Cloning and expressions of chop in loach (Misgurnus anguillicaudatus) and its response to hydrogen peroxide (HO) stress.

C/EBP [CCAAT/enhancer-binding protein]-homologous protein gene (chop) which plays an important role in endoplasmic reticulum stress-induced apoptosis was investigated here by RACE and qPCR in an aquaculture animal for the first time. The full-length cDNA sequence of loach (Misgurnus anguillicaudatus) chop was 2533 bp, encoding 266 amino acids. The expression level of loach chop changed during different early life stages, with the highest expression at the 8-cell stage. Among different tissues, loach chop predominantly was expressed in gill, spleen, and gonad. We performed a hydrogen peroxide (HO, a common-used disinfectant) stress trial to explore the role of loach chop, with three different concentrations (0 μM, 50 μM, and 100 μM) of HO. The 100-μM dose was lethal for half the population but the other concentrations did not result in mortality. The activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX) in loach gill, liver, and spleen decreased with extended stress time and increased HO concentration. The expression levels of gill chop in loaches from the 100-μM group were significantly higher than those from the other two treatment groups at 12 and 24 h of exposure. atf4 and bax, two proapoptotic genes, were significantly upregulated in gills of loaches from the 100-μM group compared to the other two groups 18 h and 24 h after treatment. bcl2, an antiapoptotic gene, presented an opposite trend. These results indicated a close relationship between HO stress and fish apoptosis with loach chop playing an important role in HO stress response.