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At least 109 records · Page 6Linked to original sources
PubMed2001

Light-dependent induction of cFos during subjective day and night in PACAP-containing ganglion cells of the retinohypothalamic tract.

Environmental light stimulation via the retinohypothalamic tract (RHT) is necessary for stable entrainment of circadian rhythms generated in the suprachiasmatic nucleus (SCN). In the current report, the authors characterized the functional activity and phenotype of retinal ganglion cells that give rise to the RHT of the rat. Retinal ganglion cells that give rise to the RHT were identified by transsynaptic passage of an attenuated alpha herpesvirus known to have selective affinity for this pathway. Dual labeling immunocytochemistry demonstrated co-localization of viral antigen and pituitary adenylate cyclase activating polypeptide (PACAP) in retinal ganglion cells. This was confirmed using the anterograde tracer cholera toxin subunit B (ChB). In normal and retinally degenerated monosodium glutamate (MSG)-treated rats, ChB co-localized with PACAP in axons of the retinorecipient zone of the SCN. Light-induced Fos-immunoreactivity (Fos-IR) was apparent in all PACAP-containing retinal ganglion cells and a population of non-PACAP-containing retinal ganglion cells at dawn of normal and MSG-treated animals. Within the next 3 h, Fos disappeared in all non-PACAP-immunoreactive cells but persisted in all PACAP-containing retinal ganglion cells until dusk. When animals were exposed to constant light, Fos-IR was sustained only in the PACAP-immunoreactive (PACAP-IR) retinal ganglion cells. Darkness eliminated Fos-IR in all PACAP-IR retinal ganglion cells, demonstrating that the induction of Fos gene expression was light dependent. When animals were maintained in constant darkness and exposed to light pulses at ZT 14, ZT 19, or ZT 6, Fos-IR was induced in PACAP-IR retinal ganglion cells in a pattern similar to that seen at dawn. Collectively, these data indicate that PACAP is present in ganglion cells that give rise to the RHT and suggest a role for this peptide in the light entrainment of the clock.

Animals↗
PubMed2001

Dissection of the light signal transduction pathways regulating the two early light-induced protein genes in Arabidopsis.

The expression of light-regulated genes in plants is controlled by different classes of photoreceptors that act through a variety of signaling molecules. During photomorphogenesis, the early light-induced protein (Elip) genes are among the first to be induced. To understand the light signal transduction pathways that regulate Elip expression, the two Elip genes, Elip1 and Elip2, in Arabidopsis were studied, taking advantage of the genetic tools available for studying light signaling in Arabidopsis. Using two independent quantitative reverse transcriptase-PCR techniques, we found that red, far-red, and blue lights positively regulate expression of the Elip genes. Phytochrome A and phytochrome B are involved in this signaling. The cryptochrome or phototropin photoreceptors are not required for blue-light induction of either Elip gene, suggesting the involvement of an additional, unidentified, blue-light receptor. Although the COP9 signalosome, a downstream regulator, is involved in dark repression of both Elips, Elip1 and Elip2 show different expression patterns in the dark. The transcription factor HY5 promotes the light induction of Elip1, but not Elip2. A defect in photosystem II activity in greening of hy5 seedlings may result from the loss of Elip1. Heat shock positively controlled Elip1 and Elip2 in a light-independent fashion. This induction is independent of HY5, indicating that heat shock and light activate transcription of the Elip genes through independent pathways.

Arabidopsis↗
PubMed2003

cGMP-dependent protein kinase II modulates mPer1 and mPer2 gene induction and influences phase shifts of the circadian clock.

BACKGROUND: In mammals, the master circadian clock that drives many biochemical, physiological, and behavioral rhythms is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Generation and maintenance of circadian rhythmicity rely on complex interlocked transcriptional/translational feedback loops involving a set of clock genes. Among the molecular components driving the mammalian circadian clock are the Period 1 and 2 (mPer1 and mPer2) genes. Because the periodicity of the clock is not exactly 24 hr, it has to be adjusted periodically. The major stimulus for adjustment (resetting) of the clock is nocturnal light. It evokes activation of signaling pathways in the SCN that ultimately lead to expression of mPer1 and mPer2 genes conveying adjustment of the clock. RESULTS: We show that mice deficient in cGMP-dependent protein kinase II (cGKII, also known as PKGII), despite regular retinal function, are defective in resetting the circadian clock, as assessed by changes in the onset of wheel running activity after a light pulse. At the molecular level, light induction of mPer2 in the SCN is strongly reduced in the early period of the night, whereas mPer1 induction is elevated in cGKII-deficient mice. Additionally, we show that light induction of cfos and light-dependent phosphorylation of CREB at serine 133 are not affected in these animals. CONCLUSIONS: cGKII plays a role in the clock-resetting mechanism. In particular, the ability to delay clock phase is affected in cGKII-deficient mice. It seems that the signaling pathway involving cGKII influences in an opposite manner the light-induced induction of mPer1 and mPer2 genes and thereby influences the direction of a phase shift of the circadian clock.

Animals↗
PubMed2002

Per and neuropeptide expression in the rat suprachiasmatic nuclei: compartmentalization and differential cellular induction by light.

Per1 and Per2, two clock genes rhythmically expressed in the suprachiasmatic nucleus (SCN), are implicated in the molecular mechanism of the circadian pacemaker and play a major role in its entrainment by light. To date, it is not known if every cell of the SCN, a heterogeneous structure in respect of neuropeptide content, expresses clock genes equally. The aim of this study was to identify, by single and double non-radioactive and/or radioactive hybridizations, the cell types (AVP, VIP and GRP) expressing Per1 or Per2 in the SCN of rats, (1) when Per are highly expressed during the daytime, and (2) after induction of Per expression by a light pulse at night. Our results indicate that, during the daytime, Per1 and Per2 genes are both mainly expressed in the AVP cells of the dorso-median part of the SCN, whereas only a few VIP cells in the ventral part of the SCN exhibit Per gene expression. In contrast, following a light pulse at night, there is differential induction of the two Per genes. Per1 expression essentially occurs in the ventro-lateral GRP cells, while Per2 expression is not restricted to the retinorecipient part of the SCN as it also occurs in AVP cells. Altogether, our results suggest that Per1 and Per2 are mainly expressed in AVP cells during the daytime and suggest that GRP cells play an important role in resetting of the clock by light.

Animals↗
PubMedDate not supplied

[Kinetic model of primary processes of photosynthesis in chloroplasts. Fast phase of chlorophyll fluorescence induction under light of various intensity].

A kinetic model was developed, which describing the system of generation and consumption of the transmembrane electrochemical proton potential delta mu H+ in primary photosynthetic processes. The model describes the catalytic cycles of photosystems I and II and the cytochrome b/f complex, as well as the ATP synthesis and passive leakage of H+, K+ [symbol: see text] Cl- ions through the thylakoid membrane. The dependence of the electron transfer rates on the value of transmembrane electric potential was taken into account. The model was applied to describe the experimental data on the registration of the fast phase of fluorescence induction. The model gives a realistic description of the fast phase of induction curves at different light intensities (from high to low).

Adenosine Triphosphate↗
PubMed1994

Ontogeny of light-induced Fos-like immunoreactivity in the hamster suprachiasmatic nucleus.

Light induction of Fos within the Syrian hamster suprachiasmatic nucleus (SCN) occurred first at postnatal day 4. The number of cells with light-induced Fos-like immunoreactivity (Fos-LI) per unit volume of SCN increased with age. Blinding experiments were used to demonstrate that the eye, though possessing an immature retina, appears to be necessary for light induction of Fos. In neonatal hamsters, environmental cycles (e.g., light and darkness) may be able to reinforce the effect of maternal melatonin in synchronizing the pup's clock.

Aging↗
PubMed1995

Isolation of Arabidopsis mutants altered in the light-regulation of chalcone synthase gene expression using a transgenic screening approach.

Transgenic Arabidopsis expressing beta-glucuronidase (GUS) driven by a chalcone synthase gene (CHS) promoter were produced. GUS activity in the leaves increased with increasing fluence rates of white light in parallel with endogenous CHS transcript levels. An isogenic line homozygous for the transgene was obtained and mutagenized seedlings of this line were screened for altered light-induction of the transgene. Putative mutants with low GUS activity were not altered in the light-induction of endogenous CHS transcripts and are therefore not regulatory mutants. Two mutant lines (A12 and C10) with elevated levels of GUS activity in the light show a corresponding increase in CHS transcript levels. The A12 mutant was focussed upon and designated icx1 (increased chalcone synthase expression). This mutant has enhanced light-stimulation of CHS expression since CHS transcript levels in darkness in icx1 are very low, as in the wild-type. The transcript levels of two other genes involved in flavonoid biosynthesis are elevated in the light in icx1 as is anthocyanin formation. However, there is no alteration in LHCII chlorophyll a/b-binding protein gene (CAB) transcript levels under the same conditions. The altered gene expression phenotype of icx1 co-segregates with several other phenotypic characteristics, including fewer leaf trichomes and alterations to the seed coat. On the basis of these data and comparison with the Arabidopsis ttg (transparent testa glabra) mutant, it is suggested that the ICX1 gene product may be concerned both with the light-regulation of gene expression and with developmental processes occurring in the epidermis.

Acyltransferases↗
PubMed1994

Light-dependent induction of early-response gene expression by calphostin-C.

Calphostin-C is a compound possessing the ability to inhibit protein kinase C (PKC) by oxidative modification in vitro and to enhance the epidermal growth factor (EGF) receptor phosphorylation in vivo in a light-dependent manner. Here, we found that calphostin-C induced c-fos and c-jun mRNA accumulation in the lung adenocarcinoma cell line A549 in a light-dependent manner. Nuclear run-on assay revealed that this mRNA accumulation took place at the transcription level. However, unlike in vitro, calphostin-C did not inhibit cytosolic PKC activity in vivo, and the gene expression induced by calphostin-C was inhibited by another PKC inhibitor, staurosporine. Thus, it was suggested that calphostin-C activates cytosolic PKC-dependent signaling pathway to the induction of "early-response gene" expression in a light-dependent manner.

Adenocarcinoma↗
PubMed1993

Light-induced phase shifts and Fos expression in the hamster circadian system: the effects of anesthetics.

In the present study, we examined the effect of administration of anesthetics on light-induced phase shifts of the circadian system. This information is of critical importance, because many studies of light input to the mammalian suprachiasmatic nucleus (SCN) have been performed on anesthetized animals. We found that light-induced phase shifts were blocked by all drugs used at anesthetic doses. We then determined the effect of two of these agents on light induction of Fos-like immunoreactivity in the SCN. We found that the administration of sodium pentobarbital prevented light induction of Fos expression in the SCN, whereas the administration of urethane did not. These results raise cautions about the use of anesthetized animals to answer questions about the photic regulation of neuronal activity in the SCN.

Animals↗
PubMed2003

Expression and regulation of the crucial plant-like ferredoxin of cyanobacteria.

The Synechocystis fedI gene (petF, ssl0020) was found to be strongly expressed under the negative control of H2O2 or heavy metals, and the positive control of light fluence (regulation dependent on active photosynthesis) or carbon availability [under the control of NdhR, the regulator of the ndh3 operon encoding NAD(P)H dehydrogenase subunits]. The basic and constitutive promoter (BP) of fedI extending from -62 to +25 (relative to the transcription start point) is weakly active, presumably because it harbours a long (30 bp) spacer between the two crucial motifs: the -10 box (5'-TAgtAT-3', -13 to -8) and the '-35' box (5'-TTGctA-3', -49 to -44). BP strength is strongly enhanced by the two upstream regions, -113 to -82 and -151 to -114, mediating the 30-fold constitutive stimulation and the fourfold light activation respectively. Three well-conserved transcriptional elements were characterized for the first time, namely the -19 box (5'-TTTT-3') that is essential to transcription, and the two twice repeated elements that are both critical to light induction: the TTGyCA-3' box (-35 to -30, and -125 to -120) and the 5'-ATTTyA-3' box (-55 to -50, and -134 to -129). That two of these light induction motifs (5'-TTGtCA-3', -35 to -30; 5'-ATTTcA-3', -55 to -50) occur in the constitutive BP promoter indicate that in the fedI gene light activation and transcription per se are closely interacting. Interestingly, the fedI gene from marine strains was found to lack the three transcriptional elements presently described, as well as the 5'-AGGA-3' Shine-Dalgarno sequence, which are all conserved among the fedI from non-marine strains.

Bacterial Proteins↗
PubMed1994

Characterization of cis-acting elements in light regulation of the nuclear gene encoding the A subunit of chloroplast isozymes of glyceraldehyde-3-phosphate dehydrogenase from Arabidopsis thaliana.

We have characterized cis-acting elements involved in light regulation of the nuclear gene (GapA) encoding the A subunit of chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in Arabidopsis thaliana. Our results show that a 1.1-kb promoter fragment of the GapA gene is sufficient to confer light inducibility and organ specificity in transgenic Nicotiana tabacum (tobacco) plants, using the beta-glucuronidase gene of Escherichia coli as the reporter gene. Deletion analysis indicates that the -359 to -110 bp region of the GapA gene is necessary for light responsiveness. Within this region there are three copies of a decamer repeat (termed the Gap box) having the consensus sequence 5'-CAAATGAA(A/G)A-3', which has not been characterized in the promoter regions of other light-regulated genes. A deletion (to -247) producing loss of one copy of these elements from the GapA promoter reduces light induction by two- to threefold compared with a promoter deletion (to -359) with all three Gap boxes present, while deletion of all three Gap boxes (to -110) abolishes light induction completely. Gel mobility shift experiments using tobacco nuclei as the source of nuclear proteins show that GapA promoter fragments that contain these repeats bind strongly to a factor in the nuclear extract and that binding can be abolished by synthetic competitors consisting only of a monomer or dimer of the Gap box. Furthermore, a trimer, dimer, and monomer of the Gap box show binding activity and, like the authentic GapA promoter-derived probes, show binding activities that are correlated with Gap box copy number. These results strongly suggest that these repeats play important roles in light regulation of the GapA gene of A. thaliana.

Arabidopsis↗
PubMed2001

Perceptual continuation and depth in visual phantoms can be explained by perceptual transparency.

We try to explain perceptual continuation and depth in the visual-phantom illusion in terms of perceptual transparency. Perceptual continuation of inducing gratings across the occluder in stationary phantoms could be explained with unique transparency, a notion proposed by Anderson (1997 Perception 26 419-453). This view is consistent with a number of previous reports including that of McCourt (1994 Vision Research 34 1609-1617) who criticized the stationary phantom illusion from the viewpoint of his counterphase lightness induction or grating induction, which might involve invalid transparency. Here we confirm that the photopic phantom illusion (Kitaoka et al, 1999 Perception 28 825-834) really gives in-phase lightness induction and involves bistable transparency. It is thus suggested that perceptual continuation and depth in the visual-phantom illusion depend on perceptual transparency.

Analysis of Variance↗
PubMed1990

Early Changes in Gene Expression during the Transition from Vegetative to Generative Growth in the Long-Day Plant Sinapis alba.

Changes in gene expression during flower formation were studied in the long-day plant Sinapis alba. The day length dependence was exploited to synchronize flower formation in a large population of mustard plants. After an inductive light treatment, apices were harvested after different lengths of time, and changes in gene expression were analyzed. Two major groups of genes were identified whose expression was affected during flower formation. Transcripts of the first group (group I) were present at low concentration in the apex of noninduced plants. They began to accumulate strongly after the end of the inductive light period. They reached a maximum 2 days to 10 days after flower induction and then declined slowly. Transcripts of the second group of genes (group II) could be detected for the first time 10 days after flower induction. Within a very short time, these transcripts accumulated dramatically and reached a maximum 15 days after flower induction before beginning to decline. They dropped beyond the limit of detection before the flower reached maturity.

Journal Article↗
PubMed1996

bli-4, a gene that is rapidly induced by blue light, encodes a novel mitochondrial, short-chain alcohol dehydrogenase-like protein in Neurospora crassa.

Blue light plays an important role in developmental control throughout nature. The bli-4 gene of Neurospora crassa, together with bli-3, al-1 and al-2, is rapidly inducible by blue light. Induction leads to a ninety-fold increase in transcription rate over the dark control level, and the gene therefore appears to be of prime importance in the blue-light induction pathway of N. crassa. We describe the sequencing and analysis of bli-4 and the 38 kDa protein it encodes. We show that the protein is very rapidly imported into the mitochondria and exhibits high homology with the family of short-chain alcohol dehydrogenases.

Alcohol Dehydrogenase↗
PubMed2002

Light-dependent induction of strongly increased microalgal growth by methanol.

Low methanol concentrations (about 0.5% v/v) induce biomass production in cultures of the unicellular green alga Scenedesmus obliquus by more than 300%, compared to controls without this solvent. This effect on the microalgal growth was found to be dependent on the solvent concentration, the packed cell volume (PCV), light intensity and light quality. It could be shown that methanol addition leads to a decrease in size of the light harvesting complex (LHC) on the basis of chlorophylls and proteins, and thus to changes in structure and functioning of the photosynthetic apparatus. These alterations lead to enhanced photosynthesis and respiration rates. The action of methanol on the photosynthetic apparatus is thus comparable to the effect of enhanced CO(2) concentrations. These findings support the previously proposed pathway for methanol metabolization with CO(2) as the final product. We conclude that the subsequent assimilation of the increased CO(2) amounts by the Calvin-Benson cycle is a possible explanation for the methanol-mediated increase in biomass production in terms of PCV. The methanol effect is observed only in the light and in the presence of a functioning photosynthetic apparatus. Preliminary action spectra suggest that the primary photoreceptor is a chlorophyll-protein complex with two absorption maxima at 680 and 430 nm, which may possibly be attributed to the reaction center of photosystem II (PSII).

Biomass↗
PubMed1996

Cis-acting elements essential for light regulation of the nuclear gene encoding the A subunit of chloroplast glyceraldehyde 3-phosphate dehydrogenase in Arabidopsis thaliana.

We report the characterization of cis-acting elements involved in light regulation of the nuclear gene (GapA) that encodes the A subunit of glyceraldehyde 3-phosphate dehydrogenase in Arabidopsis thaliana. Our previous deletion analyses indicate that the -277 to -195 upstream region of GapA is essential for light induction of the beta-glucuronidase reporter gene in transgenic tobacco (Nicotiana tabacum) plants. This region contains three direct repeats with the consensus sequence 5'-CAAATGAA(A/G)A-3' (Gap boxes). Our results show that 2-bp substitutions of the last four nucleotides (AA or GA) of the Gap boxes by CC abolish light induction of the beta-glucuronidase reporter gene in vivo and affect binding of the Gap box binding factor in vitro. We have also identified an additional cis-acting element, AE (Activation Element) box, that is involved in regulation of GapA. A combination of a Gap box trimer and an AE box dimer can confer light responsiveness of the cauliflower mosaic virus 35S promoter containing the -92 to +6 upstream sequence, whereas oligomers of Gap boxes or AE boxes alone cannot confer light responsiveness on the same promoter. These results suggest that Gap boxes and AE boxes function together as the light-responsive element of GapA.

Arabidopsis↗
PubMed1994

In vivo and in vitro characterization of the light-regulated cpcB2A2 promoter of Fremyella diplosiphon.

When exposed to different spectral qualities of light, many cyanobacteria dramatically alter their phycobilisome rod composition in a process termed complementary chromatic adaptation. In the cyanobacterium Fremyella diplosiphon, this response is associated with differential expression of the cpcB2A2, cpeBA, and cpeCDE operons, which code for the phycobiliproteins phycocyanin and phycoerythrin and the phycoerythrin linker polypeptides, respectively. To define components of the signal transduction pathway involved in light-regulated expression of genes encoding phycobilisome polypeptides, we have used in vivo and in vitro techniques to identify cis-acting sequences and trans-acting factors necessary for the regulation of the red-light-inducible cpcB2A2 operon. Deletion of the cpcB2A2 upstream sequences to -76 bp with respect to the transcription start site had no effect on red-light induction of a cpcB2A2-beta-glucuronidase (GUS) chimeric gene, while deletion to -37 bp abolished GUS expression. Furthermore, a fragment of the cpcB2A2 gene from -76 to +25 bp linked to the untranslated leader of cpcB1A1 (a constitutively expressed operon encoding phycocyanin) is sufficient to drive high-level GUS expression in red light. Therefore, the sequence between positions -76 and -37 is necessary for the expression of cpcB2A2, and the region extending from -76 to +25 is sufficient for red-light induction of the operon. Attempts were made to correlate the in vivo data with protein binding in the region upstream of the transcription start site of cpcB2A2. Using in vitro analysis, we detected two protein-binding sites in the cpcB2A2 promoter which were localized to positions -162 to -122 and -37 to +25. Proteins from both red- and green-light-grown cells interacted with the former site, while only proteins present in extracts from red-light-grown cells interacted with the latter site. The data from both the in vivo and in vitro analyses suggest that while two regions upstream of the cpcB2A2 transcription initiation site specifically bind proteins, only the binding site bordering the transcription start site is important for complementary chromatic adaptation.

Amino Acid Sequence↗