Biomedical subjects

S K Cho

Publications and source records attributed to S K Cho.

At least 19 recordsLinked to original sources

PubMed2005

Analysis of differentially expressed transcripts from planthopper-infested wild rice (Oryza minuta).

A subtracted library was constructed from planthopper-infested wild rice (Oryza minuta) by suppression subtractive hybridization in combination with mirror orientation selection. To screen the differentially expressed transcripts in the library, we applied a cDNA microarray containing 960 random clones in a reverse Northern blot analysis using cDNA probes prepared from the mRNAs of control and planthopper-infested samples. On the basis of the signal intensities and expression ratios obtained from experiments performed in triplicate, we selected 383 clones. The elevated expression levels and overall profiles over time were verified by Northern blot analysis. Although Southern blot analysis showed similar copy numbers of the screened genes in O. minuta and O. sativa, it also revealed that the expression profiles had a different pattern. Functional categorization placed the identified transcripts in the categories of subcellular localization, metabolism, and protein fate. The presence of these expressed sequence tags implies that resistance of O. minuta to insect infestation can be achieved not only by an elevated expression of defense-related genes but also by enhanced metabolic activities.

Animals↗

PubMed2004

Comparative analysis of 5,211 leaf ESTs of wild rice (Oryza minuta).

The expressed sequence tags (ESTs) presented in this report are the first transcriptomes of wild rice. A cDNA library was constructed from 4-week-old leaf samples of greenhouse-grown Oryza minuta. The 5,211 cDNA clones of O. minuta represent 3,401 unique sequences, consisting of 2,787 singletons and 614 assembled sequences. Database comparisons of the cDNAs in GenBank's non-redundant databases using BLAST revealed that 4,957 of the 5,211 cDNAs (95.1%) showed a high degree of sequence homology to genes from other organisms. Most of the transcripts identified were genes related to metabolism, energy, protein biosynthesis and subcellular localization. The metabolism and energy categories of the O. minuta ESTs showed a considerably higher gene expression level than those of O. sativa ESTs. These data and genes can be utilized in rice breeding.

Arabidopsis↗

PubMed2003

Identification of fungal ( Magnaporthe grisea) stress-induced genes in wild rice ( Oryza minuta).

To identify fungal stress-related genes in wild rice, Oryza minuta, we constructed a subtracted library using suppression subtractive hybridization in combination with mirror orientation selection. DNA chips containing 960 randomly selected cDNA clones were applied by reverse Northern analysis to eliminate false positive clones from the library and to prescreen differentially expressed genes. In total, 377 cDNA clones were selected on the basis of their signal intensities and expression ratios. Sequence analyses of these 377 cDNA fragments revealed that 180 of them (47.7%) represented unique genes. Of these 180 cDNAs, 89 clones (49.6%) showed significant homologies to previously known genes, while the remaining 91 did not match any known sequences. The putative functions of the 180 unique ESTs were categorized by aligning them with MIPS data. They were classified into seven different groups using microarray data-derived expression patterns and verified by Northern blotting.

Blotting, Northern↗

PubMed2002

Long-term neuropsychological effects and MRI findings in patients with CS2 poisoning.

OBJECTIVES: To evaluate the long-term neuropsychological effects and magnetic resonance imaging (MRI) findings among retired patients with a history of exposure to carbon disulfide (CS2). MATERIAL AND METHODS: Seventy-four patients with a history of exposure to CS2 were divided into two equal groups according to their level of exposure, and they completed a questionnaire and were evaluated for neuropsychological symptoms using the Korean version of the revised Wechsler Adult Intelligence Scale. Thirty-one MRI images were reviewed retrospectively. RESULTS: There were no statistically significant differences in total, verbal and performance IQs between high- and low-exposure groups. MRI findings revealed a significantly larger number of cerebral lacunae (five of 12 subjects) in the high-exposure group. Periventricular hyperintensities were mostly located in frontal and occipital areas, and white-matter hyperintensities were mostly in frontal and parietal areas. CONCLUSION: The higher prevalence of lacunae in the high-exposure group as revealed by MRI suggests that further MRI studies are needed into long-term neuropsychological effects induced by CS2.

Aged↗

PubMed2001

Expression and function of CD105 during the onset of hematopoiesis from Flk1(+) precursors.

During ontogeny, the hematopoietic system is established from mesoderm-derived precursors; however, molecular events regulating the onset of hematopoiesis are not well characterized. Several members of the transforming growth factor beta (TGF-beta) superfamily have been implicated as playing a role during mesoderm specification and hematopoiesis. CD105 (endoglin) is an accessory receptor for members of the TGF-beta superfamily. Here it is reported that during the differentiation of murine embryonic stem (ES) cells in vitro, hematopoietic commitment within Flk1(+) mesodermal precursor populations is characterized by CD105 expression. In particular, CD105 is expressed during the progression from the Flk1(+)CD45(-) to Flk1(-)CD45(+) stage. The developmentally regulated expression of CD105 suggests that it may play a role during early hematopoiesis from Flk1(+) precursors. To determine whether CD105 plays a functional role during early hematopoietic development, the potential of CD105-deficient ES cells to differentiate into various hematopoietic lineages in vitro was assessed. In the absence of CD105, myelopoiesis and definitive erythropoiesis were severely impaired. In contrast, lymphopoiesis appeared to be only mildly affected. Thus, these findings suggest that the regulated expression of CD105 functions to support lineage-specific hematopoietic development from Flk1(+) precursors.

Animals↗

PubMed2001

The stress kinase mitogen-activated protein kinase kinase (MKK)7 is a negative regulator of antigen receptor and growth factor receptor-induced proliferation in hematopoietic cells.

The dual specificity kinases mitogen-activated protein kinase (MAPK) kinase (MKK)7 and MKK4 are the only molecules known to directly activate the stress kinases stress-activated protein kinases (SAPKs)/c-Jun N-terminal kinases (JNKs) in response to environmental or mitogenic stimuli. To examine the physiological role of MKK7 in hematopoietic cells, we used a gene targeting strategy to mutate MKK7 in murine T and B cells and non-lymphoid mast cells. Loss of MKK7 in thymocytes and mature B cells results in hyperproliferation in response to growth factor and antigen receptor stimulation and increased thymic cellularity. Mutation of mkk7 in mast cells resulted in hyperproliferation in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF). SAPK/JNK activation was completely abolished in the absence of MKK7, even though expression of MKK4 was strongly upregulated in mkk7(-/-) mast cell lines, and phosphorylation of MKK4 occurred normally in response to multiple stress stimuli. Loss of MKK7 did not affect activation of extracellular signal-regulated kinase (ERK)1/2 or p38 MAPK. mkk7(-/-) mast cells display reduced expression of JunB and the cell cycle inhibitor p16INK4a and upregulation of cyclinD1. Reexpression of p16INK4a in mkk7(-/-) mast cells abrogates the hyperproliferative response. Apoptotic responses to a variety of stimuli were not affected. Thus, MKK7 is an essential and specific regulator of stress-induced SAPK/JNK activation in mast cells and MKK7 negatively regulates growth factor and antigen receptor-driven proliferation in hematopoietic cells. These results indicate that the MKK7-regulated stress signaling pathway can function as negative regulator of cell growth in multiple hematopoietic lineages.

Animals↗

PubMed2001

Interaction of the Arabidopsis receptor protein kinase Wak1 with a glycine-rich protein, AtGRP-3.

The Arabidopsis wall-associated receptor kinase, Wak1, is a member of the Wak family (Wak1-5) that links the plasma membrane to the extracellular matrix. By the yeast two-hybrid screen, we found that a glycine-rich extracellular protein, AtGRP-3, binds to the extracellular domain of Wak1. Further in vitro binding studies indicated that AtGRP-3 is the only isoform among the six tested AtGRPs that specifically interacts with Waks, and the cysteine-rich carboxyl terminus of AtGRP-3 is essential for its binding to Wak1. We also show that Wak1 and AtGRP-3 form a complex with a molecular size of approximately 500 kDa in vivo in conjunction with the kinase-associated protein phosphatase, KAPP, that has been shown to interact with a number of plant receptor-like kinases. Binding of AtGRP-3 to Wak1 is shown to be crucial for the integrity of the complex. Wak1 and AtGRP-3 are both induced by salicylic acid treatment. Moreover, exogenously added AtGRP-3 up-regulates the expression of Wak1, AtGRP-3, and PR-1 (for pathogenesis-related) in protoplasts. Taken together, our data suggest that AtGRP-3 regulates Wak1 function through binding to the cell wall domain of Wak1 and that the interaction of Wak1 with AtGRP-3 occurs in a pathogenesis-related process in planta.

Arabidopsis↗

PubMed2001

Essential role of the mitochondrial apoptosis-inducing factor in programmed cell death.

Programmed cell death is a fundamental requirement for embryogenesis, organ metamorphosis and tissue homeostasis. In mammals, release of mitochondrial cytochrome c leads to the cytosolic assembly of the apoptosome-a caspase activation complex involving Apaf1 and caspase-9 that induces hallmarks of apoptosis. There are, however, mitochondrially regulated cell death pathways that are independent of Apaf1/caspase-9. We have previously cloned a molecule associated with programmed cell death called apoptosis-inducing factor (AIF). Like cytochrome c, AIF is localized to mitochondria and released in response to death stimuli. Here we show that genetic inactivation of AIF renders embryonic stem cells resistant to cell death after serum deprivation. Moreover, AIF is essential for programmed cell death during cavitation of embryoid bodies-the very first wave of cell death indispensable for mouse morphogenesis. AIF-dependent cell death displays structural features of apoptosis, and can be genetically uncoupled from Apaf1 and caspase-9 expression. Our data provide genetic evidence for a caspase-independent pathway of programmed cell death that controls early morphogenesis.

Animals↗

PubMed2001

Arthroscopic suture fixation for bony avulsion of the posterior cruciate ligament.

We describe a new arthroscopic technique for suture fixation of a posterior cruciate ligament (PCL) avulsion fracture from the tibia. This technique is indicated when the size of the avulsed fragment is small and fixation with a screw or pins is inadequate. Three portals are used: a parapatellar anteromedial portal, a high posteromedial portal, and a posterolateral portal. Using a PCL tibial guide, 2 bone tunnels are made from the anterior cortex of the tibia to the medial and lateral border of the avulsed site. One or 2 strands of 23-gauge wire or multiple nonabsorbable sutures are used for fixation through the tunnels. If the bony fragment is small or comminuted, fixation with wires or sutures leads to rigid fixation and early rehabilitation.

Arthroscopy↗

PubMed2001

gly gene cloning and expression and purification of glycinecin A, a bacteriocin produced by Xanthomonas campestris pv. glycines 8ra.

Glycinecin A, a bacteriocin produced by Xanthomonas campestris pv. glycines, inhibits the growth of X. campestris pv. vesicatoria. We have cloned and expressed the genes encoding glycinecin A in Escherichia coli. Recombinant glycinecin A was purified from cell extracts by ammonium sulfate precipitation followed by chromatography on Q-Sepharose, Mono Q (ion exchange), and size exclusion columns. Purified glycinecin A is composed of two polypeptides, is active over a wide pH range (6 to 9), and is stable at temperatures up to 60 degrees C. Glycinecin A is a heterodimer consisting of 39- and 14-kDa subunits, as revealed through size exclusion chromatography and cross-linking analysis. Two genes, glyA and glyB, encoding the 39- and 14-kDa subunits, respectively, were identified based on the N-terminal sequences of the subunits. From the nucleotide sequences of glyA and glyB, we conclude that both genes are translated as bacteriocin precursors that include N-terminal leader sequences. When expressed in E. coli, recombinant glycinecin A was found primarily in cell extracts. In contrast, most glycinecin A from Xanthomonas was found in the culture media. E. coli transformed with either glyA or glyB separately did not show the bacteriocin activity.

Bacteriocins↗

PubMed2001

Conspicuity of hepatocellular nodular lesions in cirrhotic livers at ferumoxides-enhanced MR imaging: importance of Kupffer cell number.

PURPOSE: To correlate the conspicuity of hepatocellular carcinomas and dysplastic nodules on ferumoxides-enhanced magnetic resonance (MR) images with the number of Kupffer cells in the hepatic lesions, as compared with that in background liver in histopathologic findings. MATERIALS AND METHODS: Sixty-nine histopathologically proved moderately or poorly differentiated hepatocellular carcinomas, 10 well-differentiated hepatocellular carcinomas, and 19 dysplastic nodules were retrospectively studied in 68 patients with cirrhosis who underwent ferumoxides-enhanced MR imaging. The contrast-to-noise ratio between the nodules and surrounding parenchyma was calculated at T2-weighted fast spin-echo imaging, and the difference in the number of Kupffer cells between the nodules and surrounding hepatic tissue was calculated histopathologically. The results of MR imaging and histopathologic examination were correlated. RESULTS: All 69 moderately or poorly differentiated hepatocellular carcinomas had high contrast-to-noise ratios at MR imaging and large differences in the number of Kupffer cells. Six of the 10 well-differentiated hepatocellular carcinomas had contrast-to-noise ratios of zero or nearly zero, and five of these had little difference in the number of Kupffer cells. All 19 dysplastic nodules had contrast-to-noise ratios of zero or nearly zero, and there were virtually no differences in the number of Kupffer cells. CONCLUSION: Hepatocellular nodule conspicuity at ferumoxides-enhanced MR imaging depends on differences in the number of Kupffer cells within a nodule and the surrounding cirrhotic liver; moderately or poorly differentiated hepatocellular carcinomas can be distinguished from well-differentiated hepatocellular carcinomas and dysplastic nodules.

Adult↗

PubMed2001

Pulsatile flow regulates monocyte adhesion to oxidized lipid-induced endothelial cells.

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC), a component of minimally modified low density lipoprotein, induces monocyte adhesion to endothelial cells. It is not known whether the upstroke slopes of pulsatile flow, defined as shear stress slew rates (tau(r)/tauT)), can regulate monocyte binding to ox-PAPC-treated bovine aortic endothelial cells (BAECs). At 60 cycles per minute, ox-PAPC-treated BAECs were exposed to 3 conditions representing known vascular conditions: (1) high shear stress slew rates (tau(r)/tau(T)=293 dyne. cm(-2). s(-1)), with time-averaged shear stress=50 dyne/cm(2); (2) low shear stress slew rate (tau(r)/tau(t)=71 dyne. cm(-2). s(-1)), with identical time-averaged shear stress; and (3) reversing oscillating flow (0+/-2.6 mm Hg). Reverse transcription-polymerase chain reaction and quantification were performed for monocyte chemoattractant protein-1 (MCP-1) mRNA expression. High tau(r)/tau(t) reduced monocyte binding to ox-PAPC-treated BAECs by 64+/-3.2% compared with static conditions, and low tau(r)/tau(t) reduced monocyte binding by 31+/-3.4%, whereas oscillating flow increased monocyte binding by 22+/-1.7% (P<0.005). High partial tau(r)/tau(t) downregulated MCP-1 expression by 33+/-8%, and low partial tau(r)/tau(t) downregulated MCP-1 expression by 15+/-4%, but oscillating flow upregulated MCP-1 by 13+/-5%. These results suggest that shear stress slew rates regulate monocyte binding by modulating the expression of a potent monocyte chemoattractant.

Animals↗

PubMed2001

Arthroscopically assisted treatment of avulsion fractures of the posterior cruciate ligament from the tibia.

BACKGROUND: The attachment of the posterior cruciate ligament to the posterior intercondylar fossa of the tibia is in a location that is difficult to access for arthroscopic surgical procedures. This report presents a variety of arthroscopically assisted reduction and fixation methods for managing avulsion fractures of the posterior cruciate ligament from the tibia. METHODS: Thirteen patients (fourteen knees) who had an avulsion fracture of the posterior cruciate ligament were treated with an arthroscopic procedure. Eleven patients underwent the operation in the acute phase (four to ten days after the injury), and two patients had delayed surgery (at nineteen and twenty months after the injury) because of nonunion. The choice of fixation method was based on the size of the avulsed fragment. Six knees that had a small bone fragment (<10 mm) with comminution were fixed with use of multiple sutures. Two knees that had a small bone fragment without comminution were fixed with 23-gauge wires. Two knees that had a medium-sized fragment (10 to 20 mm) were fixed with Kirschner wires. Four knees that had a large single fragment of bone (>20 mm) that involved the condyles were fixed with one or two cannulated screws. RESULTS: All patients had osseous union as determined on radiographs. Three injured knees in two patients showed limitation of motion after the operation. These patients had been immobilized for two or three months after the surgery because of concomitant fractures. The eleven patients who had undergone the operation in the acute phase, including two in whom postoperative arthrofibrosis had developed, showed no or trace posterior instability following the procedure. However, the two patients in whom the surgery had been delayed had residual grade-I posterior instability. The postoperative side-to-side differences, when measured with use of the KT-2000 arthrometer and posterior stress radiographs, showed better results in the patients in whom the surgery had been performed in the acute phase than in the patients in whom the operation had been delayed. CONCLUSION: Arthroscopic procedures can be used to treat tibial avulsion fractures of the posterior cruciate ligament.

Accidental Falls↗

PubMed2001

Tissue-engineered heart valve leaflets: an animal study.

BACKGROUND: Tissue-engineered heart valve leaflets are a promising way to overcome the inherent limitations of current prosthetic valves. The aim of this study was to compare the biological responses of an autologous cell seeded scaffold and an acellular scaffold implanted in the pulmonary valve leaflet in the same animal. METHODS: Myofibroblasts and endothelial cells were isolated and cultured from an ovine artery. A synthetic biodegradable scaffold consisting of polyglycolic acid and polylactic acid was initially seeded with the myofibroblasts, then coated with endothelial cells. Cells were seeded using a medium containing collagen and cultured. A tissue-engineered construct and a plain scaffold were implanted as double pulmonary valve leaflet replacement in the same animal in an ovine model (n=3). Additionally, the tissue-engineered construct (n=2) and the plain scaffold (n=2) were implanted as single valve leaflet replacements for long-term analysis. After sacrifice, the implanted valve leaflet tissues were retrieved, analyzed visually and using light microscopy. RESULTS: Three animals that underwent replacement of two valve leaflets with a tissue-engineered construct and a plain scaffold, survived only a short-time (12, 24, 36 hours). The death was attributed to heart failure caused by severe pulmonary insufficiency. Animals that underwent single valve leaflet replacement survived longer and were electively sacrificed at 6 and 9 weeks after operation. The analysis of the leaflets from the short-term survivors showed that the tissue-engineered constructs contained less fibrins and protein exudates than the plain scaffold. In contrast, leaflets obtained from animals surviving 6 and 9 weeks showed similar well organized granulation tissues in the tissue-engineered constructs and the plain scaffolds. CONCLUSION: This animal experiment demonstrates that in the early phase of implantation, the tissue-engineered construct shows a better biological response in terms of antithrombogenicity than the plain scaffold, although both of them have similar results in the later reparative phase.

Animals↗

PubMed2000

Immunocytochemical localization of neuronal and inducible nitric oxide synthase in the retina of zebrafish, Brachydanio rerio.

Several previous studies have revealed the distribution of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in the retina of various species. However, nothing has been reported on the nNOS and iNOS expression in zebrafish retina, even though it has been used as an effective model for developmental studies. In this study on nNOS and iNOS immunoreactivity (IR) in the zebrafish retina, iNOS-IR signals were detected in the ganglion cell layer (GC), the inner plexiform layer (IP), the outer plexiform layer (OP) and the photoreceptor layer (PR). nNOS-IR signals were also intensely detected in the GC, IP, OP and PR. These signals were very similar to the iNOS-IR signals, except for some minor differences in relative intensities. This could be explained by the speculation that the synthesis of nitric oxide by iNOS may represent a compensatory mechanism in the absence of nNOS. We described for the first time the distribution of nNOS and iNOS-IR cells in zebrafish retina. This could provide the basis for further study on the nNOS and iNOS properties of zebrafish retina.

Animals↗

PubMed2000

Clonal characterization of a bipotent T cell and NK cell progenitor in the mouse fetal thymus.

We recently described a population of fetal thymocytes with a CD117+NK1.1+CD90lowCD25- phenotype, which were shown to contain committed T cell and NK cell progenitors. However, the characterization of a single cell with a restricted T and NK cell precursor potential was lacking. Here, using an in vitro model for T and NK cell differentiation, we provide conclusive evidence demonstrating the existence of a clonal lineage-restricted T and NK cell progenitor. These results establish that fetal thymocytes with a CD117+NK1.1+CD90lowCD25- phenotype represent bipotent T and NK cell progenitors.

Animals↗

PubMed2000

Comparison of open pulled straw (OPS) vs glass micropipette (GMP) vitrification in mouse blastocysts.

The purpose of this study was to investigate the use of a glass micropipette (GMP) as a vessel for vitrification of mouse blastocysts, and to compare the post-thaw survival of these blastocysts with those cooled in open pulled straws (OPS). The GMP vessel permits higher freezing and warming rates than OPS due to the higher heat conductivity of glass and lower mass of the solution containing the embryos. Groups of 6 mouse blastocysts were sequentially placed into 2 vitrification solutions before being loaded into either the OPS or GMP vessels and immersed into LN2 within 20 to 25 sec. Post-thaw blastocysts were serially washed in 0.25 and 0.15 M sucrose in holding medium (HM) and modified human tubal fluid medium (mHTF), each for 5 min, and then cultured in mHTF supplemented with 10% FCS for 24 h. The rate of blastocyst re-expansion did not differ significantly for OPS (93.5%) and GMP (95.0%) methods (P<0.05). The hatching rate in OPS (88.7%) was similar to that in GMP (90.0%) but was lower than for the unvitrified control embryos (98.3%, P<0.05). To determine the optimal embryo population per GMP vessel, the pipettes were loaded with 2 to 10 embryos. The rate of blastocyst re-expansion after vitrification was significant for 2 to 4 embryos than for 6 to 10 embryos per vessel. In addition, the rate of blastocyst re-expansion was significantly lower if blastocysts were vitrified in the wide rather than the narrow portion of the micropipette (100 vs 87.5%; P<0.05) even when only 4 blastocysts were loaded per vessel. These results indicate that both vitrification vessels can provide high rates of embryo survival. However, the GMP vessel does not need a cap to protect the vessel from floating after immersion in LN2. The number and location of the embryos (narrow versus wide portion of capillary) were considered to be limiting factors to the viability of mouse embryos.

Animals↗

PubMed2000

The distribution and requirements of microtubules and microfilaments in bovine oocytes during in vitro maturation.

Microtubules and microfilaments are major cytoskeletal components and important modulators for chromosomal movement and cellular division in mammalian oocytes. In this study we observed microtubule and microfilament organisation in bovine oocytes by laser scanning confocal microscopy, and determined requirements of their assembly during in vitro maturation. After germinal vesicle breakdown, small microtubular asters were observed near the condensed chromatin. The asters appeared to elongate and encompass condensed chromatin particles. At the metaphase stage, microtubules were observed in the second meiotic spindle at the metaphase stage. The meiotic spindle was a symmetrical, barrel-shaped structure containing anastral broad poles, located peripherally and radially oriented. Treatment with nocodazole did not inhibit germinal vesicle breakdown. However, progression to metaphase failed to occur in oocytes treated with nocodazole. In contrast, microfilaments were observed as a relatively thick uniform area around the cell cortex and overlying chromatin following germinal vesicle breakdown. Treatment with cytochalasin B inhibited microfilament polymerisation but did not prevent either germinal vesicle breakdown or metaphase formation. However, movement of chromatin to the proper position was inhibited in oocytes treated with cytochalasin B. These results suggest that both microtubules and microfilaments are closely associated with reconstruction and proper positioning of chromatin during meiotic maturation in bovine oocytes.

Actin Cytoskeleton↗