National Demonstration Center for Experimental Fisheries Science Education, Genetics and Breeding Center for Blunt Snout Bream, Key Laboratory of Freshwater Aquatic Genetic Resources, Ministry of Agriculture, Shanghai Ocean University, Shanghai, 201306, China.
Zhejiang Ocean University, Zhejiang, 316022, China.
Fish Physiol Biochem. 2023 Apr;49(2):239-251. doi: 10.1007/s10695-023-01173-w. Epub 2023 Mar 2.
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 hifα genes in blunt snout bream that demonstrated different expressions under hypoxia conditions. In HEK293T cells, all six hifαs 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 hif2αb gene in blunt snout bream. Haplotype II (AA) and its homozygous diplotype II (AAAA) 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 (LOE) 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 hif2αb has the potential to be used as a molecular marker in future genetic breeding of hypoxia-tolerant strain.
团头鲂对低氧环境敏感。低氧诱导因子（HIF）是 HIF 通路中最关键的因素，严格调控鱼类的低氧应激过程。本研究在团头鲂中发现了 6 个 hifα基因，它们在低氧条件下表现出不同的表达。在 HEK293T 细胞中，通过荧光素酶报告基因检测，发现这 6 个 hifα均能激活 HRE 区域。更重要的是，我们在团头鲂 hif2αb 基因的外显子 203 和 752 处鉴定出了两个连锁不平衡 SNP 位点。在具有低氧耐受能力的团头鲂选择品系中，hif2αb 基因的外显子 203 和 752 处的 SNP 位点出现了两种连锁不平衡单倍型（AA）及其纯合二倍型（AAAA）。在相似的温度范围内，二倍型 II（AAAA）的失衡失能（LOE）氧张力阈值较低。此外，在低氧 48 h 时，其红细胞数量明显高于二倍型 I 和三倍型的红细胞数量（p<0.05）。与低氧耐受性状相关的酶，即还原型谷胱甘肽、超氧化物歧化酶和过氧化氢酶，在二倍型 II 中的表达也明显高于二倍型 I 或三倍型（p<0.05）。此外，在低氧 48 h 时，二倍型 II 肝脏中 epo 的表达明显高于二倍型 I 或三倍型（p<0.01）。综上所述，我们的研究结果发现，hif2αb 的低氧耐受相关二倍型 II 具有作为未来低氧耐受品系遗传育种的分子标记的潜力。
