Interlocked feedback loops contribute to the robustness of the Neurospora circadian clock

Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 07/2001; 98(13). DOI: 10.1073/pnas.121170298
Source: PubMed Central


Interlocked feedback loops may represent a common feature among the regulatory systems controlling circadian rhythms. The Neurospora circadian feedback loops involve white collar-1 (wc-1), wc-2, and frequency (frq) genes. We show that WC-1 and WC-2 proteins activate the transcription of frq gene, whereas FRQ protein plays dual roles: repressing its own transcription, probably by interacting with the WC-1/WC-2 complex, and activating the expression of both WC proteins. Thus, they form two interlocked feedback loops: one negative and one positive. We establish the physiological significance of the interlocked positive feedback loops by showing that the levels of WC-1 and WC-2 determine the robustness and stability of the clock. Our data demonstrate that with WC-1 being the limiting factor in the WC-1/WC-2 complex, the greater the levels of WC-1 and WC-2, the higher the level of the FRQ oscillation and the more robust the overt rhythms. Our data also show that, despite considerable changes in the levels of WC-1, WC-2, and FRQ, the period of the clock has been limited to a small range, suggesting that the interlocked circadian feedback loops are also important for determining the circadian period length of the clock.

Download full-text


Available from: Yuhong Yang, Sep 29, 2015
13 Reads
  • Source
    • "For example, the circadian clock network of the model fungal species Neurospora crassa is built around a central negative feedback loop augmented by an interlocking positive loop (Baker et al., 2012). It has been shown experimentally that the positive loop reduces the variability in the free-running period of the clock (Cheng et al., 2001; Smolen et al., 2001), thereby promoting its robust synchronization to the external LD cycle. Subsequent ODE modeling of the Neurospora clock has demonstrated that this interlocked feedback structure also imparts the flexibility necessary to tune the dependence of oscillator phase on both day length (Akman et al., 2008) and ambient temperature (Akman et al., 2010b), yielding a potentially generic mechanism by which temperature compensation can be achieved in a clock network (Akman et al., 2010b). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Rhythmic behavior is essential for plants; for example, daily (circadian) rhythms control photosynthesis and seasonal rhythms regulate their life cycle. The core of the circadian clock is a genetic network that coordinates the expression of specific clock genes in a circadian rhythm reflecting the 24-h day/night cycle. Circadian clocks exhibit stochastic noise due to the low copy numbers of clock genes and the consequent cell-to-cell variation: this intrinsic noise plays a major role in circadian clocks by inducing more robust oscillatory behavior. Another source of noise is the environment, which causes variation in temperature and light intensity: this extrinsic noise is part of the requirement for the structural complexity of clock networks. Advances in experimental techniques now permit single-cell measurements and the development of single-cell models. Here we present some modeling studies showing the importance of considering both types of noise in understanding how plants adapt to regular and irregular light variations. Stochastic models have proven useful for understanding the effect of regular variations. By contrast, the impact of irregular variations and the interaction of different noise sources are less well studied.
    Frontiers in Plant Science 10/2014; 5:564. DOI:10.3389/fpls.2014.00564 · 3.95 Impact Factor
  • Source
    • "The lag-1 + -coding region was amplified from genomic DNA of OR74A. The PCR product was cloned into pDE3dBH-qa-2 (Cheng et al. 2001) and confirmed by sequencing. The lag-1 KO (lag-1-1-2-1) (Colot et al. 2006) was crossed to his-3, A (FGSC 261, see crosses above) on cornmeal agar to obtain a homokaryotic lag-1 KO hygromycin-resistant his-3 (NCU00008-61) strain. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The biological clock affects aging through ras-1 (bd) and lag-1, and these two longevity genes together affect a clock phenotype and the clock oscillator in Neurospora crassa. Using an automated cell-counting technique for measuring conidial longevity, we show that the clock-associated genes lag-1 and ras-1 (bd) are true chronological longevity genes. For example, wild type (WT) has an estimated median life span of 24 days, while the double mutant lag-1, ras-1 (bd) has an estimated median life span of 120 days for macroconidia. We establish the biochemical function of lag-1 by complementing LAG1 and LAC1 in Saccharomyces cerevisiae with lag-1 in N. crassa. Longevity genes can affect the clock as well in that, the double mutant lag-1, ras-1 (bd) can stop the circadian rhythm in asexual reproduction (i.e., banding in race tubes) and lengthen the period of the frequency oscillator to 41 h. In contrast to the ras-1 (bd), lag-1 effects on chronological longevity, we find that this double mutant undergoes replicative senescence (i.e., the loss of replication function with time), unlike WT or the single mutants, lag-1 and ras-1 (bd). These results support the hypothesis that sphingolipid metabolism links aging and the biological clock through a common stress response
    Ecology and Evolution 09/2014; 4(17). DOI:10.1002/ece3.1202 · 2.32 Impact Factor
  • Source
    • "The wc-1 KO mutant (matA; his-3; bd; wc-1null; FGSC 3081) was a gift from J. Dunlap (Dartmouth Medical School, Hanover, NH). The WC-1 Myc strain was a wc-1 KO transformed with pDE3dBH derivative (Cheng et al., 2001) containing the entire wc-1 Myc tagged under the qa2 promoter. The WMN strain expresses a WC-1 protein truncated at the carboxy-terminus (from aa 764 to the end of the protein; Cheng et al., 2003). "
    [Show abstract] [Hide abstract]
    ABSTRACT: In Neurospora crassa and other filamentous fungi, light-dependent-specific phenomena are regulated by transcription factors WC-1 and WC-2. In addition to its transcriptional activity, WC-1 is able to directly sense light stimuli through a LOV sensor domain. Its location in the nucleus and heterodimerization with WC-2, together with the presence of a zinc-finger DNA-binding domain and an environmental sensor domain, all resemble the functional evolutionary architecture adopted by vertebrate nuclear receptors (NRs). Here we describe a scenario in which WC-1 represents a functional orthologue of NRs and acts through association with the chromatin-modifying coactivator NGF-1, which encodes a homologue of the yeast Gcn5p acetyltransferase. To support this view, we show a direct association between WC-1 and NGF-1 that depends on a WC-1 region containing a conserved functional LXXLL motif, a signature previously described as being an exclusive feature of NR/coactivator interaction. Our data suggest that a WC-1/NGF-1 complex is preassembled in the dark on light-inducible promoters and that, after exposure to light stimulation, NGF-1-associated HAT activity leads to histone H3 acetylation and transcriptional activation. Finally, we provide evidence for a NGF-1-independent acetylated form of WC-1. Overall our data indicate that Neurospora and higher eukaryotes share a common mechanism for the signal transduction of environmental stimuli.
    Molecular biology of the cell 08/2012; 23(19):3863-72. DOI:10.1091/mbc.E12-02-0142 · 4.47 Impact Factor
Show more