The energetic cost of protein synthesis in isolated hepatocytes of rainbow trout (Oncorhynchus mykiss)

Warm and thermally variable incubation conditions reduce embryonic performance and carry over to influence hatchling tradeoffs

Animals' thermal sensitivities have long been characterized by thermal performance curves (TPCs) or reaction norms, and TPCs may predict animals' responses to climate change. Typically, TPCs are parameterized by measuring performance at a range of constant temperatures. Yet, animals encounter a range of thermal environments, and temperature variability is an aspect of climate change that may affect animals more than gradual warming. Daily temperature variability is particularly important for eggs in most taxa because they are highly sensitive to temperature and cannot behaviorally avoid stressful temperatures. Thus, the legacy of thermal conditions experienced during incubation may carryover to subsequent life stages. Here, I factorially manipulated mean temperature (20, 25, or 30 °C) and daily temperature range (DTR; ±0, 5, or 10 °C) during incubation for eggs of the variable field cricket (Gryllus lineaticeps) to integrate the role of DTR into the established paradigm of TPCs. Low DTR (±5 °C) was not generally costly, and it even improved hatchling starvation resistance (sensu hormesis). However, high DTR (±10 °C) reduced and delayed hatching at a warm mean temperature (30 °C). The effects of high DTR carried over to accelerate hatchling development at an expense to hatchling starvation resistance-therefore, thermal conditions during incubation can shape tradeoffs among important traits related to life history and stress tolerance later in life. In sum, animals may exhibit complex responses to their increasingly warmer, more thermally variable environments.

Surviving without oxygen involves major tissue specific changes in the proteome of crucian carp (Carassius carassius)

The crucian carp (Carassius carassius) can survive complete oxygen depletion (anoxia) for several months at low temperatures, making it an excellent model for studying molecular adaptations to anoxia. Still, little is known about how its global proteome responds to anoxia and reoxygenation. By applying mass spectrometry-based proteome analyses on brain, heart and liver tissue from crucian carp exposed to normoxia, five days anoxia, and reoxygenation, we found major changes in particularly cardiac and hepatic protein levels in response to anoxia and reoxygenation. These included tissue-specific differences in mitochondrial proteins involved in aerobic respiration and mitochondrial membrane integrity. Enzymes in the electron transport system (ETS) decreased in heart and increased massively in liver during anoxia and reoxygenation but did not change in the brain. Importantly, the data support a special role for the liver in succinate handling upon reoxygenation, as suggested by a drastic increase of components of the ETS and uncoupling protein 2, which could allow for succinate metabolism without excessive formation of reactive oxygen species (ROS). Also during reoxygenation, the levels of proteins involved in the cristae junction organization of the mitochondria changed in the heart, possibly functioning to suppress ROS formation. Furthermore, proteins involved in immune (complement) system activation changed in the anoxic heart compared to normoxic controls. The results emphasize that responses to anoxia are highly tissue-specific and related to organ function.

Predator-induced maternal effects determine adaptive antipredator behaviors via egg composition

In high-risk environments with frequent predator encounters, efficient antipredator behavior is key to survival. Parental effects are a powerful mechanism to prepare offspring for coping with such environments, yet clear evidence for adaptive parental effects on offspring antipredator behaviors is missing. Rapid escape reflexes, or "C-start reflexes," are a key adaptation in fish and amphibians to escape predator strikes. We hypothesized that mothers living in high-risk environments might induce faster C-start reflexes in offspring by modifying egg composition. Here, we show that offspring of the cichlid fish Neolamprologus pulcher developed faster C-start reflexes and were more risk averse if their parents had been exposed to cues of their most dangerous natural predator during egg production. This effect was mediated by differences in egg composition. Eggs of predator-exposed mothers were heavier with higher net protein content, and the resulting offspring were heavier and had lower igf-1 gene expression than control offspring shortly after hatching. Thus, changes in egg composition can relay multiple putative pathways by which mothers can influence adaptive antipredator behaviors such as faster escape reflexes.

eIF4E3 forms an active eIF4F complex during stresses (eIF4FS) targeting mTOR and re-programs the translatome

The eIF4E are a family of initiation factors that bind the mRNA 5' cap, regulating the proteome and the cellular phenotype. eIF4E1 mediates global translation and its activity is controlled via the PI3K/AKT/mTOR pathway. mTOR down-regulation results in eIF4E1 sequestration into an inactive complex with the 4E binding proteins (4EBPs). The second member, eIF4E2, regulates the translatome during hypoxia. However, the exact function of the third member, eIF4E3, has remained elusive. We have dissected its function using a range of techniques. Starting from the observation that it does not interact with 4EBP1, we demonstrate that eIF4E3 recruitment into an eIF4F complex occurs when Torin1 inhibits the mTOR pathway. Ribo-seq studies demonstrate that this complex (eIF4FS) is translationally active during stress and that it selects specific mRNA populations based on 5' TL (UTR) length. The interactome reveals that it associates with cellular proteins beyond the cognate initiation factors, suggesting that it may have 'moon-lighting' functions. Finally, we provide evidence that cellular metabolism is altered in an eIF4E3 KO background but only upon Torin1 treatment. We propose that eIF4E3 acts as a second branch of the integrated stress response, re-programming the translatome to promote 'stress resistance' and adaptation.

Thermal sensitivity of cell metabolism of different Antarctic fish species mirrors organism temperature tolerance

Despite cold adaptation, Antarctic fish show lower growth than expected from the van’t Hoff’s Q10 rule. Protein synthesis is one of the main energy-consuming processes, which is downregulated under energy deficiency. Considering the effect of temperature on growth performance, we tested if temperature-dependent cellular energy allocation to protein synthesis correlates with temperature-dependent whole-animal growth and thus thermal tolerance. Cell respiration and energy expenditure for protein synthesis were determined in hepatocytes of the circumpolar-distributed Antarctic eelpout Pachycara brachycephalum after warm acclimation (0 °C vs 5 °C) and, of two notothenioids the sub-Antarctic Lepidonotothen squamifrons and the high-Antarctic icefish Chionodraco hamatus. We used intermittent-flow respirometry to analyse cellular response to acute warming from 5 to 10 °C (P. brachycephalum) and from 1 to 5 °C (L. squamifrons, C. hamatus). Warming-induced rise in respiration was similar between 0- and 5 °C-acclimated P. brachycephalum and between L. squamifrons and C. hamatus. Irrespective of acclimation, warming decreased energy expenditure for protein synthesis in P. brachycephalum, which corresponds to reduced whole-animal growth at temperatures > 5 °C. Warming doubled energy expenditure for protein synthesis in L. squamifrons but had no effect on C. hamatus indicating that L. squamifrons might benefit from warmer waters. The species-specific temperature effect on energy expenditure for protein synthesis is discussed to mirror thermal sensitivity of whole-animal growth performance, thereby paralleling the degree of cold adaptation. Clearly more data are necessary including measurements at narrower temperature steps particularly for C. hamatus and an increased species’ number per ecotype to reinforce presented link between cellular and whole-animal thermal sensitivity.

Species vulnerability under climate change: Study of two sea urchins at their distribution margin

In order to develop powerful predictions on the impact of climate change on marine organisms, it is critical to understand how abiotic drivers such as temperature can directly and indirectly affect marine organisms. Here, we evaluated and compared the physiological vulnerability of the leading-edge populations of two species of sea urchins Loxechinus albus and Pseudechinus magellanicus in response to predicted ocean warming and food limitation. After exposing sea urchins to a 60-day experimental period to contrasting temperature (1 °C, 7 °C and 14 °C corresponding respectively to the actual average summer temperature in Antarctica, the control treatment temperature and the predicted future temperature in the Strait of Magellan) and diet levels (ad libitum or food limitation), sea urchin stress tolerance was assessed. Sea urchins' physiology was measured at the organismal and sub-cellular level by studying the organisms energy balance (behavior, growth, gonad index, ingestion rate, O₂ uptake, energy reserves) and the expression of genes associated with aerobic metabolism. Our results showed that at their distribution edge, and despite their distinct geographical repartition, both species might be resilient to ocean warming. However, the combination of ocean warming and food limitation reduced the stress tolerance of sea urchins. In a warming ocean, another strategy could be to migrate toward the pole to a cooler environment but incubation at 1 °C resulted in a diminution of both species' aerobic scope. Overall, if these engineer species are unable to acclimate to food limitation under future climate, population fitness could be affected with ecological and economic consequences.

An appetite for invasion: digestive physiology, thermal performance and food intake in lionfish (Pterois spp.)

Species invasions threaten global biodiversity, and physiological characteristics may determine their impact. Specific dynamic action (SDA; the increase in metabolic rate associated with feeding and digestion) is one such characteristic, strongly influencing an animal's energy budget and feeding ecology. We investigated the relationship between SDA, scope for activity, metabolic phenotype, temperature and feeding frequency in lionfish (Pterois spp.), which are invasive to western Atlantic marine ecosystems. Intermittent-flow respirometry was used to determine SDA, scope for activity and metabolic phenotype at 26°C and 32°C. Maximum metabolic rate occurred during digestion, as opposed to exhaustive exercise, as in more athletic species. SDA and its duration (SDA_dur) were 30% and 45% lower at 32°C than at 26°C, respectively, and lionfish ate 42% more at 32°C. Despite a 32% decline in scope for activity from 26°C to 32°C, aerobic scope may have increased by 24%, as there was a higher range between standard metabolic rate (SMR) and peak SDA (SDA_peak; the maximum postprandial metabolic rate). Individuals with high SMR and low scope for activity phenotypes had a less costly SDA and shorter SDA_dur but a higher SDA_peak Feeding frequently had a lower and more consistent cost than consuming a single meal, but increased SDA_peak These findings demonstrate that: (1) lionfish are robust physiological performers in terms of SDA and possibly aerobic scope at temperatures approaching their thermal maximum, (2) lionfish may consume more prey as oceans warm with climate change, and (3) metabolic phenotype and feeding frequency may be important mediators of feeding ecology in fish.

Effect of protein synthesis inhibitor cycloheximide on starvation, fasting and feeding oxygen consumption in juvenile spiny lobster Sagmariasus verreauxi

Metabolism in aquatic ectotherms evaluated by oxygen consumption rates reflects energetic costs including those associated with protein synthesis. Metabolism is influenced by nutritional status governed by feeding, nutrient intake and quality, and time without food. However, little is understood about contribution of protein synthesis to crustacean energy metabolism. This study is the first using a protein synthesis inhibitor cycloheximide to research contribution of cycloheximide-sensitive protein synthesis to decapod crustacean metabolism. Juvenile Sagmariasus verreauxi were subject to five treatments: 2-day fasted lobsters sham injected with saline; 2-day fasted lobsters injected with cycloheximide; 10-day starved lobsters injected with cycloheximide; post-prandial lobsters fed with squid Nototodarus sloanii with no further treatment; and post-prandial lobsters injected with cycloheximide. Standard and routine metabolic rates in starved lobsters were reduced by 32% and 41%, respectively, compared to fasted lobsters, demonstrating metabolic downregulation with starvation. Oxygen consumption rates of fasted and starved lobsters following cycloheximide injection were reduced by 29% and 13%, respectively, demonstrating protein synthesis represents only a minor component of energy metabolism in unfed lobsters. Oxygen consumption rate of fed lobsters was reduced by 96% following cycloheximide injection, demonstrating protein synthesis in decapods contributes a major proportion of specific dynamic action (SDA). SDA in decapods is predominantly a post-absorptive process likely related to somatic growth. This work extends previously limited knowledge on contribution of protein synthesis to crustacean metabolism, which is crucial to explore the relationship between nutritional status and diet quality and how this will affect growth potential in aquaculture species.

Ingestion of artificial sweeteners leads to caloric frustration memory in Drosophila

Non-caloric artificial sweeteners (NAS) are widely used in modern human food, raising the question about their health impact. Here we have asked whether NAS consumption is a neutral experience at neural and behavioral level, or if NAS can be interpreted and remembered as negative experience. We used behavioral and imaging approaches to demonstrate that Drosophila melanogaster learn the non-caloric property of NAS through post-ingestion process. These results show that sweet taste is predictive of an energy value, and its absence leads to the formation of what we call Caloric Frustration Memory (CFM) that devalues the NAS or its caloric enantiomer. CFM formation involves activity of the associative memory brain structure, the mushroom bodies (MBs). In vivo calcium imaging of MB-input dopaminergic neurons that respond to sugar showed a reduced response to NAS after CFM formation. Altogether, these findings demonstrate that NAS are a negative experience for the brain.

While non-caloric artificial sweeteners (NAS) are used as food additives, it’s unclear whether animals perceive NAS as positive or negative percept. Here, Musso and colleagues show in Drosophila that NAS is a negative percept, encoded in a new type of memory.

Biochemical Foundations of Health and Energy Conservation in Hibernating Free-ranging Subadult Brown Bear Ursus arctos

Brown bears (Ursus arctos) hibernate for 5-7 months without eating, drinking, urinating, and defecating at a metabolic rate of only 25% of the summer activity rate. Nonetheless, they emerge healthy and alert in spring. We quantified the biochemical adaptations for hibernation by comparing the proteome, metabolome, and hematological features of blood from hibernating and active free-ranging subadult brown bears with a focus on conservation of health and energy. We found that total plasma protein concentration increased during hibernation, even though the concentrations of most individual plasma proteins decreased, as did the white blood cell types. Strikingly, antimicrobial defense proteins increased in concentration. Central functions in hibernation involving the coagulation response and protease inhibition, as well as lipid transport and metabolism, were upheld by increased levels of very few key or broad specificity proteins. The changes in coagulation factor levels matched the changes in activity measurements. A dramatic 45-fold increase in sex hormone-binding globulin levels during hibernation draws, for the first time, attention to its significant but unknown role in maintaining hibernation physiology. We propose that energy for the costly protein synthesis is reduced by three mechanisms as follows: (i) dehydration, which increases protein concentration without de novo synthesis; (ii) reduced protein degradation rates due to a 6 °C reduction in body temperature and decreased protease activity; and (iii) a marked redistribution of energy resources only increasing de novo synthesis of a few key proteins. The comprehensive global data identified novel biochemical strategies for bear adaptations to the extreme condition of hibernation and have implications for our understanding of physiology in general.

The small molecule '1-(4-biphenylylcarbonyl)-4-(5-bromo-2-methoxybenzyl) piperazine oxalate' and its derivatives regulate global protein synthesis by inactivating eukaryotic translation initiation factor 2-alpha

By environmental stresses, cells can initiate a signaling pathway in which eukaryotic translation initiation factor 2-alpha (eIF2-α) is involved to regulate the response. Phosphorylation of eIF2-α results in the reduction of overall protein neogenesis, which allows cells to conserve resources and to reprogram energy usage for effective stress control. To investigate the role of eIF2-α in cell stress responses, we conducted a viability-based compound screen under endoplasmic reticulum (ER) stress condition, and identified 1-(4-biphenylylcarbonyl)-4-(5-bromo-2-methoxybenzyl) piperazine oxalate (AMC-01) and its derivatives as eIF2-α-inactivating chemical. Molecular characterization of this signaling pathway revealed that AMC-01 induced inactivation of eIF2-α by phosphorylating serine residue 51 in a dose- and time-dependent manner, while the negative control compounds did not affect eIF2-α phosphorylation. In contrast with ER stress induction by thapsigargin, phosphorylation of eIF2-α persisted for the duration of incubation with AMC-01. By pathway analysis, AMC-01 clearly induced the activation of protein kinase RNA-activated (PKR) kinase and nuclear factor-κB (NF-κB), whereas it did not modulate the activity of PERK or heme-regulated inhibitor (HRI). Finally, we could detect a lower protein translation rate in cells incubated with AMC-01, establishing AMC-01 as a potent chemical probe that can regulate eIF2-α activity. We suggest from these data that AMC-01 and its derivative compounds can be used as chemical probes in future studies of the role of eIF2-α in protein synthesis-related cell physiology.

The effect of hatching time on the bioenergetics of northern pike (Esox lucius) larvae from a single egg batch during the endogenous feeding period

Size, caloric value and chemical composition were measured separately in the progeny of two northern pike (Esox lucius) females at 3-day intervals during the endogenous feeding period from hatching to final yolk resorption. Tissue, yolk and entire larvae were analysed separately in three groups of larvae that hatched at different times (between 88 and 106 degree-days post-fertilization). An integrated approach with the Gompertz model was used to compute the yolk conversion efficiency and time to maximum tissue size in early, mid and late hatched larvae. At hatching, unresorbed yolk of early hatched larvae contained more energy (39.20 J) and more protein (0.99 mg) compared to the yolk of larvae that hatched later (38.13 J and 0.92 mg protein for late hatched larvae, p < 0.05). In contrast, a significant reduction in tissue weight (-0.7 mg DW) and protein content (-0.5 mg) was found in early hatched larvae compared to those which hatched later (p < 0.05). Between days 9 and 12 post-hatching (108 and 144 degree-days post-hatching), close to the final yolk resorption, late hatched larvae stopped growing and their tissue began to be resorbed. This tissue resorption time was delayed in early hatched larvae which presented at the end of the experiment a greater tissue weight than late hatched ones. Yolk conversion efficiency in term of energy from hatching to complete yolk resorption stage was significantly higher for early and mid hatched larvae (51%) compared to late hatched ones (44%) (p = 0.004). Furthermore, the time to maximum tissue size was found to be negatively related to hatching time which implies that early hatched larvae take longer time to switch from one developmental stage to the next. The maximum tissue dry weight and energy content were found to be reached at approximately the same age post-fertilization for both early hatched and late hatched larvae, suggesting that the principal steps in a fish's lifespan are better correlated with time of fertilization than hatching time.

Effects of repeated handling and air exposure on the immune response and the disease resistance of gibel carp (Carassius auratus gibelio) over winter

High mortalities and suppressed immune functions of farmed fish over winter are the universal problems in aquaculture. It is necessary to improve the immune response and disease resistance in the overwintering fish. A recent study suggested that repeated handling increased innate immune mechanisms and disease resistance in Senegalese sole. Therefore, the present study evaluated the hypothesis that appropriate repeated handling could compromise the immune depression and increase the disease resistance in gibel carp over winter. The experiment was executed in field net cages (2 m × 2 m × 2 m) from Dec. 4, 2012 to Apr. 2, 2013. Three cages with 50 fish per cage were randomly designed as the control group and did not receive any interfere over winter. The other three cages received repeated handling with an air exposure for 5 min every week during the experiment. Fish were not fed over winter. At the end of the trial, fish were challenged with Aeromonas hydrophila at a dose of 1.5 × 10(8) CFU ml(-1). The results showed that no significant difference of final body weight was found between groups. The spleen and kidney somatic index increased in the control fish after bacterial challenge and showed a rising trend but not a statistical change in repeated handled fish. Plasma cortisol levels significantly increased in the control fish at 6 h post bacterial challenge and then declined. However, repeated handled fish did not show any significant change in plasma cortisol levels after challenge. The reduced inducement of heat shock protein 70 (HSP70) expressions by repeated handling was found in gibel carp post bacterial challenge. After overwintering, the repeated handled fish exhibited increased catalase (CAT) and superoxide dismutase (SOD) activities. Enhanced plasma CAT activities and reduced plasma malondialdehyde (MDA) contents were found in repeated handled fish over time against invading bacteria. Up-regulation of myeloid differentiation primary response gene 88 (MyD88) and interleukin 11 (IL11) was observed in repeated handled fish over time after bacterial challenge. The overexpression of IL11 was significantly reduced by repeated handling against invading bacteria compared to the control group. The present results implied that a MyD88-dependent signaling pathway was involved in the innate immune responses of gibel carp by repeated handling over winter against invading bacteria.

Repeated handling compromises the immune suppression and improves the disease resistance in overwintering channel catfish (Ictalurus punctatus)

In winter, fish have suppressed immune functions and are susceptible to bacteria or virus which may lead to a high mortality. It is necessary to improve the immune response and disease resistance for overwintering fish. A recent study suggested that repeated handling increased the innate immune mechanisms and disease resistance in Senegalese sole. Therefore, the present study tested the hypothesis that appropriate repeated handling could compromise the immune depression and increase the disease resistance in channel catfish over winter. The experiment was carried out in field cages from Nov. 2012 to April 2013. Before the experiment, 35 fish with an average weight of 188.4 g were randomly assigned to one of six cages (2 m × 2 m × 2 m). Three cages were designed as the control group and did not receive any interfere. Fish in the other three cages received a weekly repeated handling of an air exposure for 5 min. Fish were not fed over winter. At the end of the trial, fish were challenged with Aeromonas hydrophila at a dose of 5.6 × 10(8) CFU ml(-1). The results showed that final body weight was not changed between groups. The spleen somatic index increased while the head kidney somatic index decreased in the unhandled fish after bacterial challenge, but these indices were not significantly changed in the repeated handled fish. Plasma cortisol levels in the control fish were induced at 6 h post challenge and then declined to the normal levels. However, plasma cortisol levels in the repeated handled fish did not show any significant change after bacteria challenge. The reduced inducement of heat shock protein 70 (HSP70) expression by repeated handling was observed in fish post bacterial challenge. After overwintering, repeated handled fish exhibited increased catalase (CAT) activities and reduced malondialdehyde (MDA) contents. Plasma total antioxidant capacity (TAOC), CAT and superoxide dismutase (SOD) activities of channel catfish were enhanced by repeated handling post bacterial challenge. The enhanced up-regulation of Interleukin 8 (IL8), IL1β-a, IL1β-b together with the immune related genes of Toll-like receptor 2 (TLR2), TLR3, nucleotide-binding oligomerization domain 1 (NOD1) and NOD2 by repeated handling was found in catfish after bacterial challenge. The present results indicated that a combination of signaling pathways through TLRs and NODs was involved in the innate immune response of the overwintering repeated handled channel catfish against invading bacteria.

The impact of the phosphomimetic eIF2αS/D on global translation, reinitiation and the integrated stress response is attenuated in N2a cells

A plethora of stresses trigger a rapid downregulation of protein synthesis. However, a fraction of mRNAs continue to be recruited onto polysomes and their protein products play a key role in deciding cell fate. These transcripts are characterized by the presence of uORFs within their 5' TL coupling protein expression to reinitiation. The translational brake arises due to the activation of a family of kinases targeting the α subunit of the trimolecular eIF2(αβγ) initiation factor. Phosphorylation of eIF2αSer51 inhibits ternary complex regeneration reducing the pool of 43S ribosomes. It is popular to mimic this event, and hence the integrated stress response (ISR), by the expression of the phosphomimetic eIF2αS51D. However, we report that whereas the ISR is reproduced by eIF2αS51D expression in human HEK293T cells this is not the case in N2a mouse neuroblastoma cells. With regards to translational downregulation, this arises due to the failure of the phosphomimetic protein to assemble an eIF2 complex with endogenous eIF2β/γ. This can be compensated for by the transient co-expression of all three subunits. Curiously, these conditions do not modulate reinitiation and consequently fail to trigger the ISR. This is the first demonstration that the inhibitory and reinitiation functions of eIF2αS/D can be separated.

Energetic costs of protein synthesis do not differ between red- and white-blooded Antarctic notothenioid fishes

Antarctic icefishes (Family Channichthyidae) within the suborder Notothenioidei lack the oxygen-binding protein hemoglobin (Hb), and six of the 16 species of icefishes lack myoglobin (Mb) in heart ventricle. As iron-centered proteins, Hb and Mb can promote the formation of reactive oxygen species (ROS) that damage biological macromolecules. Consistent with this, our previous studies have shown that icefishes have lower levels of oxidized proteins and lipids in oxidative muscle compared to red-blooded notothenioids. Because oxidized proteins are usually degraded by the 20S proteasome and must be resynthesized, we hypothesized that rates of protein synthesis would be lower in icefishes compared to red-blooded notothenioids, thereby reducing the energetic costs of protein synthesis and conferring a benefit to the loss of Hb and Mb. Rates of protein synthesis were quantified in hearts, and the fraction of oxygen consumption devoted to protein synthesis was measured in isolated hepatocytes and cardiomyocytes of notothenioids differing in the expression of Hb and cardiac Mb. Neither rates of protein synthesis nor the energetic costs of protein synthesis differed among species, suggesting that red-blooded species do not degrade and replace oxidatively modified proteins at a higher rate compared to icefishes but rather, persist with higher levels of oxidized proteins.

Differential impacts of elevated CO2 and acidosis on the energy budget of gill and liver cells from Atlantic cod, Gadus morhua

Ocean acidification impacts fish and other marine species through increased seawater PCO2 levels (hypercapnia). Knowledge of the physiological mechanisms mediating effects in various tissues of fish is incomplete. Here we tested the effects of extracellular hypercapnia and acidosis on energy metabolism of gill and liver cells of Atlantic cod. Exposure media mimicked blood conditions in vivo, either during normo- or hypercapnia and at control or acidic extracellular pH (pHe). We determined metabolic rate and energy expenditure for protein biosynthesis, Na(+)/K(+)-ATPase and H(+)-ATPase and considered nutrition status by measurements of metabolic rate and protein biosynthesis in media with and without free amino acids (FAA). Addition of FAA stimulated hepatic but not branchial oxygen consumption. Normo- and hypercapnic acidosis as well as hypercapnia at control pHe depressed metabolic stimulation of hepatocytes. In gill cells, acidosis depressed respiration independent of PCO2 and FAA levels. For both cell types, depressed respiration was not correlated with the same reduction in energy allocated to protein biosynthesis or Na(+)/K(+)-ATPase. Hepatic energy expenditure for protein synthesis and Na(+)/K(+)-ATPase was even elevated at acidic compared to control pHe suggesting increased costs for ion regulation and cellular reorganization. Hypercapnia at control pHe strongly reduced oxygen demand of branchial Na(+)/K(+)-ATPase with a similar trend for H(+)-ATPase. We conclude that extracellular acidosis triggers metabolic depression in gill and metabolically stimulated liver cells. Additionally, hypercapnia itself seems to limit capacities for metabolic usage of amino acids in liver cells while it decreases the use and costs of ion regulatory ATPases in gill cells.

Effects of temperature on specific dynamic action in Atlantic cod Gadus morhua

Growth requires that energy is directed towards ingestion, digestion, absorption and assimilation of a meal; energy expenditures are often expressed as the specific dynamic action (SDA). While SDA is an important part of fish energy budgets and strongly affected by water temperature, temperature effects are not known across a wide temperature range in Atlantic cod Gadus morhua. The objective of this study was to examine effects of temperature (2, 5, 10, 15 or 20 °C) on the energetic cost and time used for SDA in juvenile G. morhua by intermittent flow respirometry. At each temperature, G. morhua were fed a meal of herring (Clupea harengus) corresponding to 5 % of the body mass. Standard metabolic rates measured pre-feeding and post-feeding metabolic rates were measured to determine SDA. The study showed that SDA coefficients (%, SDA energy divided by meal energy) were significantly lower at 2 and 10 °C (5.4-6.3 %) compared to 5, 15 and 20 °C (10.4-12.4 %), while SDA duration increased significantly from 80 h at 10 °C to 130-160 h at 2, 15 and 20 °C and reached a maximum of 250 h at 5 °C. The significant decrease in SDA duration at 10 °C combined with a low SDA coefficient suggests that water temperatures close to 10 °C may represent the optimum temperatures for SDA in this population of G. morhua. Our results suggest that SDA is not a simple function of temperature, but may vary with temperature in a more complex fashion.

Cost, effectiveness and environmental relevance of multidrug transporters in sea urchin embryos

ATP-binding cassette transporters protect cells via efflux of xenobiotics and endogenous byproducts of detoxification. While the cost of this ATP-dependent extrusion is known at the molecular level, i.e. the ATP used for each efflux event, the overall cost to a cell or organism of operating this defense is unclear, especially as the cost of efflux changes depending on environmental conditions. During prolonged exposure to xenobiotics, multidrug transporter activity could be costly and ineffective because effluxed substrate molecules are not modified in the process and could thus undergo repeated cycles of efflux and re-entry. Here we use embryos of the purple sea urchin, Strongylocentrotus purpuratus, as a model to determine transport costs and benefits under environmentally relevant xenobiotic concentrations. Strikingly, our results show that efflux transporter activity costs less than 0.2% of total ATP usage, as a proportion of oxygen consumption. The benefits of transport, defined as the reduction in substrate accumulation due to transporter activity, depended largely, but not entirely, on the rate of passive flux of each substrate across the plasma membrane. One of the substrates tested exhibited rapid membrane permeation coupled with high rates of efflux, thus inducing rapid and futile cycles of efflux followed by re-entry of the substrate. This combination significantly reduced transporter effectiveness as a defense and increased costs even at relatively low substrate concentrations. Despite these effects with certain substrates, our results show that efflux transporters are a remarkably effective and low-cost first line of defense against exposure to environmentally relevant concentrations of xenobiotics.

Starvation and re-feeding affect Hsp expression, MAPK activation and antioxidant enzymes activity of European sea bass (Dicentrarchus labrax)

In the context of food deprivation in fish (wild and farmed), understanding of cellular responses is necessary in order to develop strategies to minimize stress caused by starvation in the aquaculture section. The present study evaluates the effects of long term starvation (1F-3S: one-month feeding-three-month starvation) and starvation/re-feeding (2S-2F: two-month starvation-two-month re-feeding) compared to the control group (4F-0S: four-month feeding-zero month starvation) on cellular stress response and antioxidant defense in organs, like the intestine, the liver, the red and white muscle of European sea bass Dicentrarchus labrax. Molecular responses were addressed through the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases and particularly p38 mitogen-activated protein kinase (p38 MAPK) and the extracellular signal-regulated kinases (ERK-1/2). For the determination of the effect of the oxidative stress caused by food deprivation and/or re-feeding, the (maximum) activities of antioxidant enzymes such as glutathione peroxidise (GPx), catalase (CAT) and superoxide dismutase (SOD) as well as the determination of thiobarbituric acid reactive substances (TBARS) were studied. The experimental feeding trials caused a tissue distinct and differential response on the cellular and antioxidant capacity of sea bass not only during the stressful process of starvation but also in re-feeding. Specifically, the intestine phosphorylation of ERKs and antioxidant enzymatic activities increased in the 2S-2F fish group, while in the 1F-3S group an increase was detected in the levels of the same proteins except for GPx. In the liver and the red muscle of 2S-2F fish, decreased Hsp70 and phosphorylated p38 MAPK levels and increased Hsp90 levels were observed. Additionally, SOD activity decreased in the red muscle of 2S-2F and 1F-3S groups. In the liver and red muscle of 1F-3S group Hsp70 levels increased, while the activation of p38 MAPK in the liver decreased. In the white muscle, Hsp90 levels decreased and the phosphorylation of p38 MAPK increased in both feeding regimes compared to control. In the same tissue, GPx and catalase levels were decreased in 2S-2F regime, while SOD levels were decreased in 1F-3S regime.

Effects of 17α-ethynylestradiol on sexual differentiation and development of the African clawed frog (Xenopus laevis)

Several studies have shown that exposure of amphibians, including the African clawed frog (Xenopus laevis), to potent estrogens at critical times during development results in feminization and/or demasculinization. However, genotyping of X. laevis has only recently become possible, so studies performed in the past were rarely able to make explicit linkages between genetic and phenotypic sex. Therefore, to further characterize this relationship, X. laevis tadpoles were exposed during development to 0.09, 0.84, or 8.81 μg/L 17α-ethynylestradiol (EE2), which is the estrogen analog commonly used in oral contraceptives. Exposure to all concentrations of EE2 tested resulted in significant delays in time to metamorphosis. Genotyping showed that genetic sex ratios were similar among treatments. However, morphological evaluation revealed that a significant number of individuals with a male genotype displayed mixed sex and abnormal phenotypes. Additionally, both genetic males and females exposed to EE2 exhibited greater presence of vitellogenin protein relative to the respective controls. Since estrogens function downstream of the initial molecular signals of sexual differentiation, it is likely that genetic male animals received mixed endogenous male and exogenous female signals that caused disordered sexual development. The production of vitellogenin was probably temporally separated and independent from primary effects on sexual differentiation, and might have contributed to delays in metamorphosis observed in individuals exposed to EE2.

Towards a more representative in vitro method for fish ecotoxicology: morphological and biochemical characterisation of three-dimensional spheroidal hepatocytes

The use of fish primary cells and cell lines offer an in vitro alternative for assessment of chemical toxicity and the evaluation of environmental samples in ecotoxicology. However, their uses are not without limitations such as short culture periods and loss of functionality, particularly with primary tissue. While three-dimensional (spheroid) technology is now established for in vitro mammalian toxicity studies, to date it has not been considered for environmental applications in a model aquatic species. In this study we report development of a reproducible six-well plate, gyratory-mediated method for rainbow trout (Oncorhynchus mykiss) hepatocyte spheroid culture and compare their functional and biochemical status with two-dimensional (2D) monolayer hepatocytes. Primary liver spheroid formation was divided into two stages, immature (1-5 days) and mature (≥6 days) according to size, shape and changes in functional and biochemical parameters (protein, glucose, albumin and lactate dehydrogenase). Mature spheroids retained the morphological characteristics (smooth outer surface, tight cell-cell contacts) previously described for mammalian spheroids as demonstrated by light and scanning electron microscopy. Glucose production and albumin synthesis were significantly higher in mature spheroids when compared to conventional 2D monolayer cultures (P < 0.01) and increased as spheroids matured (P < 0.01). Basal lactate dehydrogenase (LDH) leakage significantly decreased during spheroid formation and was significantly lower than 2D cultures (P < 0.01). It is therefore suggested that mature spheroids can maintain a high degree of functional, biochemical and morphological status over-time in culture that is superior to conventional 2D models and can provide realistic organotypic responses in vitro. Trout spheroids that take ~6-8 days to reach maturity would be suitable for use in acute toxicological tests and since it is possible to culture individual spheroids for over a month, there is potential for this work to lead towards in vitro bioaccumulation alternatives and to conduct high throughput screens of chronic exposure. This is an important step forward for developing alternative in vitro tools in future fish ecotoxicological studies.

Cortisol modulates the expression of cytokines and suppressors of cytokine signaling (SOCS) in rainbow trout hepatocytes

Although liver is a key target for corticosteroid action, its role in immune function is largely unknown. We tested the hypothesis that stress levels of cortisol down regulate immune-relevant genes in rainbow trout (Oncorhynchus mykiss) liver. Hepatocytes were treated with lipopolysaccharide (LPS) for 24h either in the presence or absence of cortisol. LPS stimulated heat shock protein 70 expression, enhanced glycolytic capacity, and reduced glucose output. LPS stimulated mRNA abundance of cytokines and serum amyloid protein A (SAA), while suppressors of cytokine signaling (SOCS)-3 was reduced. Cortisol increased mRNA abundances of IL-1β, SOCS-1 and SOCS-2, while inhibiting either basal or LPS-stimulated IL-8, TNF α2 and SAA. These cortisol-mediated effects were rescued by Mifepristone, a glucocorticoid receptor antagonist. Altogether, cortisol modulates the molecular immune response in trout hepatocytes. The upregulation of SOCS-1 and SOCS-2 by cortisol may be playing a key role in suppressing cytokine signaling and the associated inflammatory response.

Salinity acclimation modulates copper toxicity in the sheepshead minnow, Cyprinodon variegatus

The sheepshead minnow (Cyprinodon variegatus) is able to withstand a wide range of salinities. Salinity acclimation involves physiological and biochemical changes, which may influence how organisms respond to a stressor. The present study investigated effects of salinity acclimation on subsequent Cu toxicity. In experiment 1, fish were acclimated to a hyposmotic, isosmotic, or hyperosmotic salinity for 14 d and then exposed at these salinities to 16.6 µM Cu(2+) for 12 h. Survival differed during this Cu challenge; fish acclimated to 2.5 ppt salinity were much more sensitive to Cu than those acclimated to 10.5 or 18.5 ppt seawater. In experiment 2, fish were exposed to 14.6 µM Cu(2+) for 6 h after the 14-d salinity acclimation. Whole-body Cu, whole-body Na, liver lipid peroxidation (LPO), liver catalase activity, and liver glucose levels were determined before and after Cu exposure. Prior to Cu exposure, the acclimation groups differed only for liver glucose levels, which were higher in the 2.5 ppt acclimated fish than in the others. These same 2.5 ppt acclimated fish were markedly affected by Cu, having increased whole-body Cu and liver LPO and decreased whole-body Na levels. Copper exposure had generally insignificant effects for the 10.5 ppt and the 18.5 ppt acclimated fish. This study showed that even in euryhaline fish, salinity acclimation can have a drastic effect on Cu toxicity.

Aroclor 1254 disrupts liver glycogen metabolism and enhances acute stressor-mediated glycogenolysis in rainbow trout

The objective of this study was to investigate the impact of short-term exposure to polychlorinated biphenyls on the acute stress response in rainbow trout. Fish were exposed to dietary Aroclor1254 (10mg kg(-1) body mass/day) for 3 days and then subjected to a 3-min handling disturbance and sampled over a 24h recovery after the stressor exposure. In the pre-stress fish, PCB exposure significantly elevated aryl hydrocarbon receptor (AhR) and cytochrome P4501A1 (Cyp1A1) mRNA abundance and Cyp1A protein expression confirming AhR activation. There was no significant effect of PCB on plasma cortisol and glucose levels, while plasma lactate levels were significantly elevated compared to the sham group. PCB exposure significantly elevated liver glycogen content and hexokinase activity, whereas lactate dehydrogenase activity was depressed. Short-term PCB exposure did not modify the acute stressor-induced plasma cortisol, glucose and lactate responses. Liver glycogen content dropped significantly after stressor exposure in the PCB group but not in the sham group. This was matched by a significantly higher liver LDH activity and a lower HK activity during recovery in the PCB group suggesting enhanced glycolytic capacity to fuel hepatic metabolism. Liver AhR, but not Cyp1A1, transcript levels were significantly reduced during recovery from handling stressor in the Aroclor fed fish. Collectively, this study demonstrates that short-term PCB exposure may impair the liver metabolic performance that is critical to cope with the enhanced energy demand associated with additional stressor exposure in rainbow trout.

Development, validation and field application of an RNA-based growth index in juvenile plaice Pleuronectes platessa

A general mechanism relating RNA concentration and growth rate is derived from four physiological assumptions and developed into a growth index for juvenile plaice Pleuronectes platessa. The index describing instantaneous growth rates (G, day⁻¹) in the laboratory with the lowest Akaike information criterion with small-sample bias adjustment was a function of RNA concentration (R, g(RNA)g⁻¹(wet mass)), temperature (T, ° K), body mass (M, g) and DNA concentration (D, g(DNA)g⁻¹(wet mass)): G = β₀ + β(R) R + β(T)T + β(T2)T² + β(M)M + β(D)D + β(RT)RT. RNA concentration began to respond to changes in feeding conditions within 8 days, suggesting that the index reflects growth rate in the short-term. Furthermore, the index distinguished between rapid growth and negative growth of juvenile P. platessa measured directly in laboratory and field enclosures, respectively. An application of the RNA-based growth index at two beaches on the west coast of Scotland suggested that the growth of juvenile P. platessa varies considerably in space and time and is submaximum in late summer.

Effect of correlated tRNA abundances on translation errors and evolution of codon usage bias

Despite the fact that tRNA abundances are thought to play a major role in determining translation error rates, their distribution across the genetic code and the resulting implications have received little attention. In general, studies of codon usage bias (CUB) assume that codons with higher tRNA abundance have lower missense error rates. Using a model of protein translation based on tRNA competition and intra-ribosomal kinetics, we show that this assumption can be violated when tRNA abundances are positively correlated across the genetic code. Examining the distribution of tRNA abundances across 73 bacterial genomes from 20 different genera, we find a consistent positive correlation between tRNA abundances across the genetic code. This work challenges one of the fundamental assumptions made in over 30 years of research on CUB that codons with higher tRNA abundances have lower missense error rates and that missense errors are the primary selective force responsible for CUB.

Codon usage bias (CUB) is a ubiquitous and important phenomenon. CUB is thought to be driven primarily due to selection against missense errors. For over 30 years, the standard model of translation errors has implicitly assumed that the relationship between translation errors and tRNA abundances are inversely related. This is based on an implicit and unstated assumption that the distribution of tRNA abundances across the genetic code are uncorrelated. Examining these abundance distributions across 73 bacterial genomes from 20 different genera, we find a consistent positive correlation between tRNA abundances across the genetic code. We further show that codons with higher tRNA abundances are not always “optimal” with respect to reducing the missense error rate and hence cannot explain the observed patterns of CUB.

Molecular mechanisms of metabolic regulation by insulin in Drosophila

The insulin signalling pathway is highly conserved from mammals to Drosophila. Insulin signalling in the fly, as in mammals, regulates a number of physiological functions, including carbohydrate and lipid metabolism, tissue growth and longevity. In the present review, I discuss the molecular mechanisms by which insulin signalling regulates metabolism in Drosophila, comparing and contrasting with the mammalian system. I discuss both the intracellular signalling network, as well as the communication between organs in the fly.

Specific dynamic action: a review of the postprandial metabolic response

For more than 200 years, the metabolic response that accompanies meal digestion has been characterized, theorized, and experimentally studied. Historically labeled "specific dynamic action" or "SDA", this physiological phenomenon represents the energy expended on all activities of the body incidental to the ingestion, digestion, absorption, and assimilation of a meal. Specific dynamic action or a component of postprandial metabolism has been quantified for more than 250 invertebrate and vertebrate species. Characteristic among all of these species is a rapid postprandial increase in metabolic rate that upon peaking returns more slowly to prefeeding levels. The average maximum increase in metabolic rate stemming from digestion ranges from a modest 25% for humans to 136% for fishes, and to an impressive 687% for snakes. The type, size, composition, and temperature of the meal, as well as body size, body composition, and several environmental factors (e.g., ambient temperature and gas concentration) can each significantly impact the magnitude and duration of the SDA response. Meals that are large, intact or possess a tough exoskeleton require more digestive effort and thus generate a larger SDA than small, fragmented, or soft-bodied meals. Differences in the individual effort of preabsorptive (e.g., swallowing, gastric breakdown, and intestinal transport) and postabsorptive (e.g., catabolism and synthesis) events underlie much of the variation in SDA. Specific dynamic action is an integral part of an organism's energy budget, exemplified by accounting for 19-43% of the daily energy expenditure of free-ranging snakes. There are innumerable opportunities for research in SDA including coverage of unexplored taxa, investigating the underlying sources, determinants, and the central control of postprandial metabolism, and examining the integration of SDA across other physiological systems.

Tissue-specific suppression of estrogen, androgen and glucocorticoid receptor gene expression in feral vitellogenic male Mozambique tilapia

While vitellogenesis in male fish is commonly used as a biomarker of xenoestrogen exposure, very little is known about the impacts associated with this unusual protein synthesis in feral populations. To this end, a recent study showed elevated circulating vitellogenin (VTG) levels in male Mozambique tilapia (Oreochromis mossambicus) collected from the Aja but not Tengan Rivers in Okinawa, Japan. Here we investigated whether this unusual protein synthesis in male fish from the Aja River affect transcript abundance of estrogen (ER), androgen (AR) and glucocorticoid (GR) receptors in the liver, brain and testis. The detection of plasma VTG levels ( approximately 100 microg ml(-1)) in male tilapia confirmed xenoestrogenic exposure in the Aja, but not the Tengan River. This protein induction was not associated with any changes in the reproductive capacity as assessed by sperm mobility and testis histology in the Aja fish. Plasma levels of estradiol-17beta, 11-ketotestosterone and cortisol were not significantly different between fish from the two rivers. Quantitative real-time PCR revealed a significant reduction in transcript levels of ERalpha and ERbeta, GR and ARalpha but not ARbeta, in the livers of tilapia from the Aja compared with the Tengan River. There were no significant changes in any of the steroid receptor transcript levels in either the brain or testis between the two rivers. Overall, our results imply that xenoestrogen exposure and VTG synthesis may lead to disruption of liver responsiveness to sex steroids and glucocorticoid stimulation in feral male fish.

Cost of protein synthesis and energy allocation during development of antarctic sea urchin embryos and larvae

Cold environments represent a substantial volume of the biosphere. To study developmental physiology in subzero seawater temperatures typically found in the Southern Ocean, rates and costs of protein synthesis were measured in embryos and larvae of Sterechinus neumayeri, the Antarctic sea urchin. Our analysis of the "cost of living" in extreme cold for this species shows (1) that cost of protein synthesis is strikingly low during development, at 0.41 +/- 0.05 J (mg protein synthesized)(-1) (n = 16); (2) that synthesis cost is fixed and independent of synthesis rate; and (3) that a low synthesis cost permits high rates of protein turnover at -1 degrees C, at rates comparable to those of temperate species of sea urchin embryos developing at 15 degrees C. With a low synthesis cost, even at the highest synthesis rates measured (gastrulae), the proportion of total metabolism accounted for by protein synthesis in the Antarctic sea urchin was 54%-a value similar to that of temperate sea urchin embryos. In the Antarctic sea urchin, up to 87% of metabolic rate can be accounted for by the combined energy costs of protein synthesis and the sodium pump. We conclude that, in Antarctic sea urchin embryos, high rates of protein synthesis can be supported in extreme-cold environments while still maintaining low rates of respiration.

Oxygen availability regulates metabolism and gene expression in trout hepatocyte cultures

We studied the metabolic rate, cellular energetic state, hypoxia-inducible factor-1 (HIF-1) activation, and expression of enzymes involved in energy metabolism using rainbow trout (Oncorhynchus mykiss) hepatocytes over the oxygen range from 21 to 1 kPa. Oxygen dependence of these factors was assessed by gradually reducing oxygen supply to cells from 21 kPa to 10, 5, 2, and 1 kPa. Moreover, time course experiments for up to 20 h at oxygen tensions of 1 and 2 kPa were carried out. Reduction of oxygen from 21 kPa to 10, 5, 2, and 1 kPa decreased metabolic rate of the cells by 14, 24, 37, and 46%, respectively. This response was instantaneous and fully reversible upon reoxygenation. Cellular ATP content and the expression of all mRNAs studied decreased when oxygen was reduced from 21 to 5 and 2 kPa. The lowest ATP levels, approximately 43% of the initial value, were measured at 5 kPa of oxygen, whereas the reduction in mRNA amounts was most pronounced at 2 kPa. At 1 kPa oxygen tension, both ATP content and mRNA amounts returned to normoxic (21 kPa) levels with a concomitant activation of HIF-1, indicating reorganization of energy metabolism in adaptation of cells to low oxygen supply. These results show that oxygen has a direct regulatory effect on metabolism of trout hepatocyte cultures, supporting the view that oxygen has a profound role in metabolic regulation in cells.

Fixed metabolic costs for highly variable rates of protein synthesis in sea urchin embryos and larvae

Defining the physiological mechanisms that set metabolic rates and the`cost of living' is important for understanding the energy costs of development. Embryos and larvae of the sea urchin Lytechinus pictus(Verrill) were used to test hypotheses regarding differential costs of protein synthesis in animals differing in size, rates of protein synthesis, and physiological feeding states. For embryos, the rate of protein synthesis was 0.22±0.014 ng protein embryo-1 h-1 (mean ±s.e.m.) and decreased in unfed larvae to an average rate of 0.05±0.001 ng protein larva-1 h-1. Fed larvae had rates of synthesis that were up to 194 times faster than unfed larvae (9.7±0.81 ng protein larva-1 h-1). There was no significant difference, however, in the cost of protein synthesis between these larvae with very different physiological states. Furthermore, the cost of synthesis in the larval stages was also similar to costs measured for blastula and gastrula embryos of 8.4±0.99 J mg-1 protein synthesized. The cost of protein synthesis was obtained using both direct (`inhibitor') and indirect (`correlative') measurements; both methods gave essentially identical results. Protein synthesis accounted for up to 54±8% of metabolic rate in embryos. Percent of metabolism accounted for by protein synthesis in larvae was dependent on their physiological feeding state, with protein synthesis accounting for 16±4% in unfed larvae and 75±11% in fed larvae. This regulation of metabolic rate was due to differential rates of synthesis for a fixed energy cost per unit mass of protein synthesized. The cost of synthesizing a unit of protein did not change with increasing rates of protein synthesis. We conclude that the cost of protein synthesis is independent of the rate of synthesis, developmental stage, size and physiological feeding state during sea urchin development.

Host regulation and release of parasitism-specific proteins in the system Toxoneuron nigriceps–Heliothis virescens

The braconid wasp Toxoneuron nigriceps induced qualitative and quantitative changes in the protein composition of the moth Heliothis virescens host hemolymph. Total protein concentration was found to be higher in parasitized host 4 days after parasitism as compared to control hosts, mainly due to changes in a particular group of proteins. Host proteins with a molecular mass of 173 and 72 kDa were found in higher levels in the hemolymph of parasitized larvae as control hosts approached pupation, while an 80 kDa peptide was found in reduced concentration in the hemolymph of parasitized hosts. Levels of these three peptides were maintained throughout parasitoid development, while two of them (173 and 72 kDa) were cleared from the host hemolymph close to pupation. Besides the regulation of host proteins, three parasitism-specific proteins (PSPs) were released into the host hemolymph. Two of them (PSP1-MW=116 kDa, pI=6.3; PSP2-MW=114 kDa, pI=6.2) first appeared in the hemolymph of parasitized hosts soon after pupation of control host and increased in concentration as the parasitoid developed. The third PSP (PSP3-MW=56 kDa, pI=5.8) was produced towards the end of parasitoid larval development, close to parasitoid egression. Database searches based on the amino acid composition and amino terminal sequence of PSP1 and PSP2 did not produce any significant matches, while PSP3 was identified as a putative chitinase. Incubation of host derived tissues, parasitoid larvae and teratocytes in 35S conditioned media suggested PSPs were a product of teratocytes. The role of the regulation of host proteins and release of PSPs by teratocytes for the successful development of T. nigriceps are discussed.

Influence of oxygen partial pressures on protein synthesis in feeding crabs

Many water-breathing animals have a strategy that consists of maintaining low blood PO2 values in a large range of water oxygenation level (4-40 kPa). This study examines the postprandial changes in O2 consumption, arterial blood PO2, and tissue protein synthesis in the shore crab Carcinus maenas in normoxic, O2-depleted, and O2-enriched waters to study the effects of this strategy on the O2 consumption and peptide bond formation after feeding. In normoxic water (21 kPa), the arterial PO2 was 1.1 kPa before feeding and 1.2 kPa 24 h later. In water with a PO2 of 3 kPa (arterial PO2 0.6 kPa), postprandial stimulation of protein synthesis and O2 consumption were blocked. The blockade was partial at a water PO2 of 4 kPa (arterial PO2 0.8 kPa). An increase in environmental PO2 (60 kPa, arterial PO2 10 kPa) resulted in an increase in protein synthesis compared with normoxic rates. It is concluded that the arterial PO2 spontaneously set in normoxic Carcinus limits the rates of protein synthesis. The rationale for such a strategy is discussed.

Hypometabolism, antioxidant defenses and free radical metabolism in the pulmonate land snail Helix aspersa

The aim of this work was to evaluate the effect of a cycle of estivation and awakening on free radical metabolism in selected organs of the land snail Helix aspersa. Estivation for 20 days induced a 4.9- and 1.8-fold increase in selenium-dependent glutathione peroxidase activity (Se-GPX) and in total glutathione levels (GSH-eq), respectively, in hepatopancreas when compared to activity in active animals 24 h after awakening. Foot muscle Se-GPX activity was also increased 3.9-fold during estivation, whereas GSH-eq did not vary. The activities of other antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase and glutathione S-transferase) and glucose 6-phosphate dehydrogenase were unchanged in both organs. After 15 min of awakening, the glutathione disulphide (GSSG)/GSH-eq ratio increased significantly by 55% in hepatopancreas, slowly returning to the levels observed during estivation. The higher GSSG/GSH-eq ratio may be caused by increased formation of reactive oxygen species (ROS) during awakening. The levels of thiobarbituric acid reactive substances (TBARS) decreased from 49 to 30.7 nmol g(-1) wet mass in hepatopancreas after 5 min arousal and, after 30 min, TBARS rose significantly to 39.6 nmol g(-1) wet mass, gradually declining thereafter. The levels of lipid hydroperoxides in hepatopancreas and of carbonyl protein in foot muscle both decreased during awakening. The higher levels of products of free radical damage during estivation may have resulted from low levels of ROS formation associated with decreased rates of lipid hydroperoxide detoxification and oxidized protein turnover caused by metabolic depression. The regulation of the antioxidant system during hypometabolism may constitute a mechanism to minimize oxidative stress during cycles of estivation and awakening.

In vivo downregulation of protein synthesis in the snail Helix apersa during estivation

Protein synthesis is downregulated during metabolic depression in a number of systems where the metabolic depression is effected by obvious extrinsic cues. The metabolic depression of the estivating land snail Helix apersa occurs in the absence of any obvious physiological stress and has an intrinsic component independent of temperature, pH, O(2) status, or osmolality. We show that this metabolic depression is accompanied by a downregulation of protein synthesis in vivo. The rate of protein synthesis decreases in two major tissues during estivation: to 23% and 53% of the awake rate in hepatopancreas and foot muscle, respectively. We show from calculations of the theoretical contribution of protein synthesis to total O(2) consumption that the depression of protein synthesis must be a significant, obligate, in vivo component of metabolic depression in H. aspersa.

Mechanisms of metabolic defense against hypoxia in hibernating frogs

The cold submerged frog (Rana temporaria) serves as a useful model for many hibernating ectotherms that take refuge in hypoxic ponds and lakes until more favourable conditions of climate and food availability return. In all such animals, entry into a hypometabolic state effectively extends their survival time by lessening the impact of ATP demands on endogenous substrates. At the cellular level, metabolic depression may be brought about by decreasing energy-consuming processes and/or by increasing the efficiency of energy-producing pathways. Since the mitochondrion is the major contributor to the total energy production during aerobic metabolism and frog survival during winter depends on entry into a hypometabolic state, this review focuses on the respiratory properties of mitochondria that serve to increase the efficiency of energy production in hibernation. Energy conservation during overwintering also occurs through decreases in the ATP demand of the energy-consuming processes. For example, hibernating frogs decrease their ATP demands for Na(+)/K(+)-ATPase activity as part of a coordinated process of energy conservation wherein O(2)-limitation initiates a generalised suppression of ion channel densities and/or channel leak activities. The net result is that cell membrane permeabilities are reduced, thereby lowering the energetic costs of maintaining transmembrane ion gradients.

The acute phase response and innate immunity of fish

Tissue trauma or invasion by pathogens or parasites induce changes in the quantities of several macromolecules in animal body fluids. These changes comprise one aspect of the acute phase response (APR), which in toto involves metabolic changes in several organ systems. One clear indication of the response is the increase in synthesis and secretion by the liver of several plasma proteins, with simultaneous decreases in others. These acute phase proteins (APP) function in a variety of defense-related activities such as limiting the dispersal of infectious agents, repair of tissue damage, inactivation of proteases, killing of microbes and other potential pathogens, and restoration of the healthy state. Some APP are directly harmful to microbes, while others modify targets thus marking them for cell responses. Some work alone while others contribute to cascades. Proteins that are APP in mammals, and that have been identified in both teleosts and elasmobranchs include C-reactive protein, serum amyloid P, and several components of the Complement system. Others reported in teleosts include transferrin and thrombin. Of these, only CRP has been reported to increase in acute phase plasma. In trout, a precerebellin-like protein is an APP with unknown functions. A cDNA library enriched in fragments of transcripts that were more abundant in livers from fish undergoing an APR recently yielded sequences resembling 12 additional known APP, and as many others either not known to be APP, or not similar to others yet in public databases. It appears that, as in mammals, hepatocytes are the prime source of APP in fish, and that pro-inflammatory cytokines induce transcription of their genes.

Estradiol impairs hyposmoregulatory capacity in the euryhaline tilapia, Oreochromis mossambicus

Freshwater (FW)-adapted tilapia (Oreochromis mossambicus) were treated with estradiol (E(2)) for 4 days to stimulate protein synthesis and sampled at 0, 4, and 24 h after exposure to 50% seawater (SW). E(2) increased circulating vitellogenin (VTG) levels in large amounts, indicative of unusually high rates of hepatic protein synthesis. E(2) treatment prevented the recovery of plasma osmolality in 50% SW that was evident in the sham group. Plasma sodium concentration was significantly elevated with E(2) in FW, but the levels did not change in 50% SW. Gill Na(+)-K(+)-ATPase activity was significantly lower in the E(2) group compared with sham-injected tilapia in 50% SW. No significant differences were noted in plasma cortisol, thyroxine, triiodothyronine, or glucose concentration with E(2) in 50% SW. E(2) significantly lowered several key liver enzyme activities and also decreased gill lactate dehydrogenase and malate dehydrogenase activities over a 24-h period. Together, our results suggest that E(2) impairs ion regulation in tilapia, partially mediated by a decreased metabolic capacity in liver and gill. The decreased tissue metabolic capacity is likely due to E(2)-induced energy repartitioning processes that are geared toward VTG synthesis at the expense of other energy-demanding pathways.

Protein synthesis costs could account for the tissue-specific effects of sub-lethal copper on protein synthesis in rainbow trout (Oncorhynchus mykiss)

This study investigates protein synthesis, following exposure to sub-lethal Cu, in rainbow trout in vivo and in vitro. The investigation has two aims: to determine if perturbations in protein synthesis, compared with other physiological changes, are a biomarker of Cu pollution and to evaluate the most productive role of cellular models in ecotoxicology. Protein synthesis rates were measured by labelling with 3H-phenylalanine. In vivo this was applied by a single (i.p.) injection and in vitro by bathing the cells in 3H-phenylalanine labelled culture media. The effects in vivo were tissue specific. After 3 weeks' exposure to 0.7 microM Cu only skin protein synthesis was reduced. Gills and liver from the same fish were unaffected. This reduction in skin protein synthesis appears to be more sensitive than some other biomarkers reported in the literature. However, Cu concentrations greater by orders of magnitude were required to reproduce this reduction in protein synthesis in skin cell explants (200 and 400 microM). Hepatocyte protein synthesis was unaffected by 10, 20 and 40 microM Cu and a separate investigation has also shown that 25 and 75 microM Cu does not effect protein synthesis in cultured gill cells. Oxygen consumption rates were also measured in vitro by monitoring the decline in O2 partial pressure. The Cu concentrations given above resulted in a decline in O2 consumption rates in the respective cell types. By measuring protein synthesis and O2 consumption after treatment with a protein synthesis inhibitor (cycloheximide), the costs of protein synthesis were also determined. Synthesis costs in hepatocytes are close to the theoretical minimum and are only marginally affected by Cu. Gill cell synthesis costs are also minimal and are unaffected. In skin explants, the reduction in protein synthesis was accompanied by greatly increased synthesis costs. This in vitro result offers a hypothesis as to the tissue-specific effects in vivo; i.e. the energetic demand of protein synthesis may determine tissue sensitivity or susceptibility. Cell or tissue types with high protein synthesis rates are able to avoid detrimental increases in the synthesis cost when exposed to Cu. In tissues with a low protein synthesis rate any further reduction is more likely to incur a potentially damaging increase in protein synthesis costs. Thus, whilst in vitro models may have little practical use in environmental monitoring, they may be best used as a mechanistic tool in understanding susceptibility or tolerance to sub-lethal Cu.

Hierarchies of ATP-consuming processes: direct compared with indirect measurements, and comparative aspects

The original aim of the present study was to deal with two problems that had emerged from a study on hierarchies of ATP-consuming processes in cells [Buttgereit and Brand (1995) Biochem. J. 312, 163-167]. Firstly, we wanted to find out whether the results of that study had been influenced by the method used for the determination of process activity and, secondly, we wondered whether and to what extent the structure of the hierarchy established for cell suspensions under energy-limiting conditions might depend on the type of cell or on the lifestyle, ecology and phylogenetic status of the species from which the cells were derived. We confined our study to the two most prominent ATP consumers of cells: protein synthesis and the Na(+)/K(+)-ATPase, measuring their activity directly by [3H]leucine incorporation and Rb(+)-flux respectively. We found large differences in the sensitivity of protein synthesis to energy limitation between hepatocytes from an anoxia-tolerant fish species and an anoxia-sensitive fish species (goldfish and rainbow trout respectively). On the other hand, Na(+)/K(+)-ATPase activity was hardly affected by energy limitation in the hepatocytes from both fish species. We also studied the response of a human hepatoma cell line, HepG2, to energy limitation and found both protein synthesis and Na(+)/K(+)-ATPase activity to be equally sensitive to energy limitation, but more sensitive than the Na(+)/K(+)-ATPase of the two fish species. A comparison of the indirect and direct methods for measuring protein synthesis revealed the rate of oxygen consumption to be functionally related to the concentration of cycloheximide, the inhibitor used. It was found that at 15 mM cycloheximide [three orders of magnitude higher than the concentration at which the incorporation of free amino acids (FAA) into protein is inhibited] total oxygen consumption was suppressed by 71-75%, whereas the measured rate of [3H]leucine incorporation into protein suggested that the cycloheximide-sensitive fraction should have amounted to not more than approx. 10% of the total oxygen consumption. On the other hand, the amount of oxygen consumption suppressed with the high concentration of cycloheximide corresponded almost exactly to the increase in oxygen consumption of cells incubated in an FAA-enriched medium compared with cells incubated in a standard, FAA-free medium. Our major conclusions are, firstly, that high concentrations of cycloheximide disrupt cellular metabolism, bringing to a standstill all those processes that can be stimulated by incubating starved cells in an FAA-enriched medium, secondly, that the attempt to estimate the metabolic cost of protein synthesis by inhibiting oxygen consumption with cycloheximide leads to spurious results, and, thirdly, that the structure of a 'hierarchy' of ATP-consumers may reflect the lifestyle and physiology of the species studied.

Meeting energy budgets by modulation of behaviour and physiology in the eel (Anguilla anguilla L.)

Availability of energy for feeding, and the scope to accommodate the associated increase in oxygen demand (SDA: specific dynamic action) can, to a large degree, regulate the future feeding and energy availability of an animal. There is a fundamental conflict between locomotion and SDA within the physiological capacity of a mobile organism to respire sufficiently in order to simultaneously meet both requirements. This paper is a first attempt to integrate the costs of behaviour and physiology and produce a testable model of energy allocation in the eel. Total oxygen consumption (metabolic rate MO2) of the eel (Anguilla anguilla L.) was 109 micromol O2 x g(-1) x day(-1) with a cost of measured protein synthesis representing 49% of this value, and measured routine swimming (locomotor) activity representing approximately 34%. By allocating periods of reduced activity, the eel is able to develop a strategy to prudently meet the costs of feeding and temporally balance energy budgets (in terms of oxygen) by modulation of the behaviour and demands of physiology.

Protein synthesis and specific dynamic action in crustaceans: effects of temperature

Temperature influences the specific dynamic action (SDA), or rise in oxygen uptake rate after feeding, in eurythermal and stenothermal crustaceans by changing the timing and the magnitude of the response. Intra-specific studies on the eurythermal crab, Carcinus maenas, show that a reduction in acclimation temperature is associated with a decrease in SDA magnitude, resulting from an increase in SDA duration but a decrease in peak factorial scope (the factorial rise in peak SDA over prefeeding values). Inter-specific feeding studies on stenothermal polar isopods revealed marked differences in SDA response between the Antarctic species, Glyptonotus antarcticus and the Arctic species, Saduria entomon. Compared to S. entomon held at 4 and 13 degrees C, the SDA response in G. antarcticus held at 1 degrees C was characterised by a lower absolute oxygen uptake rate at peak SDA and an extended SDA duration. At peak SDA, whole animal rates of protein synthesis increased in proportion to the postprandial increase in oxygen uptake rate in the Antarctic and the Arctic species. Rates of oxygen uptake plotted against whole animal rates of protein synthesis gave similar relationships in both isopod species, indicating similar costs of protein synthesis after a meal, despite their differences in SDA response and thermal habitat.