Developmental stage-specific regulation of the circadian clock by temperature in zebrafish (original) (raw)
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Temperature Regulates Transcription in the Zebrafish Circadian Clock
PLoS Biology, 2005
It has been well-documented that temperature influences key aspects of the circadian clock. Temperature cycles entrain the clock, while the period length of the circadian cycle is adjusted so that it remains relatively constant over a wide range of temperatures (temperature compensation). In vertebrates, the molecular basis of these properties is poorly understood. Here, using the zebrafish as an ectothermic model, we demonstrate first that in the absence of light, exposure of embryos and primary cell lines to temperature cycles entrains circadian rhythms of clock gene expression. Temperature steps drive changes in the basal expression of certain clock genes in a gene-specific manner, a mechanism potentially contributing to entrainment. In the case of the per4 gene, while E-box promoter elements mediate circadian clock regulation, they do not direct the temperature-driven changes in transcription. Second, by studying E-box-regulated transcription as a reporter of the core clock mechanism, we reveal that the zebrafish clock is temperature-compensated. In addition, temperature strongly influences the amplitude of circadian transcriptional rhythms during and following entrainment by light-dark cycles, a property that could confer temperature compensation. Finally, we show temperature-dependent changes in the expression levels, phosphorylation, and function of the clock protein, CLK. This suggests a mechanism that could account for changes in the amplitude of the Ebox-directed rhythm. Together, our results imply that several key transcriptional regulatory elements at the core of the zebrafish clock respond to temperature. Citation: Lahiri K, Vallone D, Gondi SB, Santoriello C, Dickmeis T, et al (2005) Temperature regulates transcription in the zebrafish circadian clock. PLoS Biol 3(11): e351.
Autonomous onset of the circadian clock in the zebrafish embryo
The EMBO Journal, 2008
On the first day of development a circadian clock becomes functional in the zebrafish embryo. How this oscillator is set in motion remains unclear. We demonstrate that zygotic period1 transcription begins independent of light exposure. Pooled embryos maintained in darkness and under constant temperature show elevated non-oscillating levels of period1 expression. Consequently, there is no maternal effect or developmental event that sets the phase of the circadian clock. Analysis of period1 transcription, at the cellular level in the absence of environmental stimuli, reveals oscillations in cells that are asynchronous within the embryo. Demonstrating an autonomous onset to rhythmic period1 expression. Transcription of clock1 and bmal1 is rhythmic in the adult, but constant during development in light-entrained embryos. Transient expression of dominant-negative DCLOCK blocks period1 transcription, thus showing that endogenous CLOCK is essential for the transcriptional regulation of period1 in the embryo. We demonstrate a default mechanism in the embryo that initiates the autonomous onset of the circadian clock. This embryonic clock is differentially regulated from that in the adult, the transition coinciding with the appearance of several clock output processes.
Zebrafish circadian clocks: cells that see light
In the classical view of circadian clock organization, the daily rhythms of most organisms were thought to be regulated by a central, 'master' pacemaker, usually located within neural structures of the animal. However, with the results of experiments performed in zebrafish, mammalian cell lines and, more recently, mammalian tissues, this view has changed to one where clock organization is now seen as being highly decentralized. It is clear that clocks exist in the peripheral tissues of animals as diverse as Drosophila, zebrafish and mammals. In the case of Drosophila and zebrafish, these tissues are also directly lightresponsive. This light sensitivity and direct clock entrainability is also true for zebrafish cell lines and earlystage embryos. Using luminescent reporter cell lines containing clock gene promoters driving the expression of luciferase and single-cell imaging techniques, we have been able to show how each cell responds rapidly to a single light pulse by being shifted to a common phase, equivalent to the early day. This direct light sensitivity might be related to the requirement for light in these cells to activate the transcription of genes involved in DNA repair. It is also clear that the circadian clock in zebrafish regulates the timing of the cell cycle, demonstrating the wide impact that this light sensitivity and daily rhythmicity has on the biology of zebrafish.
CLOCK:BMAL-Independent Circadian Oscillation of Zebrafish Cryptochrome1a Gene
Biological & Pharmaceutical Bulletin, 2009
Organisms ranging from bacteria to humans have daily rhythms driven by endogenous oscillators called circadian clocks, which regulate various biochemical, physiological, and behavioral processes. 1) Under natural conditions, circadian rhythms are entrained to a 24-h cycle by environmental time cues, of which light is the most important. Over the past few years, the molecular mechanisms responsible for these oscillations have been thoroughly investigated and specific "clock genes" that control this rhythm have been identified. The core of the clock mechanism in Drosophila, Neurospora, and mammals is commonly represented by a transcription/ translation-based negative-feedback loop that relies on positive and negative oscillator elements. 2,3) Although the organization of the negative feedback loop in Drosophila, Neurospora, and mammals is conceptually similar, its components differ among species. 3) In mammals, two basic helix-loop-helix PAS (PER-ARNT-SIM) domain-containing transcription factors, CLOCK and BMAL, constitute the positive elements. 4,5) Upon heterodimerization, the CLOCK: BMAL complex drives the transcription of the negative components of the clock machinery, two Cryptochrome genes (Cry1 and Cry2). CRYs negatively regulate their own expression, therefore setting up the rhythmic oscillations of gene expression that drive the circadian clock. 6) Zebrafish possess an intrinsic autonomous oscillator that consists of components similar to those of mammals. 7) zCLOCK and zBMAL act as positive elements and zCRYs act as negative regulators. As the result of whole-genome duplication during the evolution of the teleost lineage, the circadian oscillator of zebrafish contains duplications for most of the clock genes. Interestingly, zebrafish have four repressor types of CRYs (zCRY1a, zCRY1b, zCRY2a, and zCRY2b). Despite the structural and functional similarities seen in vitro, their expression profiles are quite different. 7) Expression of zCry1b, zCry2a and zCry2b are under the control of CLOCK:BMAL heterodimer, showing a clear circadian oscillation both in light-dark (LD) and constant dark (DD) conditions. 8) In contrast, although zCry1a exhibits a circadian oscillation in cultured cells exposed to a LD cycle, this oscillation dampens quickly after the transfer of the cells to a DD condition. 9-11) Thus, transcriptional regulation of zCry1a is believed to be CLOCK:BMAL-independent. Zebrafish oscillators in peripheral tissues and cell lines derived from zebrafish tissues display direct-light responsiveness. 12) In fact, zebrafish cultured cells constitute an attractive alternative to the mammalian system to study the complexity of the circadian clock machinery and the influence that light has on it. In zebrafish cells, light directly activates the expression of zCry1a. 10,11) Light-induced zCRY1a in turn inhibits CLOCK:BMAL-dependent transcription, thereby participating in the light entrainment of the circadian clock. 10,11) Moreover, a critical role for extracellular signalregulated kinase (ERK) signaling pathway in the circadian transcriptional regulation has been established in a variety of species. 9,13) Indeed, we have previously reported that lightinduced zCry1a expression is achieved through activation of the ERK signaling cascade, 11) showing the critical role of ERK pathway in transcriptional regulation of zCry1a gene. Here we report that the oscillation of zCry1a gene expression does not depend on CLOCK:BMAL transcriptional activation. Indeed, the abolishment of CLOCK:BMAL-transactivation capacity through the expression of a dominant negative form of zCLOCK3 (zCLOCK3-DeltaC) lacking its transactivation domain does not show any impact on the cir
Analysis of a Gene Regulatory Cascade Mediating Circadian Rhythm in Zebrafish
PLoS Computational Biology, 2013
In the study of circadian rhythms, it has been a puzzle how a limited number of circadian clock genes can control diverse aspects of physiology. Here we investigate circadian gene expression genome-wide using larval zebrafish as a model system. We made use of a spatial gene expression atlas to investigate the expression of circadian genes in various tissues and cell types. Comparison of genome-wide circadian gene expression data between zebrafish and mouse revealed a nearly anti-phase relationship and allowed us to detect novel evolutionarily conserved circadian genes in vertebrates. We identified three groups of zebrafish genes with distinct responses to light entrainment: fast light-induced genes, slow lightinduced genes, and dark-induced genes. Our computational analysis of the circadian gene regulatory network revealed several transcription factors (TFs) involved in diverse aspects of circadian physiology through transcriptional cascade. Of these, microphthalmia-associated transcription factor a (mitfa), a dark-induced TF, mediates a circadian rhythm of melanin synthesis, which may be involved in zebrafish's adaptation to daily light cycling. Our study describes a systematic method to discover previously unidentified TFs involved in circadian physiology in complex organisms.
Circadian rhythmicity and light sensitivity of the zebrafish brain
PloS one, 2014
Traditionally, circadian clocks have been thought of as a neurobiological phenomenon. This view changed somewhat over recent years with the discovery of peripheral tissue circadian oscillators. In mammals, however, the suprachiasmatic nucleus (SCN) in the hypothalamus still retains the critical role of a central synchronizer of biological timing. Zebrafish, in contrast, have always reflected a more highly decentralized level of clock organization, as individual cells and tissues contain directly light responsive circadian pacemakers. As a consequence, clock function in the zebrafish brain has remained largely unexplored, and the precise organization of rhythmic and light-sensitive neurons within the brain is unknown. To address this issue, we used the period3 (per3)-luciferase transgenic zebrafish to confirm that multiple brain regions contain endogenous circadian oscillators that are directly light responsive. In addition, in situ hybridization revealed localised neural expression ...
Starting the Zebrafish Pineal Circadian Clock with a Single Photic Transition
Endocrinology, 2006
The issue of what starts the circadian clock ticking was addressed by studying the developmental appearance of the daily rhythm in the expression of two genes in the zebrafish pineal gland that are part of the circadian clock system. One encodes the photopigment exorhodopsin and the other the melatonin synthesizing enzyme arylalkylamine N-acetyltransferase (AANAT2). Significant daily rhythms in AANAT2 mRNA abundance were detectable for several days after fertilization in animals maintained in a normal or reversed lighting cycle providing 12 h of light and 12 h of dark. In contrast, these rhythms do not develop if animals are maintained in
Biochemical and Biophysical Research Communications, 2006
To elucidate the roles of DEC1 and DEC2, basic helix-loop-helix transcription factors, in the circadian clock of photosensitive zebrafish peripheral cells, zebrafish Dec1 and Dec2 (zDec1 and zDec2) were cloned and their functions and expression patterns were examined in BRF41, a zebrafish cell line. zDEC1 and zDEC2 have high sequence similarity to mammalian counterparts and the molecular phylogenetic analysis of the zDEC1 and zDEC2 sequences reflected the predicted pattern of species classification. zDEC1 and zDEC2 inhibited zCLOCK1:zBMAL3 mediated transcription as CRY1a. zDec1 and zDec2 mRNA showed robust circadian oscillation in BRF41 cells. However, zDec1 and zDec2 mRNA was not strongly induced by exposure to light. These results indicate that zDec1 and zDec2 are involved in the circadian clock mechanism in photosensitive zebrafish peripheral cells by suppressing CLOCK/BMAL-induced gene expression and that the feedback loops of zDEC1 and zDEC2 may be interlocked with the PER/CRY core circadian feedback loops.
Genetically Blocking the Zebrafish Pineal Clock Affects Circadian Behavior
PLOS Genetics, 2016
The master circadian clock in fish has been considered to reside in the pineal gland. This dogma is challenged, however, by the finding that most zebrafish tissues contain molecular clocks that are directly reset by light. To further examine the role of the pineal gland oscillator in the zebrafish circadian system, we generated a transgenic line in which the molecular clock is selectively blocked in the melatonin-producing cells of the pineal gland by a dominant-negative strategy. As a result, clock-controlled rhythms of melatonin production in the adult pineal gland were disrupted. Moreover, transcriptome analysis revealed that the circadian expression pattern of the majority of clock-controlled genes in the adult pineal gland is abolished. Importantly, circadian rhythms of behavior in zebrafish larvae were affected: rhythms of place preference under constant darkness were eliminated, and rhythms of locomotor activity under constant dark and constant dim light conditions were markedly attenuated. On the other hand, global peripheral molecular oscillators, as measured in whole larvae, were unaffected in this model. In conclusion, characterization of this novel transgenic model provides evidence that the molecular clock in the melatonin-producing cells of the pineal gland plays a key role, possibly as part of a multiple pacemaker system, in modulating circadian rhythms of behavior.