The juvenile hormone analogue, methoprene, inhibits ecdysterone induction of small heat shock protein gene expression

HSP gene superfamily in Aspongopus chinensis Dallas: unravelling identification, characterisation and expression patterns during diapause and non-diapause stages

Aspongopus chinensis Dallas 1851, an insect of important economic value, faces challenges in artificial breeding due to mandatory diapause and limited access to wild resources. Heat shock proteins (Hsps) are thought to influence diapause in insects, but little is known about their role in A. chinensis during diapause. This study used genomic methods to identify 25 Hsp genes in A. chinensis, including two Hsp90, 14 Hsp70, four Hsp60 and five small Hsp genes, were located on seven chromosomes, respectively. The gene structures among the same families are relatively conserved. Meanwhile, the motif compositions and secondary structures of A. chinensis Hsps (AcHsps) were predicted. RNA-seq data and fluorescence quantitative PCR analysis showed that there were differences in the expression patterns of AcHsps in diapause and non-diapause stages, and AcHsp70-5 was significantly differentially expressed in both analysis, which was enriched in the pathway of response to hormone. All the results showed that Hsps play an important role in the diapause mechanism of A. chinensis. Our observations highlight the molecular evolution of the Hsp gene and their effect on diapause in A. chinensis.

Ecdysone and gene expressions for chromatin remodeling, histone modification, and Broad Complex in relation to pupal commitment in Bombyx mori

In the present study, we tried to clarify when and how pupal commitment (PT) better to use PC occurs and what is involved in the PT of Bombyx mori. To clarify this, we examined the responsiveness of a wing disc to ecdysone, referring to metamorphosis-related BR-C, development-related Myc and Wnt, and chromatin remodeling-related genes at around the predicted PT stage of the Bombyx wing disc. Wing disc responsiveness to juvenile hormone (JH) and ecdysone was examined using Methoprene and 20-hydroxyecdysone (20E) in vitro. The body weight of B. mori increased after the last larval ecdysis, peaked at Day 5 of the fifth larval instar (D5L5), and then decreased. The responsiveness of the wing disc to JH decreased after the last larval ecdysis up to D3L5. Bmbr-c (the Broad Complex of B. mori) showed enhanced expression in D4L5 wing discs with 20E treatment. Some chromatin remodeler and histone modifier genes (Bmsnr1, Bmutx, and Bmtip60) showed upregulation after being cultured with 20E in D4L5 wing discs. A low concentration of 20E is suggested to induce responsiveness to 20E in D4L5 wing discs. Bmbr-c, Bmsnr1, Bmutx, and Bmtip60 were upregulated after being cultured with a low concentration of 20E in D4L5 wing discs. The expression of Bmmyc and Bmwnt1 did not show a change after being cultured with or without 20E in D4L5 wing discs, while enhanced expression was observed with 20E in D5L5 wing discs. From the present results, we concluded that PT of the wing disc of B. mori occurred beginning on D4L5 with the secretion of low concentrations of ecdysteroids. Bmsnr1, Bmutx, Bmtip60, and BR-C are also involved.

A Crucial Caste Regulation Gene Detected by Comparing Termites and Sister Group Cockroaches

Sterile castes are a defining criterion of eusociality; investigating their evolutionary origins can critically advance theory. In termites, the soldier caste is regarded as the first acquired permanently sterile caste. Previous studies showed that juvenile hormone (JH) is the primary factor inducing soldier differentiation, and treatment of workers with artificial JH can generate presoldier differentiation. It follows that a shift from a typical hemimetabolous JH response might be required for soldier formation during the course of termite evolution within the cockroach clade. To address this possibility, analysis of the role of JH and its signaling pathway was performed in the termite Zootermopsis nevadensis and compared with the wood roach Cryptocercus punctulatus, a member of the sister group of termites. Treatment with a JH analog (JHA) induced a nymphal molt in C. punctulatus RNA interference (RNAi) of JH receptor Methoprene tolerant (Met) was then performed, and it inhibited the presoldier molt in Z. nevadensis and the nymphal molt in C. punctulatus Knockdown of Met in both species inhibited expression of 20-hydroxyecdysone (20E; the active form of ecdysone) synthesis genes. However, in Z. nevadensis, several 20E signaling genes were specifically inhibited by Met RNAi. Consequently, RNAi of these genes were performed in JHA-treated termite individuals. Knockdown of 20E signaling and nuclear receptor gene, Hormone receptor 39 (HR39/FTZ-F1β) resulted in newly molted individuals with normal worker phenotypes. This is the first report of the JH-Met signaling feature in termites and Cryptocercus JH-dependent molting activation is shared by both taxa and mediation between JH receptor and 20E signalings for soldier morphogenesis is specific to termites.

The Insect Growth Regulator Pyriproxyfen Terminates Egg Diapause in the Asian Tiger Mosquito, Aedes albopictus

The Asian tiger mosquito, Aedes albopictus, is a highly invasive mosquito species that transmits chikungunya and dengue. This species overwinters as diapausing eggs in temperate climates. Early diapause termination may be a beneficial strategy for winter mosquito control; however, a mechanism to terminate the diapause process using chemicals is not known. We tested the hypothesis that a hormonal imbalance caused by the administration of juvenile hormone analog would terminate egg diapause in A. albopictus. We tested the insect growth regulator pyriproxyfen on all developmental stages to identify a susceptible stage for diapause termination. We found that pyriproxyfen treatment of mosquito eggs terminated embryonic diapause. The highest rates of diapause termination were recorded in newly deposited (78.9%) and fully embryonated (74.7%) eggs at 0.1 and 1 ppm, respectively. Hatching was completed earlier in newly deposited eggs (25-30 days) compared to fully embryonated eggs (71-80 days). The combined mortality from premature diapause termination and ovicidal activity was 98.2% in newly deposited and >98.9% in fully embryonated eggs at 1 ppm. The control diapause eggs did not hatch under diapausing conditions. Pyriproxyfen exposure to larvae, pupae and adults did not prevent the females from ovipositing diapausing eggs. There was no effect of pyriproxyfen on diapausing egg embryonic developmental time. We also observed mortality in diapausing eggs laid by females exposed to pyriproxyfen immediately after blood feeding. There was no mortality in eggs laid by females that survived larval and pupal exposures. In conclusion, diapausing eggs were the more susceptible to pyriproxyfen diapause termination compared to other life stages. This is the first report of diapause termination in A. albopictus with a juvenile hormone analog. We believe our findings will be useful in developing a new control strategy against overwintering mosquito populations.

Differentially expressed genes in the ovary of the sixth day of pupal "Ming" lethal egg mutant of silkworm, Bombyx mori

The "Ming" lethal egg mutant (l-em) is a vitelline membrane mutant in silkworm, Bombyx mori. The eggs laid by the l-em mutant lose water, ultimately causing death within an hour. Previous studies have shown that the deletion of BmEP80 is responsible for the l-em mutation in silkworm, B. mori. In the current study, digital gene expression (DGE) was performed to investigate the difference of gene expression in ovaries between wild type and l-em mutant on the sixth day of the pupal stage to obtain a global view of gene expression profiles using the ovaries of three l-em mutants and three wild types. The results showed a total of 3,463,495 and 3,607,936 clean tags in the wild type and the l-em mutant libraries, respectively. Compared with those of wild type, 239 differentially expressed genes were detected in the l-em mutant, wherein 181 genes are up-regulated and 58 genes are down-regulated in the mutant strain. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis results showed that no pathway was significantly enriched and three pathways are tightly related to protein synthesis among the five leading pathways. Moreover, the expression profiles of eight important differentially expressed genes related to oogenesis changed. These results provide a comprehensive gene expression analysis of oogenesis and vitellogenesis in B. mori which facilitates understanding of both the specific molecular mechanism of the 1-em mutant and Lepidopteran oogenesis in general.

Early manipulation of juvenile hormone has sexually dimorphic effects on mature adult behavior in Drosophila melanogaster

Hormones are critical for the development, maturation, and maintenance of physiological systems; therefore, understanding their involvement during maturation of the brain is important for the elucidation of mechanisms by which adults become behaviorally competent. Changes in exogenous and endogenous factors encountered during sexual maturation can have long lasting effects in mature adults. In this study, we investigated the role of the gonadotropic hormone, juvenile hormone (JH), in the modulation of adult behaviors in Drosophila. Here we utilized methoprene (a synthetic JH analog) and precocene (a JH synthesis inhibitor) to manipulate levels of JH in sexually immature male and female Drosophila with or without decreased synthesis of neuronal dopamine (DA). Locomotion and courtship behavior were assayed once the animals had grown to sexual maturity. The results demonstrate a sexually dimorphic role for JH in the modulation of these centrally controlled behaviors in mature animals that is dependent on the age of the animals assayed, and present DA as a candidate neuronal factor that differentially interacts with JH depending on the sex of the animal. The data also suggest that JH modulates these behaviors through an indirect mechanism. Since gonadotropic hormones and DA interact in mammals to affect brain development and later function, our results suggest that this mechanism for the development of adult behavioral competence may be evolutionarily conserved.

Juvenile hormone action through a defined enhancer motif to modulate ecdysteroid-activation of natural core promoters

We have established a model system of hormone action, in an Sf9 cell transfection system, using defined enhancer motifs and natural core promoters of metamorphosis-associated genes. The DR1 enhancer, that is an established DNA binding site for the ecdysone receptor/ultraspiracle heterodimer, was necessary for transcriptional activation by 20-OH ecdysone. For this activated transcription, a natural sequence closely 5' to the TATA box is necessary. Cotreatment with juvenile hormone III strongly suppressed the steroid activation of transcription. However, in the absence of the sequence located closely 5' to the TATA box, cotreatment with juvenile hormone instead increased transcription over that occurring due to 20-hydroxy-ecdysone alone. This sensitivity to activation by cotreatment with juvenile hormone could be transferred to a related, but otherwise unresponsive, hexamerin core promoter simply by transferring to the unresponsive promoter the five base transcription start site (ACAGT) from the responsive hexamerin gene. These are the first reports that the direction of JH action on 20-OH ecdysone-activated transcription can be reversed by removal of a sequence at the core promoter, and that modulatory action of juvenile hormone can be transferred to a different gene by transferring the transcription start site motif.

Identification and characterization of a juvenile hormone response element and its binding proteins

Juvenile hormones (JH) regulate a wide variety of developmental and physiological processes in insects. Comparison of microarray data on JH-induced genes in the fruit fly, Drosophila melanogaster, L57 cells and in the honey bee, Apis mellifera, identified 16 genes that are induced in both species. Analysis of promoter regions of these 16 D. melanogaster genes identified DmJHRE1 (D. melanogaster JH response element 1). In L57 cells, the reporter gene regulated by DmJHRE1 was induced by JH III. Two proteins (FKBP39 and Chd64) that bind to DmJHRE1 were identified. FKBP39 and Chd64 double-stranded RNA inhibited JH III induction of a reporter gene regulated by DmJHRE1. FKBP39 and Chd64 proteins expressed in yeast bound to DmJHRE1. Two-hybrid and pull-down assays showed that these two proteins interact with each other as well as with ecdysone receptor, ultraspiracle, and methoprene-tolerant protein. Developmental expression profiles and JH induction of mRNA for FKBP39 and Chd64 proteins and their interaction with proteins known to be involved in both JH (methoprene-tolerant protein) and ecdysteroid action (ecdysone receptor and ultraspiracle) suggest that these proteins probably play important roles in cross-talk between JH and ecdysteroids.

Characterization and expression patterns of let-7 microRNA in the silkworm (Bombyx mori)

BACKGROUND

lin-4 and let-7, the two founding members of heterochronic microRNA genes, are firstly confirmed in Caenorhabditis elegans to control the proper timing of developmental programs in a heterochronic pathway. let-7 has been thought to trigger the onset of adulthood across animal phyla. Ecdysone and Broad-Complex are required for the temporal expression of let-7 in Drosophila melanogaster. For a better understanding of the conservation and functions of let-7, we seek to explore how it is expressed in the silkworm (Bombyx mori).

RESULTS

One member of let-7 family has been identified in silkworm computationally and experimentally. All known members of this family share the same nucleotides at ten positions within the mature sequences. Sequence logo and phylogenetic tree show that they are not only conserved but diversify to some extent among some species. The bmo-let-7 was very lowly expressed in ova harvested from newborn unmated female adult and in individuals from the first molt to the early third instar, highly expressed after the third molt, and the most abundant expression was observed after mounting, particularly after pupation. The expression levels were higher at the end of each instar and at the beginning of each molt than at other periods, coinciding with the pulse of ecdysone and BR-C as a whole. Using cultured ovary cell line, BmN-SWU1, we examined the effect of altered ecdysone levels on bmo-let-7 expression. The expression was also detected in various tissues of day 3 of the fifth instar and of from day 7 of the fifth to pupa, suggesting a wide distributing pattern with various signal intensities.

CONCLUSION

bmo-let-7 is stage- and tissue-specifically expressed in the silkworm. Although no signals were detected during embryonic development and first larval instar stages, the expression of bmo-let-7 was observed from the first molt, suggesting that it might also function at early larval stage of the silkworm. The detailed expression profiles in the whole life cycle and cultured cell line of silkworm showed a clear association with ecdysone pulse and a variety of biological processes.

Evolution of sexual dimorphism and male dimorphism in the expression of beetle horns: phylogenetic evidence for modularity, evolutionary lability, and constraint

Beetle horns are enlarged outgrowths of the head or thorax that are used as weapons in contests over access to mates. Horn development is typically confined to males (sexual dimorphism) and often only to the largest males (male dimorphism). Both types of dimorphism result from endocrine threshold mechanisms that coordinate cell proliferation near the end of the larval period. Here, we map the presence/absence of each type of dimorphism onto a recent phylogeny for the genus Onthophagus (Coleoptera: Scarabaeidae) to explore how horn development has changed over time. Our results provide empirical support for several recent predictions regarding the evolutionary lability of developmental thresholds, including uncoupled evolution of alternative phenotypes and repeated fixation of phenotypes. We also report striking evidence of a possible developmental constraint. We show that male dimorphism and sexual dimorphism map together on the phylogeny; whenever small males have horns, females also have horns (and vice versa). We raise the possibility that correlated evolution of these two phenomena results from a shared element in their endocrine regulatory mechanisms rather than a history of common selection pressures. These results illustrate the type of insight that can be gained only from the integration of developmental and evolutionary perspectives.

Molecular Chaperones and the Epigenetics of Longevity and Cancer Resistance

The inherent immortality of embryonic stem cells demonstrates that replicative senescence as possibly the aging of species are epigenetic phenomena. The cellular level of expression of the housekeeping molecular chaperones correlates with longevity and cancer resistance of species. The chaperones are cancer antagonists by acting as genetic buffers, stabilizing the normal phenotype. Probably the progressive age-related silencing of the housekeeping genes contributes to the phenotype of aging, with the associated increase in cancer incidence. The present review concerns epigenetic chemical, immunological, and hormonal mechanisms, activating chaperone- and immune-response genes, which have proved effective in increasing longevity and cancer resistance. The relation of steroid hormone levels to species longevity, the anticarcinogenic activity of pregnancy hormones, and the influence of hormones on the longevity of social insects, illustrates the importance of hormonal mechanisms for the activation of longevity genes.

Glycine-rich protein genes, which encode a major component of the cuticle, have different developmental profiles from other cuticle protein genes in Bombyx mori

Three types of GRP (glycine-rich proteins) cDNAs were identified in the EST database of Bombyx mori. These came from 21 ESTs in the W3-stage wing disc EST library. We named them BmGRP1, BmGRP2 and BmGRP3. BmGRP1 and BmGRP2 had 57% identity in deduced amino acid sequences. Expression of all BmGRPs was observed in the epidermis at the fourth molting stage, and in the wing at pupation and mid-pupal stage. It is suggested that BmGRPs contribute to larval, pupal and adult cuticles together with other cuticle proteins. Transcripts of BmGRP2 increased after 7 days of pupal stage. BmGRP2 is suggested to construct adult trachea in the wing. Hormonal response of BmGRPs was compared with that of another group of cuticular protein genes, BMWCPs. BmGRPs were induced by a pulse of 20E. Induction of BmGRP3 was observed in W1 wing discs in the presence of JHA which was added with 20E, whereas that of BMWCP2 was inhibited in the presence of JHA. Induction of BmGRPs was observed in the wing discs of V3 and W1 stages, while that of BMWCP2 was not observed in the V3 wing discs. These differences between BMWCPs and BmGRPs in response to hormones at different developmental stages are discussed.

Characterization of the Drosophila Methoprene -tolerant gene product. Juvenile hormone binding and ligand-dependent gene regulation

Juvenile hormones (JHs) of insects are sesquiterpenoids that regulate a great diversity of processes in development and reproduction. As yet the molecular modes of action of JH are poorly understood. The Methoprene-tolerant (Met) gene of Drosophila melanogaster has been found to be responsible for resistance to a JH analogue (JHA) insecticide, methoprene. Previous studies on Met have implicated its involvement in JH signaling, although direct evidence is lacking. We have now examined the product of Met (MET) in terms of its binding to JH and ligand-dependent gene regulation. In vitro synthesized MET directly bound to JH III with high affinity (Kd = 5.3 +/- 1.5 nm, mean +/- SD), consistent with the physiological JH concentration. In transient transfection assays using Drosophila S2 cells the yeast GAL4-DNA binding domain fused to MET exerted JH- or JHA-dependent activation of a reporter gene. Activation of the reporter gene was highly JH- or JHA-specific with the order of effectiveness: JH III >> JH II > JH I > methoprene; compounds which are only structurally related to JH or JHA did not induce any activation. Localization of MET in the S2 cells was nuclear irrespective of the presence or absence of JH. These results suggest that MET may function as a JH-dependent transcription factor.

The homeodomain protein PBX participates in JH-related suppressive regulation on the expression of major plasma protein genes in the silkworm, Bombyx mori

In the silkworm, Bombyx mori, major plasma proteins referred to as 30K proteins are the most abundant proteins in the hemolymph of final (fifth) instar larvae. Surgical extirpation of corpora allata, the source of a juvenile hormone (JH), causes rapid accumulation of 30K proteins in the hemolymph of fourth instar larvae. The 30K protein 6G1 (30K6G1) gene was repressed in primary cultured fat body cells treated with a JH analog (JHA), methoprene. To identify the JH response element present in the promoter region of the 30K6G1 gene, we performed transfection analyses of the 5'-deletion mutants of the 30K6G1 gene using primary cultured fat body cells, gel retardation assays and in vivo footprinting analysis. The results from those analyses revealed that a JH response element exists in the sequence between positions -147 and -140. When the promoter construct mutated at positions -143, -142, and -141 was transfected to fat body primary cultured cells, the suppression effect on the reporter gene expression caused by JHA was reduced. Gel retardation assay using specific antibody revealed that a PBX protein binds to the JH response element. Northern blot analysis revealed that the gene expression of Bombyx PBX is enhanced in the fat body cells by JHA treatment. These results indicate that PBX proteins are involved in the JH signaling pathway and play an important role in suppressing 30K protein gene expression in the fat body of B. mori.

Cross communication between signaling pathways: juvenoid hormones modulate ecdysteroid activity in a crustacean

Methyl farnesoate is a juvenoid hormone that regulates a variety of processes in crustaceans including male sex determination among daphnids (Branchiopoda, Cladocera). The synthetic juvenoids pyriproxyfen and fenoxycarb mimic the action of methyl farnesoate in daphnids. In the present study we tested the hypothesis that juvenoids also can regulate ecdysteroid activity in a crustacean (Daphnia magna). Methyl farnesoate, pyriproxyfen, and fenoxycarb all disrupted ecdysteroid-regulated aspects of embryo development in daphnids. Exposure of ecdysteroid-responsive cells to 20-hydroxyecdysone reduced cell proliferation and increased mRNA levels of the ecdysone receptor and its partner protein ultraspiracle. Co-treatment of cells with the juvenoid pyriproxyfen attenuated all of these ecdysteroid mediated responses. While juvenoids functioned as anti-ecdysteroids in both intact embryos and in cultured cells, 20-hydroxyecdysone showed no evidence of acting as an anti-juvenoid. The combined effects of pyroproxyfen with the ecdysteroid synthesis inhibitor fenarimol and the ecdysteroid receptor antagonist testosterone were evaluated in an effort to discern whether the action of the juvenoids were additive with those of know anti-ecdysteroids. The anti-ecdysteroid effects of pyriproxyfen were non-additive with those of either anti-ecdysteroid. Rather, joint effects conformed to a model of synergy. These results demonstrated that juvenoids elicit anti-ecdysteroidal activity in a crustacean through a unique mechanism of action. A model involving receptor partner deprivation is proposed that explains the synergistic interactions observed.

Hormonal regulation and functional role of Drosophila E75A orphan nuclear receptor in the juvenile hormone signaling pathway

Ecdysone and juvenile hormone (JH) are important regulators of insect growth and development. While ecdysone initiates a transition from one developmental stage to another, JH determines the nature of the transition. How these two hormones interact at the molecular level is not known. Here we report the JH inducibility of the E75A nuclear receptor encoded by the E75 early ecdysone-inducible gene. In Drosophila S2 cells, E75A transcription is specifically activated by JH at concentrations well within the physiological range found in larvae and adults. The induction is rapid and does not require a concurrent protein synthesis, and thus represents a primary hormone response. Consistent with JH regulation, E75A mRNA levels are reduced in ovaries of apterous(4) mutant adults defective in JH secretion. Expression is rescued by topical methoprene application. We further provide evidence that ectopic E75A is sufficient to perform several functions in the JH signaling pathway. First, it can down-regulate its own transcription. Second, E75A can potentiate the JH inducibility of a secondary response gene, JhI-21. Finally, in the presence of JH, E75A can repress ecdysone activation of early genes including Broad-Complex. Based on these data, we propose a model for the role of E75A in the ecdysone-JH regulatory interplay.

The molecular site of action of juvenile hormone and juvenile hormone insecticides during metamorphosis: how these compounds kill insects

Studies in a variety of insects during the past four decades has deepened our understanding of juvenile hormone (JH) physiology, but how this hormone works at the molecular level remains elusive. Similarly, the mechanism of toxicity of JH analogue insecticides is still in question. There is much evidence from laboratory usage that JHAs act as JH agonists and generally show the highest toxicity when applied at the onset of metamorphosis. A physiological basis for the toxicity and morphogenetic effects has been suggested by recent work linking these effects with interference with the expression or action of certain genes, particularly the Broad-Complex (BR-C) transcription factor gene, that direct metamorphic change. Misexpressed BR-C then leads to improper expression of one or more downstream effector genes controlled by BR-C gene products, resulting in abnormal developmental and physiological changes that disrupt metamorphosis. Therefore, JH is a necessary molecule at certain times in insect development but becomes toxic when present during metamorphosis.

Temporal regulation of microRNA expression in Drosophila melanogaster mediated by hormonal signals and broad-Complex gene activity

lin-4 and let-7 are founding members of an extensive family of genes that produce small transcripts, termed microRNAs (miRNAs). In Caenorhabditis elegans, lin-4 and let-7 control the timing of postembryonic events by translational repression of target genes, permitting progression from early to late developmental programs. To identify Drosophila melanogaster miRNAs that could play similar roles in the control of developmental timing, we characterized the developmental expression profile of 24 miRNAs in Drosophila, and found 7 miRNAs that are either upregulated or downregulated in conjunction with metamorphosis. The upregulation of three of these miRNAs (mir-100, mir-125, and let-7), and the downregulation of a fourth (mir-34) requires the hormone ecdysone (Ecd) and the activity of the Ecd-inducible gene Broad-Complex. Interestingly, mir-125 is a putative homologue of lin-4. mir-100, -125, and let-7 are clustered within an 800-bp region on chromosome 2L, suggesting that these three miRNAs may be coordinately regulated via common cis-acting elements during metamorphosis. In S2 cells, Ecd and the juvenile hormone analog methoprene exert opposite effects on the expression of these four miRNAs, indicating the participation of both these hormones in the temporal regulation of mir-34, -100, -125, and let-7 expression in vivo.

The isolation of two juvenile hormone-inducible genes in Drosophila melanogaster

Juvenile hormone (JH) is an important regulator of both insect development and reproductive maturation. Although the molecular mechanism of JH action is not yet known, there is growing circumstantial evidence that JH directly regulates gene expression. In the absence of a JH target gene, however, this suggestion has remained speculative. Cultured Drosophila S2 cells have been used to identify genes whose expression is regulated by JH. Employing differential display we identified several genes whose transcripts accumulate in cells treated with the JH agonist methoprene. Two of the genes-JhI-1 and JhI-26-were cloned and characterized in detail. For both genes, transcripts showed rapid and specific induction in the presence of either methoprene or JHIII, but not in the presence of other biologically inactive compounds of similar chemical structure. Accumulation of JhI-1 and JhI-26 RNAs requires continuous hormone presence. The developmental expression of the two JH-inducible genes corresponds to the abundance profile of JH in vivo. Furthermore, topical methoprene application to pupae leads to the ectopic accumulation of JhI-1 and JhI-26 transcripts.

Stress-reactivity and juvenile hormone degradation in Drosophila melanogaster strains having stress-related mutations

Juvenile hormone (JH) degradation was studied under normal and stress conditions in young and matured females of Drosophila melanogaster strains having mutations in different genes involved in responses to stress It was shown that (1) the impairment in heat shock response elicits an alteration in stress-reactivity of the JH system; (2) the impairment JH reception causes a decrease of JH-hydrolysing activity and of stress-reactivity in young females, while in mature ones stress reactivity is completely absent; (3) the absence of octopamine results in higher JH-hydrolysis level under normal conditions and altered JH stress-reactivity; (4) the higher dopamine content elicits a dramatic decrease of JH degradation under normal conditions and of JH stress-reactivity. Thus, the impairments in any component of the Drosophila stress reaction result in changes in the reponse of JH degradation system to stress. The role of JH in the development of the insect stress reaction is discussed.

A juvenile hormone agonist reveals distinct developmental pathways mediated by ecdysone-inducible broad complex transcription factors

Juvenile hormone (JH) is an important regulator of insect development that, by unknown mechanisms, modifies molecular, cellular, and organismal responses to the molting hormone, 20-hydroxyecdysone (20E). In dipteran insects such as Drosophila, JH or JH agonists, administered at times near the onset of metamorphosis, cause lethality. We tested the hypothesis that the JH agonist methoprene acts by interfering with function of the Broad Complex (BRC), a 20E-regulated locus encoding BTB/POZ-zinc finger transcription factors essential for metamorphosis of many tissues. We found that methoprene, administered by feeding or by topical application, disrupts the metamorphic reorganization of the central nervous system, salivary glands, and musculature in a dose-dependent manner. As we predicted, methoprene phenocopies a subset of previously described BRC defects; it also phenocopies Deformed and produces abnormalities not associated with known mutations. Interestingly, methoprene specifically disrupts those metamorphic events dependent on the combined action of all BRC isoforms, while sparing those that require specific isoform subsets. Thus, our data provide independent pharmacological evidence for the model, originally based on genetic studies, that BRC proteins function in two developmental pathways. Mutations of Methoprene-tolerant (Met), a gene involved in the action of JH, protect against all features of the "methoprene syndrome." These findings have allowed us to propose novel alternative models linking BRC, juvenile hormone, and MET.

The effect of juvenile hormone on the response of the Drosophila imaginal disc cell line Cl 8+ to moulting hormone

The Drosophila wing imaginal disc cell line Cl 8+ was used to investigate the interaction between juvenile hormone III (JH) and 20-hydroxyecdysone (20HE). Cell cultures were exposed to either or both hormones at a range of concentrations and cell growth was observed. JH was found to ameliorate the effects of 20HE on cell growth, even when added after the cells had been exposed to 20HE for 4 or 24h.

Cloning and characterization of an ecdysone receptor cDNA from Locusta migratoria

To facilitate studies on the hormonal control of development in the migratory locust, Locusta migratoria, we have undertaken the cloning of cDNAs for nuclear hormone receptors. Sequences obtained by polymerase chain reaction (PCR) showed homology with receptor family members including the ecdysteroid receptor (EcR). A cDNA clone corresponding to the EcR fragment includes an open reading frame of 1622 nucleotides, predicting a 59 kDa protein showing clear homology with EcRs and distinct from other classes of nuclear receptors. Northern analysis revealed a major transcript of 9.2 kb. In fifth instar fat body, the transcript was most abundant at the end of the instar when ecdysone titres are highest. There was no obvious evidence of EcR regulation by a juvenile hormone analog. Although its role in development may be similar, the locust ecdysone receptor (LmEcR) is divergent from EcRs characterized from insects belonging to the dipteran and lepidopteran orders, presumably reflecting the more ancestral sequence in the relatively primitive locust.

Insect juvenile hormone resistance gene homology with the bHLH-PAS family of transcriptional regulators

Juvenile hormone analog (JHA) insecticides are relatively nontoxic to vertebrates and offer effective control of certain insect pests. Recent reports of resistance in whiteflies and mosquitoes demonstrate the need to identify and understand genes for resistance to this class of insect growth regulators. Mutants of the Methoprene-tolerant (Met) gene in Drosophila melanogaster show resistance to both JHAs and JH, and previous biochemical studies have demonstrated a mechanism of resistance involving an intracellular JH binding-protein that has reduced ligand affinity in Met flies. We cloned the Met+ gene by transposable P-element tagging and found reduced transcript level in several mutant alleles, showing that underproduction of the normal gene product can lead to insecticide resistance. Transformation of Met flies with a Met+ cDNA resulted in susceptibility to methoprene, indicating that the cDNA encodes a functional Met+ protein. MET shows homology to the basic helix-loop-helix (bHLH)-PAS family of transcriptional regulators, implicating MET in the action of JH at the gene level in insects. This family also includes the vertebrate dioxin receptor, a transcriptional regulator known to bind a variety of environmental toxicants. Because JHAs include a diverse array of chemicals with JH activity, a mechanism whereby they can exert effects in insects through a common pathway is suggested.

Juvenile hormone regulation of an insect gene: a specific transcription factor and a DNA response element

We have used locust fat body nuclear protein extracts and upstream DNA of the juvenile hormone (JH)-inducible locust gene, jhp21, to examine the regulation of specific transcription by JH. Promoter activity was assayed with G-free cassette reporter constructs. Nuclear extracts from adult female fat body, previously exposed to JH or an analog, actively transcribe from the jhp21 promoter and a control adenovirus major late (AdML) promoter, whereas extracts from JH-deprived female fat body, or other tissues, transcribe strongly from the AdML promoter but weakly or not at all from the jhp21 promoter. Transcription is enhanced by sequences between -140 and -211 nt from the jhp21 transcription start point (tsp), which include a CAAT box, and also by sequences between -1056 and -1200. A 15-nt partially palindromic sequence element found at -1152, resembling known hormone response elements, was shown to stimulate transcription when restored to truncated jhp21 DNA. Two very similar sequences occur further upstream. In electrophoretic mobility shift assays (EMSA), the same sequence element was shown to specifically bind a protein that was present in nuclear extracts from JH-exposed, but not from JH-deprived, fat body. Several lines of evidence suggest that the DNA element may be a JH response element (JHRE). The JH-induced protein that binds to it appears to be a transcription factor that activates the initiation of JH target gene (jhp21) transcription, and could be a JH receptor.

Insect nuclear receptors: a developmental and comparative perspective

The appearance of puffs on the polytene chromosomes of insect salivary glands incubated with 20-hydroxyecdysone provided the first demonstration that steroids act directly at the gene transcriptional level to bring about subsequent cellular changes (Becker, 1959; Clever and Karlson, 1960). Despite that auspicious beginning, learning about the molecular mechanisms that underlie the hormonal regulation of insect development was impeded for many years by the difficulty associated with isolating and identifying rare regulatory factors from limited tissue sources. The advent of recombinant DNA methodology and powerful techniques such as the polymerase chain reaction (PCR) along with the recognition that many important endocrine factors are structurally conserved across a wide range of species has, however, all but eliminated the technical obstacles once facing the insect endocrinologist trying to isolate and study these regulatory molecules. This review will discuss recent progress and recall some earlier experiments concerning the molecular basis of hormonal action in insects focusing primarily on the members of the nuclear hormone receptor superfamily in Drosophila melanogaster. Two members of this family comprise the functional ecdysteroid receptor and at least a dozen other "orphans" have been identified in Drosophila for which no cognate ligand has yet been found. Many of these orphans are regulated by ecdysteroids. A discussion of juvenile hormone binding proteins that are not family members has been included because of their potential impact on nuclear receptor function. As receptor homologues have been identified in other insects, several general ideas concerning insect hormonal regulation have begun to emerge and these will be examined from a comparative point of view.

Ecdysteroid-dependent protein synthesis in caste-specific development of the larval honey bee ovary

In the honey bee, Apis mellifera, the fifth larval instar is a critical period for caste differentiation. During this premetamorphic phase the hormonal milieu shows pronounced caste differences and several organs, particularly the ovaries, enter different developmental pathways leading to highly fertile queens and nearly sterile workers. Developmental profiles of total protein synthesis in larval ovaries showed marked caste differences starting with the early fifth instar. By two-dimensional electrophoresis, caste-specific patterns could be detected in the synthesis of a 29 kDa/pI 4.6 and two 24 kDa/pI 5.2-5.5. proteins (pI=isoelectric point). A marked decrease in the expression of these proteins was found to coincide with caste-specific differences in the haemolymph ecdysteroid titer. In vitro exposure of larval worker ovaries to physiological (10^-7 M) concentrations of synthetic makisterone A elicited an identical response. Juvenile hormone did not affect protein synthesis patterns in larval ovaries, and also did not inhibit or reverse the ecdysteroid-induced effects. Heat shock experiments revealed that the 29 kDa/pI 4.6 ecdysteroid-regulated protein belongs to the class of small heat shock proteins.

Regulation of juvenile hormone esterase gene transcription by juvenile hormone

Juvenile hormone (JH) is a major hormone regulating insect development. We have obtained a cDNA and a genomic clone for juvenile hormone esterase (JHE), the enzyme that is involved in the degradation of juvenile hormone and which is critical for insect development. Analysis of the regulation of JHE during the final larval stadium in the cabbage looper, Trichoplusia ni, showed that the JHE mRNA levels are maximal on days 2 and 4 of the final stadium. Nuclear run-on analyses demonstrated that changes in JHE mRNA levels are primarily due to changes in the transcription rate of the gene, which may be a single copy in the genome. Treatment with a JH analog resulted in induction of JHE gene transcription, which could be detected within three hours after treatment. Salient features present in the 5' flanking region of this JH-sensitive gene are presented, including the presence of sequences closely resembling binding sites for members of the family of nuclear receptors. This report is the first direct demonstration, by nuclear run-on analysis, of JH induction of gene transcription.