Regulation of insect steroid hormone biosynthesis by innervating peptidergic neurons

Differential expression of ITP and ITPL indicate multiple functions in the silkworm Bombyx mori

Ion transport peptide (ITP) and a longer ITP-like (ITPL) are alternatively spliced insect neuropeptides involved in the regulation of development and water homeostasis. Using in situ hybridisation and immunohistochemistry, we determined site- and stage-specific expression of each peptide in Bombyx mori. Each peptide was differentially expressed, except for the prominent overlapping expression of both peptides in six pairs of the brain neurosecretory cells Ia₂. After metamorphosis, ITP appeared in the male-specific neurons of the abdominal neuromere 9 (MAN₉) that innervate the reproductive organs. ITPL was detected in a pair of dorsolateral interneurons (IN-DL) in each thoracic and abdominal ganglion, and in the thoracic neurosecretory cells (NS-VTL₂) which terminate in the vicinity of the prothoracic gland. Feeding larvae showed ITPL expression in the abdominal neurosecretory cells M5. ITPL was also expressed in the peripheral L1 neurons that project axons into the thoracic and abdominal transverse nerves. Our results suggest that ITP and ITPL exhibit different sex- and stage-specific functions that may include regulation of reproduction and steroid production. For future functional studies, we identified an upstream regulatory region controlling ITP/ITPL expression in the brain and L1 neurons, and prepared stable transgenic line pITP-Gal4.2 using the piggyBac system.

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.

The FMRFamide-like peptide FLP-2 is involved in the modulation of larval development and adult lifespan by regulating the secretion of the insulin-like peptide INS-35 in Caenorhabditis elegans

In the animal kingdom, neuropeptides regulate diverse physiological functions. In invertebrates, FMRFamide and its related peptides, a family of neuropeptides, play an important role as neurotransmitters. The FMRFamide-like peptides (FLPs) are one of the most diverse neuropeptide families and are conserved in nematodes. Our screen for flp genes of the free-living soil nematode Caenorhabditis elegans revealed that the flp-2 gene is involved in larval development. The gene is also conserved in plant-parasitic root-knot nematodes. Our molecular genetic analyses of the C. elegans flp-2 gene demonstrated as follows: 1) the production and secretion of FLP-2, produced in the head neurons, are controlled by environmental factors (growth density and food); 2) the FLP-2 is involved in not only larval development but also adult lifespan by regulating the secretion of one of the insulin-like peptides INS-35, produced in the intestine. These findings provide new insight into the development of new nematicides.

Neuropeptidergic control of neurosteroids biosynthesis

Neurosteroids are steroids synthesized within the central nervous system either from cholesterol or by metabolic reactions of circulating steroid hormone precursors. It has been suggested that neurosteroids exert pleiotropic activities within the central nervous system, such as organization and activation of the central nervous system and behavioral regulation. It is also increasingly becoming clear that neuropeptides exert pleiotropic activities within the central nervous system, such as modulation of neuronal functions and regulation of behavior, besides traditional neuroendocrinological functions. It was hypothesized that some of the physiological functions of neuropeptides acting within the central nervous system may be through the regulation of neurosteroids biosynthesis. Various neuropeptides reviewed in this study possibly regulate neurosteroids biosynthesis by controlling the activities of enzymes that catalyze the production of neurosteroids. It is now required to thoroughly investigate the neuropeptidergic control mechanisms of neurosteroids biosynthesis to characterize the physiological significance of this new neuroendocrinological phenomenon.

Regulation of ecdysone production in Drosophila by neuropeptides and peptide hormones

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

Genome-wide identification of neuropeptides and their receptor genes in Bemisia tabaci and their transcript accumulation change in response to temperature stresses

Insect neuropeptides play an important role in regulating physiological functions such as growth, development, behavior and reproduction. We identified temperature-sensitive neuropeptides and receptor genes of the cotton whitefly, Bemisia tabaci. We identified 38 neuropeptide precursor genes and 35 neuropeptide receptors and constructed a phylogenetic tree using additional data from other insects. As temperature adaptability enables B. tabaci to colonize a diversity of habitats, we performed quantitative polymerase chain reaction with two temperature stresses (low = 4 °C and high = 40 °C) to screen for temperature-sensitive neuropeptides. We found many neuropeptides and receptors that may be involved in the temperature adaptability of B. tabaci. This study is the first to identify B. tabaci neuropeptides and their receptors, and it will help to reveal the roles of neuropeptides in temperature adaptation of B. tabaci.

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.

The TRH-ortholog EFLamide in the migratory locust

Arthropod EFLamide genes in chelicerates, myriapods, decapods and non pterygote hexapods encode various EFLamide paracopies on a single precursor. However, in more advanced insect species such multiple EFLamide paracopies encoding genes are absent. In some Hemiptera putative exons of an EFLamide gene coding for a single EFLamide have been identified, while in the migratory locust a similar exon could potentially code for two EFLamide peptides. The recent identification of an EFLGamide from Platynereis dumerilii as the ligand for an ortholog of the TRH GPCR, suggested that the arthropod EFLamides might similarly activate TRH GPCR orthologs. We here identify the TRH GPCR ortholog from Locusta migratoria and show that it is activated in nanomolar concentrations by the two EFLamides previously predicted from this species. We also show that in the central nervous system there seems to be only a single bilateral neuron in the protocerebrum expressing this peptide. Given this very limited expression of EFLamide in locusts, it is perhaps not surprising that this gene and its receptor have been lost in many other insect species. This shows again that although neuropeptides and their receptors may persist in different evoltionary lineages, their functions can change dramatically.

Coleoptera genome and transcriptome sequences reveal numerous differences in neuropeptide signaling between species

Background

Insect neuropeptides are interesting for the potential their receptors hold as plausible targets for a novel generation of pesticides. Neuropeptide genes have been identified in a number of different species belonging to a variety of insects. Results suggest significant neuropeptide variation between different orders, but much less is known of neuropeptidome variability within an insect order. I therefore compared the neuropeptidomes of a number of Coleoptera.

Methodology

Publicly available genome sequences, transcriptomes and the original sequence data in the form of short sequence read archives were analyzed for the presence or absence of genes coding neuropeptides as well as some neuropeptide receptors in seventeen beetle species.

Results

Significant differences exist between the Coleoptera analyzed here, while many neuropeptides that were previously characterized from Tribolium castaneum appear very similar in all species, some are not and others are lacking in one or more species. On the other hand, leucokinin, which was presumed to be universally absent from Coleoptera, is still present in non-Polyphaga beetles.

Conclusion

The variability in neuropeptidome composition between species from the same insect order may be as large as the one that exists between species from different orders.

Characterization of G-protein coupled receptors from the blackback land crab Gecarcinus lateralis Y organ transcriptome over the molt cycle

BACKGROUND

G-protein coupled receptors (GPCRs) are ancient, ubiquitous, constitute the largest family of transducing cell surface proteins, and are integral to cell communication via an array of ligands/neuropeptides. Molt inhibiting hormone (MIH) is a key neuropeptide that controls growth and reproduction in crustaceans by regulating the molt cycle. It inhibits ecdysone biosynthesis by a pair of endocrine glands (Y-organs; YOs) through binding a yet uncharacterized GPCR, which triggers a signalling cascade, leading to inhibition of the ecdysis sequence. When MIH release stops, ecdysone is synthesized and released to the hemolymph. A peak in ecdysone titer is followed by a molting event. A transcriptome of the blackback land crab Gecarcinus lateralis YOs across molt was utilized in this study to curate the list of GPCRs and their expression in order to better assess which GPCRs are involved in the molt process.

RESULTS

Ninety-nine G. lateralis putative GPCRs were obtained by screening the YO transcriptome against the Pfam database. Phylogenetic analysis classified 49 as class A (Rhodopsin-like receptor), 35 as class B (Secretin receptor), and 9 as class C (metabotropic glutamate). Further phylogenetic analysis of class A GPCRs identified neuropeptide GPCRs, including those for Allatostatin A, Allatostatin B, Bursicon, CCHamide, FMRFamide, Proctolin, Corazonin, Relaxin, and the biogenic amine Serotonin. Three GPCRs clustered with recently identified putative CHH receptors (CHHRs), and differential expression over the molt cycle suggests that they are associated with ecdysteroidogenesis regulation. Two putative Corazonin receptors showed much higher expression in the YOs compared with all other GPCRs, suggesting an important role in molt regulation.

CONCLUSIONS

Molting requires an orchestrated regulation of YO ecdysteroid synthesis by multiple neuropeptides. In this study, we curated a comprehensive list of GPCRs expressed in the YO and followed their expression across the molt cycle. Three putative CHH receptors were identified and could include an MIH receptor whose activation negatively regulates molting. Orthologs of receptors that were found to be involved in molt regulation in insects were also identified, including LGR3 and Corazonin receptor, the latter of which was expressed at much higher level than all other receptors, suggesting a key role in YO regulation.

De novo characterization of Phenacoccus solenopsis transcriptome and analysis of gene expression profiling during development and hormone biosynthesis

The cotton mealybug Phenacoccus solenopsis is a devastating pest of cotton causing tremendous loss in the yield of crops each year. Widespread physiological and biological studies on P. solenopsis have been carried out, but the lack of genetic information has constrained our understanding of the molecular mechanisms behind its growth and development. To understand and characterize the different developmental stages, RNA-Seq platform was used to execute de-novo transcriptome assembly and differential gene expression profiling for the eggs, first, second, third instar and adult female stages. About 182.67 million reads were assembled into 93,781 unigenes with an average length of 871.4 bp and an N50 length of 1899 bp. These unigenes sequences were annotated and classified by performing NCBI non-redundant (Nr) database, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Clusters of Orthologous Groups (COG), Gene ontology (GO), the Swiss-Prot protein database (Swiss-Prot), and nearest related organism Acyrthosiphon pisum (pea aphid) database. To get more information regarding the process of metamorphosis, we performed a pairwise comparison of four developmental stages and obtained 29,415 differentially expressed genes. Some of the differentially expressed genes were associated with functional protein synthesis, anti-microbial protection, development and hormone biosynthesis. Functional pathway enrichment analysis of differentially expressed genes showed the positive correlation with specific physiological activities of each stage, and these results were confirmed by qRT-PCR experiments. This study gives a valuable genomics resource of P. solenopsis covering all its developmental stages and will promote future studies on biological processes at the molecular level.

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.

Neuropeptide Evolution: Chelicerate Neurohormone and Neuropeptide Genes may reflect one or more whole genome duplications

Four genomes and two transcriptomes from six Chelicerate species were analyzed for the presence of neuropeptide and neurohormone precursors and their GPCRs. The genome from the spider Stegodyphus mimosarum yielded 87 neuropeptide precursors and 101 neuropeptide GPCRs. High neuropeptide transcripts were also found in the trancriptomes of three other spiders, Latrodectus hesperus, Parasteatoda tepidariorum and Acanthoscurria geniculata. For the scorpion Mesobuthus martensii the numbers are 79 and 74 respectively. The very small genome of the house dust mite, Dermatophagoides farinae, on the other hand contains a much smaller number of such genes. A few new putative Arthropod neuropeptide genes were discovered. Thus, both spiders and the scorpion have an achatin gene and in spiders there are two different genes encoding myosuppressin-like peptides while spiders also have two genes encoding novel LGamides. Another finding is the presence of trissin in spiders and scorpions, while neuropeptide genes that seem to be orthologs of Lottia LFRYamide and Platynereis CCRFamide were also found. Such genes were also found in various insect species, but seem to be lacking from the Holometabola. The Chelicerate neuropeptide and neuropeptide GPCR genes often have paralogs. As the large majority of these are probably not due to local gene duplications, is not impossible that they reflect the effects of one or more ancient whole genome duplications.

Expression of RYamide in the nervous and endocrine system of Bombyx mori

RYamides are neuropeptides encoded by a gene whose precise expression and function have not yet been determined. We identified the RYamide gene transcript (fmgV1g15f, SilkBase database) and predicted two candidates for G-protein coupled RYamide receptors (A19-BAG68418 and A22-BAG68421) in the silkworm Bombyx mori. We cloned the RYamide transcript and described its spatial expression using in situ hybridisation. In the larval central nervous system (CNS) expression of RYamide was restricted to 12-14 small neurons in the brain and two posterior neurons in the terminal abdominal ganglion. During metamorphosis their number decreased to eight protocerebral neurons in the adults. Multiple staining, using various insect neuropeptide antibodies, revealed that neurons expressing RYamide are different from other peptidergic cells in the CNS. We also found RYamide expression in the enteroendocrine cells (EC) of the anterior midgut of larvae, pupae and adults. Two minor subpopulations of these EC were also immunoreactive to antibodies against tachykinin and myosupressin. This expression pattern suggests RYamides may play a role in the regulation of feeding and digestion.

Neuropeptide evolution: Chelicerate neurohormone and neuropeptide genes may reflect one or more whole genome duplications

Four genomes and two transcriptomes from six Chelicerate species were analyzed for the presence of neuropeptide and neurohormone precursors and their GPCRs. The genome from the spider Stegodyphus mimosarum yielded 87 neuropeptide precursors and 120 neuropeptide GPCRs. Many neuropeptide transcripts were also found in the transcriptomes of three other spiders, Latrodectus hesperus, Parasteatoda tepidariorum and Acanthoscurria geniculata. For the scorpion Mesobuthus martensii the numbers are 79 and 93 respectively. The very small genome of the house dust mite, Dermatophagoides farinae, on the other hand contains a much smaller number of such genes. A few new putative Arthropod neuropeptide genes were discovered. Thus, both spiders and the scorpion have an achatin gene and in spiders there are two different genes encoding myosuppressin-like peptides while spiders also have two genes encoding novel LGamides. Another finding is the presence of trissin in spiders and scorpions, while neuropeptide genes that seem to be orthologs of Lottia LFRYamide and Platynereis CCRFamide were also found. Such genes were also found in various insect species, but seem to be lacking from the Holometabola. The Chelicerate neuropeptide and neuropeptide GPCR genes often have paralogs. As the large majority of these are probably not due to local gene duplications, is plausible that they reflect the effects of one or more ancient whole genome duplications.

Expression of a sugar clade gustatory receptor, BmGr6, in the oral sensory organs, midgut, and central nervous system of larvae of the silkworm Bombyx mori

Insects taste nonvolatile chemicals through gustatory receptors (Grs) and make choices for feeding, mating, and oviposition. To date, genome projects have identified 69 Gr genes in the silkworm, Bombyx mori; however, the expression sites of these Grs remain to be explored. In this study, we used reverse transcription (RT)-PCR to investigate expression of the B. mori Gr-6 (BmGr6) gene, a member of the putative sugar clade gene family in various tissues. BmGr6 is expressed in the midgut, central nervous system (CNS), and oral sensory organs. Moreover, immunohistochemistry using an anti-BmGr6 antiserum demonstrated that BmGr6 is expressed in cells by oral sensory organs, midgut and nervous system. Furthermore, double-immunohistochemistry indicated that BmGr6 is expressed in midgut enteroendocrine cells, also in CNS neurosecretory cells. In particular, a portion of BmGr6-expressing cells, in both midgut and CNS, secretes FMRFamide-related peptides (FaRPs). These results suggest that BmGr6 functions not only as a taste receptor, but also as a chemical sensor such as for the regulation of gut movement, physiological conditions, and feeding behavior of larvae.

Conserved molecular switch interactions in modeled cardioactive RF-NH2 peptide receptors: Ligand binding and activation

Peptides may act through G protein-coupled receptors to influence cardiovascular performance; thus, delineating mechanisms involved in signaling is a molecular-based strategy to influence health. Molecular switches, often represented by conserved motifs, maintain a receptor in an inactive state. However, once the switch is broken, the transmembrane regions move and activation occurs. The molecular switches of Drosophila melanogaster myosuppressin (MS) receptors were previously identified to include a unique ionic lock and novel 3-6 lock, as well as transmission and tyrosine toggle switches. In addition to MS, cardioactive ligands structurally related by a C-terminal RF-NH2 include sulfakinin, neuropeptide F (NPF), short NPF, and FMRF-NH2-containing peptide subfamilies. We hypothesized receptor molecular switch motifs were conserved within a RF-NH2 subfamily and across species. Thus, we investigated RF-NH2 receptor (RFa-R) molecular switches in D. melanogaster, Tribolium castaneum, Anopheles gambiae, Rhodnius prolixus, and Bombyx mori. Adipokinetic hormone (AKH), which does not contain a RF-NH2, was also examined. The tyrosine toggle switch and ionic lock showed a higher degree of conservation within a RF-NH2 subfamily than the transmission switch and 3-7 lock. AKH receptor motifs were not representative of a RF-NH2 subfamily. The motifs and interactions of switches in the RFa-Rs were consistent with receptor activation and ligand-specific binding.

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.

Structural Characterization ofN-Glycans of Cauxin by MALDI-TOF Mass Spectrometry and Nano LC-ESI-Mass Spectrometry

Cauxin is a carboxylesterase-like glycoprotein excreted as a major component of cat urine. Cauxin contains four putative N-glycosylation sites. We characterized the structure of an N-linked oligosaccharide of cauxin using nano liquid chromatography (LC)-electrospray ionization (ESI) and matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry (MALDI-QIT-TOF MS) and MS/MS, and high-performance liquid chromatography (HPLC) with an octadecylsilica (ODS) column. The structure of the N-linked oligosaccharide of cauxin attached to (83)Asn was a bisecting complex type, Galbeta1-4GlcNAcbeta1-2Manalpha1-3(Galbeta1-4GlcNAcbeta1-2Manalpha1-6)(GlcNAcbeta1-4)Manbeta1-4GlcNAcbeta1-4(Fucalpha1-6)GlcNAc.

Natalisin, a tachykinin-like signaling system, regulates sexual activity and fecundity in insects

An arthropod-specific peptidergic system, the neuropeptide designated here as natalisin and its receptor, was identified and investigated in three holometabolous insect species: Drosophila melanogaster, Tribolium castaneum, and Bombyx mori. In all three species, natalisin expression was observed in 3-4 pairs of the brain neurons: the anterior dorso-lateral interneurons, inferior contralateral interneurons, and small pars intercerebralis neurons. In B. mori, natalisin also was expressed in two additional pairs of contralateral interneurons in the subesophageal ganglion. Natalisin-RNAi and the activation or silencing of the neural activities in the natalisin-specific cells in D. melanogaster induced significant defects in the mating behaviors of both males and females. Knockdown of natalisin expression in T. castaneum resulted in significant reduction in the fecundity. The similarity of the natalisin C-terminal motifs to those of vertebrate tachykinins and of tachykinin-related peptides in arthropods led us to identify the natalisin receptor. A G protein-coupled receptor, previously known as tachykinin receptor 86C (also known as the neurokinin K receptor of D. melanogaster), now has been recognized as a bona fide natalisin receptor. Taken together, the taxonomic distribution pattern of the natalisin gene and the phylogeny of the receptor suggest that natalisin is an ancestral sibling of tachykinin that evolved only in the arthropod lineage.

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

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

Ecdysone control of developmental transitions: lessons from Drosophila research

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

Developmental checkpoints and feedback circuits time insect maturation

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

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.

20-hydroxyecdysone and juvenile hormone analog prevent precocious metamorphosis in recessive trimolter mutants of Bombyx mori

The trimolter mutants of Bombyx mori have four instead of five larval instars of normal tetramolters. Here, we show that the tetramolter was induced in the recessive trimolter European No.7 mutant (rt-E7) by application of either the juvenile hormone analog (JHA) or 20-hydroxyecdysone (20E). However, treatments with JHA or 20E did not change the number of larval instars of the dominant trimolter Si Chuan mutant (DT-SC). Krüppel-homolog 1 (Kr-h1) is an early JH-response gene that mediates the anti-metamorphic action of JH. In the wing disc of tetramolter B. mori, Kr-h1 RNAs decreased shortly after ecdysis to the fifth instar, while pupal specifier gene, Broad Complex Z1 (BR-Z1) RNAs slightly increased and coincided with the onset of metamorphic competence of wing discs. Analysis of the developmental profile of Kr-h1 in the wing disc of rt-E7 showed that its transcript slightly increased from 12 to 24 h and gradually decreased between 24 and 72 h in the fourth (last) larval instar, while Kr-h1 mRNA decreased rapidly between 12 and 72 h in DT-SC. In addition, the expression of BR-Z1 in DT-SC during the early fourth (last) larval instar is relatively higher than that in rt-E7. These results indicated that the occurrence of pupal commitment of the wing disc in DT-SC was much earlier than that in rt-E7. In the early fourth larval instar of rt-E7, feeding on 20E or treatments with exogenous JHA caused up-regulation of Kr-h1, suppressed premature induction of BR-Z1, and then induced an additional larval instar. By contrast, in DT-SC mutant, since pupal commitment immediately occurred after third ecdysis, precocious metamorphosis was not successfully rescued. The results suggest that Kr-h1 and BR-Z1 involved in the prevention of precocious metamorphosis in recessive trimolter mutants by application of 20E and JHA. The result indicated that Kr-h1 and BR-Z1 expression reflected larval-pupal transition of the recessive trimolter of B. mori.

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.

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

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

Role of the Halloween genes, Spook and Phantom in ecdysteroidogenesis in the desert locust, Schistocerca gregaria

The functional characterization of the Halloween genes represented a major breakthrough in the elucidation of the ecdysteroid biosynthetic pathway. These genes encode cytochrome P450 enzymes catalyzing the final steps of ecdysteroid biosynthesis in the dipteran Drosophila melanogaster and the Lepidoptera Manduca sexta and Bombyx mori. This is the first report on the identification of two Halloween genes, spook (spo) and phantom (phm), from a hemimetabolous orthopteran insect, the desert locust Schistocerca gregaria. Using q-RT-PCR, their spatial and temporal transcript profiles were analyzed in both final larval stage and adult locusts. The circulating ecdysteroid titers in the hemolymph were measured and found to correlate well with changes in the temporal transcript profiles of spo and phm. Moreover, an RNA interference (RNAi)-based approach was employed to study knockdown effects upon silencing of both transcripts in the fifth larval stage. Circulating ecdysteroid levels were found to be significantly reduced upon dsRNA treatment.

Effects of neuropeptides on feeding initiation in larvae of the silkworm, Bombyx mori

In insects, especially phytophagous insects, feeding behavior occurs at a regular frequency. Although a number of physiological studies have revealed various causal factors leading to feeding behavior in insects, little has been demonstrated regarding the regulatory mechanisms underlying insect feeding behavior. To confirm the presence of an endocrinological regulatory mechanism in feeding behavior, we tested the effects of several biologically active peptides on silkworm, Bombyx mori larvae feeding behaviors. To evaluate the effects of the biologically active peptides, we measured the period of latency to the first bite following sample injection into starved Bombyx larvae. Of the chemically synthesized peptides tested, myosuppressin exhibited a prolonged latency, indicating that myosuppressin is a possible inhibitory peptide in Bombyx larvae. In contrast, injections of tachykinin and short neuropeptide F, which are members of the structurally related RF-amide peptide family, had a shorter latency period, indicating that these two peptides are possible stimulatory peptides. In addition, the present study suggests that this bioassay will be advantageous for screening for peptides that regulate insect feeding behavior.

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.

Insulin signaling, lifespan and stress resistance are modulated by metabotropic GABA receptors on insulin producing cells in the brain of Drosophila

Insulin-like peptides (ILPs) regulate growth, reproduction, metabolic homeostasis, life span and stress resistance in worms, flies and mammals. A set of insulin producing cells (IPCs) in the Drosophila brain that express three ILPs (DILP2, 3 and 5) have been the main focus of interest in hormonal DILP signaling. Little is, however, known about factors that regulate DILP production and release by these IPCs. Here we show that the IPCs express the metabotropic GABA_B receptor (GBR), but not the ionotropic GABA_A receptor subunit RDL. Diminishing the GBR expression on these cells by targeted RNA interference abbreviates life span, decreases metabolic stress resistance and alters carbohydrate and lipid metabolism at stress, but not growth in Drosophila. A direct effect of diminishing GBR on IPCs is an increase in DILP immunofluorescence in these cells, an effect that is accentuated at starvation. Knockdown of irk3, possibly part of a G protein-activated inwardly rectifying K⁺ channel that may link to GBRs, phenocopies GBR knockdown in starvation experiments. Our experiments suggest that the GBR is involved in inhibitory control of DILP production and release in adult flies at metabolic stress and that this receptor mediates a GABA signal from brain interneurons that may convey nutritional signals. This is the first demonstration of a neurotransmitter that inhibits insulin signaling in its regulation of metabolism, stress and life span in an invertebrate brain.

Multiple neuropeptides in the Drosophila antennal lobe suggest complex modulatory circuits

The fruitfly, Drosophila, is dependent on its olfactory sense in food search and reproduction. Processing of odorant information takes place in the antennal lobes, the primary olfactory center in the insect brain. Besides classical neurotransmitters, earlier studies have indicated the presence of a few neuropeptides in the olfactory system. In the present study we made an extensive analysis of the expression of neuropeptides in the Drosophila antennal lobes by direct profiling using matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) mass spectrometry and immunocytochemistry. Neuropeptides from seven different precursor genes were unambiguously identified and their localization in neurons was subsequently revealed by immunocytochemistry. These were short neuropeptide F, tachykinin related peptide, allatostatin A, myoinhibitory peptide, SIFamide, IPNamide, and myosuppressin. The neuropeptides were expressed in subsets of olfactory sensory cells and different populations of local interneurons and extrinsic (centrifugal) neurons. In some neuron types neuropeptides were colocalized with classical neurotransmitters. Our findings suggest a huge complexity in peptidergic signaling in different circuits of the antennal lobe.

Regulatory actions of neuropeptides and peptide hormones on the reproduction of molluscsThe present review is one of a series of occasional review articles that have been invited by the Editors and will feature the broad range of disciplines and expertise represented in our Editorial Advisory Board

Reproductive success of individual animals is essential for the survival of any species. Molluscs have adapted to a wide variety of environments (freshwater, brackish water, seawater, and terrestrial habits) and have evolved unique tactics for reproduction. Both of these features attract the academic interests of scientists. Because neuropeptides and peptide hormones play critical roles in neural and neurohormonal regulation of physiological functions and behaviors in this animal group, the regulatory actions of these messengers in reproduction have been extensively investigated. In this review, we will briefly summarize how peptidergic messengers are involved in various aspects of reproduction, using some peptides such as egg-laying hormone, caudo-dorsal cell hormone, APGWamide, and gonadotropin-releasing hormone as typical examples.

The G protein-coupled receptors in the silkworm, Bombyx mori

G protein-coupled receptors (GPCRs) are the largest and most versatile family of transmembrane receptors in the cell, occupying the highest hierarchical positions in the regulation of many physiological processes. Although they have been extensively studied in a number of model insects, there have been few investigations of GPCRs in large Lepidopterans, such as Bombyx mori, an organism that provides a means to perform detailed tissue expression analyses, which may help to characterize GPCRs and their ligands. In addition, B. mori, also known as the silkworm, is an insect of substantial economic importance, due to its use in silk production and traditional medicines. In this work, we computationally identified 90 putative GPCRs in B. mori, 33 of which represent novel proteins. These GPCRs were annotated and compared with their homologs in Drosophila melanogaster and Anopheles gambiae. Phylogenetics analyses of the GPCRs from these three insects showed that GPCRs may easily duplicate or disappear during insect evolution, especially in the neuropeptide and protein hormone receptor subfamily. Interestingly, we observed a decrease in the quantity and diversity of the stress-tolerance gene, Methuselah, in B. mori, which may be related to its long history of domestication. Moreover, the presence of many Bombyx-specific GPCRs suggests that neither Drosophila nor Anopheles is good representatives for the GPCRs in the Class Insecta.

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.

Control of ecdysteroidogenesis in prothoracic glands of insects: a review

The very first step in the study of the endocrine control of insect molting was taken in 1922. Stefan Kopec characterized a factor in the brain of the gypsy moth, Lymantria dispar which appeared to be essential for metamorphosis. This factor was later identified as the neuropeptide prothoracicotropic hormone (PTTH), the first discovery of a series of factors involved in the regulation of ecdysteroid biosynthesis in insects. It is now accepted that PTTH is the most important regulator of prothoracic gland (PG) ecdysteroidogenesis. The periodic increases in ecdysteroid titer necessary for insect development can basically be explained by the episodic activation of the PGs by PTTH. However, since the characterization of the prothoracicostatic hormone (PTSH), it has become clear that in addition to 'tropic factors', also 'static factors', which are responsible for the 'fine-tuning' of the hemolymph ecdysteroid titer, are at play. Many of these regulatory factors are peptides originating from the brain, but also other, extracerebral factors both of peptidic and non-peptidic nature are able to affect PG ecdysteroidogenesis, such as the 'classic' insect hormones, juvenile hormone (JH) and the molting hormone (20E) itself. The complex secretory pattern of ecdysteroids as observed in vivo is the result of the delicate balance and interplay between these ecdysiotropic and ecdysiostatic factors.

A fat body-derived IGF-like peptide regulates postfeeding growth in Drosophila

Members of the insulin family of peptides have conserved roles in the regulation of growth and metabolism in a wide variety of metazoans. Here we show that Drosophila insulin-like peptide 6 (DILP6), which is structurally similar to vertebrate insulin-like growth factor (IGF), is predominantly expressed in the fat body, a functional equivalent of the vertebrate liver and adipocytes. This expression occurs during the postfeeding stage under the direct regulation of ecdysteroid. We further reveal that dilp6 mutants show growth defects during the postfeeding stage, which results in reduced adult body size through a decrease in cell number. This phenotype is rescued by fat body-specific expression of dilp6. These data indicate that DILP6 is a functional, as well as a structural, counterpart of vertebrate IGFs. Our data provide in vivo evidence for a role of ILPs in determining adult body size through the regulation of postfeeding growth.

Bombyx prothoracicostatic peptides activate the sex peptide receptor to regulate ecdysteroid biosynthesis

Insect molting and metamorphosis are induced by steroid hormones named ecdysteroids, whose production is regulated by various neuropeptides. We cloned the gene and analyzed the expression of the prothoracicostatic peptide, a unique neuropeptide shown to suppress the production of ecdysteroids in the prothoracic gland of the silkworm, Bombyx mori. We also characterized a Bombyx G protein-coupled receptor, which has previously been identified as an ortholog of the Drosophila sex peptide receptor, as a functional prothoracicostatic peptide receptor. This receptor responded specifically to the prothoracicostatic peptides when examined using a heterologous expression system. The receptor was highly expressed in the prothoracic gland on the day before each larval and pupal ecdysis, when prothoracicostatic peptides are synthesized at a high level in the epiproctodeal glands. These results suggest that the sex peptide receptor functions as a prothoracicostatic peptide receptor in Bombyx and that the peripheral neurosecretory cells as well as the central neuroendocrine system play stage-specific roles in regulating ecdysteroidogenesis.

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

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

Presence and distribution of FMRFamide-like immunoreactivity in the cyprid of the barnacle Balanus amphitrite (Cirripedia, Crustacea)

The presence and distribution of FMRFamide-like peptides (FLPs) in the cyprid larvae of the barnacle Balanus amphitrite were investigated using immunohistochemical methods. Barnacles are considered to be one of the most important constituents of animal fouling communities, and the cyprid stage is specialized for settlement and metamorphosis in to the sessile adult condition. FLPs immunoreactive (IR) neuronal cell bodies were detected in both the central and the peripheral nervous system. One bilateral group of neurons somata was immunodetected in the brain, and IR nerve fibers were observed in the neuropil area and optic lobes. Intense immunostaining was also observed in the frontal filament complex: frontal filament tracts leaving the optic lobes and projecting towards the compound eyes, swollen nerve endings in the frontal filament vesicles, and thin nerve endings in the external frontal filament. Thin IR nerve fibers were also present in the cement glands. Two pairs of neuronal cell bodies were immunodetected in the posterior ganglion; some of their axons appear to project to the cirri. FLPs IR neuronal cell bodies were also localized in the wall of the dilated midgut and in the narrow hindgut; their processes surround the gut wall and allow gut neurons to synapse with one another. Our data demonstrated the presence of FLPs IR substances in the barnacle cyprid. We hypothesize that these peptides act as integrators in the central nervous system, perform neuromuscular functions for thoracic limbs, trigger intestinal movements and, at the level of the frontal filament, play a neurosecretory role.

Identification of a complex peptidergic neuroendocrine network in the hard tick, Rhipicephalus appendiculatus

Neuropeptides are crucial regulators of development and various physiological functions but little is known about their identity, expression and function in vectors of pathogens causing serious diseases, such as ticks. Therefore, we have used antibodies against multiple insect and crustacean neuropeptides to reveal the presence of these bioactive molecules in peptidergic neurons and cells of the ixodid tick Rhipicephalus appendiculatus. These antibodies have detected 15 different immunoreactive compounds expressed in specific central and peripheral neurons associated with the synganglion. Most central neurons arborize in distinct areas of the neuropile or the putative neurohaemal periganglionic sheath of the synganglion. Several large identified neurons in the synganglion project multiple processes through peripheral nerves to form elaborate axonal arborizations on the surface of salivary glands or to terminate in the lateral segmental organs (LSO). Additional neuropeptide immunoreactivity has been observed in intrinsic secretory cells of the LSO. We have also identified two novel clusters of peripheral neurons embedded in the cheliceral and paraspiracular nerves. These neurons project branching axons into the synganglion and into the periphery. Our study has thus revealed a complex network of central and peripheral peptidergic neurons, putative neurohaemal and neuromodulatory structures and endocrine cells in the tick comparable with those found in insect and crustacean neuroendocrine systems. Strong specific staining with a large variety of antibodies also indicates that the tick nervous system and adjacent secretory organs are rich sources of diverse neuropeptides related to those identified in insects, crustaceans or even vertebrates.

Proteomic identification of the silkworm (Bombyx mori L) prothoracic glands during the fifth instar stage

Although the ecdysteroid of the silkworm had been studied for decades, the proteome of the prothoracic gland, the primary source of ecdysteroid hormones, has not been studied previously. In the present paper, we utilized a proteomic approach to investigate the fifth instar prothoracic gland during the growth and development of the silkworm, Bombyx mori L. The two-dimensional electrophoresis results showed that the majority of proteins were acidic proteins, especially concentrated in the area of 25–65 kDa, with pI values of between 4 and 7, and the difference was not distinct. When compared with Qiufeng (Japanese strain), the interspecific distinction was larger than the intraspecific distinction, and 19 particular spots, excized from the third, fifth and ninth days of p50 (Chinese strain) and Qiufeng were subjected to MALDI-TOF–MS (matrix-assisted laser-desorption ionization–time-of-flight MS) analysis. We sorted them into seven catagories: energetics and/or metabolism, storage proteins, protection, lipid metabolism, signal transduction, cell function and unknown function proteins. Of these proteins, arginine methyltransferase is discussed as playing an important role in regulating the activation of ecdysteroidogenesis via transcription or translation.

Neuropeptide receptor transcriptome reveals unidentified neuroendocrine pathways

Neuropeptides are an important class of molecules involved in diverse aspects of metazoan development and homeostasis. Insects are ideal model systems to investigate neuropeptide functions, and the major focus of insect neuropeptide research in the last decade has been on the identification of their receptors. Despite these vigorous efforts, receptors for some key neuropeptides in insect development such as prothoracicotropic hormone, eclosion hormone and allatotropin (AT), remain undefined. In this paper, we report the comprehensive cloning of neuropeptide G protein-coupled receptors from the silkworm, Bombyx mori, and systematic analyses of their expression. Based on the expression patterns of orphan receptors, we identified the long-sought receptor for AT, which is thought to stimulate juvenile hormone biosynthesis in the corpora allata (CA). Surprisingly, however, the AT receptor was not highly expressed in the CA, but instead was predominantly transcribed in the corpora cardiaca (CC), an organ adjacent to the CA. Indeed, by using a reverse-physiological approach, we purified and characterized novel allatoregulatory peptides produced in AT receptor-expressing CC cells, which may indirectly mediate AT activity on the CA. All of the above findings confirm the effectiveness of a systematic analysis of the receptor transcriptome, not only in characterizing orphan receptors, but also in identifying novel players and hidden mechanisms in important biological processes. This work illustrates how using a combinatorial approach employing bioinformatic, molecular, biochemical and physiological methods can help solve recalcitrant problems in neuropeptide research.

A genome-wide inventory of neurohormone GPCRs in the red flour beetle Tribolium castaneum

Insect neurohormones (biogenic amines, neuropeptides, and protein hormones) and their G protein-coupled receptors (GPCRs) play a central role in the control of behavior, reproduction, development, feeding and many other physiological processes. The recent completion of several insect genome projects has enabled us to obtain a complete inventory of neurohormone GPCRs in these insects and, by a comparative genomics approach, to analyze the evolution of these proteins. The red flour beetle Tribolium castaneum is the latest addition to the list of insects with a sequenced genome and the first coleopteran (beetle) to be sequenced. Coleoptera is the largest insect order and about 30% of all animal species living on earth are coleopterans. Some coleopterans are severe agricultural pests, which is also true for T. castaneum, a global pest for stored grain and other dried commodities for human consumption. In addition, T. castaneum is a model for insect development. Here, we have investigated the presence of neurohormone GPCRs in Tribolium and compared them with those from the fruit fly Drosophila melanogaster (Diptera) and the honey bee Apis mellifera (Hymenoptera). We found 20 biogenic amine GPCRs in Tribolium (21 in Drosophila; 19 in the honey bee), 48 neuropeptide GPCRs (45 in Drosophila; 35 in the honey bee), and 4 protein hormone GPCRs (4 in Drosophila; 2 in the honey bee). Furthermore, we identified the likely ligands for 45 of these 72 Tribolium GPCRs. A highly interesting finding in Tribolium was the occurrence of a vasopressin GPCR and a vasopressin peptide. So far, the vasopressin/GPCR couple has not been detected in any other insect with a sequenced genome (D. melanogaster and six other Drosophila species, Anopheles gambiae, Aedes aegypti, Bombyx mori, and A. mellifera). Tribolium lives in very dry environments. Vasopressin in mammals is the major neurohormone steering water reabsorption in the kidneys. Its presence in Tribolium, therefore, might be related to the animal's need to effectively control water reabsorption. Other striking differences between Tribolium and the other two insects are the absence of the allatostatin-A, kinin, and corazonin neuropeptide/receptor couples and the duplications of other hormonal systems. Our survey of 340 million years of insect neurohormone GPCR evolution shows that neuropeptide/receptor couples can easily duplicate or disappear during insect evolution. It also shows that Drosophila is not a good representative of all insects, because several of the hormonal systems that we now find in Tribolium do not exist in Drosophila.

Ecdysteroids, juvenile hormone and insect neuropeptides: Recent successes and remaining major challenges

In the recent decade, tremendous progress has been realized in insect endocrinology as the result of the application of a variety of advanced methods in neuropeptidome- and receptor research. Hormones of which the existence had been shown by bioassays four decades ago, e.g. bursicon (a member of the glycoprotein hormone family) and pupariation factor (Neb-pyrokinin 2, a myotropin), could be identified, along with their respective receptors. In control of diurnal rhythms, clock genes got company from the neuropeptide Pigment Dispersing Factor (PDF), of which the receptor could also be identified. The discovery of Inka cells and their function in metamorphosis was a true hallmark. Analysis of the genomes of Caenorhabditis elegans, Drosophila melanogaster and Apis mellifera yielded about 75, 100 and 200 genes coding for putative signaling peptides, respectively, corresponding to approximately 57, 100 and 100 peptides of which the expression could already be proven by means of mass spectrometry. The comparative approach invertebrates-vertebrates recently yielded indications for the existence of counterparts in insects for prolactin, atrial natriuretic hormone and Growth Hormone Releasing Hormone (GRH). Substantial progress has been realized in identifying the Halloween genes, a membrane receptor(s) for ecdysteroids, a nuclear receptor for methylfarnesoate, and dozens of GPCRs for insect neuropeptides. The major remaining challenges concern the making match numerous orphan GPCRs with orphan peptidic ligands, and elucidating their functions. Furthermore, the endocrine control of growth, feeding-digestion, and of sexual differentiation, in particular of males, is still poorly understood. The finding that the prothoracic glands produce an autocrine factor with growth factor-like properties and secrete proteins necessitates a reevaluation of their role in development.

Prothoracicotropic hormone regulates developmental timing and body size in Drosophila

In insects, control of body size is intimately linked to nutritional quality as well as environmental and genetic cues that regulate the timing of developmental transitions. Prothoracicotropic hormone (PTTH) has been proposed to play an essential role in regulating the production and/or release of ecdysone, a steroid hormone that stimulates molting and metamorphosis. In this report, we examine the consequences on Drosophila development of ablating the PTTH-producing neurons. Surprisingly, PTTH production is not essential for molting or metamorphosis. Instead, loss of PTTH results in delayed larval development and eclosion of larger flies with more cells. Prolonged feeding, without changing the rate of growth, causes the overgrowth and is a consequence of low ecdysteroid titers. These results indicate that final body size in insects is determined by a balance between growth-rate regulators such as insulin and developmental timing cues such as PTTH that set the duration of the feeding interval.

FXPRL-amide peptides induce ecdysteroidogenesis through a G-protein coupled receptor expressed in the prothoracic gland of Bombyx mori

The FXPRL-amide peptide family (pyrokinin/PBAN family) consists of insect peptides that function broadly in insect life processes and are characterized by a conserved C-terminal motif. In the silkworm, Bombyx mori, sex pheromone biosynthesis and induction of embryonic diapause are regulated by peptides from this family. To elucidate other functions of Bombyx FXPRL-amide peptides, we analyzed the tissue expression patterns of two known Bombyx G-protein coupled receptors for these peptides. We found that the Bombyx diapause hormone receptor (BmDHR), is expressed in the prothoracic gland (PG), the organ which synthesizes and releases the insect molting hormones, ecdysteroids. Furthermore, diapause hormone (DH), a member of the Bombyx FXPRL-amide peptides, increases both intracellular Ca(2+) and cAMP concentrations and induces ecdysteroidogenesis in late fifth instar PGs coincident with BmDHR expression in the PGs. DH also has the highest prothoracicotropic activity among the FXPRL-amide peptides, which corresponds well to the ligand specificity of heterologously expressed BmDHR. These results demonstrate that FXPRL-amide peptides can function as prothoracicotropic factors through the activation of BmDHR and may play an important role in controlling molting and metamorphosis.