Antagonistic actions of juvenile hormone and 20-hydroxyecdysone within the ring gland determine developmental transitions in Drosophila

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.

Caterpillar-Induced Rice Volatile (E)-β-Farnesene Impairs the Development and Survival of Chilo suppressalis Larvae by Disrupting Insect Hormone Balance

Significant research progress has recently been made on establishing the roles of tps46 in rice defense. (E)-β-farnesene (Eβf) is a major product of tps46 activity but its physiological functions and potential mechanisms against Chilo suppressalis have not yet been clarified. In the present study, C. suppressalis larvae were artificially fed a diet containing 0.8 g/kg Eβf and the physiological performance of the larvae was evaluated. In response to Eβf treatment, the average 2nd instar duration significantly increased from 4.78 d to 6.31 d while that of the 3rd instar significantly increased from 5.70 d to 8.00 d compared with the control. There were no significant differences between the control and Eβf-fed 4th and 5th instars in terms of their durations. The mortalities of the 2nd and 3rd Eβf-fed instars were 21.00-fold and 6.39-fold higher, respectively, than that of the control. A comparative transcriptome analysis revealed that multiple differentially expressed genes are involved in insect hormone biosynthesis. An insect hormone assay on the 3rd instars disclosed that Eβf disrupted the balance between the juvenile hormone and ecdysteroid levels. Eβf treatment increased the juvenile hormones titers but not those of the ecdysteroids. The qPCR results were consistent with those of the RNA-Seq. The foregoing findings suggested that Eβf impairs development and survival in C. suppressalis larvae by disrupting their hormone balance. Moreover, Eβf altered the pathways associated with carbohydrate and xenobiotic metabolism as well as those related to cofactors and vitamins in C. suppressalis larvae. The discoveries of this study may contribute to the development and implementation of an integrated control system for C. suppressalis infestations in rice.

Kr-h1, a Cornerstone Gene in Insect Life History

Insect life cycle is coordinated by hormones and their downstream effectors. Krüppel homolog1 (Kr-h1) is one of the crucial effectors which mediates the actions of the two critical hormones of insects, the juvenile hormone (JH) and 20-hydroxyecdysone (20E). It is a transcription factor with a DNA-binding motif of eight C₂H₂ zinc fingers which is found to be conserved among insect orders. The expression of Kr-h1 is fluctuant during insect development with high abundance in juvenile instars and lower levels in the final instar and pupal stage, and reappearance in adults, which is governed by the coordination of JH, 20E, and miRNAs. The dynamic expression pattern of Kr-h1 is closely linked to its function in the entire life of insects. Over the past several years, accumulating studies have advanced our understanding of the role of Kr-h1 during insect development. It acts as a universal antimetamorphic factor in both hemimetabolous and holometabolous species by directly inhibiting the transcription of 20E signaling genes Broad-Complex (Br-C) and Ecdysone induced protein 93F (E93), and steroidogenic enzyme genes involved in ecdysone biosynthesis. Meanwhile, it promotes vitellogenesis and ovarian development in the majority of studied insects. In addition, Kr-h1 regulates insect behavioral plasticity and caste identity, neuronal morphogenesis, maturation of sexual behavior, as well as embryogenesis and metabolic homeostasis. Hence, Kr-h1 acts as a cornerstone regulator in insect life.

WAKE-mediated modulation of cVA perception via a hierarchical neuro-endocrine axis in Drosophila male-male courtship behaviour

The nervous and endocrine systems coordinate with each other to closely influence physiological and behavioural responses in animals. Here we show that WAKE (encoded by wide awake, also known as wake) modulates membrane levels of GABA_A receptor Resistance to Dieldrin (Rdl), in insulin-producing cells of adult male Drosophila melanogaster. This results in changes to secretion of insulin-like peptides which is associated with changes in juvenile hormone biosynthesis in the corpus allatum, which in turn leads to a decrease in 20-hydroxyecdysone levels. A reduction in ecdysone signalling changes neural architecture and lowers the perception of the male-specific sex pheromone 11-cis-vaccenyl acetate by odorant receptor 67d olfactory neurons. These finding explain why WAKE-deficient in Drosophila elicits significant male-male courtship behaviour.

The authors show that the Drosophila master regulator WAKE modulates the secretion of insulin-like peptides, triggering a decrease in 20-hydroxyecdysone levels. This lowers the perception of a male-specific sex pheromone and explains why WAKE-deficient Drosophila flies show male-male courtship behaviour.

The cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function in mosquitoes

This study's aim was to investigate whether the cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function among mosquitoes. BLAST and phylogenetic analysis revealed that three mosquito cecropin Bs, namely Aedes albopictus cecropin B (Aalcec B), Armigeres subalbatus cecropin B2 (Ascec B2), and Culex quinquefasciatus cecropin B1 (Cqcec B1), play crucial roles in cuticle formation during pupal development via the regulation of prophenoloxidase 3 (PPO 3). The effects of cecropin B knockdown were rescued in a cross-species manner by injecting synthetic cecropin B peptide into pupae. Further investigations showed that these three cecropin B peptides bind to TTGG(A/C)A motifs within each of the PPO 3 DNA fragments obtained from these three mosquitoes. These results suggest that Aalcec B, Ascec B2, and Cqcec B1 each play an important role as a transcription factor in cuticle formation and that similar cecropin-prophenoloxidase regulatory mechanisms exist in multiple mosquito species.

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Cecropin B is able to regulate PPO 3 expression in the pupae

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Cecropin B binds to TTGG(A/C)A motifs within the PPO 3 DNA

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The knockdown of cecropin B was rescued by sequence-similar cecropin B peptides

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The cecropin B-prophenoloxidase 3 regulatory mechanism is conserved 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.

Juvenile Hormone Membrane Signaling Enhances its Intracellular Signaling Through Phosphorylation of Met and Hsp83

Juvenile hormone (JH) regulates insect development and reproduction through both intracellular and membrane signaling, and the two pathways might crosstalk with each other. Recent studies have reported that JH membrane signaling induces phosphorylation of the JH intracellular receptor Met, thus enhancing its transcriptional activity. To gain more insights into JH-induced Met phosphorylation, we here performed phosphoproteomics to identify potential phosphorylation sites of Met and its paralog Germ-cell expressed (Gce) in Drosophila Kc cells. In vitro experiments demonstrate that JH-induced phosphorylation sites in the basic helix-loop-helix (bHLH) domain, but not in the Per-Arnt-Sim-B (PAS-B) domain, are required for maximization of Met transcriptional activity. Moreover, phosphoproteomics analysis reveale that JH also induces the phosphorylation of Hsp83, a chaperone protein involved in JH-activated Met nuclear import. The JH-induced Hsp83 phosphorylation at S219 facilitates Hsp83-Met binding, thus promoting Met nuclear import and its transcription. By using proteomics, subcellular distribution, and co-immunoprecipitation approaches, we further characterized 14-3-3 proteins as negative regulators of Met nuclear import through physical interaction with Hsp83. These results show that JH membrane signaling induces phosphorylation of the key components in JH intracellular signaling, such as Met and Hsp83, and consequently facilitating JH intracellular signaling.

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.

FKBP39 Controls the Larval Stage JH Activity and Development in Drosophila melanogaster

Simple Summary

Two endocrine hormones, ecdysone and juvenile hormone (JH), control insect development and reproduction. Some studies in the literature have suggested that FKBP39 functions as a transcriptional factor and regulates the JH pathway in Drosophila. However, the physiological roles of FKBP39 are still elusive. To determine the FKBP39 roles in vivo, we first developed an antibody to check the FKBP39 expression pattern and then detected JH activity-related phenotypes in fkbp39 mutants, such as pupariation, reproduction, and Kr-h1 expression. We found that FKBP39 expresses at a high level and controls JH activity at the larval stage. Moreover, we found that rp49, the most widely used reference gene for Real-time quantitative PCR (qRT-PCR), significantly decreased in the fkbp39 mutant. This work will provide valuable information for studies on JH activity and insect development.

Abstract

FK506-binding protein 39kD (FKBP39) localizes in the nucleus and contains multiple functional domains. Structural analysis suggests that FKBP39 might function as a transcriptional factor and control juvenile hormone (JH) activity. Here, we show that FKBP39 expresses at a high level and localizes in the nucleolus of fat body cells during the first two larval stages and early third larval stage. The fkbp39 mutant displays delayed larval-pupal transition and an increased expression of Kr-h1, the main mediator of the JH pathway, at the early third larval stage. Moreover, the fkbp39 mutant has a fertility defect that is independent of JH activity. Interestingly, the expression of rp49, the most widely used reference gene for qRT-PCR in Drosophila, significantly decreased in the fkbp39 mutant, suggesting that FKBP39 might regulate ribosome assembly. Taken together, our data demonstrate the expression pattern and physiological roles of FKBP39 in Drosophila.

Drosophila Sirtuin 6 mediates developmental diet-dependent programming of adult physiology and survival

Organisms in the wild experience unpredictable and diverse food availability throughout their lifespan. Over-/under-nutrition during development and in adulthood is known to dictate organismal survival and fitness. Studies using model systems have also established long-term effects of developmental dietary alterations on life-history traits. However, the underlining genetic/molecular factors, which differentially couple nutrient inputs during development with fitness later in life are far less understood. Using Drosophila and loss/gain of function perturbations, our serendipitous findings demonstrate an essential role of Sirtuin 6 in regulating larval developmental kinetics, in a nutrient-dependent manner. The absence of Sirt6 affected ecdysone and insulin signalling and led to accelerated larval development. Moreover, varying dietary glucose and yeast during larval stages resulted in enhanced susceptibility to metabolic and oxidative stress in adults. We also demonstrate an evolutionarily conserved role for Sirt6 in regulating physiological homeostasis, physical activity and organismal lifespan, known only in mammals until now. Our results highlight gene-diet interactions that dictate thresholding of nutrient inputs and physiological plasticity, operative across development and adulthood. In summary, besides showing its role in invertebrate ageing, our study also identifies Sirt6 as a key factor that programs macronutrient-dependent life-history traits.

Transcriptomic Alterations in Water Flea (Daphnia magna) following Pravastatin Treatments: Insect Hormone Biosynthesis and Energy Metabolism

Pravastatin, used for lowering cholesterol and further decreasing blood lipid, has been frequently detected in the contaminated freshwaters, whereas its long-term exposure effects on non-target aquatic invertebrates remains undetermined. Therefore, the purpose of this study was to evaluate the toxic effects of pravastatin (PRA) with the concentration gradients (0, 0.5, 50, 5000 μg/L) on a model water flea Daphnia magna (D. magna) over 21 d based on phenotypic and genome-wide transcriptomic analyses. After 21 d, exposure to PRA at 5000 μg/L significantly reduced the body length and increased the number of offspring. The 76, 167, and 499 differentially expressed genes (DEGs) were identified by using absolute log2 fold change < 1 and adj p < 0.05 as a cutoff in the 0.5, 50, and 5000 μg/L PRA treatment groups, respectively. Three pathways, including xenobiotic metabolism, insect hormone biosynthesis pathway, and energy metabolism were significantly (p < 0.05) enriched after exposure to PRA. These suggested that the upregulation of genes in insect biosynthetic hormone pathway increased the juvenile hormone III content, which further reduced the body length of D. magna. The positive effect of methyl farnesoate synthesis on the ovarian may result in the increased number of offspring. Furthermore, energy tended to be allocated to detoxification process and survival under stress conditions, as the amount of energy that an individual can invest in maintenance and growth is limited. Taken together, our results unraveled the toxic mechanism of cardiovascular and lipid pharmaceuticals in aquatic invertebrate.

Juvenile Hormone Studies in Drosophila melanogaster

In the field of insect endocrinology, juvenile hormone (JH) is one of the most wondrous entomological terms. As a unique sesquiterpenoid hormone produced and released by the endocrine gland, corpus allatum (CA), JH is a critical regulator in multiple developmental and physiological processes, such as metamorphosis, reproduction, and behavior. Benefited from the precise genetic interventions and simplicity, the fruit fly, Drosophila melanogaster, is an indispensable model in JH studies. This review is aimed to present the regulatory factors on JH biosynthesis and an overview of the regulatory roles of JH in Drosophila. The future directions of JH studies are also discussed, and a few hot spots are highlighted.

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.

Improving Polysaccharide-Based Chitin/Chitosan-Aerogel Materials by Learning from Genetics and Molecular Biology

Improved wound healing of burnt skin and skin lesions, as well as medical implants and replacement products, requires the support of synthetical matrices. Yet, producing synthetic biocompatible matrices that exhibit specialized flexibility, stability, and biodegradability is challenging. Synthetic chitin/chitosan matrices may provide the desired advantages for producing specialized grafts but must be modified to improve their properties. Synthetic chitin/chitosan hydrogel and aerogel techniques provide the advantages for improvement with a bioinspired view adapted from the natural molecular toolbox. To this end, animal genetics provide deep knowledge into which molecular key factors decisively influence the properties of natural chitin matrices. The genetically identified proteins and enzymes control chitin matrix assembly, architecture, and degradation. Combining synthetic chitin matrices with critical biological factors may point to the future direction with engineering materials of specific properties for biomedical applications such as burned skin or skin blistering and extensive lesions due to genetic diseases.

Transcriptomic analysis of Bombyx mori corpora allata with comparison to prothoracic glands in the final instar larvae

The corpus allatum (CA) is an endocrine organ of insects that synthesizes juvenile hormone (JH). Yet little is known regarding the global gene expression profile for the CA, although JH signaling pathway has been well-studied in insects. Here, we report the availability of the transcriptome resource of the isolated CA from the final (fifth) instar larvae of the silkworm, Bombyx mori when the JH titer is low. We also compare it with prothoracic gland (PG) that produces the precursor of 20-hydroxyecdysone (20E), to find some common features in the JH and 20E related genes between the two organs. A total of 17,262 genes were generated using a combination of genome-guided assembly and annotation, in which 10,878 unigenes were enriched in 58 Gene Ontology terms, representing almost all expressed genes in the CA of the 5th instar larvae of B. mori. Transcriptome analysis confirmed that gene for Torso, the receptor of prothoracicotropic hormone (PTTH), is present in the PG but not in the CA. Transcriptome comparison and quantitative real time-PCR indicated that 11 genes related to JH biosynthesis and regulation and six genes for 20E are expressed in both the CA and PG, suggesting that the two organs may cross talk with each other through these genes. The temporal expression profiles of the two genes for the multifunctional neurohormonal factor sericotropin precursor and the uncharacterized protein LOC114249572, the most abundant in the CA and PG transcriptomes respectively, suggested that they might play important roles in the JH and 20E biosynthesis. The present work provides new insights into the CA and PG.

Molecular biomarkers as tool for early warning by chlorpyrifos exposure on Alpine chironomids

Pesticides used in agriculture can be transported at a medium-high distance due to the drift effect, reaching even remote areas as mountain regions, glaciers, and snow cover. With the melting process, pesticides enter freshwater glacier ecosystems, becoming a threat to wildlife fauna, mainly dominated by Diptera Chironomidae. Chlorpyrifos (CPF), as one of the most commonly used pesticides in alpine vineyards and apple orchards, is frequently detected in icemelt waters. We selected as target species, larvae of the cold stenothermal chironomid Diamesa zernyi, collected in two glacier-fed streams (Presena and Amola) in the Italian Alps. Firstly, a de novo transcriptome was obtained, and secondly, a gene array was designed to study the molecular response of a wild population of D. zernyi exposed to three sub-lethal CPF concentrations corresponding to 1/100 LC10 (0.011 μg/L), 1/10 LC10 (0.11 μg/L), and LC10 (1.1 μg/L), for 24 h. The sub-organismal response was evaluated by Real-Time Polymerase Chain Reaction (RT-PCR), employing 40 genes related to essential metabolic routes as future candidates for biomarkers in wildlife chironomids. After 24 h, the endocrine system (E75, E93, EcR, and Met), detoxification response (GSTO3, GSTS1), and stress response (hsp75, hsp83, HYOU1) were altered. CPF seems to act as an endocrine disruptor and could lead to defective larval development, disrupted cellular homeostasis through heat shock proteins (HSPs) alteration (defective protein folding and mitochondrial functions), as well as oxidative damage (confirmed by increased GST expression). For the first time, molecular studies detected early alarm signals in wildlife in glacier environments. Our findings confirm the high environmental risk of CPF affecting aquatic insect metabolism and raise the level of concern about this pesticide in high altitude water bodies, generally considered pristine. Furthermore, this study emphasizes the incipient need to use non-model organisms for the evaluation of natural ecosystems. We also highlight the demand for research into new molecular biomarkers, and the importance of including molecular approaches in toxicology evaluations to detect the early adverse effects of pollutants.

The steroid-induced microRNA let-7 regulates developmental growth by targeting cdc7 in the Drosophila fat body

In insects, 20-hydroxyecdysone (20E) limits systemic growth by triggering developmental transitions. Previous studies have shown that 20E-induced let-7 exhibits crosstalk with the cell cycle. Here, we examined the underlying molecular mechanisms and physiological functions of 20E-induced let-7 in the fat body, an organ for energy storage and nutrient mobilization which plays a critical role in the larval growth. First, the overexpression of let-7 decreased the body size and led to the reduction of both nucleolus and cell sizes in the larval fat body. In contrast, the overexpression of let-7-Sponge increased the nucleolus and cell sizes. Moreover, we found that cdc7, encoding a conserved protein kinase that controls the endocycle, is a target of let-7. Notably, the mutation of cdc7 in the fat body resulted in growth defects. Overall, our findings revealed a novel role of let-7 in the control of endoreduplication-related growth during larval-prepupal transition in Drosophila.

Intrinsic and damage-induced JAK/STAT signaling regulate developmental timing by the Drosophila prothoracic gland

Development involves tightly paced, reproducible sequences of events, yet it must adjust to conditions external to it, such as resource availability and organismal damage. A major mediator of damage-induced immune responses in vertebrates and insects is JAK/STAT signaling. At the same time, JAK/STAT activation by the Drosophila Upd cytokines is pleiotropically involved in normal development of multiple organs. Whether inflammatory and developmental JAK/STAT roles intersect is unknown. Here, we show that JAK/STAT is active during development of the prothoracic gland (PG), which controls metamorphosis onset through ecdysone production. Reducing JAK/STAT signaling decreased PG size and advanced metamorphosis. Conversely, JAK/STAT hyperactivation by overexpression of pathway components or SUMOylation loss caused PG hypertrophy and metamorphosis delay. Tissue damage and tumors, known to secrete Upd cytokines, also activated JAK/STAT in the PG and delayed metamorphosis, at least in part by inducing expression of the JAK/STAT target Apontic. JAK/STAT damage signaling, therefore, regulates metamorphosis onset by co-opting its developmental role in the PG. Our findings in Drosophila provide insights on how systemic effects of damage and cancer can interfere with hormonally controlled development and developmental transitions.

Summary: Damage signaling from tumors mediated by JAK/STAT-activating Upd cytokines delays the Drosophila larva–pupa transition through co-option of a JAK/STAT developmental role in the prothoracic gland.

Juvenile hormone signaling promotes ovulation and maintains egg shape by inducing expression of extracellular matrix genes

It is well documented that the juvenile hormone (JH) can function as a gonadotropic hormone that stimulates vitellogenesis by activating the production and uptake of vitellogenin in insects. Here, we describe a phenotype associated with mutations in the Drosophila JH receptor genes, Met and Gce: the accumulation of mature eggs with reduced egg length in the ovary. JH signaling is mainly activated in ovarian muscle cells and induces laminin gene expression in these cells. Meanwhile, JH signaling induces collagen IV gene expression in the adult fat body, from which collagen IV is secreted and deposited onto the ovarian muscles. Laminin locally and collagen IV remotely contribute to the assembly of ovarian muscle extracellular matrix (ECM); moreover, the ECM components are indispensable for ovarian muscle contraction. Furthermore, ovarian muscle contraction externally generates a mechanical force to promote ovulation and maintain egg shape. This work reveals an important mechanism for JH-regulated insect reproduction.

Tramtrack acts during late pupal development to direct ant caste identity

A key question in the rising field of neuroepigenetics is how behavioral plasticity is established and maintained in the developing CNS of multicellular organisms. Behavior is controlled through systemic changes in hormonal signaling, cell-specific regulation of gene expression, and changes in neuronal connections in the nervous system, however the link between these pathways is unclear. In the ant Camponotus floridanus, the epigenetic corepressor CoREST is a central player in experimentally-induced reprogramming of caste-specific behavior, from soldier (Major worker) to forager (Minor worker). Here, we show this pathway is engaged naturally on a large genomic scale during late pupal development targeting multiple genes differentially expressed between castes, and central to this mechanism is the protein tramtrack (ttk), a DNA binding partner of CoREST. Caste-specific differences in DNA binding of ttk co-binding with CoREST correlate with caste-biased gene expression both in the late pupal stage and immediately after eclosion. However, we find a unique set of exclusive Minor-bound genes that show ttk pre-binding in the late pupal stage preceding CoREST binding, followed by caste-specific gene repression on the first day of eclosion. In addition, we show that ttk binding correlates with neurogenic Notch signaling, and that specific ttk binding between castes is enriched for regulatory sites associated with hormonal function. Overall our findings elucidate a pathway of transcription factor binding leading to a repressive epigenetic axis that lies at the crux of development and hormonal signaling to define worker caste identity in C. floridanus.

Role of juvenile hormone receptor Methoprene-tolerant 1 in silkworm larval brain development and domestication

The insect brain is the central part of the neurosecretory system, which controls morphology, physiology, and behavior during the insect's lifecycle. Lepidoptera are holometabolous insects, and their brains develop during the larval period and metamorphosis into the adult form. As the only fully domesticated insect, the Lepidoptera silkworm Bombyx mori experienced changes in larval brain morphology and certain behaviors during the domestication process. Hormonal regulation in insects is a key factor in multiple processes. However, how juvenile hormone (JH) signals regulate brain development in Lepidoptera species, especially in the larval stage, remains elusive. We recently identified the JH receptor Methoprene tolerant 1 ( Met1) as a putative domestication gene. How artificial selection on Met1 impacts brain and behavioral domestication is another important issue addressing Darwin's theory on domestication. Here, CRISPR/Cas9-mediated knockout of Bombyx Met1 caused developmental retardation in the brain, unlike precocious pupation of the cuticle. At the whole transcriptome level, the ecdysteroid (20-hydroxyecdysone, 20E) signaling and downstream pathways were overactivated in the mutant cuticle but not in the brain. Pathways related to cell proliferation and specialization processes, such as extracellular matrix (ECM)-receptor interaction and tyrosine metabolism pathways, were suppressed in the brain. Molecular evolutionary analysis and in vitro assay identified an amino acid replacement located in a novel motif under positive selection in B. mori, which decreased transcriptional binding activity. The B. mori MET1 protein showed a changed structure and dynamic features, as well as a weakened co-expression gene network, compared with B. mandarina. Based on comparative transcriptomic analyses, we proposed a pathway downstream of JH signaling (i.e., tyrosine metabolism pathway) that likely contributed to silkworm larval brain development and domestication and highlighted the importance of the biogenic amine system in larval evolution during silkworm domestication.

Involvement of Cis-Acting Elements in Molecular Regulation of JH-Mediated Vitellogenin Gene 2 of Female Periplaneta americana

Vitellogenins (Vgs) are yolk protein precursors that are regulated by juvenile hormone (JH) and/or 20-hydroxyecdysone (20E) in insects. JH acts as the principal gonadotropin that stimulates vitellogenesis in hemimetabolous insects. In this study, we cloned and characterized the Periplaneta americana Vitellogenin 2 (Vg2) promoter. Multiple sites for putative transcription factor binding were predicted for the 1,804 bp Vg2 promoter region, such as the Broad-Complex, ecdysone response element (EcRE), GATA, Hairy, JH response element (JHRE), and Methoprene (Met)-binding motif, among others. Luciferase reporter assay has identified that construct -177 bp is enough to support JH III induction but not 20E suppression. This 38 bp region (from -177 to -139 bp) contains two conserved response element half-sites separated by 2 nucleotides spacer (DR2) and is designated as Vg2RE (^-168GAGTCACGGAGTCGCCGCTG^-149). Mutation assay and luciferase assay data using mutated constructs verified the crucial role of G residues in Vg2RE for binding the isolated fat body nuclear protein. In Sf9 cells, a luciferase reporter placed under the control of a minimal promoter containing Vg2RE was induced by JH III in a dose- and time-dependent manner. Nuclear proteins isolated from previtellogenic female fat body cells bound to Vg2RE, and this binding was outcompeted by a 50-fold excess of cold Drosophila melanogaster DR4 and Galleria mellonella JH binding protein response elements (Chorion factor-I/Ultraspiracle). Affinity pull-down experiment with nuclear extracts of previtellogenic female fat body, using 31-bp probe Vg2RE as bait, yielded a 71 kDa candidate nuclear protein that may mediate the regulatory action of the JH III.

The effects of cadmium on the development of Drosophila and its transgenerational inheritance effects

A new focus in toxicology research is the impact of parental exposure to environmental toxic substances on the characteristics of offspring. In the present study, newly produced eggs of Drosophila melanogaster were treated with different concentrations of cadmium (0, 1, 2, 4, 8 mg/kg) to study the effects of development. The results showed that cadmium changed the larval body length and weight, prolonged the pupation and eclosion time, and changed the relative expression levels of development-related genes (baz, β-Tub60D, tj). Furthermore, the parental Drosophila (F₀) were treated with cadmium (4.5 mg/kg) from egg stage, and when grows to adults, they mated in standard medium to produce the de-stressed offspring (F₁-F₄) to assess the transgenerational effects of developmental delay. The results showed that the delayed effects of the pupation and eclosion time could be maintained for two generations, and the inhibiting effects of juvenile hormone (JH) and ecdysone (20-hydroxyecdysone, 20E) could be maintained for two or three generations. More importantly, cadmium increased the expression of DNA methylation-related genes (dDnmt2, dMBD2/3) in the ovaries (F₀-F₂) and testicles (F₀ and F₁). In addition, cadmium accumulated in parental Drosophila (F₀) was not transmitted to offspring through reproductive pathway. These results demonstrate that the developmental toxicity caused by cadmium could be transmitted to the de-stressed offspring, and the observed transgenerational inheritance effects may be associated with epigenetic regulation, underscoring the need to consider fitness of future generations in evaluating the toxicity and environmental risks of cadmium.

MicroRNA miR-8 promotes cell growth of corpus allatum and juvenile hormone biosynthesis independent of insulin/IGF signaling in Drosophila melanogaster

The Drosophila melanogaster corpus allatum (CA) produces and releases three types of sesquiterpenoid hormones, including juvenile hormone III bisepoxide (JHB3), juvenile hormone III (JH III), and methyl farnesoate (MF). JH biosynthesis involves multiple discrete enzymatic reactions and is subjected to a comprehensive regulatory network including microRNAs (miRNAs). Using a high throughput sequencing approach, we have identified abundant miRNAs in the D. melanogaster ring gland, which consists of the CA, prothoracic gland, and corpus cardiaca. Genetic and qPCR screens were then performed in an attempt to uncover the full repertoire of CA miRNAs that are involved in regulating metamorphosis. miR-8 was identified as a potential candidate and further studied for its role in the CA. Overexpression of miR-8 in the CA increased cell size of the gland and expression of Jhamt (a gene coding for a key regulatory enzyme in JH biosynthesis), resulting in pupal lethality. By contrast, sponge-mediated reduction of miR-8 in the CA decreased cell size and Jhamt expression, but did not cause lethality. Further investigation revealed that miR-8 promotes cell growth independent of insulin/IGF signaling. Taken together, these experiments show that miR-8 is highly expressed in the CA and exerts its positive effects on cell growth and JH biosynthesis. The miRNAs data in the ring gland also provide a useful resource to study how miRNAs collaboratively regulate hormone synthesis in D. melanogaster.

Histone H3K27 methylation-mediated repression of Hairy regulates insect developmental transition by modulating ecdysone biosynthesis

Insect development is cooperatively orchestrated by the steroid hormone ecdysone and juvenile hormone (JH). The polycomb repressive complex 2 (PRC2)-mediated histone H3K27 trimethylation (H3K27me3) epigenetically silences gene transcription and is essential for a range of biological processes, but the functions of H3K27 methylation in insect hormone action are poorly understood. Here, we demonstrate that H3K27 methylation-mediated repression of Hairy transcription in the larval prothoracic gland (PG) is required for ecdysone biosynthesis in Bombyx and Drosophila H3K27me3 levels in the PG are dynamically increased during the last larval instar. H3K27me3 reduction induced by the down-regulation of PRC2 activity via inhibitor treatment in Bombyx or PG-specific knockdown of the PRC2 component Su(z)12 in Drosophila diminishes ecdysone biosynthesis and disturbs the larval-pupal transition. Mechanistically, H3K27 methylation targets the JH signal transducer Hairy to repress its transcription in the PG; PG-specific knockdown or overexpression of the Hairy gene disrupts ecdysone biosynthesis and developmental transition; and developmental defects caused by PG-specific Su(z)12 knockdown can be partially rescued by Hairy down-regulation. The application of JH mimic to the PG decreases both H3K27me3 levels and Su(z)12 expression. Altogether, our study reveals that PRC2-mediated H3K27 methylation at Hairy in the PG during the larval period is required for ecdysone biosynthesis and the larval-pupal transition and provides insights into epigenetic regulation of the crosstalk between JH and ecdysone during insect development.

Transcriptome Analysis of Hormone-and Cuticle-Related Genes in the Development Process of Deutonymph in Tetranychus urticae

Tetranychus urticae is an important agricultural pest that feeds on more than 1100 plant species. To investigate gene expression network in development process of deutonymph, a comprehensive transcriptome analysis of different developmental time points of deutonymph in T. urticae was performed. Comparing with expression profile of 7 h, 309, 876, 2736, and 3432 differential expression genes were detected at time points 14 h, 21 h, 28 h, and 35 h, respectively. The expression dynamic analysis indicated that genes in hormone- (ecdysteroid and juvenile hormone) and cuticle- (chitin and cuticle proteins) related pathways were indispensable for development process in deutonymph. Among hormone related pathway genes, the ecdysteroid biosynthesis pathway genes were highly expressed at the growth period of development process, which is opposite to the expression patterns of juvenile hormone biosynthesis pathway genes. For cuticle related pathway genes, 13 chitinase genes were identified in the genome of T. urticae, and 8 chitinase genes were highly expressed in different time points of developmental process in the deutonymph of T. urticae. Additionally, 59 cuticle protein genes were identified from genome, and most of the cuticle protein genes were expressed in the molting period of developmental process in deutonymph. This study reveals critical genes involved in the development process of deutonymph and also provides comprehensive development transcriptome information for finding more molecular targets to control this pest.

Function and Evolution of Nuclear Receptors in Environmental-Dependent Postembryonic Development

Nuclear receptors (NRs) fulfill key roles in the coordination of postembryonal developmental transitions in animal species. They control the metamorphosis and sexual maturation in virtually all animals and by that the two main environmental-dependent developmental decision points. Sexual maturation and metamorphosis are controlled by steroid receptors and thyroid receptors, respectively in vertebrates, while both processes are orchestrated by the ecdysone receptor (EcR) in insects. The regulation of these processes depends on environmental factors like nutrition, temperature, or photoperiods and by that NRs form evolutionary conserved mediators of phenotypic plasticity. While the mechanism of action for metamorphosis and sexual maturation are well studied in model organisms, the evolution of these systems is not entirely understood and requires further investigation. We here review the current knowledge of NR involvement in metamorphosis and sexual maturation across the animal tree of life with special attention to environmental integration and evolution of the signaling mechanism. Furthermore, we compare commonalities and differences of the different signaling systems. Finally, we identify key gaps in our knowledge of NR evolution, which, if sufficiently investigated, would lead to an importantly improved understanding of the evolution of complex signaling systems, the evolution of life history decision points, and, ultimately, speciation events in the metazoan kingdom.

Persistent pesticides: effects of endosulfan at the molecular level on the aquatic invertebrate Chironomus riparius

Although banned in multiple areas, due to its persistence in the environment, endosulfan constitutes a significant environmental concern. In this work, fourth instar Chironomus riparius larvae were exposed at environmentally relevant endosulfan concentrations of 0.1, 1, and 10 μg/L for 24 h to analyze the possible effects of this acaricide on gene expression and enzymatic activity. Transcriptional changes were studied through the implementation of a real-time polymerase chain reaction array with 42 genes related to several metabolic pathways (endocrine system, detoxification response, stress response, DNA reparation, and immune system). Moreover, glutathione-S-transferase (GST), phenoloxidase (PO), and acetylcholinesterase (AChE) activities were assessed. The five pathways were differentially altered by endosulfan exposure with significant changes in the E93, Dis, MAPR, Met, InR, GSTd3, GSTt3, MRP1, hsp70, hsp40, hsp24, ATM, PARP, Proph, and Def genes. Besides, all of the measured enzymatic activities were modified, with increased activity of GST, followed by PO and AChE. In summary, the results reflected the effects provoked in C. riparius at molecular level despite the absence of lethality. These data raise concerns about the strong alteration on different metabolic routes despite the low concentrations used. Therefore, new risk assessment strategies should consider include the effects at the sub-organismal level as endpoints in addition to the classical ecologically relevant parameters (such as survival). This endeavor will facilitate a comprehensive evaluation of toxicants in the environment.

Anopheles coluzzii stearoyl-CoA desaturase is essential for adult female survival and reproduction upon blood feeding

Vitellogenesis and oocyte maturation require anautogenous female Anopheles mosquitoes to obtain a bloodmeal from a vertebrate host. The bloodmeal is rich in proteins that are readily broken down into amino acids in the midgut lumen and absorbed by the midgut epithelial cells where they are converted into lipids and then transported to other tissues including ovaries. The stearoyl-CoA desaturase (SCD) plays a pivotal role in this process by converting saturated (SFAs) to unsaturated (UFAs) fatty acids; the latter being essential for maintaining cell membrane fluidity amongst other housekeeping functions. Here, we report the functional and phenotypic characterization of SCD1 in the malaria vector mosquito Anopheles coluzzii. We show that RNA interference (RNAi) silencing of SCD1 and administration of sterculic acid (SA), a small molecule inhibitor of SCD1, significantly impact on the survival and reproduction of female mosquitoes following blood feeding. Microscopic observations reveal that the mosquito thorax is quickly filled with blood, a phenomenon likely caused by the collapse of midgut epithelial cell membranes, and that epithelial cells are depleted of lipid droplets and oocytes fail to mature. Transcriptional profiling shows that genes involved in protein, lipid and carbohydrate metabolism and immunity-related genes are the most affected by SCD1 knock down (KD) in blood-fed mosquitoes. Metabolic profiling reveals that these mosquitoes exhibit increased amounts of saturated fatty acids and TCA cycle intermediates, highlighting the biochemical framework by which the SCD1 KD phenotype manifests as a result of a detrimental metabolic syndrome. Accumulation of SFAs is also the likely cause of the potent immune response observed in the absence of infection, which resembles an auto-inflammatory condition. These data provide insights into mosquito bloodmeal metabolism and lipid homeostasis and could inform efforts to develop novel interventions against mosquito-borne diseases.

Female mosquitoes can become infected with malaria parasites upon ingestion of blood from an infected person and can transmit the disease when they bite another person some days later. The bloodmeal is rich in proteins which female mosquitoes use to develop their eggs after converting them first to saturated and then to unsaturated fatty acids inside their gut cells. Here, we present the characterization of the enzyme that mosquitoes use to convert saturated to unsaturated fatty acids and show that when this enzyme is eliminated or inhibited mosquitoes cannot produce eggs and die soon after they feed on blood. The mosquito death appears to be primarily associated with the collapse of their gut epithelial barrier due to the loss of cell membrane integrity, leading to their inner body cavity being filled with the ingested blood. These mosquitoes also suffer from an acute and detrimental auto-inflammatory condition due to mounting of a potent immune response in the absence of any infection. We conclude that this enzyme and the mechanism of converting blood-derived proteins to unsaturated fatty acids as a whole can be a good target of interventions aiming at limiting the mosquito abundance and blocking malaria transmission.

Genome and transcriptome analysis of the mealybug Maconellicoccus hirsutus: Correlation with its unique phenotypes

Mealybugs are aggressive pests with world-wide distribution and are suitable for the study of different phenomena like genomic imprinting and epigenetics. Genomic approaches facilitate these studies in absence of robust genetics in this system. We sequenced, de novo assembled, annotated Maconellicoccus hirsutus genome. We carried out comparative genomics it with four mealybug and eight other insect species, to identify expanded, specific and contracted gene classes that relate to pesticide and desiccation resistance. We identified horizontally transferred genes adding to the mutualism between the mealybug and its endosymbionts. Male and female transcriptome analysis indicates differential expression of metabolic pathway genes correlating with their physiology and the genes for sexual dimorphism. The significantly lower expression of endosymbiont genes in males relates to the depletion of endosymbionts in males during development.

Susceptibility of South Texas Aedes aegypti to Pyriproxyfen

Simple Summary

We evaluated the susceptibility of an Ae. aegypti strain from the Lower Rio Grande Valley (LRGV) of South Texas to the insect growth regulator pyriproxyfen. We observed a difference in the inhibition of emergence to the lowest doses of pyriproxyfen tested between our field strain and a susceptible strain. However, the doses used are 10 times lower from the recommended application of <50 ppb for vector control programs. Our results suggest that pyriproxyfen should be an effective active ingredient in the LRGV to help reduce Ae. aegypti populations in the LRGV.

Abstract

An integral part to integrated mosquito management is to ensure chemical products used for area-wide control are effective against a susceptible population of mosquitoes. Prior to conducting an intervention trial using an insect growth regulator, pyriproxyfen, in South Texas to control Aedes aegypti, we conducted a larval bioassay to evaluate baseline levels of susceptibility. We used seven serially-diluted doses ranging from 2.5 ppb to 6.3 × 10⁻⁴ ppb. We observed 100% inhibition emergence (IE) at even the lowest dose of 6.3 × 10⁻⁴ ppb in our susceptible reference colony of Ae. aegypti Liverpool. In our field strain of Ae. aegypti (F5 colonized from South Texas) we observed 79.8% IE at 6.3 × 10⁻⁴ ppb, 17.7% IE at 1.25 × 10⁻³ ppb, 98.7% IE at 1.25 × 10⁻² ppb, and 100% emergence inhibition for the remainder of the doses. Given that commercial pyriproxyfen products are labeled for doses ranging to 50 ppb, we conclude that the field population sampled by this study are susceptible to this insect growth regulator.

Methoxyfenozide, a Molting Hormone Agonist, Affects Autogeny Capacity, Oviposition, Fecundity, and Fertility in Culex pipiens (Diptera: Culicidae)

The current study aimed to evaluate the effects of methoxyfenozide (RH-2485), an insect growth disrupter (IGD) belonging to molting hormone agonist class, against female adults of Culex pipiens L. under laboratory conditions. Lethal concentrations (LC50 = 24.54 µg/liter and LC90 = 70.79 µg/liter), previously determined against fourth instar larvae, were tested for adult female fertility, fecundity and oviposition after tarsal contact before mating and any bloodmeal. Methoxyfenozide was found to alter negatively their autogeny capacity and oviposition. A strong reduction of 56% and 72% (P < 0.001) in females' autogeny capacity was observed in both treated series, respectively. Alteration in oviposition were found to be higher with LC90 (OAI-LC90 = -0.62) than with the LC50 (OAI-LC50 = -0.42). Also fecundity and hatching rate (fertility) were significantly reduced in treated series as compared to controls. A significant reduction of 37.65 and 28.23% in fecundity and decrease of 56.85 and 71.87% in fertility were found, respectively in LC50 and LC90 treated series. Obtained data clearly demonstrated that methoxyfenozide have significant depressive effect on reproductive potential against medically important vector with minimizing ecotoxicological risks in mosquitoes management.

Autophagy triggers CTSD (cathepsin D) maturation and localization inside cells to promote apoptosis

CTSD/CathD/CATD (cathepsin D) is a lysosomal aspartic protease. A distinguishing characteristic of CTSD is its dual functions of promoting cell proliferation via secreting a pro-enzyme outside the cells as a ligand, and promoting apoptosis via the mature form of this enzyme inside cells; however, the regulation of its secretion, expression, and maturation is undetermined. Using the lepidopteran insect Helicoverpa armigera, a serious agricultural pest, as a model, we revealed the dual functions and regulatory mechanisms of CTSD secretion, expression, and maturation. Glycosylation of asparagine 233 (N233) determined pro-CTSD secretion. The steroid hormone 20-hydroxyecdysone (20E) promoted CTSD expression. Macroautophagy/autophagy triggered CTSD maturation and localization inside midgut cells to activate CASP3 (caspase 3) and promote apoptosis. Pro-CTSD was expressed in the pupal epidermis and was secreted into the hemolymph to promote adult fat body endoreplication/endoreduplication, cell proliferation, and association. Our study revealed that the differential expression and autophagy-mediated maturation of CTSD in tissues determine its roles in apoptosis and cell proliferation, thereby determining the cell fates of tissues during lepidopteran metamorphosis.Abbreviations: 20E: 20-hydroxyecdysone; 3-MA: 3-methyladenine; ACTB/β-actin: actin beta; AKT: protein kinase B; ATG1: autophagy-related 1; ATG4: autophagy-related 4; ATG5: autophagy-related 5; ATG7: autophagy-related 7; ATG14: autophagy-related 14; BSA: bovine serum albumin; CASP3: caspase 3; CQ: choroquine; CTSD: cathepsin D; DAPI: 4',6-diamidino-2-phenylindole; DMSO: dimethyl sulfoxide; DPBS: dulbecco's phosphate-buffered saline; DsRNA: double-stranded RNA; EcR: ecdysone receptor; EcRE: ecdysone response element; EdU: 5-ethynyl-2´-deoxyuridine; G-m-CTSD: glycosylated-mautre-CTSD; G-pro-CTSD: glycosylated-pro-CTSD; HaEpi: Helicoverpa armigera epidermal cell line; HE staining: hematoxylin and eosin staining; IgG: immunoglobin G; IM: imaginal midgut; JH: juvenile hormone; Kr-h1: krueppel homologous protein 1; LM: larval midgut; M6P: mannose-6-phosphate; PBS: phosphate-buffered saline; PCD: programmed cell death; PNGase: peptide-N-glycosidase F; RFP: red fluorescent protein; RNAi: RNA interference; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SYX17: syntaxin 17; USP1: ultraspiracle isoform 1.

Involvement of Methoprene-tolerant and Krüppel homolog 1 in juvenile hormone-signaling regulating the maturation of male accessory glands in the moth Agrotis ipsilon

Male accessory glands (MAGs) produce seminal fluid proteins that are essential for the fertility and also influence the reproductive physiology and behavior of mated females. In many insect species, and especially in the moth Agrotis ipsilon, juvenile hormone (JH) promotes the maturation of the MAGs but the underlying molecular mechanisms in this hormonal regulation are not yet well identified. Here, we examined the role of the JH receptor, Methoprene-tolerant (Met) and the JH-inducible transcription factor, Krüppel homolog 1 (Kr-h1) in transmitting the JH signal that upregulates the growth and synthetic activity of the MAGs in A. ipsilon. We cloned two full length cDNAs encoding Met1 and Met2 which are co-expressed with Kr-h1 in the MAGs where their expression levels increase with age in parallel with the length and protein content of the MAGs. RNAi-mediated knockdown of either Met1, Met2, or Kr-h1 resulted in reduced MAG length and protein amount. Moreover, injection of JH-II into newly emerged adult males induced the transcription of Met1, Met2 and Kr-h1 associated to an increase in the length and protein content of the MAGs. By contrast, JH deficiency decreased Met1, Met2 and Kr-h1 mRNA levels as well as the length and protein reserves of the MAGs of allatectomized old males and these declines were partly compensated by a combined injection of JH-II in operated males. Taken together, our results highlighted an involvement of the JH-Met-Kr-h1 signaling pathway in the development and secretory activity of the MAGs in A. ipsilon.

20E-mediated regulation of BmKr-h1 by BmKRP promotes oocyte maturation

BACKGROUND

Krüppel homolog 1 (Kr-h1) is a critical transcription factor for juvenile hormone (JH) signaling, known to play a key role in regulating metamorphosis and adult reproduction in insects. Kr-h1 can also be induced by molting hormone 20-hydroxyecdysone (20E), however, the underlying mechanism of 20E-induced Kr-h1 expression remains unclear. In the present study, we investigated the molecular mechanism of Kr-h1 induction by 20E in the reproductive system of a model lepidopteran insect, Bombyx mori.

RESULTS

Developmental and tissue-specific expression analysis revealed that BmKr-h1 was highly expressed in ovaries during the late pupal and adult stages and the expression was induced by 20E. RNA interference (RNAi)-mediated depletion of BmKr-h1 in female pupae severely repressed the transcription of vitellogenin receptor (VgR), resulting in the reduction in vitellogenin (Vg) deposition in oocytes. BmKr-h1 specifically bound the Kr-h1 binding site (KBS) between - 2818 and - 2805 nt upstream of BmVgR and enhanced the transcription of BmVgR. A 20E cis-regulatory element (CRE) was identified in the promoter of BmKr-h1 and functionally verified using luciferase reporter assay, EMSA and DNA-ChIP. Using pull-down assays, we identified a novel transcription factor B. mori Kr-h1 regulatory protein (BmKRP) that specifically bound the BmKr-h1 CRE and activated its transcription. CRISPR/Cas9-mediated knockout of BmKRP in female pupae suppressed the transcription of BmKr-h1 and BmVgR, resulting in arrested oogenesis.

CONCLUSION

We identified BmKRP as a new transcription factor mediating 20E regulation of B. mori oogenesis. Our data suggests that induction of BmKRP by 20E regulates BmKr-h1 expression, which in turn induces BmVgR expression to facilitate Vg uptake and oogenesis.

Integrating animal development: How hormones and metabolism regulate developmental transitions and brain formation

Our current knowledge on how individual tissues or organs are formed during animal development is considerable. However, the development of each organ does not occur in isolation and thus their formation needs to be done in a coordinated manner. This coordination is regulated by hormones, systemic signals that instruct the simultaneous development of all organs and direct tissue specific developmental programs. In addition, multi- and individual-organ development requires the integration of the nutritional state of the animal, since this affects nutrient availability necessary for the progression of development and growth. Variations in the nutritional state of the animal are normal during development, as the sources and access to nutrients greatly differ depending on the animal stage. Furthermore, adversities of the external environment also exert major alterations in extrinsic nutritional conditions. Thus, both in normal and malnutrition circumstances, the animal needs to trigger metabolic changes to maintain energy homeostasis and sustain growth and development. This metabolic flexibility is mediated by hormones, that drive both developmental encoded metabolic transitions throughout development and adaptation responses according to the nutritional state of the animal. This review aims to provide a comprehensive summary of the current knowledge of how endocrine regulation coordinates multi-organ development by orchestrating metabolic transitions and how it integrates metabolic adaptation responses to starvation. We also focus on the particular case of brain development, as it is extremely sensitive to hormonally induced metabolic changes. Finally, we discuss how brain development is prioritized over the development of other organs, as its growth can be spared from nutrient deprivation.

Steroid hormone ecdysone deficiency stimulates preparation for photoperiodic reproductive diapause

Diapause, a programmed developmental arrest primarily induced by seasonal environmental changes, is very common in the animal kingdom, and found in vertebrates and invertebrates alike. Diapause provides an adaptive advantage to animals, as it increases the odds of surviving adverse conditions. In insects, individuals perceive photoperiodic cues and modify endocrine signaling to direct reproductive diapause traits, such as ovary arrest and increased fat accumulation. However, it remains unclear as to which endocrine factors are involved in this process and how they regulate the onset of reproductive diapause. Here, we found that the long day-mediated drop in the concentration of the steroid hormone ecdysone is essential for the preparation of photoperiodic reproductive diapause in Colaphellus bowringi, an economically important cabbage beetle. The diapause-inducing long-day condition reduced the expression of ecdysone biosynthetic genes, explaining the drop in the titer of 20-hydroxyecdysone (20E, the active form of ecdysone) in female adults. Application of exogenous 20E induced vitellogenesis and ovarian development but reduced fat accumulation in the diapause-destined females. Knocking down the ecdysone receptor (EcR) in females destined for reproduction blocked reproductive development and induced diapause traits. RNA-seq and hormone measurements indicated that 20E stimulates the production of juvenile hormone (JH), a key endocrine factor in reproductive diapause. To verify this, we depleted three ecdysone biosynthetic enzymes via RNAi, which confirmed that 20E is critical for JH biosynthesis and reproductive diapause. Importantly, impairing Met function, a component of the JH intracellular receptor, partially blocked the 20E-regulated reproductive diapause preparation, indicating that 20E regulates reproductive diapause in both JH-dependent and -independent manners. Finally, we found that 20E deficiency decreased ecdysis-triggering hormone signaling and reduced JH production, thereby inducing diapause. Together, these results suggest that 20E signaling is a pivotal regulator that coordinates reproductive plasticity in response to environmental inputs.

Developmental arrest pervades organismal development and physiology where it facilitates an enormous range of adaptive responses to stressful conditions. Many animals exhibit various forms of developmental arrest that ensures survival under the most adverse environments. Reproductive diapause occurs when adults temporarily suspend reproduction in response to environmental stress and has been documented for a variety of invertebrates, particularly insects. Endocrine signals play a central role in translating environmental cues such as photoperiod into reproductive diapause-related physiology and behavior. However, it has been an unresolved issue as to which endocrine factors can respond to photoperiodic inputs and regulate diapause outputs. In this study, we found that a decrease in ecdysone levels is critical for reproductive diapause to occur. Also, ecdysone could interact with juvenile hormone to regulate the occurrence of reproductive diapause in response to photoperiodic cues. Our findings provide new insight into endocrine mechanisms of photoperiodic reproductive diapause and an example of phenotypic plasticity in animals.

Control of the insect metamorphic transition by ecdysteroid production and secretion

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

Juvenile hormone pathway in honey bee larvae: A source of possible signal molecules for the reproductive behavior of Varroa destructor

The parasitic mite Varroa destructor devastates honey bee (Apis mellifera) colonies around the world. Entering a brood cell shortly before capping, the Varroa mother feeds on the honey bee larvae. The hormones 20-hydroxyecdysone (20E) and juvenile hormone (JH), acquired from the host, have been considered to play a key role in initiating Varroa's reproductive cycle. This study focuses on differential expression of the genes involved in the biosynthesis of JH and ecdysone at six time points during the first 30 hr after cell capping in both drone and worker larvae of A. mellifera. This time frame, covering the conclusion of the honey bee brood cell invasion and the start of Varroa's ovogenesis, is critical to the successful initiation of a reproductive cycle. Our findings support a later activation of the ecdysteroid cascade in honey bee drones compared to worker larvae, which could account for the increased egg production of Varroa in A. mellifera drone cells. The JH pathway was generally downregulated confirming its activity is antagonistic to the ecdysteroid pathway during the larva development. Nevertheless, the genes involved in JH synthesis revealed an increased expression in drones. The upregulation of jhamt gene involved in methyl farnesoate (MF) synthesis came into attention since the MF is not only a precursor of JH but it is also an insect pheromone in its own right as well as JH-like hormone in Acari. This could indicate a possible kairomone effect of MF for attracting the mites into the drone brood cells, along with its potential involvement in ovogenesis after the cell capping, stimulating Varroa's initiation of egg laying.

Identification and Analysis of MicroRNAs Associated with Wing Polyphenism in the Brown Planthopper, Nilaparvata lugens

Many insects are capable of developing two types of wings (i.e., wing polyphenism) to adapt to various environments. Though the roles of microRNAs (miRNAs) in regulating animal growth and development have been well studied, their potential roles in modulating wing polyphenism remain largely elusive. To identify wing polyphenism-related miRNAs, we isolated small RNAs from 1st to 5th instar nymphs of long-wing (LW) and short-wing (SW) strains of the brown planthopper (BPH), Nilaparvata lugens. Small RNA libraries were then constructed and sequenced, yielding 158 conserved and 96 novel miRNAs. Among these, 122 miRNAs were differentially expressed between the two BPH strains. Specifically, 47, 2, 27 and 41 miRNAs were more highly expressed in the 1st, 3rd, 4th and 5th instars, respectively, of the LW strain compared with the SW strain. In contrast, 47, 3, 29 and 25 miRNAs were more highly expressed in the 1st, 3rd, 4th and 5th instars, respectively, of the SW strain compared with the LW strain. Next, we predicted the targets of these miRNAs and carried out Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis. We found that a number of pathways might be involved in wing form determination, such as the insulin, MAPK, mTOR, FoxO and thyroid hormone signaling pathways and the thyroid hormone synthesis pathway. Thirty and 45 differentially expressed miRNAs targeted genes in the insulin signaling and insect hormone biosynthesis pathways, respectively, which are related to wing dimorphism. Among these miRNAs, Nlu-miR-14-3p, Nlu-miR-9a-5p and Nlu-miR-315-5p, were confirmed to interact with insulin receptors (NlInRs) in dual luciferase reporter assays. These discoveries are helpful for understanding the miRNA-mediated regulatory mechanism of wing polyphenism in BPHs and shed new light on how insects respond to environmental cues through developmental plasticity.

MicroRNA miR-927 targets the juvenile hormone primary response gene Krüppel homolog1 to control Drosophila developmental growth

Krüppel homolog1 (Kr-h1) is a juvenile hormone (JH) response transcriptional factor that transduces JH signalling to repress insect metamorphosis in both hemimetabolous and holometabolous insects. While few studies about microRNAs (miRNAs) downregulating Kr-h1 expression to mediate insect metamorphosis have been demonstrated in hemimetabolous insects, the miRNAs that target the Kr-h1 of holometabolous insects have not been reported. Here, we identified two miR-927 binding sites within the 3'UTR region of Kr-h1 in Drosophila melanogaster, and miR-927 was found to downregulate the expression of Kr-h1. The expression profiles of miR-927 and Kr-h1 displayed relatively opposite pattern during most of the larval development stages. Overexpression of miR-927 in the fat body significantly decreased the expression of Kr-h1 and resulted in reduced oviposition, increased mortality, delayed pupation, and reduced pupal size. Notably, the co-overexpression of Kr-h1 rescued the developmental and growth defects associated with miR-927 overexpression, indicating that Kr-h1 is a biologically relevant target of miR-927. Moreover, the expression of miR-927 was found to be repressed by JH and its receptor Met/gce, forming a positive regulatory loop of JH signalling. Overall, our studies support a conserved role for the JH/miRNA/Kr-h1 regulatory axis in growth control during insect development.

Effect of ethylparaben on the growth and development of Drosophila melanogaster on preadult

Parabens are esters of p-hydroxybenzoic acid, including methylparaben (MP), ethylparaben (EP), propylparaben (PP), and the like. This substance has estrogenic and antiandrogenic effects, and a putative role in promoting cancer through endocrine disruption. By exposing Drosophila melanogaster to different concentrations of EP (300 mg/L, 700 mg/L, and 1000 mg/L), we investigated the effect of EP on the growth and development of D. melanogaster before emergence. We found that EP prolonged the development cycle of D. melanogaster, and changed the relative expression levels of Met, Gce, EcR, Kr-h1, and Br. In addition, EP reduced the titer of juvenile hormone Ⅲ (JH Ⅲ) and 20-hydroxyecdysone (20E), and delayed the peak of hormone secretion. This study provided a more objective and thorough assessment of safety for the parabens.

Roles of and cross-talk between ecdysteroid and sesquiterpenoid pathways in embryogenesis of branchiopod crustacean Daphnia magna

The ecdysteroid and sesquiterpenoid pathways control growth, developmental transition, and embryogenesis in insects. However, the function of orthologous genes and the cross-talk between both pathways remain largely uncharacterized in non-insect arthropods. Spook (Spo) and Juvenile hormone acid o-methyltransferase (Jhamt) have been suggested to function as rate-limiting factors in ecdysteroid and sesquiterpenoid biosynthesis, respectively, in insects. In this study, we report on the functions of Spo and Jhamt and the cross-talk between them in embryos of the branchiopod crustacean Daphnia magna. Spo expression was activated at the onset of gastrulation, with the depletion of Spo transcript by RNAi resulting in developmental arrest at this stage. This phenotype could be partially rescued by supplementation with 20-hydroxyecdysone, indicating that Spo may play the same role in ecdysteroid biosynthesis in early embryos, as reported in insects. After hatching, Spo expression was repressed, while Jhamt expression was activated transiently, despite its silencing during other embryonic stages. Jhamt RNAi showed little effect on survival, but shortened the embryonic period. Exposure to the sesquiterpenoid analog Fenoxycarb extended the embryonic period and rescued the Jhamt RNAi phenotype, demonstrating a previously unidentified role of sesquiterpenoid in the repression of precocious embryogenesis. Interestingly, the knockdown of Jhamt resulted in the derepression of ecdysteroid biosynthesis genes, including Spo, similar to regulation during insect hormonal biosynthesis. Sesquiterpenoid signaling via the Methoprene-tolerant gene was found to be responsible for the repression of ecdysteroid biosynthesis genes. It upregulated an ortholog of CYP18a1 that degrades ecdysteroid in insects. These results illuminate the conserved and specific functions of the ecdysteroid and sesquiterpenoid pathways in Daphnia embryos. We also infer that the common ancestor of branchiopod crustaceans and insects exhibited antagonism between the two endocrine hormones before their divergence 400 million years ago.

Diversity of Insect Sesquiterpenoid Regulation

Insects are arguably the most successful group of animals in the world in terms of both species numbers and diverse habitats. The sesquiterpenoids juvenile hormone, methyl farnesoate, and farnesoic acid are well known to regulate metamorphosis, reproduction, sexual dimorphism, eusociality, and defense in insects. Nevertheless, different insects have evolved with different sesquiterpenoid biosynthetic pathway as well as products. On the other hand, non-coding RNAs such as microRNAs have been implicated in regulation of many important biological processes, and have recently been explored in the regulation of sesquiterpenoid production. In this review, we summarize the latest findings on the diversity of sesquiterpenoids reported in different groups of insects, as well as the recent advancements in the understanding of regulation of sesquiterpenoid production by microRNAs.

Upregulation of E93 Gene Expression Acts as the Trigger for Metamorphosis Independently of the Threshold Size in the Beetle Tribolium castaneum

Body size in holometabolous insects is determined by the size at which the juvenile larva undergoes metamorphosis to the pupal stage. To undergo larva-pupa transition, larva must reach a critical developmental checkpoint, the threshold size (TS); however, the molecular mechanisms through which the TS cues this transition remain to be fully characterized. Here, we use the flour beetle Tribolium castaneum to characterize the molecular mechanisms underlying entry into metamorphosis. We found that T. castaneum reaches a TS at the beginning of the last larval instar, which is associated with the downregulation of TcKr-h1 and the upregulation of TcE93 and TcBr-C. Unexpectedly, we found that while there is an association between TS and TcE93 upregulation, it is the latter that constitutes the molecular trigger for metamorphosis initiation. In light of our results, we evaluate the interactions that control the larva-pupa transition and suggest alternative models.

MAPK-dependent hormonal signaling plasticity contributes to overcoming Bacillus thuringiensis toxin action in an insect host

The arms race between entomopathogenic bacteria and their insect hosts is an excellent model for decoding the intricate coevolutionary processes of host-pathogen interaction. Here, we demonstrate that the MAPK signaling pathway is a general switch to trans-regulate differential expression of aminopeptidase N and other midgut genes in an insect host, diamondback moth (Plutella xylostella), thereby countering the virulence effect of Bacillus thuringiensis (Bt) toxins. Moreover, the MAPK cascade is activated and fine-tuned by the crosstalk between two major insect hormones, 20-hydroxyecdysone (20E) and juvenile hormone (JH) to elicit an important physiological response (i.e. Bt resistance) without incurring the significant fitness costs often associated with pathogen resistance. Hormones are well known to orchestrate physiological trade-offs in a wide variety of organisms, and our work decodes a hitherto undescribed function of these classic hormones and suggests that hormonal signaling plasticity is a general cross-kingdom strategy to fend off pathogens.

Bacillus thuringiensis (Bt) is an important bioinsecticide, but high-level resistance has been rapidly evolving in agricultural pests. Here, Guo et al. show that the MAPK cascade can be activated by enhanced upstream insect hormone signals to counter Bt virulence in the diamondback moth.

Regulatory Mechanisms of Cell Polyploidy in Insects

Polyploidy cells undergo the endocycle to generate DNA amplification without cell division and have important biological functions in growth, development, reproduction, immune response, nutrient support, and conferring resistance to DNA damage in animals. In this paper, we have specially summarized current research progresses in the regulatory mechanisms of cell polyploidy in insects. First, insect hormones including juvenile hormone and 20-hydroxyecdysone regulate the endocycle of variant cells in diverse insect species. Second, cells skip mitotic division in response to developmental programming and conditional stimuli such as wound healing, regeneration, and aging. Third, the reported regulatory pathways of mitotic to endocycle switch (MES), including Notch, Hippo, and JNK signaling pathways, are summarized and constructed into genetic network. Thus, we think that the studies in crosstalk of hormones and their effects on canonical pathways will shed light on the mechanism of cell polyploidy and elucidate the evolutionary adaptions of MES through diverse insect species.

CREB-binding protein regulates metamorphosis and compound eye development in the yellow fever mosquito, Aedes aegypti

Juvenile hormones (JH) and ecdysone coordinately regulate metamorphosis in Aedes aegypti. We studied the function of an epigenetic regulator and multifunctional transactivator, CREB binding protein (CBP) in A. aegypti. RNAi-mediated knockdown of CBP in Ae. aegypti larvae resulted in suppression of JH primary response gene, Krüppel-homolog 1 (Kr-h1), and induction of primary ecdysone response gene, E93, resulting in multiple effects including early metamorphosis, larval-pupal intermediate formation, mortality and inhibition of compound eye development. RNA sequencing identified hundreds of genes, including JH and ecdysone response genes regulated by CBP. In the presence of JH, CBP upregulates Kr-h1 by acetylating core histones at the Kr-h1 promoter and facilitating the recruitment of JH receptor and other proteins. CBP suppresses metamorphosis regulators, EcR-A, USP-A, BR-C, and E93 through the upregulation of Kr-h1 and E75A. CBP regulates the expression of core eye specification genes including those involved in TGF-β and EGFR signaling. These studies demonstrate that CBP is an essential player in JH and 20E action and regulates metamorphosis and compound eye development in Ae. aegypti.

Post-transcriptional regulation of insect metamorphosis and oogenesis

Metamorphic transformation from larvae to adults along with the high fecundity is key to insect success. Insect metamorphosis and reproduction are governed by two critical endocrines, juvenile hormone (JH), and 20-hydroxyecdysone (20E). Recent studies have established a crucial role of microRNA (miRNA) in insect metamorphosis and oogenesis. While miRNAs target genes involved in JH and 20E-signaling pathways, these two hormones reciprocally regulate miRNA expression, forming regulatory loops of miRNA with JH and 20E-signaling cascades. Insect metamorphosis and oogenesis rely on the coordination of hormones, cognate genes, and miRNAs for precise regulation. In addition, the alternative splicing of genes in JH and 20E-signaling pathways has distinct functions in insect metamorphosis and oogenesis. We, therefore, focus in this review on recent advances in post-transcriptional regulation, with the emphasis on the regulatory role of miRNA and alternative splicing, in insect metamorphosis and oogenesis. We will highlight important new findings of miRNA interactions with hormonal signaling and alternative splicing of JH receptor heterodimer gene Taiman.