Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, Guangdong 511458, China.
Jiangsu Key Laboratory for Biodiversity and Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210023, China.
Sleep. 2024 Apr 12;47(4). doi: 10.1093/sleep/zsae018.
Marine mammals, especially cetaceans, have evolved a very special form of sleep characterized by unihemispheric slow-wave sleep (USWS) and a negligible amount or complete absence of rapid-eye-movement sleep; however, the underlying genetic mechanisms remain unclear. Here, we detected unique, significant selection signatures in basic helix-loop-helix ARNT like 2 (BMAL2; also called ARNTL2), a key circadian regulator, in marine mammal lineages, and identified two nonsynonymous amino acid substitutions (K204E and K346Q) in the important PER-ARNT-SIM domain of cetacean BMAL2 via sequence comparison with other mammals. In vitro assays revealed that these cetacean-specific mutations specifically enhanced the response to E-box-like enhancer and consequently promoted the transcriptional activation of PER2, which is closely linked to sleep regulation. The increased PER2 expression, which was further confirmed both in vitro and in vivo, is beneficial for allowing cetaceans to maintain continuous movement and alertness during sleep. Concordantly, the locomotor activities of zebrafish overexpressing the cetacean-specific mutant bmal2 were significantly higher than the zebrafish overexpressing the wild-type gene. Subsequently, transcriptome analyses revealed that cetacean-specific mutations caused the upregulation of arousal-related genes and the downregulation of several sleep-promoting genes, which is consistent with the need to maintain hemispheric arousal during USWS. Our findings suggest a potential close relationship between adaptive changes in BMAL2 and the remarkable adaptation of USWS and may provide novel insights into the genetic basis of the evolution of animal sleep.
海洋哺乳动物，尤其是鲸目动物，进化出一种非常特殊的睡眠形式，其特征是单侧慢波睡眠（USWS）和极少量或完全不存在快速眼动睡眠；然而，潜在的遗传机制仍不清楚。在这里，我们在生物钟调节因子基本螺旋-环-螺旋 ARNT 样 2（BMAL2；也称为 ARNTL2）的海洋哺乳动物谱系中检测到独特的、显著的选择特征，并通过与其他哺乳动物的序列比较，在鲸目动物的 BMAL2 中重要的 PER-ARNT-SIM 结构域中鉴定出两个非同义氨基酸取代（K204E 和 K346Q）。体外实验表明，这些鲸目动物特有的突变特异性地增强了对 E 盒样增强子的反应，从而促进了 PER2 的转录激活，PER2 与睡眠调节密切相关。进一步在体外和体内证实的 PER2 表达增加有利于鲸目动物在睡眠期间保持持续的运动和警觉。一致地，过表达鲸目动物特异性突变 bmal2 的斑马鱼的运动活动明显高于过表达野生型基因的斑马鱼。随后，转录组分析显示，鲸目动物特异性突变导致觉醒相关基因的上调和几个促进睡眠的基因的下调，这与在 USWS 期间保持半球觉醒的需要一致。我们的研究结果表明，BMAL2 的适应性变化与 USWS 的显著适应之间可能存在密切关系，并可能为动物睡眠进化的遗传基础提供新的见解。
