Prostaglandin signaling and ovarian follicle development in the silkmoth, Bombyx mori

A PLA2 deletion mutant using CRISPR/Cas9 coupled to RNASeq reveals insect immune genes associated with eicosanoid signaling

Eicosanoids mediate insect immune responses and synthesized by the catalytic activity of phospholipase A2 (PLA2). A uniquely encoded secretory PLA2 (sPLA2) is associated with immune responses of a lepidopteran insect, Spodoptera exigua. Its deletion mutant was generated using a CRISPR/Cas9 genome editing technology. Both wild and mutant lines were then immune-challenged, and the resulting transcripts were compared with their naïve transcripts by RNASeq using the Illumina-HiSeq platform. In total, 12,878 unigenes were further analyzed by differentially expressed gene tools. Over 69% of the expressed genes in S. exigua larvae are modulated in their expression levels by eicosanoids, recorded from CRISPR/Cas9 mutagenesis against an eicosanoid-synthetic gene, Se-sPLA2. Further, about 36% of the immune-associated genes are controlled by the eicosanoids in S. exigua. Indeed, the deletion mutant suffered significant immunosuppression in both cellular and humoral responses in response to bacterial challenge as well as severely reduced developmental and reproductive potentials.

Prostaglandin A3 regulates the colony development of Odontotermes formosanus by reducing worker proportion

Subterranean termites cause significant economic losses worldwide due to their destruction of agricultural and forest plants. In the past, soil termiticides were commonly used to control subterranean termites because they were effective and affordable. However, due to growing environmental concerns, these harmful substances have become less popular as they cause damage to non-target organisms and lead to environmental contamination. Baits crafted from plants and other easily metabolized compounds serve as excellent alternatives. In this study, we gathered branches from the promising plant, Magnolia grandiflora L. (MGL), along with branches from five other tree species that are potential food for termites. These branches were used as food to observe the population growth of Odontotermes formosanus. Additionally, a mix of branches from all six species was used to feed the control group (MIX). The study results showed that MGL nutrition significantly inhibited worker development, resulting in a significantly lower worker-to-soldier ratio (WSR). Furthermore, LC‒MS/MS analysis revealed that the level of prostaglandin A3 (PGA3) in workers significantly increased when they were under MGL nutrition. Additionally, ICP-MS analysis indicated a significant increase in calcium concentrations in the branches of MGL and combs under MGL nutrition. Moreover, there was a significant increase in peroxidase (POD) activity in workers under MGL nutrition. These findings suggest that the inhibitory effect of MGL nutrition on worker development may be due to excessive PGA3 synthesis, as Ca2+ and POD are involved in the synthesis process of PGs in insects. Subsequent verification experiments strongly support this hypothesis, as the WSR of colonies fed PGA3-added MIX was significantly lower than that of the MIX alone. This study introduces a new concept for developing environmentally friendly biological control methods for O. formosanus and sheds light on the potential role of PGs in termite development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44297-024-00030-3.

Lipids in Insect Reproduction: Where, How, and Why

Modern insects have inhabited the earth for hundreds of millions of years, and part of their successful adaptation lies in their many reproductive strategies. Insect reproduction is linked to a high metabolic rate that provides viable eggs in a relatively short time. In this context, an accurate interplay between the endocrine system and the nutrients synthetized and metabolized is essential to produce healthy offspring. Lipids guarantee the metabolic energy needed for egg formation and represent the main energy source consumed during embryogenesis. Lipids availability is tightly regulated by a complex network of endocrine signals primarily controlled by the central nervous system (CNS) and associated endocrine glands, the corpora allata (CA) and corpora cardiaca (CC). This endocrine axis provides hormones and neuropeptides that significatively affect tissues closely involved in successful reproduction: the fat body, which is the metabolic center supplying the lipid resources and energy demanded in egg formation, and the ovaries, where the developing oocytes recruit lipids that will be used for optimal embryogenesis. The post-genomic era and the availability of modern experimental approaches have advanced our understanding of many processes involved in lipid homeostasis; therefore, it is crucial to integrate the findings of recent years into the knowledge already acquired in the last decades. The present chapter is devoted to reviewing major recent contributions made in elucidating the impact of the CNS/CA/CC-fat body-ovary axis on lipid metabolism in the context of insect reproduction, highlighting areas of fruitful research.

BmPxt1 mediated immune response by regulating PGE2 in silkworm, Bombyx mori

Prostaglandins (PGs) mediates the immune response of insects to multiple stimuli. Mammalian cyclooxygenase (COXs) is a key enzyme in the synthesis of PGs, and peroxinectin (Pxt) may have similar functions in some sequenced insect genomes. As a representative of Lepidoptera, the silkworm also contains PGs, but its synthetic pathway is not clear. We cloned a full-length cDNA encoding a Pxt, designated as BmPxt1, from silkworm. Sequence alignment analysis showed that the protein encoded by BmPxt1 has a conserved domain similar to Pxts, and its catalytic site is shared with the Pxt of Manduca sexta, which also produces PGs. The expression of BmPxt1 gene was the highest in the hemocytes and was induced by Nuclear Polyhedrosis Virus (NPV) challenge in the detected tissues. Moreover, we found that dsPxt1 treatment deficiency down-regulated BmPxt1 transcript levels and efficiently inhibiting hemocyte-spreading and nodule formation in silkworm. Hemocyte-spreading, nodule formation, phenoloxidase (PO) and AMP genes (attacin, defencin and moricin) were also inhibited by aspirin, a COX inhibitor. Treatment by PGE2 but not arachidonic acid (AA) rescued the immunosuppression; PGs concentrations was also inhibited by aspirin. PGE2, but not AA, treatment rescued the PGs concentrations. The COX inhibitor, aspirin, impaired the innate immune response including nodulation, encapsulation, and melanization in silkworm, while PGE2, but not arachidonic acid (AA), partially reversed these effects of aspirin. Recombinant BmsPxt1 significantly induced PO activation in larvae hemolymph, PGs concentrations and encapsulation of agarose beads. Injection of recombinant BmsPxt1 into larvae resulted in increased transcript levels of AMP genes. Our results confirmed that BmPxt1 was involved in the synthesis of PGs in the innate immune response of silkworm larvae, and provided new information for the role of BmsPxt1 secreted by silkworm in activating PO and antimicrobial peptides.

Prostaglandin E2 mediates chorion formation of the Asian tiger mosquito, Aedes albopictus, at late oogenesis

Chorion-i.e., the eggshell-is formed during the late stage of oogenesis by follicular epithelium in the ovary. Although the endocrine signal(s) driving choriogenesis remain unclear in mosquitoes, this process in other insects has been suspected to involve the mediation of prostaglandins (PGs). This study tested the role of PG in the choriogenesis of the Asian tiger mosquito, Aedes albopictus, and its influence on controlling the expressions of genes associated with chorion formation by a transcriptome analysis. An immunofluorescence assay showed that PGE2 is localised in follicular epithelium. With the treatment of aspirin, an inhibitor of PG biosynthesis, at mid oogenesis, the PGE2 signal disappeared in the follicular epithelium led to significantly inhibited chorion formation along with a malformed eggshell. Ovary transcriptomes were assessed by RNASeq at the mid and late ovarian developmental stages. Differentially expressed genes (DEGs) exhibiting more than twofold changes in expression levels included 297 genes at mid stage and 500 genes at late stage. These DEGs at these two developmental stages commonly included genes associated with egg and chorion proteins of Ae. albopictus. Most chorion-associated genes were clustered in the 168 Mb region on a chromosome and exhibited significantly induced expressions at both ovarian developmental stages. The inhibition of PG biosynthesis significantly suppressed the expression of the chorion-associated genes while the addition of PGE2 rescued the gene expressions and led to recovery of choriogenesis. These results suggest that PGE2 mediates the choriogenesis of Ae. albopictus.

PGE2 mediation of egg development in Western flower thrip, Frankliniella occidentalis

Eicosanoids mediate various insect physiological processes, including reproduction. Especially, the eicosanoid prostaglandin E₂  (PGE₂ ) is known to mediate oocyte development in some insects. The explosive reproductive potential of the Western flower thrips, Frankliniella occidentalis, damages various agricultural crops. However, little is known about the underlying physiological processes of egg development in this pest. This study found that treatment with aspirin (ASP) (a specific cyclooxygenase (COX) inhibitor) used to inhibit PGE₂ biosynthesis during ovarian development significantly suppressed the reproduction of female F. occidentalis. However, the addition of PGE₂ to ASP-treated females significantly rescued the suppressed reproduction. PGE₂ was detected in growing ovarian follicles in an immunofluorescence assay. The hypothetical biosynthetic machinery of PGE₂ was predicted from the F. occidentalis genome and included phospholipase A₂  (PLA₂ ), COX-like peroxidase (POX), and PGE₂ synthase (PGES). Three specific PLA₂ s were highly expressed in female adults during active oogenesis. Specific POX and PGES genes also showed high expression during active oogenesis. The adverse effect of ASP treatment on oogenesis was observed in follicle formation in the germarium where the follicle numbers in an ovariole were decreased, which resulted in hypotrophied ovaries. This impairment was rescued by the addition of PGE₂ . ASP treatment also significantly inhibited chorion formation and suppressed gene expression associated with choriogenesis, which included chorion protein, mucin, and yellow while it did not inhibit vitellogenin gene expression. However, the addition of PGE₂ induced the expression of the target genes suppressed by ASP treatment and rescued chorion formation. These results suggest that PGE₂ mediated ovarian development by affecting follicle formation and choriogenesis in F. occidentalis.

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.

Effects of urea application on the reproduction of Pardosa pseudoannulata: Field and laboratory studies

As an important chemical fertilizer, urea can greatly increase crop yields, but it also has negative effects on beneficial arthropods in the agricultural field, such as spiders. Here, we reported that urea application reduced the reproductive performance in Pardosa pseudoannulata, a dominant species of spider in rice fields, which preys on a range of insect pests, based on both field and laboratory studies. In a field test, urea application significantly reduced the egg production of adult and subadult females collected from the urea-treated fields. A laboratory test was set up to further evaluate the impact of urea application on P. pseudoannulata reproduction. In consistent with field test results, the spiders treated by urea for 14 d and 28 d had lower reproduction ability than their control counterparts, with regard to the mating rate, egg production, and egg hatchability. The transcriptomic sequencing of individuals treated by urea for 28 d showed that urea application caused a number of differentially expressed transcripts with several downregulated unigenes related to basic enzymes and several upregulated unigenes involved in stress resistance. The knockdown of a metalloproteinase gene caused a significant decrease in egg production, and the silencing of a carboxylesterase gene significantly reduced both the egg production and egg hatchability. Taken together, the present study found that urea application reduced P. pseudoannulata reproduction ability and the negative impact partially resulted from the downregulation of certain basic enzyme genes. The study provided a fresh view of fertilizers on beneficial arthropods with great potential in the protection of P. pseudoannulata in fields.

Identification and function analysis of BmPxtA in the immune response regulated by PGE2 of silkworm, Bombyx mori

Prostaglandins (PGs) can mediate the immune response of insects to infection. Mammalian cyclooxygenase (COXs) is a key enzyme in the synthesis of PGs, and Pxt may be its homologous gene in some sequenced insect genomes. As a representative of Lepidoptera, the silkworm also contains PGs, but the biosynthetic source of PGs is still unclear. In this study, Sequence analysis showed that peroxinectin (BmPxtA) gene of silkworm was closely related to human COX gene, and its homologous protein had conserved domains corresponding to human COX. The expression of BmPxtA gene was the highest in the hemocytes and was induced by Nuclear Polyhedrosis Virus (NPV) challenge in the detected tissues. The quantitative polymerase chain reaction (qPCR) results showed that silencing BmPxtA mediated by RNA interference (RNAi) inhibited the expression of immune-related pathway genes, and specifically suppressed hemocyte-spreading and nodule formation in silkworm; Hemocyte-spreading and nodule formation were also inhibited by aspirin, a COX inhibitor. Treatment by PGE₂ but not arachidonic acid (AA) rescued the immunosuppression; PGs concentrations was also inhibited by aspirin. PGE₂, but not AA, treatment rescued the PGs concentrations. These results suggest that BmPxtA gene is associated with PG biosynthesis in silkworm and the immune response of silkworm was affected by regulating the concentrations of PGs.

Silkworm FoxL21 plays important roles as a regulator of ovarian development in both oogenesis and ovariole development

The ovary is an important organ in reproduction. In insects, especially lepidopteran insects, the oocytes and reproductive organs develop rapidly during the pupal stage. Despite their drastic morphological changes, the molecular mechanisms of ovary development are not fully understood. In this study, it is found that forkhead box transcription factor L2, member 1 (FoxL21), which is known to be involved in ovarian differentiation and maintenance in vertebrates, is required for the development of the ovary in the silkworm, Bombyx mori. FoxL21 was expressed in the ovary and ovariole during the larval and pupal stage, respectively. In silkworms in which FoxL21 was knocked out by genome editing, multiple ovarian dysfunctions, such as, abnormal egg formation, thinning of the ovariole sheaths, and defective connection of the oviductus geminus with the ovariole were observed. Finally, ovarian transplantation experiments using the knockout silkworms revealed that FoxL21 functions in the ovariole, but not in the oviductus geminus.

The prostanoids, thromboxanes, mediate hemocytic immunity to bacterial infection in the lepidopteran Spodoptera exigua

We report on a new insect prostanoid in a lepidopteran insect, Spodoptera exigua. Thromboxane B₂ (TXB₂) was detected by LC-MS/MS in extracts of larval epidermis, midgut, fat body and hemocytes, with highest amounts in hemocytes (about 300 ng/g tissue with substantial variation). Thromboxane A₂ (TXA₂) is an unstable intermediate that is non-enzymatically hydrolyzed into the stable TXB_2. In S. exigua, both thromboxanes mediate at least two cellular immune responses to bacterial infection, hemocyte-spreading behavior and nodule formation. At the molecular level, a TXA₂ synthase (SeTXAS) was identified from a group of 139 S. exigua cytochrome P450 monooxygenases. SeTXAS was highly similar to mammalian TXAS genes and is expressed in all developmental stages and four tested larval tissues. Immune challenge significantly enhanced SeTXAS expression, especially in hemocytes. RNA interference (RNAi) injections using gene-specific double stranded RNA led to reduced SeTXAS expression and suppressed the cellular immune responses, which were rescued following TXA₂ or TXB₂ injections. Unlike other PGs, TXA₂ or TXB₂ did not influence oocyte development in adult females. We infer that thromboxanes are present in insect tissues, where they mediate innate immune responses.

The first report of prostacyclin and its physiological roles in insects

Prostaglandins (PGs) mediate physiological processes of insects as well as mammals. Prostaglandin I₂ (PGI₂) is a relatively well-known eicosanoid with potent hormone-like actions on various tissues of vertebrates, however, its presence and biosynthetic pathway have not been described in insects. This study demonstrated that fat bodies of the lepidopteran species, Spodoptera exigua, contained ~ 3.6 pg/g PGI₂. To identify its biosynthetic pathway, a PGI₂ synthase gene of S. exigua (Se-PGIS) was predicted from a transcriptome of S. exigua; 25.6% homology with human PGIS was demonstrated. Furthermore, a predicted three-dimensional structure of Se-PGIS was demonstrated to be 38.3% similar to the human PGIS ortholog, including catalytic residues. Se-PGIS was expressed in all developmental stages of S. exigua and most abundant larval and adult stages; immune challenging of larvae significantly up-regulated these expression levels. The inducible expression of Se-PGIS expression was followed by a greater than four-fold increase in the concentration of PGI₂ in fat bodies 10 h after immune challenge. RNA interference (RNAi) against Se-PGIS was performed by injecting double-stranded RNA (dsRNA). Under these RNAi conditions, cellular immune responses (e.g., hemocyte-spreading behavior, nodulation, phenoloxidase activity) were not affected by bacterial challenge. The addition of PGI₂ to larvae treated with an eicosanoid biosynthesis inhibitor did not rescue the immunosuppression. Interestingly, PGI₂ injection significantly suppressed nodule formation in response to bacterial challenge. In addition to the negative effect of PGI₂ against immunity, the Se-PGIS-RNAi treatment significantly interfered with immature development and severely impaired oocyte development in female adults; the addition of PGI₂ to RNAi-treated females significantly recovered oocyte development. Se-PGIS RNAi treatment also impaired male fertility by reducing fecundity after mating with untreated females. These results suggest that PGI₂ acts as a negative regulator of immune responses initiated by other factors and mediates S. exigua development and reproduction.

An ovary-specific mucin is associated with choriogenesis mediated by prostaglandin signaling in Spodoptera exigua

Polytrophic ovarioles of Spodoptera exigua, a lepidopteran insect, begins with the development of oocytes and differentiation of nurse cells followed by vitellogenesis and choriogenesis. Compared with previtellogenic and vitellogenic developments, choriogenesis has not been clearly understood yet in endocrine control. This study investigated the expression and function of a mucin-like structural protein of S. exigua called Se-Mucin1 in choriogenesis. It was highly expressed in ovarioles containing chorionated oocytes. The expression level of Se-Mucin1 was increased during adult stage as early as 18 h after adult emergence, reaching the maximal level at 24 h and later. Interestingly, DNA amount of Se-Mucin1 was increased by almost four folds during early adult stage while other genes (hexokinase and glyceraldehyde-3-phosphate dehydrogenase) not directly associated with chorion formation did not show genomic DNA increase, suggesting specific gene amplification of Se-Mucin1. RNA interference (RNAi) suppressed Se-Mucin1 expression by injecting 1 μg of double-strand RNA to teneral females (<5 h after emergence), which exhibited significantly impaired fecundity and egg hatching rate. Eggs laid by RNAi-treated females were malformed in eggshell structures with loss of mesh-like fibers. Treatment with aspirin, a prostaglandin (PG) biosynthesis inhibitor, suppressed the induction of Se-Mucin1 expression during early adult stage and impaired egg development. An addition of PGE₂ significantly rescued such impairment in Se-Mucin1 expression and subsequent egg development. These results suggest that PGs mediate choriogenesis of S. exigua by activating the expression of chorion-associated genes including Se-Mucin1.

Lipidomic analyses reveal enhanced lipolysis in planthoppers feeding on resistant host plants

The brown planthopper (BPH) (Nilaparvata lugens Stål) is a highly destructive pest that seriously damages rice (Oryza sativa L.) and causes severe yield losses. To better understand the physiological and metabolic mechanisms through which BPHs respond to resistant rice, we combined mass-spectrometry-based lipidomics with transcriptomic analysis and gene knockdown techniques to compare the lipidomes of BPHs feeding on either of the two resistant (NIL-Bph6 and NIL-Bph9) plants or a wild-type, BPH susceptible (9311) plant. Insects that were fed on resistant rice transformed triglyceride (TG) to phosphatidylcholine (PC) and digalactosyldiacylglycerol (DGDG), with these lipid classes showing significant alterations in fatty acid composition. Moreover, the insects that were fed on resistant rice were characterized by prominent expression changes in genes involved in lipid metabolism processes. Knockdown of the NlBmm gene, which encodes a lipase that regulates the mobilization of lipid reserves, significantly increased TG content and feeding performance of BPHs on resistant plants relative to dsGFP-injected BPHs. Our study provides the first detailed description of lipid changes in BPHs fed on resistant and susceptible rice genotypes. Results from BPHs fed on resistant rice plants reveal that these insects can accelerate TG mobilization to provide energy for cell proliferation, body maintenance, growth and oviposition.

Diet quality and NSAIDs promote changes in formation of prostaglandins by an aquatic invertebrate

We used the freshwater insect Hydropsyche sp. to investigate the impact of diets lacking arachidonic acid (ARA) and an environmentally relevant mixture of NSAIDs (Ibuprofen, Ketoprofen, Diclofenac and Naproxen at a nominal concentration of all compounds together 16.75 μg L^-1) on their metabolism of ARA and prostaglandins (PGs). The organisms were exposed for 16 days to four different treatments: a reference (FF), a diet lacking ARA (O), to NSAIDs in water (FFN) and to the combination of the two factors (ON). Mortality, biomass and bioconcentration of pharmaceuticals were investigated. The ARA and PGs levels in the organisms were monitored by utilising a targeted metabolomics approach. NSAIDs or dietary constraints did not produce significant differences in biomass or mortality of Hydropsyche sp. among treatments. In organisms exposed to NSAIDs, all pharmaceuticals were detected, except for Ketoprofen. Metabolomic approach determined the presence of PGH₂, PGE₁ and PGD₁. Levels of ARA diminished significantly in those organisms in treatment ON. The levels of PGs responded negatively to the absence of ARA in diet: PGH₂ diminished significantly with respect to the reference in treatment O while PGE₁ diminished significantly in treatment ON. Regarding the effects of NSAIDs on ARA metabolism, our results suggest that it was sensitive to NSAIDs, but effects were weak and did not imply a general decrease in the PGs. We confirmed that ARA was the main substrate for the synthesis of PGs in Hydropsyche sp, their absence or poor levels of ARA in diet, produced changes in the PG levels.

Deletion mutant of PGE2 receptor using CRISPR-Cas9 exhibits larval immunosuppression and adult infertility in a lepidopteran insect, Spodoptera exigua

Prostaglandins (PGs) mediate various physiological processes in insects and other invertebrates, but there is very little information on PG receptors. This study identified a PGE₂ receptor (SePGE₂R) in the lepidopteran insect, Spodoptera exigua, and addressed its functional association with cellular immunity, development, and reproduction. SePGE₂R is expressed in most developmental stages and tissues. After SePGR₂R expression knock down by RNA interference (RNAi), larval nodule formation (clears bacterial infections from circulating hemolymph) was severely suppressed coupled with reduced F-actin growth in hemocytes. Treating female adults with RNAi prevented nurse cell dumping in follicles and interfered with oocyte development. SePGE₂R was heterologously expressed in Sf9 cells, in which the endogenous S. frugiperda PGE₂R was knocked down by small interfering RNA. This transiently expressed SePGE₂R responded to PGE₂, but not other PGs, with dose-dependent up-regulation of intracellular cAMP concentrations. Treating S. exigua larvae with PGE₂ led to activation of a trimeric Gαs subunit, protein kinase A (PKA), and Rho family small intracellular G proteins in hemocytes. A deletion mutant of SePGE₂R was generated using CRISPR/Cas9 which exhibited severely retarded larval development and adult reproduction. We infer that PGE₂R mediates insect immune and reproductive processes via a PKA signal pathway.

Prostaglandins influence protein phosphorylation in established insect cell line

Prostaglandins (PGs) are oxygenated metabolites of arachidonic acid and two other C20 polyunsaturated fatty acids. Among other actions in invertebrates, PGs act in ovarian development, renal functions, immunity, hemocyte migration, and gene/protein expression. Reversible phosphorylation is a major mechanism of regulating protein functions in eukaryotic cells and for some mammalian proteins it is influenced by PGs. We posed the hypothesis that PGs influence protein phosphorylation within insect cells, which we tested with the established insect cell line, BCIRL-HzAM1. After 20, 30, or 40 min incubations in the presence of one of three PGs (at 15 μM), PGA₂ , PGE₁ , or PGF_2α , separate sets of cells were processed for analysis by two-dimensional electrophoresis followed by tandem mass spectrometry. We recorded significant phosphorylation changes in 31 proteins, decreases in 15, and increases in 15, and one protein with increased or decreased phosphorylation, depending on PG treatment. Increasing PG exposure times led to changes in fewer proteins, 20 min incubations led to changes in 16 proteins, 30 min to changes in 13, and 40 min to changes in 2 proteins. The proteins were identified by bioinformatic analyses, including transcript description, calculated molecular weights and isoelectric points, MOlecular Weight SEarch score, total ion score, numbers of peptides, percent protein coverage, E-value, and highest peptide score. The data presented in this paper firmly support our hypothesis that PGs influence protein phosphorylation within insect cells and adds a novel PG-signaled function to insect biology.

Changes in emergence phenology, fatty acid composition, and xenobiotic-metabolizing enzyme expression is associated with increased insecticide resistance in the Colorado potato beetle

The Colorado potato beetle (Leptinotarsa decemlineata) is a major agricultural pest of solanaceous crops. An effective management strategy employed by agricultural producers to control this pest species is the use of systemic insecticides. Recent emphasis has been placed on the use of neonicotinoid insecticides. Despite efforts to curb resistance development through integrated pest management approaches, resistance to neonicotinoids in L. decemlineata populations continues to increase. One contributing factor may be alterations in insect fatty acids, which have multiple metabolic functions and are associated with the synthesis of xenobiotic-metabolizing enzymes to mitigate the effects of insecticide exposure. In this study, we analyzed the fatty acid composition of L. decemlineata populations collected from an organic production field and from a commercially managed field to determine if fatty acid composition varied between the two populations. We demonstrate that a population of L. decemlineata that has a history of systemic neonicotinoid exposure (commercially managed) has a different lipid composition and differential expression of known metabolic detoxification mechanisms relative to a population that has not been exposed to neonicotinoids (organically managed). The fatty acid data indicated an upregulation of Δ⁶ desaturase in the commercially managed L. decemlineata population and suggest a role for eicosanoids and associated metabolic enzymes as potential modulators of insecticide resistance. We further observed a pattern of delayed emergence within the commercially managed population compared with the organically managed population. Variations in emergence timing together with specific fatty acid regulation may significantly influence the capacity of L. decemlineata to develop insecticide resistance.

Prostaglandin D2 synthase and its functional association with immune and reproductive processes in a lepidopteran insect, Spodoptera exigua

Several prostaglandins (PGs) have been identified in different insect species. However, their biosynthesis and physiological roles in insects remain unclear. PGD₂ is synthesized by isomerization from PGH₂ in mammals. This study identified a PGD₂ synthase (SePGDS) in a lepidopteran insect, Spodoptera exigua. It showed sequence homology (32.8%) with human PGDS. Based on its conserved active site residues, its N-terminal tyrosine (Y8) was predicted to mediate electron relay from glutathione to PGH₂ substrate, which was distinct from the catalysis of PGE₂ (=PGD₂ isomer) synthase (SePGES). SePGDS was highly expressed in larval and adult stages. RNA interference (RNAi) of SePGDS expression resulted in immunosuppression of cellular immune responses by suppressing the expression of actin polymerization-associated genes. It also suppressed the expression of some antimicrobial genes. Such immunosuppression induced by RNAi treatment was specifically rescued by the addition of PGD₂, but not its precursor, arachidonic acid. Such RNAi treatment in adults prevented egg development in females by inhibiting choriogenesis. RNAi treatment also suppressed nurse cell dumping to growing oocytes. However, the addition of PGD₂ rescued egg development of RNAi-treated females. These results suggest that SePGDS is responsible for the production of PGD₂ which mediates immune and reproductive processes of S. exigua.

Deletion mutant of sPLA2 using CRISPR/Cas9 exhibits immunosuppression, developmental retardation, and failure of oocyte development in legume pod borer, Maruca vitrata

Phospholipase A₂ (PLA₂) catalyzes release of free fatty acids linked to phospholipids at sn-2 position. Some of these released free fatty acids are used to synthesize eicosanoids that mediate various physiological processes in insects. Although a large number of PLA₂s form a superfamily consisting of at least 16 groups, few PLA₂s have been identified and characterized in insects. Furthermore, physiological functions of insect PLA₂s remain unclear. Clustered regularly interspaced short parlindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) has been a useful research tool to validate gene function. This study identified and characterized a secretory PLA₂ (sPLA₂) from legume pod borer, Maruca vitrata (Lepidoptera: Crambidae), and validated its physiological functions using CRISPR/Cas9. An open reading frame of M. vitrata sPLA₂ (Mv-sPLA₂) encoding 192 amino acids contained signal peptide, calcium-binding domain, and catalytic site. Phylogenetic analysis indicated that Mv-sPLA₂ was related to other Group III sPLA₂s. Mv-sPLA₂ was expressed in both larval and adult stages. It was inducible by immune challenge. RNA interference (RNAi) of Mv-sPLA₂ significantly suppressed cellular immunity and impaired larval development. Furthermore, RNAi treatment in female adults prevented oocyte development. These physiological alterations were also observed in a mutant line of M. vitrata with Mv-sPLA₂ deleted by using CRISPR/Cas9. Mv-sPLA₂ was not detected in the mutant line from western blot analysis. Addition of an eicosanoid, PGE₂, significantly rescued oocyte development of females of the mutant line. These results suggest that Mv-sPLA₂ plays crucial role in immune, developmental, and reproductive processes of M. vitrata.

Expression Analysis of mRNA Decay of Maternal Genes during Bombyx mori Maternal-to-Zygotic Transition

Maternal genes play an important role in the early embryonic development of the silkworm. Early embryonic development without new transcription depends on maternal components stored in the egg during oocyte maturation. The maternal-to-zygotic transition (MZT) is a tightly regulated process that includes maternal mRNAs elimination and zygotic transcription initiation. This process has been extensively studied within model species. Each model organism has a unique pattern of maternal transcriptional clearance classes in MZT. In this study, we identified 66 maternal genes through bioinformatics analysis and expression analysis in the eggs of silkworm virgin moths (Bombyx mori). All 66 maternal genes were expressed in vitellogenesis in day eight female pupae. During MZT, the degradation of maternal gene mRNAs could be divided into three clusters. We found that eight maternal genes of cluster 1 remained stable from 0 to 3.0 h, 17 maternal genes of cluster 2 were significantly decayed from 0.5 to 1.0 h and 41 maternal genes of cluster 3 were significantly decayed after 1.5 h. Therefore, the initial time-point of degradation of cluster 2 was earlier than that of cluster 3. The maternal gene mRNAs decay of clusters 2 and 3 is first initiated by maternal degradation activity. Our study expands upon the identification of silkworm maternal genes and provides a perspective for further research of the embryo development in Bombyx mori.

Toll/IMD signal pathways mediate cellular immune responses via induction of intracellular PLA 2 expression

Phospholipase A₂ (PLA₂ ) hydrolyzes fatty acids from phospholipids at the sn-2 position. Two intracellular PLA₂ s, iPLA₂ A and iPLA₂ B, have been found in Spodoptera exigua. Both are calcium-independent cellular PLA₂ . Their orthologs have been found in other insects. These two iPLA₂ s are different in ankyrin motif of N terminal region. The objective of this study was to determine whether Toll/immune deficiency (IMD) signal pathways could mediate cellular immune responses via induction of iPLA₂ expression. Both iPLA ₂ s were expressed in all developmental stages of S. exigua, showing the highest expression in the adult stage. During larval stage, hemocyte is the main tissue showing expression of these iPLA₂ s. Both iPLA₂ s exhibited similar expression patterns after immune challenge with different microbial pathogens such as virus, bacteria, and fungi. Promoter component analysis of orthologs encoded in S. frugiperda indicated nuclear factor-κB- and Relish-responsible elements on their promoters, suggesting their expression in S. exigua under Toll/IMD immune signaling pathways. RNA interference (RNAi) of MyD88 or Pelle under Toll pathway suppressed inducible expression levels of both iPLA₂ s in response to Gram-positive bacteria containing Lys-type peptidoglycan or fungal infection. In contrast, RNAi against Relish under IMD pathway suppressed both iPLA₂ s in response to infection with Gram-negative bacteria. Under RNAi conditions, hemocytes significantly lost cellular immune response measured by nodule formation. However, addition of arachidonic acid (a catalytic product of PLA₂ ) rescued such immunosuppression. These results suggest that Toll/IMD signal pathways can mediate cellular immune responses via eicosanoid signaling by inducing iPLA₂ expression.

Inhibition of prostaglandin biosynthesis leads to suppressed ovarian development in Spodoptera exigua

Prostaglandins (PGs) are a group of eicosanoids that are C20 oxygenated polyunsaturated fatty acids. PGs can mediate various physiological processes such as immunity, salivary secretion, excretion, and reproduction in insects. The objective of this study was to determine the effect of PG on oocyte development in Spodoptera exigua, a lepidopteran insect known to biosynthesize PGs. Polytrophic ovarioles of S. exigua females exhibited follicle development in germarium, in which oocytes were distinct from nurse cells. During vitellogenesis, nurse cells degenerated by losing cytoplasm called "nurse cell dumping" while oocytes showed increase in cell volume. When PG biosynthesis inhibitors such as ibuprofen or aspirin were applied, nurse cell dumping was not complete and no chorion was formed, thus preventing egg formation. However, addition of PGE₂ significantly rescued such inhibition and resumed oocyte development and choriogenesis. To support the observation with genetic factor, RNA interference (RNAi) specific to peroxynectins (Pxts: Se-Pxt1 and Se-Pxt2) known to act as insect cyclooxygenase was performed to suppress PG biosynthesis. Both Se-Pxt1 and Se-Pxt2 were highly expressed in the ovary of control female. RNAi treatment against Se-Pxt1 or Se-Pxt2 specifically suppressed target genes and inhibited oocyte development. Addition of PGE₂ to adults treated with RNAi rescued the suppressed development of oocytes. Results of this study suggest that PGs can stimulate oocyte development as autocrine/paracrine mediators of vitellogenesis and choriogenesis in insects.

Prostaglandins and Other Eicosanoids in Insects: Biosynthesis and Biological Actions

This essay reviews the discoveries, synthesis, and biological significance of prostaglandins (PGs) and other eicosanoids in insect biology. It presents the most current - and growing - understanding of the insect mechanism of PG biosynthesis, provides an updated treatment of known insect phospholipase A2 (PLA2), and details contemporary findings on the biological roles of PGs and other eicosanoids in insect physiology, including reproduction, fluid secretion, hormone actions in fat body, immunity and eicosanoid signaling and cross-talk in immunity. It completes the essay with a prospectus meant to illuminate research opportunities for interested readers. In more detail, cellular and secretory types of PLA2, similar to those known on the biomedical background, have been identified in insects and their roles in eicosanoid biosynthesis documented. It highlights recent findings showing that eicosanoid biosynthetic pathway in insects is not identical to the solidly established biomedical picture. The relatively low concentrations of arachidonic acid (AA) present in insect phospholipids (PLs) (< 0.1% in some species) indicate that PLA2 may hydrolyze linoleic acid (LA) as a precursor of eicosanoid biosynthesis. The free LA is desaturated and elongated into AA. Unlike vertebrates, AA is not oxidized by cyclooxygenase, but by a specific peroxidase called peroxinectin to produce PGH2, which is then isomerized into cell-specific PGs. In particular, PGE2 synthase recently identified converts PGH2 into PGE2. In the cross-talks with other immune mediators, eicosanoids act as downstream signals because any inhibition of eicosanoid signaling leads to significant immunosuppression. Because host immunosuppression favors pathogens and parasitoids, some entomopathogens evolved a PLA2 inhibitory strategy activity to express their virulence.

Ecdysone oxidase and 3-dehydroecdysone-3β-reductase contribute to the synthesis of ecdysone during early embryonic development of the silkworm

Maternal ecdysteroids regulate a variety of cellular processes during early embryonic development of insects, yet little is known about the genes involved in the biosynthesis of these hormones. In this study, we found that ecdysone oxidase (EO) gene, which encodes an enzyme to catalyze ecdysone (or 20-hydroxyecdysone, 20E) to 3-dehydroecdysone (3DE), was highly expressed in the mature ovaries of the domestic silkworm, Bombyx mori. B. mori EO (BmEO) was localized in the cytoplasm around the yolk granules of oocyte. Furthermore, the down-regulated expression of the BmEO gene using RNA interference could not affect normal development of the female silkworm, but lower the 20E titer and hatching rate of its offspring. Rescue experiments by injecting the product (3DE) of BmEO can significantly elevate the 20E level and hatching rate of the BmEO RNAi offspring. Meanwhile, during embryonic stage, the down-regulating expression of 3DE-3β-reductase, which can reduce 3DE into ecdysone, also lowered the 20E titer. Taken together, our results prove that 3DE can be synthesized from ecdysone in maternal ovary yolk granules, and then the maternal 3DE is converted into active ecdysone during the early embryonic development of offspring. Thus, our findings reveal a new pathway to explain the origin of high 20E level before the formation the prothoracic gland in the silkworm.

Lipids in Insect Oocytes: From the Storage Pathways to Their Multiple Functions

In insect physiology, the mechanisms involved in the buildup and regulation of yolk proteins in developing oocytes have been thoroughly researched during the last three decades. Comparatively, the study of lipid metabolism in oocytes had received less attention. The importance of this issue lies in the fact that lipids make up to 40% of the dry weight of an insect egg, being the most important supply of energy for the developing embryo. Since the oocyte has a very limited capacity to synthesize lipids de novo, most of the lipids in the mature eggs arise from the circulation. The main lipid carriers in the insect circulatory system are the lipoproteins lipophorin and vitellogenin. In some species, the endocytosis of lipophorin and vitellogenin may account for about 10% of the lipids present in mature eggs. Thus, most of the lipids are transferred by a lipophorin-mediated pathway, in which the lipoprotein unloads its lipid cargo at the surface of oocytes without internalization. This chapter recapitulates the current status on lipid storage and its utilization in insect oocytes and discusses the participation of key factors including lipoproteins, transfer proteins, lipolytic enzymes, and dynamic organelles such as lipid droplets. The new findings in the field of lipophorin receptors are presented in the context of lipid accumulation during egg maturation, and the roles of lipids beyond energy source are summarized from the perspective of oogenesis and embryogenesis. Finally, prospective and fruitful areas of future research are suggested.

Persistent RNA virus infection of lepidopteran cell lines: Interactions with the RNAi machinery

RNAi is broadly used as a technique for specific gene silencing in insects but few studies have investigated the factors that can affect its efficiency. Viral infections have the potential to interfere with RNAi through their production of viral suppressors of RNAi (VSRs) and the production of viral small RNAs that can saturate and inactivate the RNAi machinery. In this study, the impact of persistent infection of the RNA viruses Flock house virus (FHV) and Macula-like virus (MLV) on RNAi efficiency was investigated in selected lepidopteran cell lines. Lepidopteran cell lines were found to be readily infected by both viruses without any apparent pathogenic effects, with the exception of Bombyx-derived Bm5 and BmN4 cells, which could not be infected by FHV. Because Sf21 cells were free from both FHV and MLV and Hi5-SF were free from FHV and only contained low levels of MLV, they were tested to evaluate the impact of the presence of the virus. Two types of RNAi reporter assays however did not detect a significant interference with gene silencing in infected Sf21 and Hi5-SF cells when compared to virus-free cells. In Hi5 cells, the presence of FHV could be easily cleared through the expression of an RNA hairpin that targets its VSR gene, confirming that the RNAi mechanism was not inhibited. Sequencing indicated that the B2 RNAi inhibitor gene of FHV and a putative VSR gene from MLV were intact in persistently infected cell lines, indicating that protection against RNAi remains essential for virus survival. It is proposed that infection levels of persistent viruses in the cell lines are too low to have an impact on RNAi efficiency in the lepidopteran cell lines and that encoded VSRs act locally at the sites of viral replication (mitochondrial membranes) without affecting the rest of the cytoplasm.

Variation of prostaglandin E2 concentrations in ovaries and its effects on ovarian maturation and oocyte proliferation in the giant fresh water prawn, Macrobrachium rosenbergii

Prostaglandins (PGs) are important bioactive mediators for many physiological functions. In some decapod crustaceans, prostaglandin E2 (PGE2) has been detected in reproductive organs, and may play a role in the control of ovarian maturation. However, in the freshwater prawn, Macrobrachium rosenbergii, the presences of PGE2 and key enzymes for PGE2 biosynthesis, as well as its effects on ovarian maturation have not yet been investigated. In this study we reported the presence of PGE2, cyclooxygenase1 (COX1) and prostaglandin E synthase (PGES) in the ovarian tissues of M. rosenbergii, using immunohistochemistry. Intense immunoreactivities of PGE2 (PGE2-ir), COX1 (Cox1-ir) and PGES (PGES-ir) were detected in previtellogenic oocytes (Oc1 and Oc2), while the immunoreactivities were absent in the late vitellogenic oocytes (Oc4). This finding supports the hypothesis that the PGE2 biosynthesis occurs in the ovary of this prawn. To ascertain this finding we used LC-MS/MS to quantitate PGE2 concentrations during ovarian developmental cycle. The levels of PGE2 were significantly higher in the early ovarian stages (St I and II) than in the late stages (St III and IV). Moreover, we found that administration of PGE2 stimulated the ovarian maturation in this species by shortening the length of the ovarian cycle, increasing ovarian-somatic index, oocyte proliferation, and vitellogenin (Vg) level in the hemolymph.

BmECM25, from the silkworm Bombyx mori, is an extracellular matrix protein

BmECM25 (previously reported as BmVMP25) was previously predicted as a gene encoding the vitelline membrane protein in silkworm, Bombyx mori. In this study, we investigated the detail temporal and spatial patterns of BmECM25 protein. Western blot results showed that BmECM25 was expressed in the follicular epithelium cells from stages -6 to +1, and was then secreted into the oocytes. However, the abundance of BmECM25 decreased during the subsequent oogenesis and finally disappeared in the mature follicles. Immunofluorescence detection showed that BmECM25 locates inside the VM layer and forms a discontinuous layer. These features of BmECM25 suggest that it is an oocyte membrane matrix protein, not a vitelline membrane protein.

Mating for male-derived prostaglandin: a functional explanation for the increased fecundity of mated female crickets?

Direct benefits are considered to be the driving force of high female mating rates, yet species in which females do not receive material resources from males still experience increased fitness from mating frequently. One hypothesis suggests that substances within the ejaculate may boost survival or offspring production. If these materials are limiting to females, they will require continual renewal via mating and could provide a functional understanding of how high mating rates lead to increased female fitness. Using the Texas field cricket, Gryllus texensis, we investigated the sexual transfer of prostaglandin E2, an important mediator of invertebrate reproduction. We determined that like other gryllid species, males include significant quantities of prostaglandin E2 (PGE2) and its precursor molecule, arachidonic acid (AA), within the spermatophore. These components are passed to females during copulation and then stored within the spermatheca. We then tested the novel hypothesis that PGE2 is ephemerally available after mating and that females must frequently mate to maintain access to this limiting compound. We found that PGE2 within the spermatheca is indeed depleted through time, with only a small amount remaining 1 week after mating, but that its presence can be maintained at high quantities and for prolonged periods of time by remating. Our results support the hypothesis that high female mating rates increase the amount and availability of PGE2 throughout the breeding season, which could explain the positive relationship between female mating rate and fecundity.

Chorion genes: a landscape of their evolution, structure, and regulation

Differential regulation at the level of transcription provides a means for controlling gene expression in eukaryotes, especially during development. Insect model systems have been extensively used to decipher the molecular basis of such regulatory cascades, and one of the oldest such model systems is the regulation of chorion gene expression during ovarian follicle maturation. Recent experimental and technological advances have shed new light onto the system, allowing us to revisit it. Thus, in this review we try to summarize almost 40 years' worth of studies on chorion gene regulation while-by comparing Bombyx mori and Drosophila melanogaster models-attempting to present a comprehensive, unified model of the various regulatory aspects of choriogenesis that takes into account the evolutionary conservation and divergence of the underlying mechanisms.

Roles of peroxinectin in PGE2-mediated cellular immunity in Spodoptera exigua

BACKGROUND

Prostaglandins (PGs) mediate insect immune responses to infections and invasions. Although the presence of PGs has been confirmed in several insect species, their biosynthesis in insects remains a conundrum because orthologs of the mammalian cyclooxygenases (COXs) have not been found in the known insect genomes. PG-mediated immune reactions have been documented in the beet armyworm, Spodoptera exigua. The purpose of this research is to identify the source of PGs in S. exigua.

PRINCIPAL FINDINGS

Peroxidases (POXs) are a sister group of COX genes. Ten putative POXs (SePOX-A ∼ SePOX-J) were expressed in S. exigua. Expressions of SePOX-F and -H were induced by bacterial challenge and expressed in the hemocytes and the fat body. RNAi of each POX was performed by hemocoelic injection of their specific double-stranded RNAs. dsPOX-F or, separately, dsPOX-H, but not the other eight dsRNA constructs, specifically suppressed hemocyte-spreading behavior and nodule formation; these two reactions were also inhibited by aspirin, a COX inhibitor. PGE2, but not arachidonic acid, treatment rescued the immunosuppression. Sequence analysis indicated that both POX genes were clustered with peroxinectin (Pxt) and their cognate proteins shared some conserved domains corresponding to the Pxt of Drosophila melanogaster.

CONCLUSIONS

SePOX-F and -H are Pxt-like genes associated with PG biosynthesis in S. exigua.

Transfection of BmCPV genomic dsRNA in silkmoth-derived Bm5 cells: stability and interactions with the core RNAi machinery

While several studies have been conducted to investigate the stability of dsRNA in the extracellular medium (hemolymph, gut content, saliva), little is known regarding the persistence of dsRNA once it has been introduced into the cell. Here, we investigate the stability of Bombyx mori cytoplasmic polyhedrosis virus (BmCPV) genomic dsRNA fragments after transfection into Bombyx-derived Bm5 cells. Using RT-PCR as a detection method, we found that dsRNA could persist for long periods (up to 8 days) in the intracellular environment. While the BmCPV genomic dsRNA was processed by the RNAi machinery, its presence had no effects on other RNAi processes, such as the silencing of a luciferase reporter by dsLuc. We also found that transfection of BmCPV genomic dsRNA could not establish a viral infection in the Bm5 cells, even when co-transfections were carried out with dsRNAs targeting Dicer and Argonaute genes, suggesting that the neutralization by RNAi does not play a role in the establishment of an in vitro culture system. The mechanism of the dsRNA stability in Bm5 cells is discussed, as well as the implications for the establishment for an in vitro culture system for BmCPV.

Transcriptional response of BmToll9-1 and RNAi machinery genes to exogenous dsRNA in the midgut of Bombyx mori

Injection of dsRNA is widely applied to silence endogenous genes and study gene function in insects. However, it is not yet clear to what extent it can also exert non-specific effects, for instance by interference with the innate immune response. In this study, we report on the transcriptional response of BmToll9-1 to lipopolysaccharide (LPS) and dsRNA in the silkmoth, Bombyx mori. BmToll9-1 encodes a Toll receptor highly expressed in midgut tissue and that shows limited similarity to the mammalian TLR3 endolysosome receptor for dsRNA; while Dcr2 and Ago2 encode two key components of the RNAi machinery. An expression pattern study of all 14 Toll receptors in B. mori showed that BmToll9-1 was expressed in different larval and pupal tissues with the highest expression level detected in the midgut, indicating a possible function in immunity against pathogens taken up by the food. In order to investigate the response of BmToll9-1, different ways to deliver dsRNA, specific for GFP (dsGFP), and LPS were applied in Bombyx 5th instar larvae. The feeding experiments suggested that dsGFP did not suppress the expression of BmToll9-1 significantly, while LPS could suppress the expression of BmToll9-1 after 3h of feeding. On the other hand, the injection experiments showed that dsGFP, as well as LPS, could significantly inhibit the expression of BmToll9-1 in 3h. Bacteria that constantly expressed dsGFP could also down-regulate the expression of BmToll9-1 to a greater extent than bacteria that do not express dsGFP. The failure of dsGFP by feeding to affect the expression of BmToll9-1 was correlated with the rapid degradation of dsGFP by dsRNase in the midgut juice. Expression of the RNAi machinery genes Dcr2 and Ago2, as well as dsRNase, was also affected by injection of dsRNA and not by feeding, but in these cases an induction was observed instead of a down-regulation. Because LPS is a well-known pathogen-associated molecular pattern (PAMP), it suggested that the decrease in BmToll9-1 expression is a consequence of the activation of the innate immune response by LPS. The similar response of BmToll9-1 between the two triggers, LPS and dsRNA, suggests that dsRNA can also act as a PAMP in the midgut of Bombyx. Furthermore, induction of the genes Dcr2, Ago2 and dsRNase may also constitute a defense mechanism against invading dsRNA.

BmVMP90, a large vitelline membrane protein of the domesticated silkmoth Bombyx mori, is an essential component of the developing ovarian follicle

We present the characterization of BmVMP90, a vitelline membrane protein (VMP) of the silkmoth Bombyx mori bearing similarities with dipteran VMPs whose existence had recently been suggested by an in silico analysis of the silkmoth genome and follicular cell RNA expression analyses. Using a specific antibody, we determine the presence of BmVMP90 protein in ovarian follicular cell extracts at the end of vitellogenesis and in vitelline membrane extracts but not in the chorion of fractionated eggshells isolated from ovulated follicles. Whole mount follicle immunofluorescence studies reveal a pattern of BmVMP90 deposition matching the «imprinted» pattern of follicular cells on the vitelline membrane surface. Antisense DNA-directed inhibition BmVMP90 expression in ex vivo cultures of early vitellogenic follicles produced a phenotype of kidney- or bean-shaped follicles with detached follicular epithelia, suggestive of the importance of BmVMP90 for the integrity of developing follicles and normal deposition of the chorion structure that follows vitelline membrane formation but no adverse effects on the execution of the follicular cell-imprinted program of choriogenesis per se.

Bombyx mori DNA/RNA non-specific nuclease: expression of isoforms in insect culture cells, subcellular localization and functional assays

A DNA/RNA non-specific alkaline nuclease (BmdsRNase) was isolated from the digestive juice of Bombyx mori. While originally reported to be produced by the midgut only, in this project it was found that the mRNA of this enzyme was also expressed in the epidermis, fat body, gut, thoracic muscles, Malpighian tubules, brain, and silk glands of 5th instar larvae, indicating additional functions to its reported role in nucleic acid digestion in the midgut. In order to study the functional properties of BmdsRNase, three pEA-BmdsRNase expression constructs were generated, characterized by presence or absence of a signal peptide and a propeptide, and used for expression in lepidopteran Hi5 tissue culture cells. Western blot indicated that these different forms of BmdsRNase protein were not secreted into the growth medium, while they were detected in the pellets and supernatants of Hi5 cell extracts. Nucleic acids cleavage experiments indicated that full-length BmdsRNase could digest dsRNA and that the processed form (absence of signal peptide and propeptide) of BmdsRNase could degrade both DNA and dsRNA in Hi5 cell culture. Using a reporter assay targeted by transfected homologous dsRNA, it was shown that the digestive property of the processed form could interfere with the RNAi response. Immunostaining of processed BmdsRNase protein showed asymmetric localization in the cellular cytoplasm and co-localization with Flag-tagged Dicer-2 was also observed. In conclusion, our in vitro studies indicated that intracellular protein isoforms of BmdsRNase can be functional and involved in the regulation of nucleic acid metabolism in the cytoplasm. In particular, because of its propensity to degrade dsRNA, the enzyme might be involved in the innate immune response against invading nucleic acids such as RNA viruses.

Prostaglandin A2 influences gene expression in an established insect cell line (BCIRL-HzAM1) cells

Prostaglandins (PGs) and other eicosanoids are oxygenated metabolites of arachidonic acid and two other C(20) polyunsaturated fatty acids. While most well studied in mammals, PGs exert important actions in insects and virtually all other invertebrates. We have been researching the mechanisms of PG actions in established insect cell lines and reported earlier that two PGs, PGA(1) and PGE(1), influence gene and protein expression in HzAM1 cells. Here we report on further experiments with three 2-series PGs, PGA(2), PGE(2) and PGF(2α). In separate experiments we treated cells with each of the three PGs for 12 and 24h and then analyzed cell lysates by 2-D electrophoresis. Analysis of the gels by Delta2D software showed that PGA(2) influenced expression of 60 proteins while PGE(2) and PGF(2α) treatments led to expression changes for only a few proteins. All spots representing changes in protein expression were processed for analysis by MALDI TOF/TOF mass spectrometry. Bioinformatic analysis of the resulting sequences yielded in silico identifications of all proteins. The apparent changes in some proteins were confirmed by quantitative PCR, which demonstrated that changes in protein expression were parallel to changes in mRNA expression. We assorted the proteins into functional categories, including 1/cell structure and function; 2/cell protection and immunity; 3/energetics and metabolism; 4/nucleotide processing; 5/protein action and processing and 6/signal transduction. These findings substantially extend our idea that one mechanism of PG actions in insect cells is the modulation of gene and protein expression.

Modeling bidirectional transcription using silkmoth chorion gene promoters

Bidirectional transcription is an interesting feature of eukaryotic genomes; yet not all aspects of its mechanism are understood. Silkmoth choriogenesis is a model system for studying transcriptional regulation at the initiation level. As chorion genes comprise a large group of divergently transcribed gene pairs, we are presented with the possibility of investigating the intricacies of bidirectional transcription. Their well characterized 5' regulatory regions and expression profiles lay the foundation for investigating protein:protein and protein:DNA interactions, and RNA polymerase function during oocyte development. In this article we summarize current knowledge on chorion gene regulation and propose an approach to modeling bidirectional transcription using chorion promoters.

Microscopic and molecular characterization of ovarian follicle atresia in Rhodnius prolixus Stahl under immune challenge

In this work we characterized the degenerative process of ovarian follicles of the bug Rhodnius prolixus challenged with the non-entomopathogenic fungus Aspergillus niger. An injection of A. niger conidia directly into the hemocoel of adult R. prolixus females at the onset of vitellogenesis caused no effect on host lifespan but elicited a net reduction in egg batch size. Direct inspection of ovaries from the mycosed insects revealed that fungal challenge led to atresia of the vitellogenic follicles. Light microscopy and DAPI staining showed follicle shrinkage, ooplasm alteration and disorganization of the monolayer of follicle cells in the atretic follicles. Transmission electron microscopy of thin sections of follicle epithelium also showed nuclei with condensed chromatin, electron dense mitochondria and large autophagic vacuoles. Occurrence of apoptosis of follicle cells in these follicles was visualized by TUNEL labeling. Resorption of the yolk involved an increase in protease activities (aspartyl and cysteinyl proteases) which were associated with precocious acidification of yolk granules and degradation of yolk protein content. The role of follicle atresia in nonspecific host-pathogen associations and the origin of protease activity that led to yolk resorption are discussed.

Drosophila eggshell production: identification of new genes and coordination by Pxt

Drosophila ovarian follicles complete development using a spatially and temporally controlled maturation process in which they resume meiosis and secrete a multi-layered, protective eggshell before undergoing arrest and/or ovulation. Microarray analysis revealed more than 150 genes that are expressed in a stage-specific manner during the last 24 hours of follicle development. These include all 30 previously known eggshell genes, as well as 19 new candidate chorion genes and 100 other genes likely to participate in maturation. Mutations in pxt, encoding a putative Drosophila cyclooxygenase, cause many transcripts to begin expression prematurely, and are associated with eggshell defects. Somatic activity of Pxt is required, as RNAi knockdown of pxt in the follicle cells recapitulates both the temporal expression and eggshell defects. One of the temporally regulated genes, cyp18a1, which encodes a cytochromome P450 protein mediating ecdysone turnover, is downregulated in pxt mutant follicles, and cyp18a1 mutation itself alters eggshell gene expression. These studies further define the molecular program of Drosophila follicle maturation and support the idea that it is coordinated by lipid and steroid hormonal signals.

Search for limiting factors in the RNAi pathway in silkmoth tissues and the Bm5 cell line: the RNA-binding proteins R2D2 and Translin

RNA interference (RNAi), an RNA-dependent gene silencing process that is initiated by double-stranded RNA (dsRNA) molecules, has been applied with variable success in lepidopteran insects, in contrast to the high efficiency achieved in the coleopteran Tribolium castaneum. To gain insight into the factors that determine the efficiency of RNAi, a survey was carried out to check the expression of factors that constitute the machinery of the small interfering RNA (siRNA) and microRNA (miRNA) pathways in different tissues and stages of the silkmoth, Bombyx mori. It was found that the dsRNA-binding protein R2D2, an essential component in the siRNA pathway in Drosophila, was expressed at minimal levels in silkmoth tissues. The silkmoth-derived Bm5 cell line was also deficient in expression of mRNA encoding full-length BmTranslin, an RNA-binding factor that has been shown to stimulate the efficiency of RNAi. However, despite the lack of expression of the RNA-binding proteins, silencing of a luciferase reporter gene was observed by co-transfection of luc dsRNA using a lipophilic reagent. In contrast, gene silencing was not detected when the cells were soaked in culture medium supplemented with dsRNA. The introduction of an expression construct for Tribolium R2D2 (TcR2D2) did not influence the potency of luc dsRNA to silence the luciferase reporter. Immunostaining experiments further showed that both TcR2D2 and BmTranslin accumulated at defined locations within the cytoplasm of transfected cells. Our results offer a first evaluation of the expression of the RNAi machinery in silkmoth tissues and Bm5 cells and provide evidence for a functional RNAi response to intracellular dsRNA in the absence of R2D2 and Translin. The failure of TcR2D2 to stimulate the intracellular RNAi pathway in Bombyx cells is discussed.

The influence of chronic eicosanoid biosynthesis inhibition on life history of the greater waxmoth, Galleria mellonella and its ectoparasitoid, Bracon hebetor

Eicosanoids are oxygenated metabolites of three C20 polyunsaturated fatty acids, mainly arachidonic acid (AA; 20:4n-6), but also 20:3n-6 and 20:5n-3. Aside from their importance in biomedicine, eicosanoids act in invertebrate biology. Prostaglandins (PGs) influence salt and water transport physiology in insect rectal epithelia and in Malpighian tubules. PGs also influence a few insect behaviors, including releasing oviposition behavior and behavioral fever. Eicosanoids act in ovarian development and in insect immunity. Because eicosanoids act in several areas of insect biology, we posed the hypothesis that chronic inhibition of eicosanoid biosynthesis, in the absence of microbial challenge, can influence insect life table parameters, including developmental time, survival, adult longevity and parasitoid fecundity. Here we report that inhibiting eicosanoid biosynthesis throughout the larval life exerted minor influences on some life table parameters of the greater wax moth, Galleria mellonella and its ectoparasitoid, Bracon hebetor, however, the inhibitors strongly reduced the production and hatchability of the parasitoids' eggs. The significance of the work relates to the potentials of understanding and targeting eicosanoid systems as a platform for developing new technologies of insect pest management. As seen here, the impact of targeting eicosanoid systems is seen in crucial moments of insect life histories, such as reproduction or immune challenge rather than in overall larval development.

Prostaglandins and their receptors in insect biology

We treat the biological significance of prostaglandins (PGs) and their known receptors in insect biology. PGs and related eicosanoids are oxygenated derivatives of arachidonic acid (AA) and two other C20 polyunsaturated fatty acids. PGs are mostly appreciated in the context of biomedicine, but a growing body of literature indicates the biological significance of these compounds extends throughout the animal kingdom, and possibly beyond. The actions of most PGs are mediated by specific receptors. Biomedical research has discovered a great deal of knowledge about PG receptors in mammals, including their structures, pharmacology, molecular biology and cellular locations. Studies of PG receptors in insects lag behind the biomedical background, however, recent results hold the promise of accelerated research in this area. A PG receptor has been identified in a class of lepidopteran hemocytes and experimentally linked to the release of prophenoloxidase. PGs act in several crucial areas of insect biology. In reproduction, a specific PG, PGE(2), releases oviposition behavior in most crickets and a few other insect species; PGs also mediate events in egg development in some species, which may represent all insects. PGs play major roles in modulating fluid secretion in Malpighian tubules, rectum and salivary glands, although, again, this has been studied in only a few insect species that may represent the Class. Insect immunity is a very complex defense system. PGs and other eicosanoids mediate a large number of immune reactions to infection and invasion. We conclude that research into PGs and their receptors in insects will lead to important advances in our understanding of insect biology.