Juvenile Hormone Synthesis Research Articles

An anti-juvenile hormone agent, ethyl 4-(2-benzylhexyloxy)benzoate, inhibits juvenile hormone synthesis through the suppression of the transcription of juvenile hormone biosynthetic enzymes in the corpora allata in Bombyx mori

Ethyl 4-[(S)-2-benzylhexyloxy)]benzoate (KF-13S), derived from ethyl 4-[2-( tert-butylcarbonyloxy)butoxy]benzoate (ETB), has strong anti-juvenile hormone (JH) activity which causes precocious metamorphosis in Bombyx mori, and the mode of action of this compound was studied. Application of KF-13S inhibited JH biosynthesis by the corpora allata (CA) in a reversible manner, and in vitro culture experiments showed that this inhibition was due to the direct action of this compound on the CA. When mRNA expression of the JH biosynthetic enzymes were studied, KF-13S strongly suppressed those of HMG Co-A synthase and HMG Co-A reductase. mRNA levels of other mevalonate enzymes and JH acid O-methyltransferase were also suppressed but were less sensitive to the compound. These studies showed that KF-13S prevents the transcription of many of the JH biosynthetic enzymes so that JH synthesis is suppressed.

A coordinated expression of biosynthetic enzymes controls the flux of juvenile hormone precursors in the corpora allata of mosquitoes

Juvenile hormone (JH) is a key regulator of metamorphosis and ovarian development in mosquitoes. Adult female Aedes aegypti mosquitoes show developmental and dynamically regulated changes of JH synthesis. Newly emerged females have corpora allata (CA) with low biosynthetic activity, but they produce high amounts of JH a day later; blood feeding results in a striking decrease in JH synthesis, but the CA returns to a high level of JH synthesis three days later. To understand the molecular bases of these dynamic changes we combined transcriptional studies of 11 of the 13 enzymes of the JH pathway with a functional analysis of JH synthesis. We detected up to a 1000-fold difference in the levels of mRNA in the CA among the JH biosynthetic enzymes studied. There was a coordinated expression of the 11 JH biosynthetic enzymes in female pupae and adult mosquito. Increases or decreases in transcript levels for all the enzymes resulted in increases or decreases of JH synthesis; suggesting that transcript changes are at least partially responsible for the dynamic changes of JH biosynthesis observed. JH synthesis by the CA was progressively increased in vitro by addition of exogenous precursors such as geranyl-diphosphate, farnesyl-diphosphate, farnesol, farnesal and farnesoic acid. These results suggest that the supply of these precursors and not the activity of the last 6 pathway enzymes is rate limiting in these glands. Nutrient reserves play a key role in the regulation of JH synthesis. Nutritionally deficient females had reduced transcript levels for the genes encoding JH biosynthetic enzymes and reduced JH synthesis. Our studies suggest that JH synthesis is controlled by the rate of flux of isoprenoids, which is the outcome of a complex interplay of changes in precursor pools, enzyme levels and external regulators such as nutrients and brain factors. Enzyme levels might need to surpass a minimum threshold to achieve a net flux of precursors through the biosynthetic pathway. In glands with low synthetic activity, the flux of isoprenoids might be limited by the activity of enzymes with low levels of expression.

Inhibition of DD2R gene expression in the corpus allatum activates alkaline phosphatase in female Drosophila melanogaster

Tissue-specific inhibition of the expression of the D2-like dopamine receptor gene (DD2R) in the corpus allatum (CA), which is a gland that synthesizes the juvenile hormone (JH), was tested for effect on alkaline phosphatase (AP) activity and the intensity of the AP response to heat stress (stress reactivity) in female Drosophila melanogaster. AP activity and AP stress reactivity in transgenic females with lower DD2R expression in the CA were higher than in control flies. A pharmacological elevation in JH increased AP activity in females of the control strains. DD2R was assumed to mediate the inhibitory effect of dopamine of JH synthesis in the CA of D. melanogaster.

Molecular analysis of nutritional and hormonal regulation of female reproduction in the red flour beetle, Tribolium castaneum

Female reproduction includes maturation of oocytes and the synthesis of yolk proteins (vitellogenin, Vg) in the fat body and their deposition into the oocytes. Our recent studies showed that juvenile hormone (JH) regulates Vg synthesis and 20-hydroxyecdysone (20E) regulates oocyte maturation in the red flour beetle ( Tribolium castaneum). Here, we report on the role of nutritional signaling on vitellogenesis and oogenesis. Comparison of gene expression between fed and starved beetles by microarray analysis showed the up-regulation of genes involved in energy homeostasis and down-regulation of genes involved in egg production in the starved beetles. The RNA interference (RNAi) aided knock-down in the expression of genes involved in insulin and TOR signaling pathways showed that both these signaling pathways play key roles in Vg synthesis and oocyte maturation. Starvation of female beetles resulted in a block in Vg synthesis but not in the progression of primary oocyte development to the resting stage. Feeding after starvation induced Vg synthesis and the progression of primary oocytes from the resting stage to the mature stage. However, in the beetles where JH or 20E synthesis or action was blocked by RNAi, both Vg synthesis and oocyte maturation were affected suggesting that both these hormones (JH and 20E) and nutritional signaling and their cross-talk regulate vitellogenesis and oogenesis.

Stage-specific regulation of juvenile hormone biosynthesis by ecdysteroid in Bombyx mori

In the penultimate (4th) instar larvae of Bombyx mori, juvenile hormone (JH) synthesis by corpora allata (CA) fluctuates. When diet containing 20-hydroxyecdysone (20E) was fed, JH synthetic activity of the CA was first stimulated as the ecdysteroid titer increased, then suppressed slightly by the higher molting concentration of ecdysteroids (>250ng/ml). The overall JH biosynthetic activity was modulated by the expression of JH biosynthetic enzymes in the CA: primarily JH acid O-methyltransferase (JHAMT), isopentenyl diphosphate isomerase, and farnesyl diphosphate synthase 1. After the last (5th) larval ecdysis, the artificially increased high ecdysteroid level due to the 20E diet activated JH synthesis by the CA, which required intact nervous connections with the brain. A factor(s) from the 20E-activated brain controls mainly JHAMT and HMG Co-A reductase expression to stimulate the JH synthesis. In the normal last instar larvae, the ecdysteroid titer declines so that these activation mechanisms are absent; therefore the decline of the ecdysteroid titer after the final larval ecdysis is one of the factors which induces the cessation of the JH synthesis by CA.

Juvenile hormone synthesis: “esterify then epoxidize” or “epoxidize then esterify”? Insights from the structural characterization of juvenile hormone acid methyltransferase

Juvenile hormones (JHs) play key roles in regulating metamorphosis and reproduction in insects. The last two steps of JH synthesis diverge depending on the insect order. In Lepidoptera, epoxidation by a P450 monooxygenase precedes esterification by a juvenile hormone acid methyltransferase (JHAMT). In Orthoptera, Dictyoptera, Coleoptera and Diptera epoxidation follows methylation. The aim of our study was to gain insight into the structural basis of JHAMT’s substrate recognition as a means to understand the divergence of these pathways. Homology modeling was used to build the structure of Aedes aegypti JHAMT. The substrate binding site was identified, as well as the residues that interact with the methyl donor ( S-adenosylmethionine) and the carboxylic acid of the substrate methyl acceptors, farnesoic acid (FA) and juvenile hormone acid (JHA). To gain further insight we generated the structures of Anopheles gambiae, Bombyx mori, Drosophila melanogaster and Tribolium castaneum JHAMTs. The modeling results were compared with previous experimental studies using recombinant proteins, whole insects, corpora allata or tissue extracts. The computational study helps explain the selectivity toward the ( 10R)-JHA isomer and the reduced activity for palmitic and lauric acids. The analysis of our results supports the hypothesis that all insect JHAMTs are able to recognize both FA and JHA as substrates. Therefore, the order of the methylation/epoxidation reactions may be primarily imposed by the epoxidase’s substrate specificity. In Lepidoptera, epoxidase might have higher affinity than JHAMT for FA, so epoxidation precedes methylation, while in most other insects there is no epoxidation of FA, but esterification of FA to form MF, followed by epoxidation to JH III.

Final steps in juvenile hormone biosynthesis in the desert locust, Schistocerca gregaria

Two genes coding for enzymes previously reported to be involved in the final steps of juvenile hormone (JH) biosynthesis in different insect species, were characterised in the desert locust, Schistocerca gregaria. Juvenile hormone acid O-methyltransferase (JHAMT) was previously described to catalyse the conversion of farnesoic acid (FA) and JH acid to their methyl esters, methyl farnesoate (MF) and JH respectively. A second gene, CYP15A1 was reported to encode a cytochrome P450 enzyme responsible for the epoxidation of MF to JH. Additionally, a third gene, FAMeT (originally reported to encode a farnesoic acid methyltransferase) was included in this study. Using q-RT-PCR, all three genes ( JHAMT, CYP15A1 and FAMeT) were found to be primarily expressed in the CA of the desert locust, the main biosynthetic tissue of JH. An RNA interference approach was used to verify the orthologous function of these genes in S. gregaria. Knockdown of the three genes in adult animals followed by the radiochemical assay (RCA) for JH biosynthesis and release showed that SgJHAMT and SgCYP15A1 are responsible for synthesis of MF and JH respectively. Our experiments did not show any involvement of SgFAMeT in JH biosynthesis in the desert locust. Effective and selective inhibitors of SgJHAMT and SgCYP15A1 would likely represent selective biorational locust control agents.

Fine structure of corpora allata of castes with different rates of juvenile hormone production in the termite Reticulitermes flavipes

The aim of this work is to describe corpora allata (CA) of several castes of the termite Reticulitermes flavipes that have different rates of juvenile hormone (JH) synthesis, with respect to differences in fine structure, volume, and intensity of allatostatin immunoreactivity in their innervation. The castes chosen are workers and their potential derivatives, apterous secondary reproductives and pre-soldiers (the precursors of soldiers). These castes, at the stages chosen, produce JH at low, high and intermediate rates respectively. Hormone production is positively correlated with volume and negatively correlated with intensity of allatostatin immunoreactivity in axons within the glands. Characteristics of fine structure that correlate with increased activity are increase in abundance and width of mitochondria, decrease in ability to fix and visualize smooth endoplasmic reticulum. These features have previously been described for CA of cockroaches and other insects. Glycogen in the CA of all of the castes studied, especially the large amounts in highly active glands of physogastric apterous reproductive females, is the most striking difference between the CA cells of R. flavipes and previously described CA of cockroaches, in which glycogen is absent throughout the reproductive cycles. This suggests that glycogen is an important source of energy for hormone production by termite CA.

Cloning and Characterization of a Putative Farnesoic Acid Omethyltransferase Gene from the Brown Planthopper,Nilaparvata lugens

Juvenile hormone (JH) plays key roles in both metamorphosis and adult reproductive processes. Farnesoic acid O-methyltransferase (FAMeT) is thought to be an important enzyme in the JH biosynthetic pathway, catalyzing methylation of farnesoic acid (FA) to methyl farnesoate (MF). A full-length cDNA (NlFAMeT) encoding a 299 amino acid putative FAMeT was isolated from the brown planthopper, Nilaparvata lugens (Stal) (Hemiptera: Geometroidea), a major rice pest in many parts of Asia. NlFAMeT showed high amino acid identities (52–54%) with other insect FAMeTs. Although the NlFAMeT transcript was expressed highly in corpus allatum (CA) and brain (without CA), no correlation was found between NlFAMeT transcript and JH titers. Although only a low level of NlFAMeT transcript was detected in the ovary, a high level was found in the abdomen and should be in one or more tissues undefined in the abdomen. Also, NlFAMeT transcript had a positive change during the vitellogenesis in female adults. These data indicated that NlFAMeT might not be a key enzyme in JH synthesis in N. lugens, but that it may play an important role in the ovary development. It might also be important in some unknown process in a so-far unidentified tissue in the abdomen.

Neuropeptide regulators of the juvenile hormone biosynthesis (in vitro) in the beetle, Tenebrio molitor (Coleoptera, Tenebrionidae)

The genome of Tribolium castaneum encodes two allatostatin [AS type B; W(X)(6)Wamide and AS type C; PISCF-OH] and one allatotropin (AT) precursor, but no AS type A (FGLamide) (Tribolium Genome Sequencing Consortium, 2008: Nature 452:949-955). Here we studied the activity (in vitro) of peptides derived from these precursors on the synthesis/release of juvenile hormone (JH) III. The corpora cardiaca-corpora allata (CC-CA) complexes of adult females of another tenebrionid beetle, the mealworm Tenebrio molitor, were used. Incubating the gland complexes in a medium containing Trica-AS B3 peptide, we showed that the peptide has allatostatic function in T. molitor. The activity of the type C AS depended on the age of the test animals and their intrinsic rate of JH III biosynthesis. The Trica-AS C peptide inhibited the JH release from CA of 3-day-old females with a high intrinsic rate of JH synthesis, but activated JH release from the CA of 7-day-old females with a lower intrinsic rate of JH production. The allatotropin peptide (Trica-AT) also activated the JH release from the CA of 7-day-old females in a dose-dependent and reversible manner. Unexpectedly, a type A AS derived from the precursor of the American cockroach Periplaneta americana (Peram-AS A2b) inhibited the JH release from the CA of younger and older females in the concentration range of 10(-8) to 10(-4) M, and the effects were fully reversible in the absence of peptide. These data suggest a complex role of allatoactive neuropeptides in the regulation of JH III biosynthesis in beetles.

NADP + -dependent farnesol dehydrogenase, a corpora allata enzyme involved in juvenile hormone synthesis

The synthesis of juvenile hormone (JH) is an attractive target for control of insect pests and vectors of disease, but the minute size of the corpora allata (CA), the glands that synthesize JH, has made it difficult to identify important biosynthetic enzymes by classical biochemical approaches. Here, we report identification and characterization of an insect farnesol dehydrogenase (AaSDR-1) that oxidizes farnesol into farnesal, a precursor of JH, in the CA. AaSDR-1 was isolated as an EST in a library of the corpora allata-corpora cardiaca of the mosquito Aedes aegypti. The 245-amino acid protein presents the typical short-chain dehydrogenase (SDR) Rossmann-fold motif for nucleotide binding. This feature, together with other conserved sequence motifs, place AaSDR-1 into the "classical" NADP(+)-dependent cP2 SDR subfamily. The gene is part of a group of highly conserved paralogs that cluster together in the mosquito genome; similar clusters of orthologs were found in other insect species. AaSDR-1 acts as a homodimer and efficiently oxidizes C(10) to C(15) isoprenoid and aliphatic alcohols, showing the highest affinity for the conversion of farnesol into farnesal. Farnesol dehydrogenase activity was not detected in the CA of newly emerged mosquitoes but significant activity was detected 24 h later. Real time PCR experiments revealed that AaSDR-1 mRNA levels were very low in the inactive CA of the newly emerged female, but increased >30-fold 24 h later during the peak of JH synthesis. These results suggest that oxidation of farnesol might be a rate-limiting step in JH III synthesis in adult mosquitoes.

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.

Age‐ and division‐of‐labour‐dependent differential expression of a novel non‐coding RNA, Nb‐1, in the brain of worker honeybees, Apis mellifera L.

To elucidate the molecular mechanisms underlying honeybee social behaviours, we identified a novel gene, Nb-1, whose expression in the worker brain changes according to the age-dependent division of labour in normal colonies. The open reading frames contained in the Nb-1 cDNA were not conserved in the homologue of a related species, suggesting that the Nb-1 gene product is a non-coding RNA. The distribution of Nb-1-expressing cells partially overlapped that of octopamine-immunoreactive cells and neurosecretory cells, the latter of which are involved in the synthesis and secretion of juvenile hormone (JH). Octopamine and JH control worker task transition, and thus Nb-1 might be involved in task transition through the modulation of octopamine/JH synthesis and secretion.

Evidence for a Phe-Gly-Leu-amide-like allatostatin in the beetle Tenebrio molitor

The allatostatins (ASTs) with Phe-Gly-Leu-amide C-terminal sequence are multifunctional neuropeptides discovered as inhibitors of juvenile hormone (JH) synthesis by corpora allata (CA) of cockroaches. Although these ASTs inhibit JH synthesis only in cockroaches, crickets, termites and locusts, isolation of peptides or of cDNA/genomic DNA or analysis of genomes indicates their occurrence in many orders of insects with the exception of coleopterans. The gene for these ASTs has not been found in the genome of the red flour beetle Tribolium castaneum (Family Tenebrionidae). Yet, in view of widespread occurrence of these peptides in insects, crustaceans and nematodes, they would be expected to occur in beetles. This study provides evidence for the presence of FGLa-like ASTs in the tenebrionid beetle, Tenebrio molitor, and scarabid beetle, Popillia japonica. Extract of brain from both beetles inhibited JH synthesis by cockroach CA dose dependently and reversibly. 20 brain equivalents of T. molitor and P. japonica extracts inhibited JH synthesis 64 ± 5 and 65 ± 0.6% respectively. Antibody against cockroach allatostatin ( Diploptera punctata AST-7) used in an enzyme-linked immunosorbent assay reacted with brain extract of these beetles. Antibody against D. punctata AST-5 localized FGLa-like ASTs in the brain and subesophageal ganglion of T. molitor and P. japonica. In addition, pretreatment of T. molitor brain extract with anti- D. punctata AST-5 reduced the inhibition of JH synthesis and pretreatment of anti- D. punctata AST-5 with D. punctata AST-5 diminished the immunoreactivity of the antibody. Thus we predict that FGLa-like allatostatins will be found in beetles.

Neuropeptide Regulators of Juvenile Hormone Synthesis

Juvenile hormones (JH), produced by the corpora allata, have an essential role in growth and development, morphogenesis, and reproductive processes of insects. The output of JH and circulating titer are required to be precisely regulated throughout the insect's life in response to developmental requirements and environmental factors. The synthesis of JH must be periodically turned off and on, or finely tuned, in a highly coordinated way. Except for a few key or intensely studied insect species, the control of synthesis of JH by regulatory peptides remains largely undefined and many of the details remain obscure. Several different classes of neuropeptide are believed to be involved in the regulation of corpus allatum function and hence JH output. In different insect species and at different stages of development, these regulatory peptides may include at least three types of inhibitory allatostatins, at least one type of stimulatory allatotropin, and perhaps several other, as yet largely undefined, additional neuropeptides. The details of how each of these peptides acts to affect JH production and their relationship to each other in the coordination of JH synthesis remain to be established. There are several insect orders for which almost nothing is known concerning the regulation of JH synthesis and the peptides that might be involved. Current proteomic and genomic studies are helping to redress this balance but at the same time posing new questions. Other neuropeptides are implicated in the regulation of JH production, and there is new evidence concerning the mode of action of allatotropins.

Target of Rapamycin (TOR) Mediates the Transduction of Nutritional Signals into Juvenile Hormone Production

Anautogeny is a reproductive strategy by which females do not reproduce until they feed. Therefore, nutritional signals must inform the reproductive tissues, and cells that the organism has reached a nutritional status suitable for triggering reproductive processes. One of the possible pathways involved in anautogeny is the "target of rapamycin" (TOR) pathway, which has been described as connecting the nutritional status with growth, proliferation, and cancer. The German cockroach, Blattella germanica, is an anautogenous species whose vitellogenesis is governed by juvenile hormone. In the present report, we describe the cloning of TOR cDNA from B. germanica (BgTOR). Expression studies showed that BgTOR is expressed in adult female corpora allata and fat body. BgTOR knockdown using systemic RNAi in vivo produced a severe inhibition of juvenile hormone synthesis in adult female corpora allata, together with a reduction of mRNA levels corresponding to 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase-1, HMG-CoA synthase-2, and HMG-CoA reductase. In addition, there was a reduction of vitellogenin mRNA in the fat body, and ovaries did not grow. Analysis of TOR expression in corpora allata of fed and starved females suggested that TOR is not regulated at the transcriptional level. Nevertheless, there was a reduction in HMG-CoA synthases and reductase mRNA in corpora allata (but not in the fat body) of starved females, together with a dramatic reduction of juvenile hormone production and ovary development. Taken together, our results indicate that TOR knockdown mimics starvation in terms of corpora allata activity, and suggest that nutritional signals that activate juvenile hormone biosynthesis and vitellogenin production are mediated by the TOR pathway.

Sensory Neurons in the Drosophila Genital Tract Regulate Female Reproductive Behavior

Females of many animal species behave very differently before and after mating. In Drosophila melanogaster, changes in female behavior upon mating are triggered by the sex peptide (SP), a small peptide present in the male's seminal fluid. SP activates a specific receptor, the sex peptide receptor (SPR), which is broadly expressed in the female reproductive tract and nervous system. Here, we pinpoint the action of SPR to a small subset of internal sensory neurons that innervate the female uterus and oviduct. These neurons express both fruitless (fru), a marker for neurons likely to have sex-specific functions, and pickpocket (ppk), a marker for proprioceptive neurons. We show that SPR expression in these fru+ ppk+ neurons is both necessary and sufficient for behavioral changes induced by mating. These neurons project to regions of the central nervous system that have been implicated in the control of reproductive behaviors in Drosophila and other insects.

Isolation of the gene for the precursor of Phe-Gly-Leu-amide allatostatins in the termite Reticulitermes flavipes

Allatostatins (ASTs), with a C-terminal sequence Tyr/Phe-Xaa-Phe-Gly-Leu/Ile-amide, are multifunctional neuropeptides that were first discovered by their ability to inhibit juvenile hormone (JH) synthesis by the corpora allata (CA) in cockroaches. These A-type ASTs have since been demonstrated to inhibit JH synthesis in crickets, termites and more recently locusts. The gene for the precursor of A-type ASTs has been identified in several species of cockroaches, in crickets and in locusts, but not yet in termites, although 5 AST peptides were isolated from the lower termite Reticulitermes flavipes that are identical to known cockroach ASTs. In this study, primers designed from AST amino acid sequences of cockroaches are used to identify the gene for the preproAST peptides in R. flavipes. In addition, the expression of the gene in brain tissues is demonstrated for egg-laying and non-egg-laying neotenic reproductives. The gene codes for 14 individual peptides and its sequence is closer to that of cockroaches and the cricket than to that of other insect orders in which these peptides do not act as allatostatins. Among the known cockroach AST genes, the termite AST gene is most similar to that of Periplaneta americana, a species belonging to the primitive family Blattidae.

Roles of ecdysteroid and juvenile hormone in vitellogenesis in an endoparasitic wasp, Pteromalus puparum (Hymenoptera: Pteromalidae)

To elucidate the endocrine regulation of vitellogenesis in an endoparastic wasp ( Pteromalus puparum), the titers of ecdysteroid and juvenile hormone (JH) from the whole bodies are measured using the method of radioimmunoassay and GC–MS, and compared with the levels of vitellogenin (Vg) mRNA in the fat bodies, hemolymph Vg and ovarian vitellin (Vt), respectively. The results show that the ecdysteroid titer and fat body Vg mRNA level have a similar dynamics tendency, and the peak titer is at adult eclosion. The titer of JH III and ovarian Vt also have a similar dynamics tendency, and the peak titer is at 48 h after eclosion. The profiles of hemolymph Vg, Vg mRNA in fat bodies and ovarian Vt, are also measured in the wasps after treated with different amounts of 20-hydroxyecdysone (20HE) or JH III in female pupa and adults. The results show that 20HE stimulates Vg synthesis in the fat bodies and its release into the hemolymph, and that JH III only accelerates Vg sequestration in the oocytes. Decapitation, which is believed to terminate synthesis of JH in insects, can not inhibit vitellogenesis and oocyte maturation in P. puparum. Furthermore, Vg gene is expressed with a lower titer of JH and depressed by a higher titer of JH III. These studies suggest that ecdysteroids play a role in Vg synthesis and believed to be the dominant hormones in regulation of vitellogenesis in P. puparum, and JHs are not the essential factors to female reproduction in this wasp.

Juvenile hormone acid methyl transferase is a key regulatory enzyme for juvenile hormone synthesis in the Eri silkworm, Samia cynthica ricini

During the period of adult emergence in the Eri silkworm, Samia cynthia ricini, the corpora allata (CA) are apparently reactivated in females, but not males. This creates a significant sexual dimorphism in juvenile hormone (JH) synthesis by CA. To determine the underlying molecular mechanisms in this process, we cloned cDNAs of two enzymes involved in the JH synthesis pathway: 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) and juvenile hormone acid methyl transferase (JHAMT). Both Samcri-HMGR and -JHAMT mRNAs were detected in CA almost exclusively. However, their expression patterns were different from each other. During the period of adult emergence, Samcri-HMGR was expressed in CA at a constantly high level suggesting it plays little role for the regulation of JH synthesis. In contrast, the patterns of both Samcri-JHAMT mRNA level and enzyme activity were closely correlated with the patterns of JH synthesis, CA reactivation, and sexual dimorphism of JH synthesis. In addition, JHAMT mRNA levels were paralleled JH synthesis in the fifth-instar larvae of S. cynthia ricini and the pharate adults of the silkworm Bombyx mori. We infer from these results that JHAMT is a key regulatory enzyme for JH synthesis in the Eri silkworm.