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的预期变化能够 促进适应日常环境周期。昼夜节律程序在真核生物中的普遍存在 蓝藻表明，生物钟为暴露在波动中的生物提供了健康优势。 成长环境。尽管生物钟无处不在，但生物钟系统对整体 健康状况仍然难以捉摸。模型蓝藻细长聚球藻PCC的研究进展 7942表明，昼夜节律周期与外部光周期密切匹配的蓝藻较多 与不同时期的菌株相比，它们更适合。重要的是，这些研究依赖于核心时钟有缺陷的突变体， 这导致了以前未被认识到的多效性后果。在这里，我们建议测试一下健身的益处 利用一株不能产生基因表达振荡的菌株研究蓝藻的昼夜节律 尽管拥有完整的生物钟，但为了避免时钟突变体遇到的偏差。这个 先前描述的CRM1突变体在CRM(昼夜节律调节器)中包含一个转座子插入 ORF导致时钟控制基因的心律失常表达。CRM1等位基因引起不同的表型 来自心律失常的kaiC零和RpaA零的菌株，并且CRM1突变体在交替的明暗周期中生长， 提供了一种具有中度心律失常基因表达的菌株，非常适合健康研究。竞赛实验 在心律失常CRM1突变体和WT或其他心律失常突变体之间，结合代谢谱和 在CRM1背景下基于TnSeq的高通量遗传交互屏幕，将改善我们的 对蓝藻不能保持节律基因的适应性后果的理解 表情。此外，这项工作旨在表征RpaA的调节活动的谜团 CRM肽，添加到我们影响时钟输出的因素模型中。总而言之，这项工作具有 有可能为未来关于人体时钟控制健康的研究提供信息。它正变得越来越多 显然，现代生活的代价--包括倒班、蓝光照射、喷气式飞机旅行和其他行为-- 可以深刻地扰乱各种哺乳动物组织的昼夜节律，从而导致疾病。我们的能力 要评估生物钟在哺乳动物组织中的适合性优势是有限的，有必要进行处理。 模型生物，如长链球菌，以研究时钟网络的健康成分。这项工作可能 为未来理解和治疗人类昼夜节律紊乱提供一个框架。

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.