Conversion of ecdysone and 20-hydroxyecdysone into 3-dehydroecdysteroids is a major pathway in third instar Drosophila melanogaster larvae

Cis-regulatory polymorphism at fiz ecdysone oxidase contributes to polygenic evolutionary response to malnutrition in Drosophila

We investigate the contribution of a candidate gene, fiz (fezzik), to complex polygenic adaptation to juvenile malnutrition in Drosophila melanogaster. Experimental populations maintained for >250 generations of experimental evolution to a nutritionally poor larval diet (Selected populations) evolved several-fold lower fiz expression compared to unselected Control populations. Here we show that this divergence in fiz expression is mediated by a cis-regulatory polymorphism. This polymorphism, originally sampled from a natural population in Switzerland, is distinct from a second cis-regulatory SNP previously identified in non-African D. melanogaster populations, implying that two independent cis-regulatory variants promoting high fiz expression segregate in non-African populations. Enzymatic analyses of Fiz protein expressed in E. coli demonstrate that it has ecdysone oxidase activity acting on both ecdysone and 20-hydroxyecdysone. Four of five fiz paralogs annotated to ecdysteroid metabolism also show reduced expression in Selected larvae, implying that malnutrition-driven selection favored general downregulation of ecdysone oxidases. Finally, as an independent test of the role of fiz in poor diet adaptation, we show that fiz knockdown by RNAi results in faster larval growth on the poor diet, but at the cost of greatly reduced survival. These results imply that downregulation of fiz in Selected populations was favored by selection on the nutritionally poor diet because of its role in suppressing growth in response to nutrient shortage. However, they suggest that fiz downregulation is only adaptive in combination with other changes evolved by Selected populations, which ensure that the organism can sustain the faster growth promoted by fiz downregulation.

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.

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Crustacean oxi-reductases protein sequences derived from a functional genomic project potentially involved in ecdysteroid hormones metabolism - a starting point for function examination

A transcriptomic assembly originated from hypodermis and Y organ of the crustacean Pontastacus leptodactylus is used here for in silico characterization of oxi-reductase enzymes potentially involved in the metabolism of ecdysteroid molting hormones. RNA samples were extracted from male Y organ and its neighboring hypodermis in all stages of the molt cycle. An equimolar RNA mix from all stages was sequenced using next generation sequencing technologies and de novo assembled, resulting with 74,877 unique contigs. These transcript sequences were annotated by examining their resemblance to all GenBank translated transcripts, determining their Gene Ontology terms and their characterizing domains. Based on the present knowledge of arthropod ecdysteroid metabolism and more generally on steroid metabolism in other taxa, transcripts potentially related to ecdysteroid metabolism were identified and their longest possible conceptual protein sequences were constructed in two stages, correct reading frame was deduced from BLASTX resemblances, followed by elongation of the protein sequence by identifying the correct translation frame of the original transcript. The analyzed genes belonged to several oxi-reductase superfamilies including the Rieske non heme iron oxygenases, cytochrome P450s, short-chained hydroxysteroid oxi-reductases, aldo/keto oxireductases, lamin B receptor/sterol reductases and glucose-methanol-cholin oxi-reductatses. A total of 68 proteins were characterized and the most probable participants in the ecdysteroid metabolism where indicated. The study provides transcript and protein structural information, a starting point for further functional studies, using a variety of gene-specific methods to demonstrate or disprove the roles of these proteins in relation to ecdysteroid metabolism in P. leptodactylus.

Diversity of detoxification pathways of ingested ecdysteroids among phytophagous insects

The metabolic pathways of ingested ecdysteroids have been investigated in three insect species, the aphid Myzus persicae and two Lepidoptera, Plodia interpunctella and Ostrinia nubilalis. M. persicae produces mainly a 22-glucoside conjugate, whereas P. interpunctella eliminates a mixture of 20E and its 3-oxo and 3-epi derivatives, both in free form and as conjugates with various fatty acids. O. nubilalis only produces fatty acyl ester conjugates. These data point out the great diversity of detoxification mechanisms used by phytophagous insects in order to overcome the potential harmful effects of ecdysteroids present in their food.

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.

Study of steroidogenesis in pupae of the forensically important blow fly Protophormia terraenovae (Robineau-Desvoidy) (Diptera: Calliphoridae)

Protophormia terraenovae is a forensically important fly whose development time is studied by forensic entomologists to establish the time elapsed since death (post-mortem interval, PMI). Quantity and nature of ecdysteroid hormones present in P. terraenovae pupae were analysed in order to determine if they could be correlated to the age of pupae found on corpses and thereby could give information on the PMI. Ecdysteroid levels were quantified during the pupal-adult development of synchronised animals using enzyme immunoassay (EIA), a sensitive method allowing acurate quantification in one pupa. Two types of pupae were compared: "fresh" pupae, kept frozen until analysis and "experimentally dried" pupae, which were left for several weeks at ambient temperature. A peak of ecdysteroids was detected between 36 and 96 h after pupariation in fresh animals. It was not observed in "experimentally dried" pupae. High-pressure liquid chromatography (HPLC) analyses combined with EIA showed that 20-hydroxyecdysone (20E) was the major free ecdysteroid at various pupal ages. Enzymatic hydrolysis experiments revealed the presence of apolar conjugates at all ages tested. However, neither qualitative nor quantitative difference was detected between early and late pupae. This study gives precise information on the nature and quantity of ecdysteroids in the course of pupal development of a calliphorid fly. The limits of using ecdysteroid measurement as a tool in forensic entomology are discussed.

Regulation of ecdysteroid signalling during Drosophila development: identification, characterization and modelling of ecdysone oxidase, an enzyme involved in control of ligand concentration

The steroidal moulting hormones (ecdysteroids) mediate developmental transitions in insects, and their regulation is mainly controlled by the production and inactivation of these steroid hormones at the appropriate developmental times. One route of metabolism of ecdysteroids in insects involves EO (ecdysone oxidase)-catalysed conversion into 3-dehydroecdysteroid, which undergoes reduction to the corresponding 3-epiecdysteroid. By a twin-stranded bioinformatics approach, employing both phylogenomics and model structure-based analysis, we first predicted that DmEO (the EO of Drosophila melanogaster) corresponds to the protein product of gene CG9504. When CG9504 was expressed in COS7 cells, significant conversion of ecdysone into 3-dehydroecdysone was observed. Quantitative PCR and enzyme assay showed that DmEO was mainly expressed in the midgut during the late instars at a time corresponding to a hormone titre peak. DmEO shares only 27% amino acid sequence identity with Spodoptera littoralis (Lepidoptera) EO, yet key substrate-binding residues are well conserved. A model of DmEO is consistent with an inability to catalyse reaction of cholesterol derivatives. The significance of DmEO in ligand activation is discussed in relation to new evidence suggesting that 3-dehydro- and 3-epiecdysteroids may be functionally active as ligands in a novel, atypical ecdysteroid signalling pathway involving the Drosophila orphan nuclear receptor, DHR38, rather than being merely hormone inactivation products.

Shade is the Drosophila P450 enzyme that mediates the hydroxylation of ecdysone to the steroid insect molting hormone 20-hydroxyecdysone

The steroid 20-hydroxyecdysone (20E) is the primary regulatory hormone that mediates developmental transitions in insects and other arthropods. 20E is produced from ecdysone (E) by the action of a P450 monooxygenase that hydroxylates E at carbon 20. The gene coding for this key enzyme of ecdysteroidogenesis has not been identified definitively in any insect. We show here that the Drosophila E-20-monooxygenase (E20MO) is the product of the shade (shd) locus (cytochrome p450, CYP314a1). When shd is transfected into Drosophila S2 cells, extensive conversion of E to 20E is observed, whereas in sorted homozygous shd embryos, no E20MO activity is apparent either in vivo or in vitro. Mutations in shd lead to severe disruptions in late embryonic morphogenesis and exhibit phenotypes identical to those seen in disembodied (dib) and shadow (sad) mutants, two other genes of the Halloween class that code for P450 enzymes that catalyze the final two steps in the synthesis of E from 2,22-dideoxyecdysone. Unlike dib and sad, shd is not expressed in the ring gland but is expressed in peripheral tissues such as the epidermis, midgut, Malpighian tubules, and fat body, i.e., tissues known to be major sites of E20MO activity in a variety of insects. However, the tissue in which shd is expressed does not appear to be important for developmental function because misexpression of shd in the embryonic mesoderm instead of the epidermis, the normal embryonic tissue in which shd is expressed, rescues embryonic lethality.

The Drosophila orphan nuclear receptor DHR38 mediates an atypical ecdysteroid signaling pathway

Ecdysteroid pulses trigger the major developmental transitions during the Drosophila life cycle. These hormonal responses are thought to be mediated by the ecdysteroid receptor (EcR) and its heterodimeric partner Ultraspiracle (USP). We provide evidence for a second ecdysteroid signaling pathway mediated by DHR38, the Drosophila ortholog of the mammalian NGFI-B subfamily of orphan nuclear receptors. DHR38 also heterodimerizes with USP, and this complex responds to a distinct class of ecdysteroids in a manner that is independent of EcR. This response is unusual in that it does not involve direct binding of ecdysteroids to either DHR38 or USP. X-ray crystallographic analysis of DHR38 reveals the absence of both a classic ligand binding pocket and coactivator binding site, features that seem to be common to all NGFI-B subfamily members. Taken together, these data reveal the existence of a separate structural class of nuclear receptors that is conserved from fly to humans.

Regulation of Ecdysteroid Signaling: Cloning and Characterization of Ecdysone Oxidase

One route of inactivation of ecdysteroids in insects involves ecdysone oxidase-catalyzed conversion into 3-dehydroecdysteroid followed by irreversible reduction by 3-dehydroecdysone 3alpha-reductase to 3-epiecdysone. We have purified from Spodoptera littoralis the first ecdysone oxidase and subjected it to limited amino acid sequencing. A reverse-transcriptase polymerase chain reaction-based approach has been used to clone the cDNA (2.8 kilobases) encoding this 65-kDa protein. Northern blotting showed that the mRNA transcript was expressed in midgut during the prepupal stage of the last larval instar at a time corresponding to an ecdysteroid titer peak. Conceptual translation of the ecdysone oxidase cDNA and data base searching revealed that the enzyme is an FAD flavoprotein that belongs to the glucose-methanol-choline oxidoreductase superfamily. Ecdysone oxidase represents the only oxidase in eukaryotic animals known to catalyze oxygen-dependent oxidation of steroids; by contrast, oxidation of steroids in vertebrates occurs via NAD(P)(+)-linked dehydrogenases. The injection of RH-5992, an ecdysteroid agonist, induced the transcription of ecdysone oxidase, suggesting that ecdysone oxidase is an ecdysteroid-responsive gene. The gene encoding this enzyme, consisting of five exons, has also been isolated. Sequences similar to the binding motifs for Broad-Complex and FTZ-F1 have been found in the 5'-flanking region. Southern blotting indicated that ecdysone oxidase is encoded by a single-copy gene. We have determined the kinetic characteristics of this novel recombinant ecdysone oxidase produced using a baculovirus expression system.

Transcriptional activation of the Drosophila ecdysone receptor by insect and plant ecdysteroids

A number of insect ecdysteroids, plant ecdysteroids and juvenoids were assayed for their ability to activate Drosophila nuclear receptors in transfected tissue culture cells. Discrete modifications to 20-hydroxyecdysone, the apparent natural ligand for the ecdysone receptor (EcR), conferred dramatic changes on the transcriptional activity of this receptor, suggesting that other biologically relevant EcR ligands may exist. Conversely, none of the compounds tested had a significant effect on the activity of three Drosophila orphan nuclear receptors: DHR38, DHR78 or DHR96. Taken together, these results demonstrate the selectivity of EcR for a series of natural and synthetic ecdysone agonists and suggest that as yet untested compounds may be responsible for activating DHR38, DHR78 and DHR96.

Action of different ecdysteroids on the regulation of mRNAs for the ecdysone receptor, MHR3, dopa decarboxylase, and a larval cuticle protein in the larval epidermis of the tobacco hornworm, Manduca sexta

To determine which ecdysteroids may be biologically active in the larval epidermis of the tobacco hornworm, Manduca sexta, we studied the action of several known ecdysteroids and metabolites on the expression of the genes encoding the ecdysone receptor (EcR), Manduca hormone receptor 3 (MHR3), dopa decarboxylase (DDC), and a larval cuticle protein (LCP-14). Both Day 2 fourth- and Day 2 fifth-instar larval epidermis contained significant 3 beta-reductase activity which metabolized 3-dehydroecdysone (3DE) and 3-dehydro-20-hydroxyecdysone (3D20E) to ecdysone (E) and 20-hydroxyecdysone (20E), respectively, but had only very low amounts of ecdysone oxidase activity (E to 3DE) and no detectable ecdysone 20-monooxygenase activity (E to 20E). When the expression of the various genes was studied in the epidermis in vitro, 20E and 3D20E had similar effects, whereas E, 3DE, 26-hydroxyecdysone and 20,26-dihydroxyecdysone were ineffective. Exposure of Day 2 fifth-instar epidermis to 500 ng/ml of either 20E or 3D20E for 24 hr caused a rapid, biphasic increase in EcR-B1 mRNA. By contrast, EcR-A mRNA showed a less rapid initial increase followed by a slow steady rise and was less responsive to 3D20E. Ecdysone in a 1:1 mixture with 20E effectively halved the concentration of 20E needed to induce EcR-B1 mRNA but showed no synergism in the induction of EcR-A mRNA. The induction of MHR3 mRNA and of DDC mRNA in Day 2 fourth-instar epidermis as well as the suppression of DDC and LCP-14 gene expression by 3D20E was indistinguishable from that of 20E. Therefore, for Manduca larval epidermis, only 20E and 3D20E are biologically active ecdysteroids. Since the 3D20E can be converted to 20E by the epidermis, its effects are likely mediated by 20E.

Differential incorporation of cholesterol and cholesterol derivatives into ecdysteroids by the larval ring glands and adult ovaries of Drosophila melanogaster: a putative explanation for the l(3)ecd1 mutation

Studies in vitro revealed that intact ring glands of Drosophila melanogaster convert tritiated cholesterol (C) and 25-hydroxycholesterol (25C) via 7-dehydrocholesterol (7dC) and 7-dehydro-25-hydroxycholesterol (7d25C), respectively, to ecdysone (E) and 2-deoxyecdysone (2dE), while both intact and homogenized ovaries synthesize only 2dE from these precursors. Emulsified 7d25C was incorporated directly into ecdysteroids by these tissue preparations at a much greater rate than was 7d25C made in situ from 25C. To probe the basis of the biochemical defect in the ecdysteroid deficient conditional mutant ecdysoneless (ecd1), the differential incorporation into ecdysteroids of C (via 7dC), and particularly of 25C (via 7d25C), was measured relative to that observed after the incubation of 7d25C directly with both wild type and mutant tissues in vitro at 30 degrees C, the restrictive temperature. Both C and 25C were equally 7,8-dehydrogenated in situ to 7dC or 7d25C, respectively, by both wild type and mutant tissues at 30 degrees C. However, the rate of subsequent conversion of either of these delta 5,7-sterol intermediates synthesized in situ to ecdysteroids was reduced an average of 50% in the mutant tissues relative to the wild type. Yet, when emulsified 7d25C was incubated directly with either the wild type or mutant tissues at the restrictive temperature, the amplified rate of conversion of the freely available 7d25C to ecdysteroid by these tissues was identical. These data suggest that the defect in ecd1 tissue-mediated ecdysteroidogenesis does not involve a "hit" on any of the enzymes involved in either the 7,8-dehydrogenation of C or 25C or in the subsequent oxidation of 7d25C or 7dC to ecdysteroid. Rather, the mutation appears to affect the expression of a gene governing the translocation of delta 5,7-sterol intermediates from the subcellular compartment where they are synthesized and/or stored to the site of subsequent oxidation to ecdysteroid.

Insect nuclear receptors: a developmental and comparative perspective

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

Metabolism of ecdysone and 20-hydroxyecdysone in adult Drosophila melanogaster

The metabolism of [3H]ecdysone injected into adult female and male Drosophila melanogaster was investigated. The metabolites present in flies and faeces were analysed separately after incubation times of 1, 2 or 4 h. In female flies ecdysone-22-fatty acid acyl esters were the major metabolites followed by 3-dehydroecdysone, 26-hydroxyecdysone, ecdysonoic acid, 20-hydroxyecdysone and a negatively charged conjugate of ecdysone. In male flies the same compounds were formed, but their relative concentrations were somewhat different from those in female flies. All metabolites formed can be excreted. [3H]20-hydroxyecdysone was metabolized in much the same way: 20-hydroxyecdysone-22-acyl esters, 3-dehydro-20-hydroxyecdysone, 20-hydroxy-ecdysonoic acid and a negatively charged conjugate of 20-hydroxyecdysone were formed. However, 20,26-dihydroxyecdysone could not be detected after injection of [3H]20-hydroxyecdysone.

Developmental requirements for the ecdysoneless (ecd) locus in Drosophila melanogaster

The ecdysoneless locus in Drosophila melanogaster has been defined previously by a single conditional mutation, I(3)ecd1, that causes an ecdysteroid deficit and larval death at the restrictive temperature, 29 degrees C, although the primary role of the mutation in developmental processes has been unclear. Gene dosage and complementation studies reported here for ecd1 and five nonconditional lethal alleles indicate that the ecd locus plays prezygotic and postzygotic roles essential for normal embryonic development, the successful completion of each larval molt, adult eclosion, and female fertility. The ecd locus is also required for normal macrochaete differentiation. For each observed phenotype, the severity of mutational effects was correlated with ecd mutant genotypes. In all cases, ecd1 homozygotes were least affected. Mutants heteroallelic for ecd1 and any one of four nonconditional recessive mutations were more severely affected than ecd1 homozygotes, revealing these as hypomorphic alleles. For all phenotypic effects, mutants heteroallelic for ecd1 and a dominant mutation (ecd3D) were most severely affected. These individuals died during embryogenesis at 29 degrees C and developed no macrochaetes on the dorsal thorax when transferred to 29 degrees C during the white prepupal stage. The ecd3D mutation also caused female semisterility in heterozygotes. Ecdysteroid regulation has been implicated previously in all the developmental processes disrupted by these ecd mutations except for macrochaete differentiation.

Evidence that Y-organs of the crab Cancer antennarius secrete 3-dehydroecdysone

Y-organs are paired glands in crustaceans that secrete a class of steroid hormones (ecdysteroids) that regulate growth, molting and development. The glandular secretion has been assumed to be solely the ecdysteroid, ecdysone, a polyhydroxylated derivative of cholesterol. We previously reported that Y-organs of a crab (Cancer antennarius) additionally secreted an ecdysteroid that is less polar than ecdysone. Evidence is presented here that the other secretion product is 3-dehydroecdysone (3-dhE). The compound co-chromatographed with authentic 3-dhE in both normal-phase, and reversed-phase, high-performance liquid chromatography. Mass spectrometry of the ecdysteroid gave results consistent with its identity as 3-dhE. The putative 3-dhE was radiolabeled by injecting crabs with [3H]cholesterol and then incubating the Y-organs. The putative [3H]3-dhE secretion was then subjected to chemical reduction. The reaction yielded labeled products that co-chromatographed with authentic ecdysone and 3-epiecdysone. Results of other experiments gave the following results: (1) Putative 3-dhE was not altered (chromatographic criteria) by incubations with snail hydrolases. (2) Putative [3H]3-dhE, added to incubations of Y-organ halves or homogenates, was not significantly converted to ecdysone; also, no conversion was evident after incubation in medium alone in which the hemolymph serum supplement was raised to 50% of the volume. (3) [3H]Ecdysone was not converted to putative 3-dhE in vitro by Y-organ halves or homogenates.(ABSTRACT TRUNCATED AT 250 WORDS)

Larval fat body-specific gene expression in D. melanogaster

The Pl gene, together with the LSP-1 alpha, -1 beta, and -1 gamma, LSP-2, and P6 genes, is expressed exclusively in the larval fat body of D. melanogaster during the third instar. In vivo mapping of the cis-acting regulatory sequences of the P1 gene was carried out using hybrid constructs with three different reporter genes and a combination of transient and germline transformation assays. This revealed that regulatory elements involved in the setting up of the temporal and spatial specificities of transcription of the P1 gene are located in a short DNA region immediately upstream of the mRNA transcription start. This region includes an element that behaves as a fat-body transcriptional enhancer and element(s) required for ecdysone inducibility of transcription of the P1 gene.