Confined within the cold-stable Southern Ocean, Antarctic notothenioid fishes have undergone an evolutionary loss of the inducible heat shock response (HSR), while facing perpetual low-temperature challenges to cellular proteostasis. This study examines how evolution in chronic cold has affected the shared cellular apparatus that mediates proteostasis under normal and heat stressed states. To deduce Antarctic-specific changes, we compared native expression levels across the full suite of chaperome genes and assessed the structural integrity of two crucial HSR regulators - Heat Shock Factor 1 (HSF1) that activates HSR, and heat shock elements (HSEs), the binding sites for HSF1 - between Antarctic fishes and the basal temperate notothenioid Eleginops maclovinus. Native expression levels of Antarctic fish chaperomes showed very modest changes overall, contrary to the common view of constitutive upregulation in the cold. Only a few cytosolic HSP70 genes showed greater transcription, with only the ancestrally-inducible HSPA6 strongly upregulated across all Antarctic species. Additionally, the constant cold has apparently not relaxed the selective pressures on maintaining HSF1 and HSEs in Antarctic fish. Instead, we found HSF1 experienced intensified selective pressure, with conserved sequence changes in Antarctic species suggesting optimization for non-heat-stress functional roles. HSEs of the HSP70 gene family have largely remained conserved in canonical sequence motifs and copy numbers as in E. maclovinus, showing limited impact of relaxed selective pressure. This study shows that evolution in chronic cold has led to both subtle and distinctive changes in the cellular apparatus for proteostasis and HSR, with functional consequences amenable to experimental evaluation.

中文翻译：

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南极鱼群伴侣基因表达和调控元件的进化

被限制在寒冷稳定的南大洋内，南极类鲸鱼经历了诱导热休克反应 (HSR) 的进化损失，同时面临着对细胞蛋白质稳态的永久低温挑战。这项研究探讨了慢性感冒的进化如何影响在正常和热应激状态下介导蛋白质稳态的共享细胞装置。为了推断南极特有的变化，我们比较了全套伴侣基因的天然表达水平，并评估了两个关键的 HSR 调节因子——激活 HSR 的热激因子 1 (HSF1) 和热激元素 (HSE) 的结构完整性。 HSF1 的结合位点 - 在南极鱼类和基底温带 notothenioid Eleginops maclovinus 之间。南极鱼伴侣的原生表达水平总体上表现出非常温和的变化，与寒冷中组成性上调的普遍观点相反。只有少数细胞溶质 HSP70 基因表现出更大的转录，只有祖先诱导的 HSPA6 在所有南极物种中强烈上调。此外，持续的寒冷显然并没有减轻维持南极鱼类 HSF1 和 HSE 的选择压力。相反，我们发现 HSF1 经历了增强的选择压力，南极物种的保守序列变化表明对非热应激功能作用的优化。HSP70 基因家族的 HSE 在标准序列基序和拷贝数中基本上保持保守，与 E. maclovinus 一样，显示出放松选择压力的有限影响。