edge of the medulla, and mayfly, waterstrider, and 1 of the blowfly species in the central brain. PDH-positive fibers form a fanlike arrangement over the frontal side of the medulla. Two or just 1 bundle of PDH-positive fibers run from the optic lobe to the protocerebrum, with collaterals passing over to the contralateral optic lobe. Antisera to the prothoracicotropic (PTTH) and the eclosion (EH) hormones, which in some insects regulate the molting and ecdysis rhythms, respectively, typically react with a few neurons in the frontal protocerebrum. However, the PTTH-positive neurons of the mayfly and the damselfly and the EH-positive neurons of the caddisfly are located in the suboesophageal ganglion. No PTTH-like antigen was detected in locusts, and no EH-like antigens were detected in the damselfly, stonefly, locusts, and the honeybee. There are no signs of co-localization of the PER-, PDH-, PTTH-, and EH-like antigens in identical neurons.

Cellular localization of bursicon using antisera against partial peptide sequences of this insect cuticle-sclerotizing neurohormone

Bursicon is the final neurohormone released at the end of the molting cycle. It triggers the sclerotization (tanning) of the insect cuticle. Until now, its existence has been verified only by bioassays. In an attempt to identify this important neurohormone, bursicon was purified from homogenates of 2,850 nerve cords of the cockroach Periplaneta americana by using high performance liquid chromatography technology and two-dimensional gel electrophoresis. Bursicon bioactivity was found in four distinct protein spots at approximately 30 kDa between pH 5.3 and 5.9. The protein of one of these spots at pH 5.7 was subsequently microsequenced, and five partial amino acid sequences were retrieved. Evidence is presented that two of these sequences are derived from bursicon. Antibodies raised against the two sequences labeled bursicon-containing neurons in the central nervous systems of P. americana. One of these antisera labeled bursicon-containing neurons in the crickets Teleogryllus commodus and Gryllus bimaculatus, and the moth Manduca sexta. A cluster of four bilaterally paired neurons in the brain of Drososphila melanogaster was also labeled. In addition, this antiserum detected three spots corresponding to bursicon in Western blots of two-dimensional gels. The 12-amino acid sequence detected by this antiserum, thus, seems to be conserved even among species that are distantly related.

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.

Integration of endocrine signals that regulate insect ecdysis

The extremely large number of insects and members of allied groups alive today suggests that molting--shedding of an old cuticle--may be one of the most commonly performed behaviors on our planet. Removal of an old cuticle in insects is associated with stereotyped, species-specific patterns of behavior referred to as ecdysis. It has been recognized for decades that the initiation of ecdysis is under hormonal control, but until recently many of the key peptides that regulate ecdysis were unknown. The report in 1996 of a new ecdysis-triggering hormone (ETH) sparked an era of significant advances in our understanding of the regulation of molting. This article summarizes the current model of peptide regulation of ecdysis, a model that is based on a positive feedback loop between ETH and a brain peptide, eclosion hormone. Then the relationship of these regulatory peptides to the neural circuitry that is the ultimate driver of the behavior are described. Because insects can undergo both status quo (larval-larval) and metamorphic (larval-pupal and pupal-adult) molts, differences in ecdysis behavior at different life stages are described and potential sources of these differences are identified. Most of the work described is based on studies of ecdysis in the hawkmoth, Manduca sexta, but results from studies of ecdysis in the fruit fly Drosophila melanogaster are also discussed.

Mono- and dibasic proteolytic cleavage sites in insect neuroendocrine peptide precursors

Regulatory peptides are synthesized as part of larger precursors that are subsequently processed into the active substances. After cleavage of the signal peptide, further proteolytic processing occurs predominantly at basic amino acid residues. Rules have been proposed in order to predict which putative proteolytic processing sites are actually used, but these rules have been established for vertebrate peptide precursors and it is unclear whether they are also valid for insects. The aim of this paper is to establish the validity of these rules to predict proteolytic cleavage sites at basic amino acids in insect neuropeptide precursors. Rules describing the cleavage of mono- and dibasic potential processing sites in insect neuropeptide precursors are summarized below. Lys-Arg pairs not followed by an aliphatic or basic amino acid residue are virtually always cleaved in insect regulatory peptide precursors, but cleavages of Lys-Arg pairs followed by either an aliphatic or a basic amino acid residue are ambiguous, as is processing at Arg-Arg pairs. Processing at Arg-Lys pairs has so far not been demonstrated in insects and processing at Lys-Lys pairs appears very rare. Processing at single Arg residues occurs only when there is a basic amino acid residue in position -4, -6, or -8, usually an Arg, but Lys or His residues work also. Although the current number of such sites is too limited to draw definitive conclusions, it seems plausible that cleavage at these sites is inhibited by the presence of aliphatic residues in the +1 position. However, cleavage at single Arg residues is ambiguous. When several potential cleavage sites overlap the one most easily cleaved appears to be processed. It cannot be excluded that some of the rules formulated here will prove less than universal, as only a limited number of cleavage sites have so far been identified. It is likely that, as in vertebrates, ambiguous processing sites exist to allow differential cleavage of the same precursor by different convertases and it seems possible that the precursors of allatostatins and PBAN are differentially cleaved in different cell types. Arch. Insect Biochem. Physiol. 43:49-63, 2000.

Structural study on silkworm eclosion hormone fragment (1-34) in solution by proton nuclear magnetic resonance spectroscopy

Eclosion hormone (EH) is a neuropeptide hormone which controls the ecdysis behavior in insect. The three dimensional structure of the N-terminal fragment (1-34) of the eclosion hormone which was predicted to contain a compact region crucial for the EH activity was studied in 50% d3-trifluoroethanol(TFE)/50% H2O at pH 3 and 298 K by 1H NMR spectroscopy with the combined use of distance geometry and molecular dynamics calculations. NMR results indicated that the fragment actually assumes an alpha-helix between Ala10 and Gln20, but no rigid structure is present from Cys21 through the C-terminus and for the N-terminal region (Ser1-Asp9). The elucidated structure was compared with the predicted structure of the native EH for the further development of the design of the insecticide.

Insect neuropeptides and their receptors new leads for medical and agricultural applications

Diversification of messenger and receptor molecules is the result of evolution; however, the principles of intercellular signaling mechanisms are very similar in all metazoans. Recent discoveries of insect peptides provide new leads for applications in medicine and agriculture. (Trends Endocrinol Metab 1997;8:321-326). (c) 1997, Elsevier Science Inc.

Disruption of a behavioral sequence by targeted death of peptidergic neurons in Drosophila

The neuropeptide eclosion hormone (EH) is a key regulator of insect ecdysis. We tested the role of the two EH-producing neurons in Drosophila by using an EH cell-specific enhancer to activate cell death genes reaper and head involution defective to ablate the EH cells. In the EH cell knockout flies, larval and adult ecdyses were disrupted, yet a third of the knockouts emerged as adults, demonstrating that EH has a significant but nonessential role in ecdysis. The EH cell knockouts had discrete behavioral deficits, including slow, uncoordinated eclosion and an insensitivity to ecdysis-triggering hormone. The knockouts lacked the lights-on eclosion response despite having a normal circadian eclosion rhythm. This study represents a novel approach to the dissection of neuropeptide regulation of a complex behavioral program.

MALDI-MS as a monitor of the purification and folding of synthetic eclosion hormone

Analogues of the small protein Manduca sexta eclosion hormone (62 amino acids) were synthesized by Fmoc solid-phase methodology. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) was used to analyze the products of the syntheses and this information was used to design an efficient purification scheme. MALDI-MS was used to monitor the target products through purification and it was also used to monitor folding of the purified materials. The folded EH analogues were shown to be biologically active proteins with an in vivo bioassay using pharate adult moths, Heliothis virescens.

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.

Neuropeptide-stimulated cyclic guanosine monophosphate immunoreactivity in the neurosecretory terminals of a neurohemal organ

The neuropeptide eclosion hormone acts on the nervous system of the tobacco hornworm, Manduca sexta, to increase cyclic guanosine monophosphate (cGMP) levels. In this study I describe the localization of some of the sites where these increases occur. Prior to pupal ecdysis, eclosion hormone stimulates an increase in cGMP in a network of fibers in the transverse nerve of each abdominal ganglion. Double-label experiments with propidium iodide suggest that the cGMP immunoreactivity is primarily localized in neurosecretory nerve endings. The time course of the increase in cGMP immunoreactivity and its requirement for lipid metabolism is similar to that of the cGMP increase measured by radioimmunoassay. The cGMP response in the transverse nerve is stage-specific, occurring prior to pupal ecdysis and not prior to larval or adult ecdysis.

Accumulation of neuropeptides in the cerebral neurosecretory system of Manduca sexta larvae parasitized by the braconid wasp Cotesia congregata

Fifth instar larvae of Manduca sexta that were parasitized by the braconid wasp Cotesia congregata failed to develop after the parasitoid larvae emerged, and these host larvae lingered for 2-3 weeks in a quiescent, nonfeeding state without initiating a larval molt or metamorphosis. This study was focused on the neuroendocrine changes associated with the host's developmental arrest. Immunohistochemical studies suggested that the host brain neurosecretory cells as well as their axon terminals in the corpora cardiaca-corpora allata complex accumulated multiple neuropeptides. The extent of accumulation in cells and axons increased with time, so that hosts examined 7-14 days after the wasps emerged showed the most intense staining with antibodies against prothoracicotropic hormone, bombyxin, allatotropin, allatostatin, diuretic hormone, eclosion hormone, proctolin, and FMRFamide. Increased levels of prothoracicotropic hormone and FMRFamide-like peptides in the brains of parasitized larvae were confirmed using Western blots and enzyme-linked immunosorbent assay (ELISA), respectively. Starvation of the unparasitized larvae induced some accumulation of the neuropeptides; however, the intensity of staining and number of immunopositive cells and axons were in most cases clearly higher in the parasitized larvae. Our results suggest that accumulation of the neuropeptides is associated with developmental arrest of parasitized larvae. Because a similar developmental arrest occurs in a wide range of parasitized insects, our findings may have relevance for many other species. Moreover, these data illustrate the potential value of using parasitized M. sexta larvae as a model for studying the mechanisms governing the rates of neuropeptide expression, processing, packaging, and release, as well as providing a rich source of neuropeptides, thus facilitating their isolation and characterization.

Isolation, identification, and synthesis of Mas-MG-MT I, a novel peptide from the larval midgut of Manduca sexta (Lepidoptera: Sphingidae)

A five-residue myotropic peptide, Manduca sexta midgut myotropin I (Mas-MG-MT I), was isolated from an extract of 800 midguts of fifth instar larvae of the tobacco hornworm, Manduca sexta. It was purified by reverse phase and normal phase HPLC. Myotropic activity was screened by a heterologous Locusta migratoria oviduct bioassay. Sequence analysis, amino acid composition analysis, and comparison of candidate synthetic peptides in the amide and acid form revealed the following primary structure: Ala-Glu-Pro-Tyr-Thr-NH2. This is the first fully identified peptide isolated directly from the midgut of an insect species. Few significant sequence homologies with known vertebrate and invertebrate peptides have been found.

Isolation, characterization and expression of the eclosion hormone gene of Drosophila melanogaster

Eclosion hormone (EH) is a neuropeptide that triggers the performance of ecdysis behaviors at the end of a molt. We have isolated the EH gene from Drosophila melanogaster, and localized the gene to the right arm of chromosome 3 at band position 90B1-2. The 97-amino-acid translation product contains a signal peptide followed by a 73-amino-acid prohormone. The N-terminus of the prohormone has diverged from lepidopteran EH both in its length and amino acid composition, and contains a potential endoproteolytic cleavage site. The deduced sequence of Drosophila EH is 58% identical (36 of 62 amino acids) to that of Manduca EH. The EH gene is expressed as a 0.8-kb transcript in a single pair of brain neurons which extend their processes the entire length of the central nervous system and also to the corpora cardiaca portion of the ring gland. These cells show massive depletion of immunoreactive EH at ecdysis.

Immunoaffinity purification of the neuropeptide prothoracicotropic hormone from Manduca sexta

The prothoracicotropic hormones (PTTH) are cerebral peptides that control insect postembryonic development by stimulating the prothoracic glands to synthesize ecdysteroids. Using immunoaffinity chromatography and SDS-PAGE, a 25.5 kDa big PTTH has been purified from Manduca sexta. Based upon SDS-PAGE and Western blot analysis, the native form of big PTTH appears to be a dimer with monomers of 16.5 kDa. Four HPLC-separated fragments of this acidic peptide were sequenced and exhibited no sequence similarity with Bombyx mori PTTH. In agreement with this finding, the basic Bombyx PTTH had no PTTH bioactivity in Manduca. One sequenced fragment of the Manduca PTTH is approximately 70% similar to the vertebrate cellular retinoid binding proteins, suggesting these binding proteins may be present in insects.

Insect neuropeptides: discovery and application in insect management

New approaches to the development of insect control agents have been revealed through the molecular description of neuropeptides, their biogenesis, action, and degradation. Prerequisite to the exploitation of a neuropeptide as a lead to control agent development is a thorough understanding of the biochemistry of the neuropeptide and appreciation of its physiological impact. Reliable bioassays must be coupled with advanced biochemical and molecular genetic technologies to overcome limitations imposed by the typically low endogenous levels of individual neuropeptides. Purification, amino acid sequencing, and gene cloning provide the molecular tools necessary for studies on neuropeptide synthesis, processing, secretion, receptor binding, and inactivation. Each of these areas consists of a number of amino acid sequence-, and enzyme-dependent steps which may be considered as targets for the development of highly specific control agents. These agents will include antagonist and superagonists, peptidomimetics, recombinant peptides delivered through the baculovirus technology, receptor blockers, and enzyme inhibitors.

Eclosion Hormone Stimulates Cyclic GMP Levels in Manduca sexta Nervous Tissue via Arachidonic Acid Metabolism with Little or No Contribution from the Production of Nitric Oxide

The neuropeptide eclosion hormone acts directly on the nervous system of the tobacco hornworm, Manduca sexta, to trigger ecdysis behavior at the end of each molt. Previous studies have shown that the action of eclosion hormone is mediated via the intracellular messenger cyclic GMP. In the present study we have investigated the mechanisms involved in the eclosion hormone-stimulated increases in cyclic GMP. No stimulation of guanylate cyclase was seen in homogenized nervous tissue, suggesting that eclosion hormone does not directly stimulate a membrane-bound form of guanylate cyclase. Nitric oxide synthase inhibitors, N-methylarginine and nitroarginine, had no effect on eclosion hormone-stimulated cyclic GMP levels. By contrast, 4-bromophenacyl bromide, an inhibitor of arachidonic acid release, and nordihydroguaiaretic acid, an inhibitor of arachidonic acid metabolism, almost completely abolished the eclosion hormone-stimulated cyclic GMP increase. We hypothesize that eclosion hormone receptors are coupled to a lipase, activation of which causes the release of arachidonic acid. Either the arachidonic acid directly stimulates the soluble guanylate cyclase or further metabolism of arachidonic acid yields compounds that activate guanylate cyclase.

Growth of axon collaterals of eclosion hormone neurons into a new release site during metamorphosis of Bombyx mori

Eclosion hormone (EH) is a peptide triggering ecdysis in insects. Injection of Lucifer dye into EH producing cells in the silkworm at various stages of adult development revealed that after pupation the EH cells produced many axon collaterals to form a new neurohaemal structure in the corpora cardiaca (CC), the corpora allata and the associated nerves of the CC. The axon collaterals may serve as a major release site of EH at adult ecdysis.

Nucleotide sequence of cDNA for the eclosion hormone of the silkworm, Bombyx mori, and the expression in a brain

The cDNAs encoding eclosion hormone (EH) of the silkworm, Bombyx mori, were isolated and sequenced. The results showed that the pre-EH molecule contains a 26-amino acid signal peptide and a 62-amino acid mature EH. The deduced amino acid sequence agreed with that previously determined by the peptide analysis. The presence of leucine residue at the carboxyl terminal of EH, which had not been detected directly by the peptide analysis, was proved. Primer extension and Northern hybridization analyses revealed that 0.9 kb mRNA is transcribed and it has a 66-nucleotide non-translated sequence at the 5'-end region. In situ hybridization showed that the EH gene is expressed in two pairs of nuerosecretory cells in the brain of 5th instar larva.

Complete structure of eclosion hormone of Manduca sexta. Assignment of disulfide bond location

The locations of the three disulfide bonds of eclosion hormone (EH) isolated from Manduca sexta were assigned by sequence analysis of thermolysin fragments and by comparison of a key heterodimeric fragment to regiospecifically synthesized parallel and antiparallel isomers. We elucidated the complete structure of Manduca EH as a 62-residue peptide which has three disulfide bonds between Cys14-Cys38, Cys18-Cys34, and Cys21-Cys49.

Purification and chemical characterization of peptide G1, an invertebrate neuropeptide that stimulates cyclic GMP metabolism

Bioassay analysis of extracts of the major neurosecretory structures of the American lobster have revealed several different agents with stimulatory effects on the cyclic GMP metabolism of various lobster tissues. The most potent of these is a peptide extracted from the sinus gland, a neurohemal organ found in the animal's eyestalk. This molecule, called peptide G1 (for its effects on cyclic GMP metabolism), can increase the cyclic GMP content of every lobster tissue tested, sometimes by as much as 200-fold. In this article, we describe the purification and some of the chemical properties of peptide G1. Purification was accomplished by sequential anion exchange and reverse-phase HPLC. The purified peptide is a large, extremely hydrophobic molecule. Its apparent molecular mass on a reducing sodium dodecyl sulfate-containing gel is 6.4 kDa, and its calculated molecular mass (based on an amino acid analysis of the purified material) is 8.2 kDa. Amino acid analysis reveals a high proportion of leucine and valine residues. The amino terminus of the molecule is not susceptible to Edman degradation, but sequencing studies were successfully carried out on tryptic fragments. Based on the estimated size of the molecule, these studies provide approximately 60% of the total sequence. No homologies with any previously sequenced peptide were observed, but biochemical similarities to as yet unsequenced peptides found in extracts of sinus glands from other crustaceans (hyperglycemic hormone and moult-inhibiting hormone) are described.

A new peptide in the FMRFamide family isolated from the CNS of the hawkmoth, Manduca sexta

We have purified a FMRFamide-like peptide from extracts of brain-subesophageal ganglion of the moth, Manduca sexta. The purification was monitored with a new, competitive ELISA, and accomplished with ion exchange and reverse-phase HPLC. The peptide structure was determined by a combination of tandem mass spectrometry and automated Edman degradation. The amino acid sequence of the peptide is less than Glu-Asp-Val-Val-His-Ser-Phe-Leu-Arg-Phe-amide (pEDVVHSFLRF-NH2). In a separate purification, an identical peptide was isolated from extracts of brain-associated neurohemal structures. We have named this peptide ManducaFLRFamide, to indicate its homology with other members of the "FMRFamide" family. In bioassays, chemically synthesized peptide increased the force of neurally evoked contractions in the major power-producing flight muscles, the dorsal longitudinal muscles. This observation suggests that hormonally released ManducaFLRFamide may play a role in sustaining or promoting the flight behavior necessary for mate-seeking (in males) or oviposition (in females) in sphingid moths.

Eclosion hormone of the silkworm Bombyx mori. Expression in Escherichia coli and location of disulfide bonds

A gene encoding eclosion hormone (EH) from the silkworm, Bombyx mori was chemically synthesized, inserted into a secretion vector and expressed in Escherichia coli, leading to the production of biologically active EH. Sequence analysis of cystine-containing peptides in a thermolysin digest of this EH established the locations of 3 disulfide bonds in the molecule. Evidence was also obtained that the 6 residues at the NH2-terminal are dispensable but 4 residues at the COOH-terminal play an important role in EH activity.

Isolation and expression of the eclosion hormone gene from the tobacco hornworm, Manduca sexta

Eclosion hormone (EH) is a 62-amino acid neuropeptide that initiates the ecdysis behavior of insects. The EH-encoding gene of the tobacco hornworm, Manduca sexta, was isolated by using a designed 72-mer oligonucleotide probe. Sequence analysis of this gene and its corresponding cDNA showed that the EH gene is 7.8 kilobases and consists of three exons. Exon I is totally nontranslated; exon II contains a 26-amino acid signal peptide and amino acids 1-4 of the EH peptide, and exon III encodes the remainder of the peptide. The EH gene is present in a single copy per haploid genome and transcribes an 0.8-kb mRNA that is expressed in larval, diapausing pupal, and developing adult brains but not in the ventral nerve cord or in nonneural tissues. In situ hybridization showed that the EH gene is expressed in two pairs of ventromedial neurosecretory cells in brains of both larvae and developing adults.

Amino acid sequence of the crustacean hyperglycemic hormone (CHH) from the shore crab, Carcinus maenas

Crustacean hyperglycemic hormone (CHH) was isolated from sinus glands of Carcinus maenas, and its primary structure was determined by manual microsequencing, using the DABITC-PITC double-coupling method. The neurohormone consists of 72 amino acid residues (8524 Da). Three disulfide bridges are present and both the N- and C-terminus are blocked. CHH does not show significant sequence homology to any known peptide hormone or protein.