INHIBITION OF FATTY ACID DESATURASES IN Drosophila melanogaster LARVAE BLOCKS FEEDING AND DEVELOPMENTAL PROGRESSION

Mating-induced increase of kynurenine in Drosophila ovary enhances starvation resistance of progeny

The maternal nutritional environment can impact progeny development, stress tolerance, and longevity. Such phenotypic variation of offspring resulting from the maternal environment is often referred to as the 'maternal effect' and is observed across taxa, including in humans. While some mechanisms behind maternal effects have been revealed, such as histone modification, many studies rely on drastic genetic or nutritional manipulation in describing these mechanisms. Here we aimed to reveal how the maternal environment is regulated under physiological conditions to affect the progeny. Specifically, we detailed metabolic regulation in oocytes in response to mating using Drosophila melanogaster fruit flies. Using liquid chromatography-mass spectrometry, we found that upon mating, the ovary metabolites shifted, predominantly toward increasing amino acids and the tryptophan/kynurenine (Kyn) pathway. This mating-induced increase in ovary Kyn was driven by increased Kyn production in the fat body, a functional counterpart of the mammalian liver and white adipose tissue and the source of Kyn storage for the ovary after mating. Furthermore, we show that maternal Kyn repression decreased the starvation resistance of progeny and that administering exogenous Kyn to the maternal generation enhanced the starvation resistance of female progeny. Taken together, these findings point to a previously unidentified role of fat body Kyn distribution during reproduction on progeny survival.

The influence of first desaturase subfamily genes on fatty acid synthesis, desiccation tolerance and inter-caste nutrient transfer in the termite Coptotermes formosanus

Desaturase enzymes play an essential role in the biosynthesis of unsaturated fatty acids (UFAs). In this study, we identified seven "first desaturase" subfamily genes (Cfor-desatA1, Cfor-desatA2-a, Cfor-desatA2-b, Cfor-desatB-a, Cfor-desatB-b, Cfor-desatD and Cfor-desatE) from the Formosan subterranean termite Coptotermes formosanus. These desaturases were highly expressed in the cuticle and fat body of C. formosanus. Inhibition of either the Cfor-desatA2-a or Cfor-desatA2-b gene resulted in a significant decrease in the contents of fatty acids (C16:0, C18:0, C18:1 and C18:2) in worker castes. Moreover, we observed that inhibition of most of desaturase genes identified in this study had a negative impact on the survival rate and desiccation tolerance of workers. Interestingly, when normal soldiers were reared together with dsCfor-desatA2-b-treated workers, they exhibited higher mortality, suggesting that desaturase had an impact on trophallaxis among C. formosanus castes. Our findings shed light on the novel roles of desaturase family genes in the eusocial termite C. formosanus.

Insect cuticle and insecticide development

Insecticide resistance poses a significant challenge, diminishing the effectiveness of chemical insecticides. To address this global concern, the development of novel and efficient pest management technologies based on chemical insecticides is an ongoing necessity. The insect cuticle, a highly complex and continuously renewing organ, plays a crucial role in this context. On one hand, as the most vital structure, it serves as a suitable target for insecticides. On the other hand, it acts as the outermost barrier, isolating the insect's inner organs from the environment, and thus offering resistance to contact with insecticides, preventing their entry into insect bodies. Our work focuses on key targets concerning cuticle formation and the interaction between the cuticle and contact insecticides. Deeper studying insect cuticles and understanding their structure-function relationship, formation process, and regulatory mechanisms during cuticle development, as well as investigating insecticide resistance related to the barrier properties of insect cuticles, are promising strategies not only for developing novel insecticides but also for discovering general synergists for contact insecticides. With this comprehensive review, we hope to contribute valuable insights into the development of effective pest management solutions and the mitigation of insecticide resistance.

Transcriptome analysis reveals the role of Zelda in the regulation of embryonic and wing development of Tribolium castaneum

Zinc finger protein (Zelda) of Tribolium castaneum (TcZelda) has been showed to play pivotal roles in embryonic development and metamorphosis. However, the regulatory mechanism of TcZelda associated with these physiology processes is unclear. Herein, the developmental expression profile showed that Zelda of T. castaneum was highly expressed in early eggs. Tissue expression profiling revealed that TcZelda was mainly expressed in the larval head and adult ovary of late adults and late larvae. TcZelda knockdown led to a 95% mortality rate in adults. These results suggested that TcZelda is related to the activation of the zygote genome in early embryonic development. Furthermore, 592 differentially expressed genes were identified from the dsZelda treated group. Compared with the control group, altered disjunction (ALD) and AGAP005368-PA (GAP) in the dsZelda group were significantly down-regulated, while TGF-beta, propeptide (TGF) was significantly up-regulated, suggesting that TcZelda may be involved in insect embryonic development. In addition, the expression of Ubx ultrabithorax (UBX), Cx cephalothorax (CX), En engrailed (EN), and two Endocuticle structural glycoprotein sgabd (ABD) genes were significantly down-regulated, suggesting that they may cooperate with TcZelda to regulate the development of insect wings. Additionally, Elongation (ELO), fatty acid synthase (FAS), and fatty acyl-CoA desaturase (FAD) expression was inhibited in dsZelda insects, which could disturb the lipase signaling pathways, thus, disrupting the insect reproductive system and pheromone synthesis. These results may help reveal the function of TcZelda in insects and the role of certain genes in the gene regulatory network and provide new ideas for the prevention and control of T. castaneum.

Unraveling the Role of Lac Insects in Providing Natural Industrial Products

In the current era, products made from organic materials enjoy a privileged position because of their inherent safety. The eco-friendly properties of natural lac resins have increased their demand in many industries. It is secreted by sucking insects (Hemiptera, Kerriidae) and comprises three major components, viz., resin, dye, and wax. Lac insects are generally bivoltine in nature and are distributed in tropical and sub-tropical regions with complex multi-trophic habitats. Because of their sedentary habits, lac insects are more vulnerable to predators, parasitoids, squirrels, and rats, leading to a more than 50% reduction in production yield. To increase lac production, advanced-level molecular research is required to figure out the mechanism behind lac synthesis and secretion to improve lac yield and quality. The present review highlights metamorphosis, sexual dimorphism, multi-trophic habitat, host plants, and natural enemies of lac insects, lac composition, and applications, emphasizing the role of microbes, potential lac genes, and lac synthesis mechanisms in enhancing lac quality and production. The information provided here might be useful for lac researchers and for stakeholders aiming to make their products more eco-friendly.

CYP311A1 in the anterior midgut is involved in lipid distribution and microvillus integrity in Drosophila melanogaster

Lipids are either taken up from food sources or produced internally in specialized tissues such as the liver. Among others, both routes of lipid metabolism involve cytochrome P450 monooxygenases (CYPs). We sought to analyze the function of Cyp311a1 that has been shown to be expressed in the midgut of the fruit fly Drosophila melanogaster. Using a GFP-tagged version of CYP311A1 that is expressed under the control of its endogenous promoter, we show that Cyp311a1 localizes to the endoplasmic reticulum in epithelial cells of the anterior midgut. In larvae with reduced Cyp311a1 expression in the anterior midgut, compared to control larvae, the apical plasma membrane of the respective epithelial cells contains less and shorter microvilli. In addition, we observed reduction of neutral lipids in the fat body, the insect liver, and decreased phosphatidylethanolamine (PE) and triacylglycerols (TAG) amounts in the whole body of these larvae. Probably as a consequence, they cease to grow and eventually die. The microvillus defects in larvae with reduced Cyp311a1 expression are restored by supplying PE, a major phospholipid of plasma membranes, to the food. Moreover, the growth arrest phenotype of these larvae is partially rescued. Together, these results suggest that the anterior midgut is an import hub in lipid distribution and that the midgut-specific CYP311A1 contributes to this function by participating in shaping microvilli in a PE-dependent manner.

Loss of Stearoyl-CoA desaturase 1 leads to cardiac dysfunction and lipotoxicity

Diets high in carbohydrates are associated with type 2 diabetes and its co-morbidities, including hyperglycemia, hyperlipidemia, obesity, hepatic steatosis and cardiovascular disease. We used a high-sugar diet to study the pathophysiology of diet-induced metabolic disease in Drosophila melanogaster. High-sugar diets produce hyperglycemia, obesity, insulin resistance and cardiomyopathy in flies, along with ectopic accumulation of toxic lipids, or lipotoxicity. Stearoyl-CoA desaturase 1 is an enzyme that contributes to long-chain fatty acid metabolism by introducing a double bond into the acyl chain. Knockdown of stearoyl-CoA desaturase 1 in the fat body reduced lipogenesis and exacerbated pathophysiology in flies reared on high-sucrose diets. These flies exhibited dyslipidemia and growth deficiency in addition to defects in cardiac and gut function. We assessed the lipidome of these flies using tandem mass spectrometry to provide insight into the relationship between potentially lipotoxic species and type 2 diabetes-like pathophysiology. Oleic acid supplementation is able to rescue a variety of phenotypes produced by stearoyl-CoA desaturase 1 RNAi, including fly mass, triglyceride storage, gut development and cardiac failure. Taken together, these data suggest a protective role for monounsaturated fatty acids in diet-induced metabolic disease phenotypes.

Genome-Wide Characterization and Identification of Long Non-Coding RNAs during the Molting Process of a Spider Mite, Panonychus citri

Molting is essential for arthropods to grow. As one of the important arthropod pests in agriculture, key spider mite species (Tetranychus and Panonychus) can normally molt three times from the larva to adult stage within a week. This physiological strategy results in the short lifecycle of spider mites and difficulties in their control in the field. Long non-coding RNAs (lncRNAs) regulate transcriptional editing, cellular function, and biological processes. Thus, analysis of the lncRNAs in the spider mite molting process may provide new insights into their roles in the molting mechanism. For this purpose, we used high-throughput RNA-seq to examine the expression dynamics of lncRNAs and mRNAs in the molting process of different development stages in Panonychus citri. We identified 9199 lncRNAs from 18 transcriptomes. Analysis of the lncRNAs suggested that they were shorter and had fewer exons and transcripts than mRNAs. Among these, 356 lncRNAs were differentially expressed during three molting processes: late larva to early protonymph, late protonymph to early deutonymph, and late deutonymph to early adult. A time series profile analysis of differentially expressed lncRNAs showed that 77 lncRNAs were clustered into two dynamic expression profiles (Pattern a and Pattern c), implying that lncRNAs were involved in the molting process of spider mites. Furthermore, the lncRNA-mRNA co-expression networks showed that several differentially expressed hub lncRNAs were predicted to be functionally associated with typical molting-related proteins, such as cuticle protein and chitin biosynthesis. These data reveal the potential regulatory function of lncRNAs in the molting process and provide datasets for further analysis of lncRNAs and mRNAs in spider mites.

Eco-genetics of desiccation resistance in Drosophila

Climate change globally perturbs water circulation thereby influencing ecosystems including cultivated land. Both harmful and beneficial species of insects are likely to be vulnerable to such changes in climate. As small animals with a disadvantageous surface area to body mass ratio, they face a risk of desiccation. A number of behavioural, physiological and genetic strategies are deployed to solve these problems during adaptation in various Drosophila species. Over 100 desiccation-related genes have been identified in laboratory and wild populations of the cosmopolitan fruit fly Drosophila melanogaster and its sister species in large-scale and single-gene approaches. These genes are involved in water sensing and homeostasis, and barrier formation and function via the production and composition of surface lipids and via pigmentation. Interestingly, the genetic strategy implemented in a given population appears to be unpredictable. In part, this may be due to different experimental approaches in different studies. The observed variability may also reflect a rich standing genetic variation in Drosophila allowing a quasi-random choice of response strategies through soft-sweep events, although further studies are needed to unravel any underlying principles. These findings underline that D. melanogaster is a robust species well adapted to resist climate change-related desiccation. The rich data obtained in Drosophila research provide a framework to address and understand desiccation resistance in other insects. Through the application of powerful genetic tools in the model organism D. melanogaster, the functions of desiccation-related genes revealed by correlative studies can be tested and the underlying molecular mechanisms of desiccation tolerance understood. The combination of the wealth of available data and its genetic accessibility makes Drosophila an ideal bioindicator. Accumulation of data on desiccation resistance in Drosophila may allow us to create a world map of genetic evolution in response to climate change in an insect genome. Ultimately these efforts may provide guidelines for dealing with the effects of climate-related perturbations on insect population dynamics in the future.

The Desaturase Gene Nlug-desatA2 Regulates the Performance of the Brown Planthopper Nilaparvata lugens and Its Relationship with Rice

Insect desaturases are known to play an important role in chemical communication between individuals. However, their roles in insect growth, development and fecundity, and in regulating interactions of insects with plants, remain largely unknown. In this study, we explored the functions of Nlug-desatA2, a desaturase gene of the brown planthopper (BPH), Nilaparvata lugens (Stål). The RNA interference-based knockdown of Nlug-desatA2 decreased the ratio of monounsaturated fatty acids to saturated fatty acids, and the level of fatty acids and triglycerides in BPH. Nlug-desatA2-knockdown also reduced the food intake, body mass and fecundity of female BPH adults, and led to abdomen atrophy and ovarian agenesis. Nlug-desatA2-knockdown suppressed the transcription of TOR (target of rapamycin), Lpp (Lipophorin) and AKHR (adipokinetic hormone receptor) in female adults. Moreover, the corrected survival rate of BPH with Nlug-desatA2-knockdown fed an artificial diet was higher than the survival rate of those fed on rice plants. Higher levels of salicylic acid in rice infested by Nlug-desatA2-knockdown female BPH adults than in rice infested by control BPH may be the reason. These findings demonstrate that Nlug-desatA2 has an essential role in lipid metabolism and is involved in the food intake, survival, development and fecundity of BPH. In addition, this gene is likely involved in regulating the responses of rice to BPH infestation.

Inhibition of fatty acid desaturation impairs cuticle differentiation in Drosophila melanogaster

Previously, we showed that inhibition of the activity of fatty acid desaturases (Desat) perturbs signalling of the developmental timing hormone ecdysone in the fruit fly Drosophila melanogaster. To understand the impact of this effect on cuticle differentiation, a process regulated by ecdysone, we analysed the cuticle of D. melanogaster larvae fed with the Desat inhibitor CA10556. In these larvae, the expression of most of the key cuticle genes is normal or slightly elevated at day one of CA10556 feeding. As an exception, expression of twdlM coding for a yet uncharacterised cuticle protein is completely suppressed. The cuticle of these larvae appears to be normal at the morphological level. However, these animals are sensitive to desiccation, a trait that according to our data, among others, may be associated with reduced TwdlM amounts. At day two of CA10556 feeding, expression of most of the cuticle genes tested including twdlM is suppressed. Expression of cpr47Eb coding for a chitin-binding protein is, by contrast, highly elevated suggesting that Cpr47Eb participates at a specific compensation program. Overall, the cuticle of these larvae is thinner than the cuticle of control larvae. Taken together, lipid desaturation is necessary for a coordinated deployment of a normal cuticle differentiation program.

The Desaturase Gene Family is Crucially Required for Fatty Acid Metabolism and Survival of the Brown Planthopper, Nilaparvata lugens

Desaturases are essentially required for unsaturated fatty acid (UFA) biosynthesis. We identified 10 genes encoding putative desaturases in the transcriptome database of the brown planthopper (BPH), Nilaparvata lugens. These include eight First Desaturase family genes, one cytochrome b5 fused desaturase gene (Nlug-Cytb5r) and one Sphingolipid Desaturase gene (Nlug-ifc). Transcript level profiling revealed significant variation in the expression patterns of these genes across tissues and developmental stages, which occur in a gene-specific manner. Interestingly, their expression was also modulated by the insect food source: the mRNA levels of Nlug-desatC and Nlug-Cytb5r were down-regulated, but the expression level of Nlug-desatA1-b and Nlug-desatA1-c were elevated in the BPH fed on the resistant rice variety Babawee as compared to the non-resistant variety Taichun Native 1 (TN1). Silencing Nlug-desatA1-b, Nlug-desatA1-c, or Nlug-Ifc reduced fatty acid composition and abundance in female BPH 1-d-old-adults compared to controls. Whereas, single knockdown of all ten desaturase genes significantly increased mortality of BPH nymphs compared with controls. Of the ten desaturase genes, knockdown of Nlug-desatA1-b and Nlug-desatA2 caused the highest mortality in BPH (91% and 97%, respectively). Our findings offer a base for expression and functional characterization of newly identified desaturase genes in BPH, and may contribute to RNA interference-based pest management strategies.

The fruit fly Drosophila melanogaster as an innovative preclinical ADME model for solute carrier membrane transporters, with consequences for pharmacology and drug therapy

Solute carrier membrane transporters (SLCs) control cell exposure to small-molecule drugs, thereby contributing to drug efficacy and failure and/or adverse effects. Moreover, SLCs are genetically linked to various diseases. Hence, in-depth knowledge of SLC function is fundamental for a better understanding of disease pathophysiology and the drug development process. Given that the model organism Drosophila melanogaster (fruit fly) expresses SLCs, such as for the excretion of endogenous and toxic compounds by the hindgut and Malpighian tubules, equivalent to human intestine and kidney, this system appears to be a promising preclinical model to use to study human SLCs. Here, we systematically compare current knowledge of SLCs in Drosophila and humans and describe the Drosophila model as an innovative tool for drug development.

The ABC transporter ABCH-9C is needed for cuticle barrier construction in Locusta migratoria

ATP-binding cassette (ABC) transporters constitute a large superfamily of proteins that mediate transport of a diverse number of substrates including nutrients, lipids and xenobiotics across membranes serving a variety of developmental and physiological functions. Here, we report on the molecular properties and biological roles of the ABC transporter LmABCH-9C in the migratory locust Locusta migratoria. LmABCH-9C was expressed continuously during nymphal development in all tissues including the integument. Expression was highest just after molting. Suppression of LmABCH-9C transcript levels by RNA interference (RNAi) in nymphs provoked death during or soon after molting to the next stage. These nymphs lost weight within minutes after molting. Moreover, high humidity rescued the lethality of molted dsLmABCH-9C-injected nymphs. In histological experiments, we find that the amounts of inner-cuticular lipids are reduced in nymphs with suppressed LmABCH-9C expression. These data together indicate that LmABCH-9C is needed for lipid-dependent desiccation resistance, paralleling the function of ABCH-9C in Tribolium castaneum. Hence, the function of this ABC transporter seems to be conserved across insect species ranging from hemimetabolous (L. migratoria) to holometabolous (T. castaneum) species. In addition, we find that cuticle inward impermeability is compromised in nymphs with reduced LmABCH-9C function. In summary, consistent with the model that cuticular lipids are necessary to prevent desiccation and penetration of xenobiotics in insects, we hypothesize that LmABCH-9C is involved in the construction of a lipid-based barrier at the surface of the cuticle especially after molting to protect the animal against uncontrolled water loss and entry. Susceptibility of this ABC transporter to RNAi-mediated knockdown designates it as an excellent target for RNAi-based insect pest control.

Regulation of cuticular hydrocarbon profile maturation by Drosophila tanning hormone, bursicon, and its interaction with desaturase activity

Shortly after emergence the exoskeleton (cuticle) of adult insects is rapidly expanded, hardened (sclerotized), and pigmented (melanized). In parallel with this process, the oenocytes, which are large polyploid cells located below the abdominal epidermis, secrete onto the cuticle a cocktail of cuticular hydrocarbons (CHs) and waxes. These improve the waterproofing of the cuticle, and also provide important chemosensory and pheromonal cues linked with gender, age, and species differentiation. The hardening and pigmentation of the new cuticle are controlled by the neurohormone, bursicon, and its receptor, encoded by the DLGR2 receptor, rickets (rk); by contrast, little is known about the timecourse of changes in CH profile and about the role of bursicon in this process. Here we show in Drosophila that rk function is also required for the normal maturation of the fly's CH profile, with flies mutant for rk function showing dramatically elevated levels of CHs. Interestingly, this effect is mostly abrogated by mutations in the Δ9 desaturase encoded by the desaturase1 gene, which introduces a first double bond into elongated fatty-acid chains, suggesting that desaturase1 acts downstream of rk. In addition, flies mutant for rk showed changes in the absolute and relative levels of specific 7-monoenes (in males) and 7,11-dienes (in females). The fact that these differences in CH amounts were obtained using extractions of very different durations suggests that the particular CH profile of flies mutant for rk is not simply due to their unsclerotized cuticle but that bursicon may be involved in the process of CH biosynthesis itself.