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At least 973 records · Page 54Linked to original sources
PubMed1994

Expression of nitrate assimilation related genes in Chlamydomonas reinhardtii.

The mRNA accumulation pattern of the Chlamydomonas reinhardtii nitrate assimilation-related gene cluster has been elucidated. In ammonium-grown wild-type cells, nit-1 (nitrate reductase, NR), nar-1, nar-2 and nar-3 (nitrate transporter) genes showed very similar kinetics of expression when transferred to nitrate medium. Transcripts of all these genes accumulated transiently in ammonium-grown wild-type cells after a one-hour incubation in nitrogen-free medium, and practically disappeared at about 2 hours. Mutant strains lacking functional nitrate reductase showed similar accumulation kinetics of these transcripts during both nitrate induction and derepression in nitrogen-free media. In contrast to the other nar transcripts, that nar-4, a gene sharing similar sequences with nar-3, accumulated in small amounts in wild-type cells, and only increased after a long nitrate induction period. Nitrate and light showed a strong positive effect on the accumulation of nit-1 gene transcripts. Acetate as a carbon source allowed accumulation of nit-1 mRNA in the dark, indicating the existence of interactions between light and carbon metabolism in nit-1 gene expression. Our data strongly suggest that NR negatively autoregulates its own expression and that of nar genes.

Animals↗
PubMed1987

UV-induced damage and repair in centromere DNA of yeast.

The centromere is the region within a chromosome that is required for proper segregation during mitosis and meiosis. Lesions in this sequence represent a unique type of damage, as loss of function could result in catastrophic loss of the genetic material of an entire chromosome. We have measured the induction by ultraviolet (UV) light of pyrimidine dimers in a 2550-bp restriction fragment that includes the centromere region of chromosome III in Saccharomyces cerevisiae. Yeast cells were exposed to ultraviolet light, cellular DNA was gently extracted, and subsequently treated with a UV-specific endonuclease to cleave all pyrimidine dimers. The sites of UV-specific nuclease scission within the centromere were determined by separating the DNA according to molecular weight, transferring the fragments to nitrocellulose, and hybridizing to a radiolabeled 624-bp fragment homologous to the centromere DNA from chromosome III. Several hotspots were identified in chromatin DNA from cells, as well as in irradiated deproteinized DNA. Double strand damage due to closely opposed pyrimidine dimers was also observed. At biological doses (35% survival) there are approximately 0.1 to 0.2 pyrimidine dimers per centromere. These dimers are efficiently repaired in the centromere and surrounding region.

Base Sequence↗
PubMed2005

A marvel of mucosal T cells and secretory antibodies for the creation of first lines of defense.

The mucosal immune system acts as a first line of defense against bacterial and viral infections while also playing a crucial role in the establishment and maintenance of mucosal homeostasis between the host and the outside environment. In addition to epithelial cells and antigen-presenting cells (dendritic cells and macrophages), B and T lymphocytes form a dynamic mucosal network for the induction and regulation of secretory IgA (S-IgA) and cytotoxic T lymphocyte (CTL) responses. This review seeks to shed light on the pathways of induction and regulation of these responses and to elucidate the role they simultaneously play in fending off pathogen invasion and maintaining mucosal homeostasis.

Animals↗
PubMed2000

[The UV record. Document for quality control, therapy planning and risk assessment in dermatologic photo- and photochemotherapy].

Ultraviolet (UV-) radiation therapy as a mono- or combination therapy (UV-A, UV-A1, UV-B, SUP, UV-B311) or as photochemotherapy with photosensitization (systemic PUVA-, bath PUVA-, topical PUVA-therapy) are successfully used for the treatment of several dermatological disorders. Long-term side effects of natural UV (sun light) include photoaging and induction of skin tumors. At present, the relevance of in-vitro findings of potential tumor induction in animals through therapeutic levels of UV radiation is a matter of debate. To assess these risks, information on treated location, kind of UV radiation and cumulative UV doses are required. Practically this information is barely accessible. This makes decisions on possible therapies difficult. To solve this problem we propose to use an "UV pass". At the end of each UV radiation cycle, the body location, the type of radiation and the cumulative dose are documented and this pass is given to the patient. This will improve the information transfer if the doctor is changed, as well as facilitating decisions about certain therapies and calculation of long-term risks of UV radiation. Finally it will improve the quality of UV photo- and photochemotherapy.

Dose-Response Relationship, Radiation↗
PubMed2003

Shoot production per responsive leaf explant increases exponentially with explant organogenic potential in Nicotiana species.

As part of the effort to develop optimal plant varieties for the production and molecular farming of plant-made pharmaceuticals, this study evaluated shoot organogenic potential of a total of 115 Nicotiana accessions, representing 53 species. To induce shoots, leaves from seedling grown in vitro were cut into pieces, cultured on shoot-induction medium under low light for 3 weeks, and then subcultured onto the same medium for another 4 weeks under normal light. Statistical analysis detected significant differences among the 115 accessions for the percentage of leaf explants producing shoots and the number of shoots produced per responsive leaf explant. Importantly, regression analysis also found an exponential relationship between the number of shoots produced per responsive leaf explant and the percentage of leaf explants producing shoots. The number of shoots produced per responsive leaf explant increased rather slowly, ranging from zero to around five, as the percentage of leaf explants producing shoots increased from 0 to 80%, but the increase became dramatic as the percentage increased from 80% to 100%, reaching as high as 35 shoots per responsive leaf explant. This exponential relationship is the first of its kind to be established in plant regeneration studies using either organogenesis or somatic embryogenesis systems. A possible mechanism that governs the establishment of the exponential relationship is discussed.

Culture Techniques↗
PubMed1977

Effects of sodium azide on photosystem II of Chlorella pyrenoidosa.

The action of sodium azide on the electron transport chain was investigated by means of oxygen evolution, fluorescence and luminescence measurements. (1) The damping of the oxygen oscillations is progressively reduced with increasing azide concentration in the range of 10(-5) - 10(-1) M. (2) The rate of the dark decay of the S2 and S3 states is considerably slowed. The degree of slowing is dependent on concentration. (3) Luminescence is inhibited by azide both in the presence and absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). (4) The fluorescence induction curve in strong light is modified in the presence of azide and its shape depends on azide concentration and on incubation time. (5) At a given time after a saturating flash, the fluorescence yield in the presence of azide is much higher than that of the control. It seems to be due to a general fluorescence increase rather than to a slower Q- reduction. (6) We tentatively propose an accelerated reduction of the primary donor P+ in state S2 and S3, by the intermediate donor Z in the presence of azide. Additionally, we have to assume that in the S2 and S3 states, some centers are blocked in an inactive low fluorescent form and that azide decreases their concentration.

Azides↗
PubMed1980

The induction of benzo[a]pyrene-3-mono-oxygenase by singlet oxygen in liver cell culture is mediated by oxidation products of histidine.

The photochemical generation of excited states of oxygen by the mild illumination of culture medium containing 15 microM riboflavin results in a typical induction of benzo[a]pyrene-3-mono-oxygenase in cell lines derived from liver. However, the induction of the mono-oxygenase is not due to an excited state of oxygen directly activating the inducing mechanism inside the cell but is due to the oxidation of a component of the culture medium forming a stable inducer. The present work unequivocably shows that the component oxidised is histidine. The mild illumination of culture medium containing riboflavin therefore converts a physiological component of the medium which is not normally an inducer of the mono-oxygenase into a compound which is as effective an inducer as the classical inducer. The finding that singlet oxygen will oxidise a cell constituent into a powerful inducer is compatible with the hypothesis that excited states of oxygen and their oxidation products may play a central role in the induction of cytochrome P-450 and associated enzyme activities by many chemically unrelated inducers.

Amino Acids↗
PubMed1992

In vivo assessment of drug sensitivity of African trypanosomes using the akinetoplastic induction test.

Following treatment of mice infected with Trypanosoma congolense or T brucei brucei with various doses of isometamidium chloride or diminazene aceturate, the induction of akinetoplastic (AK) forms was observed in the trypomastigotes of both species within 10 hours of drug administration. The levels of AK-induction were closely correlated with the levels of resistance to each compound found using a standard in vivo drug assay in mice. In general, ineffective doses of either compound conferred AK-induction rates of less than 30 per cent; relapsing cases had between 30 and 50 per cent while curative doses had AK-induction rates of 50 per cent or more. In vivo determination of AK-induction rates using ordinary light microscopy is thus a potentially feasible alternative indicator to the conventional use of mice infection and treatment methods for assessing drug sensitivity in African trypanosomes.

Animals↗
PubMed1986

Comparison of MHC antigen expression on PHA- and MLC-induced T cell lines with that on T and B lymphoblastoid cell lines by cell cycle dependency.

Although it is well known that the expression of major histocompatibility complex (MHC) antigens on the surface of lymphoblastoid cell lines are cell cycle dependent, the way in which the MHC antigen expression on activated T cells varies with cell cycle phase has not previously been described. Using 11 lymphoblastoid cell lines from malignant and nonmalignant tissues (B cells, T cells, and myeloid cells) and five activated T cell lines (two cell lines activated by phytohemagglutinin and three alloreactive T cell clones), MHC antigen expression was quantitatively studied by dual-beam flow cytometry. Correlated measurements of surface antigen quantity (immunofluorescence), DNA content (Hoechst 33342), and cell size (light scatter), uninfluenced by induction synchrony and cell fixation, were performed. The data indicate that cell surface antigen quantity and cell surface area demonstrate specific values at each phase of the cell cycle when the cells are in logarithmic growth. Examining cells in logarithmic growth, it was confirmed, for all lymphoblastoid cell lines, that the quantity of MHC antigens on G2 (S + G2 + M) cells was greater than that on G1 cells. In addition, it was found, by analyzing antigen quantity and surface area, that class I antigen density in the G2 phase is 17% less than that in the G1 phase in leukemic T cell lines, and that both class I and class II antigen densities in the G2 phase were 21% less than that in the G1 phase in lymphoblastoid B cell lines. In activated T cells, class I antigen density in the G2 phase was 11% less than that in the G1 phase, while class II antigen density in the G2 phase was 12% greater than that in the G1 phase. We describe four important observations in this report. In both G1 and G2 phases, activated T cells express: quantitatively fewer class I antigens than lymphoblastoid B cell lines; similar quantity of class I antigens as that of leukemic T cell lines; and similar quantity of class II antigens as that of lymphoblastoid B cell lines. Also, class II antigens are expressed in greater density in the G2 phase than in the G1 phase in activated T cells. In contrast, lymphoblastoid B cell lines express greater density of class II antigens in the G1 phase than in the G2 phase of the cell cycle. These findings differ from previous reports, suggesting that G1 phase cells may have a more significant role than G2 phase cells as target cells for MHC restricted cytotoxic cells.

B-Lymphocytes↗
PubMed1989

Proliferative response of renal pelvic epithelium in rats to oral administration of ortho-phenylphenol, sodium ortho-phenylphenate and diphenyl.

Changes in DNA synthesis levels and morphology as observed by scanning electron microscopy (SEM) and light microscopy in rat renal papilla and pelvis following oral administration of ortho-phenylphenol (OPP), sodium ortho-phenylphenate (OPP-Na) and diphenyl, were investigated in F344 rats. OPP and OPP-Na treatment for 4 weeks was associated with elevated DNA synthesis in both renal papilla and pelvis, in addition to distinct morphological cell surface alterations. Sequential light microscope observation revealed induction of renal papillary necrosis from week 4, followed by regeneration hyperplasia at weeks 16 and 24, but no changes in the renal pelvis in the OPP case. OPP-Na not only similarly affected the renal papilla, but also brought about development of hyperplasia in the renal pelvis. No proliferative response of the kidney was apparent in rats fed diphenyl. The present study indicated that the proliferative responses in the renal pelvic epithelium following OPP-Na are similar to those induced by this chemical in the urinary bladder, and that in both cases they are indicative of promoting or carcinogenic potential.

Administration, Oral↗
PubMed2003

Importance of ascorbate peroxidases OsAPX1 and OsAPX2 in the rice pathogen response pathways and growth and reproduction revealed by their transcriptional profiling.

We have identified and characterized two rice ascorbate peroxidase (OsAPX1 and OsAPX2) genes against diverse signals known to involve in defense/stress responses, using "2-week-old rice seedling in vitro model system". Oryza sativa ascorbate peroxidase 1 and 2 (OsAPX1/2) share 83% similarity to each other at amino acid level and belong to a small gene family in the rice genome. OsAPX1/2 show a weak constitutive expression in leaves. Their transcripts were up-regulated upon wounding (by cut), and diverse signals such as salicylic acid (SA), ethylene (using the ethylene generator, ethephon), abscisic acid (ABA), hydrogen peroxide, copper sulfate, protein phosphatase (PP) inhibitors, cantharidin (CN), endothall (EN) and okadaic acid (OA), and blast pathogen (Magnaporthe grisea) attack, but surprisingly not by jasmonic acid (JA). Interestingly, the OsAPX2 inductions were more potent and rapid than OsAPX1, whose expression increased gradually with time. These inductions were influenced by light signal(s), and showed requirement for certain de novo synthesized protein factor(s). Intriguingly, OsAPX1/2 mRNAs expression manifested a clear rhythmicity under light/dark cycle. Differential regulation of the OsAPX1/2 expressions by diverse environmental cues, including pathogen, and their developmental regulation in both young and reproductive stages strongly suggests their role in stress-signaling pathways and development in rice.

Amino Acid Sequence↗