Biochemistry of proteins that bind and metabolize juvenile hormones

Suppression of Gene Juvenile Hormone Diol Kinase Delays Pupation in Heortia vitessoides Moore

Juvenile hormone diol kinase (JHDK) is a critical enzyme involved in juvenile hormone degradation in insects. In this study, HvJHDK in the Heortia vitessoides Moore (Lepidoptera: Crambidae) transcriptional library was cloned. Stage-specific expression patterns of HvJHDK, HvJHEH, and HvJHE as well as juvenile hormone titers were determined. The three tested enzymes participated in juvenile hormone degradation. Moreover, juvenile hormone titers peaked after larval–larval molts, consistent with a role for juvenile hormone in inhibition of metamorphosis. HvJHDK was subsequently suppressed using RNA interference (RNAi) to reveal its functions. Different concentrations of dsJHDK elicited the optimal interference efficiency at different life stages of H. vitessoides. Suppression of HvJHDK decreased HvJHDK content and increased the juvenile hormone titer, thereby resulting in reduced triglyceride content, sharply declined survival rate, clearly lethal phenotypes, and extended larval growth. Moreover, suppression of HvJHDK upregulated HvJHEH and HvJHE expression levels, suggesting that there is feedback regulation in the juvenile hormone metabolic pathway. Taken together, our findings provide molecular references for the selection of novel insecticidal targets.

Daywake, an Anti-siesta Gene Linked to a Splicing-Based Thermostat from an Adjoining Clock Gene

Sleep is fundamental to animal survival but is a vulnerable state that also limits how much time can be devoted to critical wake-dependent activities [1]. Although many animals are day-active and sleep at night, they exhibit a midday nap, or "siesta," that can vary in intensity and is usually more prominent on warm days. In humans, the balance between maintaining the wake state or sleeping during the day has important health implications [2], but the mechanisms underlying this dynamic regulation are poorly understood. Using the well-established Drosophila melanogaster animal model to study sleep [3], we identify a new wake-sleep regulator that we term daywake (dyw). dyw encodes a juvenile hormone-binding protein [4] that functions in neurons as a day-specific anti-siesta gene, with little effect on sleep levels during the nighttime or in the absence of light. Remarkably, dyw expression is stimulated in trans via cold-enhanced splicing of the dmpi8 intron [5] from the reverse-oriented but slightly overlapping period (per) clock gene [6]. The functionally integrated dmpi8-dyw genetic unit operates as a "behavioral temperate acclimator" by increasingly counterbalancing siesta-promoting pathways as daily temperatures become cooler and carry reduced risks from daytime heat exposure. While daily patterns of when animals are awake and when they sleep are largely scheduled by the circadian timing system, dyw implicates a less recognized class of modulatory wake-sleep regulators that primarily function to enhance flexibility in wake-sleep preference, a behavioral plasticity that is commonly observed in animals during the midday, raising the possibility of shared mechanisms.

Mode of Action of Farnesol, the "Noble Unknown" in Particular in Ca2+ Homeostasis, and Its Juvenile Hormone-Esters in Evolutionary Retrospect

Farnesol, the sesquiterpenoid precursor of insect juvenile hormones (JH) that itself has JH activity, existed already long before animals and their hormones came into being. Although it is omnipresent in all eukaryotes, this molecule remains a "noble unknown" in cell physiology. It is neither documented as a hormone nor as another type of signaling molecule. To date, its function as an intermediate in the synthesis of squalene-cholesterol-steroids in chordates/vertebrates, and of the insect/arthropod JHs, esters of farnesol, in the mevalonate biosynthetic pathway is assumed to be the only one. This assumption neglects that already two decades ago, farnesol has been shown to be a potent endogenous inhibitor of N-type voltage-gated Ca²⁺ channels in some mammalian cell types. The tandem mevalonate pathway and Ca²⁺ channels originated early in eukaryotic evolution, and has since been well conserved, "promoting" it as a ubiquitous player in Ca²⁺ homeostasis in all eukaryotes. This paper accentuates how this drastic change in thinking gained momentum after the discovery by Paroulek and Sláma that the huge amounts of JH I in male accessory glands of the Cecropia moth, are actually synthesized in these glands themselves and not in the corpora allata, the hitherto assumed unique synthesis site of such compounds. In addition, MAG-JHs have no hormonal- but an exocrine function. Here we hypothesize that MAG-JHs may function in protecting the spermatozoa against toxic Ca²⁺ concentrations, and in enabling their flagellum to undulate. They may do so by acting through membrane receptors. Our novel paradigm assigns to farnesol/JHs a function of flexible hydrophobic molecular valves for restricting untimely Ca²⁺-passage through some types of canonical Ca²⁺channels, using covalently bound farnesyl- or geranyl-geranyl group attachment as well as GPCRs-G proteins all containing a prenyl group. The high rotatable bond count, and their horseshoe-shape are instrumental to their valve function. In our paradigm, Met/Tai and Gce, to date generally thought to be the (only) functional (nuclear) receptors for JHs, are classified as probable Ca²⁺-sensitive transcription factors. Some theoretical and practical considerations for possible applications in a medical context will be discussed.

Expression and characterization of an epoxide hydrolase from Anopheles gambiae with high activity on epoxy fatty acids

In insects, epoxide hydrolases (EHs) play critical roles in the metabolism of xenobiotic epoxides from the food resources and in the regulation of endogenous chemical mediators, such as juvenile hormones. Using the baculovirus expression system, we expressed and characterized an epoxide hydrolase from Anopheles gambiae (AgEH) that is distinct in evolutionary history from insect juvenile hormone epoxide hydrolases (JHEHs). We partially purified the enzyme by ion exchange chromatography and isoelectric focusing. The experimentally determined molecular weight and pI were estimated to be 35 kD and 6.3 respectively, different than the theoretical ones. The AgEH had the greatest activity on long chain epoxy fatty acids such as 14,15-epoxyeicosatrienoic acids (14,15-EET) and 9,10-epoxy-12Z-octadecenoic acids (9,10-EpOME or leukotoxin) among the substrates evaluated. Juvenile hormone III, a terpenoid insect growth regulator, was the next best substrate tested. The AgEH showed kinetics comparable to the mammalian soluble epoxide hydrolases, and the activity could be inhibited by AUDA [12-(3-adamantan-1-yl-ureido) dodecanoic acid], a urea-based inhibitor designed to inhibit the mammalian soluble epoxide hydrolases. The rabbit serum generated against the soluble epoxide hydrolase of Mus musculus can both cross-react with natural and denatured forms of the AgEH, suggesting immunologically they are similar. The study suggests there are mammalian sEH homologs in insects, and epoxy fatty acids may be important chemical mediators in insects.

Four-way regulation of mosquito yolk protein precursor genes by juvenile hormone-, ecdysone-, nutrient-, and insulin-like peptide signaling pathways

Anautogenous mosquito females require a meal of vertebrate blood in order to initiate the production of yolk protein precursors by the fat body. Yolk protein precursor gene expression is tightly repressed in a state-of-arrest before blood meal-related signals activate it and expression levels rise rapidly. The best understood example of yolk protein precursor gene regulation is the vitellogenin-A gene (vg) of the yellow fever mosquito Aedes aegypti. Vg-A is regulated by (1) juvenile hormone signaling, (2) the ecdysone-signaling cascade, (3) the nutrient sensitive target-of-rapamycin signaling pathway, and (4) the insulin-like peptide (ILP) signaling pathway. A plethora of new studies have refined our understanding of the regulation of yolk protein precursor genes since the last review on this topic in 2005 (Attardo et al., 2005). This review summarizes the role of these four signaling pathways in the regulation of vg-A and focuses upon new findings regarding the interplay between them on an organismal level.

Precise RNAi-mediated silencing of metabolically active proteins in the defence secretions of juvenile leaf beetles

Allomones are widely used by insects to impede predation. Frequently these chemical stimuli are released from specialized glands. The larvae of Chrysomelina leaf beetles produce allomones in gland reservoirs into which the required precursors and also the enzymes are secreted from attached gland cells. Hence, the reservoirs can be considered as closed bio-reactors for producing defensive secretions. We used RNA interference (RNAi) to analyse in vivo functions of proteins in biosynthetic pathways occurring in insect secretions. After a salicyl alcohol oxidase was silenced in juveniles of the poplar leaf beetles, Chrysomela populi, the precursor salicyl alcohol increased to 98 per cent, while salicyl aldehyde was reduced to 2 per cent within 5 days. By analogy, we have silenced a novel protein annotated as a member of the juvenile hormone-binding protein superfamily in the juvenile defensive glands of the related mustard leaf beetle, Phaedon cochleariae. The protein is associated with the cyclization of 8-oxogeranial to iridoids (methylcyclopentanoid monoterpenes) in the larval exudates made clear by the accumulation of the acylic precursor 5 days after RNAi triggering. A similar cyclization reaction produces the secologanin part of indole alkaloids in plants.

The juvenile hormone (JH) epoxide hydrolase gene in the honey bee (Apis mellifera) genome encodes a protein which has negligible participation in JH degradation

Epoxide hydrolases are multifunctional enzymes that are best known in insects for their role in juvenile hormone (JH) degradation. Enzymes involved in JH catabolism can play major roles during metamorphosis and reproduction, such as the JH epoxide hydrolase (JHEH), which degrades JH through hydration of the epoxide moiety to form JH diol, and JH esterase (JHE), which hydrolyzes the methyl ester to produce JH acid. In the honey bee, JH has been co-opted for additional functions, mainly in caste differentiation and in age-related behavioral development of workers, where the activity of both enzymes could be important for JH titer regulation. Similarity searches for jheh candidate genes in the honey bee genome revealed a single Amjheh gene. Sequence analysis, quantification of Amjheh transcript levels and Western blot assays using an AmJHEH-specific antibody generated during this study revealed that the AmJHEH found in the fat body shares features with the microsomal JHEHs from several insect species. Using a partition assay we demonstrated that AmJHEH has a negligible role in JH degradation, which, in the honey bee, is thus performed primarily by JHE. High AmJHEH levels in larvae and adults were related to the ingestion of high loads of lipids, suggesting that AmJHEH has a role in dietary lipid catabolism.

A genome-wide survey for host response of silkworm, Bombyx mori during pathogen Bacillus bombyseptieus infection

Host-pathogen interactions are complex relationships, and a central challenge is to reveal the interactions between pathogens and their hosts. Bacillus bombysepticus (Bb) which can produces spores and parasporal crystals was firstly separated from the corpses of the infected silkworms (Bombyx mori). Bb naturally infects the silkworm can cause an acute fuliginosa septicaemia and kill the silkworm larvae generally within one day in the hot and humid season. Bb pathogen of the silkworm can be used for investigating the host responses after the infection. Gene expression profiling during four time-points of silkworm whole larvae after Bb infection was performed to gain insight into the mechanism of Bb-associated host whole body effect. Genome-wide survey of the host genes demonstrated many genes and pathways modulated after the infection. GO analysis of the induced genes indicated that their functions could be divided into 14 categories. KEGG pathway analysis identified that six types of basal metabolic pathway were regulated, including genetic information processing and transcription, carbohydrate metabolism, amino acid and nitrogen metabolism, nucleotide metabolism, metabolism of cofactors and vitamins, and xenobiotic biodegradation and metabolism. Similar to Bacillus thuringiensis (Bt), Bb can also induce a silkworm poisoning-related response. In this process, genes encoding midgut peritrophic membrane proteins, aminopeptidase N receptors and sodium/calcium exchange protein showed modulation. For the first time, we found that Bb induced a lot of genes involved in juvenile hormone synthesis and metabolism pathway upregulated. Bb also triggered the host immune responses, including cellular immune response and serine protease cascade melanization response. Real time PCR analysis showed that Bb can induce the silkworm systemic immune response, mainly by the Toll pathway. Anti-microorganism peptides (AMPs), including of Attacin, Lebocin, Enbocin, Gloverin and Moricin families, were upregulated at 24 hours post the infection.

Gerry Brooks and epoxide hydrolases: four decades to a pharmaceutical

The pioneering work of Gerry Brooks on cyclodiene insecticides led to the discovery of a class of enzymes known as epoxide hydrolases. The results from four decades of work confirm Brooks' first observations that the microsomal epoxide hydrolase is important in foreign compound metabolism. Brooks and associates went on to be the first to carry out a systematic study of the inhibition of this enzyme. A second role for this enzyme family was in the degradation of insect juvenile hormone (JH). JH epoxide hydrolases have now been cloned and expressed from several species, and there is interest in developing inhibitors for them. Interestingly, the distantly related mammalian soluble epoxide hydrolase has emerged as a promising pharmacological target for treating hypertension, inflammatory disease and pain. Tight-binding transition-state inhibitors were developed with good ADME (absorption, distribution, metabolism and excretion). These compounds stabilize endogenous epoxides of fatty acids, including arachidonic acid, which have profound therapeutic effects. Now EHs from microorganisms and plants are used in green chemistry. From his seminal work, Dr Brooks opened the field of epoxide hydrolase research in many directions including xenobiotic metabolism, insect physiology and human health, as well as asymmetric organic synthesis.

Genes encoding putative Takeout/juvenile hormone binding proteins in the honeybee (Apis mellifera) and modulation by age and juvenile hormone of the takeout-like gene GB19811

We identified and characterized eight genes encoding putative Takeout/juvenile hormone binding proteins (To/JHBP) in the honeybee genome. Phylogenetic analyses revealed nine distinct lineages within this gene family, including those containing Takeout (To) and JHBP for which there are no honeybee homologs. Their diversity and ubiquitous expression suggest that To/JHBP proteins are involved in diverse and important processes in insects. We further characterized the expression of one of these genes, GB19811 that is ubiquitously expressed. GB19811 transcript levels in the abdomen increased, and decreased in the head with worker age. There was no influence of colony environment or brood care behavior on GB19811 expression in young bees. Young bees treated with juvenile hormone (JH) showed a decrease in head GB19811 mRNA levels. This finding is consistent with the premise that JH, for which titers typically increase with age, is involved in age-related modulation of GB19811 expression. In contrast to Drosophila Takeout, the expression of GB19811 did not vary with diurnal or circadian rhythms. Taken together, these findings suggest that GB19811 is not an ortholog of Takeout, and is involved in JH-mediated regulation of adult honeybee worker development.

Investigation of hormone activity in butterfly imaginal wing discs by protein expression pattern changes

In a proteomic approach using 2-DE, the changes in protein expression patterns in wing imaginal discs induced by hormone treatment have been studied. Here we show the response of butterfly imaginal wing disc tissue taken from late fifth instar larvae of the African-Mocker swallowtail Papilio dardanus (Lepidoptera) to the insect hormones 20-hydroxyecdysone (20-HE) and juvenile hormone (JH). The tissues were cultured in the presence of one hormone or a combination of both and their protein expression was compared to the pattern obtained from untreated wing discs. All the treatments resulted in changes in the expression pattern distinct from the uninduced control, indicating a distinct protein regulation induced by the hormones. The treatment with both of the hormones, which are known to have antagonistic physiological effects, did show a unique pattern, presumably the result, in part, of synergistic effects on protein expression mediated by the combined effects of both the hormones. The extent of the interaction between JH and 20-HE indicates a complex molecular regulation, far beyond a simple antagonistic effect.

A perspective for understanding the modes of juvenile hormone action as a lipid signaling system

The juvenile hormones of insects regulate an unusually large diversity of processes during postembryonic development and adult reproduction. It is a long-standing puzzle in insect developmental biology and physiology how one hormone can have such diverse effects. The search for molecular mechanisms of juvenile hormone action has been guided by classical models for hormone-receptor interaction. Yet, despite substantial effort, the search for a juvenile hormone receptor has been frustrating and has yielded limited results. We note here that a number of lipid-soluble signaling molecules in vertebrates, invertebrates and plants show curious similarities to the properties of juvenile hormones of insects. Until now, these signaling molecules have been thought of as uniquely evolved mechanisms that perform specialized regulatory functions in the taxon where they were discovered. We show that this array of lipid signaling molecules share interesting properties and suggest that they constitute a large set of signal control and transduction mechanisms that include, but range far beyond, the classical steroid hormone signaling mechanism. Juvenile hormone is the insect representative of this widespread and diverse system of lipid signaling molecules that regulate protein activity in a variety of ways. We propose a synthetic perspective for understanding juvenile hormone action in light of other lipid signaling systems and suggest that lipid activation of proteins has evolved to modulate existing signal activation and transduction mechanisms in animals and plants. Since small lipids can be inserted into many different pathways, lipid-activated proteins have evolved to play a great diversity of roles in physiology and development.

Insect juvenile hormone: from "status quo" to high society

Juvenile hormone (JH) exerts pleiotropic functions during insect life cycles. The regulation of JH biosynthesis by neuropeptides and biogenic amines, as well as the transport of JH by specific binding proteins is now well understood. In contrast, comprehending its mode of action on target organs is still hampered by the difficulties in isolating specific receptors. In concert with ecdysteroids, JH orchestrates molting and metamorphosis, and its modulatory function in molting processes has gained it the attribute "status quo" hormone. Whereas the metamorphic role of JH appears to have been widely conserved, its role in reproduction has been subject to many modifications. In many species, JH stimulates vitellogenin synthesis and uptake. In mosquitoes, however, this function has been transferred to ecdysteroids, and JH primes the ecdysteroid response of developing follicles. As reproduction includes a variety of specific behaviors, including migration and diapause, JH has come to function as a master regulator in insect reproduction. The peak of pleiotropy was definitely reached in insects exhibiting facultative polymorphisms. In wing-dimorphic crickets, differential activation of JH esterase determines wing length. The evolution of sociality in Isoptera and Hymenoptera has also extensively relied on JH. In primitively social wasps and bumble bees, JH integrates dominance position with reproductive status. In highly social insects, such as the honey bee, JH has lost its gonadotropic role and now regulates division of labor in the worker caste. Its metamorphic role has been extensively explored in the morphological differentiation of queens and workers, and in the generation of worker polymorphism, such as observed in ants.