Identification of a prothoracicostatic peptide in the larval brain of the silkworm, Bombyx mori

Sex peptide receptor is not required for refractoriness to remating or induction of egg laying in Aedes aegypti

Across diverse insect taxa, the behavior and physiology of females dramatically changes after mating-processes largely triggered by the transfer of seminal proteins from their mates. In the vinegar fly Drosophila melanogaster, the seminal protein sex peptide (SP) decreases the likelihood of female flies remating and causes additional behavioral and physiological changes that promote fertility including increasing egg production. Although SP is only found in the Drosophila genus, its receptor, sex peptide receptor (SPR), is the widely conserved myoinhibitory peptide (MIP) receptor. To test the functional role of SPR in mediating postmating responses in a non-Drosophila dipteran, we generated 2 independent Spr-knockout alleles in the yellow fever mosquito, Aedes aegypti. Although SPR is needed for postmating responses in Drosophila and the cotton bollworm Helicoverpa armigera, Spr mutant Ae. aegypti show completely normal postmating decreases in remating propensity and increases in egg laying. In addition, injection of synthetic SP or accessory gland homogenate from D. melanogaster into virgin female mosquitoes did not elicit these postmating responses. Our results demonstrate that Spr is not required for these canonical postmating responses in Ae. aegypti, indicating that other, as yet unknown, signaling pathways are likely responsible for these behavioral switches in this disease vector.

Identification of the principal neuropeptide MIP and its action pathway in larval settlement of the echiuran worm Urechis unicinctus

BACKGROUND

Larval settlement and metamorphosis represent critical events in the life history of marine benthic animals. Myoinhibitory peptide (MIP) plays a pivotal role in larval settlement of marine invertebrates. However, the molecular mechanisms of MIP involved in this process are not well understood.

RESULTS

In this study, we evaluated the effects of thirteen MIP mature peptides on triggering the larval settlement of Urechis unicinctus (Xenopneusta, Urechidae), and determined that MIP2 was the principal neuropeptide. Transcriptomic analysis was employed to identify differentially expressed genes (DEGs) between the MIP2-treated larvae and normal early-segmentation larvae. Both cAMP and calcium signaling pathways were enriched in the DEGs of the MIP2-treated larvae, and two neuropeptide receptor genes (Spr, Fmrfar) were up-regulated in the MIP2-treated larvae. The activation of the SPR-cAMP pathway by MIP2 was experimentally validated in HEK293T cells. Furthermore, fourteen cilia-related genes, including Tctex1d2, Cfap45, Ift43, Ift74, Ift22, Cav1 and Mns1, etc. exhibited down-regulated expression in the MIP2-treated larvae. Whole-mount in situ hybridization identified two selected ciliary genes, Tctex1d2 and Cfap45, were specially expressed in circumoral ciliary cells of the early-segmentation larvae. Knocking down Tctex1d2 mRNA levels by in vivo RNA interference significantly increased the larval settlement rate.

CONCLUSION

Our findings suggest that MIP2 inhibits the function of the cilia-related genes, such as Tctex1d2, through the SPR-cAMP-PKA pathway, thereby inducing larval settlement in U. unicinctus. The study contributes important data to the understanding of neuropeptide regulation in larval settlement.

Molecular Characterization of Two Wamide Neuropeptide Signaling Systems in Mollusk Aplysia

Neuropeptides with the C-terminal Wamide (Trp-NH₂) are one of the last common ancestors of peptide families of eumetazoans and play various physiological roles. In this study, we sought to characterize the ancient Wamide peptides signaling systems in the marine mollusk Aplysia californica, i.e., APGWamide (APGWa) and myoinhibitory peptide (MIP)/Allatostatin B (AST-B) signaling systems. A common feature of protostome APGWa and MIP/AST-B peptides is the presence of a conserved Wamide motif in the C-terminus. Although orthologs of the APGWa and MIP signaling systems have been studied to various extents in annelids or other protostomes, no complete signaling systems have yet been characterized in mollusks. Here, through bioinformatics, molecular and cellular biology, we identified three receptors for APGWa, namely, APGWa-R1, APGWa-R2, and APGWa-R3. The EC₅₀ values for APGWa-R1, APGWa-R2, and APGWa-R3 are 45, 2100, and 2600 nM, respectively. For the MIP signaling system, we predicted 13 forms of peptides, i.e., MIP1-13 that could be generated from the precursor identified in our study, with MIP5 (WKQMAVWa) having the largest number of copies (4 copies). Then, a complete MIP receptor (MIPR) was identified and the MIP1-13 peptides activated the MIPR in a dose-dependent manner, with EC₅₀ values ranging from 40 to 3000 nM. Peptide analogs with alanine substitution experiments demonstrated that the Wamide motif at the C-terminus is necessary for receptor activity in both the APGWa and MIP systems. Moreover, cross-activity between the two signaling systems showed that MIP1, 4, 7, and 8 ligands could activate APGWa-R1 with a low potency (EC₅₀ values: 2800-22,000 nM), which further supported that the APGWa and MIP signaling systems are somewhat related. In summary, our successful characterization of Aplysia APGWa and MIP signaling systems represents the first example in mollusks and provides an important basis for further functional studies in this and other protostome species. Moreover, this study may be useful for elucidating and clarifying the evolutionary relationship between the two Wamide signaling systems (i.e., APGWa and MIP systems) and their other extended neuropeptide signaling systems.

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.

Myoinhibitory peptides in the central complex of the locust Schistocerca gregaria and colocalization with locustatachykinin-related peptides

The central complex in the brain of insects provides a neural network for sensorimotor processing that is essential for spatial navigation and locomotion and plays a role in sleep control. Studies on the neurochemical architecture of the central complex have been performed especially in the fruit fly Drosophila melangoaster and the desert locust, Schistocerca gregaria. In several insect species, myoinhibitory peptides (MIPs) are involved in circadian control and sleep-wake regulation. To identify neurons that might underlie these functions, we investigated the distribution of MIPs in the central complex of the locust. In silico transcript analysis suggests the presence of eight different MIPs in the desert locust. Through immunolabeling, we identified five systems of central-complex neurons that express MIP-like peptides. Two systems constitute columnar neurons of the protocerebral bridge and the lower division of the central body, while the other three systems are columnar neurons (two systems) and tangential neurons (one system) of the upper division of the central body. The innervation pattern and cell count of two systems of columnar neurons revealed the existence of 18 instead of 16 columns of the protocerebral bridge. Immunostaining of preparations containing intracellularly stained single cells allowed us to further specify subtypes of labeled columnar neurons. Double-label experiments showed that three systems of MIP-immunostained columnar neurons are also locustatachykinin-immunoreactive. No colocalization was found with serotonin immunostaining. The data provide novel insights into the architecture of the locust central complex and suggest that MIPs play a prominent role within the central-complex network.

Immunoreactive Response of Plast-MIPs to Fasting and Their Functional Role in the Reduction of Hemolymph Reducing Sugars in the Brown-Winged Green Bug, Plautia stali

Animals survive nutrient deficiency by controlling their physiology, such as sugar metabolism and energy-consuming developmental events. Although research on the insect neural mechanisms of the starvation-induced modulation has progressed, the mechanisms have not been fully understood due to their complexity. Myoinhibitory peptides are known to be neuropeptides involved in various physiological activities, development, and behavior. Here, we analyzed the responsiveness of Plautia stali myoinhibitory peptides (Plast-MIPs) to starvation and their physiological role in the brown-winged green bug, P. stali. First, we performed immunohistochemical analyses to investigate the response of Plast-MIP neurons in the cephalic ganglion to fasting under long day conditions. Fasting significantly enhanced the immunoreactivity to Plast-MIPs in the pars intercerebralis (PI), which is known to be a brain region related to various endocrine regulations. Next, to analyze the physiological role of Plast-MIPs, we performed RNA interference-mediated knockdown of Plast-Mip and injection of synthetic Plast-MIP in normally fed and fasted females. The knockdown of Plast-Mip did not have significant effects on the body weight or proportions of ovarian development in each feeding condition. On the other hand, the knockdown of Plast-Mip increased the gonadosomatic index of normally fed females whereas it did not have a significant effect on food intake. Notably, the knockdown of Plast-Mip diminished the fasting-induced reduction of hemolymph reducing sugar levels. Additionally, injection of synthetic Plast-MIP acutely decreased the hemolymph reducing sugar level. Our results suggested responsiveness of Plast-MIPs in the PI to fasting and their functional role in reduction of the hemolymph reducing sugar level.

Evolution and Potential Function in Molluscs of Neuropeptide and Receptor Homologues of the Insect Allatostatins

The allatostatins (ASTs), AST-A, AST-B and AST-C, have mainly been investigated in insects. They are a large group of small pleotropic alloregulatory neuropeptides that are unrelated in sequence and activate receptors of the rhodopsin G-protein coupled receptor family (GPCRs). The characteristics and functions of the homologue systems in the molluscs (Buccalin, MIP and AST-C-like), the second most diverse group of protostomes after the arthropods, and of high interest for evolutionary studies due to their less rearranged genomes remains to be explored. In the present study their evolution is deciphered in molluscs and putative functions assigned in bivalves through meta-analysis of transcriptomes and experiments. Homologues of the three arthropod AST-type peptide precursors were identified in molluscs and produce a larger number of mature peptides than in insects. The number of putative receptors were also distinct across mollusc species due to lineage and species-specific duplications. Our evolutionary analysis of the receptors identified for the first time in a mollusc, the cephalopod, GALR-like genes, which challenges the accepted paradigm that AST-AR/buccalin-Rs are the orthologues of vertebrate GALRs in protostomes. Tissue transcriptomes revealed the peptides, and their putative receptors have a widespread distribution in bivalves and in the bivalve Mytilus galloprovincialis, elements of the three peptide-receptor systems are highly abundant in the mantle an innate immune barrier tissue. Exposure of M. galloprovincialis to lipopolysaccharide or a marine pathogenic bacterium, Vibrio harveyi, provoked significant modifications in the expression of genes of the peptide precursor and receptors of the AST-C-like system in the mantle suggesting involvement in the immune response. Overall, our study reveals that homologues of the arthropod AST-systems in molluscs are potentially more complex due to the greater number of putative mature peptides and receptor genes. In bivalves they have a broad and varying tissue distribution and abundance, and the elements of the AST-C-like family may have a putative function in the immune response.

Identification of the neuropeptide precursor genes potentially involved in the larval settlement in the Echiuran worm Urechis unicinctus

BACKGROUND

In marine invertebrate life cycles, which often consist of planktonic larval and benthonic adult stages, settlement of the free-swimming larva to the sea floor in response to environmental cues is a key life cycle transition. Settlement is regulated by a specialized sensory-neurosecretory system, the larval apical organ. The neuroendocrine mechanisms through which the apical organ transduces environmental cues into behavioral responses during settlement are not fully understood yet.

RESULTS

In this study, a total of 54 neuropeptide precursors (pNPs) were identified in the Urechis unicinctus larva and adult transcriptome databases using local BLAST and NpSearch prediction, of which 10 pNPs belonging to the ancient eumetazoa, 24 pNPs belonging to the ancient bilaterian, 3 pNPs belonging to the ancient protostome, 9 pNPs exclusive in lophotrochozoa, 3 pNPs exclusive in annelid, and 5 pNPs only found in U. unicinctus. Furthermore, four pNPs (MIP, FRWamide, FxFamide and FILamide) which may be associated with the settlement and metamorphosis of U. unicinctus larvae were analysed by qRT-PCR. Whole-mount in situ hybridization results showed that all the four pNPs were expressed in the region of the apical organ of the larva, and the positive signals were also detected in the ciliary band and abdomen chaetae. We speculated that these pNPs may regulate the movement of larval cilia and chaeta by sensing external attachment signals.

CONCLUSIONS

This study represents the first comprehensive identification of neuropeptides in Echiura, and would contribute to a complete understanding on the roles of various neuropeptides in larval settlement of most marine benthonic invertebrates.

Genomics- and Peptidomics-Based Discovery of Conserved and Novel Neuropeptides in the American Cockroach

As a model hemimetabolous insect species and an invasive urban pest that is globally distributed, the American cockroach, Periplaneta americana, is of great interest in both basic and applied research. Previous studies on P. americana neuropeptide identification have been based on biochemical isolation and molecular cloning. In the present study, an integrated approach of genomics- and peptidomics-based discovery was performed for neuropeptide identification in this insect species. First, 67 conserved neuropeptide or neurohormone precursor genes were predicted via an in silico analysis of the P. americana genome and transcriptome. Using a large-scale peptidomic analysis of peptide extracts from four different tissues (the central nervous system, corpora cardiac and corpora allata complex, midgut, and male accessory gland), 35 conserved (predicted) neuropeptides and a potential (novel) neuropeptide were then identified. Subsequent experiments revealed the tissue distribution, sex difference, and developmental patterns of two conserved neuropeptides (allatostatin B and short neuropeptide F) and a novel neuropeptide (PaOGS36577). Our study shows a comprehensive neuropeptidome and detailed spatiotemporal distribution patterns, providing a solid basis for future functional studies of neuropeptides in the American cockroach (data are available via ProteomeXchange with identifier PXD021660).

Plodia interpunctella (Lepidoptera: Pyralidae): Intoxication with essential oils isolated from Lippia turbinata (Griseb.) and analysis of neuropeptides and neuropeptide receptors, putative targets for pest control

The Indian meal moth Plodia interpunctella is a pest of stored products worldwide. Plant-derived essential oils with insecticidal activity could be safe products to control this species. The scarce information about the mode of action of most plant-derived products limits their use for the control of insect pests. Here, we demonstrate that an essential oil distilled from Lippia turbinata ("poleo") has insecticidal activity on P. interpunctella larvae. Furthermore, we performed a comprehensive characterization of P. interpunctella neuroendocrine system, in comparison with other lepidopteran species.

Function and Distribution of the Wamide Neuropeptide Superfamily in Metazoans

The Wamide neuropeptide superfamily is of interest due to its distinctive functions in regulating life cycle transitions, metamorphic hormone signaling, and several aspects of digestive system function, from gut muscle contraction to satiety and fat storage. Due to variation among researchers in naming conventions, a global view of Wamide signaling in animals in terms of conservation or diversification of function is currently lacking. Here, I summarize the phylogenetic distribution of Wamide neuropeptides based on current data and describe recent findings in the areas of Wamide receptors and biological functions. Common trends that emerge across Cnidarians and protostomes are the presence of multiple Wamide receptors within a single organism, and the fact that Wamide signaling likely functions across an extensive variety of biological systems, including visual, circadian, and reproductive systems. Important areas of focus for future research are the further identification of Wamide-receptor pairs, confirmation of the phylogenetic distribution of Wamides through largescale sequencing and mass spectrometry, and assignment of different functions to specific subsets of Wamide-expressing neurons. More extensive study of Wamide signaling throughout larval development in a greater number of phyla is also important in order to understand the role of Wamides in hormonal regulation. Defining the evolution and function of neuropeptide signaling in animal nervous systems will benefit from an increased understanding of Wamide function and signaling mechanisms in a wider variety of organisms, beyond the traditional model systems.

Ecdysteroidogenesis in Heliothis virescens (Lepidoptera: Noctuidae): Recombinant Prothoracicotropic Hormone and Brain Extract Show Comparable Effects

Prothoracicotropic hormone (PTTH) is a neuropeptide that triggers a cascade of events within the prothoracic gland (PG) cells, leading to the activation of all the crucial enzymes involved in ecdysone biosynthesis, the main insect steroid hormone. Studies concerning ecdysteroidogenesis predicted PTTH action using brain extract (BE), consisting in a complex mixture in which some components positively or negatively interfere with PTTH-stimulated ecdysteroidogenesis. Consequently, the integration of these opposing factors in steroidogenic tissues leads to a complex secretory pattern. A recombinant form of prothoracicotropic hormone (rPTTH) from the tobacco budworm Heliothis virescens (F.) (Lepidoptera: Noctuidae) was expressed and purified to perform in vitro tests in a standard and repeatable manner. A characterization of rPTTH primary and secondary structures was performed. The ability of rPTTH and H. virescens BE to stimulate ecdysteroidogenesis was investigated on the third day of fifth larval stage. rPTTH activity was compared with the BE mixture by enzyme immunoassay and western blot, revealing that they equally stimulate the production of significant amount of ecdysone, through a transduction cascade that includes the TOR pathway, by the phosphorylation of 4E binding protein (4E-BP) and S6 kinase (S6K), the main targets of TOR protein. The results of these experiments suggest the importance of obtaining a functional pure hormone to perform further studies, not depending on the crude brain extract, composed by different elements and susceptible to different uncontrollable variables.

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.

Developmental studies provide new insights into the evolution of sense organs in Sabellariidae (Annelida)

BACKGROUND

Sabellarids, also known as honeycomb or sandcastle worms, when building their tubes, produce chemical signals (free fatty acids) that are responsible for larval settlement and the formation of three-dimensional aggregations. The larval palps and the dorsal hump (becoming the median organ in adults) are presumed to participate in such a substrate selection during settlement. Notably, the sabellariid median organ is an apparently unique organ among annelids that has been attributed with a sensory function and perhaps with some affinities to the nuchal organs of other polychaetes. Nevertheless, detailed investigations of this prominent character complex including ultrastructural examinations are lacking so far.

RESULTS

Our comprehensive investigations provide data about the anterior sensory organs in Sabellariidae and inform about their transformation during pelagic larval development. We used a comparative approach including immunostaining with subsequent confocal laser scanning microscopy (clsm), histological sections as well as electron microscopy in a range of larval and adult stages of two sabellariid species. We find that the neuronal innervation as well as the ultrastructure of the sabellariid ciliary structures along the median organ are highly comparable with that of nuchal organs known from other polychaetes. Furthermore, the myoinhibitory protein (MIP) - a protein known to be also involved into chemo-sensation - was detected in the region of the larval median organ. Moreover, we reveal the presence of an unusual type of photoreceptor as part of the median organ in Idanthyrsus australiensis with a corrugated sensory membrane ultrastructure unlike those observed in the segmental ocelli of other polychaetes.

CONCLUSIONS

We are describing for the first time the nuchal organ-like structures in different developmental stages of two species of Sabellariidae. The external morphology, neuronal innervation, developmental fate and ultrastructure of the newly-discovered median organ-based ciliary pits are comparable with the characteristics known for annelid nuchal organs and therefore indicate a homology of both sensory complexes. The presence of myoinhibitory peptide (MIP) in the respective region supports such a hypothesis and exhibits the possibility of an involvement of the entire sabellariid median organ complex, and in particular the prominent ciliated pits, in chemo-sensation.

Extensive characterization and differential analysis of endogenous peptides from Bombyx batryticatus using mass spectrometric approach

Bombyx batryticatus, the dried larva of Bombyx mori L. (4th-5th instars) infected with Beauveria bassiana Vuill, is an important animal-derived medicine effective against several diseases. The metamorphosis of silkworm can result insignificant changes in the levels of proteins and polypeptides in the 4^th and 5^th instar larvae. Here, we performed extensive characterization of Bombyx batryticatus peptides, including polypeptides containing cysteines, using an MS-based data mining strategy. A total of 779 peptides with various PTMs (post-translational modifications) were identified through database search and de novo sequencing. Some of these peptides might have important biological activities. Besides, the differential analysis of polypeptides between the head and body of Bombyx batryticatus was performed to provide a clinical basis for rational use of the drugs derived from it. This study illustrates the abundance and sequences of endogenous Bombyx batryticatus polypeptides, and thus, provides potential candidates for the screening of active compounds for future biological research and drug discovery studies.

CRISPR knockouts reveal an endogenous role for ancient neuropeptides in regulating developmental timing in a sea anemone

Neuropeptides are evolutionarily ancient peptide hormones of the nervous and neuroendocrine systems, and are thought to have regulated metamorphosis in early animal ancestors. In particular, the deeply conserved Wamide family of neuropeptides—shared across Bilateria (e.g. insects and worms) and its sister group Cnidaria (e.g. jellyfishes and corals)—has been implicated in mediating life-cycle transitions, yet their endogenous roles remain poorly understood. By using CRISPR-Cas9-mediated reverse genetics, we show that cnidarian Wamide—referred to as GLWamide—regulates the timing of life cycle transition in the sea anemone cnidarian Nematostella vectensis. We find that mutant planula larvae lacking GLWamides transform into morphologically normal polyps at a rate slower than that of the wildtype control larvae. Treatment of GLWamide null mutant larvae with synthetic GLWamide peptides is sufficient to restore a normal rate of metamorphosis. These results demonstrate that GLWamide plays a dispensable, modulatory role in accelerating metamorphosis in a sea anemone.

The silkrose of Bombyx mori effectively prevents vibriosis in penaeid prawns via the activation of innate immunity

We previously identified novel bioactive polysaccharides from Bactrocera cucurbitae and Antheraea yamamai that activate innate immunity in RAW264 murine macrophages. However, in terms of potential applications in the cultivation of prawns, there were problems with the availability of these insects. However, we have now identified a polysaccharide from Bombyx mori that activates innate immunity in RAW264 cells and penaeid prawns. This purified polysaccharide, termed silkrose of B. mori (silkrose-BM), has a molecular weight of 1,150,000 and produces a single symmetrical peak on HPLC. Eight of nine constitutive monosaccharides of silkrose-BM are concomitant with dipterose of B. cucurbitae (dipterose-BC) and silkrose of A. yamamai (silkrose-AY). The major differences are found in the molar ratios of the monosaccharides. Silkrose-BM is approximately 500-fold less potent than silkrose-AY (EC₅₀: 2.5 and 0.0043 μg/mL, respectively) in a nitrite oxide (NO) production assay using RAW264 cells. However, the maximum NO production for silkrose-BM and AY were comparable and higher than that of the lipopolysaccharide of Escherichia coli. The survival of penaeid prawns (Litopenaeus vannamei and Marsupenaeus japonicus) after infection with Vibrio penaecida was significantly improved by both dietary silkrose-BM and B. mori pupae. This suggests that silkrose-BM effectively prevents vibriosis in penaeid prawns via the activation of innate immunity.

Reference genes validation in Phenacoccus solenopsis under various biotic and abiotic stress conditions

Real-time PCR (RT-qPCR) expression analysis is a powerful analytical technique, but for normalization of data requires the use of stable reference genes. However, suitable reference genes are still not known in the case of Phenacoccus solenopsis under variable experimental treatments. The present study focused on the identification of stable housekeeping genes as a reference for analysis under different abiotic and biotic factors in P. solenopsis. We analyzed the relative expression of six commonly used candidate reference genes in different developmental stages, host-feeding assay, temperature treatments and field distribution conditions. Expression stabilities were analyzed by geNorm, NormFinder, and RefFinder. Under developmental and field distribution conditions, β-Tubulin was found to be most stable reference genes followed by rpl32 and α-Tubulin. In the case host feeding treatment conditions, β-Tubulin and α-tubulin identified to be the most stable reference genes, while in temperature stress, a combination of α-Tubulin and rpl32 found to be suitable for normalizing the RT-qPCR data. Further, the above-identified genes were validated using RT-qPCR based gene expression analysis of four objective genes namely, Myoinhibitory peptides (MIPs), Zinc_metalloprotease (Zn_Mp), fatty acid synthase (fas) and alpha-glucosidase. Identified reference genes will facilitate gene expression studies in future under different stress treatments in P. solenopsis.

Conserved Transcription Factors Steer Growth-Related Genomic Programs in Daphnia

Ecological genomics aims to understand the functional association between environmental gradients and the genes underlying adaptive traits. Many genes that are identified by genome-wide screening in ecologically relevant species lack functional annotations. Although gene functions can be inferred from sequence homology, such approaches have limited power. Here, we introduce ecological regulatory genomics by presenting an ontology-free gene prioritization method. Specifically, our method combines transcriptome profiling with high-throughput cis-regulatory sequence analysis in the water fleas Daphnia pulex and Daphnia magna. It screens coexpressed genes for overrepresented DNA motifs that serve as transcription factor binding sites, thereby providing insight into conserved transcription factors and gene regulatory networks shaping the expression profile. We first validated our method, called Daphnia-cisTarget, on a D. pulex heat shock data set, which revealed a network driven by the heat shock factor. Next, we performed RNA-Seq in D. magna exposed to the cyanobacterium Microcystis aeruginosa. Daphnia-cisTarget identified coregulated gene networks that associate with the moulting cycle and potentially regulate life history changes in growth rate and age at maturity. These networks are predicted to be regulated by evolutionary conserved transcription factors such as the homologues of Drosophila Shavenbaby and Grainyhead, nuclear receptors, and a GATA family member. In conclusion, our approach allows prioritising candidate genes in Daphnia without bias towards prior knowledge about functional gene annotation and represents an important step towards exploring the molecular mechanisms of ecological responses in organisms with poorly annotated genomes.

Ecdysone signaling underlies the pea aphid transgenerational wing polyphenism

The wing polyphenism of pea aphids is a compelling laboratory model with which to study the molecular mechanisms underlying phenotypic plasticity. In this polyphenism, environmental stressors such as high aphid density cause asexual, viviparous adult female aphids to alter the developmental fate of their embryos from wingless to winged morphs. This polyphenism is transgenerational, in that the pea aphid mother experiences the environmental signals, but it is her offspring that are affected. Previous research suggested that the steroid hormone ecdysone may play a role in this polyphenism. Here, we analyzed ecdysone-related gene expression patterns and found that they were consistent with a down-regulation of the ecdysone pathway being involved in the production of winged offspring. We therefore predicted that reduced ecdysone signaling would result in more winged offspring. Experimental injections of ecdysone or its analog resulted in a decreased production of winged offspring. Conversely, interfering with ecdysone signaling using an ecdysone receptor antagonist or knocking down the ecdysone receptor gene with RNAi resulted in an increased production of winged offspring. Our results are therefore consistent with the idea that ecdysone plays a causative role in the regulation of the proportion of winged offspring produced in response to crowding in this polyphenism. Our results also show that an environmentally regulated maternal hormone can mediate phenotype production in the next generation, as well as provide significant insight into the molecular mechanisms underlying the functioning of transgenerational phenotypic plasticity.

Myosuppressin is involved in the regulation of pupal diapause in the cabbage army moth Mamestra brassicae

Diapause, a programmed developmental arrest, is common in insects, enabling them to survive adverse seasons. It is well established that pupal diapause is regulated by ecdysteroids secreted by the prothoracic glands (PGs), with cessation of ecdysteroid secretion after pupal ecdysis leading to pupal diapause. A major factor regulating the gland activity is prothoracicotropic hormone (PTTH) secreted from the brain. In our previous study, we demonstrated that the cessation of PTTH release after pupal ecdysis resulted in the inactivation of the PGs, leading to pupal diapause in the cabbage army moth Mamestra brassicae. Here we show that a neuropeptide myosuppressin also contributes to the inactivation of PGs at the initiation of diapause. Myosuppressin suppresses PTTH-stimulated activation of the PGs in vitro. Concentrations of myosuppressin in the hemolymph after pupal ecdysis are higher in diapause pupae than in nondiapause pupae.

Newly identified allatostatin Bs and their receptor in the two-spotted cricket, Gryllus bimaculatus

A cDNA encoding allatostatin Bs (ASTBs) containing the W(X)6W motif was identified using a database generated by a next generation sequencer (NGS) in the two-spotted cricket, Gryllus bimaculatus. The contig sequence revealed the presence of five novel putative ASTBs (GbASTBs) in addition to GbASTBs previously identified in G. bimaculatus. MALDI-TOF MS analyses revealed the presence of these novel and previously identified GbASTBs with three missing GbASTBs. We also identified a cDNA encoding G. bimaculatus GbASTB receptor (GbASTBR) in the NGS data. Phylogenetic analysis demonstrated that this receptor was highly conserved with other insect ASTBRs, including the sex peptide receptor of Drosophila melanogaster. Calcium imaging analyses indicated that the GbASTBR heterologously expressed in HEK293 cells exhibited responses to all identified GbASTBs at a concentration range of 10(-10)-10(-5)M.

G protein coupled receptors as targets for next generation pesticides

There is an on-going need for the discovery and development of new pesticides due to the loss of existing products through the continuing development of resistance, the desire for products with more favourable environmental and toxicological profiles and the need to implement the principles of integrated pest management. Insect G protein coupled receptors (GPCRs) have important roles in modulating biology, physiology and behaviour, including reproduction, osmoregulation, growth and development. Modifying normal receptor function by blocking or over stimulating its actions may either result in the death of a pest or disrupt its normal fitness or reproductive capacity to reduce pest populations. Hence GPCRs offer potential targets for the development of next generation pesticides providing opportunities to discover new chemistries for invertebrate pest control. Such receptors are important targets for pharmaceutical drugs, but are under-exploited by the agro-chemical industry. The octopamine receptor agonists are the only pesticides with a recognized mode of action, as described in the classification scheme developed by the Insecticide Resistance Action Committee, that act via a GPCR. The availability of sequenced insect genomes has facilitated the characterization of insect GPCRs, but the development and utilization of screening assays to identify lead compounds has been slow. Various studies using knock-down technologies or applying the native ligands and/or neuropeptide analogues to pest insects in vivo, have however demonstrated that modifying normal receptor function can have an insecticidal effect. This review presents examples of potential insect neuropeptide receptors that are potential targets for lead compound development, using case studies from three representative pest species, Tribolium castaneum, Acyrthosiphon pisum, and Drosophila suzukii. Functional analysis studies on T. castaneum suggest that GPCRs involved in growth and development (eclosion hormone, ecdysis triggering hormone and crustacean cardioacceleratory peptide receptors) as well as the dopamine-2 like, latrophilin-like, starry night, frizzled-like, methuselah-like and the smoothened receptors may be suitable pesticide targets. From in vivo studies using native ligands and peptide analogues, receptors which appear to have a role in the regulation of feeding in the pea aphid, such as the PISCF-allatostatin and the various "kinin" receptors, are also potential targets. In Drosophila melanogaster various neuropeptides and their signalling pathways have been studied extensively. This may provide insights into potential pesticide targets that could be exploited in D. suzukii. Examples include the sex peptide receptor, which is involved in reproduction and host seeking behaviours, and those responsible for osmoregulation such as the diuretic hormone receptors. However the neuropeptides and their receptors in insects are often poorly characterized, especially in pest species. Although data from closely related species may be transferable (e.g. D. melanogaster to D. suzukii), peptides and receptors may have different roles in different insects, and hence a target in one insect may not be appropriate in another. Hence fundamental knowledge of the roles and functions of receptors is vital for development to proceed.

The pleiotropic allatoregulatory neuropeptides and their receptors: A mini-review

Juvenile hormones (JH) are highly pleiotropic insect hormones essential for post-embryonic development. The circulating JH titer in the hemolymph of insects is influenced by enzymatic degradation, binding to JH carrier proteins, uptake and storage in target organs, but evidently also by rates of production at its site of synthesis, the corpora allata (CA). The multiple processes in which JH is involved alongside the critical significance of JH in insect development emphasize the importance for elucidating the control of JH production. Production of JH in CA cells is regulated by different factors: by neurotransmitters, such as dopamine and glutamate, but also by allatoregulatory neuropeptides originating from the brain and axonally transported to the CA where they bind to their G protein-coupled receptors (GPCRs). Different classes of allatoregulatory peptides exist which have other functions aside from acting as influencers of JH production. These pleiotropic neuropeptides regulate different processes in different insect orders. In this mini-review, we will give an overview of allatotropins and allatostatins, and their recently characterized GPCRs with a view to better understand their modes of action and different action sites.

The homeodomain transcription factors antennapedia and POU-M2 regulate the transcription of the steroidogenic enzyme gene Phantom in the silkworm

The steroid hormone ecdysone, which controls insect molting and metamorphosis, is synthesized in the prothoracic gland (PG), and several steroidogenic enzymes that are expressed specifically in the PG are involved in ecdysteroidogenesis. In this study, we identified new regulators that are involved in the transcriptional control of the silkworm steroidogenic enzyme genes. In silico analysis predicted several potential cis-regulatory elements (CREs) for the homeodomain transcription factors Antennapedia (Antp) and POU-M2 in the proximal promoters of steroidogenic enzyme genes. Antp and POU-M2 are expressed dynamically in the PG during larval development, and their overexpression in silkworm embryo-derived (BmE) cells induced the expression of steroidogenic enzyme genes. Importantly, luciferase reporter analyses, electrophoretic mobility shift assays, and chromatin immunoprecipitation assays revealed that Antp and POU-M2 promote the transcription of the silkworm steroidogenic enzyme gene Phantom (Phm) by binding directly to specific motifs within overlapping CREs in the Phm promoter. Mutations of these CREs in the Phm promoter suppressed the transcriptional activities of both Antp and POU-M2 in BmE cells and decreased the activities of mutated Phm promoters in the silkworm PG. In addition, pulldown and co-immunoprecipitation assays demonstrated that Antp can interact with POU-M2. Moreover, RNA interference-mediated down-regulation of either Antp or POU-M2 during silkworm wandering not only decreased the ecdysone titer but also led to the failure of metamorphosis. In summary, our results suggest that Antp and POU-M2 coordinate the transcription of the silkworm Phm gene directly, indicating new roles for homeodomain proteins in regulating insect ecdysteroidogenesis.

Bombyx mori prothoracicostatic peptide receptor is allosterically activated via a Gαi/o-protein-biased signalling cascade by Drosophila sex peptide

We here demonstrated that Bombyx mori prothoracicostatic peptide was allosterically activated by Drosophila sex peptide leading to Gαi-independent inhibition of cAMP, while its activation resulted in Ca2+ mobilization and kurtz-dependent receptor internalization in response to the endogenous agonist prothoracicostatic peptide.

Myoinhibitory peptide regulates feeding in the marine annelid Platynereis

Background

During larval settlement and metamorphosis, marine invertebrates undergo changes in habitat, morphology, behavior and physiology. This change between life-cycle stages is often associated with a change in diet or a transition between a non-feeding and a feeding form. How larvae regulate changes in feeding during this life-cycle transition is not well understood. Neuropeptides are known to regulate several aspects of feeding, such as food search, ingestion and digestion. The marine annelid Platynereis dumerilii has a complex life cycle with a pelagic non-feeding larval stage and a benthic feeding postlarval stage, linked by the process of settlement. The conserved neuropeptide myoinhibitory peptide (MIP) is a key regulator of larval settlement behavior in Platynereis. Whether MIP also regulates the initiation of feeding, another aspect of the pelagic-to-benthic transition in Platynereis, is currently unknown.

Results

Here, we explore the contribution of MIP to the regulation of feeding behavior in settled Platynereis postlarvae. We find that in addition to expression in the brain, MIP is expressed in the gut of developing larvae in sensory neurons that densely innervate the hindgut, the foregut, and the midgut. Activating MIP signaling by synthetic neuropeptide addition causes increased gut peristalsis and more frequent pharynx extensions leading to increased food intake. Conversely, morpholino-mediated knockdown of MIP expression inhibits feeding. In the long-term, treatment of Platynereis postlarvae with synthetic MIP increases growth rate and results in earlier cephalic metamorphosis.

Conclusions

Our results show that MIP activates ingestion and gut peristalsis in Platynereis postlarvae. MIP is expressed in enteroendocrine cells of the digestive system suggesting that following larval settlement, feeding may be initiated by a direct sensory-neurosecretory mechanism. This is similar to the mechanism by which MIP induces larval settlement. The pleiotropic roles of MIP may thus have evolved by redeploying the same signaling mechanism in different aspects of a life-cycle transition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-014-0093-6) contains supplementary material, which is available to authorized users.

Functional characterization and expression analysis of the myoinhibiting peptide receptor in the Chagas disease vector, Rhodnius prolixus

Myoinhibiting peptides (MIPs), which are also known as B-type allatostatins, are a family of neuropeptides found in protostomes. Their primary structure is characterized by an amidated carboxyl-terminal motif consisting of a conserved pair of tryptophan residues normally separated by six non-conserved amino acids (W(X6)Wamide). In the fruit fly Drosophila melanogaster, MIPs are likely the ancestral ligands of the sex peptide receptor, which plays an important role in courtship and reproduction. Recently, several endogenous MIPs were discovered in the Chagas disease vector, Rhodnius prolixus, having both conserved (W(X6)Wamide) and atypical (W(X7)Wamide) carboxyl-terminal motifs. Physiological functions of MIPs are plentiful and include inhibition of visceral muscle activity; a role that has been illustrated on hindgut in R. prolixus. In order to identify novel physiological targets and elucidate biological actions for the MIPs in R. prolixus, we have isolated and examined the spatial expression profile of the MIP receptor transcript in various fifth instar tissues and have additionally determined the expression profile in reproductive tissues of fifth instar as well as adult insects. The most abundant MIP receptor transcript expression was found in the salivary glands and central nervous system, which corroborates roles previously determined for MIPs in other insects. We functionally-characterized the endogenous MIP receptor and examined its activation by R. prolixus MIPs containing the typical W(X6)Wamide and atypical W(X7)Wamide carboxyl-terminal motifs. These peptides dose-dependently activated the MIP receptor (RhoprMIPr1) with EC50 values in the mid-nanomolar range. We also examined the activity of these RhoprMIPs on spontaneous muscle contractions of oviducts from female adult R. prolixus. Our findings confirm the myoinhibitory nature of the MIP peptides, which dose-dependently reduced spontaneous oviduct contractions by nearly 70%, again having mid-nanomolar EC50 values. Finally, we utilized a heterologous receptor assay and oviduct bioassay to examine the activity of several MIP structural analogs, which independently confirmed the requirement of the highly conserved tryptophan residues as well as the amidated C-terminus for retaining full biological activity.

Identification and characterization of a sex peptide receptor-like transcript from the western tarnished plant bug Lygus hesperus

Lygus hesperus females exhibit a post-mating behavioural switch that triggers increased egg laying and decreased sexual interest. In Drosophila melanogaster, these changes are controlled by sex peptide (SP) and the sex peptide receptor (DmSPR). In Helicoverpa armigera, SPR (HaSPR) also regulates some post-mating behaviour; however, myoinhibiting peptides (MIPs) have been identified as the SPR ancestral ligand, indicating that SPR is a pleiotropic receptor. In the present study, we identified a transcript, designated L. hesperus SPR (LhSPR), that is homologous to known SPRs and which is expressed throughout development and in most adult tissues. LhSPR was most abundant in female seminal depositories and heads as well as the hindgut/midgut of both sexes. In vitro analyses revealed that fluorescent chimeras of LhSPR, DmSPR and HaSPR localized to the cell surface of cultured insect cells, but only DmSPR and HaSPR bound carboxytetramethylrhodamine-labelled analogues of DmSP21-36 and DmMIP4. Injected DmSP21-36 also failed to have an effect on L. hesperus mating receptivity. Potential divergence in the LhSPR binding pocket may be linked to receptor-ligand co-evolution as 9 of 13 MIPs encoded by a putative L. hesperus MIP precursor exhibit an atypical W-X7 -Wamide motif vs the W-X6 -Wamide and W-X8 -Wamide motifs of Drosophila MIPs and SP.

The degradome and the evolution of Drosophila sex peptide as a ligand for the MIP receptor

The male sex peptide (SP) of Drosophila melanogaster has wide ranging effects on females, including rejection of courting males, increased egg production, changes to the feeding habit, increased synthesis of antimicrobial peptides and elevated locomotor activity during day-time. The peptide activates receptors in sensory neurons of the female reproductive tract and can also traverse into the hemolymph and reach the central nervous system. The SP receptor involved in rejection and egg-laying responses has been shown to be identical to the receptor for the evolutionary conserved myoinhibitory peptides (MIPs) that function as neuropeptides in both males and females. Intriguingly, MIPs cannot substitute for SP when either expressed in the male accessory glands or injected into virgin females. MIPs are linear peptides with an amidated C-terminus which protects them from cleavage by carboxypeptidases, but leaves them exposed to potential attack from aminopeptidase and endopeptidase activities. In contrast, the SP region responsible for eliciting the post-mating response is cyclic and has several hydroxyproline residues N-terminal to the disulfide bridge which is expected to protect the biological activity of SP from peptidases of the male accessory gland and seminal fluid. We now present in vitro data showing that SP is metabolically stable, whereas MIPs are much more susceptible to degradation by peptidases of the male accessory gland and the hemolymph of virgin female D. melanogaster. SP has evolved relatively recently as a MIP receptor ligand that is particularly well adapted to surviving in the hostile degradome of the male accessory gland and seminal fluid.

Conserved MIP receptor-ligand pair regulates Platynereis larval settlement

Life-cycle transitions connecting larval and juvenile stages in metazoans are orchestrated by neuroendocrine signals including neuropeptides and hormones. In marine invertebrate life cycles, which often consist of planktonic larval and benthic adult stages, settlement of the free-swimming larva to the sea floor in response to environmental cues is a key life cycle transition. Settlement is regulated by a specialized sensory-neurosecretory system, the larval apical organ. The neuroendocrine mechanisms through which the apical organ transduces environmental cues into behavioral responses during settlement are not yet understood. Here we show that myoinhibitory peptide (MIP)/allatostatin-B, a pleiotropic neuropeptide widespread among protostomes, regulates larval settlement in the marine annelid Platynereis dumerilii. MIP is expressed in chemosensory-neurosecretory cells in the annelid larval apical organ and signals to its receptor, an orthologue of the Drosophila sex peptide receptor, expressed in neighboring apical organ cells. We demonstrate by morpholino-mediated knockdown that MIP signals via this receptor to trigger settlement. These results reveal a role for a conserved MIP receptor-ligand pair in regulating marine annelid settlement.

Receptors for the neuropeptides, myoinhibitory peptide and SIFamide, in control of the salivary glands of the blacklegged tick Ixodes scapularis

Tick salivary glands are important organs that enable the hematophagous feeding of the tick. We previously described the innervation of the salivary gland acini types II and III by a pair of protocerebral salivary gland neurons that produce both myoinhibitory peptide (MIP) and SIFamide (Šimo et al., 2009b). In this study we identified authentic receptors expressed in the salivary glands for these neuropeptides. Homology-based searches for these receptors in the Ixodes scapularis genome sequence were followed by gene cloning and functional expression of the receptors. Both receptors were activated by low nanomolar concentrations of their respective ligands. The temporal expression patterns of the two ligands and their respective receptors suggest that the SIFamide signaling system pre-exists in unfed salivary glands, while the MIP system is activated upon initiation of feeding. Immunoreactivity for the SIFamide receptor in the salivary gland was detected in acini types II and III, surrounding the acinar valve and extending to the basal region of the acinar lumen. The location of the SIFamide receptor in the salivary glands suggests three potential target cell types and their probable functions: myoepithelial cell that may function in the contraction of the acini and/or the control of the valve; large, basally located dopaminergic granular cells for regulation of paracrine dopamine; and neck cells that may be involved in the control of the acinar duct and its valve.

Peptidomic Analysis of the Brain and Corpora Cardiaca-Corpora Allata Complex in the Bombyx mori

The silkworm, Bombyx mori, is an important economic insect for silk production. However, many of the mature peptides relevant to its various life stages remain unknown. Using RP-HPLC, MALDI-TOF MS, and previously identified peptides from B. mori and other insects in the transcriptome database, we created peptide profiles showing a total of 6 ion masses that could be assigned to peptides in eggs, including one previously unidentified peptide. A further 49 peptides were assigned to larval brains. 17 new mature peptides were identified in isolated masses. 39 peptides were found in pupal brains with 8 unidentified peptides. 48 were found in adult brains with 12 unidentified peptides. These new unidentified peptides showed highly significant matches in all MS analysis. These matches were then searched against the National Center for Biotechnology Information (NCBI) database to provide new annotations for these mature peptides. In total, 59 mature peptides in 19 categories were found in the brains of silkworms at the larval, pupal, and adult stages. These results demonstrate that peptidomic variation across different developmental stages can be dramatic. Moreover, the corpora cardiaca-corpora allata (CC-CA) complex was examined during the fifth larval instar. A total of 41 ion masses were assigned to peptides.

The distribution and physiological effects of the myoinhibiting peptides in the kissing bug, rhodnius prolixus

The myoinhibiting peptides (MIPs), also designated as allatostatin-Bs or prothoracicostatic peptides in some insects, are neuropeptides that are characterized by two tryptophan (W) residues at the C-terminal, denoted as the W(X₆)Wamide motif. They are believed to be the ancestral ligands for the Drosophila sex peptide (SP) receptor. Physiological functions of MIPs include the inhibition of contraction of insect visceral muscles, in addition to allatostatic and prothoracicostatic activities. The MIP precursor in Rhodnius prolixus encodes MIPs that have an unusual W(X₇)Wamide motif. In the present study, MIP-like immunoreactivity was detected within neurons in the central nervous system and within the innervation to the salivary glands, hindgut, and female and male reproductive systems of adult R. prolixus. The effects of peptides with the unusual W(X₇)Wamide motif (Rhopr-MIP-4) and with the typical W(X₆)Wamide motif (Rhopr-MIP-7) were tested for physiological activity on R. prolixus hindgut contractions. Both peptides reduce the frequency and amplitude of hindgut contractions in a dose-dependent manner. In addition, both peptides activate the Drosophila SP receptor. The MIP/SP receptors are therefore activated by peptides with the unusual W(X₇)Wamide motif.

Families of allatoregulator sequences: a 2011 perspective1This 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

Three different peptide families have been named “allatostatins” (ASTs), based on their initial purifications which were based on their ability to inhibit juvenile hormone (JH) biosynthesis. These include (i) a family of peptides that have a consensus C-terminal sequence Y/FXFGL-NH2; (ii) a family of peptides with a conserved C-terminal sequence W(X)6W-NH2; and(iii) a family of peptides with C-terminal sequence PISCF, some of which are C-terminally-amidated. Each allatostatin family has functions distinct and apart from the inhibition of JH biosynthesis. A peptide family known as the “allatotropins” serve to stimulate JH biosynthesis. This family of peptides also has been proven to exert multiple effects dependent on the species in question. Genome and peptidome projects are uncovering new members of these families and it is clear that these structures are not just confined to Insecta but are found in a range of invertebrates. The receptors for these neuropeptides have been identified and tested experimentally for specific ligand binding. The Y/FXFGLa-ASTs exert their action through galanin-like receptors, W(X)6Wa-ASTs through a sex peptide-binding receptor, and PISCF-ASTs through somatostatin-like receptors. These receptors are conserved through evolutionary time and are being identified in numerous invertebrates by way of genome projects.

Peptidergic control of food intake and digestion in insects 1This 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

Like all heterotrophic organisms, insects require a strict control of food intake and efficient digestion of food into nutrients to maintain homeostasis and to fulfill physiological tasks. Feeding and digestion are steered by both external and internal signals that are transduced by a multitude of regulatory factors, delivered either by neurons innervating the gut or mouthparts, or by midgut endocrine cells. The present review gives an overview of peptide regulators known to control feeding and digestion in insects. We describe the discovery and functional role in these processes for insect allatoregulatory peptides, diuretic hormones, FMRFamide-related peptides, (short) neuropeptide F, proctolin, saliva production stimulating peptides, kinins, and tachykinins. These peptides control either gut myoactivity, food intake, and (or) release of digestive enzymes. Some peptides exert their action at multiple levels, possibly having a biological function that depends on their site of delivery. Many regulatory peptides have been physically extracted from different insect species. However, multiple peptidomics, proteomics, transcriptomics, and genome sequencing projects have led to increased discovery and prediction of peptide (precursor) and receptor sequences. In combination with physiological experiments, these large-scale projects have already led to important steps forward in unraveling the physiology of feeding and digestion in insects.

Recent topics on the regulatory mechanism of ecdysteroidogenesis by the prothoracic glands in insects

Molting and metamorphosis are strictly regulated by steroid hormones known as ecdysteroids. It is now widely recognized that ecdysteroid biosynthesis (ecdysteroidogenesis) in the prothoracic gland (PG) is regulated by the tropic factor prothoracicotropic hormone (PTTH). However, the importance of PTTH in the induction of molting and metamorphosis remains unclear, and other mechanisms are thought to be involved in the regulation of ecdysteroidogenesis by the PG. Recently, new regulatory mechanisms, prothoracicostatic factors, and neural regulation have been explored using the silkworm, Bombyx mori, and two circulating prothoracicostatic factors, prothoracicostatic peptide (PTSP) and Bommo-myosuppressin (BMS), have been identified. Whereas PTTH and BMS are secreted from the brain, PTSP is secreted from the peripheral neurosecretory system - the epiproctodeal gland - during the molting stage. The molecular basis of neural regulation of ecdysteroidogenesis has been revealed for the first time in B. mori. The innervating neurons supply both Bommo-FMRF related peptide (BRFa) and orcokinin to maintain low levels of ecdysteroids during the feeding stage. These complex regulatory mechanisms - involving tropic and static factors, peripheral neurosecretory cells as well as the central neuroendocrine system, and neural regulation in addition to circulating factors collaborate to regulate ecdysteroidogenesis. Thus, together they create the finely tuned fluctuations in ecdysteroid titers needed in the hemolymph during insect development.

Identification and differential expression of a sex-peptide receptor in Helicoverpa armigera

Sex-pheromone production in the night flying female moth, Helicoverpa armigera is under neuroendocrine control due to the timely release of Pheromone Biosynthesis-Activating Neuropeptide (PBAN). Males orient to the females by upwind anemotaxis which usually leads to a successful mating. During copulation insect males transfer seminal peptides, produced in Male Accessory Glands (MAGs) which are implicated in post-mating behavioral changes of the females. These changes include the termination of pheromone biosynthesis and thus females do not re-mate. In previous studies we showed that synthetic Drosophila melanogaster Sex-Peptide (DrmSP), which is responsible for terminating receptivity in female flies, can terminate PBAN-stimulated pheromone production by pheromone glands of the female moth, H. armigera. In addition, we demonstrated that at least one fraction of the H. armigera MAG extract is both immunoreactive to DrmSP antibody and is pheromonostatic, we also showed that different sets of DrmSP-like immunoreactive peptides are up-regulated in the central nervous system of mated females. In the present study, we identify a putative receptor for sex-peptide (SP-R) in H. armigera on the basis of sequence homologies deposited in the GenBank. In addition, in an attempt to draw some light on the physiological significance of SP-like peptides in this moth, we conducted a differential expression study of this receptor comparing gene expression levels in relation to different photoperiods, sex and mating status of the moth. Photoperiod and mating influence SP-R gene expression levels and sexual dimorphic changes were observed in neural tissues due to the different physiological states. After mating SP-R transcript levels in female neural tissues and pheromone glands are up-regulated. Physiological studies in vivo confirm the up-regulation of gene expression levels in pheromone glands isolated from mated females.

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.

Bombyx orcokinins are brain-gut peptides involved in the neuronal regulation of ecdysteroidogenesis

Biosynthesis of ecdysteroids, the insect steroid hormones controlling gene expression during molting and metamorphosis, takes place primarily in the prothoracic gland (PG). The activity of the PG is regulated by various neuropeptides. In the silkworm Bombyx mori, these neuropeptides utilize both hormonal and neuronal pathways to regulate the activity of the PG, making the insect an excellent model system to investigate the complex signaling network controlling ecdysteroid biosynthesis. Here we report another group of neuropeptides, orcokinins, as neuronal prothoracicotropic factors. Using direct mass spectrometric profiling of the axons associated with the PG, we detected several peptide peaks which correspond to orcokinin gene products in addition to the previously described Bommo-FMRFamides (BRFas). In situ hybridization and immunohistochemistry revealed that orcokinins are produced in the prominent neurosecretory cells in the ventral ganglia, as well as in numerous small neurons throughout the central nervous system and in midgut endocrine cells. One of the two pairs of BRFa-expressing neurosecretory cells in the prothoracic ganglion coexpresses orcokinin, and these neurons project axons through the transverse nerve and terminate on the surface of the PG. Using an in vitro PG bioassay, we show that orcokinins have a clear prothoracicotropic activity and are able to cancel the static effect of BRFas on ecdysteroid biosynthesis, whereas the suppressive effect of BRFas on cAMP production remained unchanged in the presence of orcokinins. The discovery of a second regulator of PG activity in these neurons further illustrates the potential importance of the PG innervation in the regulation of insect development.

Toward a consensus nomenclature for insect neuropeptides and peptide hormones

The nomenclature currently in use for insect neuropeptide and peptide hormone families is reviewed and suggestions are made as to how it can be rationalized. Based upon this review, a number of conventions are advanced as a guide to a more rationale nomenclature. The scheme that is put forward builds upon the binomial nomenclature scheme proposed by Raina and Gäde in 1988, when just over 20 insect neuropeptides had been identified. Known neuropeptides and peptide hormones are assigned to 32 structurally distinct families, frequently with overlapping functions. The names given to these families are those that are currently in use, and describe a biological function, homology to known invertebrate/vertebrate peptides, or a conserved structural motif. Interspecific isoforms are identified using a five-letter code to indicate genus and species names, and intraspecific isoforms are identified by Roman or Arabic numerals, with the latter used to signify the order in which sequences are encoded on a prepropeptide. The proposed scheme is sufficiently flexible to allow the incorporation of novel peptides, and could be extended to other arthropods and non-arthropod invertebrates.

Neuropeptide physiology in insects

In a search for more environmentally benign alternatives to chemical pesticides, insect neuropeptides have been suggested as ideal candidates. Neuropeptides are neuromodulators and/or neurohormones that regulate most major physiological and behavioral processes in insects. The major neuropeptide structures have been identified through peptide purification in insects (peptidomics) and insect genome projects. Neuropeptide receptors have been identified and characterized in Drosophila and similar receptors are being targeted in other insects considered to be economically detrimental pests in agriculture and forestry. Defining neuropeptide action in different insect systems has been more challenging and as a consequence, identifying unique targets for potential pest control is also a challenge. In this chapter, neuropeptide biosynthesis as well as select physiological processes are examined with a view to pest control targets. The application of molecular techniques to transform insects with neuropeptide or neuropeptide receptor genes, or knockout genes to identify potential pest control targets, is a relatively new area that offers promise to insect control. Insect immune systems may also be manipulated through neuropeptides which may aid in compromising the insects ability to defend against foreign invasion.

Neuropeptide precursor gene discovery in the Chagas disease vector Rhodnius prolixus

We show a straightforward workflow combining homology search in Rhodnius prolixus genome sequence with cloning by rapid amplification of cDNA ends and mass spectrometry. We have identified 32 genes and their transcripts that encode a number of neuropeptide precursors leading to 194 putative peptides. We validated by mass spectrometry 82 of those predicted neuropeptides in the brain of R. prolixus to achieve the first comprehensive genomic, transcriptomic and neuropeptidomic analysis of an insect disease vector. Comparisons of available insect neuropeptide sequences revealed that the R. prolixus genome contains most of the conserved neuropeptides in insects, many of them displaying specific features at the sequence level. Some gene families reported here are identified for the first time in the order Hemiptera, a highly biodiverse group of insects that includes many human, animal and plant disease agents.

Microarray-based gene expression profiles of silkworm brains

Background

Molecular genetic studies of Bombyx mori have led to profound advances in our understanding of the regulation of development. Bombyx mori brain, as a main endocrine organ, plays important regulatory roles in various biological processes. Microarray technology will allow the genome-wide analysis of gene expression patterns in silkworm brains.

Results

We reported microarray-based gene expression profiles in silkworm brains at four stages including V7, P1, P3 and P5. A total of 4,550 genes were transcribed in at least one selected stage. Of these, clustering algorithms separated the expressed genes into stably expressed genes and variably expressed genes. The results of the gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analysis of stably expressed genes showed that the ribosomal and oxidative phosphorylation pathways were principal pathways. Secondly, four clusters of genes with significantly different expression patterns were observed in the 1,175 variably expressed genes. Thirdly, thirty-two neuropeptide genes, six neuropeptide-like precursor genes, and 117 cuticular protein genes were expressed in selected developmental stages.

Conclusion

Major characteristics of the transcriptional profiles in the brains of Bombyx mori at specific development stages were present in this study. Our data provided useful information for future research.

Myoinhibiting peptides are the ancestral ligands of the promiscuous Drosophila sex peptide receptor

Male insects change behaviors of female partners by co-transferring accessory gland proteins (Acps) like sex peptide (SP), with their sperm. The Drosophila sex peptide receptor (SPR) is a G protein-coupled receptor expressed in the female's nervous system and genital tract. While most Acps show a fast rate of evolution, SPRs are highly conserved in insects. We report activation of SPRs by evolutionary conserved myoinhibiting peptides (MIPs). Structural determinants in SP and MIPs responsible for this dual receptor activation are characterized. Drosophila SPR is also expressed in embryonic and larval stages and in the adult male nervous system, whereas SP expression is restricted to the male reproductive system. MIP transcripts occur in male and female central nervous system, possibly acting as endogenous SPR ligands. Evolutionary consequences of the promiscuous nature of SPRs are discussed. MIPs likely function as ancestral ligands of SPRs and could place evolutionary constraints on the MIP/SPR class.

Brain-independent development in the moth Sesamia nonagrioides

The caterpillars of Sesamia nonagrioides developing under long-day (LD) photoperiod pupate in the 5th or 6th instar whereas under short day (SD) conditions they enter diapause and undergo several extra larval molts. The diapause is terminated within 1-3 instars upon transfer of SD larvae to the LD conditions. Brain removal from the 6th instar larvae promotes pupation followed by imaginal development; however, one third of the SD larvae and 12% of the LD larvae debrained at the start of the instar first undergo 1-2 larval molts. The incidence of larval molts is enhanced by the brain implants. Exclusively pupal molts occur in the LD larvae debrained late in the 6th instar. Decapitation elicits pupation in both LD and SD larvae, except for some of the 4th and 5th and rarely 6th instar that are induced to a fast larval molt. The pupation of decapitated larvae is reverted to a larval molt by application of a juvenile hormone (JH) agonist. No molts occur in abdomens isolated from the head and thorax prior to the wandering stage. Abdomens isolated later undergo a larval (SD insects) or a pupal (LD insects) molt. Taken together the data reveal that in S. nonagrioides (1) several larval molts followed by a pupal and imaginal molt can occur without brain; (2) an unknown head factor outside the brain is needed for the pupal-adult molt; (3) brain exerts both stimulatory and inhibitory effect on the corpora allata (CA); (4) larval molts induced in CA absence suggest considerable JH persistence.

MIPs are ancestral ligands for the sex peptide receptor

Upon mating, females of many animal species undergo dramatic changes in their behavior. In Drosophila melanogaster, postmating behaviors are triggered by sex peptide (SP), which is produced in the male seminal fluid and transferred to female during copulation. SP modulates female behaviors via sex peptide receptor (SPR) located in a small subset of internal sensory neurons that innervate the female uterus and project to the CNS. Although required for postmating responses only in these female sensory neurons, SPR is expressed broadly in the CNS of both sexes. Moreover, SPR is also encoded in the genomes of insects that lack obvious SP orthologs. These observations suggest that SPR may have additional ligands and functions. Here, we identify myoinhibitory peptides (MIPs) as a second family of SPR ligands that is conserved across a wide range of invertebrate species. MIPs are potent agonists for Drosophila, Aedes, and Aplysia SPRs in vitro, yet are unable to trigger postmating responses in vivo. In contrast to SP, MIPs are not produced in male reproductive organs, and are not required for postmating behaviors in Drosophila females. We conclude that MIPs are evolutionarily conserved ligands for SPR, which are likely to mediate functions other than the regulation of female reproductive behaviors.