粗糙脉孢菌及其他真菌中生物钟系统研究进展

地球自转形成的昼夜交替促使地球上的生物在体内进化出了能够测量时间的"生物钟"系统,此系统由输入途径、核心振荡器和输出途径3部分组成。"光逃避"假说为生物钟的进化提供了一种合理的解释。作为研究生物钟的理想模式生物之一,粗糙脉孢菌生物钟的核心振荡器是由正调控因子WC-1、WC-2和负调控因子FRQ、FRH组成的一个基于转录/翻译的负反馈调控环路。输入途径感知光照、温度等环境信号并将其传递到核心振荡器,进而调控下游一系列钟控基因表达,输出昼夜节律。此外,粗糙脉孢菌中还存在不依赖于WC复合体的frq基因的转录,其调控方式的解析进一步丰富了生物钟的调控网络。最后,通过比较并探索其他真菌中生物钟系统组成及运行机制,使我们对真菌生物钟的进化历程及生物体对环境的整体适应性有了更加全面而深刻的认识。     

KaiA调控蓝藻生物钟的分子机制研究进展

蓝藻生物钟系统主要包括输入途径、核心振荡器和输出途径3部分,核心振荡器主要由时钟蛋白KaiA、KaiB、KaiC构成。3种蛋白之间的相互作用产生节律信号及调控输入、输出信号进而维持生物振荡的精确与稳定。文中围绕蓝藻生物钟核心振荡器及核心振荡器组成蛋白的结构、功能与相互作用特点,结合本实验室近期取得的研究成果,针对时钟蛋白KaiA调节KaiC的酶活性、介导核心振荡器的时相重置、与CikA竞争KaiB的结合位点等方面近年来的研究进展进行了综述。     

蓝藻生物钟信号输出途径分子机制的研究进展

昼夜节律生物钟包括信号输入途径、核心振荡器和信号输出途径。在生物钟振荡周期与环境信号的同步过程中,信号输入途径感应外界环境的时间变化信号致使生物钟振荡周期和环境同步,并将其输入途径接受的外界信息传递给核心振荡器,核心振荡器再通过不同输出途径将周期性时间信号传递出去,产生周期性的信号调控作用。主要对蓝藻生物钟已知的三条主要输出途径KaiC-SasA-RpaA、KaiC-LabARpaA和KaiC-CikA-RpaA及其相关调节因子的分子机制研究进展进行综述。     

昆虫生物钟分子调控研究进展

昆虫生物钟节律的研究是人类了解生物节律的重要途径。昆虫在生理和行为上具有广泛的节律活动,如运动、睡眠、学习记忆、交配、嗅觉等节律活动,其中昼夜活动行为节律的研究广泛而深入。昆虫乃至高等动物普遍具有保守的昼夜节律系统,昼夜生物钟节律主要包括输入系统:用于接受外界光和温度等环境信号并传入核心振荡器,使得生物时钟与环境同步;核心时钟系统:自我维持的昼夜振荡器;输出系统:将生物钟产生的信号传递出去而控制生物行为和生理的节律变化。早期分子和遗传学研究主要关注昼夜节律振荡器的分子机制及神经生物学,阐明了昼夜生物钟节律的主要分子机制及相关神经网络。最近更多的研究关注生物钟信号是如何输入和输出。本文以果蝇运动节律的相关研究为主要内容,围绕生物钟输入系统、振荡器、输出系统这3个组成部分对昆虫生物钟研究进展进行总结。     

生物发光成像无损伤研究植物生物钟的方法

植物生物钟系统是植物为了适应地球自转进化出的以约24小时为周期的分子系统, 通过感知并整合外界周期性变化的环境信号进而协调细胞内相应基因的表达和能量状态, 赋予植物对生存环境的适应性并参与调控多个植物生长发育过程。目前, 越来越多的研究聚焦于解析植物生物钟的分子机制, 基于此也衍生出很多研究生物钟表型的方法。该文在总结已有生物钟检测方法的基础上, 重点介绍生物钟表型实验中最常用且比较稳定可靠的实验方法, 以期为生物钟的表型研究尤其是生物钟机制研究提供技术支持与借鉴。     

生物发光成像无损伤研究植物生物钟的方法

植物生物钟系统是植物为了适应地球自转进化出的以约24小时为周期的分子系统,通过感知并整合外界周期性变化的环境信号进而协调细胞内相应基因的表达和能量状态,赋予植物对生存环境的适应性并参与调控多个植物生长发育过程。目前,越来越多的研究聚焦于解析植物生物钟的分子机制,基于此也衍生出很多研究生物钟表型的方法。该文在总结已有生物钟检测方法的基础上,重点介绍生物钟表型实验中最常用且比较稳定可靠的实验方法,以期为生物钟的表型研究尤其是生物钟机制研究提供技术支持与借鉴。     

生物钟对植物非生物胁迫应答调控的进展

生物钟是一种控制植物节律性生长发育的内源性系统,可以辅助植物预知周围光照、温度和湿度环境的变化,以其核心振荡器为主要调控元件,通过细胞内关键基因的表达水平、蛋白互作从而形成信号转导通路和反馈调节回路,指导植物作出相应的表型调整,对提高植物在逆境条件下的生存适应能力具有重要的作用。本研究综述了植物在寒冷、干旱、高盐的极端环境下,生物钟关键基因CCA1/LHY、PRRs和GI等参与胁迫应答的调控方式,以及在调控过程中生物钟对脱落酸、乙烯、细胞分裂素和茉莉酸合成及代谢的影响。以植物的基因功能和激素调节为切入点,为运用现代分子生物技术手段提高植物非生物抗逆性的研究提供理论依据。     

PRRs家族功能基因的研究进展

PRRs家族基因作为生物钟核心振荡器的主要组分,在植物光周期控制开花途径中起抑制作用,并通过调控ABA等方式影响植物抗逆性,对植物生物量的积累有重要影响,在植物生长发育过程中起重要作用。综述了PRRs家族基因的结构特征、光周期调控作用模型及其对逆境的响应方式,将为进一步研究PRRs家族基因的功能和培育优质广适性作物品种提供理论参考。     

光对植物生物钟的调节

植物中的许多生理和生化反应都表现出一种内源的近似于24小时的昼夜节律现象,这些昼夜节律现象受生物钟的调节。高等植物的生物钟系统由输入途径、中央振荡器、输出途径以及一个阀门效应器组成。光信号通过光敏色素和隐花色素进入生物钟,使中央振荡器产生振荡,改变生物钟的输出信号,引起各种生理反应。本文综述了光信号对高等植物生物钟的调节作用和转导途径。     

光对植物生物钟的调节

植物中的许多生理和生化反应都表现出一种内源的近似于24小时的昼夜节律现象,这些昼夜节律现象受生物钟的调节.高等植物的生物钟系统由输入途径、中央振荡器、输出途径以及一个阀门效应器组成.光信号通过光敏色素和隐花色素进入生物钟,使中央振荡器产生振荡,改变生物钟的输出信号,引起各种生理反应.本文综述了光信号对高等植物生物钟的调节作用和转导途径.     

Regulation of output from the plant circadian clock

Plants, like many other organisms, have endogenous biological clocks that enable them to organize their physiological, metabolic and developmental processes so that they occur at optimal times. The best studied of these biological clocks are the circadian systems that regulate daily (approximately 24 h) rhythms. At the core of the circadian system in every organism are oscillators responsible for generating circadian rhythms. These oscillators can be entrained (set) by cues from the environment, such as daily changes in light and temperature. Completing the circadian clock model are the output pathways that provide a link between the oscillator and the various biological processes whose rhythms it controls. Over the past few years there has been a tremendous increase in our understanding of the mechanisms of the oscillator and entrainment pathways in plants and many useful reviews on the subject. In this review we focus on the output pathways by which the oscillator regulates rhythmic plant processes. In the first part of the review we describe the role of the circadian system in regulation at all stages of a plant's development, from germination and growth to reproductive development as well as in multiple cellular processes. Indeed, the importance of a circadian clock for plants can be gauged by the fact that so many facets of plant development are under its control. In the second part of the review we describe what is known about the mechanisms by which the circadian system regulates these output processes.     

CUL1 regulates TOC1 protein stability in the Arabidopsis circadian clock

The circadian clock is the endogenous timer that coordinates physiological processes with daily and seasonal environmental changes. In Arabidopsis thaliana , establishment of the circadian period relies on targeted degradation of TIMING OF CAB EXPRESSION 1 (TOC1) by the 26S proteasome. ZEITLUPE (ZTL) is the F-box protein that associates with the SCF (Skp/Cullin/F-box) E3 ubiquitin ligase that is responsible for marking TOC1 for turnover. CULLIN1 (CUL1) is a core component of SCF complexes and is involved in multiple signaling pathways. To assess the contribution of CUL1-containing SCF complexes to signaling within the plant oscillator, circadian rhythms were examined in the recessive, temperature-sensitive CUL1 allele axr6-3 . The activity of CUL1 in this mutant declines progressively with increasing ambient temperature, resulting in more severe defects in CUL1-dependent activities at elevated temperature. Examination of circadian rhythms in axr6-3 revealed circadian phenotypes comparable to those observed in ztl null mutants; namely, lengthened circadian period, altered expression of core oscillator genes, and limited degradation of TOC1. In addition, treatment of seedlings with exogenous auxin did not alter TOC1 stability. These results demonstrate that CUL1 is required for TOC1 degradation and further suggest that this protein is the functional cullin for the SCF^ZTL complex.     

Four easy pieces: mechanisms underlying circadian regulation of growth and development

The circadian clock confers rhythms of approximately 24 hours to biological events. It elevates plant fitness by allowing plants to anticipate predictable environmental changes and organize life process to coincide with the most favorable environmental conditions. Many developmental events are circadian regulated to ensure that growth occurs at the ideal time or season relative to available resources. Circadian clock control over growth and development is often achieved through regulation of key phytohormone action. Circadian influence over the genome is widespread and the clock modulates genes involved in phytohormone synthesis and signaling, in addition to other pathways shaping growth and development. This review presents four nonmutually exclusive mechanisms by which temporal information is gleaned from the core oscillator and passed to pathways regulating plant growth and development.     

Biological clocks in Arabidopsis thaliana

Biological rhythms are ubiquitous in eukaryotes, and the best understood of these occur with a period of approximately a day – circadian rhythms. Such rhythms persist even when the organism is placed under constant conditions, with a period that is close, but not exactly equal, to 24 h, and are driven by an endogenous timer – one of the many 'biological clocks'. In plants, research into circadian rhythms has been driven forward by genetic experiments using Arabidopsis . Higher plant genomes include a particularly large number of genes involved in metabolism, and circadian rhythms may well provide the necessary coordination for the control of these – for example, around the diurnal rhythm of photosynthesis – to suit changing developmental or environmental conditions. The endogenous timer must be flexible enough to support these requirements. Current research supports this notion most strongly for the input pathway, in which multiple photoreceptors have been shown to mediate light input to the clock. Both input and output components are now related to putative circadian oscillator mechanisms by sequence homology or by experimental observation. It appears that the pathways linking some domains of the basic clock model may be very short indeed, or the mechanisms of these domains may overlap. Components of the first plant circadian output pathway to be identified unequivocally will help to determine exactly how many output pathways control the various phases of overt rhythms in plants.     

Rhythmic regulation of retinal melatonin: Metabolic pathways,neurochemical mechanisms,and the ocular circadian clock

1. Current knowledge of the mechanisms of circadian and photic regulation of retinal melatonin in vertebrates is reviewed, with a focus on recent progress and unanswered questions. 2. Retinal melatonin synthesis is elevated at night, as a result of acute suppression by light and rhythmic regulation by a circadian oscillator, or clock, which has been localized to the eye in some species. 3. The development of suitable in vitro retinal preparations, particularly the eyecup from the African clawed frog, Xenopus laevis, has enabled identification of neural, cellular, and molecular mechanisms of retinal melatonin regulation. 4. Recent findings indicate that retinal melatonin levels can be regulated at multiple points in indoleamine metabolic pathways, including synthesis and availability of the precursor serotonin, activity of the enzyme serotonin N-acetyltransferase, and a novel pathway for degradation of melatonin within the retina. 5. Retinal dopamine appears to act through D2 receptors as a signal for light in this system, both in the acute suppression of melatonin synthesis and in the entrainment of the ocular circadian oscillator. 6. A recently developed in vitro system that enables high-resolution measurement of retinal circadian rhythmicity for mechanistic analysis of the circadian oscillator is described, along with preliminary results that suggest its potential for elucidating general circadian mechanisms. 7. A model describing hypothesized interactions among circadian, neurochemical, and cellular mechanisms in regulation of retinal melatonin is presented.     

Toward construction of a self-sustained clock-like expression system based on the mammalian circadian clock

Despite recent advances in circadian biology, detailed understanding of how a biological pacemaker system is assembled, maintained, and regulated continues to be a significant challenge. We have assembled and characterized a first-generation, regulatable, self-sustained clock-like expression system based on key components of the mammalian circadian clock. The molecular setup of the clock-like oscillator was reduced to the core set of positive and negative elements common to all known circadian pacemakers. Sophisticated tetracycline-responsive multi-cistronic expression integrated with forefront lentiviral transduction tools enabled autoregulated reporter transgene expression in a human cell line. We characterized transgene expression kinetics of an artificial oscillator and showed that its expression profiles could be modulated by a serum shock and administration of regulating tetracycline antibiotics. Design of a generic mammalian clock-like expression system will offer novel opportunities to study circadian biology and may provide a unique tool for rhythmic expression of desired transgenes fostering advances in biopharmaceutical manufacturing, gene therapy, and tissue engineering.