Shortened lifespan induced by a high-glucose diet is associated with intestinal immune dysfunction in Drosophila sechellia.

Organisms can generally be divided into two nutritional groups: generalists that consume various types of food and specialists that consume specific types of food. However, it remains unclear how specialists adapt to only limited nutritional conditions in nature. In this study, we addressed this question by focusing on Drosophila fruit flies. The generalist Drosophila melanogaster can consume a wide variety of foods that contain high glucose levels. In contrast, the specialist Drosophila sechellia consumes only the Indian mulberry, known as noni (Morinda citrifolia), which contains relatively little glucose. We showed that the lifespan of D. sechellia was significantly shortened under a high-glucose diet, but this effect was not observed for D. melanogaster. In D. sechellia, a high-glucose diet induced disorganization of the gut epithelia and visceral muscles, which was associated with abnormal digestion and constipation. RNA-sequencing analysis revealed that many immune-responsive genes were suppressed in the gut of D. sechellia fed a high-glucose diet compared with those fed a control diet. Consistent with this difference in the expression of immune-responsive genes, high glucose-induced phenotypes were restored by the addition of tetracycline or scopoletin, a major nutritional component of noni, each of which suppresses gut bacterial growth. We propose that, in D. sechellia, a high-glucose diet impairs gut immune function, which leads to a change in gut microbiota, disorganization of the gut epithelial structure and a shortened lifespan.

The Drosophila CCR4-NOT complex is required for cholesterol homeostasis and steroid hormone synthesis.

CCR4-NOT is a highly conserved protein complex that regulates gene expression at multiple levels. In yeast, CCR4-NOT functions in transcriptional initiation, heterochromatin formation, mRNA deadenylation and other processes. The range of functions for Drosophila CCR4-NOT is less clear, except for a well-established role as a deadenylase for maternal mRNAs during early embryogenesis. We report here that CCR4-NOT has an essential function in the Drosophila prothoracic gland (PG), a tissue that predominantly produces the steroid hormone ecdysone. Interfering with the expression of the CCR4-NOT components twin, Pop2, Not1, and Not3 in a PG-specific manner resulted in larval arrest and a failure to initiate metamorphosis. Transcriptome analysis of PG-specific Pop2-RNAi samples revealed that Pop2 is required for the normal expression of ecdysone biosynthetic gene spookier (spok) as well as cholesterol homeostasis genes of the NPC2 family. Interestingly, dietary supplementation with ecdysone and its various sterol precursors showed that 7-dehydrocholesterol and cholesterol completely rescued the larval arrest phenotype, allowing Pop2-RNAi animals to reach pupal stage, and, to a low degree, even survival to adulthood, while the biologically active hormone, 20-Hydroxyecdysone (20E), was significantly less effective. Also, we present genetic evidence that CCR4-NOT has a nuclear function where CCR4-NOT-depleted cells exhibit aberrant chromatin and nucleoli structures. In summary, our findings indicate that the Drosophila CCR4-NOT complex has essential roles in the PG, where it is required for Drosophila steroid hormone production and cholesterol homeostasis, and likely has functions beyond a mere mRNA deadenylase in Drosophila.

The intestinal stem cell/enteroblast-GAL4 driver, escargot-GAL4, also manipulates gene expression in the juvenile hormone-synthesizing organ of Drosophila melanogaster.

Intestinal stem cells (ISCs) of the fruit fly, Drosophila melanogaster, offer an excellent genetic model to explore homeostatic roles of ISCs in animal physiology. Among available genetic tools, the escargot (esg)-GAL4 driver, expressing the yeast transcription factor gene, GAL4, under control of the esg gene promoter, has contributed significantly to ISC studies. This driver facilitates activation of genes of interest in proximity to a GAL4-binding element, Upstream Activating Sequence, in ISCs and progenitor enteroblasts (EBs). While esg-GAL4 has been considered an ISC/EB-specific driver, recent studies have shown that esg-GAL4 is also active in other tissues, such as neurons and ovaries. Therefore, the ISC/EB specificity of esg-GAL4 is questionable. In this study, we reveal esg-GAL4 expression in the corpus allatum (CA), responsible for juvenile hormone (JH) production. When driving the oncogenic gene, RasV12, esg-GAL4 induces overgrowth in ISCs/EBs as reported, but also increases CA cell number and size. Consistent with this observation, animals alter expression of JH-response genes. Our data show that esg-GAL4-driven gene manipulation can systemically influence JH-mediated animal physiology, arguing for cautious use of esg-GAL4 as a "specific" ISC/EB driver to examine ISC/EB-mediated animal physiology.

Transcriptional Regulators of Ecdysteroid Biosynthetic Enzymes and Their Roles in Insect Development.

Steroid hormones are responsible for coordinating many aspects of biological processes in most multicellular organisms, including insects. Ecdysteroid, the principal insect steroid hormone, is biosynthesized from dietary cholesterol or plant sterols. In the last 20 years, a number of ecdysteroidogenic enzymes, including Noppera-bo, Neverland, Shroud, Spook/Spookier, Cyp6t3, Phantom, Disembodied, Shadow, and Shade, have been identified and characterized in molecular genetic studies using the fruit fly Drosophila melanogaster. These enzymes are encoded by genes collectively called the Halloween genes. The transcriptional regulatory network, governed by multiple regulators of transcription, chromatin remodeling, and endoreplication, has been shown to be essential for the spatiotemporal expression control of Halloween genes in D. melanogaster. In this review, we summarize the latest information on transcriptional regulators that are crucial for controlling the expression of ecdysteroid biosynthetic enzymes and their roles in insect development.

Su(var)2-10- and Su(var)205-dependent upregulation of the heterochromatic gene neverland is required for developmental transition in Drosophila.

Animals develop from juveniles to sexually mature adults through the action of steroid hormones. In insect metamorphosis, a surge of the steroid hormone ecdysone prompts the transition from the larval to the adult stage. Ecdysone is synthesized by a series of biosynthetic enzymes that are specifically expressed in an endocrine organ, the prothoracic gland. At the late larval stage, the expression levels of ecdysone biosynthetic enzymes are upregulated through the action of numerous transcription factors, thus initiating metamorphosis. In contrast, the mechanism by which chromatin regulators support the expression of ecdysone biosynthetic genes is largely unknown. Here, we demonstrate that Su(var)2-10 and Su(var)205, suppressor of variegation [Su(var)] genes encoding a chromatin regulator Su(var)2-10 and nonhistone heterochromatic protein 1a, respectively, regulate the transcription of one of the heterochromatic ecdysone biosynthetic genes, neverland, in Drosophila melanogaster. Knockdown of Su(var)2-10 and Su(var)205 in the prothoracic gland caused a decrease in neverland expression, resulting in a defect in larval-to-prepupal transition. Furthermore, overexpression of neverland and administration of 7-dehydrocholesterol, a biosynthetic precursor of ecdysone produced by Neverland, rescued developmental defects in Su(var)2-10 and Su(var)205 knockdown animals. These results indicate that Su(var)2-10- and Su(var)205-mediated proper expression of neverland is required for the initiation of metamorphosis. Given that Su(var)2-10-positive puncta are juxtaposed with the pericentromeric heterochromatic region, we propose that Su(var)2-10- and Su(var)205-dependent regulation of inherent heterochromatin structure at the neverland gene locus is essential for its transcriptional activation.

Whole-genome sequencing analysis and protocol for RNA interference of the endoparasitoid wasp Asobara japonica.

Asobara japonica is an endoparasitic wasp that parasitizes Drosophila flies. It synthesizes various toxic components in the venom gland and injects them into host larvae during oviposition. To identify and characterize these toxic components for enabling parasitism, we performed the whole-genome sequencing (WGS) and devised a protocol for RNA interference (RNAi) with A. japonica. Because it has a parthenogenetic lineage due to Wolbachia infection, we generated a clonal strain from a single wasp to obtain highly homogenous genomic DNA. The WGS analysis revealed that the estimated genome size was 322 Mb with a heterozygosity of 0.132%. We also performed RNA-seq analyses for gene annotation. Based on the qualified WGS platform, we cloned ebony-Aj, which encodes the enzyme N-ß-alanyl dopamine synthetase, which is involved in melanin production. The microinjection of double-stranded RNA (dsRNA) targeting ebony-Aj led to body colour changes in adult wasps, phenocopying ebony-Dm mutants. Furthermore, we identified putative venom genes as a target of RNAi, confirming that dsRNA injection-based RNAi specifically suppressed the expression of the target gene in wasp adults. Taken together, our results provide a powerful genetic toolkit for studying the molecular mechanisms of parasitism.

The sugar-responsive enteroendocrine neuropeptide F regulates lipid metabolism through glucagon-like and insulin-like hormones in Drosophila melanogaster.

The enteroendocrine cell (EEC)-derived incretins play a pivotal role in regulating the secretion of glucagon and insulins in mammals. Although glucagon-like and insulin-like hormones have been found across animal phyla, incretin-like EEC-derived hormones have not yet been characterised in invertebrates. Here, we show that the midgut-derived hormone, neuropeptide F (NPF), acts as the sugar-responsive, incretin-like hormone in the fruit fly, Drosophila melanogaster. Secreted NPF is received by NPF receptor in the corpora cardiaca and in insulin-producing cells. NPF-NPFR signalling resulted in the suppression of the glucagon-like hormone production and the enhancement of the insulin-like peptide secretion, eventually promoting lipid anabolism. Similar to the loss of incretin function in mammals, loss of midgut NPF led to significant metabolic dysfunction, accompanied by lipodystrophy, hyperphagia, and hypoglycaemia. These results suggest that enteroendocrine hormones regulate sugar-dependent metabolism through glucagon-like and insulin-like hormones not only in mammals but also in insects.

Poly(A) Binding Protein Is Required for Nuclear Localization of the Ecdysteroidogenic Transcription Factor Molting Defective in the Prothoracic Gland of Drosophila melanogaster.

Steroid hormone signaling contributes to the development of multicellular organisms. In insects, ecdysteroids, like ecdysone and the more biologically-active derivative 20-hydroxyecdysone (20E), promote molting and metamorphosis. Ecdysone is biosynthesized in the prothoracic gland (PG), via several steps catalyzed by ecdysteroidogenic enzymes that are encoded by Halloween genes. The spatio-temporal expression pattern of ecdysteroidogenic genes is strictly controlled, resulting in a proper fluctuation of the 20E titer during insect development. However, their transcriptional regulatory mechanism is still elusive. A previous study has found that the polyadenylated tail [poly(A)] deadenylation complex, called Carbon catabolite repressor 4-Negative on TATA (CCR4-NOT) regulates the expression of spookier (spok), which encodes one of the ecdysteroidogenic enzymes in the fruit fly Drosophila melanogaster. Based on this finding, we speculated whether any other poly(A)-related protein also regulates spok expression. In this study, we reported that poly(A) binding protein (Pabp) is involved in spok expression by regulating nuclear localization of the transcription factor molting defective (Mld). When pabp was knocked down specifically in the PG by transgenic RNAi, both spok mRNA and Spok protein levels were significantly reduced. In addition, the spok promoter-driven green fluorescence protein (GFP) signal was also reduced in the pabp-RNAi PG, suggesting that Pabp is involved in the transcriptional regulation of spok. We next examined which transcription factors are responsible for Pabp-dependent transcriptional regulation. Among the transcription factors acting in the PG, we primarily focused on the zinc-finger transcription factor Mld, as Mld is essential for spok transcription. Mld was localized in the nucleus of the control PG cells, while Mld abnormally accumulated in the cytoplasm of pabp-RNAi PG cells. In contrast, pabp-RNAi did not affect the nuclear localization of other transcription factors, including ventral vein lacking (Vvl) and POU domain motif 3 (Pdm3), in PG cells. From these results, we propose that Pabp regulates subcellular localization in the PG, specifically of the transcription factor Mld, in the context of ecdysone biosynthesis.

Cooperative Control of Ecdysone Biosynthesis in Drosophila by Transcription Factors Séance, Ouija Board, and Molting Defective.

Ecdysteroids are steroid hormones that control many aspects of development and physiology. During larval development, ecdysone is synthesized in an endocrine organ called the prothoracic gland through a series of ecdysteroidogenic enzymes encoded by the Halloween genes. The expression of the Halloween genes is highly restricted and dynamic, indicating that their spatiotemporal regulation is mediated by their tight transcriptional control. In this study, we report that three zinc finger-associated domain (ZAD)-C2H2 zinc finger transcription factors-Séance (Séan), Ouija board (Ouib), and Molting defective (Mld)-cooperatively control ecdysone biosynthesis in the fruit fly Drosophila melanogaster Séan and Ouib act in cooperation with Mld to positively regulate the transcription of neverland and spookier, respectively, two Halloween genes. Remarkably, loss-of-function mutations in séan, ouib, or mld can be rescued by the expression of neverland, spookier, or both, respectively. These results suggest that the three transcription factors have distinct roles in coordinating the expression of just two genes in Drosophila Given that neverland and spookier are located in constitutive heterochromatin, Séan, Ouib, and Mld represent the first example of a transcription factor subset that regulates genes located in constitutive heterochromatin.