Marine Science Institute, The University of Texas at Austin, Port Aransas, TX, USA.
Department of Zoology, The University of British Columbia, British Columbia, Canada.
Sci Rep. 2017 Aug 10;7(1):7834. doi: 10.1038/s41598-017-07696-6.
Hemoglobin (Hb) multiplicity is common in fish, yet despite its ubiquitous nature, the functional significance is unclear. Here we explore the hypothesis that Hb multiplicity plays a role in hypoxia tolerance using the red drum (Sciaenops ocellatus). Red drum is an economically and ecologically important species native to coastal regions and estuaries of the Gulf of Mexico - habitats that routinely experience pronounced hypoxic events. Using a transcriptomic approach, we demonstrate that red drum red blood cells express 7 and 5 Hbα and Hbβ isoforms, respectively. Phylogenetic analysis grouped these isoforms into distinct isoHb clades, and provided evidence of lineage specific expression of particular isoHbs. In normoxia, three isoHbs predominated (Hbα-3.1, -3.2, and Hbβ-3.1). A three-week hypoxia acclimation (48 mmHg) resulted in significant up-regulation of Hbα-2, Hbα-3.2, and Hbβ-3.1, effectively switching the predominantly expressed isoforms. Changes in subunit expression were correlated with a decrease in non-stripped hemolysate P. Similarly, hypoxia acclimation resulted in a 20% reduction in whole animal critical oxygen threshold (P). Hypoxia acclimation was not associated with changes in gill morphology, hematocrit, or relative ventricular mass. Overall, these data provide support for the hypothesis that Hb isoform switching can provide a physiological benefit to counteract environmental stress in fishes.
血红蛋白（Hb）多样性在鱼类中很常见，但尽管其普遍存在，但其功能意义尚不清楚。在这里，我们使用红鼓鱼（Sciaenops ocellatus）来验证血红蛋白多样性在耐低氧能力中发挥作用的假说。红鼓鱼是一种经济和生态上都很重要的物种，原产于墨西哥湾沿海地区和河口——这些栖息地经常会发生明显的低氧事件。通过转录组学方法，我们证明红鼓鱼的红细胞分别表达 7 种和 5 种 Hbα和 Hbβ同工型。系统发育分析将这些同工型分为不同的同工 Hb 分支，并提供了特定同工 Hb 在线系特异性表达的证据。在常氧条件下，三种同工 Hb 占主导地位（Hbα-3.1、-3.2 和 Hbβ-3.1）。经过三周的低氧适应（48mmHg），Hbα-2、Hbα-3.2 和 Hbβ-3.1 的表达显著上调，有效地切换了主要表达的同工型。亚基表达的变化与非条纹溶血物 P 的减少相关。同样，低氧适应导致动物整体临界氧阈值（P）降低 20%。低氧适应与鳃形态、红细胞压积或相对心室质量的变化无关。总的来说，这些数据支持血红蛋白同工型转换可以为鱼类应对环境压力提供生理益处的假说。
