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

Receptor tyrosine kinases CAD96CA and FGFR1 function as the cell membrane receptors of insect juvenile hormone

Juvenile hormone (JH) is important to maintain insect larval status; however, its cell membrane receptor has not been identified. Using the lepidopteran insect Helicoverpa armigera (cotton bollworm), a serious agricultural pest, as a model, we determined that receptor tyrosine kinases (RTKs) cadherin 96ca (CAD96CA) and fibroblast growth factor receptor homologue (FGFR1) function as JH cell membrane receptors by their roles in JH-regulated gene expression, larval status maintaining, rapid intracellular calcium increase, phosphorylation of JH intracellular receptor MET1 and cofactor Taiman, and high affinity to JH III. Gene knockout of Cad96ca and Fgfr1 by CRISPR/Cas9 in embryo and knockdown in various insect cells, and overexpression of CAD96CA and FGFR1 in mammalian HEK-293T cells all supported CAD96CA and FGFR1 transmitting JH signal as JH cell membrane receptors.

Phylogenomics of the Ecdysteroid Kinase-like (EcKL) Gene Family in Insects Highlights Roles in Both Steroid Hormone Metabolism and Detoxification

The evolutionary dynamics of large gene families can offer important insights into the functions of their individual members. While the ecdysteroid kinase-like (EcKL) gene family has previously been linked to the metabolism of both steroid molting hormones and xenobiotic toxins, the functions of nearly all EcKL genes are unknown, and there is little information on their evolution across all insects. Here, we perform comprehensive phylogenetic analyses on a manually annotated set of EcKL genes from 140 insect genomes, revealing the gene family is comprised of at least 13 subfamilies that differ in retention and stability. Our results show the only two genes known to encode ecdysteroid kinases belong to different subfamilies and therefore ecdysteroid metabolism functions must be spread throughout the EcKL family. We provide comparative phylogenomic evidence that EcKLs are involved in detoxification across insects, with positive associations between family size and dietary chemical complexity, and we also find similar evidence for the cytochrome P450 and glutathione S-transferase gene families. Unexpectedly, we find that the size of the clade containing a known ecdysteroid kinase is positively associated with host plant taxonomic diversity in Lepidoptera, possibly suggesting multiple functional shifts between hormone and xenobiotic metabolism. Our evolutionary analyses provide hypotheses of function and a robust framework for future experimental studies of the EcKL gene family. They also open promising new avenues for exploring the genomic basis of dietary adaptation in insects, including the classically studied coevolution of butterflies with their host plants.

Social modulation of oogenesis and egg laying in Drosophila melanogaster

Being part of a group facilitates cooperation between group members but also creates competition for resources. This is a conundrum for gravid females, whose future offspring benefit from being in a group only if there are enough resources relative to group size. Females may therefore be expected to modulate reproductive output depending on social context. In the fruit fly Drosophila melanogaster, females actively attract conspecifics to lay eggs on the same resources, generating groups in which individuals may cooperate or compete. The genetic tractability of this species allows dissecting the mechanisms underlying physiological adaptation to social context. Here, we show that females produce eggs increasingly faster as group size increases. By laying eggs faster when grouped than when isolated, females reduce competition between offspring and increase offspring survival. In addition, grouped females lay eggs during the day, while isolated females lay them at night. We show that responses to the presence of others requires visual input and that flies from any sex, mating status, or species can trigger these responses. The mechanisms of this modulation of egg laying by group is connected to a lifting of the inhibition of light on oogenesis and egg laying, possibly mediated in part by an increase in juvenile hormone activity. Because modulation of reproduction by social context is a hallmark of animals with higher levels of sociality, our findings in a species considered solitary question the validity of this nomenclature and suggest a widespread and profound influence of social context on reproduction.

Brain adiponectin signaling controls peripheral insulin response in Drosophila

The brain plays a key role in energy homeostasis, detecting nutrients, metabolites and circulating hormones from peripheral organs and integrating this information to control food intake and energy expenditure. Here, we show that a group of neurons in the Drosophila larval brain expresses the adiponectin receptor (AdipoR) and controls systemic growth and metabolism through insulin signaling. We identify glucose-regulated protein 78 (Grp78) as a circulating antagonist of AdipoR function produced by fat cells in response to dietary sugar. We further show that central AdipoR signaling inhibits peripheral Juvenile Hormone (JH) response, promoting insulin signaling. In conclusion, we identify a neuroendocrine axis whereby AdipoR-positive neurons control systemic insulin response.

Circulating adiponectin controls sensitivity to insulin in tissues. Here, Arquier et al. show that adiponectin receptor activity in neurons of the Drosophila brain controls insulin response in peripheral tissues via juvenile hormone signaling.

Profiling Transcriptional Response of Dengue-2 Virus Infection in Midgut Tissue of Aedes aegypti

Understanding the mosquito antiviral response could reveal target pathways or genes of interest that could form the basis of new disease control applications. However, there is a paucity of data in the current literature in understanding antiviral response during the replication period. To illuminate the gene expression patterns in the replication stage, we collected gene expression data at 2.5 days after Dengue-2 virus (DENV-2) infection. We sequenced the whole transcriptome of the midgut tissue and compared gene expression levels between the control and virus-infected group. We identified 31 differentially expressed genes. Based on their function, we identified that those genes fell into two major functional categories - (1) nucleic acid/protein process and (2) immunity/oxidative stress response. Our study has identified candidate genes that can be followed up for gene overexpression/inhibition experiments to examine if the perturbed gene interaction may impact the mosquito’s immune response against DENV. This is an important step to understanding how mosquitoes eliminate the virus and provides an important foundation for further research in developing novel dengue control strategies.

Acetone application for administration of bioactive substances has no negative effects on longevity, fitness, and sexual communication in a parasitic wasp

Administration of defined amounts of bioactive substances is a perseverative problem in physiological studies on insects. Apart from feeding and injection, topical application of solutions of the chemicals is most commonly used for this purpose. The solvents used should be non-toxic and have least possible effects on the studied parameters. Acetone is widely used for administration of chemical substances to insects, but possible side-effects of acetone application on fitness and behavioral parameters have been rarely investigated. Here we study the effects of acetone application (207 nl) on fitness and sexual communication in the parasitic wasp Nasonia giraulti Darling. Application of acetone had neither negative effects on longevity nor on offspring number and offspring sex ratio of treated wasps. Treatment of females hampered courtship and mating of N. giraulti couples neither directly after application nor one day after. Male sex pheromone titers were not influenced by acetone treatment. Three application examples demonstrate that topical acetone application is capable of bringing active amounts of insect hormones, neuromodulators, and biosynthetic precursors even in tiny insects. We advocate the use of acetone as a convenient, conservative, and broadly applicable vehicle for studying the effects of bioactive substances in insects.

Genomic and transcriptomic analyses in Drosophila suggest that the ecdysteroid kinase-like (EcKL) gene family encodes the 'detoxification-by-phosphorylation' enzymes of insects

Phosphorylation is a phase II detoxification reaction that, among animals, occurs near exclusively in insects, but the enzymes responsible have never been cloned or otherwise identified. We propose the hypothesis that members of the arthropod-specific ecdysteroid kinase-like (EcKL) gene family encode detoxicative kinases. To test this hypothesis, we annotated the EcKL gene family in 12 species of Drosophila and explored their evolution within the genus. Many ancestral EcKL clades are evolutionarily unstable and have experienced repeated gene gain and loss events, while others are conserved as single-copy orthologs. Leveraging multiple published gene expression datasets from D. melanogaster, and using the cytochrome P450s-a classical detoxification family-as a test case, we demonstrate relationships between xenobiotic induction, detoxification tissue-enriched expression and evolutionary instability in the EcKLs and the P450s. We devised a systematic method for identifying candidate detoxification genes in large gene families that is concordant with experimentally determined functions of P450 genes in D. melanogaster. Applying this method to the EcKLs suggested a significant proportion of these genes play roles in detoxification, and that the EcKLs may constitute a detoxification gene family in insects. Additionally, we estimate that between 11 and 16 uncharacterised D. melanogaster P450s are strong detoxification candidates. Lastly, we also found previously unreported genomic and transcriptomic variation in a number of EcKLs and P450s associated with toxic stress phenotypes using a targeted phenome-wide association study (PheWAS) approach in D. melanogaster, presenting multiple future avenues of research for detoxification genetics in this species.

Drosophila female fertility and juvenile hormone metabolism depends on the type of Wolbachia infection

Maternally inherited intracellular bacteria Wolbachia cause both parasitic and mutualistic effects on their numerous insect hosts, including manipulating the host reproductive system in order to increase the bacteria spreading in a host population, and increasing the host fitness. Here, we demonstrate that the type of Wolbachia infection determines the effect on Drosophila melanogaster egg production as a proxy for fecundity, and metabolism of juvenile hormone (JH), which acts as gonadotropin in adult insects. For this study, we used six D. melanogaster lineages carrying the nuclear background of interbred Bi90 lineage and cytoplasmic backgrounds with or without Wolbachia of different genotype variants. The wMelCS genotype of Wolbachia decreases egg production in infected D. melanogaster females in the beginning of oviposition and increases it later (from the sixth day after eclosion), whereas the wMelPop Wolbachia strain causes the opposite effect, and the wMel, wMel2 and wMel4 genotypes of Wolbachia do not show any effect on these traits compared with uninfected Bi90 D. melanogaster females. The intensity of JH catabolism negatively correlates with the fecundity level in the flies carrying both wMelCS and wMelPop Wolbachia The JH catabolism in females infected with genotypes of the wMel group does not differ from that in uninfected females. The effects of wMelCS and wMelPop infection on egg production can be levelled by the modulation of JH titre (via precocene/JH treatment of the flies). Thus, at least one of the mechanisms promoting the effect of Wolbachia on D. melanogaster female fecundity is mediated by JH.

Wound healing, calcium signaling, and other novel pathways are associated with the formation of butterfly eyespots

Background

One hypothesis surrounding the origin of novel traits is that they originate from the co-option of pre-existing genes or larger gene regulatory networks into novel developmental contexts. Insights into a trait’s evolutionary origins can, thus, be gained via identification of the genes underlying trait development, and exploring whether those genes also function in other developmental contexts. Here we investigate the set of genes associated with the development of eyespot color patterns, a trait that originated once within the Nymphalid family of butterflies. Although several genes associated with eyespot development have been identified, the eyespot gene regulatory network remains largely unknown.

Results

In this study, next-generation sequencing and transcriptome analyses were used to identify a large set of genes associated with eyespot development of Bicyclus anynana butterflies, at 3-6 h after pupation, prior to the differentiation of the color rings. Eyespot-associated genes were identified by comparing the transcriptomes of homologous micro-dissected wing tissues that either develop or do not develop eyespots in wild-type and a mutant line of butterflies, Spotty, with extra eyespots. Overall, 186 genes were significantly up and down-regulated in wing tissues that develop eyespots compared to wing tissues that do not. Many of the differentially expressed genes have yet to be annotated. New signaling pathways, including the Toll, Fibroblast Growth Factor (FGF), extracellular signal–regulated kinase (ERK) and/or Jun N-terminal kinase (JNK) signaling pathways are associated for the first time with eyespot development. In addition, several genes involved in wound healing and calcium signaling were also found to be associated with eyespots.

Conclusions

Overall, this study provides the identity of many new genes and signaling pathways associated with eyespots, and suggests that the ancient wound healing gene regulatory network may have been co-opted to cells at the center of the pattern to aid in eyespot origins. New transcription factors that may be providing different identities to distinct wing sectors, and genes with sexually dimorphic expression in the eyespots were also identified.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4175-7) contains supplementary material, which is available to authorized users.

Targeted mutagenesis of Drosophila RNaseZ gene by homologous recombination

For the first time we used a homologous recombination method to obtain complete and precise deletion of Drosophila dRNaseZ gene. In the founder line of flies in which the RNaseZ sequence was replaced by attP site, the full-length sequence of the gene was reintegrated, and its functionality was shown. This approach will allow us to generate further gene mutations in different domains of dRNaseZ protein and discover a broad spectrum and uncover functions outside of tRNA processing.

The Amino Acid Transporter JhI-21 Coevolves with Glutamate Receptors, Impacts NMJ Physiology, and Influences Locomotor Activity in Drosophila Larvae

Changes in synaptic physiology underlie neuronal network plasticity and behavioral phenomena, which are adjusted during development. The Drosophila larval glutamatergic neuromuscular junction (NMJ) represents a powerful synaptic model to investigate factors impacting these processes. Amino acids such as glutamate have been shown to regulate Drosophila NMJ physiology by modulating the clustering of postsynaptic glutamate receptors and thereby regulating the strength of signal transmission from the motor neuron to the muscle cell. To identify amino acid transporters impacting glutmatergic signal transmission, we used Evolutionary Rate Covariation (ERC), a recently developed bioinformatic tool. Our screen identified ten proteins co-evolving with NMJ glutamate receptors. We selected one candidate transporter, the SLC7 (Solute Carrier) transporter family member JhI-21 (Juvenile hormone Inducible-21), which is expressed in Drosophila larval motor neurons. We show that JhI-21 suppresses postsynaptic muscle glutamate receptor abundance, and that JhI-21 expression in motor neurons regulates larval crawling behavior in a developmental stage-specific manner.

CDK8-Cyclin C Mediates Nutritional Regulation of Developmental Transitions through the Ecdysone Receptor in Drosophila

The steroid hormone ecdysone and its receptor (EcR) play critical roles in orchestrating developmental transitions in arthropods. However, the mechanism by which EcR integrates nutritional and developmental cues to correctly activate transcription remains poorly understood. Here, we show that EcR-dependent transcription, and thus, developmental timing in Drosophila, is regulated by CDK8 and its regulatory partner Cyclin C (CycC), and the level of CDK8 is affected by nutrient availability. We observed that cdk8 and cycC mutants resemble EcR mutants and EcR-target genes are systematically down-regulated in both mutants. Indeed, the ability of the EcR-Ultraspiracle (USP) heterodimer to bind to polytene chromosomes and the promoters of EcR target genes is also diminished. Mass spectrometry analysis of proteins that co-immunoprecipitate with EcR and USP identified multiple Mediator subunits, including CDK8 and CycC. Consistently, CDK8-CycC interacts with EcR-USP in vivo; in particular, CDK8 and Med14 can directly interact with the AF1 domain of EcR. These results suggest that CDK8-CycC may serve as transcriptional cofactors for EcR-dependent transcription. During the larval–pupal transition, the levels of CDK8 protein positively correlate with EcR and USP levels, but inversely correlate with the activity of sterol regulatory element binding protein (SREBP), the master regulator of intracellular lipid homeostasis. Likewise, starvation of early third instar larvae precociously increases the levels of CDK8, EcR and USP, yet down-regulates SREBP activity. Conversely, refeeding the starved larvae strongly reduces CDK8 levels but increases SREBP activity. Importantly, these changes correlate with the timing for the larval–pupal transition. Taken together, these results suggest that CDK8-CycC links nutrient intake to developmental transitions (EcR activity) and fat metabolism (SREBP activity) during the larval–pupal transition.

During the larval-pupal transition in Drosophila, CDK8-CycC helps to link nutrient intake to development by activating ecdysone receptor-dependent transcription and to fat metabolism by inhibiting SREBP-activated gene expression.

Arthropods are estimated to account for over 80% of animal species on earth. Characterized by their rigid exoskeletons, juvenile arthropods must periodically shed their thick outer cuticles by molting in order to grow. The steroid hormone ecdysone plays an essential role in regulating the timing of developmental transitions, but exactly how ecdysone and its receptor EcR activates transcription correctly after integrating nutritional and developmental cues remains unknown. Our developmental genetic analyses of two Drosophila mutants, cdk8 and cycC, show that they are lethal during the prepupal stage, with aberrant accumulation of fat and a severely delayed larval–pupal transition. As we have reported previously, CDK8-CycC inhibits fat accumulation by directly inactivating SREBP, a master transcription factor that controls the expression of lipogenic genes, which explains the abnormal fat accumulation in the cdk8 and cycC mutants. We find that CDK8 and CycC are required for EcR to bind to its target genes, serving as transcriptional cofactors for EcR-dependent gene expression. The expression of EcR target genes is compromised in cdk8 and cycC mutants and underpins the retarded pupariation phenotype. Starvation of feeding larvae precociously up-regulates CDK8 and EcR, prematurely down-regulates SREBP activity, and leads to early pupariation, whereas re-feeding starved larvae has opposite effects. Taken together, these results suggest that CDK8 and CycC play important roles in coordinating nutrition intake with fat metabolism by directly inhibiting SREBP-dependent gene expression and regulating developmental timing by activating EcR-dependent transcription in Drosophila.

Significant fluctuations in ecdysteroid receptor gene (EcR) expression in relation to seasons of molt and reproduction in the grapsid crab, Metopograpsus messor (Brachyura: Decapoda)

Metopograpsus messor, a brachyuran crab inhabiting the estuaries of North Kerala (India), is a prolific breeder releasing approximately 14-16 broods a year. The present paper reports the sequence information on the DNA binding domain (C domain, DBD), linker (D domain) and ligand binding domain (E domain, LBD) of M. messor ecdysteroid receptor (MmEcR) gene, the first grapsid brachyuran crab EcR examined. We have also measured MmEcR transcript levels in the ovary and the hepatopancreas throughout the annual cycle, with special reference to seasons of molt and reproduction. MmEcR expression in both the tissues is found to be at its peak (P<0.05) in late premolt crabs (January/May, molt/reproduction season); the expression levels are lowest (P<0.05) during June/July, when the females would neither molt nor reproduce (season for molt/reproduction repose). Intermediate levels of expression were found during the breeding season (August/December). Interestingly, this pattern of gene expression is in concordance with the fluctuating ecdysteroid levels of the hemolymph and Y organ secretory activity. The significant levels of fluctuation in the ovarian expression of MmEcR strongly suggest the ovary as a potential target for ecdysteroid action. A season-wise comparison of the gene expression reveals that ovarian MmEcR transcript levels are higher in breeding crabs (August/December) than the non-breeding animals (June/July), implicating a possible ecdysteroid role in reproduction in M. messor.

Wolbachia-induced paternal defect in Drosophila is likely by interaction with the juvenile hormone pathway

Wolbachia are endosymbionts that infect many insect species. They can manipulate the host's reproduction to increase their own maternal transmission. Cytoplasmic incompatibility (CI) is one such manipulation, which is expressed as embryonic lethality when Wolbachia-infected males mate with uninfected females. However, matings between males and females carrying the same Wolbachia strain result in viable progeny. The molecular mechanisms of CI are currently not clear. We have previously reported that the gene Juvenile hormone-inducible protein 26 (JhI-26) exhibited the highest upregulation in the 3rd instar larval testes of Drosophila melanogaster when infected by Wolbachia. This is reminiscent of an interaction between Wolbachia and juvenile hormone (JH) pathway in flies. Considering that Jhamt gene encodes JH acid methyltransferase, a key regulatory enzyme of JH biosynthesis, and that methoprene-tolerant (Met) has been regarded as the best JH receptor candidate, we first compared the expression of Jhamt and Met between Wolbachia-infected and uninfected fly testes to investigate whether Wolbachia infection influence the JH signaling pathway. We found that the expressions of Jhamt and Met were significantly increased in the presence of Wolbachia, suggesting an interaction of Wolbachia with the JH signaling pathway. Then, we found that overexpression of JhI-26 in Wolbachia-free transgenic male flies caused paternal-effect lethality that mimics the defects associated with CI. JhI-26 overexpressing males resulted in significantly decrease in hatch rate. Surprisingly, Wolbachia-infected females could rescue the egg hatch. In addition, we showed that overexpression of JhI-26 caused upregulation of the male accessory gland protein (Acp) gene CG10433, but not vice versa. This result suggests that JhI-26 may function at the upstream of CG10433. Likewise, overexpression of CG10433 also resulted in paternal-effect lethality. Both JhI-26 and CG10433 overexpressing males resulted in nuclear division defects in the early embryos. Finally, we found that Wolbachia-infected males decreased the propensity of the mated females to remating, a phenotype also caused by both JhI-26 and CG10433 overexpressing males. Taken together, our results provide a working hypothesis whereby Wolbachia induce paternal defects in Drosophila probably by interaction with the JH pathway via JH response genes JhI-26 and CG10433.

Biased gene expression in early honeybee larval development

Background

Female larvae of the honeybee (Apis mellifera) develop into either queens or workers depending on nutrition. This nutritional stimulus triggers different developmental trajectories, resulting in adults that differ from each other in physiology, behaviour and life span.

Results

To understand how these trajectories are established we have generated a comprehensive atlas of gene expression throughout larval development. We found substantial differences in gene expression between worker and queen-destined larvae at 6 hours after hatching. Some of these early changes in gene expression are maintained throughout larval development, indicating that caste-specific developmental trajectories are established much earlier than previously thought. Within our gene expression data we identified processes that potentially underlie caste differentiation. Queen-destined larvae have higher expression of genes involved in transcription, translation and protein folding early in development with a later switch to genes involved in energy generation. Using RNA interference, we were able to demonstrate that one of these genes, hexamerin 70b, has a role in caste differentiation. Both queen and worker developmental trajectories are associated with the expression of genes that have alternative splice variants, although only a single variant of a gene tends to be differentially expressed in a given caste.

Conclusions

Our data, based on the biases in gene expression early in development together with published data, supports the idea that caste development in the honeybee consists of two phases; an initial biased phase of development, where larvae can still switch to the other caste by differential feeding, followed by commitment to a particular developmental trajectory.

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.

Tethered domains and flexible regions in tRNase Z(L), the long form of tRNase Z

tRNase Z, a member of the metallo-β-lactamase family, endonucleolytically removes the pre-tRNA 3′ trailer in a step central to tRNA maturation. The short form (tRNase Z^S) is the only one found in bacteria and archaebacteria and is also present in some eukaryotes. The homologous long form (tRNase Z^L), exclusively found in eukaryotes, consists of related amino- and carboxy-domains, suggesting that tRNase Z^L arose from a tandem duplication of tRNase Z^S followed by interdependent divergence of the domains. X-ray crystallographic structures of tRNase Z^S reveal a flexible arm (FA) extruded from the body of tRNase Z remote from the active site that binds tRNA far from the scissile bond. No tRNase Z^L structures have been solved; alternative biophysical studies are therefore needed to illuminate its functional characteristics. Structural analyses of tRNase Z^L performed by limited proteolysis, two dimensional gel electrophoresis and mass spectrometry establish stability of the amino and carboxy domains and flexibility of the FA and inter-domain tether, with implications for tRNase Z^L function.

Identification and sequence analysis of metazoan tRNA 3'-end processing enzymes tRNase Zs

tRNase Z is the endonuclease responsible for removing the 3'-trailer sequences from precursor tRNAs, a prerequisite for the addition of the CCA sequence. It occurs in the short (tRNase Z^S) and long (tRNase Z^L) forms. Here we report the identification and sequence analysis of candidate tRNase Zs from 81 metazoan species. We found that the vast majority of deuterostomes, lophotrochozoans and lower metazoans have one tRNase Z^S and one tRNase Z^L genes, whereas ecdysozoans possess only a single tRNase Z^L gene. Sequence analysis revealed that in metazoans, a single nuclear tRNase Z^L gene is likely to encode both the nuclear and mitochondrial forms of tRNA 3′-end processing enzyme through mechanisms that include alternative translation initiation from two in-frame start codons and alternative splicing. Sequence conservation analysis revealed a variant PxKxRN motif, PxPxRG, which is located in the N-terminal region of tRNase Z^Ss. We also identified a previously unappreciated motif, AxDx, present in the C-terminal region of both tRNase Z^Ss and tRNase Z^Ls. The AxDx motif consisting mainly of a very short loop is potentially close enough to form hydrogen bonds with the loop containing the PxKxRN or PxPxRG motif. Through complementation analysis, we demonstrated the likely functional importance of the AxDx motif. In conclusion, our analysis supports the notion that in metazoans a single tRNase Z^L has evolved to participate in both nuclear and mitochondrial tRNA 3′-end processing, whereas tRNase Z^S may have evolved new functions. Our analysis also unveils new evolutionarily conserved motifs in tRNase Zs, including the C-terminal AxDx motif, which may have functional significance.

Expression profiling of attenuated mitochondrial function identifies retrograde signals in Drosophila

Mitochondria are able to modulate cell state and fate during normal and pathophysiologic conditions through a nuclear-mediated mechanism collectively termed as a retrograde response. Our previous studies in Drosophila melanogaster have clearly established that progress through the cell cycle is precisely regulated by the intrinsic activity of the mitochondrion by specific signaling cascades mounted by the cell. As a means to further our understanding of how mitochondrial energy status affects nuclear control of basic cell decisions, we have employed Affymetrix microarray-based transcriptional profiling of Drosophila S2 cells knocked down for the gene encoding subunit Va of the complex IV of the mitochondrial electron transport chain. The profiling data identify transcriptional upregulation of glycolytic genes, and metabolic studies confirm this increase in glycolysis. The data provide a model of the shift of metabolism from a predominately oxidative state toward a predominately aerobic glycolytic state mediated through transcriptional control. The transcriptional changes alter many signaling systems, including p53, insulin, hypoxia-induced factor α, and conserved mitochondrial retrograde responses. This rich dataset provides many novel targets for further understanding the mechanism whereby the mitochondrion manages energy substrate disposition and directs cellular fate decisions.

Transcriptional regulation of juvenile hormone-mediated induction of Krüppel homolog 1, a repressor of insect metamorphosis

The Krüppel homolog 1 gene (Kr-h1) has been proposed to play a key role in the repression of insect metamorphosis. Kr-h1 is assumed to be induced by juvenile hormone (JH) via a JH receptor, methoprene-tolerant (Met), but the mechanism of induction is unclear. To elucidate the molecular mechanism of Kr-h1 induction, we first cloned cDNAs encoding Kr-h1 (BmKr-h1) and Met (BmMet1 and BmMet2) homologs from Bombyx mori. In a B. mori cell line, BmKr-h1 was rapidly induced by subnanomolar levels of natural JHs. Reporter assays identified a JH response element (kJHRE), comprising 141 nucleotides, located ∼2 kb upstream from the BmKr-h1 transcription start site. The core region of kJHRE (GGCCTCCACGTG) contains a canonical E-box sequence to which Met, a basic helix-loop-helix Per-ARNT-Sim (bHLH-PAS) transcription factor, is likely to bind. In mammalian HEK293 cells, which lack an intrinsic JH receptor, ectopic expression of BmMet2 fused with Gal4DBD induced JH-dependent activity of an upstream activation sequence reporter. Meanwhile, the kJHRE reporter was activated JH-dependently in HEK293 cells only when cotransfected with BmMet2 and BmSRC, another bHLH-PAS family member, suggesting that BmMet2 and BmSRC jointly interact with kJHRE. We also found that the interaction between BmMet2 and BmSRC is dependent on JH. Therefore, we propose the following hypothesis for the mechanism of JH-mediated induction of BmKr-h1: BmMet2 accepts JH as a ligand, JH-liganded BmMet2 interacts with BmSRC, and the JH/BmMet2/BmSRC complex activates BmKr-h1 by interacting with kJHRE.

Molecular Mechanisms of Transcription Activation by Juvenile Hormone: A Critical Role for bHLH-PAS and Nuclear Receptor Proteins

Juvenile hormone (JH) is responsible for controlling many biological processes. In several insect species JH has been implicated as a key regulator of developmental timing, preventing the premature onset of metamorphosis during larval growth periods. However, the molecular basis of JH action is not well-understood. In this review, we highlight recent advances which demonstrate the importance of transcription factors from the bHLH-PAS and nuclear receptor families in mediating the response to JH.

Assigning a function to a conserved archaeal metallo-β-lactamase from Haloferax volcanii

The metallo-β-lactamase family of enzymes comprises a large group of proteins with diverse functions in the metabolism of the cell. Among others, this superfamily contains proteins which are involved in DNA and RNA metabolism, acting as nucleases in e.g. repair and maturation. Many proteins have been annotated in prokaryotic genomes as being potential metallo-β-lactamases, but very often the function has not been proven. The protein HVO_2763 from Haloferax volcanii is such a potential metallo-β-lactamase. HVO_2763 has sequence similarity to the metallo-β-lactamase tRNase Z, a tRNA 3′ processing endonuclease. Here, we report the characterisation of this metallo-β-lactamase HVO_2763 in the halophilic archaeon Haloferax volcanii. Using different in vitro assays with the recombinant HVO_2763, we could show that the protein does not have tRNA 3′ processing or exonuclease activity. According to transcriptome analyses of the HVO_2763 deletion strain, expression of proteins involved in membrane transport is downregulated in the mutant. Therefore, HVO_2763 might be involved directly or indirectly in membrane transport.

Differentially expressed profiles in the larval testes of Wolbachia infected and uninfected Drosophila

Background

Wolbachia are endosymbiotic bacteria that are frequently found in arthropods and nematodes. These maternally inherited bacteria manipulate host reproduction by several mechanisms including cytoplasmic incompatibility (CI). CI is the most common phenotype induced by Wolbachia and results in the developmental arrest of embryos derived from crosses between Wolbachia-infected males and uninfected females. Although the molecular mechanisms of CI are currently unknown, several studies suggest that host sperm is modified by Wolbachia during spermatogenesis.

Results

We compared the gene expression of Drosophila melanogaster larval testes with and without the wMel strain of Wolbachia to identify candidate genes that could be involved in the interaction between Wolbachia and the insect host. Microarray, quantitative RT-PCR and in situ hybridization analyses were carried out on D. melanogaster larval testes to determine the effect of Wolbachia infection on host gene expression. A total of 296 genes were identified by microarray analysis to have at least a 1.5 fold change [q-value < 5%] in expression. When comparing Wolbachia-infected flies to uninfected flies, 167 genes were up-regulated and 129 genes down-regulated. Differential expression of genes related to metabolism, immunity, reproduction and other functions were observed. Quantitative RT-PCR (qRT-PCR) confirmed 12 genes are differentially expressed in the testes of the 3^rd instar larvae of Wolbachia-infected and uninfected flies. In situ hybridization demonstrated that Wolbachia infection changes the expression of several genes putatively associated with spermatogenesis including JH induced protein-26 and Mst84Db, or involved in immune (kenny) or metabolism (CG4988-RA).

Conclusions

Wolbachia change the gene expression of 296 genes in the larval testes of D. melanogaster including genes related to metabolism, immunity and reproduction. Interestingly, most of the genes putatively involved in immunity were up-regulated in the presence of Wolbachia. In contrast, most of the genes putatively associated with reproduction (especially spermatogenesis) were down-regulated in the presence of Wolbachia. These results suggest Wolbachia may activate the immune pathway but inhibit spermatogenesis. Our data provide a significant panel of candidate genes that may be involved in the interaction between Wolbachia and their insect hosts. This forms a basis to help elucidate the underlying mechanisms of Wolbachia-induced CI in Drosophila and the influence of Wolbachia on spermatogenesis.

Sequences that direct subcellular traffic of the Drosophila methoprene-tolerant protein (MET) are located predominantly in the PAS domains

Methoprene-tolerant protein (MET) is a key mediator of antimetamorphic signaling in insects. MET belongs to the family of bHLH-PAS transcription factors which regulate gene expression and determine essential physiological and developmental processes. The ability of many bHLH-PAS proteins to carry out their functions is related to the patterns of intracellular trafficking, which are determined by specific sequences and indicate that a nuclear localization signal (NLS) or a nuclear export signal (NES) is present and active. Therefore, the identification of NLS and NES signals is fundamental in order to understand the intracellular signaling role of MET. Nevertheless, data on the intracellular trafficking of MET are inconsistent, and until now there hasn't been any data on potential NLS and NES sequences. To analyze the trafficking of MET we designed a number of expression vectors encoding full-length MET, as well as various derivatives, that were fused to yellow fluorescent protein (YFP). Confocal microscopy analysis of the subcellular distribution of YFP-MET indicated that while this protein was localized mainly in the nucleus, it was also observed in the cytoplasm. This suggested the presence of both an NLS and NES in MET. Our work has shown that each of the two PAS domains of MET (PAS-A and PAS-B, respectively) contain one NLS and one NES sequence. Additional NES activity was present in the C-terminal fragment. The NLS activity located in PAS-B was dependent on the presence of juvenile hormone (JH), the potential ligand for MET. In contrast to this, JH didn't seem to be required for the NLS in PAS-A to be active. However, on the basis of current knowledge about the function of PAS-A in other bHLH-PAS proteins, we suggest there might be other proteins that control the activity of the NLS and possibly the NES located in the PAS-A of MET. Thus, the intracellular trafficking of MET seems to be regulated by a rather complicated network of different factors.

Alterations in the Aedes aegypti transcriptome during infection with West Nile, dengue and yellow fever viruses

West Nile (WNV), dengue (DENV) and yellow fever (YFV) viruses are (re)emerging, mosquito-borne flaviviruses that cause human disease and mortality worldwide. Alterations in mosquito gene expression common and unique to individual flaviviral infections are poorly understood. Here, we present a microarray analysis of the Aedes aegypti transcriptome over time during infection with DENV, WNV or YFV. We identified 203 mosquito genes that were ≥5-fold differentially up-regulated (DUR) and 202 genes that were ≥10-fold differentially down-regulated (DDR) during infection with one of the three flaviviruses. Comparative analysis revealed that the expression profile of 20 DUR genes and 15 DDR genes was quite similar between the three flaviviruses on D1 of infection, indicating a potentially conserved transcriptomic signature of flaviviral infection. Bioinformatics analysis revealed changes in expression of genes from diverse cellular processes, including ion binding, transport, metabolic processes and peptidase activity. We also demonstrate that virally-regulated gene expression is tissue-specific. The overexpression of several virally down-regulated genes decreased WNV infection in mosquito cells and Aedes aegypti mosquitoes. Among these, a pupal cuticle protein was shown to bind WNV envelope protein, leading to inhibition of infection in vitro and the prevention of lethal WNV encephalitis in mice. This work provides an extensive list of targets for controlling flaviviral infection in mosquitoes that may also be used to develop broad preventative and therapeutic measures for multiple flaviviruses.

Dengue (DENV), West Nile (WNV) and Yellow Fever (YFV) viruses are responsible for severe human disease and mortality worldwide. There is no vaccine available for dengue or West Nile virus and no specific antiviral is available for any of these viral infections. These viruses are transmitted to humans through the bite of a mosquito vector. Understanding the effects of viral infection on gene expression in the mosquito is crucial to the development of effective antiviral treatments for mosquitoes and may enable researchers to interrupt the human-insect infection cycle. Here we investigate the alterations in gene expression across the entire Aedes aegypti genome during infection with DENV, YFV and WNV over time. We describe several genes that share a similar expression profile during infection with all three viruses. We also use a WNV mosquito cell, mosquito and mouse model to show that virally downregulated genes are inhibitory to infection when overexpressed and that viral regulation of mosquito genes is tissue-specific. Our results provide an extensive amount of data highlighting viral gene targets in the mosquito during infection. This data may also be used to develop broad-spectrum anti-flaviviral treatments in mosquitoes.

The Drosophila FTZ-F1 nuclear receptor mediates juvenile hormone activation of E75A gene expression through an intracellular pathway

Juvenile hormone (JH) regulates a wide variety of biological activities in holometabolous insects, ranging from vitellogenesis and caste determination in adults to the timing of metamorphosis in larvae. The mechanism of JH signaling in such a diverse array of processes remains either unknown or contentious. We previously found that the nuclear receptor gene E75A is activated in S2 cells as a primary response to JH. Here, by expressing an intracellular form of JH esterase, we demonstrate that JH must enter the cell in order to activate E75A. To find intracellular receptors involved in the JH response, we performed an RNAi screen against nuclear receptor genes expressed in this cell line and identified the orphan receptor FTZ-F1. Removal of FTZ-F1 prevents JH activation of E75A, whereas overexpression enhances activation, implicating FTZ-F1 as a critical component of the JH response. FTZ-F1 is bound in vivo to multiple enhancers upstream of E75A, suggesting that it participates in direct JH-mediated gene activation. To better define the role of FTZ-F1 in JH signaling, we investigated interactions with candidate JH receptors and found that the bHLH-PAS proteins MET and GCE both interact with FTZ-F1 and can activate transcription through the FTZ-F1 response element. Removal of endogenous GCE, but not MET, prevents JH activation of E75A. We propose that FTZ-F1 functions as a competence factor by loading JH signaling components to the promoter, thus facilitating the direct regulation of E75A gene expression by JH.

The participation of calponin in the cross talk between 20-hydroxyecdysone and juvenile hormone signaling pathways by phosphorylation variation

20-hydroxyecdysone (20E) and juvenile hormone (JH) signaling pathways interact to mediate insect development, but the mechanism of this interaction is poorly understood. Here, a calponin homologue domain (Chd) containing protein (HaCal) is reported to play a key role in the cross talk between 20E and JH signaling by varying its phosphorylation. Chd is known as an actin binding domain present in many proteins including some signaling proteins. Using an epidermal cell line (HaEpi), HaCal was found to be up-regulated by either 20E or the JH analog methoprene (JHA). 20E induced rapid phosphorylation of HaCal whereas no phosphorylation occurred with JHA. HaCal could be quickly translocated into the nuclei through 20E or JH signaling but interacted with USP1 only under the mediation of JHA. Knockdown of HaCal by RNAi blocked the 20E inducibility of USP1, PKC and HR3, and also blocked the JHA inducibility of USP1, PKC and JHi. After gene silencing of HaCal by ingestion of dsHaCal expressed by Escherichia coli, the larval development was arrested and the gene expression of USP1, PKC, HR3 and JHi were blocked. These composite data suggest that HaCal plays roles in hormonal signaling by quickly transferring into nucleus to function as a phosphorylated form in the 20E pathway and as a non-phosphorylated form interacting with USP1 in the JH pathway to facilitate 20E or JH signaling cascade, in short, by switching its phosphorylation status to regulate insect development.

The fission yeast Schizosaccharomyces pombe has two distinct tRNase ZLs encoded by two different genes and differentially targeted to the nucleus and mitochondria

tRNase Z is the endonuclease that is involved in tRNA 3′-end maturation by removal of the 3′-trailer sequences from tRNA precursors. Most eukaryotes examined to date, including the budding yeast Saccharomyces cerevisiae and humans, have a single long form of tRNase Z (tRNase ZL). In contrast, the fission yeast Schizosaccharomyces pombe contains two candidate tRNase ZLs encoded by the essential genes sptrz1+ and sptrz2+. In the present study, we have expressed recombinant SpTrz1p and SpTrz2p in S. pombe. Both recombinant proteins possess precursor tRNA 3′-endonucleolytic activity in vitro. SpTrz1p localizes to the nucleus and has a simian virus 40 NLS (nuclear localization signal)-like NLS at its N-terminus, which contains four consecutive arginine and lysine residues between residues 208 and 211 that are critical for the NLS function. In contrast, SpTrz2p is a mitochondrial protein with an N-terminal MTS (mitochondrial-targeting signal). High-level overexpression of sptrz1+ has no detectable phenotypes. In contrast, strong overexpression of sptrz2+ is lethal in wild-type cells and results in morphological abnormalities, including swollen and round cells, demonstrating that the correct expression level of sptrz2+ is critical. The present study provides evidence for partitioning of tRNase Z function between two different proteins in S. pombe, although we cannot rule out specialized functions for each protein.

Comparative transcriptional pathway bioinformatic analysis of dietary restriction, Sir2, p53 and resveratrol life span extension in Drosophila

A multiple comparison approach using whole genome transcriptional arrays was used to identify genes and pathways involved in calorie restriction/dietary restriction (DR) life span extension in Drosophila. Starting with a gene centric analysis comparing the changes in common between DR and two DR related molecular genetic life span extending manipulations, Sir2 and p53, lead to a molecular confirmation of Sir2 and p53's similarity with DR and the identification of a small set of commonly regulated genes. One of the identified upregulated genes, takeout, known to be involved in feeding and starvation behavior, and to have sequence homology with Juvenile Hormone (JH) binding protein, was shown to directly extend life span when specifically overexpressed. Here we show that a pathway centric approach can be used to identify shared physiological pathways between DR and Sir2, p53 and resveratrol life span extending interventions. The set of physiological pathways in common among these life span extending interventions provides an initial step toward defining molecular genetic and physiological changes important in life span extension. The large overlap in shared pathways between DR, Sir2, p53 and resveratrol provide strong molecular evidence supporting the genetic studies linking these specific life span extending interventions.

RNAi knockdown of dRNaseZ, the Drosophila homolog of ELAC2, impairs growth of mitotic and endoreplicating tissues

The Drosophila RNase Z(L) (dRNaseZ) gene encodes a member of the ELAC1/ELAC2 protein family with homologs in every living organism. All RNase Z proteins tested so far were found to possess endoribonuclease activity, which is responsible for the removal of a 3' trailer from a primary tRNA transcript. Given that tRNA 3'-end processing has been delineated using in vitro, bacterial and cell culture models, its relevance to RNase Z functions in vivo has yet to be established. In this study, we employed heritable RNA interference (RNAi) in combination with the GAL4/UAS system to spatiotemporally knockdown the dRNaseZ gene and study its biological role in cells of a developing fruit fly. We found that dRNaseZ is an essential gene, as ubiquitous knockdown caused growth arrest and early larval lethality. Molecular analysis confirmed that dRNaseZ is necessary for 3'-end processing of nuclear and mitochondrial tRNAs: knockdown larvae displayed significant accumulation of both types of processing intermediates with extensions at the 3' end. This is the first in vivo demonstration of RNase Z(L) dependent tRNA processing in the context of a metazoan model organism. Using tissue-specific GAL4 drivers, we also showed that in mitotically growing imaginal discs dRNaseZ is required for cell proliferation and/or viability, but not for the maintenance of their differentiated progeny. In endoreplicating salivary glands, dRNaseZ controls organ size by supporting cell growth but not DNA replication. Although the mechanisms remain unclear, our results support the notion that RNase Z(L) is involved in biological pathways regulating cell growth and proliferation.

Heterodimer of two bHLH-PAS proteins mediates juvenile hormone-induced gene expression

Juvenile hormone (JH) plays crucial roles in many aspects of insect life. The Methoprene-tolerant (Met) gene product, a member of the bHLH-PAS family of transcriptional regulators, has been demonstrated to be a key component of the JH signaling pathway. However, the molecular function of Met in JH-induced signal transduction and gene regulation remains to be fully elucidated. Here we show that a transcriptional coactivator of the ecdysteroid receptor complex, FISC, acts as a functional partner of Met in mediating JH-induced gene expression. Met and FISC appear to use their PAS domains to form a dimer only in the presence of JH or JH analogs. In newly emerged adult female mosquitoes, expression of some JH responsive genes is considerably dampened when Met or FISC is depleted by RNAi. Met and FISC are found to be associated with the promoter of the early trypsin gene (AaET) when transcription of this gene is activated by JH. A juvenile hormone response element (JHRE) has been identified in the AaET upstream regulatory region and is bound in vitro by the Met-FISC complex present in the nuclear protein extracts of previtellogenic adult female mosquitoes. In addition, the Drosophila homologs of Met and FISC can also use this mosquito JHRE to activate gene transcription in response to JH in a cell transfection assay. Together, the evidence indicates that Met and FISC form a functional complex on the JHRE in the presence of JH and directly activate transcription of JH target genes.

Paralogous genes involved in juvenile hormone action in Drosophila melanogaster

Juvenile hormone (JH) is critical for multiple aspects of insect development and physiology. Although roles for the hormone have received considerable study, an understanding of the molecules necessary for JH action in insects has been frustratingly slow to evolve. Methoprene-tolerant (Met) in Drosophila melanogaster fulfills many of the requirements for a hormone receptor gene. A paralogous gene, germ-cell expressed (gce), possesses homology and is a candidate as a Met partner in JH action. Expression of gce was found to occur at multiple times and in multiple tissues during development, similar to that previously found for Met. To probe roles of this gene in JH action, we carried out in vivo gce over- and underexpression studies. We show by overexpression studies that gce can substitute in vivo for Met, alleviating preadult but not adult phenotypic characters. We also demonstrate that RNA interference-driven knockdown of gce expression in transgenic flies results in preadult lethality in the absence of MET. These results show that (1) unlike Met, gce is a vital gene and shows functional flexibility and (2) both gene products appear to promote JH action in preadult but not adult development.

Hormonal regulation of the E75 gene in Drosophila: identifying functional regulatory elements through computational and biological analysis

Drosophila development is regulated by two hormones, 20-hydroxyecdysone (ecdysone) and juvenile hormone. We previously found that expression of the E75 gene is induced by both hormones in cultured S2 cells. E75 occupies over 100 kb of genomic DNA; it has four alternative promoters producing isoforms E75A, E75B, E75C, and E75D. To identify hormone response elements in the 60-kb noncoding area upstream of the E75A transcription start site, we developed a novel approach combining in vitro, in vivo, and in silico techniques. Using chromatin immunoprecipitation coupled with quantitative real-time PCR, we identified five putative enhancers marked with H3K4 monomethylation and depletion of H3. Four of these are ecdysone-regulated enhancers, which possess hormone-responsive chromatin and contain sequences sufficient to confer ecdysone inducibility to a reporter gene. Using EvoPrinterHD- and Multiple Expectation Maximization for Motif Elicitation-based computational analysis, we first created a database of short sequences that are highly conserved among 12 Drosophila species. Within this database, we then identified a set of putative ecdysone response elements (EcREs). Seven of these elements represent in vivo binding sites for the ecdysone receptor and are necessary for hormone-mediated activation of gene expression in cultured cells. We found that each EcRE exhibits different binding and activation properties, and at least some of them function cooperatively.We propose that the presence of multiple EcREs with distinct features provides flexibility to the rapid and powerful response of E75A to ecdysone during Drosophila development.

Genomic structure and expression analysis of the RNase kappa family ortholog gene in the insect Ceratitis capitata

Cc RNase is the founding member of the recently identified RNase kappa family, which is represented by a single ortholog in a wide range of animal taxonomic groups. Although the precise biological role of this protein is still unknown, it has been shown that the recombinant proteins isolated so far from the insect Ceratitis capitata and from human exhibit ribonucleolytic activity. In this work, we report the genomic organization and molecular evolution of the RNase kappa gene from various animal species, as well as expression analysis of the ortholog gene in C. capitata. The high degree of amino acid sequence similarity, in combination with the fact that exon sizes and intronic positions are extremely conserved among RNase kappa orthologs in 15 diverse genomes from sea anemone to human, imply a very significant biological function for this enzyme. In C. capitata, two forms of RNase kappa mRNA (0.9 and 1.5 kb) with various lengths of 3' UTR were identified as alternative products of a single gene, resulting from the use of different polyadenylation signals. Both transcripts are expressed in all insect tissues and developmental stages. Sequence analysis of the extended region of the longer transcript revealed the existence of three mRNA instability motifs (AUUUA) and five poly(U) tracts, whose functional importance in RNase kappa mRNA decay remains to be explored.

Mutations of the withered (whd) gene in Drosophila melanogaster confer hypersensitivity to oxidative stress and are lesions of the carnitine palmitoyltransferase I (CPT I) gene

Since some oxygen defense mutants of Drosophila melanogaster exhibit a crinkled wing phenotype, a screen was performed on strains bearing mutant alleles conferring a visible wing phenotype to determine whether any were hypersensitive to oxidative stress. One mutant, withered (whd), was found to be sensitive to both dietary paraquat and hyperoxia. New alleles of whd were induced on a defined genetic background and strains carrying these alleles were also found to be sensitive to oxidative stress. To identify the product of the whd gene we used a sequence-based positional candidate approach and by this method we determined that whd encodes carnitine palmitoyltransferase I (CPT I), an enzyme of the outer mitochondrial membrane that is required for the import of long-chain fatty acids into the mitochondria for beta-oxidation. Although this function is not vital under laboratory conditions, whd adults were found to be highly sensitive to starvation and to heavy metal toxicity relative to controls. This work uncovers a novel relationship between fatty acid metabolism and reactive oxygen metabolism. Further, these results in conjunction with past research on whd and on mammalian CPT I support the hypothesis that CPT I serves a vital function in the response to thymine supplementation.

Isolation, endocrine regulation and transcript distribution of a putative primary JH-responsive gene from the pine engraver, Ips pini (Coleoptera: Scolytidae)

We isolated a cDNA of unknown function from a juvenile hormone III (JH III)-treated male midgut cDNA library prepared from the pine engraver beetle, Ips pini, and examined its genomic structure. The gene, tentatively named "Ipi10G08", encoded a 410 amino acid translation product that shared 26-37% identity with unannotated matches from several insects. Semi-quantitative RT-PCR analysis of Ipi10G08 following application of a 10 microg dose of JH III demonstrated an early induction for both male and female beetles, with transcripts being detectable after 45 min. An expression profile of male midgut tissue indicated Ipi10G08 transcript levels reach a maximum induction of approximately 22.5-fold control levels at 4h post-treatment. Tissue distribution studies displayed a large induction of Ipi10G08 mRNA in the alimentary canal of JH III-treated beetles, especially in males. A dose curve from both sexes suggested there may be a difference in the ability to respond to lower levels of JH III and immunoblot analysis indicated that although JH III highly induces transcript levels in females, protein levels are not similarly induced, while protein levels are induced in males. Ipi10G08 is likely a primary JH response gene and may provide insight into how this hormone exerts its actions.

Juvenile hormone analogs do not affect directly the activity of the ecdysteroid receptor complex in insect culture cell lines

During insect development, ecdysteroids and juvenile hormones (JHs) interact to regulate larval growth, metamorphosis and reproduction but the molecular mechanisms by which both hormones influence each other's activity remain unknown. Because of their ease of use and straightforward genetic manipulation, insect cell lines often have been used to clarify the actions and interactions of hormones at the molecular level. Here we report on the use of two insect culture cell lines, Drosophila melanogaster S2 and Bombyx mori Bm5 cells, to investigate two molecular processes in which ecdysteroids and JH have been shown to interact: (1) direct modulation of the activity of the ecdysteroid receptor transcription complex and (2) interference at the level of induction of the primary gene E75. Our data do not support JH analogs (JHAs) acting through the above processes: 'antagonism' of ecdysteroid receptor activity by JHAs correlated with cytotoxicity and induction of E75 expression by JHAs was not demonstrated. However, we confirm previous studies in which it was observed that methoprene can partially reverse the growth inhibition by 20E in S2 cells (but not Bm5 cells). Therefore, the molecular mechanism by which both hormones influence each other's activity to regulate cell growth in S2 cells remains unknown.

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.

Specific transcriptional responses to juvenile hormone and ecdysone in Drosophila

Previous studies have shown that ecdysone (E), and its immediate downstream product 20-hydroxyecdysone (20E), can have different biological functions in insects, suggesting that E acts as a distinct hormone. Here, we use Drosophila larval organ culture in combination with microarray technology to identify genes that are transcriptionally regulated by E, but which show little or no response to 20E. These genes are coordinately expressed for a brief temporal interval at the onset of metamorphosis, suggesting that E acts together with 20E to direct puparium formation. We also show that E74B, pepck, and CG14949 can be induced by juvenile hormone III (JH III) in organ culture, and that CG14949 can be induced by JH independently of protein synthesis. In contrast, E74A and E75A show no response to JH in this system. These studies demonstrate that larval organ culture can be used to identify Drosophila genes that are regulated by hormones other than 20E, and provide a basis for studying crosstalk between multiple hormone signaling pathways.

The tRNase Z family of proteins: physiological functions, substrate specificity and structural properties

tRNase Z is the endoribonuclease that generates the mature 3'-end of tRNA molecules by removal of the 3'-trailer elements of precursor tRNAs. This enzyme has been characterized from representatives of all three domains of life (Bacteria, Archaea and Eukarya), as well as from mitochondria and chloroplasts. tRNase Z enzymes come in two forms: short versions (280-360 amino acids in length), present in all three kingdoms, and long versions (750-930 amino acids), present only in eukaryotes. The recently solved crystal structure of the bacterial tRNase Z provides the structural basis for the understanding of central functional elements. The substrate is recognized by an exosite that protrudes from the main protein body and consists of a metallo-beta-lactamase domain. Cleavage of the precursor tRNA occurs at the binuclear zinc site located in the other subunit of the functional homodimer. The first gene of the tRNase Z family was cloned in 2002. Since then a comprehensive set of data has been acquired concerning this new enzyme, including detailed functional studies on purified recombinant enzymes, mutagenesis studies and finally the determination of the crystal structure of three bacterial enzymes. This review summarizes the current knowledge about these exciting enzymes.

Wide mutational spectrum of a gene involved in hormone action and insecticide resistance in Drosophila melanogaster

The Methoprene-tolerant (Met) bHLH-PAS gene in Drosophila melanogaster is involved in the molecular action of juvenile hormone (JH), and mutants result in resistance to the toxic and morphogenetic effects of JH and JH agonist insecticides such as methoprene. A detailed study of Met mutants can shed light on the poorly understood action of JH as well as the molecular basis of Met resistance to JH insecticides. Nine mutant alleles bearing point mutations in Met were examined for penetrance and expressivity of three phenotypic characters: resistance, defective oogenesis, and a novel eye defect. The collection ranged from two weak alleles having less severe phenotypes to strong alleles with severe phenotypes similar to that of a null allele. The point mutations were located in both conserved and nonconserved domains. Both the eye defect, seen as severely malformed ommatidial facets in the posterior margin of the compound eye, and the oogenesis phenotype are nonconditional, whereas expression of the resistance phenotype requires treatment with JH or JH analogs (JHAs) during early metamorphosis. A proposed basis for all the phenotypic characters centers on MET action as a transcriptional regulator of ecdysone secondary-response target genes during metamorphosis. Disruption of MET function either by mutation or by JHA presence during early metamorphosis results in transcriptional misregulation of different target genes, resulting in the pathology seen in either instance. The variety of amino acid changes in MET that resulted in resistance may portend a rapid rise in resistance in response to increased use of JH insecticides in field insect populations.

Can juvenogens, biochemically targeted hormonogen compounds, assist in environmentally safe insect pest management?

Two different types of juvenogens, biochemically targeted hormonogen compounds were tested for their potency to act as insect pest management agents. In the performed biological screening, wax-like esteric juvenogens (3-10) proved to be convenient agents for controlling blowfly and termites, and displayed species selectivity: cis-N-{2-[4-(2-butanoyloxycyclohexyl)methyl]phenoxy}ethyl carbamate (3) was highly active on blowfly (Neobellieria bullata), while trans-N-{2-[4-(2-hexadecanoyloxycyclohexyl)methyl]-phenoxy}ethyl carbamate (6) showed high activity on termite (Prorhinotermes simplex). Glycosidic juvenogens, isomeric N-{2-{4-{[2-(beta-D-galactopyranosyloxy)cyclohexyl]methyl}phenoxy}ethyl carbamates (13 and 14), were proved to act as systemic agents, suitable for protecting plants against phytophagous insects (e.g. aphids). Due to the prolonged action of juvenogens, which is connected with the sequential liberating of the biologically active molecule of the insect juvenile hormone bioanalog from the juvenogen molecule by means of enzymic systems of target insects and/or their host plants, more insect individuals can be treated by juvenogens, which are species-targeted structures due to their different physicochemical properties. The results achieved with both types of juvenogens were promising, concerning their final effect on the tested insect species, and the compounds 3-6, 9 (cis-(9Z)-N-{2-[4-(2-(octadec-9-enoyl)oxycyclohexyl)methyl]phenoxy}ethyl carbamate), 13 and 14 proved to represent convenient insect pest management agents for potential practical applications against different insect pests.

Mechanisms of midgut remodeling: juvenile hormone analog methoprene blocks midgut metamorphosis by modulating ecdysone action

In holometabolous insects such as mosquito, Aedes aegypti, midgut undergoes remodeling during metamorphosis. Insect metamorphosis is regulated by several hormones including juvenile hormone (JH) and 20-hydroxyecdysone (20E). The cellular and molecular events that occur during midgut remodeling were investigated by studying nuclear stained whole mounts and cross-sections of midguts and by monitoring the mRNA levels of genes involved in 20E action in methoprene-treated and untreated Ae. aegypti. We used JH analog, methoprene, to mimic JH action. In Ae. aegypti larvae, the programmed cell death (PCD) of larval midgut cells and the proliferation and differentiation of imaginal cells were initiated at about 36h after ecdysis to the 4th instar larval stage (AEFL) and were completed by 12h after ecdysis to the pupal stage (AEPS). In methoprene-treated larvae, the proliferation and differentiation of imaginal cells was initiated at 36h AEFL, but the PCD was initiated only after ecdysis to the pupal stage. However, the terminal events that occur for completion of PCD during pupal stage were blocked. As a result, the pupae developed from methoprene-treated larvae contained two midgut epithelial layers until they died during the pupal stage. Quantitative PCR analyses showed that methoprene affected midgut remodeling by modulating the expression of ecdysone receptor B, ultraspiracle A, broad complex, E93, ftz-f1, dronc and drice, the genes that are shown to play key roles in 20E action and PCD. Thus, JH analog, methoprene acts on Ae. aegypti by interfering with the expression of genes involved in 20E action resulting in a block in midgut remodeling and death during pupal stage.

Interaction of bHLH-PAS proteins involved in juvenile hormone reception in Drosophila

The Methoprene-tolerant (Met) bHLH-PAS gene is involved in juvenile hormone (JH) action in Drosophila melanogaster as a likely component of a JH receptor. We expressed Met in Drosophila S2 cells and explored for MET partners using pull-down assays. MET-MET interaction was found to occur. The germ-cell expressed (gce) gene is another D. melanogaster bHLH-PAS gene with high homology to Met, and GCE formed heterodimers with MET. In the presence of JH or either of two JH agonists, MET-MET and MET-GCE formation was drastically reduced. Interaction between GCE and MET having N- or C-terminus truncations, bHLH or PAS-A domain deletions, or a point mutation in the PAS-B domain failed to occur. However, JH-dependent interaction occurred between GCE and MET having point mutations in bHLH or PAS-A. During development, changes in JH titer may alter partner binding by MET and result in different gene expression patterns.

Protein kinase C mediated phosphorylation blocks juvenile hormone action

Juvenile hormones (JH) regulate a wide variety of developmental and physiological processes in insects. Although the biological actions of JH are well documented, the molecular mechanisms underlying JH action are poorly understood. We studied the molecular basis of JH action using a JH response element (JHRE) identified in the promoter region of JH esterase gene cloned from Choristoneura fumiferana, which is responsive to JH and 20-hydroxyecdysone (20E). In Drosophila melanogaster L57 cells, the JHRE-regulated reporter gene was induced by JH I, JH III, methoprene, and hydroprene. Nuclear proteins isolated from L57 cells bound to the JHRE and exposure of these proteins to ATP resulted in a reduction in their DNA binding. Either JH III or calf intestinal alkaline phosphatase (CIAP) was able to restore the binding of nuclear proteins to the DNA. In addition, protein kinase C inhibitors increased and protein kinase C activators reduced the binding of nuclear proteins to the JHRE. In transactivation assays, protein kinase C inhibitors induced the luciferase gene placed under the control of a minimal promoter and the JHRE. These data suggest that protein kinase C mediated phosphorylation prevents binding of nuclear proteins to juvenile hormone responsive promoters resulting in suppression of JH action.

Interaction between hormonal signaling pathways in Drosophila melanogaster as revealed by genetic interaction between methoprene-tolerant and broad-complex

Juvenile hormone (JH) regulates insect development by a poorly understood mechanism. Application of JH agonist insecticides to Drosophila melanogaster during the ecdysone-driven onset of metamorphosis results in lethality and specific morphogenetic defects, some of which resemble those in mutants of the ecdysone-regulated Broad-Complex (BR-C). The Methoprene-tolerant (Met) bHLH-PAS gene mediates JH action, and Met mutations protect against the lethality and defects. To explore relationships among these two genes and JH, double mutants were constructed between Met alleles and alleles of each of the BR-C complementation groups: broad (br), reduced bristles on palpus (rbp), and 2Bc. Defects in viability and oogenesis were consistently more severe in rbp Met or br Met double mutants than would be expected if these genes act independently. Additionally, complementation between BR-C mutant alleles often failed when MET was absent. Patterns of BRC protein accumulation during metamorphosis revealed essentially no difference between wild-type and Met-null individuals. JH agonist treatment did not block accumulation of BRC proteins. We propose that MET and BRC interact to control transcription of one or more downstream effector genes, which can be disrupted either by mutations in Met or BR-C or by application of JH/JH agonist, which alters MET interaction with BRC.