Functional exploration of SNP mutations in HIF2ab gene correlated with hypoxia tolerance in blunt snout bream (Megalobrama amblycephala)

Blunt snout bream (Megalobrama amblycephala) is sensitive to hypoxia environment. Hypoxia-inducible factor (HIF) is the most critical factor in the HIF pathway, which strictly regulates the hypoxia stress process of fish. In this study, we found six hif alpha genes in blunt snout bream that demonstrated different expressions under hypoxia conditions. In HEK293T cells, all six hif alpha s were detected to activate the HRE region by luciferase reporter assay. More importantly, we identified two linkage-disequilibrium SNP sites at exon 203 and 752 of the hif2 alpha b gene in blunt snout bream. Haplotype II (A(203)A(752)) and its homozygous diplotype II (A(203)A(203)A(752)A(752)) appeared frequently in a selected strain of blunt snout bream with hypoxia tolerance. Diplotype II has a lower oxygen tension threshold for loss of equilibrium (LOEcrit) over a similar range of temperatures. Moreover, its erythrocyte number increased significantly (p < 0.05) than those in diplotype I and diplotype III strains at 48 h of hypoxia. The enzymes related with hypoxia tolerant traits, i.e., reduced glutathione, superoxide dismutase, and catalase, were also significantly (p < 0.05) induced in diplotype II than in diplotype I or III. In addition, the expression of epo in the liver of diplotype II was significantly (p < 0.01) higher than that in the diplotype I or III strains at 48 h of hypoxia. Taken together, our results found that the hypoxia-tolerant-related diplotype II of hif2 alpha b has the potential to be used as a molecular marker in future genetic breeding of hypoxia-tolerant strain.

Automated summary

This study identified six hif alpha genes in blunt snout bream, with different expressions under hypoxia conditions. Two SNP sites in hif2 alpha b gene were associated with hypoxia tolerance in a selected strain of blunt snout bream. Diplotype II of hif2 alpha b gene showed better hypoxia tolerance, increased erythrocyte count, enhanced enzyme expression, and higher expression of epo gene.