Nosema ceranae alters a highly conserved hormonal stress pathway in honeybees

Nosema ceranae, an emerging pathogen of the western honeybee (Apis mellifera), is implicated in recent pollinator losses and causes severe energetic stress. However, whether precocious foraging and accelerated behavioural maturation in infected bees are caused by the infection itself or via indirect energetic stress remains unknown. Using a combination of nutritional and infection treatments, we investigated how starvation and infection alters the regulation of adipokinetic hormone (AKH) and octopamine, two highly conserved physiological pathways that respond to energetic stress by mobilizing fat stores and increasing search activity for food. Although there was no response from AKH when bees were experimentally infected with N. ceranae or starved, supporting the notion that honeybees have lost this pathway, there were significant regulatory changes in the octopamine pathway. Significantly, we found no evidence of acute energetic stress being the only cause of symptoms associated with N. ceranae infection. Therefore, the parasite itself appears to alter regulatory components along a highly conserved physiological pathway in an infection-specific manner. This indicates that pathogen-induced behavioural alteration of chronically infected bees should not just be viewed as a coincidental short-term by-product of pathogenesis (acute energetic stress) and may be a result of a generalist manipulation strategy to obtain energy for reproduction.

Identification and functional characterization of a novel locust peptide belonging to the family of insect growth blocking peptides

Growth blocking peptides (GBPs) are recognized as insect cytokines that take part in multifaceted functions including immune system activation and growth retardation. The peptides induce hemocyte spreading in vitro, which is considered as the initial step in hemocyte activation against infection in many insect species. Therefore, in this study, we carried out a series of in vitro bioassay driven fractionations of Locusta migratoria hemolymph combined with mass spectrometry to identify locust hemocyte activation factors belonging to the family of insect GBPs. We identified the locust hemocyte spreading peptide (locust GBP) as a 28-mer peptide encoded at the C-terminus of a 64 amino acid long precursor polypeptide. As demonstrated by QRT-PCR, the gene encoding the locust GBP precursor (proGBP) was expressed in large quantities in diverse locust tissues including fat body, endocrine glands, central nervous system, reproductive tissues and flight muscles. In contrary, hemocytes, gut tissues and Malpighian tubules displayed little expression of the proGBP transcript. The bioactive peptide induces transient depletion of hemocytes in vivo and when injected in last instar nymphs it extends the larval growth phase and postpones adult molting. In addition, we identified a functional homologous hemocyte spreading peptide in Schistocerca gregaria.

Multiple factors contribute to anautogenous reproduction by the mosquito Aedes aegypti

Aedes aegypti is an anautogenous mosquito that must blood feed on a vertebrate host to produce and lay a clutch of eggs. The rockpool mosquito, Georgecraigius atropalpus, is related to A. aegypti but is a facultatively autogenous species that produces its first clutch of eggs shortly after emerging without blood feeding. Consumption of a blood meal by A. aegypti triggers the release of ovary ecdysteroidogenic hormone (OEH) and insulin-like peptide 3 (ILP3) from the brain, which stimulate egg formation. OEH and ILP3 also stimulate egg formation in G. atropalpus but are released at eclosion independently of blood feeding. These results collectively suggest that blood meal dependent release of OEH and ILP3 is one factor that prevents A. aegypti from reproducing autogenously. Here, we examined two other factors that potentially inhibit autogeny in A. aegypti: teneral nutrient reserves and the ability of OEH and ILP3 to stimulate egg formation in the absence of blood feeding. Measures of nutrient reserves showed that newly emerged A. aegypti females had similar wet weights but significantly lower protein and glycogen reserves than G. atropalpus females when larvae were reared under identical conditions. OEH stimulated non-blood fed A. aegypti females to produce ecdysteroid hormone and package yolk into oocytes more strongly than ILP3. OEH also reduced host seeking and blood feeding behavior, yet females produced few mature eggs. Overall, our results indicate that multiple factors prevent A. aegypti from reproducing autogenously.

Characterization and expression analysis of adipokinetic hormone and its receptor in eusocial aphid Pseudoregma bambucicola

Aphids display an extraordinary phenotypic plasticity ranging from widespread reproductive and wing polyphenisms to the occurrence of sterile or subfertile soldier morphs restricted to eusocial species of the subfamilies Eriosomatinae and Hormaphidinae. Individual morphs are specialized by their behavior, anatomy, and physiology to perform different roles in aphid societies at different stages of the life cycle. The capacity of the insects to cope with environmental stressors is under the control of a group of neuropeptides of the adipokinetic hormone/red pigment-concentrating hormone family (AKH/RPCH) that bind to a specific receptor (AKHR). Here, we describe the molecular characteristics of AKH and AKHR in the eusocial aphid Pseudoregma bambucicola. The sequence of the bioactive AKH decapeptide and the intron position in P. bambucicola AKH preprohormone were found to be identical to those in a phylogenetically distant aphid Dreyfusia spp. (Adelgidae). We detected four transcript variants of AKHR that are translated into three protein isoforms. Further, we analyzed AKH/AKHR expression in different tissues and insects of different castes. In wingless females, a remarkable amount of AKH mRNA was only expressed in the heads. In contrast, AKHR transcript levels increased in the order gut<ovary<fat body<head. In aphids from both the primary and secondary hosts (Styrax suberifolia and Bambusa spp., respectively), the highest AKH expression levels were recorded in winged, migratory females and soldiers, whereas reduced levels were found in wingless, sedentary females that are functionally oriented to reproduction. The highest AKHR expression was found in soldiers in gall-dwelling populations, whereas in bamboo colonies the highest transcript level was detected in winged females. We propose a possible explanation for the correlation between AKH and AKHR transcript levels and task partitioning among individual forms in P. bambucicola colonies.

Hormonal Regulation of Response to Oxidative Stress in Insects-An Update

Insects, like other organisms, must deal with a wide variety of potentially challenging environmental factors during the course of their life. An important example of such a challenge is the phenomenon of oxidative stress. This review summarizes the current knowledge on the role of adipokinetic hormones (AKH) as principal stress responsive hormones in insects involved in activation of anti-oxidative stress response pathways. Emphasis is placed on an analysis of oxidative stress experimentally induced by various stressors and monitored by suitable biomarkers, and on detailed characterization of AKH’s role in the anti-stress reactions. These reactions are characterized by a significant increase of AKH levels in the insect body, and by effective reversal of the markers—disturbed by the stressors—after co-application of the stressor with AKH. A plausible mechanism of AKH action in the anti-oxidative stress response is discussed as well: this probably involves simultaneous employment of both protein kinase C and cyclic adenosine 3′,5′-monophosphate pathways in the presence of extra and intra-cellular Ca²⁺ stores, with the possible involvement of the FoxO transcription factors. The role of other insect hormones in the anti-oxidative defense reactions is also discussed.

Diapause hormone in the Helicoverpa/Heliothis complex: A review of gene expression, peptide structure and activity, analog and antagonist development, and the receptor

This review summarizes recent studies focusing on diapause hormone (DH) in the Helicoverpa/Heliothis complex of agricultural pests. Moths in this complex overwinter in pupal diapause, a form of developmental arrest used to circumvent unfavorable seasons. DH was originally reported in the silkmoth Bombyx mori, a species that relies on DH to induce an embryonic diapause. But, in the case of Helicoverpa/Heliothis, levels of dh transcripts and DH peptides are more abundant in nondiapausing pupae than in diapausing individuals, and DH effectively terminates diapause within a specific temperature range. A structure activity relationship study indicated that the active core of DH is the C-terminal hepta-peptide, LWFGPRLa. We designed and synthesized a first generation of DH agonists and identified two agonists (PK-2Abf and PK-Etz) that were nearly 50- and 13-fold more potent than the native hormone. These studies revealed two structural characteristics of DH and its agonists that are essential for interaction with the receptor: a trans-Pro configuration to form a type I β-turn and a hydrophobic moiety involved in ligand binding. Modification of DH at the active core yielded a potent DH antagonist (DH-Jo, acetyl-GLWA[Jo]RLa) as well as an agonist (DH-2Abf-K). Three compounds (Decyl-1963, Dodecyl-1967, Heptyl-1965) were identified as agents capable of penetrating the cuticle of young pupae and thereby preventing the entry into diapause. DH receptor cDNA was cloned and an effective in vitro high throughput screen system was established for future use. This work sets the stage for further development of DH analogs and antagonists that have the potential to disrupt insect diapause as a tool for pest management.

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

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

Allatotropin inhibits juvenile hormone biosynthesis by the corpora allata of adult Bombyx mori

Juvenile hormone (JH) synthesis by the corpora allata (CA) does not occur during the pupal stage in both male and female Bombyx mori but begins shortly before adult ecdysis and thereafter only in females. JH biosynthesis in female adults was prevented by allatotropin (AT) through the corpora cardiaca (CC) and the tightly attached oesophagus before adult ecdysis, but after ecdysis, removal of the CC had little effect and only the oesophagus was necessary for AT to prevent JH synthesis. AT could not prevent JH synthesis by the CA alone in either stage. Short neuropeptide F (sNPF) acted directly on the CA, preventing JH biosynthesis without preventing the JH biosynthetic enzymes before adult ecdysis, but had little effect after ecdysis, indicating that the action of AT was not via sNPF. The inhibition of JH synthesis by AT was indirect. Both AT and a factor(s) from the AT-stimulated oesophagus through the CC were necessary for the inhibitory action, which was due to the prevention of some of the JH biosynthetic enzymes. These results clearly show that AT prevents JH synthesis in adult CA in B. mori, although AT stimulates JH biosynthesis by the CA in several insect species.

Rescheduling Behavioral Subunits of a Fixed Action Pattern by Genetic Manipulation of Peptidergic Signaling

The ecdysis behavioral sequence in insects is a classic fixed action pattern (FAP) initiated by hormonal signaling. Ecdysis triggering hormones (ETHs) release the FAP through direct actions on the CNS. Here we present evidence implicating two groups of central ETH receptor (ETHR) neurons in scheduling the first two steps of the FAP: kinin (aka drosokinin, leucokinin) neurons regulate pre-ecdysis behavior and CAMB neurons (CCAP, AstCC, MIP, and Bursicon) initiate the switch to ecdysis behavior. Ablation of kinin neurons or altering levels of ETH receptor (ETHR) expression in these neurons modifies timing and intensity of pre-ecdysis behavior. Cell ablation or ETHR knockdown in CAMB neurons delays the switch to ecdysis, whereas overexpression of ETHR or expression of pertussis toxin in these neurons accelerates timing of the switch. Calcium dynamics in kinin neurons are temporally aligned with pre-ecdysis behavior, whereas activity of CAMB neurons coincides with the switch from pre-ecdysis to ecdysis behavior. Activation of CCAP or CAMB neurons through temperature-sensitive TRPM8 gating is sufficient to trigger ecdysis behavior. Our findings demonstrate that kinin and CAMB neurons are direct targets of ETH and play critical roles in scheduling successive behavioral steps in the ecdysis FAP. Moreover, temporal organization of the FAP is likely a function of ETH receptor density in target neurons.

Food odors trigger an endocrine response that affects food ingestion and metabolism

Food odors stimulate appetite and innate food-seeking behavior in hungry animals. The smell of food also induces salivation and release of gastric acid and insulin. Conversely, sustained odor exposure may induce satiation. We demonstrate novel effects of food odors on food ingestion, metabolism and endocrine signaling in Drosophila melanogaster. Acute exposure to attractive vinegar odor triggers a rapid and transient increase in circulating glucose, and a rapid upregulation of genes encoding the glucagon-like hormone adipokinetic hormone (AKH), four insulin-like peptides (DILPs) and some target genes in peripheral tissues. Sustained exposure to food odors, however, decreases food intake. Hunger-induced strengthening of synaptic signaling from olfactory sensory neurons (OSNs) to brain neurons increases food-seeking behavior, and conversely fed flies display reduced food odor sensitivity and feeding. We show that increasing the strength of OSN signaling chronically by genetic manipulation of local peptide neuromodulation reduces feeding, elevates carbohydrates and diminishes lipids. Furthermore, constitutively strengthened odor sensitivity altered gene transcripts for AKH, DILPs and some of their targets. Thus, we show that food odor can induce a transient anticipatory endocrine response, and that boosted sensitivity to this odor affects food intake, as well as metabolism and hormonal signaling.

The activity of the nonsulfated sulfakinin Zopat-SK-1 in the neck-ligated larvae of the beetle Zophobas atratus

Insect sulfakinins (SKs) are multifunctional neuropeptides structurally and functionally homologous to the mammalian gastrin/cholecystokinin (CCK). It has been proposed that SKs play a role in modulating energy management in insects by interacting with adipokinetic hormone (AKH), the principle hormone controlling insect intermediary metabolism. To exclude head factors (including AKH) that influence the activity of the nonsulfated sulfakinin Zopat-SK-1 in the larvae of the beetle Zophobas atratus, ligature and in vitro bioassays were used. Our study showed that in the neck-ligated larvae, Zopat-SK-1 evoked a much more pronounced glycogenolytic effect in fat body tissue and a significantly higher hypertrahelosemic effect in hemolymph than in larvae without ligation. We found that the concentration of the sugar trehalose increased under hormonal treatment but no changes in glucose levels were observed. Under in vitro conditions, the maximal glycogenolytic effect of Zopat-SK-1 in fat body was observed at 10 pmol of hormone. Ligature and in vitro bioassays indicated that Zopat-SK-1 activity in the Z. atratus larvae is modulated by head signals and/or factors from the gastrointestinal tract. Our data indicate the existence of a brain-gastrointestinal axis that has a role in controlling of energy (carbohydrate) metabolism in the insect body. Moreover, these results, together with immunological evidence of a cholecystokinin-like (sulfakinin) receptor in the Z. atratus fat body, help us to better understand the SK signaling pathways and its physiological role in insect biology.

The Neuropeptide Allatostatin A Regulates Metabolism and Feeding Decisions in Drosophila

Coordinating metabolism and feeding is important to avoid obesity and metabolic diseases, yet the underlying mechanisms, balancing nutrient intake and metabolic expenditure, are poorly understood. Several mechanisms controlling these processes are conserved in Drosophila, where homeostasis and energy mobilization are regulated by the glucagon-related adipokinetic hormone (AKH) and the Drosophila insulin-like peptides (DILPs). Here, we provide evidence that the Drosophila neuropeptide Allatostatin A (AstA) regulates AKH and DILP signaling. The AstA receptor gene, Dar-2, is expressed in both the insulin and AKH producing cells. Silencing of Dar-2 in these cells results in changes in gene expression and physiology associated with reduced DILP and AKH signaling and animals lacking AstA accumulate high lipid levels. This suggests that AstA is regulating the balance between DILP and AKH, believed to be important for the maintenance of nutrient homeostasis in response to changing ratios of dietary sugar and protein. Furthermore, AstA and Dar-2 are regulated differentially by dietary carbohydrates and protein and AstA-neuronal activity modulates feeding choices between these types of nutrients. Our results suggest that AstA is involved in assigning value to these nutrients to coordinate metabolic and feeding decisions, responses that are important to balance food intake according to metabolic needs.

Targeted mutagenesis and functional analysis of adipokinetic hormone-encoding gene in Drosophila

Adipokinetic hormones (Akhs) are small peptides (8-10 amino acid [aa] residues long) found in insects that regulate metabolic responses to stress by stimulating catabolic reactions and mobilizing energy stores. We employed Transcription activator-like effector nuclease (TALEN) mutagenesis and isolated an Akh(1) mutant carrying a small deletion in the gene that resulted in a truncated peptide; the second aa (Leu) was missing from the functional octapeptide. This null Dmel/Akh mutant is suitable to study Akh function without any effect on the C-terminal associated peptide encoded by the same gene. The mutant flies were fully viable and compared to the control flies, had significantly low levels of hemolymph saccharides including trehalose and were resistant to starvation. These characteristics are similar to those obtained from the flies carrying targeted ablation of Akh-expressing neurons (reported earlier). We also found that the Akh(1) mutants are slightly heavy and had a slow metabolic rate. Furthermore, we showed that the ectopic expression of Dmel∖Akh reverses the Akh(1) phenotype and restores the wild-type characteristics. Our results confirmed that Akh is an important regulator of metabolic homeostasis in Drosophila.

Knockdown of adipokinetic hormone synthesis increases susceptibility to oxidative stress in Drosophila--a role for dFoxO?

Insect adipokinetic hormones (AKHs) are pleiotropic hormones known to play a protective role in response to oxidative stress (OS). However, the precise signaling pathways are unclear. We present evidence that AKH may primarily employ the Forkhead box class O transcription factor (FoxO) to exert this effect. The impact of knocking down AKH synthesis or its over-expression in its response to OS was studied in Drosophila melanogaster. AKH knockdown (AKH-RNAi) as well as AKH overexpression (AKH-oex) was achieved using the Gal-4/UAS system and controls were w(1118) (+/+), AKH-Gal4/+, UAS-AKH/+ and UAS-AKH-RNAi/+. Exposure to 80 μM hydrogen peroxide (HP) revealed that AKH-RNAi flies showed significantly higher mortality than AKH-oex or the respective control lines. This susceptibility was evidenced by significantly enhanced levels of protein carbonyls - a biomarker of OS, in AKH-RNAi flies compared to controls and AKH-oex flies. Interestingly, AKH-oex flies had the least amount of protein carbonyls. AKH-RNAi flies had significantly less dFoxO transcript and translated protein compared to control and AKH-oex flies in un-challenged condition as well as when challenged with HP. Sestrin - a major antioxidant defense protein and one of the targets of dFoxO - was also significantly down-regulated (both at mRNA and protein level) in AKH-RNAi flies (both unchallenged and challenged with HP) compared to control flies and flies with over-expressed AKH. These findings imply that dFoxO may act downstream of AKH as a transcription factor to mediate response to OS in D. melanogaster.

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.