cDNA structure and expression of bombyxin, an insulin-like brain secretory peptide of the silkmoth Bombyx mori

Insulin-like and mimetic molecules from non-mammalian organisms: potential relevance for drug discovery

Insulin was first discovered in extracts of vertebrate pancreas during a focused search for a therapy for diabetes. Subsequent efforts to discover and isolate a similar active principle from yeast and plants driven by the hope to identify insulin-like/mimetic molecules with critical advantages in the pharmacokinetic profile and expenditure of production compared to authentic human insulin were not successful. As a consequence, it has generally been assumed that hormones evolved exclusively during course of the evolution of vertebrate endocrine organs, implying a rather recent origin. Concomitantly, the existence and physiological role of vertebrate hormones in lower multi- and unicellular eukaryotes have remained a rather controversial subject over decades, albeit there is some evidence that hormones and hormone-binding proteins resembling those of vertebrates are expressed in fungi and yeast. Past and recent findings on the existence of insulin-like and mimetic materials, such as the glucose tolerance factor, in lower eukaryotes, in particular Neurospora crassa and yeast, will be presented. These data provide further evidence for the provocative view that the evolutionary roots of the vertebrate endocrine system may be far more ancient than is generally believed and that the identification and characterisation of insulin-like/mimetic molecules from lower eukaryotes may be useful for future drug discovery efforts.

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

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

Insulin/IGF signaling and its regulation in Drosophila

Taking advantage of Drosophila as a genetically tractable experimental animal much progress has been made in our understanding of how the insulin/IGF signaling (IIS) pathway regulates development, growth, metabolism, stress responses and lifespan. The role of IIS in regulation of neuronal activity and behavior has also become apparent from experiments in Drosophila. This review briefly summarizes these functional roles of IIS, and also how the insulin producing cells (IPCs) are regulated in the fly. Furthermore, we discuss functional aspects of the spatio-temporal production of eight different insulin-like peptides (DILP1-8) that are thought to act on one known receptor (dInR) in Drosophila.

DNA synthesis during endomitosis is stimulated by insulin via the PI3K/Akt and TOR signaling pathways in the silk gland cells of Bombyx mori

Silk gland cells undergo multiple endomitotic cell cycles during silkworm larval ontogeny. Our previous study demonstrated that feeding is required for continued endomitosis in the silk gland cells of silkworm larvae. Furthermore, the insulin signaling pathway is closely related to nutritional signals. To investigate whether the insulin signaling pathway is involved in endomitosis in silk gland cells, in this study, we initially analyzed the effects of bovine insulin on DNA synthesis in endomitotic silk gland cells using 5-bromo-2'-deoxyuridine (BrdU) labeling technology, and found that bovine insulin can stimulate DNA synthesis. Insulin signal transduction is mainly mediated via phosphoinositide 3-kinase (PI3K)/Akt, the target of rapamycin (TOR) and the extracellular signal-regulated kinase (ERK) pathways in vertebrates. We ascertained that these three pathways are involved in DNA synthesis in endomitotic silk gland cells using specific inhibitors against each pathway. Moreover, we investigated whether these three pathways are involved in insulin-stimulated DNA synthesis in endomitotic silk gland cells, and found that the PI3K/Akt and TOR pathways, but not the ERK pathway, are involved in this process. These results provide an important theoretical foundation for the further investigations of the mechanism underlying efficient endomitosis in silk gland cells.

Signalling properties and pharmacology of a 5-HT7 -type serotonin receptor from Tribolium castaneum

In the last decade, genome sequence data and gene structure information on invertebrate receptors has been greatly expanded by large sequencing projects and cloning studies. This information is of great value for the identification of receptors; however, functional and pharmacological data are necessary for an accurate receptor classification and for practical applications. In insects, an important group of neurotransmitter and neurohormone receptors, for which ample sequence information is available but pharmacological information is missing, are the biogenic amine G protein-coupled receptors (GPCRs). In the present study, we investigated the sequence information, pharmacology and signalling properties of a 5-HT7 -type serotonin receptor from the red flour beetle, Tribolium castaneum (Trica5-HT7 ). The receptor encoding cDNA shows considerable sequence similarity with cognate 5-HT7 receptors and phylogenetic analysis also clusters the receptor within this 5-HT receptor group. Real-time reverse transcription PCR demonstrated high expression levels in the brain, indicating the possible importance of this receptor in neural processes. Trica5-HT7 was dose-dependently activated by 5-HT, which induced elevated intracellular cyclic AMP levels but had no effect on calcium signalling. The synthetic agonists, α-methyl 5-HT, 5-methoxytryptamine, 5-carboxamidotryptamine and 8-hydroxy-2-(dipropylamino)tetralin hydrobromide, showed a response, although with a much lower potency and efficacy than 5-HT. Ketanserin and methiothepin were the most potent antagonists. Both showed characteristics of competitive inhibition on Trica5-HT7 . The signalling pathway and pharmacological profile offer important information that will facilitate functional and comparative studies of 5-HT receptors in insects and other invertebrates. The pharmacology of invertebrate 5-HT receptors differs considerably from that of vertebrates. The present study may therefore contribute to establishing a more reliable classification of invertebrate 5-HT receptors.

Feeding on a begomovirus-infected plant enhances fecundity via increased expression of an insulin-like peptide in the whitefly, MEAM1

The Middle East-Minor 1 cryptic species (MEAM1), Bemisia tabaci (Gennadius) is a globally invasive pest. It spreads widely due to its high fecundity and mutualistic interactions with the virus they vector. Feeding on virus (tomato yellow leaf curl China virus, TYLCCNV)-infected host plants improves their fecundity, however, the key factor regulating the signaling transduction in reproduction of whitefly remains to be identified. Here, we cloned a full length cDNA encoding an insulin-like peptide in MEAM1 (BtILP1) and investigated its expression profile, functions, and the expression induced by feeding on virus-infected tobacco plants. The full length cDNA of BtILP1 was 590 bps and encoded an open reading frame containing 149 amino acid residues. Multiple sequences alignment results showed BtILP1 contained the structural features typical of the insulin family. Expression dynamics associated with development showed the expression level of BtILP1 peaked at 5 days posteclosion (PE). During 1 to 3 days PE, BtILP1 was expressed highly in the head and abdomen of female adults and highly in the head during 5 to 7 days PE. Knockdown of the BtILP1 expression also impaired vitellogenin gene expression at both transcript and protein levels. Downregulating BtILP1 expression decreased fecundity of female adults and hatching rate of eggs. Feeding on virus-infected tobacco increased BtILP1 expression in MEAM1 female adults. We infer feeding on begomovirus-infected tobacco enhances the reproduction of MEAM1 by inducing BtILP1 expression. Our results give a new sight into the mutualistic interactions between virus and its insect vector.

Identification of putative insulin-like peptides and components of insulin signaling pathways in parasitic platyhelminths by the use of genome-wide screening

No endogenous insulin-like peptides in parasitic flatworms have been reported. Insulin receptors from flukes and tapeworms have been shown to interact directly with the host-derived insulin molecule, which suggests the exploitation of host-derived insulin. In this study, a strategy of genome-wide searches followed by comprehensive analyses of strictly conserved features of the insulin family was used to demonstrate the presence of putative insulin-like peptides in the genomes of six tapeworms and two flukes. In addition, whole insulin signaling pathways were annotated on a genome-wide scale. Two putative insulin-like peptide genes in each genome of tapeworms and one insulin-like peptide gene in each genome of flukes were identified. The comprehensive analyses revealed that all of these peptides showed the common features shared by other members of the insulin family, and the phylogenetic analysis implied a putative gene duplication event in the Cestoda during the evolution of insulin-like peptide genes. The quantitative expression analysis and immunolocalization results suggested a putative role of these peptides in reproduction. Entire sets of major components of the classic insulin signaling pathway were successfully identified, suggesting that this pathway in parasitic flatworms might also regulate many other important biological activities. We believe that the identification of the insulin-like peptides gives us a better understanding of the insulin signaling pathway in these parasites, as well as host-parasite interactions.

A new theraphosid spider toxin causes early insect cell death by necrosis when expressed in vitro during recombinant baculovirus infection

Baculoviruses are the most studied insect viruses in the world and are used for biological control of agricultural and forest insect pests. They are also used as versatile vectors for expression of heterologous proteins. One of the major problems of their use as biopesticides is their slow speed to kill insects. Thus, to address this shortcoming, insect-specific neurotoxins from arachnids have been introduced into the baculovirus genome solely aiming to improve its virulence. In this work, an insecticide-like toxin gene was obtained from a cDNA derived from the venom glands of the theraphosid spider Brachypelma albiceps. The mature form of the peptide toxin (called Ba3) has a high content of basic amino acid residues, potential for three possible disulfide bonds, and a predicted three-stranded β-sheetDifferent constructions of the gene were engineered for recombinant baculovirus Autographa californica multiple nuclepolyhedrovirus (AcMNPV) expression. Five different forms of Ba3 were assessed; (1) the full-length sequence, (2) the pro-peptide and mature region, (3) only the mature region, and the mature region fused to an (4) insect or a (5) virus-derived signal peptide were inserted separately into the genome of the baculovirus. All the recombinant viruses induced cell death by necrosis earlier in infection relative to a control virus lacking the toxin gene. However, the recombinant virus containing the mature portion of the toxin gene induced a faster cell death than the other recombinants. We found that the toxin construct with the signal peptide and/or pro-peptide regions delayed the necrosis phenotype. When infected cells were subjected to ultrastructural analysis, the cells showed loss of plasma membrane integrity and structural changes in mitochondria before death. Our results suggest this use of baculovirus is a potential tool to help understand or to identify the effect of insect-specific toxic peptides when produced during infection of insect cells.

Insulin-producing cells and their regulation in physiology and behavior ofDrosophila1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

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

Partial synchronization dynamics of coupled ultradian oscillators comprising an insect neurosecretory cell system

An insulin-related peptide, bombyxin, in the silkmoth Bombyx mori is secreted by four pairs of cerebral neurosecretory cells that form a weakly coupled oscillator system to produce a pulsatile pattern of hormone secretion. The activity of individual bombyxin-producing (BP) cells oscillated with different periods (20-70 min). The population of BP cells exhibited complex phase dynamics, including spontaneous synchronization and desynchronization of different combinations of cells. Statistical cross-correlation analyses of oscillation patterns between BP cells revealed that one cell usually correlated closely with a few particular cells of similar periodicity. Close investigation of the phase differences between individual active phases of the related cell pairs revealed that an inphase synchronous state was usually maintained for many cycles, whereas an antiphase state was transient, lasting for a few cycles. In contrast, antiphase synchronous states often occurred between several cell pairs when the brain containing the cerebral neurosecretory cell system was disconnected from the ventral nerve cord containing the neuronal mechanism that induced periodic heartbeat reversals at intervals of 80-110 min and exerted a periodic suppressive or phase-resetting effect on individual BP cells. These results suggest that the internal coupling mechanism in the BP cell system is not sufficient to maintain an in-phase synchronous state in the heterogeneous cell population, and that the external phase resetting mechanism may assist in-phase synchronization of many neurosecretory cells to generate an overall pulsatile pattern of bombyxin secretion.

Insulin-like peptides in Spodoptera littoralis (Lepidoptera): Detection, localization and identification

Insulin is an extensively studied peptide hormone in mammals. However, insulin is not restricted to vertebrates, but has also been identified in invertebrates, among whom several insect species. These insulin-like peptides (ILPs) show structural and-at least some-functional homology with mammalian insulin and act through a conserved pathway. Yet many aspects of insulin function in insects remain to be unveiled. We analyzed the presence of ILPs in the cotton leafworm, Spodoptera littoralis, at two levels: (1) cellular localization of ILPs in whole tissues of the central nervous system from S. littoralis, and (2) detection and identification of ILPs at nucleotide level. To our knowledge, nothing about the presence of ILPs in S. littoralis has been described so far. By whole mount in situ immunolocalization, we localized bombyxin-like material in S. littoralis in four pairs of pars intercerebralis cells and in the corpus cardiacum-corpus allatum complexes. In addition, we have cloned two different S. littoralis ILP precursor cDNAs by a combination of PCR and RAcE. The corresponding precursor polypeptides ('Sl-ILPP1' and 'Sl-ILPP2') show significant sequence homology with precursors for bombyxin and other bombyxin-related peptides. Our results strongly suggest that the S. littoralis ILPs belong to the category of bombyxin-analogs.

The morphostatic actions of juvenile hormone

The maintenance of "status quo" in larvae by juvenile hormone (JH) involves both the programming of ecdysteroid-dependent synthesis during the molt and the suppression of morphogenetic growth during the intermolt. The latter morphostatic action does not require ecdysteroids, and has been studied in the formation of imaginal discs in Manduca sexta. Preultimate larval instars have both invaginated discs and imaginal primordia, both of which grow isomorphically with the larva. In the last instar, the young discs/primordia initiate the morphogenesis and patterning that results in a mature disc. JH suppresses both the initiation and progression of the signaling that transforms immature discs or primordia into a fully patterned imaginal disc. This transformation normally occurs in the context of the rapid growth of the last larval stage, and nutrient-dependent factors appear to be able to override the JH suppression. The morphostatic action of JH may have been important for the evolution of the larval stage. Studies on embryos of basal, hemimetabolous insects show that their premature exposure to JH can truncate patterning programs and cause precocious tissue maturation, factors essential for organizing a novel larval form. This suppression of embryonic patterning then results in embryonic fields that remain dormant as long as JH is present. These are the primordia that can transform into imaginal discs once JH disappears in preparation for metamorphosis.

Construction of a cysteine protease deficient Bombyx mori multiple nucleopolyhedrovirus bacmid and its application to improve expression of a fusion protein

The bacmid system of BmMNPV with cysteine protease gene deletion (CPD-BmMNPV bacmid) was constructed using the lambda recombination system. The protease activities of Bombyx mori cells and silkworm larvae infected with this CPD-BmMNPV bacmid were reduced by 94% and 85%, respectively. By using this system, a GFP(uv)-beta1,3-N-acetylglucosaminyltransferase 2 (GFP(uv)-beta3GnT2) fusion protein was successfully expressed in silkworm larvae with less protein degradation and without larvae liquefaction; beta3GnT activity improved 30%. This CPD-BmMNPV bacmid system provides rapid protein production in silkworms and can be used for the production of recombinant eukaryotic proteins without proteolytic degradation.

Enhanced production of secretory beta1,3-N-acetylglucosaminyltransferase 2 fusion protein into hemolymph of Bombyx mori larvae using recombinant BmNPV bacmid integrated signal sequence

The enhanced secretion of beta1,3-N-acetylglucosaminyltransferase 2 (beta3GnT2) fusion protein into the hemolymph of Bombyx mori larvae was studied using a recombinant B. mori nucleopolyhedrovirus (BmNPV) bacmid integrating seven signal sequences. When the BmNPV bacmid encoding the signal sequences from the silkworm B. mori bombyxin (bx) and B. mori prophenoloxidase-activating enzyme (ppae) was injected into silkworm larvae, 56.1 and 51.5mU/ml beta3GnT, respectively, were secreted into the hemolymph of silkworm larvae. For bx, 97.3% of the total beta3GnT activity was secreted into hemolymph, and only 1.1% remained in the intestines of silkworm larvae. For ppae, 90.8% of the total beta3GnT activity was secreted to the hemolymph, but 7.8% remained in the intestines of silkworm larvae. Using the BmNPV bacmid encoding bx, the amount of secreted beta3GnT was 91mug per larva, which was 2.5% of the total amount of protein in the hemolymph.

Three insulin-relaxin-like genes in Ciona intestinalis

The Ciona intestinalis genome harbors three insulin-like genes: INS-L1, -L2 and -L3. Conserved synteny between the Ciona-human genomes predicts that Ciona INS-Ls are orthologous to the vertebrate insulin-relaxin family, but this relation cannot be inferred from molecular phylogeny. A conserved protein core with six cysteines; typical arrangement of B-, C- and A-protein domains; pro-protein maturation mode; and putative insulin receptor-binding sites were identified in Ciona INS-L proteins. ESTs used to assemble exonic sequences of INS-Ls combined with qRT-PCR analysis provided evidence that the predicted genes are expressed in the developing and adult Ciona. Our results support that Ciona INS-L1 is orthologous to the vertebrate insulin-like/relaxin genes, INS-L2 to insulin genes and INS-L3 to IGF genes. Our analysis also implies that the insulin-like/relaxin ancestor switched receptor type from tyrosine kinase- to GPCR-type, whereas insulin-IGF subfamily retained the tyrosine kinase-type of receptor. We propose that this receptor-switch occurred after the time when urochordates branched from the common chordate lineage, but before the two genome-duplications at the root of the vertebrates.

Signaling and function of insulin-like peptides in insects

Insulin-like peptides (ILPs) exist in insects and are encoded by multigene families that are expressed in the brain and other tissues. Upon secretion, these peptides likely serve as hormones, neurotransmitters, and growth factors, but to date, few direct functions have been demonstrated. In Drosophila melanogaster, molecular genetic studies have revealed elements of a conserved insulin signaling pathway, and as in other animal models, it appears to play a key role in metabolism, growth, reproduction, and aging. This review offers (a) an integrated summary of the efforts to characterize the distribution of ILPs in insects and to define this pathway and its functions in Drosophila and (b) a few considerations for future studies of ILP endocrinology in insects.

Functional expression of lepidopteran-selective neurotoxin in baculovirus: potential for effective pest management

Recombinant baculovirus expressing insect-selective neurotoxins derived from venomous animals are considered as an attractive alternative to chemical insecticides for efficient insect control agents. Recently we identified and characterized a novel lepidopteran-selective toxin, Buthus tamulus insect-selective toxin (ButaIT), having 37 amino acids and eight half cysteine residues from the venom of the South Indian red scorpion, Mesobuthus tamulus. The synthetic toxin gene containing the ButaIT sequence in frame to the bombyxin signal sequence was engineered into a polyhedrin positive Autographa californica nuclear polyhedrosis virus (AcMNPV) genome under the control of the p10 promoter. Toxin expression in the haemolymph of infected larvae of Heliothis virescens and also in an insect cell culture system was confirmed by western blot analysis using antibody raised against the GST-ButaIT fusion protein. The recombinant NPV (ButaIT-NPV) showed enhanced insecticidal activity on the larvae of Heliothis virescens as evidenced by a significant reduction in median survival time (ST50) and also a greater reduction in feeding damage as compared to the wild-type AcMNPV.

Novel fish-derived adrenomedullin in mammals: structure and possible function

Adrenomedullin (AM) has been recognized as a member of the calcitonin (CT)/CT gene-related peptide (CGRP) family. However, an independent AM family consisting of five paralogous peptides exists in teleost fish. Among them, the peptide named AM1 is an ortholog of mammalian AM as determined by the linkage analysis of orthologous genes and the presence of proAM N-terminal 20 peptide (PAMP)-like sequence in the prosegment. Since the peptides named AM2 and 3 are distinct from other members with respect to the precursor sequence, tissue distribution of the transcripts, and exon-intron organization, we searched for their mammalian orthologs from genome databases, which resulted in an identification of AM2 in human, rat, and mouse. AM2 was expressed abundantly in the submaxillary gland, kidney, and some vascular and digestive tissues of mice. AM2 injected in vivo induced potent cardiovascular and renal effects in mice. In the heart and kidney of mice, AM2 was localized in endothelial cells of the coronary vessels and in glomeruli and vasa recta, respectively. AM2 increased cAMP accumulation in cells expressing human CT receptor-like receptor (CRLR) and one of receptor activity-modifying proteins (RAMPs), but it was no more potent than CGRP and AM. AM2 was also less potent than CT in cells expressing CT receptor and RAMP. There remains a possibility that a new AM2-specific receptor or an additional RAMP that enables CRLR to be an AM2-specific receptor, exists in mammals.

Heterologous expression of maize (Zea mays L.) Mir1 cysteine proteinase in eukaryotic and prokaryotic expression systems

Several heterologous expression systems were tested for their ability to express a unique maize cysteine proteinase Mir1. A baculovirus-based expression system using Trichoplusia ni larvae as host resulted in the expression of Mir1 that was correctly processed and exhibited proteinase activity. Expression in Escherichia coli resulted in accumulation of Mir1, but it had limited solubility and enzymatic activity. Large quantities of Mir1 were produced when Pichia pastoris was used as the host, but the enzyme was insoluble and inactive.

Insulin-like system and growth regulation in the Pacific oyster Crassostrea gigas: hrIGF-1 effect on protein synthesis of mantle edge cells and expression of an homologous insulin receptor-related receptor

The involvement of molecules belonging to the insulin/IGF family in regulation of growth has been investigated in the Pacific oyster Crassostrea gigas. In vitro biological effects of human recombinant IGF-1 (hrIGF-1) on mantle edge cells, involved in oyster shell and soft body growth, were studied over an annual cycle. In mantle edge cells hrIGF-1 stimulates protein synthesis of 56+/-5.1% over basal for 10(-10) M in September with in addition a clear dose-effect corresponding to the highest shell growth period, and 57.5+/-3.45% over basal for 10(-11) M in March and 51+/-5.4% over basal for 10(-10) M in April corresponding to the period of mantle growth. These insulin-like effects were associated with the expression of a recently identified C. gigas insulin receptor-related receptor (CIR) in mantle edge cells as demonstrated by RT-PCR. Moreover, in situ hybridisation (ISH) confirmed this expression at the level of the inner and outer epithelia involved in mantle growth and shell formation.

Isolation and biological characterization of a 6-kDa protein from hepatopancreas of lobster Panulirus argus with insulin-like effects

A protein with insulin-like effects was isolated from the hepatopancreas of the lobster Panulirus argus following a classic method for mammalian insulin purification from the pancreas. After acid-alcoholic extraction and ethanol-ether precipitation followed by molecular filtration chromatography, a protein with an apparent molecular weight of 6 kDa was isolated. This protein is characterized by its ability to interact with anti-insulin antibodies and by mimicking insulin actions as the stimulation of glucose oxidation to CO(2) and lipogenesis in isolated rat adipocytes. In addition, this insulin immunoreactive protein (IIP) was able to stimulate the autophosphorylation of the insulin receptor present in rat adipocyte plasma membranes, in a dose-dependent manner. The immunological and biochemical results obtained are consistent with the hypothesis that protein(s) with insulin-like effects occur in the digestive gland of the lobster P. argus and may be of significance to control metabolic and growth related processes in crustaceans.

Cloning, characterization, and embryonic expression analysis of the Drosophila melanogaster gene encoding insulin/relaxin-like peptide

Insulin is one of the key peptide hormones that regulates growth and metabolism in vertebrates. Evolutionary conservation of many elements of the insulin/IGF signaling network makes it possible to study the basic genetic function of this pathway in lower metazoan models such as Drosophila. Here we report the cloning and characterization of the gene for Drosophila insulin/relaxin-like peptide (DIRLP). The predicted protein structure of DIRLP greatly resembles typical insulin structure and contains features that differentiate it from the Drosophila juvenile hormone, another member of the insulin family. The Dirlp gene is represented as a single copy in the Drosophila melanogaster genome (compared to multiple copies for Drosophila juvenile hormone) and shows evolutionary conservation of genetic structure. The gene was mapped to the Drosophila chromosome 3, region 67D2. In situ hybridization of whole-mount Drosophila embryos with Dirlp antisense RNA probe reveals early embryonic mesodermal/ventral furrow expression pattern, consistent with earlier observation of the insulin protein immunoreactivity in Drosophila embryos. The in situ hybridization pattern was found to be identical to that obtained during immunohistochemistry analysis of the Drosophila embryos using various insulin monoclonal and polyclonal antibodies that do not recognize Drosophila juvenile hormone, supporting the idea that Dirlp is a possible Drosophila insulin ortholog. Identification of the gene for DIRLP provides a new approach for study of the regulatory pathway of the insulin family of peptides.

Platelet-derived growth factor and transforming growth factor-beta in invertebrate immune and neuroendocrine interactions: another sign of conservation in evolution

Growth factor-like molecules have been found in various invertebrate species. In particular, we have reported the presence of platelet-derived growth factor (PDGF)-AB and transforming growth factor-beta (TGF-beta)1 immunoreactive molecules in molluscs, insects and annelids. Moreover, PDGF-AB and TGF-beta1 affect the main immune functions, such as phagocytosis, chemotaxis and cell motility. Changes in cell shape are induced via interactions of growth factors with their respective specific receptors. The extracellular signals are transduced by the activation of classical signal transduction pathways, such as those involving PKA and PKC, and pivotal transcription regulators, i.e. the Fos, Jun and SMAD proteins. The two growth factors intervene in stress responses by activating the CRH-ACTH-biogenic amine axis. Exogenous administration of PDGF-AB and TGF-beta1 in a molluscan wound provokes an accelerated migration of immunocytes and fibroblasts to the injured area, stimulating granulation tissue formation and wound re-epithelialization. These findings suggest that these molecules are ancestral and that their function is well conserved and crucial in the maintenance of invertebrate homeostasis.

The characterization of prepro-Insulin-like growth factor-1 Ea-2 expression and Insulin-like growth factor-1 genes (devoid 81 bp) in the zebrafish ( Danio rerio )

In this study, we cloned zebrafish (Danio rerio) IGF-1 cDNA and gene from zebrafish brain cDNA library and adult zebrafish genomic library, respectively. Based on two cDNAs sequence with different length of 5'- and 3'-untranslated region (5UTR and 3UTR) and one nucleotide difference at glutamine (A9, CAG) of A domain represented at IGF-1 sequence. One of zebrafish IGF-1 genes named as IGF-1a gene. The zebrafish IGF-1a gene spanned approximately 15 kb and is divided into five exons. The results of IGF-1 cDNA and genomic Southern blotting, all indicated that the zebrafish have more than one IGF-1 gene. The genomic organization of zebrafish IGF-1a gene in an exon is devoid of 81 bp segment which is located at 3' end of exon 3 encoded 27 amino acid of E domain. The segment of 27 amino acid exists in known teleost IGF-1 genes but is absent in zebrafish IGF-1 gene. The E domain of zebrafish IGF-1 Ea-2 is encoded by 3' end of exon 3 (16 amino acid), full of exon 4 (12 amino acid) and exon 5 (19 amino acid). The sequence data revealed the zebrafish IGF-1a gene encoded IGF-1a Ea-2 mRNA. In combination RT-PCR with Southern blotting, zebrafish IGF-1 genes abundantly expressed IGF-1 Ea-2 mRNA in all tested adult tissues and developmental stages of embryo. The IGF-1 Ea-2 mRNA was first detected during embryo development from blastula stage to hatching, during yolk absorption and at feeding. All these findings suggest that the expression of pro-IGF-1 Ea-2 is not controlled by alternative splicing but alternative gene usage in the zebrafish.

Neuropeptides and their precursors in the fruitfly, Drosophila melanogaster

Neuropeptides form the most diverse class of chemical messenger molecules in metazoan nervous systems. They are usually generated from biosynthetic precursor polypeptides by enzymatic processing and modification. Many different peptides belonging to a number of distinct neuropeptide families have already been characterized from various insect species. The Drosophila Genome Sequencing Project has important implications for the future of neurobiological research. This paper describes the discovery of several new fruitfly neuropeptides by an in silico data mining approach. In addition, the state-of-the-art of Drosophila peptide research is reviewed.

Molecular cloning and characterization of a new insulin/IGF-like peptide of the nematode Caenorhabditis elegans

Diapause, aging, and fat accumulation in Caenorhabditis elegans are regulated by DAF-2, a homolog of mammalian insulin/insulin-like growth factor-I (IGF-I) receptors. We have cloned and characterized a C. elegans gene encoding a new insulin/IGF-like peptide. The gene containing three exons encodes a precursor protein 95 residue long. Although the putative precursor contains a signal peptide, B chain, C peptide, and A chain like the preproinsulin, the mature peptide consists of one polypeptide-like IGF. The predicted tertiary structure seems similar to crystal structure of insulin. Therefore, the peptide may be a hybrid molecule of insulin and IGF. The peptide expression was detected at the embryonic and several larval stages. Disruption of the peptide production led to an extended life span like the daf-2 mutation, suggesting that the peptide should be one of the ligands of the DAF-2. This is the first description of the peptide that mediates animal longevity.

Prothoracicotropic activity of SBRPs, the insulin-like peptides of the saturniid silkworm Samia cynthia ricini

Synthesis and secretion of the insect molting hormone ecdysteroid in the prothoracic glands (PGs) are stimulated by the prothoracicotropic hormone (PTTH) secreted by the brain. Bombyxins, insulin-like peptides of the silkworm Bombyx mori, show prothoracicotropic activity when administered to the saturniid silkworm Samia cynthia ricini, but they are inactive to B. mori itself. Recently, the genes for the bombyxin homologs of S. cynthia ricini (referred to as Samia bombyxin-related peptides, SBRPs) were cloned. To examine the prothoracicotropic activity of SBRPs on S. cynthia ricini, we synthesized two representative molecules, SBRP-A1 and -B1. They promoted pupa-to-adult development with ED(50) of 50 and 10 ng/pupa (EC(50) of 5 and 1 nM), respectively.

The phylogeny of the insulin-like growth factors

The insulin-like growth factors are major regulators of growth and development in mammals and their presence in lower vertebrates suggests that they played a similarly fundamental role throughout vertebrate evolution. While originally perceived simply as mediators of growth hormone, on-going research in mammals has revealed several hierarchical layers of complexity in the regulation of ligand bioavailability and signal transduction. Our understanding of the biological role and mechanisms of action of these important growth factors in mammals patently requires further elucidation of the IGF hormone system in the simple model systems that can be found in lower vertebrates and protochordates. This review contrasts our knowledge of the IGF hormone system in mammalian and nonmammalian models through comparison of tissue and developmental distributions and gene structures of IGF system components in different taxa. We also discuss the evolutionary origins of the system components and their possible evolutionary pathways.

Baculovirus expression of an insect gene that encodes multiple neuropeptides

Sex pheromone production in the corn earworm, Helicoverpa zea, is regulated by a 33-amino-acid neuropeptide named Hez-PBAN (pheromone biosynthesis activating neuropeptide). Hez-PBAN is encoded in a preprohormone that also contains four other structurally related peptides. Two recombinant baculoviruses that contain two different sequences of Hez-PBAN cDNA under the control of a strong polyhedrin promotor were constructed. The first virus, AcWT-PBAN, contains the entire prepro-Hez-PBAN coding sequence. The second virus, AcBX-PBAN, contains a synthetic chimera gene encoding a bombyxin signal peptide sequence fused to a pro-Hez-PBAN sequence. Cell extracts, culture medium of BTI-TN-5B1-4 cells, and hemolymph from 4th instar Trichoplusia ni larvae, all infected with AcBX-PBAN, showed a high level of pheromonotropic activity. Pheromonotropic activity was not detected in the cells infected with AcWT-PBAN. Results of chromatographic and immunochemical studies showed that some of the potential processing sites in the expressed pro-Hez-PBAN sequence were not used during posttranslational processing in the AcBX-PBAN-4-infected BTI-TN-5B1-4 cells and 4th instar T. ni larvae. However, the processing pattern of the recombinant pro-Hez-PBAN in AcBX-PBAN-infected 4th instar T. ni larvae was similar to that exhibited in the central nervous system of H. zea adult females, since a PBAN-like immunoreactive-peptide-band was found in the hemolymph of Ac-BX-PBAN-4-infected 4th instar T. ni larvae. In a droplet feeding assay, neonate and 3rd instar T. ni larvae infected with AcBX-PBAN-4 showed a significant reduction in survival time (26% and 19%, respectively) when compared to control larvae that were infected with a polyhedrin-deficient virus, Ac-E10.

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.

Bombyxin, an insulin-related peptide of insects, reduces the major storage carbohydrates in the silkworm Bombyx mori

The effects of an insect insulin-related peptide, bombyxin, on carbohydrate metabolism were investigated in the silkworm Bombyx mori. Bombyxin lowered the concentration of the major hemolymph sugar, trehalose, in a dose-dependent manner when injected into neck-ligated larvae. Bombyxin also caused elevated trehalase activity in the midgut and muscle, suggesting that bombyxin induces hypotrehalosemia by promoting the hydrolysis of hemolymph trehalose to glucose and thereby facilitating its transport into tissues. In addition, bombyxin reduced the glycogen content in the fat body and concurrently raised the percentage of active glycogen phosphorylase in this tissue. Because hemolymph trehalose is also a major storage form of carbohydrate in insects, our results indicate that bombyxin reduces the amount of both principal storage carbohydrates in B. mori larvae. It is therefore suggested that although bombyxin is involved in the control of carbohydrate metabolism like insulin, the physiological role of bombyxin in insects is different from that of insulin in mammals.

Ancient divergence of insulin and insulin-like growth factor

Studies on the evolutionary pathway of the insulin gene family suggest that insulin and insulin-like growth factor (IGF) became distinct molecules only after the vertebrates arose. A single molecule with identity to both insulin and IGF was reported in amphioxus. To study the origin of insulin, we selected tunicates because their ancestors are thought to be a nodal point in the evolution of vertebrates. This is the first report of separate insulin and IGF molecules from invertebrates. Two cDNAs were isolated from the tunicate Chelyosoma productum: One cDNA encodes a distinct preproinsulin with B, C, and A domains, whereas the other encodes tunicate preproIGF, including all five domains in their proper sequence. Both mRNAs are expressed in the nervous system, digestive tract, heart, and possibly the gonad but not in branchial basket or tunic. Hence, insulin and igf genes have similar expression patterns. In situ methods confirm the polymerase chain reaction evidence that tunicate insulin and igf mRNAs are expressed in cortical cells of the neural ganglion. We conclude that insulin and IGF have maintained separate gene lineages in both vertebrate and protochordate evolution and, thus, a distinct evolutionary history of more than 600 million years.

Structure and expression of bombyxin E1 gene: a novel family gene that encodes bombyxin-IV, an insect insulin-related neurosecretory peptide

A bombyxin gene encoding precursor molecule for bombyxin-IV, one of the insulin-related neurosecretory peptide of the silkmoth Bombyx mori, has been cloned and characterized. The nucleotide sequence of this gene and its deduced amino acid sequence deviate moderately from those characterized previously for the family A, B, C and D bombyxin genes. The gene encoding the bombyxin-IV precursor was therefore defined into a novel family E and designated as gene E1. The bombyxin E1 transcript in Bombyx brain was shown to locate in four pairs of medial neurosecretory cells, which also produce other bombyxin family mRNAs, and the amount of the E1 transcript did not change markedly during the fifth larval instar. Genomic Southern hybridization indicated that the Bombyx haploid genome contained a single copy of the bombyxin family E gene.

The prothoracicotropic hormone bombyxin has specific receptors on insect ovarian cells

Bombyxin II, a product of the brain of the adult silkmoth, Bombyx mori, binds to ovarian cells of three different species of lepidoptera, i.e. B. mori (silkmoth), Samia cynthia ricini (ailanthus moth), and an ovarian cell line of Spodoptera frugiperda (Sf9) (fall armyworm). Crude Sf9 cell membrane preparations were used to show that the purported bombyxin receptor binds its ligand in a specific, saturable, and reversible manner. The dissociation constant of the bombyxin-receptor complex is 260+/-90 pM. Quantitative binding studies and Scatchard analysis suggest that every Sf9 cell displays 20000 receptors on the surface. The cross-linked bombyxin-receptor ligand complex has an apparent molecular mass of about 300 kDa as determined by SDS/PAGE. Reduction causes the bombyxin receptor to dissociate into two subunits with molecular masses of 90 kDa and 116 kDa. The size and subunit structure of the putative bombyxin receptor on Sf9 cells show some similarities to the mammalian insulin receptor.

The effects of insulin/IGF-I on glucose and leucine metabolism in the redclaw crayfish (Cherax quadricarinatus)

In recent years, invertebrate peptides have been identified which share substantial homologies with vertebrate insulin and insulin-like growth factors (IGFs), indicating a high degree of conservation of insulin/IGF systems through animal evolution. In a previous study, we provided evidence for the presence of IGF-I-like peptides in the redclaw (Cherax quadricarinatus), a species of freshwater crayfish endemic to northern Australia river systems which has attained support as a culture species. The general aim of the current study was to elucidate the functional significance of IGF-I-like peptides in this species by examining the effects of mammalian IGF-I on glucose and leucine metabolism. Juvenile redclaw were injected with a single dose of purified human insulin, recombinant human (rh) IGF-I, or Des-1-3-IGF-I. Glucose levels in redclaw tissues were then determined over an 8-hr period using enzymatic approaches. It was shown that injection of rhIGF-I induced an acute increase in free glucose content in hepatopancreas while Des-1-3-IGF-I and insulin raised free glucose levels in abdominal muscle. Radiolabel tracer approaches also demonstrated that injection of rhIGF-I increased glycogen synthesis in abdominal muscle and elevated the incorporation of leucine into protein in both abdominal muscle and hepatopancreas. Taken together, the findings of this study suggest that IGF-I-like peptides are biologically active in this species and may be of significance to metabolic and growth-related processes.

Life cycle expression of a bombyxin-like neuropeptide in the tobacco hornworm, Manduca sexta

Immunocytochemistry was used to investigate the developmental expression of the insulin-like neuropeptide bombyxin in the tobacco hornworm, Manduca sexta. A mouse monoclonal antibody raised against a synthetic peptide corresponding to bombyxin's A-chain N-terminus was used to localize a bombyxin-like peptide to a group of cerebral medial neurosecretory cells, the M-NSC IIa(2). Immunostaining was first detected on day 0 of the second larval instar, localized in the M-NSC IIa(2) somata and in the neurohemal organ, the corpora allata (CA). By day 0 of the fourth larval instar, the peptide was present throughout the M-NSC IIa(2) somata, axons, dendritic fields and CA. Between days 7 and 9 of the fifth instar, a dramatic reduction in the dendritic fields and CA staining occurred, suggesting the peptide is released. After day 2 of the pupal period, only M-NSC IIa(2) somata immunostained, a pattern that persisted through day 2 of the adult stage. The specificity of immunostaining was demonstrated by using a synthetic bombyxin peptide to block staining. These developmental data reveal times of potential Manduca bombyxin-like peptide release which should provide insight into the peptide's function.

Bombyxin-related peptides: cDNA structure and expression in the brain of the hornworm Agrius convolvuli [corrected]

We have cloned three cDNAs from the sweet potato hornworm Agrius convolvuli that encode precursor molecules for peptides structurally related to bombyxin, an insulin-related brain secretory peptide in Bombyx mori. The Agrius bombyxin-related peptide (ABRP) cDNAs are classified into type A and B according to their sequence similarity. The prepro-ABRPs deduced from the cDNA sequences have the insulin-like domain organization of signal peptide/B chain/C peptide/A chain. The ABRP transcripts in Agrius brain were shown to locate in four pairs of medial neurosecretory cells, the homologous group of neurosecretory cells that produce bombyxins in Bombyx brain. Genomic Southern analysis indicated the presence of multiple copies of ABRP gene in the Agrius genome. Results showed that the ABRP genes are remarkably different from the vertebrate insulin genes in the number of copy and spatial localization of the transcripts.

Structure and expression of the gene for the prothoracicotropic hormone of the silkmoth Bombyx mori

We cloned and characterized two allelic variants of the gene for the Bombyx mori prothoracicotropic hormone (PTTH), a homodimeric 30-kDa brain secretory protein. These PTTH genes contain five exons that encode a precursor protein consisting of 224 amino acid residues whose C-terminal 109 residues represent the PTTH subunit. The Bombyx haploid genome contains a single copy of the PTTH gene. The major site of PTTH expression is the brain but expression at a very low level occurs in the gut. One Bombyx brain at day 0 of the fifth larval instar contained 2.4-2.8 pg PTTH mRNA, and this amount did not change markedly during larval-pupal development.

Insulin-like molecules in the beetle Tenebrio molitor

Immunocytochemical staining of the nervous system of larva, pupa, and adult stage of Tenebrio molitor with anti-insulin serum demonstrated insulin-like peptides in the protocerebrum, corpora allata, and suboesophageal ganglion. During pupal development, marked changes in staining intensity of the protocerebral cells were detected. The staining pattern suggests release of insulin-like peptides early on day 0 and again on day 3 of the stadium. Injections of anti-insulin at these times caused significant delays in the timing of pupal/adult ecdysis. An immunoblot of haemolymph from day-3 pupae revealed a 6.5-kDa insulin-like molecule. These results suggest that the prothoracicotropic hormone of T. molitor is an insulin-like molecule.

Mitogenicity of the earthworm's (Eisenia foetida) insulin-like proteins

1. Biologically active glycolipoprotein complex (G-90), isolated from whole earthworm tissue extract (Eisenia foetida), was separated into seven fractions by gel-filtration. 2. It has been shown by radioimmunoassay that each of the fractions, except the lightest one, is cross-reactive with porcine anti-insulin antibodies. Molecules that possess such activity were detected by immunoblotting. 3. All fractions, except the heaviest and the lightest one, stimulate mammalian normal and transformed cell proliferation in serum-free conditions in vitro. The intensity of stimulation depends on cell type. Stimulation is completely abolished if the medium is supplemented with fetal calf serum.

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.