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, PGE2, 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

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

Identification of four secretory phospholipase A2s in a lepidopteran insect, Acrolepiopsis sapporensis, and their functional association with cellular immune responses

BackgroundEicosanoids are a group of the oxygenated C20 polyunsaturated fatty acids and play crucial roles in mediating various insect physiological processes. Catalytic activity of phospholipase A2 (PLA2) provides an initial substrate, arachidonic acid (AA), for subsequent eicosanoid biosynthesis.ResultsThis study identified four different secretory PLA2 (As-PLA2A–As-PLA2D) genes encoded in the Asian onion moth, Acrolepiopsis sapporensis. A phylogenetic analysis indicated that As-PLA2A and As-PLA2D are clustered with Group III PLA2s while As-PLA2B and As-PLA2C are clustered with Group XII and Group X PLA2s, respectively. Expression levels of these PLA2 genes increased along with larval development, especially in the fat body. A bacterial immune challenge upregulated the basal expression levels of the four PLA2 genes, which resulted in significant increases of the PLA2 enzyme activity. The enzyme activity was susceptible to a calcium chelator or reducing agent, suggesting Ca2+ dependency and disulfide linkage required for the catalytic activities of the secretory type of PLA2s. In addition, the PLA2 activity was also susceptible to bromophenacyl bromide (BPB), a specific inhibitor to sPLA2, but not to intracellular PLA2 inhibitors. An addition of BPB to the immune challenge significantly prevented hemocyte-spreading behavior of A. sapporensis. BPB treatment also suppressed a cellular immune response measured by hemocyte nodule formation. However, the immunosuppression was significantly rescued by the AA addition. To determine the PLA2(s) responsible for the immunity, individual RNA interference (RNAi) treatments specific to each of the four PLA2s were performed. Injection of gene-specific double-stranded RNAs caused significant reductions in the transcript level in all four PLA2s. In all four PLA2s, the RNAi treatments prevented the cellular immune response even after the immune challenge.ConclusionThis study reports four secretory PLA2s encoded in A. sapporensis and their function in mediating cellular immunity

Coagulation-Ceramic Membrane Filtrati on for U.S. Surface Water Treatment Summary

The objective of this project was to conduct a systematic pilot-scale investigation of a hybrid coagulation-ceramic membrane treatment system to gain fundamental insights about necessary pretreatment conditions, fouling mechanisms, and contaminant removal capabilities, using two U.S. surface water sources. A two-phase plan was implemented for each of the three coagulants considered in this study: aluminum sulfate, aluminum chlorohydrate, and ferric chloride. The first phase involved the optimization of the coagulation pretreatment conditions that provided the best performance in terms of particle removal, organics removal, and membrane fouling. The second phase involved a comprehensive performance evaluation of the optimized system. The removal of precursors of selected regulated and emerging disinfection by-products as well as selected microorganisms and surrogates from the two U.S. surface waters was determined

Manipulation of GameXPeptide synthetase gene expression by a promoter exchange alters the virulence of an entomopathogenic bacterium, Photorhabdus temperata temperata, by modulating insect immune responses

An entomopathogenic bacterium, Photorhabdus temperata subsp. temperata, is mutualistic to its host nematode, Heterorhabditis megidis. The infective juvenile nematodes enter target insects through natural openings and release the symbiotic bacteria into the insect hemocoel. The released bacteria suppress the insect immune responses and cause septicemia through their secondary metabolites. GameXPeptide (GXP) is one of the common secondary metabolites of most Photorhabdus species and is produced by the catalytic activity of a specific non-ribosomal peptide synthetase called GxpS encoded by the gxpS gene. This study confirmed gxpS to be encoded in the P. temperata temperata genome and analyzed its expression during bacterial growth. LC-MS/MS analysis of the bacterial culture broth contained at least four different GXPs (GXP-A to GXP-D), in which GXP-A was the most abundant. To investigate GXP synthesis following gxpS expression, the gxpS promoter of P. temperata temperata was replaced with an inducible arabinose promoter by homologous recombination. The gxpS transcript levels in the mutant were altered by the addition of l-arabinose. Without the inducer, the gxpS transcript level was significantly lower compared to the wild type and produced significantly lower amounts of the four GXPs. The addition of the inducer to the mutant significantly increased gxpS expression and produced significantly higher levels of the four GXPs compared to the wild type. The metabolite extracts obtained from wild-type and mutant bacteria showed differential immunosuppressive activities according to their GXP contents against the cellular and humoral immune responses of a lepidopteran insect, Spodoptera exigua. Interestingly, the gxpS-mutant bacteria showed less insecticidal activity compared to the wild type, whereas the addition of GXP to the mutant significantly restored insecticidal activity. These results suggest that the gxpS gene encoded in P. temperata temperata is responsible for the production of at least four different GXPs, which play crucial roles in bacterial virulence

ABCC transporters mediate insect resistance to multiple Bt toxins revealed by bulk segregant analysis

[EN] Background: Relatively recent evidence indicates that ABCC2 transporters play a main role in the mode of action of Bacillus thuringiensis (Bt) Cry1A-type proteins. Mapping of major Cry1A resistance genes has linked resistance to the ABCC2 locus in Heliothis virescens, Plutella xylostella, Trichoplusia ni and Bombyx mori, and mutations in this gene have been found in three of these Bt-resistant strains. Results: We have used a colony of Spodoptera exigua (Xen-R) highly resistant to a Bt commercial bioinsecticide to identify regions in the S. exigua genome containing loci for major resistance genes by using bulk segregant analysis (BSA). Results reveal a region containing three genes from the ABCC family (ABBC1, ABBC2 and ABBC3) and a mutation in one of them (ABBC2) as responsible for the resistance of S. exigua to the Bt commercial product and to its key Spodoptera-active ingredients, Cry1Ca. In contrast to all previously described mutations in ABCC2 genes that directly or indirectly affect the extracellular domains of the membrane protein, the ABCC2 mutation found in S. exigua affects an intracellular domain involved in ATP binding. Functional analyses of ABBC2 and ABBC3 support the role of both proteins in the mode of action of Bt toxins in S. exigua. Partial silencing of these genes with dsRNA decreased the susceptibility of wild type larvae to both Cry1Ac and Cry1Ca. In addition, reduction of ABBC2 and ABBC3 expression negatively affected some fitness components and induced up-regulation of arylphorin and repat5, genes that respond to Bt intoxication and that are found constitutively up-regulated in the Xen-R strain. Conclusions: The current results show the involvement of different members of the ABCC family in the mode of action of B. thuringiensis proteins and expand the role of the ABCC2 transporter in B. thuringiensis resistance beyond the Cry1A family of proteins to include Cry1Ca.We want to thank C. S. Hern ndez-Rodr guez for her comments on binding assays, Ismael Mingarro for his help in determination of ABCC domains and William Moar (Auburn University, Auburn, AL) for his comments on the manuscript and generating the Xen-R colony. This research was partially supported by IPET (Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries), Ministry of Agriculture, Food and Rural Affairs to YK. Research at the University of Valencia was supported by Generalitat Valenciana (prometeo/2011/044) and Ministry of Science and Innovation (AGL2011-30352-C02-02 and AGL2012-39946-C02-01).Park, Y.; González Martínez, RM.; Navarro Cerrillo, G.; Chakroun, M.; Kim, Y.; Ziarsolo Areitioaurtena, P.; Blanca Postigo, JM.... (2014). ABCC transporters mediate insect resistance to multiple Bt toxins revealed by bulk segregant analysis. BMC Biology. 12(46):1-15. https://doi.org/10.1186/1741-7007-12-46S115124

The Bacterium \u3ci\u3eXenorhabdus nematophila\u3c/i\u3e Inhibits Phospholipases A\u3csub\u3e2\u3c/sub\u3e from Insect, Prokaryote, and Vertebrate Sources

The bacterium Xenorhabdus nematophila is a virulent insect pathogen. Part of its pathogenicity is due to impairing cellular immunity by blocking biosynthesis of eicosanoids, the major recognized signal transduction system in insect cellular immunity. X. nematophila inhibits the first step in eicosanoid biosynthesis, phospholipase A2 (PLA2). Here we report that the bacterium inhibits PLA2 from two insect immune tissues, hemocytes and fat body, as well as PLA2s selected to represent a wide range of organisms, including prokaryotes, insects, reptiles, and mammals. Our finding on a bacterial in-hibitor of PLA2 activity contributes new insight into the chemical ecology of microbe-host interactions, which usually involve actions rather than inhibitors of PLA2s

Genetical and physiological mechanisms of face fly, Musca autumnalis DeGeer, diapause

Face flies, Musca autumnalis DeGeer (Diptera: Muscidae), overwinter as adults in reproductive diapause. The onset of diapause in face fly populations varies with longitude and is regulated by photoperiod. Therefore, the threshold of diapause response must be under genetic control. The mode of diapause inheritance in face flies was analyzed by crosses between high and low diapause strains. The endocrinology of diapause and reproductive developments was investigated by using in vivo and in vitro hormonal applications to see how juvenile hormone and ecdysteroid levels are regulated;Face fly diapause was polygenic with a small number of genes. Diapause inheritance did not fit a simple additive model because of incomplete dominance and sex-linkage. The incidence of face fly diapause was correlated with genes controlling developmental rates. A progressive decrease of diapause incidence in laboratory colonies was a correlated response to selection for increased developmental rates;Vitellogenin and vitellin of face flies were characterized by SDS-PAGE and Western blotting and quantified in hemolymph from reproductive and diapausing flies by using indirect ELISA. Reproductive females began to synthesize vitellogenin soon after adult eclosion, between 0 and 15 degree-days above a 12°C threshold. Vitellogenin synthesis was sigmoid with respect to time. Pre-diapause, teneral adults also synthesized small amounts of vitellogenin;Methoprene (a juvenile hormone analog) and 20-hydroxyecdysone induced diapausing flies to undergo reproductive development even when maintained in diapause conditions. The effects of both hormones were additive. Newly synthesized vitellogenin was measured in fat body culture medium by indirect ELISA. Fat body from diapausing flies synthesized vitellogenin in vitro in the presence of methoprene or 20-hydroxyecdysone. The foregoing data suggest that both hormones must be maintained at low levels during diapause development.</p

Eicosanoids rescue Spodoptera exigua infected with Xenorhabdus nematophilus, the symbiotic bacteria to the entomopathogenic nematode Steinernema carpocapsae

Abstract Xenorhabdus nematophilus is a pathogenic bacterium causing insect haemolymph septicemia, which leads to host insect death. To address the fundamental mechanisms underlying this haemolymph septicemia, or the immunodepressive response of the host insects following bacterial infection, we tested a hypothesis that the insect immune-mediating eicosanoid pathway is blocked by inhibitory action of the bacterium. Haemocoelic injection of the bacteria into the fifth instar larvae of Spodoptera exigua reduced the total number of living haemocytes with postinjection time and resulted in host death in 16 h at 25°C. The lethal efficacy, described by the median lethal bacterial dose (LD 50 ), was estimated as 33 colony-forming units per fifth instar larva of S. exigua. The lethal effect of the bacteria on the infected larvae decreased significantly with the addition of exogenous arachidonic acid (10 µg), a precursor of eicosanoids. In comparison, injections of dexamethasone (10 µg), a specific inhibitor of phospholipase A 2 , and other eicosanoid biosynthesis inhibitors elevated significantly the bacterial pathogenicity. Live X. nematophilus induced the infected larvae to form less nodules than did the heat-killed bacteria, but the addition of arachidonic acid increased the number of nodules formed significantly in response to live bacterial injection. The treatment with dexamethasone and other inhibitors, however, decreased the nodule formation after injection of heat-killed bacteria. These results indicate that eicosanoids play a role in the immune response of S. exigua, and suggest strongly that X. nematophilus inhibits its eicosanoid pathway, which then results in immunodepressive haemolymph septicemia