A nuclear juvenile hormone-binding protein from larvae of Manduca sexta: a putative receptor for the metamorphic action of juvenile hormone

Cloning, expression analysis and RNAi of farnesoic acid O-methylransferase gene from Neocaridina denticulata sinensis

Methyl farnesoate (MF) is an essential endocrine hormone in crustaceans, which can promote the occurrence of crustaceans molting, control morphogenesis, affect gonad development, and regulate the stress stimulation to the external environment. The farnesoic acid O-methyltransferase (FAMeT) is a key rate-limiting enzyme in MF synthesis, catalyzing the conversion of farnesoic acid (FA) into MF. Neocaridina denticulata sinensis [Decapoda] is a suitable animal model for studying crustaceans because it can reproduce many times under artificial control and has a short reproductive cycle. According to its transcriptomic and genomic information, the full-length cDNA sequence of FAMeT from N. denticulata sinensis (NdFAMeT) was cloned and the characterization of its deduced amino acid sequence was also analyzed. The relative expression of NdFAMeT in different tissues was determined. The NdFAMeT protein was recombinantly expressed in E. coli and its enzyme activity was determined. After gene knockdown by RNAi technology, the protein activity of shrimp was decreased and the individual phenotype was also observed.

Rhodnius, Golden Oil, and Met: A History of Juvenile Hormone Research

Juvenile hormone (JH) is a unique sesquiterpenoid hormone which regulates both insect metamorphosis and insect reproduction. It also may be utilized by some insects to mediate polyphenisms and other life history events that are environmentally regulated. This article details the history of the research on this versatile hormone that began with studies by V. B. Wigglesworth on the "kissing bug" Rhodnius prolixus in 1934, through the discovery of a natural source of JH in the abdomen of male Hyalophora cecropia moths by C. M. Williams that allowed its isolation ("golden oil") and identification, to the recent research on its receptor, termed Methoprene-tolerant (Met). Our present knowledge of cellular actions of JH in metamorphosis springs primarily from studies on Rhodnius and the tobacco hornworm Manduca sexta, with recent studies on the flour beetle Tribolium castaneum, the silkworm Bombyx mori, and the fruit fly Drosophila melanogaster contributing to the molecular understanding of these actions. Many questions still need to be resolved including the molecular basis of competence to metamorphose, differential tissue responses to JH, and the interaction of nutrition and other environmental signals regulating JH synthesis and degradation.

A Life's Journey Through Insect Metamorphosis

This autobiographical article describes the research career of Lynn M. Riddiford from its early beginnings in a summer program for high school students at Jackson Laboratory to the present "retirement" at the Friday Harbor Laboratories. The emphasis is on her forays into many areas of insect endocrinology, supported by her graduate students and postdoctoral associates. The main theme is the hormonal regulation of metamorphosis, especially the roles of juvenile hormone (JH). The article describes the work of her laboratory first in the elucidation of the endocrinology of the tobacco hornworm, Manduca sexta, and later in the molecular aspects of the regulation of cuticular and pigment proteins and of the ecdysone-induced transcription factor cascade during molting and metamorphosis. Later studies utilized Drosophila melanogaster to answer further questions about the actions of JH.

Combining RNA-seq and proteomic profiling to identify seminal fluid proteins in the migratory grasshopper Melanoplus sanguinipes (F)

BACKGROUND

Seminal fluid proteins control many aspects of fertilization and in turn, they play a key role in post-mating sexual selection and possibly reproductive isolation. Because effective proteome profiling relies on the availability of high-quality DNA reference databases, our knowledge of these proteins is still largely limited to model organisms with ample genetic resources. New advances in sequencing technology allow for the rapid characterization of transcriptomes at low cost. By combining high throughput RNA-seq and shotgun proteomic profiling, we have characterized the seminal fluid proteins secreted by the primary male accessory gland of the migratory grasshopper (Melanoplus sanguinipes), one of the main agricultural pests in central North America.

RESULTS

Using RNA sequencing, we characterized the transcripts of ~ 8,100 genes expressed in the long hyaline tubules (LHT) of the accessory glands. Proteomic profiling identified 353 proteins expressed in the long hyaline tubules (LHT). Of special interest are seminal fluid proteins (SFPs), such as EJAC-SP, ACE and prostaglandin synthetases, which are known to regulate female oviposition in insects.

CONCLUSIONS

Our study provides new insights into the proteomic components of male ejaculate in Orthopterans, and highlights several important patterns. First, the presence of proteins that lack predicted classical secretory tags in accessory gland proteomes is common in male accessory glands. Second, the products of a few highly expressed genes dominate the accessory gland secretions. Third, accessory gland transcriptomes are enriched for novel transcripts. Fourth, there is conservation of SFPs' functional classes across distantly related taxonomic groups with very different life histories, mating systems and sperm transferring mechanisms. The identified SFPs may serve as targets of future efforts to develop species- specific genetic control strategies.

Effects of retinoids and juvenoids on moult and on phenoloxidase activity in the blood-sucking insect Rhodnius prolixus

Retinoic acid and insect juvenile hormone (JH) are structurally related terpenoids which are widespread in nature and are involved in many biological events such as morphogenesis, embryogenesis and cellular differentiation. Here, we investigated the effects of the retinoids 9-cis retinoic acid (9cisRA), all trans retinol (atROH), all trans retinoic acid (atRA) and the juvenoids methoprene (Met) and JH injection on moult and on phenoloxidase activity in the blood-sucking insect Rhodnius prolixus. Overall, we observed that injection of retinoids or juvenoids (120 pmols) in the hemocoel of 4th instar nymphs reduced the percentage of insects which appeared normal in morphology upon moult. Noteworthy, insects exposed to 9cisRA or JH underwent profound morphological changes upon moult, generating abnormal 5th instar nymphs and also markedly increased the death of insects during the moulting process. In addition, reduction in the percentage of insects that moult without any morphological alteration, induced by retinoids or juvenoids treatment, was negatively correlated with insects that both display abnormal moult and those that die during moult. Hemolymphatic phenoloxidase activity in adult male insects injected with 9cisRA, Met and JH were significantly reduced after a bacterial challenge. Together, these results indicate that not only juvenoids but also retinoids play an important role on morphogenesis and on immune response in R. prolixus, suggesting that the molecular mechanisms involved in these events recognize the terpenoid backbone as an important structural determinant in insects.

Control of juvenile hormone biosynthesis in Bombyx mori: cloning of the enzymes in the mevalonate pathway and assessment of their developmental expression in the corpora allata

We have isolated the cDNAs of all enzymes involved in the mevalonate pathway portion of the juvenile hormone (JH) biosynthetic pathway in Bombyx mori, i.e., those responsible for the formation of farnesyl diphosphate from acetyl-CoA. There is a single gene encoding each enzyme of this pathway, with the exception of farnesyl diphosphate synthase (FPPS), for which we identified three homologs. All but two of these enzymes are expressed almost exclusively in the corpora allata (CA), as indicated by quantitative RT-PCR analyses. Phosphomevalonate kinase (MevPK) was expressed in many tissues, including the CA. In day 2 4th instars, FPPS1 expression was detected primarily in the Malpighian tubules, but expression of the structurally related FPPS2 and FPPS3 occurred mainly in the CA. Since FPPS3 transcripts were 55 times less abundant than those of FPPS2, the latter is expected to play a major role in JH biosynthesis at this stage. Studies on the developmental expression of these enzymes in the CA showed that the levels of all transcripts were high during the 4th instar larvae, a stage at which in vitro JH biosynthesis was high. However, the transcripts of all the mevalonate enzymes declined to low levels and JH acid O-methyltransferase (JHAMT) transcript disappeared by day 3 when CA ceased JH production after the final larval molt. The CA did not synthesize JH during the pupal stage, coincident with the limited expression of mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate kinase and isopentenyl diphosphate isomerase, and the inactivation of the JHAMT gene. Only female CA produced JH in the adult stage, a feature associated with the re-expression of JHAMT in female but little in male adult CA. Altogether, our results point to a relationship between JH biosynthesis and expression of most JH biosynthetic enzymes in the CA.

Development of a real-time PCR assay for measurement of yellow protein mRNA transcription in the desert locust Schistocerca gregaria: a basis for isolation of a peptidergic regulatory factor

A major unresolved issue in insect endocrinology concerns the question of whether or not insects have sex hormones. Conclusive evidence in favor of the presence of such hormones awaits the establishment of appropriate bioassays in males. The cuticle of sexually mature males of the desert locust Schistocerca gregaria turns yellow in gregarious conditions only. Neither females nor isolated males ever turn yellow. The yellowing is due to the deposition in the cuticle of a male-specific Yellow Protein (YP), of which the amino acid sequence is known. In this paper, we describe the partial cloning of the cDNA encoding this Yellow Protein. The tissue distribution and temporal expression of the YP-mRNA is studied in detail using RT-PCR. Furthermore, an RT-PCR based bioassay was developed, which may serve as a reliable tool to help identify the hormones controlling the yellowing process. In addition to juvenile hormone, we have shown that a factor present in the brain-corpora cardiaca is involved in the yellow coloration, as injection of an extract induces the expression of YP-mRNA in isolated gregarious males.

Cloning and expression analysis of takeout/JHBP family genes of silkworm, Bombyx mori

A Bombyx EST cDNA database was searched using the Drosophila takeout gene and nine cDNAs were obtained. The homology search suggested that these genes are widespread in insects and organize a large gene family, and that they have hydrophobic ligands. A phylogenetic tree indicated that the genes are first divided into two large groups, juvenile hormone binding protein and other protein genes, and the latter group diversified within a short time at an early stage. The expression study of five Bombyx genes indicated that they are expressed in various tissues and are regulated by development and feeding conditions. The Bombyx genes might have roles related to the regulation of metabolism, growth or development related to nutritional conditions.

Comparative genomics of insect juvenile hormone biosynthesis

The biosynthesis of insect juvenile hormone (JH) and its neuroendocrine control are attractive targets for chemical control of insect pests and vectors of disease. To facilitate the molecular study of JH biosynthesis, we analyzed ESTs from the glands producing JH, the corpora allata (CA) in the cockroach Diploptera punctata, an insect long used as a physiological model species and compared them with ESTs from the CA of the mosquitoes Aedes aegypti and Anopheles albimanus. The predicted genes were analyzed according to their probable functions with the Gene Ontology classification, and compared to Drosophila and Anopheles gambiae genes. A large number of reciprocal matches in the cDNA libraries of cockroach and mosquito CA were found. These matches defined known and suspected enzymes of the JH biosynthetic pathway, but also several proteins associated with signal transduction that might play a role in the modulation of JH synthesis by neuropeptides. The identification in both cockroach and mosquito CA of homologs of the small ligand binding proteins from insects, Takeout/JH binding protein and retinol-binding protein highlights a hitherto unsuspected complexity of metabolite trafficking, perhaps JH precursor trafficking, in these endocrine glands. Furthermore, many reciprocal matches for genes of unknown function may provide a fertile ground for an in-depth study of allatal-specific cell physiology. ESTs are deposited in GenBank under the accession numbers DV 017592-DV 018447 (Diploptera punctata); DR 746432-DV 747949 (Aedes aegypti); and DR 747950-DR 748310 (Anopheles albimanus).

Microarray-based survey of a subset of putative olfactory genes in the mosquito Anopheles gambiae

Female Anopheles gambiae mosquitoes respond to odours emitted from humans in order to find a blood meal, while males are nectar feeders. This complex behaviour is controlled at several levels, but is probably initiated by the interaction of various molecules in the antennal sensilla. Important molecules in the early odour recognition events include odourant binding proteins (OBPs), which may be involved in odour molecule transport, odourant receptors (ORs) that are expressed in the chemosensory neurones and odour degrading enzymes (ODEs). To obtain a better understanding of the expression patterns of genes that may be involved in host odour reception in females, we generated a custom microarray to study their steady state mRNA levels in chemosensory tissues, antennae and palps. These results were supported by quantitative RT PCR. Our study detected several OBPs that are expressed at significantly higher levels in antennae and palps of females vs. males, while others showed the opposite expression pattern. Most OBPs are slightly down-regulated 24 h after blood feeding, but some, especially those with higher expression levels in males, are up-regulated in blood-fed females, suggesting a shift in blood-fed females from human host seeking to nectar feeding.

Identification and characterization of a juvenile hormone (JH) response region in the JH esterase gene from the spruce budworm, Choristoneura fumiferana

Using a differential display of mRNA technique we discovered that the juvenile hormone (JH) esterase gene (Cfjhe) from Choristoneura fumiferana is directly induced by juvenile hormone I (JH I), and the JH I induction is suppressed by 20-hydroxyecdysone (20E). To study the mechanism of action of these two hormones in the regulation of expression of this gene, we cloned the 1270-bp promoter region of the Cfjhe gene and identified a 30-bp region that is located between -604 and -574 and is sufficient to support both JH I induction and 20E suppression. This 30-bp region contains two conserved hormone response element half-sites separated by a 4-nucleotide spacer similar to the direct repeat 4 element and is designated as a putative juvenile hormone response element (JHRE). In CF-203 cells, a luciferase reporter placed under the control of JHRE and a minimal promoter was induced by JH I in a dose- and time-dependent manner. Moreover, 20E suppressed this JH I-induced luciferase activity in a dose- and time-dependent manner. Nuclear proteins isolated from JH I-treated CF-203 cells bound to JHRE and the binding was competed by a 100-fold excess of the cold probe but not by 100-fold excess of double-stranded oligonucleotides of unrelated sequence. JH I induced/modified nuclear proteins prior to their binding to JHRE and 20E suppressed this JH I induction/modification. These results suggest that the 30-bp JHRE identified in the Cfjhe gene promoter is sufficient to support JH induction and 20E suppression of the Cfjhe gene.

Sexual dimorphic expression of putative antennal carrier protein genes in the malaria vector Anopheles gambiae

To obtain a better understanding of the olfactory processes that allow mosquitoes to identify human hosts, a molecular study has been performed to identify and characterize molecules in the olfactory signalling pathway of the African malaria vector Anopheles gambiae. Using cDNA libraries from antennae of females and males, a collection of cDNAs encoding odorant binding proteins and other novel antennal proteins were isolated and characterized, which represent various families of putative carrier proteins with homologues in other insects. Using filter array hybridizations and quantitative RT PCR, regulation and gender specificity of expression of these genes was investigated. Significant differences in steady-state levels of some of these putative carrier protein genes were detected between the sexes and after blood feeding in females.

A novel gene in the takeout gene family is regulated by hormones and nutrients in Manduca larval epidermis

A novel gene, moling, was cloned from epidermal RNA of the tobacco hornworm, Manduca sexta, using PCR-based suppression subtractive hybridization. moling belongs to a gene family that includes several lepidopteran hemolymph juvenile hormone (JH) binding proteins and takeout of Drosophila melanogaster. The mRNA first appears in the epidermis on day 0 of the fifth instar and rises to its peak expression by mid-day 2, then declines rapidly and is gone by the onset of wandering. moling is expressed exclusively in the last instar larval epidermis and not in the imaginal discs or any other tissues. Allatectomy early in the fourth instar induces precocious metamorphosis and causes the appearance of moling mRNA by 33 h. Allatectomy after the critical period for JH in the final larval molt had no effect on the timing of the onset of moling expression in the final instar but caused a more rapid up-regulation once begun. The JH mimic pyriproxifen given at the outset of the final instar suppressed the expression of moling mRNA to low levels, in both intact and allatectomized larvae. Starvation immediately after ecdysis to the fifth instar prevented the onset of expression. Thus, initiation of transcription requires both nutrient intake and decline in JH. Infusion of 20-hydroxyecdysone (20E) into ligated abdomens of day 2 fifth instar larvae and culture of the day 2 fifth instar larval abdominal epidermis with 20E in vitro both caused a rapid decline of moling mRNA. The slower and variable decline that occurred in mid-day 2 fifth instar larval epidermis in the ligated abdomens or when incubated in hormone-free medium indicated that the increase of 20E on day 2 had already initiated the decline of expression. The role of Moling may be to stabilize JH in the epidermal cell during the final intermolt when the JH esterase activity increases.

Methoprene interferes with mosquito midgut remodeling during metamorphosis

Many juvenile hormone analogs interfere with insect metamorphosis, a property that makes them useful in insect control and as investigatorial tools with which to study metamorphic mechanisms. We report that one such analog, methoprene, interferes with mosquito metamorphic midgut remodeling. Methoprene treated Aedes aegypti (L.), Aedes albopictus (Skuse), and Culex quinquefasciatus (Say) fourth instars pupate, but the pupal midguts are morphologically similar to larval midguts. The degree of midgut remodeling is affected by the dose of methoprene applied and the extent of fourth instar development when methoprene exposure is initiated. DNA staining indicates that high methoprene concentrations interfere with diploid cell division and programmed death of polytene cells. Lower methoprene concentrations do not interfere with diploid cell division but the removal of polytene cells is incomplete. The effect of methoprene dose on the extent of midgut remodeling correlates well with its effect on pupal and adult survival. Metamorphic midgut remodeling offers a mosquito system with which to study the effect of ecdysone, juvenile hormone and juvenile hormone analogs on metamorphosis. An understanding of the molecular mechanisms by which methoprene affects mosquito metamorphosis might lead to the development of more effective mosquito control chemicals having fewer deleterious environmental effects and to genetic strategies by which mosquito populations might be controlled.

Sequence, structure and expression of the hemolymph juvenile hormone binding protein gene in the tobacco hornworm, Manduca sexta

The hemolymph juvenile hormone binding protein (hJHBP) gene of Manduca sexta is a key target of its specific ligand, juvenile hormone (JH). While the cDNA for hJHBP has been partially characterized, little is known about the hJHBP gene structure or its promoter(s) and enhancers(s). Previous studies have demonstrated that JH stimulates a rapid accumulation of hJHBP mRNA in the fat body. To better understand the underlying molecular events affecting regulation, we sequenced the M. sexta hJHBP gene and its mRNA transcript, characterized its genomic organization, and determined the spatial and temporal expression patterns of the hJHBP gene. The gene is composed of 5 exons spanning 6.7 kb. Southern blot analysis indicates that the gene is present as a single copy. The earliest expression of hJHBP occurs 24 to 48 h after fertilization. Distribution studies indicate that fat body is the only site for hJHBP expression. Elements displaying similarity with sequences of other lepidopteran genes were discovered outside the open reading frame and may represent mobile insertion elements.

Endocrine insights into the evolution of metamorphosis in insects

This review explores the roles of ecdysone and juvenile hormone (JH) in the evolution of complete metamorphosis and how metamorphosis, in turn, has impacted endocrine signaling. JH is a key player in the evolution of metamorphosis because it can act on embryos from more basal insect groups to suppress morphogenesis and cause premature differentiation, functions needed for transforming the transitional pronymphal stage of hemimetabolous insects into a functional larval stage. In the ancestral condition, imaginal-related growth is then delayed until JH finally disappears during the last larval instar. In the more derived groups of the Holometabola, selective tissues have escaped this JH suppression to form early-growing imaginal discs. We discuss how complete metamorphosis may have influenced the molecular aspects of both ecdysone and JH signaling.

Purification and sequence determination of a yellow protein from sexually mature males of the desert locust, Schistocerca gregaria

A yellow protein from abdominal cuticle of the desert locust, Schistocerca gregaria, has been purified and its amino acid sequence determined. The yellow color comes from bound carotene, the protein is only deposited in the epidermis and cuticle of male locusts during their sexual maturation, and the deposition is dependent upon a sufficiently high titer of juvenile hormone. The sequence of the protein is atypical for a cuticular protein, but it has some similarity to a putative juvenile hormone binding protein from Manduca sexta. It is suggested that the protein is involved in the transport of carotenes from internal tissues to epidermis and cuticle of the locust.

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.

Considerations on the structural evidence of a ligand-binding function of ultraspiracle, an insect homolog of vertebrate RXR

This analysis considers the structural evidence of a ligand-binding function of the nuclear receptor ultraspiracle (USP). The positions and nature of residues in the ligand-binding domain of USP from six higher insects is evaluated in comparison to the function of conserved residues vertebrate receptors that have been co-crystallized with ligand. USP appears to conserve residues that in vertebrate receptors (1) form the hydrophobic ligand-binding pocket, (2) contact oxygen-containing moieties on ligands, such as hydroxyl, keto and carboxyl groups, and (3) in response to ligand-binding conformationally change to form a multi-helix hydrophobic groove for recruitment of transcriptional co-activators. These structural features are consistent with the recent report that USP can bind the epoxymethylfarnesoates (juvenile hormones) and thereupon is induced to change conformation.

Insect pheromones--an overview of biosynthesis and endocrine regulation

This overview describes, compares, and attempts to unify major themes related to the biosynthetic pathways and endocrine regulation of insect pheromone production. Rather than developing and dedicating an entirely unique set of enzymes for pheromone biosynthesis, insects appear to have evolved to add one or a few tissue-specific auxiliary or modified enzymes that transform the products of "normal" metabolism to pheromone compounds of high stereochemical and quantitative specificity. This general understanding is derived from research on model species from one exopterygote insect order (Blattodea) and three endopterygote insect orders (Coleoptera, Diptera, and Lepidoptera). For instance, the ketone hydrocarbon contact sex pheromone of the female German cockroach, Blattella germanica, derives its origins from fatty acid biosynthesis, arising from elongation of a methyl-branched fatty acyl-CoA moiety followed by decarboxylation, hydroxylation, and oxidation. Coleopteran sex and aggregation pheromones also arise from modifications of fatty acid biosynthesis or other biosynthetic pathways, such as the isoprenoid pathway (e.g. Cucujidae, Curculionidae, and Scolytidae), or from simple transformations of amino acids or other highly elaborated host precursors (e.g. Scarabaeidae and Scolytidae). Like the sex pheromone of B. germanica, female-produced dipteran (e.g. Drosophilidae and Muscidae) sex pheromone components originate from elongation of fatty acyl-CoA moieties followed by loss of the carbonyl carbon and the formation of the corresponding hydrocarbon. Female-produced lepidopteran sex pheromones are also derived from fatty acids, but many moths utilize a species-specific combination of desaturation and chain-shortening reactions followed by reductive modification of the carbonyl carbon. Carbon skeletons derived from amino acids can also be used as chain initiating units and elongated to lepidopteran pheromones by this pathway (e.g. Arctiidae and Noctuidae). Insects utilize at least three hormonal messengers to regulate pheromone biosynthesis. Blattodean and coleopteran pheromone production is induced by juvenile hormone III (JH III). In the female common house fly, Musca domestica, and possibly other species of Diptera, it appears that during hydrocarbon sex pheromone biosynthesis, ovarian-produced ecdysteroids regulate synthesis by affecting the activities of one or more fatty acyl-CoA elongation enzyme(s) (elongases). Lepidopteran sex pheromone biosynthesis is often mediated by a 33 or 34 amino acid pheromone biosynthesis activating neuropeptide (PBAN) through alteration of enzyme activities at one or more steps prior to or during fatty acid synthesis or during modification of the carbonyl group. Although a molecular level understanding of the regulation of insect pheromone biosynthesis is in its infancy, in the male California fivespined ips, Ips paraconfusus (Coleoptera: Scolytidae), JH III acts at the transcriptional level by increasing the abundance of mRNA for 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme in de novo isoprenoid aggregation pheromone biosynthesis.

Juvenile hormone prevents ecdysteroid-induced expression of broad complex RNAs in the epidermis of the tobacco hornworm, Manduca sexta

A cDNA homolog of the Drosophila melanogaster Broad Complex (BRC) gene was isolated from the tobacco hornworm, Manduca sexta, which shows a predicted 88% amino acid identity with Drosophila BRC in the N-terminal BTB domain. Three zinc finger domains encoding homologs of the Drosophila Z2, Z3, and Z4 domains (93, 100, and 85% identity, respectively) were obtained by RT-PCR. In Manduca dorsal abdominal epidermis, BRC RNAs were not observed during the larval molt. Three BRC transcripts-6.0, 7.0, and 9.0 kb-first appeared at the end of the feeding stage of the fifth (final) instar when the epidermis is exposed to ecdysteroids in the absence of juvenile hormone (JH) and becomes committed to pupal differentiation. These RNAs were induced in day 2 fifth larval epidermis in vitro by 20-hydroxyecdysone (20E) in the absence of JH with dose-response and time courses similar to the induction of pupal commitment. This induction by 20E in vitro was prevented by the presence of JH I at levels seen in vivo during the larval molt. In the wing discs, the BRC RNAs appeared shortly after ecdysis to the fifth instar and coincided with the onset of metamorphic competence of these discs. Application of a JH analogue pyriproxifen during the fourth instar molt delayed and reduced the levels of BRC mRNAs seen in the wing discs in the early fifth instar, but did not completely prevent their appearance in this tissue that first differentiates at metamorphosis. The expression of the BRC transcription factors thus appears to be one of the first molecular indications of the genetic reprogramming of the epidermis necessary for insect metamorphosis. How JH prevents BRC expression in this epidermis may provide the key to understanding how this hormone controls metamorphosis.

Juvenile hormone: the status of its "status quo" action

Juvenile hormone (JH) allows larval molting in response to ecdysteroids but prevents the switching of gene expression necessary for metamorphosis. I first review our efforts to isolate the nuclear receptor for JH in the larval epidermis of Manduca sexta using photoaffinity analogs and our recent findings that the molecule isolated does not bind JH I with high affinity. The reported apparent high affinity binding of JH I by the recombinant 29 kDa protein (rJP29) was artifactual due to the presence of contaminating esterases. Purified rJP29 bound little detectable JH I, but its binding of the photoaffinity analog was prevented by JH I as well as other isoprenoids, indicating a low affinity for these compounds. Our recent studies focus on the effects of JH on the early molecular events induced by 20-hydroxyecdysone (20E). Culture of day 2 5th larval epidermis with 10(-6)M 20E for 24 h caused first pupal commitment, then the onset of the predifferentiative events necessary for pupation. Biphasic increases in the mRNAs of the two isoforms of the ecdysone receptor (EcR-A and EcR-B1) and of E75A, an ecdysteroid-induced transcription factor, coincided with these two phases. The mRNAs for Ultraspiracle (USP) and the metamorphosis-specific Broad-Complex (BR-C) increased only during the second phase. The presence of JH had no effect on the initial increases in EcR mRNAs but caused an increased accumulation of E75A mRNA. This JH also prevented the later changes in EcR, USP, and BR-C mRNAs. Thus, JH influences only certain of the early actions of 20E which then result in its preservation of the "status quo."

Biochemistry of proteins that bind and metabolize juvenile hormones

A diverse group of proteins has evolved to bind and metabolize insect juvenile hormones (JHs). Synthetic radiolabeled JHs and their photoaffinity analogs have enabled us to isolate and characterize JH binding proteins (JHBPs), a putative nuclear JH receptor, JH esterases (JHEs), JH epoxide hydrolases (JHEHs), and methyl farnesoate binding proteins (MFBPs). Highlights of recent progress on structural characterization of JHBPs and JHEHs of two lepidopterans will be described. Efforts to identify MFBPs of penaeid shrimp will be discussed, and the discovery of a possible vertebrate JHBP will be presented.

Seasonal changes in juvenile hormone titers and rates of biosynthesis in honey bees

Honey bee colonies can respond to changing environmental conditions by showing plasticity in age related division of labor, and these responses are associated with changes in juvenile hormone. The shift from nest tasks to foraging has been especially well characterized; foraging is associated with high juvenile hormone titers and high rates of juvenile hormone biosynthesis, and can be induced prematurely in young bees by juvenile hormone treatment or by a shortage of foragers. However, very few studies have been conducted that study plasticity in division of labor under naturally occurring changes in the environment. To gain further insight into how the environment and juvenile hormone influence foraging behavior, we measured juvenile hormone titers and rates of biosynthesis in workers during times of the year when colony activity in temperature climates is reduced: late fall, winter, and early spring. Juvenile hormone titers and rates of biosynthesis decreased in foragers in the fall as foraging diminished and bees became less active. This demonstration of a natural drop in juvenile hormone confirms and extends previous findings when bees were experimentally induced to revert from foraging to within-hive tasks. In addition, endocrine changes in foragers in the fall are part of a larger seasonally related phenomenon in which juvenile hormone levels in younger, pre-foraging bees also decline in the fall and then increase the following spring as colony activity increases. The seasonal decline in juvenile hormone in foragers was mimicked in summer by placing a honey bee colony in a cold room for 8 days. This suggests that seasonal changes in juvenile hormone are not related to photoperiod changes, but rather to changes in temperature and/or colony social structure that in turn influence endocrine and behavioral development. We also found that active foragers in the late winter and early spring had lower juvenile hormone levels than active foragers in late spring. In light of recent findings of a possible link between juvenile hormone and neuroanatomical plasticity in the bee brain, these results suggest that bees can forage with low juvenile hormone, after previous exposure to some threshold level of juvenile hormone leads to changes in brain structure.

Molecular analysis of the Methoprene-tolerant gene region of Drosophila melanogaster

Adult functions of juvenile hormone (JH) have been described for Drosophila melanogaster and other dipteran insects, but preadult function for this hormone remains largely unknown in this order of insects. We have identified a mutation of Drosophila, Methoprene-tolerant (Met), which appears to alter JH reception during late larval development. The molecular cloning of Met will be a step toward understanding this gene and possibly identifying a preadult role(s) for JH. Molecular cloning was initiated using the technique of transposon-tagging with a transposable P element. P-element insertional alleles of Met were generated, and genomic libraries were constructed from two of these alleles. From these libraries P-element-bearing clones were isolated that in situ hybridized to the cytogenetic region where Met had been previously localized by genetic methods. Two of the alleles were shown to have complete P-elements inserted in similar, but not identical, locations in the predicted cytogenetic region where Met is located. A late-larval cDNA library was screened to identify transcriptional units in this region, and clones were recovered with homology to a DNA fragment abutting the P-element insertion site. These clones may represent Met cDNA molecules.

Effects of experience and juvenile hormone on the organization of the mushroom bodies of honey bees

There is an age-related division of labor in the honey bee colony that is regulated by juvenile hormone. After completing metamorphosis, young workers have low titers of juvenile hormone and spend the first several weeks of their adult lives performing tasks within the hive. Older workers, approximately 3 weeks of age, have high titers of juvenile hormone and forage outside the hive for nectar and pollen. We have previously reported that changes in the volume of the mushroom bodies of the honey bee brain are temporally associated with the performance of foraging. The neuropil of the mushroom bodies is increased in volume, whereas the volume occupied by the somata of the Kenyon cells is significantly decreased in foragers relative to younger workers. To study the effect of flight experience and juvenile hormone on these changes within the mushroom bodies, young worker bees were treated with the juvenile hormone analog methoprene but a subset was prevented from foraging (big back bees). Stereological volume estimates revealed that, regardless of foraging experience, bees treated with methoprene had a significantly larger volume of neuropil in the mushroom bodies and a significantly smaller Kenyon cell somal region volume than did 1-day-old bees. The bees treated with methoprene did not differ on these volume estimates from untreated foragers (presumed to have high endogenous levels of juvenile hormone) of the same age sampled from the same colony. Bees prevented from flying and foraging nonetheless received visual stimulation as they gathered at the hive entrance. These results, coupled with a subregional analysis of the neuropil, suggest a potentially important role of visual stimulation, possibly interacting with juvenile hormone, as an organizer of the mushroom bodies. In an independent study, the brains of worker bees in which the transition to foraging was delayed (overaged nurse bees) were also studied. The mushroom bodies of overaged nurse bees had a Kenyon cell somal region volume typical of normal aged nurse bees. However, they displayed a significantly expanded neuropil relative to normal aged nurse bees. Analysis of the big back bees demonstrates that certain aspects of adult brain plasticity associated with foraging can be displayed by worker bees treated with methoprene independent of foraging experience. Analysis of the overaged nurse bees suggests that the post-metamorphic expansion of the neuropil of the mushroom bodies of worker honey bees is not a result of foraging experience.

Larva lights: a decade of photoaffinity labeling with juvenile hormone analogues

The introduction of photoaffinity labeling into the mode of action of insect hormones and pheromones started 12 yr ago with the photoaffinity labeling of juvenile hormone binding proteins (JHBPs) from cockroaches in the laboratory of the late John K. Koeppe. Applying this technique to Manduca sexta led ultimately to a three-laboratory collaborative project that has begun to dissect the molecular basis for JH transport, metabolism, and nuclear binding and gene activation in Lepidoptera. This review provides (1) a history of the first experiments; (2) an idea of the breadth of the technique in the arthropod classes Insecta, Crustacea, and Arachnida; and (3) evidence for the depth of the technique in unearthing key details about three different types of the molecular action of JH in M. sexta.