A critical role of the nuclear receptor HR3 in regulation of gonadotrophic cycles of the mosquito Aedes aegypti

Effect of nanoformulation Azadirachta indica on some factors associated with the vectorial capacity and competence of Anopheles aquasalis experimentally infected with Plasmodium vivax

Malaria remains a highly prevalent infectious disease worldwide, particularly in tropical and subtropical regions. Effectively controlling of mosquitoes transmitting of Plasmodium spp. is crucial in to control this disease. A promising strategy involves utilizing plant-derived products, such as the Neem tree (Azadirachta indica), known for its secondary metabolites with biological activity against various insect groups of agricultural and public health importance. This study investigated the effects of a nanoformulation prototype Neem on factors linked to the vector competence of Anopheles aquasalis, a malaria vector in Latin America. Different concentrations of the nanoformulation were supplied through sugar solution and blood feeding, assessing impacts on longevity, fecundity, fertility, and transgenerational survival from larvae to adults. Additionally, the effects of the Neem nanoformulation and NeemAZAL® formulation on the sporogonic cycle of P. vivax were evaluated. Overall, significant impacts were observed at 100 ppm and 1,000 ppm concentrations on adult survival patterns and on survival of the F1 generation. A trend of reduced oviposition and hatching rates was also noted in nanoformulation-consuming groups, with fertility and fecundity declining proportionally to the concentration. Additionally, a significant decrease in the infection rate and intensity of P. vivax was observed in the 1,000 ppm group, with a mean of 3 oocysts per female compared to the control's 27 oocysts per female. In the commercial formulation, the highest tested concentration of 3 ppm yielded 5.36 oocysts per female. Concerning sporozoite numbers, there was a reduction of 52 % and 87 % at the highest concentrations compared to the control group. In conclusion, these findings suggest that the A. indica nanoformulation is a potential as a tool for malaria control through reduction in the vector longevity and reproductive capacity, possibly leading to decreased vector population densities. Moreover, the nanoformulation interfered with the sporogonic development of P. vivax. However, further basic research on Neem formulations, their effects, and mechanisms of action is imperative to gain a more specific perspective for safe field implementation.

Endocrine factors modulating vitellogenesis and oogenesis in insects: An update

The endocrine system plays a pivotal role in shaping the mechanisms that ensure successful reproduction. With over a million known insect species, understanding the endocrine control of reproduction has become increasingly complex. Some of the key players include the classic insect lipid hormones juvenile hormone (JH) and ecdysteroids, and neuropeptides such as insulin-like peptides (ILPs). Individual endocrine factors not only modulate their own target tissue but also play crucial roles in crosstalk among themselves, ensuring successful vitellogenesis and oogenesis. Recent advances in omics, gene silencing, and genome editing approaches have accelerated research, offering both fundamental insights and practical applications for studying in-depth endocrine signaling pathways. This review provides an updated and integrated view of endocrine factors modulating vitellogenesis and oogenesis in insect females.

Ecdysone-controlled nuclear receptor ERR regulates metabolic homeostasis in the disease vector mosquito Aedes aegypti

Hematophagous mosquitoes require vertebrate blood for their reproductive cycles, making them effective vectors for transmitting dangerous human diseases. Thus, high-intensity metabolism is needed to support reproductive events of female mosquitoes. However, the regulatory mechanism linking metabolism and reproduction in mosquitoes remains largely unclear. In this study, we found that the expression of estrogen-related receptor (ERR), a nuclear receptor, is activated by the direct binding of 20-hydroxyecdysone (20E) and ecdysone receptor (EcR) to the ecdysone response element (EcRE) in the ERR promoter region during the gonadotropic cycle of Aedes aegypti (named AaERR). RNA interference (RNAi) of AaERR in female mosquitoes led to delayed development of ovaries. mRNA abundance of genes encoding key enzymes involved in carbohydrate metabolism (CM)-glucose-6-phosphate isomerase (GPI) and pyruvate kinase (PYK)-was significantly decreased in AaERR knockdown mosquitoes, while the levels of metabolites, such as glycogen, glucose, and trehalose, were elevated. The expression of fatty acid synthase (FAS) was notably downregulated, and lipid accumulation was reduced in response to AaERR depletion. Dual luciferase reporter assays and electrophoretic mobility shift assays (EMSA) determined that AaERR directly activated the expression of metabolic genes, such as GPI, PYK, and FAS, by binding to the corresponding AaERR-responsive motif in the promoter region of these genes. Our results have revealed an important role of AaERR in the regulation of metabolism during mosquito reproduction and offer a novel target for mosquito control.

The Juvenile-Hormone-Responsive Factor AmKr-h1 Regulates Caste Differentiation in Honey Bees

Honey bees are typical model organisms for the study of caste differentiation, and the juvenile hormone (JH) is a crucial link in the regulatory network of caste differentiation in honey bees. To investigate the mechanism of JH-mediated caste differentiation, we analyzed the effect of the JH response gene AmKr-h1 on this process. We observed that AmKr-h1 expression levels were significantly higher in queen larvae than in worker larvae at the 48 h, 84 h, and 120 h larval stages, and were regulated by JH. Inhibiting AmKr-h1 expression in honey bee larvae using RNAi could lead to the development of larvae toward workers. We also analyzed the transcriptome changes in honey bee larvae after AmKr-h1 RNAi and identified 191 differentially expressed genes (DEGs) and 682 differentially expressed alternative splicing events (DEASEs); of these, many were related to honey bee caste differentiation. Our results indicate that AmKr-h1 regulates caste differentiation in honey bees by acting as a JH-responsive gene.

A Hepatocyte Nuclear Factor BtabHNF4 Mediates Desiccation Tolerance and Fecundity in Whitefly (Bemisia tabaci)

Hepatocyte nuclear factor 4 (HNF4) is essential for glucose homeostasis and lipid metabolism in insects. However, little is known about the role of HNF4 in whiteflies. In the present study, we identified a hepatocyte nuclear factor protein from Bemsia tabaci (Diptera: Drosophilidae) and named it BtabHNF4. The full-length of BtabHNF4 was 3,006 bp, encoding a sequence of 434 amino acids that contains a conserved zinc-finger DNA-binding domain (DBD) and a well-conserved ligand-binding domain (LBD). The temporal and spatial expression showed that BtabHNF4 was highly expressed in the female adult stage and abdominal tissues of B. tabaci. A leaf-mediated RNA interference method was used to explore the function of BtabHNF4 in whiteflies. Our results showed that the knockdown of BtabHNF4 influences the desiccation tolerance, egg production, and egg hatching rate of whiteflies. Additionally, BtabHNF4 silencing significantly inhibited the expression level of vitellogenin. These results expand the function of HNF4 and pave the way for understanding the molecular mechanisms of HNF4 in regulating multiple physiological processes.

A critical role for ecdysone response genes in regulating egg production in adult female Rhodnius prolixus

Ecdysteroids control ovary growth and egg production through a complex gene hierarchy. In the female Rhodnius prolixus, a blood-gorging triatomine and the vector of Chagas disease, we have identified the ecdysone response genes in the ovary using transcriptomic data. We then quantified the expression of the ecdysone response gene transcripts (E75, E74, BR-C, HR3, HR4, and FTZ-F1) in several tissues, including the ovary, following a blood meal. These results confirm the presence of these transcripts in several tissues in R. prolixus and show that the ecdysone response genes in the ovary are mostly upregulated during the first three days post blood meal (PBM). Knockdown of E75, E74, or FTZ-F1 transcripts using RNA interference (RNAi) was used to understand the role of the ecdysone response genes in vitellogenesis and egg production. Knockdown significantly decreases the expression of the transcripts for the ecdysone receptor and Halloween genes in the fat body and the ovaries and reduces the titer of ecdysteroid in the hemolymph. Knockdown of each of these transcription factors typically alters the expression of the other transcription factors. Knockdown also significantly decreases the expression of vitellogenin transcripts, Vg1 and Vg2, in the fat body and ovaries and reduces the number of eggs produced and laid. Some of the laid eggs have an irregular shape and smaller volume, and their hatching rate is decreased. Knockdown also influences the expression of the chorion gene transcripts Rp30 and Rp45. The overall effect of knockdown is a decrease in number of eggs produced and a severe reduction in number of eggs laid and their hatching rate. Clearly, ecdysteroids and ecdysone response genes play a significant role in reproduction in R. prolixus.

Aspirin Inhibition of Prostaglandin Synthesis Impairs Mosquito Egg Development

Several endocrine signals mediate mosquito egg development, including 20-hydroxyecdysone (20E). This study reports on prostaglandin E₂ (PGE₂) as an additional, but core, mediator of oogenesis in a human disease-vectoring mosquito, Aedes albopictus. Injection of aspirin (an inhibitor of cyclooxygenase (COX)) after blood-feeding (BF) inhibited oogenesis by preventing nurse cell dumping into a growing oocyte. The inhibitory effect was rescued by PGE₂ addition. PGE₂ was found to be rich in nurse cells and follicular epithelium after BF. RNA interference (RNAi) treatments of PG biosynthetic genes, including PLA₂ and two COX-like peroxidases, prevented egg development. Interestingly, 20E treatment significantly increased the expressions of PG biosynthetic genes, while the RNAi of Shade (which is a 20E biosynthetic gene) expression prevented inducible expressions after BF. Furthermore, RNAi treatments of PGE₂ receptor genes suppressed egg production, even under PGE₂. These results suggest that a signaling pathway of BF-20E-PGE₂ is required for early vitellogenesis in the mosquito.

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.

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.

The KNRL nuclear receptor controls hydrolase-mediated vitellin breakdown during embryogenesis in the brown planthopper, Nilaparvata lugens

Vitellin (Vn) homeostasis is central to the fecundity of oviparous insects. Most studies have focused on the synthesis and transportation of Vn as a building block for developing eggs during vitellogenesis; however, less is known about how the utilization of this nutrient reserve affects embryonic development. Here, we show that the single ortholog of the knirps and knirps-like nuclear receptors, KNRL, negatively regulates Vn breakdown by suppressing the expression of hydrolase genes in the brown planthopper, Nilaparvata lugens. KNRL was highly expressed in the ovary of adult females, and knockdown of KNRL by RNA interference resulted in the acceleration of Vn breakdown and the inhibition of embryonic development. Transcriptome sequencing analysis revealed that numerous hydrolase genes, including cathepsins and trypsins were up-regulated after KNRL knockdown. At least eight of the nine significantly enriched Gene Ontology terms for the up-regulated genes were in proteolysis-related categories. The expression levels of five selected trypsin genes and the enzymatic activities of trypsin in the embryos were significantly increased after KNRL knockdown. Moreover, trypsin injection prolonged egg duration, delayed embryonic development, accelerated Vn breakdown and severely reduced egg hatchability, a pattern similar to that observed in KNRL-silenced N. lugens. These observations suggest that KNRL controls Vn breakdown in embryos via the transcriptional inhibition of hydrolases. Generally, this study provides a foundation for understanding how embryo nutrient reserves are mobilized during embryogenesis and identifies several genes and pathways that may prove valuable targets for pest control.

The ecdysone-induced protein 93 is a key factor regulating gonadotrophic cycles in the adult female mosquito Aedes aegypti

Repeated blood feedings are required for adult female mosquitoes to maintain their gonadotrophic cycles, enabling them to be important pathogen carriers of human diseases. Elucidating the molecular mechanism underlying developmental switches between these mosquito gonadotrophic cycles will provide valuable insight into mosquito reproduction and could aid in the identification of targets to disrupt these cycles, thereby reducing disease transmission. We report here that the transcription factor ecdysone-induced protein 93 (E93), previously implicated in insect metamorphic transitions, plays a key role in determining the gonadotrophic cyclicity in adult females of the major arboviral vector Aedes aegypti Expression of the E93 gene in mosquitoes is down-regulated by juvenile hormone (JH) and up-regulated by 20-hydroxyecdysone (20E). We find that E93 controls Hormone Receptor 3 (HR3), the transcription factor linked to the termination of reproductive cycles. Moreover, knockdown of E93 expression via RNAi impaired fat body autophagy, suggesting that E93 governs autophagy-induced termination of vitellogenesis. E93 RNAi silencing prior to the first gonadotrophic cycle affected normal progression of the second cycle. Finally, transcriptomic analysis showed a considerable E93-dependent decline in the expression of genes involved in translation and metabolism at the end of a reproductive cycle. In conclusion, our data demonstrate that E93 acts as a crucial factor in regulating reproductive cycle switches in adult female mosquitoes.

20-Hydroxyecdysone (20E) signaling as a promising target for the chemical control of malaria vectors

With the rapid development and spread of resistance to insecticides among anopheline malaria vectors, the efficacy of current World Health Organization (WHO)-approved insecticides targeting these vectors is under threat. This has led to the development of novel interventions, including improved and enhanced insecticide formulations with new targets or synergists or with added sterilants and/or antimalarials, among others. To date, several studies in mosquitoes have revealed that the 20-hydroxyecdysone (20E) signaling pathway regulates both vector abundance and competence, two parameters that influence malaria transmission. Therefore, insecticides which target 20E signaling (e.g. methoxyfenozide and halofenozide) may be an asset for malaria vector control. While such insecticides are already commercially available for lepidopteran and coleopteran pests, they still need to be approved by the WHO for malaria vector control programs. Until recently, chemicals targeting 20E signaling were considered to be insect growth regulators, and their effect was mostly studied against immature mosquito stages. However, in the last few years, promising results have been obtained by applying methoxyfenozide or halofenozide (two compounds that boost 20E signaling) to Anopheles populations at different phases of their life-cycle. In addition, preliminary studies suggest that methoxyfenozide resistance is unstable, causing the insects substantial fitness costs, thereby potentially circumventing one of the biggest challenges faced by current vector control efforts. In this review, we first describe the 20E signaling pathway in mosquitoes and then summarize the mechanisms whereby 20E signaling regulates the physiological processes associated with vector competence and vector abundance. Finally, we discuss the potential of using chemicals targeting 20E signaling to control malaria vectors.

Controlling the development of the dengue vector Aedes aegypti using HR3 RNAi transgenic Chlamydomonas

The Aedes aegypti mosquito plays an important role in the spread of diseases, including epidemic ones, such as dengue fever, Zika virus disease, yellow fever, and chikungunya disease. To control the population of Ae.aegypti, we transferred an HR3 RNAi fragment into the microalgae Chlamydomonas, which serves as food for Ae.aegypti larvae. Results showed that the HR3 RNAi transgenic algal strains were lethal to Ae.aegypti. The integumentary system of larvae fed with HR3 RNAi transgenic algal strains was severely damaged. Muscles of the larvae were unevenly distributed and disordered, and their midgut showed disintegration of the intestinal cavity. RNA-Seq results demonstrated that on the 4th day of inoculation with the transgenic algae, the abundance of early expressed genes in the 20E signal transduction pathway of larvae fed with the HR3 RNAi transgenic algal strain significantly reduced. These genes include E74, E75, E93, and 20E receptor complex EcR/USP and FTZ-F1 gene regulated by HR3. In later experiments, a scale test of 300 Ae.aegypti eggs per group was carried out for 30 days, and the survival rate of Ae.aegypti fed with the HR3 RNAi transgenic strain was only 1.3%. These results indicate that the HR3 RNAi transgenic strain exerts obvious insecticidal effect.

Conidiobolus coronatus induces oxidative stress and autophagy response in Galleria mellonella larvae

Cell homeostasis requires the correct levels of reactive oxygen species (ROS) to be maintained as these regulate the proliferation and differentiation of cells, and control the immune response and inflammation. High levels of ROS can cause oxidative stress, leading to protein, lipid and DNA damage, or even cell death. Under physiological conditions, the rate of autophagy remains stable; however, it can be accelerated by a number of exogenous stimuli such as oxidative stress, starvation or hypoxia, leading to cell death. The present paper examines the effect of Conidiobolus coronatus infection on the immune response, oxidative stress processes and autophagy in the greater wax moth, Galleria mellonella. Fungal infection was found to result in the disorganization of the cytoskeleton of the larval immune cells and the enhancement of oxidative defense processes. Lipid peroxidation and autophagy were also induced in the hemocytes. Our findings show that G. mellonella is an ideal model for exploring immune mechanisms.

Metabolic balancing by miR-276 shapes the mosquito reproductive cycle and Plasmodium falciparum development

The blood-feeding behavior of Anopheles females delivers essential nutrients for egg development and drives parasite transmission between humans. Plasmodium growth is adapted to the vector reproductive cycle, but how changes in the reproductive cycle impact parasite development remains unclear. Here, we show that the bloodmeal-induced miR-276-5p fine-tunes the expression of branched-chain amino acid transferase to terminate the reproductive cycle. Silencing of miR-276 prolongs high rates of amino acid (AA) catabolism and increases female fertility, suggesting that timely termination of AA catabolism restricts mosquito investment into reproduction. Prolongation of AA catabolism in P. falciparum-infected females also compromises the development of the transmissible sporozoite forms. Our results suggest that Plasmodium sporogony exploits the surplus mosquito resources available after reproductive investment and demonstrate the crucial role of the mosquito AA metabolism in within-vector parasite proliferation and malaria transmission.

Plasmodium growth is adapted to the reproductive cycle of mosquitoes, but underlying mechanisms are unclear. Here, Lampe et al. show that the blood-meal induced miR-276 balances the termination of the mosquito amino acid catabolism and egg development, providing nutrients for Plasmodium sporozoite development.

The genome-wide transcriptional regulatory landscape of ecdysone in the silkworm

BACKGROUND

The silkworm, Bombyx mori, a typical representative of metamorphic insects, is of great agricultural and economic importance. The steroid hormone ecdysone (20-hydroxyecdysone, 20E) is the central regulator of insect developmental transitions, and its nuclear receptors are crucial for numerous biological processes, including reproduction, metabolism, and immunity. However, genome-wide DNA regulatory elements and the ecdysone receptor (EcR) that control these programs of gene expression are not well defined.

RESULTS

In this study, we investigated the alterations in three types of histone modification in silkworm embryonic cells treated with 20E by chromatin immunoprecipitation sequencing (ChIP-seq). We identified enhancers using histone modifications and derived genome-wide ecdysone-dependent enhancer activity maps in the silkworm. We found enhancers enriched for monomethylation of histone H3 Lys4 (H3K4me1) that showed dynamic changes in acetylation of histone H3 Lys27 (H3K27ac) after 20E treatment and functioned to regulate the transcription of specific genes. EcR regulated transcription by binding not only to proximal promoters but also to the distal enhancers of target genes. Moreover, only 52.65% EcR peaks contained ecdysone response element (EcRE) motif, suggesting that EcR regulates the expression of target genes not only by binding directly to EcRE, but also by binding with other transcription factor.

CONCLUSIONS

Our findings provide novel insights into the complex regulatory landscape of hormone-responsive cell activity and a basis for understanding the complex transcriptional regulatory processes of ecdysone.

Regulatory Pathways Controlling Female Insect Reproduction

The synthesis of vitellogenin and its uptake by maturing oocytes during egg maturation are essential for successful female reproduction. These events are regulated by the juvenile hormones and ecdysteroids and by the nutritional signaling pathway regulated by neuropeptides. Juvenile hormones act as gonadotropins, regulating vitellogenesis in most insects, but ecdysteroids control this process in Diptera and some Hymenoptera and Lepidoptera. The complex crosstalk between the juvenile hormones, ecdysteroids, and nutritional signaling pathways differs distinctly depending on the reproductive strategies adopted by various insects. Molecular studies within the past decade have revealed much about the relationships among, and the role of, these pathways with respect to regulation of insect reproduction. Here, we review the role of juvenile hormones, ecdysteroids, and nutritional signaling, along with that of microRNAs, in regulating female insect reproduction at the molecular level.

Nuclear receptor HR3 controls locust molt by regulating chitin synthesis and degradation genes of Locusta migratoria

During growth and development of insects, the steroid hormone 20-Hydroxyecdysone (20E) regulates the molting process through activation of a series of genes including E74, E75 and HR3 by the 20E receptor EcR. Here, we analyzed the function of LmHR3 in the migratory locust Locusta migratoria. By sequence comparison, we first identified and characterized the putative nuclear receptor protein (LmHR3) based on L. migratoria transcriptome data. The full length cDNA is 2272 bp long encoding a protein of 455 amino acids that contains a DNA binding domain (zinc finger) and a ligand binding domain. Phylogenetic analyses showed that LmHR3 has a high homology with the ortholog from Blattaria. RT-qPCR results revealed that LmHR3 has a low level expression in the early days of 5th instar nymphs, and then increases and peaks at day 6, followed by a decrease to low levels before ecdysis. The LmHR3, hence, coincides with the profile of circulating 20E levels. Indeed, we show that transcription of LmHR3 is induced by 20E in vivo, and significantly suppressed by successfully knocking down expression of LmEcR. After injection of dsRNA for LmHR3 (dsLmHR3) at day 2 of earlier instar nymphs (3rd and 4th instar) and final instar nymphs (5th instar), none of the nymphs were able to molt normally, and eventually died. Chitin staining and ultra-structural analysis showed that both the synthesis of the new cuticle and the degradation of the old cuticle were blocked in the dsLmHR3 treated nymphs. Especially, chitin synthesis genes (LmUAP1 and LmCHS1) and chitinase genes (LmCHT5 and LmCHT10) were significantly down-regulated in the dsLmHR3 treatment group. Together, our results suggest that LmHR3 is involved in the control of chitin synthesis and degradation during L. migratoria molting.

Implications of autophagy on arbovirus infection of mosquitoes

Arthropod-borne (arbo-) viruses, like all viruses, are obligate intracellular parasites that have evolved mechanisms to subvert cellular processes and evade anti-viral defenses to replicate and persist. An increasing body of research is beginning to recognize the intimate relationship between arboviruses and the cellular autophagy pathway. As a result, new therapeutic approaches that modify the autophagic response to viral infection have shown great promise. The preponderance of work thus far, however, has originated from vertebrate systems. Efforts to elucidate the role of autophagy during arbovirus infection of invertebrates have emerged, providing new insights into arbovirus-vector interactions; interactions that could be exploited for novel control strategies.

WAFs lead molting retardation of naupliar stages with down-regulated expression profiles of chitin metabolic pathway and related genes in the copepod Tigriopus japonicus

Oil pollution is considered being disastrous to marine organisms and ecosystems. As molting is critical in the developmental process of arthropods in general and copepods, in particular, the impact will be adverse if the target of spilled oil is on molting. Thus, we investigated the harmful effects of water accommodated fractions (WAFs) of crude oil with an emphasis on inhibition of chitin metabolic pathways related genes and developmental retardation in the copepod Tigriopus japonicus. Also, we analysed the ontology and domain of chitin metabolic pathway genes and mRNA expression patterns of developmental stage-specific genes. Further, the developmental retardation followed by transcriptional modulations in nuclear receptor genes (NR) and chitin metabolic pathway-related genes were observed in the WAFs-exposed T. japonicus. As a result, the developmental time was found significantly (P<0.05) delayed in response to 40% WAFs in comparison with that of control. Moreover, the NR gene, HR3 and chitinases (CHT9 and CHT10) were up-regulated in N4-5 stages, while chitin synthase genes (CHS-1, CHS-2-1, and CHS-2-2) down-regulated in response to WAFs. In brief, a high concentration of WAFs repressed nuclear receptor genes but elicited activation of some of the transcription factors at low concentration of WAFs, resulting in suppression of chitin synthesis. Thus, we suggest that WAF can lead molting retardation of naupliar stages in T. japonicus through down-regulations of chitin metabolism. These findings will provide a better understanding of the mode of action of chitin biosynthesis associated with molting mechanism in WAF-exposed T. japonicus.

Ecdysone receptor (EcR) and ultraspiracle (USP) genes from the cyclopoid copepod Paracyclopina nana: Identification and expression in response to water accommodated fractions (WAFs)

Ecdysteroid hormones are pivotal in the development, growth, and molting of arthropods, and the hormone pathway is triggered by binding ecdysteroid to a heterodimer of the two nuclear receptors; ecdysone receptors (EcR) and ultraspiracle (USP). We have characterized EcR and USP genes, and their 5'-untranslated region (5'-UTR) from the copepod Paracyclopina nana, and studied mRNA transcription levels in post-embryonic stages and in response to water accommodated fractions (WAFs) of crude oil. The open reading frames (ORF) of EcR and USP were 1470 and 1287bp that encoded 490 and 429 amino acids with molecular weight of 121.18 and 105.03kDa, respectively. Also, a well conserved DNA-binding domain (DBD) and ligand-binding domain (LBD) were identified which confirmed by phylogenetic analysis. Messenger RNA transcriptional levels of EcR and USP were developmental stage-specific in early post-embryonic stages (N3-4). However, an evoked expression of USP was observed throughout copepodid stage and in adult females. WAFs (40 and 80%) were acted as an ecdysone agonist in P. nana, and elicited the mRNA transcription levels in adults. Developmental stage-specific transcriptional activation of EcR and USP in response to WAFs was observed. USP gene was down-regulated in the nauplius in response to WAF, whereas up-regulation of USP was observed in the adults. This study represents the first data of molecular elucidation of EcR and USP genes and their regulatory elements from P. nana and the developmental stage specific expression in response to WAFs, which can be used as potential biomarkers for environmental stressors with ecotoxicological evaluations in copepods.

Apoptosis-related genes control autophagy and influence DENV-2 infection in the mosquito vector, Aedes aegypti

The mosquito Aedes aegypti is the primary urban vector for dengue virus (DENV) worldwide. Insight into interactions occurring between host and pathogen is important in understanding what factors contribute to vector competence. However, many of the molecular mechanisms for vector competence remain unknown. Our previous global transcriptional analysis suggested that differential expression of apoptotic proteins is involved in determining refractoriness vs susceptibility to DENV-2 infection in Ae. aegypti females following a DENV-infected blood meal. To determine whether DENV-refractory Ae. aegypti showed more robust apoptosis upon infection, we compared numbers of apoptotic cells from midguts of refractory and susceptible strains and observed increased numbers of apoptotic cells in only the refractory strain upon DENV-2 infection. Thereafter, we manipulated apoptosis through dsRNA interference of the initiator caspase, Aedronc. Unexpectedly, dsAedronc-treated females showed both decreased frequency of disseminated infection and decreased virus titer in infected individuals. Insect caspases have also previously been identified as regulators of the cellular recycling process known as autophagy. We observed activation of autophagy in midgut and fat body tissues following a blood meal, as well as programmed activation of several apoptosis-related genes, including the effector caspase, Casps7. To determine whether autophagy was affected by caspase knockdown, we silenced Aedronc and Casps7, and observed reduced activation of autophagy upon silencing. Our results provide evidence that apoptosis-related genes are also involved in regulating autophagy, and that Aedronc may play an important role in DENV-2 infection success in Ae. aegypti, possibly through its regulation of autophagy.

The Steroid Hormone 20-Hydroxyecdysone Enhances Gene Transcription through the cAMP Response Element-binding Protein (CREB) Signaling Pathway

Animal steroid hormones regulate gene transcription through genomic pathways by binding to nuclear receptors. These steroid hormones also rapidly increase intracellular calcium and cyclic adenosine monophosphate (cAMP) levels and activate the protein kinase C (PKC) and protein kinase A (PKA) nongenomic pathways. However, the function and mechanism of the nongenomic pathways of the steroid hormones are unclear, and the relationship between the PKC and PKA pathways is also unclear. We propose that the steroid hormone 20-hydroxyecdysone (20E) activates the PKA pathway to enhance 20E-induced gene transcription in the lepidopteran insect Helicoverpa armigera The expression of the catalytic subunit 1 of PKA (PKAC1) increased during metamorphosis, and PKAC1 knockdown blocked pupation and repressed 20E-responsive gene expression. 20E regulated PKAC1 phosphorylation at threonine 200 and nuclear translocation through an ecdysone-responsive G-protein-coupled receptor 2. PKAC1 induced cAMP response element-binding protein (CREB) phosphorylation at serine 143, which bound to the cAMP response element on DNA to enhance 20E-responsive gene transcription. Through ecdysone-responsive G-protein-coupled receptor 2, 20E increased cAMP levels, which induced CREB PKA phosphorylation and 20E-responsive gene expression. This study demonstrates that the PKA/CREB pathway tightly and critically regulates 20E-induced gene transcription as well as its relationship with the 20E-induced PKC pathway.

Hairy and Groucho mediate the action of juvenile hormone receptor Methoprene-tolerant in gene repression

The arthropod-specific juvenile hormone (JH) controls numerous essential functions. Its involvement in gene activation is known to be mediated by the transcription factor Methoprene-tolerant (Met), which turns on JH-controlled genes by directly binding to E-box-like motifs in their regulatory regions. However, it remains unclear how JH represses genes. We used the Aedes aegypti female mosquito, in which JH is necessary for reproductive maturation, to show that a repressor, Hairy, is required for the gene-repressive action of JH and Met. The RNA interference (RNAi) screen for Met and Hairy in the Aedes female fat body revealed a large cohort of Met- and Hairy-corepressed genes. Analysis of selected genes from this cohort demonstrated that they are repressed by JH, but RNAi of either Met or Hairy renders JH ineffective in repressing these genes in an in vitro fat-body culture assay. Moreover, this JH action was prevented by the addition of the translational inhibitor cycloheximide (CHX) to the culture, indicating the existence of an indirect regulatory hierarchy. The lack of Hairy protein in the CHX-treated tissue was verified using immunoblot analysis, and the upstream regions of Met/Hairy-corepressed genes were shown to contain common binding motifs that interact with Hairy. Groucho (gro) RNAi silencing phenocopied the effect of Hairy RNAi knockdown, indicating that it is involved in the JH/Met/Hairy hierarchy. Finally, the requirement of Hairy and Gro for gene repression was confirmed in a cell transfection assay. Thus, our study has established that Hairy and its cofactor Gro mediate the repressive function of JH and Met.

Regulation of Gene Expression Patterns in Mosquito Reproduction

In multicellular organisms, development, growth and reproduction require coordinated expression of numerous functional and regulatory genes. Insects, in addition to being the most speciose animal group with enormous biological and economical significance, represent outstanding model organisms for studying regulation of synchronized gene expression due to their rapid development and reproduction. Disease-transmitting female mosquitoes have adapted uniquely for ingestion and utilization of the huge blood meal required for swift reproductive events to complete egg development within a 72-h period. We investigated the network of regulatory factors mediating sequential gene expression in the fat body, a multifunctional organ analogous to the vertebrate liver and adipose tissue, of the female Aedes aegypti mosquito. Transcriptomic and bioinformatics analyses revealed that ~7500 transcripts are differentially expressed in four sequential waves during the 72-h reproductive period. A combination of RNA-interference gene-silencing and in-vitro organ culture identified the major regulators for each of these waves. Amino acids (AAs) regulate the first wave of gene activation between 3 h and 12 h post-blood meal (PBM). During the second wave, between 12 h and 36 h, most genes are highly upregulated by a synergistic action of AAs, 20-hydroxyecdysone (20E) and the Ecdysone-Receptor (EcR). Between 36 h and 48 h, the third wave of gene activation—regulated mainly by HR3—occurs. Juvenile Hormone (JH) and its receptor Methoprene-Tolerant (Met) are major regulators for the final wave between 48 h and 72 h. Each of these key regulators also has repressive effects on one or more gene sets. Our study provides a better understanding of the complexity of the regulatory mechanisms related to temporal coordination of gene expression during reproduction. We have detected the novel function of 20E/EcR responsible for transcriptional repression. This study also reveals the previously unidentified large-scale effects of HR3 and JH/Met on transcriptional regulation during the termination of vitellogenesis and remodeling of the fat body.

In addition to being vectors of devastating human diseases, mosquitoes represent outstanding model organisms for studying regulatory mechanisms of differential gene expression due to their rapid reproductive cycles. About 7500 transcripts are differentially expressed in four sequential waves during the 72-h reproductive period in the fat body, a critical reproductive organ. The major regulators for these waves of gene expression are the two very important insect hormones, 20-hydroxyecdysone (20E) and Juvenile hormone (JH), their respective receptors Ecdysone Receptor (EcR) and Methoprene-Tolerant (Met), amino acids and the orphan nuclear receptor HR3. These key regulators are responsible for activation and repression of co-regulated gene sets, at different time points, within the 72-h reproductive period. Importantly, this study, apart from providing an insight into the regulatory complexity involved in the temporal coordination of gene expression, also reveals the previously unidentified roles of 20E/EcR, JH/Met and HR3 during the 72-h period post blood meal.

Temporal Coordination of Carbohydrate Metabolism during Mosquito Reproduction

Hematophagous mosquitoes serve as vectors of multiple devastating human diseases, and many unique physiological features contribute to the incredible evolutionary success of these insects. These functions place high-energy demands on a reproducing female mosquito, and carbohydrate metabolism (CM) must be synchronized with these needs. Functional analysis of metabolic gene profiling showed that major CM pathways, including glycolysis, glycogen and sugar metabolism, and citrate cycle, are dramatically repressed at post eclosion (PE) stage in mosquito fat body followed by a sharply increase at post-blood meal (PBM) stage, which were also verified by Real-time RT-PCR. Consistent to the change of transcript and protein level of CM genes, the level of glycogen, glucose and trehalose and other secondary metabolites are also periodically accumulated and degraded during the reproductive cycle respectively. Levels of triacylglycerols (TAG), which represent another important energy storage form in the mosquito fat body, followed a similar tendency. On the other hand, ATP, which is generated by catabolism of these secondary metabolites, showed an opposite trend. Additionally, we used RNA interference studies for the juvenile hormone and ecdysone receptors, Met and EcR, coupled with transcriptomics and metabolomics analyses to show that these hormone receptors function as major regulatory switches coordinating CM with the differing energy requirements of the female mosquito throughout its reproductive cycle. Our study demonstrates how, by metabolic reprogramming, a multicellular organism adapts to drastic and rapid functional changes.

Mosquitoes transmit numerous devastating human diseases due to their obligatory hematophagy that is required for the efficient reproduction. Metabolism must be synchronized with high energetic needs of a female mosquito for host seeking, blood feeding and rapid egg development. Each reproductive cycle is divided into two phases that are sequentially governed by juvenile hormone (JH) and 20-hydroxyecdysone. During the pre-blood meal phase, the JH receptor Methoprene-tolerant (Met) controls carbohydrate metabolism (CM) pathways and its RNA interference (RNAi) silencing caused up-regulation of CM enzymes at the transcript and protein levels activating glycolytic flux and depletion of storage and circulating sugars. During the second, post blood meal phase, CM was regulated by the ecdysone receptor EcR and its RNAi silencing had a dramatic effect opposite to that of Met RNAi. Thus, we show that Met and EcR function as regulatory switches coordinating carbohydrate metabolism with energetic requirements of the female mosquito reproductive cycle.

The steroid hormone 20-hydroxyecdysone via nongenomic pathway activates Ca2+/calmodulin-dependent protein kinase II to regulate gene expression

The steroid hormone 20-hydroxyecdysone (20E) triggers calcium signaling pathway to regulate 20E response gene expression, but the mechanism underlying this process remains unclear. We propose that the 20E-induced phosphorylation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) serves an important function in 20E response gene transcription in the lepidopteran insect Helicoverpa armigera. CaMKII showed increased expression and phosphorylation during metamorphosis. 20E elevated CaMKII phosphorylation. However, the G protein-coupled receptor (GPCR) and ryanodine receptor inhibitor suramin, the phospholipase C inhibitor U73122, and the inositol 1,4,5-triphosphate receptor inhibitor xestospongin C suppressed 20E-induced CaMKII phosphorylation. Two ecdysone-responsible GPCRs and Gαq protein were involved in 20E-induced CaMKII phosphorylation by RNA interference analysis. 20E regulated CaMKII threonine phosphorylation at amino acid 290, thereby inducing CaMKII nuclear translocation. CaMKII knockdown by dsCaMKII injection into the larvae prevented the occurrence of larval-pupal transition and suppressed 20E response gene expression. CaMKII phosphorylation and nuclear translocation maintained USP1 lysine acetylation at amino acid 303 by inducing histone deacetylase 3 phosphorylation and nuclear export. The lysine acetylation of USP1 was necessary for the interaction of USP1 with EcRB1 and their binding to the ecdysone response element. Results suggest that 20E (via GPCR activation and calcium signaling) activates CaMKII phosphorylation and nuclear translocation, which regulate USP1 lysine acetylation to form an EcRB1-USP1 complex for 20E response gene transcription.

Juvenile hormone and its receptor, methoprene-tolerant, control the dynamics of mosquito gene expression

Juvenile hormone III (JH) plays a key role in regulating the reproduction of female mosquitoes. Microarray time-course analysis revealed dynamic changes in gene expression during posteclosion (PE) development in the fat body of female Aedes aegypti. Hierarchical clustering identified three major gene clusters: 1,843 early-PE (EPE) genes maximally expressed at 6 h PE, 457 mid-PE (MPE) genes at 24 h PE, and 1,815 late-PE (LPE) genes at 66 h PE. The RNAi microarray screen for the JH receptor Methoprene-tolerant (Met) showed that 27% of EPE and 40% of MPE genes were up-regulated whereas 36% of LPE genes were down-regulated in the absence of this receptor. Met repression of EPE and MPE and activation of LPE genes were validated by an in vitro fat-body culture experiment using Met RNAi. Sequence motif analysis revealed the consensus for a 9-mer Met-binding motif, CACG(C)/TG(A)/G(T)/AG. Met-binding motif variants were overrepresented within the first 300 bases of the promoters of Met RNAi-down-regulated (LPE) genes but not in Met RNAi-up-regulated (EPE) genes. EMSAs using a combination of mutational and anti-Met antibody supershift analyses confirmed the binding properties of the Met consensus motif variants. There was a striking temporal separation of expression profiles among major functional gene groups, with carbohydrate, lipid, and xenobiotics metabolism belonging to the EPE and MPE clusters and transcription and translation to the LPE cluster. This study represents a significant advancement in the understanding of the regulation of gene expression by JH and its receptor Met during female mosquito reproduction.