Time-space trade-offs in population protocols for the majority problem.

Population protocols are a model for distributed computing that is focused on simplicity and robustness. A system of n identical agents (finite state machines) performs a global task like electing a unique leader or determining the majority opinion when each agent has one of two opinions. Agents communicate in pairwise interactions with randomly assigned communication partners. Quality is measured in two ways: the number of interactions to complete the task and the number of states per agent. We present protocols for the majority problem that allow for a trade-off between these two measures. Compared to the only other trade-off result (Alistarh et al. in Proceedings of the 2015 ACM symposium on principles of distributed computing, Donostia-San Sebastián, 2015), we improve the number of interactions by almost a linear factor. Furthermore, our protocols can be made uniform (working correctly without any information on the population size n), yielding the first uniform majority protocols that stabilize in a subquadratic number of interactions.

Effects of increased CO2 on fish gill and plasma proteome.

Ocean acidification and warming are both primarily caused by increased levels of atmospheric CO2, and marine organisms are exposed to these two stressors simultaneously. Although the effects of temperature on fish have been investigated over the last century, the long-term effects of moderate CO2 exposure and the combination of both stressors are almost entirely unknown. A proteomics approach was used to assess the adverse physiological and biochemical changes that may occur from the exposure to these two environmental stressors. We analysed gills and blood plasma of Atlantic halibut (Hippoglossus hippoglossus) exposed to temperatures of 12 °C (control) and 18 °C (impaired growth) in combination with control (400 µatm) or high-CO2 water (1000 µatm) for 14 weeks. The proteomic analysis was performed using two-dimensional gel electrophoresis (2DE) followed by Nanoflow LC-MS/MS using a LTQ-Orbitrap. The high-CO2 treatment induced the up-regulation of immune system-related proteins, as indicated by the up-regulation of the plasma proteins complement component C3 and fibrinogen ß chain precursor in both temperature treatments. Changes in gill proteome in the high-CO2 (18 °C) group were mostly related to increased energy metabolism proteins (ATP synthase, malate dehydrogenase, malate dehydrogenase thermostable, and fructose-1,6-bisphosphate aldolase), possibly coupled to a higher energy demand. Gills from fish exposed to high-CO2 at both temperature treatments showed changes in proteins associated with increased cellular turnover and apoptosis signalling (annexin 5, eukaryotic translation elongation factor 1γ, receptor for protein kinase C, and putative ribosomal protein S27). This study indicates that moderate CO2-driven acidification, alone and combined with high temperature, can elicit biochemical changes that may affect fish health.

Differential regulation of the rainbow trout (Oncorhynchus mykiss) MT-A gene by nuclear factor interleukin-6 and activator protein-1.

BACKGROUND: Previously we have identified a distal region of the rainbow trout (Oncorhynchus mykiss) metallothionein-A (rtMT-A) enhancer region, being essential for free radical activation of the rtMT-A gene. The distal promoter region included four activator protein 1 (AP1) cis-acting elements and a single nuclear factor interleukin-6 (NF-IL6) element. In the present study we used the rainbow trout hepatoma (RTH-149) cell line to further examine the involvement of NF-IL6 and AP1 in rtMT-A gene expression following exposure to oxidative stress and tumour promotion. RESULTS: Using enhancer deletion studies we observed strong paraquat (PQ)-induced rtMT-A activation via NF-IL6 while the AP1 cis-elements showed a weak but significant activation. In contrast to mammals the metal responsive elements were not activated by oxidative stress. Electrophoretic mobility shift assay (EMSA) mutation analysis revealed that the two most proximal AP1 elements, AP11,2, exhibited strong binding to the AP1 consensus sequence, while the more distal AP1 elements, AP13,4 were ineffective. Phorbol-12-myristate-13-acetate (PMA), a known tumor promoter, resulted in a robust induction of rtMT-A via the AP1 elements alone. To determine the conservation of regulatory functions we transfected human Hep G2 cells with the rtMT-A enhancer constructs and were able to demonstrate that the cis-elements were functionally conserved. The importance of NF-IL6 in regulation of teleost MT is supported by the conservation of these elements in MT genes from different teleosts. In addition, PMA and PQ injection of rainbow trout resulted in increased hepatic rtMT-A mRNA levels. CONCLUSIONS: These studies suggest that AP1 primarily is involved in PMA regulation of the rtMT-A gene while NF-IL6 is involved in free radical regulation. Taken together this study demonstrates the functionality of the NF-IL6 and AP-1 elements and suggests an involvement of MT in protection during pathological processes such as inflammation and cancer.

The impact of temperature on the metabolome and endocrine metabolic signals in Atlantic salmon (Salmo salar).

The aim was to elucidate the effects of elevated temperature on growth performance, growth- and appetite-regulating hormones and metabolism in Atlantic salmon, Salmo salar. Post-smolts in seawater (average mass 175g) that had been reared at 12°C were kept at three temperatures (8, 12 and 18°C) and sampled after one and three months. After three months, the fish kept in 18°C had decreased growth rate and condition factor, and elevated plasma levels of growth hormone (GH) and leptin, compared with fish kept at the lower temperatures. Food conversion efficiency was also decreased at 18°C, while at the same time protein uptake was improved and thus was not a limiting mechanism for growth. Redistribution of energy stores in fish at the highest temperature is evident as a preference of maintaining length growth during times of limited energy availability. NMR-based metabolomics analyses of plasma revealed that several metabolites involved in energy metabolism were negatively affected by temperature in the upper temperature range of Atlantic salmon. Specifically, the high temperature induced a decline of several amino acids (glutamine, tyrosine and phenylalanine) and a shift in lipid metabolism. It appears likely that the decreased food intake at the highest temperature is linked to an anorexigenic function of leptin, but also that the decreased food intake, feed conversion efficiency and condition factor can be linked to changes in GH endocrinology.

Seasonal appetite regulation in the anadromous Arctic charr: evidence for a role of adiposity in the regulation of appetite but not for leptin in signalling adiposity.

The aim of this study was to investigate whether the seasonal feeding cycle of the anadromous Arctic charr (Salvelinus alpinus) is regulated by a lipostatic mechanism and if leptin (Lep) might act as an endocrine signal of adiposity. Offspring of anadromous Arctic charr with a body mass of 121 g were divided into two treatment groups; one was given feed in excess from March to November, and the other was fasted between April and early June and fed in excess thereafter. In the continuously fed group there was an 8-fold increase in body mass, and a doubling of percentage body fat, from March to August, after which there was no further increase. Fish in the other group lost weight and body fat during fasting, but grew rapidly on being fed, and had partially compensated for their deficit in body mass by August. Differences in percentage body fat between treatment groups were eliminated by August, providing evidence for a lipostatic regulation of feeding and energy homeostasis in Arctic charr. Neither liver total LepA gene expression nor plasma Lep concentrations correlated positively with fish adiposity, so there was no evidence that Lep acts as a signal of adiposity in this species. On the other hand, there was a strong increase in liver LepA1 gene expression at the end of the fasting period, concomitant with fat mobilization and increased plasma glucose, indicating that LepA1 may play a role in regulating metabolic processes associated with fasting.

Plasma leptin and growth hormone levels in the fine flounder (Paralichthys adspersus) increase gradually during fasting and decline rapidly after refeeding.

In fish, recent studies have indicated an anorexigenic role of leptin and thus its possible involvement in regulation of energy balance and growth. In the present study, the effects of fasting and refeeding periods on plasma leptin levels were studied in the fine flounder, a flatfish with remarkably slow growth. To further assess the endocrine status of the fish during periods of catabolism and anabolism, plasma growth hormone (GH) levels were also analyzed. Under normal feeding condition, plasma leptin and GH levels remained stable and relatively high in comparison with other teleost species. For the three separate groups of fish, fasted for 2, 3, and 4 weeks, respectively, plasma leptin levels increase gradually, becoming significantly elevated after 3 weeks, and reaching highest levels after 4-week fasting. Plasma GH levels were significantly elevated after 2-week fasting. At the onset of refeeding, following a single meal, leptin levels decline rapidly to lower than initial levels within 2 h, irrespective of the length of fasting. Plasma GH also decline, the decrease being significant after 4, 24 and 2 h for the 2, 3 and 4-week fasted groups, respectively. This study shows that plasma leptin levels in the fine flounder are strongly linked to nutritional status and suggests that leptin secretion is regulated by fast-acting mechanisms. Elevated leptin levels in fasted fish may contribute to a passive survival strategy of species which experience natural food shortage periods by lowering appetite and limiting physical foraging activity.

The role of growth hormone in growth, lipid homeostasis, energy utilization and partitioning in rainbow trout: interactions with leptin, ghrelin and insulin-like growth factor I.

The growth-promoting effects of in vivo growth hormone (GH) treatment were studied in relation to size and lipid content of energy stores including liver, mesentery, white muscle and belly flap in rainbow trout. In order to elucidate endocrine interactions and links to regulation of growth, adiposity and energy metabolism, plasma levels of GH, insulin-like growth factor I (IGF-I), leptin (Lep) and ghrelin, were assessed and correlated to growth and energy status. In addition tissue-specific expression of lepa1 mRNA was examined. Juvenile rainbow trout were implanted with sustained-release bovine GH implants and terminally sub-sampled at 1, 3 and 6 weeks. GH increased specific growth rate, reduced condition factor (CF) and increased feed conversion efficiency resulting in a redistribution of energy stores. Thus, GH decreased mesenteric (MSI) and liver somatic index (LSI). Lipid content of the belly flap increased following GH-treatment while liver and muscle lipid content decreased. Independent of GH substantial growth was accompanied by an increase in muscle lipids and a decrease in belly flap lipids. The data suggest that the belly flap may function as an energy buffering tissue during episodes of feeding and lean growth. Liver and muscle lipids were positively correlated to body weight, indicating a size-dependent change in adiposity. Hepatic lepa1 mRNA positively correlated to MSI and CF and its expression decreased following GH treatment, coinciding with decreased hepatic lipid content. Plasma Lep was positively correlated to MSI and belly flap lipid content, suggesting that Lep may communicate energy status. In summary, the observed GH tissue-specific effects on lipid metabolism in rainbow trout highlight the complex physiology of the energy reserves and their endocrine control.

Effects of long-term restricted feeding on plasma leptin, hepatic leptin expression and leptin receptor expression in juvenile Atlantic salmon (Salmo salar L.).

Leptin is a pleiotropic hormone and plays a key role in body weight regulation, energy homeostasis and lipid store utilization in mammals. In this study, we investigated the effect of feed-restriction on leptin genes (lepa1 and lepa2), leptin receptor (lepr) gene expression and plasma leptin levels in juvenile Atlantic salmon parr. Feed restriction was performed from late April to mid-June, in order to gain insight into the role of the leptin system in energy balance regulation and adiposity in juvenile salmon. A significant increase in lepa1 expression as well as higher levels of plasma leptin was found in feed-restricted fish in June compared to fully fed controls, while lepa2 gene expression decreased in both groups during the treatment period. Lepa2 was, however significantly higher in the feed-restricted group in June. Leptin receptor expression was up regulated during the period of enhanced growth and lipid deposition in the fully fed control, indicating a seasonal effect on the receptor expression in the brain. Both lepa1 and lepa2 genes very mainly expressed in the liver in juvenile salmon, while lepr was expressed in the brain but showed also considerable expression in various peripheral tissues. The study provides evidence that the leptin system is sensitive to the metabolic status of the fish as both season and restricted feeding affect lepa1 and lepa2 gene expression in the liver and brain leptin receptor expression, however, for lepa1 expression and leptin plasma level in an opposite way as that observed in the mammalian system.

Physiology and mRNA expression in rainbow trout (Oncorhynchus mykiss) after long-term exposure to the new antifoulant medetomidine.

Medetomidine is under evaluation for use as an antifouling agent, and its effects on non-target aquatic organisms are therefore of interest. In this study, rainbow trout was exposed to low (0.5 and 5.0nM) concentrations of medetomidine for up to 54 days. Recently we have reported on effects on paleness and melanophore aggregation of medetomidine in these fish. Here, specific growth rates were investigated together with a broad set of physiological parameters including plasma levels of growth hormone (GH), insulin-like growth factor-I (IGF-I) and leptin, glucose and haemoglobin (Hb), hematocrit (Ht), condition factor, liver and heart somatic indexes (LSI, HSI). Hepatic enzyme activities of CYP1A (EROD activity), glutathione S-transferases (GST) and glutathione reductase (GR) were also measured. Additionally, hepatic mRNA expression was analysed through microarray and quantitative PCR in fish sampled after 31 days of exposure. Medetomidine at both concentrations significantly lowered blood glucose levels and the higher concentration significantly reduced the LSI. The mRNA expression analysis revealed few differentially expressed genes in the liver and the false discovery rate was high. Taken together, the results suggest that medetomidine at investigated concentrations could interfere with carbohydrate metabolism of exposed fish but without any clear consequences for growth.

Interactions of pharmaceuticals and other xenobiotics on hepatic pregnane X receptor and cytochrome P450 3A signaling pathway in rainbow trout (Oncorhynchus mykiss).

The pregnane X receptor (PXR) belongs to the nuclear hormone receptor (NR) superfamily and is commonly described as a xenophore or a pharmacophore, as it can be activated by a wide array of xenobiotics, including numerous pharmaceuticals and other environmental pollutants. The PXR regulates expression of e.g. cytochrome P450 3A (CYP3A) and the P-glycoprotein (P-gp) that are involved in excretion of lipophilic xenobiotics and endobiotics. A full length PXR cDNA was isolated from rainbow trout liver and it was expressed in a descending order of magnitude in liver>intestine>kidney>heart. A rainbow trout PXR reporter assay was developed and a suite of pharmaceuticals and other xenobiotics were screened. However, no specific activation of rainbow trout PXR was observed with the substances tested. Interactions of prototypical PXR agonists on PXR signaling in rainbow trout were further investigated in cells of hepatic origin exposed in vitro and in juvenile rainbow trout exposed in vivo. The rainbow trout hepatoma cell line (RTH-149), displayed 600 times lower expression of CYP3A mRNA compared to primary cultures of hepatocytes, and did not respond to treatment with either pregnenolone 16α-carbonitrile (PCN), ketoconazole (KCZ) or rifampicin (RIF), which implies a non-functional PXR in this cell line. Exposure of hepatocytes to PCN and lithocholic acid (LA), resulted in a weak concentration-dependent induction of CYP3A and P-gp mRNA levels, though, exposure to the higher concentration of LA (50 µM) decreased PXR mRNA levels. Exposure to dexamethasone (DEX) resulted in a decrease in PXR mRNA, without affecting CYP3A mRNA levels in hepatocytes in vitro. Injections of rainbow trout in vivo with 1 mg LA/kg fish resulted in a slight (albeit not significant) increase in CYP3A mRNA levels without affecting PXR mRNA levels. Although, injection with 10mg omeprazole (OME)/kg fish had no effect on PXR and CYP3A mRNA levels, a 60% inhibition of CYP3A enzyme activities was evident. An in vitro screening of the chemicals used showed that OME and RIF acted as weak CYP3A inhibitors whereas LA and DEX did not affect the CYP3A activity. In contrast, PCN acted as an activator of the CYP3A enzyme activity in vitro. Taken together, these data show that some prototypical PXR agonists weakly affect PXR activation in rainbow trout. Besides, some of these agonists have a stronger effect on the CYP3A catalyst. This study demonstrates the importance of investigation effects of pharmaceuticals on the PXR signaling pathway in non-target animals such as fish.

Leptin and leptin receptor genes in Atlantic salmon: Cloning, phylogeny, tissue distribution and expression correlated to long-term feeding status.

The present study reports the complete coding sequences for two paralogues for leptin (sLepA1 and sLepA2) and leptin receptor (sLepR) in Atlantic salmon. The deduced 171-amino acid (aa) sequence of sLepA1 and 175 aa sequence for sLepA2 shows 71.6% identity to each other and clusters phylogenetically with teleost Lep type A, with 22.4% and 24.1% identity to human Lep. Both sLep proteins are predicted to consist of four helixes showing strong conservation of tertiary structure with other vertebrates. The highest mRNA levels for sLepA1 in fed fish (satiation ration=100%) were observed in the brain, white muscle, liver, and ovaries. In most tissues sLepA2 generally had a lower expression than sLepA1 except for the gastrointestinal tract (stomach and mid-gut) and kidney. Only one leptin receptor ortholog was identified and it shares 24.2% aa sequence similarity with human LepR, with stretches of highest sequence similarity corresponding to domains considered important for LepR signaling. The sLepR was abundantly expressed in the ovary, and was also high in the brain, pituitary, eye, gill, skin, visceral adipose tissue, belly flap, red muscle, kidney, and testis. Fish reared on a rationed feeding regime (60% of satiation) for 10 months grew less than control (100%) and tended to have a lower sLepA1 mRNA expression in the fat-depositing tissues visceral adipose tissue (p<0.05) and white muscle (n.s.). sLepA2 mRNA levels was very low in these tissues and feeding regime tended to affect its expression in an opposite manner. Expression in liver differed from that of the other tissues with a higher sLepA2 mRNA in the feed-rationed group (p<0.01). Plasma levels of sLep did not differ between fish fed restricted and full feeding regimes. No difference in brain sLepR mRNA levels was observed between fish fed reduced and full feeding regimes. This study in part supports that sLepA1 is involved in signaling the energy status in fat-depositing tissues in line with the mammalian model, whereas sLepA2 may possibly play important roles in the digestive tract and liver. At present, data on Lep in teleosts are too scarce to allow generalization about how the Lep system is influenced by tissue-specific energy status and, in turn, may regulate functions related to feed intake, growth, and adiposity in fish. In tetraploid species like Atlantic salmon, different Lep paralogues seems to serve different physiological roles.

Proteomic studies in zebrafish liver cells exposed to the brominated flame retardants HBCD and TBBPA.

Proteomic effect screening in zebrafish liver cells was performed to generate hypotheses regarding single and mixed exposure to the BFRs HBCD and TBBPA. Responses at sublethal exposure were analysed by two-dimensional gel electrophoresis followed by MALDI-TOF and FT-ICR protein identification. Mixing of HBCD and TBBPA at sublethal doses of individual substances seemed to increase toxicity. Proteomic analyses revealed distinct exposure-specific and overlapping responses suggesting novel mechanisms with regard to HBCD and TBBPA exposure. While distinct HBCD responses were related to decreased protein metabolism, TBBPA revealed effects related to protein folding and NADPH production. Overlapping responses suggest increased gluconeogenesis (GAPDH and aldolase) while distinct mixture effects suggest a pronounced NADPH production and changes in proteins related to cell cycle control (prohibitin and crk-like oncogene). We conclude that mixtures containing HBCD and TBBPA may result in unexpected effects highlighting proteomics as a sensitive tool for detecting and hypothesis generation of mixture effects.

A homologous salmonid leptin radioimmunoassay indicates elevated plasma leptin levels during fasting of rainbow trout.

The present study was conducted to establish a homologous radioimmunoassay (RIA) for quantifying plasma leptin (Lep) levels in salmonid species, and to study Lep levels in relation to nutritional status. A part of the Lep peptide, a 14 amino acid long sequence, identical between a Salmo and an Oncorhynchus species was synthesised. Polyclonal antibodies were raised in rabbit against this antigen and both were subsequently used in the development of a RIA protocol for assessing plasma Lep levels. The limit of detection of the assay was 0.3 nM, and intra- and interassay coefficient of variation (CV) were 8.4% and 13%, respectively. Apart from Atlantic salmon and rainbow trout, the assay exhibits measuring parallelism for a range of fish species, including arctic char, Atlantic cod and turbot, suggesting that the established RIA is useful for quantifying Lep levels in several fish species. The RIA indicates that Lep is found in salmonid plasma at levels of 0.5-5 nM, which is comparable with other peptide hormones, and well within the measuring range of the RIA. A study of fed and fasted rainbow trout showed elevated plasma Lep levels during fasting. In addition there was no correlation between Lep levels and condition factor. These data suggest that the relation between circulating Lep levels and energy status differs from that in mammals. While Lep is linked to energy balance, it may not act as an adiposity signal in salmonids, possibly pointing to functional divergence among ectothermic and endothermic vertebrates.

Activation of the rainbow trout metallothionein-A promoter by silver and zinc.

In fish, the synthesis of metallothionein (MT) is increased by a number of heavy metals. The rainbow trout MT-A gene promoter region contains six known metal responsive elements (MREs), that mediate promoter activation by metals. In the present study, two fish cell lines differing in their ability to produce MT, RTG-2 (produce MT protein) and CHSE-214 (produce no detectable MT protein), were used to help elucidate the roles of Zn, Ag and MT in the activation of the MT promoter. The hypothesis tested was that Ag activates the MT-A promoter indirectly by displacing Zn from pre-existing Zn-MT and that this liberated Zn subsequently induces MT synthesis. Both cell lines were transfected with a luciferase reporter gene construct containing the rainbow trout MT-A promoter, exposed to various concentrations of Zn or Ag, and assayed for luciferase activity. CHSE-214 cells showed five times greater production of luciferase than RTG-2 cells when exposed to identical concentrations of Ag. Thus, Ag can likely induce MT transcription without displacing Zn from pre-existing Zn-MT. Furthermore, Ag activated the MT promoter at concentrations 100-fold lower than those required for Zn to initiate transcription, suggesting that zinc displaced from other sites by such low concentrations of Ag would not be sufficient to initiate MT transcription. This interpretation was further supported by radiotracer studies indicating that Ag did not cause a redistribution of 65Zn within either of the two cell types. These combined results indicate that Ag may be a direct inducer of MT.