Characterization of duplicated heme oxygenase-1 genes and their responses to hypoxic stress in blunt snout bream ( Megalobrama amblycephala )

The heme oxygenase (HO)-1 is a cytoprotective enzyme that can be involved in cytoprotection against hypoxia stress. In this study, we cloned duplicated HO-1a and HO-1b cDNAs in hypoxia-sensitive blunt snout bream ( Megalobrama amblycephala ). HO-1a and HO-1b encode peptides with 272 amino acids and 246 amino acids, respectively, and they share a low sequence identity of 55%. HO-1a and HO-1b mRNAs were maternally deposited in the zygote, and the mRNAs decreased to the lowest levels at 8 hpf. Both mRNAs were significantly ( p < 0.01) expressed from 12 hpf and fluctuated but maintained a high level after 16 hpf. Using in situ hybridization, HO-1a and HO-1b mRNAs were ubiquitously expressed in embryos at 12 hpf. At 24 and 36 hpf, HO-1b transcripts were detected in the mid- and hindbrain, respectively, whereas HO-1a was mainly transcribed in the eyes and endoderm at 24 hpf and in the brain at 36 hpf. In adult fish, HO-1a was abundantly expressed in the heart, liver, gill, kidney, spleen, and brain, while HO-1b mRNA was detected mainly in the kidney. After exposure to hypoxic stress, both HO-1a and HO-1b mRNAs were upregulated significantly in the gill and liver but downregulated significantly in the brain ( p < 0.01). These findings suggest that duplicated HO genes have evolved divergently and yet play overlapping biological roles in regulating the response to hypoxia in M. amblycephala .