2,849 research outputs found
A survey of children's interests from grade IV through grade VIII in the fields of active recreation, entertainment, reading, school subjects, and vocations.
Thesis (Ed.M.)--Boston Universit
Increased camptothecin toxicity induced in mammalian cells expressing Saccharomyces cerevisiae DNA topoisomerase I
The yeast Saccharomyces cerevisiae has been useful in establishing the phenotypic effects of specific mutations on the enzymatic activity and camptothecin sensitivity of yeast and human DNA topoisomerase I. To determine whether these phenotypes were faithfully reiterated in higher eukaryotic cells, wild-type and mutant yeast Top1 proteins were epitope-tagged at the amino terminus and transiently overexpressed in mammalian COS cells. Camptothecin preferentially induced apoptosis in cells expressing wild-type eScTop1p yet did not appreciably increase the cytotoxic response of cells expressing a catalytically inactive (eSctop1Y727F) or a catalytically active, camptothecin-resistant eSctop1vac mutant. Using an epitope-specific antibody, immobilized precipitates of eScTop1p were active in DNA relaxation assays, whereas immunoprecipitates of eScTop1Y727Fp were not. Thus, the enzyme retained catalytic activity while tethered to a support. Interestingly, the mutant eSctop1T722A, which mimics camptothecin-induced cytotoxicity in yeast through stabilization of the covalent enzyme-DNA intermediate, induced apoptosis in COS cells in the absence of camptothecin. This correlated with increased DNA cleavage in immunoprecipitates of eScTop1T722Ap, in the absence of the drug. The observation that the phenotypic consequences of expressing wild-type and mutant yeast enzymes were reiterated in mammalian cells suggests that the mechanisms underlying cellular responses to DNA topoisomerase I-mediated DNA damage are conserved between yeast and mammalian cells
Suprachiasmatic Nucleus Neurons Are Glucose Sensitive
The suprachiasmatic nucleus (SCN) in the hypothalamus serves as the pacemaker for mammalian circadian rhythms. In a hamster brain slice preparation, the authors were able to record spontaneous activity from SCN cells for up to 4 days in vitro and verify a self-sustained rhythm in firing. The phase of this rhythm was altered by the concentration of glucose in the bathing medium, with time of peak firing advanced for a 20 mM glucose condition and slightly delayed for a 5 mM glucose condition, relative to 10 mM. The advancing effect of 20 mM glucose and the delaying effect of 5 mM glucose were not maintained during a 2nd day in vitro after changing the bathing medium back to 10 mM glucose, thus indicating the effect was not a permanent phase shift of the underlying oscillation. In experiments recording from cell-attached membrane patches on acutely dissociated hamster SCN neurons, exchanging the bathing medium from high (20 mM) to zero glucose increased potassium (K+)-selective channel activity. With inside-out membrane patches, the authors revealed the presence of a glybenclamide-sensitive K+ channel (190 pS) and a larger conductance (260 pS) Ca2+- dependent K+ channel that were both reversibly inhibited by ATP at the cytoplasmic surface. Furthermore, 1 mM tetraethylammonium chloride was demonstrated to advance peak firing time in the brain slice in a similar manner to a high concentration of glucose (20 mM). The authors interpret the results to imply that SCNs are sensitive to glucose, most probably via ATP modulation of K+ channel activity in these neurons. Tonic modulation of K+ channel activity appears to alter output of the pacemaker but does not reset the phase
Transduction of a dominant-negative H-Ras into human eosinophils attenuates extracellular signal-regulated kinase activation and interleukin-5-mediated cell viability
Inhibition of eosinophil apoptosis by exposure
to interleukin-5 (IL-5) is associated
with the development of tissue eosinophilia
and may contribute to the
inflammation characteristic of asthma.
Analysis of the signaling events associated
with this process has been hampered
by the inability to efficiently manipulate
eosinophils by the introduction of
active or inhibitory effector molecules.
Evidence is provided, using a dominantnegative
N17 H-Ras protein (dn-H-Ras)
and MEK inhibitor U0126, that activation
of the Ras-Raf-MEK-ERK pathway plays a
determining role in the prolongation of
eosinophil survival by IL-5. For these
studies, a small region of the human
immunodeficiency virus Tat protein, a protein
transduction domain known to enter
mammalian cells efficiently, was fused to
the N-terminus of dn-H-Ras. The Tat-dn-HRas
protein generated from this construct
transduced isolated human blood
eosinophils at more than 95% efficiency.
When Tat-dn-H-Ras-transduced eosinophils
were treated with IL-5, they exhibited
a time- and dosage-dependent reduction
in extracellular regulated kinase 1
and 2 activation and an inhibition of p90
Rsk1 phosphorylation and IL-5-mediated
eosinophil survival in vitro. In contrast,
Tat-dn-H-Ras did not inhibit CD11b upregulation
or STAT5 tyrosine phosphorylation.
These data demonstrate that Tat
dominant-negative protein transduction
can serve as an important and novel tool
in studying primary myeloid cell signal
transduction in primary leukocytes and
can implicate the Ras-Raf-MEK-ERK pathway
in IL-5-initiated eosinophil survival
Prompt neutrino fluxes from atmospheric charm
We calculate the prompt neutrino flux from atmospheric charm production by
cosmic rays, using the dipole picture in a perturbative QCD framework, which
incorporates the parton saturation effects present at high energies. We compare
our results with the next-to-leading order perturbative QCD result and find
that saturation effects are large for neutrino energies above 10^6 GeV, leading
to a substantial suppression of the prompt neutrino flux. We comment on the
range of prompt neutrino fluxes due to theoretical uncertainties.Comment: 13 pages with 11 figures; expanded discussion, added references,
version to be published in Phys. Rev.
Differential modulation of microglia superoxide anion and thromboxane B(2 )generation by the marine manzamines
BACKGROUND: Thromboxane B(2 )(TXB(2)) and superoxide anion (O(2)(-)) are neuroinflammatory mediators that appear to be involved in the pathogenesis of several neurodegenerative diseases. Because activated-microglia are the main source of TXB(2 )and O(2)(- )in these disorders, modulation of their synthesis has been hypothesized as a potential therapeutic approach for neuroinflammatory disorders. Marine natural products have become a source of novel agents that modulate eicosanoids and O(2)(- )generation from activated murine and human leukocytes. With the exception of manzamine C, all other manzamines tested are characterized by a complex pentacyclic diamine linked to C-1 of the β-carboline moiety. These marine-derived alkaloids have been reported to possess a diverse range of bioactivities including anticancer, immunostimulatory, insecticidal, antibacterial, antimalarial and antituberculosis activities. The purpose of this investigation was to conduct a structure-activity relationship study with manzamines (MZ) A, B, C, D, E and F on agonist-stimulated release of TXB(2 )and O(2)(- )from E. coli LPS-activated rat neonatal microglia in vitro. RESULTS: The manzamines differentially attenuated PMA (phorbol 12-myristate 13-acetate)-stimulated TXB(2 )generation in the following order of decreasing potency: MZA (IC(50 )<0.016 μM) >MZD (IC(50 )= 0.23 μM) >MZB (IC(50 )= 1.6 μM) >MZC (IC(50 )= 2.98 μM) >MZE and F (IC(50 )>10 μM). In contrast, there was less effect on OPZ (opsonized zymosan)-stimulated TXB(2 )generation: MZB (IC(50 )= 1.44 μM) >MZA (IC(50 )= 3.16 μM) >MZC (IC(50 )= 3.34 μM) >MZD, MZE and MZF (IC(50 )>10 μM). Similarly, PMA-stimulated O(2)(- )generation was affected differentially as follows: MZD (apparent IC(50)<0.1 μM) >MZA (IC(50 )= 0.1 μM) >MZB (IC(50 )= 3.16 μM) >MZC (IC(50 )= 3.43 μM) >MZE and MZF (IC(50 )>10 μM). In contrast, OPZ-stimulated O(2)(- )generation was minimally affected: MZB (IC(50 )= 4.17 μM) >MZC (IC(50 )= 9.3 μM) >MZA, MZD, MZE and MZF (IC(50 )> 10 μM). From the structure-activity relationship perspective, contributing factors to the observed differential bioactivity on TXB(2 )and O(2)(- )generation are the solubility or ionic forms of MZA and D as well as changes such as saturation or oxidation of the β carboline or 8-membered amine ring. In contrast, the fused 13-membered macrocyclic and isoquinoline ring system, and any substitutions in these rings would not appear to be factors contributing to bioactivity. CONCLUSION: To our knowledge, this is the first experimental study that demonstrates that MZA, at in vitro concentrations that are non toxic to E. coli LPS-activated rat neonatal microglia, potently modulates PMA-stimulated TXB(2 )and O(2)(- )generation. MZA may thus be a lead candidate for the development of novel therapeutic agents for the modulation of TXB(2 )and O(2)(- )release in neuroinflammatory diseases. Marine natural products provide a novel and rich source of chemical diversity that can contribute to the design and development of new and potentially useful anti-inflammatory agents to treat neurodegenerative diseases
Searching for Oscillations with Extragalactic Neutrinos
We propose a novel approach for studying oscillations
with extragalactic neutrinos. Active Galactic Nuclei and Gamma Ray Bursts are
believed to be sources of ultrahigh energy muon neutrinos. With distances of
100 Mpc or more, they provide an unusually long baseline for possible detection
of with mixing parameters down to
eV, many orders of magnitude below the current accelerator
experiments. By solving the coupled transport equations, we show that
high-energy 's, as they propagate through the earth, cascade down in
energy, producing the enhancement of the incoming flux in the low
energy region, in contrast to the high-energy 's, which get absorbed.
For an AGN quasar model we find the flux to be a factor of 2 to 2.5
larger than the incoming flux in the energy range between GeV and
GeV, while for a GRB fireball model, the enhancement is 10%-27% in the same
energy range and for zero nadir angle. This enhancement decreases with larger
nadir angle, thus providing a novel way to search for appearance by
measuring the angular dependence of the muons. To illustrate how the cascade
effect and the final flux depend on the steepness of the incoming
, we show the energy and angular distributions for several generic
cases of the incoming tau neutrino flux, for n=1,2 and
3.6. We show that for the incoming flux that is not too steep, the signal for
the appearance of high-energy is the enhanced production of lower
energy and their distinctive angular dependence, due to the contribution
from the decay into just below the detector.Comment: 11 pages, including 4 color figure
Effects of Heating on Teflon(Registered Trademark) FEP Thermal Control Material from the Hubble Space Telescope
Metallized Teflon(Registered Trademark) FEP (fluorinated ethylene propylene) thermal control material on the Hubble Space Telescope (HST) is degrading in the space environment. Teflon(Registered Trademark) FEP thermal control blankets (space-facing FEP) retrieved during the first servicing mission (SM1) were found to be embrittled on solar facing surfaces and contained microscopic cracks. During the second servicing mission (SM2) astronauts noticed that the FEP outer layer of the multi-layer insulation (MLI) covering the telescope was cracked in many locations around the telescope. Large cracks were observed on the light shield, forward shell and equipment bays. A tightly curled piece of cracked FEP from the light shield was retrieved during SM2 and was severely embrittled, as witnessed by ground testing. A Failure Review Board (FRB) was organized to determine the mechanism causing the MLI degradation. Density, x-ray crystallinity and solid state nuclear magnetic resonance (NMR) analyses of FEP retrieved during SM1 were inconsistent with results of FEP retrieved during SM2. Because the retrieved SM2 material curled while in space, it experienced a higher temperature extreme during thermal cycling, estimated at 200 C, than the SM1 material, estimated at 50 C. An investigation on the effects of heating pristine and FEP exposed on HST was therefore conducted. Samples of pristine. SM1, and SM2 FEP were heated to 200 C and evaluated for changes in density and morphology. Elevated temperature exposure was found to have a major impact on the density of the retrieved materials. Characterization of polymer morphology of as-received and heated FEP samples by NMR provided results that were consistent with the density results. These findings have provided insight to the damage mechanisms of FEP in the space environment
Insights Developed Into the Damage Mechanism of Teflon FEP Thermal Control Material on the Hubble Space Telescope
Metalized Teflon FEP (DuPont; fluorinated ethylene propylene) thermal control material on the Hubble Space Telescope (HST) has been found to degrade in the space environment. Teflon FEP thermal control blankets retrieved during the first servicing mission were found to be embrittled on solar-facing surfaces and to contain microscopic cracks (the FEP surface is exposed to the space environment). During the second servicing mission, astronauts noticed that the FEP outer layer of the multilayer insulation blanketing covering the telescope was cracked in many locations. Large cracks were observed on the light shield, forward shell, and equipment bays. A tightly curled piece of cracked FEP from the light shield was retrieved during the second mission. This piece was severely embrittled, as witnessed by ground testing. A Failure Review Board was organized by NASA Goddard Space Flight Center to determine the mechanism causing the multilayer insulation degradation. This board included members of the Electro-Physics Branch of the NASA Glenn Research Center at Lewis Field. Density measurements of the retrieved materials obtained under the review board's investigations indicated that FEP from the first servicing mission was essentially unchanged from pristine FEP but that the second servicing mission FEP had increased in density in comparison to pristine FEP (ref. 1). The results were consistent with crystallinity measurements taken using x-ray diffraction and with results from solid-state nuclear magnetic resonance tests (see the table and ref. 1). Because the second servicing mission FEP was embrittled and its density and crystallinity had increased in comparison to pristine FEP, board researchers expected that the first servicing mission FEP, which was also embrittled, would also have increased in crystallinity and density, but it did not. Because the retrieved second servicing mission material curled while in space, it experienced a higher temperature extreme during thermal cycling (estimated at 200 C) than the first servicing mission material (estimated at 50 C). Therefore, Glenn initiated and conducted an investigation of the effects of heating pristine FEP and FEP that had been exposed on the Hubble Space Telescope. Samples of pristine and first and second servicing mission FEP were heated to 200 C and evaluated for changes in density and morphology. We hoped that the results would help explain why FEP degrades in the Hubble Space Telescope space environment
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