Ecdysone signaling mediates the trade-off between immunity and reproduction via suppression of amyloids in the mosquito Aedes aegypti.

The balance between immunity and reproduction is essential for many key physiological functions. We report that to maintain an optimal fertility, 20-hydroxyecdysone (20E) and the ecdysone receptor (EcR) downregulate the immune deficiency (IMD) pathway during the post blood meal phase (PBM) of the Aedes aegypti reproductive cycle. RNA interference-mediated depletion of EcR elicited an increased expression of the IMD pathway components, and these mosquitoes were more resistant to infection by Gram-negative bacteria. Moreover, 20E and EcR recruit Pirk-like, the mosquito ortholog of Drosophila melanogaster Pirk. CRISPR-Cas9 knockout of Pirk-like has shown that it represses the IMD pathway by interfering with IMD-mediated formation of amyloid aggregates. 20E and EcR disruption of the amyloid formation is pivotal for maintaining normal yolk protein production and fertility. Additionally, 20E and its receptor EcR directly induce Pirk-like to interfere with cRHIM-mediated formation of amyloid. Our study highlights the vital role of 20E in governing the trade-off between immunity and reproduction. Pirk-like might be a potential target for new methods to control mosquito reproduction and pathogen transmission.

The role of 20E biosynthesis relative gene Shadow in the reproduction of the predatory mirid bug, Cyrtorhinus lividipennis (Hemiptera: Miridae).

Cytorhinus lividipennis is a natural enemy of rice planthoppers and leafhoppers. Improving the fecundity of C. lividipennis will be helpful to improve its control effect on pests. However, little is known about the hormonal regulatory mechanism of reproduction in C. lividipennis. In the current study, we examined the role of 20-hydroxyecdysone (20E) biosynthesis relative gene Shadow in the reproduction of C. lividipennis. The complementary DNA sequence of ClSad is 2018 -bp in length with an open reading frame of 1398-bp encoding 465 amino acid residues. ClSad was readily detected in nymphal and adult stages, and highly expressed in the adult stage. ClSad was highly expressed in the midgut and ovaries of adult females. Moreover, RNA interference-mediated knockdown of ClSad reduced the 20E titers and ClVg transcript level, resulting in fewer fully developed eggs and a decrease in the number of eggs laid by dsSad-injected adult females within 15 days. These results suggest that ClSad plays a critical role in the reproduction of C. lividipennis. The present study provides insights into the molecular mechanism of the ClSad gene for the reproduction of C. lividipennis.

Co-option of immune effectors by the hormonal signalling system triggering metamorphosis in Drosophila melanogaster.

Insect metamorphosis is triggered by the production, secretion and degradation of 20-hydroxyecdysone (ecdysone). In addition to its role in developmental regulation, increasing evidence suggests that ecdysone is involved in innate immunity processes, such as phagocytosis and the induction of antimicrobial peptide (AMP) production. AMP regulation includes systemic responses as well as local responses at surface epithelia that contact with the external environment. At pupariation, Drosophila melanogaster increases dramatically the expression of three AMP genes, drosomycin (drs), drosomycin-like 2 (drsl2) and drosomycin-like 5 (drsl5). We show that the systemic action of drs at pupariation is dependent on ecdysone signalling in the fat body and operates via the ecdysone downstream target, Broad. In parallel, ecdysone also regulates local responses, specifically through the activation of drsl2 expression in the gut. Finally, we confirm the relevance of this ecdysone dependent AMP expression for the control of bacterial load by showing that flies lacking drs expression in the fat body have higher bacterial persistence over metamorphosis. In contrast, local responses may be redundant with the systemic effect of drs since reduction of ecdysone signalling or of drsl2 expression has no measurable negative effect on bacterial load control in the pupa. Together, our data emphasize the importance of the association between ecdysone signalling and immunity using in vivo studies and establish a new role for ecdysone at pupariation, which impacts developmental success by regulating the immune system in a stage-dependent manner. We speculate that this co-option of immune effectors by the hormonal system may constitute an anticipatory mechanism to control bacterial numbers in the pupa, at the core of metamorphosis evolution.

RNA interference shows that Spook, the precursor gene of 20-hydroxyecdysone (20E), regulates the molting of Macrobrachium nipponense.

The aim of this study was to explore the function of the Mn-Spook gene, which was found in the ovary transcriptome of the Oriental river prawn (Macrobrachium nipponense). The Spook gene, which is the precursor gene of 20-hydroxyecdysone (20E), plays an important role in the process of molting in many arthropods, but its function in M. nipponense is unclear. We cloned the full-length Mn-Spook gene from the ovary of M. nipponense and found that it had the same conserved domains as the P450 gene of the Halloween family of genes. The Mn-Spook gene was highly expressed in ovary and gill tissue during the breeding period. During ovarian development, Mn-spook gene expression was highest at the nearly-ripe stage, and it also was highly expressed in the zoea developmental stage. Cellular localization analysis showed that Mn-Spook signals accumulated in the cytoplasmic membrane and nucleus of oocytes. Finally, we used RNA interference to evaluate the function of the Mn-Spook gene. Compared with the control group, in vivo injection of Mn-Spook dsRNA effectively downregulated the expression of Mn-Spook and the content of 20E. The molting frequency of M. nipponense in the experimental group also was significantly inhibited. These results demonstrated that the Mn-Spook gene played an important role in the molting process of M. nipponense.

Expression of 20-hydroxyecdysone-related genes during gonadal development of Teleogryllus emma (Orthoptera: Gryllidae).

Insect gonads develop under endocrine signals. In this study, we assessed the characters of partial complementary DNAs encoding the Teleogryllus emma orthologs of 20-hydroxyecdysone (20E)-related genes (RXR, E75, HR3, Hsc70, and Hsp90) and analyzed their expression patterns in both nymph and adult crickets. 20E treatment suppressed expression of TeEcR, TeRXR, TeE75, TeHR3, TeHsc70, and TeHsp90. Temporal expression analysis demonstrated that TeERR and 20E-related genes were expressed in four stages of gonadal development from the fourth-instar nymph stage to the adult stage. The expression pattern of these genes differed in testicular and ovarian development. TeRXR, HR3, TeHsc70, and TeHsp90 were irregularly expressed in gonads of the same developmental stages, while mRNAs encoding TeERR, TeEcR, and TeE75 accumulated in higher levels in ovaries than in testes. RNA interference (RNAi) of TeEcR expression led to decrease of the expression levels of TeEcR, TeRXR, TeHR3, and TeHsc70, while it enhanced TeE75 and TeHsp90 expressions. These results demonstrate that the TeERR and 20E-related genes help regulate gonadal development, while TeEcR appears to inhibit TeE75 expression, TeE75 inhibits HR3 expression. Hsc70 indirectly regulated the expression of the primary and secondary response genes E74A, E75B, and HR3. Hsp90 regulated Usp expression with no direct regulatory relationship with EcR.

Subunit P60 of phosphatidylinositol 3-kinase promotes cell proliferation or apoptosis depending on its phosphorylation status.

The regulatory subunits (P60 in insects, P85 in mammals) determine the activation of the catalytic subunits P110 in phosphatidylinositol 3-kinases (PI3Ks) in the insulin pathway for cell proliferation and body growth. However, the regulatory subunits also promote apoptosis via an unclear regulatory mechanism. Using Helicoverpa armigera, an agricultural pest, we showed that H. armigera P60 (HaP60) was phosphorylated under insulin-like peptides (ILPs) regulation at larval growth stages and played roles in the insulin/ insulin-like growth factor (IGF) signaling (IIS) to determine HaP110 phosphorylation and cell membrane translocation; whereas, HaP60 was dephosphorylated and its expression increased under steroid hormone 20-hydroxyecdysone (20E) regulation during metamorphosis. Protein tyrosine phosphatase non-receptor type 6 (HaPTPN6, also named tyrosine-protein phosphatase corkscrew-like isoform X1 in the genome) was upregulated by 20E to dephosphorylate HaP60 and HaP110. 20E blocked HaP60 and HaP110 translocation to the cell membrane and reduced their interaction. The phosphorylated HaP60 mediated a cascade of protein phosphorylation and forkhead box protein O (HaFOXO) cytosol localization in the IIS to promote cell proliferation. However, 20E, via G protein-coupled-receptor-, ecdysone receptor-, and HaFOXO signaling axis, upregulated HaP60 expression, and the non-phosphorylated HaP60 interacted with phosphatase and tensin homolog (HaPTEN) to induce apoptosis. RNA interference-mediated knockdown of HaP60 and HaP110 in larvae repressed larval growth and apoptosis. Thus, HaP60 plays dual functions to promote cell proliferation and apoptosis by changing its phosphorylation status under ILPs and 20E regulation, respectively.

A 14-amino acids deletion in BmShadow results to non-moult on the 2nd instar in the bivoltine silkworm, Bombyx mori.

The Bombyx mori Shadow gene (BmShadow) belongs to the superfamily of cytochrome P450 genes. To elucidate the function of the BmShadow gene and its association with diapause, we employed the CRISPR/Cas9 system to knock out the BmShadow gene in the bivoltine strain Qiufeng. The mutant (BmShadow-/-) was obtained in G2, exhibiting a 42-base deletion corresponded exactly to the amino acids regions from positions 155 to 168. The larvae of BmShadow-/- cannot moult at the pre-moulting stage of the 2nd instar. When the BmShadow-/- larvae were fed with 20E analogue at the late stage of the 2nd instar, they were rescued and developed into the 3rd instar. Rescue experiments indicated that the 20E concentration of BmShadow-/- larvae was significantly lower than that in WT larvae, and the 20E concentration of BmShadow-/- larvae which fed 20E analogue was restored to normal levels. Interestingly, the BmShadow-/- larvae could not moult on the 1st instar when they hatched from eggs after being stored at 5 °C for 40 days or after hibernation, suggesting that the 20E transported from the mother was partially consumed in the diapause maintenance phase. Our study confirmed that BmShadow is involved in 20E synthesis and a 14-amino acids region from position 155 to 168 was essential for its function, also there appears to be no other compensation pathway in vivo, which offered an important potential target locus for the control of silkworm development and the biological control of agricultural and forestry pests.

The steroid hormone 20-hydroxyecdysone counteracts insulin signaling via insulin receptor dephosphorylation.

The insulin receptor (INSR) binds insulin to promote body growth and maintain normal blood glucose levels. While it is known that steroid hormones such as estrogen and 20-hydroxyecdysone counteract insulin function, the molecular mechanisms responsible for this attenuation remain unclear. In the present study, using the agricultural pest lepidopteran Helicoverpa armigera as a model, we proposed that the steroid hormone 20-hydroxyecdysone (20E) induces dephosphorylation of INSR to counteract insulin function. We observed high expression and phosphorylation of INSR during larval feeding stages that decreased during metamorphosis. Insulin upregulated INSR expression and phosphorylation, whereas 20E repressed INSR expression and induced INSR dephosphorylation in vivo. Protein tyrosine phosphatase 1B (PTP1B, encoded by Ptpn1) dephosphorylated INSR in vivo. PTEN (phosphatase and tensin homolog deleted on chromosome 10) was critical for 20E-induced INSR dephosphorylation by maintaining the transcription factor Forkhead box O (FoxO) in the nucleus, where FoxO promoted Ptpn1 expression and repressed Insr expression. Knockdown of Ptpn1 using RNA interference maintained INSR phosphorylation, increased 20E production, and accelerated pupation. RNA interference of Insr in larvae repressed larval growth, decreased 20E production, delayed pupation, and accumulated hemolymph glucose levels. Taken together, these results suggest that a high 20E titer counteracts the insulin pathway by dephosphorylating INSR to stop larval growth and accumulate glucose in the hemolymph.

A mating-induced reproductive gene promotes Anopheles tolerance to Plasmodium falciparum infection.

Anopheles mosquitoes have transmitted Plasmodium parasites for millions of years, yet it remains unclear whether they suffer fitness costs to infection. Here we report that the fecundity of virgin and mated females of two important vectors-Anopheles gambiae and Anopheles stephensi-is not affected by infection with Plasmodium falciparum, demonstrating that these human malaria parasites do not inflict this reproductive cost on their natural mosquito hosts. Additionally, parasite development is not impacted by mating status. However, in field studies using different P. falciparum isolates in Anopheles coluzzii, we find that Mating-Induced Stimulator of Oogenesis (MISO), a female reproductive gene strongly induced after mating by the sexual transfer of the steroid hormone 20-hydroxyecdysone (20E), protects females from incurring fecundity costs to infection. MISO-silenced females produce fewer eggs as they become increasingly infected with P. falciparum, while parasite development is not impacted by this gene silencing. Interestingly, previous work had shown that sexual transfer of 20E has specifically evolved in Cellia species of the Anopheles genus, driving the co-adaptation of MISO. Our data therefore suggest that evolution of male-female sexual interactions may have promoted Anopheles tolerance to P. falciparum infection in the Cellia subgenus, which comprises the most important malaria vectors.

Functional analysis of ecdysteroid biosynthetic enzymes of the rice planthopper, Nilaparvata lugens.

Ecdysteroids, insect steroid hormones, play key roles in regulating insect development and reproduction. Hemipteran insects require ecdysteroids for egg production; however, ecdysteroid synthesis (ecdysteroidogenesis) details have not been elucidated. We identified all known genes encoding ecdysteroidogenic enzymes in Nilaparvata lugens and clarified their necessity during nymphal and ovarian development. We confirmed that N. lugens utilized 20-hydroxyecdysone as an active hormone. Assays using heterologous expression of enzymes in Drosophila S2 cells showed conserved functions of enzymes Neverland, CYP306A2, CYP314A1 and CYP315A1, but not CYP302A1. RNA interference and rescue analysis using 20-hydroxyecdysone demonstrated that most of the genes were necessary for nymphal development. The identified N. lugens enzymes showed conserved functions and pathways for ecdysteroidogenesis. Knockdown of ecdysteroidogenic enzyme genes in newly molted females caused failure of egg production: less vitellogenic and mature eggs in ovaries, fewer laid eggs and embryonic development deficiency of laid eggs. Considering the high expressions of ecdysteroidogenic enzyme genes in adults and ovaries, ecdysteroidogenesis in ovaries was critical for N. lugens ovarian development. Our study presents initial evidence that hemipteran insects require ecdysteroidogenesis for ovarian development.

Sex-specific expression profiles of ecdysteroid biosynthesis and ecdysone response genes in extreme sexual dimorphism of the mealybug Planococcus kraunhiae (Kuwana).

Insect molting hormone (ecdysteroids) and juvenile hormone regulate molting and metamorphic events in a variety of insect species. Mealybugs undergo sexually dimorphic metamorphosis: males develop into winged adults through non-feeding, pupa-like stages called prepupa and pupa, while females emerge as neotenic wingless adults. We previously demonstrated, in the Japanese mealybug Planococcus kraunhiae (Kuwana), that the juvenile hormone titer is higher in males than in females at the end of the juvenile stage, which suggests that juvenile hormone may regulate male-specific adult morphogenesis. Here, we examined the involvement of ecdysteroids in sexually dimorphic metamorphosis. To estimate ecdysteroid titers, quantitative RT-PCR analyses of four Halloween genes encoding for cytochrome P450 monooxygenases in ecdysteroid biosynthesis, i.e., spook, disembodied, shadow and shade, were performed. Overall, their expression levels peaked before each nymphal molt. Transcript levels of spook, disembodied and shadow, genes that catalyze the steps in ecdysteroid biosynthesis in the prothoracic gland, were higher in males from the middle of the second nymphal instar to adult emergence. In contrast, the expression of shade, which was reported to be involved in the conversion of ecdysone into 20-hydroxyecdysone in peripheral tissues, was similar between males and females. These results suggest that ecdysteroid biosynthesis in the prothoracic gland is more active in males than in females, although the final conversion into 20-hydroxyecdysone occurs at similar levels in both sexes. Moreover, expression profiles of ecdysone response genes, ecdysone receptor and ecdysone-induced protein 75B, were also analyzed. Based on these expression profiles, we propose that the changes in ecdysteroid titer differ between males and females, and that high ecdysteroid titer is essential for directing male adult development.

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.

miR-34 modulates wing polyphenism in planthopper.

Polyphenism is a successful strategy adopted by organisms to adapt to environmental changes. Brown planthoppers (BPH, Nilaparvata lugens) develop two wing phenotypes, including long-winged (LW) and short-winged (SW) morphs. Though insulin receptor (InR) and juvenile hormone (JH) have been known to regulate wing polyphenism in BPH, the interaction between these regulators remains largely elusive. Here, we discovered that a conserved microRNA, miR-34, modulates a positive autoregulatory feedback loop of JH and insulin/IGF signaling (IIS) pathway to control wing polyphenism in BPH. Nlu-miR-34 is abundant in SW BPHs and suppresses NlInR1 by targeting at two binding sites in the 3'UTR of NlInR1. Overexpressing miR-34 in LW BPHs by injecting agomir-34 induces the development towards SW BPHs, whereas knocking down miR-34 in SW BPHs by injecting antagomir-34 induces more LW BPHs when another NlInR1 suppressor, NlInR2, is also suppressed simultaneously. A cis-response element of Broad Complex (Br-C) is found in the promoter region of Nlu-miR-34, suggesting that 20-hydroxyecdysone (20E) might be involved in wing polyphenism regulation. Topic application of 20E downregulates miR-34 expression but does not change wing morphs. On the other hand, JH application upregulates miR-34 expression and induces more SW BPHs. Moreover, knocking down genes in IIS pathway changes JH titers and miR-34 abundance. In all, we showed that miRNA mediates the cross talk between JH, 20E and IIS pathway by forming a positive feedback loop, uncovering a comprehensive regulation mechanism which integrates almost all known regulators controlling wing polyphenism in insects.

MicroRNA let-7 regulates the expression of ecdysteroid receptor (ECR) in Hyalomma asiaticum (Acari: Ixodidae) ticks.

BACKGROUND: Ticks are blood-sucking arthropods that can transmit diseases to humans and animals. These arthropods are the second most important vectors of pathogens. MicroRNAs are a class of conserved small noncoding RNAs that play regulatory roles in gene expression at the post-transcriptional level. Molting is an important biological process in arthropods. Research on the molting process is important for understanding tick physiology and control. METHODS: Dual-luciferase reporter assays were used to assess the role of miRNA let-7 in ecdysteroid receptor (ECR) biology. The expression levels of ECR and let-7 were measured by real-time qPCR before and after tick molting. To explore the function of let-7 and ECR, we performed overexpression and knocking down of let-7 and RNAi of ECR in tick nymphs. The biological function of let-7 in molting was explored by injecting nymphs, ten days after engorgement, with let-7 agomir for overexpression and let-7 antagomir for knocking down. The rate of molting was then determined. ECR dsRNA was injected into ticks to evaluate the function of ECR by gene silencing. The expression of ECR and let-7 was measured using RT-qPCR. All data were analyzed using GraphPad Prism v.6. RESULTS: The results of the luciferase assay using a eukaryotic expression system revealed that ECR was a natural target of let-7. Let-7 overexpressed by agomir affected the rate of molting (P < 0.01) and the period of molting (P < 0.01). Let-7 antagomir for knockdown affected the period of molting (P < 0.01), but there was no effect on the rate of molting (P = 0.27). ECR dsRNA gene silencing significantly affected the rate of molting (P < 0.05). CONCLUSIONS: This study demonstrated that let-7 can regulate the expression of ECR and that let-7 can affect molting in ticks. Our results help to understand the regulation of let-7 by 20-hydroxyecdysone (20E) and will provide a reference for functional analysis studies of microRNAs in ticks.

ß­ecdysterone protects against apoptosis by promoting autophagy in nucleus pulposus cells and ameliorates disc degeneration.

Increasing cell apoptosis is one of the major causes of intervertebral disc degeneration (IDD). ß-ecdysterone has been demonstrated to protect PC12 cells against neurotoxicity. A previous study revealed that ß­ecdysterone may be involved in the regulation of autophagy in osteoblasts. Therefore, we hypothesized that ß­ecdysterone may possess therapeutic effects on IDD via autophagy stimulation. The effect of ß­ecdysterone on IDD was explored by in vitro experiments. The results demonstrated that ß­ecdysterone attenuated the apoptosis induced by tert­butyl hydroperoxide via promoting autophagy in nucleus pulposus cells. Beclin­1, an indispensable protein for the stimulation of autophagy, is upregulated and stabilized by ß­ecdysterone in a dose­ and time­dependent manner in nucleus pulposus cells. Inhibition of autophagy with 3­methyladenine partially abrogated the protective function of ß­ecdysterone against apoptosis of nucleus pulposus cells, indicating that autophagy participated in the protective effect of ß­ecdysterone on IDD. Additionally, ß­ecdysterone promoted the expression of anabolic genes while inhibiting the expression of catabolic genes in nucleus pulposus cells. Collectively, the present study demonstrated that ß­ecdysterone may protect nucleus pulposus cells against apoptosis by autophagy stimulation and ameliorate disc degeneration, which indicates that ß­ecdysterone may be a potential therapeutic agent for IDD.

RNA interference against the putative insulin receptor substrate gene chico affects metamorphosis in Leptinotarsa decemlineata.

It is noted that insect insulin/insulin-like growth factor/target of rapamycin signaling is critical for the regulation of metamorphosis in holometabolous insects. However, the molecular mechanism remains undetermined. Our previous findings reveal that RNA interference (RNAi)-mediated knockdown of an insulin gene (LdILP2) in Leptinotarsa decemlineata disturbs both 20-hydroxyecdysone (20E) and juvenile hormone (JH) signaling, and impairs pupation. In the present paper, we further observed that the expression of the insulin receptor substrate gene chico (Ldchico) and the phosphoinositide-3-kinase gene pi3k (Ldpi3k92E) was repressed in LdILP2 depleted larvae. Moreover, RNAi of Ldchico or Ldpi3k92E decreased food consumption, affected absorption and metabolism of amino acids and sugars, and reduced expression of several 20E (LdEcR, LdHR3 and LdE75) and JH (LdJHAMT, LdKr-h1 and LdHairy) signaling genes. As a result, larval development was postponed and larval growth was inhibited. Intriguingly, knockdown of Ldchico, rather than Ldpi3k92E, impaired larval-pupal and pupal-adult ecdysis, and specifically repressed transcription of another 20E signaling gene LdUSP. Ingestion of 20E rescued the expression of LdEcR, LdHR3 and LdE75, whereas 20E feeding restored neither the decreased LdUSP mRNA level, nor the reduced pupation and adult emergence rates in Ldchico RNAi larvae. Therefore, Chico is critical for the regulation of larval-pupal-adult transition by a PI3K-independent pathway, perhaps through activation of USP in L. decemlineata.

Juvenile hormone-regulated alternative splicing of the taiman gene primes the ecdysteroid response in adult mosquitoes.

Juvenile hormone (JH) regulates many aspects of insect development and reproduction. In some processes, JH plays a critical role in defining the action of the steroid hormone 20-hydroxyecdysone (20E). In Aedes aegypti mosquitoes, JH prepares newly emerged female adults to become competent to synthesize vitellogenin in response to 20E after blood ingestion. The molecular basis of this competence is still not well understood. Here, we report that JH regulates pre-mRNA splicing of the taiman gene, which encodes a key transcriptional regulator required for both JH- and 20E-controlled gene expression. JH stimulated the production of the Taiman isoforms A/B, while reducing the levels of the isoforms C/D, in the fat body after adult eclosion. The appearance of the A/B isoforms in maturing mosquitoes was accompanied by acquisition of the competence to respond to 20E. Depletion of the A/B isoforms, by inhibiting the alternative splicing or by isoform-specific RNA interference, considerably diminished the 20E-induced gene expression after a blood meal and substantially impaired oocyte development. In accordance with this observation, further studies indicated that in the presence of 20E, the Taiman A/B isoforms showed much stronger interactions with the 20E receptor complex than the Taiman C/D isoforms. In contrast, all four isoforms displayed similar capabilities of forming active JH receptor complexes with the methoprene-tolerant protein (Met). This study suggested that JH confers the competence to newly emerged female mosquitoes by regulating mRNA splicing to generate the Taiman isoforms that are essential for the vitellogenic 20E response.

HR38, an ortholog of NR4A family nuclear receptors, mediates 20-hydroxyecdysone regulation of carbohydrate metabolism during mosquito reproduction.

The Aedes aegypti mosquito is the principal vector for many dangerous human viral diseases. Carbohydrate metabolism (CM) is essential for supplying the energy necessary for host seeking, blood digestion and rapid egg development of this vector insect. The steroid hormone 20-hydroxyecdysone (20E) and the ecdysone receptor (EcR) are important regulators of CM, coordinating it with female reproductive events. We report here that the NR4A nuclear receptor AHR38 plays a critical role in mediating these actions of 20E and EcR. AHR38 RNA interference (RNAi) depletion in female mosquitoes blocked the transcriptional activation of CM genes encoding phosphoglucomutase (PGM) and trehalose-6-phophate synthase (TPS); it caused an increase of glycogen accumulation and a decrease of the circulating sugar trehalose. This treatment also resulted in a dramatic reduction in fecundity. Considering that these phenotypes resulting from AHR38 RNAi depletion are similar to those of EcR RNAi, we investigated a possible connection between these transcription factors in CM regulation. EcR RNAi inhibits the AHR38 gene expression. Moreover, the 20E-induced EcR complex directly activates AHR38 by binding to the ecdysone response element (EcRE) in the upstream regulatory region of this gene. The present work has implicated AHR38 in the 20E-mediated control of CM and provided new insight into mechanisms of 20E regulation of metabolism during female mosquito reproduction.

Host miRNAs are involved in hormonal regulation of HaSNPV-triggered climbing behaviour in Helicoverpa armigera.

Baculoviruses manipulate host climbing behaviour to ensure that the hosts die at elevated positions on host plants to facilitate virus proliferation and transmission, which is a process referred to as tree-top disease. However, the detailed molecular mechanism underlying tree-top disease has not been elucidated. Using transcriptome analysis, we showed that two hormone signals, juvenile hormone (JH) and 20-hydroxyecdysone (20E), are key components involved in HaSNPV-induced tree-top disease in Helicoverpa armigera larvae. RNAi-mediated knockdown and exogenous hormone treatment assays demonstrated that 20E inhibits virus-induced tree-top disease, while JH mediates tree-top disease behaviour. Knockdown of BrZ2, a downstream signal of JH and 20E, promoted HaSNPV-induced tree-top disease. We also found that two miRNAs target BrZ2 and are involved in the cross-talk regulation between 20E and JH manipulating HaSNPV replication, time to death and HaSNPV-induced tree-top disease.

Desiccation stress induces developmental heterochrony in Drosophila melanogaster.

Stressful environments are known to perturb developmental patterns in insects. In the purview of desiccation as a stressor, relatively little is known about the developmental consequences linked with desiccation tolerance. In this study, we have particularly focused on the exploration of the temporal profile of postembryonic development in response to desiccation exposure in Drosophila melanogaster and the associated trade-offs. We document a correlation between variations in 20-hydroxyecdysone levels and the altered timing of metamorphic events during the life cycle. Following desiccation, we observed an extension in the larval longevity whereas the duration of the pupal and adult stages was significantly shortened. Alternately, feeding of 20-hydroxyecdysone apparently led to the restoration of the normal temporal pattern of development in the desiccated group. In spite of the desiccation-responsive heterochronic shifts in development, the overall lifespan post recovery remained almost unaltered among the desiccated and undesiccated groups suggesting plasticity in developmental control. This observation reminisces 'canalization-like' phenomenon that buffers alterations in the overall lifespan. We thus identified a desiccationresponsive period in the lifespan of D. melanogaster during which variations in ecdysone levels are capable to alter the temporal course of development.