Spook and Spookier code for stage-specific components of the ecdysone biosynthetic pathway in Diptera

Ovarian Ecdysteroidogenesis in Both Immature and Mature Stages of an Acari, Ornithodoros moubata

Ecdysteroidogenesis is essential for arthropod development and reproduction. Although the importance of ecdysteroids has been demonstrated, there is little information on the sites and enzymes for synthesis of ecdysteroids from Chelicerates. Ecdysteroid functions have been well studied in the soft tick Ornithodoros moubata, making this species an excellent candidate for elucidating ecdysteroidogenesis in Chelicerates. Results showed that O. moubata has at least two ecdysteroidogenic enzymes, Spook (OmSpo) and Shade (OmShd). RNAi showed both enzymes were required for ecdysteroidogenesis. Enzymatic assays demonstrated OmShd has the conserved functions of ecdysone 20-hydroxylase. OmSpo showed specific expression in the ovaries of final nymphal and adult stages, indicating O. moubata utilizes the ovary as an ecdysteroidogenic tissue instead of specific tissues as seen in other arthropods. On the other hand, OmShd expression was observed in various tissues including the midgut, indicating functional ecdysteroids can be produced in these tissues. In nymphal stages, expression of both OmSpo and OmShd peaked before molting corresponding with high ecdysteroid titers in the hemolymph. In fed adult females, OmSpo expression peaked at 8–10 days after engorgement, while OmShd expression peaked immediately after engorgement. Mated females showed more frequent surges of OmShd than virgin females. These results indicate that the regulation of synthesis of ecdysteroids differs in nymphs and adult females, and mating modifies adult female ecdysteroidogenesis. This is the first report to focus on synthesis of ecdysteroids in ticks and provides essential knowledge for understanding the evolution of ecdysteroidogenesis in arthropods.

The genomes of two key bumblebee species with primitive eusocial organization

Background

The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats.

Results

We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits.

Conclusions

These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0623-3) contains supplementary material, which is available to authorized users.

RNA interference-mediated silencing of a Halloween gene spookier affects nymph performance in the small brown planthopper Laodelphax striatellus

Post-embryonic development of insects is highly dependent on ecdysteroid hormone 20-hydroxyecdysone. Halloween gene spookier (spok, cyp307a2) has been documented to be involved in ecdysteroidogenesis in Drosophila melanogaster and Bombyx mori. We describe here the cloning and characterization of Halloween gene spookier (Lsspok, Lscyp307a2) in the small brown planthopper Laodelphax striatellus, a hemipteran insect species. LsSPOK has three insect-conserved P450 motifs, that is, Helix-K, PERF motif and heme-binding domain. Temporal and spatial expression patterns of Lsspok were evaluated by quantitative polymerase chain reaction. Through the fouth-instar and the early fifth-instar stages, Lsspok showed two expression peaks in the second- and fifth-day fourth-instar nymphs, and two troughs in the first-day fourth and fifth instars. On day 5 of the fourth-instar nymphs, Lsspok clearly had a high transcript level in the thorax where prothoracic glands were located. Dietary introduction of double-stranded RNA of Lsspok in the nymph stage successfully knocked down the target gene, decreased expression level of ecdysone receptor (LsEcR) gene, caused nymphal lethality and delayed development. Ingestion of 20-hydroxyecdysone in Lsspok-dsRNA-exposed nymphs did not increase Lsspok expression level, but almost completely rescued the LsEcR mRNA level and relieved the negative effects on survival and development. Thus, our data suggest that the ecdysteroidogenic pathway is conserved in insects and LsSPOK is responsible for specific steps in ecdysteroidogenesis in L. striatellus.

Steroid Signaling Establishes a Female Metabolic State and Regulates SREBP to Control Oocyte Lipid Accumulation

Disruptions in energy homeostasis severely affect reproduction in many organisms and are linked to several reproductive disorders in humans. As a result, understanding the mechanisms that control nutrient accumulation in the oocyte will provide valuable insights into the links between metabolic disease and reproductive dysfunction. We show that the steroid hormone ecdysone functions in Drosophila to control lipid metabolism and support oocyte production. First, local EcR-mediated signaling induces a stage-specific accumulation of lipids in stage-10 oocytes. EcR induces lipid accumulation by promoting the activation of the lipogenic transcription factor SREBP and by controlling the expression of the low-density lipoprotein (LDL) receptor homolog, LpR2. Second, global signaling via the ecdysone receptor, EcR, establishes a female metabolic state and promotes whole-body triglyceride and glycogen storage at high levels. EcR acts in the CNS to mediate these effects, in part by promoting higher levels of feeding in females. Thus, ecdysone functions at two levels to support reproduction: first by inducing lipid accumulation in the late stages of oocyte development and second by providing a signal that coordinates lipid metabolism in the germline with whole-animal lipid homeostasis. Ecdysone regulation allows females to assess the demands of oogenesis and alter their behavior and metabolic state to support the biosynthetic requirements of oocyte production.

Knockdown of Cs-Spook induces delayed larval molting in rice striped stem borer Chilo suppressalis

Spook has essential roles in the biogenesis of the molting hormone 20-hydroxyecdysone (20-E). The function of spook in the rice striped stem borer (SSB) Chilo suppressalis remains unclear, prompting our hypothesis that it exerts actions similar to those reported for other insect species. Here we amplified the full-length transcript of spook (Cs-Spook) in SSB by 5' and 3' rapid amplification of cDNA ends. Cs-Spook has conserved P450 motifs such as Helix-C, Helix-I, Helix-K, and PERF motif (PxxFxPxRF). It was highly expressed in late instar larvae but less so in newly molted larvae. Cs-Spook was highly expressed in prothoracic glands. Cs-Spook was knocked down by dsRNA treatments. Compared with controls, the gene expression level was reduced to 9% at 24 h post injection (PI), 33% at 48 h PI, and 24% at 72 h PI. The ecdysteroid titer decreased significantly in the dsRNA-treated group (P < 0.05), resulting in delayed larval development. The delayed development in dsRNA-treatment group was rescued by treating with 20-E. Our work demonstrates that Cs-Spook participates in the biogenesis of 20-E and regulates the molt of SSB, as seen in other species.

Production of systemically circulating Hedgehog by the intestine couples nutrition to growth and development

Rodenfels et al. show that the Drosophila intestine responds to nutrient availability by regulating production of a circulating lipoprotein-associated form of Hedgehog (Hh). Levels of circulating Hh tune the rates of growth and developmental timing in a coordinated fashion. Circulating Hh is especially important during starvation, when it is also required for mobilization of fat body triacylglycerol stores.

In Drosophila larvae, growth and developmental timing are regulated by nutrition in a tightly coordinated fashion. The networks that couple these processes are far from understood. Here, we show that the intestine responds to nutrient availability by regulating production of a circulating lipoprotein-associated form of the signaling protein Hedgehog (Hh). Levels of circulating Hh tune the rates of growth and developmental timing in a coordinated fashion. Circulating Hh signals to the fat body to control larval growth. It regulates developmental timing by controlling ecdysteroid production in the prothoracic gland. Circulating Hh is especially important during starvation, when it is also required for mobilization of fat body triacylglycerol (TAG) stores. Thus, we demonstrate that Hh, previously known only for its local morphogenetic functions, also acts as a lipoprotein-associated endocrine hormone, coordinating the response of multiple tissues to nutrient availability.

Silencing D. melanogaster lgr1 impairs transition from larval to pupal stage

G protein-coupled receptors (GPCRs) play key roles in a wide diversity of physiological processes and signalling pathways. The leucine-rich repeats containing GPCRs (LGRs) are a subfamily that is well-conserved throughout most metazoan phyla and have important regulatory roles in vertebrates. Here, we report on the critical role of Drosophila melanogaster LGR1, the fruit fly homologue of the vertebrate glycoprotein hormone receptors, in development as a factor involved in the regulation of pupariation. Transcript profiling revealed that lgr1 transcripts are most abundant in third instar larvae and adult flies. The tissues displaying the highest transcript levels were the hindgut, the rectum and the salivary glands. Knockdown using RNA interference (RNAi) demonstrated that white pupa formation was severely suppressed in D. melanogaster lgr1 RNAi larvae. Associated with this developmental defect was a reduced ecdysteroid titer, which is in line with significantly reduced transcript levels detected for the Halloween genes shadow (sad) and spookier (spok) in the third instar lgr1 RNAi larvae compared to the control condition.

CYP18A1 regulates tissue-specific steroid hormone inactivation in Bombyx mori

Insect development and metamorphosis are regulated by two major hormones, juvenile hormone and ecdysteroids. Despite being the key regulator of insect developmental transitions, the metabolic pathway of the primary steroid hormone, 20-hydroxyecdysone (20E), especially its inactivation pathway, is still not completely elucidated. A cytochrome P450 enzyme, CYP18A1, has been shown to play key roles in insect steroid hormone inactivation through 26-hydroxylation. Here, we identified two CYP18 (BmCYP18A1 and BmCYP18B1) orthologs in the lepidopteran model insect, Bombyx mori. Interestingly, BmCYP18A1 gene is predominantly expressed in the middle silk gland (MSG) while BmCYP18B1 expresses ubiquitously in B. mori. BmCYP18A1 is induced by 20E in vitro, suggesting its role in 20E metabolism. Using the binary Gal4/UAS transgenic system, we ectopically overexpressed BmCYP18A1 in a MSG-specific manner with a Sericin1-Gal4 (Ser-Gal4) driver or in a ubiquitous manner with an Actin3-Gal4 (A3-Gal4) driver. Ectopic overexpression of BmCYP18A1 in MSG or in all tissues resulted in developmental arrestment of transgenic animals during the final instar larval stage. The 20E titers in the transgenic animals expressing BmCYP18A1 were lower compared to the levels in the control animals. Although the biological significance of MSG-specific expression of BmCYP18A1 is unclear, our results provide the first evidence that BmCYP18A1, which is conserved in most arthropods, is involved in a tissue-specific steroid hormone inactivation in B. mori.

A Halloween gene noppera-bo encodes a glutathione S-transferase essential for ecdysteroid biosynthesis via regulating the behaviour of cholesterol in Drosophila

In insects, the precise timing of moulting and metamorphosis is strictly guided by ecdysteroids that are synthesised from dietary cholesterol in the prothoracic gland (PG). In the past decade, several ecdysteroidogenic enzymes, some of which are encoded by the Halloween genes, have been identified and characterised. Here, we report a novel Halloween gene, noppera-bo (nobo), that encodes a member of the glutathione S-transferase family. nobo was identified as a gene that is predominantly expressed in the PG of the fruit fly Drosophila melanogaster. We generated a nobo knock-out mutant, which displayed embryonic lethality and a naked cuticle structure. These phenotypes are typical for Halloween mutants showing embryonic ecdysteroid deficiency. In addition, the PG-specific nobo knock-down larvae displayed an arrested phenotype and reduced 20-hydroxyecdysone (20E) titres. Importantly, both embryonic and larval phenotypes were rescued by the administration of 20E or cholesterol. We also confirm that PG cells in nobo loss-of-function larvae abnormally accumulate cholesterol. Considering that cholesterol is the most upstream material for ecdysteroid biosynthesis in the PG, our results raise the possibility that nobo plays a crucial role in regulating the behaviour of cholesterol in steroid biosynthesis in insects.

Enzymes for ecdysteroid biosynthesis: their biological functions in insects and beyond

Steroid hormones are responsible for the coordinated regulation of many aspects of biological processes in multicellular organisms. Since the last century, many studies have identified and characterized steroidogenic enzymes in vertebrates, including mammals. However, much less is known about invertebrate steroidogenic enzymes. In the last 15 years, a number of steroidogenic enzymes and their functions have been characterized in ecdysozoan animals, especially in the fruit fly Drosophila melanogaster. In this review, we summarize the latest knowledge of enzymes crucial for synthesizing ecdysteroids, the principal insect steroid hormones. We also discuss the functional conservation and diversity of ecdysteroidogenic enzymes in other insects and even non-insect species, such as nematodes, vertebrates, and lower eukaryotes.

Pigment dispersing factor regulates ecdysone biosynthesis via bombyx neuropeptide G protein coupled receptor-B2 in the prothoracic glands of Bombyx mori

Ecdysone is the key hormone regulating insect growth and development. Ecdysone synthesis occurs in the prothoracic glands (PGs) and is regulated by several neuropeptides. Four prothoracicotropic and three prothoracicostatic factors have been identified to date, suggesting that ecdysone biosynthesis is intricately regulated. Here, we demonstrate that the neuropeptide pigment dispersing factor (PDF) stimulates ecdysone biosynthesis and that this novel signaling pathway partially overlaps with the prothoracicotropic hormone (PTTH) signaling pathway. We performed transcriptome analysis and focused on receptors predominantly expressed in the PGs. From this screen, we identified a candidate orphan G protein coupled receptor (GPCR), Bombyx neuropeptide GPCR-B2 (BNGR-B2). BNGR-B2 was predominantly expressed in ecdysteroidogenic tissues, and the expression pattern in the PGs corresponded to the ecdysteroid titer in the hemolymph. Furthermore, we identified PDF as a ligand for BNGR-B2. PDF stimulated ecdysone biosynthesis in the PGs, but the stimulation was only observed in the PGs during a specific larval stage. PDF did not affect the transcript level of known ecdysone biosynthetic enzymes, and inhibiting transcription did not suppress ecdysone biosynthesis, suggesting that the effects of PDF might be mediated by translational regulation and/or post-translational modification. In addition, the participation of protein kinase A (PKA), phosphatidylinositol 3-kinase (PI3K), target of rapamycin (TOR) and eukaryotic translation initiation factor 4E (eIF4E)-binding protein (4E-BP) in the PDF signaling pathway was discovered.

Transcriptome survey of the lipid metabolic pathways involved in energy production and ecdysteroid synthesis in the salmon louse Caligus rogercresseyi (Crustacea: Copepoda)

The goal of this study was to identify and analyze the lipid metabolic pathways involved in energy production and ecdysteroid synthesis in the ectoparasite copepod Caligus rogercresseyi. Massive transcriptome sequencing analysis was performed during the infectious copepodid larval stage, during the attached chalimus larval stage, and also in female and male adults. Thirty genes were selected for describing the pathways, and these were annotated for proteins or enzymes involved in lipid digestion, absorption, and transport; fatty acid degradation; the synthesis and degradation of ketone bodies; and steroid and ecdysteroid syntheses. Differential expression of these genes was analyzed by ontogenic stage and discussed considering each stage's feeding habits and energetic needs. Copepodids showed a low expression of fatty acid digestion genes, reflected by a non-feeding behavior, and the upregulation of genes involved in steroid biosynthesis, which was consistent with a pathway for cholesterol synthesis during ecdysis. The chalimus stage showed an upregulation of genes related to fatty acid digestion, absorption, and transport, as well as to fatty acid degradation and the synthesis of ketone bodies, therefore suggesting that lipids ingested from the mucus and skin of the host fish are metabolized as important sources of energy. Adult females also showed a pattern of high lipid metabolism for energy supply and mobilization in relation to reproduction and vitellogenesis. Adult females and males revealed different lipid metabolism patterns that reflected different energetic needs. This study reports for the first time the probable lipid metabolic pathways involved in the energy production and ecdysteroid synthesis of C. rogercresseyi.

The putative Halloween gene phantom involved in ecdysteroidogenesis in the white-backed planthopper Sogatella furcifera

Postembryonic development of insects is highly dependent on ecdysteroid hormones ecdysone (E) and 20-hydroxyecdysone (20E). A cytochrome P450 monooxygenase CYP306A1, the product of the Halloween gene phantom (phm), is involved in the ecdysteroidogenesis in representative insects in Diptera, Lepidoptera and Orthoptera. In the present paper, Sfphm was cloned from a hemipteran insect species, the white-backed planthopper Sogatella furcifera. SfPHM has five insect conserved P450 motifs, i.e., Helix-C, Helix-I, Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of Sfphm were evaluated by q-PCR. Sfphm showed three expression peaks in late second-, third- and fourth-instar stages. In contrast, the expression levels were lower and formed three troughs in the newly-molted second-, third- and fourth-instar nymphs. The relative 20E levels exhibited similar temporal patterns to Sfphm expression levels. On day 3 of the fourth-instar nymphs, Sfphm clearly had a high transcript level in the thorax where PGs were located. Dietary introduction of double-stranded RNA of Sfphm into the second instars successfully knocked down the target gene, and greatly reduced 20E level and ecdysone receptor (EcR) expression level. Moreover, knockdown of Sfphm caused lethality and slowed down ecdysis during nymphal stages. Furthermore, ingestion of 20-hydroxyecdysone did not alter Sfphm expression level, but almost completely rescued SfEcR expression level, and relieved the negative effects on nymphal survival and ecdysis in Sfphm-dsRNA-exposed planthoppers. Thus, our results suggest that Sfphm plays a critical role in ecdysteroidogenesis in S. furcifera.

Transcriptional control of steroid biosynthesis genes in the Drosophila prothoracic gland by ventral veins lacking and knirps

Specialized endocrine cells produce and release steroid hormones that govern development, metabolism and reproduction. In order to synthesize steroids, all the genes in the biosynthetic pathway must be coordinately turned on in steroidogenic cells. In Drosophila, the steroid producing endocrine cells are located in the prothoracic gland (PG) that releases the steroid hormone ecdysone. The transcriptional regulatory network that specifies the unique PG specific expression pattern of the ecdysone biosynthetic genes remains unknown. Here, we show that two transcription factors, the POU-domain Ventral veins lacking (Vvl) and the nuclear receptor Knirps (Kni), have essential roles in the PG during larval development. Vvl is highly expressed in the PG during embryogenesis and is enriched in the gland during larval development, suggesting that Vvl might function as a master transcriptional regulator in this tissue. Vvl and Kni bind to PG specific cis-regulatory elements that are required for expression of the ecdysone biosynthetic genes. Knock down of either vvl or kni in the PG results in a larval developmental arrest due to failure in ecdysone production. Furthermore, Vvl and Kni are also required for maintenance of TOR/S6K and prothoracicotropic hormone (PTTH) signaling in the PG, two major pathways that control ecdysone biosynthesis and PG cell growth. We also show that the transcriptional regulator, Molting defective (Mld), controls early biosynthetic pathway steps. Our data show that Vvl and Kni directly regulate ecdysone biosynthesis by transcriptional control of biosynthetic gene expression and indirectly by affecting PTTH and TOR/S6K signaling. This provides new insight into the regulatory network of transcription factors involved in the coordinated regulation of steroidogenic cell specific transcription, and identifies a new function of Vvl and Knirps in endocrine cells during post-embryonic development.

Unexpected role of the steroid-deficiency protein ecdysoneless in pre-mRNA splicing

The steroid hormone ecdysone coordinates insect growth and development, directing the major postembryonic transition of forms, metamorphosis. The steroid-deficient ecdysoneless1 (ecd1) strain of Drosophila melanogaster has long served to assess the impact of ecdysone on gene regulation, morphogenesis, or reproduction. However, ecd also exerts cell-autonomous effects independently of the hormone, and mammalian Ecd homologs have been implicated in cell cycle regulation and cancer. Why the Drosophila ecd1 mutants lack ecdysone has not been resolved. Here, we show that in Drosophila cells, Ecd directly interacts with core components of the U5 snRNP spliceosomal complex, including the conserved Prp8 protein. In accord with a function in pre-mRNA splicing, Ecd and Prp8 are cell-autonomously required for survival of proliferating cells within the larval imaginal discs. In the steroidogenic prothoracic gland, loss of Ecd or Prp8 prevents splicing of a large intron from CYP307A2/spookier (spok) pre-mRNA, thus eliminating this essential ecdysone-biosynthetic enzyme and blocking the entry to metamorphosis. Human Ecd (hEcd) can substitute for its missing fly ortholog. When expressed in the Ecd-deficient prothoracic gland, hEcd re-establishes spok pre-mRNA splicing and protein expression, restoring ecdysone synthesis and normal development. Our work identifies Ecd as a novel pre-mRNA splicing factor whose function has been conserved in its human counterpart. Whether the role of mammalian Ecd in cancer involves pre-mRNA splicing remains to be discovered.

Signaling of reactive oxygen species in PTTH-stimulated ecdysteroidogenesis in prothoracic glands of the silkworm, Bombyx mori

Our previous study demonstrated that mitochondria-derived reactive oxygen species (ROS) generation is involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in Bombyx mori prothoracic glands (PGs). In the present study, we further investigated the mechanism of ROS production and the signaling pathway mediated by ROS. PTTH-stimulated ROS production was markedly attenuated in a Ca(2+)-free medium. The phospholipase C (PLC) inhibitor, U73122, greatly inhibited PTTH-stimulated ROS production, indicating the involvement of Ca(2+) and PLC. When the PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187, or the protein kinase C (PKC) activator, phorbol 12-myristate acetate (PMA)), a great increase in ROS production was observed. We further investigated the action mechanism of PTTH-stimulated ROS signaling. Results showed that in the presence of either an antioxidant (N-acetylcysteine, NAC), or the mitochondrial oxidative phosphorylation inhibitors (rotenone, antimycin A, the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP), and diphenyleneiodonium (DPI)), PTTH-regulated phosphorylation of ERK, 4E-BP, and AMPK was blocked. Treatment with 1mM of H2O2 alone activated the phosphorylation of ERK and 4E-BP, and inhibited AMPK phosphorylation. From these results, we conclude that PTTH-stimulated ROS signaling is Ca(2+)- and PLC-dependent and that ROS signaling appears to lie upstream of the phosphorylation of ERK, 4E-BP, and AMPK.

Phantom, a cytochrome P450 enzyme essential for ecdysone biosynthesis, plays a critical role in the control of border cell migration in Drosophila

The border cells of Drosophila are a model system for coordinated cell migration. Ecdysone signaling has been shown to act as the timing signal to initiate the migration process. Here we find that mutations in phantom (phm), encoding an enzyme in the ecdysone biosynthesis pathway, block border cell migration when the entire follicular epithelium of an egg chamber is mutant, even when the associated germline cells (nurse cells and oocyte) are wild-type. Conversely, mutant germline cells survive and do not affect border cell migration, as long as the surrounding follicle cells are wild-type. Interestingly, even small patches of wild-type follicle cells in a mosaic epithelium are sufficient to allow the production of above-threshold levels of ecdysone to promote border cell migration. The same phenotype is observed with mutations in shade (shd), encoding the last enzyme in the pathway that converts ecdysone to the active 20-hydroxyecdysone. Administration of high 20-hydroxyecdysone titers in the medium can also rescue the border cell migration phenotype in cultured egg chambers with an entirely phm mutant follicular epithelium. These results indicate that in normal oogenesis, the follicle cell epithelium of each individual egg chamber must supply sufficient ecdysone precursors, leading ultimately to high enough levels of mature 20-hydroxyecdysone to the border cells to initiate their migration. Neither the germline, nor the neighboring egg chambers, nor the surrounding hemolymph appear to provide threshold amounts of 20-hydroxyecdysone to do so. This "egg chamber autonomous" ecdysone synthesis constitutes a useful way to regulate the individual maturation of the asynchronous egg chambers present in the Drosophila ovary.

Common origin of insect trachea and endocrine organs from a segmentally repeated precursor

Segmented organisms have serially repeated structures [1] that become specialized in some segments [2]. We show here that the Drosophila corpora allata, prothoracic glands, and trachea have a homologous origin and can convert into each other. The tracheal epithelial tubes develop from ten trunk placodes [3, 4], and homologous ectodermal cells in the maxilla and labium form the corpora allata and the prothoracic glands. The early endocrine and trachea gene networks are similar, with STAT and Hox genes inducing their activation. The initial invagination of the trachea and the endocrine primordia is identical, but activation of Snail in the glands induces an epithelial-mesenchymal transition (EMT), after which the corpora allata and prothoracic gland primordia coalesce and migrate dorsally, joining the corpora cardiaca to form the ring gland. We propose that the arthropod ectodermal endocrine glands and respiratory organs arose through an extreme process of divergent evolution from a metameric repeated structure.

Microarray and RNAi analysis of P450s in Anopheles gambiae male and female steroidogenic tissues: CYP307A1 is required for ecdysteroid synthesis

In insects, the steroid hormone 20-hydroxyecdysone (20E) coordinates major developmental transitions. While the first and the final steps of 20E biosynthesis are characterized, the pathway from 7-dehydrocholesterol to 5β-ketodiol, commonly referred as the “black box”, remains hypothetical and whether there are still unidentified enzymes is unknown. The black box would include some oxidative steps, which are believed to be mediated by P450 enzymes. To identify new enzyme(s) involved in steroid synthesis, we analyzed by small-scale microarray the expression of all the genes encoding P450 enzymes of the malaria mosquito Anopheles gambiae in active steroidogenic organs of adults, ovaries from blood-fed females and male reproductive tracts, compared to inactive steroidogenic organs, ovaries from non-blood-fed females. Some genes encoding P450 enzymes were specifically overexpressed in female ovaries after a blood-meal or in male reproductive tracts but only three genes were found to be overexpressed in active steroidogenic organs of both females and males: cyp307a1, cyp4g16 and cyp6n1. Among these genes, only cyp307a1 has an expression pattern similar to other mosquito steroidogenic genes. Moreover, loss-of-function by transient RNAi targeting cyp307a1 disrupted ecdysteroid production demonstrating that this gene is required for ecdysteroid biosynthesis in Anopheles gambiae.

Identification of cytochrome P450 monooxygenase genes and their expression profiles in cyhalothrin-treated Colorado potato beetle, Leptinotarsa decemlineata

Based on a Leptinotarsa decemlineata transcriptome dataset and the GenBank sequences, a total of 74 cytochrome P450 monooxygenase genes (Cyps) were identified. These genes fell into CYP2 clan, mitochondrial clan, CYP3 clan and CYP4 clan, and were classified into 19 families and 35 subfamilies according to standard nomenclature. Two new families were discovered in CYP4 clan, and were named CYP412 and CYP413 respectively. Four new families that were recently discovered in Tribolium castaneum, including mitochondrial family CYP353, CYP3 clan families CYP345 and CYP347, and CYP4 clan family CYP350, were also found in L. decemlineata. The phylogenetic trees of CYPs from L. decemlineata and other representative insect species were constructed, and these trees provided evolutionary insight for the genetic distance. Our results facilitate further researches to understand the functions and evolution of L. decemlineata Cyp genes. In order to find cyhalothrin-inducible Cyp genes, the expression levels of Cyps belonging to CYP12, CYP6, CYP9 and CYP4 families were determined by quantitative reverse transcriptase-PCR in cyhalothrin-treated and control fourth-instar larvae. Nine Cyp genes, i.e., Cyp12H2, Cyp6BH2, Cyp6BJ1, Cyp6BQ17, Cyp6EG1, Cyp6EH1, Cyp6EJ1 Cyp4BN13v1 and Cyp4BN15, were highly expressed in cyhalothrin-treated larvae. These CYPs are the candidates that are involved in cyhalothrin detoxification.

Dynamic feedback circuits function as a switch for shaping a maturation-inducing steroid pulse in Drosophila

Steroid hormones trigger the onset of sexual maturation in animals by initiating genetic response programs that are determined by steroid pulse frequency, amplitude and duration. Although steroid pulses coordinate growth and timing of maturation during development, the mechanisms generating these pulses are not known. Here we show that the ecdysone steroid pulse that drives the juvenile-adult transition in Drosophila is determined by feedback circuits in the prothoracic gland (PG), the major steroid-producing tissue of insect larvae. These circuits coordinate the activation and repression of hormone synthesis, the two key parameters determining pulse shape (amplitude and duration). We show that ecdysone has a positive-feedback effect on the PG, rapidly amplifying its own synthesis to trigger pupariation as the onset of maturation. During the prepupal stage, a negative-feedback signal ensures the decline in ecdysone levels required to produce a temporal steroid pulse that drives developmental progression to adulthood. The feedback circuits rely on a developmental switch in the expression of Broad isoforms that transcriptionally activate or silence components in the ecdysone biosynthetic pathway. Remarkably, our study shows that the same well-defined genetic program that stimulates a systemic downstream response to ecdysone is also utilized upstream to set the duration and amplitude of the ecdysone pulse. Activation of this switch-like mechanism ensures a rapid, self-limiting PG response that functions in producing steroid oscillations that can guide the decision to terminate growth and promote maturation.

Molecular cloning and RNA interference-mediated functional characterization of a Halloween gene spook in the white-backed planthopper Sogatella furcifera

Background

Ecdysteroid hormones ecdysone and 20-hydroxyecdysone play fundamental roles in insect postembryonic development and reproduction. Five cytochrome P450 monooxygenases (CYPs), encoded by Halloween genes, have been documented to be involved in the ecdysteroidogenesis in insect species of diverse orders such as Diptera, Lepidoptera and Orthoptera. Up to now, however, the involvement of the Halloween genes in ecdysteroid synthesis has not been confirmed in hemipteran insect species.

Results

In the present paper, a Halloween gene spook (Sfspo, Sfcyp307a1) was cloned in the hemipteran Sogatella furcifera. SfSPO has three insect conserved P450 motifs, i.e., Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of Sfspo were evaluated by qPCR. Sfspo showed three expression peaks in late second-, third- and fourth-instar stages. In contrast, the expression levels were lower and formed three troughs in the newly-molted second-, third- and fourth-instar nymphs. On day 3 of the fourth-instar nymphs, Sfspo clearly had a high transcript level in the thorax where PGs were located. Dietary introduction of double-stranded RNA (dsRNA) of Sfspo into the second instars successfully knocked down the target gene, and greatly reduced expression level of ecdysone receptor (EcR) gene. Moreover, knockdown of Sfspo caused lethality and delayed development during nymphal stages. Furthermore, application of 20-hydroxyecdysone on Sfspo-dsRNA-exposed nymphs did not increase Sfspo expression, but could almost completely rescue SfEcR expression, and relieved the negative effects on nymphal survival and development.

Conclusion

In S. furcifera, Sfspo was cloned and the conservation of SfSPO is valid. Thus, SfSPO is probably also involved in ecdysteroidogenesis for hemiptera.

Silencing the ecdysone synthesis and signaling pathway genes disrupts nymphal development in the whitefly

Sap-sucking insects are important pests in agriculture and good models to study insect biology. The role of ecdysone pathway genes in the life history of this group of insects is largely unknown likely due to a lack of efficient gene silencing methods allowing functional genetic analyses. Here, we developed a new and high throughput method to silence whitefly genes using a leaf-mediated dsRNA feeding method. We have applied this method to explore the roles of genes within the molting hormone-ecdysone synthesis and signaling pathway for the survival, reproduction and development of whiteflies. Silencing of genes in the ecdysone pathway had a limited effect on the survival and fecundity of adult whiteflies. However, gene silencing reduced survival and delayed development of the whitefly during nymphal stages. These data suggest that the silencing method developed here provides a useful tool for functional gene discovery studies of sap-sucking insects, and further indicate the potential of regulating the ecdysone pathway in whitefly control.

Integrated analysis of cytochrome P450 gene superfamily in the red flour beetle, Tribolium castaneum

Background

The functional and evolutionary diversification of insect cytochrome P450s (CYPs) shaped the success of insects. CYPs constitute one of the largest and oldest gene superfamilies that are found in virtually all aerobic organisms. Because of the availability of whole genome sequence and well functioning RNA interference (RNAi), the red flour beetle, Tribolium castaneum serves as an ideal insect model for conducting functional genomics studies. Although several T. castaneum CYPs had been functionally investigated in our previous studies, the roles of the majority of CYPs remain largely unknown. Here, we comprehensively analyzed the phylogenetic relationship of all T. castaneum CYPs with genes in other insect species, investigated the CYP6BQ gene cluster organization, function and evolution, as well as examined the mitochondrial CYPs gene expression patterns and intron-exon organization.

Results

A total 143 CYPs were identified and classified into 26 families and 59 subfamilies. The phylogenetic trees of CYPs among insects across taxa provided evolutionary insight for the genetic distance and function. The percentage of singleton (33.3%) in T. castaneum CYPs is much less than those in Drosophila melanogaster (52.5%) and Bombyx mori (51.2%). Most members in the largest CYP6BQ gene cluster may make contribution to deltamethrin resistance in QTC279 strain. T. castaneum genome encodes nine mitochondrial CYPs, among them CYP12H1 is only expressed in the final instar larval stage. The intron-exon organizations of these mitochondrial CYPs are highly diverse.

Conclusion

Our studies provide a platform to understand the evolution and functions of T. castaneum CYP gene superfamily which will help reveal the strategies employed by insects to cope with their environment.

Activin receptor inhibition by Smad2 regulates Drosophila wing disc patterning through BMP-response elements

Imaginal disc development in Drosophila requires coordinated cellular proliferation and tissue patterning. In our studies of TGFβ superfamily signaling components, we found that a protein null mutation of Smad2, the only Activin subfamily R-Smad in the fruit fly, produces overgrown wing discs that resemble gain of function for BMP subfamily signaling. The wing discs are expanded specifically along the anterior-posterior axis, with increased proliferation in lateral regions. The morphological defect is not observed in mutants for the TGFβ receptor baboon, and epistasis tests showed that baboon is epistatic to Smad2 for disc overgrowth. Rescue experiments indicate that Baboon binding, but not canonical transcription factor activity, of Smad2 is required for normal disc growth. Smad2 mutant discs generate a P-Mad stripe that is narrower and sharper than the normal gradient, and activation targets are correspondingly expressed in narrowed domains. Repression targets of P-Mad are profoundly mis-regulated, with brinker and pentagone reporter expression eliminated in Smad2 mutants. Loss of expression requires a silencer element previously shown to be controlled by BMP signaling. Epistasis experiments show that Baboon, Mad and Schnurri are required to mediate the ectopic silencer output in the absence of Smad2. Taken together, our results show that loss of Smad2 permits promiscuous Baboon activity, which represses genes subject to control by Mad-dependent silencer elements. The absence of Brinker and Pentagone in Smad2 mutants explains the compound wing disc phenotype. Our results highlight the physiological relevance of substrate inhibition of a kinase, and reveal a novel interplay between the Activin and BMP pathways.

Accessory gland as a site for prothoracicotropic hormone controlled ecdysone synthesis in adult male insects

Insect steroid hormones (ecdysteroids) are important for female reproduction in many insect species and are required for the initiation and coordination of vital developmental processes. Ecdysteroids are also important for adult male physiology and behavior, but their exact function and site of synthesis remains unclear, although previous studies suggest that the reproductive system may be their source. We have examined expression profiles of the ecdysteroidogenic Halloween genes, during development and in adults of the flour beetle Tribolium castaneum. Genes required for the biosynthesis of ecdysone (E), the precursor of the molting hormone 20-hydroxyecdysone (20E), are expressed in the tubular accessory glands (TAGs) of adult males. In contrast, expression of the gene encoding the enzyme mediating 20E synthesis was detected in the ovaries of females. Further, Spookiest (Spot), an enzyme presumably required for endowing tissues with competence to produce ecdysteroids, is male specific and predominantly expressed in the TAGs. We also show that prothoracicotropic hormone (PTTH), a regulator of E synthesis during larval development, regulates ecdysteroid levels in the adult stage in Drosophila melanogaster and the gene for its receptor Torso seems to be expressed specifically in the accessory glands of males. The composite results suggest strongly that the accessory glands of adult male insects are the main source of E, but not 20E. The finding of a possible male-specific source of E raises the possibility that E and 20E have sex-specific roles analogous to the vertebrate sex steroids, where males produce primarily testosterone, the precursor of estradiol. Furthermore this study provides the first evidence that PTTH regulates ecdysteroid synthesis in the adult stage and could explain the original finding that some adult insects are a rich source of PTTH.

Origins of P450 diversity

The P450 enzymes maintain a conserved P450 fold despite a considerable variation in sequence. The P450 family even includes proteins that lack the single conserved cysteine and are therefore no longer haem-thiolate proteins. The mechanisms of successive gene duplications leading to large families in plants and animals are well established. Comparisons of P450 CYP gene clusters in related species illustrate the rapid changes in CYPome sizes. Examples of CYP copy number variation with effects on fitness are emerging, and these provide an opportunity to study the proximal causes of duplication or pseudogenization. Birth and death models can explain the proliferation of CYP genes that is amply illustrated by the sequence of every new genome. Thus, the distribution of P450 diversity within the CYPome of plants and animals, a few families with many genes (P450 blooms) and many families with few genes, follows similar power laws in both groups. A closer look at some families with few genes shows that these, often single member families, are not stable during evolution. The enzymatic prowess of P450 may predispose them to switch back and forth between metabolism of critical structural or signal molecules and metabolism dedicated to environmental response.

Study on ecdysteroid levels and gene expression of enzymes related to ecdysteroid biosynthesis in the larval testis of Spodoptera littoralis

We investigated here the ecdysteroid titers and the expression of six genes coding for known enzymes of the ecdysteroid biosynthesis in the testes of last instar larvae of the pest cotton leafworm, Spodoptera littoralis. We showed that the timing of the ecdysteroid profile was the same in testes and in hemolymph, with a small peak at day 2 and a large one at day 4 after ecdysis. Ecdysone and 20-hydroxyecdysone (20E) were detected in both tissues. 20E was the major ecdysteroid in testes and in hemolymph from day 4. Interestingly, the gene expression of the steroidogenetic enzymes, Neverland, and the five cytochrome P450 enzymes encoded by the Halloween genes was confirmed in the testes, and varied during the instar. However, from the data obtained so far, we cannot conclude that the measured ecdysteroids in the testes result from the activity of the genes under study. Indeed, it is suggested that the ecdysone produced centrally in the prothoracic glands, could have been transformed into 20E in the testes, where Sl-shade is well expressed.

Molecular cloning and expression profile of a Halloween gene encoding Cyp307A1 from the seabuckthorn carpenterworm, Holcocerus hippophaecolus

20-Hydroxyecdyone, an active form of ecdysteroid, is the key hormone in insect growth and development. Halloween genes encode ecdysteroidogenic enzymes, including cytochrome P450 monooxygenase. CYP307A1 (spook) is accepted as an enzyme acting in the so-called 'black box' that includes a series of hypothetical and unproven reactions that finally result in the oxidation of 7-dehydrocholesterol to diketol. In this study, the Holcocerus hippophaecolus Hua (Lepidoptera: Cossidae) CYP307A1 (HhSpo) gene was identified and characterized. The obtained cDNA sequence was 2084 base pairs with an open reading frame of 537 animo acids, in which existed conserved motifs of CYP450 enzymes. The transcript profiles of HhSpo were analyzed in various tissues of final instar larvae. The highest expression was observed in the prothoracic gland, while expression level was low but significant in other tissues. These results suggest that the sequence character and expression profile of HhSpo were well conserved and provided the basic information for its functional analysis.

What goes up must come down: transcription factors have their say in making ecdysone pulses

Insect metamorphosis is one of the most fascinating biological processes in the animal kingdom. The dramatic transition from an immature juvenile to a reproductive adult is under the control of the steroid hormone ecdysone, also known as the insect molting hormone. During Drosophila development, periodic pulses of ecdysone are released from the prothoracic glands, upon which the hormone is rapidly converted in peripheral tissues to its biologically active form, 20-hydroxyecdysone. Each hormone pulse has a unique profile and causes different developmental events, but we only have a rudimentary understanding of how the timing, amplitude, and duration of a given pulse are controlled. A key component involved in the timing of ecdysone pulses is PTTH, a brain-derived neuropeptide. PTTH stimulates ecdysone production through a Ras/Raf/ERK signaling cascade; however, comparatively little is known about the downstream targets of this pathway. In recent years, it has become apparent that transcriptional regulation plays a critical role in regulating the synthesis of ecdysone, but only one transcription factor has a well-defined link to PTTH. Interestingly, many of the ecdysteroidogenic transcription factors were originally characterized as primary response genes in the ecdysone signaling cascade that elicits the biological responses to the hormone in target tissues. To review these developments, we will first provide an overview of the transcription factors that act in the Drosophila ecdysone regulatory hierarchy. We will then discuss the roles of these transcriptional regulators in controlling ecdysone synthesis. In the last section, we will briefly outline transcription factors that likely have roles in regulating ecdysone synthesis but have not been formally identified as downstream effectors of ecdysone.

Developmental checkpoints and feedback circuits time insect maturation

The transition from juvenile to adult is a fundamental process that allows animals to allocate resource toward reproduction after completing a certain amount of growth. In insects, growth to a species-specific target size induces pulses of the steroid hormone ecdysone that triggers metamorphosis and reproductive maturation. The past few years have seen significant progress in understanding the interplay of mechanisms that coordinate timing of ecdysone production and release. These studies show that the neuroendocrine system monitors complex size-related and nutritional signals, as well as external cues, to time production and release of ecdysone. Based on results discussed here, we suggest that developmental progression to adulthood is controlled by checkpoints that regulate the genetic timing program enabling it to adapt to different environmental conditions. These checkpoints utilize a number of signaling pathways to modulate ecdysone production in the prothoracic gland. Release of ecdysone activates an autonomous cascade of both feedforward and feedback signals that determine the duration of the ecdysone pulse at each developmental transitions. Conservation of the genetic mechanisms that coordinate the juvenile-adult transition suggests that insights from the fruit fly Drosophila will provide a framework for future investigation of developmental timing in metazoans.

Tissue damage disrupts developmental progression and ecdysteroid biosynthesis in Drosophila

In humans, chronic inflammation, severe injury, infection and disease can result in changes in steroid hormone titers and delayed onset of puberty; however the pathway by which this occurs remains largely unknown. Similarly, in insects injury to specific tissues can result in a global developmental delay (e.g. prolonged larval/pupal stages) often associated with decreased levels of ecdysone – a steroid hormone that regulates developmental transitions in insects. We use Drosophila melanogaster as a model to examine the pathway by which tissue injury disrupts developmental progression. Imaginal disc damage inflicted early in larval development triggers developmental delays while the effects are minimized in older larvae. We find that the switch in injury response (e.g. delay/no delay) is coincident with the mid-3rd instar transition – a developmental time-point that is characterized by widespread changes in gene expression and marks the initial steps of metamorphosis. Finally, we show that developmental delays induced by tissue damage are associated with decreased expression of genes involved in ecdysteroid synthesis and signaling.

Conserved and divergent elements in Torso RTK activation in Drosophila development

The repeated use of signalling pathways is a common phenomenon but little is known about how they become co-opted in different contexts. Here we examined this issue by analysing the activation of Drosophila Torso receptor in embryogenesis and in pupariation. While its putative ligand differs in each case, we show that Torso-like, but not other proteins required for Torso activation in embryogenesis, is also required for Torso activation in pupariation. In addition, we demonstrate that distinct enhancers control torso-like expression in both scenarios. We conclude that repeated Torso activation is linked to a duplication and differential expression of a ligand-encoding gene, the acquisition of distinct enhancers in the torso-like promoter and the recruitment of proteins independently required for embryogenesis. A combination of these mechanisms is likely to allow the repeated activation of a single receptor in different contexts.

Analysis of the transcriptomes downstream of Eyeless and the Hedgehog, Decapentaplegic and Notch signaling pathways in Drosophila melanogaster

Tissue-specific transcription factors are thought to cooperate with signaling pathways to promote patterned tissue specification, in part by co-regulating transcription. The Drosophila melanogaster Pax6 homolog Eyeless forms a complex, incompletely understood regulatory network with the Hedgehog, Decapentaplegic and Notch signaling pathways to control eye-specific gene expression. We report a combinatorial approach, including mRNAseq and microarray analyses, to identify targets co-regulated by Eyeless and Hedgehog, Decapentaplegic or Notch. Multiple analyses suggest that the transcriptomes resulting from co-misexpression of Eyeless+signaling factors provide a more complete picture of eye development compared to previous efforts involving Eyeless alone: (1) Principal components analysis and two-way hierarchical clustering revealed that the Eyeless+signaling factor transcriptomes are closer to the eye control transcriptome than when Eyeless is misexpressed alone; (2) more genes are upregulated at least three-fold in response to Eyeless+signaling factors compared to Eyeless alone; (3) based on gene ontology analysis, the genes upregulated in response to Eyeless+signaling factors had a greater diversity of functions compared to Eyeless alone. Through a secondary screen that utilized RNA interference, we show that the predicted gene CG4721 has a role in eye development. CG4721 encodes a neprilysin family metalloprotease that is highly up-regulated in response to Eyeless+Notch, confirming the validity of our approach. Given the similarity between D. melanogaster and vertebrate eye development, the large number of novel genes identified as potential targets of Ey+signaling factors will provide novel insights to our understanding of eye development in D. melanogaster and humans.

Fungal ecdysteroid-22-oxidase, a new tool for manipulating ecdysteroid signaling and insect development

Steroid hormones ecdysteroids regulate varieties of developmental processes in insects. Although the ecdysteroid titer can be increased experimentally with ease, its artificial reduction, although desirable, is very difficult to achieve. Here we characterized the ecdysteroid-inactivating enzyme ecdysteroid-22-oxidase (E22O) from the entomopathogenic fungus Nomuraea rileyi and used it to develop methods for reducing ecdysteroid titer and thereby controlling insect development. K(m) and K(cat) values of the purified E22O for oxidizing ecdysone were 4.4 μM and 8.4/s, respectively, indicating that E22O can inactivate ecdysone more efficiently than other ecdysteroid inactivating enzymes characterized so far. The cloned E22O cDNA encoded a FAD-dependent oxidoreductase. Injection of recombinant E22O into the silkworm Bombyx mori interfered with larval molting and metamorphosis. In the hemolymph of E22O-injected pupae, the titer of hormonally active 20-hydroxyecdysone decreased and concomitantly large amounts of inactive 22-dehydroecdysteroids accumulated. E22O injection also prevented molting of various other insects. In the larvae of the crambid moth Haritalodes basipunctalis, E22O injection induced a diapause-like developmental arrest, which, as in normal diapause, was broken by chilling. Transient expression of the E22O gene by in vivo lipofection effectively decreased the 20-hydroxyecdysone titer and blocked molting in B. mori. Transgenic expression of E22O in Drosophila melanogaster caused embryonic morphological defects, phenotypes of which were very similar to those of the ecdysteroid synthesis deficient mutants. Thus, as the first available simple but versatile tool for reducing the internal ecdysteroid titer, E22O could find use in controlling a broad range of ecdysteroid-associated developmental and physiological phenomena.

A cytochrome p450 conserved in insects is involved in cuticle formation

The sequencing of numerous insect genomes has revealed dynamic changes in the number and identity of cytochrome P450 genes in different insects. In the evolutionary sense, the rapid birth and death of many P450 genes is observed, with only a small number of P450 genes showing orthology between insects with sequenced genomes. It is likely that these conserved P450s function in conserved pathways. In this study, we demonstrate the P450 gene, Cyp301a1, present in all insect genomes sequenced to date, affects the formation of the adult cuticle in Drosophila melanogaster. A Cyp301a1 piggyBac insertion mutant and RNAi of Cyp301a1 both show a similar cuticle malformation phenotype, which can be reduced by 20-hydroxyecdysone, suggesting that Cyp301a1 is an important gene involved in the formation of the adult cuticle and may be involved in ecdysone regulation in this tissue.

Synergism between altered cortical polarity and the PI3K/TOR pathway in the suppression of tumour growth

Loss of function of pins (partner of inscuteable) partially disrupts neuroblast (NB) polarity and asymmetric division, results in fewer and smaller NBs and inhibits Drosophila larval brain growth. Food deprivation also inhibits growth. However, we find that the combination of loss of function of pins and dietary restriction results in loss of NB asymmetry, overproliferation of Miranda-expressing cells, brain overgrowth and increased frequency of tumour growth on allograft transplantation. The same effects are observed in well-fed pins larvae that are mutant for pi3k (phosphatidylinositol 3-kinase) or exposed to the TOR inhibitor rapamycin. Thus, pathways that are sensitive to food deprivation and dependent on PI3K and TOR are essential to suppress tumour growth in Drosophila larval brains with compromised pins function. These results highlight an unexpected crosstalk whereby the normally growth-promoting, nutrient-sensing PI3K/TOR pathway suppresses tumour formation in neural stem cells with compromised cell polarity.

Novel cytochrome P450, cyp6a17, is required for temperature preference behavior in Drosophila

Perception of temperature is an important brain function for organisms to survive. Evidence suggests that temperature preference behavior (TPB) in Drosophila melanogaster, one of poikilothermal animals, is regulated by cAMP-dependent protein kinase (PKA) signaling in mushroom bodies of the brain. However, downstream targets for the PKA signaling in this behavior have not been identified. From a genome-wide search for the genes regulated by PKA activity in the mushroom bodies, we identified the cyp6a17 Cytochrome P450 gene as a new target for PKA. Our detailed analysis of mutants by genetic, molecular and behavioral assays shows that cyp6a17 is essential for temperature preference behavior. cyp6a17 expression is enriched in the mushroom bodies of the adult brain. Tissue-specific knockdown and rescue experiments demonstrate that cyp6a17 is required in the mushroom bodies for normal temperature preference behavior. This is the first study, to our knowledge, to show PKA-dependent expression of a cytochrome P450 gene in the mushroom bodies and its role as a key factor for temperature preference behavior. Taken together, this study reveals a new PKA-Cytochrome P450 pathway that regulates the temperature preference behavior.

Nuclear receptor DHR4 controls the timing of steroid hormone pulses during Drosophila development

Pulses of the steroid hormone ecdysone are turned off periodically through nucleo-cytoplasmic oscillations of a nuclear receptor that counteracts the neuropeptide signaling pathway responsible for activating hormone pulses in Drosophila melanogaster.

In insects, precisely timed periodic pulses of the molting hormone ecdysone control major developmental transitions such as molts and metamorphosis. The synthesis and release of ecdysone, a steroid hormone, is itself controlled by PTTH (prothoracicotopic hormone). PTTH transcript levels oscillate with an 8 h rhythm, but its significance regarding the timing of ecdysone pulses is unclear. PTTH acts on its target tissue, the prothoracic gland (PG), by activating the Ras/Raf/ERK pathway through its receptor Torso, however direct targets of this pathway have yet to be identified. Here, we demonstrate that Drosophila Hormone Receptor 4 (DHR4), a nuclear receptor, is a key target of the PTTH pathway and establishes temporal boundaries by terminating ecdysone pulses. Specifically, we show that DHR4 oscillates between the nucleus and cytoplasm of PG cells, and that the protein is absent from PG nuclei at developmental times when low titer ecdysone pulses occur. This oscillatory behavior is blocked when PTTH or torso function is abolished, resulting in nuclear accumulation of DHR4, while hyperactivating the PTTH pathway results in cytoplasmic retention of the protein. Increasing DHR4 levels in the PG can delay or arrest development. In contrast, reducing DHR4 function in the PG triggers accelerated development, which is caused by precocious ecdysone signaling due to a failure to repress ecdysone pulses. Finally, we show that DHR4 negatively regulates the expression of a hitherto uncharacterized cytochrome P450 gene, Cyp6t3. Disruption of Cyp6t3 function causes low ecdysteroid titers and results in heterochronic phenotypes and molting defects, indicating a novel role in the ecdysone biosynthesis pathway. We propose a model whereby nuclear DHR4 controls the duration of ecdysone pulses by negatively regulating ecdysone biosynthesis through repression of Cyp6t3, and that this repressive function is temporarily overturned via the PTTH pathway by removing DHR4 from the nuclear compartment.

Steroid hormones play fundamental roles in development and disease. They are often released as pulses, thereby orchestrating multiple physiological and developmental changes throughout the body. Hormone pulses must be regulated in a way so that they have a defined beginning, peak, and end. In Drosophila, pulses of the steroid hormone ecdysone govern all major developmental transitions, such as the molts or the transformation of a larva to a pupa. While we have a relatively good understanding of how an ecdysone pulse is initiated, little is known about how hormone production is turned off. In this study, we identify a critical regulator of this process, the nuclear receptor DHR4. When we interfere with the function of DHR4 specifically in the ecdysone-producing gland, we find that larvae develop much faster than normal, and that this is caused by the inability to turn off ecdysone production. We show that DHR4 oscillates between cytoplasm and nucleus of ecdysone-producing cells under the control of a neuropeptide that regulates ecdysone production. When the neuropeptide pathway is inactive, DHR4 enters the nucleus and represses another gene, Cyp6t3, for which we show a novel role in the production of ecdysone.

Role of the Halloween genes, Spook and Phantom in ecdysteroidogenesis in the desert locust, Schistocerca gregaria

The functional characterization of the Halloween genes represented a major breakthrough in the elucidation of the ecdysteroid biosynthetic pathway. These genes encode cytochrome P450 enzymes catalyzing the final steps of ecdysteroid biosynthesis in the dipteran Drosophila melanogaster and the Lepidoptera Manduca sexta and Bombyx mori. This is the first report on the identification of two Halloween genes, spook (spo) and phantom (phm), from a hemimetabolous orthopteran insect, the desert locust Schistocerca gregaria. Using q-RT-PCR, their spatial and temporal transcript profiles were analyzed in both final larval stage and adult locusts. The circulating ecdysteroid titers in the hemolymph were measured and found to correlate well with changes in the temporal transcript profiles of spo and phm. Moreover, an RNA interference (RNAi)-based approach was employed to study knockdown effects upon silencing of both transcripts in the fifth larval stage. Circulating ecdysteroid levels were found to be significantly reduced upon dsRNA treatment.

Nitric oxide coordinates metabolism, growth, and development via the nuclear receptor E75

Nitric oxide gas acts as a short-range signaling molecule in a vast array of important physiological processes, many of which include major changes in gene expression. How these genomic responses are induced, however, is poorly understood. Here, using genetic and chemical manipulations, we show that nitric oxide is produced in the Drosophila prothoracic gland, where it acts via the nuclear receptor ecdysone-induced protein 75 (E75), reversing its ability to interfere with its heterodimer partner, Drosophila hormone receptor 3 (DHR3). Manipulation of these interactions leads to gross alterations in feeding behavior, fat deposition, and developmental timing. These neuroendocrine interactions and consequences appear to be conserved in vertebrates.

Neuroendocrine regulation of Drosophila metamorphosis requires TGFbeta/Activin signaling

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

Ecdysteroid biosynthesis in workers of the European honeybee Apis mellifera L

We previously reported preferential expression of genes for ecdysteroid signaling in the mushroom bodies of honeybee workers, suggesting a role of ecdysteroid signaling in regulating honeybee behaviors. The organs that produce ecdysteroids in worker honeybees, however, remain unknown. We show here that the expression of neverland and Non-molting glossy/shroud, which are involved in early steps of ecdysteroid synthesis, was enhanced in the ovary, while the expression of CYP306A1 and CYP302A1, which are involved in later steps of ecdysone synthesis, was enhanced in the brain, and the expression of CYP314A1, which is involved in converting ecdysone into active 20-hydroxyecdysone (20E), was enhanced in the brain, fat body, and ovary. In in vitro organ culture, a significant amount of ecdysteroids was detected in the culture medium of the brain, fat body, and hypopharyngeal glands. The ecdysteroids detected in the culture medium of the fat body were identified as ecdysone and 20E. These findings suggest that, in worker honeybees, cholesterol is converted into intermediate ecdysteroids in the ovary, whereas ecdysone is synthesized and secreted mainly by the brain and converted into 20E in the brain and fat body.