CLOCK-mediated acetylation of BMAL1 controls circadian function.
ABSTRACT Regulation of circadian physiology relies on the interplay of interconnected transcriptional-translational feedback loops. The CLOCK-BMAL1 complex activates clock-controlled genes, including cryptochromes (Crys), the products of which act as repressors by interacting directly with CLOCK-BMAL1. We have demonstrated that CLOCK possesses intrinsic histone acetyltransferase activity and that this enzymatic function contributes to chromatin-remodelling events implicated in circadian control of gene expression. Here we show that CLOCK also acetylates a non-histone substrate: its own partner, BMAL1, is specifically acetylated on a unique, highly conserved Lys 537 residue. BMAL1 undergoes rhythmic acetylation in mouse liver, with a timing that parallels the downregulation of circadian transcription of clock-controlled genes. BMAL1 acetylation facilitates recruitment of CRY1 to CLOCK-BMAL1, thereby promoting transcriptional repression. Importantly, ectopic expression of a K537R-mutated BMAL1 is not able to rescue circadian rhythmicity in a cellular model of peripheral clock. These findings reveal that the enzymatic interplay between two clock core components is crucial for the circadian machinery.
Article: CHD1 remodels chromatin and influences transient DNA methylation at the clock gene frequency.[show abstract] [hide abstract]
ABSTRACT: Circadian-regulated gene expression is predominantly controlled by a transcriptional negative feedback loop, and it is evident that chromatin modifications and chromatin remodeling are integral to this process in eukaryotes. We previously determined that multiple ATP-dependent chromatin-remodeling enzymes function at frequency (frq). In this report, we demonstrate that the Neurospora homologue of chd1 is required for normal remodeling of chromatin at frq and is required for normal frq expression and sustained rhythmicity. Surprisingly, our studies of CHD1 also revealed that DNA sequences within the frq promoter are methylated, and deletion of chd1 results in expansion of this methylated domain. DNA methylation of the frq locus is altered in strains bearing mutations in a variety of circadian clock genes, including frq, frh, wc-1, and the gene encoding the frq antisense transcript (qrf). Furthermore, frq methylation depends on the DNA methyltransferase, DIM-2. Phenotypic characterization of Δdim-2 strains revealed an approximate WT period length and a phase advance of approximately 2 hours, indicating that methylation plays only an ancillary role in clock-regulated gene expression. This suggests that DNA methylation, like the antisense transcript, is necessary to establish proper clock phasing but does not control overt rhythmicity. These data demonstrate that the epigenetic state of clock genes is dependent on normal regulation of clock components.PLoS Genetics 07/2011; 7(7):e1002166. · 8.69 Impact Factor
Article: Altered behavioral and metabolic circadian rhythms in mice with disrupted NAD+ oscillation.[show abstract] [hide abstract]
ABSTRACT: The Intracellular levels of nicotinamide adenine dinucleotide (NAD(+)) are rhythmic and controlled by the circadian clock. However, whether NAD(+) oscillation in turn contributes to circadian physiology is not fully understood. To address this question we analyzed mice mutated for the NAD(+) hydrolase CD38. We found that rhythmicity of NAD(+) was altered in the CD38-deficient mice. The high, chronic levels of NAD(+) results in several anomalies in circadian behavior and metabolism. CD38-null mice display a shortened period length of locomotor activity and alteration in the rest-activity rhythm. Several clock genes and, interestingly, genes involved in amino acid metabolism were deregulated in CD38-null livers. Metabolomic analysis identified alterations in the circadian levels of several amino acids, specifically tryptophan levels were reduced in the CD38-null mice at a circadian time paralleling with elevated NAD(+) levels. Thus, CD38 contributes to behavioral and metabolic circadian rhythms and altered NAD(+) levels influence the circadian clock.Aging 08/2011; 3(8):794-802. · 5.13 Impact Factor
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ABSTRACT: The circadian clock is accountable for the regulation of internal rhythms in most living organisms. It allows the anticipation of environmental changes during the day and a better adaptation of physiological processes. In mammals the main clock is located in the suprachiasmatic nucleus (SCN) and synchronizes secondary clocks throughout the body. Its molecular constituents form an intracellular network which dictates circadian time and regulates clock-controlled genes. These clock-controlled genes are involved in crucial biological processes including metabolism and cell cycle regulation. Its malfunction can lead to disruption of biological rhythms and cause severe damage to the organism. The detailed mechanisms that govern the circadian system are not yet completely understood. Mathematical models can be of great help to exploit the mechanism of the circadian circuitry. We built a mathematical model for the core clock system using available data on phases and amplitudes of clock components obtained from an extensive literature search. This model was used to answer complex questions for example: how does the degradation rate of Per affect the period of the system and what is the role of the ROR/Bmal/REV-ERB (RBR) loop? Our findings indicate that an increase in the RNA degradation rate of the clock gene Period (Per) can contribute to increase or decrease of the period--a consequence of a non-monotonic effect of Per transcript stability on the circadian period identified by our model. Furthermore, we provide theoretical evidence for a potential role of the RBR loop as an independent oscillator. We carried out overexpression experiments on members of the RBR loop which lead to loss of oscillations consistent with our predictions. These findings challenge the role of the RBR loop as a merely auxiliary loop and might change our view of the clock molecular circuitry and of the function of the nuclear receptors (REV-ERB and ROR) as a putative driving force of molecular oscillations.PLoS Computational Biology 12/2011; 7(12):e1002309. · 5.22 Impact Factor