Proteomic Basis of Stress Responses in the Gills of the Pacific OysterCrassostrea gigas

Abstract

The Pacific oyster Crassostrea gigas is one of the dominant sessile inhabitants of the estuarine intertidal zone, which is a physically harsh environment due to the presence of a number of stressors. Oysters have adapted to highly dynamic and stressful environments, but the molecular mechanisms underlying such stress adaptation are largely unknown. In the present study, we examined the proteomic responses in the gills of C. gigas exposed to three stressors (high temperature, low salinity, and aerial exposure) they often encounter in the field. We quantitatively compared the gill proteome profiles using iTRAQ-coupled 2-D LC-MS/MS. There were 3165 identified proteins among which 2379 proteins could be quantified. Heat shock, hyposalinity, and aerial exposure resulted in 50, 15, and 33 differentially expressed gill proteins, respectively. Venn diagram analysis revealed substantial different responses to the three stressors. Only xanthine dehydrogenase/oxidase showed a similar expression pattern across the three stress treatments, suggesting that reduction of ROS accumulation may be a conserved response to these stressors. Heat shock caused significant overexpression of molecular chaperones and production of S-adenosyl-l-methionine, indicating their crucial protective roles against protein denature. In addition, heat shock also activated immune responses, Ca(2+) binding protein expression. By contrast, hyposalinity and aerial exposure resulted in the up-regulation of 3-demethylubiquinone-9 3-methyltransferase, indicating that increase in ubiquinone synthesis may contribute to withstanding both the osmotic and desiccation stress. Strikingly, the majority of desiccation-responsive proteins, including those involved in metabolism, ion transportation, immune responses, DNA duplication, and protein synthesis, were down-regulated, indicating conservation of energy as an important strategy to cope with desiccation stress. There was a high consistency between the expression levels determined by iTRAQ and Western blotting, highlighting the high reproducibility of our proteomic approach and its great value in revealing molecular mechanisms of stress responses.

Contrasting impacts of ocean acidification and warming on the molecular responses of CO2-resilient oysters

“…Higher levels of PDI have also been observed in thermally-stressed sea cucumbers [62] and in larvae from Pacific oysters ( C. gigas ) exposed to the combination of elevated temperature (+2  ° C relative to control) and elevated CO 2 (pH 7.9, 656 μatm p CO 2 ) [63]. In line with our results, stress-induced protein 1, another molecular chaperone, was also found to be up-regulated in the gills of C. gigas following acute heat stress (+ 20  ° C for 1 h) [27]. It has been extensively reported that elevated temperature triggers oxidative stress in different species of marine invertebrates [23, 24, 26].…”

“…Hence, they have been used for proteomic and transcriptomic analyses in numerous previous studies (e.g. [12, 21, 27, 29]). For proteomics, oyster gills were immediately frozen at −80 °C ( n  = 15 per treatment), while gill samples for transcriptional analysis were stored in RNA later (Ambion) at −20 °C ( n  = 21 per treatment; including same oysters used for proteomics).…”

“…Acute heat stress (+12 °C relative to ambient) also induced changes in the transcriptional levels of other genes involved in cellular homeostasis and protein synthesis (gills and mantle; 3–24 day exposure) [26]. At the protein level, increased concentrations of Hsp, as well as changes in the concentrations of proteins involved in energy metabolism, calcium binding and immune responses, were observed in the gills of C. gigas following exposure to temperature extremes (+20 °C relative to ambient; 1 h exposure) [27]. Although relevant given the broad temperature ranges oysters encounter in their natural environment, these studies have focused on acute heat stress (+12 °C to 20 °C relative to control) and so do not reflect near-future climate change scenarios where projected temperature increases span between 1.5 °C and 3.2 °C by the end of this century [1].…”

The modulation role of serotonin in Pacific oyster Crassostrea gigas in response to air exposure

“…Marine molluscs living in the intertidal zones must face the harsh and dynamically environments, which can be influenced by a variety of physical factors such as salinity, pH, dissolved oxygen and temperature [18,19]. Among all these environmental factors, air exposure is considered as one of the most deathful threats for molluscs [20].…”

“…Pacific oyster Crassostrea gigas, living in the intertidal zones, is distributed all over the world, which is one of the most important marine molluscs with the highest production [27]. The special habitat and wide distribution indicate the successful adaptation of oyster to the environment, making it an ideal experimental model for the investigation of the stress response of marine molluscs in estuarine regions [18,19].…”