Autonomous onset of the circadian clock in the zebrafish embryo

• Published in: The EMBO journal 2008-10, Vol.27 (20), p.2757-2765
• Main Authors: Dekens, Marcus PS, Whitmore, David
• Format: Article
• Language: English
• Subjects: Animals; ARNTL Transcription Factors; Basic Helix-Loop-Helix Transcription Factors - metabolism; bmal; Cellular biology; circadian clock; Circadian Rhythm; Circadian rhythms; clock; CLOCK Proteins; Danio rerio; Embryos; Fish; Freshwater; Gene Expression Regulation, Developmental; Light; Models, Biological; Models, Genetic; ontogeny; Oscillometry; period; Prenatal development; Temperature; Time Factors; Trans-Activators - metabolism; Transcription Factors - metabolism; Transcription, Genetic; Zebrafish; Zebrafish Proteins - metabolism
• ISSN: 0261-4189; 1460-2075
• DOI: 10.1038/emboj.2008.183

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 ΔCLOCK 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.