Signaling and function of insulin-like peptides in insects

Regulation of insulin-like peptide expression in adult Blattella germanica females

The insulin-IGF-signalling (IIS) pathway regulates key processes in metazoans. The pathway is activated through the binding of the ligands, which in insects are usually referred to as insulin-like peptides (ILPs), to a class of receptor tyrosine kinases, the insect insulin receptor. To study the pathway regulation, it is therefore essential to understand how ILPs are produced and released. In this study we analysed the factors that regulate the expression of the seven ILPs (BgILPs) expressed in adult females of the German cockroach, Blattella germanica. The results showed that the starvation-induced expression reduction of brain BgILP3, 5 and 6 and fat body BgILP7 is not due to reduced juvenile hormone (JH) or decreased TOR pathway activity. In addition, depletion of FoxO in starved females did not correct the low levels of these BgILPs, but even reduced further BgILP5 expression, indicating the need to maintain certain basal levels of BgILP5 even during starvation. Furthermore, JH promoted increased BgILP5 and decreased BgILP3 expression in the brain, an effect that required Methoprene-tolerant (Met), the JH receptor, but not Krüppel homolog 1 (Kr-h1), the main JH transducer. On the other hand, JH inhibited the expression of BgILP7 in the fat body, although in this case, the action required both Met and Kr-h1. In addition, JH reduction treatments produced a decrease in the expression of the insulin receptor in the fat body, which suggests an increase in IIS. The results show a peculiar regulation of ILP expression in adult B. germanica females, which is clearly different than that seen in other species. This is understandable given that gene duplications in recent clades have resulted in different sets of ILP genes, involving substantial changes in gene regulatory networks.

Evolutionary diversification of insulin-related peptides (IRPs) in aphids and spatiotemporal distribution in Acyrthosiphon pisum

Members of the insulin superfamily activate the evolutionarily highly conserved insulin/insulin-like growth factor signaling pathway, involved in regulation of growth, energy homeostasis, and longevity. In the current study we focus on aphids to gain more insight into the evolution of the IRPs and how they may contribute to regulation of the insulin-signaling pathway. Using the latest annotation of the pea aphid (Acyrthosiphon pisum) genome, and combining sequence alignments and phylogenetic analyses, we identified seven putative IRP encoding-genes, with IRP1-IRP4 resembling the classical insulin and insulin-like protein structures, and IRP5 and IRP6 bearing insulin-like growth factor (IGF) features. We also identified IRP11 as a new and structurally divergent IRP present in at least eight aphid genomes. Globally the ten aphid genomes analyzed in this work contain four to 15 IRPs, while only three IRPs were found in the genome of the grape phylloxera, a hemipteran insect representing an earlier evolutionary branch of the aphid group. Expression analyses revealed spatial and temporal variation in the expression patterns of the different A. pisum IRPs. IRP1 and IRP4 are expressed throughout all developmental stages and morphs in neuroendocrine cells of the brain, while IRP5 and IRP6 are expressed in the fat body. IRP2 is expressed in specific cells of the gut in aphids in non-crowded conditions and in the head of aphids under crowded conditions, IRP3 in salivary glands, and both IRP2 and IRP3 in the male morph. IRP11 expression is enriched in the carcass. This complex spatiotemporal expression pattern suggests functional diversification of the IRPs.

A proctolin-like peptide is regulated after baculovirus infection and mediates in caterpillar locomotion and digestion

Baculoviruses constitute a large group of invertebrate DNA viruses, predominantly infecting larvae of the insect order Lepidoptera. During a baculovirus infection, the virus spreads throughout the insect body producing a systemic infection in multiple larval tissues, included the central nervous system (CNS). As a main component of the CNS, neuropeptides are small protein-like molecules functioning as neurohormones, neurotransmitters, or neuromodulators. These peptides are involved in regulating animal physiology and behavior and could be altered after baculovirus infection. In this study, we have investigated the effect of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) infection on expression of Spodoptera exigua neuropeptides and neuropeptide-like genes. Expression of the gene encoding a polypeptide that resembles the well-known insect neuropeptide proctolin and named as proctolin-like peptide (PLP), was downregulated in the larval brain following infection and was chosen for further analysis. A recombinant Autographa californica multiple nucleopolyhedrovirus (AcMNPV) overexpressing the C-terminal part of the PLP was generated and used in bioassays using S. exigua larvae to study its influence on the viral infection and insect behavior. AcMNPV-PLP-infected larvae showed less locomotion activity and a reduction in growth compared to larvae infected with wild type AcMNPV or mock-infected larvae. These results are indicative of this new peptide as a neuromodulator that regulates visceral and skeletal muscle contractions and offers a novel effector involved in the behavioral changes during baculovirus infection.

CRISPR/Cas9-mediated mutation on an insulin-like peptide encoding gene affects the growth of the ridgetail white prawn Exopalaemon carinicauda

Insulin-like peptides (ILPs) play key roles in animal growth, metabolism and reproduction in vertebrates. In crustaceans, one type of ILPs, insulin-like androgenic gland hormone (IAG) had been reported to be related to the sex differentiations. However, the function of other types of ILPs is rarely reported. Here, we identified another type of ILPs in the ridgetail white prawn Exopalaemon carinicauda (EcILP), which is an ortholog of Drosophila melanogaster ILP7. Sequence characterization and expression analyses showed that EcILP is similar to vertebrate insulin/IGFs and insect ILPs in its heterodimeric structure and expression profile. Using CRISPR/Cas9 genome editing technology, we generated EcILP knockout (KO) prawns. EcILP-KO individuals have a significant higher growth-inhibitory trait and mortality than those in the normal group. In addition, knockdown of EcILP by RNA interference (RNAi) resulted in slower growth rate and higher mortality. These results indicated that EcILP was an important growth regulator in E. carinicauda.

The genome of the black cutworm Agrotis ipsilon

The black cutworm (BCW), Agrotis ipsilon, is a worldwide polyphagous and underground pest that causes a high level of economic loss to a wide range of crops through the damage of roots. This species performs non-directed migration throughout East and Southeast Asia seasonally. Lack of a genome information has limited further studies on its unique biology and the development of novel management approaches. In this study, we present a 476 Mb de novo assembly of BCW, along with a consensus gene set of 14,801 protein-coding gene models. Quality controls show that both genome assembly and annotations are high-quality and mostly complete. We focus manual annotation and comparative genomics on gene families that related to the unique attributes of this species, such as nocturnality, long-distance migration, and host adaptation. We find that the BCW genome encodes a similar gene repertoire in various migration-related gene families to the diural migratory butterfly Danaus plexiipus, with additional copies of long wavelength opsin and two eye development-related genes. On the other hand, we find that the genomes of BCW and many other polyphagous lepidopterans encode many more gustatory receptor genes, particularly the lineage-specific expanded bitter receptor genes, than the mono- or oligo-phagous species, suggesting a common role of gustatory receptors (GRs) expansion in host range expansion. The availability of a BCW genome provides valuable resources to study the molecular mechanisms of non-directed migration in lepidopteran pests and to develop novel strategies to control migratory nocturnal pests.

Identification, Synthesis, Conformation and Activity of an Insulin-like Peptide from a Sea Anemone

The role of insulin and insulin-like peptides (ILPs) in vertebrate animals is well studied. Numerous ILPs are also found in invertebrates, although there is uncertainty as to the function and role of many of these peptides. We have identified transcripts with similarity to the insulin family in the tentacle transcriptomes of the sea anemone Oulactis sp. (Actiniaria: Actiniidae). The translated transcripts showed that these insulin-like peptides have highly conserved A- and B-chains among individuals of this species, as well as other Anthozoa. An Oulactis sp. ILP sequence (IlO1_i1) was synthesized using Fmoc solid-phase peptide synthesis of the individual chains, followed by regioselective disulfide bond formation of the intra-A and two interchain disulfide bonds. Bioactivity studies of IlO1_i1 were conducted on human insulin and insulin-like growth factor receptors, and on voltage-gated potassium, sodium, and calcium channels. IlO1_i1 did not bind to the insulin or insulin-like growth factor receptors, but showed weak activity against KV1.2, 1.3, 3.1, and 11.1 (hERG) channels, as well as NaV1.4 channels. Further functional studies are required to determine the role of this peptide in the sea anemone.

An overview of the insulin signaling pathway in model organisms Drosophila melanogaster and Caenorhabditis elegans

The insulin/insulin-like growth factor signaling pathway is an evolutionary conserved pathway across metazoans and is required for development, metabolism and behavior. This pathway is associated with various human metabolic disorders and cancers. Thus, model organisms including Drosophila melanogaster and Caenorhabditis elegans provide excellent opportunities to examine the structure and function of this pathway and its influence on cellular metabolism and proliferation. In this review, we will provide an overview of human insulin and the human insulin signaling pathway and explore the recent discoveries in model organisms Drosophila melanogaster and Caenorhabditis elegans. Our review will provide information regarding the various insulin-like peptides in model organisms as well as the conserved functions of insulin signaling pathways. Further investigation of the insulin signaling pathway in model organisms could provide a promising opportunity to develop novel therapies for various metabolic disorders and insulin-mediated cancers.

Dietary chromium modulates glucose homeostasis and induces oxidative stress in Pacific white shrimp (Litopenaeus vannamei)

While chromium (Cr) has been recognized as an essential nutrient for all animals, and dietary supplementation can be beneficial, it can also be toxic. The present study aimed to investigate the contrasting effects of dietary chromium in Pacific white shrimp Litopenaeus vannamei. Five experimental diets were formulated to contain Cr at levels of 0.82 (Cr0.82, unsupplemented diet), 1.01 (Cr1.01), 1.22 (Cu1.22), 1.43 (Cr1.43) and 1.63 (Cr1.63) mg/kg and were fed to shrimp for 8 weeks. Highest weight gain was recorded in shrimp fed the diet containing 1.22 mg/kg Cr. Shrimp fed the diet containing the highest level of Cr (1.63 mg/kg) showed the lowest weight gain and clear signs of oxidative stress and apoptosis as evidenced by higher levels of H₂O₂, malondialdehyde and 8-hydroxydeoxyguanosine, and expression of caspase 2, 3, 5, and lower contents of total and oxidized glutathione, and expression of Cu/Zn sod, cat, gpx, mt, bcl2. Chromium supplementation promoted glycolysis and inhibited gluconeogenesis as shown by increased activities of hexokinase, phosphofructokinase and pyruvate kinase, and reduced activity of phosphoenolpyruvate carboxykinase in shrimp fed the diet containing 1.43 mg/kg Cr. Shrimp fed the diet with 1.63 mg/kg Cr had lowest contents of crustacean hyperglycemic hormone and insulin like peptide in hemolymph. Expression of genes involved in insulin signaling pathway and glycose metabolism including insr, irs1, pik3ca, pdpk1, akt, acc1, gys, glut1, pk, hk were up-regulated, and foxO1, gsk-3β, g6pc, pepck were down-regulated in shrimp fed the diets supplemented with Cr. This study demonstrated that optimum dietary supplementation of Cr had beneficial effects on glucose homeostasis and growth, whereas excess caused oxidative damage and impaired growth. The results contribute to our understanding of the biological functions of chromium in shrimp.

The effects of high-monosaccharide diets on development and biochemical composition of white-eyed mutant strain of house cricket (Acheta domesticus)

Tryptophan (TRP) is one of the essential amino acids in the animal body. Its exogenicity and low concentrations mean that it can be regarded as one of the key regulatory molecules at the cellular as well as physiological level. It has been shown to have a number of essential functions, such as in the production of other biologically active molecules. The main objective of this project was to investigate the effects of a high monosaccharide diet (HMD) on a hemimetabolic insect-house cricket (Acheta domesticus) and a mutant strain with impaired visual pigment synthesis (closely related to the tryptophan and kynurenine (KYN) metabolic pathway)-white eye. This study was aimed at determining the effects of glucose and fructose on cricket development and biochemical composition. A parallel goal was to compare the response of both cricket strains to HMD. ELISA assays indicated dysfunction of the TRP-KYN pathway in white strain insects and an elevated KYN/TRP ratio. Biochemical analyses demonstrated the effects of HMD mainly on fat and glycogen content. A decrease in food intake was also observed in the groups on HMD. However, no changes in imago body weight and water content were observed. The results of the study indicate a stronger response of the white strain to HMD compared to the wild-type strain. At the same time, a stronger detrimental effect of fructose than of glucose was apparent. Sex was found to be a modulating factor in the response to HMD.

Disruption of the Serine/Threonine Kinase Akt Gene Affects Ovarian Development and Fecundity in the Cigarette Beetle, Lasioderma serricorne

Serine/threonine kinase Akt, an important component of the insulin signaling pathway, plays an essential role in many physiological processes. In this study, we identified and characterized an Akt gene (designated LsAkt) from the cigarette beetle, Lasioderma serricorne. LsAkt contains a 1614 bp open reading frame encoding a 537 amino acid protein that possesses a conserved pleckstrin homology domain and a serine/threonine kinase domain. The expression of LsAkt was high in pupal stages and peaked in day-4 female pupae. In adult tissues, LsAkt was highly expressed in the thorax, ovary, and midgut. The expression of LsAkt was induced by methoprene or bovine insulin in vivo, but significantly decreased by 20-hydroxyecdysone. RNA interference-mediated knockdown of LsAkt resulted in severely blocked ovarian development and reduced fecundity and hatchability. The vitellogenin (Vg) content and juvenile hormone (JH) titers of LsAkt-depletion beetles were decreased, and expressions of Vg and four JH signaling and biosynthetic genes were significantly decreased. Silencing of LsAkt reduced the amounts of glucose, glycogen, and trehalose in female adults and affected the expressions of seven key carbohydrate metabolic genes. Taken together, it is inferred that Akt implicates in L. serricorne reproduction by modification of Vg synthesis, juvenile hormone production and carbohydrate metabolism.

Insects as a New Complex Model in Hormonal Basis of Obesity

Nowadays, one of the biggest problems in healthcare is an obesity epidemic. Consumption of cheap and low-quality energy-rich diets, low physical activity, and sedentary work favor an increase in the number of obesity cases within many populations/nations. This is a burden on society, public health, and the economy with many deleterious consequences. Thus, studies concerning this disorder are extremely needed, including searching for new, effective, and fitting models. Obesity may be related, among other factors, to disrupting adipocytes activity, disturbance of metabolic homeostasis, dysregulation of hormonal balance, cardiovascular problems, or disorders in nutrition which may lead to death. Because of the high complexity of obesity, it is not easy to find an ideal model for its studies which will be suitable for genetic and physiological analysis including specification of different compounds’ (hormones, neuropeptides) functions, as well as for signaling pathways analysis. In recent times, in search of new models for human diseases there has been more and more attention paid to insects, especially in neuro-endocrine regulation. It seems that this group of animals might also be a new model for human obesity. There are many arguments that insects are a good, multidirectional, and complex model for this disease. For example, insect models can have similar conservative signaling pathways (e.g., JAK-STAT signaling pathway), the presence of similar hormonal axis (e.g., brain–gut axis), or occurrence of structural and functional homologues between neuropeptides (e.g., neuropeptide F and human neuropeptide Y, insulin-like peptides, and human insulin) compared to humans. Here we give a hint to use insects as a model for obesity that can be used in multiple ways: as a source of genetic and peptidomic data about etiology and development correlated with obesity occurrence as well as a model for novel hormonal-based drug activity and their impact on mechanism of disease occurrence.

High MEK/ERK signalling is a key regulator of diapause maintenance in the cotton bollworm, Helicoverpa armigera

MEK/ERK signalling has been identified as a key factor that terminates diapause in Sarcophaga crassipalpis and Bombyx mori. Paradoxically, high p-MEK/p-ERK signalling induces diapause in pupae of the moth Helicoverpa armigera; however, the regulatory mechanism is unknown. In the present study, we show that p-MEK and p-ERK are elevated in the brain of diapause-destined pupae and suppression of MEK/ERK activity terminates diapause progress. Reactive oxygen species (ROS) activate MEK/ERK signalling, causing large-scale phosphorylation of downstream proteins. The levels of ubiquitin-conjugated proteins are also significantly reduced when ROS or p-ERK level decreased. Moreover, terminated diapause progress by 20-hydroxyecdysone injection significantly decreases p-MEK, p-ERK and phospho-ribosomal S6 kinase levels, while phospho-MAPK substrates and ubiquitin-conjugated protein levels increase. Our data demonstrate that high MEK/ERK signalling mediated by ROS promotes diapause maintenance via increasing phosphorylation and degradation of downstream substrates. The results of this study may provide important information for understanding the regulatory mechanisms during insect diapause.

The effect of pyriproxyfen on the concentration of circulating metabolic fuel molecules and chemical elements in the hemolymph of Acraea horta L. (Lepidoptera: Nymphalidae): A quantitative analysis

Many pollinating insects expand their niche to adjacent agricultural areas and are, therefore, exposed to chemical insecticides. Acraea horta L. (Lepidoptera: Nymphalidae) is a pollinator butterfly widely distributed in the Southern African region. The objectives of this work were to evaluate carbohydrate, lipid and chemical elements in the hemolymph of A. horta exposed to pyriproxyfen, a juvenile hormone analog (JHA). Last instar larvae (L6: day 1 or day 2) were topically exposed to an aqueous solution of pyriproxyfen (100 μg of the active ingredient per insect) or to diluent (control group). Hemolymph was collected after adult eclosion to determine total carbohydrate and lipid concentrations: in the control group lipids were present in lower concentrations than carbohydrates and there was no significant difference in metabolite levels between sexes; a similar pattern with similar levels were measured in the treated group, except that lipid concentrations in treated males were lower, and carbohydrate concentrations in treated females were lower than the control values. Morphologically intact adult males from treated larvae were subjected to free flight; their hemolymph carbohydrate levels were significantly reduced and did not recover to starting levels in a 30 min rest period following the exhaustive flight episode. To assess the effect of pyriproxyfen on a different stage of development, 48 h old butterflies were treated in the same way as described for the L6 larvae above; hemolymph samples were taken 48 h later for metabolite measurements and for quantification of chemical elements: carbohydrate levels decreased significantly after pyriproxyfen exposure, while lipid levels increased; inorganic elements measured in untreated adults were more abundant in females, with a general decrease in concentration following pyriproxyfen exposure, except for an increase in Fe levels in males and Cl levels in females. The quantitative changes measured in A. horta hemolymph via biochemical and chemical element analyses may indicate distinct physiological interferences beyond the main mode of action of pyriproxyfen on JH activity. In conclusion, the use and quantification of pyriproxyfen should be carefully evaluated prior to application in areas where A. horta and other pollinator species occur.

Factors that regulate expression patterns of insulin-like peptides and their association with physiological and metabolic traits in Drosophila

Insulin-like peptides (ILPs) and components of the insulin signaling pathway are conserved across different animal phyla. Eight ILPs (called DILPs) and two receptors, dInR and Lgr3, have been described in Drosophila. DILPs regulate varied physiological traits including lifespan, reproduction, development, feeding behavior, stress resistance and metabolism. At the same time, different conditions such as nutrition, dietary supplements and environmental factors affect the expression of DILPs. This review focuses primarily on DILP2, DILP3, and DILP5 which are produced by insulin-producing cells in the brain of Drosophila. Although they are produced by the same cells and can potentially compensate for each other, DILP2, DILP3, and DILP5 expression may be differentially regulated at the mRNA level. Thus, we summarized available data on the conditions affecting the expression profiles of these DILPs in adult Drosophila. The accumulated data indicate that transcript levels of DILPs are determined by (a) nutritional conditions such as the protein-to-carbohydrate ratio, (b) carbohydrate type within the diet, (c) malnutrition or complete starvation; (d) environmental factors such as stress or temperature; (e) mutations of single peptides that induce changes in the expression of the other peptides; and (f) dietary supplements of drugs or natural substances. Furthermore, manipulation of specific genes in a cell- and tissue-specific manner affects mRNA levels for DILPs and, thereby, modulates various physiological traits and metabolism in Drosophila.

Evolution-Based Protein Engineering for Antifungal Peptide Improvement

Antimicrobial peptides (AMPs) have been considered as the alternatives to antibiotics because of their less susceptibility to microbial resistance. However, compared with conventional antibiotics they show relatively low activity and the consequent high cost and nonspecific cytotoxicity, hindering their clinical application. What’s more, engineering of AMPs is a great challenge due to the inherent complexity in their sequence, structure, and function relationships. Here, we report an evolution-based strategy for improving the antifungal activity of a nematode-sourced defensin (Cremycin-5). This strategy utilizes a sequence-activity comparison between Cremycin-5 and its functionally diverged paralogs to identify sites associated with antifungal activity for screening of enhanceable activity-modulating sites for subsequent saturation mutagenesis. Using this strategy, we identified a site (Glu-15) whose mutations with nearly all other types of amino acids resulted in a universally enhanced activity against multiple fungal species, which is thereby defined as a Universally Enhanceable Activity-Modulating Site (UEAMS). Especially, Glu15Lys even exhibited >9-fold increased fungicidal potency against several clinical isolates of Candida albicans through inhibiting cytokinesis. This mutant showed high thermal and serum stability and quicker killing kinetics than clotrimazole without detectable hemolysis. Molecular dynamic simulations suggest that the mutations at the UEAMS likely limit the conformational flexibility of a distant functional residue via allostery, enabling a better peptide–fungus interaction. Further sequence, structural, and mutational analyses of the Cremycin-5 ortholog uncover an epistatic interaction between the UEAMS and another site that may constrain its evolution. Our work lights one new road to success of engineering AMP drug leads.

Physiological Alterations in Deletion Mutants of Two Insulin-Like Peptides Encoded in Maruca vitrata Using CRISPR/Cas9

Most insect species encode multiple insulin-like peptides (ILPs) that exhibit functional overlaps in mediating physiological processes such as development and reproduction. Why do they need multiple ILPs? To address this question, we tested a hypothesis of the requirement of multiple ILPs by generating mutants lacking individual ILP genes using the CRISPR/Cas9 technology. Two ILPs (ILP1 and ILP2) in the legume pod borer, Maruca vitrata, mediate similar physiological processes such as hemolymph sugar level, larval development, and adult reproduction. Individual knock-out mutants (ΔILP1 and ΔILP2) were generated. They showed successful development from larvae to adults. However, they suffered from high hemolymph sugar levels by enhancing trehalose titers in the hemolymph. The hyperglycemic effect was more evident in ΔILP2 mutants than in ΔILP1 mutants. Both mutants showed increased expression of trehalose-6-phosphate synthase but suppressed expression of trehalase. These mutants also showed altered expression patterns of insulin signaling components. Expression levels of insulin receptor and Akt genes were upregulated, while those of FOXO and Target of rapamycin genes were downregulated in these mutants. These alterations of signal components resulted in significant retardation of immature development and reduced body sizes. ΔILP1 or ΔILP2 females exhibited poor oocyte development. Bromo-uridine incorporation was much reduced at the germarium of ovarioles of these mutants compared with wild females. Expression of the vitellogenin gene was also reduced in these mutants. Furthermore, males of these deletion mutants showed impaired reproductive activities when they mated with wild-type females. These results suggest that both ILPs are required for mediating larval development and adult reproduction in M. vitrata.

Insulin-Like Peptides and Cross-Talk With Other Factors in the Regulation of Insect Metabolism

The insulin-like peptide (ILP) and insulin-like growth factor (IGF) signalling pathways play a crucial role in the regulation of metabolism, growth and development, fecundity, stress resistance, and lifespan. ILPs are encoded by multigene families that are expressed in nervous and non-nervous organs, including the midgut, salivary glands, and fat body, in a tissue- and stage-specific manner. Thus, more multidirectional and more complex control of insect metabolism can occur. ILPs are not the only factors that regulate metabolism. ILPs interact in many cross-talk interactions of different factors, for example, hormones (peptide and nonpeptide), neurotransmitters and growth factors. These interactions are observed at different levels, and three interactions appear to be the most prominent/significant: (1) coinfluence of ILPs and other factors on the same target cells, (2) influence of ILPs on synthesis/secretion of other factors regulating metabolism, and (3) regulation of activity of cells producing/secreting ILPs by various factors. For example, brain insulin-producing cells co-express sulfakinins (SKs), which are cholecystokinin-like peptides, another key regulator of metabolism, and express receptors for tachykinin-related peptides, the next peptide hormones involved in the control of metabolism. It was also shown that ILPs in Drosophila melanogaster can directly and indirectly regulate AKH. This review presents an overview of the regulatory role of insulin-like peptides in insect metabolism and how these factors interact with other players involved in its regulation.

Neofunctionalization of a second insulin receptor gene in the wing-dimorphic planthopper, Nilaparvata lugens

A single insulin receptor (InR) gene has been identified and extensively studied in model species ranging from nematodes to mice. However, most insects possess additional copies of InR, yet the functional significance, if any, of alternate InRs is unknown. Here, we used the wing-dimorphic brown planthopper (BPH) as a model system to query the role of a second InR copy in insects. NlInR2 resembled the BPH InR homologue (NlInR1) in terms of nymph development and reproduction, but revealed distinct regulatory roles in fuel metabolism, lifespan, and starvation tolerance. Unlike a lethal phenotype derived from NlInR1 null, homozygous NlInR2 null mutants were viable and accelerated DNA replication and cell proliferation in wing cells, thus redirecting short-winged–destined BPHs to develop into long-winged morphs. Additionally, the proper expression of NlInR2 was needed to maintain symmetric vein patterning in wings. Our findings provide the first direct evidence for the regulatory complexity of the two InR paralogues in insects, implying the functionally independent evolution of multiple InRs in invertebrates.

The highly conserved insulin/insulin-like growth factor signaling pathway plays a pivotal role in growth, development, and various physiological processes across a wide phylogeny of organisms. Unlike a single InR in the model species such as the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans, most insect lineages have two or even three InR copies. However, the function of the alternative InRs remains elusive. Here, we created a homozygous mutation for a second insulin receptor (InR2) in the wing-dimorphic brown planthopper (BPH), Nilaparvata lugens, using the clustered regularly interspaced palindromic repeats/CRISPR-associated (CRISPR/Cas9) system. Our findings revealed that InR2 possesses functions distinct from the BPH InR homologue (NlInR1), indicating that multiple InR paralogues may have evolved independently and may have functionally diversified in ways more complex than previously expected in invertebrates.

Larval feeding status regulates the transcript levels of genes encoding PTTH and allatoregulatory peptides in silkworm Bombyx mori

In Bombyx mori, two dorsolateral neurosecretory cells (NSCs) in each of the two brain lobes have been identified as prothoracicotropic hormone (PTTH) producing cells. This neuropeptide in insects stimulates the prothoracic gland for the synthesis and release of ecdysone, responsible for the molting events. Allatotropin (AT) and allatostatin (AST) are allatoregulatory neuropeptides that regulate juvenile hormone biosynthesis. Here, by using RT-qPCR, we showed that in B. mori, nutritional stress modulates the mRNA expression of AT and AST-C (allatostain type C) in the central nervous system consisting of the brain lobes and all the associated ganglia. Using whole-mount in situ hybridization, we showed that the feeding status of Bombyx larvae also influences the expression of PTTH in the NSCs of the brain. Food deprivation significantly decreased the mRNA expression levels of PTTH in larvae at active or terminal growth period. Further, we showed that insulin modulates the expression level of PTTH. However, its action was dependent on the feeding status of the larvae. At feeding, the insulin decreased the PTTH expression level, while at food deprivation, the insulin increased the PTTH expression level. The data thus indicates that larval feeding status plays an important role in altering the mRNA expression levels of allatoregulatory peptide genes and PTTH.

Persistent pesticides: effects of endosulfan at the molecular level on the aquatic invertebrate Chironomus riparius

Although banned in multiple areas, due to its persistence in the environment, endosulfan constitutes a significant environmental concern. In this work, fourth instar Chironomus riparius larvae were exposed at environmentally relevant endosulfan concentrations of 0.1, 1, and 10 μg/L for 24 h to analyze the possible effects of this acaricide on gene expression and enzymatic activity. Transcriptional changes were studied through the implementation of a real-time polymerase chain reaction array with 42 genes related to several metabolic pathways (endocrine system, detoxification response, stress response, DNA reparation, and immune system). Moreover, glutathione-S-transferase (GST), phenoloxidase (PO), and acetylcholinesterase (AChE) activities were assessed. The five pathways were differentially altered by endosulfan exposure with significant changes in the E93, Dis, MAPR, Met, InR, GSTd3, GSTt3, MRP1, hsp70, hsp40, hsp24, ATM, PARP, Proph, and Def genes. Besides, all of the measured enzymatic activities were modified, with increased activity of GST, followed by PO and AChE. In summary, the results reflected the effects provoked in C. riparius at molecular level despite the absence of lethality. These data raise concerns about the strong alteration on different metabolic routes despite the low concentrations used. Therefore, new risk assessment strategies should consider include the effects at the sub-organismal level as endpoints in addition to the classical ecologically relevant parameters (such as survival). This endeavor will facilitate a comprehensive evaluation of toxicants in the environment.

Insects Provide Unique Systems to Investigate How Early-Life Experience Alters the Brain and Behavior

Early-life experiences have strong and long-lasting consequences for behavior in a surprising diversity of animals. Determining which environmental inputs cause behavioral change, how this information becomes neurobiologically encoded, and the functional consequences of these changes remain fundamental puzzles relevant to diverse fields from evolutionary biology to the health sciences. Here we explore how insects provide unique opportunities for comparative study of developmental behavioral plasticity. Insects have sophisticated behavior and cognitive abilities, and they are frequently studied in their natural environments, which provides an ecological and adaptive perspective that is often more limited in lab-based vertebrate models. A range of cues, from relatively simple cues like temperature to complex social information, influence insect behavior. This variety provides experimentally tractable opportunities to study diverse neural plasticity mechanisms. Insects also have a wide range of neurodevelopmental trajectories while sharing many developmental plasticity mechanisms with vertebrates. In addition, some insects retain only subsets of their juvenile neuronal population in adulthood, narrowing the targets for detailed study of cellular plasticity mechanisms. Insects and vertebrates share many of the same knowledge gaps pertaining to developmental behavioral plasticity. Combined with the extensive study of insect behavior under natural conditions and their experimental tractability, insect systems may be uniquely qualified to address some of the biggest unanswered questions in this field.

Complex Evolution of Insect Insulin Receptors and Homologous Decoy Receptors, and Functional Significance of Their Multiplicity

Evidence accumulates that the functional plasticity of insulin and insulin-like growth factor signaling in insects could spring, among others, from the multiplicity of insulin receptors (InRs). Their multiple variants may be implemented in the control of insect polyphenism, such as wing or caste polyphenism. Here, we present a comprehensive phylogenetic analysis of insect InR sequences in 118 species from 23 orders and investigate the role of three InRs identified in the linden bug, Pyrrhocoris apterus, in wing polymorphism control. We identified two gene clusters (Clusters I and II) resulting from an ancestral duplication in a late ancestor of winged insects, which remained conserved in most lineages, only in some of them being subject to further duplications or losses. One remarkable yet neglected feature of InR evolution is the loss of the tyrosine kinase catalytic domain, giving rise to decoys of InR in both clusters. Within the Cluster I, we confirmed the presence of the secreted decoy of insulin receptor in all studied Muscomorpha. More importantly, we described a new tyrosine kinase-less gene (DR2) in the Cluster II, conserved in apical Holometabola for ∼300 My. We differentially silenced the three P. apterus InRs and confirmed their participation in wing polymorphism control. We observed a pattern of Cluster I and Cluster II InRs impact on wing development, which differed from that postulated in planthoppers, suggesting an independent establishment of insulin/insulin-like growth factor signaling control over wing development, leading to idiosyncrasies in the co-option of multiple InRs in polyphenism control in different taxa.

Hormonal Regulation of Reproductive Diapause That Occurs in the Year-Round Mass Rearing of Bombus terrestris Queens

Adult reproductive diapause is an adaptive strategy under adverse environments for insects and other arthropod species, including bumblebees, which enables queens to survive through a harsh winter and then build new colonies in the following spring. Little research has been done on the molecular regulatory mechanism of reproductive diapause in Bombus terrestris, which is an important pollinator of wild plants and crops. Our previous research identified the conditions that induced reproductive diapause during the year-round mass rearing of B. terrestris. Here, we performed combined transcriptomics and proteomics analyses of reproductive diapause in B. terrestris during and after diapause at three different ecophysiological phases, diapause, postdiapause, and founder postdiapause. The analyses showed that differentially expressed proteins/genes acted in the citrate cycle, insect hormone biosynthesis, insulin and mTOR signaling pathway. To further understand the mechanisms that regulated the reproductive diapause, genes involved in the regulation of JH synthesis, insulin/TOR signal pathway were determined. The BtRheb, BtTOR, BtVg, and BtJHAMT had lower expression levels in diapause queens. The JH III titer levels and the activities of the metabolic enzymes were significantly up-regulated in postdiapause queens. Also, after the microinjection of insulin-like peptides (ILPs) and JH analogue (JHA), hormones, cold-tolerance metabolites, metabolic enzymes, and reproduction showed significant changes. Together with results from other related research, a model of the regulation of reproductive diapause during the year-round mass rearing of B. terrestris was proposed. This study contributes to a comprehensive insight into the molecular regulatory mechanism of reproductive diapause in eusocial insects.

Overwintering conditions impact insulin pathway gene expression in diapausing Megachile rotundata

Diapause is a non-feeding state that many insects undergo to survive the winter months. With fixed resources, overall metabolism and insulin signaling (IIS) are maintained at low levels, but whether those change in response to seasonal temperature fluctuations remains unknown. The focus of this study was to determine 1) how genes in the insulin signaling pathway vary throughout diapause and 2) if that variation changes in response to temperature. To test the hypothesis that expression of IIS pathway genes vary in response to temperature fluctuations during overwintering, alfalfa leafcutting bees, Megachile rotundata, were overwintered at either a constant 4 °C in the lab or in naturally fluctuating temperatures in the field. Expression levels of genes in the IIS pathway, cell cycle regulators, and transcription factors were measured. Overall our findings showed that a few key targets of the insulin signaling pathway, along with growth regulators, change during overwintering, suggesting that only cell cycle regulators, and not the IIS pathway as a whole, change across the phases of diapause. To answer our second question, we compared gene expression levels between temperature treatments at each month for a given gene. We observed significantly more differences in expression of IIS pathway targets, indicating that overwintering conditions impact insulin pathway gene expression and leads to altered expression profiles. With differences seen between temperature treatment groups, these findings indicate that constant temperatures like those used in agricultural storage protocols, lead to different expression profiles and possibly different diapause phenotypes for alfalfa leafcutting bees.

The involvement of insulin/ToR signaling pathway in reproductive performance of Rhodnius prolixus

Insulins are peptide hormones widely studied for their important regulatory roles in metabolism, growth and development. In insects, insulin signaling along with the target of rapamycin (ToR) are involved in detecting and interpreting nutrient levels. Recently, by transcriptome analysis we reported an up-regulation of transcripts involved in insulin/ToR signaling in unfed Rhodnius prolixus; however, this signaling pathway is only activated in fed insects. Here, continuing with the blood-gorging triatomine R. prolixus as a model, we report the direct effect of insulin/ToR signaling on reproductive performance. By immunofluorescence we identified cells in the brain with positive signal to the R. prolixus ILP (Rhopr-ILP1) and show that the insulin receptor and protein effectors downstream of insulin/ToR signaling activation, are differentially expressed in ovarian follicles dependent on their developmental stage. Using qPCR we find that the expression of transcripts involved in insulin signaling in the central nervous system (CNS), fat body and ovaries increase as the state of starvation progresses, promoting a more highly sensitized state to respond rapidly to ILP/IGF levels. In addition, using dsRNA injection and in vivo and ex vivo assays to promote signaling activation we demonstrate a direct participation of insulin/ToR signaling in coordinating the synthesis of the main yolk protein precursor, vitellogenin, thereby influencing the numbers of eggs laid per female. We thereby show a mechanism by which nutritional signaling regulates reproductive performance in a vector of Chagas disease. As reproduction is responsible for propagation of insect populations, this work is important for the development of innovative biocontrol methods.

Functional characterization of the insulin signaling pathway in the hard tick Ixodes ricinus

Ticks are blood-feeding arachnids transmitting a variety of pathogens to humans and animals. A unique trait in tick physiology is their ability to engorge and digest large amounts of host blood, ensuring their high reproductive potential. Activation of the blood digestive machinery in the tick gut, as well as processes controlling maturation of ovaries, are triggered upon blood meal uptake by still largely unknown mechanisms. Sensing of the nutritional status in metazoan organisms is facilitated by the evolutionarily conserved Insulin Signaling Pathway (ISP) and the interlinked Target of Rapamycin (TOR) pathway. Recently, we have identified three components of these pathways in the hard tick Ixodes ricinus midgut transcriptome, namely a putative insulin receptor (InR), and the downstream intracellular serine/threonine kinases AKT and TOR. In this study, we primarily focus on the molecular and functional characterization of the I. ricinus insulin receptor (IrInR), the first InR characterized in Chelicerates. A phylogenetic analysis across the major Arthropod lineages demonstrated that ticks possess only one gene encoding an InR-related molecule. Tissue expression profiling by quantitative PCR in semi-engorged I. ricinus females revealed that the IrInR, as well as AKT (IrAKT) and TOR (IrTOR) are expressed in various organs, with the highest expression being detected in ovaries. We have further evaluated the impact of RNAi-mediated knock-down (KD) of IrInR, IrAKT, and IrTOR on tick blood-feeding and reproductive capacity. Weights of engorged IrInR KD females and laid egg clutches were reduced compared to the control group, and these quantitative parameters clearly correlated with the efficiency of RNAi-KD achieved in individual ticks. The most striking phenotype was observed for IrAKT KD that impaired tick feeding and completely aborted egg production. A recombinant extracellular fragment of the IrInR α-subunit was used to produce antibodies in experimental rabbits to assess its potential as a protective antigen against tick feeding and reproduction. Our data clearly indicate the functionality of the ISP in ticks and demonstrate the need for further investigation of specific roles played by the endogenous insulin-like peptides in tick physiological processes.

Regulation of a Trehalose-Specific Facilitated Transporter (TRET) by Insulin and Adipokinetic Hormone in Rhodnius prolixus, a Vector of Chagas Disease

Using the blood-sucking kissing bug, Rhodnius prolixus as an experimental model, we have studied the involvement of insulin-like peptides (ILPs) and adipokinetic hormone (AKH) signaling in carbohydrate metabolism, focusing on the regulation of the trehalose-specific facilitated transporter (Rhopr-TRET), particularly in the ovaries. We find that trehalose stores in ovaries increase after feeding, synchronously with the beginning of vitellogenesis, but that the transcript expression of enzymes involved in trehalose synthesis show no changes between unfed and blood-fed animals. However, an eightfold increase in Rhopr-TRET transcript expression is observed in the ovaries post-blood meal. In vivo and ex vivo assays using exogenous insulins and Rhopr-AKH, reveal that Rhopr-TRET is up-regulated in ovaries by both peptide families. In accordance with these results, when ILP and AKH signaling cascades are impaired using RNA interference, Rhopr-TRET transcript is down-regulated. In addition, trehalose injection induces an up-regulation of Rhopr-TRET transcript expression and suggests an activation of insulin signaling. Overall, the results support the hypothesis of a direct trehalose uptake by ovaries from the hemolymph through Rhopr-TRET, regulated by ILP and/or AKH. We also show that Rhopr-TRET may work cooperatively with AKH signaling to support the release of trehalose from the ovaries into the hemolymph during the unfed (starved) condition. In conclusion, the results indicate that in females of R. prolixus, trehalose metabolism and its hormonal regulation by ILP and AKH play critical roles in adapting to different nutritional conditions and physiological states.

Domeless receptor loss in fat body tissue reverts insulin resistance induced by a high-sugar diet in Drosophila melanogaster

Insulin resistance is a hallmark of type 2 diabetes resulting from the confluence of several factors, including genetic susceptibility, inflammation, and diet. Under this pathophysiological condition, the dysfunction of the adipose tissue triggered by the excess caloric supply promotes the loss of sensitivity to insulin at the local and peripheral level, a process in which different signaling pathways are involved that are part of the metabolic response to the diet. Besides, the dysregulation of insulin signaling is strongly associated with inflammatory processes in which the JAK/STAT pathway plays a central role. To better understand the role of JAK/STAT signaling in the development of insulin resistance, we used a simple organism, Drosophila melanogaster, as a type 2 diabetes model generated by the consumption of a high-sugar diet. In this model, we studied the effects of inhibiting the expression of the JAK/STAT pathway receptor Domeless, in fat body, on adipose metabolism and glycemic control. Our results show that the Domeless receptor loss in fat body cells reverses both hyperglycemia and the increase in the expression of the insulin resistance marker Nlaz, observed in larvae fed a high sugar diet. This effect is consistent with a significant reduction in Dilp2 mRNA expression and an increase in body weight compared to wild-type flies fed high sugar diets. Additionally, the loss of Domeless reduced the accumulation of triglycerides in the fat body cells of larvae fed HSD and also significantly increased the lifespan of adult flies. Taken together, our results show that the loss of Domeless in the fat body reverses at least in part the dysmetabolism induced by a high sugar diet in a Drosophila type 2 diabetes model.

The origin of wing polyphenism in ants: An eco-evo-devo perspective

The evolution of eusociality, where solitary individuals integrate into a single colony, is a major transition in individuality. In ants, the origin of eusociality coincided with the origin of a wing polyphenism approximately 160 million years ago, giving rise to colonies with winged queens and wingless workers. As a consequence, both eusociality and wing polyphenism are nearly universal features of all ants. Here, we synthesize fossil, ecological, developmental, and evolutionary data in an attempt to understand the factors that contributed to the origin of wing polyphenism in ants. We propose multiple models and hypotheses to explain how wing polyphenism is orchestrated at multiple levels, from environmental cues to gene networks. Furthermore, we argue that the origin of wing polyphenism enabled the subsequent evolution of morphological diversity across the ants. We finally conclude by outlining several outstanding questions for future work.

1 H NMR-based metabonomic evaluation of the pesticides camptothecin and matrine against larvae of Spodoptera litura

BACKGROUND

Camptothecin (CPT) and matrine (MAT) have potential as botanical pesticides against several pest species. However, the mechanisms of metabolic and physiological changes in pests induced by CPT and MAT are unknown. In this study, a toxicological test, an NMR-based metabolomic study, an enzymatic test, and an RT quantitative PCR (RT-qPCR) experiment were all conducted to examine the effect of CPT and MAT on Spodoptera litura.

RESULTS

CPT (0.5-1%) exerted high toxicity against larvae of S. litura and caused growth stagnation and high mortality of larvae. A variety of metabolites were significantly influenced by 0.5% CPT, including several energy-related metabolites such as trehalose, lactate, succinate, citrate, malate, and fumarate. In contrast, MAT showed low toxicity against larvae and induced almost no changes in hemolymph metabolites of S. litura. Enzymatic tests showed that trehalase activity was significantly decreased in larvae after feeding with 0.5% CPT. RT-qPCR showed that the transcription levels of alanine aminotransferase, malate dehydrogenase, and isocitrate dehydrogenase were decreased while lactate dehydrogenase was increased in the 0.5% CPT-treated group.

CONCLUSIONS

These data indicate that one of the important mechanisms of CPT against S. litura larvae is via the inhibition of trehalose hydrolysis and glycolysis. Our findings also suggest that CPT exhibits a stronger toxicological effect than MAT against S. litura, which provides basic information for the application of CPT in the control of S. litura or other lepidoptera pests.

Evolution of the Insulin Gene: Changes in Gene Number, Sequence, and Processing

Insulin has not only made major contributions to the field of clinical medicine but has also played central roles in the advancement of fundamental molecular biology, including evolution. Insulin is essential for the health of vertebrate species, yet its function has been modified in species-specific manners. With the advent of genome sequencing, large numbers of insulin coding sequences have been identified in genomes of diverse vertebrates and have revealed unexpected changes in the numbers of genes within genomes and in their sequence that likely impact biological function. The presence of multiple insulin genes within a genome potentially allows specialization of an insulin gene. Discovery of changes in proteolytic processing suggests that the typical two-chain hormone structure is not necessary for all of inulin's biological activities.

Prediction of neuropeptide precursors and differential expression of adipokinetic hormone/corazonin-related peptide, hugin and corazonin in the brain of malaria vector Nyssorhynchus albimanus during a Plasmodium berghei infection

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We describe precursors that predicted at least sixty neuropeptides in Ny. albimanus.

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At least 16 precursors are encoded in the Ny. albimanus brain.

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Myosuppressin neuropeptide precursor was identified in Ny albimanus.

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acp and hugin transcripts increased in Ny. albimanus brains infected with P. berghei.

Insect neuropeptides, play a central role in the control of many physiological processes. Based on an analysis of Nyssorhynchus albimanus brain transcriptome a neuropeptide precursor database of the mosquito was described. Also, we observed that adipokinetic hormone/corazonin-related peptide (ACP), hugin and corazonin encoding genes were differentially expressed during Plasmodium infection. Transcriptomic data from Ny. albimanus brain identified 29 pre-propeptides deduced from the sequences that allowed the prediction of at least 60 neuropeptides. The predicted peptides include isoforms of allatostatin C, orcokinin, corazonin, adipokinetic hormone (AKH), SIFamide, capa, hugin, pigment-dispersing factor, adipokinetic hormone/corazonin-related peptide (ACP), tachykinin-related peptide, trissin, neuropeptide F, diuretic hormone 31, bursicon, crustacean cardioactive peptide (CCAP), allatotropin, allatostatin A, ecdysis triggering hormone (ETH), diuretic hormone 44 (Dh44), insulin-like peptides (ILPs) and eclosion hormone (EH). The analysis of the genome of An. albimanus and the generated transcriptome, provided evidence for the identification of myosuppressin neuropeptide precursor. A quantitative analysis documented increased expression of precursors encoding ACP peptide, hugin and corazonin in the mosquito brain after Plasmodium berghei infection. This work represents an initial effort to characterize the neuropeptide precursors repertoire of Ny. albimanus and provides information for understanding neuroregulation of the mosquito response during Plasmodium infection.

Aging Regulated Through a Stability Model of Insulin/Insulin Growth Factor Receptor Function

Mutations of the insulin-like receptor in Drosophila extend lifespan. New research suggests this receptor operates in two modes. The first extends lifespan while slowing reproduction and reducing growth. The second strongly extends lifespan without impairing growth or reproduction; it confers longevity assurance. The mutation that confers longevity assurance resides in the kinase insert domain, which contains a potential SH2 binding site for substrate proteins. We apply a recent model for the function of receptor tyrosine kinases to propose how insulin receptor structure can modulate aging. This concept hypothesizes that strong insulin-like ligands promote phosphorylation of high threshold substrate binding sites to robustly induce reproduction, which impairs survival as a consequence of trade-offs. Lower levels of receptor stimulation provide less kinase dimer stability, which reduces reproduction and extends lifespan by avoiding reproductive costs. Environmental conditions that favor diapause alter the expression of insulin ligands to further repress the stability of the interacting kinase domains, block phosphorylation of low threshold substrates and thus induce a unique molecular program that confers longevity assurance. Mutations of the insulin receptor that block low-phosphorylation site interactions, such as within the kinase insert domain, can extend lifespan while maintaining overall dimer stability. These flies are long-lived while maintaining reproduction and growth. The kinase insert domain of Drosophila provides a novel avenue from which to seek signaling of the insulin/insulin-like growth factor system of humans that modulate aging without impacting reproduction and growth, or incurring insulin resistance pathology.

Protein synthesis with conformationally constrained cyclic dipeptides

We have synthesized several conformationally constrained dipeptide analogues as possible substrates for incorporation into proteins. These have included three cyclic dipeptides formed from Boc derivatives of 2,4-diaminobutyric acid, ornithine and lysine, having 5-, 6-, and 7-membered lactam rings, respectively. These dipeptides were used to activate a suppressor tRNA transcript, the latter of which had been prepared by in vitro transcription. Using modified E. coli ribosomes described previously, these activated suppressor tRNAs enabled the incorporation of the three cyclic dipeptides into dihydrofolate reductase (DHFR) at positions 18 and 49. The suppression yields increased with increasing lactam ring size and were found to proceed in suppression yields ranging from 3.4 to 8.9% at two different protein sites for the 5-, 6- and 7-membered lactam dipeptides. The greater facility of incorporation of the 7-membered lactam prompted us to prepare two 7-membered cyclic acylhydrazides (4 and 5) by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI)-mediated cyclization of amino acids having selectively protected hydrazine functional groups in their side chains. In common with the lactam dipeptides, acylhydrazide dipeptides 4 and 5 could be used to activate the same suppressor tRNA transcript and to incorporate the cyclic dipeptides into DHFR. They were incorporated into the same two DHFR sites in suppression yields ranging from 8.3 to 11.2%.

Insulin receptor deficiency reduces lipid synthesis and reproductive function in the insect Rhodnius prolixus

Rhodnius prolixus, a vector of Chagas disease, is a hematophagous insect that feeds exclusively on blood. Each blood meal is digested within the first fourteen days after feeding, providing substrates for lipid synthesis for storage and egg production. These events are precisely regulated and emerging evidence points to a key function of insulin-like peptides (ILPs) in this control. Here we investigated the role of insulin receptor in the regulation of nutrient metabolism in fed adult females. The expression of insulin receptor (RhoprIR) gene was determined in adult organs, and it was highest in ovaries and previtellogenic follicles. We generated insects with RNAi-mediated knockdown of RhoprIR to address the physiological role of this receptor. RhoprIR deficiency improved longevity and reduced triacylglycerol storage in the fat body, whereas blood digestion remained unchanged for seven days after blood meal. The lower lipid content was attributable to decreased de novo lipogenesis as well as reduced incorporation of hemolymph-derived fatty acids into newly synthesized lipids within this organ. Consistent with that, fat bodies from RhoprIR-deficient insects exhibited decreased gene expression levels of lipophorin receptor (RhoprLpR), glycerol-3-phosphate acyltransferase 1 and 4 (RhoprGpat1 and RhoprGpat4), and carnitine palmitoyltransferase 1 (RhoprCpt1). Although hemolymph lipid profile was not affected by RhoprIR disruption, the concentration of circulating vitellogenin was increased. In line with these changes, RhoprIR-deficient females exhibited smaller ovaries and a marked reduction in oviposition. Taken together, these findings support a key role of insulin receptor in nutrient homeostasis, lipid synthesis and egg production following a blood meal.

Insulin/IGF signaling and TORC1 promote vitellogenesis via inducing juvenile hormone biosynthesis in the American cockroach

Vitellogenesis, including vitellogenin (Vg) production in the fat body and Vg uptake by maturing oocytes, is of great importance for the successful reproduction of adult females. The endocrinal and nutritional regulation of vitellogenesis differs distinctly in insects. Here, the complex crosstalk between juvenile hormone (JH) and the two nutrient sensors insulin/IGF signaling (IIS) and target of rapamycin complex1 (TORC1), was investigated to elucidate the molecular mechanisms of vitellogenesis regulation in the American cockroach, Periplaneta americana Our data showed that a block of JH biosynthesis or JH action arrested vitellogenesis, in part by inhibiting the expression of doublesex (Dsx), a key transcription factor gene involved in the sex determination cascade. Depletion of IIS or TORC1 blocked both JH biosynthesis and vitellogenesis. Importantly, the JH analog methoprene, but not bovine insulin (to restore IIS) and amino acids (to restore TORC1 activity), restored vitellogenesis in the neck-ligated (IIS-, TORC1- and JH-deficient) and rapamycin-treated (TORC1- and JH-deficient) cockroaches. Combining classic physiology with modern molecular techniques, we have demonstrated that IIS and TORC1 promote vitellogenesis, mainly via inducing JH biosynthesis in the American cockroach.

Tyramine and its receptor TYR1 linked behavior QTL to reproductive physiology in honey bee workers (Apis mellifera)

Honey bees (Apis mellifera) provide an excellent model for studying how complex social behavior evolves and is regulated. Social behavioral traits such as the division of labor have been mapped to specific genomic regions in quantitative trait locus (QTL) studies. However, relating genomic mapping to gene function and regulatory mechanism remains a big challenge for geneticists. In honey bee workers, division of labor is known to be regulated by reproductive physiology, but the genetic basis of this regulation remains unknown. In this case, QTL studies have identified tyramine receptor 1 (TYR1) as a candidate gene in region pln2, which is associated with multiple worker social traits and reproductive anatomy. Tyramine (TA), a neurotransmitter, regulates physiology and behavior in diverse insect species including honey bees. Here, we examine directly the effects of TYR1 and TA on worker reproductive physiology, including ovariole number, ovary function and the production of vitellogenin (VG, an egg yolk precursor). First, we used a pharmacology approach to demonstrate that TA affects ovariole number during worker larval development and increases ovary maturation during the adult stage. Second, we used a gene knockdown approach to show that TYR1 regulates vg transcription in adult workers. Finally, we estimated correlations in gene expression and propose that TYR1 may regulate vg transcription by coordinating hormonal and nutritional signals. Taken together, our results suggest TYR1 and TA play important roles in regulating worker reproductive physiology, which in turn regulates social behavior. Our study exemplifies a successful forward-genetic strategy going from QTL mapping to gene function.

Transcriptome analysis of pituitary gland revealed candidate genes and gene networks regulating the growth and development in goose

Goose is important meat poultry and its growth and development has always been the focus of attention, but the regulation mechanisms of genes and gene network underlying growth and development of goose are still unclear. Three males of large-size Shitou goose and three males of small size Wuzong goose at 5 weeks of age were used for transcriptome analysis with deep sequencing. After slaughter, their pituitary gland was taken for RNA-seq. A total of 290 DEGs were identified by fold change ≥2 and false discovery rate (FDR) <0.05, where there were 148 upregulated genes and 142 downregulated genes in Shitou goose compared to Wuzong goose. Results also showed that the DEGs related to insulin signaling pathway could increase protein synthesis and fat production, and the interaction network of DEGs was mainly related to development, endocrine system, inflammatory diseases, tissue damage and abnormality. The DEGs involved in the growth and function of the pituitary organs may regulate the growth and development of the body by affecting the synthesis and secretion of pituitary hormones. The results of this study will help to understand the regulatory mechanism of goose growth and development.

Chromatin accessibility and transcriptome landscapes of Monomorium pharaonis brain

The emergence of social organization (eusociality) is a major event in insect evolution. Although previous studies have investigated the mechanisms underlying caste differentiation and social behavior of eusocial insects including ants and honeybees, the molecular circuits governing sociality in these insects remain obscure. In this study, we profiled the transcriptome and chromatin accessibility of brain tissues in three Monomorium pharaonis ant castes: queens (including mature and un-mated queens), males and workers. We provide a comprehensive dataset including 16 RNA-sequencing and 16 assay for transposase accessible chromatin (ATAC)-sequencing profiles. We also demonstrate strong reproducibility of the datasets and have identified specific genes and open chromatin regions in the genome that may be associated with the social function of these castes. Our data will be a valuable resource for further studies of insect behaviour, particularly the role of brain in the control of eusociality.

Insights into carbohydrate metabolism from an insulin-like peptide in Macrobrachium rosenbergii

This study identified an insulin-like peptide (ILP) in Macrobrachium rosenbergii termed Mr-ILP and further investigated its function through glucose injection and RNAi. With the analysis of five other glucose metabolism related genes, this study shed light on the molecular mechanism of carbohydrate metabolism in crustaceans. Mr-ILP shared the typical skeleton with six conserved cysteine and mainly expressed in neuroendocrine system. In M. rosenbergii, the elevated hemolymph glucose concentration after glucose injection returned to basal levels in short time, implying an efficient regulatory system in carbohydrate metabolism. Hyperglycemic related genes answered the elevated hemolymph glucose concentration quickly with significant decreased expression level, while Mr-ILP showed delayed response. Instead, glycolysis increased after glucose injection, which indicated glycolysis might play an important role in lowering the abnormally high glucose level. In vivo silencing of Mr-ILP, by injecting the prawns with double-stranded RNA (dsRNA) for 21 days reduced its expression by approximately 75%. Accordingly, glycogen synthase decreased and the trehalose and glycogen level in the hepatopancreas were significantly reduced, indicating the function of Mr-ILP in oligosaccharide and polysaccharide accumulation. When Mr-ILP was silenced, the expression of hyperglycemic related genes were enhanced, but the hemolymph glucose level was not elevated significantly, which might attribute to the increased glycolysis to keep a balanced glucose level in hemolymph.

The antibiotic jinggangmycin increases brown planthopper (BPH) fecundity by enhancing rice plant sugar concentrations and BPH insulin-like signaling

The brown planthopper (BPH), Nilaparvata lugens, is a resurgent pest with an unexpected response to jinggangmycin (JGM), a broadly applied antibiotic used to control rice sheath blight disease. JGM stimulates BPH fecundity, but the underlining molecular mechanisms remain unclear. Here we report that JGM sprays led to increased glucose concentrations, photosynthesis and gene expression, specifically Rubsico, sucrose phosphate synthase, invertase 2 (INV2) and INV3 in rice plants. JGM sprays led to high-glucose rice plants. Feeding BPH on these plants led to increased insulin-like signaling and vitellogenin synthesis. Treating BPH with metformin, a gluconeogenesis inhibitor, reversed the influence of feeding on high-glucose rice, which was rescued by glucose injections. Silencing insulin-like peptide 2 using per os dsRNA led to reduction in juvenile hormone (JH) III titers and other fecundity parameters, which were reversed by topical applications of the JH analog, methoprene. We infer that JGM acts via two broad mechanisms, one through increasing rice plant sugar concentrations and a second by upregulating BPH insulin-like signaling.

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.

Functional diversification of three delta-class glutathione S-transferases involved in development and detoxification in Tribolium castaneum

Glutathione S-transferases (GSTs) are members of a multifunctional enzyme superfamily. Forty-one GSTs have been identified in Tribolium castaneum; however, none of the 41 GSTs has been functionally characterized. Here, three delta-class GSTs, TcGSTd1, TcGSTd2 and TcGSTd3, of T. castaneum were successfully cloned and expressed in Escherichia coli. All of the studied GSTs catalysed the conjugation of reduced glutathione with 1-chloro-2,4-dinitrobenzene. Insecticide treatment showed that the expression levels of TcGSTd3 and TcGSTd2 were significantly increased after exposure to phoxim and lambda-cyhalothrin, whereas TcGSTd1 was slightly upregulated only in response to phoxim. A disc diffusion assay showed that overexpression of TcGSTD3, but not TcGSTD1 or TcGSTD2, in E. coli increased resistance to paraquat-induced oxidative stress. RNA interference knockdown of TcGSTd1 caused metamorphosis deficiencies and reduced fecundity by regulating insulin/target-of-rapamycin signalling pathway-mediated ecdysteroid biosynthesis, and knockdown of TcGSTd3 led to reduced fertility and a decreased hatch rate of the offspring, probably caused by the reduced antioxidative activity in the reproductive organs. These results indicate that TcGSTd3 and TcGSTd2 may play vital roles in cellular detoxification, whereas TcGSTd1 may play essential roles in normal development of T. castaneum. These delta-class GSTs in T. castaneum have obtained different functions during the evolution.

Performance and Transcriptional Response of the Green Peach Aphid Myzus persicae to the Restriction of Dietary Amino Acids

Free amino acids in the phloem sap are the dominant nitrogen source for aphids, but their availability is usually poor. Although some studies have explored the effect of dietary amino acid restriction on aphid performance, little is known about the molecular basis of these effects. Here, we examined the performance and transcriptome of the green peach aphid, Myzus persicae, fed a standard diet (Control diet) or a diet containing 50% of the total amino acids of the Control diet (Half diet). Aphid weight and fecundity were significantly reduced in the Half diet group. Transcriptomic analysis showed that a total of 1460 genes were differentially expressed between the groups were fed on the two diets, which many of them were associated with nutrient and energy metabolism. When feeding on the Half diet, aphids upregulated genes associated with the amino acid biosynthetic pathway (predominantly amino acid biosynthesis genes and some amino acid transporter genes) as well as the cysteine and serine protease genes. Furthermore, these aphids displayed increased expression of genes associated with glycolysis, which could generate intermediates for de novo amino acid biosynthesis. Consistent with this, elevated glucose levels were observed in aphids in the Half diet group. Additionally, the expression levels of several genes associated with hormonal signaling pathway were altered. Several genes related to juvenile hormone and insulin-like peptide (ILP) signaling were downregulated, including Krüppel homolog 1 (Kr-h1) and insulin-like peptide 5 (Ilp5), respectively. In contrast, several genes related to ecdysone signaling were upregulated including broad-complex core protein (Br-c) and shade (Shd). Despite their poor performances, M. persicae adapted to dietary restriction of amino acids, through upregulation of genes involved in amino acid biosynthesis, glycolysis, and protein degradation, as well as by altering the expression level of genes involved in hormone signaling pathways.

The Role of Peptide Hormones in Insect Lipid Metabolism

Lipids are the primary storage molecules and an essential source of energy in insects during reproduction, prolonged periods of flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. The fat body is primarily composed of adipocytes, which accumulate triacylglycerols in intracellular lipid droplets. Genomics and proteomics, together with functional analyses, such as RNA interference and CRISPR/Cas9-targeted genome editing, identified various genes involved in lipid metabolism and elucidated their functions. However, the endocrine control of insect lipid metabolism, in particular the roles of peptide hormones in lipogenesis and lipolysis are relatively less-known topics. In the current review, the neuropeptides that directly or indirectly affect insect lipid metabolism are introduced. The primary lipolytic and lipogenic peptide hormones are adipokinetic hormone and the brain insulin-like peptides (ILP2, ILP3, ILP5). Other neuropeptides, such as insulin-growth factor ILP6, neuropeptide F, allatostatin-A, corazonin, leucokinin, tachykinins and limostatin, might stimulate lipolysis, while diapause hormone-pheromone biosynthesis activating neuropeptide, short neuropeptide F, CCHamide-2, and the cytokines Unpaired 1 and Unpaired 2 might induce lipogenesis. Most of these peptides interact with one another, but mostly with insulin signaling, and therefore affect lipid metabolism indirectly. Peptide hormones are also involved in lipid metabolism during reproduction, flight, diapause, starvation, infections and immunity; these are also highlighted. The review concludes with a discussion of the potential of lipid metabolism-related peptide hormones in pest management.

Two insulin receptors coordinate oogenesis and oviposition via two pathways in the green lacewing, Chrysopa pallens

Insulin signalling in insects, as in mammals, regulates various physiological functions, such as reproduction. However, the molecular mechanism by which insulin signals orchestrate ovarian stem cell proliferation, vitellogenesis, and oviposition remains elusive. Here, we investigate the functions of the phosphoinositide 3-kinase (PI3K)-serine/threonine kinase (Akt) pathway, GTPase Ras/mitogen-activated protein kinase (MAPK) pathway, and their downstream messengers in a natural predator, Chrysopa pallens, by the RNAi method. When C. pallens vitellogenin gene 1 (CpVg1) expression was knocked down, the follicle maturation was arrested and total fecundity was reduced. Silencing C. pallens insulin receptor 1 (CpInR1) suppressed Vg transcription and reduced egg mass and hatching rate. Depletion of C. pallens insulin receptor 2 (CpInR2) transcripts lowered Vg transcript level, hampered ovarian development and decreased reproductive output. Knockdown of C. pallens Akt (CpAkt) and C. pallens extracellular-signal-regulated kinase (Cperk) caused phenotypes similar to those caused by knockdown of CpInR2. Disruption of C. pallens transcription factor forkhead box O (CpFoxO) expression caused no significant effects on ovarian development, but sharply impaired total fecundity. Interference with the expression of C. pallens target of rapamycin (CpTor) gene and C. pallens cAMP-response element binding protein (CpCreb) gene led to a down-regulation of Vg transcription, blocking of ovariole growth, and decrease in egg quality. These results suggested the two CpInRs orchestrate oogenesis and oviposition via two signalling pathways to guarantee natural reproduction in the green lacewing, C. pallens.

The miR-9b microRNA mediates dimorphism and development of wing in aphids

Wing dimorphism is a phenomenon of phenotypic plasticity in aphid dispersal. However, the signal transduction for perceiving environmental cues (e.g., crowding) and the regulation mechanism remain elusive. Here, we found that aci-miR-9b was the only down-regulated microRNA (miRNA) in both crowding-induced wing dimorphism and during wing development in the brown citrus aphid Aphis citricidus We determined a targeted regulatory relationship between aci-miR-9b and an ABC transporter (AcABCG4). Inhibition of aci-miR-9b increased the proportion of winged offspring under normal conditions. Overexpression of aci-miR-9b resulted in decline of the proportion of winged offspring under crowding conditions. In addition, overexpression of aci-miR-9b also resulted in malformed wings during wing development. This role of aci-miR-9b mediating wing dimorphism and development was also confirmed in the pea aphid Acyrthosiphon pisum The downstream action of aci-miR-9b-AcABCG4 was based on the interaction with the insulin and insulin-like signaling pathway. A model for aphid wing dimorphism and development was demonstrated as the following: maternal aphids experience crowding, which results in the decrease of aci-miR-9b. This is followed by the increase of ABCG4, which then activates the insulin and insulin-like signaling pathway, thereby causing a high proportion of winged offspring. Later, the same cascade, "miR-9b-ABCG4-insulin signaling," is again involved in wing development. Taken together, our results reveal that a signal transduction cascade mediates both wing dimorphism and development in aphids via miRNA. These findings would be useful in developing potential strategies for blocking the aphid dispersal and reducing viral transmission.

Genome of the webworm Hyphantria cunea unveils genetic adaptations supporting its rapid invasion and spread

BACKGROUND

The fall webworm Hyphantria cunea is an invasive and polyphagous defoliator pest that feeds on nearly any type of deciduous tree worldwide. The silk web of H. cunea aids its aggregating behavior, provides thermal regulation and is regarded as one of causes for its rapid spread. In addition, both chemosensory and detoxification genes are vital for host adaptation in insects.

RESULTS

Here, a high-quality genome of H. cunea was obtained. Silk-web-related genes were identified from the genome, and successful silencing of the silk protein gene HcunFib-H resulted in a significant decrease in silk web shelter production. The CAFE analysis showed that some chemosensory and detoxification gene families, such as CSPs, CCEs, GSTs and UGTs, were expanded. A transcriptome analysis using the newly sequenced H. cunea genome showed that most chemosensory genes were specifically expressed in the antennae, while most detoxification genes were highly expressed during the feeding peak. Moreover, we found that many nutrient-related genes and one detoxification gene, HcunP450 (CYP306A1), were under significant positive selection, suggesting a crucial role of these genes in host adaptation in H. cunea. At the metagenomic level, several microbial communities in H. cunea gut and their metabolic pathways might be beneficial to H. cunea for nutrient metabolism and detoxification, and might also contribute to its host adaptation.

CONCLUSIONS

These findings explain the host and environmental adaptations of H. cunea at the genetic level and provide partial evidence for the cause of its rapid invasion and potential gene targets for innovative pest management strategies.

Alteration of insulin signaling to control insect pest by using transformed bacteria expressing dsRNA

BACKGROUND

Insulin/insulin-like growth factor signaling (IIS) is known to mediate larval growth and adult reproduction in the legume pod borer, Maruca vitrata (Lepidoptera: Crambidae). Four IIS components (InR, FOXO, Akt, and TOR) play crucial roles in the IIS pathway.

RESULTS

RNA interference (RNAi) against any of these four IIS component genes was effective in suppressing each target mRNA level by either hemocoelic injection or oral administration using gene-specific double-stranded RNAs (dsRNAs). These RNAi treatments interfered with larval growth, leading to small pupae or significant larval mortality. For massive production of dsRNA, transformed bacteria expressing dsRNAs of these four IIS components were prepared with L4440 expression vector and HT115 strain of Escherichia coli. The transformed bacteria killed the larvae in a dose-dependent manner by feeding administration. An ultra-sonication pretreatment was performed to impair bacterial membrane and increase dsRNA release from the bacteria in insect intestine. This pretreatment increased the insecticidal activity of these recombinant bacteria. To further increase dsRNA toxicity, its mixture with Bacillus thuringiensis (Bt) was prepared and showed significant increase of Bt insecticidal activity in the laboratory. The bacterial mixture also showed a high control efficacy (83.3%) in an adzuki bean (Vigna angularis) field infested by M. vitrata. Furthermore, such a dsRNA effect was specific for M. vitrata, but not for non-target insects.

CONCLUSION

The bacteria expressing dsRNA specific to IIS components can be used to develop dsRNA insecticide. © 2019 Society of Chemical Industry.