Oscillating molecules and how they move circadian clocks across evolutionary boundaries.
Oscillating molecules and how they move circadian clocks across evolutionary boundaries.
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振荡分子以及它们如何使生物钟跨越进化界限。
DOI：
10.1073/pnas.90.12.5382
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发表时间：
1993
影响因子：
11.1
通讯作者：
Rosbash,M
中科院分区：
文献类型：
--
作者：
Hall,JC;Rosbash,M
生物钟随处可见，至少在生物体上是这样。除了在鸟类松果体和哺乳动物视交叉上核(1)等系统中广为人知之外，现在人们认识到，为了运行日常起搏器，生物体不必是复杂的后生动物。我们从大量的研究中了解到这一点，这些研究记录了微生物中真实的昼夜节律起搏器，如脉孢子虫、圆环菌和裸眼线虫(参考文献综述)。1和2)。因为时间生物学家已经向下推断了他们对这些节律的研究(从1729年的高等植物开始；参考文献。3)，因此，他们中的一些人推断了他们对细胞水平(包括微生物)时钟向上返回到更高形式的想法。因此，调节24小时节律的起搏器实体不必由细胞间网络或类似物组成。如果生物复杂性不是昼夜节律系统的标志，那么这样的生物钟可能在进化的早期就出现了。然而，人们似乎认为，日常节律无法跨越可怕的真核-原核边界。像往常一样，这种调查和情报障碍消失了(4，5)。蓝藻的昼夜节律已被发现，并被常规地(如果不是偶然地)报道了8年(4-6)。在这些原核生物中，以及在真核微生物中，起搏器保留了它们的定义特征(例如，参考文献)。7和8)：它们在接近一天的周期的恒定条件下“自由运行”；它们的相位由光设置(环境因素主要负责在自然光/暗周期中每天将生物钟重新设置到准确的24小时周期；参考文献)。1)，表现为温度补偿。尽管我们似乎很好地利用了我们体内的闹钟，发育中的果蝇足够聪明，可以在有益的时间窗内从变态中脱颖而出，但为什么细菌需要时钟来处理它沉闷的事情(借用很久以前一位评论作家的话；参考文献。9)?一个有趣的原理伴随着关于蓝藻代谢昼夜节律的最早报告之一：细胞需要在时间上将不相容的生化反应--包括光合作用和固氮--划分为一天中的不同部分(5)。随后的一项研究表明，支撑原核生物固氮的亚硝酸酶节律是由催化因子数量的每日波动调节的，而催化因子的量又由编码酶的mRNA的昼夜节律控制(10)。所有这一切和更多的内容都发表在本期《美国医学会会刊》上的一篇关于蓝藻节律的论文中；它源于近藤等人(11)对参与光合作用的一种因子的节律性进行了分子分析的实验。这种“光系统II”基因产物的节律被监测的主要方式涉及一种报告转基因聚球菌：该基因的上游调节区被融合到荧光素酶编码序列中，这使得转录速度的昼夜节律性能够被实时跟踪为生物柱的每日振荡(11)。在高等植物中也有类似的观察，其中涉及叶绿素a/b结合蛋白(Cab)mRNAs的节律性通过产生类似的转基因菌株而被转录介导(12)。这种方法最近达到了顶峰，证明了在拟南芥中，发光节律的昼夜循环可以被“在线”监测；实验涉及将Cab基因启动子融合到萤火虫荧光素酶报告(13)。…中mRNAs水平的钟控变化
Circadian clocks are all over the place, at least organismically speaking. In addition to being well known in systems such as the avian pineal gland and the mammalian suprachiasmatic nucleus (1), it is now appreciated that an organism need not be a complex metazoan in order to run a daily pacemaker. We know this from a host of studies that have documented bona fide circadian pacemakers in micro-bial organisms such as Neurospora, Gon-yaulax, and Euglena (reviewed in refs. 1 and 2). As chronobiologists have extrapolated their investigations of these rhythms downward (starting with a higher plant in 1729; ref. 3), so have some ofthem extrapolated their thinking about cellularlevel (including microbial) clocks back upward to higher forms. Thus, a pacemaker entity that mediates 24-hr rhythms would not have to be composed of an intercellular networkor the like. If biological complexity is not the hallmark of a circadian system, such clocks could have arisen early in evolution. Yet it seemed to have been assumed that daily rhythms couldnot cross the dread eukaryotic-prokaryotic boundary. As usual, that kind of investigatory and in-tellectual barrier fell (4, 5). Circadian rhythms in cyanobacteria were discov-ered and have been routinely, if not sa-liently, reported upon for 8 years (4-6). In these prokaryotes, and in eukaryotic microbes as well, the pacemakers retain their defining features (eg, refs. 7 and 8): they" free-run" in constant condi-tions with periods close to a day; they have their phases set by light (the environmental factor that is principally responsible for daily resetting of circadian clocks to precisely 24-hr periods in nat-ural light/dark cycles; ref. 1), and they manifest temperature compensation. Although we seem to make good use of our internal alarm clock, and developing fruit flies are smart enough to emerge from metamorphosis during a salutary window of time, why would a bacterium need a clock to conduct its dreary affairs (borrowing the words of a review writer from long ago; ref. 9)? An interesting rationale accompanied one of the first reports of a metabolic circadian rhythm in a cyanobacterium: The cells need to temporally compartmentalize incompati-ble biochemical reactions-involving photosynthesis and nitrogen fixationinto different halves of the day (5). A subsequent study showed that a nitroge-nase rhythm, which underpins that of prokaryotic nitrogen fixation, is mediated by daily fluctuations in the amount of that catalytic factor, this being in turn controlled by a circadian rhythm of the enzyme-encoding mRNA (10). All of this and more is presented in a paper on cyanobacterial rhythms that appears in the current issue of these Pro-ceedings; it resulted from experiments in which Kondo et al.(11) molecularly an-alyzed the rhythmicity ofa factor involved in photosynthesis. The primary manner in which the rhythm ofthis" photosystem II" gene product was monitored involved a reporter-transgenic strain of Synechococcus: an upstream regulatory region of the genewas fused to luciferase-encoding sequences, which permitted the circadian rhythmicity of the transcription rate to be tracked in real time as daily oscillations of biolumines-cence (11). Similar observations had been made in higher plants, where rhythmicity involving chlorophyll a/b-binding protein (Cab) mRNAwas shown, by the creation of analogous transgenic strains, to be transcriptionally mediated (12). This approach recently culminated in the demonstration that circadian cycling of a glow rhythm can be monitored" on-line" in Arabidopsis; the experiments involved fusing a Cab gene promoter to a firefly luciferase reporter (13). Clock-controlled changes in the levels of mRNAs …