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PubMed1983

Light and agonists alter pineal N-acetyltransferase induction by vasoactive intestinal polypeptide.

Vasoactive intestinal polypeptide stimulated serotonin N-acetyltransferase activity in rat pineal glands in organ culture by a postsynaptic action that was independent of the beta-receptor. The magnitude of stimulation could be altered by environmental lighting conditions and by prior exposure to the agonist. Such up- and down-regulation, well known for catecholaminergic stimulation of this system, is compatible with a possible control of the pineal by vasoactive intestinal polypeptide as well as by catecholamines.

Acetyltransferases↗
PubMed2001

Control mechanisms of diel vertical migration: theoretical assumptions.

We explore control mechanisms underlying the vertical migration of zooplankton in the water column under the predator-avoidance hypothesis. Two groups of assumptions in which the organisms are assumed to migrate vertically in order to minimize realized or effective predation pressure (type-I) and to minimize changes in realized or effective predation pressure (type-II), respectively, are investigated. Realized predation pressure is defined as the product of light intensity and relative predation abundance and the part of realized predation pressure that really affects organisms is termed as effective predation pressure. Although both types of assumptions can lead to the migration of zooplankton to avoid the mortality from predators, only the mechanisms based on type-II assumptions permit zooplankton to undergo a normal diel vertical migration (morning descent and evening ascent). The assumption of minimizing changes in realized predation pressure is based on consideration of DVM induction only by light intensity and predators. The assumption of minimizing changes in effective predation pressure takes into account, apart from light and predators also the effects of food and temperature. The latter assumption results in the same expression of migration velocity as the former one when both food and temperature are constant over water depth. A significant characteristic of the two type-II assumptions is that the relative change in light intensity plays a primary role in determining the migration velocity. The photoresponse is modified by other environmental variables: predation pressure, food and temperature. Both light and predation pressure are necessary for organisms to undertake DVM. We analyse the effect of each single variable. The modification of the phototaxis of migratory organisms depends on the vertical distribution of these variables.

Animals↗
PubMed2000

Quantitative structure-activity relationships in a series of endogenous and synthetic steroids exhibiting induction of CYP3A activity and hepatomegaly associated with increased DNA synthesis.

The results of a quantitative structure-activity relationship (QSAR) study on a total of 14 steroids exhibiting induction of a CYP3A-associated activity and increase in liver weight/DNA synthesis is reported. It is found that different, but related, structural descriptors correlate with increase in ethylmorphine N-demethylase activity (r=0.92) and with the increase in liver weight (r=0.78) and DNA synthesis (r=0.78). Although there is a strong correlation between increase in liver weight and DNA content (r=0.999), neither of these correlated with ethylmorphine N-demethylase activity. These findings are discussed in the light of CYP3A induction, substrate specificity and inhibition; a proposed model of human CYP3A4 based on sequence homology with CYP102, a bacterial P450 of known crystal structure, demonstrates the possible mode of interaction between substrates and inhibitors within the putative active site.

Aryl Hydrocarbon Hydroxylases↗
PubMed2003

Are NADP-dependent isocitrate dehydrogenases and ferredoxin-dependent glutamate synthase co-regulated by the same photoreceptors?

Activities of NADP-dependent isocitrate dehydrogenases (cytosolic and plastidic isoforms, ICDH1 and ICDH2; EC 1.1.1.42) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) in turions of Spirodela polyrhiza were all stimulated by light. Single or repeated red light (R) pulses induced the activity of the enzymes and this effect was reverted by subsequent far-red light (FR) pulses. The enzymes are, therefore, co-regulated by the low-fluence response of phytochrome. For ICDH, this is reported here for the first time. Neither an effect of the very low-fluence response nor of the FR-mediated high-irradiance response was detectable. Irradiance with continuous R resulted in enhanced enzyme activities and protein levels (Western analysis using polyclonal antibodies against ICDH1 and Fd-GOGAT). These additional effects of continuous R (called a "non-induction effect") could be inhibited for ICDH1 and ICDH2 by the inhibitor of photosynthetic electron transport, 3-(3',4'-dichlorophenyl)-1,1-dimethylurea, and are therefore related to the effect of photosynthesis. In contrast, the non-induction effect of Fd-GOGAT was resistant against this inhibitor. Moreover, hourly R pulses did not replace the effect of continuous R. The non-induction effect of light on the activity and protein level of Fd-GOGAT was therefore tentatively classified as an R-mediated high-irradiance response. The activity of Fd-GOGAT but not that of ICDHs was additionally regulated by a specific blue-light receptor. It can be concluded that the levels of ICDHs and Fd-GOGAT were coordinated by light but were not co-regulated by the same photoreceptors. Nitrate is necessary for the light regulation of both enzymes, contributing to the coordinated expression of the relevant genes.

Amino Acid Oxidoreductases↗
PubMed2007

Induction of a high-CO2-inducible, periplasmic protein, H43, and its application as a high-CO2-responsive marker for study of the high-CO2-sensing mechanism in Chlamydomonas reinhardtii.

The unicellular green alga Chlamydomonas reinhardtii can acclimate to a broad range of environmental CO(2) concentrations. We observed that the cells synthesized a specific 43 kDa protein, H43, in the periplasmic space under photoautotrophic high-CO(2) conditions. Under low-CO(2) conditions, H43 disappeared. However, H43 mRNA expression was observed even under heterotrophic low-CO(2) conditions when the cells were grown with 17.4 mM acetate in darkness. When the cells were treated with 4,4'-dithiocyanatostilbene-2,2'-disulfonate (DIDS) and mersalyl to modify cell surface proteins, H43 mRNA expression was strongly affected under both heterotrophic and photoautotrophic conditions. The H43 induction pattern in a mitochondrial respiration-deficient mutant dum-1 that lacks cytochrome c oxidase was the same, but the level was much lower than that in the wild type. Even under illumination, the dissolved CO(2) concentration in the culture rapidly increased slightly following the addition of acetate and dramatically increased even further by the inhibition of photosynthesis with DCMU. Radiotracer experiments with [U-(14)C]acetate revealed that (14)CO(2) release from cells was greater in darkness than in the light due to the great stimulation of internal CO(2) evolution, resulting in an increase in external CO(2) concentration. Strong light inhibited H43 induction and DCMU promoted the induction under photoheterotrophic low-CO(2) conditions. The results demonstrate that H43 is strictly regulated by a concentration of CO(2) resulting from respiration and photosynthesis. Our results suggest that Chlamydomonas induces high-CO(2)-responsive protein H43 by sensing the concentration of ambient CO(2) with the contribution of cell surface protein.

Animals↗
PubMed1992

Bioluminescence detection system of mutagen using firefly luciferase genes introduced in Escherichia coli lysogenic strain.

A rapid and convenient microbial sensing system for mutagens was developed based upon the induction of prophage from Escherichia coli lysogenic strain and bioluminescence. The system consisted of lysogenic E. coli encoding firefly luciferase genes and a photodetection system. Measurement of mutagen mitomycin C was achieved by measuring the luminescence intensity emitted from E. coli lysogenic strain for the recombinant phage in the presence of luminescence substrates. Approximately 1 h after addition of mitomycin C, the luminescence began to be observed, and 3 h after, it attained a level of 2 times greater than that of 1 h. Irradiation with ultraviolet light also produced light based on induction of phage from the E. coli lysogenic strain for the recombinant phage. On the other hand, when nonmutagenic toxic compounds like sodium azide were added to the reaction medium, luminescence was not observed. Mitomycin C could be detected within 1 h with this sensing system, at concentrations down to 10(2) ng/assay.

Bacteriophage lambda↗
PubMed2002

A luminescent Escherichia coli biosensor for the high throughput detection of beta-lactams.

A group-specific bioluminescent Escherichia coli strain for studying the action of beta-lactam antibiotics is described. The strain contains a plasmid, pBlaLux1, in which the luciferase genes from Photorhabdus luminescens are inserted under the control of the beta-lactam-responsive element ampR/ampC from Citrobacter freundii. In the presence of beta-lactams, the bacterial cells are induced to express the luciferase enzyme and three additional enzymes generating the substrate for the luciferase reaction. This biosensor for beta-lactams does not need any substrate or cofactor additions, and the bioluminescence can be measured very sensitively in real time by using a luminometer. Basic parameters affecting the light production and induction in the gram-negative model organism E. coli SNO301/pBlaLux1 by various beta-lactams were studied. The dose-response curves were bell shaped, indicating toxic effects for the sensor strain at high concentrations of beta-lactams. Various beta-lactams had fairly different assay ranges: ampicillin, 0.05-1.0 microg/ml; piperacillin, 0.0025-25 microg/ml; imipenem, 0.0025-0.25 microg/ml; cephapirin, 0.025-2.5 microg/ml; cefoxitin, 0.0025-1.5 microg/ml; and oxacillin, 25-500 microg/ml. Also, the induction coefficients (signal over background noninduced control) varied considerably from 3 to 158 in a 2-hour assay. Different non-beta-lactam antibiotics did not cause induction. Because the assay can be automated using microplate technologies, the approach may be suitable for higher throughput analysis of beta-lactam action.

Ampicillin↗
PubMed1980

Studies on the influence of photoreactivation on the frequencies of UV-induced chromosomal aberrations, sister-chromatid exchanges and pyrimidine dimers in chicken embryonic fibroblasts.

Chicken embryonic fibroblasts, which possess photoreactivating enzyme were used to study the influence of photoreactivating light on the induction of pyrimidine dimers, sister-chromatid exchanges (SCEs) and chromosomal aberrations by 254 nm UV. While photoreactivation (PR) efficiently removed most of the induced dimers (75-95%), the frequencies of SCEs and chromosomal aberrations were reduced only by about 30-65%, in parallel experiments. Since pyrimidine dimers are the only photoreactivable photolesions known, the reduction in the frequencies of SCEs and chromosomal aberrations on PR has been interpreted as due to disappearance of pyrimidine dimers, implying that these lesions are the primary events responsible for the induction of the biological end points studied. The possible reasons for the lack of quantitative relationship between the frequencies of dimers and the frequencies of SCEs and chromosomal aberrations are discussed.

Animals↗
PubMed2005

Hahb-10, a sunflower homeobox-leucine zipper gene, is regulated by light quality and quantity, and promotes early flowering when expressed in Arabidopsis.

Homeodomain-leucine zipper proteins constitute a family of transcription factors found only in plants. Expression patterns of the sunflower homeobox-leucine zipper gene Hahb-10 (Helianthus annuus homeobox-10), that belongs to the HD-Zip II subfamily, were analysed. Northern blots showed that Hahb-10 is expressed primarily in mature leaves, although expression is clearly detectable in younger leaves and also in stems. Considerably higher expression levels were detected in etiolated seedlings compared with light-grown seedlings. Induction of Hahb-10 expression was observed when seedlings were subjected to treatment with gibberellins. Transgenic Arabidopsis thaliana plants that express Hahb-10 under the 35S cauliflower mosaic virus promoter show special phenotypic characteristics such as darker cotyledons and planar leaves. A reduction in the life cycle of about 25% allowing earlier seed collection was also observed, and this phenomenon is clearly related to a shortened flowering time. When the number of plants per pot increased, the difference in developmental rate between transgenic and non-transformed individuals became larger. After gibberellin treatment, the relative difference in life cycle duration was considerably reduced. Several light-regulated genes have been tested as possible target genes of Hahb-10. One of them, PsbS, shows a different response to illumination conditions in transgenic plants compared with the response in wild-type plants while the other genes behave similarly in both genotypes. We propose that Hahb-10 functions in a signalling cascade(s) that control(s) plant responses to light quality and quantity, and may also be involved in gibberellin transduction pathways.

Arabidopsis↗
PubMed1985

Cerebrovascular hypoxic and autoregulatory responses during reduced brain metabolism.

The effect of reducing cerebral oxygen consumption (CMRO2) on the cerebral blood flow (CBF) responses to isocapnic hypoxic hypoxia and hypotension was examined in sheep. Newborn and adult animals were studied because of their different base-line CMRO2. Microsphere-measured CBF responses during pentobarbital coma (i.e., electroencephalographic silence) were compared with responses in conscious or lightly sedated animals. Induction of barbiturate coma reduced both CMRO2 and CBF by 50% from the awake value and by 25% from the value obtained in animals sedated with pentobarbital. The CBF response to 30 and 50% reductions in arterial O2 content (CaO2) was attenuated during coma, but only in proportion to the decrease in CMRO2. Whether CMRO2 was normal or reduced, the normoxic cerebral O2 delivery (CaO2 X CBF) was maintained during hypoxia in both newborns and adults. The relative autoregulatory index (fractional change in CBF divided by fractional change in perfusion pressure) was determined during graded hemorrhage. The index was not significantly different from zero (which represents perfect autoregulation) in awake, lightly sedated, or comatose animals. The data demonstrate that both base-line CBF and responses to hypoxia are closely tied to CMRO2 and that 50% reduction of CMRO2 does not impair cerebrovascular autoregulation.

Animals↗
PubMed2006

Increased ascorbate content delays flowering in long-day grown Arabidopsis thaliana (L.) Heynh.

Flowering requires the integration of different inductive stimuli, including light, temperature and hormones. In an attempt to assess whether ascorbate (ASC) could contribute to the control of flowering time, we analyzed the effects of increased ASC content on the transition to the reproductive stage in the facultative long-day plant Arabidopsis thaliana. ASC content was increased by spraying leaves with the ASC precursor L-galactono-gamma-lactone. Our data show that increased ASC content did not affect vegetative growth, whereas a significant delay (5 days in average) in flower production occurred in ASC-overproducing plants. Higher ASC availability resulted in delayed expression of LEAFY (LFY), the gene encoding for a key transcription factor integrating different flowering-inductive pathways. On the contrary, spraying with gibberellin under the same condition caused both early LFY expression and early flowering. The possible role of ASC in the transition to the reproductive stage is discussed.

Arabidopsis↗
PubMed1993

An ultrastructural study of experimentally induced microliths in rat proximal and distal tubules.

Calcium oxalate stone formation was induced in rats by oral application of ethylene glycol and ammonium chloride for 4, 8 and 24 days. After each induction period, light-microscopically, birefringent crystals were seen in the tubular lumen and, intracellularly, in proximal and distal tubular cells. After a postfixation which partially removed the crystalline material crystal ghosts were seen by electron microscopy. In the lumen, crystal ghosts were observed ranging from single crystals to crystal agglomerates. The large intraluminal agglomerates were surrounded by epithelial cells and cellular debris. Both crystal types had an organic interior. In the cytoplasm of ultrastructurally changed proximal tubular cells, small (200 to 600 nm. in diameter) single crystal ghosts were present in the terminal web at the basis of the microvilli. Others were present in large vacuolar structures, with a fine granular matrix. After the prolonged microlith induction periods, such vacuolar structures were seen throughout the cell. The organic matrix of the crystal ghosts therein had acquired a more aggregated and complex structure.

Ammonium Chloride↗
PubMed2004

Plant body weight-induced secondary growth in Arabidopsis and its transcription phenotype revealed by whole-transcriptome profiling.

Wood is an important raw material and environmentally cost-effective renewable source of energy. However, the molecular biology of wood formation (i.e. secondary growth) is surprisingly understudied. A novel experimental system was employed to study the molecular regulation of secondary xylem formation in Arabidopsis. First, we demonstrate that the weight carried by the stem is a primary signal for the induction of cambium differentiation and the plant hormone, auxin, is a downstream carrier of the signal for this process. We used Arabidopsis whole-transcriptome (23 K) GeneChip analysis to examine gene expression profile changes in the inflorescent stems treated for wood formation by cultural manipulation or artificial weight application. Many of the genes up-regulated in wood-forming stems had auxin responsive cis-acting elements in their promoter region, indicating auxin-mediated regulation of secondary growth. We identified 700 genes that were differentially expressed during the transition from primary growth to secondary growth. More than 40% of the genes that were up-regulated (>5x) were associated with signal transduction and transcriptional regulation. Biological significance of these regulatory genes is discussed in light of the induction and development of secondary xylem.

Arabidopsis↗
PubMed1992

Phospholipid metabolism and second messenger system after brain ischemia.

To evaluate possible involvement of phospholipid metabolism and related second messenger systems in the selective neuronal damage after ischemia, we measured changes of polyphosphoinositides (PPIs) and free fatty acids (FFAs) in a model of 5-min or 10-min ischemia and reperfusion in gerbils. The binding activity of 3H-phorbol 12,13-dibutyrate (PDBu) for protein kinase C (PKC) and 3H-inositol 1,4,5-triphosphate (IP3) for IP3 receptors was demonstrated autoradiographically. Induction of 70 KDa heat shock protein (HSP70) mRNA and amyloid precursor protein (APP) mRNA was also examined using Northern blot analysis. In the parietal cortex (an area resistant to transient ischemia), PPIs decreased during ischemia and recovered rapidly after reperfusion. However, recovery did not occur in the hippocampal CA1 area (an area more vulnerable to transient ischemia). In the cortex, arachidonic acid (AA) increased during ischemia and returned to baseline by 7 days after reperfusion; in the CA1 area, the AA level remained elevated even after 7 days of reperfusion. PDBu binding decreased in CA1 cells after 2 days of reperfusion. IP3 binding began to decrease at 5 hr of reperfusion, which is far earlier than either the onset of decreased PDBu binding or the observation of neuronal damage by light microscopy. The induction of HSP70 mRNA occurred, but the induction of APP mRNA did not. Regional differences in the induction of HSP70 mRNA were found; CA1 cells produced less HSP70 mRNA than cortical cells 8 hr after transient ischemia. These results suggest that CA1 cell membranes may not recover after transient ischemic attack, and that the membranes of the endoplasmic reticulum, which have IP3 receptors, may undergo alterations earlier than cytoplasmic membranes. The variable induction of HSP70 mRNA may be related to regional differences in vulnerability in cortical and hippocampal CA1 cells after transient ischemia. Involvement of excitatory neurotransmission in the induction of HSP70 has been suggested. The combined data may support a role for inositol phospholipid metabolism, changes in related second messenger systems, and induction of HSP70 in the excitotoxic mechanism of hippocampal CA1 neuronal damage, death, and repair.

Amyloid beta-Protein Precursor↗
PubMedDate not supplied

Role of soluble and cell surface molecules in the pathogenesis of autoimmune skin diseases.

The skin is one of the most commonly involved tissue in rheumatic autoimmune diseases. Different mechanisms are thought to be implicated in the pathogenesis of skin lesions. In genetically predisposed individuals, ultraviolet (UV) light can contribute to the induction of skin lesions via an inflammatory process. UV light promotes the release of cytokines by keratinocytes and the induction of adhesion molecules on the surface of epidermal cells initiating a cascade of inflammatory events and recruiting immunoinflammatory cells into the skin. In this review data regarding the expression of TNF-alpha in lesional skin tissue from subacute cutaneous lupus erythematosus patients and the role of interferons in the pathogenesis of skin manifestations of rheumatic autoimmune diseases are reported. In addition, an overview on the expression of cellular adhesion molecules in these diseases is provided.UV light can also induce apoptosis in keratinocytes. During this cell death several enzymes became activated. Among them, desoxyribonuclease (DNase) is an enzyme involved in degrading DNA during apoptosis. Data regarding the activity of DNAse in patients with cutaneous lupus erythematosus as a possible risk factor for the development of systemic disease are here reported.

Apoptosis↗
PubMed2002

Immunoglobulin light chain gene rearrangements display hierarchy in absence of selection for functionality in precursor-B-ALL.

The general order of the immunoglobulin (Ig) gene rearrangement process in human precursor-B cells is largely known. However, the exact Ig rearrangement patterns reflecting this process, especially those of the Ig light chain genes, are not well established. This requires detailed analysis of the gene configuration of all six IGH, IGK and IGL alleles at the single cell level. As such extensive analyses are difficult to perform in a reliable way within a single normal precursor-B cell, we used 169 precursor-B-ALL (ie six pro-B-ALL, 112 common ALL, and 51 pre-B-ALL) as clonal 'single cell' model system. The Ig gene recombinations show hierarchy starting with IGH gene rearrangements in all cases, followed by IGK rearrangements, IGK deletions and/or IGL rearrangements in 71% of cases. IGK deletions were found in the absence of IGL rearrangements in 34% of cases, which might be explained by the continuous recombinase activity in precursor-B-ALL, resulting in 'end-stage' IGK rearrangements, together with an apparently limited accessibility of the IGL locus. Remarkably, in 5% of cases IGL rearrangements took place in the absence of IGK rearrangements. In addition we found that in-frame IGH rearrangements are not necessarily required for the induction of Ig light chain gene rearrangements and that IGL rearrangements can be induced irrespective of the frame of the accompanying IGK rearrangements. In conclusion, precursor-B-ALL constitute a model system for studying Ig gene rearrangement processes without selection for functionality of the rearrangements or the influence of somatic hypermutations. Nevertheless, the hierarchy of IGH, IGK and IGL rearrrangements is apparent in precursor-B-ALL.

B-Lymphocytes↗
PubMed1992

Photosynthetic Light Utilization Efficiency, Photosystem II Heterogeneity, and Fluorescence Quenching in Chlamydomonas reinhardtii during the Induction of the CO(2)-Concentrating Mechanism.

The photosynthetic light-response curve, the relative amounts of the different photosystem II (PSII) units, and fluorescence quenching were altered in an adaptive manner when CO(2)-enriched wild-type Chlamydomonas reinhardtii cells were transferred to low levels of CO(2). This treatment is known to result in the induction of an energy-dependent CO(2)-concentrating mechanism (CCM) that increases the internal inorganic carbon concentration and thus the photosynthetic CO(2) utilization efficiency. After 3 to 6 h of low inorganic carbon treatment, several changes in the photosynthetic energy-transducing reactions appeared and proceeded for about 12 h. After this time, the fluorescence parameter variable/maximal fluorescence yield and the amounts of both PSIIalpha and PSIIbeta (secondary quinone electron acceptor of PSII-reducing) centers had decreased, whereas the amount of PSIIbeta (secondary quinone electron acceptor of PSII-nonreducing) centers had increased. The yield of noncyclic electron transport also decreased during the induction of the CCM, whereas both photochemical and nonphotochemical quenching of PSII fluorescence increased. Concurrent with these changes, the photosynthetic light-utilization efficiency also decreased significantly, largely attributed to a decline in the curvature parameter theta, the convexity of the photosynthetic light-response curve. Thus, it is concluded that the increased CO(2) utilization efficiency in algal cells possessing the CCM is maintained at the cost of a reduced light utilization efficiency, most probably due to the reduced energy flow through PSII.

Journal Article↗
PubMed1978

Functional and structural organization of chlorophyll in the developing photosynthetic membranes of Euglena gracilis Z. II. Formation of system II photosynthetic units during greening under optimal light intensity.

The relationships between light-harvesting chlorophyll and reaction centers in Photosystem II were analyzed during the chloroplast development of dark-grown, non-dividing Euglena gracilis Z. Comparative measurements included light saturation of photosynthesis, oxygen evolution under flashing-light and fluorescence induction. The results obtained can be summarized as follows: (1) Photosystem II photocenters are formed in parallel with chlorophyll synthesis, but after a long lag phase. (2) As a consequence, the chlorophyll reaction center ratio (Emerson's type photosynthetic unit) decreases during greening. (3) This decrease is accompanied by considerable changes in the energy transfer and trapping properties of Photosystem II. Most of the initially synthesized chlorophylls are inactive in the transfer of excitations to active photochemical centers and are shared among newly formed Photosystem II photocenters; as a consequence, the number of chlorophylls functionally connected to each Photosystem II photocenter decreases and cooperatively between these centers appears. Results are discussed in terms of chlorophyll organization in developing photosynthetic membranes with reference to the lake or puddle models of photosynthetic unit organization.

Chlorophyll↗