Biomedical subjects

C Heintzen

Publications and source records attributed to C Heintzen.

9 recordsLinked to original sources

PubMed2005

Synchronizing the Neurospora crassa circadian clock with the rhythmic environment.

The metronomic predictability of the environment has elicited strong selection pressures for the evolution of endogenous circadian clocks. Circadian clocks drive molecular and behavioural rhythms that approximate the 24 h periodicity of our environment. Found almost ubiquitously among phyla, circadian clocks allow preadaptation to rhythms concomitant with the natural cycles of the Earth. Cycles in light intensity and temperature for example act as important cues that couple circadian clocks to the environment via a process called entrainment. This review summarizes our current understanding of the general and molecular principles of entrainment in the model organism Neurospora crassa, a simple eukaryote that has one of the best-studied circadian systems and light-signalling pathways.

Biological Clocks↗

PubMed2001

The PAS protein VIVID defines a clock-associated feedback loop that represses light input, modulates gating, and regulates clock resetting.

vvd, a gene regulating light responses in Neurospora, encodes a novel member of the PAS/LOV protein superfamily. VVD defines a circadian clock-associated autoregulatory feedback loop that influences light resetting, modulates circadian gating of input by connecting output and input, and regulates light adaptation. Rapidly light induced, vvd is an early repressor of light-regulated processes. Further, vvd is clock controlled; the clock gates light induction of vvd and the clock gene frq so identical signals yield greater induction in the morning. Mutation of vvd severely dampens gating, especially of frq, consistent with VVD modulating gating and phasing light-resetting responses. vvd null strains display distinct alterations in the phase-response curve to light. Thus VVD, although not part of the clock, contributes significantly to regulation within the Neurospora circadian system.

Amino Acid Sequence↗

PubMed2001

Coiled-coil domain-mediated FRQ-FRQ interaction is essential for its circadian clock function in Neurospora.

The frequency (frq) gene, the central component of the frq-based circadian negative feedback loop, regulates various aspects of the circadian clock in NEUROSPORA: However, the biochemical function of its protein products, FRQ, is poorly understood. In this study, we demonstrated that the most conserved region of FRQ forms a coiled-coil domain. FRQ interacts with itself in vivo, and the deletion of the coiled-coil region results in loss of the interaction. Point mutations, which are designed to disrupt the coiled-coil structure, weaken or completely abolish the FRQ self-association and lead to the arrhythmicity of the overt rhythm. Mutations of the FRQ coiled-coil that inhibit self-association also prevent its interaction with two other key components of the NEUROSPORA: circadian clock, namely WC-1 and WC-2, the two PAS domain-containing transcription factors. Taken together, these data strongly suggest that the formation of the FRQ-FRQ and FRQ-WC complexes is essential for the function of the NEUROSPORA: clock.

Amino Acid Sequence↗

PubMed1999

Regulation of clock genes.

A recent explosion in the identification of new clock components in cyanobacteria, fungi, insects, mammals as well as potential candidates in plants has uncovered common themes among the structure, function and regulation of these components. Positive and negative interactions that are organized in negative feedback loops have been found crucial for clock function. Both transcriptional and posttranscriptional mechanisms appear to be important for circadian rhythm generation in all of these organisms.

Animals↗

PubMed1999

The circadian system of Arabidopsis thaliana: forward and reverse genetic approaches.

It is now widely accepted that autoregulatory circuits involving transcription/translation of clock genes form the molecular basis of the endogenous circadian clock in different organisms. In Arabidopsis thaliana, the RNA-binding protein AtGRP7 (Arabidopsis thaliana glycine-rich protein) has been identified as part of a negative-feedback loop through which AtGRP7 regulates the circadian oscillations of its own transcript. Experimental evidence indicates that this feedback loop also is influenced by another oscillator. Support for this hypothesis comes from the characterization of the clock mutant toc1 (timing of cab expression) and the recent isolation of two candidate clock molecules, LHY (late elongated hypocotyl) and CCA1 (circadian clock associated). TOC1, as well as the LHY and CCA1 oscillatory feedback loops, influence several rhythmic physiological and molecular processes in Arabidopsis, including cyclic Atgrp7 gene expression. We discuss the features of these feedback loops with relation to the organization of the circadian system in Arabidopsis.

Arabidopsis↗

PubMed1997

AtGRP7, a nuclear RNA-binding protein as a component of a circadian-regulated negative feedback loop in Arabidopsis thaliana.

The endogenous clock that drives circadian rhythms is thought to communicate temporal information within the cell via cycling downstream transcripts. A transcript encoding a glycine-rich RNA-binding protein, Atgrp7, in Arabidopsis thaliana undergoes circadian oscillations with peak levels in the evening. The AtGRP7 protein also cycles with a time delay so that Atgrp7 transcript levels decline when the AtGRP7 protein accumulates to high levels. After AtGRP7 protein concentration has fallen to trough levels, Atgrp7 transcript starts to reaccumulate. Overexpression of AtGRP7 in transgenic Arabidopsis plants severely depresses cycling of the endogenous Atgrp7 transcript. These data establish both transcript and protein as components of a negative feedback circuit capable of generating a stable oscillation. AtGRP7 overexpression also depresses the oscillation of the circadian-regulated transcript encoding the related RNA-binding protein AtGRP8 but does not affect the oscillation of transcripts such as cab or catalase mRNAs. We propose that the AtGRP7 autoregulatory loop represents a "slave" oscillator in Arabidopsis that receives temporal information from a central "master" oscillator, conserves the rhythmicity by negative feedback, and transduces it to the output pathway by regulating a subset of clock-controlled transcripts.

Arabidopsis↗

PubMed1994

A light- and temperature-entrained circadian clock controls expression of transcripts encoding nuclear proteins with homology to RNA-binding proteins in meristematic tissue.

To investigate physiological processes generated by endogenous circadian rhythms on the molecular level, we have identified clock-controlled genes in the long-day plant Sinapis alba L. A cDNA library was differentially screened using cDNA probes representing transcripts expressed at either the middle of the light period or the middle of the dark period. Two closely related groups of transcripts, Sagrp1 and Sagrp2, controlled by a circadian rhythm have been isolated. RNA blot analysis verified that transcript levels oscillate in plants grown in light/dark cycles with maxima between 'Zeitgeber' time (zt)8 and zt12 (8-12 h after onset of illumination) and minima around zt20. Steady-state mRNA levels continue to oscillate in plants shifted from light/dark cycles to constant light. No synchronous mRNA oscillations are found in plants grown from seed in constant light at constant temperature, suggesting that the clock has to be entrained initially. In contrast, when plants grown in constant light are exposed to rhythmic temperature shifts oscillations of steady-state Sagrp mRNA levels are induced, indicating that temperature acts as an alternative external stimulus (zeitgeber) other than light to entrain the oscillator. In situ hybridization reveals that both transcript groups are expressed predominantly in meristematic and growing tissue. Strong expression is observed in the leaf primordia of the shoot apex, the procambial strands, cambium and in all cell layers of young leaves around zt12. In contrast, little or no signal is found on tissue sections isolated at zt20. This indicates that the oscillator(s) regulating Sagrp transcript fluctuations operate(s) synchronously in different organs. For both transcript groups cDNAs were isolated corresponding to unspliced pre-mRNAs or to transcripts generated by the use of a second 5' splice site. The cDNAs corresponding to the fully spliced transcripts contain open reading frames for polypeptides of 16 kDa, each containing a putative N-terminal RNA recognition motif and a C-terminal region rich in glycine. The predicted proteins show strong homology to an ABA-inducible glycine-rich protein from maize embryos and to the mammalian RNA-binding protein A1 of the heterogeneous nuclear ribonucleoprotein complex involved in pre-mRNA splicing. The SaGRP protein fluctuates with a very low amplitude over light/dark cycles. Immunogold labeling demonstrates the presence of the SaGRP protein within the nucleus of the investigated meristematic cells of young leaves.

Amino Acid Sequence↗

PubMed1994

Circadian oscillations of a transcript encoding a germin-like protein that is associated with cell walls in young leaves of the long-day plant Sinapis alba L.

As part of an attempt to analyze rhythmic phenomena in the long-day plant Sinapis alba L. at the molecular level, we have searched for mRNAs whose concentration varies as a function of time of day. Differential screening of a cDNA library established from mRNAs expressed at the end of the daily light phase with probes representing transcripts expressed predominantly in the morning or evening has identified one major transcript. The cDNA, Saglp, encodes a predicted 22-kD protein with an N-terminal signal sequence. The protein shows homology to germin, a protein expressed in wheat embryos after onset of germination. The Saglp mRNA level undergoes circadian oscillations in light/dark cycles with maxima between 8 and 12 PM (zeitgeber time [zt]12-zt16) and minima around 8 PM (zt0). In plants grown from seed in constant light, transcript levels are constitutive. In constant light regular temperature shifts function as an alternative "zeitgeber" to initiate Saglp transcript oscillations. At the cellular level, Saglp transcripts are expressed in the epidermis and spongy parenchyma of young leaves, and in distinct regions of the epidermis and the cortex in stems and petioles. Strong signals are observed in these tissues around zt12, whereas little expression is found around zt20, suggesting that the underlying oscillatory mechanism(s) operate(s) synchronously in different plant organs. The SaGLP steady-state protein concentration remains constant over light/dark cycles. Immunogold labeling shows that the SaGLP protein is associated with primary cell walls.

Amino Acid Sequence↗

PubMed1993

A methyl jasmonate-induced shift in the length of the 5' untranslated region impairs translation of the plastid rbcL transcript in barley.

The plant growth substance (-)-jasmonic acid methyl ester (methyl jasmonate, JaMe) affects plastid gene expression at the protein and mRNA levels when applied exogenously to detached leaf segments of Hordeum vulgare L. cv. Salome. Translation of the large subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (LSU, rbcL gene products) and of the 65 and 68 kDa proteins of photosystem I (psaA and psaB gene products, respectively) ceased, whereas synthesis of the 32 kDa photosystem II protein (D1, psbA gene product) continued in JaMe-treated leaf tissues. These changes were not caused by corresponding alterations in transcript abundances. The loss of LSU protein synthesis, occurring within 24 h of JaMe treatment, correlated with a decline in the in vitro-translatable rbcL mRNA, but contrasted with an almost constant transcript level. The 5' ends of the rbcL transcripts shifted from '-59' in freshly harvested or water-treated leaves to '-94' in JaMe-treated leaf tissues. Transcripts ending at these positions presumably arise from alternative processing of the primary transcript ending at position '-316'. The '-94' transcript contains, within the 5' untranslated region, a 35-base motif with remarkable complementarity to the extreme 3' terminal part of the 16S rRNA, involved in intramolecular base pairing within the ribosome and can associate with 30S but not 70S complexes in organello, suggesting that intermolecular base pairing impairs translation initiation, probably by competing for ribosome binding at the Shine-Dalgarno sequence. In contrast, transcripts ending at '-59' lack the 5' terminal 'extra' sequence and are active in terms of translation initiation.

Acetates↗