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

Function Analysis of Cholesterol 7-Desaturase in Ovarian Maturation and Molting in Macrobrachium nipponense: Providing Evidence for Reproductive Molting Progress

The Cholesterol 7-desaturase gene plays an important role in insect ecdysone synthesis, but its role in ovarian development has not been reported. In this study, characteristics and the phylogenetic relationship of Cholesterol 7-desaturase were identified by bioinformatics. qPCR showed that the Mn-CH7D gene was highly expressed in the ovary, which was much higher than that in other tissues, and the expression level of Mn-CH7D reached the highest level at the third stage of the ovarian development stage (O-III). During embryonic development, the Mn-CH7D gene expression was highest in the zoea stage. The function of the Mn-CH7D gene was explored by RNA interference. The experimental group was injected with Mn-CH7D dsRNA through the pericardial cavity of M. nipponense, while the control group was injected with the same volume of dsGFP. Statistical analysis of gonadal development and GSI calculation showed that the silencing of Mn-CH7D resulted in the suppression of gonadal development. In addition, the molting frequency of the experimental group was significantly lower than that of the control group during the second molting cycle after silencing Mn-CH7D. On the seventh day after silencing, ecdysone content in the experimental group was significantly reduced. These results demonstrated that the Mn-CH7D gene played a dual role in ovarian maturation and molting of M. nipponense.

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.

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.

Transcriptome analysis of chloride intracellular channel knockdown in Drosophila identifies oxidation-reduction function as possible mechanism of altered sensitivity to ethanol sedation

Chloride intracellular channels (CLICs) are a unique family of evolutionarily conserved metamorphic proteins, switching between stable conformations based on redox conditions. CLICs have been implicated in a wide variety biological processes including ion channel activity, apoptosis, membrane trafficking, and enzymatic oxidoreductase activity. Understanding the molecular mechanisms by which CLICs engage in these activities is an area of active research. Here, the sole Drosophila melanogaster ortholog, Clic, was targeted for RNAi knockdown to identify genes and biological processes associated with Clic expression. Clic knockdown had a substantial impact on global transcription, altering expression of over 7% of transcribed Drosophila genes. Overrepresentation analysis of differentially expressed genes identified enrichment of Gene Ontology terms including Cytoplasmic Translation, Oxidation-Reduction Process, Heme Binding, Membrane, Cell Junction, and Nucleolus. The top term, Cytoplasmic Translation, was enriched almost exclusively with downregulated genes. Drosophila Clic and vertebrate ortholog Clic4 have previously been tied to ethanol sensitivity and ethanol-regulated expression. Clic knockdown-responsive genes from the present study were found to overlap significantly with gene sets from 4 independently published studies related to ethanol exposure and sensitivity in Drosophila. Bioinformatic analysis of genes shared between these studies revealed an enrichment of genes related to amino acid metabolism, protein processing, oxidation-reduction processes, and lipid particles among others. To determine whether the modulation of ethanol sensitivity by Clic may be related to co-regulated oxidation-reduction processes, we evaluated the effect of hyperoxia on ethanol sedation in Clic knockdown flies. Consistent with previous findings, Clic knockdown reduced acute ethanol sedation sensitivity in flies housed under normoxia. However, this effect was reversed by exposure to hyperoxia, suggesting a common set of molecular-genetic mechanism may modulate each of these processes. This study suggests that Drosophila Clic has a major influence on regulation of oxidative stress signaling and that this function overlaps with the molecular mechanisms of acute ethanol sensitivity in the fly.

A Genetic Study of Cerebral Atherosclerosis Reveals Novel Associations with NTNG1 and CNOT3

Cerebral atherosclerosis is a leading cause of stroke and an important contributor to dementia. Yet little is known about its genetic basis. To examine the association of common single nucleotide polymorphisms with cerebral atherosclerosis severity, we conducted a genomewide association study (GWAS) using data collected as part of two community-based cohort studies in the United States, the Religious Orders Study (ROS) and Rush Memory and Aging Project (MAP). Both studies enroll older individuals and exclude participants with signs of dementia at baseline. From our analysis of 1325 participants of European ancestry who had genotype and neuropathologically assessed cerebral atherosclerosis measures available, we found a novel locus for cerebral atherosclerosis in NTNG1. The locus comprises eight SNPs, including two independent significant SNPs: rs6664221 (β = -0.27, 95% CI = (-0.35, -0.19), p = 1.29 × 10^-10) and rs10881463 (β = -0.20, 95% CI = (-0.27, -0.13), p = 3.40 × 10^-8). We further found that the SNPs may influence cerebral atherosclerosis by regulating brain protein expression of CNOT3. CNOT3 is a subunit of CCR4-NOT, which has been shown to be a master regulator of mRNA stability and translation and an important complex for cholesterol homeostasis. In summary, we identify a novel genetic locus for cerebral atherosclerosis and a potential mechanism linking this variation to cerebral atherosclerosis progression. These findings offer insights into the genetic effects on cerebral atherosclerosis.

Regulation of ecdysone production in Drosophila by neuropeptides and peptide hormones

In both mammals and insects, steroid hormones play a major role in directing the animal's progression through developmental stages. To maximize fitness outcomes, steroid hormone production is regulated by the environmental conditions experienced by the animal. In insects, the steroid hormone ecdysone mediates transitions between developmental stages and is regulated in response to environmental factors such as nutrition. These environmental signals are communicated to the ecdysone-producing gland via the action of neuropeptide and peptide hormone signalling pathways. While some of these pathways have been well characterized, there is evidence to suggest more signalling pathways than has previously been thought function to control ecdysone production, potentially in response to a greater range of environmental conditions. Here, we review the neuropeptide and peptide hormone signalling pathways known to regulate the production of ecdysone in the model genetic insect Drosophila melanogaster, as well as what is known regarding the environmental signals that trigger these pathways. Areas for future research are highlighted that can further contribute to our overall understanding of the complex orchestration of environmental, physiological and developmental cues that together produce a functioning adult organism.

Control of the insect metamorphic transition by ecdysteroid production and secretion

Ecdysteroids are a class of steroid hormones that controls molting and metamorphic transitions in Ecdysozoan species including insects, in which ecdysteroid biosynthesis and its regulation have been extensively studied. Insect ecdysteroids are produced from dietary sterols by a series of reduction-oxidation reactions in the prothoracic gland and in Drosophila they are released into the hemolymph via vesicle-mediated secretion at the time of metamorphosis. To initiate precisely controlled ecdysteroid pulses, the prothoracic gland functions as a central node integrating both intrinsic and extrinsic signals to control ecdysteroid biosynthesis and secretion. In this review, we outline recent progress in the characterization of ecdysone biosynthesis and steroid trafficking pathways and the discoveries of novel factors regulating prothoracic gland function.

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.

Sterol Characteristics in Silkworm Brain and Various Tissues Characterized by Precise Sterol Profiling Using LC-MS/MS

Sterols, especially cholesterol (Chl), are fundamental for animal survival. Insects lacking the ability to synthesize Chl are sterol auxotrophic animals and utilize dietary Chl and phytosterols to survive. The sterols obtained from a diet are distributed to the tissues; however, sterol homeostasis in insect tissues remains to be elucidated. This study sought to understand the sterol characteristics of insect tissues through detailed sterol quantification and statistics. The combination of sterol quantification using liquid chromatography tandem mass spectrometry (LC-MS/MS) and principal component analysis (PCA) revealed tissue-specific sterol characteristics in the silkworm, Bombyx mori, a phytophagous insect. We found that insect tissues have tissue-intrinsic sterol profiles. The brain has a unique sterol composition as compared to other tissues—high concentration of Chl and less accumulation of phytosterols. Other tissues also have intrinsic sterol characteristics, which when defined by dietary sterols or Chl metabolites, indicate preference for a sterol and consistently manage their own sterol homeostasis. Though most tissues never change sterol profiles during development, the brain drastically changes its sterol profile at the wandering stage, indicating that it could alter sterol composition in preparation for metamorphosis. These results suggest the existence of tissue- and sterol-specific systems for sterol homeostasis in insects.