Biomedical subjects

K Moon

Publications and source records attributed to K Moon.

At least 19 recordsLinked to original sources

PubMed2005

Theory of microwave parametric down-conversion and squeezing using circuit QED.

We study theoretically the parametric down-conversion and squeezing of microwaves using cavity quantum electrodynamics of a superconducting Cooper-pair box (CPB) qubit located inside a transmission line resonator. The nonlinear susceptibility chi2 describing three-wave mixing can be tuned by dc gate voltage applied to the CPB and vanishes by symmetry at the charge degeneracy point. We show that the coherent coupling of different cavity modes through the qubit can generate a squeezed state. Based on parameters realized in recent successful circuit QED experiments, squeezing of 95% approximately 13 dB below the vacuum noise level should be readily achievable.

Journal Article↗

PubMed2001

Enhanced regeneration of rice (Oryza sativa L.) embryogenic callus by light irradiation in growth phase.

The effect of light irradiation on the growth and regeneration of embryogenic rice calli was investigated. Rice calli grew slightly better in the light than in the dark during the growth stage. When calli subcultured under light irradiation were transferred into a liquid regeneration culture system, the number of plantlets with shoots regenerated from calli subcultured in the light was higher than in the case of those subcultured in the dark, whereas there was no obvious difference between the light and dark subcultures when a solid medium was used for the regeneration. The number of regenerated plantlets increased with increasing light intensity up to 2000 lx, but remained the same when the light intensity was raised further. The maximum number of regenerated plantlets was obtained under a photoperiod of 16 h/d. About 8800 plantlets per liter-medium were regenerated from light-cultured calli, which is 1.5 times more than the number regenerated from calli grown in the conventional dark culture.

Journal Article↗

PubMed2001

In situ regeneration of rice (Oryza sativa L.) callus immobilized in polyurethane foam.

An in situ regeneration system for rice calli comprised of a callus growth stage and two regeneration stages was developed. After the first stage of regeneration, the medium is changed and the calli are immobilized in polyurethane foam supports, in each of which 3-5 regenerated plantlets develop from the immobilized calli during the second stage. While no significant change in callus size was observed during the first stage of regeneration, in the second stage callus enlargement and shoot regeneration predominated. In the light of these findings, calli were immobilized in the second stage after medium exchange. The use of 10-mm support cubes with an average pore size of 3.6 mm resulted in the most efficient immobilization and in situ regeneration. Medium exchange after 15 d gave the largest number of support cubes with shoots. When rice calli were cultivated in support cubes placed in 60 ml second-stage medium in a 500-ml flask, the immobilization ratio was 83%, and 82% of the support cubes contained 3-5 regenerated plantlets after 25 d. The shoot lengths of the regenerated plantlets obtained from the in situ regeneration culture were longer than those from a suspension culture. When support cubes with 3-5 regenerated plantlets were transferred from the flask to 1 4 MS solid medium supplemented with 10 g/l sorbitol and 5 g/l sucrose, the regenerated plantlets developed quickly into plants with a length above 10 cm after 10 d.

Journal Article↗

PubMed2000

Phosphatidylinositol 3-kinase stimulates muscle differentiation by activating p38 mitogen-activated protein kinase.

The activation of both phosphatidylinositol 3-kinase (PI3-kinase) and p38 mitogen-activated protein kinase (p38 MAPK) is required for muscle differentiation. However, it is not known whether the signals from these two kinases interact during this process. In this work, we have investigated this using H9c2 cardiac myoblasts. The p38 MAPK-specific inhibitor SB203580 blocked muscle differentiation and suppressed the expression of myogenin and myosin heavy chain in a concentration-dependent manner. Consistent with this, expression of a wild-type p38 MAPK (Ha-p38) or a constitutively active MAPK kinase 6 (MKK6(glu)) promoted the rate of differentiation into multinucleated myotubes. LY294002, a PI3-kinase inhibitor, suppressed in a dose-dependent manner not only muscle differentiation but also activation of p38 MAPK. In addition, expression of a constitutively active form of PI3-kinase (p110*) enhanced myotube formation and p38 MAPK activation, while expression of a dominant negative form of PI3-kinase (Deltap85) attenuated these responses. Furthermore, SB203580 suppressed differentiation of H9c2 cells expressing p110*. Interestingly, LY294002 also suppressed differentiation of H9c2 cells expressing Ha-p38 or MKK6(glu). However, SB203580 did not affect PI3-kinase activity, suggesting that PI3-kinase myogenic signaling to p38 MAPK is unidirectional. Taken together, we concluded that PI3-kinase activates p38 MAPK, which in turn stimulates muscle differentiation, but that p38 MAPK does not substitute for PI3-kinase in this process.

Animals↗

PubMed2000

In vitro cloning of complex mixtures of DNA on microbeads: physical separation of differentially expressed cDNAs.

We describe a method for cloning nucleic acid molecules onto the surfaces of 5-micrometer microbeads rather than in biological hosts. A unique tag sequence is attached to each molecule, and the tagged library is amplified. Unique tagging of the molecules is achieved by sampling a small fraction (1%) of a very large repertoire of tag sequences. The resulting library is hybridized to microbeads that each carry approximately 10(6) strands complementary to one of the tags. About 10(5) copies of each molecule are collected on each microbead. Because such clones are segregated on microbeads, they can be operated on simultaneously and then assayed separately. To demonstrate the utility of this approach, we show how to label and extract microbeads bearing clones differentially expressed between two libraries by using a fluorescence-activated cell sorter (FACS). Because no prior information about the cloned molecules is required, this process is obviously useful where sequence databases are incomplete or nonexistent. More importantly, the process also permits the isolation of clones that are expressed only in given tissues or that are differentially expressed between normal and diseased states. Such clones then may be spotted on much more cost-effective, tissue- or disease-directed, low-density planar microarrays.

Cloning, Molecular↗

PubMed2000

Thermodynamic phase diagram of the quantum hall skyrmion system

We numerically study the interacting quantum Hall Skyrmion system based on the Chern-Simons action. By noticing that the action is invariant under global spin rotations in the spin space with respect to the magnetic field direction, we obtain the low-energy effective action for a many-Skyrmion system. Performing extensive molecular dynamics simulations, we establish the thermodynamic phase diagram for a many-Skyrmion system.

Journal Article↗

PubMed2000

Gene expression analysis by massively parallel signature sequencing (MPSS) on microbead arrays.

We describe a novel sequencing approach that combines non-gel-based signature sequencing with in vitro cloning of millions of templates on separate 5 microm diameter microbeads. After constructing a microbead library of DNA templates by in vitro cloning, we assembled a planar array of a million template-containing microbeads in a flow cell at a density greater than 3x10(6) microbeads/cm2. Sequences of the free ends of the cloned templates on each microbead were then simultaneously analyzed using a fluorescence-based signature sequencing method that does not require DNA fragment separation. Signature sequences of 16-20 bases were obtained by repeated cycles of enzymatic cleavage with a type IIs restriction endonuclease, adaptor ligation, and sequence interrogation by encoded hybridization probes. The approach was validated by sequencing over 269,000 signatures from two cDNA libraries constructed from a fully sequenced strain of Saccharomyces cerevisiae, and by measuring gene expression levels in the human cell line THP-1. The approach provides an unprecedented depth of analysis permitting application of powerful statistical techniques for discovery of functional relationships among genes, whether known or unknown beforehand, or whether expressed at high or very low levels.

Cell Line↗

PubMed2000

Evidence for the role of high density lipoproteins in mediating the antioxidant effect of estrogens.

Estrogens possess strong antioxidant effects in vitro, but in vivo studies in humans have yielded conflicting results. Little is known regarding factors that mediate the antioxidant effect of estrogens in vivo. In this study the potential role of high density lipoprotein (HDL) was examined. The antioxidant effect of estradiol-17beta (E2) added to low density lipoprotein (LDL) was lost after dialysis. In contrast, the antioxidant effect of E2 added to HDL was conserved after dialysis, suggesting that E2 was bound to HDL. Binding of E2 to LDL increased after esterification (especially to long chain fatty acids). In the presence of HDL, an increased amount of E2 was transferred to LDL. E2-17 ester was as potent as E2 in preventing LDL oxidation in vitro, but 3,17-diesters were not as effective (E2=E2-17 ester>E2-3 ester>E2-3,17 diester). This was also supported by experiments which showed that estrogens with masked 3-OH groups were not effective as antioxidants. These studies provide evidence that HDL could facilitate the antioxidant effect of E2 through initial association, esterification and eventual transfer of E2 esters to LDL. Therefore it is critical that HDL peroxidation parameters be evaluated in subjects receiving estrogen replacement therapy.

Antioxidants↗

PubMed1997

In vitro characterization of the anti-human cytomegalovirus activity of PMEA (Adefovir).

PMEA [9-[2-(phosphonomethoxy)ethyl]adenine; adefovir] has shown anti-cytomegalovirus activity in animal models and in preliminary human trials. PMEA diphosphate (PMEApp), the active antiviral metabolite of PMEA, is a potent inhibitor of human cytomegalovirus (HCMV) DNA polymerase. PMEA is efficiently taken up and phosphorylated to PMEApp in numerous human cell lines. In vitro replication of wild type and drug resistant HCMV clinical isolates is effectively inhibited by PMEA. PMEA in combination with other anti-HCMV agents shows additive inhibition of HCMV replication.

Adenine↗

PubMed1997

Conversion of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine to cidofovir by an intracellular cyclic CMP phosphodiesterase.

Cidofovir (HPMPC) [1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]-cytosine] is an acyclic nucleotide analog with potent and selective activity against herpesviruses. The prodrug, cyclic HPMPC (cHPMPC) [1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl) methyl]cytosine], has antiviral activity similar to that of the parent compound but exhibits reduced toxicity in animal models. cHPMPC is converted to cidofovir by a cellular cyclic CMP phosphodiesterase (EC 3.1.4.37) which hydrolyzes a variety of substrates, including adenosine 3',5'-cyclic monophosphate (cAMP) and cytidine 3',5'-cyclic monophosphate (cCMP). The K(m) and Vmax values for hydrolysis of cHPMPC by cCMP phosphodiesterase purified from human liver are 250 microM and 0.66 nmol.min-1.unit-1, respectively. These values are similar to the K(m) and Vmax values for cAMP (23 microM and 1.16 nmol.min-1.unit-1, respectively) and cCMP (75 microM and 2.32 nmol.min-1.unit of enzyme-1, respectively). The catalytic efficiency (Vmax/K(m) ratio) of this enzyme for the cHPMPC substrate is only 10- to 20-fold lower than those for the natural cyclic nucleotides, indicating that cHPMPC is a viable intracellular substrate for the human enzyme. Kinetic analysis indicates that cHPMPC, cAMP, and cCMP are competitive with respect to each other and that they are hydrolyzed by the same enzyme. cHPMPC is hydrolyzed to cidofovir in all primary human cell systems tested, including those derived from target organs that might be infected in patients with human cytomegalovirus (HCMV) disease. Importantly, hydrolysis of cHPMPC is not diminished in cells infected with HCMV.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗

PubMed1996