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PubMed2000

Reducing agents and light break an S-S bond activating rhodopsin in vivo in Chlamydomonas.

Light induces retinal synthesis via photoactivation of a small amount of Chlamydomonas rhodopsin pigment (Foster et al., Proc. Natl. Acad. Sci. USA 85, 6379-6383). A reducing agent [dithiothreitol (DDT) or mercaptoacetic acid (MAA)] also induces retinal synthesis in the dark via a rhodopsin with a chromophore. If the opsin is saturated with retinal and is bleached with light in the presence of a thiol trapping agent, the bleaching becomes irreversible. We conclude that the reducing agent as well as light break a disulfide bond resulting in activation of the rhodopsin and induction of carotenogenesis. Both the chemical and light induction is inhibited by GDPbetaS and pertussis toxin. Breaking the bridge between the 3rd and 5th helix may lead to increased proton accessibility of Asp134 leading to the rolling of the 3rd helix and MetaIIb formation.

Animals↗
PubMed2004

Induction and detection of bystander effects after combined treatment of cells with 5-bromo-2'-deoxyurine, Hoechst 33 258 and ultraviolet A light.

PURPOSE: A combined treatment of cells with 5-bromo-2'-deoxyurine (BrdU), Hoechst 33 258 and ultraviolet A (UVA) light was used to introduce chromosomal aberrations in cells for the study of bystander effects in non-labelled cells. MATERIALS AND METHODS: Mixtures of BrdU-labelled and non-labelled Chinese hamster cells (V79) in S phase were exposed to Hoechst 33 258 and/or UVA light. Metaphase cells were collected and analysed for chromosomal aberrations by Giemsa staining. BrdU immunostaining was performed to verify BrdU incorporation in the cells. RESULTS: Combined treatment with BrdU, Hoechst dye and UVA light induced reduced cell survival and increased chromosomal aberrations, whereas treatment with Hoechst 33 258 and/or UVA light had no effect on cells. Elevated frequencies of chromosomal aberrations were found in non-labelled cells mixed with BrdU-labelled cells and exposed to Hoechst dye and UVA light, suggesting the induction of bystander effects by damaged BrdU-labelled cells. These bystander clastogenic effects were also observed in non-labelled cells mixed with dying cells, indicating a contribution of dying cells in the induction of the bystander effects. CONCLUSIONS: The combined treatment with BrdU, Hoechst 33 258 and UVA light is a valid method for the study of bystander effects as it enables both induction of DNA damage and discrimination of targeted cells and bystander cells.

Animals↗
PubMed1978

Role of ultraviolet light and UV DNA in the induction of skin lesions in experimental animals.

In vivo and in vitro animal experiments have been performed to clarify the role of ultraviolet light denatured DNA (UV DNA) and ultraviolet light (UVL) in the pathogenesis of the dermal lesions of human SLE. Rabbits immunized with UV DNA show deposition of immunoglobulin at the dermal-epidermal junction following exposure to UVL. We have also shown that UV DNA appears concomitantly with the antibody at the dermal-epidermal junction subsequent to the UVL exposure. Both n DNA and UV DNA have been shown to bind to the dermal-epidermal junction in vitro which could result in the persistence of these antigens at this site. These studies lend further support to the hypothesis that the release of UV DNA and its subsequent deposition at the dermal-epidermal junction may result in binding of both immunoglobulin and complement, leading to the development of histological lesions of SLE.

Animals↗
PubMedDate not supplied

Regulation of seasonality in the migratory male blackheaded bunting (Emberiza melanocephala).

The present study was carried out on a Palearctic-Indian migratory species, the blackheaded bunting (Emberiza melanocephala), to understand the importance of photoperiodism and circannual rhythms in determining seasonality in changes in body mass and testis size in birds. An initial experiment determined the effects of duration and intensity of light on photoperiodic induction. The birds were exposed to different photoperiods (hours of light:hours of darkness; 11.5L:12.5D, 12L:12D, 12.5L:11.5D and 13L:11D) at the same (approximately 450 lux) light intensity, and to 13L:11D at different light intensities (50-, 100-, 400-, 800- and 1000-lux). The induction and subsequent regression of photoperiodic responses were dependent upon duration and intensity of the light period until these reached threshold. A second experiment investigated if an endogenous seasonal rhythm underlies photoperiodism in buntings. Birds maintained since February on a 8L: 16D photoperiod (a non-inductive short day length invariably used to ensure photosensitivity in photoperiodic species) were subjected periodically to 16L:8D (a long day length), one group every month from mid-March to mid-August. The magnitude of long day response in body mass and testes decreased as the duration of the short days progressed, but testicular response was restored in birds that were exposed to long days in July and August. The birds exposed simultaneously to short, long, and natural day lengths for 32 weeks underwent an induction-regression cycle under long days and natural day lengths, but not under short days in which a decrease in body mass occurred after about 20 weeks. The last experiment examined the importance of latitudinal migration on photoperiodism, by comparing the response to long days of three groups which included birds from populations those were held in the outdoor aviary for 1 or 2 years at 27 degrees N and those immediately arrived from their breeding grounds (approximately 40 degrees N). There was no difference in the photoperiodic induction among the three groups, indicating that neither experience to changing photoperiods during a migratory journey, nor to long photoperiods at breeding grounds, were critical for a subsequent response (initiation-termination-reinitiation) cycle. Taken together, these findings suggest that (1) the blackheaded bunting has its own endogenous timing program, which is regulated by the photoperiod, and (2) the photoperiodic programs of bunting are flexible enough to accommodate variations in the amplitude of environmental cycles. Thus, it appears that photoperiodism has evolved independently of the evolution of migration in this species.

Adaptation, Physiological↗
PubMed1994

Analysis of the parsley chalcone-synthase promoter in response to different light qualities.

We examined the chalcone synthase (chs) promoter from parsley [Petroselinum crispum Miller (A.W. Hill)] for the existence of separate promoter elements responsible for transcriptional activation of the chs gene by UV-B and by blue light. A combination of in-vivo foot-printing in parsley cells and light-induced transient expression assays with different chs promoter constructs in parsley protoplasts was used. Dark controls and blue-light-irradiated cells gave identical in-vivo footprints on the chs promoter. Pre-irradiation with blue light prior to a UV-B-light pulse is known to cause a shift in the timing of UV-B-light-induced increase in chs transcription rates. This shift was also manifested on the DNA template, since UV-B-light-induced in-vivo footprints in cells pretreated with blue light were detected earlier than in cells which had been irradiated with a UV-B-light pulse only. Although there was a clear shift in the timing of footprint appearance, the patterns of footprinting did not change. Light-induced transient-expression assays revealed that the shortest tested chs promoter which retained any light responsiveness, was sufficient for mediating both induction by UV light and the blue-light-mediated kinetic shift. These findings argue against a spatial separation of UV-B- and blue-light-responsive elements on the chs promoter. We interpret these data by postulating that the signal transduction pathways originating from the excitation of UV-B- and blue-light receptors merge at the chs promoter, or somewhere between light perception and protein-DNA interaction.

Acyltransferases↗
PubMed1981

Morphological changes in the hypothalamic-hypophyseal-gonadal axis of male rats after twelve months of streptozotocin-induced diabetes.

The hypothalami, pituitaries and testes from streptozotocin-treated and control male Wistar rats were examined by light and electron microscopy 12 months after induction of diabetes. Light and electron microscopic immunohistochemical techniques were employed for the localization of luteinizing hormone-releasing hormone and luteinizing hormone in the hypothalami and the pituitaries. In the hypothalami of diabetic animals swollen neuronal processes containing anti-luteinizing hormone-releasing-hormone positive material were frequent. In the pituitaries of the same animals a large number of small luteinizing hormone-gonadotrophs was found. These cells contained numerous secretory granules and were deficient in endoplasmic reticulum. The average testicular weight of the diabetic rats was significantly reduced but with marked individual variations. Histologically, the testes with the highest weights appeared normal, those with the lowest weights atrophic with few degenerating Leydig cells. these hypothalamic-hypophyseal changes are probably responsible for the testicular lesions found in experimental diabetes mellitus and may have relevance to the problem of infertility in human diabetes.

Animals↗
PubMed1978

Photosensitized inhibition of nitrate reductase induction by 4,5',8-trimethylpsoralen and near ultraviolet light.

4,5' ,8-trimethylpsoralen photosensitizes the inhibition of the induction of nitrate reductase in XD cells of tobacco, by near ultraviolet light. The photosensitization depends on the concentration of 4,5' ,8-trimethylpsoralen and the near ultraviolet light dose. Concomitant with the inhibition of nitrate reductase induction there is a severe inhibition of DNA and RNA synthesis. Oxygen uptake and protein synthesis are not affected. Translation of preexisting mRNA coding for nitrate reductase is insesitive to 4,5' ,8-trimethylpsoralen and near ultraviolet light. It is concluded that the DNA of these cells is the target for the photochemical reaction of 4,5' ,8-trimethylpsoralen. The template activity of the DNA is inhibited, and the expression of the genome thereby prevented. Translation of preexisting nRNA is not affected.

Coumarins↗
PubMed1986

Effect of Different Carbon Sources on the Ammonium Induction of Different Forms of NADP-Specific Glutamate Dehydrogenase in Chlorella sorokiniana Cells Cultured in the Light and Dark.

The ammonium induction of the chloroplast-localized NADP-specific glutamate dehydrogenase (NADP-GDH) was shown not to be a light-dependent process per se in Chlorella sorokiniana. In the dark without exogenous organic substrates, the cells synthesized low levels of fully active NADP-GDH, provided endogenous starch reserves had not been depleted. When cells were supplied with exogenous acetate, the rate of induction of NADP-GDH activity per milliliter of culture in the dark was equal to or slightly greater than the rate observed under photosynthetic conditions without an organic carbon source. Glucose supported only a low rate of induction of NADP-GDH activity in the dark. Both acetate and glucose inhibited induction of enzyme activity in the light. The NADP-GDH holoenzyme had at least 7 different electrophoretic forms. These forms differed in net charge and/or molecular weight. Their difference in molecular weight was due to the presence of 2 subunits with similar antigenic properties but different molecular weights (M(r) = 55,500 and 53,000; alpha-and beta-subunits, respectively). Depending upon the cultural conditions and length of the induction period, a wide variation was observed in the alpha:beta subunit ratio and in the numbers and sizes of the NADP-GDH holoenzymes.

Journal Article↗
PubMed1993

The neurophysiological correlates of colour induction, colour and brightness contrast.

Psychophysical experiments suggest that colour contrast and colour induction by surround lights can be explained as brightness contrasts (darkness induction) in the spectral region of the surround colour. It follows from this model that a chromatic surround reduces the gain of receptor-ganglion cell channels if the surround colour is in their excitatory spectral region. Thus, a green-sensitive cell (G+/R- or WS in our nomenclature) would respond less to a blue-green stimulus flashed into its receptive field when the surround (5 degrees/20 degrees inner/outer diameter) is illuminated with blue light. Neurophysiological experiments show that this is indeed the case and that such surround-induced response changes are present already in relay cells of the parvocellular layers of the lateral geniculate nucleus (P-LGN) and their retinal afferents. These surround-induced response changes are in qualitative and quantitative agreement with psychophysical experiments. Since the neuronal signal for white consists of a balanced excitation of the M-cone excited, green-blue-sensitive WS-cells and the L-cone excited, yellow-red-sensitive WL-cells, the findings also explain colour induction on white surfaces as well as coloured shadows: during blue surround illumination, white signals from the WS-cells, and during red surround the white signals from the WL-cells are reduced. The neurophysiological surround effects on P-LGN cells are identical but weaker than those produced by light of the same colour shone into the receptive field centres. They are therefore undistinguishable from direct adaptation of those receptors which feed directly into the receptive field of the respective cells. This suggests that they are caused by scattered light reaching the receptive field from the surround.

Animals↗
PubMed1982

Far-Red Reversal of Red Light Effect during Long-Night Induction of Potato (Solanum tuberosum L.) Tuberization.

The hypothesis that phytochrome is involved in the regulation of potato (Solanum tuberosum L.) tuberization was tested. When 5 minutes of red light were given in the middle of the 16-hour dark period to which whole plants were exposed daily for 14 days before making cuttings, the percentage of tuberization on cuttings decreased. The effect of red light was significantly reversed by 2 minutes of far-red light given immediately after the red in each of two separate experiments. This supports the hypothesis that phytochrome is at least indirectly involved.Longer exposures to red light were not always as effective as a 5-minute exposure in reducing tuberization and were not reversible by far-red light.

Journal Article↗
PubMedDate not supplied

[Theoretical analysis of inductive effects in higher plant photosynthesis].

The proposed mathematical model of the light stages of photosynthesis in higher plants takes into account the regulatory process of excitation energy redistribution between photosystems depending on the redox state of electron carriers. Nonmonotonic changes in the intensity of pigment fluorescence upon switching on the excitation light (delayed fluorescence induction) are described. The time required for fluorescence to reach its peak intensity and the degree of fluorescence quenching depending on light intensity are analyzed. Th kinetics of light-induced changes in EPR I signal upon switching from the far-red to white light is simulated.

Electron Spin Resonance Spectroscopy↗
PubMed2004

Contribution of UVB and UVA to UV-dependent stimulation of cyclooxygenase-2 expression in artificial epidermis.

Both UVB (280-320 nm) and UVA (320-400 nm) radiation lead to an enhanced expression of cyclooxygenase-2 (COX-2) in epidermal cells in various in-vitro and in-vivo models. It is demonstrated here that the expression of COX-2 is induced in artificial human epidermis exposed to simulated solar light (>290 nm). Employing filters eliminating specified regions from the simulated solar spectrum, the UVB and UVA-2 (320-350 nm) regions are shown to fully account for induction of COX-2 mRNA and protein as well as the enhanced production of prostaglandin E(2) after irradiation. At the protein level, approximately 70% of the total induction by solar light is due to light in the UVA-2 region. UVA-1 (350-400 nm), visible light and IR radiation are practically ineffective. COX-2 induction by simulated solar light is attenuated in the presence of inhibitors of p38(MAPK) or of c-Jun-N-terminal kinases (JNK), whereas COX-2 induction by UVA is blocked only by inhibition of JNK. UV-induced COX-2 expression is not affected by inhibition of the MEK 1,2/ERK 1,2 pathways.

Cyclooxygenase 2↗
PubMed2005

Envoy, a PAS/LOV domain protein of Hypocrea jecorina (Anamorph Trichoderma reesei), modulates cellulase gene transcription in response to light.

Envoy, a PAS/LOV domain protein with similarity to the Neurospora light regulator Vivid, which has been cloned due to its lack of expression in a cellulase-negative mutant, links cellulase induction by cellulose to light signaling in Hypocrea jecorina. Despite their similarity, env1 could not compensate for the lack of vvd function. Besides the effect of light on sporulation, we observed a reduced growth rate in constant light. An env1(PAS-) mutant of H. jecorina grows significantly slower in the presence of light but remains unaffected in darkness compared to the wild-type strain QM9414. env1 rapidly responds to a light pulse, with this response being different upon growth on glucose or glycerol, and it encodes a regulator essential for H. jecorina light tolerance. The induction of cellulase transcription in H. jecorina by cellulose is enhanced by light in the wild-type strain QM9414 compared to that in constant darkness, whereas a delayed induction in light and only a transient up-regulation in constant darkness of cbh1 was observed in the env1(PAS-) mutant. However, light does not lead to cellulase expression in the absence of an inducer. We conclude that Envoy connects the light response to carbon source signaling and thus that light must be considered an additional external factor influencing gene expression analysis in this fungus.

Amino Acid Sequence↗
PubMed1986

Light-dependent activity of the antitumor antibiotics ravidomycin and desacetylravidomycin.

The antitumor antibiotics ravidomycin and desacetylravidomycin were studied by the biochemical lambda prophage induction assay. In this assay, induction of the enzyme beta-galactosidase is measured as a specific indication of the ability of an agent to directly or indirectly damage DNA. Induction was observed only when these two antibiotics were irradiated with light in the presence of the indicator organism. Drug treated with light followed by incubation with the indicator organism in the dark did not cause induction. Light in both the near UV and visible wave length ranges activated these antibiotics; near UV and visible blue wavelengths were most effective, while 597-nm light was totally ineffective. The amount of induction caused by these drugs varied directly with the dosage of light provided. Bacterial growth inhibition, as well as cytotoxicity for a human colon carcinoma cell line, was also dramatically enhanced by light. These data suggest that ravidomycin and desacetylravidomycin are potent photosensitizing, DNA-damaging agents.

Aminoglycosides↗
PubMed1990

Fast induction of translatable mRNA by blue light in Neurospora crassa wt: the wc-1 and wc-2 mutants are blind.

After blue-light irradiation of Neurospora crassa (wt) mycelia we observed an increase of about 13 translatable mRNA species within a period of 30 min. The induction of translatable mRNA species followed a specific temporal pattern which permitted the identification of four distinct classes. One of the translatable mRNAs was induced in less than 2 min, while the others showed lag periods of 5, 10 or 20 min from the beginning of illumination. The white collar mutants, wc-1 and wc-2, which do not display any of the blue-light-induced physiological effects tested until now were found to be defective for the photoinduction of translatable mRNAs.

Electrophoresis, Gel, Two-Dimensional↗
PubMed2006

Paradoxical effects of NPY in the suprachiasmatic nucleus.

The circadian clock in the suprachiasmatic nucleus (SCN) is synchronized by the 24 h, light : dark cycle, and is reset by photic and non-photic cues. The acute effects of light in the SCN include the increase of mRNA levels of the circadian clock gene Per1 and a dramatic reduction of pineal melatonin. Neuropeptide Y (NPY), which appears to mediate the phase-resetting effects of non-photic stimuli, prevents the ability of light, and stimuli that mimic light, to phase shift the circadian clock when injected into the SCN. The purpose of the present study was to determine if NPY inhibits the ability of light to suppress pineal melatonin. Surprisingly, NPY injected into the SCN of hamsters mimicked the effects of light by suppressing pineal melatonin levels. To confirm that NPY inhibited the effects of light on the induction of Per1 mRNA levels, Per1 mRNA levels in the SCN were measured in these same animals. NPY significantly reduced Per1 mRNA levels induced by the light pulse. The suppression of melatonin by NPY appears to be mediated by the same subtype of NPY receptors in the SCN that mediate the modulation of phase shifts. Injection of Y5 receptor agonists mimicked the effects of NPY on pineal melatonin, while injection of a Y2 agonist did not. Thus, these data are the first to demonstrate the paradoxical effects of NPY within the SCN. NPY mimics the effects of light on pineal melatonin and inhibits the effects of light on the induction of Per1 mRNA.

Animals↗
PubMed1992

Induction in mice of human light-chain-associated amyloidosis.

Primary (idiopathic) or multiple myeloma-associated amyloidosis is characterized by the deposition in tissue of monoclonal light chains or light-chain fragments (AL amyloidosis). In contrast to other types of amyloidosis, information regarding the pathogenesis of light-chain-related amyloid has heretofore been limited due to the lack of a suitable in vivo model. The authors report the successful experimental induction of human AL amyloid deposits. The repeated injection into mice of Bence Jones proteins obtained from two patients with AL amyloidosis produced the histopathologic lesions characteristic of this disease. Partial dehydration of animals before protein injection resulted in the acceleration of amyloid formation. The human proteins were deposited as amyloid within the mouse renal blood vessel walls and parenchymal tissue, as well as in other organs. The deposits were Congo red-positive, exhibited green birefringence, and had a fibrillar ultrastructure. As evidenced immunohistochemically, the experimentally induced amyloid deposits consisted of the injected human light chains, and in addition, contained mouse amyloid P component (AP); mouse immunoglobulin (Ig) or inflammatory-associated amyloid A protein was not detected. Extraction and characterization of the amyloid deposits found within the mouse kidney revealed the presence of a predominantly intact human light polypeptide chain. Mice injected in identical manner with a non-amyloid-associated Bence Jones protein had no or only rare amyloid deposits. The experimental mouse model provides a means to ascertain the amyloidogenic potential of human monoclonal light chains and to study further the pathogenesis of AL amyloidosis.

Amyloid↗
PubMedDate not supplied

Induction of DNA-protein crosslinks in melanotic cloudman S91 mouse melanoma cells and EMT6 mouse mammary carcinoma cells by monochromatic 254 and 405 nm light.

The rates of induction of DNA-protein crosslinks (DPC) by monochromatic radiation at 254 and 405 nm were compared in melanotic S91 mouse melanoma cells and EMT6 mouse mammary carcinoma cells. At 254 nm, the rates of induction of DPC are the same in the two cell lines, whereas, at 405 nm, the rate of induction of DPC in the melanotic cells is considerably less than that in the nonmelanotic cells. Since the major difference in the two cell lines with respect to absorption is melanin, the latter finding implies that intracellular melanin can protect against this DNA damage caused by a component of environmental carcinogenic solar radiation.

Animals↗