-
[show abstract]
[hide abstract]
ABSTRACT: Conidial separation 1 (CSP1) is a global transcription repressor. It is expressed under control of the white collar complex (WCC), the core transcription factor of the circadian clock of Neurospora. Here we report that the length of the circadian period decreases with increasing glucose concentrations in csp1 mutant strains, while the period is compensated for changes in glucose concentration in wild-type strains. Glucose stimulated CSP1 expression. Overexpression of CSP1 caused period lengthening and, eventually, complete dampening of the clock rhythm. We show that CSP1 inhibits expression of the WHITE COLLAR 1 (WC1) subunit of the WCC by repressing the wc1 promoter. Glucose-dependent repression of wc1 transcription by CSP1 compensated for the enhanced translation of WC1 at high glucose levels, resulting in glucose-independent expression of the WCC and, hence, metabolic compensation that maintained a constant circadian period. Thus, the negative feedback of CSP1 on WC1 expression constitutes a molecular pathway that coordinates energy metabolism and the circadian clock.
Genes & development 11/2012; 26(21):2435-42. · 12.08 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Timekeeping by circadian clocks relies upon precise adjustment of expression levels of clock proteins. Here we identify GLYCOGEN SYNTHASE KINASE (GSK) as a novel and critical component of the circadian clock of Neurospora crassa that regulates the abundance of its core transcription factor WHITE COLLAR COMPLEX (WCC) on a posttranscriptional level. We show that GSK specifically binds and phosphorylates both subunits of the WCC. Reduced expression of GSK promotes an increased accumulation of WC-1, the limiting factor of the WCC, causing an acceleration of the circadian clock and a shorter free-running period.
Journal of Biological Chemistry 09/2012; · 4.77 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this issue of Genes & Development, Kim and colleagues (pp. 490-502) report that the Drosophila circadian repressor dPER undergoes O-linked GlcNAcylation (O-GlcNAc). Their data show that manipulation of the relevant O-GlcNAc transferase (OGT) regulates behavioral rhythmicity by affecting the stability and nuclear translocation of dPER.
Genes & development 03/2012; 26(5):415-6. · 12.08 Impact Factor
-
Gencer Sancar,
Cigdem Sancar,
Britta Brügger,
Nati Ha,
Timo Sachsenheimer,
Elan Gin,
Simon Wdowik,
Ingrid Lohmann,
Felix Wieland,
Thomas Höfer,
Axel Diernfellner, Michael Brunner
[show abstract]
[hide abstract]
ABSTRACT: The white-collar complex (WCC), the core transcription factor of the circadian clock of Neurospora, activates morning-specific expression of the transcription repressor CSP1. Newly synthesized CSP1 exists in a transient complex with the corepressor RCM1/RCO1 and the ubiquitin ligase UBR1. CSP1 is rapidly hyperphosphorylated and degraded via UBR1 and its ubiquitin conjugase RAD6. Genes controlled by CSP1 are rhythmically expressed and peak in the evening (i.e., in antiphase to morning-specific genes directly controlled by WCC). Rhythmic expression of these second-tier genes depends crucially on phosphorylation and rapid turnover of CSP1, which ensures tight coupling of CSP1 abundance and function to the circadian activity of WCC. Negative feedback of CSP1 on its own transcription buffers the amplitude of CSP1-dependent oscillations against fluctuations of WCC activity. CSP1 predominantly regulates genes involved in metabolism. It controls ergosterol synthesis and fatty acid desaturases and thereby modulates the lipid composition of membranes.
Molecular cell 12/2011; 44(5):687-97. · 14.61 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In the course of a day, the Neurospora clock protein FREQUENCY (FRQ) is progressively phosphorylated at up to 113 sites and eventually degraded. Phosphorylation and degradation are crucial for circadian time keeping, but it is not known how phosphorylation of a large number of sites correlates with circadian degradation of FRQ. We show that two amphipathic motifs in FRQ interact over a long distance, bringing the positively charged N-terminal portion in spatial proximity to the negatively charged middle and C-terminal portion of FRQ. The interaction is essential for the recruitment of casein kinase 1a (CK1a) into a stable complex with FRQ. FRQ-bound CK1a progressively phosphorylates the positively charged N-terminal domain of FRQ at up to 46 nonconsensus sites, triggering a conformational change, presumably by electrostatic repulsion, that commits the protein for degradation via the PEST1 signal in the negatively charged central portion of FRQ.
Molecular cell 09/2011; 43(5):713-22. · 14.61 Impact Factor
-
FEBS letters 05/2011; 585(10):1383. · 3.54 Impact Factor
-
Kristina M Smith,
Gencer Sancar,
Rigzin Dekhang,
Christopher M Sullivan,
Shaojie Li,
Andrew G Tag,
Cigdem Sancar,
Erin L Bredeweg,
Henry D Priest,
Ryan F McCormick,
Terry L Thomas,
James C Carrington,
Jason E Stajich,
Deborah Bell-Pedersen, Michael Brunner,
Michael Freitag
[show abstract]
[hide abstract]
ABSTRACT: Light signaling pathways and circadian clocks are inextricably linked and have profound effects on behavior in most organisms. Here, we used chromatin immunoprecipitation (ChIP) sequencing to uncover direct targets of the Neurospora crassa circadian regulator White Collar Complex (WCC). The WCC is a blue-light receptor and the key transcription factor of the circadian oscillator. It controls a transcriptional network that regulates ∼20% of all genes, generating daily rhythms and responses to light. We found that in response to light, WCC binds to hundreds of genomic regions, including the promoters of previously identified clock- and light-regulated genes. We show that WCC directly controls the expression of 24 transcription factor genes, including the clock-controlled adv-1 gene, which controls a circadian output pathway required for daily rhythms in development. Our findings provide links between the key circadian activator and effectors in downstream regulatory pathways.
Eukaryotic Cell 10/2010; 9(10):1549-56. · 3.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Light responses and photoadaptation of Neurospora depend on the photosensory light-oxygen-voltage (LOV) domains of the circadian transcription factor White Collar Complex (WCC) and its negative regulator VIVID (VVD). We found that light triggers LOV-mediated dimerization of the WCC. The activated WCC induces expression of VVD, which then disrupts and inactivates the WCC homodimers by the competitive formation of WCC-VVD heterodimers, leading to photoadaptation. During the day, expression levels of VVD correlate with light intensity, allowing photoadaptation over several orders of magnitude. At night, previously synthesized VVD serves as a molecular memory of the brightness of the preceding day and suppresses responses to light cues of lower intensity. We show that VVD is essential to discriminate between day and night, even in naturally ambiguous photoperiods with moonlight.
Cell 09/2010; 142(5):762-72. · 32.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The Neurospora clock protein FREQUENCY (FRQ) is an essential regulator of the circadian transcription factor WHITE COLLAR COMPLEX (WCC). In the course of a circadian period, the subcellular distribution of FRQ shifts from mainly nuclear to mainly cytosolic. This shift is crucial for coordinating the negative and positive limbs of the clock. We show that the subcellular redistribution of FRQ on a circadian time scale is governed by rapid, noncircadian cycles of nuclear import and export. The rate of nuclear import of newly synthesized FRQ is progressively reduced in a phosphorylation-dependent manner, leading to an increase in the steady-state level of cytoplasmic FRQ. The long-period frq(7) mutant displays reduced kinetics of FRQ(7) protein phosphorylation and a prolonged accumulation in the nucleus. We present a mathematical model that describes the cytoplasmic accumulation of wild-type and mutant FRQ on a circadian time scale on the basis of frequency-modulated rapid nucleocytoplasmic shuttling cycles.
Genes & development 09/2009; 23(18):2192-200. · 12.08 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Posttranslational modifications, particularly phosphorylation, regulate activity, stability and localization of proteins in circadian clocks, thereby contributing to a stable oscillation with a period of approximately 24h. The White Collar Complex (WCC) is the central transcription factor of the circadian clock of Neurospora crassa. Its activity is regulated in a circadian manner by rhythmic phosphorylation, mediated by the clock protein Frequency (FRQ). Here we present purification of TAP-tagged WCC and identification of novel phosphorylation sites of WC-1 and WC-2, all of which appear to be proline directed. Exchange of a single WC-2 serine residue (S433) to alanine or aspartate affects WCC-dependent transcription and circadian period, suggesting an important role of WC-2 S433 phosphorylation for WCC activity and circadian timing.
FEBS letters 06/2009; 583(12):1833-40. · 3.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The Neurospora clock protein FREQUENCY (FRQ) inhibits its transcriptional activator WHITE COLLAR COMPLEX (WCC) in a negative feedback loop and supports its accumulation in a positive loop. We show that positive feedback is a delayed effect of negative feedback underlying the same post-translational mechanisms: DNA-binding-competent active WCC commits rapidly to degradation. FRQ-dependent phosphorylation of WCC, which interferes with DNA binding (negative feedback), leads to reduced turnover and slow accumulation of newly expressed WCC (positive feedback). When DNA binding of WCC is compromised by mutation, its accumulation is independent of FRQ. Cycles of FRQ-dependent inactivation and PP2A-dependent reactivation of WCC occur in the minute range and are coupled to obligate rapid cycles of nucleo-cytoplasmic shuttling. WCC shuttling and activity cycles are modulated by FRQ in circadian fashion.
Genes & Development 01/2009; 22(24):3397-402. · 11.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: FREQUENCY (FRQ) and the White Collar Complex (WCC), consisting of WC1 and WC2 subunits, are crucial components of positive and negative feedback loops of the circadian clock of Neurospora. In the positive limb, FRQ supports the accumulation of WC1 on a post-translational level and activates transcription of wc2. We analysed the transcriptional regulation of wc2. The WCC indirectly inhibits wc2 by controlling expression of a putative repressor. FRQ activates wc2 transcription by inhibiting WCC. A putative transcriptional activator binds to the wc2 promoter and antagonizes the repressor function. Furthermore, an internal promoter in the wc2 coding region drives expression of an amino-terminally shortened isoform, sWC2. Full-length WC2 and sWC2 are expressed in an antagonistic manner; thus, sWC2 expression seems to be a fail-safe mechanism that maintains total WC2 levels above a threshold.
EMBO Reports 07/2008; 9(8):788-94. · 7.36 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new finding opens up speculation that the molecular mechanism of circadian clocks in Synechococcus elongatus is composed of multiple oscillator systems (Kitayama and colleagues, this issue, pp. 1513-1521), as has been described in many eukaryotic clock model systems. However, an alternative intepretation is that the pacemaker mechanism-as previously suggested-lies primarily in the rate of ATP hydrolysis by the clock protein KaiC.
Genes & Development 06/2008; 22(11):1422-6. · 11.66 Impact Factor
-
Genes & Development 05/2008; 22(7):825-31. · 11.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Circadian clocks drive daily rhythms in physiology and behaviour, and thus allow organisms to better adapt to rhythmic changes in the environment. Circadian oscillators are cell-autonomous systems, which generate via transcriptional, post-transcriptional, translational and post-translational control mechanisms a daily activity-rhythm of a circadian transcription factor complex. According to recent models, this complex of transcription factors controls directly or indirectly expression of a large number of genes, and thus generates the potential to modulate physiological processes in a rhythmic fashion. The basic principles of the generation of circadian oscillation are similar in all eukaryotic systems. The circadian clock of the filamentous fungus Neurospora crassa is well characterized at the molecular level. Focusing on the molecular properties, interactions and post-translational modifications of the core Neurospora clock proteins WHITE COLLAR-1, WHITE COLLAR-2, FREQUENCY and VIVID, this review summarizes our knowledge of the molecular basis of circadian time keeping in Neurospora. Moreover, we discuss the mechanisms by which environmental cues like light and temperature entrain and reset this circadian system.
Molecular Microbiology 05/2008; 68(2):255-62. · 5.01 Impact Factor
-
03/2008; , ISBN: 9783527610754
-
01/2008: pages 987 - 1019; , ISBN: 9783527619498
-
[show abstract]
[hide abstract]
ABSTRACT: The large (l) and small (s) isoforms of FREQUENCY (FRQ) are elements of interconnected feedback loops of the Neurospora circadian clock. The expression ratio of l-FRQ vs. s-FRQ is regulated by thermosensitive splicing of an intron containing the initiation codon for l-FRQ. We show that this splicing is dependent on light and temperature and displays a circadian rhythm. Strains expressing only l-FRQ or s-FRQ support short and long temperature-compensated circadian rhythms, respectively. The thermosensitive expression ratio of FRQ isoforms influences period length in wt. Our data indicate that differential expression of FRQ isoforms is not required for temperature compensation but rather provides a means to fine-tune period length in response to ambient temperature.
FEBS Letters 01/2008; 581(30):5759-64. · 3.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Circadian clocks are self-sustained oscillators modulating rhythmic transcription of large numbers of genes. Clock-controlled gene expression manifests in circadian rhythmicity of many physiological and behavioral functions. In eukaryotes, expression of core clock components is organized in a network of interconnected positive and negative feedback loops. This network is thought to constitute the pacemaker that generates circadian rhythmicity. The network of interconnected loops is embedded in a supra-net via a large number of interacting factors that affect expression and function of core clock components on transcriptional and post-transcriptional levels. In particular, phosphorylation and dephosphorylation of clock components are critical processes ensuring robust self-sustained circadian rhythmicity and entrainment of clocks to external cues. In cyanobacteria, three clock proteins have the capacity to generate a self-sustained circadian rhythm of autophosphorylation and dephosphorylation independent of transcription and translation. This phosphorylation rhythm regulates the function of these clock components, which then facilitate rhythmic gene transcription, including negative feedback on their own genes. In this article, we briefly present the mechanism of clock function in cyanobacteria. We then discuss in detail the contribution of transcriptional feedback and protein phosphorylation to various functional aspects of the circadian clock of Neurospora crassa.
Genes & Development 06/2006; 20(9):1061-74. · 11.66 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Frequency (FRQ) is a central component of interconnected negative and positive limbs of feedback loops of the circadian clock of Neurospora. In the negative limb, FRQ inhibits its transcriptional activator White Collar Complex (WCC) and in the positive limb, FRQ supports accumulation of WCC. We show that these conflicting functions are confined to distinct subcellular compartments and coordinated in temporal fashion. Inactivation of the transcriptional activator WCC requires nuclear FRQ and occurs early after the onset of FRQ expression. Support of WCC accumulation requires cytosolic FRQ and occurs on a post-translational level, when high amounts of FRQ have accumulated. The transcriptional function of FRQ in the negative loop and its post-translational function in the positive loop are independent and associated with distinct regions of FRQ. Phosphorylation of FRQ at the PEST-2 region triggers its maturation from a nuclear repressor toward a cytoplasmic activator.
Genes & Development 03/2006; 20(3):297-306. · 11.66 Impact Factor
