Ecdysone receptors and their biological actions

Synchronizing Drosophila larvae with the salivary gland reporter Sgs3-GFP for discovery of phenotypes in the late third instar stage

The larval stage of the Drosophila melanogaster life cycle is characterized by rapid growth and nutrient storage that occur over three instar stages separated by molts. In the third instar, the steroid hormone ecdysone drives key developmental processes and behaviors that occur in a temporally-controlled sequence and prepare the animal to undergo metamorphosis. Accurately staging Drosophila larvae within the final third instar is critical due to the rapid developmental progress at this stage, but it is challenging because the rate of development varies widely across a population of animals even if eggs are laid within a short period of time. Moreover, many methods to stage third instar larvae are cumbersome, and inherent variability in the rate of development confounds some of these approaches. Here we demonstrate the usefulness of the Sgs3-GFP transgene, a fusion of the Salivary gland secretion 3 (Sgs3) and GFP proteins, for staging third instar larvae. Sgs3-GFP is expressed in the salivary glands in an ecdysone-dependent manner from the midpoint of the third instar, and its expression pattern changes reproducibly as larvae progress through the third instar. We show that Sgs3-GFP can easily be incorporated into experiments, that it allows collection of developmentally-equivalent individuals from a mixed population of larvae, and that its use enables precise assessment of changing levels of hormones, metabolites, and gene expression during the second half of the third instar.

Effect of silencing the E74B gene on the development and metamorphosis of Helicoverpa armigera

BACKGROUND

The growth and development transition of insects are mainly mediated by ecdysone. As one of the ecdysone-induced transcription factors, E74 is involved in many physiological processes of insect growth and development. However, E74 and its function in Helicoverpa armigera remains unclear.

RESULTS

In this study, E74B, a subtype of the E74, was identified for the first time in H. armigera. Bioinformatics analysis showed that H. armigera E74B shared the highest homology with E74B in Bombyx mori, which belongs to the E26 transformation-specific (ETS) superfamily. The expression profile showed that the transcription level of HaE74B increased in the late stages of fourth to sixth instars compared with the early stages; it was also high in the pupa and midgut. Moreover, we investigated the function of HaE74B through RNA interference and 20E rescue experiments. The results showed silencing of E74B affected the molting and growth of larvae, resulting in the death of more than 60% of larvae. In addition, it also seriously affected the metamorphosis of H. armigera, which reduced the pupae rate, the eclosion rate of the pupae, and fecundity. Application of 20E partially restored the defects in the molting, development and pupae rate of H. armigera.

CONCLUSION

Taken together, these results demonstrated that HaE74B plays a critical role in the growth, development, and metamorphosis of H. armigera, which serves as a molecular target and sets out a theoretical foundation for RNAi-mediated control of this key pest. © 2023 Society of Chemical Industry.

Unveiling Molecular Effects of the Secondary Metabolite 2-Dodecanone in the Model Hymenopteran Nasonia vitripennis

Over the past decade, multiple studies have suggested that the secondary metabolites produced by plants against herbivorous insects could be used as biopesticides. However, as the molecular mechanism of action of these compounds remains unknown, it is difficult to predict how they would affect non-target insects; thus, their innocuity needs to be clarified. Here, we investigate, from the molecular level to the organism, the responses of a useful parasitic insect Nasonia vitripennis (Walker, 1836) being exposed at the pupae stage for 48 h (up to 6 days) to sublethal doses (5 µg/L and 500 µg/L) of 2-Dodecanone. 2-Dodecanone altered the gene expression of genes related to ecdysone-related pathways, biotransformation, and cell homeostasis. A significant induction of ecdysone response-genes (EcR, usp, E78, Hr4, Hr38) was detected, despite no significant differences in ecdysteroid levels. Regarding the cell homeostasis processes, the gene l(2)efl was differentially altered in both experimental conditions, and a dose-dependent induction of hex81 was observed. 2-Dodecanone also triggered an induction of Cyp6aQ5 activity. Finally, 2-Dodecanone exposure had a significant effect on neither development time, energy reserves, nor egg-laying capacity; no potential genotoxicity was detected. For the first time, this study shows evidence that 2-Dodecanone can modulate gene expression and interfere with the ecdysone signalling pathway in N. vitripennis. This could lead to potential endocrine alterations and highlight the suitability of this organism to improve our general understanding of the molecular effects of plant defences in insects. Our findings provide new insights into the toxicity of 2-Dodecanone that could potentially be explored in other species and under field conditions for plant protection and pest management as a means to reduce reliance on synthetic pesticides.

Finishing the egg

Gamete development is a fundamental process that is highly conserved from early eukaryotes to mammals. As germ cells develop, they must coordinate a dynamic series of cellular processes that support growth, cell specification, patterning, the loading of maternal factors (RNAs, proteins, and nutrients), differentiation of structures to enable fertilization and ensure embryonic survival, and other processes that make a functional oocyte. To achieve these goals, germ cells integrate a complex milieu of environmental and developmental signals to produce fertilizable eggs. Over the past 50 years, Drosophila oogenesis has risen to the forefront as a system to interrogate the sophisticated mechanisms that drive oocyte development. Studies in Drosophila have defined mechanisms in germ cells that control meiosis, protect genome integrity, facilitate mRNA trafficking, and support the maternal loading of nutrients. Work in this system has provided key insights into the mechanisms that establish egg chamber polarity and patterning as well as the mechanisms that drive ovulation and egg activation. Using the power of Drosophila genetics, the field has begun to define the molecular mechanisms that coordinate environmental stresses and nutrient availability with oocyte development. Importantly, the majority of these reproductive mechanisms are highly conserved throughout evolution, and many play critical roles in the development of somatic tissues as well. In this chapter, we summarize the recent progress in several key areas that impact egg chamber development and ovulation. First, we discuss the mechanisms that drive nutrient storage and trafficking during oocyte maturation and vitellogenesis. Second, we examine the processes that regulate follicle cell patterning and how that patterning impacts the construction of the egg shell and the establishment of embryonic polarity. Finally, we examine regulatory factors that control ovulation, egg activation, and successful fertilization.

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.

Innate functions of natural products: A promising path for the identification of novel therapeutics

In the course of evolution, living organisms have become well equipped with diverse natural products that serve important functions, including defence from biotic and abiotic stress, growth regulation, reproduction, metabolism, and epigenetic regulation. It seems to be the organism's ecological niche that influences the natural product's structural and functional diversity. Indeed, natural products constitute the nuts and bolts of molecular co-evolution and ecological relationships among different life forms. Since natural products in the form of specialized secondary metabolites exhibit biological functions via interactions with specific target proteins, they can provide a simultaneous glimpse of both new therapeutics and therapeutic targets in humans as well. In this review, we have discussed the innate role of natural products in the ecosystem and how this intrinsic role provides a futuristic opportunity to identify new drugs and therapeutic targets rapidly.

Azadirachtin Inhibits Nuclear Receptor HR3 in the Prothoracic Gland to Block Larval Ecdysis in the Fall Armyworm, Spodoptera frugiperda

Azadirachtin has been used to control agricultural pests for a long time; however, the molecular mechanism of azadirachtin on lepidopterans is still not clear. In this study, the fourth instar larvae of fall armyworm were fed with azadirachtin, and then the ecdysis was blocked in the fourth instar larval stage (L4). The prothoracic glands (PGs) of the treated larvae were dissected for RNA sequencing to determine the effect of azadirachtin on ecdysis inhibition. Interestingly, one of the PG-enriched genes, the nuclear hormone receptor 3 (HR3), was decreased after azadirachtin treatment, which plays a critical role in the 20-hydroxyecdysone action during ecdysis. To deepen the understanding of azadirachtin on ecdysis, the HR3 was knocked out by using the CRISPR/Cas9 system, while the HR3 mutants displayed embryonic lethal phenotype; thus, the stage-specific function of HR3 during larval molting was not enabled to unfold. Hence, the siRNA was injected into the 24 h L4 larvae to knock down HR3. After 96 h, the injected larvae were blocked in the old cuticle during ecdysis which is consistent with the azadirachtin-treated larvae. Taken together, we envisioned that the inhibition of ecdysis in the fall armyworm after the azadirachtin treatment is due to an interference with the expression of HR3 in PG, resulting in larval mortality. The results in this study specified the understanding of azadirachtin on insect ecdysis and the function of HR3 in lepidopteran in vivo.

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.

Hormonal gatekeeping via the blood-brain barrier governs caste-specific behavior in ants

Here, we reveal an unanticipated role of the blood-brain barrier (BBB) in regulating complex social behavior in ants. Using scRNA-seq, we find localization in the BBB of a key hormone-degrading enzyme called juvenile hormone esterase (Jhe), and we show that this localization governs the level of juvenile hormone (JH3) entering the brain. Manipulation of the Jhe level reprograms the brain transcriptome between ant castes. Although ant Jhe is retained and functions intracellularly within the BBB, we show that Drosophila Jhe is naturally extracellular. Heterologous expression of ant Jhe into the Drosophila BBB alters behavior in fly to mimic what is seen in ants. Most strikingly, manipulation of Jhe levels in ants reprograms complex behavior between worker castes. Our study thus uncovers a remarkable, potentially conserved role of the BBB serving as a molecular gatekeeper for a neurohormonal pathway that regulates social behavior.

Steroid receptor coactivator TAIMAN is a new modulator of insect circadian clock

TAIMAN (TAI), the only insect ortholog of mammalian Steroid Receptor Coactivators (SRCs), is a critical modulator of ecdysone and juvenile hormone (JH) signaling pathways, which govern insect development and reproduction. The modulatory effect is mediated by JH-dependent TAI's heterodimerization with JH receptor Methoprene-tolerant and association with the Ecdysone Receptor complex. Insect hormones regulate insect physiology and development in concert with abiotic cues, such as photo- and thermoperiod. Here we tested the effects of JH and ecdysone signaling on the circadian clock by a combination of microsurgical operations, application of hormones and hormone mimics, and gene knockdowns in the linden bug Pyrrhocoris apterus males. Silencing taiman by each of three non-overlapping double-strand RNA fragments dramatically slowed the free-running period (FRP) to 27-29 hours, contrasting to 24 hours in controls. To further corroborate TAIMAN's clock modulatory function in the insect circadian clock, we performed taiman knockdown in the cockroach Blattella germanica. Although Blattella and Pyrrhocoris lineages separated ~380 mya, B. germanica taiman silencing slowed the FRP by more than 2 hours, suggesting a conserved TAI clock function in (at least) some insect groups. Interestingly, the pace of the linden bug circadian clock was neither changed by blocking JH and ecdysone synthesis, by application of the hormones or their mimics nor by the knockdown of corresponding hormone receptors. Our results promote TAI as a new circadian clock modulator, a role described for the first time in insects. We speculate that TAI participation in the clock is congruent with the mammalian SRC-2 role in orchestrating metabolism and circadian rhythms, and that TAI/SRCs might be conserved components of the circadian clock in animals.

Dual roles of CYP302A1 in regulating ovarian maturation and molting in Macrobrachium nipponense

CYP302A1 is a member of the Halloween genes in the cytochrome P450 supergene family, which play an important regulatory role in the synthesis of 20-hydroxyecdysone (20E) in crustaceans and insects. In this study, we found that the Mn-CYP302A1sequence included typical CYP450 conserved domains. Phylogenic showed that it is closely related to crustaceans and insects. q-PCR analysis indicated that Mn-CYP302A1 was highly expressed in the ovaries and peaked before ovarian maturation. Mn-CYP302A1 expression was higher at the post-larval stage of day 15 than at other stages of embryogenesis. In situ hybridization indicated that Mn-CYP302A1 was mainly distributed in the nucleus, yolk granules, cell membrane and cytoplasm To further establish the function of CYP302A1, a 21-day RNA interference experiment was conducted. On day 16, the Gonad Somatic Index of the control group and the experimental group showed significant differences, with GSI of 11.72% in the control group and 3.21% in the experimental group. The cumulative proportion of the second entry into stage O-Ⅲ was 100% in the control group, while it was 41.67% in the experimental group on day 21. The ecdysone content was 8.91nmol/L in the control group and 6.11nmol/L in the experimental group on day 9. A significant difference in the molting proportion between the control group and the experimental group was also observed (49% in the control group and 34% in the experimental group) on day 16. Statistical results showed that the average molting cycle of the control group was 14.5 days, while that of the experimental group was 16.5 days. However, the morphological structure of ovarian tissue did not abnormal change. Therefore, the results of this study suggest that Mn-CYP302A1 can promote ovarian maturation and molting in female M. nipponense.

Sublethal effects of halofenozide on larval development and detoxification in Phaedon brassicae (Coleoptera: Chrysomelidae)

The brassica leaf beetle, Phaedon brassicae, is a serious defoliator of cruciferous crops. Halofenozide (Hal), an ecdysone agonist, is a new class of insect growth-regulating insecticide. Our preliminary experiment revealed the outstanding larval toxicity of Hal against P. brassicae. However, the metabolic degradation of this compound in insects remains unclear. In this study, oral administration of Hal at LC10 and LC25 caused severe separation of the cuticle and epidermis, leading to larval molting failure. Sublethal dose exposure also significantly reduced the larval respiration rate as well as their pupation rates and pupal weights. Conversely, the activities of the multifunctional oxidase, carboxylesterase (CarE), and glutathione S-transferase (GST) were significantly enhanced in Hal-treated larvae. Further analysis using RNA sequencing identified 64 differentially expressed detoxifying enzyme genes, including 31 P450s, 13 GSTs, and 20 CarEs. Among the 25 upregulated P450s, 22 genes were clustered into the CYP3 clan, and the other 3 genes belonged to the CYP4 clan. Meanwhile, 3 sigma class GSTs and 7 epsilon class GSTs were dramatically increased, accounting for the majority of the upregulated GSTs. Moreover, 16 of the 18 overexpressed CarEs were clustered into the coleopteran xenobiotic-metabolizing group. These results showed the augmented expression of detoxification genes in P. brassicae after exposed to sublethal dose of Hal, and helped to better understand the potential metabolic pathways that could contribute to the reduced sensitivity to Hal in this pest. Overall, a deep insight into the detoxification mechanisms would provide practical guidance for the field management of P. brassicae.

Identification of ecdysone receptor target genes in the worker honey bee brains during foraging behavior

Ecdysone signaling plays central roles in morphogenesis and female ovarian development in holometabolous insects. In the European honey bee (Apis mellifera L.), however, ecdysone receptor (EcR) is expressed in the brains of adult workers, which have already undergone metamorphosis and are sterile with shrunken ovaries, during foraging behavior. Aiming at unveiling the significance of EcR signaling in the worker brain, we performed chromatin-immunoprecipitation sequencing of EcR to search for its target genes using the brains of nurse bees and foragers. The majority of the EcR targets were common between the nurse bee and forager brains and some of them were known ecdysone signaling-related genes. RNA-sequencing analysis revealed that some EcR target genes were upregulated in forager brains during foraging behavior and some were implicated in the repression of metabolic processes. Single-cell RNA-sequencing analysis revealed that EcR and its target genes were expressed mostly in neurons and partly in glial cells in the optic lobes of the forager brain. These findings suggest that in addition to its role during development, EcR transcriptionally represses metabolic processes during foraging behavior in the adult worker honey bee brain.

Temporal control of neuronal wiring

Wiring an animal brain is a complex process involving a staggering number of cell-types born at different times and locations in the developing brain. Incorporation of these cells into precise circuits with high fidelity is critical for animal survival and behavior. Assembly of neuronal circuits is heavily dependent upon proper timing of wiring programs, requiring neurons to express specific sets of genes (sometimes transiently) at the right time in development. While cell-type specificity of genetic programs regulating wiring has been studied in detail, mechanisms regulating proper timing and coordination of these programs across cell-types are only just beginning to emerge. In this review, we discuss some temporal regulators of wiring programs and how their activity is controlled over time and space. A common feature emerges from these temporal regulators - they are induced by cell-extrinsic cues and control transcription factors capable of regulating a highly cell-type specific set of target genes. Target specificity in these contexts comes from cell-type specific transcription factors. We propose that the spatiotemporal specificity of wiring programs is controlled by the combinatorial activity of temporal programs and cell-type specific transcription factors. Going forward, a better understanding of temporal regulators will be key to understanding the mechanisms underlying brain wiring, and will be critical for the development of in vitro models like brain organoids.

Flubendiamide induced genetic and cellular damages directly influence the life cycle of the oriental leaf worm, Spodoptera litura

Indiscriminate uses of insecticide greatly damage the environment as well as non-target organisms. Thus, multiple levels of bioassays can help better management of our environment. Flubendiamide is a phthalic acid diamide insecticide that ceases the function of insect muscle leading to paralysis and death. Here, we aimed to explore the effects of Flubendiamide on the life cycle of Spodoptera litura vis-a-vis the mode of action. Fourth instar larvae of the same age (120 ± 2 h) and size were fed with different concentrations (20-80 μg/mL) of Flubendiamide for 12-72 h. We performed a pharmacokinetics study, different biochemical assays, p450, Ecdysone receptor (EcR) and other genes expression analyses by Real-Time PCR and gross damages by Dye exclusion assay and histopathology. Our results demonstrate that the mean concentration of Flubendiamide after 48 h is 9.907 μg/mL and (i) altered the molting, metamorphosis, and reproduction at 80 μg/mL (24 h) (ii) increases all oxidative stress parameters (ROS/RNS, MDA, 8OHdG), decreases oxidative defense mechanisms (SOD, CAT, GST) at 80 μg/mL (48 h) and p450 in a time and concentration-dependent manner, (iii) activates CncC/Maf apoptotic pathways at 80 μg/mL concentration at 24 h while the expression declined from 48 h onwards, (iii) downregulates the EcR expression in a time and concentration-dependent manner, which might be responsible for disturbed molting, metamorphosis, and reproduction, and (iv) increase the expression of apoptotic genes (Caspase 1, -3, and - 5), in time and concentration-dependent manner causing gross morphological and histological damages. In conclusion, indiscriminate use of this insecticide can affect the ecosystem and have the capacity to cause multiple hazardous effects on experimental organisms. Thus, it warrants further investigations to improve and optimize the integrated pest management packages, including Flubendiamide for better management.

Identification and functional characterisation of N-acetylglucosamine kinase from Helicoverpa armigera divulge its potential role in growth and development via UDP-GlcNAc salvage pathway

N-acetylglucosamine kinase (NAGK), a major enzyme of sugar-kinase/Hsp70/actin superfamily, catalyses the conversion of N-acetylglucosamine to GlcNAc-6-phosphate, the first step leading to the salvage synthesis of uridine diphosphate N-acetylglucosamine. Here, we present the first report on identification, cloning, recombinant expression and functional characterisation of NAGK from Helicoverpa armigera (HaNAGK). The purified soluble HaNAGK exhibited a molecular mass of ~39 kDa with monomeric conformation. It catalysed the sequential transformation of GlcNAc into UDP-GlcNAc, indicating its role as the initiator of UDP-GlcNAc salvage pathway. HaNAGK exhibited ubiquitous expressions across all the developmental stages and major tissues of H. armigera. The gene was significantly upregulated (80 %; p < 0.01) by the moulting hormone 20-hydroxyecdysone and significantly downregulated (89 %; p < 0.001) by the chitin synthesis inhibitor novaluron, indicating its involvement in ecdysis and chitin metabolism. Furthermore, RNAi of HaNAGK caused poor weight gain, deformed insect bodies, aberrant metamorphosis and pronounced wing abnormalities in >55 % of surviving adults, while recording 7.79 ± 1.52 % and 24.25 ± 7.21 % mortality during larval and pupal stages, respectively. Altogether, the present findings suggest that HaNAGK plays a crucial role in the growth and development of H. armigera and thus, could be considered as a compelling gene of interest while formulating novel pest management strategies.

Mechanistic effects of microwave radiation on pupal emergence in the leafminer fly, Liriomyza trifolii

Liriomyza trifolii is a significant pest of vegetable and ornamental crops across the globe. Microwave radiation has been used for controlling pests in stored products; however, there are few reports on the use of microwaves for eradicating agricultural pests such as L. trifolii, and its effects on pests at the molecular level is unclear. In this study, we show that microwave radiation inhibited the emergence of L. trifolii pupae. Transcriptomic studies of L. trifolii indicated significant enrichment of differentially expressed genes (DEGs) in 'post-translational modification, protein turnover, chaperones', 'sensory perception of pain/transcription repressor complex/zinc ion binding' and 'insulin signaling pathway' when analyzed with the Clusters of Orthologous Groups, Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes databases, respectively. The top DEGs were related to reproduction, immunity and development and were significantly expressed after microwave radiation. Interestingly, there was no significant difference in the expression of genes encoding heat shock proteins or antioxidant enzymes in L. trifolii treated with microwave radiation as compared to the untreated control. The expression of DEGs encoding cuticular protein and protein takeout were silenced by RNA interference, and the results showed that knockdown of these two DEGs reduced the survival of L. trifolii exposed to microwave radiation. The results of this study help elucidate the molecular response of L. trifolii exposed to microwave radiation and provide novel ideas for control.

BmMD-2A responds to 20-hydroxyecdysone and regulates Bombyx mori silkworm innate immunity in larva-to-pupa metamorphosis

20E-hydroxyecdysone (20E) plays important roles in larval molting and metamorphosis in insects and is also involved in the insect innate immune response. Insect metamorphosis is a highly successful strategy for environmental adaptation and is the most vulnerable stage during which the insect is susceptible to various pathogens. 20E regulates a series of antimicrobial peptides (AMPs) through the immunodeficiency (IMD) pathway activation in Drosophila; nevertheless, whether other immune pathways are involved in 20E-regulated insect immunity is unknown. Our previous studies showed that BmMD-2A is a member of the MD-2-related lipid recognition (ML) family of proteins that are involved in the Bombyx mori innate immunity Toll signaling pathway. In this study, we further demonstrate that BmMD-2A is also positively regulated by 20E, and the BmMD-2A neutralization experiment suggested that 20E activates some downstream immune effect factors, the AMP genes against Escherichia coli and Staphylococcus aureus, through the regulation of BmMD-2A in larval metamorphosis, implying that B. mori may use the Toll-ML signaling pathway to maintain innate immune balance in the larval-pupal metamorphosis stage, which is a different innate immunity pathway regulated by 20E compared to the IMD pathway in Drosophila.

The MicroRNA Ame-Bantam-3p Controls Larval Pupal Development by Targeting the Multiple Epidermal Growth Factor-like Domains 8 Gene (megf8) in the Honeybee, Apis mellifera

20-Hydroxyecdysone (20E) plays an essential role in coordinating developmental transitions in insects through responsive protein-coding genes and microRNAs (miRNAs). However, the interplay between 20E and miRNAs during insect metamorphosis is unknown. In this study, using small RNA sequencing, a comparative miRNA transcriptomic analysis in different development stages, and 20E treatment, we identified ame-bantam-3p as a key candidate miRNA involved in honeybee metamorphosis. Target prediction and in vitro dual-luciferase assays confirmed that ame-bantam-3p interacts with the coding region of the megf8 gene and promotes its expression. Meanwhile, temporal expression analysis revealed that the expression of ame-bantam-3p is higher in the larval stage than in prepupal and pupal stages, and that this expression pattern is similar to that of megf8. In vivo, we found that the mRNA level of megf8 was significantly increased after the injection of ame-bantam-3p agomir. A 20E feeding assay showed that 20E downregulated the expression of both ame-bantam-3p and its target gene megf8 on larval days five, six, and seven. Meanwhile, the injection of ame-bantam-3p agomir also reduced the 20E titer, as well as the transcript levels of essential ecdysteroid synthesis genes, including Dib, Phm, Sad, and Nvd. The transcript levels of 20E cascade genes, including EcRA, ECRB1, USP, E75, E93, and Br-c, were also significantly decreased after ame-bantam-3p agomir injection. However, ame-bantam-3p antagomir injection and dsmegf8 injection showed the opposite effect to ame-bantam-3p agomir injection. Ame-bantam-3p agomir treatment ultimately led to mortality and the failure of larval pupation by inhibiting ecdysteroid synthesis and the 20E signaling pathway. However, the expression of 20E signaling-related genes was significantly increased after megf8 knockdown, and larvae injected with dsmegf8 showed early pupation. Combined, our results indicate that ame-bantam-3p is involved in the 20E signaling pathway through positively regulating its target gene megf8 and is indispensable for larval–pupal development in the honeybee. These findings may enhance our understanding of the relationship between 20E signaling and small RNAs during honeybee development.

Ammonia Stress Disturbs Moult Signaling in Juvenile Swimming Crab Portunus trituberculatus

Ammonia is a significant concern during hatchery culture in brachyuran species, and its accumulation may lead to abortive moulting and large-scale deaths of the early juveniles. To date, the underlying mechanism for ammonia-induced alteration of the moulting process is still unknown. In this study, we aimed to investigate the effects of ammonia on the moulting as well as the potential mechanisms in early juveniles of the swimming crab Portunus trituberculatus, an important aquaculture species in China. We evaluated the survival rate and moulting rate of the juvenile crabs (C2) and analyzed the expression pattern of the genes in key components of molt signaling during a complete moulting cycle under different concentrations of ammonia nitrogen (the control group: <0.1 mg/L; the LA group: 5 mg/L; and the HA group: 20 mg/L). The results showed that: (1) the survival rate in the LA and HA groups was lower than that in the control group at the end of the experiment, and moulting death syndrome (MDS) was only observed in the HA group; (2) the moulting rate was higher in the LA group and lower in the HA group compared to the control group; (3) consistent with the results of the moulting experiment, MIH showed decreased expression, and genes related to ecdysteroid synthesis, ecdysteroid receptors, and responsive effectors exhibited increased expression in the LA group compared to the control group; and (4) although MIH expression was upregulated, increased expression of the genes associated with ecdysteroid synthesis, ecdysteroid receptors and downstream effectors still observed in the HA group. Our results indicated that low levels of ammonia can promote moulting in juvenile swimming crabs by inhibiting the expression of MIH and activating moult signaling, whereas high levels of ammonia inhibit moulting and lead to MDS through impairing moult signaling.

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.

Low GSK3β activity is required for insect diapause through responding to ROS/AKT signaling and down-regulation of Smad1/EcR/HR3 cascade

Glycogen synthase kinase 3β (GSK3β) plays important roles in gene transcription, metabolism, apoptosis, development, and signal transduction. However, its role in the regulation of pupal diapause remains unclear. In this paper, we find that low GSK3β activity in brains of diapause-destined pupae of Helicoverpa armigera is caused by elevated AKT activity. In response to ROS, AKT phosphorylates GSK3β to decrease its activity. In developing pupal brains, GSK3β can activate the transcription factor Smad1, which binds to the promoter region of the ecdysone receptor (EcR) gene and increases its expression. In the presence of 20-hydroxyecdysone (20E), EcR can bind to USP and increase the expression of 20E-response genes, including HR3, for pupal-adult development. In contrast, high levels of ROS in brains of diapause-destined pupae up-regulate p-AKT, which in turn decreases GSK3β activity. Low GSK3β activity causes low expression of EcR/HR3 via down-regulation of Smad1 activity, leading to diapause initiation. These results suggest that low GSK3β activity plays a key role in pupal diapause via ROS/AKT/GSK3β/Smad/EcR/HR3 signaling.

Field recommended concentrations of pyraclostrobin exposure disturb the development and immune response of worker bees (Apis mellifera L.) larvae and pupae

The strobilurin fungicide pyraclostrobin is widely used to prevent and control the fungal diseases of various nectar and pollen plants. Honeybees also directly or indirectly contact this fungicide with a long-term exposure period. However, the effects of pyraclostrobin on the development and physiology of Apis mellifera larvae and pupae during continuous exposure have been rarely known. To investigate the effects of field-realistic concentrations of pyraclostrobin on honeybee survival and development, the 2-day-old larvae were continuously fed with different pyraclostrobin solutions (100 mg/L and 83.3 mg/L), and the expression of development-, nutrient-, and immune-related genes in larvae and pupae were examined. The results showed that two field-realistic concentrations of pyraclostrobin (100 and 83.3 mg/L) significantly decreased the survival and capped rate of larvae, the weight of pupae and newly emerged adults, and such decrease was a positive correlation to the treatment concentrations. qPCR results showed that pyraclostrobin could induce the expression of Usp, ILP2, Vg, Defensin1, and Hymenoptaecin, decrease the expression of Hex100, Apidaecin, and Abaecin in larvae, could increase the expression of Ecr, Usp, Hex70b, Vg, Apidaecin, and Hymenoptaecin, and decreased the expression of ILP1, Hex100 and Defensin1in pupae. These results reflect pyraclostrobin could decrease nutrient metabolism, immune competence and seriously affect the development of honeybees. It should be used cautiously in agricultural practices, especially in the process of bee pollination.

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.

Using Drosophila Genetics to Identify Factors that Affect PARP1 Activity In Vivo

PARP1 is the enzyme responsible for the majority of the poly(ADP-ribose) (pADPr) synthesis in Drosophila. Its activity can be easily evaluated in vitro by measuring the level of pADPr, which allow to study the effect of potential PARP1 upstream factors on PARP1 activity. However, PARP1 activity can be challenging to measure in vivo, due to the presence of PARG, since pADPr level is a consequence of the activity of both PARP1 that synthetizes pADPr and PARG that degrades it. An increase in PARG activity can hide an increase of PARP1 activity. In this context, the effect of potential upstream factors on PARP1 activity can be hard to measure. Here, we describe a genetic background where PARG is absent to study changes in PARP1 activity at different developmental time points.

Functional characterization of chitin synthesis pathway genes, HaAGM and HaUAP, reveal their crucial roles in ecdysis and survival of Helicoverpa armigera (Hübner)

The chitin metabolic pathway is one of the most lucrative targets for designing pest management regimes. Inhibition of the chitin synthesis pathway causes detrimental effects on the normal growth and development of insects. Phospho-N-acetylglucosamine mutase (AGM) and UDP-N-acetylglucosamine pyrophosphorylase (UAP) are two key chitin biosynthesis enzymes in insects including Helicoverpa armigera, a pest of global significance. In the present study, we have identified, cloned and recombinantly expressed AGM and UAP from H. armigera (HaAGM and HaUAP). Biochemical characterization of recombinant HaAGM and HaUAP exhibited high affinities for their natural substrates N-acetyl glucosamine-6-phosphate (K_m 38.72 ± 2.41) and N-acetyl glucosamine-1-phosphate (K_m 3.66 ± 0.13), respectively. In the coupled enzyme-catalytic assay, HaAGM and HaUAP yielded the end-products, inorganic pyrophosphate and UDP-GlcNAc, confirming their active participation in the chitin synthesis pathway of H. armigera. Gene expression profiling revealed that HaAGM and HaUAP genes were expressed in all developmental stages and key tissues. These genes also showed substantial responses towards the moulting hormone 20-hydroxyecdysone and chitin biosynthesis inhibitor, novaluron. Remarkably, the RNAi-mediated knockdown of either HaAGM or HaUAP led to severe developmental deformities and significant mortality ranging from 65.61 to 72.54%. Overall findings suggest that HaAGM and HaUAP play crucial roles in the ecdysis and survival of H. armigera. Further, these genes could serve as potential targets for designing pest management strategies for H. armigera.

Insect hormones affect the toxicity of the insecticidal growth regulator cyromazine in Liriomyza trifolii (Diptera: Agromyzidae)

The leafminer Liriomyza trifolii is an important insect pest of ornamental and vegetable crops worldwide. Cyromazine is an effective, commonly-used insecticide that functions as a growth regulator, but its effect on L. trifolii has not been previously reported. In this study, transcriptome analysis was undertaken in L. trifolii exposed to cyromazine. Clusters of orthologous groups analysis indicated that a large number of differentially expressed genes responding to cyromazine were categorized as "lipid transport and metabolism", "post-translational modification, protein turnover, chaperones", and "cell wall/membrane/envelope biogenesis". Gene ontology analysis indicated that pathways associated with insect hormones, growth and development, and cuticle synthesis were significantly enriched. In general, the transcriptome results showed that the genes related to insect hormones were significantly expressed after treatment with cyromazine. Furthermore, the combined exposure of L. trifolii to cyromazine and the hormone analogues 20-hydroxyecdysone (20E) or juvenile hormone (JH) indicated that hormone analogues can change the expression pattern of hormone-related genes (20EP and JHEH) and pupal length. The combined application of cyromazine with 20E improved the survival rate of L. trifolii, whereas the combination of JH and cyromazine reduced survival. The results of this study help elucidate the mechanistic basis for cyromazine toxicity and provide a foundation for understanding cyromazine resistance.

Cloning and Characterization of Drosophila melanogaster Juvenile Hormone Epoxide Hydrolases (JHEH) and Their Promoters

Juvenile hormone epoxide hydrolase (JHEH) plays an important role in the metabolism of JH III in insects. To study the control of JHEH in female Drosophila melanogaster, JHEH 1, 2 and 3 cDNAs were cloned and sequenced. Northern blot analyses showed that the three transcripts are expressed in the head thorax, the gut, the ovaries and the fat body of females. Molecular modeling shows that the enzyme is a homodimer that binds juvenile hormone III acid (JH IIIA) at the catalytic groove better than JH III. Analyses of the three JHEH promoters and expressing short promoter sequences behind a reporter gene (lacZ) in D. melanogaster cell culture identified a JHEH 3 promoter sequence (626 bp) that is 10- and 25-fold more active than the most active promoter sequences of JHEH 2 and JHEH 1, respectively. A transcription factor (TF) Sp1 that is involved in the activation of JHEH 3 promoter sequence was identified. Knocking down Sp1 using dsRNA inhibited the transcriptional activity of this promoter in transfected D. melanogaster cells and JH III and 20HE downregulated the JHEH 3 promoter. On the other hand, JH IIIA and farnesoic acid did not affect the promoter, indicating that JH IIIA is JHEH's preferred substrate. A transgenic D. melanogaster expressing a highly activated JHEH 3 promoter behind a lacZ reporter gene showed promoter transcriptional activity in many D. melanogaster tissues.

Sodium Benzoate Delays the Development of Drosophila melanogaster Larvae and Alters Commensal Microbiota in Adult Flies

Sodium benzoate (SB), the sodium salt of benzoic acid, is widely used as a preservative in foods and drinks. The toxicity of SB to the human body attracted people’s attention due to the excessive use of preservatives and the increased consumption of processed and fast foods in modern society. The SB can inhibit the growth of bacteria, fungi, and yeast. However, less is known of the effect of SB on host commensal microbial community compositions and their functions. In this study, we investigated the effect of SB on the growth and development of Drosophila melanogaster larvae and whether SB affects the commensal microbial compositions and functions. We also attempted to clarify the interaction between SB, commensal microbiota and host development by detecting the response of commensal microbiota after the intervention. The results show that SB significantly retarded the development of D. melanogaster larvae, shortened the life span, and changed the commensal microbial community. In addition, SB changed the transcription level of endocrine coding genes such as ERR and DmJHAMT. These results indicate that the slow down in D. melanogaster larvae developmental timing and shortened life span of adult flies caused by SB intake may result from the changes in endocrine hormone levels and commensal microbiota. This study provided experimental data that indicate SB could affect host growth and development of D. melanogaster through altering endocrine hormone levels and commensal microbial composition.

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.

Interorgan communication through peripherally derived peptide hormones in Drosophila

In multicellular organisms, endocrine factors such as hormones and cytokines regulate development and homoeostasis through communication between different organs. For understanding such interorgan communications through endocrine factors, the fruit fly Drosophila melanogaster serves as an excellent model system due to conservation of essential endocrine systems between flies and mammals and availability of powerful genetic tools. In Drosophila and other insects, functions of neuropeptides or peptide hormones from the central nervous system have been extensively studied. However, a series of recent studies conducted in Drosophila revealed that peptide hormones derived from peripheral tissues also play critical roles in regulating multiple biological processes, including growth, metabolism, reproduction, and behaviour. Here, we summarise recent advances in understanding target organs/tissues and functions of peripherally derived peptide hormones in Drosophila and describe how these hormones contribute to various biological events through interorgan communications.

Roles of Krüppel Homolog 1 and Broad-Complex in the Development of Dendroctonus armandi (Coleoptera: Scolytinae)

In insects, metamorphosis is controlled by juvenile hormone (JH) and 20-hydroxyecdysone (20E). Krüppel homolog 1 (Kr-h1), a key JH-early inducible gene, is responsible for the suppression of metamorphosis and the regulation of the Broad-Complex (Br-C) gene, which is induced by 20E and functions as a “pupal specifier”. In this study, we identified and characterized the expression patterns and tissue distribution of DaKr-h1 and DaBr-C at various developmental stages of Dendroctonus armandi. The expression of the two genes was induced by JH analog (JHA) methoprene and 20E, and their functions were investigated by RNA interference. DaKr-h1 and DaBr-C were predominantly expressed in the heads of larvae and were significantly downregulated during the molting stage. In contrast, the DaKr-h1 transcript level was highest in the adult anterior midgut. DaBr-C was mainly expressed in female adults, with the highest transcript levels in the ovaries. In the larval and pupal stages, both JHA and 20E significantly induced DaKr-h1, but only 20E significantly induced DaBr-C, indicating the importance of hormones in metamorphosis. DaKr-h1 knockdown in larvae upregulated DaBr-C expression, resulting in precocious metamorphosis from larvae to pupae and the formation of miniature pupae. DaKr-h1 knockdown in pupae suppressed DaBr-C expression, increased emergence, caused abnormal morphology, and caused the formation of small-winged adults. These results suggest that DaKr-h1 is required for the metamorphosis of D. armandi. Our findings provide insight into the roles of DaKr-h1 and DaBr-C in JH-induced transcriptional repression and highlight DaKr-h1 as a potential target for metamorphosis suppression in D. armandi.

Molting process revealed by the detailed expression profiles of RXR1/RXR2 and mining the associated genes in a spider mite, Panonychus citri

Spider mites have one ecdysone receptor (EcR) and multiple retinoid X receptors (RXRs). However, the function of these RXRs in spider mite development is unknown. Here, we screened the expression dynamics of two PcRXR isoforms at 4 h intervals in the deutonymphal stage of Panonychus citri. The results showed that PcEcR had an expression pattern similar to that of PcRXR2. For PcRXR1, its expression remained at a certain high level, when there was a decrease of both PcEcR and PcRXR2. In situ hybridization showed that PcRXR2 was detected in the central nervous mass, while the ecdysteroid biosynthesis gene PcSpo was mainly expressed at the edge of the central nervous mass. RNAi-based silencing of PcRXR1 or PcRXR2 showed the same phenotype as in mites with that of silencing PcEcR. Furthermore, RNA-seq was used to mine the genes associated with the expression dynamics of PcRXR1 or PcRXR2, which revealed that the heterodimer of EcR-RXR2 in spider mites might be linked with the cell autophagy and tissue remodeling during apolysis, and RXR1 might be linked with new epicuticle and exocuticle secretion during ecdysis. Taken together, these results increase our understanding of the regulation mechanism of ecdysteroid signal pathway in spider mite development.

Silencing of transcription factor E93 inhibits adult morphogenesis and disrupts cuticle, wing and ovary development in Locusta migratoria

Ecdysone-induced protein 93F (E93) plays important roles during the metamorphosis process in insects. In this study, a cDNA of the LmE93 gene was identified from the transcriptome of Locusta migratoria, which consists of the 3378-nucleotide open-reading frame (ORF) and encodes 1125 amino acids with helix-turn-helix (HTH) motifs. Reverse transcription quantitative polymerase chain reaction analysis revealed that LmE93 was highest expressed in ovary. The LmE93 expression level was markedly low from the 3rd to 4th instar nymphs, and greatly increased in 1-day-old 5th instar nymphs with a peak on middle nymphal days, then declined in the late nymphal days. Moreover, injected dsLmE93 into 4th and 5th instar nymphs greatly reduced LmE93 transcripts, respectively, and prevented the process of metamorphosis, causing supernumerary nymphal stages. Hematoxylin-eosin staining of the integument showed that the apolysis occurred in advance in 4th instar nymphs, and old cuticle degradation was decreased in dsLmE93-injected locusts of 5th instar nymphs. Smaller and no fully developed wings with reduced columns between the anterior and posterior regions were found in N6 and N7 supernumerary nymphs. In addition, the development of the ovary in dsLmE93-injected locusts was severely blocked, the yolk was almost not formed and there was no development of ovarioles. The results indicated that LmE93 play key roles in the metamorphosis, cuticle, wing and ovarian development of locusts.

A global timing mechanism regulates cell-type-specific wiring programmes

The assembly of neural circuits is dependent on precise spatiotemporal expression of cell recognition molecules^1-5. Factors controlling cell type specificity have been identified^6-8, but how timing is determined remains unknown. Here we describe induction of a cascade of transcription factors by a steroid hormone (ecdysone) in all fly visual system neurons spanning target recognition and synaptogenesis. We demonstrate through single-cell sequencing that the ecdysone pathway regulates the expression of a common set of targets required for synaptic maturation and cell-type-specific targets enriched for cell-surface proteins regulating wiring specificity. Transcription factors in the cascade regulate the expression of the same wiring genes in complex ways, including activation in one cell type and repression in another. We show that disruption of the ecdysone pathway generates specific defects in dendritic and axonal processes and synaptic connectivity, with the order of transcription factor expression correlating with sequential steps in wiring. We also identify shared targets of a cell-type-specific transcription factor and the ecdysone pathway that regulate specificity. We propose that neurons integrate a global temporal transcriptional module with cell-type-specific transcription factors to generate different cell-type-specific patterns of cell recognition molecules regulating wiring.

iTRAQ Proteomic Analysis of Interactions Between 20E and Phospholipase C in Apolygus lucorum (Meyer-Dür)

Polyphagous Apolygus lucorum has become the dominant insect in Bacillus thuringiensis (Bt) cotton fields. Hormone 20-hydroxyecdysone (20E) regulates multiple insect development and physiology events. 20E responses are controlled by pathways triggered by phospholipase C (PLC)-associated proteins. However, 20E-modulated genes and related proteins that can be affected by PLC still remain unknown. Here, isobaric tag for relative and absolute quantitation (iTRAQ) and immunoblotting techniques were used to compare differentially expressed proteins (DEPs) in A. lucorum in response to the treatment of 20E and the PLC inhibitor U73122 as well as their combination. A total of 1,624 non-redundant proteins and 97, 248, 266 DEPs were identified in the 20E/control, U73122/control, and 20E + U73122/control groups, respectively. Only 8 DEPs, including pathogenesis-related protein 5-like, cuticle protein 19.8, trans-sialidase, larval cuticle protein A2B-like, cathepsin L1, hemolymph juvenile hormone-binding protein, ATP-dependent RNA helicase p62-like, and myosin-9 isoform X1, were detected in all three groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEPs were involved in diverse signaling pathways. The results were validated by immunoblotting, which highlighted the reliability of proteomics analysis. These findings provided novel insights into the function of PLC in 20E signaling pathway in A. lucorum.

Juvenile hormone membrane signaling phosphorylates USP and thus potentiates 20-hydroxyecdysone action in Drosophila

Juvenile hormone (JH) and 20-hydroxyecdysone (20E) coordinately regulate development and metamorphosis in insects. Two JH intracellular receptors, methoprene-tolerant (Met) and germ-cell expressed (Gce), have been identified in the fruit fly Drosophila melanogaster. To investigate JH membrane signaling pathway without the interference from JH intracellular signaling, we characterized phosphoproteome profiles of the Met gce double mutant in the absence or presence of JH in both chronic and acute phases. Functioning through a potential receptor tyrosine kinase and phospholipase C pathway, JH membrane signaling activated protein kinase C (PKC) which phosphorylated ultraspiracle (USP) at Ser35, the PKC phosphorylation site required for the maximal action of 20E through its nuclear receptor complex EcR-USP. The usp^S35A mutant, in which Ser was replaced with Ala at position 35 by genome editing, showed decreased expression of Halloween genes that are responsible for ecdysone biosynthesis and thus attenuated 20E signaling that delayed developmental timing. The usp^S35A mutant also showed lower Yorkie activity that reduced body size. Altogether, JH membrane signaling phosphorylates USP at Ser35 and thus potentiates 20E action that regulates the normal fly development. This study helps better understand the complex JH signaling network.

Rapid Assessment of Insect Steroid Hormone Entry Into Cultured Cells

Steroid hormones control development and homeostasis in a wide variety of animals by interacting with intracellular nuclear receptors. Recent discoveries in the fruit fly Drosophila melanogaster revealed that insect steroid hormones or ecdysteroids are incorporated into cells through a membrane transporter named Ecdysone Importer (EcI), which may become a novel target for manipulating steroid hormone signaling in insects. In this study, we established an assay system that can rapidly assess EcI-mediated ecdysteroid entry into cultured cells. Using NanoLuc Binary Technology (NanoBiT), we first developed an assay to detect ligand-dependent heterodimerization of the ecdysone receptor (EcR) and retinoid X receptor (RXR) in human embryonic kidney (HEK) 293T cells. We also developed HEK293 cells that stably express EcI. By combining these tools, we can monitor ecdysteroid entry into the cells in real time, making it a reliable system to assess EcI-mediated steroid hormone incorporation into animal cells.

The Hox gene Antennapedia is essential for wing development in insects

A long-standing view in the field of evo-devo is that insect forewings develop without any Hox gene input. The Hox gene Antennapedia (Antp), despite being expressed in the thoracic segments of insects, has no effect on wing development. This view has been obtained from studies in two main model species: Drosophila and Tribolium. Here, we show that partial loss of function of Antp resulted in reduced and malformed adult wings in Bombyx, Drosophila and Tribolium. Antp mediates wing growth in Bombyx by directly regulating the ecdysteriod biosynthesis enzyme gene (shade) in the wing tissue, which leads to local production of the growth hormone 20-hydroxyecdysone. Additional targets of Antp are wing cuticular protein genes CPG24, CPH28 and CPG9, which are essential for wing development. We propose, therefore, that insect wing development occurs in an Antp-dependent manner. This article has an associated 'The people behind the papers' interview.

Hsp27, a potential EcR target, protects nonylphenol-induced cellular and organismal toxicity in Drosophila melanogaster

Deciphering the potential mechanism of chemical-induced toxicity enables us to alleviate the cellular and organismal dysfunction. The environmental presence of nonylphenol (endocrine disruptor) has a major health concern due to its widespread usage in our day-to-day life. The current study establishes a novel functional link among nonylphenol-induced oxidative stress, Heat shock protein 27 (Hsp27, member of stress protein family), and Ecdysone receptor (EcR, a nuclear receptor), which eventually coordinates the nonylphenol-induced sub-cellular and organismal level toxicity in a genetically tractable model Drosophila melanogaster. Drosophila larvae exposed to nonylphenol (0.05, 0.5 and 5.0 μg/mL) showed a significant decrease in Hsp27 and EcR mRNA levels in the midgut. In concurrence, reactive oxygen species (ROS) levels were increased with a corresponding decline in glutathione (GSH) level and Thioredoxin reductase (TrxR) activity. Increased lipid peroxidation (LPO), protein carbonyl (PC) contents, and cell death were also observed in a correlation with the nonylphenol concentrations. Sub-cellular toxicity poses a negative organismal response, which was evident by delayed larval development and reduced Drosophila emergence. Subsequently, a positive genetic correlation (p < 0.001) between EcR and Hsp27 revealed that nonylphenol-dependent EcR reduction is a possible link for the downregulation of Hsp27. Further, Hsp27 overexpression in midgut cells showed a reduction in nonylphenol-induced intracellular ROS, LPO, PC content, and cell death through the TrxR mediated regenerative pathway and reduced GSH level improving the organismal response to the nonylphenol exposure. Altogether, the study elucidates the potential EcR-Hsp27 molecular interactions in mitigating the nonylphenol-induced cellular and organismal toxicity.

From Extrapolation to Precision Chemical Hazard Assessment: The Ecdysone Receptor Case Study

Hazard assessment strategies are often supported by extrapolation of damage probabilities, regarding chemical action and species susceptibilities. Yet, growing evidence suggests that an adequate sampling of physiological responses across a representative taxonomic scope is of paramount importance. This is particularly relevant for Nuclear Receptors (NR), a family of transcription factors, often triggered by ligands and thus, commonly exploited by environmental chemicals. Within NRs, the ligand-induced Ecdysone Receptor (EcR) provides a remarkable example. Long regarded as arthropod specific, this receptor has been extensively targeted by pesticides, seemingly innocuous to non-target organisms. Yet, current evidence clearly suggests a wider presence of EcR orthologues across metazoan lineages, with unknown physiological consequences. Here, we address the state-of-the-art regarding the phylogenetic distribution and functional characterization of metazoan EcRs and provide a critical analysis of the potential disruption of such EcRs by environmental chemical exposure. Using EcR as a case study, hazard assessment strategies are also discussed in view of the development of a novel "precision hazard assessment paradigm.

Calcium signaling and regulation of ecdysteroidogenesis in crustacean Y-organs

Crustacean Y-organs secrete ecdysteroid molting hormones. Ecdysteroids are released in increased amount during premolt, circulate in hemolymph, and stimulate the events in target cells that lead to molting. During much of the molting cycle, ecdysteroid production is suppressed by molt-inhibiting hormone (MIH), a peptide neurohormone produced in the eyestalks. The suppressive effect of MIH is mediated by a cyclic nucleotide second messenger. A decrease in circulating MIH is associated with an increase in the hemolymphatic ecdysteroid titer during pre-molt. Nevertheless, it has long been hypothesized that a positive regulatory signal or stimulus is also involved in promoting ecdysteroidogenensis during premolt. Data reviewed here are consistent with the hypothesis that an intracellular Ca²⁺ signal provides that stimulus. Pharmacological agents that increase intracellular Ca²⁺ in Y-organs promote ecdysteroidogenesis, while agents that lower intracellular Ca²⁺ or disrupt Ca²⁺ signaling suppress ecdysteroidogenesis. Further, an increase in the hemolymphatic ecdysteroid titer after eyestalk ablation or during natural premolt is associated with an increase in intracellular free Ca²⁺ in Y-organ cells. Several lines of evidence suggest elevated intracellular calcium is linked to enhanced ecdysteroidogenesis through activation of Ca²⁺/calmodulin dependent cyclic nucleotide phosphodiesterase, thereby lowering intracellular cyclic nucleotide second messenger levels and promoting ecdysteroidogenesis. Results of transcriptomic studies show genes involved in Ca²⁺ signaling are well represented in Y-organs. Several recent studies have focused on Ca²⁺ transport proteins in Y-organs. Complementary DNAs encoding a plasma membrane Ca²⁺ ATPase (PMCA) and a sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) have been cloned from crab Y-organs. The relative abundance of PMCA and SERCA transcripts in Y-organs is elevated during premolt, a time when Ca²⁺ levels in Y-organs are likewise elevated. The results are consistent with the notion that these transport proteins act to maintain the Ca²⁺ gradient across the cell membrane and re-set the cell for future Ca²⁺ signals.

3-Bromopyruvate-induced glycolysis inhibition impacts larval growth and development and carbohydrate homeostasis in fall webworm, Hyphantria cunea Drury

As a typical glycolytic inhibitor, 3-bromopyruvate (3-BrPA) has been extensively studied in cancer therapy in recent decades. However, few studies focused on 3-BrPA in regulating the growth and development of insects, and the relationship and regulatory mechanism between glycolysis and chitin biosynthesis remain largely unknown. The Hyphantria cunea, named fall webworm, is a notorious defoliator, which caused a huge economic loss to agriculture and forestry. Here, we investigated the effects of 3-BrPA on the growth and development, glycolysis, carbohydrate homeostasis, as well as chitin synthesis in H. cunea larvae. To elucidate the action mechanism of 3-BrPA on H. cunea will provide a new insight for the control of this pest. The results showed that 3-BrPA dramatically restrained the growth and development of H. cunea larvae and resulted in larval lethality. Meanwhile, we confirmed that 3-BrPA caused a significant decrease in carbohydrate, adenosine triphosphate (ATP), pyruvic acid (PA), and triglyceride (TG) levels by inhibiting glycolysis in H. cunea larvae. Further studies indicated that 3-BrPA significantly affected the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), glucose 6-phosphate dehydrogenase (G6PDH) and trehalase, as well as expressions of the genes related to glycolysis, resulting in carbohydrate homeostasis disorder. Moreover, it was found that 3-BrPA enhanced 20-hydroxyecdysone (20E) signaling by upregulating HcCYP306A1 and HcCYP314A1, two critical genes in 20E synthesis pathway, and accelerated chitin synthesis by upregulating transcriptional levels of genes in the chitin synthesis pathway in H. cunea larvae. Taken together, our findings provide a novel insight into the mechanism of glycolytic inhibitor in regulating the growth and development of insects, and lay a foundation for the potential application of glycolytic inhibitors in pest control as well.

Constraints and Opportunities for the Evolution of Metamorphic Organisms in a Changing Climate

We argue that developmental hormones facilitate the evolution of novel phenotypic innovations and timing of life history events by genetic accommodation. Within an individual’s life cycle, metamorphic hormones respond readily to environmental conditions and alter adult phenotypes. Across generations, the many effects of hormones can bias and at times constrain the evolution of traits during metamorphosis; yet, hormonal systems can overcome constraints through shifts in timing of, and acquisition of tissue specific responses to, endocrine regulation. Because of these actions of hormones, metamorphic hormones can shape the evolution of metamorphic organisms. We present a model called a developmental goblet, which provides a visual representation of how metamorphic organisms might evolve. In addition, because developmental hormones often respond to environmental changes, we discuss how endocrine regulation of postembryonic development may impact how organisms evolve in response to climate change. Thus, we propose that developmental hormones may provide a mechanistic link between climate change and organismal adaptation.

Characterization of the detrimental effects of type IV glandular trichomes on the aphid Macrosiphum euphorbiae in tomato

BACKGROUND

Glandular trichomes are essential in plants' defence against pests however, the mechanisms of action are not completely understood. While there is considerable evidence of feeding and movement impairment by trichomes, the effect on other traits is less clear. We combined laboratory and greenhouse experiments with molecular analysis to understand how glandular trichomes affect the behavior, population growth, and the expression of biomarkers involved in detoxification, primary metabolism, and developmental pathways of the aphid Macrosiphum euphorbiae. We used two isogenic tomato lines that differ in the presence of type IV glandular trichomes and production of acylsucroses; i.e.,Solanum lycopersicum cv. 'Moneymaker' and an introgressed line from Solanum pimpinellifolium (with trichomes type IV).

RESULTS

Type IV glandular trichomes affected host selection and aphid proliferation with aphids avoiding, and showing impaired multiplication on the genotype with trichomes. The exposure to type IV glandular trichomes resulted in the overexpression of detoxication markers (i.e., Hsp70, Hsp17, Hsp10); the repression of the energetic metabolism (GAPDH), and the activation of the ecdysone pathway; all these, underlying the key adaptations and metabolic trade-offs in aphids exposed to glandular trichomes.

CONCLUSION

Our results demonstrate the detrimental effect of glandular trichomes (type IV) on the aphid and put forward their mode of action. Given the prevalence of glandular trichomes in wild and cultivated Solanaceae; and of the investigated molecular biomarkers in insects in general, our results provide relevant mechanisms to understand the effect of trichomes not only on herbivorous insects but also on other trophic levels.

Accelerated cell cycles enable organ regeneration under developmental time constraints in the Drosophila hindgut

Individual organ development must be temporally coordinated with development of the rest of the organism. As a result, cell division cycles in a developing organ occur on a relatively fixed timescale. Despite this, many developing organs can regenerate cells lost to injury. How organs regenerate within the time constraints of organism development remains unclear. Here, we show that the developing Drosophila hindgut regenerates by accelerating the mitotic cell cycle. This process is achieved by decreasing G1 length and requires the JAK/STAT ligand unpaired-3. Mitotic capacity is then terminated by the steroid hormone ecdysone receptor and the Sox transcription factor Dichaete. These two factors converge on regulation of a hindgut-specific enhancer of fizzy-related, a negative regulator of mitotic cyclins. Our findings reveal how the cell-cycle machinery and cytokine signaling can be adapted to accomplish developmental organ regeneration.

Anatomy and evolution of a DNA replication origin

DNA amplification occurs at the DNA puff II/9A locus in the fungus fly Sciara coprophila. As a foundation to study the molecular mechanism for the initiating events of II/9A DNA re-replication, we have sequenced 14 kb spanning a DNase hypersensitive site (DHS) upstream of the 1 kb amplification origin and through transcription units II/9-1 and II/9-2 downstream of the origin. These elements are annotated as well as the ORC binding site at the origin and the transition point (TP) between continuous and discontinuous DNA syntheses that marks the origin of bidirectional replication at the nucleotide level. A 9 bp motif found at the TP is repeated near the other end of the 1 kb ORI and may identify a putative second TP. The steroid hormone ecdysone induces DNA amplification as well as transcription and puffing at locus II/9A. Within the 14 kb, several matches to the ecdysone response element (EcRE) consensus sequence were identified, including some in the amplification origin region. EcRE O-P is at a central axis of a remarkable symmetry, equidistant to the TPs that are themselves equidistant to EcRE O-1 and EcRE O-2. DNA sequence alterations have occurred throughout the II/9A region in a newly discovered polymorphism (#2). Polymorphism #2 is not specific to developmental stage, sex, or tissue, and it does not impair DNA amplification. The DHS, both 9 bp TP sequences, and EcREs O-1, O-P, and O-2 are conserved between the polymorphism #1 and #2 sequences, suggesting their functional importance and retention during evolutionary selection. Moreover, a 72 bp sequence in the Sciara DHS at DNA puff II/9A is conserved in DNA puff C-3 of Rhynchosciara americana. Comparisons are discussed between the Sciara II/9A amplicon and the chorion locus amplicon on the third chromosome of Drosophila.

Juvenile hormone in spiders. Is this the solution to a mystery?

The juvenile hormone (JH) plays a crucial role in arthropod physiological processes, e.g., the regulation of metamorphosis, development, and reproduction (the vitellogenesis, the development of gonads, egg production). Still, data about this sesquiterpenoid hormone in spiders (Araneae) are rudimentary and equivocal. The presence of the JH or its precursors (e.g. methyl farnesoate) is not confirmed in spiders. The site of synthesis of its is still undetermined. No receptors of the JH are identified in spiders and thus, the molecular mechanism of action of this group of hormones is still unknown. Here we show by using the phylogenetic analysis and qPCR method the presence of the transcript of the enzyme catalyzing the last phase of the JH biosynthesis pathway (epox CYP15A1), the JH receptor (Met), and a possible candidate to the methyl farnesoate receptor (USP) in the various tissues and stages of ontogenesis in both sexes of spider Parasteatoda tepidariorum. Our results indicate that the juvenile hormone and/or methyl farnesoate presence is possible in the species of spider P. tepidariorum. The presence of the Ptepox CYP15A1 gene suggests that the main site of the juvenile hormone synthesis can be the integument and not the Schneider organ 2. It also seems that the juvenile hormone and/or methyl farnesoate can be hormones with biological activity due to the presence of the transcript of insect and crustacean JH/MG receptor - Met. The Ptepox CYP15A1, PtMet, and Ptusp expression are sex-, tissue-and time-specific. This study is the first report about the presence of the Ptepox CYP15A1 and PtMet transcripts in the Arachnida, which may indicate the presence of the juvenile hormone and/or methyl farnesoate in spiders.