Functional Development of the Zebrafish Pineal Gland: Light-Induced Expression of Period2 is Required for Onset of the Circadian Clock (original) (raw)
Related papers
Circadian Photoreception in the Zebrafish (Danio rerio) Pineal Gland
2006
The zebrafish pineal gland is a photoreceptive organ that contains an intrinsic circadian oscillator which drives daily rhythms of gene expression and the melatonin hormonal signal. Circadian rhythms of melatonin in the blood, peaking at night are design to modulate circadian and annual rhythms in all vertebrates. The source of rhythmic melatonin secretion is daily changes in the activity of Arylalkylamin Nacetyl transferase (AANAT). Zebrafish AANAT (zfAANAT2) activity is regulated by light and by the circadian oscillator in the pineal gland. Light pulse during the night triggers an acute degradation of AANAT protein in the pineal photoreceptor cell. In addition, daily-rhythmic transcription of zfaanat2 is regulated by the circadian oscillator. In zebrafish embryos, zfAanat2 mRNA expression begins at 22 h postfertilization (hpf), soon after the pineal is formed and clock-controlled rhythm of its transcript begins on the second day of development. In the studies presented here, I hav...
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
Endocrinology, 1999
Serotonin N-acetyltransferase (AANAT), the penultimate enzyme in melatonin synthesis, is typically found only at significant levels in the pineal gland and retina. Large changes in the activity of this enzyme drive the circadian rhythm in circulating melatonin seen in all vertebrates. In this study, we examined the utility of using AANAT messenger RNA (mRNA) as a marker to monitor the very early development of pineal photoreceptors and circadian clock function in zebrafish. Zebrafish AANAT-2 (zfAANAT-2) cDNA was isolated and used for in situ hybridization. In the adult, zfAANAT-2 mRNA is expressed exclusively in pineal cells and retinal photoreceptors. Developmental analysis, using whole mount in situ hybridization, indicated that pineal zfAANAT-2 mRNA expression is first detected at 22 h post fertilization. Retinal zfAANAT-2 mRNA was first detected
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
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.
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.
Circadian time-keeping during early stages of development
Proceedings of the National Academy of Sciences, 2006
The zebrafish pineal gland is a photoreceptive organ containing an intrinsic central circadian oscillator, which drives daily rhythms of gene expression and the melatonin hormonal signal. Here we investigated the effect of light, given at early developmental stages before pineal gland formation, on the pineal circadian oscillator. Embryos that were exposed to light at 0–6, 10–13, or 10–16 h after fertilization exhibited clock-controlled rhythms of arylalkylamine- N -acetyltransferase ( zfaanat2 ) mRNA in the pineal gland during the third and fourth day of development. This rhythm was absent in embryos that were placed in continuous dark within 2 h after fertilization (before blastula stage). Differences in the phases of these rhythms indicate that they are determined by the time of illumination. Light treatments at these stages also caused a transient increase in period2 mRNA levels, and the development of zfaanat2 mRNA rhythm was abolished by PERIOD2 knock-down. These results indic...
Light-Dependent Regulation of Circadian Clocks in Vertebrates
Chronobiology [Working Title]
Circadian clocks are intrinsic time-tracking systems that endow organisms with a survival advantage. The core of the circadian clock mechanism is a cellautonomous and self-sustained oscillator called a cellular clock, which operates via a transcription-/translation-based negative feedback loop. Under natural conditions, circadian clocks are entrained to a 24-hour day by environmental time cues, most commonly light. In mammals, circadian clocks are regulated by cellular clocks located in the central nervous system, such as the suprachiasmatic nucleus (SCN), and in other peripheral tissues. Importantly, mammals have no photoreceptors in the peripheral tissues; therefore the effect of light on peripheral clocks is indirect. By striking contrast, zebrafish peripheral cellular clocks are directly light responsive. This characteristic of the zebrafish cellular clock has contributed to the identification of molecules and signaling pathways that are involved in the lightdependent regulation of the cellular clock. Here, selected light-dependent regulatory mechanisms of circadian clocks in mammals and zebrafish are described.
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.
Proceedings of the National Academy of Sciences, 2007
Light is the key entraining stimulus for the circadian clock, but several features of the signaling pathways that convert the photic signal to clock entrainment remain to be deciphered. Here, we show that light induces the production of hydrogen peroxide (H 2 O 2 ) that acts as the second messenger coupling photoreception to the zebrafish circadian clock. Treatment of light-responsive Z3 cells with H 2 O 2 triggers the induction of zCry1a and zPer2 genes and the subsequent circadian oscillation of zPer1 . Remarkably, the induction kinetics and oscillation profile in response to H 2 O 2 are identical to those initiated by light. Catalase ( Cat ), an antioxidant enzyme degrading H 2 O 2 , shows an oscillating pattern of expression and activity, antiphasic to zCry1a and zPer2 . Interestingly, overexpression of zCAT results in a reduced light-dependent zCry1a and zPer2 gene induction. In contrast, inhibition of zCAT function enhances light-mediated inducibility of these clock genes. The...