Amino acid sequence of a prothoracicotropic hormone of the silkworm Bombyx mori

Identification and functional characterization of insulin-like peptides in a pine beetle

Insulin - including insulin-like peptides (ILPs), relaxins and insulin-like growth factors (IGFs) - is an evolutionarily conserved hormone in all metazoans It is involved in various physiological processes, such as metabolism, growth, reproduction, lifespan and stress resistance. However, there are no reports on the functional role of ILPs in the Chinese white pine beetle, Dendroctonus armandi. In this study, we have cloned and identified two ILP cDNAs in D. armandi. The expression levels of DaILP1 and DaILP2 were significantly changed in different developmental stages. Both ILPs were expressed mostly in the head and fat body. Moreover, starvation induces the reduction of ILP1 mRNA level in adults and larvae, while ILP2 only in larvae of D. armandi, respectively. Additionally, RNA-interference (RNAi) using double stranded RNA to knock down ILP1 and ILP2 reduced the mRNA levels of the target genes, and caused a significant reduction in body weight of D. armandi. Moreover, silencing ILP1 led to an increase of trehalose and glycogen and significantly enhanced starvation resistance in both adults and larvae. The results show that the ILP signaling pathway plays a significant role in growth and carbohydrate metabolism of D. armandi and may provide a potential molecular target for pest control.

Localization of SNARE proteins in the brain and corpus allatum of Bombyx mori

Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) make up the core machinery that mediates membrane fusion. SNAREs, syntaxin, synaptosome-associated protein (SNAP), and synaptobrevin form a tight SNARE complex that brings the vesicle and plasma membranes together and is essential for membrane fusion. The cDNAs of SNAP-25, VAMP2, and Syntaxin 1A from Bombyx mori were inserted into a plasmid, transformed into Escherichia coli, and purified. We then produced antibodies against the SNAP-25, VAMP2, and Syntaxin 1A of Bombyx mori of rabbits and rats, which were used for immunohistochemistry. Immunohistochemistry results revealed that the expression of VAMP2 was restricted to neurons in the pars intercerebralis (PI), dorsolateral protocerebrum (DL), and central complex (CX) of the brain. SNAP-25 was restricted to neurons in the PI and the CX of the brain. Syntaxin 1A was restricted to neurons in the PI and DL of the brain. VAMP2 co-localized with SNAP-25 in the CX, and with Syntaxin 1A in the PI and DL. VAMP2, SNAP-25, and Syntaxin 1A are present in the CA. Bombyxin-immunohistochemical reactivities (IRs) of brain and CA overlapped with VAMP2-, SNAP-25, and Syntaxin 1A-IRs. VAMP2 and Syntaxin 1A are present in the prothoracicotropic hormone (PTTH)-secretory neurons of the brain.

The insulin signaling pathway a century after its discovery: Sexual dimorphism in insulin signaling

Since practically a century ago, the insulin pathway was discovered in both vertebrates and invertebrates, implying an evolutionarily ancient origin. After a century of research, it is now clear that the insulin signal transduction pathway is a critical, flexible and pleiotropic pathway, evolving into multiple anabolic functions besides glucose homeostasis. It regulates paramount aspects of organismal well-being like growth, longevity, intermediate metabolism, and reproduction. Part of this diversification has been attained by duplications and divergence of both ligands and receptors riding on a common general signal transduction system. One of the aspects that is strikingly different is its usage in reproduction, particularly in male versus female development and fertility within the same species. This review highlights sexual divergence in metabolism and reproductive tract differences, the occurrence of sexually "exaggerated" traits, and sex size differences that are due to the sexes' differential activity/response to the insulin signaling pathway.

Molecular identification and putative role of insulin growth factor binding protein-related protein (IGFBP-rp) in the swimming crab Portunus trituberculatus

The insulin-like growth factor/insulin-like polypeptide (IGF/ILP) signaling is vital for growth, physiological metabolism, development, and reproduction. Insulin-like growth factor-binding protein (IGFBP) is involved in the insulin signaling pathway in both vertebrates and invertebrates and is critical for various physiology functions. Herein, we cloned and characterized the full-length cDNA of IGFBP-rp in the swimming crab, Portunus trituberculatus (PtIGFBP-rp). The deduced amino acid sequence of PtIGFBP-rp was found to contain three key domains (insulin-like binding (IB) domain, the kazale-type serine protease inhibitor (KAZAL) domain, and the immunoglobulin-like C2 (IGc2) domain). Results showed that PtIGFBP-rp shared the same expression pattern as P. trituberculatus insulin androgenic gland hormone (PtIAG) transcripts during the embryonic larval, juvenile crab stage and the androgenic gland (AG) developmental cycle. Moreover, PtIGFBP-rp transcripts were also present in high abundance in hepatopancreas, muscle, and androgenic glands. The regulatory relationship between PtIGFBP-rp and PtIAG was investigated by RNA interference and co-localization assays, which showed a co-localization relationship and feedback regulation between them. Bilateral eye stalk ablation (ESA) increased the expression of PtIGFBP-rp in the AG at 7 d after surgery. These results demonstrate the involvement of PtIGFBP-rp in the signaling regulatory network of IAG in P. trituberculatus.

Interorgan communication through peripherally derived peptide hormones in Drosophila

In multicellular organisms, endocrine factors such as hormones and cytokines regulate development and homoeostasis through communication between different organs. For understanding such interorgan communications through endocrine factors, the fruit fly Drosophila melanogaster serves as an excellent model system due to conservation of essential endocrine systems between flies and mammals and availability of powerful genetic tools. In Drosophila and other insects, functions of neuropeptides or peptide hormones from the central nervous system have been extensively studied. However, a series of recent studies conducted in Drosophila revealed that peptide hormones derived from peripheral tissues also play critical roles in regulating multiple biological processes, including growth, metabolism, reproduction, and behaviour. Here, we summarise recent advances in understanding target organs/tissues and functions of peripherally derived peptide hormones in Drosophila and describe how these hormones contribute to various biological events through interorgan communications.

Insulin and Memory in Invertebrates

Insulin and insulin-like peptides (ILP) help to maintain glucose homeostasis, whereas insulin-like growth factor (IGF) promotes the growth and differentiation of cells in both vertebrates and invertebrates. It is sometimes difficult to distinguish between ILP and IGF in invertebrates, however, because in some cases ILP has the same function as IGF. In the present review, therefore, we refer to these peptides as ILP/IGF signaling (IIS) in invertebrates, and discuss the role of IIS in memory formation after classical conditioning in invertebrates. In the arthropod Drosophila melanogaster, IIS is involved in aversive olfactory memory, and in the nematode Caenorhabditis elegans, IIS controls appetitive/aversive response to NaCl depending on the duration of starvation. In the mollusk Lymnaea stagnalis, IIS has a critical role in conditioned taste aversion. Insulin in mammals is also known to play an important role in cognitive function, and many studies in humans have focused on insulin as a potential treatment for Alzheimer’s disease. Although analyses of tissue and cellular levels have progressed in mammals, the molecular mechanisms, such as transcriptional and translational levels, of IIS function in cognition have been far advanced in studies using invertebrates. We anticipate that the present review will help to pave the way for studying the effects of insulin, ILPs, and IGFs in cognitive function across phyla.

Bombyxin II Regulates Glucose Absorption and Glycogen Synthesis through the PI3K Signaling Pathway in HepG2 Cells

Bombyxin, as an insulin-like insect hormone, was discovered in the silkmoth Bombyx mori. It can regulate the metabolism of trehalose and glycogen in Bombyx mori, but whether it has glucose absorption and glycogen synthesis effect on mammalian cells was not clear. BombyxinII (BbxII) and mutant BbxII (mBbxII) genes were cloned into pcDNA3.1(+) vector, respectively; then, gene vectors were transfected into 293FT cells using Lipofectamine 2000. Levels of mRNA and protein expression of BbxII and mBbxII were detected by PCR and Western blot in 293FT cells, respectively. Glucose consumption and glycogenesis were determined by glucose oxidase-peroxidase (GOD-POD) and periodic acid-Schiff (PAS) staining in HepG2 cells; the PI3K signaling pathway was inhibited with wortmannin S1952 in HepG2 cells. Result showed that BbxII and mBbxII genes were being successfully expressed in 293FT cells, respectively. The expression protein of BbxII gene is 10kd pre-bombyxinII, and yet, the expression protein of mBbxII gene is 4kd mature bombyxinII. Only the 4kd bombyxinII showed increased glucose uptake and glycogenesis in HepG2 cells, and the ability of increasing glucose uptake was equal to the human insulin (10 nM). PI3K-wortmannin S1952 inhibitor can decrease the glycogen synthesis induced by bombyxin II protein in HepG2 cells. In conclusion, mature bombyxin II may adjust glucose absorption and glycogen synthesis in HepG2 cells through the PI3K signaling pathway.

Regulation of ecdysone production in Drosophila by neuropeptides and peptide hormones

In both mammals and insects, steroid hormones play a major role in directing the animal's progression through developmental stages. To maximize fitness outcomes, steroid hormone production is regulated by the environmental conditions experienced by the animal. In insects, the steroid hormone ecdysone mediates transitions between developmental stages and is regulated in response to environmental factors such as nutrition. These environmental signals are communicated to the ecdysone-producing gland via the action of neuropeptide and peptide hormone signalling pathways. While some of these pathways have been well characterized, there is evidence to suggest more signalling pathways than has previously been thought function to control ecdysone production, potentially in response to a greater range of environmental conditions. Here, we review the neuropeptide and peptide hormone signalling pathways known to regulate the production of ecdysone in the model genetic insect Drosophila melanogaster, as well as what is known regarding the environmental signals that trigger these pathways. Areas for future research are highlighted that can further contribute to our overall understanding of the complex orchestration of environmental, physiological and developmental cues that together produce a functioning adult organism.

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.

Arthropod IGF, relaxin and gonadulin, putative orthologs of Drosophila insulin-like peptides 6, 7 and 8, likely originated from an ancient gene triplication

BACKGROUND

Insects have several genes coding for insulin-like peptides and they have been particularly well studied in Drosophila. Some of these hormones function as growth hormones and are produced by the fat body and the brain. These act through a typical insulin receptor tyrosine kinase. Two other Drosophila insulin-like hormones are either known or suspected to act through a G-protein coupled receptor. Although insulin-related peptides are known from other insect species, Drosophila insulin-like peptide 8, one that uses a G-protein coupled receptor, has so far only been identified from Drosophila and other flies. However, its receptor is widespread within arthropods and hence it should have orthologs. Such putative orthologs were recently identified in decapods and have been called gonadulins.

METHODOLOGY

In an effort to identify gonadulins in other arthropods public genome assemblies and short-read archives from insects and other arthropods were explored for the presence of genes and transcripts coding insulin-like peptides and their putative receptors.

RESULTS

Gonadulins were detected in a number of arthropods. In those species for which transcriptome data from the gonads is available insect gonadulin genes are expressed in the ovaries and at least in some species also in the testes. In some insects differences in gonadulin expression in the ovary between actively reproducing and non-reproducing females differs more than 100-fold. Putative orthologs of Drosophila ilp 6 were also identified. In several non-Dipteran insects these peptides have C-terminally extensions that are alternatively spliced. The predicted peptides have been called arthropod insulin-like growth factors. In cockroaches, termites and stick insects genes coding for the arthropod insulin-like growth factors, gonadulin and relaxin, a third insulin-like peptide, are encoded by genes that are next to one another suggesting that they are the result of a local gene triplication. Such a close chromosomal association was also found for the arthropod insulin-like growth factor and gonadulin genes in spiders. Phylogenetic tree analysis of the typical insulin receptor tyrosine kinases from insects, decapods and chelicerates shows that the insulin signaling pathway evolved differently in these three groups. The G-protein coupled receptors that are related to the Drosophila ilp 8 receptor similarly show significant differences between those groups.

CONCLUSION

A local gene triplication in an early ancestor likely yielded three genes coding gonadulin, arthropod insulin-like growth factor and relaxin. Orthologs of these genes are now commonly present in arthropods and almost certainly include the Drosophila insulin-like peptides 6, 7 and 8.

Molecular characterization of insulin-like peptides in the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

Insulin-like peptides (ILPs) including insulin, insulin-like growth factor (IGF) and relaxin are evolutionarily conserved hormones in metazoans, and they are involved in diverse physiological processes. The migratory brown planthopper (BPH), Nilaparvata lugens, encodes four ILP genes (Nlilp1, Nlilp2, Nlilp3 and Nlilp4) but their physiological roles are largely unknown. Sequence analysis showed that NlILP1 contained a relaxin-specific G protein-coupled receptor-binding motif and a variant motif of cysteine residues, and NlILP2 and NlILP4 resembled vertebrate IGFs. RNA interference (RNAi)-mediated gene silencing showed that depletion of each of Nlilp1, 2 and 3 significantly delayed the developmental duration of nymphs, and this effect could be exacerbated by double or triple gene depletion. Depletion of Nlilp1, Nlilp2 or Nlilp3 induces the accumulation of glucose, trehalose and glycogen, which is contradictory to depletion of the insulin receptor (NlInR1) in the BPH. Depletion of Nlilp1 significantly enhanced starvation resistance in both females and males although its extent was smaller than NlInR1 depletion. A parental RNAi assay showed that depletion of each of Nlilp1-4 dramatically impaired female fecundity. These findings indicate that NlILP1-4 have redundant and distinct roles in physiological processes in the BPH, thereby enhancing our understanding of the contribution of each NlILP to the ecological success of this species in natural habitats.

An insulin-like growth factor-like peptide promotes ovarian development in the silkmoth Bombyx mori

Insulin family peptides are known to be key regulators of growth and metabolism in insects and vertebrates. Insects have two types of insulin family peptides: insulin-like peptides and insulin-like growth factor (IGF)-like peptides (IGFLPs). We recently demonstrated that an IGFLP in the silkmoth, Bombyx mori (BIGFLP) promotes the growth of the genital imaginal disc ex vivo. However, the role of BIGFLP in the regulation of insect growth remains unclear because no in vivo study has been performed. Therefore, we analysed the functions of BIGFLP in vivo by constructing BIGFLP knock-out (KO) B. mori using the clustered regularly interspaced palindromic repeats (CRISPR) and CRISPR-associated protein 9 (CRISPR-Cas9) system. The KO moths exhibited decreased body weights and size of the appendages compared wild-type (wt) moths. Interestingly, KO females also had drastically lower ovary weights and number of eggs than wt females. However, mutant ovaries that were transplanted into wt host pupae reached a similar weight to wt ovaries that were transplanted into the wt hosts, suggesting that IGFLP in the haemolymph promotes ovarian development. These findings show that BIGFLP regulates the growth and development of adult organs, particularly the ovaries, in B. mori.

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.

Regulation of antimicrobial peptide genes via insulin-like signaling pathway in the silkworm Bombyx mori

Antimicrobial peptides (AMPs) are important effector molecules of insect humoral immunity, and expression of AMPs is mainly regulated by the Toll and immune deficiency (IMD) pathways. FoxO, a key downstream regulator of the insulin-like signaling (ILS) pathway, has been recently reported to be involved in the regulation of AMPs in Drosophila melanogaster. In the present study, we investigated AMP gene expression and the regulation pathway controlled by the starvation in the silkworm Bombyx mori. We discovered that antibacterial activity in the hemolymph of B. mori larvae was increased by starvation, and expression of AMP genes (BmCecB6, BmAtta1, BmLeb3 and BmDefB) as well as the ILS target genes (FoxO, InR and Brummer) were strongly activated in the fat body by starvation. Moreover, phosphorylation of Akt kinase was reduced in the Bm-12 cells after starvation, suggesting that the ILS pathway was inhibited by starvation. We then showed that more FoxO protein was present in the cytoplasm than in the nucleus of Bm-12 cells under normal conditions, but more FoxO was detected in the nucleus after cells were starved for 8 h, indicating that FoxO was activated by starvation. In summary, our results indicated that starvation can activate AMP gene expression in B. mori via the ILS/FoxO signaling pathway.

Application of insulin signaling to predict insect growth rate in Maruca vitrata (Lepidoptera: Crambidae)

Insect growth is influenced by two major environmental factors: temperature and nutrient. These environmental factors are internally mediated by insulin/insulin-like growth factor signal (IIS) to coordinate tissue or organ growth. Maruca vitrata, a subtropical lepidopteran insect, migrates to different climate regions and feeds on various crops. The objective of this study was to determine molecular tools to predict growth rate of M. vitrata using IIS components. Four genes [insulin receptor (InR), Forkhead Box O (FOXO), Target of Rapamycin (TOR), and serine-threonine protein kinase (Akt)] were used to correlate their expression levels with larval growth rates under different environmental conditions. The functional association of IIS and larval growth was confirmed because RNA interference of these genes significantly decreased larval growth rate and pupal weight. Different rearing temperatures altered expression levels of these four IIS genes and changed their growth rate. Different nutrient conditions also significantly changed larval growth and altered expression levels of IIS components. Different local populations of M. vitrata exhibited significantly different larval growth rates under the same nutrient and temperature conditions along with different expression levels of IIS components. Under a constant temperature (25°C), larval growth rates showed significant correlations with IIS gene expression levels. Subsequent regression formulas of expression levels of four IIS components against larval growth rate were applied to predict growth patterns of M. vitrata larvae reared on different natural hosts and natural local populations reared on the same diet. All four formulas well predicted larval growth rates with some deviations. These results indicate that the IIS expression analysis explains the growth variation at the same temperature due to nutrient and genetic background.

Molecular identification of an insulin growth factor binding protein (IGFBP) and its potential role in an insulin-like peptide system of the pearl oyster, Pinctada fucata

Insulin-like growth factors (IGFs) play critical roles in regulating metabolism, growth, and reproduction in invertebrates. IGF binding proteins (IGFBPs) serve as major regulators of IGF activity and regulate endocrine system. In the present study, the full-length cDNA of an igfbp was identified from the pearl oyster, Pinctada fucata, using expressed sequence tag (EST) sequence. The 1124bp Pfigfbp cDNA contains a 465bp open reading frame (ORF) encoding a putative protein of 154 amino acids, a 5'-untranslated region (UTR) of 238bp, and a 3'-UTR of 394bp (not including polyA+). Multiple sequence alignment of the deduced IB domain sequences revealed that twelve conserved Cys and ILP binding site in PfIGFBP were well aligned with human IGFBPs1-7, Mizuhopecten yessoensis IGFBP5 and Eriocheir sinensis IGFBP7. Gene expression analysis indicated that Pfigfbp mRNA was expressed in all the tissues and developmental stages examined, with a higher level in the foot than in other tissues and a higher level in the polar body stage and 32-cell stage than in the other stages. Pfigfbp and PfILP (insulin-like peptide) mRNA levels significantly increased in the digestive gland after feeding, while levels were dramatically reduced during a week of food deprivation and increased upon refeeding. In vitro experiments indicated that Pfigfbp mRNA expression in mantle cells was affected by insulin/IGFs (IGF-I, IGF-II). Our data suggests that Pfigfbp may be involved in endocrine signaling in P. fucata via the regulation of insulin-like peptide signaling.

Localization and functional analysis of the insect-specific RabX4 in the brain of Bombyx mori

Rab proteins are small monomeric GTPases/GTP-binding proteins, which form the largest branch of the Ras superfamily. The different Rab GTPases are localized to the cytosolic face of specific intracellular membranes, where they function as regulators of distinct steps in membrane trafficking. RabX4 is an insect-specific Rab protein that has no close homolog in vertebrates. There is little information about insect-specific Rab proteins. RabX4 was expressed in Escherichia coli and subsequently purified. Antibodies against Bombyx mori RabX4 were produced in rabbits for western immunoblotting and immunohistochemistry. Western blotting of neural tissues revealed a single band, at approximately 26 kD. RabX4-like immunohistochemical reactivity was restricted to neurons of the pars intercerebralis and dorsolateral protocerebrum in the brain. Further immunohistochemical analysis revealed that RabX4 colocalized with Rab6 and bombyxin in the corpus allatum, a neuronal organ that secretes neuropeptides synthesized in the brain into the hemolymph. RabX4 expression in the frontal ganglion, part of the insect stomatogastric nervous system that is found in most insect orders, was restricted to two neurons on the outer region and did not colocalize with allatotropin or Rab6. Furthermore, RNA interference of RabX4 decreased bombyxin expression levels in the brain. These findings suggest that RabX4 is involved in the neurosecretion of a secretory organ in Bombyx mori.

In vitro stimulation of vitellogenin expression by insulin in the mud crab, Scylla paramamosain, mediated through PI3K/Akt/TOR pathway

Vitellogenin (vtg) synthesis, known as vitellogenesis, is one of most important processes in the ovarian development of oviparous animals. Recently, multiple insulin-like peptides (ILPs) have been reported in crustacean species due to the application of transcriptome sequencing. In this context, the present study reports that the addition of an exogenous ILP, bovine insulin, stimulates vtg (termed Sp-vtg) expression in hepatopancreatic explants from the mud crab, Scylla paramamosain, by in vitro experiments. Homologous genes of key factors in ILP signaling, Sp-PI3K, Sp-Akt, Sp-Rheb and Sp-TOR, have been isolated in S. paramamosain based on a transcriptome database. Further experiments reveal that the RNAi-mediated Sp-Akt gene knockdown and the inhibitors of Sp-PI3K and Sp-TOR block the stimulation of Sp-vtg expression by insulin. The combined results implicate the endogenous ILP and its corresponding signaling in the regulation of Sp-vtg synthesis in S. paramamosain.

Insulin-like growth factor (IGF)-like peptide and 20-hydroxyecdysone regulate the growth and development of the male genital disk through different mechanisms in the silkmoth, Bombyx mori

It is well established that ecdysteroids play pivotal roles in the regulation of insect molting and metamorphosis. However, the mechanisms by which ecdysteroids regulate the growth and development of adult organs after pupation are poorly understood. Recently, we have identified insulin-like growth factor (IGF)-like peptides (IGFLPs), which are secreted after pupation under the control of 20-hydroxyecdysone (20E). In the silkmoth, Bombyx mori, massive amounts of Bombyx-IGFLP (BIGFLP) are present in the hemolymph during pupal-adult development, suggesting its importance in the regulation of adult tissue growth. Thus, we hypothesized that the growth and development of adult tissues including imaginal disks are regulated by the combined effects of BIGFLP and 20E. In this study, we investigated the growth-promoting effects of BIGFLP and 20E using the male genital disks of B. mori cultured ex vivo, and further analyzed the cell signaling pathways mediating hormone actions. We demonstrate that 20E induces the elongation of genital disks, that both hormones stimulate protein synthesis in an additive manner, and that BIGFLP and 20E exert their effects through the insulin/IGF signaling pathway and mitogen-activated protein kinase pathway, respectively. These results show that the growth and development of the genital disk are coordinately regulated by both BIGFLP and 20E.

A viral histone H4 suppresses insect insulin signal and delays host development

Parasitization by an endoparasitoid wasp, Cotesia plutellae, alters host development of Plutella xylostella by extending larval period and preventing metamorphosis. Insulin signal plays a crucial role in mediating insect development and controlling blood sugar level in insects. In this study, three insulin-like peptide genes (PxILP1-3) were predicted from the genome of P. xylostella. However, only PxILP1 was confirmed to be expressed in P. xylostella. Starvation suppressed the expression level of PxILP1 and up-regulated plasma trehalose level. RNA interference against PxILP1 mimicked starvation effect and extended the larval period of P. xylostella. Parasitized larvae exhibited significantly lower levels of PxILP1 expression compared to nonparasitized larvae. Injection of wasp-symbiotic polydnavirus C. plutellae bracovirus (CpBV) also suppressed PxILP1 expression and extended the larval period. Injection of a viral segment (CpBV-S30) containing a viral histone H4 (CpBV-H4) also suppressed PxILP1 expression. Co-injection of CpBV-S30 and double-stranded RNA (dsCpBV-H4) specific to CpBV-H4 rescued the suppression of PxILP1 expression. Injection of CpBV-S30 significantly extended larval development. Co-injection of CpBV-S30 with dsCpBV-H4 rescued the delay of larval development. Injection of a bovine insulin to parasitized larvae prevented parasitoid development. These results indicate that parasitism of C. plutellae can down-regulate host insulin signaling with the help of parasitic factor CpBV-H4.

Rab proteins in the brain and corpus allatum of Bombyx mori

In eukaryotic cells, Rab guanosine triphosphate-ases serve as key regulators of membrane-trafficking events, such as exocytosis and endocytosis. Rab3, Rab6, and Rab27 control the regulatory secretory pathway of neuropeptides and neurotransmitters. The cDNAs of Rab3, Rab6, and Rab27 from B. mori were inserted into a plasmid, transformed into Escherichia coli, and then subsequently purified. We then produced antibodies against Rab3, Rab6, and Rab27 of Bombyx mori in rabbits and rats for use in western immunoblotting and immunohistochemistry. Western immunoblotting of brain tissue revealed a single band at approximately 26 kDa. Immunohistochemistry results revealed that Rab3, Rab6, and Rab27 expression was restricted to neurons in the pars intercerebralis and dorsolateral protocerebrum of the brain. Rab3 and Rab6 co-localized with bombyxin, an insect neuropeptide. However, there was no Rab that co-localized with prothoracicotropic hormone. The corpus allatum secretes neuropeptides synthesized in the brain into the hemolymph. Results showed that Rab3 and Rab6 co-localized with bombyxin in the corpus allatum. These findings suggest that Rab3 and Rab6 are involved in neurosecretion in B. mori. This study is the first to report a possible relationship between Rab and neurosecretion in the insect corpus allatum.

Insulin/IGF signaling in Drosophila and other insects: factors that regulate production, release and post-release action of the insulin-like peptides

Insulin, insulin-like growth factors (IGFs) and insulin-like peptides (ILPs) are important regulators of metabolism, growth, reproduction and lifespan, and mechanisms of insulin/IGF signaling (IIS) have been well conserved over evolution. In insects, between one and 38 ILPs have been identified in each species. Relatively few insect species have been investigated in depth with respect to ILP functions, and therefore we focus mainly on the well-studied fruitfly Drosophila melanogaster. In Drosophila eight ILPs (DILP1-8), but only two receptors (dInR and Lgr3) are known. DILP2, 3 and 5 are produced by a set of neurosecretory cells (IPCs) in the brain and their biosynthesis and release are controlled by a number of mechanisms differing between larvae and adults. Adult IPCs display cell-autonomous sensing of circulating glucose, coupled to evolutionarily conserved mechanisms for DILP release. The glucose-mediated DILP secretion is modulated by neurotransmitters and neuropeptides, as well as by factors released from the intestine and adipocytes. Larval IPCs, however, are indirectly regulated by glucose-sensing endocrine cells producing adipokinetic hormone, or by circulating factors from the intestine and fat body. Furthermore, IIS is situated within a complex physiological regulatory network that also encompasses the lipophilic hormones, 20-hydroxyecdysone and juvenile hormone. After release from IPCs, the ILP action can be modulated by circulating proteins that act either as protective carriers (binding proteins), or competitive inhibitors. Some of these proteins appear to have additional functions that are independent of ILPs. Taken together, the signaling with multiple ILPs is under complex control, ensuring tightly regulated IIS in the organism.

Insights into insulin-like peptide system in invertebrates from studies on IGF binding domain-containing proteins in the female mud crab, Scylla paramamosain

Insulin-like peptides (ILPs) have been proved to exist extensively in invertebrates and play critical roles in regulating growth, metabolism and reproduction. ILP signaling system has been well defined in insects, with all key components homologous with vertebrate IGF signaling; however, counterparts of IGF binding proteins (IGFBPs) in vertebrates are not included in this system because of lacking sufficient researches in the related aspect. The present study firstly reports the identification of three kinds of invertebrate IGF binding (IB) domain-containing protein genes from the mud crab Scylla paramamosain. Gene expression analysis suggested that they might be closely involved in ovarian development, but with separate roles. Subsequent bioinformatics analysis and in vitro experiments indicated that they are likely to serve as endogenous ILP-specific binding proteins in invertebrates. More importantly, based on the current evidence we inferred that in invertebrate, ILP system might take the place of IGF system in vertebrate species.

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.

Regulation of hemolymph trehalose level by an insulin-like peptide through diel feeding rhythm of the beet armyworm, Spodoptera exigua

Like vertebrate insulins, some insect insulin-like peptides (ILPs) play crucial roles in controlling immature growth, adult lifespan, and hemolymph sugar level. An ILP gene (SeILP1) was predicted from a transcriptome database of Spodoptera exigua. SeILP1 encodes 95 amino acid sequence and shares sequence homologies (33-83%) with other insect ILPs, in which six conserved cysteine residues are found in the predicted B-A chains. SeILP1 was expressed in all developmental stages of S. exigua. However, SeILP1 expression was tissue-specific because the transcript was detected in fat body and epidermis, but not in hemocytes and gut. Its expression increased with feeding activity. Hemolymph trehalose levels of the fifth instar larvae maintained a relatively constant level at 2.31±0.62mM. However, starvation induced a significant increase of the hemolymph trehalose level by more than twofold in 48h, at which few SeILP1 was transcribed. RNA interference of SeILP1 using its specific double-stranded RNA induced a significant increase of hemolymph trehalose level. Interestingly, a bovine insulin decreased hemolymph trehalose level in a dose-dependent manner. These results indicate that SeILP1 plays a role in suppressing hemolymph trehalose level in S. exigua.

Characterization of Rab-interacting lysosomal protein in the brain of Bombyx mori

Rab guanosine triphosphatases in eukaryotic cells are key regulators of membrane-trafficking events, such as exocytosis and endocytosis. Rab7 regulates traffic from early to late endosomes and from late endosomes to vacuoles/lysosomes. The Rab7-interacting lysosomal protein (RILP) was extracted from the silkworm, Bombyx mori (B. mori), and expressed in Escherichia coli (E. coli), followed by its purification. The glutathione sulfotransferase pull-down assay revealed that Rab7 of B. mori interacted with RILP of B. mori. We then produced antibodies against RILP of B. mori in rabbits for their use in Western immunoblotting and immunohistochemistry. Western immunoblotting of brain tissue for RILP revealed a single band, at approximately 50 kD. RILP-like immunohistochemical reactivity (RILP-ir) was restricted to neurons of the pars intercerebralis and dorsolateral protocerebrum. Furthermore, RILP-ir was colocalized with the eclosion hormone-ir and bombyxin-ir. However, RILP-ir was not colocalized with prothoracicotropic hormone-ir. These results were similar to those of Rab7 from our previous study. These findings suggest that RILP and Rab7 are involved in the neurosecretion in a restricted subtype of neurons in B. mori. Thus, our study is the first to report of a possible relationship between an insect Rab effector and neurosecretion.

Insulin-like and IGF-like peptides in the silkmoth Bombyx mori: discovery, structure, secretion, and function

A quarter of a century has passed since bombyxin, the first insulin-like peptide identified in insects, was discovered in the silkmoth Bombyx mori. During these years, bombyxin has been studied for its structure, genes, distribution, hemolymph titers, secretion control, as well as physiological functions, thereby stimulating a wide range of studies on insulin-like peptides in other insects. Moreover, recent studies have identified a new class of insulin family peptides, IGF-like peptides, in B. mori and Drosophila melanogaster, broadening the base of the research area of the insulin-related peptides in insects. In this review, we describe the achievements of the studies on insulin-like and IGF-like peptides mainly in B. mori with short histories of their discovery. Our emphasis is that bombyxins, secreted by the brain neurosecretory cells, regulate nutrient-dependent growth and metabolism, whereas the IGF-like peptides, secreted by the fat body and other peripheral tissues, regulate stage-dependent growth of tissues.

Body size determination in insects: a review and synthesis of size- and brain-dependent and independent mechanisms

Body size determination requires a mechanism for sensing size and a mechanism for linking size information to the termination of growth. Although the hormonal mechanisms that terminate growth are well elucidated, the mechanisms by which a body senses its own size are only partially understood; most of this understanding has come from the study of the mechanisms that control insect moulting and metamorphosis. We first review and discuss advances in our understanding of the physiological mechanisms by which insect larvae sense their size. Second, we present new findings on how larvae in which the size-sensing mechanism has been disrupted eventually terminate growth (in a size-independent manner). We synthesize recent insights into the genetic and molecular mechanisms of ecdysteroid regulation in Drosophila melanogaster with developmental physiology findings in Manduca sexta, paving the way for an integrated understanding of the mechanisms of body size regulation.

Ecdysone control of developmental transitions: lessons from Drosophila research

The steroid hormone ecdysone is the central regulator of insect developmental transitions. Recent new advances in our understanding of ecdysone action have relied heavily on the application of Drosophila melanogaster molecular genetic tools to study insect metamorphosis. In this review, we focus on three major aspects of Drosophila ecdysone biology: (a) factors that regulate the timing of ecdysone release, (b) molecular basis of stage- and tissue-specific responses to ecdysone, and (c) feedback regulation and coordination of ecdysone signaling.

Developmental checkpoints and feedback circuits time insect maturation

The transition from juvenile to adult is a fundamental process that allows animals to allocate resource toward reproduction after completing a certain amount of growth. In insects, growth to a species-specific target size induces pulses of the steroid hormone ecdysone that triggers metamorphosis and reproductive maturation. The past few years have seen significant progress in understanding the interplay of mechanisms that coordinate timing of ecdysone production and release. These studies show that the neuroendocrine system monitors complex size-related and nutritional signals, as well as external cues, to time production and release of ecdysone. Based on results discussed here, we suggest that developmental progression to adulthood is controlled by checkpoints that regulate the genetic timing program enabling it to adapt to different environmental conditions. These checkpoints utilize a number of signaling pathways to modulate ecdysone production in the prothoracic gland. Release of ecdysone activates an autonomous cascade of both feedforward and feedback signals that determine the duration of the ecdysone pulse at each developmental transitions. Conservation of the genetic mechanisms that coordinate the juvenile-adult transition suggests that insights from the fruit fly Drosophila will provide a framework for future investigation of developmental timing in metazoans.

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.

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.

Identification of novel bombyxin genes from the genome of the silkmoth Bombyx mori and analysis of their expression

Insulin family peptide members play key roles in regulating growth, metabolism, and reproduction. Bombyxin is an insulin-related peptide of the silkmoth Bombyx mori. We analyzed the full genome of B. mori and identified five novel bombyxin families, V to Z. We characterized the genomic organization and chromosomal location of the novel bombyxin family genes. In contrast to previously identified bombyxin genes, bombyxin-V and -Z genes had intervening introns at almost the same positions as vertebrate insulin genes. We performed reverse transcription-polymerase chain reaction and in situ hybridization in different tissues and developmental stages to observe their temporal and spatial expression patterns. The newly identified bombyxin genes were expressed in diverse tissues: bombyxin-V, -W, and -Y mRNAs were expressed in the brain and bombyxin-X mRNA in fat bodies. Bombyxin-Y gene was expressed in both brain and ovary of larval stages. High level of bombyxin-Z gene expression in the follicular cells may suggest its function in reproduction. The presence of a short C-peptide domain and an extended A chain domain, and high expression of bombyxin-X gene in the fat body cells during non-feeding stages suggest its insulin-like growth factor-like function. These results suggest that the bombyxin genes originated from a common ancestral gene, similar to the vertebrate insulin gene, and evolved into a diverse gene family with multiple functions.

Genomics, transcriptomics, and peptidomics of Daphnia pulex neuropeptides and protein hormones

We report 43 novel genes in the water flea Daphnia pulex encoding 73 predicted neuropeptide and protein hormones as partly confirmed by RT-PCR. MALDI-TOF mass spectrometry identified 40 neuropeptides by mass matches and 30 neuropeptides by fragmentation sequencing. Single genes encode adipokinetic hormone, allatostatin-A, allatostatin-B, allatotropin, Ala(7)-CCAP, CCHamide, Arg(7)-corazonin, DENamides, CRF-like (DH52) and calcitonin-like (DH31) diuretic hormones, two ecdysis-triggering hormones, two FIRFamides, one insulin, two alternative splice forms of ion transport peptide (ITP), myosuppressin, neuroparsin, two neuropeptide-F splice forms, three periviscerokinins (but no pyrokinins), pigment dispersing hormone, proctolin, Met(4)-proctolin, short neuropeptide-F, three RYamides, SIFamide, two sulfakinins, and three tachykinins. There are two genes for a preprohormone containing orcomyotropin-like peptides and orcokinins, two genes for N-terminally elongated ITPs, two genes (clustered) for eclosion hormones, two genes (clustered) for bursicons alpha, beta, and two genes (clustered) for glycoproteins GPA2, GPB5, three genes for different allatostatins-C (two of them clustered) and three genes for IGF-related peptides. Detailed comparisons of genes or their products with those from insects and decapod crustaceans revealed that the D. pulex peptides are often closer related to their insect than to their decapod crustacean homologues, confirming that branchiopods, to which Daphnia belongs, are the ancestor group of insects.

Historical view of development of comparative endocrinology in Japan

This article describing a brief history of development of comparative endocrinology in Japan is contributed to the journal General and Comparative Endocrinology, in commemoration of the 50th anniversary of its publication. It covers significant works in the field of comparative endocrinology that have been done by Japanese endocrinologists, focusing those achieved during the past 70 years. The contents were arranged according to the taxonomical order of the experimental animals with which individual researchers or research groups have contributed to the acquisition of important knowledge in comparative endocrinology.

A switch in the control of growth of the wing imaginal disks of Manduca sexta

BACKGROUND

Insulin and ecdysone are the key extrinsic regulators of growth for the wing imaginal disks of insects. In vitro tissue culture studies have shown that these two growth regulators act synergistically: either factor alone stimulates only limited growth, but together they stimulate disks to grow at a rate identical to that observed in situ. It is generally thought that insulin signaling links growth to nutrition, and that starvation stops growth because it inhibits insulin secretion. At the end of larval life feeding stops but the disks continue to grow, so at that time disk growth has become uncoupled from nutrition. We sought to determine at exactly what point in development this uncoupling occurs.

METHODOLOGY

Growth and cell proliferation in the wing imaginal disks and hemolymph carbohydrate concentrations were measured at various stages in the last larval instar under experimental conditions of starvation, ligation, rescue, and hormone treatment.

PRINCIPAL FINDINGS

Here we show that in the last larval instar of M. sexta, the uncoupling of nutrition and growth occurs as the larva passes the critical weight. Before this time, starvation causes a decline in hemolymph glucose and trehalose and a cessation of wing imaginal disks growth, which can be rescued by injections of trehalose. After the critical weight the trehalose response to starvation disappears, and the expression of insulin becomes decoupled from nutrition. After the critical weight the wing disks loose their sensitivity to repression by juvenile hormone, and factors from the abdomen, but not the brain, are required to drive continued growth.

CONCLUSIONS

During the last larval instar imaginal disk growth becomes decoupled from somatic growth at the time that the endocrine events of metamorphosis are initiated. These regulatory changes ensure that disk growth continues uninterrupted when the nutritive and endocrine signals undergo the drastic changes associated with metamorphosis.

An ecdysteroid-inducible insulin-like growth factor-like peptide regulates adult development of the silkmoth Bombyx mori

Insulin-like growth factors (IGFs) play essential roles in fetal and postnatal growth and development of mammals. They are secreted by a wide variety of tissues, with the liver being the major source of circulating IGFs, and regulate cell growth, differentiation and survival. IGFs share some biological activities with insulin but are secreted in distinct physiological and developmental contexts, having specific functions. Although recent analyses of invertebrate genomes have revealed the presence of multiple insulin family peptide genes in each genome, little is known about functional diversification of the gene products. Here we show that a novel insulin family peptide of the silkmoth Bombyx mori, which was purified and sequenced from the hemolymph, is more like IGFs than like insulin, in contrast to bombyxins, which are previously identified insulin-like peptides in B. mori. Expression analysis reveals that this IGF-like peptide is predominantly produced by the fat body, a functional equivalent of the vertebrate liver and adipocytes, and is massively released during pupa-adult development. Studies using in vitro tissue culture systems show that secretion of the peptide is stimulated by ecdysteroid and that the secreted peptide promotes the growth of adult-specific tissues. These observations suggest that this peptide is a Bombyx counterpart of vertebrate IGFs and that functionally IGF-like peptides may be more ubiquitous in the animal kingdom than previously thought. Our results also suggest that the known effects of ecdysteroid on insect adult development may be in part mediated by IGF-like peptides.

The in vitro oxidative folding of the insulin superfamily

Insulin and related proteins, which have been found not only in mammals, birds, reptiles, amphibians, fish, and cephalochordate, but also in mollusca, insects, and Caenorhabditis elegans, form a large protein family, the insulin superfamily. In comparing their amino acid sequences, a common sequence characteristic, the insulin structural motif, is found in all members of the superfamily. The structural motif is deduced to be the sequence basis of the identical disulfide linkages and similar three-dimensional structures of the superfamily. The insulin superfamily provides a series of disulfide-containing proteins for the studies of in vitro oxidative folding. The in vitro folding pathways of insulin-like growth factor-1 (IGF-1), porcine insulin precursor (PIP), human proinsulin, and Amphioxus insulin-like peptide (AILP) have been established by capture and analysis of the folding intermediates during their in vitro oxidative folding process. The family also provides an excellent system for study of the sequence structure relation: insulin and IGF-1 share high amino acid sequence homology, but they have evolved different folding behaviors. The sequence determinants of their different folding behaviors have been revealed by analyzing the folding behaviors of those global and local insulin/IGF-1 hybrids.

Insulin and gender: an insulin-like gene expressed exclusively in the androgenic gland of the male crayfish

Members of the insulin family of hormones are generally not regarded as gender-specific, although there is sporadic evidence for the possible involvement of insulin pathways in sexual differentiation. In crustaceans, sexual differentiation is controlled by the androgenic gland (AG), an organ unique to males. To date, attempts to identify active AG factors in decapods through either classical purification methods or sequence similarity with isopod AG hormones have proven unsuccessful. In the present study, the first subtractive cDNA library from a decapod AG was constructed from the red-claw crayfish Cherax quadricarinatus. During library screening, an AG-specific gene, expressed exclusively in males even at early stages of maturation and termed Cq-IAG (C. quadricarinatus insulin-like AG factor), was discovered. In situ hybridization of Cq-IAG confirmed the exclusive localization of its expression to the AG. Following cloning and complete sequencing of the gene, its cDNA was found to contain 1445 nucleotides encoding a deduced translation product of 176 amino acids. The proposed protein sequence encompasses Cys residue and putative cleaved peptide patterns whose linear and 3D organization are similar to those of members of the insulin/insulin-like growth factor/relaxin family and their receptor recognition surface. The identification of Cq-IAG is the first report of a pro-insulin-like gene expressed in a decapod crustacean in a gender-specific manner. Its expression in a male-specific endocrine gland controlling sex differentiation supports the notion that insulin may have evolved in the context of regulating sexual differentiation.

Molecular characterization of insulin-like peptides in the yellow fever mosquito, Aedes aegypti: expression, cellular localization, and phylogeny

Insulin-like peptides are key regulators of metabolism, reproduction, and senescence in higher eukaryotic organisms. Here we present the identification, expression, and tissue localization of eight genes encoding insulin-like peptides (ILPs) in the yellow fever mosquito, Aedes aegypti. All eight ILPs share the conserved features of the insulin superfamily as prepropeptides consisting of contiguous signal, B, C, and A peptides. However, one of the ILPs has a truncated C peptide and a carboxy terminal extension, features consistent with insulin growth factors. Transcripts for five of the ILPs occurred predominantly in the heads (brains) of larval, pupal, and adult mosquitoes. Transcripts of two other genes, one of which was the putative insulin growth factor, were present in the head, thorax and abdomens of all stages. The final ILP was predominantly expressed in abdomen. Results from immunocytochemistry with two different ILP antisera showed cellular localizations in the nervous system and midgut that corroborated the existence of these expression patterns. Three of the ILP genes are so closely linked that only the 5' region of the first ILP gene likely suffices as a promoter, indicating that these genes form a eukaryotic operon. The nearly identical expression pattern of these three ILPs supported this idea. Finally, the phylogenetic relationship of ILPs from three dipteran species, Ae. aegypti, the African malaria mosquito (Anopheles gambiae), and Drosophila melanogaster is presented as a step towards understanding the structural and functional diversity of insect ILPs.

Insulin-like growth factor signaling in fish

The insulin-like growth factor (IGF) system plays a central role in the neuroendocrine regulation of growth in all vertebrates. Evidence from studies in a variety of vertebrate species suggest that this growth factor complex, composed of ligands, receptors, and high-affinity binding proteins, evolved early during vertebrate evolution. Among nonmammalian vertebrates, IGF signaling has been studied most extensively in fish, particularly teleosts of commercial importance. The unique life history characteristics associated with their primarily aquatic existence has fortuitously led to the identification of novel functions of the IGF system that are not evident from studies in mammals and other tetrapod vertebrates. Furthermore, the emergence of the zebrafish as a preferred model for development genetics has spawned progress in determining the requirements for IGF signaling during vertebrate embryonic development. This review is intended as a summary of our understanding of IGF signaling, as revealed through research into the expression, function, and evolution of IGF ligands, receptors, and binding proteins in fish.

Evolution of the relaxin-like peptide family

BACKGROUND

The relaxin-like peptide family belongs in the insulin superfamily and consists of 7 peptides of high structural but low sequence similarity; relaxin-1, 2 and 3, and the insulin-like (INSL) peptides, INSL3, INSL4, INSL5 and INSL6. The functions of relaxin-3, INSL4, INSL5, INSL6 remain uncharacterised. The evolution of this family has been contentious; high sequence variability is seen between closely related species, while distantly related species show high similarity; an invertebrate relaxin sequence has been reported, while a relaxin gene has not been found in the avian and ruminant lineages.

RESULTS

Sequence similarity searches of genomic and EST data identified homologs of relaxin-like peptides in mammals, and non-mammalian vertebrates such as fish. Phylogenetic analysis was used to resolve the evolution of the family. Searches were unable to identify an invertebrate relaxin-like peptide. The published relaxin cDNA sequence in the tunicate, Ciona intestinalis was not present in the completed C. intestinalis genome. The newly discovered relaxin-3 is likely to be the ancestral relaxin. Multiple relaxin-3-like sequences are present in fugu fish (Takifugu rubripes) and zebrafish (Danio rerio), but these appear to be specific to the fish lineage. Possible relaxin-1 and INSL5 homologs were also identified in fish and frog species, placing their emergence prior to mammalia, earlier than previously believed. Furthermore, estimates of synonymous and nonsynonymous substitution rates (dN/dS) suggest that the emergence of relaxin-1, INSL4 and INSL6 during mammalia was driven by positive Darwinian selection, hence these peptides are likely to have novel and in the case of relaxin-1, which is still under positive selection in humans and the great apes, possibly still evolving functions. In contrast, relaxin-3 is constrained by strong purifying selection, demonstrating it must have a highly conserved function, supporting its hypothesized important neuropeptide role.

CONCLUSIONS

We present a phylogeny describing the evolutionary history of the relaxin-like peptide family and show that positive selection has driven the evolution of the most recent members of the family.

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.

Bombyxin is a growth factor for wing imaginal disks in Lepidoptera

The mechanisms that control the growth rate of internal tissues during postembryonic development are poorly understood. In insects, the growth rate of imaginal disks varies with nutrition and keeps pace with variation in somatic growth. We describe here a mechanism by which the growth of wing imaginal disks is controlled. When wing imaginal disks of the butterfly Precis coenia are removed from the larva and placed in a standard nutrient-rich tissue culture medium they stop growing, suggesting that nutrients alone are not sufficient to support normal growth. Such disks can be made to grow at a normal rate by supplementing the culture medium with an optimal concentration of the steroid hormone 20-hydroxyecdysone and with hemolymph taken from growing larvae. The growth-promoting activity of the hemolymph is caused by a heat-stable factor that can be extracted from the CNS and appears to be identical to the neurohormone bombyxin, a member of the insulin family of proteins. Synthetic bombyxin stimulates growth at concentrations as low as 30 ngml, and specific antibodies to bombyxin completely remove growth-promoting activity from the hemolymph. Bombyxin evidently acts together with 20-hydroxyecdysone to stimulate cell division and growth of wing imaginal disks. It appears that the level of bombyxin in the hemolymph is modulated by the brain in response to variation in nutrition and is part of the mechanism that coordinates the growth of internal organs with overall somatic growth.

Insulin and Neuroparsin Promote Neurite Outgrowth in Cultured Locust CNS

Organotypic cultures of locust embryo central nervous system (CNS) were used to study the influence of hormonal factors on neurite outgrowth. Explants from the third thoracic ganglion (embryonic day 9) were grown in a serum-free medium and exposed to insulin, neuroparsin, a recently characterized insect neurohormone, somatostatin and two insect hormones: 20-hydroxyecdysone and juvenile hormone. These hormonal factors were tested either alone or in several combinations. In our culture system both insulin and neuroparsin promoted extensive neurite outgrowth. Their effects were quantitatively similar. Somatostatin had no effect on neurite formation, but was a growth factor for glial cells. 20-hydroxyecdysone was a required factor for glial cell and neurite survival. Juvenile hormone did not have any observable effects in this culture system. When insulin was added in combination with 20-hydroxyecdysone the stimulation of neurite outgrowth exceeded that seen when insulin was added alone. A similar enhancement was observed with the combination of neuroparsin and 20-hydroxyecdysone. We conclude that in locusts: (i) insulin can be implicated as a neurotrophic factor as in vertebrates; and (ii) neuroparsin, a locust neurohormone, can also be characterized as a neurotrophic factor for the locust. Moreover, both neurohormones interact synergistically with the steroid hormone 20-hydroxyecdysone to enhance neurite growth.