Farnesoid secretions of dipteran ring glands: what we do know and what we can know

Simultaneous Detection and Distribution of Five Juvenile Hormones in 58 Insect Species and the Absolute Configuration in 32 Insect Species

Juvenile hormone (JH) plays an important role in regulating various insect physiological processes. Herein, a novel method (chiral and achiral) for the simultaneous detection of five JHs was established by processing a whole insect without complicated hemolymph extraction. The proposed method was used to determine the distribution of JHs in 58 insect species and the absolute configuration of JHs in 32 species. The results showed that JHSB₃ was uniquely synthesized in Hemiptera, JHB₃ was unique to Diptera, and JH I and JH II were unique to Lepidoptera. JH III was present in most insect species surveyed, with social insects having generally higher JH III titers. Interestingly, JHSB₃ and JHB₃, both double epoxidation JHs, were found in insects with sucking mouthparts. The absolute conformation of JH III and the 10C of the detected JHs were all R stereoisomers.

Juvenile hormone signaling - a mini review

Since it was first postulated by Wigglesworth in 1934, juvenile hormone (JH) is considered a status quo hormone in insects because it prevents metamorphosis that is initiated by the molting hormone 20-hydroxyecdysone (20E). During the last decade, significant advances have been made regarding JH signaling. First, the bHLH-PAS transcription factor Met/Gce was identified as the JH intracellular receptor. In the presence of JH, with the assistance of Hsp83, and through physical association with a bHLH-PAS transcriptional co-activator, Met/Gce enters the nucleus and binds to E-box-like motifs in promoter regions of JH primary-response genes for inducing gene expression. Second, the zinc finger transcription factor Kr-h1 was identified as the anti-metamorphic factor which transduces JH signaling. Via Kr-h1 binding sites, Kr-h1 represses expression of 20E primary-response genes (i.e. Br, E93 and E75) to prevent 20E-induced metamorphosis. Third, through the intracellular signaling, JH promotes different aspects of female reproduction. Nevertheless, this action varies greatly from species to species. Last, a hypothetical JH membrane receptor has been predicted to be either a GPCR or a tyrosine kinase receptor. In future, it will be a great challenge to understand how the JH intracellular receptor Met/Gce and the yet unidentified JH membrane receptor coordinate to regulate metamorphosis and reproduction in insects.

Juvenile hormone-activated phospholipase C pathway enhances transcriptional activation by the methoprene-tolerant protein

Juvenile hormone (JH) is a key regulator of a wide diversity of developmental and physiological events in insects. Although the intracellular JH receptor methoprene-tolerant protein (MET) functions in the nucleus as a transcriptional activator for specific JH-regulated genes, some JH responses are mediated by signaling pathways that are initiated by proteins associated with plasma membrane. It is unknown whether the JH-regulated gene expression depends on the membrane-mediated signal transduction. In Aedes aegypti mosquitoes, we found that JH activated the phospholipase C (PLC) pathway and quickly increased the levels of inositol 1,4,5-trisphosphate, diacylglycerol, and intracellular calcium, leading to activation and autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII). When abdomens from newly emerged mosquitoes were cultured in vitro, the JH-activated gene expression was repressed substantially if specific inhibitors of PLC or CaMKII were added to the medium together with JH. In newly emerged female mosquitoes, RNAi-mediated depletion of PLC or CaMKII considerably reduced the expression of JH-responsive genes, including the Krüppel homolog 1 gene (AaKr-h1) and the early trypsin gene (AaET). JH-induced loading of MET to the promoters of AaKr-h1 and AaET was weakened drastically when either PLC or CaMKII was inactivated in the cultured tissues. Therefore, the results suggest that the membrane-initiated signaling pathway modifies the DNA-binding activity of MET via phosphorylation and thus facilitates the genomic responses to JH. In summary, this study reveals an interplay of genomic and nongenomic signaling mechanisms of JH.

Juvenile Hormone Biosynthesis in Insects: What Is New, What Do We Know, and What Questions Remain?

Our understanding of JH biosynthesis has significantly changed in the last years. In this review I would like to discuss the following topics: (1) the progresses in understanding the JH biosynthesis pathway. Access to genome sequences has facilitated the identification of all the genes encoding biosynthetic enzymes and the completion of comprehensive transcriptional studies, as well as the expression and characterization of recombinant enzymes. Now the existence of different flux directionalites, feed-back loops and pathway branching points in the JH biosynthesis pathways can be explored; (2) the new concepts in the modulation of JH synthesis by allatoregulators. The list of putative JH modulators is increasing. I will discuss their possible role during the different physiological states of the CA; (3) the new theoretical and physiological frameworks for JH synthesis analysis. I will discuss the bases of the flux model for JH biosynthesis. JH plays multiple roles in the control of ovary development in female mosquitoes; therefore, the CA presents different physiological states, where JH synthesis is altered by gating the flux at distinctive points in the pathway; (4) in the final section I will identify new challenges and future directions on JH synthesis research.

Sesquiterpene action, and morphogenetic signaling through the ortholog of retinoid X receptor, in higher Diptera

Morphogenetic signaling by small terpenoid hormones is a common feature of both vertebrate and invertebrate development. Most attention on insect developmental signaling by small terpenoids has focused on signaling by juvenile hormone through bHLH-PAS proteins (e.g., the MET protein), especially as that signaling axis intersects with ecdysteroid action through the receptor EcR. However, a series of endocrine and pharmacological studies on pupariation in cyclorrhaphous Diptera have remained persistently refractory to explanation with the above two-axis model. Recently, the terpenoid compound methyl farnesoate has been physicochemically demonstrated to exist in circulation at physiological concentrations, in several mecopterid orders, including Diptera. In addition, it has also been recently demonstrated that the receptor to which methyl farnesoate binds with nanomolar affinity (ultraspiracle, an ortholog of retinoid X receptor) requires a functioning ligand binding pocket to sustain the morphogenetic transition to puparium formation. This review evaluates endocrine and pharmacological evidence for developmental pathways reached by methyl farnesoate action, and assesses the participation of the retinoid X receptor ligand pocket in signal transduction to those developmental endpoints.

Life-history evolution and the polyphenic regulation of somatic maintenance and survival

Here we discuss life-history evolution from the perspective of adaptive phenotypic plasticity, with a focus on polyphenisms for somatic maintenance and survival. Polyphenisms are adaptive discrete alternative phenotypes that develop in response to changes in the environment. We suggest that dauer larval diapause and its associated adult phenotypes in the nematode (Caenorhabditis elegans), reproductive dormancy in the fruit fly (Drosophila melanogaster) and other insects, and the worker castes of the honey bee (Apis mellifera) are examples of what may be viewed as the polyphenic regulation of somatic maintenance and survival. In these and other cases, the same genotype can--depending upon its environment--express either of two alternative sets of life-history phenotypes that differ markedly with respect to somatic maintenance, survival ability, and thus life span. This plastic modulation of somatic maintenance and survival has traditionally been underappreciated by researchers working on aging and life history. We review the current evidence for such adaptive life-history switches and their molecular regulation and suggest that they are caused by temporally and/or spatially varying, stressful environments that impose diversifying selection, thereby favoring the evolution of plasticity of somatic maintenance and survival under strong regulatory control. By considering somatic maintenance and survivorship from the perspective of adaptive life-history switches, we may gain novel insights into the mechanisms and evolution of aging.

Ligand binding pocket function of Drosophila USP is necessary for metamorphosis

The widely accepted paradigm that epoxidized methyl farnesoates ("juvenile hormones," JHs) are the principal sesquiterpenoid hormones regulating insect metamorphosis was assessed in Drosophila melanogaster. GC-MS analysis of circulating methyl farnesoids during the mid to late 3rd instar showed that methyl farnesoate is predominant over methyl epoxyfarnesoate (=JH III). The circulating concentration of methyl farnesoate (reaching nearly 500 nM), was easily high enough on a kinetic basis to load the Drosophila ortholog of the nuclear hormone receptor RXR (also known as "ultraspiracle," USP), whereas the circulating concentrations of JH III and methyl bisepoxyfarnesoate (bisepoxyJH III) were not. The hypothesis that the ligand pocket of USP necessarily binds an endogenous ligand for differentiation of the immature to the adult was tested with USP mutated at residue that normally extends a side chain into the ligand binding pocket. An equilibrium binding assay confirmed that the mutation (Q288A) strongly altered methyl farnesoate interaction with USP, while a heterologous cell-line transfection assay confirmed that the mutation did not allosterically alter the transcriptional response of the ultraspiracle/ecdysone receptor heterodimer to ecdysteroid signaling. Transgenic wildtype USP driven by the cognate natural promoter rescued null animals to develop to the adult inside a normally formed puparium, while in contrast animals transgenically expressing instead the ligand pocket mutant exhibited developmental derangement at the larval to pupal transition, including failure to form a properly shaped or sclerotized puparium. Other point mutations to the pocket strongly reducing affinity for methyl farnesoate similarly disrupted the larval to pupal metamorphosis. These results suggest that normal larval to pupal maturation in this mecopteran model insect requires the involvement of a distinct endocrine axis of USP binding to its own endogenous terpenoid ligand.

Phospholipid--driven gene regulation

Phospholipids (PLs), well known for their fundamental role in cellular structure, play critical signaling roles via their derivatives and cleavage products acting as second messengers in signaling cascades. Recent work has shown that intact PLs act as signaling molecules in their own right by modulating the activity of nuclear hormone transcription factors responsible for tuning genes involved in metabolism, lipid flux, steroid synthesis and inflammation. As such, PLs have been classified as novel hormones. This review highlights recent work in PL-driven gene regulation with a focus on the unique structural features of phospholipid-sensing transcription factors and what sets them apart from well known soluble phospholipid transporters.

Function, diversity, and application of insect juvenile hormone epoxidases (CYP15)

Juvenile hormones (JHs) represent a family of sesquiterpenoid hormones in insects, and they play a key role in regulating development, metamorphosis, and reproduction. The last two steps of the JH biosynthetic pathway, epoxidation and methyl esterification of farnesoic acid to JH, are insect specific, and thus have long been considered a promising target for biorational insecticides. Recently, the enzymes involved in the last two steps have been molecularly identified: JH acid methyltransferase catalyzes the esterification step and the cytochrome P450 CYP15 enzyme catalyzes the epoxidation step. In this review, we describe the recent progress on the characterization of JH biosynthetic enzymes, with special focus on the function and diversity of the CYP15 family. CYP15 genes have evolved lineage-specific substrate specificity and regulatory mechanisms in insects, which appear to be associated with the lineage-specific acquisition of unique JH structure and function. In addition, the lack of CYP15 genes in crustacean (Daphnia pulex) and arachnid (Tetranychus urticae) species, whose genomes have been fully sequenced, may imply that CYP15 enzymes are an evolutionary innovation in insects to use the epoxide forms of methylated farnesoid molecules as their principal JHs. Molecular identification and characterization of CYP15 genes from broad taxa of insects have paved the way to the design of target-specific, biorational anti-JH agents.

How does juvenile hormone control insect metamorphosis and reproduction?

In insects juvenile hormone (JH) regulates both metamorphosis and reproduction. This lecture focuses on our current understanding of JH action at the molecular level in both of these processes based primarily on studies in the tobacco hornworm Manduca sexta, the flour beetle Tribolium castaneum, the mosquito Aedes aegypti, and the fruit fly Drosophila melanogaster. The roles of the JH receptor complex and the transcription factors that it regulates during larval molting and metamorphosis are summarized. Also highlighted are the intriguing interactions of the JH and insulin signaling pathways in both imaginal disc development and vitellogenesis. Critical actions of JH and its receptor in the timing of maturation of the adult optic lobe and of female receptivity in Drosophila are also discussed.

The juvenile hormone signaling pathway in insect development

The molecular action of juvenile hormone (JH), a regulator of vital importance to insects, was until recently regarded as a mystery. The past few years have seen an explosion of studies of JH signaling, sparked by a finding that a JH-resistance gene, Methoprene-tolerant (Met), plays a critical role in insect metamorphosis. Here, we summarize the recently acquired knowledge on the capacity of Met to bind JH, which has been mapped to a particular ligand-binding domain, thus establishing this bHLH-PAS protein as a novel type of an intracellular hormone receptor. Next, we consider the significance of JH-dependent interactions of Met with other transcription factors and signaling pathways. We examine the regulation and biological roles of genes acting downstream of JH and Met in insect metamorphosis. Finally, we discuss the current gaps in our understanding of JH action and outline directions for future research.

cDNA isolation, expression, and hormonal regulation of yolk protein genes in the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Yolk protein (YP) or vitellogenin (Vg), the main component of yolk, is the key nutrient for embryonic development. YPs, encoded from uncleaved genes existing mainly in cyclorraphan flies, are different from VGs that are present in most non-cyclorraphan dipterans and other insects. In this study, cDNAs of two YPs, namely Bdyp1 and Bdyp2 (GenBank accession Nos. AF368053 and AF368054), were isolated in the oriental fruit fly, Bactrocera dorsalis (Hendel). RT-PCR analysis revealed that Bdyp1 and 2 are expressed in the fat body and ovary during egg development. However, the expression profiles of Bdyp1 and 2 in the fat body are different, indicating that divergent mechanisms might exist in the regulation of these two genes. Twenty-hydroxyecdysone (20E) plays a major role in promoting Bdyp1 expression, yet the expression of Bdyp2 exhibits a greater response to juvenile hormone (JH) in fat body in vitro. Unexpectedly, 20E-induced expression of both Bdyp1 and 2 is suppressed by JH prior to 20E treatment of in vitro fat body; conversely, it is enhanced by the addition of JH following 20E treatment.

Precocious metamorphosis in the juvenile hormone-deficient mutant of the silkworm, Bombyx mori

Insect molting and metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent precocious metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes precocious metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and metamorphosis.

The number of larval instars in insects varies greatly across insect taxa and can even vary at the intraspecific level. However, little is known about how the number of larval instars is fixed in each species or modified by the environment. The silkworm, Bombyx mori, provides a unique bioresource for investigating this question, as there are several “moltinism” strains that exhibit variations in the number of larval molts. The present study describes the first positional cloning of a moltinism gene. We performed genetic and biochemical analyses on the dimolting (mod) mutant, which shows precocious metamorphosis with fewer larval–larval molts. We found that mod is a juvenile hormone (JH)–deficient mutant that is unable to synthesize JH, a hormone that prevents precocious metamorphosis and allows the larvae to undergo multiple rounds of larval–larval molts. This JH–deficient mutation is the first described to date in any insect species and, therefore, the mod strain will serve as a useful model for elucidating the molecular mechanism of JH action. Remarkably, precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that morphostatic action of JH is not necessary for young larvae of B. mori.

Neuroendocrine regulation of Drosophila metamorphosis requires TGFbeta/Activin signaling

In insects, initiation of metamorphosis requires a surge in the production of the steroid hormone 20-hydroxyecdysone from the prothoracic gland, the primary endocrine organ of juvenile larvae. Here, we show that blocking TGFβ/Activin signaling, specifically in the Drosophila prothoracic gland, results in developmental arrest prior to metamorphosis. The terminal, giant third instar larval phenotype results from a failure to induce the large rise in ecdysteroid titer that triggers metamorphosis. We further demonstrate that activin signaling regulates competence of the prothoracic gland to receive PTTH and insulin signals, and that these two pathways act at the mRNA and post-transcriptional levels, respectively, to control ecdysone biosynthetic enzyme expression. This dual regulatory circuitry may provide a cross-check mechanism to ensure that both developmental and nutritional inputs are synchronized before initiating the final genetic program leading to reproductive adult development. As steroid hormone production in C. elegans and mammals is also influenced by TGFβ/Activin signaling, this family of secreted factors may play a general role in regulating developmental transitions across phyla.

Evidence for differential biosynthesis of juvenile hormone (and related) sesquiterpenoids in Drosophila melanogaster

Previous studies in Drosophila melanogaster have demonstrated that biosynthesis and regulation of juvenile hormone bisepoxide (JHB(3)) may not be coordinated with that of juvenile hormone (JH III). In this study, we have used the radiochemical assay to confirm the coordinated developmental sesquiterpenoid profile during adult life and analyze the effect of farnesol and farnesoic acid addition on methyl farnesoate, JH III and JHB(3) production by isolated ring glands of Drosophila third instar larvae or corpora allata of adult females. Application of exogenous farnesol or farnesoic acid to glands in vitro stimulated MF and JH III biosynthesis in both larvae and adults. Farnesol and farnesoic acid were inhibitory to JHB(3) biosynthesis in larvae. N-acetyl-geranyl-L-cysteine (NAGC) and S-farnesyl-thioacetic acid (SFTA) are farnesyl pyrophosphatase inhibitors that have specificity towards two different ring gland phosphatases. NAGC and SFTA had no effect on MF or JH III biosynthesis, whereas SFTA inhibited JHB(3) biosynthesis. SFTA shows specificity for a ring gland phosphatase, Phos2680, which has not been previously implicated as a contributor to JHB(3) biosynthesis. This finding suggests that farnesol production occurs in two alternate pools; one pool utilized for MF and JH III production and the other for JHB(3) production. Finally, we have used the UAS-GAL4 system in Drosophila to express juvenile hormone acid methyltransferase (JHAMT) in vivo. In contrast to in vitro studies, JHAMT expression had no effect on MF or JH III biosynthesis but stimulated JHB(3) in both larvae and adults.

Activities of natural methyl farnesoids on pupariation and metamorphosis of Drosophila melanogaster

Methyl farnesoate (MF) and juvenile hormone (JH III), which bind with high affinity to the receptors USP and MET, respectively, and bisepoxy JH III (bisJH III) were assessed for several activities during Drosophila larval development, and during prepupal development to eclosed adults. Dietary MF and JH III were similarly active, and more active than bisJH III, in lengthening larval development prior to pupariation. However, the order of activity was changed (JH III>bisJH III>MF) with respect to preventing prepupae from eclosing as normal adults, whether administered in the larval diet or as topically applied at the white puparium stage. If endogenous production of all three larval methyl farnesoids was suppressed by a strongly driven RNAi against HMGCR in the corpora allata cells, most larvae did not attain pupariation. Farnesol (which has no demonstrated life-necessary function in larval life except in corpora allata cells as a precursor to methyl farnesoid biosynthesis) when incorporated into the diet rescued attainment of pupariation in a dose-dependent manner, presumably by rescuing endogenous production of all three hormones. A more mild suppression of endogenous methyl farnesoid production enabled larval attainment of pupariation. However, in this background dietary MF had increased activity in preventing puparia from attaining normal adult eclosion. The physiological relevance of using exogenous methyl farnesoids to block prepupal development to normally eclosed adults was tested by, instead, protecting in prepupae the endogenous titer of methyl farnesoids. JH esterase normally increases during the mid-late prepupal stage, presumably to clear endogenous methyl farnesoids. When JH esterase was inhibited with an RNAi, it prevented attainment of adult eclosion. Cultured adult corpora allata from male and female Aedes aegypti released both MF and JH III, and the A. aegypti nuclear receptor USP bound MF with nanomolar affinity. These A. aegypti data support the use of Drosophila as a model for mosquitoes of the binding of secreted MF to USP.

Bioassays of compounds with potential juvenoid activity on Drosophila melanogaster: juvenile hormone III, bisepoxide juvenile hormone III and methyl farnesoates

Metabolites of the 6,7,10,11 bisepoxide juvenile hormone III (JHB(3)), and other potential juvenoids, were tested for juvenile hormone activity using early instar or early stage pupae of Drosophila melanogaster. Importantly, methyl farnesoates were tested as they might have JH-like activity on Dipteran juveniles. Larvae were exposed to compounds in medium, or the compounds were applied to white puparia. In the assays employed in the present study, there was no indication for JH activity associated with the metabolites of JHB(3). The activity of methyl farnesoate (MF) was higher than that of JH III and far greater than bisepoxide JH III. As opposed to the two endogenous juvenile hormones, methyl farnesoate has weak activity in the white puparial bioassay. When fluorinated forms of methyl farnesoate, which is unlikely to be converted to JH, were applied to Drosophila medium to which fly eggs were introduced, there was a high degree of larval mortality, but no evidence of subsequent mortality at the pupal stage. One possible explanation for the results is that methyl farnesoate is active as a hormone in larval stages, but has little activity at the pupal stage where only juvenile hormone has a major effect.

Suppressed production of methyl farnesoid hormones yields developmental defects and lethality in Drosophila larvae

A long-unresolved question in the developmental biology of Drosophila melanogaster has been whether methyl farnesoid hormones secreted by the ring gland are necessary for larval maturation and metamorphosis. In this study, we have used RNAi techniques to inhibit 3-Hydroxy-3-Methylglutaryl CoA Reductase (HMGCR) expression selectively in the corpora allatal cells that produce the circulating farnesoid hormones. The developing larvae manifest a number of developmental, metabolic and morphogenetic derangements. These defects included the exhibition of an "ultraspiracle" death phenotype at the 1st to 2nd instar larval molt, similar to that exhibited by animals that are null for the farnesoid receptor ultraspiracle. The few larvae surviving past a second lethal period at the 2nd to 3rd instar larval molt, again with "ultraspiracle" phenotype, often became developmentally arrested after either attaining a misformed puparium or after formation of the white pupa. Survival past the "ultraspiracle" lethal phenotype could be rescued by dietary provision of an endogenous dedicated precursor to the three naturally secreted methyl farnesoid hormones. In addition to these developmental and morphogenetic defects, most larvae that survived to the late second instar exhibited a posterior-originating melanization of the tracheal system. These results support the hypothesis that larval methyl farnesoid hormones are necessary for larval survival and morphogenetic transformation through the larval and pupal metamorphic processes.

Drosophila FoxO regulates organism size and stress resistance through an adenylate cyclase

Forkhead box class O (FoxO) transcription factors are a family of conserved proteins that regulate the cellular responses to various stimuli, such as energy deprivation, stress, and developmental cues. FoxO proteins are important mediators of the insulin signaling pathway, adjusting growth and metabolism to nutrient availability. Insulin signaling acts together with the glucagon-stimulated cAMP signaling pathway to orchestrate the organism response to various nutritional conditions. In this study, we demonstrate that Drosophila melanogaster FoxO (dFoxO) regulates cAMP signaling by directly inducing the expression of an adenylate cyclase gene, ac76e. Interestingly, ac76e is expressed in a highly restricted pattern throughout fly development, limited to the corpus allatum (CA), gastric cecum, and malpighian tubules. dFoxO activation of AC76E in the CA increases starvation resistance and limits growth. Our results unravel a new role for dFoxO, integrating cAMP and insulin signaling to adapt organism growth to the existing nutritional conditions.

The cis-regulatory sequences required for expression of the Drosophila melanogaster adult cuticle gene ACP65A

Post-embryonic development in insects requires successive molts. Molts are triggered by ecdysteroids, and the nature of the molt (larval, pupal or adult) is determined by juvenile hormones. The genes encoding cuticle proteins are targets of both classes of hormones, and therefore are interesting models to study hormone action at the molecular level. The Drosophila ACP65A cuticle gene is expressed exclusively during the synthesis of the adult exoskeleton, in epidermal domains synthesising flexible cuticle. We have examined the cis-regulatory sequences of ACP65A using phylogenetic comparisons and functional analysis, and find that only about 180 bp are essential, including an 81 bp intron. The restriction of ACP65A expression appears to depend on a strong repression mechanism.

Juvenile hormone regulation of Drosophila Epac--a guanine nucleotide exchange factor

Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to characterize the effects of juvenile hormone (JH) on Epac (Exchange Protein directly Activated by Cyclic AMP; NM_001103732), a guanine nucleotide exchange factor for Rap1 in Drosophila S2 cells. JH treatment led to a rapid, dose-dependent increase in Epac relative expression ratio (RER) when compared to treatment with methyl linoleate (MLA) that lacks biological activity. The minimal level of hormone needed to elicit a response was 100 ng/ml. Time-course studies indicated a significant rise in the RER 1h after treatment. S2 cells were challenged with 20-hydroxyecdysone and a series of compounds similar in structure to JH to determine the specificity of the response. Methoprene and JH III displayed the greatest increases in RER. Late third instar (96 h) Drosophila were exposed to diet containing methoprene (500 ng/g diet); significantly higher RERs for Epac were observed 12h after exposure. JH had no effect on Epac RERs in the human cell line HEK-293.

Hormonal regulation of the humoral innate immune response in Drosophila melanogaster

Juvenile hormone (JH) and 20-hydroxy-ecdysone (20E) are highly versatile hormones, coordinating development, growth, reproduction and aging in insects. Pulses of 20E provide key signals for initiating developmental and physiological transitions, while JH promotes or inhibits these signals in a stage-specific manner. Previous evidence suggests that JH and 20E might modulate innate immunity, but whether and how these hormones interact to regulate the immune response remains unclear. Here we show that JH and 20E have antagonistic effects on the induction of antimicrobial peptide (AMP) genes in Drosophila melanogaster. 20E pretreatment of Schneider S2 cells promoted the robust induction of AMP genes, following immune stimulation. On the other hand, JH III, and its synthetic analogs (JHa) methoprene and pyriproxyfen, strongly interfered with this 20E-dependent immune potentiation, although these hormones did not inhibit other 20E-induced cellular changes. Similarly, in vivo analyses in adult flies confirmed that JH is a hormonal immuno-suppressor. RNA silencing of either partner of the ecdysone receptor heterodimer (EcR or Usp) in S2 cells prevented the 20E-induced immune potentiation. In contrast, silencing methoprene-tolerant (Met), a candidate JH receptor, did not impair immuno-suppression by JH III and JHa, indicating that in this context MET is not a necessary JH receptor. Our results suggest that 20E and JH play major roles in the regulation of gene expression in response to immune challenge.

Juvenile hormone acid O-methyltransferase in Drosophila melanogaster

Juvenile hormone (JH) acid O-methyltransferase (JHAMT) is the enzyme that transfers a methyl group from S-adenosyl-l-methionine (SAM) to the carboxyl group of JH acids to produce active JHs in the corpora allata. While the JHAMT gene was originally identified and characterized in the silkworm Bombyx mori, no orthologs from other insects have been studied until now. Here we report on the functional characterization of the CG17330/DmJHAMT gene in the fruit fly Drosophila melanogaster. Recombinant DmJHAMT protein expressed in Escherichia coli catalyzes the conversion of farnesoic acid and JH III acid to their cognate methyl esters in the presence of SAM. DmJHAMT is predominantly expressed in corpora allata, and its developmental expression profile correlates with changes in the JH titer. While a transgenic RNA interference against DmJHAMT has no visible effect, overexpression of DmJHAMT results in a pharate adult lethal phenotype, similar to that obtained with application of JH analogs, suggesting that the temporal regulation of DmJHAMT is critical for Drosophila development.

Juvenile hormone action: a 2007 perspective

Juvenile hormone (JH) is a key hormone in regulation of the insect's life history, both in maintaining the larval state during molts and in directing reproductive maturation. This short review highlights the recent papers of the past year that lend new insight into the role of this hormone in the larva and the mechanisms whereby it achieves this role.

rosy Function is required for juvenile hormone effects in Drosophila melanogaster

Application of a high dose of juvenile hormone (JH) III or its mimics (JHM) to Drosophila at the white puparium stage causes the formation of a pupal-like abdomen with few or no short bristles. We report here that the rosy (ry) gene encoding the enzyme xanthine dehydrogenase (XDH), which catalyzes the final two-step oxidation in purine catabolism, is required for this effect of JH on the epidermis. In ry506 (null allele) homozygotes or hemizygotes, JH III or pyriproxifen (a JHM) had little effect on abdominal bristle or cuticle formation, but disrupted the development of the central nervous system as in wild-type flies. Wild-type ry rescued the JH sensitivity of the abdominal epidermis in ry506 mutants. Inhibition of XDH activity phenocopied the ry null mutant's insensitivity to JH. Larvae fed on hypoxanthine or xanthine showed a decreased JH sensitivity. ry506 clones were sensitive to JH, indicating that ry is required non-cell autonomously for the JH effects. Normally JH applied at pupariation causes the aberrant reexpression of the transcription factor broad in the abdominal epidermis during adult development, but in the ry506 mutant most of the cells in the dorsal tergite showed no broad reexpression, indicating that ry is upstream of broad in the JH signaling pathway.