Examining the impact arrhythmic gene expression has on fitness in cyanobacteria possessing a complete circadian clock

摘要 由内在生物钟控制的昼夜节律使细胞生理学的预期变化成为可能， 促进对日常环境周期的适应。真核生物中昼夜节律程序的普遍性 蓝细菌表明，生物钟赋予生物体适应优势， 成长环境。尽管生物钟无处不在，但生物钟系统对整体生物钟系统的具体益处 健康状况仍然难以捉摸。模式蓝藻细长聚球藻PCC的研究进展 7942表明，昼夜节律与外部光周期紧密匹配的蓝藻较多， 比不同时期的菌株更适合。重要的是，这些研究依赖于核心时钟有缺陷的突变体， 这导致了以前未被重视的多效性后果。在这里，我们建议测试健身效益 利用一种不能在基因表达中产生振荡的菌株， 尽管拥有完整的生物钟，以避免生物钟突变体遇到的偏差。的 先前描述的crm 1突变体在crm（昼夜节律调节剂）中含有转座子插入， 开放阅读框，导致生物钟控制基因的表达。crm 1等位基因的表型不同， 来自无kaiC和无rpaA的菌株，crm 1突变体在交替的光-暗循环中生长， 为适合性研究提供了理想的具有适度的代谢基因表达的菌株。竞争实验 突变型crm 1与野生型或其他突变型之间的差异，再加上代谢特征， 在crm 1背景下进行高通量的基于TnSeq的遗传相互作用筛选，将提高我们的 理解蓝藻不能维持节律基因的适应性后果 表情此外，这项工作的目的是表征RpaA调节活性的神秘的 Crm肽，加入到我们的影响时钟输出的因素模型中。总的来说，这项工作具有 有可能为未来关于人类生物钟控制健身的研究提供信息。变得越来越 显然，现代生活的代价--包括轮班工作、蓝光照射、喷气式飞机旅行和其他行为-- 会严重扰乱多种哺乳动物组织的昼夜节律，从而导致疾病。我们的能力 评估哺乳动物组织中生物钟的适应性优势是有限的，需要易于处理的 模式生物如S. elongatus来研究生物钟网络的适应度组件。这项工作可能 为未来理解和治疗人类昼夜节律紊乱提供了一个框架。

ABSTRACT Circadian rhythms controlled by intrinsic biological clocks enable anticipatory changes in cellular physiology to promote adaptation to daily environmental cycles. The pervasiveness of circadian programs among eukaryotes and cyanobacteria suggests that circadian clocks confer a fitness advantage to organisms exposed to fluctuating growth environments. Despite the ubiquity of circadian clocks, the specific benefits of circadian systems to overall fitness have remained elusive. Previous studies in the model cyanobacterium Synechococcus elongatus PCC 7942 demonstrated that cyanobacteria whose circadian period closely matches the external light cycle are more fit than strains with periods that differ. Importantly, these studies relied on mutants with defective core clocks, which resulted in previously unappreciated pleiotropic consequences. Here, we propose to test the fitness benefit of circadian rhythms in cyanobacteria using a strain that is unable to produce oscillations in gene expression despite possessing an intact circadian clock, in order to avoid biases encountered by clock mutants. The previously described crm1 mutant contains a transposon insertion in the crm (circadian rhythmicity modulator) ORF that results in arrhythmic expression of clock controlled genes. The crm1 allele elicits phenotypes distinct from arrhythmic kaiC-null and rpaA-null strains, and the crm1 mutant grows in alternating light-dark cycles, providing a strain with moderate arrhythmic gene expression ideal for fitness studies. Competition experiments between the arrhythmic crm1 mutant and WT or other arrhythmic mutants, coupled with metabolic profiles and high-throughput TnSeq-based genetic interaction screens in the crm1 background, will improve our understanding of the fitness consequences encountered by cyanobacteria that fail to maintain rhythmic gene expression. Furthermore, this work is intended to characterize the RpaA-modulating activity of the enigmatic Crm peptide, adding to our model of factors that influence clock output. Taken together, this work has the potential to inform future studies regarding clock-controlled fitness in humans. It is becoming increasingly apparent that the toll of modern life – including shiftwork, blue-light exposure, jet travel and other behaviors – can profoundly disrupt circadian programs in a variety of mammalian tissues, contributing to disease. Our ability to assess the fitness advantage of biological clocks in mammalian tissues is limited, necessitating tractable model organisms such as S. elongatus to investigate fitness components of the clock network. The work may provide a framework for future understanding and treatment of circadian disruption in humans.