Local requirement of the Drosophila insulin binding protein imp-L2 in coordinating developmental progression with nutritional conditions

WGCNA based identification of hub genes associated with cold response and development in Apis mellifera metamorphic pupae

Honeybee is a crucial pollinator in nature, and plays an indispensable role in both agricultural production and scientific research. In recent decades, honeybee was challenged with health problems by biotic and abiotic stresses. As a key ecological factor, temperature has been proved to have an impact on the survival and production efficiency of honeybees. Previous studies have demonstrated that low temperature stress can affect honeybee pupation and shorten adult longevity. However, the molecular mechanism underlying the effects of low temperatures on honeybee growth and development during their developmental period remain poorly understood. In this paper, the weighted gene co-expression analysis (WGCNA) was employed to explore the molecular mechanisms underpinnings of honeybees' respond to low temperatures (20°C) during four distinct developmental stages: large-larvae, prepupae, early-pupae and mid-pupae. Through an extensive transcriptome analysis, thirteen gene co-expression modules were identified and analyzed in relation to honeybee development and stress responses. The darkorange module was found to be associated with low temperature stress, with its genes primarily involved in autophagy-animal, endocytosis and MAPK signaling pathways. Four hub genes were identified within this module, namely, loc726497, loc409791, loc410923, and loc550857, which may contribute to honeybee resistance to low temperature and provide insight into the underlying mechanism. The gene expression patterns of grey60 and black modules were found to correspond to the developmental stages of prepupae and early-pupae, respectively, with the hub genes loc409494, loc725756, loc552457, loc726158, Ip3k and Lcch3 in grey60 module likely involved in brain development, and the hub genes loc410555 in black module potentially related to exoskeleton development. The brown module genes exhibited a distinct pattern of overexpression in mid-pupae specimens, with genes primarily enriched in oxidative phosphorylation, citrate cycle and other pathways, which may be related to the formation of bee flying muscle. No related gene expression module was found for mature larvae stage. These findings provide valuable insights into the developmental process of honeybees at molecular level during the capped brood stage.

Isolation of a novel missense mutation in insulin receptor as a spontaneous revertant in ImpL2 mutants in Drosophila

Evolutionarily conserved insulin/insulin-like growth factor (IGF) signaling (IIS) correlates nutrient levels to metabolism and growth, thereby playing crucial roles in development and adult fitness. In the fruit fly Drosophila, ImpL2, an ortholog of IGFBP7, binds to and inhibits the function of Drosophila insulin-like peptides. In this study, we isolated a temperature-sensitive mutation in the insulin receptor (InR) gene as a spontaneous revertant in ImpL2 null mutants. The p.Y902C missense mutation is located at the functionally conserved amino acid residue of the first fibronectin type III domain of InR. The hypomorphic InR mutant animals showed a temperature-dependent reduction in IIS and body size. The mutant animals also exhibited metabolic defects, such as increased triglyceride and carbohydrate levels. Metabolomic analysis further revealed that defects in InR caused dysregulation of amino acid and ribonucleotide metabolism. We also observed that InR mutant females produced tiny irregular-shaped embryos with reduced fecundity. In summary, this novel allele of InR is a valuable tool for the Drosophila genetic model of insulin resistance and type 2 diabetes.

A bacteria-regulated gut peptide determines host dependence on specific bacteria to support host juvenile development and survival

BACKGROUND

Commensal microorganisms have a significant impact on the physiology of host animals, including Drosophila. Lactobacillus and Acetobacter, the two most common commensal bacteria in Drosophila, stimulate fly development and growth, but the mechanisms underlying their functional interactions remain elusive.

RESULTS

We found that imaginal morphogenesis protein-Late 2 (Imp-L2), a Drosophila homolog of insulin-like growth factor binding protein 7, is expressed in gut enterocytes in a bacteria-dependent manner, determining host dependence on specific bacteria for host development. Imp-L2 mutation abolished the stimulatory effects of Lactobacillus, but not of Acetobacter, on fly larval development. The lethality of the Imp-L2 mutant markedly increased under axenic conditions, which was reversed by Acetobacter, but not Lactobacillus, re-association. The host dependence on specific bacteria was determined by Imp-L2 expressed in enterocytes, which was repressed by Acetobacter, but not Lactobacillus. Mechanistically, Lactobacillus and Acetobacter differentially affected steroid hormone-mediated Imp-L2 expression and Imp-L2-specific FOXO regulation.

CONCLUSIONS

Our finding may provide a way how host switches dependence between different bacterial species when benefiting from varying microbiota.

Adipose mitochondrial metabolism controls body growth by modulating systemic cytokine and insulin signaling

Animals must adapt their growth to fluctuations in nutrient availability to ensure proper development. These adaptations often rely on specific nutrient-sensing tissues that control whole-body physiology through inter-organ communication. While the signaling mechanisms that underlie this communication are well studied, the contributions of metabolic alterations in nutrient-sensing tissues are less clear. Here, we show how the reprogramming of adipose mitochondria controls whole-body growth in Drosophila larvae. We find that dietary nutrients alter fat-body mitochondrial morphology to lower their bioenergetic activity, leading to rewiring of fat-body glucose metabolism. Strikingly, we find that genetic reduction of mitochondrial bioenergetics just in the fat body is sufficient to accelerate body growth and development. These growth effects are caused by inhibition of the fat-derived secreted peptides ImpL2 and tumor necrosis factor alpha (TNF-α)/Eiger, leading to enhanced systemic insulin signaling. Our work reveals how reprogramming of mitochondrial metabolism in one nutrient-sensing tissue can couple nutrient availability to whole-body growth.

Hemocyte Clusters Defined by scRNA-Seq in Bombyx mori: In Silico Analysis of Predicted Marker Genes and Implications for Potential Functional Roles

Within the hemolymph, insect hemocytes constitute a heterogeneous population of macrophage-like cells that play important roles in innate immunity, homeostasis and development. Classification of hemocytes in different subtypes by size, morphology and biochemical or immunological markers has been difficult and only in Drosophila extensive genetic analysis allowed the construction of a coherent picture of hemocyte differentiation from pro-hemocytes to granulocytes, crystal cells and plasmatocytes. However, the advent of high-throughput single cell technologies, such as single cell RNA sequencing (scRNA-seq), is bound to have a high impact on the study of hemocytes subtypes and their phenotypes in other insects for which a sophisticated genetic toolbox is not available. Instead of averaging gene expression across all cells as occurs in bulk-RNA-seq, scRNA-seq allows high-throughput and specific visualization of the differentiation status of individual cells. With scRNA-seq, interesting cell types can be identified in heterogeneous populations and direct analysis of rare cell types is possible. Next to its ability to profile the transcriptomes of individual cells in tissue samples, scRNA-seq can be used to propose marker genes that are characteristic of different hemocyte subtypes and predict their functions. In this perspective, the identities of the different marker genes that were identified by scRNA-seq analysis to define 13 distinct cell clusters of hemocytes in larvae of the silkworm, Bombyx mori, are discussed in detail. The analysis confirms the broad division of hemocytes in granulocytes, plasmatocytes, oenocytoids and perhaps spherulocytes but also reveals considerable complexity at the molecular level and highly specialized functions. In addition, predicted hemocyte marker genes in Bombyx generally show only limited convergence with the genes that are considered characteristic for hemocyte subtypes in Drosophila.

TOR signalling is required for host lipid metabolic remodelling and survival following enteric infection in Drosophila

When infected by enteric pathogenic bacteria, animals need to initiate local and whole-body defence strategies. Although most attention has focused on the role of innate immune anti-bacterial responses, less is known about how changes in host metabolism contribute to host defence. Using Drosophila as a model system, we identify induction of intestinal target-of-rapamycin (TOR) kinase signalling as a key adaptive metabolic response to enteric infection. We find that enteric infection induces both local and systemic induction of TOR independently of the Immune deficiency (IMD) innate immune pathway, and we see that TOR functions together with IMD signalling to promote infection survival. These protective effects of TOR signalling are associated with remodelling of host lipid metabolism. Thus, we see that TOR is required to limit excessive infection-mediated wasting of host lipid stores by promoting an increase in the levels of gut- and fat body-expressed lipid synthesis genes. Our data support a model in which induction of TOR represents a host tolerance response to counteract infection-mediated lipid wasting in order to promote survival. This article has an associated First Person interview with the first author of the paper.

Tumors overcome the action of the wasting factor ImpL2 by locally elevating Wnt/Wingless

Tumors often secrete wasting factors associated with atrophy and the degeneration of host tissues. If tumors were to be affected by the wasting factors, mechanisms allowing tumors to evade the adverse effects of the wasting factors must exist, and impairing such mechanisms may attenuate tumors. We use Drosophila midgut tumor models to show that tumors up-regulate Wingless (Wg) to oppose the growth-impeding effects caused by the wasting factor, ImpL2 (insulin-like growth factor binding protein [IGFBP]-related protein). Growth of Yorkie (Yki)-induced tumors is dependent on Wg while either elimination of ImpL2 or elevation of insulin/insulin-like growth factor signaling in tumors revokes this dependency. Notably, Wg augmentation could be a general mechanism for supporting the growth of tumors with elevated ImpL2 and exploited to attenuate muscle degeneration during wasting. Our study elucidates the mechanism by which tumors negate the action of ImpL2 to uphold their growth during cachexia-like wasting and implies that targeting the Wnt/Wg pathway might be an efficient treatment strategy for cancers with elevated IGFBPs.

Crtc modulates fasting programs associated with 1-C metabolism and inhibition of insulin signaling

Fasting in mammals promotes increases in circulating glucagon and decreases in circulating insulin that stimulate catabolic programs and facilitate a transition from glucose to lipid burning. The second messenger cAMP mediates effects of glucagon on fasting metabolism, in part by promoting the phosphorylation of CREB and the dephosphorylation of the cAMP-regulated transcriptional coactivators (CRTCs) in hepatocytes. In Drosophila, fasting also triggers activation of the single Crtc homolog in neurons, via the PKA-mediated phosphorylation and inhibition of salt-inducible kinases. Crtc mutant flies are more sensitive to starvation and oxidative stress, although the underlying mechanism remains unclear. Here we use RNA sequencing to identify Crtc target genes that are up-regulated in response to starvation. We found that Crtc stimulates a subset of fasting-inducible genes that have conserved CREB binding sites. In keeping with its role in the starvation response, Crtc was found to induce the expression of genes that inhibit insulin secretion (Lst) and insulin signaling (Impl2). In parallel, Crtc also promoted the expression of genes involved in one-carbon (1-C) metabolism. Within the 1-C pathway, Crtc stimulated the expression of enzymes that encode modulators of S-adenosyl-methionine metabolism (Gnmt and Sardh) and purine synthesis (ade2 and AdSl) Collectively, our results point to an important role for the CREB/CRTC pathway in promoting energy balance in the context of nutrient stress.

Genetic manipulation of insulin/insulin-like growth factor signaling pathway activity has sex-biased effects on Drosophila body size

In Drosophila raised in nutrient-rich conditions, female body size is approximately 30% larger than male body size due to an increased rate of growth and differential weight loss during the larval period. While the mechanisms that control this sex difference in body size remain incompletely understood, recent studies suggest that the insulin/insulin-like growth factor signaling pathway (IIS) plays a role in the sex-specific regulation of processes that influence body size during development. In larvae, IIS activity differs between the sexes, and there is evidence of sex-specific regulation of IIS ligands. Yet, we lack knowledge of how changes to IIS activity impact body size in each sex, as the majority of studies on IIS and body size use single- or mixed-sex groups of larvae and/or adult flies. The goal of our current study was to clarify the body size requirement for IIS activity in each sex. To achieve this goal, we used established genetic approaches to enhance, or inhibit, IIS activity, and quantified pupal size in males and females. Overall, genotypes that inhibited IIS activity caused a female-biased decrease in body size, whereas genotypes that augmented IIS activity caused a male-specific increase in body size. These data extend our current understanding of body size regulation by showing that most changes to IIS pathway activity have sex-biased effects, and highlights the importance of analyzing body size data according to sex.

Metabolism and growth adaptation to environmental conditions in Drosophila

Organisms adapt to changing environments by adjusting their development, metabolism, and behavior to improve their chances of survival and reproduction. To achieve such flexibility, organisms must be able to sense and respond to changes in external environmental conditions and their internal state. Metabolic adaptation in response to altered nutrient availability is key to maintaining energy homeostasis and sustaining developmental growth. Furthermore, environmental variables exert major influences on growth and final adult body size in animals. This developmental plasticity depends on adaptive responses to internal state and external cues that are essential for developmental processes. Genetic studies have shown that the fruit fly Drosophila, similarly to mammals, regulates its metabolism, growth, and behavior in response to the environment through several key hormones including insulin, peptides with glucagon-like function, and steroid hormones. Here we review emerging evidence showing that various environmental cues and internal conditions are sensed in different organs that, via inter-organ communication, relay information to neuroendocrine centers that control insulin and steroid signaling. This review focuses on endocrine regulation of development, metabolism, and behavior in Drosophila, highlighting recent advances in the role of the neuroendocrine system as a signaling hub that integrates environmental inputs and drives adaptive responses.

A developmental checkpoint directs metabolic remodelling as a strategy against starvation in Drosophila

Steroid hormones are crucial regulators of life-stage transitions during development in animals. However, the molecular mechanisms by which developmental transition through these stages is coupled with optimal metabolic homeostasis remains poorly understood. Here, we demonstrate through mathematical modelling and experimental validation that ecdysteroid-induced metabolic remodelling from resource consumption to conservation can be a successful life-history strategy to maximize fitness in Drosophila larvae in a fluctuating environment. Specifically, the ecdysteroid-inducible protein ImpL2 protects against hydrolysis of circulating trehalose following pupal commitment in larvae. Stored glycogen and triglycerides in the fat body are also conserved, even under fasting conditions. Moreover, pupal commitment dictates reduced energy expenditure upon starvation to maintain available resources, thus negotiating trade-offs in resource allocation at the physiological and behavioural levels. The optimal stage-specific metabolic shift elucidated by our predictive and empirical approaches reveals that Drosophila has developed a highly controlled system for ensuring robust development that may be conserved among higher-order organisms in response to intrinsic and extrinsic cues.

Dpp regulates autophagy-dependent midgut removal and signals to block ecdysone production

Animal development and homeostasis require the programmed removal of cells. Autophagy-dependent cell deletion is a unique form of cell death often involved in bulk degradation of tissues. In Drosophila the steroid hormone ecdysone controls developmental transitions and triggers the autophagy-dependent removal of the obsolete larval midgut. The production of ecdysone is exquisitely coordinated with signals from numerous organ systems to mediate the correct timing of such developmental programs. Here we report an unexpected role for the Drosophila bone morphogenetic protein/transforming growth factor β ligand, Decapentaplegic (Dpp), in the regulation of ecdysone-mediated midgut degradation. We show that blocking Dpp signaling induces premature autophagy, rapid cell death, and midgut degradation, whereas sustained Dpp signaling inhibits autophagy induction. Furthermore, Dpp signaling in the midgut prevents the expression of ecdysone responsive genes and impairs ecdysone production in the prothoracic gland. We propose that Dpp has dual roles: one within the midgut to prevent improper tissue degradation, and one in interorgan communication to coordinate ecdysone biosynthesis and developmental timing.

Steroid signaling mediates nutritional regulation of juvenile body growth via IGF-binding protein in Drosophila

Nutritional condition during the juvenile growth period considerably affects final adult size. The insulin/insulin-like growth factor signaling (IIS)/target of rapamycin (TOR) nutrient-sensing pathway is known to regulate growth and metabolism in response to nutritional conditions. However, there is limited information on how endocrine pathways communicate nutritional information to different metabolic organs to regulate organismal growth. Here, we show that Imaginal morphogenesis protein-Late 2 (Imp-L2), a Drosophila homolog of insulin-like growth factor-binding protein 7 (IGFBP7), plays a key role in the nutritional control of organismal growth. Nutritional restriction during the larval growth period causes undersized adults, which is largely diminished by Imp-L2 mutation. We delineate a pathway in which nutritional restriction increases levels of the steroid hormone ecdysone, which, in turn, triggers ecdysone signaling-dependent Imp-L2 production from the fat body, a fly adipose organ, thereby attenuating peripheral IIS and body growth. Surprisingly, this endocrine pathway operates independent of the fat-body-TOR internal nutrient sensor, long believed to be the control center for nutrition-dependent growth. Our study reveals a previously unrecognized endocrine circuit mediating nutrition-dependent juvenile growth, which could also potentially be related to the insulin resistance frequently observed in puberty.

Nutritional regimens with periodically recurring phases of dietary restriction extend lifespan in Drosophila

Nutritional interventions such as caloric and dietary restriction increase lifespan in various animal models. To identify alternative and less demanding nutritional interventions that extend lifespan, we subjected fruit flies ( Drosophila melanogaster) to weekly nutritional regimens that involved alternating a conventional diet with dietary restriction. Short periods of dietary restriction (up to 2 d) followed by longer periods of a conventional diet yielded minimal increases in lifespan. We found that 3 or more days of contiguous dietary restriction (DR) was necessary to yield a lifespan extension similar to that observed with persistent DR. Female flies were more responsive to these interventions than males. Physiologic changes known to be associated with prolonged DR, such as reduced metabolic rates, showed the same time course as lifespan extension. Moreover, concurrent transcriptional changes indicative of reduced insulin signaling were identified with DR. These physiologic and transcriptional changes were sustained, as they were detectable several days after switching to conventional diets. Taken together, diets with longer periods of DR extended lifespan concurrently with physiologic and transcriptional changes that may underlie this increase in lifespan.-Romey-Glüsing, R., Li, Y., Hoffmann, J., von Frieling, J., Knop, M., Pfefferkorn, R., Bruchhaus, I., Fink, C., Roeder, T. Nutritional regimens with periodically recurring phases of dietary restriction extend lifespan in Drosophila.

Organ-to-Organ Communication: A Drosophila Gastrointestinal Tract Perspective

The long-term maintenance of an organism's homeostasis and health relies on the accurate regulation of organ-organ communication. Recently, there has been growing interest in using the Drosophila gastrointestinal tract to elucidate the regulatory programs that underlie the complex interactions between organs. Data obtained in this field have dramatically improved our understanding of how organ-organ communication contributes to the regulation of various aspects of the intestine, including its metabolic and physiological status. However, although research uncovering regulatory programs associated with interorgan communication has provided key insights, the underlying mechanisms have not been extensively explored. In this review, we highlight recent findings describing gut-neighbor and neighbor-neighbor communication models in adults and larvae, respectively, with a special focus on how a range of critical strategies concerning continuous interorgan communication and adjustment can be used to manipulate different aspects of biological processes. Given the high degree of similarity between the Drosophila and mammalian intestinal epithelia, it can be anticipated that further analyses of the Drosophila gastrointestinal tract will facilitate the discovery of similar mechanisms underlying organ-organ communication in other mammalian organs, such as the human intestine.

The interplay between intestinal bacteria and host metabolism in health and disease: lessons from Drosophila melanogaster

All higher organisms negotiate a truce with their commensal microbes and battle pathogenic microbes on a daily basis. Much attention has been given to the role of the innate immune system in controlling intestinal microbes and to the strategies used by intestinal microbes to overcome the host immune response. However, it is becoming increasingly clear that the metabolisms of intestinal microbes and their hosts are linked and that this interaction is equally important for host health and well-being. For instance, an individual's array of commensal microbes can influence their predisposition to chronic metabolic diseases such as diabetes and obesity. A better understanding of host-microbe metabolic interactions is important in defining the molecular bases of these disorders and could potentially lead to new therapeutic avenues. Key advances in this area have been made using Drosophila melanogaster. Here, we review studies that have explored the impact of both commensal and pathogenic intestinal microbes on Drosophila carbohydrate and lipid metabolism. These studies have helped to elucidate the metabolites produced by intestinal microbes, the intestinal receptors that sense these metabolites, and the signaling pathways through which these metabolites manipulate host metabolism. Furthermore, they suggest that targeting microbial metabolism could represent an effective therapeutic strategy for human metabolic diseases and intestinal infection.

Deciphering the main venom components of the ectoparasitic ant-like bethylid wasp, Scleroderma guani

Similar to venom found in most venomous animals, parasitoid venoms contain a complex cocktail of proteins with potential agrichemical and pharmaceutical use. Even though parasitoids are one of the largest group of venomous animals, little is known about their venom composition. Recent few studies revealed high variated venom composition existing not only in different species but also between closely related strains, impling that increasing information on the venom proteins from more greater diversity of species of different taxa is key to comprehensively uncover the complete picture of parasitoid venom. Here, we explored the major protein components of the venom of ectoparasitic ant-like bethylid wasp, Scleroderma guani by an integrative transcriptomic-proteomic approach. Illumina deep sequencing of venom apparatus cDNA produced 49,873 transcripts. By mapping the peptide spectral data derived from venom reservoir against these transcripts, mass spectrometry analysis revealed ten main venom proteins, including serine proteinase, metalloprotease, dipeptidyl peptidase IV, esterase, antithrombin-III, acid phosphatase, neural/ectodermal development factor IMP-L2 like protein, venom allergen 3, and unknown protein. Interestingly, one serine proteinase was firstly identified with rarely high molecular weight about 200 kDa in parasitoid venom. The occurrence of abundant acid phosphatase, antithrombin-III and venom allergen 3 demonstrated that S. guani venom composition is similar to that of social wasp venoms. All identified venom genes showed abundantly biased expression in venom apparatus, indicating their virulent functions involved in parasitization. This study shed light on the more better understanding of parasitoid venom evolution across species and will facilitate the further elucidation of function and toxicity of these venom proteins.

Insulin/IGF signaling in Drosophila and other insects: factors that regulate production, release and post-release action of the insulin-like peptides

Insulin, insulin-like growth factors (IGFs) and insulin-like peptides (ILPs) are important regulators of metabolism, growth, reproduction and lifespan, and mechanisms of insulin/IGF signaling (IIS) have been well conserved over evolution. In insects, between one and 38 ILPs have been identified in each species. Relatively few insect species have been investigated in depth with respect to ILP functions, and therefore we focus mainly on the well-studied fruitfly Drosophila melanogaster. In Drosophila eight ILPs (DILP1-8), but only two receptors (dInR and Lgr3) are known. DILP2, 3 and 5 are produced by a set of neurosecretory cells (IPCs) in the brain and their biosynthesis and release are controlled by a number of mechanisms differing between larvae and adults. Adult IPCs display cell-autonomous sensing of circulating glucose, coupled to evolutionarily conserved mechanisms for DILP release. The glucose-mediated DILP secretion is modulated by neurotransmitters and neuropeptides, as well as by factors released from the intestine and adipocytes. Larval IPCs, however, are indirectly regulated by glucose-sensing endocrine cells producing adipokinetic hormone, or by circulating factors from the intestine and fat body. Furthermore, IIS is situated within a complex physiological regulatory network that also encompasses the lipophilic hormones, 20-hydroxyecdysone and juvenile hormone. After release from IPCs, the ILP action can be modulated by circulating proteins that act either as protective carriers (binding proteins), or competitive inhibitors. Some of these proteins appear to have additional functions that are independent of ILPs. Taken together, the signaling with multiple ILPs is under complex control, ensuring tightly regulated IIS in the organism.

Functional Conservation of the Glide/Gcm Regulatory Network Controlling Glia, Hemocyte, and Tendon Cell Differentiation in Drosophila

High-throughput screens allow us to understand how transcription factors trigger developmental processes, including cell specification. A major challenge is identification of their binding sites because feedback loops and homeostatic interactions may mask the direct impact of those factors in transcriptome analyses. Moreover, this approach dissects the downstream signaling cascades and facilitates identification of conserved transcriptional programs. Here we show the results and the validation of a DNA adenine methyltransferase identification (DamID) genome-wide screen that identifies the direct targets of Glide/Gcm, a potent transcription factor that controls glia, hemocyte, and tendon cell differentiation in Drosophila. The screen identifies many genes that had not been previously associated with Glide/Gcm and highlights three major signaling pathways interacting with Glide/Gcm: Notch, Hedgehog, and JAK/STAT, which all involve feedback loops. Furthermore, the screen identifies effector molecules that are necessary for cell-cell interactions during late developmental processes and/or in ontogeny. Typically, immunoglobulin (Ig) domain-containing proteins control cell adhesion and axonal navigation. This shows that early and transiently expressed fate determinants not only control other transcription factors that, in turn, implement a specific developmental program but also directly affect late developmental events and cell function. Finally, while the mammalian genome contains two orthologous Gcm genes, their function has been demonstrated in vertebrate-specific tissues, placenta, and parathyroid glands, begging questions on the evolutionary conservation of the Gcm cascade in higher organisms. Here we provide the first evidence for the conservation of Gcm direct targets in humans. In sum, this work uncovers novel aspects of cell specification and sets the basis for further understanding of the role of conserved Gcm gene regulatory cascades.

Mitochondrial iron supply is required for the developmental pulse of ecdysone biosynthesis that initiates metamorphosis in Drosophila melanogaster

Synthesis of ecdysone, the key hormone that signals the termination of larval growth and the initiation of metamorphosis in insects, is carried out in the prothoracic gland by an array of iron-containing cytochrome P450s, encoded by the halloween genes. Interference, either with iron-sulfur cluster biogenesis in the prothoracic gland or with the ferredoxins that supply electrons for steroidogenesis, causes a block in ecdysone synthesis and developmental arrest in the third instar larval stage. Here we show that mutants in Drosophila mitoferrin (dmfrn), the gene encoding a mitochondrial carrier protein implicated in mitochondrial iron import, fail to grow and initiate metamorphosis under dietary iron depletion or when ferritin function is partially compromised. In mutant dmfrn larvae reared under iron replete conditions, the expression of halloween genes is increased and 20-hydroxyecdysone (20E), the active form of ecdysone, is synthesized. In contrast, addition of an iron chelator to the diet of mutant dmfrn larvae disrupts 20E synthesis. Dietary addition of 20E has little effect on the growth defects, but enables approximately one-third of the iron-deprived dmfrn larvae to successfully turn into pupae and, in a smaller percentage, into adults. This partial rescue is not observed with dietary supply of ecdysone's precursor 7-dehydrocholesterol, a precursor in the ecdysone biosynthetic pathway. The findings reported here support the notion that a physiological supply of mitochondrial iron for the synthesis of iron-sulfur clusters and heme is required in the prothoracic glands of insect larvae for steroidogenesis. Furthermore, mitochondrial iron is also essential for normal larval growth.

Insulin/IGF signaling and its regulation in Drosophila

Taking advantage of Drosophila as a genetically tractable experimental animal much progress has been made in our understanding of how the insulin/IGF signaling (IIS) pathway regulates development, growth, metabolism, stress responses and lifespan. The role of IIS in regulation of neuronal activity and behavior has also become apparent from experiments in Drosophila. This review briefly summarizes these functional roles of IIS, and also how the insulin producing cells (IPCs) are regulated in the fly. Furthermore, we discuss functional aspects of the spatio-temporal production of eight different insulin-like peptides (DILP1-8) that are thought to act on one known receptor (dInR) in Drosophila.

Endocrine remodelling of the adult intestine sustains reproduction in Drosophila

The production of offspring is energetically costly and relies on incompletely understood mechanisms that generate a positive energy balance. In mothers of many species, changes in key energy-associated internal organs are common yet poorly characterised functionally and mechanistically. In this study, we show that, in adult Drosophila females, the midgut is dramatically remodelled to enhance reproductive output. In contrast to extant models, organ remodelling does not occur in response to increased nutrient intake and/or offspring demands, but rather precedes them. With spatially and temporally directed manipulations, we identify juvenile hormone (JH) as an anticipatory endocrine signal released after mating. Acting through intestinal bHLH-PAS domain proteins Methoprene-tolerant (Met) and Germ cell-expressed (Gce), JH signals directly to intestinal progenitors to yield a larger organ, and adjusts gene expression and sterol regulatory element-binding protein (SREBP) activity in enterocytes to support increased lipid metabolism. Our findings identify a metabolically significant paradigm of adult somatic organ remodelling linking hormonal signals, epithelial plasticity, and reproductive output.