Duplicate CgCREBL2β involved in the response of oyster upon high-temperature stress through the induction of glycolysis and haemocyte apoptosis.

The cAMP response element-binding protein-like 2 (CREBL2) is involved in the regulation of response to environmental stress. A CREBL2 homologue, CgCREBL2β, was identified in the Pacific oyster Crassostrea gigas and considered a paralog derived from CREBL2 duplication. In the present study, its evolutionary characteristics and involvement in the regulation of glucose metabolism and cell apoptosis after 6 h and 60 h of high-temperature stress were investigated. At 6 h after CgCREBL2β dsRNA injection and high-temperature stress, the mRNA expressions of CgENO1 (enolase 1) and CgPGK1L (phosphoglycerate kinase 1-like), the activities of HK (hexokinase) and PK (pyruvate kinase), and the contents of glucose and GLY (glycogen) were 0.55-fold (p < 0.01), 0.44-fold (p < 0.05), 0.60-fold (p < 0.05), 1.35-fold (p < 0.05), 1.29-fold (p < 0.05) and 0.60-fold (p < 0.05) of that in the control group, respectively. CgCREBL2β was suggested to be involved in the regulation of glucose metabolism through glycolysis at very early stage of high-temperature stress. The mRNA expressions of apoptosis-related genes CgBcl-2, CgBax and CgCaspase3 were 1.80-fold (p < 0.05), 0.53-fold (p < 0.05) and 0.62-fold (p < 0.05) of that in the control group at 6 h after high-temperature stress, respectively, and were 1.60-fold (p < 0.05), 0.57-fold (p < 0.05) and 1.00-fold (p > 0.05) of that in the control group at 60 h after high-temperature stress, respectively. The apoptosis rate in the CgCREBL2β-RNAi group was 16.70 % (p < 0.05) and 20.31 % (p > 0.05) at 6 h and 60 h after high-temperature stress, respectively, which was lower than that in the control group. It is indicated that CgCREBL2β transcript was involved in the upregulation of the mRNA expressions of pro-apoptotic genes and the downregulation of the mRNA expressions of anti-apoptotic genes, thereby promoting haemocyte apoptosis. These results collectively demonstrated that the duplicate CgCREBL2β was involved in the response to high-temperature stress through the induction of glycolysis and haemocyte apoptosis.