The 2014 Bernard B. Brodie award lecture-epoxide hydrolases: drug metabolism to therapeutics for chronic pain

Dr. Bernard Brodie's legacy is built on fundamental discoveries in pharmacology and drug metabolism that were then translated to the clinic to improve patient care. Similarly, the development of a novel class of therapeutics termed the soluble epoxide hydrolase (sEH) inhibitors was originally spurred by fundamental research exploring the biochemistry and physiology of the sEH. Here, we present an overview of the history and current state of research on epoxide hydrolases, specifically focusing on sEHs. In doing so, we start with the translational project studying the metabolism of the insect juvenile hormone mimic R-20458 [(E)-6,7-epoxy-1-(4-ethylphenoxy)-3,7-dimethyl-2-octene], which led to the identification of the mammalian sEH. Further investigation of this enzyme and its substrates, including the epoxyeicosatrienoic acids, led to insight into mechanisms of inflammation, chronic and neuropathic pain, angiogenesis, and other physiologic processes. This basic knowledge in turn led to the development of potent inhibitors of the sEH that are promising therapeutics for pain, hypertension, chronic obstructive pulmonary disorder, arthritis, and other disorders.

Adipokinetic hormone signalling system in the Chagas disease vector, Rhodnius prolixus

Neuropeptides and their G protein-coupled receptors are widespread throughout Metazoa and in several cases, clear orthologues can be identified in both protostomes and deuterostomes. One such neuropeptide is the insect adipokinetic hormone (AKH), which is related to the mammalian gonadotropin-releasing hormone. AKH has been studied extensively and is known to mobilize lipid, carbohydrates and proline for energy-consuming activities such as flight. In order to determine the possible roles for this signalling system in Rhodnius prolixus, we isolated the cDNA sequences encoding R. prolixus AKH (Rhopr-AKH) and its receptor (Rhopr-AKHR). We also examined their spatial expression pattern using quantitative PCR. Our expression analysis indicates that Rhopr-AKH is only expressed in the corpus cardiacum of fifth-instars and adults. Rhopr-AKHR, by contrast, is expressed in several peripheral tissues including the fat body. The expression of the receptor in the fat body suggests that AKH is involved in lipid mobilization, which was confirmed by knockdown of Rhopr-AKHR via RNA interference. Adult males that had been injected with double-stranded RNA (dsRNA) for Rhopr-AKHR exhibited increased lipid content in the fat body and decreased lipid levels in the haemolymph. Moreover, injection of Rhopr-AKH in Rhopr-AKHR dsRNA-treated males failed to elevate haemolymph lipid levels, confirming that this is indeed the receptor for Rhopr-AKH.

Positive feedback regulation of prothoracicotropic hormone secretion by ecdysteroid--a mechanism that determines the timing of metamorphosis

When insect larvae have fully grown, prothoracicotropic hormone (PTTH) is released from the brain, triggering the initiation of metamorphic development through stimulation of ecdysteroid secretion by the prothoracic glands. The present study analyzes the mechanism that regulates the occurrence of this PTTH surge. In the silkworm Bombyx mori, the PTTH surge occurs on day 6 of the fifth instar and is preceded by a small rise in hemolymph ecdysteroid titer, which occurs late on day 5. We therefore hypothesized that this rise of ecdysteroid titer is involved in the induction of the PTTH surge. To test this hypothesis, two experiments were conducted. First, a small amount of 20-hydroxyecdysone was injected on day 4, two days before the expected day of the PTTH surge, to simulate the small rise in hemolymph ecdysteroid titer on day 5. This injection led to a precocious surge of PTTH the next day. Next, the hemolymph ecdysteroid titer on day 5 was artificially lowered by injecting ecdysteroid-22-oxidase, which inactivates 20-hydroxyecdysone. After this treatment, the PTTH surge did not occur on day 6 in 80% of the animals. These results indicate that a small rise of the hemolymph ecdysteroid titer plays a critical role in the induction of the PTTH surge. Since basal ecdysteroidogenic activity of the prothoracic glands increases with larval growth, a circulating level of ecdysteroids may convey information about larval maturity to the brain, to coordinate larval growth and metamorphosis. This is the first report in invertebrates to demonstrate positive feedback regulation of the surge of a tropic hormone by a downstream steroid hormone.

Regulation of histone H3 phosphorylation at serine 10 in PTTH-stimulated prothoracic glands of the silkworm, Bombyx mori

A complex signaling network appears to be involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in insect prothoracic glands (PGs). In the present study, we investigated the localization of phosphorylated extracellular signal-regulated kinase (ERK) in PTTH-stimulated PGs in Bombyx mori. The nuclear effect of PTTH was further studied by examining phosphorylation of histone H3 at serine 10. Results showed that in PTTH-stimulated PGs, higher phosphorylated ERK was detected in nuclear fraction compared to that in cytosolic fraction. PTTH treatment in vitro appears to rapidly enhance the transcriptional activation-associated histone H3 phosphorylation at serine 10. PTTH stimulated histone H3 phosphorylation in a time-dependent manner. Injection of PTTH into day-6 last instar larvae greatly increased histone H3 phosphorylation, verifying the in vitro effect. The stimulation of histone H3 phosphorylation by PTTH appears to be developmentally regulated. PTTH-stimulated histone H3 phosphorylation was greatly reduced in Ca(2+)-free saline or by pretreatment with a potent and specific inhibitor of phospholipase C (PLC), U73122. When PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187 or thapsigargin), a greatly increase in histone H3 phosphorylation at serine 10 was observed, indicating Ca(2+)-dependency of histone H3 phosphorylation stimulated by PTTH. In addition, PTTH-stimulated histone H3 phosphorylation was partially reduced by U0126, a specific mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor, indicating the involvement of ERK. However, pretreatment with LY294002, a phosphoinositide 3-kinase (PI3K) inhibitor, did not inhibit PTTH-stimulated histone H3 phosphorylation, implying that PI3K signaling is not related to PTTH-stimulated histone H3 phosphorylation. Taken together, these results suggest that PTTH-stimulated histone H3 phosphorylation at serine 10 is mediated by Ca(2+)/ERK signaling in B. mori PGs.

In silico characterization of the neuropeptidome of the Western black widow spider Latrodectus hesperus

Technological advancements in high-throughput sequencing have resulted in the production/public deposition of an ever-growing number of arthropod transcriptomes. While most sequencing projects have focused on hexapods, transcriptomes have also been generated for members of the Chelicerata. One chelicerate for which a large transcriptome has recently been released is the Western black widow Latrodectus hesperus, a member of the Araneae (true spiders). Here, a neuropeptidome for L. hesperus was predicted using this resource. Thirty-eight peptide-encoding transcripts were mined from the L. hesperus transcriptome, with 216 distinct peptides predicted from the deduced pre/preprohormones. The identified peptides included members of the allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CAPA/periviscerokinin/pyrokinin, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/ion transport peptide, diuretic hormone 31, diuretic hormone 44, FMRFamide-like peptide (FLP), GSEFLamide, insulin-like peptide, neuropeptide F (NPF), orcokinin, proctolin, short neuropeptide F, SIFamide, sulfakinin and tachykinin-related peptide (TRP) families. Of particular note were the identifications of a carboxyl (C)-terminally extended corazonin, FLPs possessing -IMRFamide, -MMYFamide, and -MIHFamide C-termini, a NPF and a sulfakinin each ending in -RYamide rather than -RFamide, a precursor whose orcokinins include C-terminally amidated isoforms, and a collection of TRPs possessing -FXPXLamide rather than the stereotypical -FXGXLamide C-termini. The L. hesperus peptidome is by far the largest thus far published for any member of the Chelicerata. Taken collectively, these data serve as a reference for future neuropeptide discovery in the Araneae and provide a foundation for future studies of peptidergic control in L. hesperus and other spiders.

Molecular characterization, tissue distribution, and ultrastructural localization of adipokinetic hormones in the CNS of the firebug Pyrrhocoris apterus (Heteroptera, Insecta)

Adipokinetic hormones (AKHs) are a group of insect metabolic neurohormones, synthesized and released from an endocrine retrocerebral gland, the corpus cardiacum (CC). Small amounts of AKH have also been identified in the brain, although their role in this organ is not clear. To address this gap in the knowledge about insect brain biology, we studied the nucleotide sequence, tissue distribution, and subcellular localization of AKHs in the brain and CC of the firebug Pyrrhocoris apterus. This insect expresses two AKHs; the octapeptides Pyrap-AKH and Peram-CAH-II, the presence of which was documented in the both studied organs. In situ hybridization and quantitative reverse-transcription (q-RT)-PCR revealed the expression of the genes encoding for both AKHs not only in the CC, but also in brain. Electron microscopy analysis of the brain revealed the presence of these hormones in specialized secretory granules localized predominantly in the cellular bodies of neurons. The hormones might be transported from the granules into the axons, where they could play a role in neuronal signaling. Under acute stress induced by the injection of 3μmol KCl, the level of AKHs in the brain increased to a greater extent than that in the CC. These results might indicate an enhanced role of brain-derived AKHs in defence reaction under acute stress situations.

New insights into the evolution of vertebrate CRH (corticotropin-releasing hormone) and invertebrate DH44 (diuretic hormone 44) receptors in metazoans

The corticotropin releasing hormone receptors (CRHR) and the arthropod diuretic hormone 44 receptors (DH44R) are structurally and functionally related members of the G protein-coupled receptors (GPCR) of the secretin-like receptor superfamily. We show here that they derive from a bilaterian predecessor. In protostomes, the receptor became DH44R that has been identified and functionally characterised in several arthropods but the gene seems to be absent from nematode genomes. Duplicate DH44R genes (DH44 R1 and DH44R2) have been described in some arthropods resulting from lineage-specific duplications. Recently, CRHR-DH44R-like receptors have been identified in the genomes of some lophotrochozoans (molluscs, which have a lineage-specific gene duplication, and annelids) as well as representatives of early diverging deuterostomes. Vertebrates have previously been reported to have two CRHR receptors that were named CRHR1 and CRHR2. To resolve their origin we have analysed recently assembled genomes from representatives of early vertebrate divergencies including elephant shark, spotted gar and coelacanth. We show here by analysis of synteny conservation that the two CRHR genes arose from a common ancestral gene in the early vertebrate tetraploidizations (2R) approximately 500 million years ago. Subsequently, the teleost-specific tetraploidization (3R) resulted in a duplicate of CRHR1 that has been lost in some teleost lineages. These results help distinguish orthology and paralogy relationships and will allow studies of functional conservation and changes during evolution of the individual members of the receptor family and their multiple native peptide agonists.

Evolution of the AKH/corazonin/ACP/GnRH receptor superfamily and their ligands in the Protostomia

In this review we trace the evolutionary connections between GnRH receptors from vertebrates and the receptors for adipokinetic hormone (AKH), AKH/corazonin-related peptide (ACP), and corazonin from arthropods. We conclude that these G protein-coupled receptors (GPCRs) are closely related and have a common evolutionary origin, which dates back to the split of Proto- and Deuterostomia, about 700 million years ago. We propose that in the protostomian lineage, the ancestral GnRH-like receptor gene duplicated as did its GnRH-like ligand gene, followed by diversification, leading to (i) a corazonin receptor gene and a corazonin-like ligand gene, and (ii) an AKH receptor gene and an AKH-like ligand gene in the Mollusca and Annelida. Subsequently, the AKH receptor and ligand genes duplicated once more, yielding the situation that we know from arthropods today, where three independent hormonal systems exist, signalling with AKH, ACP, and corazonin. Our model for the evolution of GnRH signaling in the Protostomia is a striking example of receptor-ligand co-evolution. This model has been developed using several bioinformatics tools (TBLASTN searches, phylogenetic tree analyses), which also helped us to annotate six novel AKH preprohormones and their corresponding AKH sequences from the following molluscs: the sea hare Aplysia californica (AKH sequence: pQIHFSPDWGTamide), the sea slug Tritonia diomedea (pQIHFSPGWEPamide), the fresh water snail Bithynia siamensis goniomphalos (pQIHFTPGWGSamide), the owl limpet Lottia gigantea (pQIHFSPTWGSamide), the oyster Crassostrea gigas (pQVSFSTNWGSamide), and the freshwater pearl mussel Hyriopsis cumingii (pQISFSTNWGSamide). We also found AKHs in the tardigrade Hysibius dujardini (pQLSFTGWGHamide), the rotifer Brachionus calycifloros (pQLTFSSDWSGamide), and the penis worm Priapulus caudatus (pQIFFSKGWRGamide). This is the first report, showing that AKH signaling is widespread in molluscs.

Role of Phote-HrTH (Phormia terraenovae hypertrehalosemic hormone) in modulating the supercontractile muscles of the crop of adult Phormia regina Meigen

Phote-HrTH (Phormia terraenovae hypertrehalosemic hormone) has been demonstrated in the Diptera to be involved in flight metabolism, reproduction, and diapause. Each of these events needs the hormone's action and requirement for carbohydrates is the common denominator. In Diptera, carbohydrates are taken up during feeding by action of the cibarial pump and are then stored in the crop. Using adult Phormia regina, both a bioassay and electrophysiological recordings show that Phote-HrTH slows down or inhibits the crop lobe muscles (P5) and, at the same time, stimulates the muscles of the pump 4 (P4) involved in pushing fluids out of the crop and up into the midgut for digestion. The EC50 for P4 was in the nanomolar range while the IC50 for P5 was 1.4-75.1 pM. The effect of Phote-HrTH on P4/5 suggests that the peptide is important in coordinating the two pumps, which are involved in moving carbohydrates up into the midgut for digestion. The adult crop organ is an essential storage organ for carbohydrates and now should be considered an important structure capable of delivering nutrients to the midgut for digestion.

Differential peptidomics highlights adipokinetic hormone as key player in regulating digestion in anautogenous flesh fly, Sarcophaga crassipalpis

Females of anautogenous flesh flies, Sarcophaga crassipalpis, need a protein meal in order to produce their first batch of eggs. This protein meal elicits an increase in midgut proteolytic activity that is under neuropeptidergic regulation. Time series of decapitation and rescue experiments of liver fed flies evidenced the need of a peptide factor released by corpora cardiaca (CC) within 4h post protein feeding in order to assure complete protein digestion. Q-Exactive quantitative differential peptidomics analysis on CC of sugar fed flies and flies 5h post protein feeding respectively, showed a unique consistent decrease in the stored amount of adipokinetic hormone (AKH) ranging between 16% up to 63%. Injection of AKH into liver fed decapitated flies as well as sugar fed intact flies resulted in dose dependent enhanced midgut proteolytic activity up to the level of intact protein fed flies. This suggests a key role of AKH in food depended reproduction.

Ecdysis triggering hormone ensures proper timing of juvenile hormone biosynthesis in pharate adult mosquitoes

Juvenile hormones (JHs) are synthesized by the corpora allata (CA) and play a key role in insect development. A decrease of JH titer in the last instar larvae allows pupation and metamorphosis to proceed. As the anti-metamorphic role of JH comes to an end, the CA of the late pupa (or pharate adult) becomes again "competent" to synthesize JH, which would play an essential role orchestrating reproductive maturation. In the present study, we provide evidence that ecdysis triggering hormone (ETH), a key endocrine factor involved in ecdysis control, acts as an allatotropic regulator of JH biosynthesis, controlling the exact timing of CA activation in the pharate adult mosquito. Analysis of the expression of Aedes aegypti ETH receptors (AeaETHRs) revealed that they are present in the CA and the corpora cardiaca (CC), and their expression peaks 4 h before eclosion. In vitro stimulation of the pupal CA glands with ETH resulted in an increase in JH synthesis. Consistent with this finding, silencing AeaETHRs by RNA interference (RNAi) in pupa resulted in reduced JH synthesis by the CA of one day-old adult females. Stimulation with ETH resulted in increases in the activity of juvenile hormone acid methyltransferase (JHAMT), a key JH biosynthetic enzyme. Furthermore, inhibition of IP3R-operated mobilization of endoplasmic reticulum Ca(2+) stores prevented the ETH-dependent increases of JH biosynthesis and JHAMT activity. All together these findings provide compelling evidence that ETH acts as a regulatory peptide that ensures proper developmental timing of JH synthesis in pharate adult mosquitoes.

Cell death and tissue reorganization in Rhynchosciara americana (Sciaridae: Diptera) metamorphosis and their relation to molting hormone titers

Programmed cell death (PCD) is a focal topic for understanding processes underlying metamorphosis in insects, especially so in holometabolous orders. During adult morphogenesis it allows for the elimination of larva-specific tissues and the reorganization of others for their functionalities in adult life. In Rhynchosciara, this PCD process could be classified as autophagic cell death, yet the expression of apoptosis-related genes and certain morphological aspects suggest that processes, autophagy and apoptosis may be involved. Aiming to reveal the morphological changes that salivary gland and fat body cells undergo during metamorphosis we conducted microscopy analyses to detect chromatin condensation and fragmentation, as well as alterations in the cytoplasm of late pupal tissues of Rhynchosciara americana. Transmission electron microscopy and confocal microscopy revealed cells in variable stages of death. By analyzing the morphological structure of the salivary gland we observed the presence of cells with autophagic vacuoles and apoptotic bodies and DNA fragmentation was confirmed with the TUNEL assay in salivary gland. The reorganization of fat body occurs with discrete detection of cell death by TUNEL assay. However, both salivary gland histolysis and fat body reorganization occur under control of the hormone ecdysone.

Neuropeptides affecting the transfer of juvenile hormones from males to females during mating in Spodoptera frugiperda

In the polyandric moth, Spodopterafrugiperda, juvenile hormone (JH) is transferred from the male accessory reproductive glands (AG) to the female bursa copulatrix (BC) during copulation (see Hassanien et al., 2014). Here we used the RNA interference technique to study the role of allatoregulating neuropeptides in controlling the synthesis and transfer of JH during mating. Knockdown of S. frugiperda allatostatin C (Spofr-AS type C) in freshly emerged males leads to an accumulation of JH in the AG beyond that in the control and mating results in a higher transport of JH I and JH II into the female BC. Knockdown of S. frugiperda allatotropin 2 (Spofr-AT2) significantly reduces the amount of JH in the AG as well as its transfer into the female BC during copulation. Knockdown of S. frugiperda allatostatin A (Spofr-AS type A) and S. frugiperda allatotropin (Spofr-AT; Hassanien et al., 2014) only slightly affects the accumulation of JH in the AG and its transfer from the male to the female. We conclude that Spofr-AS type C and Spofr-AT2 act as true allatostatin and true allatotropin, respectively, on the synthesis of JH I and JH II in the male AG. Moreover, both peptides seem to control the synthesis of JH III in the corpora allata of adult males and its release into the hemolymph.

Transcriptional control of steroid biosynthesis genes in the Drosophila prothoracic gland by ventral veins lacking and knirps

Specialized endocrine cells produce and release steroid hormones that govern development, metabolism and reproduction. In order to synthesize steroids, all the genes in the biosynthetic pathway must be coordinately turned on in steroidogenic cells. In Drosophila, the steroid producing endocrine cells are located in the prothoracic gland (PG) that releases the steroid hormone ecdysone. The transcriptional regulatory network that specifies the unique PG specific expression pattern of the ecdysone biosynthetic genes remains unknown. Here, we show that two transcription factors, the POU-domain Ventral veins lacking (Vvl) and the nuclear receptor Knirps (Kni), have essential roles in the PG during larval development. Vvl is highly expressed in the PG during embryogenesis and is enriched in the gland during larval development, suggesting that Vvl might function as a master transcriptional regulator in this tissue. Vvl and Kni bind to PG specific cis-regulatory elements that are required for expression of the ecdysone biosynthetic genes. Knock down of either vvl or kni in the PG results in a larval developmental arrest due to failure in ecdysone production. Furthermore, Vvl and Kni are also required for maintenance of TOR/S6K and prothoracicotropic hormone (PTTH) signaling in the PG, two major pathways that control ecdysone biosynthesis and PG cell growth. We also show that the transcriptional regulator, Molting defective (Mld), controls early biosynthetic pathway steps. Our data show that Vvl and Kni directly regulate ecdysone biosynthesis by transcriptional control of biosynthetic gene expression and indirectly by affecting PTTH and TOR/S6K signaling. This provides new insight into the regulatory network of transcription factors involved in the coordinated regulation of steroidogenic cell specific transcription, and identifies a new function of Vvl and Knirps in endocrine cells during post-embryonic development.

A Novel Type of Receptor cDNA from the Prothoracic Glands of the Silkworm,Bombyx mori

A cDNA encoding a novel heptahelical receptor from the prothoracic glands of the silkworm, Bombyx mori was cloned and sequenced during screening of a prothoracicotropic hormone (PTTH) receptor. Orthologs of this receptor are found not only in insects, but also in the vertebrates. In B. mori, ubiquitous expression of the mRNA was observed in the larva. Also, a higher expression level in the prothoracic glands was observed before molting and metamorphosis and was impaired after pupal molting. But, further analysis is required to confirm whether this receptor cDNA encodes the PTTH receptor.

Responses of PTTH-producing neurosecretory neurons in Lymantria dispar caterpillars exposed to cadmium

Lymantria dispar, as most invasive insect species, is very adaptable and reacts quickly to changing environment. Neuroendocrine system first reacts to stress in insects, and specific neurohormonal reorganization may be used in early heavy metal risk assessment. Prothoracicotropic neurohormones (PTTH) control ecdysteroid synthesis (morphogenetic and stress hormones) in insects. In this article, we report the presence of PTTH immunoreactive molecules in L2' dorsolateral neurosecretory neurons (nsn) in caterpillar brains and changes after exposure to pollutant stress of different intensity. For 3 days, after molting into the 4th instar, caterpillars of Lymantria dispar were fed with a high wheat germ diet without (control) or with added cadmium (experimental groups: 10, 30, 100, 250 μg Cd/g dry food weight). Changes in PTTH producing L2' nsn and differences in the intensity of protein bands in the region of PTTH molecular mass (Mr 11-15 kDa) were analyzed. The number of L2' neurons tended to decrease except in the group given the highest cadmium concentration (250 μg). The neurons were enlarged after acute treatment especially in the group given the highest cadmium concentration. The size of L2' nsn nuclei was decreased only in the group fed with 30 μg Cd. Protein band intensity in the Mr region of PTTH remained unchanged in all groups except for the group given the diet with the highest Cd concentration.

Signaling of reactive oxygen species in PTTH-stimulated ecdysteroidogenesis in prothoracic glands of the silkworm, Bombyx mori

Our previous study demonstrated that mitochondria-derived reactive oxygen species (ROS) generation is involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in Bombyx mori prothoracic glands (PGs). In the present study, we further investigated the mechanism of ROS production and the signaling pathway mediated by ROS. PTTH-stimulated ROS production was markedly attenuated in a Ca(2+)-free medium. The phospholipase C (PLC) inhibitor, U73122, greatly inhibited PTTH-stimulated ROS production, indicating the involvement of Ca(2+) and PLC. When the PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187, or the protein kinase C (PKC) activator, phorbol 12-myristate acetate (PMA)), a great increase in ROS production was observed. We further investigated the action mechanism of PTTH-stimulated ROS signaling. Results showed that in the presence of either an antioxidant (N-acetylcysteine, NAC), or the mitochondrial oxidative phosphorylation inhibitors (rotenone, antimycin A, the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), and diphenyleneiodonium (DPI)), PTTH-regulated phosphorylation of ERK, 4E-BP, and AMPK was blocked. Treatment with 1mM of H2O2 alone activated the phosphorylation of ERK and 4E-BP, and inhibited AMPK phosphorylation. From these results, we conclude that PTTH-stimulated ROS signaling is Ca(2+)- and PLC-dependent and that ROS signaling appears to lie upstream of the phosphorylation of ERK, 4E-BP, and AMPK.

N-acetyltransferase (nat) is a critical conjunct of photoperiodism between the circadian system and endocrine axis in Antheraea pernyi

Since its discovery in 1923, the biology of photoperiodism remains a mystery in many ways. We sought the link connecting the circadian system to an endocrine switch, using Antheraea pernyi. PER-, CLK- and CYC-ir were co-expressed in two pairs of dorsolateral neurons of the protocerebrum, suggesting that these are the circadian neurons that also express melatonin-, NAT- and HIOMT-ir. The results suggest that a melatonin pathway is present in the circadian neurons. Melatonin receptor (MT2 or MEL-1B-R)-ir in PTTH-ir neurons juxtaposing clock neurons suggests that melatonin gates PTTH release. RIA showed a melatonin rhythm with a peak four hours after lights off in adult brain both under LD16:8 (LD) and LD12:12 (SD), and both the peak and the baseline levels were higher under LD than SD, suggesting a photoperiodic influence. When pupae in diapause were exposed to 10 cycles of LD, or stored at 4 °C for 4 months under constant darkness, an increase of NAT activity was observed when PTTH released ecdysone. DNA sequence upstream of nat contained E-boxes to which CYC/CLK could bind, and nat transcription was turned off by clk or cyc dsRNA. dsRNA(NAT) caused dysfunction of photoperiodism. dsRNA(PER) upregulated nat transcription as anticipated, based on findings in the Drosophila melanogaster circadian system. Transcription of nat, cyc and clk peaked at ZT12. RIA showed that dsRNA(NAT) decreased melatonin while dsRNA(PER) increased melatonin. Thus nat, a clock controlled gene, is the critical link between the circadian clock and endocrine switch. MT-binding may release PTTH, resulting in termination of diapause. This study thus examined all of the basic functional units from the clock: a photoperiodic counter as an accumulator of mRNA(NAT), to endocrine switch for photoperiodism in A. pernyi showing this system is self-complete without additional device especially for photoperiodism.

Molecular characterization and possible biological roles of allatotropin in Rhodnius prolixus

Allatotropins (ATs) are a family of neuropeptides that have been shown to stimulate the biosynthesis of juvenile hormone in certain insect species, and to have stimulatory activity on some visceral muscles. Here, we have examined the AT in Rhodnius prolixus. Molecular analysis revealed a cDNA fragment of 973 bp encoding one mature amidated AT (Rhopr-AT) with transcript levels observed in the central nervous system (CNS) and pool of fat body, trachea and associated peripheral nerves. AT-like immunoreactive neurons were found throughout the CNS and AT-like immunoreactive processes were present on some peripheral tissues. Bioassays based upon changes in hindgut and dorsal vessel contractions failed to demonstrate any myotropic effects of Rhopr-AT on these tissues; however Rhopr-AT stimulated contractions of muscles surrounding the salivary glands and secretion of saliva, as judged by the reduction in content of the cherry red saliva from the salivary glands. Serotonin stimulated an increase in peristaltic contractions of the gland though no secretion was observed. Co-application of Rhopr-AT and serotonin resulted in a more rapid secretion than either chemical alone.

Conserved residues in RF-NH₂ receptor models identify predicted contact sites in ligand-receptor binding

Peptides in the RF-NH2 family are grouped together based on an amidated dipeptide C terminus and signal through G-protein coupled receptors (GPCRs) to influence diverse physiological functions. By determining the mechanisms underlying RF-NH2 signaling targets can be identified to modulate physiological activity; yet, how RF-NH2 peptides interact with GPCRs is relatively unexplored. We predicted conserved residues played a role in Drosophila melanogaster RF-NH2 ligand-receptor interactions. In this study D. melanogaster rhodopsin-like family A peptide GPCRs alignments identified eight conserved residues unique to RF-NH2 receptors. Three of these residues were in extra-cellular loops of modeled RF-NH2 receptors and four in transmembrane helices oriented into a ligand binding pocket to allow contact with a peptide. The eighth residue was unavailable for interaction; yet its conservation suggested it played another role. A novel hydrophobic region representative of RF-NH2 receptors was also discovered. The presence of rhodopsin-like family A GPCR structural motifs including a toggle switch indicated RF-NH2s signal classically; however, some features of the DMS receptors were distinct from other RF-NH2 GPCRs. Additionally, differences in RF-NH2 receptor structures which bind the same peptide explained ligand specificity. Our novel results predicted conserved residues as RF-NH2 ligand-receptor contact sites and identified unique and classic structural features. These discoveries will aid antagonist design to modulate RF-NH2 signaling.

Functional activity of allatotropin and allatostatin in the pupal stage of a holometablous insect, Tribolium castaneum (Coleoptera, Tenebrionidae)

Allatotropin (AT) and allatostatin (AS) neuropeptides are known to regulate the biosynthesis of juvenile hormones (JH) in insects. Furthermore, they possess myoregulatory and other activities in a wide range of insect species. The genome of Tribolium castaneum encodes two AS and one AT precursors. Here we cloned the cDNAs of the precursors, followed their expression patterns during the pupal stage, and established their putative roles in adult development and oviposition of the females using RNA interference (RNAi). Cloning of the cDNA and gene structure analyses of the Tc-AT gene confirmed that the gene is expressed in three mRNA isoforms. Real-time PCR data demonstrate that the Tc-AT isoforms and the AS genes, Tc-AS C and Tc-AS B, are expressed in discerning developmental and tissue-specific patterns. Single injections of dsRNAi (targeted against the Tc-AT, Tc-AS C, and Tc-AS B, respectively), into young pupae resulted in abnormal adult phenotypes, whereby about half of the animals (P1 phenotype) looked relatively normal, but the females laid low numbers of eggs. The other halves (P2) exhibited strong developmental defects with abnormal duration of the pupal stage, abnormal head and body sizes, short elytra, and incomplete sclerotization. Moreover, these females deposited no eggs and died within one week after emergence. Individual silencing of the Tc-AT mRNA isoforms showed that Tc-AT3 had the most disruptive influence on adult development and fecundity of the females. Our findings clearly indicate a significant role of AT and AS neuropeptides in the pupa. The distinct mechanisms of action, however, remain to be determined.

Adipokinetic hormones of the two extant apterygotan insect orders, Archaeognatha and Zygentoma

Two extant apterygotan insect orders, Archaeognatha and Zygentoma, are investigated with respect to the identity of neuropeptides belonging to the adipokinetic hormone (AKH) peptide family; this is the first report on AKH peptide structures in the so-called primitive insects and the first of any peptide in the Archaeognatha. In the lepismatid, Thermobia domestica, and the machilid, Petrobius maritimus, a single AKH peptide is identified and sequenced from each species; neither sequence is novel and has previously been shown in corpora cardiaca (CC) of cockroaches (Peram-CAH-I) and dragonflies (Anaim-AKH), respectively. These octapeptides differ from each other only in one position (Asn(7) in the lepismatid and Ser(7) in the machilid). The biological relevance of these peptides was investigated and we speculate that they are likely involved in the mobilisation of lipids in the apterygotes. Immunocytochemistry with an antibody directed against an AKH revealed a well-developed pair of CC in T. domestica and another lepismatid, the fishmoth Ctenolepisma longicaudata; a cluster of immunopositive cells are located retrocerebrally in tissue sections of P. maritimus which may be the CC.

Targeting the diuretic hormone receptor to control the cotton leafworm, Spodoptera littoralis

The cotton leafworm, Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae), is one of the most devastating pests of crops worldwide. Several types of treatments have been used against this pest, but many of them failed because of the rapid development of genetic resistance in the different insect populations. G protein coupled receptors have vital functions in most organisms, including insects; thus, they are appealing targets for species-specific pest control strategies. Among the insect G protein coupled receptors, the diuretic hormone receptors have several key roles in development and metabolism, but their importance in vivo and their potential role as targets of novel pest control strategies are largely unexplored. With the goal of using DHR genes as targets to control S. littoralis, we cloned a corticotropin-releasing factor-like binding receptor in this species and expressed the corresponding dsRNA in tobacco plants to knock down the receptor activity in vivo through RNA interference. We also expressed the receptor in mammalian cells to study its signaling pathways. The results indicate that this diuretic hormone receptor gene has vital roles in S. littoralis and represents an excellent molecular target to protect agriculturally-important plants from this pest.

Serotonin receptor B may lock the gate of PTTH release/synthesis in the Chinese silk moth, Antheraea pernyi; a diapause initiation/maintenance mechanism?

The release of prothoracicotropic hormone, PTTH, or its blockade is the major endocrine switch regulating the developmental channel either to metamorphosis or to pupal diapause in the Chinese silk moth, Antheraea pernyi. We have cloned cDNAs encoding two types of serotonin receptors (5HTRA and B). 5HTRA-, and 5HTRB-like immunohistochemical reactivities (-ir) were colocalized with PTTH-ir in two pairs of neurosecretory cells at the dorsolateral region of the protocerebrum (DL). Therefore, the causal involvement of these receptors was suspected in PTTH release/synthesis. The level of mRNA(5HTRB) responded to 10 cycles of long-day activation, falling to 40% of the original level before activation, while that of 5HTRA was not affected by long-day activation. Under LD 16:8 and 12:12, the injection of dsRNA(5HTRB) resulted in early diapause termination, whereas that of dsRNA(5HTRA) did not affect the rate of diapause termination. The injection of dsRNA(5HTRB) induced PTTH accumulation, indicating that 5HTRB binding suppresses PTTH synthesis also. This conclusion was supported pharmacologically; the injection of luzindole, a melatonin receptor antagonist, plus 5th inhibited photoperiodic activation under LD 16:8, while that of 5,7-DHT, induced emergence in a dose dependent fashion under LD 12:12. The results suggest that 5HTRB may lock the PTTH release/synthesis, maintaining diapause. This could also work as diapause induction mechanism.

Characterisation of a functional allatotropin receptor in the bumblebee, Bombus terrestris (Hymenoptera, Apidae)

Allatotropins (ATs) are multifunctional neuropeptides initially isolated from the tobacco hornworm, Manduca sexta, where they were found to stimulate juvenile hormone synthesis and release from the corpora allata. ATs have been found in a wide range of insects, but appear to be absent in Drosophila. The first AT receptor (ATR) was characterised in 2008 in the lepidopteran Bombyx mori. Since then ATRs have been characterised in Coleoptera and Diptera and in 2012, an AT precursor gene was identified in hymenopteran species. ATRs show large sequence and structural similarity to vertebrate orexin receptors (OXR). Also, AT in insects and orexin in vertebrates show some overlap in functions, including modulation of feeding behaviour and reproduction. The goal of this study was to identify a functional ATR in a hymenopteran species. We used ATRs (insect sequences) and OXRs (vertebrate sequences) to search the genome of the bumblebee, Bombus terrestris. Two receptors (XP_003402490 and XP_003394933) with resemblance to ATRs and OXRs were found. Phylogenetic analysis provided the first indication that XP_003402490 was more closely related to ATRs than XP_003394933. We investigated the transcript level distribution of both receptors and the AT precursor gene by means of quantitative real-time reverse transcriptase PCR. XP_003402490 displayed a tissue distribution comparable with ATRs in other species, with high transcript levels in the male accessory glands. After pharmacological characterisation, it appeared that XP_003402490 is indeed a functional ATR. Activation of the receptor causes an increase in intracellular calcium and cyclic AMP levels with an EC50 value in the low nanomolar to picomolar range. XP_003394933 remains an orphan receptor.