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PubMed2001

Autofluorescence of melanins induced by ultraviolet radiation and near ultraviolet light. A histochemical and biochemical study.

The induction of autofluorescence of melanins by UV radiation (330-380 nm) and near UV (400-440 nm) light (jointly called UV light) was studied in tissue sections using three commercially available mounting media. Only Immu-Mount (Shandon) was found suitable for this purpose. UV irradiation of melanins in sections mounted in this medium induced strong yellow autofluorescence irrespective of the type of the polymer (eumelanin, neuromelanin, pheomelanin and ochronotic pigment). The phenomenon of autofluorescence induction was also observed with isolated natural and in vitro prepared melanins. It was inhibited by anhydrous conditions, sodium azide and catalase. In parallel experiments, rapid degradation of melanins with an intermediate fluorescent stage was achieved in UV-irradiated sections mounted in media artificially enriched with hydrogen peroxide, or directly in aqueous solutions of H2O2, Na2O2 or HIO4. Oxidations not associated with UV light led to nonfluorogenic breakdown of melanins. These observations indicate that the common mechanism may be an oxidative attack resulting from a concerted action of hydrogen peroxide and UV light leading, through strongly fluorescent intermediates, to a complete bleaching and oxidative breakdown of melanin and melanin-like polymers. Reactive oxygen species (including ozone) are considered to be important reactants in these experiments. Lipopigments differ from melanin-like pigments by their primary autofluorescence, which mostly faded during continuous prolonged irradiation. The only regular exception was melanosis coli pigment, the autofluorescence of which was considerably augmented by UV irradiation. Our results demonstrate a novel type of fluorogen in autofluorescent pigment histochemistry. The implications of the results are discussed especially in the light of the possible presence of melanin-based fluorogens in lipopigments.

Animals↗

PubMed1988

Cloning of the two chalcone flavanone isomerase genes from Petunia hybrida: coordinate, light-regulated and differential expression of flavonoid genes.

In this paper we report the isolation of cDNA clones encoding the flavonoid-biosynthetic enzyme chalcone flavanone isomerase (CHI) from Petunia hybrida. A nearly full size cDNA clone, isolated from a corolla-specific expression library, was characterized by sequence analysis. Using this CHI cDNA and the previously cloned flavonoid-specific chalcone synthase (CHS) cDNA we show that CHI and CHS genes are coordinately and tissue-specifically expressed in a developmental and light-regulated manner. Furthermore, coordinate induction of both mRNAs is observed after continuous irradiation of Petunia plantlets with UV light, probably as part of the plants UV defence mechanism. The two CHI genes, denoted A and B, were isolated from a genomic library of the Petunia inbred line V30. Both genes are transcriptionally active: gene A is transcribed in corolla, tube and UV-irradiated plantlets (1.0 kb mRNA), whereas gene B is only transcribed in immature anthers (1.0 kb mRNA). In combination with Southern blot analysis these data implicate the presence of two distinct non-allelic CHI genes in the genome of the P. hybrida line V30. Unexpectedly, mature anthers accumulate a 0.3 kb larger CHI RNA. This RNA is transcribed from CHI gene A and has a 0.3 kb 5' extension relative to the gene A transcript found in corolla tissue. Furthermore it is neither coordinately expressed with CHS mRNA nor UV inducible. Its biological function is still obscure, since no active CHI enzyme could be demonstrated in the same tissue.

Acyltransferases↗

PubMed2000

DE1, a 12-base pair cis-regulatory element sufficient to confer dark-inducible and light down-regulated expression to a minimal promoter in pea.

We found a cis-regulatory element of 12 base pairs (bp) (GGATTTTACAGT) capable of conferring light responsiveness to a minimal promoter, CaMV 35S46, in pea. The 12-bp sequence is located in the 5' upstream region of the light down-regulated gene pra2, which encodes a small GTPase belonging to the YPT/rab family. Here we examined gain-of-function analyses using synthetic promoter-luciferase constructs in a transient assay and found that the 12-bp element alone was sufficient to confer dark induction, as well as light down-regulation on the minimal promoter. We named this dark inducible element DE1. Effects of various light conditions on the reporter gene activity showed that DE1 received signals from phytochrome A, phytochrome B, and blue light photoreceptors. Using phytochrome-deficient mutants, we showed that the pra2 protein level in seedlings was also regulated by these photoreceptors. The changes in the immunoblotting pattern of the pra2 protein in these mutants were correlated with the changes in epicotyl elongation. Results from transient assays using these mutants showed that the DE1 received signals from phytochromes A and B, demonstrating that this element is indeed a light-responsive element. To our knowledge, this is the first cis-element that by itself confers light responsiveness to a minimal promoter.

Down-Regulation↗

PubMed1995

Comparison of the responses of human melanocytes with different melanin contents to ultraviolet B irradiation.

Melanin is thought to serve in photoprotection. To investigate this, we have compared the responses of cultured human melanocytes derived from different pigmentary phenotypes (skin types I-VI) to a single irradiation with different doses of UVB light, ranging between 11.7 and 70.1 mJ/cm2. After UVB irradiation, heavily pigmented melanocytes had the same percent survival but a greater capacity to resume proliferation than their lightly pigmented counterparts. A significant increase in melanin content was observed in heavily pigmented but not in lightly pigmented melanocytes. Irradiation with UVB light blocked melanocytes, regardless of their melanin content, in G1, and induced the expression of the tumor suppressor p53 protein within 4 h. This induction steadily increased up to 48 h in lightly pigmented melanocytes; however, in heavily pigmented melanocytes, p53 level peaked at 24 h after UVB treatment and declined thereafter. Additionally, DNA from lightly pigmented melanocytes contained significantly higher numbers of cyclobutane pyrimidine dimers than did DNA from heavily pigmented melanocytes after irradiation with increasing doses of UVB light. We speculate that the prolonged induction of p53 in lightly pigmented melanocytes arrests them in G1 for a long time period in order to repair extensive DNA damage. The above described differences might partially explain the increased susceptibility of individuals with lightly pigmented skin compared to individuals with dark skin to the photodamaging and photocarcinogenic effects of sun exposure.

Cell Cycle↗

PubMed1998

Apoptosis induced by fast neutrons versus 60Co gamma-rays in human peripheral blood lymphocytes.

PURPOSE: To investigate the effectiveness of high LET fast neutrons compared with low LET 60Co gamma-rays to induce apoptosis in resting lymphocytes. MATERIALS AND METHODS: Apoptosis induction was quantified by light microscopic analysis of irradiated lymphocyte samples from healthy donors after 24 h culture. For the dose-response analyses doses ranging from 0.05 to 5 Gy were applied at 1.5 Gy/min (gamma-rays) or 0.2 Gy/min (fast neutrons). To investigate the role of DNA repair in apoptosis induction a dose of 2 Gy was also given at low dose-rate (0.006 Gy/min). RESULTS: Dose-response curves obtained with both radiation qualities were characterized by an initial steep increase in the number of apoptotic cells below 1 Gy, with a flattening of the curves at higher doses towards 5 Gy. The calculated relative biological effectiveness (RBE) values for fast neutrons were close to unity. When a 2 Gy dose was administered at low rather than high dose-rate no decrease in apoptotic cell yield was observed. CONCLUSION: The dose-response data confirm the high radiosensitivity of lymphocytes and demonstrate that their response to undergo early interphase cell death by apoptosis is largely independent of LET. The observations that apoptosis induction is independent of LET and dose-rate may suggest that initial DNA damage, as opposed to DNA repair, dominate the induction of apoptosis in resting lymphocytes.

Adult↗

PubMedDate not supplied

Which induction drug for cesarean section? A comparison of thiopental sodium, propofol, and midazolam.

STUDY OBJECTIVE: To determine maternal and neonatal effects of three different induction drugs (thiopental sodium, propofol, and midazolam) for cesarean section. DESIGN: Randomized, double-blind study. SETTING: Inpatient obstetric department at a general hospital. PATIENTS: 90 healthy patients undergoing elective cesarean section with general anesthesia. INTERVENTIONS: 3 groups of 30 patients each receiving thiopental 5 mg/kg, propofol 2.4 mg/kg, or midazolam 0.3 mg/kg for induction of anesthesia. MEASUREMENTS AND MAIN RESULTS: Time to induce anesthesia, hemodynamic changes, depth of anesthesia, recovery after anesthesia, placental transfer, and neonatal outcome (Apgar and neurobehavioral examinations) were studied. In the thiopental and midazolam groups, systolic blood pressure and heart rate rose following endotracheal intubation and skin incision (p < 0.001 and p < 0.0025, respectively), while in the propofol group, there was significant hypotension after induction (p < 0.005). Electroencephalographic patterns showed a light depth of anesthesia with propofol and midazolam between anesthesia induction and delivery, confirmed by the presence of clinical signs of light anesthesia in 50% of propofol patients and 43% of midazolam patients. Time to induce anesthesia was longer with midazolam (p < 0.0001). Neonates in the midazolam and propofol groups had lower Apgar and neurobehavioral scores than those in the thiopental group. Umbilical artery to umbilical vein ratios were above 1 in the propofol and midazolam groups. CONCLUSION: Thiopental still remains the first-choice induction drug for cesarean section. The slow induction time with midazolam may put the mother at risk for pulmonary inhalation. A plane of anesthesia that may risk awareness and potential neonatal depression is the main drawback of the two newer induction drugs.

Adult↗

PubMed1987

The relationship between the activities of the pentose phosphate pathway and glycolysis during early stages of floral induction in spinach.

A quantitative cytochemical study was made of fructokinase, glucokinase, and fructokinase (both PFK-ATP and PFK-PP + F-2:6-P) activities in shoot apices of 4-week old Spinacia oleracea. The rates of activity of these enzymes in the central zone of the shoot apex of plants kept on a short day regime were compared with those from plants transferred from a range of timing up to 24 h to a continuous light regime when floral induction occurred. A mechanism is suggested explaining how no measurable change in activities of the enzymes assayed could still account for the availability of adequate levels G-6-P as substrate for pentose pathway activity which is almost doubled early on in cells of the central zone of shoot apices induced to flower.

Fructokinases↗

PubMed2006

The importance of consistent FSH delivery in infertility treatment.

The use of gonadotrophins for the treatment of infertility began in the 1930s following early work on the pituitary-ovarian axis and the discovery of FSH and LH. The technological development of pharmaceutical gonadotrophins over the last 60 years has shown improvements in specific activity, purity, degradation and detection of impurities. Throughout these pharmaceutical developments the gonadotrophin content of both urinary and recombinant preparations has been assessed using an animal in-vivo bioassay. This paper reviews the manufacturing history of recombinant human FSH (r-FSH) and follitropin-alfa filled-by-mass (FbM), and evaluates the impact of introducing a pharmaceutical product that is formulated and assayed by a physicochemical method for r-FSH protein content. This consistent gonadotrophin preparation offers the opportunity to reconsider protocols of induction in a new light, deciding the daily amount of r-FSH in relation to specific clinical parameters such as the mean ovarian volume (MOV), basal FSH concentration and body mass index (BMI). Preliminary data on the application of the formula 'basal FSH x BMI/MOV x (5.5/75)' gave interesting results as a new method to standardize the induction therapy. A formula is proposed for deciding the first 5 days of drug administration.

Animals↗

PubMed1992

Dark induction of haem oxygenase messenger RNA by haematoporphyrin derivative and zinc phthalocyanine; agents for photodynamic therapy.

Haematoporphyrin derivative is one of the main drugs currently used in clinical trials involving photodynamic therapy of cancer, and zinc phthalocyanine is being considered as one of several possible alternatives. We show that incubation of cultured human fibroblasts populations with either of the two drugs will lead to a sharp increase in the accumulation of the messenger RNA corresponding to haem oxygenase. Only cells incubated with haematoporphyrin derivative show additional enhancement of expression of this specific gene on exposure to red light. Since haem oxygenase induction appears to be a specific stress response that may be involved in cellular defence, such observations should be confirmed under conditions which would allow the clinical implications to be fully evaluated.

Cell Line↗

PubMed1984

Non-targeted mutagenesis of unirradiated lambda phage in Escherichia coli host cells irradiated with ultraviolet light.

Non-targeted mutagenesis of lambda phage by ultraviolet light is the increase over background mutagenesis when non-irradiated phage are grown in irradiated Escherichia coli host cells. Such mutagenesis is caused by different processes from targeted mutagenesis, in which mutations in irradiated phage are correlated with photoproducts in the phage DNA. Non-irradiated phage grown in heavily irradiated uvr+ host cells showed non-targeted mutations, which were 3/4 frameshifts, whereas targeted mutations were 2/3 transitions. For non-targeted mutagenesis in heavily irradiated host cells, there were one to two mutant phage per mutant burst. From this and the pathways of lambda DNA synthesis, it can be argued that non-targeted mutagenesis involves a loss of fidelity in semiconservative DNA replication. A series of experiments with various mutant host cells showed a major pathway of non-targeted mutagenesis by ultraviolet light, which acts in addition to "SOS induction" (where cleavage of the LexA repressor by RecA protease leads to din gene induction): (1) the induction of mutants has the same dependence on irradiation for wild-type and for umuC host cells; (2) a strain in which the SOS pathway is constitutively induced requires irradiation to the same level as wild-type cells in order to fully activate non-targeted mutagenesis; (3) non-targeted mutagenesis occurs to some extent in irradiated recA recB cells. In cells with very low levels of PolI, the induction of non-targeted mutagenesis by ultraviolet light is enhanced. We propose that the major pathway for non-targeted mutagenesis in irradiated host cells involves binding of the enzyme DNA polymerase I to damaged genomic DNA, and that the low polymerase activity leads to frameshift mutations during semiconservative DNA replication. The data suggest that this process will play a much smaller role in ultraviolet mutagenesis of the bacterial genome than it does in the mutagenesis of lambda phage.

Bacteriophage lambda↗

PubMed1992

Circadian rhythm of heat resistance in cotton seedlings: synthesis of heat-shock proteins.

Cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 12:12 h at 33 degrees C showed rhythmic changes in their resistance to heat shock of 53 degrees C for 40 min. The resistance was maximal at the middle of the light period and declined toward the end of the light period. One more peak of resistance developed in the middle of the dark period and declined toward the end of the dark period. Rhythmic changes in heat resistance persisted under continuous light for 3 cycles, indicating a circadian control. Under continuous light only one phase of resistance developed, lasting from the middle of the subjective night to the middle of the subjective day. The major heat shock proteins (HSPs) synthesized upon 30-min exposure to 40 degrees C, 49 degrees C or 53 degrees C were of 115, 89, 73, and 19 kDa. Their rate of synthesis depended on the inducing temperature, on previous exposure to high temperature and on the time in the light-dark cycle. The time dependency of the induction of certain HSPs persisted under continuous light, indicating a circadian control. No positive correlations was found between the rhythmic changes in heat resistance and the rhythmic changes in the synthesis of any HSP.

Circadian Rhythm↗

PubMed1971

Photomorphogenesis in Arabidopsis thaliana (L.) Heynh: Threshold Intensities and Blue-Far-red Synergism in Floral Induction.

Arabidopsis seeds were germinated on sterile mineral agar supplemented with 1% glucose and cultured under continuous light regimes. With 4-hour incandescent plus 20-hour monochromatic illumination in the region from 400 to 485 nanometers there was effective floral induction at an intensity of 100 microwatts per square centimeter. Exclusion of far red wave lengths from the 4-hour incandescent period sharply reduced the effectiveness of subsequent monochromatic blue light in promoting floral induction. Delayed floral induction occurred under continuous incandescent light lacking far red and was attributable to the blue wave lengths. Continuous 485 nanometer (100 microwatts per square centimeter) exposure without any white light treatment during the postgermination growth period was ineffective in floral induction and meristem development. Light at 730 nanometers under the same conditions was partially effective, whereas energy between 500 and 700 nanometers was completely ineffective. When continuous monochromatic light at a 3-fold higher energy level was administered, all photomorphogenic responses were accomplished with 485 nanometer light, including germination and 100% floral induction without any white light treatment at any time during the experiment. Almost equal quantum effectiveness was calculated when equivalent quantum flux densities in the region from 710 to 740 nanometers or at 485 nanometers were used. It is postulated that floral induction in Arabidopsis may be the result of a continuous excitation of a stable form of far red-absorbing phytochrome localized in or on a membrane, and that excitation can be either by direct absorption of energy by far red-absorbing phytochrome or by transfer from an accessory pigment.

Journal Article↗

PubMed1982

A B-lymphocyte-specific high-turnover protein: constitutive expression in resting B cells and induction of synthesis in proliferating cells.

A basic B-cell-specific protein of 35,000 daltons (XM1) is expressed at a high rate--comparable to actin--in resting splenic B lymphocytes of various species. Splenic or thymic T cells or fibroblasts do not express this protein. Upon polyclonal stimulation of B lymphocytes or in proliferating B-lymphocyte-derived cell lines, the synthesis of XM1 is switched off, but it is reinduced by agents that arrest replication, such as mitomycin C, hydroxyurea, ultraviolet light or gamma irradiation. Induction of XM1 after mutagen treatment is fast; the synthesis is regulated on the level of transcription or RNA processing. XM1 is turned over with half-life of less than 2 hr. XM1 is glycosylated. From compartment analysis and Triton solubilization it appears that XM1 is bound to the nuclear membrane.

Animals↗

PubMed1975

Evidence for energy migration from photosystem I to photosystem II and the effect of magnesium.

1. With Euglena chloroplasts 7722 nm light excites a fluorescence induction pattern, measured at l,u nm, typical of the Photosystem II reduction of Q. 2. Both methylviologen and phenazine methosulfate partially quench this fluorescence rise in the absence of electron transport between Photosystem II and Photosystem I, and in a manner consistent with their known role of stimulating Photosystem I photochemistry. 3. The variable fluorescence excited with 22 nm light is reduced to a greater extent than that excited by 638 nm light upon chlorophyll dilution during division in the dark. 4. These observations are interpreted to indicate that in Euglena chloroplasts light absorbed by Photosystem I is transferred energetically "uphill" to Photosystem II, where it can perform Photosystem II photochemistry. 5. Magnesium ions stimulate the variable fluorescence with both 638 nm and 722 nm light to a similar extent, which argues against the concept of magnesium ion interrupting energy transfer between Photosystem II and Photosystem I.

Chlorophyll↗

PubMed1985

Nucleotide sequence cleavages of manganese-bleomycin induced by reductant, hydrogen peroxide and ultraviolet light. Comparison with iron- and cobalt-bleomycins.

The prominent DNA breakages of bleomycin-Mn complex system were induced by reductant, hydrogen peroxide and ultraviolet light, and these three induction systems gave remarkably similar nucleotide sequence cleavage modes. The preferred DNA cleavage sites at guanine-cytosine(5'----3') and guanine-thymine(5'----3') sequences were appreciably comparable to those of the corresponding bleomycin-Fe complex systems, but not identical. In contrast, the bleomycin-Co complex system significantly degraded isolated DNA only by irradiation of ultraviolet light. The present results provide valuable information on the role of transition metals on DNA cleavage reaction of bleomycin.

Base Sequence↗

PubMed1983

Regulation of hydrogenase activity in vegetative cells of Anabaena variabilis.

Heterocyst-free (NH4+-grown) cultures of the cyanobacterium Anabaena variabilis produce a hydrogenase which is reversibly inhibited by light and O2. White or red light at an intensity of 5,000 lx inhibited greater than 95% of the activity. Oxygen at concentrations as low as 0.5% inhibited more than 85% of the hydrogenase in the vegetative cells of CO2-NH4+-grown cultures. The vegatative cell hydrogenase is also sensitive to strong oxidants like ferricyanide. In the presence of strong reductants like S2O4(2-), hydrogenase activity was not inhibited by light. However, hydrogenase activity in the heterocysts was insensitive to both light (greater than 5,000 lx) and O2 (10%). Heterocysts and light-insensitive hydrogenase activity appear simultaneously during differentiation of the vegetative cells into heterocysts (an NH4+-grown culture transferred to NH4+-free, N2-containing medium). This light-insensitive hydrogenase activity was detected several hours before the induction of nitrogenase activity. These results suggest a mode of regulation of hydrogenase in the vegetative cells of A. variabilis that is similar to "redox control" of hydrogenase and other "anaerobic" proteins in enteric bacteria like Escherichia coli.

Aerobiosis↗

PubMed2001

Daily hypothermia and torpor in a tropical primate: synchronization by 24-h light-dark cycle.

To study the temporal organization of daily hypothermia and torpor in a nocturnal Malagasy primate, the gray mouse lemur, body temperature (T(b)) and locomotor activity were recorded using telemetry on 39 males held in 24-h light-dark cycles of different photoperiods. Under free-running condition, the circadian T(b) and locomotor activity rhythms had a period shorter than 24 h. Circadian daily hypothermia started by a rapid drop in T(b) (0.24 degrees C/10 min) at the end of subjective night (13 h 25 +/- 20 min) and was characterized by minimal T(b) values 3 h 20 +/- 5 min later. Spontaneous arousal from daily hypothermia occurred at a fixed time (6 h 05 +/- 15 min, n = 7) after the beginning of subjective day. In animals exposed to 24-h light-dark cycles with night duration varying from 10 to 14 h, locomotor activity was strictly restricted to dark time, but the temporal organization of daily hypothermia was not modified, although changes in amplitude of T(b) rhythm were observed. Daily hypothermia was directly induced by light and lasted 5 h 10 +/- 10 min, with minimal T(b) values 3 h 30 +/- 30 min (n = 28) after lights on, on condition that nighttime did not exceed the duration of subjective night. However, in animals exposed to 24-h light-dark cycles with night duration varying from 10 to 5 h, the limit of induction of daily hypothermia by light was ~9 h after the beginning of night. Finally, under short days (14:10-h light-dark cycle), long bouts (6 h 50 +/- 40 min) of actual torpor (minimum T(b) 27.6 +/- 0.9 degrees C) were observed and would involve mechanisms depending on physiological changes induced by short day exposure.

Animals↗

PubMed2006

Light regulation of the photosynthetic phosphoenolpyruvate carboxylase (PEPC) in Hydrilla verticillata.

The submersed monocot, Hydrilla verticillata (L.f.) Royle, is a facultative C(4) NADP-malic enzyme (NADP-ME) plant in which the C(4) and Calvin cycles co-exist in the same cell. Futile cycling is avoided by an intracellular separation of carboxylases between the cytosol and chloroplasts. Of the two sequenced H. verticillata phosphoenolpyruvate carboxylase (PEPC) isoforms, hvpepc3 and hvpepc4, transcript expression of the latter was substantially up-regulated during C(4) induction, especially in the light. Western blots revealed two PEPC-specific bands in C(3) and C(4) leaf extracts; the lower band dominated in the C(4) and underwent post-translational phosphorylation in the light as determined by immunological studies. This band probably represents the photosynthetic isoform, HVPEPC4, despite the lack of the C(4) signature serine (Flaveria residue 774; Hydrilla 779). In C(4) leaves, PEPC activity increased 14-fold, was enhanced by leaf exposure to light, and showed allosteric regulation. Glucose-6-phosphate acted as a positive effector, but malate was inhibitory, with I(50) values of 0.4 and 0.2 mM in the light and dark, respectively, similar to those of other C(4) PEPC isoforms. In contrast, in C(3) leaves, transcript expression of both isoforms was weak, with little evidence of diel regulation, and the PEPC proteins showed essentially no indication of phosphorylation. PEPC activity in C(3) leaves was low, light independent and followed Michaelis-Menten kinetics. It was tolerant to malate, with 10-fold higher I(50) values than the PEPC from C(4) leaves. These data suggest that hvpepc4 encodes the C(4) photosynthetic PEPC, and hvpepc3 encodes an anaplerotic form.

Gene Expression Regulation, Plant↗