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Search Results: 1 - 10 of 6605 matches for " Kwang-Hwan Choi "
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Epigenetic Changes of Lentiviral Transgenes in Porcine Stem Cells Derived from Embryonic Origin
Kwang-Hwan Choi, Jin-Kyu Park, Hye-Sun Kim, Kyung-Jun Uh, Dong-Chan Son, Chang-Kyu Lee
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0072184
Abstract: Because of the physiological and immunological similarities that exist between pigs and humans, porcine pluripotent cell lines have been identified as important candidates for preliminary studies on human disease as well as a source for generating transgenic animals. Therefore, the establishment and characterization of porcine embryonic stem cells (pESCs), along with the generation of stable transgenic cell lines, is essential. In this study, we attempted to efficiently introduce transgenes into Epiblast stem cell (EpiSC)-like pESCs. Consequently, a pluripotent cell line could be derived from a porcine-hatched blastocyst. Enhanced green fluorescent protein (EGFP) was successfully introduced into the cells via lentiviral vectors under various multiplicities of infection, with pluripotency and differentiation potential unaffected after transfection. However, EGFP expression gradually declined during extended culture. This silencing effect was recovered by in vitro differentiation and treatment with 5-azadeoxycytidine. This phenomenon was related to DNA methylation as determined by bisulfite sequencing. In conclusion, we were able to successfully derive EpiSC-like pESCs and introduce transgenes into these cells using lentiviral vectors. This cell line could potentially be used as a donor cell source for transgenic pigs and may be a useful tool for studies involving EpiSC-like pESCs as well as aid in the understanding of the epigenetic regulation of transgenes.
New insights into metabolic properties of marine bacteria encoding proteorhodopsins.
Sabehi Gazalah,Loy Alexander,Jung Kwang-Hwan,Partha Ranga
PLOS Biology , 2005,
Abstract: Proteorhodopsin phototrophy was recently discovered in oceanic surface waters. In an effort to characterize uncultured proteorhodopsin-exploiting bacteria, large-insert bacterial artificial chromosome (BAC) libraries from the Mediterranean Sea and Red Sea were analyzed. Fifty-five BACs carried diverse proteorhodopsin genes, and we confirmed the function of five. We calculate that proteorhodopsin-exploiting bacteria account for 13% of microorganisms in the photic zone. We further show that some proteorhodopsin-containing bacteria possess a retinal biosynthetic pathway and a reverse sulfite reductase operon, employed by prokaryotes oxidizing sulfur compounds. Thus, these novel phototrophs are an unexpectedly large and metabolically diverse component of the marine microbial surface water.
Nonlocal Piezoresponse of LaAlO3/SrTiO3 Heterostructures
Mengchen Huang,Feng Bi,Chung-Wung Bark,Sangwoo Ryu,Kwang-Hwan Cho,Chang-Beom Eom,Jeremy Levy
Physics , 2012,
Abstract: The hysteretic piezoelectric response in LaAlO3/SrTiO3 heterostructures can provide important insights into the mechanism for interfacial conductance and its metastability under various conditions. We have performed a variety of nonlocal piezoelectric force microscopy experiments on 3 unit cell LaAlO3/SrTiO3 heterostructures. A hysteretic piezoresponse is observed under various environmental and driving conditions. The hysteresis is suppressed when either the sample is placed in vacuum or the interface is electrically grounded. We present a simple physical model which can account for the observed phenomena.
New Insights into Metabolic Properties of Marine Bacteria Encoding Proteorhodopsins
Gazalah Sabehi,Alexander Loy,Kwang-Hwan Jung,Ranga Partha,John L. Spudich,Tal Isaacson,Joseph Hirschberg,Michael Wagner,Oded Béjà
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0030273
Abstract: Proteorhodopsin phototrophy was recently discovered in oceanic surface waters. In an effort to characterize uncultured proteorhodopsin-exploiting bacteria, large-insert bacterial artificial chromosome (BAC) libraries from the Mediterranean Sea and Red Sea were analyzed. Fifty-five BACs carried diverse proteorhodopsin genes, and we confirmed the function of five. We calculate that proteorhodopsin-exploiting bacteria account for 13% of microorganisms in the photic zone. We further show that some proteorhodopsin-containing bacteria possess a retinal biosynthetic pathway and a reverse sulfite reductase operon, employed by prokaryotes oxidizing sulfur compounds. Thus, these novel phototrophs are an unexpectedly large and metabolically diverse component of the marine microbial surface water.
Radical Scavenging and Inhibition of Platelet Function by a Polyphenol-Rich Fraction from Salvia miltiorrhiza Bunge
Salvia miltiorrhizaSeun-Ah Yang, Nam-Kyung Im, Young-Joo Ji, Dong-Chan Yoo, Kwang-Hwan Jhee and In-Seon LeeSalvia miltiorrhiza
The Open Natural Products Journal , 2008, DOI: 10.2174/1874848100801010007]
Abstract: A diet rich in polyphenols has previously been shown to be associated with a lower risk for cardiovascular disease. Specifically, inhibition of platelet hyperactivation by polyphenols decreases platelet-dependent thrombosis, reducing the risk for cardiovascular disease. However, whether polyphenols in Salvia miltiorrhiza Bunge (SMB) affect platelet functions has not been clearly determined. Here, we investigated the effects of methanol and ethyl acetate (EtOAc) extracts from SMB on free radical scavenging activities, and platelet aggregation and adhesion. We found that the EtOAc fraction was the most effective at scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radicals (concentration for 50% reduction, RC50 = 2.4 ± 1.5 and 27.9 ± 1.4 μg/mL, respectively), and that, especially for DPPH radicals, the EtOAc fraction showed better scavenging activity than butylated hydroxyanisole (BHA, RC50 = 5.5 ± 0.1 μg/mL). Measurements with a turbidimetric aggregometer revealed that the EtOAc fraction was the most potent inhibitor of ADP- and collagen-induced rat platelet aggregation. In addition, the methanol and EtOAc fraction dose-dependently inhibited thrombin-stimulated platelet adhesion to collagen or fibrinogen. Collectively, these results suggest that the polyphenol-rich EtOAc fraction from SMB can reduce platelet hyperactivation by scavenging free radicals. Thus, the EtOAc fraction of SMB is a potential source of inhibitors of plateletdependent thrombosis.
New Insights into Metabolic Properties of Marine Bacteria Encoding Proteorhodopsins
Gazalah Sabehi equal contributor,Alexander Loy equal contributor,Kwang-Hwan Jung,Ranga Partha,John L Spudich,Tal Isaacson,Joseph Hirschberg,Michael Wagner ,Oded Béjà
PLOS Biology , 2005, DOI: 10.1371/journal.pbio.0030273
Abstract: Proteorhodopsin phototrophy was recently discovered in oceanic surface waters. In an effort to characterize uncultured proteorhodopsin-exploiting bacteria, large-insert bacterial artificial chromosome (BAC) libraries from the Mediterranean Sea and Red Sea were analyzed. Fifty-five BACs carried diverse proteorhodopsin genes, and we confirmed the function of five. We calculate that proteorhodopsin-exploiting bacteria account for 13% of microorganisms in the photic zone. We further show that some proteorhodopsin-containing bacteria possess a retinal biosynthetic pathway and a reverse sulfite reductase operon, employed by prokaryotes oxidizing sulfur compounds. Thus, these novel phototrophs are an unexpectedly large and metabolically diverse component of the marine microbial surface water.
Anomalous Transport in Sketched Nanostructures at the LaAlO3/SrTiO3 Interface
Guanglei Cheng,Joshua P. Veazey,Patrick Irvin,Cheng Cen1,Daniela F. Bogorin1,Feng Bi,Mengchen Huang,Shicheng Lu,Chung-Wung Bark,Sangwoo Ryu,Kwang-Hwan Cho,Chang-Beom Eom,Jeremy Levy
Physics , 2013, DOI: 10.1103/PhysRevX.3.011021
Abstract: The oxide heterostructure LaAlO3/SrTiO3 supports a two-dimensional electron liquid with a variety of competing phases including magnetism, superconductivity and weak antilocalization due to Rashba spin-orbit coupling. Further confinement of this 2D electron liquid to the quasi-one-dimensional regime can provide insight into the underlying physics of this system and reveal new behavior. Here we describe magnetotransport experiments on narrow LaAlO3/SrTiO3 structures created by a conductive atomic force microscope lithography technique. Four-terminal local transport measurements on ~10-nm-wide Hall bar structures yield longitudinal resistances that are comparable to the resistance quantum h/e2 and independent of the channel length. Large nonlocal resistances (as large as 10^4 ohms) are observed in some but not all structures with separations between current and voltage that are large compared to the 2D mean-free path. The nonlocal transport is strongly suppressed by the onset of superconductivity below ~200 mK. The origin of these anomalous transport signatures is not understood, but may arise from coherent transport defined by strong spin-orbit coupling and/or magnetic interactions.
Superconducting LaAlO3/SrTiO3 Nanowires
Joshua P. Veazey,Guanglei Cheng,Patrick Irvin,Cheng Cen,Daniela F. Bogorin,Feng Bi,Mengchen Huang,Chung-Wung Bark,Sangwoo Ryu,Kwang-Hwan Cho,Chang-Beom Eom,Jeremy Levy
Physics , 2012,
Abstract: We report superconductivity in quasi-1D nanostructures created at the LaAlO3/SrTiO3 interface. Nanostructures having line widths w~10 nm are formed from the parent two-dimensional electron liquid using conductive atomic force microscope lithography. Nanowire cross-sections are small compared to the superconducting coherence length in LaAlO3/SrTiO3 (w<
Inter-annual variability of a zooplankton community: the importance of summer concentrated rainfall in a regulated river ecosystem
Jong-Yun Choi,Kwang-Seuk Jeong,Geung-Hwan La,Hyun-Woo Kim
Journal of Ecology and Field Biology , 2011,
Abstract: We monitored the zooplankton community dynamics of a regulated river system (the Nakdong River) in South Korea,in an effort to characterize the relationship between basin rainfall quantity and changes in zooplankton communitystructure. The river studied herein has four multipurpose dams upstream and one estuarine barrage at the river mouth,resulting in intensive flow regulation. We hypothesized that flow regulation would effect zooplankton community structurechanges not only within the summer period of concentrated rainfall, but also during the subsequent seasons. Fieldmonitoring was conducted on a weekly basis (1999 to 2009) at the study site (27 km upstream from the estuary dam).The studied years were divided into two groups: rainy years with annual rainfall greater than total average annual rainfall,and dry years (years with lower than average annual rainfall). The zooplankton community data was also dividedinto two groups according to year and community structural characteristics. The summer density of zooplankton waslow during the summer concentrated rainfall period. In the autumn, zooplankton density was statistically related toriver flow (r2 = 0.30, P < 0.05, N = 11), which was affected by the summer concentrated rainfall (r2 = 0.31, P < 0.05, N = 11).Furthermore, autumn zooplankton density was positively related to that observed in the summer (r2 = 0.53, P < 0.05, N= 11). Therefore, it can be concluded that summer concentrated rainfall can affect the following seasons’ zooplanktondensities caused by dam flow control, and the potential growth rate of zooplankton
Population Growth of the Cladoceran, Daphnia magna: A Quantitative Analysis of the Effects of Different Algal Food
Jong-Yun Choi, Seong-Ki Kim, Kwang-Hyeon Chang, Myoung-Chul Kim, Geung-Hwan La, Gea-Jae Joo, Kwang-Seuk Jeong
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0095591
Abstract: In this study, we examined the effects of two phytoplankton species, Chlorella vulgaris and Stephanodiscus hantzschii, on growth of the zooplankton Daphnia magna. Our experimental approach utilized stable isotopes to determine the contribution of food algae to offspring characteristics and to the size of adult D. magna individuals. When equal amounts of food algae were provided (in terms of carbon content), the size of individuals, adult zooplankton, and their offspring increased significantly following the provision of S. hantzschii, but not after the provision of C. vulgaris or of a combination of the two species. Offspring size was unaffected when C. vulgaris or a mixture of the two algal species was delivered, whereas providing only S. hantzschii increased the production of larger-sized offspring. Stable isotope analysis revealed significant assimilation of diatom-derived materials that was important for the growth of D. magna populations. Our results confirm the applicability of stable isotope approaches for clarifying the contribution of different food algae and elucidate the importance of food quality for growth of D. magna individuals and populations. Furthermore, we expect that stable isotope analysis will help to further precisely examine the contribution of prey to predators or grazers in controlled experiments.
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