Silencing the circadian clock gene Clock using RNAi reveals dissociation of the circatidal clock from the circadian clock in the mangrove cricket

Whether a clock that generates a circatidal rhythm shares the same elements as the circadian clock is not fully understood. The mangrove cricket, Apteronemobius asahinai, shows simultaneously two endogenous rhythms in its locomotor activity; the circatidal rhythm generates active and inactive phases, and the circadian rhythm modifies activity levels by suppressing the activity during subjective day. In the present study, we silenced Clock (Clk), a master gene of the circadian clock, in A. asahinai using RNAi to investigate the link between the circatidal and circadian clocks. The abundance of Clk mRNA in the crickets injected with double-stranded RNA of Clk (dsClk) was reduced to a half of that in control crickets. dsClk injection also reduced mRNA abundance of another circadian clock gene period (per) and weakened diel oscillation in per mRNA expression. Examination of the locomotor rhythms under constant conditions revealed that the circadian modification was disrupted after silencing Clk expression, but the circatidal rhythm remained unaffected. There were no significant changes in the free-running period of the circatidal rhythm between the controls and the crickets injected with dsClk. Our results reveal that Clk is essential for the circadian clock, but is not required for the circatidal clock. From these results we propose that the circatidal rhythm of A. asahinai is driven by a clock, the molecular components of which are distinct from that of the circadian clock.     

The regulation of plant growth by the circadian clock

Circadian regulated changes in growth rates have been observed in numerous plants as well as in unicellular and multicellular algae. The circadian clock regulates a multitude of factors that affect growth in plants, such as water and carbon availability and light and hormone signalling pathways. The combination of high-resolution growth rate analyses with mutant and biochemical analysis is helping us elucidate the time-dependent interactions between these factors and discover the molecular mechanisms involved. At the molecular level, growth in plants is modulated through a complex regulatory network, in which the circadian clock acts at multiple levels.     

生物钟机制研究进展

由生物体内源性生物钟所产生的昼夜节律是近年来生命科学的研究热点之一。几种模型生物（蓝细菌、脉孢菌、拟南芥、果蝇、小鼠）的生物钟相关基因相继被克隆和鉴定,为理解昼夜节律的分子机制奠定了基础。振荡器蛋白对其编码基因的负反馈调控可能是不同生物的生物运作普遍机制,在此基础上,不同生物有不尽相同的调控方式;隐色素可能是高等生物的共同生物钟光受体。     

Synchronization of the mammalian circadian timing system: Light can control peripheral clocks independently of the SCN clock

A vast network of cellular circadian clocks regulates 24‐hour rhythms of behavior and physiology in mammals. Complex environments are characterized by multiple, and often conflicting time signals demanding flexible mechanisms of adaptation of endogenous rhythms to external time. Traditionally this process of circadian entrainment has been conceptualized in a hierarchical scheme with a light‐reset master pacemaker residing in the hypothalamus that subsequently aligns subordinate peripheral clocks with each other and with external time. Here we review new experiments using conditional mouse genetics suggesting that resetting of the circadian system occurs in a more “federated” and tissue‐specific fashion, which allows for increased noise resistance and plasticity of circadian timekeeping under natural conditions.     

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。     

Research on circadian clock genes in common abdominal malignant tumors

Circadian rhythm describes the 24-h oscillation in physiology and behavior of living organisms and presents a timing controller for life activity. Studies in recent years have reported that the abnormal expression of clock genes is closely related to the development of common abdominal malignant tumors. The expression of the 14 kinds of clock genes in 6 abdominal malignant tumors from Cancer Genome Atlas (TCGA) data was integrated and analyzed using R and Perl programming languages to show the association between clock gene expression and prognosis of cancer patients. Analysis of TCGA data indicated that the overexpression of Per1-3, Cry2, CLOCK, NR1D2 and RORA with underexpression of Timeless and NPAS2 was associated with a favorable prognosis in kidney cancer. In liver cancer, high expressions of Cry2 and RORA were correlated with prolonged overall survival (OS) in patients, while high expressions of NPAS2 and Timeless were correlated with a poor survival. High expression of CLOCK was positively correlated with OS in colon cancer patients. High expression of Cry2 and low expression of DEC1 were associated with a favorable prognosis in pancreatic cancer patients, respectively. Most of these clock-genes expressions were closely related to the clinical stage and degree of tumor differentiation of patients. Aberrant clock gene expression is related to the biological characteristics of abdominal malignant tumors, which likely has a causal role in cancer development and survival.     

松果体昼夜节律生物钟分子机制的研究进展

在各种非哺乳类脊椎动物中 ,松果体起着中枢昼夜节律振荡器的作用。近来 ,在鸟类松果体中相继发现了几种钟基因 ,如Per、Cry、Clock和Bmal等 ,其表达的时间变化规律与哺乳类视交叉上核 (SCN)的非常相似。钟的振荡由其自身调控反馈环路的转录和翻译组成 ,鸟类松果体和哺乳类SCN似乎具有共同的钟振荡基本分子构架 ;若干钟基因产物作为正向或负向调节子影响钟的振荡 ;昼夜性的控时机制同时也需要翻译后事件的参与。这些过程对钟振荡器的稳定性和 /或钟导引的光输入通路有着重要的调控作用     

Research on circadian clock genes in non-small-cell lung carcinoma

Circadian clock genes have become a hot topic in cancer research in recent years, and more and more studies are showing that clock genes are involved in regulating cell proliferation cycle and apoptosis of malignant tumors, neuroendocrine and immune function, and other processes. Lung cancer is a malignant tumor with increasing incidence worldwide. The pathogenesis of lung cancer is extremely complicated and includes genetic factors, living environment, and smoking, and the occurrence of lung cancer is related to the regulation of many oncogenes and tumor suppressor genes. But there are few studies on clock genes in lung cancer. Studies on clock genes may help to better understand the mechanism of lung cancer development for an improved treatment. The expressions of all 14 kinds of clock genes in adenocarcinoma (ADC) and squamous cell carcinoma (SCC), two main kinds of non-small-cell lung cancer (NSCLC), were studied based on integration and analysis of data from The Cancer Genome Atlas (TCGA) to show the association between clock gene expression and prognosis of cancer patients. Analysis of TCGA data indicated that overexpression of Cry2, BMAL1, and RORA with underexpression of Timeless and NPAS2 was associated with a favorable prognosis of ADC, and the expression of NPAS2 was associated with the time of patient survival. Additionally, the expression of Cry2 was related to TNM stage. In SCC, high expression of DEC1 was correlated with poor overall survival in patients and the expression of Timeless was associated with the time of patient survival. In NSCLC, circadian clock genes constitute cancer circadian rhythm by interacting with each other, showing that asynchrony with normal tissues, which collectively controlling the occurrence and development of NSCLC.     

In vitro regulation of circadian phosphorylation rhythm of cyanobacterial clock protein KaiC by KaiA and KaiB

Biochemical circadian oscillation of KaiC phosphorylation, by mixing three Kai proteins and ATP, has been proven to be the central oscillator of the cyanobacterial circadian clock. In vivo, the intracellular levels of KaiB and KaiC oscillate in a circadian fashion. By scrutinizing KaiC phosphorylation rhythm in a wide range of Kai protein concentrations, KaiA and KaiB were found to be “parameter-tuning” and “state-switching” regulators of KaiC phosphorylation rhythm, respectively. Our results also suggest a possible entrainment mechanism of the cellular circadian clock with the circadian variation of intracellular levels of Kai proteins.     

The human circadian clock and aging

The suprachiasmatic nucleus (SCN) of the hypothalamus is implicated in the timing of a wide variety of circadian processes. Since the environmental light-dark cycle is the main zeitgeber for many of the rhythms, photic information may have a synchronizing effect on the endogenous clock of the SCN by inducing periodic changes in the biological activity of certain groups of neurons. By studying the brains obtained at autopsy of human subjects, marked diurnal oscillations were observed in the neuropeptide content of the SCN. Vasopressin, for example, one of the most abundant peptides in the human SCN, exhibited a diurnal rhythm, with low values at night and peak values during the early morning. However, with advancing age, these diurnal fluctuations deteriorated, leading to a disrupted cycle with a reduced amplitude in elderly people. These findings suggest that the synthesis of some peptides in the human SCN exhibits an endogenous circadian rhythmicity, and that the temporal organization of these rhythms becomes progressively disturbed in senescence. (Chronobiology International, 17(3), 245-259, 2000)     

Light- and temperature-entrainable circadian clock in soybean development

In plants, the spatiotemporal expression of circadian oscillators provides adaptive advantages in diverse species. However, the molecular basis of circadian clock in soybean is not known. In this study, we used soybean hairy roots expression system to monitor endogenous circadian rhythms and the sensitivity of circadian clock to environmental stimuli. We discovered in experiments with constant light and temperature conditions that the promoters of clock genes GmLCLb2 and GmPRR9b1 drive a self-sustained, robust oscillation of about 24-h in soybean hairy roots. Moreover, we demonstrate that circadian clock is entrainable by ambient light/dark or temperature cycles. Specifically, we show that light and cold temperature pulses can induce phase shifts of circadian rhythm, and we found that the magnitude and direction of phase responses depends on the specific time of these two zeitgeber stimuli. We obtained a quadruple mutant lacking the soybean gene GmLCLa1, LCLa2, LCLb1, and LCLb2 using CRISPR, and found that loss-of-function of these four GmLCL orthologs leads to an extreme short-period circadian rhythm and late-flowering phenotype in transgenic soybean. Our study establishes that the morning-phased GmLCLs genes act constitutively to maintain circadian rhythmicity and demonstrates that their absence delays the transition from vegetative growth to reproductive development.     

Impact of heart-specific disruption of the circadian clock on systemic glucose metabolism in mice

The daily rhythm of glucose metabolism is governed by the circadian clock, which consists of cell-autonomous clock machineries residing in nearly every tissue in the body. Disruption of these clock machineries either environmentally or genetically induces the dysregulation of glucose metabolism. Although the roles of clock machineries in the regulation of glucose metabolism have been uncovered in major metabolic tissues, such as the pancreas, liver, and skeletal muscle, it remains unknown whether clock function in non-major metabolic tissues also affects systemic glucose metabolism. Here, we tested the hypothesis that disruption of the clock machinery in the heart might also affect systemic glucose metabolism, because heart function is known to be associated with glucose tolerance. We examined glucose and insulin tolerance as well as heart phenotypes in mice with heart-specific deletion of Bmal1, a core clock gene. Bmal1 deletion in the heart not only decreased heart function but also led to systemic insulin resistance. Moreover, hyperglycemia was induced with age. Furthermore, heart-specific Bmal1-deficient mice exhibited decreased insulin-induced phosphorylation of Akt in the liver, thus indicating that Bmal1 deletion in the heart causes hepatic insulin resistance. Our findings revealed an unexpected effect of the function of clock machinery in a non-major metabolic tissue, the heart, on systemic glucose metabolism in mammals.     

Altered expression of circadian clock genes during peripheral blood stem cell mobilization induced by granulocyte colony-stimulating factor

Circulating hematopoietic stem cells exhibit robust circadian fluctuations, which influence the mobilized cell yield, even during enforced stem cell mobilization. However, alterations in the expression of circadian clock genes during granulocyte colony-stimulating factor (G-CSF)-induced peripheral blood stem cell (PBSC) mobilization are not fully elucidated. Therefore, we measured the expression of these genes in human peripheral blood leukocytes from 21 healthy donors. While CRY1 mRNA expression significantly increased by 3.9-fold (p?<?0.01), the expression of PER3, CRY2 and BMAL1 mRNAs significantly decreased (by 0.2-fold, 0.2-fold, and 0.6-fold, respectively; p?<?0.001) after G-CSF administration. Moreover, CRY1 mRNA expression was inversely correlated with the plasma level of noradrenaline (r?=??0.36, p?<?0.05), while PER3, CRY2, and BMAL1 mRNA expression directly correlated with the plasma level of noradrenaline (r?=?0.55, r?=?0.66, and r?=?0.57, respectively; p?<?0.001). Thus, significant correlations between the levels of circadian clock gene mRNAs and the plasma level of noradrenaline, a sympathetic nervous system neurotransmitter, were established. The modulation of sympathetic activation and of the circadian clock may be novel therapeutic targets for increasing stem cell yields in PBSC donors.     

Human intestinal circadian clock: expression of clock genes in colonocytes lining the crypt

Biological clock components have been detected in many epithelial tissues of the digestive tract of mammals (oral mucosa, pancreas, and liver), suggesting the existence of peripheral circadian clocks that may be entrainable by food. Our aim was to investigate the expression of main peripheral clock genes in colonocytes of healthy humans and in human colon carcinoma cell lines. The presence of clock components was investigated in single intact colonic crypts isolated by chelation from the biopsies of 25 patients (free of any sign of colonic lesions) undergoing routine colonoscopy and in cell lines of human colon carcinoma (Caco2 and HT29 clone 19A). Per-1, per-2, and clock mRNA were detected by real-time RT-PCR. The three-dimensional distributions of PER-1, PER-2, CLOCK, and BMAL1 proteins were recorded along colonic crypts by immunofluorescent confocal imaging. We demonstrate the presence of per-1, per-2, and clock mRNA in samples prepared from colonic crypts of 5 patients and in all cell lines. We also demonstrate the presence of two circadian clock proteins, PER-1 and CLOCK, in human colonocytes on crypts isolated from 20 patients (15 patients for PER-1 and 6 for CLOCK) and in colon carcinoma cells. Establishing the presence of clock proteins in human colonic crypts is the first step toward the study of the regulation of the intestinal circadian clock by nutrients and feeding rhythms.     

How temperature affects the circadian clock of Neurospora crassa

Light and temperature are major environmental cues that influence circadian clocks. The molecular effects of these zeitgebers on the circadian clock of Neurospora crassa have been studied intensively during the last decade. While signal transduction of light into the circadian clock is quite well characterized, we have only recently begun to understand the molecular mechanisms that underlie temperature sensing. Here we summarize briefly the current knowledge about the effects of temperature on the circadian clock of Neurospora crassa.