Search

There is an accumulating body of evidence suggesting that the subzero Antarctic marine environment places physiological constraints on protein homeostasis. Levels of ubiquitin (Ub)-conjugated proteins, 20S proteasome activity and mRNA expression of many proteins involved in both the Ub tagging of damaged proteins as well as the different complexes of the 26S proteasome were measured to examine whether there is thermal compensation of the Ub-proteasome pathway in Antarctic fishes to better understand the efficiency of the protein degradation machinery in polar species. Both Antarctic (Trematomus bernacchii, Pagothenia borchgrevinki) and non-Antarctic (Notothenia angustata, Bovichtus variegatus) notothenioids were included in this study to investigate the mechanisms of cold adaptation of this pathway in polar species. Overall, there were significant differences in the levels of Ubconjugated proteins between the Antarctic notothenioids and B. variegatus, with N. angustata possessing levels very similar to those of the Antarctic fishes. Proteasome activity in the gills of Antarctic fishes demonstrated a high degree of temperature compensation such that activity levels were similar to activitiesmeasured in their temperate relatives at ecologically relevant temperatures. A similar level of thermal compensation of proteasome activity was not present in the liver of two Antarctic fishes. Higher gill proteasome activity is likely due in part to higher cellular levels of proteins involved in the Ub-proteasome pathway, as evidenced by high mRNA expression of relevant genes. Reduced activity of the Ub-proteasome pathway does not appear to be the mechanism responsible for elevated levels of denatured proteins in Antarctic fishes, at least in the gills. [ABSTRACT FROM AUTHOR]

Ocean acidification, or the increased uptake of C02 by the ocean due to elevated atmospheric C02 concentrations, may variably impact marine early life history stages, as they may be especially susceptible to changes in ocean chemistry. Investigating the regulatory mechanisms of early development in an environmental context, or ecological development, will contribute to increased understanding of potential organismal responses to such rapid, large-scale environmental changes. We examined transcript-level responses to elevated seawater C02 during gastrulation and the initiation of spiculogenesis, two crucial developmental processes in the purple sea urchin, Strongylocentrotus purpuratus. Embryos were reared at the current, accepted oceanic C02 concentration of 380 microatmospheres (&mgr;atm), and at the elevated levels of 1000 and 1350 &mgr;atm, simulating predictions for oceans and upwelling regions, respectively. The seven genes of interest comprised a subset of pathways in the primary mesenchyme cell gene regulatory network (PMC GRN) shown to be necessary for the regulation and execution of gastrulation and spiculogenesis. Of the seven genes, qPCR analysis indicated that elevated C02 concentrations only had a significant but subtle effect on two genes, one important for early embryo patterning, Wnt8, and the other an integral component in spiculogenesis and biomineralization, SM30b. Protein levels of another spicule matrix component, SM50, demonstrated significant variable responses to elevated C02. These data link the regulation of crucial early developmental processes with the environment that these embryos would be developing within, situating the study of organismal responses to ocean acidification in a developmental context. [ABSTRACT FROM AUTHOR]

Ocean acidification from the uptake of anthropogenic CO2 is expected to have deleterious consequences for many calcifying marine animals. Forecasting the vulnerability of these marine organisms to climate change is linked to an understanding of whether species possess the physiological capacity to compensate for the potentially adverse effects of ocean acidification. We carried out a microarray-based transcriptomic analysis of the physiological response of larvae of a calcifying marine invertebrate, the purple sea urchin, Strongylocentrotus purpuratus, to CO2-driven seawater acidification. In lab-based cultures, larvae were raised under conditions approximating current ocean pH conditions (pH 8.01) and at projected, more acidic pH conditions (pH7.96 and 7.88) in seawater aerated with CO2 gas. Targeting expression of ∼1000 genes involved in several biological processes, this study captured changes in gene expression patterns that characterize the transcriptomic response to CO2-driven seawater acidification of developing sea urchin larvae. In response to both elevated CO2 scenarios, larvae underwent broad scale decreases in gene expression in four major cellular processes: biomineralization, cellular stress response, metabolism and apoptosis. This study underscores that physiological processes beyond calcification are impacted greatly, suggesting that overall physiological capacity and not just a singular focus on biomineralization processes is essential for forecasting the impact of future CO2 conditions on marine organisms. Conducted on targeted and vulnerable species, genomics-based studies, such as the one highlighted here, have the potential to identify potential 'weak links' in physiological function that may ultimately determine an organism's capacity to tolerate future ocean conditions. [ABSTRACT FROM AUTHOR]

The Antarctic fishes, isolated over evolutionary history in the sub-zero waters of the Southern Ocean, are an ideal group for studying the processes of cold adaptation. One species of Antarctic notothenioid fish, Trematomus bernacchii, has lost the ability to induce heat shock proteins (Hsps) in response to exposure to acute thermal stress or to the toxic heavy metal cadmium, an important part of the cellular defense response to such stressors. To elucidate the mechanism responsible for the lack of Hsp induction, we examined several stages of the hsp gene expression pathway, including transcription factor activity, Hsp70 mRNA production and protein synthesis patterns, in hepatocytes from T. bernacchii. Hsp70 mRNA was detected, as was heat shock factor 1 (HSF1) with DNA-binding activity. However, exposure to elevated temperature and to chemical inducers of the heat shock response failed to increase Hsp70 mRNA levels, HSF1 activity or the concentration of any size class of Hsps. These results suggest that Hsps, inducible in nearly every other species, are expressed constitutively in the cold-adapted T. bernacchii. [ABSTRACT FROM AUTHOR]

The intracellular build-up of thermally damaged proteins following exposure to heat stress results in the synthesis of a family of evolutionarily conserved proteins called heat shock proteins (Hsps) that act as molecular chaperones, protecting the cell against the aggregation of denatured proteins. The transcriptional regulation of heat shock genes by heat shock factor 1 (HSF1) has been extensively studied in model systems, but little research has focused on the role HSF1 plays in Hsp gene expression in eurythermal organisms from broadly fluctuating thermal environments. The threshold temperature for Hsp induction in these organisms shifts with the recent thermal history of the individual but the mechanism by which this plasticity in Hsp induction temperature is achieved is unknown. We examined the effect of thermal acclimation on the heat-activation of HSFI in the eurythermal teleost Gillichthys mirabilis. After a 5-week acclimation period (at 13, 21 or 28°C) the temperature of HSFI activation was positively correlated with acclimation temperature. HSF1 activation peaked at 27°C in fish acclimated to 13°C, at 33°C in the 21°C group, and at 36°C in the 28°C group. Concentrations of both HSF1 and Hsp70 in the 28°C group were significantly higher than in the colder acclimated fish. Plasticity in HSF1 activation may be important to the adjustable nature of the heat shock response in eurythermal organisms and the environmental control of Hsp gene expression. [ABSTRACT FROM AUTHOR]

Examines the ability of intertidal mussels to respond to the changing thermal environment through spatio-temporal variation in heat-shock gene expression. Induction of heat-shock genes; Determination of heat-shock protein induction threshold temperatures; Quantification of the levels of activated heat-shock transcription factor one in both groups of mussels.

Studies the temperature interaction of the cytosolic molecular chaperone, Hsc70, from the eurythermal marine goby Gillichthys mirabilis. Cellular functions of molecular chaperon; Consequence of molecular proteins in a variable-temperature environment; Factors that influence the efficacy of molecular chaperons.

Investigates the occurrence of heat-shock response in the teleost fish Trematomus bernacchii in Antarctica. Use of S-labelled amino acids to indicate patterns of protein synthesis; Results of in vivo labelling experiments with isolated hepatocytes; Implications of the absence of heat-shock response in the antarctic fish.

Examines the seasonal variation in environmentally induced protein damage in natural populations of the intertidal mussel Mytilus trossulus. Comparison of protein pools state during temperature variations; Ubiquitin conjugate concentrations; Stress protein levels; Summer- and winter-collected mussels; Heat shock protein concentration; Increased energy demand.