Shade is the Drosophila P450 enzyme that mediates the hydroxylation of ecdysone to the steroid insect molting hormone 20-hydroxyecdysone

Differentially spliced mitochondrial CYP419A1 contributes to ethiprole resistance in Nilaparvata lugens

The brown planthopper Nilaparvata lugens is one of the most economically important pests of cultivated rice in Southeast Asia. Extensive use of insecticide treatments, such as imidacloprid, fipronil and ethiprole, has resulted in the emergence of multiple resistant strains of N. lugens. Previous investigation of the mechanisms of resistance to imidacloprid and ethiprole demonstrated that overexpression and qualitative changes in the cytochrome P450 gene CYP6ER1 lead to enhanced metabolic detoxification of these compounds. Here, we present the identification of a secondary mechanism enhancing ethiprole resistance mediated by differential splicing and overexpression of CYP419A1, a planthopper-specific, mitochondrial P450 gene. Although metabolic resistance to insecticides is usually mediated by overexpression of P450 genes belonging to either CYP 3 or 4 clades, we validate the protective effect of over-expression of CYP419A1, in vivo, using transgenic Drosophila melanogaster. Additionally, we report some unusual features of both the CYP419A1 gene locus and protein, which include, altered splicing associated with resistance, a non-canonical heme-binding motif and an extreme 5' end extension of the open reading frame. These results provide insight into the molecular mechanisms underpinning resistance to insecticides and have applied implications for the control of a highly damaging crop pest.

The ecdysone-induced bZIP transcription factor MafB establishes a positive feedback loop to enhance vitellogenesis and reproduction in the Aedes aegypti mosquito

Female mosquitoes require a vertebrate blood meal to activate reproduction, transmitting numerous devastating human diseases. Vitellogenesis is a central event of female reproduction that involves the massive production of vitellogenin (Vg) in the fat body and the maturation of ovaries. This process is controlled by the steroid hormone 20-hydroxyecdysone (20E); however, its molecular regulatory basis remains not completely understood. We found that the expression of Aedes aegypti muscle aponeurosis fibromatosis B (AaMafB), coding for a basic leucine zipper (bZIP) transcription factor, was significantly up-regulated after a blood meal. The 20E-bound ecdysone receptor-ultraspiracle heterodimer directly targeted the ecdysone response element in the promoter of AaMafB, activating its transcription. Coimmunoprecipitation assays illustrated the interaction between AaMafB and Cap "n" collar C (AaCncC), another bZIP transcription factor. RNA interference-mediated depletion of AaMafB or AaCncC led to impaired ovarian growth, decreased expression of AaVg and Halloween genes, and reduced 20E levels. The AaMafB-AaCncC heterodimer directly activated the transcription of AaVg and AaShade by targeting the antioxidant response element in their promoters. Together, our results indicate that AaMafB functions as an early 20E response gene, the product of which heterodimerizes with AaCncC to maintain high 20E levels and facilitates activation of AaVg in mosquitoes after a blood meal.

Overexpression of ace2 compensating for the acetylcholinesterase activity loss from ace1 mutations accelerated the development of eggs and early nymphs in Nilaparvata lugens

Acetylcholinesterase (AChE) guarantees the acetylcholine signal in insect central nervous system, and is the target of organophosphorus and carbamate insecticides, towards which resistance was often reported due to AChE mutations. In Nilaparvata lugens, a major pest on rice, two mutations (G119S and F331C) were detected in AChE1 in a chlorpyrifos-resistant (CHL) strain. The double mutations in AChE1 reduced total AChE activity in metabolizing acetylcholine, such as low protein stability, substrate affinity and catalytic efficiency, which needed compensation in a special way. In CHL strain, the transcriptional level of ace2 encoding AChE2 was systematically elevated, such as over 30-fold overexpression in brain. The ace2 overexpression not only compensated for AChE activity loss in brain due to AChE1 mutations, but also accelerated the development of eggs and early nymphs in CHL strain. When performing ace2 RNAi in CHL eggs, the egg and early nymph duration were recovered. In CHL eggs, the transcriptional levels of three basic helix-loop-helix transcription factors (Ase2, Ato1 and SCL), which were closely related to neural development, were significantly upregulated. Their respective RNAi in CHL strain also significantly recovered the egg duration, as RNAi towards ace2, which partially explained the reason for the accelerated development of eggs and early nymphs. The results revealed AChE2 non-canonical function in insect embryonic development, and uncovered a physiological effect caused by ace2 overexpression as a compensation action for resistance mechanism due to AChE1 mutations, providing a base for insecticide resistance management in insects.

Spätzle Regulates Developmental and Immune Trade-Offs Induced by Bacillus thuringiensis Priming in Rhynchophorus ferrugineus

The red palm weevil (RPW) is an invasive pest that causes devastating damage to a variety of palm plants, which exhibit specific immune priming to Bacillus thuringiensis (Bt). However, immune priming in RPW may incur a high fitness cost, and its molecular signaling pathways have not yet been reported. Here, we investigated the effect of Bt priming on RPW development and subsequently analyzed the hormonal and immune-related molecular pathways influencing the fitness cost induced by Bt priming. Bt priming delayed the body weight gain of fifth-instar larvae and prolonged their developmental duration. Bt priming significantly reduced the 20-hydroxyecdysone (20E) content in RPW hemolymph, and the expression levels of the 20E biosynthesis-related genes SHADOW and SHADE were significantly downregulated. Furthermore, we analyzed Toll pathway genes influencing Bt priming and found that only Spätzle (SPZ) transcription was significantly activated under Bt priming. After silencing SPZ expression, the negative effects of Bt priming on development, SHADOW expression, and 20E synthesis were eliminated, thereby suggesting that SPZ is a key molecular signal mediating developmental and immune trade-offs induced by Bt priming. Our results elucidate the molecular cascade pathway of immune priming and provide new targets for improving the efficiency of RPW biological controls.

A validated HPLC-MS/MS method for the simultaneous determination of ecdysteroid hormones in subminimal amounts of biological material

Ecdysteroids represent a large class of polyhydroxylated steroids which, due to their anabolic properties, are marketed as dietary supplements. Some ecdysteroids also act as important hormones in arthropods, where they regulate molting, development, and reproduction and many of these insects are miniature organisms that contain submicroliter levels of circulating biofluids. Analysis of ecdysteroids is further complicated by their very low abundance, large fluctuations during development, and difficult access to a pooled sample, which is important for quantitative measurements. In this work, we propose a new method that overcomes the described difficulties and allows validated quantification of four ecdysteroids in minimal amounts of biological material. After methanolic extraction, detectability of the ecdysteroids is increased 16- to 20-fold by conversion to their 14,15-anhydrooximes. These are further purified by pipette tip solid-phase extraction on a three-layer sorbent and subjected to HPLC-MS/MS analysis. Full validation was achieved using hemolymph from larvae of the firebug Pyrrhocoris apterus as a blank matrix and by the determination of ecdysteroids in a single Drosophila larva. The lower limit of quantifications for the four target ecdysteroids (20-hydroxyecdysone, ecdysone, makisterone A, and 2-deoxyecdysone) were 0.01; 0.1; 0.05; and 0.025 pg·ml-1 (20; 200; 100; 50 fmol ml-1), respectively, with very good accuracy, precision (expressed as relative standard deviation <15%) and recoveries (96%-119.9%). The application potential of the new method was demonstrated by quantification of ecdysteroids in various biological materials including human serum.

Effects of pyriproxyfen on development and hormone of the aphis, Aphis craccivora (Hemiptera: Aphididae)

Pyriproxyfen (PPF) has been shown to affect the pupal stage and ecdysone levels in holometabolous insects, such as silkworms and mealworms. It remains unknown whether it affects hemimetabolous insects with their hormone levels in insects lacking a pupal stage. In this laboratory study, bioassays were conducted to investigate the effects of varying doses of PPF on Aphis craccivora Koch (Hemiptera: Aphididae). Ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to determine the types and titers of juvenile hormone (JH) and 20-hydroxyecdysone (20E). Additionally, the effects of PPF on A. craccivora reproduction and molting, as well as its influence on relevant gene expression, were examined. The results revealed LC50 and LC90 values of 3.84 and 7.49 mg/l for PPF, respectively, after 48 h of exposure. The results demonstrated a significant reduction in the titer of JH III and a significant increase in the titer of 20E following treatment with PPF. However, there was no significant decrease observed in the titer of JH III skipped bisepoxide (JH SB3). A sublethal concentration of PPF was found to inhibit Krüppel homolog 1 (kr-h1) gene expression and reduce aphid reproduction, but it did not significantly impact ecdysone receptor expression and aphid molting. The results of this study demonstrate that PPF exhibits a lethal effect on aphids, thereby providing an effective means of control. Additionally, sublethal concentrations of PPF have been found to inhibit the JH in aphids, resulting in a decline in their reproductive ability and achieving the desired control objectives.

Steroid signaling controls sex-specific development in an invertebrate

In vertebrate sexual development, two important steroid hormones, testosterone and estrogen, regulate the sex-specific development of many tissues. In contrast, invertebrates utilize a single steroid hormone, ecdysone, to regulate developmental timing in both sexes. However, here we show that in Drosophila melanogaster, sex-specific ecdysone (E) signaling controls important aspects of gonad sexual dimorphism. Rather than being regulated at the level of hormone production, hormone activity is regulated cell-autonomously through sex-specific hormone reception. Ecdysone receptor (EcR) expression is restricted to the developing ovary and is repressed in the testis at a time when ecdysone initiates ovary morphogenesis. Interestingly, EcR expression is regulated downstream of the sex determination factor Doublesex (Dsx), the founding member of the Dsx/Mab3 Related Transcription Factor (DMRT) family that regulates gonad development in all animals. E signaling is required for normal ovary development1,2, and ectopic activation of E signaling in the testis antagonized stem cell niche identity and feminized somatic support cells, which were transformed into follicle-like cells. This work demonstrates that invertebrates can also use steroid hormone signaling to control sex-specific development. Further, it may help explain recent work showing that vertebrate sexual development is surprisingly cell-autonomous. For example, chickens utilize testosterone and estrogen to control sex-specific development, but when they have a mixture of cells with male and female genotypes, the male cells develop as male and the female cells develop as female despite exposure to the same circulating hormones3. Sex-specific regulation of steroid hormone signaling may well underly such cell-autonomous sexual fate choices in vertebrates as it does in Drosophila.

Local Ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila

Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, we find that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. We find that local Ec/EcR signaling is required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair.

PTTH-Torso Signaling System Controls Developmental Timing, Body Size, and Reproduction through Regulating Ecdysone Homeostasis in the Brown Planthopper, Nilaparvata lugens

In holometabolous insects, such as Drosophila and Bombyx, prothoracicotropic hormone (PTTH) is well established to be critical in controlling developmental transitions and metamorphosis by stimulating the biosynthesis of ecdysone in the prothoracic glands (PGs). However, the physiological role of PTTH and the receptor Torso in hemimetabolous insects remains largely unexplored. In this study, homozygous PTTH- and Torso-null mutants of the brown planthopper (BPH), Nilaparvata lugens, were successfully generated by employing clustered regularly interspaced short palindromic repeats/CRISPR-associated 9 (CRISPR-Cas9). Further characterization showed that both NlPTTH-/- and NlTorso-/- mutants exhibited prolonged nymphal duration and increased final adult size. Enzyme-linked immunosorbent assay (ELISA) revealed that NlPTTH-/- and NlTorso-/- mutants exhibited a significant reduction in 20-hydroxyecdysone (20E) in fifth-instar nymphs at 48 h post-ecdysis compared to Wt controls. Furthermore, our results indicated that both NlPTTH-/- and NlTorso-/- mutants had shortened lifespan, reduced female fecundity, and reduced egg hatching rates in adults. These findings suggest a conserved role for the PTTH-Torso signaling system in the regulation of developmental transitions by stimulating ecdysone biosynthesis in hemimetabolous insects.

Halloween genes are expressed with a circadian rhythm during development in prothoracic glands of the insect RHODNIUS PROLIXUS

We analyse the developmental and circadian profiles of expression of the genes responsible for ecdysteroidogenesis (Halloween genes) in the PGs of Rhodnius prolixus throughout larval-adult development. Extensive use of in vitro techniques enabled multiple different parameters to be measured in individual PGs. Expression of disembodied and spook closely paralleled the ecdysteroid synthesis of the same PGs, and the ecdysteroid titre in vivo, but with functionally significant exceptions. Various tissues other than PGs expressed one, both or neither genes. Both gonads express both genes in pharate adults (larvae close to ecdysis). Both genes were expressed at low, but significant, levels in UF Rhodnius, raising questions concerning how developmental arrest is maintained in UF animals. IHC confirmed the subcellular localisation of the coded proteins. Gene knockdown suppressed transcription of both genes and ecdysteroid synthesis, with spook apparently regulating the downstream gene disembodied. Transcription of both genes occurred with a daily rhythm (with peaks at night) that was confirmed to be under circadian control using aperiodic conditions. The complex behaviour of the rhythm in LL implied two anatomically distinct oscillators regulate this transcription rhythm. First, the circadian clock in the PGs and second, the circadian rhythm of of Rhodnius PTTH which is released rhythmically from the brain under control of the circadian clock therein, both of which were described previously. We conclude ecdysteroidogenesis in Rhodnius PGs employs a similar pathway as other insects, but its control is complex, involving mechanisms both within and outside the PGs.

Fecundity is optimized by levels of nutrient signal-dependent expression of Dve and EcR in Drosophila male accessory gland

Steroid hormones play various physiological roles including metabolism and reproduction. Steroid hormones in insects are ecdysteroids, and the major form in Drosophila melanogaster is ecdysone. In Drosophila males, the accessory gland is responsive to nutrient-dependent regulation of fertility/fecundity. The accessory gland is composed of two types of binucleated epithelial cells: a main cell and a secondary cell (SC). The transcription factors Defective proventriculus (Dve), Abdominal-B, and Ecdysone receptors (EcRs) are strongly expressed in adult SCs. We show that this EcR expression is regulated by parallel pathways of nutrient signaling and the Dve activity. Induction of Dve expression is also dependent on nutrient signaling, and it becomes nutrient signal-independent during a restricted period of development. Forced dve expression during the restricted period significantly increased the number of SCs. Here, we provide evidence that the level of nutrient signal-dependent Dve expression during the restricted period determines the number of SCs, and that ecdysone signaling is also crucial to optimize male fecundity through nutrient signal-dependent survival and maturation of SCs.

Mosquito E-20-Monooxygenase Gene Knockout Increases Dengue Virus Replication in Aedes aegypti Cells

E-20-monooxygenase (E20MO) is an enzymatic product of the shade (shd) locus (cytochrome p450, E20MO). Initially discovered in Drosophila, E20MO facilitates the conversion of ecdysone (E) into 20-hydroxyecdysone (20E) and is crucial for oogenesis. Prior research has implicated 20E in growth, development, and insecticide resistance. However, little attention has been given to the association between the E20MO gene and DENV2 infection. The transcriptome of Ae. aegypti cells (Aag2 cells) infected with DENV2 revealed the presence of the E20MO gene. The subsequent quantification of E20MO gene expression levels in Aag2 cells post-DENV infection was carried out. A CRISPR/Cas9 system was utilized to create an E20MO gene knockout cell line (KO), which was then subjected to DENV infection. Analyses of DENV2 copies in KO and wild-type (WT) cells were conducted at different days post-infection (dpi). Plasmids containing E20MO were constructed and transfected into KO cells, with pre- and post-transfection viral copy comparisons. Gene expression levels of E20MO increased after DENV infection. Subsequently, a successful generation of an E20MO gene knockout cell line and the verification of code-shifting mutations at both DNA and RNA levels were achieved. Furthermore, significantly elevated DENV2 RNA copies were observed in the mid-infection phase for the KO cell line. Viral RNA copies were lower in cells transfected with plasmids containing E20MO, compared to KO cells. Through knockout and plasmid complementation experiments in Aag2 cells, the role of E20MO in controlling DENV2 replication was demonstrated. These findings contribute to our understanding of the intricate biological interactions between mosquitoes and arboviruses.

Dietary lithium stimulates female fecundity in Drosophila melanogaster

The trace element lithium exerts a versatile bioactivity in humans, to some extend overlapping with in vivo findings in the model organism Drosophila melanogaster. A potentially essential function of lithium in reproduction has been suggested since the 1980s and multiple studies have since been published postulating a regulatory role of lithium in female gametogenesis. However, the impact of lithium on fruit fly egg production has not been at the center of attention to date. In the present study, we report that dietary lithium (0.1-5.0 mM LiCl) substantially improved life time egg production in D. melanogaster w1118 females, with a maximum increase of plus 45% when supplementing 1.0 mM LiCl. This phenomenon was not observed in the insulin receptor mutant InRE19, indicating a potential involvement of insulin-like signaling in the lithium-mediated fecundity boost. Analysis of the whole-body and ovarian transcriptome revealed that dietary lithium affects the mRNA levels of genes encoding proteins related to processes of follicular maturation. To the best of our knowledge, this is the first report on dietary lithium acting as an in vivo fecundity stimulant in D. melanogaster, further supporting the suggested benefit of the trace element in female reproduction.

Cis-regulatory polymorphism at fiz ecdysone oxidase contributes to polygenic evolutionary response to malnutrition in Drosophila

We investigate the contribution of a candidate gene, fiz (fezzik), to complex polygenic adaptation to juvenile malnutrition in Drosophila melanogaster. Experimental populations maintained for >250 generations of experimental evolution to a nutritionally poor larval diet (Selected populations) evolved several-fold lower fiz expression compared to unselected Control populations. Here we show that this divergence in fiz expression is mediated by a cis-regulatory polymorphism. This polymorphism, originally sampled from a natural population in Switzerland, is distinct from a second cis-regulatory SNP previously identified in non-African D. melanogaster populations, implying that two independent cis-regulatory variants promoting high fiz expression segregate in non-African populations. Enzymatic analyses of Fiz protein expressed in E. coli demonstrate that it has ecdysone oxidase activity acting on both ecdysone and 20-hydroxyecdysone. Four of five fiz paralogs annotated to ecdysteroid metabolism also show reduced expression in Selected larvae, implying that malnutrition-driven selection favored general downregulation of ecdysone oxidases. Finally, as an independent test of the role of fiz in poor diet adaptation, we show that fiz knockdown by RNAi results in faster larval growth on the poor diet, but at the cost of greatly reduced survival. These results imply that downregulation of fiz in Selected populations was favored by selection on the nutritionally poor diet because of its role in suppressing growth in response to nutrient shortage. However, they suggest that fiz downregulation is only adaptive in combination with other changes evolved by Selected populations, which ensure that the organism can sustain the faster growth promoted by fiz downregulation.

Local ecdysone synthesis in a wounded epithelium sustains developmental delay and promotes regeneration in Drosophila

Regenerative ability often declines as animals mature past embryonic and juvenile stages, suggesting that regeneration requires redirection of growth pathways that promote developmental growth. Intriguingly, the Drosophila larval epithelia require the hormone ecdysone (Ec) for growth but require a drop in circulating Ec levels to regenerate. Examining Ec dynamics more closely, we find that transcriptional activity of the Ec-receptor (EcR) drops in uninjured regions of wing discs, but simultaneously rises in cells around the injury-induced blastema. In parallel, blastema depletion of genes encoding Ec biosynthesis enzymes blocks EcR activity and impairs regeneration but has no effect on uninjured wings. We find that local Ec/EcR signaling is required for injury-induced pupariation delay following injury and that key regeneration regulators upd3 and Ets21c respond to Ec levels. Collectively, these data indicate that injury induces a local source of Ec within the wing blastema that sustains a transcriptional signature necessary for developmental delay and tissue repair.

Eclosion muscles secrete ecdysteroids to initiate asymmetric intestinal stem cell division in Drosophila

During organ development, tissue stem cells first expand via symmetric divisions and then switch to asymmetric divisions to minimize the time to obtain a mature tissue. In the Drosophila midgut, intestinal stem cells switch their divisions from symmetric to asymmetric at midpupal development to produce enteroendocrine cells. However, the signals that initiate this switch are unknown. Here, we identify the signal as ecdysteroids. In the presence of ecdysone, EcR and Usp promote the expression of E93 to suppress Br expression, resulting in asymmetric divisions. Surprisingly, the primary source of pupal ecdysone is not from the prothoracic gland but from dorsal internal oblique muscles (DIOMs), a group of transient skeletal muscles that are required for eclosion. Genetic analysis shows that DIOMs secrete ecdysteroids during mTOR-mediated muscle remodeling. Our findings identify sequential endocrine and mechanical roles for skeletal muscle, which ensure the timely asymmetric divisions of intestinal stem cells.

Identification of genes regulated by 20-Hydroxyecdysone in Macrobrachium nipponense using comparative transcriptomic analysis

BACKGROUND

Macrobrachium nipponense is a freshwater prawn of economic importance in China. Its reproductive molt is crucial for seedling rearing and directly impacts the industry's economic efficiency. 20-hydroxyecdysone (20E) controls various physiological behaviors in crustaceans, among which is the initiation of molt. Previous studies have shown that 20E plays a vital role in regulating molt and oviposition in M. nipponense. However, research on the molecular mechanisms underlying the reproductive molt and role of 20E in M. nipponense is still limited.

RESULTS

A total of 240.24 Gb of data was obtained from 18 tissue samples by transcriptome sequencing, with > 6 Gb of clean reads per sample. The efficiency of comparison with the reference transcriptome ranged from 87.05 to 92.48%. A total of 2532 differentially expressed genes (DEGs) were identified. Eighty-seven DEGs associated with molt or 20E were screened in the transcriptomes of the different tissues sampled in both the experimental and control groups. The reliability of the RNA sequencing data was confirmed using Quantitative Real-Time PCR. The expression levels of the eight strong candidate genes showed significant variation at the different stages of molt.

CONCLUSION

This study established the first transcriptome library for the different tissues of M. nipponense in response to 20E and demonstrated the dominant role of 20E in the molting process of this species. The discovery of a large number of 20E-regulated strong candidate DEGs further confirms the extensive regulatory role of 20E and provides a foundation for the deeper understanding of its molecular regulatory mechanisms.

Microbes control Drosophila germline stem cell increase and egg maturation through hormonal pathways

Reproduction is highly dependent on environmental and physiological factors including nutrition, mating stimuli and microbes. Among these factors, microbes facilitate vital functions for host animals such as nutritional intake, metabolic regulation, and enhancing fertility under poor nutrition conditions. However, detailed molecular mechanisms by which microbes control germline maturation, leading to reproduction, remain largely unknown. In this study, we show that environmental microbes exert a beneficial effect on Drosophila oogenesis by promoting germline stem cell (GSC) proliferation and subsequent egg maturation via acceleration of ovarian cell division and suppression of apoptosis. Moreover, insulin-related signaling is not required; rather, the ecdysone pathway is necessary for microbe-induced increase of GSCs and promotion of egg maturation, while juvenile hormone contributes only to increasing GSC numbers, suggesting that hormonal pathways are activated at different stages of oogenesis. Our findings reveal that environmental microbes can enhance host reproductivity by modulating host hormone release and promoting oogenesis.

Buprofezin affects the molting process by regulating nuclear receptors SfHR3 and SfHR4 in Sogatella furcifera

Nuclear receptors play a crucial role in various signaling and metabolic pathways, such as insect molting and development. Buprofezin (2-tert-butylimino-3-isopropyl-5-phenyl-perhydro-1, 3, 5-thiadiazin-4-one), a chitin synthesis inhibitor, causes molting deformities and slow death in insects by inhibiting chitin synthesis and interfering with their metabolism. This study investigated whether buprofezin affects insect ecdysteroid signaling pathway. The treatment of buprofezin significantly suppressed the transcription levels of SfHR3 and SfHR4, two nuclear receptor genes, in third-instar nymphs of Sogatella furcifera. Meanwhile, the transcription levels of SfHR3 and SfHR4 in first-day fifth-instar nymphs were induced at 12 h after 20E treatment. In addition, the silencing of SfHR3 and SfHR4 genes in first-day fifth-instar nymphs caused severe developmental delay and molting failure, resulting in a significant reduction of survival rates at 7.36% and 2.99% on the eighth day, respectively. Further analysis showed that the silencing SfHR3 and SfHR4 significantly inhibited the transcription levels of chitin synthesis and degradation-related genes. These results indicate that buprofezin can inhibits chitin synthesis and degradation by suppressing the signal transduction of 20E through SfHR3 and SfHR4, leading to molting failure and death. This study not only expands our understanding of the molecular mechanism of buprofezin in pest control but also lays a foundation for developing new control strategies of RNAi by targeting SfHR3 and SfHR4.

Research Progress on the Regulation of Autophagy and Apoptosis in Insects by Sterol Hormone 20-Hydroxyecdysone

20E (20-Hydroxyecdysone) is a central steroid hormone that orchestrates developmental changes and metamorphosis in arthropods. While its molecular mechanisms have been recognized for some time, detailed elucidation has primarily emerged in the past decade. PCD (Programmed cell death), including apoptosis, necrosis, efferocytosis, pyroptosis, ferroptosis, and autophagy, plays a crucial role in regulated cell elimination, which is vital for cells' development and tissue homeostasis. This review summarizes recent findings on 20E signaling regulated autophagy and apoptosis in insects, including Drosophila melanogaster, Bombyx mori, Helicoverpa armigera, and other species. Firstly, we comprehensively explore the biosynthesis of the sterol hormone 20E and its subsequent signal transduction in various species. Then, we focus on the involvement of 20E in regulating autophagy and apoptosis, elucidating its roles in both developmental contexts and bacterial infection scenarios. Furthermore, our discussion unfolds as a panoramic exposition, where we delve into the fundamental questions with our findings, anchoring them within the grander scheme of our study in insects. Deepening the understanding of 20E-autophagy/apoptosis axis not only underscores the intricate tapestry of endocrine networks, but also offers fresh perspectives on the adaptive mechanisms that have evolved in the face of environmental challenges.

Triazophos exposure on maternal Daphnia magna at environmental-related concentrations revealed toxic effects to its offspring

Due to chemical and photochemical stability, triazophos has been frequently detected in rivers and oceans over the years with extensive use for pest control in agriculture, and it has become a worldwide ecological concern to the aquatic environment. Until now, fewer data are available regarding the potential long-term adverse effects of triazophos on aquatic invertebrates, which plays an essential role in aquatic food webs, as a key group for water ecosystems. In this experiment, the F1- and F2 progenies of Daphnia magna were recovered when daphnias (F0) exposure to triazophos at environmental-related concentrations (0.1 and 1.0 μg/L) for 21 d; and the indexes related to phenotypic traits, reproduction and gene expression were measured in tested animals. The results showed that heart rate and total number of neonates in exposed F0-daphnias were significantly lower than those of control group, and the detoxification genes (HR96 and P-gp) were up-regulated while genes related reproduction (Vtg) and molting (Nvd and Shd) were significantly down-regulated. The heart rate and individual size of F1-daphnias (<24 h) were significantly reduced in the treatment group. After 21-d recovery, the heart rate and expression of HR96, P-gp, Vtg, Nvd and Shd were declined in F1-daphnias. There was no obvious difference of morphological traits and heart rate between treatment and control in F2-daphnias (<24 h). In summary, daphnias (F0) exposure to triazophos with environmental dose could raise toxic effects on its offspring (F1), which is mainly manifested by reduced heart rate, the accumulated number and individual size of offspring and decreased expression of genes related to molting and reproduction.

The Drosophila ecdysone receptor promotes or suppresses proliferation according to ligand level

The steroid hormone 20-hydroxy-ecdysone (20E) promotes proliferation in Drosophila wing precursors at low titer but triggers proliferation arrest at high doses. Remarkably, wing precursors proliferate normally in the complete absence of the 20E receptor, suggesting that low-level 20E promotes proliferation by overriding the default anti-proliferative activity of the receptor. By contrast, 20E needs its receptor to arrest proliferation. Dose-response RNA sequencing (RNA-seq) analysis of ex vivo cultured wing precursors identifies genes that are quantitatively activated by 20E across the physiological range, likely comprising positive modulators of proliferation and other genes that are only activated at high doses. We suggest that some of these "high-threshold" genes dominantly suppress the activity of the pro-proliferation genes. We then show mathematically and with synthetic reporters that combinations of basic regulatory elements can recapitulate the behavior of both types of target genes. Thus, a relatively simple genetic circuit can account for the bimodal activity of this hormone.

The Sterol Transporter Npc2c Controls Intestinal Stem Cell Mitosis and Host-Microbiome Interactions in Drosophila

Cholesterol is necessary for all cells to function. The intracellular cholesterol transporters Npc1 and Npc2 control sterol trafficking and their malfunction leads to Neimann-Pick Type C disease, a rare disorder affecting the nervous system and the intestine. Unlike humans that encode single Npc1 and Npc2 transporters, flies encompass two Npc1 (Npc1a-1b) and eight Npc2 (Npc2a-2h) members, and most of the Npc2 family genes remain unexplored. Here, we focus on the intestinal function of Npc2c in the adult. We find that Npc2c is necessary for intestinal stem cell (ISC) mitosis, maintenance of the ISC lineage, survival upon pathogenic infection, as well as tumor growth. Impaired mitosis of Npc2c-silenced midguts is accompanied by reduced expression of Cyclin genes, and genes encoding ISC regulators, such as Delta, unpaired1 and Socs36E. ISC-specific Npc2c silencing induces Attacin-A expression, a phenotype reminiscent of Gram-negative bacteria overabundance. Metagenomic analysis of Npc2c-depleted midguts indicates intestinal dysbiosis, whereby decreased commensal complexity is accompanied by increased gamma-proteobacteria. ISC-specific Npc2c silencing also results in increased cholesterol aggregation. Interestingly, administration of the non-steroidal ecdysone receptor agonist, RH5849, rescues mitosis of Npc2c-silenced midguts and increases expression of the ecdysone response gene Broad, underscoring the role of Npc2c and sterols in ecdysone signaling. Assessment of additional Npc2 family members indicates potential redundant roles with Npc2c in ISC control and response to ecdysone signaling. Our results highlight a previously unidentified essential role of Npc2c in ISC mitosis, as well as an important role in ecdysone signaling and microbiome composition in the Drosophila midgut.

Deciphering Molecular Mechanisms Governing the Reproductive Molt of Macrobrachium nipponense: A Transcriptome Analysis of Ovaries across Various Molting Stages

The relationship between molting and reproduction has received more attention in economically important crustacean decapods. Molting and reproduction are synergistic events in Macrobrachium nipponense, but the molecular regulatory mechanisms behind them are unclear. In the current study, we performed Illumina sequencing for the ovaries of M. nipponense during the molt cycle (pre-molting, Prm; mid-molting, Mm; and post-molting, Pom). A total of 66.57 Gb of transcriptome data were generated through sequencing, resulting in the identification of 105,149 unigenes whose alignment ratio with the reference genome exceeded 87.57%. Differentially expressed genes (DEGs) were annotated through the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases for gene classification and pathway analysis. A total of twenty-six molt-related DEGs were found, and their expression patterns were examined across various molting stages. The KEGG enrichment analysis revealed that the key pathways involved in regulating the molting process of M. nipponense primarily include the mTOR, insect hormone biosynthesis, TGF-beta, and Wnt signaling pathways. Our transcriptomic data suggest that these pathways crosstalk with each other to regulate the synthesis and degradation of ecdysone throughout the molt cycle. The current study has deepened our understanding of the molecular mechanisms of crustacean molting and will serve as a basis for future studies of crustaceans and other molting animals.

Sterol Regulation of Development and 20-Hydroxyecdysone Biosynthetic and Signaling Genes in Drosophila melanogaster

Ecdysteroids are crucial in regulating the growth and development of insects. In the fruit fly Drosophila melanogaster, both C27 and C28 ecdysteroids have been identified. While the biosynthetic pathway of the C27 ecdysteroid 20-hydroxyecdysone (20E) from cholesterol is relatively well understood, the biosynthetic pathway of C28 ecdysteroids from C28 or C29 dietary sterols remains unknown. In this study, we found that different dietary sterols (including the C27 sterols cholesterol and 7-dehydrocholesterol, the C28 sterols brassicasterol, campesterol, and ergosterol, and the C29 sterols β-sitosterol, α-spinasterol, and stigmasterol) differentially affected the expression of 20E biosynthetic genes to varying degrees, but similarly activated 20E primary response gene expression in D. melanogaster Kc cells. We also found that a single dietary sterol was sufficient to support D. melanogaster growth and development. Furthermore, the expression levels of some 20E biosynthetic genes were significantly altered, whereas the expression of 20E signaling primary response genes remained unaffected when flies were reared on lipid-depleted diets supplemented with single sterol types. Overall, our study provided preliminary clues to suggest that the same enzymatic system responsible for the classical C27 ecdysteroid 20E biosynthetic pathway also participated in the conversion of C28 and C29 dietary sterols into C28 ecdysteroids.

'Sharpshooter' in Botanic Garden: the tale of a rare plant-insect interaction

Here we report a unique plant-insect interaction between the leafhopper Aloka depressa (tribe Phlogisini) and the host liana, Diploclisia glaucescens, from a Botanic Garden located at the southern edge of Western Ghats in India. Field observations and SEM micrographs were employed to derive evidences on this rare plant-insect interaction. 20-Hydroxyecdysone (20E), insect moulting hormone, was detected and quantified in the host plant D. glaucescens using HPTLC-densitometry. 20E was isolated and characterized from D. glaucescens using column chromatography, 1H-, 13C-NMR and HR-MS. 20E was also detected in A. depressa excrement using HPTLC-densitometry. The leafhopper A. depressa is functioning as a 'sharpshooter' drawing nutrients from the host liana, D. glaucescens, and flinging the waste fluid as droplets through their tail ends. SEM micrographs of A. depressa revealed its external morphological features, characteristic of a sharpshooter. We quantified 20E (0.44-1.44%, dry wt.) in various parts of D. glaucescens. 20E (1.47%, dry wt.) was also detected in the excrement of A. depressa. This plant (D. glaucescens)-insect (A. depressa) association crucially is not damaging the host liana. Considering the diseases caused by sharpshooting leafhoppers in the Americas, this association and the survival of the host plant (D. glaucescens) is illustrating a unique plant-insect interaction.

Proteasome β3 subunit (PSMB3) controls female reproduction by promoting ecdysteroidogenesis during sexual maturation in Bactrocera dorsalis

Steroid hormone 20-hydroxyecdysone (20E) plays critical roles in reproductive development in dipterans and several other insect species. Ecdysteroidogenesis in the glands of larval or nymphal insects and other arthropods has been extensively studied, but that in the adult gonads remains largely unknown. Here we identified a proteasome β3 subunit (PSMB3) from a highly invasive pest Bactrocera dorsalis, and found that this gene was crucial for ecdysone production during female reproduction. PSMB3 was enriched in the ovary, and it was upregulated during sexual maturation. RNAi-mediated depletion of PSMB3 resulted in retarded ovarian development and decreased fecundity. Additionally, knockdown of PSMB3 reduced 20E titer in hemolymph of B. dorsalis. Molecularly, RNA sequencing and qPCR validation revealed that PSMB3 depletion suppressed the expression of 20E biosynthetic genes in the ovary and 20E responsive genes in the ovary and fat body. Furthermore, exogenous 20E rescued the inhibition of the ovarian development caused by PSMB3 depletion. Taken together, this study provides new insights into the adult reproductive development-related biological processes controlled by PSMB3, and proposed a potential eco-friendly control strategy against this notorious agricultural pest.

Identification and functional analysis of isopentenyl pyrophosphate isomerase genes in the whiteflies Bemisia tabaci (Hemiptera: Aleyrodidae)

The juvenile hormone (JH) plays a vital role in the regulation of a number of physiological processes, including development, reproduction, and ovarian maturation. Isopentenyl pyrophosphate isomerase (IPPI) is a key enzyme in the biosynthetic pathway of JH. In this study, we identified an isopentenyl pyrophosphate isomerase protein from Bemisia tabaci and named it BtabIPPI. The open reading frame (ORF) of BtabIPPI is 768 bp and encodes a protein of 255 amino acids that contains a conserved domain of the Nudix family. The temporal and spatial expression profiles showed that BtabIPPI was highly expressed in the female adults.RNA interference (RNAi)-mediated silencing of BtabIPPI reduced JH titers and the relative expression of vitellogenin receptor (VgR) and JH signaling pathway genes, resulting in a dramatic reduction in fecundity and hatchability. These results indicate that the BtabIPPI gene plays an important role in the female fecundity of B. tabaci. This study will broaden our understanding of the function of IPPI in regulating insect reproduction and provide a theoretical basis for targeting IPPI for pest control in the future.

Analyses of ecdysteroid transporters in the fat body of Tribolium castaneum

The control of insect moulting and metamorphosis involves ecdysteroids that orchestrate the execution of developmental genetic programs by binding to dimeric hormone receptors consisting of the ecdysone receptor (EcR) and ultraspiracle (USP). In insects, the main ecdysteroids comprise ecdysone (E), which is synthesized in the prothoracic gland and secreted into the haemolymph, and 20-hydroxyecdysone (20E), which is considered the active form by binding to the nuclear receptor of the target cell. While biosynthesis of ecdysteroids has been studied in detail in different insects, the transport systems involved in guiding these steroid hormones across cellular membranes have just recently begun to be studied. By analysing RNAi phenotypes in the red flour beetle, Tribolium castaneum, we have identified three transporter genes, TcABCG-8A, TcABCG-4D and TcOATP4-C1, whose silencing results in phenotypes similar to that observed when the ecdysone receptor gene TcEcRA is silenced, that is, abortive moulting and abnormal development of adult compound eyes during the larval stage. The genes of all three transporters are expressed at higher levels in the larval fat body of T. castaneum. We analysed potential functions of these transporters by combining RNAi and mass spectrometry. However, the analysis of gene functions is challenged by mutual RNAi effects indicating interdependent gene regulation. Based on our findings, we propose that TcABCG-8A, TcABCG-4D and TcOATP4-C1 participate in the ecdysteroid transport in fat body cells, which are involved in E → 20E conversion catalysed by the P450 enzyme TcShade.

Drosophila postembryonic nervous system development: a model for the endocrine control of development

During postembryonic life, hormones, including ecdysteroids, juvenile hormones, insulin-like peptides, and activin/TGFβ ligands act to transform the larval nervous system into an adult version, which is a fine-grained mosaic of recycled larval neurons and adult-specific neurons. Hormones provide both instructional signals that make cells competent to undergo developmental change and timing cues to evoke these changes across the nervous system. While touching on all the above hormones, our emphasis is on the ecdysteroids, ecdysone and 20-hydroxyecdysone (20E). These are the prime movers of insect molting and metamorphosis and are involved in all phases of nervous system development, including neurogenesis, pruning, arbor outgrowth, and cell death. Ecdysteroids appear as a series of steroid peaks that coordinate the larval molts and the different phases of metamorphosis. Each peak directs a stereotyped cascade of transcription factor expression. The cascade components then direct temporal programs of effector gene expression, but the latter vary markedly according to tissue and life stage. The neurons read the ecdysteroid titer through various isoforms of the ecdysone receptor, a nuclear hormone receptor. For example, at metamorphosis the pruning of larval neurons is mediated through the B isoforms, which have strong activation functions, whereas subsequent outgrowth is mediated through the A isoform through which ecdysteroids play a permissive role to allow local tissue interactions to direct outgrowth. The major circulating ecdysteroid can also change through development. During adult development ecdysone promotes early adult patterning and differentiation while its metabolite, 20E, later evokes terminal adult differentiation.

Compounds Inhibiting Noppera-bo, a Glutathione S-transferase Involved in Insect Ecdysteroid Biosynthesis: Novel Insect Growth Regulators

Glutathione S-transferases (GSTs) are conserved in a wide range of organisms, including insects. In 2014, an epsilon GST, known as Noppera-bo (Nobo), was shown to regulate the biosynthesis of ecdysteroid, the principal steroid hormone in insects. Studies on fruit flies, Drosophila melanogaster, and silkworms, Bombyx mori, demonstrated that loss-of-function mutants of nobo fail to synthesize ecdysteroid and die during development, consistent with the essential function of ecdysteroids in insect molting and metamorphosis. This genetic evidence suggests that chemical compounds that inhibit activity of Nobo could be insect growth regulators (IGRs) that kill insects by disrupting their molting and metamorphosis. In addition, because nobo is conserved only in Diptera and Lepidoptera, a Nobo inhibitor could be used to target IGRs in a narrow spectrum of insect taxa. Dipterans include mosquitoes, some of which are vectors of diseases such as malaria and dengue fever. Given that mosquito control is essential to reduce mosquito-borne diseases, new IGRs that specifically kill mosquito vectors are always in demand. We have addressed this issue by identifying and characterizing several chemical compounds that inhibit Nobo protein in both D. melanogaster and the yellow fever mosquito, Aedes aegypti. In this review, we summarize our findings from the search for Nobo inhibitors.

Domain analysis of Drosophila Blimp-1 reveals the importance of its repression function and instability in determining pupation timing

The PRDM family transcription repressor Blimp-1 is present in almost all multicellular organisms and plays important roles in various developmental processes. This factor has several conserved motifs among different species, but the function of each motif is unclear. Drosophila Blimp-1 plays an important role in determining pupation timing by acting as an unstable transcriptional repressor of the βftz-f1 gene. Thus, Drosophila provides a good system for analyzing the molecular and biological functions of each region in Blimp-1. Various Blimp-1 mutants carrying deletions at the conserved motifs were induced under the control of the heat shock promoter in prepupae, and the expression patterns of βFTZ-F1 and Blimp-1 and pupation timing were observed. The results showed that the regions with strong and weak repressor functions exist within the proline-rich middle section of the factor and near the N-terminal conserved motif, respectively. Rapid degradation was supported by multiple regions that were mainly located in a large proline-rich region. Results revealed that pupation timing was affected by the repression ability and stability of Blimp-1. This suggests that both the repression function and instability of Blimp-1 are indispensable for the precise determination of pupation timing.

A transcriptomic investigation of heat-induced transgenerational plasticity in beetles

In response to environmental stressors, parents can shape the developmental outcomes of their offspring by contributing non-genetic but heritable factors. The transmission of such factors can potentially allow offspring, from the beginning of their lives, to express phenotypes that match their anticipated environments. In this study, I ask whether enhanced growth in larvae of Onthophagus taurus (the bull-headed dung beetle) is modified by parental exposure to heat or by exposure of the offspring to heat during early life. I find that, irrespective of the early environment of the offspring, individuals produced by parents exposed to heat grow larger. Furthermore, taking a transcriptomic approach, I find that ecdysone signalling might mediate the transgenerational effect and that increased insulin signalling or reduced production of heat shock proteins might be responsible for the enhanced growth in larvae derived from parents exposed to heat. Together, my results provide evidence for a thermally induced transgenerational effect and a foundation for functional testing of candidate mechanisms mediating the effect.

A caste differentiation mutant elucidates the evolution of socially parasitic ants

Most ant species have two distinct female castes-queens and workers-yet the developmental and genetic mechanisms that produce these alternative phenotypes remain poorly understood. Working with a clonal ant, we discovered a variant strain that expresses queen-like traits in individuals that would normally become workers. The variants show changes in morphology, behavior, and fitness that cause them to rely on workers in wild-type (WT) colonies for survival. Overall, they resemble the queens of many obligately parasitic ants that have evolutionarily lost the worker caste and live inside colonies of closely related hosts. The prevailing theory for the evolution of these workerless social parasites is that they evolve from reproductively isolated populations of facultative intermediates that acquire parasitic phenotypes in a stepwise fashion. However, empirical evidence for such facultative ancestors remains weak, and it is unclear how reproductive isolation could gradually arise in sympatry. In contrast, we isolated these variants just a few generations after they arose within their WT parent colony, implying that the complex phenotype reported here was induced in a single genetic step. This suggests that a single genetic module can decouple the coordinated mechanisms of caste development, allowing an obligately parasitic variant to arise directly from a free-living ancestor. Consistent with this hypothesis, the variants have lost one of the two alleles of a putative supergene that is heterozygous in WTs. These findings provide a plausible explanation for the evolution of ant social parasites and implicate new candidate molecular mechanisms for ant caste differentiation.

Steroid hormone signaling: What we can learn from insect models

Ecdysteroids are a group of steroid hormones in arthropods with pleiotropic functions throughout their life history. Ecdysteroid research in insects has made a significant contribution to our current understanding of steroid hormone signaling in metazoans, but how far can we extrapolate our findings in insects to other systems, such as mammals? In this chapter, we compare steroid hormone signaling in insects and mammals from multiple perspectives and discuss similarities and differences between the two lineages. We also highlight a few understudied areas and remaining questions of steroid hormone biology in metazoans and propose potential future research directions.

Cloning and functional analysis of the molting gene CYP302A1 of Daphnia sinensis

BACKGROUND

Molting is an important physiological process in the growth and development of arthropoda, which is mainly regulated by juvenile hormone and ecdysone. CYP302A1 is a key enzyme which plays a critical role in the synthesis of ecdysone in insects, but it has not been identified in cladocera.

RESULTS

The CYP302Al gene of Daphnia sinensis was cloned and its function was analyzed in this paper. The CYP302Al gene of D. sinensis was 5926 bp in full-length, with an open reading frame (ORF) of 1596 bp that encoded 531 amino acids (aa), a molecular weight of 60.82 kDa and an isoelectric point of 9.29. The amino acid sequence analysis revealed that there were five characteristic conserved regions of cytochrome P450 family (namely helix-C, helix-K, helix-I, PERF and heme-binding). In dsRNA mediated experiment, the expression level of CYP302A1 gene decreased significantly (knock-down of 56.22%) in the 5% Escherichia coli concentration treatment. In addition, the expression levels of EcR and USP and HR3 genes in the downstream were also significantly decreased, whereas that of FTZ-f1 gene increased significantly. In the 5% E. coli treatment, the molting time at maturity of D. sinensis prolonged, and the development of embryos in the incubation capsule appeared abnormal or disintegrated. The whole-mount in situ hybridization showed that the CYP302A1 gene of D. sinensis had six expression sites before RNA interference (RNAi), which located in the first antennal ganglion, ovary, cecae, olfactory hair, thoracic limb and tail spine. However, the expression signal of the CYP302A1 gene of D. sinensis disappeared in the first antennal ganglion and obviously attenuated in the ovary after RNAi.

CONCLUSION

The CYP302A1 gene played an important role in the ecdysone synthesis pathway of D. sinensis, and the knock-down of the gene affected the molting and reproduction of D. sinensis.

Rethinking the ecdysteroid source during Drosophila pupal-adult development

Ecdysteroids, typified by 20-hydroxyecdysone (20E), are essential hormones for the development, reproduction and physiology of insects and other arthropods. For over half a century, the vinegar fly Drosophila melanogaster (Ephydroidea: Diptera) has been used as a model of ecdysteroid biology. Many aspects of the biosynthesis and regulation of ecdysteroids in this species are understood at the molecular level, particularly with respect to their secretion from the prothoracic gland (PG) cells of the ring gland, widely considered the dominant biosynthetic tissue during development. Discrete pulses of 20E orchestrate transitions during the D. melanogaster life cycle, the sources of which are generally well understood, apart from the large 20E pulse at the onset of pharate adult development, which has received little recent attention. As the source of this pharate adult pulse (PAP) is a curious blind spot in Drosophila endocrinology, we evaluate published biochemical and genetic data as they pertain to three hypotheses for the source of PAP 20E: the PG; an alternative biosynthetic tissue; or the recycling of stored 20E. Based on multiple lines of evidence, we contend the PAP cannot be derived from biosynthesis, with other data consistent with D. melanogaster able to recycle ecdysteroids before and during metamorphosis. Published data also suggest the PAP is conserved across Diptera, with evidence for pupal-adult ecdysteroid recycling occurring in other cyclorrhaphan flies. Further experimental work is required to test the ecdysteroid recycling hypothesis, which would establish fundamental knowledge of the function, regulation, and evolution of metamorphic hormones in dipterans and other insects.

Identification and characterization of CYP307A1 as a molecular target for controlling the small hive beetle, Aethina tumida

BACKGROUND

The molting hormone 20-hydroxyecdysone (20E) plays a key role in insect development, metamorphosis, and reproduction. Previous studies have shown that ecdysteroid metabolism is regulated by a series of CYP genes in most of the insect species. However, the roles of these CYP genes in a Coleopteran beetle, Aethina tumida (small hive beetle, SHB) have not yet been explored.

RESULTS

In the current study, we identified seven CYP genes (six Halloween genes and one AtCYP18A1 gene) related to 20E metabolism. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed that AtCYP307A1 and AtCYP307B1 were primarily expressed in the embryonic stage and in the cephalothorax of larvae. RNA interference (RNAi) screening revealed that suppression of AtCYP307A1 expression caused a lethal phenotype during the larval-pupal metamorphosis. Furthermore, Hematoxylin and Eosin staining of the integument showed that the RNAi of AtCYP307A1 inhibited the apolysis and degradation of the old cuticle. In addition, silencing of AtCYP307A1 resulted in significant down-regulation of 20E titers and the expression levels of 20E signaling pathway genes. Finally, the AtCYP307A1 RNAi phenotype was rescued by topical application of 20E.

CONCLUSION

Our studies suggest that AtCYP307A1 involved in 20E synthesis is indispensable during the larval-pupal metamorphosis of beetles, which could serve as a putative insecticide target for pest control. © 2022 Society of Chemical Industry.

A General Signal Pathway to Regulate Multiple Detoxification Genes Drives the Evolution of Helicoverpa armigera Adaptation to Xenobiotics

The study of insect adaptation to the defensive metabolites of host plants and various kinds of insecticides in order to acquire resistance is a hot topic in the pest-control field, but the mechanism is still unclear. In our study, we found that a general signal pathway exists in H. armigera which can regulate multiple P450s, GSTs and UGTs genes to help insects decrease their susceptibility to xenobiotics. Knockdown of HaNrf2 and HaAhR expression could significantly increase the toxicity of xenobiotics to H. armigera, and simultaneously decrease the gene expression of P450s, GSTs and UGTs which are related to the xenobiotic metabolism and synthesis of insect hormone pathways. Then, we used EMSA and dual luciferase assay to verify that a crosstalk exists between AhR and Nrf2 to regulate multiple P450s, GSTs and UGTs genes to mediate H. armigera susceptibility to plant allelochemicals and insecticides. The detoxification genes' expression network which can be regulated by Nrf2 and AhR is still unknown, and there were also no reports about the crosstalk between AhR and Nrf2 that exist in insects and can regulate multiple detoxification genes' expression. Our results provide a new general signaling pathway to reveal the adaptive mechanism of insects to xenobiotics and provides further insight into designing effective pest-management strategies to avoid the overuse of insecticides.

A Non-Gradual Development Process of Cicada Eyes at the End of the Fifth-Instar Nymphal Stage to Obtain Visual Ability

Insects' visual system is directly related to ecology and critical for their survival. Some cicadas present obvious differences in color and ultrastructure of compound eyes between nymphal and adult stages, but little is known about when cicadas obtain their visual ability to deal with the novel above-ground habitat. We use transcriptome analyses and reveal that cicada Meimuna mongolica has a trichromatic color vision system and that the eyes undergo a non-gradual development process at the end of the 5th-instar nymphal stage. The white-eye 5th-instar nymphs (i.e., younger 5th-instar nymphs) have no visual ability because critical components of the visual system are deficient. The transformation of eyes toward possessing visual function takes place after a tipping point in the transition phase from the white-eye period to the subsequent red-eye period, which is related to a decrease of Juvenile Hormone. The period shortly after adult emergence is also critical for eye development. Key differentially-expressed genes related to phototransduction and chromophore synthesis play positive roles for cicadas to adapt to above-ground habitat. The accumulation of ommochromes corresponds to the color change of eyes from white to red and dark brown during the end of the 5th-instar nymphal period. Cuticle tanning leads to eye color changing from dark-brown to light-brown during the early adult stage. We hypothesize that the accumulation of ommochromes occurring at the end of 5th-instar nymphal stage and the early adult stage is not only for cicadas to obtain visual ability, but also is a secure strategy to cope with potential photodamage after emergence.

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.

Impact of Imidacloprid Resistance on the Demographic Traits and Expressions of Associated Genes in Aphis gossypii Glover

Imidacloprid is one of the most widely used neonicotinoid insecticides to control sap-sucking insect pests, including Aphis gossypii. The intensive application of chemical insecticides to A. gossypii led to the development of resistance against several insecticides, including imidacloprid. Therefore, it is crucial to understand the association between imidacloprid resistance and the fitness of A. gossypii to limit the spread of the resistant population under field contexts. In this study, we used the age-stage, two-sex life table method to comprehensively investigate the fitness of imidacloprid resistant (ImR) and susceptible strains (SS) of melon aphids. Results showed that ImR aphids have prolonged developmental stages and decreased longevity, fecundity, and reproductive days. The key demographic parameters (r, λ, and R₀) were significantly reduced in ImR strain compared to SS aphids. Additionally, the molecular mechanism for fitness costs was investigated by comparing the expression profile of juvenile hormone-binding protein (JHBP), juvenile hormone epoxide hydrolase (JHEH), juvenile hormone acid O-methyltransferase (JHAMT), Vitellogenin (Vg), ecdysone receptor (EcR), and ultraspiracle protein (USP) supposed to be associated with development and reproduction in insects. The results of RT-qPCR showed that EcR, JHBP, JHAMT, JHEH, and Vg genes were downregulated, while USP was statistically the same in ImR A. gossypii compared to the SS strain. Together, these results provide in-depth information about the occurrence and magnitude of fitness costs against imidacloprid resistance that could help manage the evolution and spread of A. gossypii resistance in field populations.

MnHR4 Functions during Molting of Macrobrachium nipponense by Regulating 20E Synthesis and Mediating 20E Signaling

HR4, a member of the nuclear receptor family, has been extensively studied in insect molting and development, but reports on crustaceans are still lacking. In the current study, the MnHR4 gene was identified in Macrobrachium nipponense. To further improve the molting molecular mechanism of M. nipponense, this study investigated whether MnHR4 functions during the molting process of M. nipponense. The domain, phylogenetic relationship and 3D structure of MnHR4 were analyzed by bioinformatics. Quantitative real-time PCR (qRT-PCR) analysis showed that MnHR4 was highly expressed in the ovary. In different embryo stages, the highest mRNA expression was observed in the cleavage stage (CS). At different individual stages, the mRNA expression of MnHR4 reached its peak on the fifteenth day after hatching (L15). The in vivo injection of 20-hydroxyecdysone (20E) can effectively promote the expression of the MnHR4 gene, and the silencing of the MnHR4 gene increased the content of 20E in M. nipponense. The regulatory role of MnHR4 in 20E synthesis and 20E signaling was further investigated by RNAi. Finally, the function of the MnHR4 gene in the molting process of M. nipponense was studied by counting the molting frequency. After knocking down MnHR4, the molting frequency of M. nipponense decreased significantly. It was proved that MnHR4 plays a pivotal role in the molting process of M. nipponense.

Opportunistic binding of EcR to open chromatin drives tissue-specific developmental responses

Steroid hormones perform diverse biological functions in developing and adult animals. However, the mechanistic basis for their tissue specificity remains unclear. In Drosophila, the ecdysone steroid hormone is essential for coordinating developmental timing across physically separated tissues. Ecdysone directly impacts genome function through its nuclear receptor, a heterodimer of the EcR and ultraspiracle proteins. Ligand binding to EcR triggers a transcriptional cascade, including activation of a set of primary response transcription factors. The hierarchical organization of this pathway has left the direct role of EcR in mediating ecdysone responses obscured. Here, we investigate the role of EcR in controlling tissue-specific ecdysone responses, focusing on two tissues that diverge in their response to rising ecdysone titers: the larval salivary gland, which undergoes programmed destruction, and the wing imaginal disc, which initiates morphogenesis. We find that EcR functions bimodally, with both gene repressive and activating functions, even at the same developmental stage. EcR DNA binding profiles are highly tissue-specific, and transgenic reporter analyses demonstrate that EcR plays a direct role in controlling enhancer activity. Finally, despite a strong correlation between tissue-specific EcR binding and tissue-specific open chromatin, we find that EcR does not control chromatin accessibility at genomic targets. We conclude that EcR contributes extensively to tissue-specific ecdysone responses. However, control over access to its binding sites is subordinated to other transcription factors.

Knockdown of the Halloween Genes spook, shadow and shade Influences Oocyte Development, Egg Shape, Oviposition and Hatching in the Desert Locust

Ecdysteroids are widely investigated for their role during the molting cascade in insects; however, they are also involved in the development of the female reproductive system. Ecdysteroids are synthesized from cholesterol, which is further converted via a series of enzymatic steps into the main molting hormone, 20-hydoxyecdysone. Most of these biosynthetic conversion steps involve the activity of cytochrome P450 (CYP) hydroxylases, which are encoded by the Halloween genes. Three of these genes, spook (spo), phantom (phm) and shade (shd), were previously characterized in the desert locust, Schistocerca gregaria. Based on recent sequencing data, we have now identified the sequences of disembodied (dib) and shadow (sad), for which we also analyzed spatiotemporal expression profiles using qRT-PCR. Furthermore, we investigated the possible role(s) of five different Halloween genes in the oogenesis process by means of RNA interference mediated knockdown experiments. Our results showed that depleting the expression of SchgrSpo, SchgrSad and SchgrShd had a significant impact on oocyte development, oviposition and hatching of the eggs. Moreover, the shape of the growing oocytes, as well as the deposited eggs, was very drastically altered by the experimental treatments. Consequently, it can be proposed that these three enzymes play an important role in oogenesis.

RNAi-Mediated Silencing of Putative Halloween Gene Phantom Affects the Performance of Rice Striped Stem Borer, Chilo suppressalis

The physiological and biochemical characterization of the "Halloween" genes has fundamental importance in the biosynthesis pathway of ecdysteroids. These genes were found to catalyze the final phases of ecdysteroid biosynthesis from dietary cholesterol to the molting hormone 20-hydroxyecdysone. We report the characterization of the Cs-Phm in a major insect pest in agriculture, the rice striped stem borer, Chilo suppressalis (C. suppressalis). A full-length transcript of Cs-Phm was amplified with an open reading frame (ORF) of 478 amino acids through 5' and 3' RACE. Cs-Phm shows five insect-conserved P450 motifs: Helix-C, Helix-I, Helix-K, PERF, and heme-binding motifs. Phylogenetic analysis clearly shows high similarity to Lepidoptera and evolutionary conservation in insects. The relative spatial and temporal transcript profile shows that Cs-Phm is highly expressed in the prothoracic glands and appears throughout the larval development, but with low expression at the start of the larval instar. It seems to peak in 3-4 days and decreases again before the larvae molt. Double-stranded RNA (dsRNA) injection of Cs-Phm at the larval stage efficiently knocked down the target gene and decreased its expression level. The dsRNA-treated group showed significantly decreased ecdysteroid titers, which leads to delayed larval development and higher larval mortality. Negative effects of larval development were rescued by treating 20E in the dsRNA-treated group. Thus, in conclusion, our results suggest that Cs-Phm is functionally conserved in C. suppressalis and encodes functional CYP that contributes to the biogenesis of 20E.

The cytochrome P450 Cyp6t3 is not required for ecdysone biosynthesis in Drosophila melanogaster

The steroid hormone 20-hydroxyecdysone (20E) is essential for proper development and the timing of intermediary stage transitions in insects. As a result, there is intense interest in identifying and defining the roles of the enzymes and signaling pathways that regulate 20E production in the prothoracic gland (PG), the major endocrine organ of juvenile insect phases. Transcriptomics is one powerful tool that has been used to identify novel genes that are up- or down-regulated in the PG which may contribute to 20E regulation. Additional functional characterization of putative regulatory candidate genes typically involves qRT-PCR and/or RNAi mediated knockdown of the candidate mRNA in the PG to assess whether the gene's expression shows temporal regulation in the PG and whether its expression is essential for proper 20E production and the correct timing of developmental transitions. While these methods have proved fruitful for identifying novel regulators of 20E production, characterizing the null phenotype of putative regulatory genes is the gold standard for assigning gene function since RNAi is known to generate various types of "off target" effects. Here we describe the genetic null mutant phenotype of the Drosophila melanogaster Cyp6t3 gene . Cyp6t3 was originally identified as a differentially regulated gene in a PG microarray screen and assigned a place in the "Black Box" step of the E biosynthetic pathway based on RNAi mediated knockdown phenotypes and rescue experiments involving feeding of various intermediate compounds of the E biosynthetic pathway. In contrast, we find that Crispr generated null mutations in Cyp6t3 are viable and have normal developmental timing. Therefore, we conclude that Cyp6t3 is not required for E production under typical lab growth conditions and therefore is not an obligate enzymatic component of the Black Box.

CYP314A1-dependent 20-hydroxyecdysone biosynthesis is involved in regulating the development of pupal diapause and energy metabolism in the Chinese citrus fruit fly, Bactrocera minax

BACKGROUND

Diapause is an environmentally preprogrammed period of arrested development, and characterized by metabolic depression that can occur during any development stage of insect. The insect steroid hormone 20-hydroxyecdysone (20E), is converted from ecdysone by the cytochrome P450 enzyme shade (CYP314A1), and it exerts a potent effect on the induction and maintenance of diapause in obligatory diapause insects. However, the regulatory mechanism of 20E in obligatory diapause development remains unclear. In this study, the function of 20E in the pupal diapause of Bactrocera minax was investigated.

RESULTS

We determined the expression pattern of Halloween P450 genes from larval to adult B. minax, and found differential expression of CYP314A1 from other P450 genes, with a high level in larvae and a low level in pupae. Dysfunction of CYP314A1 by dsCYP314A1 microinjection in third-instar larvae caused significant larval mortality or abnormal pupae. Compared with dsGFP and DEPC-water, dsCYP314A1-injected larvae had significantly reduced 20E titer and altered energy metabolism, and many individuals failed to pupate. Exogenous 20E microinjected into late third-instar larvae or 20E fed to early third-instar larvae both caused similar energy metabolism changes. The 20E-treated larvae of B. minax had reduced total lipids and increased amounts of trehalose and glycogen. Furthermore, 20E-treated diapause individuals showed rapid pupal development.

CONCLUSION

The 20E biosynthesis was regulated by the expression of CYP314A1, and was involved in the induction and termination phase of obligate diapause by regulating energy metabolism in B. minax. © 2022 Society of Chemical Industry.

Essential functions of mosquito ecdysone importers in development and reproduction

Steroid hormones control sexual maturation and reproduction in insects and humans alike. The insect steroid hormone ecdysone uses a membrane transporter named Ecdysone Importer (EcI) to enter cells and promote these physiological processes, but EcI is unexpectedly missing in mosquito genomes. Using the yellow fever mosquito Aedes aegypti, here we show that mosquitoes use alternative ecdysone importers to facilitate ecdysone-dependent development and reproduction. These transporters are also present in other insects, including fruit flies, but they are dispensable for fly development and reproduction likely due to their limited expression patterns. Our results thus indicate that differential expression of steroid hormone importers enables tissue- and stage-specific hormone responses, and some importers can obtain critical physiological functions only in certain species.

The primary insect steroid hormone ecdysone requires a membrane transporter to enter its target cells. Although an organic anion-transporting polypeptide (OATP) named Ecdysone Importer (EcI) serves this role in the fruit fly Drosophila melanogaster and most likely in other arthropod species, this highly conserved transporter is apparently missing in mosquitoes. Here we report three additional OATPs that facilitate cellular incorporation of ecdysone in Drosophila and the yellow fever mosquito Aedes aegypti. These additional ecdysone importers (EcI-2, -3, and -4) are dispensable for development and reproduction in Drosophila, consistent with the predominant role of EcI. In contrast, in Aedes, EcI-2 is indispensable for ecdysone-mediated development, whereas EcI-4 is critical for vitellogenesis induced by ecdysone in adult females. Altogether, our results indicate unique and essential functions of these additional ecdysone importers in mosquito development and reproduction, making them attractive molecular targets for species- and stage-specific control of ecdysone signaling in mosquitoes.

Pupal Diapause Termination and Transcriptional Response of Antheraea pernyi (Lepidoptera: Saturniidae) Triggered by 20-Hydroxyecdysone

The pupal diapause of univoltine Antheraea pernyi hampers sericultural and biotechnological applications, which requires a high eclosion incidence after artificial diapause termination to ensure production of enough eggs. The effect of pupal diapause termination using 20-hydroxyecdysone (20E) on the eclosion incidence has not been well-documented in A. pernyi. Here, the dosage of injected 20E was optimized to efficiently terminate pupal diapause of A. pernyi, showing that inappropriate dosage of 20E can cause pupal lethality and a low eclosion incidence. The optimal ratio of 20E to 1-month-old pupae was determined as 6 μg/g. Morphological changes showed visible tissue dissociation at 3 days post-injection (dpi) and eye pigmentation at 5 dpi. Comprehensive transcriptome analysis identified 1,355/1,592, 494/203, 584/297, and 1,238/1,404 upregulated and downregulated genes at 1, 3, 6, and 9 dpi, respectively. The 117 genes enriched in the information processing pathways of “signal transduction” and “signaling molecules and interaction” were upregulated at 1 and 3 dpi, including the genes involved in FOXO signaling pathway. One chitinase, three trehalase, and five cathepsin genes related to energy metabolism and tissue dissociation showed high expression levels at the early stage, which were different from the upregulated expression of four other chitinase genes at the later stage. Simultaneously, the expression of several genes involved in molting hormone biosynthesis was also activated between 1 and 3 dpi. qRT-PCR further verified the expression patterns of two ecdysone receptor genes (EcRB1 and USP) and four downstream response genes (E93, Br-C, βFTZ-F1, and cathepsin L) at the pupal and pharate stages, respectively. Taken together, these genes serve as a resource for unraveling the mechanism underlying pupal-adult transition; these findings facilitate rearing of larvae more than once a year and biotechnological development through efficient termination of pupal diapause in A. pernyi in approximately half a month.