First evidence of laccase activity in the Pacific oyster Crassostrea gigas

Phenoloxidases (POs) are a family of enzymes including tyrosinases, catecholases and laccases, which play an important role in immune defence mechanisms in various invertebrates. The aim of this study was to thoroughly identify the PO-like activity present in the hemolymph of the Pacific oyster Crassostrea gigas, by using different substrates (i.e. dopamine and p-phenylenediamine, PPD) and different PO inhibitors. In order to go deeper in this analysis, we considered separately plasma and hemocyte lysate supernatant (HLS). In crude plasma, oxygraphic assays confirmed the presence of true oxidase activities. Moreover, the involvement of peroxidase(s) was excluded. In contrast to other molluscs, no tyrosinase-like activity was detected. With dopamine as substrate, PO-like activity was inhibited by the PO inhibitors tropolone, phenylthiourea (PTU), salicylhydroxamic acid and diethyldithio-carbamic acid, by a specific inhibitor of tyrosinases and catecholases, i.e. 4-hexylresorcinol (4-HR), and by a specific inhibitor of laccases, i.e. cetyltrimethylammonium bromide (CTAB). With PPD as substrate, PO-like activity was inhibited by PTU and CTAB. In precipitated protein fractions from plasma, and with dopamine and PPD as substrates, PTU and 4-HR, and PTU and CTAB inhibited PO-like activity, respectively. In precipitated protein fractions from hemocyte lysate supernatant, PTU and CTAB inhibited PO-like activity, independently of the substrate. Taken together, these results suggest the presence of both catecholase- and laccase-like activities in plasma, and the presence of a laccase-like activity in HLS. To the best of our knowledge, this is the first time that a laccase-like activity is identified in a mollusc by using specific substrates and inhibitors for laccase, opening new perspectives for studying the implication of this enzyme in immune defence mechanisms of molluscs of high economic value such as C. gigas.

Effects of ergothioneine from mushrooms (Flammulina velutipes) on melanosis and lipid oxidation of kuruma shrimp (Marsupenaeus japonicus)

The antimelanosic and antioxidative properties of a hot water extract prepared from the fruiting body of the edible mushroom (Flammulina velutipes) were evaluated by dietary supplementation in Kuruma shrimp (Marsupenaeus japonicus) for possible aquaculture application. The extract contained ergothioneine (ERT) at a level of 2.05 mg/mL. A commercial standard of l-ergothioneine (l-ERT) and the mushroom extract showed inhibitory activity against mushroom polyphenoloxidase (PPO). Feeding of the extract had no adverse effects on the immune systems of the shrimp under the present experimental conditions. Supplementation of the extract in the diet significantly suppressed PPO activities in the hemolymphs of the shrimp. Expression of the prophenoloxidase (proPO) gene decreased in the hemocyte of the Kuruma shrimp fed with the mushroom extract. Consequently, development of melanosis was significantly suppressed in the supplement fed shrimp during ice storage. Lipid oxidation was also effectively controlled in the supplement fed group throughout the storage period. In vitro experiments showed that l-ERT effectively inhibited the activation of proPO in the hemocyte lysate supernatant (HLS). The transcript of the proPO gene in the hemocyte showed lower expression in the l-ERT-treated HLS. It was concluded that dietary supplementation of the mushroom extract in shrimp could be a promising approach to control post mortem development of melanosis and lipid oxidation in shrimp muscles.

Oxidative stress, DNA damage and antioxidant enzyme gene expression in the Pacific white shrimp, Litopenaeus vannamei when exposed to acute pH stress

The ROS production, the percentage of dead and damaged haemocytes, the DNA Olive Tail Moment (OTM) value and the gene expression of manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPx) and thioredoxin (TRx), were studied in the Pacific white shrimp, Litopenaeus vannamei, when exposed to acute pH stress. The increased ROS production in haemocytes and the increased OTM value in both the haemocytes and the hepatopancreas cells suggest that oxidative damage occurred in shrimp exposed to pH 5.6 and pH 9.3, with apoptosis, mainly being associated with excess Ca(2+)influx and changes in cell viability. Acid and alkaline pH-induced DNA damage was time dependent in the haemocytes and the hepatopancreas cells. The concentration of intracellular free calcium [Ca(2+)] (i) after different pH treatments increased significantly over time, reaching its highest concentration after 12 h, but decreasing gradually to normal levels after 24 h. The [Ca(2+)] (i) content in shrimp cells when exposed to pH 9.3 and pH 5.6 for 12 h had increased by 58%-81%, compared with exposure to pH 7.4 (control). In addition, the gene expression of cMnSOD, CAT, GPx and TRx in the hepatopancreas of L. vannamei was induced by acid and alkaline pH stress, although there were differences in the expression response with respect to the duration of induction and the different pH treatments (acid or alkaline). Our results show that acidic or alkaline-induced oxidative stress may cause DNA damage, and cooperatively activate expression of CAT, GPx and TRx mRNA. Calcium ions appear to be important in mediating shrimp responses to pH stress.

Glutathione S-transferase in the white shrimp Litopenaeus vannamei: Characterization and regulation under pH stress

We first expressed a Mu-class GST from white shrimp Litopenaeus vannamei in Escherichia coli, and then characterized the purified recombinant enzyme with respect to the effects of pH, temperature on its catalytic (1-chloro-2, 4-dinitrobenzene-glutathione conjugation) activity. We also analyzed its expression profile in L. vannamei tissues, and assessed changes in Mu-GST expression, GST activity profiles and mortality rates following exposure of white shrimp to low and high pH (5.6 and 9.3, respectively). Realtime-PCR analysis showed that Mu-GST transcripts were expressed in all examined L. vannamei tissues, but were most abundant in the hepatopancreas. At low pH Mu-GST transcript levels in the hepatopancreas were highest after 12 h, and then declined to their original levels after 24 h. After 12 h they were also upregulated in haemocytes, but downregulated in the gills, and unchanged in the stomach following exposure to pH stress. Western blot analyses confirmed that the Mu-GST protein was strongly expressed in the hepatopancreas after 12 h at low pH and remain unchanged in the stomach after exposure to pH stress. pH-Related changes in GST activities in the shrimp hepatopancreas were similar to those displayed by the Mu-GST mRNA and protein profiles. In addition, the mortality of L. vannamei was higher at high pH than at low pH. These results suggest that L. vannamei Mu-GST expression is stimulated by acidic pH and that it may play important roles in detoxification of xenobiotics and antioxidant defenses.

A serpin from the parasitoid wasp Leptopilina boulardi targets the Drosophila phenoloxidase cascade

The insect phenoloxidase (PO) cascade is known to be tightly regulated by serine proteases and serine protease inhibitors of the serpin family. As a key component of the insect immune system, it is also suspected to be inhibited by several endoparasitoid wasps, insects that develop inside other arthropods as hosts. However, the underlying mechanisms of this inhibition are largely undescribed. Here, we report the characterization of a gene encoding a serpin, LbSPNy, highly expressed in the venom of the wasp Leptopilina boulardi (IS(y) type), and we show that either the venom or the recombinant LbSPNy inhibit the PO cascade in the hemolymph of Drosophila yakuba host larva. Altogether, our results identify the first serpin used as a virulence factor by a parasitoid wasp and show that it disrupts the activation pathway of the PO in the Drosophila host.

Investigation of EROD, CYP1A immunopositive proteins and SOD in haemocytes of Chamelea gallina and their role in response to B[a]P

CYP1A sub-family represents the main form of cytochrome P450 involved in benzo[a]pyrene (B[a]P) detoxification, but there are no clear evidences about its presence in invertebrates. 7-Ethoxy resorufin O-deethylase (EROD) activity is strictly related to CYP1A presence, at the same time P450-dependent oxidative metabolism leads to reactive oxygen species (ROS) production, thought to be an important mechanism of pollutant-mediated toxicity in aquatic organisms. Superoxide dismutases (SODs), EROD and CYP1A activities and/or expressions were detected in haemocytes of pooled clams (Chamelea gallina) and cell-free haemolymph after 24 h, 7 and 12 days of exposure to 0.5 mg/L of B[a]P. After 24 h, B[a]P content was maximum in whole tissues. A 61 kDa band was recognized in haemocytes and cell-free haemolymph by polyclonal anti-fish CYP1A, while 53.5 and 63.8 kDa CYP1A immunopositive proteins were discriminate without differences of expression. Differently, EROD, MnSOD activity/expression and ECSOD expression decreased in haemocytes and haemolymph. C. gallina immune system presents an interesting response dose/time exposure of B[a]P and the 7 days condition highlights the major effects of xenobiotic action. The identification of basal EROD levels supports the possible presence of the CYP1A, never identified in C. gallina and more specifically never isolated in immune cells, as confirmed by CYP1A-immunopositive proteins identification.

Degradation of leucomyosuppressin by enzymes in the hemolymph and midgut of Lacanobia oleracea and Spodoptera littoralis (Lepidoptera: Noctuidae) larvae

The degradation of 2 nmol synthetic leucomyosuppressin (LMS) by enzymes of the hemolymph, midgut lumen and midgut tissues of both Lacanobia oleracea and Spodoptera littoralis was investigated using reversed-phase high-performance liquid chromatography together with matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Degradation of LMS in diluted hemolymph of L. oleracea and S. littoralis was not rapid, t(1/2)=65.4 and 13.1 min, respectively, due to carboxypeptidase(s) and endopeptidase(s) present in the hemolymph. There was also some aminopeptidase activity in the hemolymph of both species. However, LMS was rapidly degraded by the diluted contents of the midgut lumen of L. oleracea and S. littoralis, t(1/2)=0.5 and 2.2 min, respectively. The enzymes most likely responsible were trypsin-like serine protease(s) and carboxypeptidase(s). Degradation of LMS by midgut tissues containing 5 microg protein was not rapid in L. oleracea or S. littoralis, t(1/2)=40.7 and 69.8 min, respectively. The most abundant degradation products probably resulted from carboxypeptidase activity, but some aminopeptidase activity was also detected.

Summer immune depression associated with increased susceptibility of the European abalone, Haliotis tuberculata to Vibrio harveyi infection

Haliotis tuberculata mortality outbreaks have occurred in France since 1998 and were attributed to a pathogenic Vibrio harveyi. These mortalities were recorded in September, a month with abalone reproduction and characterised by high seawater temperatures. The importance of gonadal maturation and temperature increase on abalone immunity and susceptibility to V. harveyi infection needed to be clarified. Therefore, an immune survey analyzing a large panel of parameters was performed from June to September 2007 on abalone from the Bay of Brest. The data obtained were put in relation with abalone reproductive status and its susceptibility to V. harveyi. Most parameters showed clear patterns from early to late summer and during gametogenesis, phagocytosis and phenoloxidase activity were reduced, whereas basal reactive oxygen species production and agglutination titres were significantly increased. Total haemocyte counts went up after the partial spawning event at the end of June, and cell complexity diminished. Using a Principal Component Analysis, the "haemolymph profile" was shown to decrease in parallel with spawning and gonadal maturation processes, and reached a minimum just after total spawning. A significant correlation between this "haemolymph profile" and disease susceptibility allowed us to establish for the first time in abalone, a clear concordance between maturation and spawning processes, immune status and abalone susceptibility to V. harveyi.

The immune response of white shrimp Litopenaeus vannamei following Vibrio alginolyticus injection

White shrimp Litopenaeus vannamei injected with saline, and injected with tryptic soy broth (TSB)-grown Vibrio alginolyticus at 1.0 x 10(5) and 1.8 x 10(5) colony-forming units (cfu) shrimp(-1) were examined for hyaline cell (HC) counts, granular cell (GC) counts, total haemocyte counts (THCs), phenoloxidase (PO) activity, respiratory burst (RB) and superoxide dismutase (SOD) activity after 1-168 h. Shrimp that received no injection served as the control. The shrimps which received V. alginolyticus at both doses showed significant decreases in these parameters after 6-96 h. The values for HC and SOD activity decreased earlier and then RB. The time to cause maximum depletion of haemocytes (haemocytopenia), PO activity, RB, and SOD activity were 12, 72, 48, and 24 h post-injection, respectively. The HC, GC, and RB returned to the original values earlier at 72 h, followed by SOD activity at 96 h, and then PO activity at 168 h post-infection. It was concluded that an injection of V. alginolyticus rapidly reduced the shrimp's immunity by decreasing HC, GC, SOD activity, RB, and PO activity within 3-24 h, followed by a slow recovery during 72-168 h post-injection. Furthermore, white shrimp L. vannamei which received V. alginolyticus showed a 6-9 h later response in PO activity, and a 72-96 h later recovery of PO activity, compared to the responses in RB and SOD activity indicating their roles in shrimp defence and immunity.

The ontogeny of immunity: development of innate immune strength in the honey bee (Apis mellifera)

Honey bees (Apis mellifera) are of vital economic and ecological importance. These eusocial animals display temporal polyethism, which is an age-driven division of labor. Younger adult bees remain in the hive and tend to developing brood, while older adult bees forage for pollen and nectar to feed the colony. As honey bees mature, the types of pathogens they experience also change. As such, pathogen pressure may affect bees differently throughout their lifespan. We provide the first direct tests of honey bee innate immune strength across developmental stages. We investigated immune strength across four developmental stages: larvae, pupae, nurses (1-day-old adults), and foragers (22-30 days old adults). The immune strength of honey bees was quantified using standard immunocompetence assays: total hemocyte count, encapsulation response, fat body quantification, and phenoloxidase activity. Larvae and pupae had the highest total hemocyte counts, while there was no difference in encapsulation response between developmental stages. Nurses had more fat body mass than foragers, while phenoloxidase activity increased directly with honey bee development. Immune strength was most vigorous in older, foraging bees and weakest in young bees. Importantly, we found that adult honey bees do not abandon cellular immunocompetence as has recently been proposed. Induced shifts in behavioral roles may increase a colony's susceptibility to disease if nurses begin foraging activity prematurely.

Effects of emersion and re-immersion on physiological and immunological variables in creel-caught and trawled Norway lobster Nephrops norvegicus

Immune defence in creel-caught and trawled Nephrops norvegicus was investigated to assess a possible relationship between phenoloxidase (PO) activation and the total haemocyte count (THC). Capture, capture method and emersion evoked physiological and immunological responses that may have implications for the ability of N. norvegicus to survive the effects of such stressors. Haemolymph THC was always negatively related to PO activity in the trawled samples, suggesting a decreased level of the plasma serine proteinase inhibitors which reportedly regulate the ProPO system (Le Moullac et al. 1998; Fish shellfish Immunol 8:621-629). In contrast, creel-caught samples showed increased levels of both PO and THC (cf. control N. norvegicus), after a 12 h emersion period. Trawling and emersion evoked progressive and significant increases (p < 0.05) in the mean levels of haemolymph L-lactate, glucose and total ammonia. The evidence of overt activity and measured haemolymph parameters suggest that creel fishing yields N. norvegicus that are more likely to survive post-harvest treatments than those that are trawled.

Clearance of white spot syndrome virus (WSSV) and immunological changes in experimentally WSSV-injected Macrobrachium rosenbergii

A time course experimental challenge of WSSV was carried out to examine the clearance of WSSV in Macrobrachium rosenbergii and the consequent immunological changes. The experimental animals were injected with WSSV and the samples of gills, pleopods, head soft tissue and hemolymph were collected at different intervals of 1, 3, 5, 10, 25, 50, 75 and 100 days post infection (p.i.). WSSV infection and clearing were confirmed by single step PCR, nested PCR and bioassay. At 3 days p.i., M. rosenbergii became lethargic and stopped feeding in contrast to the control prawns that behaved and fed normally. However, the WSSV-injected prawns suffered no mortality during the experimental period and recovered without any further gross signs of disease or any mortality over a period of 100 days p.i. The single step PCR analysis showed positive at 1, 3 and 5 days p.i. in gills, head soft tissue, pleopods and hemolymph, and all the organs showed negative at 10 days p.i. onwards. The nested PCR results showed that all organs were positive for WSSV from 3 days p.i. and extended up to 25 days p.i. At 50 days p.i, head soft tissue sample alone showed WSSV-positive while all other organs were negative by nested PCR. All the organs at 75 and 100 days p.i. showed nested PCR negative for WSSV as observed in the control prawn. The hemolymph collected from experimentally infected M. rosenbergii at 1, 3 and 5 days p.i. caused 100% mortality at 40 h p.i., 55 h p.i. and 72 h p.i, respectively in Penaeus monodon whereas hemolymph collected at 10, 25, 50, 75 and 100 days p.i. failed to cause mortality in shrimp. The moribund shrimp showed WSSV-positive and surviving shrimp showed negative by PCR. Immunological parameters such as proPO, O(2)(-) and clotting time in WSSV-injected M. rosenbergii were found to be significantly higher than those of the control groups, whereas THC and superoxide dismutase were significantly lower when compared to control groups.

A positive feedback mechanism in the Manduca sexta prophenoloxidase activation system

In Manduca sexta, pathogen recognition triggers a branched serine proteinase cascade which generates active phenoloxidase (PO) in the presence of a proPO-activating proteinase (PAP) and two noncatalytic serine proteinase homologs (SPHs). PO then catalyzes the production of reactive compounds for microbe killing, wound healing, and melanin formation. In this study, we discovered that a minute amount of PAP1 (a final component of the proteinase pathway) caused a remarkable increase in PO activity in plasma from naïve larvae, which was significantly higher than that from the same amounts of PAP1, proPO and SPHs incubated in vitro. The enhanced proPO activation concurred with the proteolytic activation of HP6, HP8, PAP1, SPH1, SPH2 and PO precursors. PAP1 cleaved proSPH2 to yield bands with mobility identical to SPH2 generated in vivo. PAP1 partially hydrolyzed proHP6 and proHP8 at a bond amino-terminal to the one cut in the PAP1-added plasma. PAP1 did not directly activate proPAP1. These results suggest that a self-reinforcing mechanism is built into the proPO activation system and other plasma proteins are required for cleaving proHP6 and proHP8 at the correct site to strengthen the defense response, perhaps in the early stage of the pathway activation.

The effect of different acclimation temperatures on the prophenoloxidase system and other defence parameters in Litopenaeus vannamei

Water temperature changes (higher and lower than 24 degrees C) were shown to have a significant effect on dopamine (DA) concentration, haemocyte count and the proPO system in the white shrimp Litopenaeus vannamei. No significant difference in any of the parameters was observed in the control group. DA concentration in haemolymph in the experimental groups increased to a peak value at 0.5 days; meanwhile serine protease (SP) activity and proteinase inhibitor (PI) activity decreased. Total haemocyte count (THC), differential haemocyte count (DHC) and PO activity were lowest at 1 day. All defence parameters became stable after 1-3 days, while the total haemocyte and large granular cell count stabilized after 6 days. After these stabilized, there was no significant difference in DA concentration and PI activity between the control and experimental groups, as was the case for the THC, DHC, PO and SP activities of shrimp held at higher temperatures. However these latter four parameters in the lower temperature groups were distinctly lower than the control group. alpha(2)-Macroglobulin activity in the experimental groups increased to a peak value after 1 day compared with the control and then stabilized after 6 days when the activity levels in higher temperature groups were higher than the control, while the lower temperature groups had no significant difference from the control. It was therefore concluded that water temperature changes modulated the immune system of L. vannamei.

Variability of haemocyte and haemolymph parameters in European flat oyster Ostrea edulis families obtained from brood stocks of different geographical origins and relation with infection by the protozoan Bonamia ostreae

A research project to compare productive traits (growth and mortality), disease susceptibility and immune capability between Ostrea edulis stocks was performed. This article reports the results on the immune capability and its relation with infection by the intrahaemocytic protozoan Bonamia ostreae. Four to five oyster spat families were produced from each of four European flat oyster populations (one from Ireland, one from Greece and two from Galicia, Spain) in a hatchery. The spat were transferred to a raft in the Ría de Arousa (Galicia) for on growing for 2 years. Total haemocyte count (THC) and differential haemocyte count (DHC) were estimated monthly through the second year of growing-out. Three types of haemocytes were distinguished: granulocytes (GH), large hyalinocytes (LHH) and small hyalinocytes (SHH). Significant correlations between the mean relative abundance of GH and SHH of the families and the mean prevalence of B. ostreae, the overall incidence of pathological conditions and the cumulative mortality of the families were found; these correlations supported the hypothesis that high %GH and low %SHH would enhance oyster immune ability and, consequently, would contribute to lower susceptibility to disease and longer lifespan. Infection by B. ostreae involved a significant increase of circulating haemocytes, which affected more markedly the LHH type. The higher the infection intensity the higher the %LHH. This illustrates the ability of B. ostreae to modulate the immune responses of the O. edulis to favour its own multiplication. A significant reduction of the phenoloxidase activity in the haemolymph of oysters O. edulis infected by B. ostreae was observed. Nineteen enzymatic activities in the haemolymph of O. edulis and Crassostrea gigas (used as a B. ostreae resistant reference) were measured using the kit api ZYM, Biomerieux. Qualitative and quantitative differences in enzyme activities in both haemocyte and plasma fractions between B. ostreae noninfected O. edulis from different origins were recorded. However, no clear positive association between enzyme activity and susceptibility to bonamiosis was found. The only enzyme detected in the resistant species C. gigas that was not found in the susceptible one O. edulis was beta-glucosidase (in plasma). B. ostreae infected O. edulis showed significant increase of some enzyme activities and the occurrence of enzymes that were not detected in noninfected oysters. These changes could be due to infection-induced enzyme synthesis by the host or to enzyme synthesis by the parasite.

Cloning and mRNA expression of antioxidant enzymes in the Pacific oyster, Crassostrea gigas in response to cadmium exposure

Cadmium (Cd) is one of the most toxic heavy metal pollutants in the aquatic environment and can induce the formation of reactive oxygen species (ROS) that cause oxidative stress. In present study, we cloned catalase (CAT) and glutathione peroxidase (GPX) cDNA, and investigated its time- and dose-related effects of three Cd concentrations (0.01, 0.05 or 0.1 ppm) on mRNA levels of antioxidant enzymes (superoxide dismutase (SOD), CAT, GPX) in the gill and changes enzyme levels in the hemolymph of the Pacific oyster, Crassostrea gigas. The cDNA indentified encoded proteins of 516 and 244 amino acids corresponding to CAT and GPX, respectively. BLAST analysis from other species indicated that the residues essential to the enzymatic function of CAT and GPX proteins of C. gigas are highly conserved. Cd treatment significantly increased antioxidant enzyme mRNA expression in the gill in a time- and dose-dependent manner. The mRNA expression at 0.1 ppm Cd concentration increased up to 3 days (CAT, GPX) or 7 days (SOD) and then decreased by 7 days (CAT, GPX) or 11 days (SOD). Aspartate aminotransferase, alanine amintransferase and hydrogen peroxide (H(2)O(2)) concentrations levels increased significantly with exposure to 0.05 or 0.1 ppm Cd for 7 days. These results suggest that antioxidant enzymes play important roles in the physiological changes related to metabolism and cell protection that occur in Pacific oysters exposed to Cd.

Effects of leucine-enkephalin on catalase activity and hydrogen peroxide levels in the haemolymph of the Pacific Oyster (Crassostrea gigas)

The nervous and immune systems of invertebrates can exchange information through neuropeptides. Furthermore, some opioid peptides can function as endogenous immune system messengers and participate in the regulation of the immune responses. The present study was designed to investigate the effects of leucine-enkephalin (L-ENK) on the activity of catalase (CAT) and hydrogen peroxide (H₂O₂) content in the haemolymph of the Pacific Oyster (Crassostrea gigas). The CAT activity and H₂O₂ content were investigated after the haemolymph of the species was exposed to 1, 5, and 50 μg/mL of L-ENK. The results indicate that the intracellular and extracellular CAT activity was increased with increasing concentration of L-ENK, while the intracellular and extracellular H₂O₂ content was decreased with increasing concentration of L-ENK. L-ENK may regulate the intracellular and extracellular CAT activity and H₂O₂ content via binding with opioid neuropeptide receptors on immunocytes of the oysters. The data strongly suggests an involvement of opioid peptides in the regulation of the antioxidant defence systems of Crassostrea gigas.

Cadmium affects the expression of heat shock protein 90 and metallothionein mRNA in the Pacific oyster, Crassostrea gigas

Cadmium (Cd) is a widespread nonessential heavy metal that enters the aquatic environment as a result of natural processes and human activities such as wastewater production, agriculture, and mining. To determine the effects of Cd on organisms, we investigated its time- and dose-related effects on mRNA levels of heat shock protein 90 (HSP90) and metallothionein (MT) in the gill and digestive gland and changes enzyme levels in the hemolymph of the Pacific oyster Crassostrea gigas. Full-length HSP90 cDNA was isolated from C. gigas by rapid amplification of cDNA end (RACE) techniques and found to contain 2154 nucleotides, including an open reading frame, and was predicted to encode a protein of 717 amino acids. BLAST analysis indicated that the HSP90 gene of C. gigas shared high homology with known HSP90 genes of other mollusks. The expression of HSP90 mRNA increased significantly with exposure to 0.01 ppm Cd for 11 days or 0.05 or 0.1 ppm Cd for 7 days. The expression of MT mRNA increased significantly with exposure to 0.01, 0.05, or 0.1 ppm Cd for 11 days. Glutamate oxaloacetate and glutamate pyruvate levels increased significantly with exposure to 0.05 or 0.1 ppm Cd for 7 days. These results indicate that HSP90 and MT play important roles in the physiological changes related to metabolism and cell protection that occur in Pacific oysters exposed to Cd.

Correlation of hemocyte counts with different developmental parameters during the last larval instar of the tobacco hornworm, Manduca sexta

We determined the changes in hemocyte titer and in the abundance of hemocyte types of the tobacco hornworm Manduca sexta during the fourth and fifth larval stadium and the beginning of the pupal stadium. As we analyzed the samples of individual insects at daily intervals, we were able to correlate phenotypical features, body weight, as well as total protein content and lysozyme activity in the hemolymph with the observations on hemocytes. In the course of the fifth larval stadium, the hemocyte titer decreased slightly and declined further after pupation. Using calculated values for total hemocyte numbers, females had about five times and males three times more hemocytes in the circulating population at the beginning of the wandering stage (in the middle of the fifth larval stadium) than immediately after the last larval--larval molt (from the fourth to the fifth larval stadium). This sexual difference was mainly due to an increase in the number of plasmatocytes, which was more prominent in females than in males. Granular cells were dominant in early fifth larval stadium while plasmatocytes were the most abundant cells in pupae. Oenocytoids and spherule cells disappeared during the wandering stage. Lysozyme activity in the hemolymph rose to a maximum during the wandering stage, with females having lysozyme values twice as high as those for males. These changes in lysozyme activity, however, did not correlate with the increase of total hemolymph protein titer which occurred already at the beginning of the wandering stage. We postulate that changes in hemocyte titers are under direct hormonal control, which has to be proven in future experiments.

Expression of Manduca sexta serine proteinase homolog precursors in insect cells and their proteolytic activation

Phenoloxidase (PO)-catalyzed reactions are crucial to the survival of insects after a pathogen or parasite infection. In Manduca sexta, active PO is generated from its precursor by a prophenoloxidase activating proteinase (PAP) in the presence of non-catalytic serine proteinase homologs (SPHs). The PAP and SPHs, located at the ends of a branched proteinase cascade, also require limited proteolysis to become functional. While the processing enzyme of M. sexta proPAP-2 and proPAP-3 is known, we are now investigating the proteolytic activation of proSPH-1 and proSPH-2. Here, we report the development of a series of Bac-to-Bac plasmid vectors for co-expression, secretion, and affinity purification of proSPH-1 and proSPH-2 from insect cells infected by one baculovirus. The purified proteins were characterized and used as substrates in a search for their activating enzymes in plasma of the larvae injected with microorganisms. Proteolytic processing occurred after the proSPHs had been incubated with hydroxyapatite or gel filtration column fractions. The cleaved proteins were active as a cofactor for proPO activation by PAP, and coexistence of SPH-1 and SPH-2 is essential for manifesting the auxiliary effect.

Phenoloxidase-associated cellular defence in the Sydney rock oyster, Saccostrea glomerata, provides resistance against QX disease infections

The enzyme phenoloxidase is a critical component of the immunological defence of invertebrates. Previously, we have shown that the activity of phenoloxidase in Sydney rock oysters (Saccostrea glomerata) correlates with the severity of QX disease outbreaks. The aetiological agent of QX disease is the opportunistic protozoan parasite, Marteilia sydneyi. In this study, we examined the response of oyster haemocytes to challenge with M. sydneyi. Granular haemocytes were able to rapidly phagocytose parasite sporonts. Phagocytosis stimulated intracellular associated phenoloxidase activity that led to the complete melanisation of phagosomes. Significant differences in phagocytic indexes and phenoloxidase activities were observed between oysters selected for resistance to QX disease (QXR) and non-selected wild-type oysters. The data suggest that phagocytosis and cellular melanisation are critical defensive responses of Sydney rock oysters infected with M. sydneyi.

Differential effects of sugar-mimic alkaloids in mulberry latex on sugar metabolism and disaccharidases of Eri and domesticated silkworms: enzymatic adaptation of Bombyx mori to mulberry defense

Mulberry leaves (Morus spp.) exude latex rich in sugar-mimic alkaloids, 1,4-dideoxy-1,4-imino-d-arabinitol (d-AB1) and 1-deoxynojirimycin (DNJ), as a defense against herbivorous insects. Sugar-mimic alkaloids are inhibitors of sugar-metabolizing enzymes, and are toxic to the Eri silkworm, Samia ricini, a generalist herbivore, but not at all to the domesticated silkworm, Bombyx mori, a mulberry specialist. To address the phenomena, we fed both larvae diets containing different sugar sources (sucrose, glucose or none) with or without sugar-mimic alkaloids from mulberry latex. In S. ricini, addition of sugar-mimic alkaloids to the sucrose (the major sugar in mulberry leaves) diet reduced both growth and the absorption ratio of sugar, but it reduced neither in B. mori. The midgut soluble sucrase activity of S. ricini was low and inhibited by very low concentrations of sugar-mimic alkaloids (IC(50)=0.9-8.2microM), but that of B. mori was high and not inhibited even by very high concentrations (IC(50)>1000microM) of sugar-mimic alkaloids. In S. ricini, the addition of sugar-mimic alkaloids to the glucose diet still had considerable negative effects on growth, although it did not reduce the absorption ratio of glucose. The hemolymph of S. ricini fed sugar-mimic alkaloids contained sugar-mimic alkaloids. The trehalose concentration in the hemolymph increased significantly in S. ricini fed sugar-mimic alkaloids, but not in B. mori. The trehalase activities of S. ricini were lower and inhibited by lower concentrations of sugar-mimic alkaloids than those of B. mori. These results suggest that sugar-mimic alkaloids in mulberry latex exert toxicity to S. ricini larvae first by inhibiting midgut sucrase and digestion of sucrose, and secondly, after being absorbed into hemolymph, by inhibiting trehalase and utilization of trehalose, the major blood sugar. Further, our results reveal that B. mori larvae evolved enzymatic adaptation to mulberry defense by developing sucrase and trehalase that are insensitive to sugar-mimic alkaloids.

Jhe in Gryllus assimilis: cloning, sequence-activity associations and phylogeny

The 458 amino acid sequence of a mature JHE protein from the cricket Gryllus assimilis was identified after isolating the partial cDNA sequence encoding this protein from a fat body and midgut cDNA library. This hemimetabolan JHE sequence shows over 40% amino acid similarity to the known JHE sequences of several holometabolous insects. It also includes previously determined peptide sequences for G. assimilis JHE as well as two other motifs associated with JHE enzymes in holometabolous insects. The predicted molecular weight of the protein agrees with that of the JHE previously purified from G. assimilis. Partial genomic sequence encoding the Jhe contains two large (1330 and 2918bp) introns. No coding DNA sequence variation was observed over a 1293bp region between selected lines differing six to eight-fold in hemolymph JHE activity. However, a 19bp indel was found in one of the introns; the insertion was strongly associated with elevated hemolymph activity, both in the selected lines and in the F(2) progeny of crosses between them. Phylogenetic analyses localised the G. assimilis JHE to a clade containing dipteran and coleopteran JHEs, with lepidopteran JHEs occurring in a separate clade.

Induction of phenoloxidase and other immunological activities in Sydney rock oysters challenged with microbial pathogen-associate molecular patterns

This study investigates the effects of two pathogen-associated molecular patterns (PAMPs), LPS and zymosan, on the Sydney rock oyster (Saccostrea glomerata) immune system. Phenoloxidase and phagocytic activities, total and differential haemocyte frequencies, as well as peroxide and superoxide concentrations were measured after the injection of lipopolysaccharide and zymosan. All of the immunological parameters were induced by both PAMPs. Phenoloxidase (monophenolase and diphenolase) and phagocytic activities, as well as the frequencies of phenoloxidase-positive haemocytes, hyalinocytes and granulocytes in the haemolymph, increased within 24 h of PAMP injection. Values for all of these parameters peaked within 48 h of challenge and began to decrease to levels that were indistinguishable from those of controls within 96h. The only exception to this pattern was diphenolase activity, which remained elevated for at least 96 h. Control saline injections that lacked PAMPs also induced responses in most of the parameters measured. However, reactions to saline injections were of far lower magnitude compared to those induced by PAMPs. All of the data suggest that the phenoloxidase and phagocytic systems of oysters are inducible components of the Sydney rock oyster immune system, and that induction is primarily due to increased frequencies of specialised haemocytes in the haemolymph.