Magnus Lucassen
Publications
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4.41Impact points
Mitochondrial function in Antarctic nototheniids with ND6 translocation.
PloS one. 01/2012; 7(2):e31860.
Fish of the suborder Notothenioidei have successfully radiated into the Southern Ocean and today comprise the dominant fish sub-order in Antarctic waters in terms of biomass and species abundance. During evolution in the cold and stable Antarctic climate, the Antarctic lineage of notothenioids devel... [more] Fish of the suborder Notothenioidei have successfully radiated into the Southern Ocean and today comprise the dominant fish sub-order in Antarctic waters in terms of biomass and species abundance. During evolution in the cold and stable Antarctic climate, the Antarctic lineage of notothenioids developed several unique physiological adaptations, which make them extremely vulnerable to the rapid warming of Antarctic waters currently observed. Only recently, a further phenomenon exclusive to notothenioid fish was reported: the translocation of the mitochondrial gene encoding the NADH Dehydrogenase subunit 6 (ND6), an indispensable part of complex I in the mitochondrial electron transport system.This study investigated the potential physiological consequences of ND6 translocation for the function and thermal sensitivity of the electron transport system in isolated liver mitochondria of the two nototheniid species Notothenia coriiceps and Notothenia rossii, with special attention to the contributions of complex I (NADH DH) and complex II (Succinate DH) to oxidative phosphorylation. Furthermore, enzymatic activities of NADH:Cytochrome c Oxidoreductase and Cytochrome C Oxidase were measured in membrane-enriched tissue extracts.During acute thermal challenge (0-15°C), capacities of mitochondrial respiration and enzymatic function in the liver could only be increased until 9°C. Mitochondrial complex I (NADH Dehydrogenase) was fully functional but displayed a higher thermal sensitivity than the other complexes of the electron transport system, which may specifically result from its unique amino acid composition, revealing a lower degree of stability in notothenioids in general. We interpret the translocation of ND6 as functionally neutral but the change in amino acid sequence as adaptive and supportive of cold stenothermy in Antarctic nototheniids. From these findings, an enhanced sensitivity to ocean warming can be deduced for Antarctic notothenioid fish.
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3.06Impact points
Thermal acclimation in Antarctic fish: transcriptomic profiling of metabolic pathways.
American journal of physiology. Regulatory, integrative and comparative physiology. 08/2011; 301(5):R1453-66.
It is widely accepted that adaptation to the extreme cold has evolved at the expense of high thermal sensitivity. However, recent studies have demonstrated significant capacities for warm acclimation in Antarctic fishes. Here, we report on hepatic metabolic reorganization and its putative molecular ... [more] It is widely accepted that adaptation to the extreme cold has evolved at the expense of high thermal sensitivity. However, recent studies have demonstrated significant capacities for warm acclimation in Antarctic fishes. Here, we report on hepatic metabolic reorganization and its putative molecular background in the Antarctic eelpout (Pachycara brachycephalum) during warm acclimation to 5°C over 6 wk. Elevated capacities of cytochrome c oxidase suggest the use of warm acclimation pathways different from those in temperate fish. The capacity of this enzyme rose by 90%, while citrate synthase (CS) activity fell by 20% from the very beginning. The capacity of lipid oxidation by hydroxyacyl-CoA dehydrogenase remained constant, whereas phosphoenolpyruvate carboxykinase as a marker for gluconeogenesis displayed 40% higher activities. These capacities in relation to CS indicate a metabolic shift from lipid to carbohydrate metabolism. The finding was supported by large rearrangements of the related transcriptome, both functional genes and potential transcription factors. A multivariate analysis (canonical correspondence analyses) of various transcripts subdivided the incubated animals in three groups, one control group and two responding on short and long timescales, respectively. A strong dichotomy in the expression of peroxisome proliferator-activated receptors-1α and -β receptors was most striking and has not previously been reported. Altogether, we identified a molecular network, which responds sensitively to warming beyond the realized ecological niche. The shift from lipid to carbohydrate stores and usage may support warm hardiness, as the latter sustain anaerobic metabolism and may prepare for hypoxemic conditions that would develop upon warming beyond the present acclimation temperature.
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3.06Impact points
Elevated seawater PCO₂ differentially affects branchial acid-base transporters over the course of development in the cephalopod Sepia officinalis.
American journal of physiology. Regulatory, integrative and comparative physiology. 02/2011; 300(5):R1100-14.
The specific transporters involved in maintenance of blood pH homeostasis in cephalopod molluscs have not been identified to date. Using in situ hybridization and immunohistochemical methods, we demonstrate that Na(+)/K(+)-ATPase (soNKA), a V-type H(+)-ATPase (soV-HA), and Na(+)/HCO(3)(-) cotranspor... [more] The specific transporters involved in maintenance of blood pH homeostasis in cephalopod molluscs have not been identified to date. Using in situ hybridization and immunohistochemical methods, we demonstrate that Na(+)/K(+)-ATPase (soNKA), a V-type H(+)-ATPase (soV-HA), and Na(+)/HCO(3)(-) cotransporter (soNBC) are colocalized in NKA-rich cells in the gills of Sepia officinalis. mRNA expression patterns of these transporters and selected metabolic genes were examined in response to moderately elevated seawater Pco(2) (0.16 and 0.35 kPa) over a time course of 6 wk in different ontogenetic stages. The applied CO(2) concentrations are relevant for ocean acidification scenarios projected for the coming decades. We determined strong expression changes in late-stage embryos and hatchlings, with one to three log2-fold reductions in soNKA, soNBCe, socCAII, and COX. In contrast, no hypercapnia-induced changes in mRNA expression were observed in juveniles during both short- and long-term exposure. However, a transiently increased ion regulatory demand was evident during the initial acclimation reaction to elevated seawater Pco(2). Gill Na(+)/K(+)-ATPase activity and protein concentration were increased by ~15% during short (2-11 days) but not long-term (42-days) exposure. Our findings support the hypothesis that the energy budget of adult cephalopods is not significantly compromised during long-term exposure to moderate environmental hypercapnia. However, the downregulation of ion regulatory and metabolic genes in late-stage embryos, taken together with a significant reduction in somatic growth, indicates that cephalopod early life stages are challenged by elevated seawater Pco(2).
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4.41Impact points
Exploring uncoupling proteins and antioxidant mechanisms under acute cold exposure in brains of fish.
PloS one. 01/2011; 6(3):e18180.
Exposure to fluctuating temperatures accelerates the mitochondrial respiration and increases the formation of mitochondrial reactive oxygen species (ROS) in ectothermic vertebrates including fish. To date, little is known on potential oxidative damage and on protective antioxidative defense mechanis... [more] Exposure to fluctuating temperatures accelerates the mitochondrial respiration and increases the formation of mitochondrial reactive oxygen species (ROS) in ectothermic vertebrates including fish. To date, little is known on potential oxidative damage and on protective antioxidative defense mechanisms in the brain of fish under cold shock. In this study, the concentration of cellular protein carbonyls in brain was significantly increased by 38% within 1 h after cold exposure (from 28 °C to 18 °C) of zebrafish (Danio rerio). In addition, the specific activity of superoxide dismutase (SOD) and the mRNA level of catalase (CAT) were increased after cold exposure by about 60% (6 h) and by 60%-90% (1 and 24 h), respectively, while the specific glutathione content as well as the ratio of glutathione disulfide to glutathione remained constant and at a very low level. In addition, cold exposure increased the protein level of hypoxia-inducible factor (HIF) by about 50% and the mRNA level of the glucose transporter zglut3 in brain by 50%-100%. To test for an involvement of uncoupling proteins (UCPs) in the cold adaptation of zebrafish, five UCP members were annotated and identified (zucp1-5). With the exception of zucp1, the mRNA levels of the other four zucps were significantly increased after cold exposure. In addition, the mRNA levels of four of the fish homologs (zppar) of the peroxisome proliferator-activated receptor (PPAR) were increased after cold exposure. These data suggest that PPARs and UCPs are involved in the alterations observed in zebrafish brain after exposure to 18°C. The observed stimulation of the PPAR-UCP axis may help to prevent oxidative damage and to maintain metabolic balance and cellular homeostasis in the brains of ectothermic zebrafish upon cold exposure.
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2.31Impact points
Localization of ion-regulatory epithelia in embryos and hatchlings of two cephalopods.
Cell and tissue research. 03/2010; 339(3):571-83.
The tissue distribution and ontogeny of Na(+)/K(+)-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immun... [more] The tissue distribution and ontogeny of Na(+)/K(+)-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immunohistochemical localization of cephalopod Na(+)/K(+)-ATPase with the polyclonal antibody alpha (H-300) raised against the human alpha1-subunit of Na(+)/K(+)-ATPase. Na(+)/K(+)-ATPase immunoreactivity was observed in several tissues (gills, pancreatic appendages, nerves), exclusively located in baso-lateral membranes lining blood sinuses. Furthermore, large single cells in the gill of adult L. vulgaris specimens closely resembled Na(+)/K(+)-ATPase-rich cells described in fish. Immunohistochemical observations indicated that the amount and distribution of Na(+)/K(+)-ATPase in late cuttlefish embryos was similar to that found in juvenile and adult stages. The ion-regulatory epithelia (e.g., gills, excretory organs) of the squid embryos and paralarvae exhibited less differentiation than adults. Na(+)/K(+)-ATPase activities for whole animals were higher in hatchlings of S. officinalis (157.0 +/- 32.4 micromol g (FM) (-1) h(-1)) than in those of L. vulgaris (31.8 +/- 3.3 micromol g (FM) (-1) h(-1)). S. officinalis gills and pancreatic appendages achieved activities of 94.8 +/- 18.5 and 421.8 +/- 102.3 micromol(ATP) g (FM) (-1) h(-1), respectively. High concentrations of Na(+)/K(+)-ATPase in late cephalopod embryos might be important in coping with the challenging abiotic conditions (low pH, high pCO(2)) that these organisms encounter inside their eggs. Our results also suggest a higher sensitivity of squid vs. cuttlefish embryos to environmental acid-base disturbances.
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1.90Impact points
Hypercapnia induced shifts in gill energy budgets of Antarctic notothenioids.
Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology. 10/2009;
Mechanisms responsive to hypercapnia (elevated CO(2) concentrations) and shaping branchial energy turnover were investigated in isolated perfused gills of two Antarctic Notothenioids (Gobionotothen gibberifrons, Notothenia coriiceps). Branchial oxygen consumption was measured under normo- versus hyp... [more] Mechanisms responsive to hypercapnia (elevated CO(2) concentrations) and shaping branchial energy turnover were investigated in isolated perfused gills of two Antarctic Notothenioids (Gobionotothen gibberifrons, Notothenia coriiceps). Branchial oxygen consumption was measured under normo- versus hypercapnic conditions (10,000 ppm CO(2)) at high extracellular pH values. The fractional costs of ion regulation, protein and RNA synthesis in the energy budgets were determined using specific inhibitors. Overall gill energy turnover was maintained under pH compensated hypercapnia in both Antarctic species as well as in a temperate zoarcid (Zoarces viviparus). However, fractional energy consumption by the examined processes rose drastically in G. gibberifrons (100-180%), and to a lesser extent in N. coriiceps gills (7-56%). In conclusion, high CO(2) concentrations under conditions of compensated acidosis induce cost increments in epithelial processes, however, at maintained overall rates of branchial energy turnover.
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3.12Impact points
Swimming performance in Atlantic Cod (Gadus morhua) following long-term (4-12 months) acclimation to elevated seawater [Formula: see text].
Aquatic toxicology (Amsterdam, Netherlands). 02/2009;
Anthropogenic CO(2) emissions lead to chronically elevated seawater CO(2) partial pressures (hypercapnia). The induced ocean acidification will very likely be a relevant factor shaping future marine environments. CO(2) exposure concomitantly challenges the animal's capacity of acid-base and ioni... [more] Anthropogenic CO(2) emissions lead to chronically elevated seawater CO(2) partial pressures (hypercapnia). The induced ocean acidification will very likely be a relevant factor shaping future marine environments. CO(2) exposure concomitantly challenges the animal's capacity of acid-base and ionic regulation as well as the ability to maintain energy metabolism and calcification. Under conditions of acute hypercapnia, numerous studies have revealed a broad range of tolerance levels displayed by various marine taxa. Thus, it is well known that, in contrast to many marine invertebrates, most teleost fish are able to fully compensate acid-base disturbances in short-term experiments (hours to several days). In order to determine whether marine fish are able to preserve aerobic scope following long-term incubation to elevated CO(2), we exposed two groups of Atlantic Cod for 4 and 12 months to 0.3 and 0.6kPa [Formula: see text] , respectively. Measurements of standard and active metabolic rates, critical swimming speeds and aerobic scope of long-term incubated cod showed no deviations from control values, indicating that locomotory performance is not compromised by the different levels of chronic hypercapnia. While the maintenance of high activity levels is supported by a 2-fold increased Na(+)/K(+)-ATPase protein expression and 2-fold elevated Na(+)/K(+)-ATPase activity in the 12 month incubated fish (0.6kPa [Formula: see text] ), no such elevation in Na(+)/K(+)-ATPase activity could be observed in the group treated with 0.3kPa [Formula: see text] . Owing to the relevance of Na(+)/K(+)-ATPase as a general indicator for ion regulatory capacity, these results point at an adjustment of enzymatic activity to cope with the CO(2) induced acid-base load at 0.6kPa [Formula: see text] while under milder hypercapnic conditions the 'standard' Na(+)/K(+)-ATPase capacity might still be sufficient to maintain acid-base status.
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3.06Impact points
Acclimation of ion regulatory capacities in gills of marine fish under environmental hypercapnia.
American journal of physiology. Regulatory, integrative and comparative physiology. 10/2008;
The preservation of ion balance and pH despite environmental fluctuations is essential for the maintenance of vital cellular functions. While several ion transporters contribute to acid-base regulation in fish, the involvement and expression of key transporters under hypercapnia remains to be establ... [more] The preservation of ion balance and pH despite environmental fluctuations is essential for the maintenance of vital cellular functions. While several ion transporters contribute to acid-base regulation in fish, the involvement and expression of key transporters under hypercapnia remains to be established. Here, two members of the HCO3(-)-transporter family (Na(+)/HCO3(-)-cotransporter: NBC1; Cl(-)/HCO3(-)-exchanger: AE1) were described for the first time in gills of marine fish. Benthic eelpout Zoarces viviparus were acclimated to 10,000 ppm CO2. Hypercapnia did not affect whole animal oxygen consumption over a period of four days. During a time series of 6 weeks NBC1 mRNA levels first decreased by about 40 % (8 to 24 h), but finally increased about threefold over control. mRNA expression of AE1 decreased transiently by 50 % at day 4, but recovered to control levels only. Reduced mRNA levels were also found for two Na(+)/H(+)-exchangers (NHE1A, NHE1B) during the first days (by 50 - 60 % at day 1/2), followed by restoration of control levels. This pattern was mirrored in a slight decrease of NHE1 protein contents and its subsequent recovery. In contrast, Na(+)/K(+)-ATPase mRNA and protein contents, as well as maximum activity rose steadily from the onset of hypercapnia, and reached up to twofold control levels at the end. These results indicate shifting acclimation patterns between short and long-term CO2 exposures. Overall, ion gradient dependent transporter mRNA levels were transiently downregulated in the beginning of the disturbance. Upregulation of NBC1 on long timescales stresses the importance of this transporter in the hypercapnia response of marine teleosts. Long-term rearrangements include Na(+)/K(+)-ATPase at higher densities and capacities indicating a shift to elevated rates of ion and acid-base regulation under environmental hypercapnia. Key words: Na+/K+-ATPase, Na+/HCO3--cotransporter (NBC1), Cl-/HCO3--anion exchanger (AE1), Na+/H+-exchanger (NHE1).
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2.72Impact points
Cold induced changes of adenosine levels in common eelpout (Zoarces viviparus): a role in modulating cytochrome c oxidase expression.
The Journal of experimental biology. 05/2008; 211(Pt 8):1262-9.
Exposure of ectothermic organisms to variations in temperatures causes a transient mismatch between energy supply and demand, which needs to be compensated for during acclimation. Adenosine accumulation from ATP breakdown indicates such an imbalance and its reversal reflects a restoration of energy ... [more] Exposure of ectothermic organisms to variations in temperatures causes a transient mismatch between energy supply and demand, which needs to be compensated for during acclimation. Adenosine accumulation from ATP breakdown indicates such an imbalance and its reversal reflects a restoration of energy status. We monitored adenosine levels in blood serum and liver of common eelpout (Zoarces viviparus) during cold exposure in vivo. Furthermore, we tested its effect on the pattern of thermal acclimation in hepatocytes isolated from cold- (4 degrees C) versus warm- (11 degrees C) exposed fish. Adenosine levels increased during cold exposure in vivo and reached a transient maximum after 24 h in serum, but remained permanently elevated in liver. Whole animal cold acclimation induced a rise of liver citrate synthase activity by 44+/-15%, but left cytochrome c oxidase activity (COX) and RNA expression of the respective genes unchanged. Cold incubation of hepatocytes from warm-acclimated fish failed to cause an increase of mitochondrial enzyme activities despite increased COX4 mRNA levels. Conversely, warm acclimation of hepatocytes from cold-acclimated fish reduced both enzyme activities and COX2 and COX4 mRNA levels by 26-37%. Adenosine treatment of both warm- and cold-acclimated hepatocytes suppressed COX activities but activated COX mRNA expression. These effects were not receptor mediated. The present findings indicate that adenosine has the potential to regulate mitochondrial functioning in vivo, albeit the pathways resulting in the contrasting effects on expression and activity need to be identified.
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2.20Impact points
Molecular characterisation and expression of Atlantic cod (Gadus morhua) myoglobin from two populations held at two different acclimation temperatures.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology. 12/2007; 148(3):681-9.
Much previous research has demonstrated the plasticity of myoglobin concentrations in both cardiac and skeletal myocytes in response to hypoxia and training. No study has yet looked at the effect of thermal acclimation on myoglobin in fish. Atlantic cod (Gadus morhua) from two different populations,... [more] Much previous research has demonstrated the plasticity of myoglobin concentrations in both cardiac and skeletal myocytes in response to hypoxia and training. No study has yet looked at the effect of thermal acclimation on myoglobin in fish. Atlantic cod (Gadus morhua) from two different populations, i.e. the North Sea and the North East Arctic, were acclimated to 10 and 4 degrees C. Both the myoglobin mRNA and myoglobin protein in cod hearts increased significantly by up to 3.7 and 2.3 fold respectively as a result of acclimation to 4 degrees C. These increments were largest in the Arctic population, which in earlier studies have been shown to possess cold compensated metabolic demands at low temperatures. These metabolic demands associated with higher mitochondrial capacities may have driven the increase in cardiac myoglobin concentrations, in order to support diffusive oxygen supply. At the same time the increase in myoglobin levels may serve further functions during cold acclimation, for example, protection of the cell against reactive oxygen species, and scavenging nitric oxide, thereby contributing to the regulation of mitochondrial volume density.
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3.04Impact points
Differential expression of duplicated LDH-A genes during temperature acclimation of weatherfish Misgurnus fossilis. Functional consequences for the enzyme.
The FEBS journal. 04/2007; 274(6):1503-13.
Temperature acclimation in poikilotherms entails metabolic rearrangements provided by variations in enzyme properties. However, in most cases the underlying molecular mechanisms that result in structural changes in the enzymes are obscure. This study reports that acclimation to low (5 degrees C) and... [more] Temperature acclimation in poikilotherms entails metabolic rearrangements provided by variations in enzyme properties. However, in most cases the underlying molecular mechanisms that result in structural changes in the enzymes are obscure. This study reports that acclimation to low (5 degrees C) and high (18 degrees C) temperatures leads to differential expression of alternative forms of the LDH-A gene in white skeletal muscle of weatherfish, Misgurnus fossilis. Two isoforms of LDH-A mRNA were isolated and characterized: a short isoform (= 1332 bp) and a long isoform ( = 1550 bp), which both have 5'-UTRs and ORFs of the same length (333 amino acid residues), but differ in the length of the 3'-UTR. In addition, these two mRNAs have 44 nucleotide point mismatches of an irregular pattern along the complete sequence, resulting in three amino acid mismatches (Gly214Val; Val304Ile and Asp312Glu) between protein products from the short and long mRNA forms, correspondingly LDH-A(alpha) and LDH-A(beta) subunits. It is expected that the beta-subunit is more aliphatic due to the properties of the mismatched amino acids and therefore sterically more restricted. According to molecular modelling of M. fossilis LDH-A, the Val304Ile mismatch is located in the subunit contact area of the tetramer, whereas the remaining two mismatches surround the contact area; this is expected to manifest in the kinetic and thermodynamic properties of the assembled tetramer. In warm-acclimated fish the relative expression between alpha and beta isoforms of the LDH-A mRNA is around 5 : 1, whereas in cold-acclimated fish expression of is reduced almost to zero. This indicates that at low temperature the pool of total tetrameric LDH-A is more homogeneous in terms of alpha/beta-subunit composition. The temperature acclimation pattern of proportional pooling of subunits with different kinetic and thermodynamic properties of the tetrameric enzyme may result in fine-tuning of the properties of skeletal LDH-A, which is in line with previously observed kinetic and thermodynamic differences between 'cold' and 'warm' LDH-A purified from weatherfish. Also, an irregular pattern of nucleotide mismatches indicates that these mRNAs are the products of two independently evolving genes, i.e. paralogues. Karyotype analysis has confirmed that the experimental population of M. fossilis is tetraploid (2n = 100), therefore gene duplication, possibly through tetraploidy, may contribute to the adaptability towards temperature variation.
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1.76Impact points
Thermal sensitivity of uncoupling protein expression in polar and temperate fish.
Comparative biochemistry and physiology. Part D, Genomics & proteomics. 09/2006; 1(3):365-74.
Uncoupling proteins (UCP), capable of increasing proton leakage across the inner mitochondrial membrane, may play a role in the temperature-dependent setting of energy turnover in animals (and their mitochondria). Therefore, the genes and expression of fish UCP were investigated in the Antarctic eel... [more] Uncoupling proteins (UCP), capable of increasing proton leakage across the inner mitochondrial membrane, may play a role in the temperature-dependent setting of energy turnover in animals (and their mitochondria). Therefore, the genes and expression of fish UCP were investigated in the Antarctic eelpout Pachycara brachycephalum and a temperate confamilial species, the common eelpout Zoarces viviparus. UCP full-length cDNA was amplified from liver and muscle using RT-PCR and rapid amplification of cDNA ends (RACE). The fish UCP mRNA consists of 1906 bp in P. brachycephalum and of 1876 bp in Z. viviparus. Both zoarcid sequences contain open reading frames of 939 bp, encoding 313 amino acids, with 98% and 99% identity, respectively. Protein sequences of zoarcid UCP are closest related to fish and mammalian UCP2. For analysis of temperature-dependent expression common eelpouts were cold-acclimated from 10 degrees C to 2 degrees C and Antarctic eelpouts were warm-acclimated from 0 degrees C to 5 degrees C. Identical cDNA probes for both species were developed to investigate fish UCP mRNA expression, and protein expression levels were detected by Western Blot in the enriched membrane fraction. During cold-acclimation in Z. viviparus, mRNA levels increased by a factor up to 2.0, protein levels increased up to 1.5, in line with mitochondrial proliferation during cold-acclimation. Despite decreased mitochondrial protein content, in Antarctic eelpout UCP levels rose upon warm acclimation by a factor up to 2.0 (mRNA) and 1.6 (protein), respectively. Besides the ongoing discussion of UCP function in vertebrates, the data are indicative of a significant role of fish UCP in thermal adaptation of fish mitochondria.
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2.72Impact points
Mitochondrial mechanisms of cold adaptation in cod (Gadus morhua L.) populations from different climatic zones.
The Journal of experimental biology. 08/2006; 209(Pt 13):2462-71.
Adjustments in mitochondrial properties and capacities are crucial in acclimatization to seasonal cold as well as in evolutionary cold adaptation of marine ectotherms. To examine whether gene expression mechanisms contribute to different settings of aerobic capacities in populations of cod (Gadus mo... [more] Adjustments in mitochondrial properties and capacities are crucial in acclimatization to seasonal cold as well as in evolutionary cold adaptation of marine ectotherms. To examine whether gene expression mechanisms contribute to different settings of aerobic capacities in populations of cod (Gadus morhua) along a latitudinal cline, maximum activities of key enzymes of mitochondrial metabolism and their respective mRNA levels were compared in white muscle and liver of cold (4 degrees C) and warm (10 degrees C) acclimated individuals from cod populations of the North Sea and the Barents Sea, respectively. In white muscle, cold acclimation caused a parallel increase in citrate synthase (CS) and in cytochrome c oxidase (COX) activities, but with a much larger effect in the cold eurythermal Arctic population. In liver, cold acclimation was accompanied by increments in CS activities, but differences between populations were minor. Overall COX activities in liver were not affected by cold acclimation, but were higher in the cold adapted population. In both populations increments in muscle CS capacities were tightly correlated with elevated mRNA levels, suggesting transcriptional control of citrate synthase levels in muscle. In liver, CS mRNA levels differed between populations but were not affected by cold acclimation, so that post-transcriptional control may contribute to elevated functional levels in this tissue. Mitochondrial-encoded COX2 mRNA levels were not limiting for functional activities in both tissues, in favour of post-transcriptional control or limitations by other transcripts of the COX complex. Altogether, the differentiation in gene expression between both populations was more strongly expressed at 4 degrees C. The comparison of functional levels and transcript levels may reflect genetic differentiation at functional sites, in line with genetic differences between the two populations previously established by non-coding genetic markers.
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2.20Impact points
Oxidative stress and HIF-1 DNA binding during stressful cold exposure and recovery in the North Sea eelpout (Zoarces viviparus).
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology. 05/2006; 143(4):494-503.
Effects of acute cold exposure (at 1 degrees C and 5 degrees C) on tissue redox state and oxidative stress parameters, as well as the onset of hypoxic signaling were investigated in the North Sea eelpout, Zoarces viviparus. Activation of the transcription factor HIF-1 (hypoxia inducible factor) was ... [more] Effects of acute cold exposure (at 1 degrees C and 5 degrees C) on tissue redox state and oxidative stress parameters, as well as the onset of hypoxic signaling were investigated in the North Sea eelpout, Zoarces viviparus. Activation of the transcription factor HIF-1 (hypoxia inducible factor) was detected in liver samples after acute cold exposure. At this temperature the cellular redox milieu was significantly reduced (below -270 mV) as compared to controls (-250 to -267 mV). Increased levels of oxidative stress parameters (TBARS and protein carbonyls) were observed mainly during recovery at control temperature (12 degrees C). This increase in oxidative stress parameters, in spite of maintained antioxidant capacity, indicates that acute cold stress and recovery mimic ischemia/reperfusion events as found in mammals. Notably the non-enzymatic antioxidant defense (e.g. glutathione) may play an important role for eelpout ROS scavenging capacity under cold stress.
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3.06Impact points
Mitochondrial proliferation in the permanent vs. temporary cold: enzyme activities and mRNA levels in Antarctic and temperate zoarcid fish.
American journal of physiology. Regulatory, integrative and comparative physiology. 01/2004; 285(6):R1410-20.
Adjustments in mitochondrial properties and capacities are crucial in acclimatization to seasonal cold and in evolutionary cold adaptation of marine ectotherms. Although long-term compensatory increments in aerobic capacity of fish tissues have frequently been described in response to cold, much les... [more] Adjustments in mitochondrial properties and capacities are crucial in acclimatization to seasonal cold and in evolutionary cold adaptation of marine ectotherms. Although long-term compensatory increments in aerobic capacity of fish tissues have frequently been described in response to cold, much less is known about transitional phases and gene expression patterns involved. We investigated the time course of adjustment to acute cold in liver of eurythermal eelpout Zoarces viviparus. Whereas citrate synthase (CS) activity rose progressively in liver, cytochrome c oxidase (COX) activity was not altered during cold acclimation. Species-specific RNA probes were used to determine mRNA levels. CS mRNA (nuclear encoded) displayed a delayed, transient increase in response to cold, such that transcript levels did not parallel the change in enzyme activity. The enzyme activities and mRNA levels in the confamilial Antarctic Pachycara brachycephalum indicate cold compensation of CS activity in this cold-adapted species. The ratio of CS and COX activities was elevated in acclimation and adaptation to cold, indicating enhanced citrate synthesis over respiratory chain capacities in cold-adapted liver mitochondria. This may support enhanced lipid synthesis typically found in cold. The ratio of enzyme activity and transcript levels differed largely between Z. viviparus populations from the Baltic and North Seas, indicating the influence of unidentified parameters other than temperature. Transcript levels may not be tightly correlated with enzyme activities during thermal adaptation and thereafter. The time course of the acclimation process indicates that regulation at the translational and posttranslational levels predominates in adjustment to moderate thermal challenges.
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Thermal sensitivity of uncoupling protein expression in polar and temperate fish
Comparative Biochemistry and Physiology Part D: Genomics and Proteomics.
Uncoupling proteins (UCP), capable of increasing proton leakage across the inner mitochondrial membrane, may play a role in the temperature-dependent setting of energy turnover in animals (and their mitochondria). Therefore, the genes and expression of fish UCP were investigated in the Antarctic eel... [more] Uncoupling proteins (UCP), capable of increasing proton leakage across the inner mitochondrial membrane, may play a role in the temperature-dependent setting of energy turnover in animals (and their mitochondria). Therefore, the genes and expression of fish UCP were investigated in the Antarctic eelpout Pachycara brachycephalum and a temperate confamilial species, the common eelpout Zoarces viviparus. UCP full-length cDNA was amplified from liver and muscle using RT–PCR and rapid amplification of cDNA ends (RACE). The fish UCP mRNA consists of 1906 bp in P. brachycephalum and of 1876 bp in Z. viviparus. Both zoarcid sequences contain open reading frames of 939 bp, encoding 313 amino acids, with 98% and 99% identity, respectively. Protein sequences of zoarcid UCP are closest related to fish and mammalian UCP2. For analysis of temperature-dependent expression common eelpouts were cold-acclimated from 10 °C to 2 °C and Antarctic eelpouts were warm-acclimated from 0 °C to 5 °C. Identical cDNA probes for both species were developed to investigate fish UCP mRNA expression, and protein expression levels were detected by Western Blot in the enriched membrane fraction. During cold-acclimation in Z. viviparus, mRNA levels increased by a factor up to 2.0, protein levels increased up to 1.5, in line with mitochondrial proliferation during cold-acclimation. Despite decreased mitochondrial protein content, in Antarctic eelpout UCP levels rose upon warm acclimation by a factor up to 2.0 (mRNA) and 1.6 (protein), respectively. Besides the ongoing discussion of UCP function in vertebrates, the data are indicative of a significant role of fish UCP in thermal adaptation of fish mitochondria.
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Microscale genetic differentiation along the vertical shore gradient in White Sea snails Littorina saxatilis (Olivi) assessed by microsatellite markers
Journal of Molluscan Studies. 69:388-391.
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Swimming performance in Atlantic Cod (Gadus morhua) following long-term (4–12 months) acclimation to elevated seawater PCO2
Aquatic Toxicology.
Anthropogenic CO2 emissions lead to chronically elevated seawater CO2 partial pressures (hypercapnia). The induced ocean acidification will very likely be a relevant factor shaping future marine environments. CO2 exposure concomitantly challenges the animal's capacity of acid-base and ionic regu... [more] Anthropogenic CO2 emissions lead to chronically elevated seawater CO2 partial pressures (hypercapnia). The induced ocean acidification will very likely be a relevant factor shaping future marine environments. CO2 exposure concomitantly challenges the animal's capacity of acid-base and ionic regulation as well as the ability to maintain energy metabolism and calcification. Under conditions of acute hypercapnia, numerous studies have revealed a broad range of tolerance levels displayed by various marine taxa. Thus, it is well known that, in contrast to many marine invertebrates, most teleost fish are able to fully compensate acid-base disturbances in short-term experiments (hours to several days).In order to determine whether marine fish are able to preserve aerobic scope following long-term incubation to elevated CO2, we exposed two groups of Atlantic Cod for 4 and 12 months to 0.3 and 0.6 kPa PCO2, respectively. Measurements of standard and active metabolic rates, critical swimming speeds and aerobic scope of long-term incubated cod showed no deviations from control values, indicating that locomotory performance is not compromised by the different levels of chronic hypercapnia. While the maintenance of high activity levels is supported by a 2-fold increased Na+/K+-ATPase protein expression and 2-fold elevated Na+/K+-ATPase activity in the 12 month incubated fish (0.6 kPa PCO2), no such elevation in Na+/K+-ATPase activity could be observed in the group treated with 0.3 kPa PCO2. Owing to the relevance of Na+/K+-ATPase as a general indicator for ion regulatory capacity, these results point at an adjustment of enzymatic activity to cope with the CO2 induced acid-base load at 0.6 kPa PCO2 while under milder hypercapnic conditions the ‘standard’ Na+/K+-ATPase capacity might still be sufficient to maintain acid-base status.
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2.19Impact points
Trade-offs in thermal adaptation: the need for a molecular to ecological integration.
Physiological and biochemical zoology : PBZ. 79(2):295-313.
Through functional analyses, integrative physiology is able to link molecular biology with ecology as well as evolutionary biology and is thereby expected to provide access to the evolution of molecular, cellular, and organismic functions; the genetic basis of adaptability; and the shaping of ecolog... [more] Through functional analyses, integrative physiology is able to link molecular biology with ecology as well as evolutionary biology and is thereby expected to provide access to the evolution of molecular, cellular, and organismic functions; the genetic basis of adaptability; and the shaping of ecological patterns. This paper compiles several exemplary studies of thermal physiology and ecology, carried out at various levels of biological organization from single genes (proteins) to ecosystems. In each of those examples, trade-offs and constraints in thermal adaptation are addressed; these trade-offs and constraints may limit species' distribution and define their level of fitness. For a more comprehensive understanding, the paper sets out to elaborate the functional and conceptual connections among these independent studies and the various organizational levels addressed. This effort illustrates the need for an overarching concept of thermal adaptation that encompasses molecular, organellar, cellular, and whole-organism information as well as the mechanistic links between fitness, ecological success, and organismal physiology. For this data, the hypothesis of oxygen- and capacity-limited thermal tolerance in animals provides such a conceptual framework and allows interpreting the mechanisms of thermal limitation of animals as relevant at the ecological level. While, ideally, evolutionary studies over multiple generations, illustrated by an example study in bacteria, are necessary to test the validity of such complex concepts and underlying hypotheses, animal physiology frequently is constrained to functional studies within one generation. Comparisons of populations in a latitudinal cline, closely related species from different climates, and ontogenetic stages from riverine clines illustrate how evolutionary information can still be gained. An understanding of temperature-dependent shifts in energy turnover, associated with adjustments in aerobic scope and performance, will result. This understanding builds on a mechanistic analysis of the width and location of thermal windows on the temperature scale and also on study of the functional properties of relevant proteins and associated gene expression mechanisms.
Following (3)
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Tomaso Patarnello
Università degli Studi di Padova -
Hans-Otto Pörtner
Alfred Wegener Institute for Polar and Marine Research
