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Results for “Light Signal Transduction”

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At least 127 records · Page 7Linked to original sources
PubMed2003

The effect of melatonin on antioxidant enzymes in human diabetic skin fibroblasts.

Melatonin plays several important physiological functions in mammals, such as immune enhancement and regulation of dark-light signal transduction. Melatonin is also known to be an endogenous free radical scavenger and an efficient antioxidant. It detoxifies a variety of free radicals and reactive oxygen intermediates, including the hydroxyl radical, singlet oxygen and nitric oxide. These radicals participate in many diseases, for example diabetes. This study determined the effect of melatonin on the antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), and the level of glutathione (GSH) in human diabetic (C2 line) skin fibroblasts. Confluent monolayers of control (S2 line) and diabetic (C2 line) skin fibroblasts were incubated with different concentrations of melatonin: 10, 50, 100 and 1000 micromol/l at 37 degrees C for 24 h. Next, the GSH level and SOD, CAT and GPx activities were measured colorimetrically. The activities of the antioxidant enzymes and the GSH level were lower in diabetic skin fibroblasts than in the control S2 line. Concentrations of melatonin of 100 and 1000 micromol/l caused a significant increase in the enzymes' activities and GSH level.

Antioxidants↗
PubMed2003

[Progress of chlamydomonas as a model organism].

The unicellular alga Chlamydomonas offers a simple life cycle, easy culture and isolation of series of mutants, established the techniques and tool kit for molecular genetics and genetics analysis. It is now becoming the model organism for studies on photosynthesis in plant, flagellar assembly and function, cell cycle and circadian rhythms, signal transduction, light perception and cell recognition. It is summarized the progress of study on Chlamydomonas as a model organism in this paper.

English Abstract↗
PubMed1998

Cell-to-cell communication in differentiation of mycelial fungi.

Electric and ionic interactions in fungal hyphae under controlled environmental conditions were characterized. The interactions were shown to be local and genetically determined. The possibility of their regulation by the blue-violet light and the membrane potential gradient between the adjacent cells was demonstrated. Septal pores providing the intercellular communication in fungi share common functional features with animal gap junctions, plant plasmodesmata, and microplasmodesmata of cyanobacteria. Integration of cells in a structurally and functionally heterogeneous ensemble takes place via local intercellular interactions due to a nonuniform distribution of ionic pumps and secondary transport systems in the apical and proximal hyphal cells. Cell differentiation during the hyphal growth results from the redistribution of functions in apical cells populations. The loss of polarity by growing intercalary hyphal fragments and equalization of ionic gradients during the regeneration of mechanically damaged intrahyphal fragments may indicate the existence of different growth mechanisms in the mycelium. Synchronization of functions of individual hyphal compartments exhibiting considerable electrophysiological heterogeneity takes place during the blue-light signal transduction, which triggers the hyphal differentiation processes.

Carotenoids↗
PubMed2005

Degradation of negative regulators: a common theme in hormone and light signaling networks?

Signal transduction pathways often modulate both positively and negatively acting components to optimize the efficiency of a signal. Recent results have shown that plants make extensive use of regulated proteolysis to modulate signal transduction pathways. An emerging theme from hormone (e.g. auxin and gibberellin) and light signaling pathways is signal or stimulus-induced degradation of negative regulators to optimize plant growth and development.

Light↗
PubMed1995

Signal-transduction pathways controlling light-regulated development in Arabidopsis.

All metazoan cells are able to make decisions about cell division or cellular differentiation based, in part, on environmental cues. Accordingly, cells express receptor systems that allow them to detect the presence of hormones, growth factors and other signals that manipulate the regulatory processes of the cell. In plants, an unusual signal-light-is required for the induction and regulation of many developmental processes. Past physiological and molecular studies have revealed the variety and complexity of plant responses to light but until recently very little was known about the mechanisms of those responses. Two major breakthroughs have allowed the identification of some photoreceptor signalling intermediates: the identification of photoreceptor and signal transduction mutants in Arabidopsis, and the development of single-cell microinjection assays in which outcomes of photoreceptor signalling can be visualized. Here, we review recent genetic advances which support the notion that light responses are not simply endpoints of linear signal transduction pathways, but are the result of the integration of a variety of input signals through a complex network of interacting signalling components.

Arabidopsis↗
PubMed1996

Dissection of the Blue-Light-Dependent Signal-Transduction Pathway Involved in Gametic Differentiation of Chlamydomonas reinhardtii.

Gametogenesis of the green alga Chlamydomonas reinhardtii may be viewed as a two-step process that is controlled by the environmental cues of nitrogen deprivation and blue light. Initiation of gametogenesis is induced by nitrogen deprivation, resulting in mating-incompetent pregametes, when cells are kept in the dark. For the completion of gametic differentiation light is required. Pregametes were treated with pharmacological compounds to influence the light-dependent conversion to mature gametes. Dibutyryl-cyclic 3[prime]5[prime] adenosinemonophosphate, papaverine, and genistein were found to inhibit the progression of gametogenesis in the light. Treatment of pregametes in the dark with either staurosporine or papaverine resulted in their conversion to mature gametes. Apparently, papaverine has different effects in the dark and in the light; the effect of staurosporine suggested that a protein kinase C-like component inhibits the conversion of pregametes to gametes, a block that normally is relieved by illumination. This hypothesis was corroborated by the observation that activators of protein kinase C, N-heptyl-5-chloro-1-naphthalenesulfonamide, N- (6-phenylhexyl)-5-chloro-1-naphthalenesulfonamide, and the phorbolester phorbol-12-myristate 13-acetate inhibited gametogenesis in the light. Genistein and dibutyryl-cyclic 3[prime]5[prime] adenosinemonophosphate were able to inhibit the dark activation caused by staurosporine treatment, suggesting that their targets work downstream from the "protein kinase C-like" kinase. Surprisingly, staurosporine and papaverine worked synergystically on the activation of pregametes in the dark.

Journal Article↗
PubMed2004

Blue light-induced chloroplast reorientations in Lemna trisulca L. (duckweed) are controlled by two separable cellular mechanisms as suggested by different sensitivity to wortmannin.

Chloroplast reorientations within mesophyll cells are among the most rapid physiological responses of higher plants to blue light. At light intensities below the saturation point of photosynthesis, chloroplasts move to the cell walls perpendicular to the direction of light and maximize light absorption (low-fluence rate response [LFR]). At light intensities above the saturation point of photosynthesis, chloroplasts redistribute to cell walls parallel to the direction of light (high-fluence rate response [HFR]). The actin-based mechanism is responsible for the light-induced chloroplast movements. We have found that an inhibitor of phosphoinositide-3-kinases, wortmannin, potently and irreversibly inhibited LFR and HFR chloroplast responses to blue light in Lemna trisulca L. mesophyll cells. Microscopic observations and photometric measurement indicated that 100 nM wortmannin specifically inhibited LFR in Lemna, whereas HFR displayed no sensitivity to the inhibitor at this concentration. A complete inhibition of the HFR could be obtained by 1 microM wortmannin. These data indicate that LFR is more sensitive to wortmannin than HFR and suggest that these two responses may be under the control of different cellular mechanisms. Our results suggest that phosphoinositide kinases and other phosphoinositide cycle enzymes may play a role in the transduction of the light signal to the actin cytoskeleton in Lemna as factors specifying the direction of chloroplast movements. A hypothetical model assuming three signaling pathways regulating light-induced chloroplast reorientations in mesophyll cells is proposed.

1-Phosphatidylinositol 4-Kinase↗
PubMed2004

Light matters: phototaxis and signal transduction in unicellular cyanobacteria.

Many photosynthetic microorganisms have evolved the ability to sense light quality and/or quantity and can steer themselves into optimal conditions within the environment. Phototaxis and gliding motility in unicellular cyanobacteria require type IV pili, which are multifunctional cell surface appendages. Screens for cells exhibiting aberrant motility uncovered several non-motile mutants as well as some that had lost positive phototaxis (consequently, they were negatively phototactic). Several negatively phototactic mutants mapped to the tax1 locus, which contains five chemotaxis-like genes. This locus includes a gene that encodes a putative photoreceptor (TaxD1) for positive phototaxis. A second chemotaxis-like cluster (tax3 locus) appears to be involved in pilus biogenesis. The biosynthesis and regulation of type IV pilus-based motility as well as the communication between the pilus motor and photosensory molecules appear to be complex and tightly regulated. Furthermore, the discovery that cyclic AMP and novel gene products are necessary for phototaxis/motility suggests that there might be additional levels of communication and signal processing.

Bacterial Proteins↗
PubMed2003

Specificity in stress response: epidermal keratinocytes exhibit specialized UV-responsive signal transduction pathways.

UV light, a paradigmatic initiator of cell stress, invokes responses that include signal transduction, activation of transcription factors, and changes in gene expression. Consequently, in epidermal keratinocytes, its principal and frequent natural target, UV regulates transcription of a distinctive set of genes. Hypothesizing that UV activates distinctive epidermal signal transduction pathways, we compared the UV-responsive activation of the JNK and NFkappaB pathways in keratinocytes, with the activation of the same pathways by other agents and in other cell types. Using of inhibitors and antisense oligonucleotides, we found that in keratinocytes only UVB/UVC activate JNK, while in other cell types UVA, heat shock, and oxidative stress do as well. Keratinocytes express JNK-1 and JNK-3, which is unexpected because JNK-3 expression is considered brain-specific. In keratinocytes, ERK1, ERK2, and p38 are activated by growth factors, but not by UV. UVB/UVC in keratinocytes activates Elk1 and AP1 exclusively through the JNK pathway. JNKK1 is essential for UVB/UVC activation of JNK in keratinocytes in vitro and in human skin in vivo. In contrast, in HeLa cells, used as a control, crosstalk among signal transduction pathways allows considerable laxity. In parallel, UVB/UVC and TNFalpha activate the NFkappaB pathway via distinct mechanisms, as shown using antisense oligonucleotides targeted against IKKbeta, the active subunit of IKK. This implies a specific UVB/UVC responsive signal transduction pathway independent from other pathways. Our results suggest that in epidermal keratinocytes specific signal transduction pathways respond to UV light. Based on these findings, we propose that the UV light is not a genetic stress response inducer in these cells, but a specific agent to which epidermis developed highly specialized responses.

Cells, Cultured↗
PubMed1997

Blue light regulation in Neurospora crassa.

The fungus Neurospora crassa has been shown to be a paradigm for photobiological, biochemical, and genetic studies of blue light perception and signal transduction. Several different developmental and morphological processes of Neurospora are regulated by blue light and can be divided into early and late blue light responses. The characterization of two central regulator proteins of blue light signal transduction in Neurospora crassa, WC1 and WC2, and the isolation of light-regulated genes, indicate transcriptional control as a central step in blue light signalling.

Color↗
PubMed2004

Photoresponsive cAMP signal transduction in cyanobacteria.

The molecular mechanism of cAMP-mediated signal transduction from light reception to the physiological response via regulation of gene expression in cyanobacteria is described based on our recent works. Cyanobacteria are known as the organisms that acquired oxygen-evolving, higher plant type photosynthesis. We have found that the cellular cAMP level in the filamentous cyanobacteria Anabaena was oppositely regulated by red and far-red light, i.e., decreasing and increasing, respectively, suggesting that a phytochrome-like red/far-red photoreversible pigment regulates the activity of a certain adenylate cyclase. On the other hand, in the unicellular cyanobacterium Synechocystis cellular cAMP content was increased by blue light irradiation, which led to stimulation of cell motility. The cAMP signaling pathway is known to play an important role in the regulation of various biological activities by altering enzyme activities or controlling gene expression levels in both prokaryotes and eukaryotes. We have isolated genes for adenylate cyclases and cAMP receptor proteins and characterized their molecular properties. Disruption of these genes resulted in the loss of cell motility. It is concluded that the light signal was transmitted by cAMP signal cascade in cyanobacteria.

Adenylyl Cyclases↗
PubMed2000

On the influence of pigment-protein interactions on energy transfer processes in photosynthetic membrane structures. 3. The FMO complex of Chlorobium tepidum at high pressure.

The low-temperature absorption spectra of the Chlorobium tepidum FMO bacteriochlorophyll-protein complex at various pressures have been calculated within the framework of mini-exciton theory. The dependences of the Qy transition energies of the monomeric pigments on pressure have been found by means of functional minimization. This functional includes the parameters of both theoretical and experimental absorption spectra at low temperatures and various pressures. The dependences obtained are compared with those derived for the exciton transition energies, which have been obtained by deconvoluting absorption spectra with seven Gaussian components at each pressure. The pressure increase has been shown to result in the increased coupling energy between both the pigment molecules themselves and pigments and amino acid residues. The pigment molecules capable of binding histidines and water molecules have been shown to have the greatest and smallest responses to increased pressure, respectively. The couplings of Bchl molecules with the surrounding amino acid residues have been shown to change both the exciton delocalization index and the exciton distribution between the pigment molecules within the protein subunit; the increased pressure does not change these parameters significantly.

Bacterial Proteins↗
PubMed1993

Chlamydomonas mutants affected in the light-dependent step of sexual differentiation.

Sexual differentiation of Chlamydomonas reinhardtii is induced by the consecutive action of two extrinsic cues--nitrogen deprivation and blue light. The definition of a blue light-dependent step in gamete formation provided a basis for the isolation of mutants altered in the signal transduction pathway by which light controls sexual differentiation. In one mutant (lrg1), gamete formation has become light independent. In the other mutant (lrg2), perception or transduction of the light signal appears to be partially impaired. In both mutants, the expression of genes activated by light in the late phase of gamete formation is affected. Genetic analyses showed that genes LRG1 and LRG2 are linked. The recessive nature of the lrg1-1 mutation implies that the gene encodes a negative factor or a protein that controls the activity of a negative factor. In the case of lrg2-1, neither wild-type nor mutant allele was dominant. Rather, two copies of the lrg2-1 gene simulate a wild-type phenotype. The identification of genetic loci in the pathway for blue light-mediated differentiation provides a basis for the isolation of signal transduction genes in Chlamydomonas.

Animals↗
PubMed1998

Current topics in signal transduction in bacteria.

Among the signal transfer systems in bacteria two types predominate: two-component regulatory systems and quorum sensing systems. Both types of system can mediate signal transfer across the bacterial cell envelope; however, the signalling molecule typically is not taken up into the cells in the former type of system, whereas it usually is in the latter. The Two-component systems include the recently described (eukaryotic) phosphorelay systems; quorum sensing systems can be based upon autoinducers of the N-acylated homoserine lactones, and on autoinducers of a peptidic nature. A single bacterial cell contains many signalling modules that primarily operate in parallel. This may give rise to neural-network behaviour. Recently, however, for both types of basic signal transfer modules, it has been demonstrated that they also can be organised in series (i.e. in a hierarchical order). Besides their hierarchical position in the signal transduction network of the cell, the spatial distribution of individual signalling modules may also be an important factor in their efficiency in signal transfer. Many challenges lie hidden in future work to understand these signal transfer processes in more detail. These are discussed here, with emphasis on the mutual interactions between different signal transfer processes. Successful contributions to this work will require rigorous mathematical modelling of the performance of signal transduction components, and -networks, as well as studies on light-sensing signal transduction systems, because of the unsurpassed time resolution obtainable in those latter systems, the opportunity to apply repeated reproducible stimuli, etc. The increased understanding of bacterial behaviour that already has resulted--and may further result--from these studies, can be used to fine-tune the beneficial activities of bacteria and/or more efficiently inhibit their deleterious ones.

Bacteria↗
PubMed1991

High intensity and blue light regulated expression of chimeric chalcone synthase genes in transgenic Arabidopsis thaliana plants.

To establish a genetic system for dissection of light-mediated signal transduction in plants, we analyzed the light wavelengths and promoter sequences responsible for the light-induced expression of the Arabidopsis thaliana chalcone synthase (CHS) promoter fused to the beta-glucuronidase (GUS) marker gene. Transgenic A. thaliana lines carrying 1975, 523, 186, and 17 bp of the CHS promoter fused to the GUS gene were generated, and the expression of these chimeric genes was monitored in response to high intensity light in mature plants and to different wavelengths of light in seedlings. Fusion constructs containing 1975 and 523 bp of CHS promoter sequence behaved identically to the endogenous CHS gene under all conditions. Expression of these constructs was induced specifically in response to high intensity white light and blue light. The response to blue light was seen in the presence of the Pfr form of phytochrome. Fusion constructs containing 186 bp of promoter sequence showed reduced basal levels of expression and only weak stimulation by blue light but were induced significantly by high intensity white light. These analyses showed that the expression of the A. thaliana CHS gene is responsive to a specific blue light receptor and that sequences between -523 and -186 bp are required for optimal basal and blue light-induced expression of this gene. The experiments lay the foundation for a simple genetic screen for light response mutants.

Acyltransferases↗