The Drosophila takeout gene is regulated by the somatic sex-determination pathway and affects male courtship behavior

Systemic corazonin signalling modulates stress responses and metabolism in Drosophila

Stress triggers cellular and systemic reactions in organisms to restore homeostasis. For instance, metabolic stress, experienced during starvation, elicits a hormonal response that reallocates resources to enable food search and readjustment of physiology. Mammalian gonadotropin-releasing hormone (GnRH) and its insect orthologue, adipokinetic hormone (AKH), are known for their roles in modulating stress-related behaviour. Here we show that corazonin (Crz), a peptide homologous to AKH/GnRH, also alters stress physiology in Drosophila. The Crz receptor (CrzR) is expressed in salivary glands and adipocytes of the liver-like fat body, and CrzR knockdown targeted simultaneously to both these tissues increases the fly's resistance to starvation, desiccation and oxidative stress, reduces feeding, alters expression of transcripts of Drosophila insulin-like peptides (DILPs), and affects gene expression in the fat body. Furthermore, in starved flies, CrzR-knockdown increases circulating and stored carbohydrates. Thus, our findings indicate that elevated systemic Crz signalling during stress coordinates increased food intake and diminished energy stores to regain metabolic homeostasis. Our study suggests that an ancient stress-peptide in Urbilateria evolved to give rise to present-day GnRH, AKH and Crz signalling systems.

Characterization of Spodoptera litura (Lepidoptera: Noctuidae) Takeout Genes and Their Differential Responses to Insecticides and Sex Pheromone

Spodoptera litura (S. litura) is one of the most serious agricultural insect pests worldwide. Takeout (TO) is involved in a variety of physiological and biochemical pathways and performs various biological functions. We characterized 18 S. litura TO genes and investigated their differential responses to insecticides and sex pheromones. All predicted TO proteins have two Cysteines that are unique to the N-terminal of the TO family proteins and contain four highly conserved Prolines, two Glycines, and one Tyrosine. The expression levels of seven TO genes in the male antennae were higher than those in the female antennae, although the expression levels of 10 TO genes in the female were higher than those in the male. We investigated the effects of the sex pheromone and three insecticides, that is, chlorpyrifos (Ch), emamectin benzoate (EB), and fipronil (Fi), on the expression levels of the TO genes in the antennae. The results showed that the insecticides and sex pheromone affect the expression levels of the TO genes. One day after the treatment, the expression levels of SlTO15 and SlTO4 were significantly induced by the Ch/EB treatment. Two days after the S. litura moths were treated with Fi, the expression of SlTO4 was significantly induced (28.35-fold). The expression of SlTO10 changed significantly after the Ch and EB treatment, although the expression of SlTO12 and SlTO15 was inhibited by the three insecticides after two days of treatment. Our results lay a foundation for studying the role of TO genes in the interaction between insecticides and sex pheromone.

Transcriptome profiling of ontogeny in the acridid grasshopper Chorthippus biguttulus

Acridid grasshoppers (Orthoptera:Acrididae) are widely used model organisms for developmental, evolutionary, and neurobiological research. Although there has been recent influx of orthopteran transcriptomic resources, many use pooled ontogenetic stages obscuring information about changes in gene expression during development. Here we developed a de novo transcriptome spanning 7 stages in the life cycle of the acridid grasshopper Chorthippus biguttulus. Samples from different stages encompassing embryonic development through adults were used for transcriptomic profiling, revealing patterns of differential gene expression that highlight processes in the different life stages. These patterns were validated with semi-quantitative RT-PCR. Embryonic development showed a strongly differentiated expression pattern compared to all of the other stages and genes upregulated in this stage were involved in signaling, cellular differentiation, and organ development. Our study is one of the first to examine gene expression during post-embryonic development in a hemimetabolous insect and we found that only the fourth and fifth instars had clusters of genes upregulated during these stages. These genes are involved in various processes ranging from synthesis of biogenic amines to chitin binding. These observations indicate that post-embryonic ontogeny is not a continuous process and that some instars are differentiated. Finally, genes upregulated in the imago were generally involved in aging and immunity. Our study highlights the importance of looking at ontogeny as a whole and indicates promising directions for future research in orthopteran development.

Distinct Roles of Met and Interacting Proteins on the Expressions of takeout Family Genes in Brown Planthopper

The takeout family genes encode relatively small proteins that are related to olfaction and are regulated by juvenile hormone (JH). The takeout genes modulate various physiological processes, such as behavioral plasticity in the migratory locust Locusta migraloria and feeding and courtship behaviors in Drosophila. Therefore, to understand the regulatory mechanism of these physiological processes, it is important to study the expressions of the takeout genes that are regulated by JH signaling. We used quantitative real-time PCR (qRTPCR) to study the role of JH signaling in the regulation of the takeout family genes in the brown planthopper Nilaparvata lugens (N. lugens) through the application of Juvenile hormone III (JHIII) and the down-regulation of key genes in the JH signaling pathway. The topical application of JHIII induced the expressions of most of the takeout family genes, and their expressions decreased 2 and 3 days after the JHIII application. Down-regulating the brown planthopper JH receptor NlMethoprene-tolerant (NlMet) and its interacting partners, NlTaiman (NlTai) and Nlß-Ftz-F1 (Nlß-Ftz), through RNAi, exhibited distinct effects on the expressions of the takeout family genes. The down-regulation of NlMet and NlKrüppel-homolog 1 (NlKr-h1) increased the expressions of the takeout family genes, while the down-regulation of the Met interacting partners NlTai and Nlß-Ftz decreased the expressions of most of the takeout family genes. This work advanced our understanding of the molecular function and the regulatory mechanism of JH signaling.

Neural and non-neural contributions to sexual dimorphism of mid-day sleep in Drosophila melanogaster: a pilot study

Many of the characteristics associated with mammalian sleep are also observed in Drosophila melanogaster Meigen, making the fruit fly a powerful model organism for studying the genetics of this important process. Included among the similarities is the presence of sexual dimorphic sleep patterns, which, in flies, are manifested as increased mid-day sleep ('siesta') in males compared with females. In the present study, targeted mis-expression of the genes transformer (tra) and tra2 is used to either feminize or masculinize specific neural and non-neural tissues in the fly. Feminization of male D. melanogaster using three different GAL4 drivers that are expressed in the mushroom bodies induces a female-like reduced siesta, whereas the masculinization of females using these drivers triggers the male-like increased siesta. A similar reversal of sex-specific sleep is also observed by mis-expressing tra in the fat body, which is a key tissue in energy metabolism and hormone secretion. In addition, the daily expression levels of takeout, an important circadian clock output gene, are sexually dimorphic. Taken together, these experiments suggest that sleep sexual dimorphism in D. melanogaster is driven by multiple neural and non-neural circuits, within and outside the brain.

Molecular mechanisms of secondary sexual trait development in insects

Secondary sexual traits are those traits other than the primary gametes that distinguish the sexes of a species. The development of secondary sexual traits occurs when sexually dimorphic factors, that is, molecules differentially produced by primary sex determination systems in males and females, are integrated into the gene regulatory networks responsible for sexual trait development. In insects, these molecular asymmetric factors were always considered to originate inside the trait-building cells, but recent work points to external factors, such as hormones, as potential candidates mediating secondary sexual trait development. Here, we review examples of the different molecular mechanisms producing sexually dimorphic traits in insects, and suggest a need to revise our understanding of secondary sexual trait development within the insect lineage.

Juvenile Hormone Is Required in Adult Males for Drosophila Courtship

Juvenile Hormone (JH) has a prominent role in the regulation of insect development. Much less is known about its roles in adults, although functions in reproductive maturation have been described. In adult females, JH has been shown to regulate egg maturation and mating. To examine a role for JH in male reproductive behavior we created males with reduced levels of Juvenile Hormone Acid O-Methyl Transferase (JHAMT) and tested them for courtship. JHAMT regulates the last step of JH biosynthesis in the Corpora Allata (CA), the organ of JH synthesis. Males with reduced levels of JHAMT showed a reduction in courtship that could be rescued by application of Methoprene, a JH analog, shortly before the courtship assays were performed. In agreement with this, reducing JHAMT conditionally in mature flies led to courtship defects that were rescuable by Methoprene. The same result was also observed when the CA were conditionally ablated by the expression of a cellular toxin. Our findings demonstrate that JH plays an important physiological role in the regulation of male mating behavior.

Transcriptomes of parents identify parenting strategies and sexual conflict in a subsocial beetle

Parenting in the burying beetle Nicrophorus vespilloides is complex and, unusually, the sex and number of parents that can be present is flexible. Such flexibility is expected to involve specialized behaviour by the two sexes under biparental conditions. Here, we show that offspring fare equally well regardless of the sex or number of parents present. Comparing transcriptomes, we find a largely overlapping set of differentially expressed genes in both uniparental and biparental females and in uniparental males including vitellogenin, associated with reproduction, and takeout, influencing sex-specific mating and feeding behaviour. Gene expression in biparental males is similar to that in non-caring states. Thus, being ‘biparental’ in N. vespilloides describes the family social organization rather than the number of directly parenting individuals. There was no specialization; instead, in biparental families, direct male parental care appears to be limited with female behaviour unchanged. This should lead to strong sexual conflict.

The burying beetle shows flexible parenting behaviour. Here, the authors show that offspring fare equally well regardless of the sex or number of parents present and find similar gene expression profiles in uniparental and biparental females and in uniparental males, which suggests no specialization in parenting.

Reproductive workers show queenlike gene expression in an intermediately eusocial insect, the buff-tailed bumble bee Bombus terrestris

Bumble bees represent a taxon with an intermediate level of eusociality within Hymenoptera. The clear division of reproduction between a single founding queen and the largely sterile workers is characteristic for highly eusocial species, whereas the morphological similarity between the bumble bee queen and the workers is typical for more primitively eusocial hymenopterans. Also, unlike other highly eusocial hymenopterans, division of labour among worker subcastes is plastic and not predetermined by morphology or age. We conducted a differential expression analysis based on RNA-seq data from 11 combinations of developmental stage and caste to investigate how a single genome can produce the distinct castes of queens, workers and males in the buff-tailed bumble bee Bombus terrestris. Based on expression patterns, we found males to be the most distinct of all adult castes (2411 transcripts differentially expressed compared to nonreproductive workers). However, only relatively few transcripts were differentially expressed between males and workers during development (larvae: 71 and pupae: 162). This indicates the need for more distinct expression patterns to control behaviour and physiology in adults compared to those required to create different morphologies. Among female castes, reproductive workers and their nonreproductive sisters displayed differential expression in over ten times more transcripts compared to the differential expression found between reproductive workers and their mother queen. This suggests a strong shift towards a more queenlike behaviour and physiology when a worker becomes fertile. This contrasts with eusocial species where reproductive workers are more similar to nonreproductive workers than the queen.

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.

Gene expression during imidacloprid-induced hormesis in green peach aphid

Imidacloprid-induced hormesis in the form of stimulated reproduction has previously been reported in green peach aphid, Myzus persicae. Changes in gene expression accompanying this hormetic response have not been previously investigated. In this study, expression of stress response (Hsp60), dispersal (OSD, TOL and ANT), and developmental (FPPS I) genes were examined for two generations during imidacloprid-induced reproductive stimulation in M. persicae. Global DNA methylation was also measured to test the hypothesis that changes in gene expression are heritable. At hormetic concentrations, down-regulation of Hsp60 was followed by up-regulation of this gene in the subsequent generation. Likewise, expression of dispersal-related genes and FPPS I varied with concentration, life stage, and generation. These results indicate that reproductive hormesis in M. persicae is accompanied by a complex transgenerational pattern of up- and down-regulation of genes that likely reflects trade-offs in gene expression and related physiological processes during the phenotypic dose-response. Moreover, DNA methylation in second generation M. persicae occurred at higher doses than in first-generation aphids, suggesting that heritable adaptability to low doses of the stressor might have occurred.

Genome wide identification of fruitless targets suggests a role in upregulating genes important for neural circuit formation

The fruitless gene (fru) encodes a set of transcription factors (Fru) that display sexually dimorphic gene expression in the brain of the fruit-fly; Drosophila melanogaster. Behavioural studies have demonstrated that fru is essential for courtship behaviour in the male fly and is thought to act by directing the development of sex-specific neural circuitry that encodes this innate behavioural response. This study reports the identification of direct regulatory targets of the sexually dimorphic isoforms of the Fru protein using an in vitro model system. Genome wide binding sites were identified for each of the isoforms using Chromatin Immunoprecipitation coupled to deep sequencing (ChIP-Seq). Putative target genes were found to be involved in processes such as neurotransmission, ion-channel signalling and neuron development. All isoforms showed a significant bias towards genes located on the X-chromosome, which may reflect a specific role for Fru in regulating x-linked genes. Taken together with expression analysis carried out in Fru positive neurons specifically isolated from the male fly brain, it appears that the Fru protein acts as a transcriptional activator. Understanding the regulatory cascades induced by Fru will help to shed light on the molecular mechanisms that are important for specification of neural circuitry underlying complex behaviour.

Transcriptome analysis in venom gland of the predatory giant ant Dinoponera quadriceps: insights into the polypeptide toxin arsenal of hymenopterans

Background

Dinoponera quadriceps is a predatory giant ant that inhabits the Neotropical region and subdues its prey (insects) with stings that deliver a toxic cocktail of molecules. Human accidents occasionally occur and cause local pain and systemic symptoms. A comprehensive study of the D. quadriceps venom gland transcriptome is required to advance our knowledge about the toxin repertoire of the giant ant venom and to understand the physiopathological basis of Hymenoptera envenomation.

Results

We conducted a transcriptome analysis of a cDNA library from the D. quadriceps venom gland with Sanger sequencing in combination with whole-transcriptome shotgun deep sequencing. From the cDNA library, a total of 420 independent clones were analyzed. Although the proportion of dinoponeratoxin isoform precursors was high, the first giant ant venom inhibitor cysteine-knot (ICK) toxin was found. The deep next generation sequencing yielded a total of 2,514,767 raw reads that were assembled into 18,546 contigs. A BLAST search of the assembled contigs against non-redundant and Swiss-Prot databases showed that 6,463 contigs corresponded to BLASTx hits and indicated an interesting diversity of transcripts related to venom gene expression. The majority of these venom-related sequences code for a major polypeptide core, which comprises venom allergens, lethal-like proteins and esterases, and a minor peptide framework composed of inter-specific structurally conserved cysteine-rich toxins. Both the cDNA library and deep sequencing yielded large proportions of contigs that showed no similarities with known sequences.

Conclusions

To our knowledge, this is the first report of the venom gland transcriptome of the New World giant ant D. quadriceps. The glandular venom system was dissected, and the toxin arsenal was revealed; this process brought to light novel sequences that included an ICK-folded toxins, allergen proteins, esterases (phospholipases and carboxylesterases), and lethal-like toxins. These findings contribute to the understanding of the ecology, behavior and venomics of hymenopterans.

CAST-ChIP maps cell-type-specific chromatin states in the Drosophila central nervous system

Chromatin organization and gene activity are responsive to developmental and environmental cues. Although many genes are transcribed throughout development and across cell types, much of gene regulation is highly cell-type specific. To readily track chromatin features at the resolution of cell types within complex tissues, we developed and validated chromatin affinity purification from specific cell types by chromatin immunoprecipitation (CAST-ChIP), a broadly applicable biochemical procedure. RNA polymerase II (Pol II) CAST-ChIP identifies ~1,500 neuronal and glia-specific genes in differentiated cells within the adult Drosophila brain. In contrast, the histone H2A.Z is distributed similarly across cell types and throughout development, marking cell-type-invariant Pol II-bound regions. Our study identifies H2A.Z as an active chromatin signature that is refractory to changes across cell fates. Thus, CAST-ChIP powerfully identifies cell-type-specific as well as cell-type-invariant chromatin states, enabling the systematic dissection of chromatin structure and gene regulation within complex tissues such as the brain.

Reduction of Cellular Lipid Content by a Knockdown of Drosophila PDP1 γ and Mammalian Hepatic Leukemia Factor

In exploring the utility of double-stranded RNA (dsRNA) injections for silencing the PAR-domain protein 1 (Pdp1) gene in adult Drosophila, we noticed a dramatic loss of fat tissue lipids. To verify that our RNAi approach produced the expected Pdp1 knockdown, the abdominal fat tissues sections were stained with PDP1 antibodies. PDP1 protein immunostaining was absent in flies injected with dsRNA targeting a sequence common to all known Pdp1 isoforms. Subsequent experiments revealed that lipid staining is reduced in flies injected with dsRNA against Pdp1 γ (fat body specific) and not against Pdp1 ε (predominantly involved in circadian mechanisms). Drosophila PDP1 γ protein shows a high homology to mammalian thyrotroph embryonic factor (TEF), albumin D site-binding protein (DBP), and hepatic leukemia factor (HLF) transcription factors. In an in vitro model of drug- (olanzapine-) induced adiposity in mouse 3T3-L1 cells, the mRNA content of HLF but not TEF and DBP was increased by the drug treatment. A knockdown of the HLF mRNA by transfecting the cultures with HLF dsRNA significantly reduced their lipid content. Furthermore, the HLF RNAi prevented olanzapine from increasing the cell lipid content. These results suggest that the PDP1/HLF system may play a role in physiological and drug-influenced lipid regulation.

Sex-switching of the Drosophila brain by two antagonistic chromatin factors

In Drosophila melanogaster, the fruitless (fru) gene encoding BTB-Zn-finger transcription factors organizes male sexual behavior by controlling the development of sexually dimorphic neuronal circuitry. However, the molecular mechanism by which fru controls the sexual fate of neurons has been unknown. Our recent study represents a first step toward clarification of this mechanism. We have shown that: (1) Fru forms a complex with the transcriptional cofactor Bonus (Bon), which recruits either of two chromatin regulators, Histone deacetylase 1 (HDAC1) or Heterochromatin protein 1a (HP1a), to Fru-target sites; (2) the Fru-Bon complex has a masculinizing effect on single sexually-dimorphic neurons when it recruits HDAC1, whereas it has a demasculinizing effect when it recruits HP1a; (3) HDAC1 or HP1a thus recruited to Fru-target sites determines the sexual fate of single neurons in an all-or-none manner, as manipulations of HDAC1 or HP1a expression levels affect the proportion of male-typical neurons and female-typical neurons without producing neurons of intersexual characteristics. Here, we hypothesize that chromatin landscape changes induced by ecdysone surges direct the HDAC1- or HP1a-containing Fru complex to distinct targets, thereby allowing them to switch the neuronal sexual fate in the brain.

Genomics of sex determination in Drosophila

Drosophilists have identified many, or perhaps most, of the key regulatory genes determining sex using classical genetics, however, regulatory genes must ultimately result in the deployment of the genome in a quantitative manner, replete with complex interactions with other regulatory pathways. In the last decade, genomics has provided a rich picture of the transcriptional profile of the sexes that underlies sexual dimorphism. The current challenge is linking transcriptional profiles with the regulatory genes. This will be a complex synthesis, but the prospects for progress are outstanding.

Sex-specific signaling in the blood-brain barrier is required for male courtship in Drosophila

Soluble circulating proteins play an important role in the regulation of mating behavior in Drosophila melanogaster. However, how these factors signal through the blood–brain barrier (bbb) to interact with the sex-specific brain circuits that control courtship is unknown. Here we show that male identity of the blood–brain barrier is necessary and that male-specific factors in the bbb are physiologically required for normal male courtship behavior. Feminization of the bbb of adult males significantly reduces male courtship. We show that the bbb–specific G-protein coupled receptor moody and bbb–specific Go signaling in adult males are necessary for normal courtship. These data identify sex-specific factors and signaling processes in the bbb as important regulators of male mating behavior.

Complex behaviors such as mating behavior are controlled by the brain. Ensembles of brain cells work in networks to ensure proper behavior at the right time. While the state of these cells plays an important role in whether and how the behavior is displayed, information from outside the brain is also required. Often, this information is provided by hormones that are present in the circulating fluid (such as the blood). However, the brain is protected by a layer of very tight cells, the so-called blood–brain barrier, that keeps unwanted molecules out. So how then do hormones and other regulatory factors “talk” to the brain? We are studying this question by examining the mating behavior of males of a model organism, the fruit fly Drosophila melanogaster. We have found that the blood–brain barrier cells themselves contain male-specific molecules that play an important role. When they are absent, courtship behavior is compromised. We have also identified how outside factors talk to the brain: by using a cellular signaling protein and a particular signaling pathway. Together they are well suited to pass on outside information to the brain network that regulates mating behavior.

doublesex functions early and late in gustatory sense organ development

Somatic sexual dimorphisms outside of the nervous system in Drosophila melanogaster are largely controlled by the male- and female-specific Doublesex transcription factors (DSX(M) and DSX(F), respectively). The DSX proteins must act at the right times and places in development to regulate the diverse array of genes that sculpt male and female characteristics across a variety of tissues. To explore how cellular and developmental contexts integrate with doublesex (dsx) gene function, we focused on the sexually dimorphic number of gustatory sense organs (GSOs) in the foreleg. We show that DSX(M) and DSX(F) promote and repress GSO formation, respectively, and that their relative contribution to this dimorphism varies along the proximodistal axis of the foreleg. Our results suggest that the DSX proteins impact specification of the gustatory sensory organ precursors (SOPs). DSX(F) then acts later in the foreleg to regulate gustatory receptor neuron axon guidance. These results suggest that the foreleg provides a unique opportunity for examining the context-dependent functions of DSX.

takeout-dependent longevity is associated with altered Juvenile Hormone signaling

In order to understand the molecular mechanisms of longevity regulation, we recently performed a screen designed to enrich for genes common to several longevity interventions. Using this approach, we identified the Drosophila melanogaster gene takeout. takeout is upregulated in a variety of long-lived flies, and extends life span when overexpressed. Here, we investigate the mechanisms of takeout-dependent longevity. takeout overexpression specifically in the fat body is sufficient to increase fly longevity and is additive to the longevity effects of Dietary Restriction. takeout long-lived flies do not show phenotypes often associated with increased longevity, such as enhanced stress resistance or major metabolic abnormalities. However, males exhibit greatly diminished courtship behavior, leading to a reduction in fertility. Interestingly, takeout contains a binding domain for Juvenile Hormone, a fly hormone that plays a role in the regulation of developmental transitions. Importantly, the longevity and courtship phenotypes of takeout overexpressing flies are reversed by treatment with the Juvenile Hormone analog methoprene. These data suggest that takeout is a key player in the tradeoff-switch between fertility and longevity. takeout may control fertility via modulation of courtship behavior. This regulation may occur through Juvenile Hormone binding to takeout and a subsequent reduction in Juvenile Hormone signaling activity.

Mio/dChREBP coordinately increases fat mass by regulating lipid synthesis and feeding behavior in Drosophila

During nutrient excess, triglycerides are synthesized and stored to provide energy during times of famine. The presence of high glucose leads to the activation of carbohydrate response element binding protein (ChREBP), a transcription factor that induces the expression of a number of glycolytic and lipogenic enzymes. ChREBP is expressed in major metabolic tissues and while we have a basic understanding of ChREBP function in liver, in vivo genetic systems to study the function of ChREBP in other tissues are lacking. In this study, we characterized the role of the Drosophila homolog of ChREBP, Mlx interactor (Mio), in controlling fat accumulation in larvae and adult flies. In Mio mutants, high sugar-induced lipogenic enzyme mRNA expression is blunted and lowering Mio levels specifically in the fat body using RNA interference leads to a lean phenotype. A lean phenotype is also observed when the gene bigmax, the fly homolog of ChREBP's binding partner Mlx, is decreased in the larval fat body. Interestingly, depleting Mio in the fat body results in decreased feeding providing a potential cause of the lowered triglycerides observed in these animals. However, Mio does not seem to function as a general regulator of hunger-induced behaviors as decreasing fat body Mio levels has no effect on sleep under fed or starved conditions. Together, these data implicate a role for Mio in controlling fat accumulation in Drosophila and suggests that it may act as a nutrient sensor in the fat body to coordinate feeding behavior with nutrient availability.

Brain sex differences and function of the fruitless gene in Drosophila

The fruitless (fru) gene in Drosophila plays a pivotal role in the formation of neural circuits underlying gender-specific behaviors. Specific labeling of fru expressing neurons has revealed a core circuit responsible for male courtship behavior.Females with a small number of masculinized neuronal clusters in their brain can initiate male-type courtship behavior. By examining the correlations between the masculinized neurons and behavioral gender type, a male-specific neuronal cluster,named P1, which coexpresses fru and double sex, was identified as a putative trigger center for male-type courtship behavior. P1 neurons extend dendrite to the lateral horn,where multimodal sensory inputs converge. Molecular studies suggest that fru determines the level of masculinization of neurons by orchestrating the transcription of a set of downstream genes, which remain to be identified.

High-throughput sequencing to reveal genes involved in reproduction and development in Bactrocera dorsalis (Diptera: Tephritidae)

BACKGROUND

Tephritid fruit flies in the genus Bactrocera are of major economic significance in agriculture causing considerable loss to the fruit and vegetable industry. Currently, there is no ideal control program. Molecular means is an effective method for pest control at present, but genomic or transcriptomic data for members of this genus remains limited. To facilitate molecular research into reproduction and development mechanisms, and finally effective control on these pests, an extensive transcriptome for the oriental fruit fly Bactrocera dorsalis was produced using the Roche 454-FLX platform.

RESULTS

We obtained over 350 million bases of cDNA derived from the whole body of B. dorsalis at different developmental stages. In a single run, 747,206 sequencing reads with a mean read length of 382 bp were obtained. These reads were assembled into 28,782 contigs and 169,966 singletons. The mean contig size was 750 bp and many nearly full-length transcripts were assembled. Additionally, we identified a great number of genes that are involved in reproduction and development as well as genes that represent nearly all major conserved metazoan signal transduction pathways, such as insulin signal transduction. Furthermore, transcriptome changes during development were analyzed. A total of 2,977 differentially expressed genes (DEGs) were detected between larvae and pupae libraries, while there were 1,621 DEGs between adults and larvae, and 2,002 between adults and pupae. These DEGs were functionally annotated with KEGG pathway annotation and 9 genes were validated by qRT-PCR.

CONCLUSION

Our data represent the extensive sequence resources available for B. dorsalis and provide for the first time access to the genetic architecture of reproduction and development as well as major signal transduction pathways in the Tephritid fruit fly pests, allowing us to elucidate the molecular mechanisms underlying courtship, ovipositing, development and detailed analyses of the signal transduction pathways.

The hector G-protein coupled receptor is required in a subset of fruitless neurons for male courtship behavior

Male courtship behavior in Drosophila melanogaster is controlled by two main regulators, fruitless (fru) and doublesex (dsx). Their sex-specific expression in brain neurons has been characterized in detail, but little is known about the downstream targets of the sex-specific FRU and DSX proteins and how they specify the function of these neurons. While sexual dimorphism in the number and connections of fru and dsx expressing neurons has been observed, a majority of the neurons that express the two regulators are present in both sexes. This poses the question which molecules define the sex-specific function of these neurons. Signaling molecules are likely to play a significant role. We have identified a predicted G-protein coupled receptor (GPCR), CG4395, that is required for male courtship behavior. The courtship defect in the mutants can be rescued by expression of the wildtype protein in fru neurons of adult males. The GPCR is expressed in a subset of fru-positive antennal glomeruli that have previously been shown to be essential for male courtship. Expression of 4395-RNAi in GH146 projection neurons lowers courtship. This suggests that signaling through the CG4395 GPCR in this subset of fru neurons is critical for male courtship behavior.

Transcriptome and gene expression profile of ovarian follicle tissue of the triatomine bug Rhodnius prolixus

Insect oocytes grow in close association with the ovarian follicular epithelium (OFE), which escorts the oocyte during oogenesis and is responsible for synthesis and secretion of the eggshell. We describe a transcriptome of OFE of the triatomine bug Rhodnius prolixus, a vector of Chagas disease, to increase our knowledge of the role of FE in egg development. Random clones were sequenced from a cDNA library of different stages of follicle development. The transcriptome showed high commitment to transcription, protein synthesis, and secretion. The most abundant cDNA was a secreted (S) small, proline-rich protein with maximal expression in the vitellogenic follicle, suggesting a role in oocyte maturation. We also found Rp45, a chorion protein already described, and a putative chitin-associated cuticle protein that was an eggshell component candidate. Six transcripts coding for proteins related to the unfolded-protein response (UPR) by were chosen and their expression analyzed. Surprisingly, transcripts related to UPR showed higher expression during early stages of development and downregulation during late stages, when transcripts coding for S proteins participating in chorion formation were highly expressed. Several transcripts with potential roles in oogenesis and embryo development are also discussed. We propose that intense protein synthesis at the FE results in reticulum stress (RS) and that lowering expression of a set of genes related to cell survival should lead to degeneration of follicular cells at oocyte maturation. This paradoxical suppression of UPR suggests that ovarian follicles may represent an interesting model for studying control of RS and cell survival in professional S cell types.

Somatic sex-specific transcriptome differences in Drosophila revealed by whole transcriptome sequencing

Background

Understanding animal development and physiology at a molecular-biological level has been advanced by the ability to determine at high resolution the repertoire of mRNA molecules by whole transcriptome resequencing. This includes the ability to detect and quantify rare abundance transcripts and isoform-specific mRNA variants produced from a gene.

The sex hierarchy consists of a pre-mRNA splicing cascade that directs the production of sex-specific transcription factors that specify nearly all sexual dimorphism. We have used deep RNA sequencing to gain insight into how the Drosophila sex hierarchy generates somatic sex differences, by examining gene and transcript isoform expression differences between the sexes in adult head tissues.

Results

Here we find 1,381 genes that differ in overall expression levels and 1,370 isoform-specific transcripts that differ between males and females. Additionally, we find 512 genes not regulated downstream of transformer that are significantly more highly expressed in males than females. These 512 genes are enriched on the × chromosome and reside adjacent to dosage compensation complex entry sites, which taken together suggests that their residence on the × chromosome might be sufficient to confer male-biased expression. There are no transcription unit structural features, from a set of features, that are robustly significantly different in the genes with significant sex differences in the ratio of isoform-specific transcripts, as compared to random isoform-specific transcripts, suggesting that there is no single molecular mechanism that generates isoform-specific transcript differences between the sexes, even though the sex hierarchy is known to include three pre-mRNA splicing factors.

Conclusions

We identify thousands of genes that show sex-specific differences in overall gene expression levels, and identify hundreds of additional genes that have differences in the abundance of isoform-specific transcripts. No transcription unit structural feature was robustly enriched in the sex-differentially expressed transcript isoforms. Additionally, we found that many genes with male-biased expression were enriched on the × chromosome and reside adjacent to dosage compensation entry sites, suggesting that differences in sex chromosome composition contributes to dimorphism in gene expression. Taken together, this study provides new insight into the molecular underpinnings of sexual differentiation.

Systems behavior: of male courtship, the nervous system and beyond in Drosophila

Male courtship in fruit flies is regulated by the same major regulatory genes that also determine general sexual differentiation of the animal. Elaborate genetics has given us insight into the roles of these master genes. These findings have suggested two separate and independent pathways for the regulation of sexual behavior and other aspects of sexual differentiation. Only recently have molecular studies started to look at the downstream effector genes and how they might control sex-specific behavior. These studies have confirmed the essential role of the previously identified male specific products of the fruitless gene in the neuronal circuits in which it is expressed. But there is increasing evidence that a number of non-neuronal tissues and pathways play a pivotal role in modulating this circuit and assuring efficient courtship.

The circadian clock interacts with metabolic physiology to influence reproductive fitness

Circadian rhythms are regulated by a synchronized system of central and peripheral clocks. Here, we show that a clock in the Drosophila fat body drives rhythmic expression of genes involved in metabolism, detoxification, the immune response, and steroid hormone regulation. Some of these genes cycle even when the fat body clock is disrupted, indicating that they are regulated by exogenous factors. Food is an important stimulus, as limiting food availability to a 6 hr interval each day drives rhythmic expression of genes in the fat body. Restricting food to a time of day when consumption is typically low desynchronizes internal rhythms because it alters the phase of rhythmic gene expression in the fat body without affecting the brain clock. Flies maintained on this paradigm produce fewer eggs than those restricted to food at the normal time. These data suggest that desynchrony of endogenous rhythms, caused by aberrant feeding patterns, affects reproductive fitness.

CSP and takeout genes modulate the switch between attraction and repulsion during behavioral phase change in the migratory locust

Behavioral plasticity is the most striking trait in locust phase transition. However, the genetic basis for behavioral plasticity in locusts is largely unknown. To unravel the molecular mechanisms underlying the behavioral phase change in the migratory locust Locusta migratoria, the gene expression patterns over the time courses of solitarization and gregarization were compared by oligonucleotide microarray analysis. Data analysis revealed that several gene categories relevant to peripheral olfactory perception are strongly regulated in a total of 1,444 differentially expressed genes during both time courses. Among these candidate genes, several CSP (chemosensory protein) genes and one takeout gene, LmigTO1, showed higher expression in gregarious and solitarious locusts, respectively, and displayed opposite expression trends during solitarization and gregarization. qRT-PCR experiments revealed that most CSP members and LmigTO1 exhibited antenna-rich expressions. RNA interference combined with olfactory behavioral experiments confirmed that the CSP gene family and one takeout gene, LmigTO1, are involved in the shift from repulsion to attraction between individuals during gregarization and in the reverse transition during solitarization. These findings suggest that the response to locust-emitted olfactory cues regulated by CSP and takeout genes is involved in the behavioral phase change in the migratory locust and provide a previously undescribed molecular mechanism linked to the formation of locust aggregations.

The migratory locust, Locusta migratoria, is a worldwide agricultural pest whose outbreaks can result in plagues during which locusts mass migrate in marching bands and flying swarms. They exhibit striking phenotypic plasticity depending on the population density. They can transform between the barely-visible solitarious phase and the swarm-forming gregarious phase. A key step in the formation of large aggregation is the initial shift from the strong mutual aversion in solitarious locusts to the attraction to each other in gregarious locusts. Previous genomics studies have revealed 532 differentially expressed genes and many regulating small RNAs between the two phases of the migratory locust. Here, we developed a large-scale oligonucleotide microarray to quantify the expression of 9,154 genes during the time courses of isolating gregarious locusts and crowding solitarious locusts. We found that several olfaction-related genes, several CSPs and one takeout, are strongly regulated during both processes and display opposite expression trends in response to population density change. We then identified that these genes mediate the rapid switch of attraction/repulsion behaviors in the migratory locust. Our findings are particularly significant for understanding the process of locust aggregation and may provide new targets to manipulate locust behavior as part of novel management strategies.

The sex-biased brain: sexual dimorphism in gene expression in two species of songbirds

Background

Despite virtually identical DNA sequences between the sexes, sexual dimorphism is a widespread phenomenon in nature. To a large extent the systematic differences between the sexes must therefore arise from processes involving gene regulation. In accordance, sexual dimorphism in gene expression is common and extensive. Genes with sexually dimorphic regulation are known to evolve rapidly, both in DNA sequence and in gene expression profile. Studies of gene expression in related species can shed light on the flexibility, or degree of conservation, of the gene expression profiles underlying sexual dimorphism.

Results

We have studied the extent of sexual dimorphism in gene expression in the brain of two species of songbirds, the zebra finch (Taeniopygia guttata) and the common whitethroat (Sylvia communis), using large-scale microarray technology. Sexual dimorphism in gene expression was extensive in both species, and predominantly sex-linked: most genes identified were male-biased and Z-linked. Interestingly, approximately 50% of the male-biased Z-linked genes were sex-biased only in one of the study species.

Conclusion

Our results corroborate the results of recent studies in chicken and zebra finch which have been interpreted as caused by a low degree of dosage compensation in female birds (i.e. the heterogametic sex). Moreover, they suggest that zebra finches and common whitethroats dosage compensate partly different sets of genes on the Z chromosome. It is possible that this pattern reflects differences in either the essentiality or the level of sexual antagonism of these genes in the respective species. Such differences might correspond to genes with different rates of evolution related to sexual dimorphism in the avian brain, and might therefore be correlated with differences between the species in sex-specific behaviours.

Socially-responsive gene expression in male Drosophila melanogaster is influenced by the sex of the interacting partner

Behavior is influenced by an organism's genes and environment, including its interactions with same or opposite sex individuals. Drosophila melanogaster perform innate, yet socially modifiable, courtship behaviors that are sex specific and require rapid integration and response to multiple sensory cues. Furthermore, males must recognize and distinguish other males from female courtship objects. It is likely that perception, integration, and response to sex-specific cues is partially mediated by changes in gene expression. Reasoning that social interactions with members of either sex would impact gene expression, we compared expression profiles in heads of males that courted females, males that interacted with other males, or males that did not interact with another fly. Expression of 281 loci changes when males interact with females, whereas 505 changes occur in response to male-male interactions. Of these genes, 265 are responsive to encounters with either sex and 240 respond specifically to male-male interactions. Interestingly, 16 genes change expression only when a male courts a female, suggesting that these changes are a specific response to male-female courtship interactions. We supported our hypothesis that socially-responsive genes can function in behavior by showing that egghead (egh) expression, which increases during social interactions, is required for robust male-to-female courtship. We predict that analyzing additional socially-responsive genes will give us insight into genes and neural signaling pathways that influence reproductive and other behavioral interactions.

Molecular genetic analysis of circadian timekeeping in Drosophila

A genetic screen for mutants that alter circadian rhythms in Drosophila identified the first clock gene-the period (per) gene. The per gene is a central player within a transcriptional feedback loop that represents the core mechanism for keeping circadian time in Drosophila and other animals. The per feedback loop, or core loop, is interlocked with the Clock (Clk) feedback loop, but whether the Clk feedback loop contributes to circadian timekeeping is not known. A series of distinct molecular events are thought to control transcriptional feedback in the core loop. The time it takes to complete these events should take much less than 24h, thus delays must be imposed at different steps within the core loop. As new clock genes are identified, the molecular mechanisms responsible for these delays have been revealed in ever-increasing detail and provide an in-depth accounting of how transcriptional feedback loops keep circadian time. The phase of these feedback loops shifts to maintain synchrony with environmental cycles, the most reliable of which is light. Although a great deal is known about cell-autonomous mechanisms of light-induced phase shifting by CRYPTOCHROME (CRY), much less is known about non-cell autonomous mechanisms. CRY mediates phase shifts through an uncharacterized mechanism in certain brain oscillator neurons and carries out a dual role as a photoreceptor and transcription factor in other tissues. Here, I review how transcriptional feedback loops function to keep time in Drosophila, how they impose delays to maintain a 24-h cycle, and how they maintain synchrony with environmental light:dark cycles. The transcriptional feedback loops that keep time in Drosophila are well conserved in other animals, thus what we learn about these loops in Drosophila should continue to provide insight into the operation of analogous transcriptional feedback loops in other animals.

The roles of fruitless and doublesex in the control of male courtship

Male courtship in Drosophila melanogaster is a robust innate behavior that is shaped by sensory input and experience. It is regulated by the general sex-determination pathway through the sex-specific forms of fruitless and doublesex. Recent findings have shown that both fruitless and doublesex are required for courtship. This chapter reviews the role of these proteins and the neurons that express them in the regulation of courtship behavior. In particular it discusses how doublesex and fruitless contribute to the generation of sexually dimorphic neurons, the role of cell death, and the emerging information about circuits that underlie the behavior.

Screening of T7 phage displayed Bactrocera dorsalis (Hendel) antenna cDNA library against chemosensory protein

Recent studies have shown that chemosensory proteins (CSPs) were involved in diverse life activities such as insect feeding, development, mating, immune regulation, as well as other important circadian rhythms, etc. To screen the proteins involved in the BdorCSP-related physiological activity, a cDNA library of the Bactrocera dorsalis (Hendel) antenna expressed on the surface of T7 phage was screened against BdorCSP. After four rounds of screening, ELISA-positive samples of selected phages were sequenced and identified as protein disulfide isomerase (PDI), trypsin-like serine protease (Ser), TakeOut (TO), and a new protein by GenBank blast, respectively. Real-time quantitative PCR results showed that the expression levels of Ser, TO, and the new protein were the highest in antenna, sharing similar expression pattern with BdorCSP. These results reveal that these proteins might be involved in the BdorCSP-related physiological or metabolic activities. This work paves a new way for exploring the function of CSPs.

Mating alters gene expression patterns in Drosophila melanogaster male heads

Background

Behavior is a complex process resulting from the integration of genetic and environmental information. Drosophila melanogaster rely on multiple sensory modalities for reproductive success, and mating causes physiological changes in both sexes that affect reproductive output or behavior. Some of these effects are likely mediated by changes in gene expression. Courtship and mating alter female transcript profiles, but it is not known how mating affects male gene expression.

Results

We used Drosophila genome arrays to identify changes in gene expression profiles that occur in mated male heads. Forty-seven genes differed between mated and control heads 2 hrs post mating. Many mating-responsive genes are highly expressed in non-neural head tissues, including an adipose tissue called the fat body. One fat body-enriched gene, female-specific independent of transformer (fit), is a downstream target of the somatic sex-determination hierarchy, a genetic pathway that regulates Drosophila reproductive behaviors as well as expression of some fat-expressed genes; three other mating-responsive loci are also downstream components of this pathway. Another mating-responsive gene expressed in fat, Juvenile hormone esterase (Jhe), is necessary for robust male courtship behavior and mating success.

Conclusions

Our study demonstrates that mating causes changes in male head gene expression profiles and supports an increasing body of work implicating adipose signaling in behavior modulation. Since several mating-induced genes are sex-determination hierarchy target genes, additional mating-responsive loci may be downstream components of this pathway as well.

Time to taste: circadian clock function in the Drosophila gustatory system

Circadian clocks keep time in the digestive, circulatory, reproductive, excretory and nervous systems even in absence of external cues. Central oscillators in the brain control locomotor activity of organisms ranging from fruit flies to man, but the functions of the clocks in peripheral nervous system are not well understood. The presence of autonomous peripheral oscillators in the major taste organ of Drosophila, the proboscis, prompted us to test whether gustatory responses are under control of the circadian clock. We find that synchronous rhythms in physiological and behavioral responses to attractive and aversive tastants are driven by oscillators in gustatory receptor neurons (GRNs); primary sensory neurons that carry taste information from the proboscis to the brain. During the middle of the night, high levels of G protein-coupled receptor kinase 2 (GPRK2) in the GRNs suppresses tastant-evoked responses. Flies with disrupted gustatory clocks are hyperphagic and hyperactive, recapitulating behaviors typically seen under the stress of starvation. Temporal plasticity in innate behaviors should offer adaptive advantages to flies. In this Extra View article we discuss how oscillators inside GRNs regulate responsiveness to tastants and influence feeding, metabolism and general activity.

Dynamic, mating-induced gene expression changes in female head and brain tissues of Drosophila melanogaster

Background

Drosophila melanogaster females show changes in behavior and physiology after mating that are thought to maximize the number of progeny resulting from the most recent copulation. Sperm and seminal fluid proteins induce post-mating changes in females, however, very little is known about the resulting gene expression changes in female head and central nervous system tissues that contribute to the post-mating response.

Results

We determined the temporal gene expression changes in female head tissues 0-2, 24, 48 and 72 hours after mating. Females from each time point had a unique post-mating gene expression response, with 72 hours post-mating having the largest number of genes with significant changes in expression. At most time points, genes expressed in the head fat body that encode products involved in metabolism showed a marked change in expression. Additional analysis of gene expression changes in dissected brain tissues 24 hours post-mating revealed changes in transcript abundance of many genes, notably, the reduced transcript abundance of genes that encode ion channels.

Conclusions

Substantial changes occur in the regulation of many genes in female head tissues after mating, which might underlie aspects of the female post-mating response. These results provide new insights into the physiological and metabolic changes that accompany changes in female behaviors.

Circadian organization of behavior and physiology in Drosophila

Circadian clocks organize behavior and physiology to adapt to daily environmental cycles. Genetic approaches in the fruit fly, Drosophila melanogaster, have revealed widely conserved molecular gears of these 24-h timers. Yet much less is known about how these cell-autonomous clocks confer temporal information to modulate cellular functions. Here we discuss our current knowledge of circadian clock function in Drosophila, providing an overview of the molecular underpinnings of circadian clocks. We then describe the neural network important for circadian rhythms of locomotor activity, including how these molecular clocks might influence neuronal function. Finally, we address a range of behaviors and physiological systems regulated by circadian clocks, including discussion of specific peripheral oscillators and key molecular effectors where they have been described. These studies reveal a remarkable complexity to circadian pathways in this "simple" model organism.

The structure of the dust mite allergen Der p 7 reveals similarities to innate immune proteins

BACKGROUND

Sensitization to house dust mite allergens is strongly correlated with asthma. Der p 7 elicits strong IgE antibody and T-cell responses in patients with mite allergy. However, the structure and biological function of this important allergen are unknown. Allergen function might contribute to allergenicity, as shown for the protease activity of group 1 mite allergens and the interaction with the innate immune system by group 2 mite allergens.

OBJECTIVE

We sought to determine the crystal structure of Der p 7 and to investigate its biological function.

METHODS

X-ray crystallography was used to determine the Der p 7 structure. Nuclear magnetic resonance analysis and biochemical assays were used to examine the binding of Der p 7 to predicted ligands.

RESULTS

Der p 7 has an elongated structure, with two 4-stranded antiparallel beta-sheets that wrap around a long C-terminal helix. The fold of Der p 7 is similar to that of LPS-binding protein (LBP), which interacts with Toll-like receptors after binding LPS and other bacterially derived lipid ligands. Nuclear magnetic resonance and biochemical assays indicate that Der p 7 does not bind LPS but binds with weak affinity to the bacterial lipopeptide polymyxin B in the predicted binding site of Der p 7.

CONCLUSIONS

Der p 7 binds a bacterially derived lipid product, a common feature of some allergens. The finding that the group 7, as well as the group 2, mite allergens are structurally similar to different proteins in the Toll-like receptor pathway further strengthens the connections between dust mites, innate immunity, and allergy.

The circadian output gene takeout is regulated by Pdp1epsilon

The circadian clock controls many circadian outputs. Although a large number of transcripts are affected by the circadian oscillator, very little is known about their regulation and function. We show here that the Drosophila takeout gene, one of the output genes of the circadian oscillator, is regulated similarly to the circadian clock genes Clock (Clk) and cry. takeout RNA levels are at constant high levels in Clk(JRK) mutants. The circadian transcription factor PAR domain protein 1 (Pdp1epsilon) is a transcription factor that had previously been postulated to control clock output genes, particularly genes regulated similarly to Clk. In agreement with this, we show here that Pdp1epsilon is a regulator of takeout. Takeout levels are low in flies with reduced Pdp1epsilon and high in flies with increased amounts of Pdp1epsilon. Furthermore, flies with reduced or elevated Pdp1epsilon levels in the fat body display courtship defects, identifying Pdp1epsilon as an important transcriptional regulator in that tissue.

Gene expression in a Drosophila model of mitochondrial disease

Background

A point mutation in the Drosophila gene technical knockout (tko), encoding mitoribosomal protein S12, was previously shown to cause a phenotype of respiratory chain deficiency, developmental delay, and neurological abnormalities similar to those presented in many human mitochondrial disorders, as well as defective courtship behavior.

Methodology/Principal Findings

Here, we describe a transcriptome-wide analysis of gene expression in tko^25t mutant flies that revealed systematic and compensatory changes in the expression of genes connected with metabolism, including up-regulation of lactate dehydrogenase and of many genes involved in the catabolism of fats and proteins, and various anaplerotic pathways. Gut-specific enzymes involved in the primary mobilization of dietary fats and proteins, as well as a number of transport functions, were also strongly up-regulated, consistent with the idea that oxidative phosphorylation OXPHOS dysfunction is perceived physiologically as a starvation for particular biomolecules. In addition, many stress-response genes were induced. Other changes may reflect a signature of developmental delay, notably a down-regulation of genes connected with reproduction, including gametogenesis, as well as courtship behavior in males; logically this represents a programmed response to a mitochondrially generated starvation signal. The underlying signalling pathway, if conserved, could influence many physiological processes in response to nutritional stress, although any such pathway involved remains unidentified.

Conclusions/Significance

These studies indicate that general and organ-specific metabolism is transformed in response to mitochondrial dysfunction, including digestive and absorptive functions, and give important clues as to how novel therapeutic strategies for mitochondrial disorders might be developed.

Regulation of energy stores and feeding by neuronal and peripheral CREB activity in Drosophila

The cAMP-responsive transcription factor CREB functions in adipose tissue and liver to regulate glycogen and lipid metabolism in mammals. While Drosophila has a homolog of mammalian CREB, dCREB2, its role in energy metabolism is not fully understood. Using tissue-specific expression of a dominant-negative form of CREB (DN-CREB), we have examined the effect of blocking CREB activity in neurons and in the fat body, the primary energy storage depot with functions of adipose tissue and the liver in flies, on energy balance, stress resistance and feeding behavior. We found that disruption of CREB function in neurons reduced glycogen and lipid stores and increased sensitivity to starvation. Expression of DN-CREB in the fat body also reduced glycogen levels, while it did not affect starvation sensitivity, presumably due to increased lipid levels in these flies. Interestingly, blocking CREB activity in the fat body increased food intake. These flies did not show a significant change in overall body size, suggesting that disruption of CREB activity in the fat body caused an obese-like phenotype. Using a transgenic CRE-luciferase reporter, we further demonstrated that disruption of the adipokinetic hormone receptor, which is functionally related to mammalian glucagon and β-adrenergic signaling, in the fat body reduced CRE-mediated transcription in flies. This study demonstrates that CREB activity in either neuronal or peripheral tissues regulates energy balance in Drosophila, and that the key signaling pathway regulating CREB activity in peripheral tissue is evolutionarily conserved.