[ ] oxide layer on the surface of each W(tungsten) nanopowder produced by the electric explosion of wire(EEW) process were formed during the 1vol.% air passivation process. The oxide layer hindered sintering densification of compacts during SPS process. The oxide phase was reduced to the pure W phase during SPS. The W nanopowder's compacts treated by the hydrogen reduction showed high sintered density of 94.5%. after SPS process at .

The zebrafish (Danio rerio) is a vertebrate model system suitable for fishing novel genes in post-genome era. Two neural mutants isolated from the ENU-based chemical mutagenesis, were characterized and the point mutations were identified by the positional cloning method. The first mutant is headless: Wnt antagonists secreted by the organizer have been identified as head inducers. The severe head defects in headless are due to a mutation in Tcf-3, a component of the Wnt pathway. The second is mind bomb: Reduced lateral inhibition in mutant permits too many neural progenitors to differentiate as neurons. Mind bomb encodes a novel gene in the Notch signaling pathway. In addition to chemical mutagenesis, we developed a novel transgene reporter system and tried to apply its use for the insertional mutagenesis. The first mutant "ondal" from this new screening approach, was characterized and mapped to a gene involved in axonal myelination and human schizophrenia. The other mutants, samdori and hayan-4 are being mapped and characterized. As a separate approach, we are challenging a genome-wide screen against the human UniGene collections. Currently, more than 15,000 human full-length cDNAs are available from the Korean UniGene Information (KUGI). After in silico screening of functionally unknown genes through database search, we performed overexpression experiments by microinjecting the single human genes into the zebrafish embryos. So far, we performed microinjections more than 2,700 human full-length cDNAs and identified 50 functionally active genes. Zebrafish embryos display variable phenotypes from developmental defects to neuronal cell death in injected embryos. Many of these genes were involved in not only developmental process but also diseases, such as cancer. After these phenotype-based screening, homologous zebrafish genes were cloned and further functional studies were performed by expression analysis, overexpression and antisense knockdown approaches. From these functionally active genes, we found that the human clone #462, now named it as "Ottogi", plays a role in vertebrate head formation during early development. Overexpression of Ottogi caused a big head phenotype, indicating its possible role in the Wnt signaling pathway. Ottogi physically interacted with the Wnt receptor Frizzled 8 within the endoplasmic reticulum. These findings suggest that Ottogi is a novel component negatively regulating the Wnt signal pathway. In addition, the human clone #498, now named as ZNF312b, plays a role in tumor progression and metastasis in gastric cancer via transcriptional activation of the K-ras oncogene. ZNF312b seems to be specifically overexpressed in gastric cancer tissues and cell lines. The overexpression of ZNF312b induces cancer-like phenotypes, including accelerated proliferation and increased tumor masses in nude mice, which are reversed by its knockdown in gastric cancer cell lines, implying involvement in gastric tumor progression.

The zebrafish (Danio rerio) is now the pre-eminent vertebrate model system for clarification of the roles of specific genes and signaling pathways in development. I will talk about positional cloning of two developmental mutants in zebrafish. The first mutant is headless: The vertebrate organizer can induce a complete body axis when transplanted to the ventral side of a host embryo by virtue of its distinct head and trunk inducing properties. Wingless/Wntantagonists secreted by the organizer have been identified as head inducers. Their ectopic expression can promote head formation, whereas ectopic activation of Wnt signalling during early gastrulation blocks head formation. These observations suggest that the ability of head inducers to inhibit Wntsignalling during formation of anterior structures is what distinguishes them from trunk inducers that permit the operation of posteriorizing Wnt signals. I describe the zebrafish headless (hdl) mutant and show that its severe head defects are due to a mutation in T-cell factor-3 (Tcf3), a member of the Tcf/Lef family. Loss of Tcf3 function in the hdl mutant reveals that hdl represses Wnt target genes. I provide genetic evidence that a component of the Wntsignalling pathway is essential in vertebrate head formation and patterning. Second mutant is mind bomb: Lateral inhibition, mediated by Notch signaling, leads to the selection of cells that are permitted to become neurons within domains defined by proneuralgene expression. Reduced lateral inhibition in zebrafish mib mutant embryos permits too many neural progenitors to differentiate as neurons. Positional cloning of mib revealed that it is a gene in the Notch pathway that encodes a RING ubiquitin ligase. Mib interacts with the intracellular domain of Delta to promote its ubiquitylation and internalization. Cell transplantation studies suggest that mib function is essential in the signaling cell for efficient activation of Notch in neighboring cells. (중략)

Nitrate in edible vegetables is converted to nitrite by nitrate reductase(NR) and/or bacteria in intestines. Nitrite and amino, in the intestine of some animals and human, bind to form nitrosamine, which is toxic and known as carcinogen. This study was carried out to examine the effect of added chlorides and their concentrations on growth, yield and nitrate content in leaf lettuce plants in hydroponics. Seeds of lettuce cv, "Samsunjokchukmyon" were planted on April 29, and seedlings were planted on June 2, and were cultured until July 5 in 1998. KCI and CaCl₂ were used as chloride source and their concentrations were 1, 2 and 4 me/L, respectively, in the lettuce standard nutrient solution for National Horticultural Research Institute(NHRI). Completely randomized design with 3 replications was used. Nitrate content and NR activity were measured 2 and 5 weeks after planting(WAP). The obtained results were summarized as the follows : Leaf weight per plant was difference from harvest dates and treatments, but total leaf weight was not significantly different among treatments. Number of leaves was higher in KCI 2 me/L, CaCl₂1 me/L and control at 2 WAP than the others, and was higher in KCI 1 me/L, and control at 3 WAP than others, and was higher in control at 5 WAP. Total number of harvested leaves was the highest in control with 14, which followed by KCI 2 me/L and CaCl₂1 me/L. Nitrate content was decreased by addition of chloride in nutrient solution. Nitrate content in the 3rd and 9th leaves was significantly decreased. NR activity was higher in control and CaCl₂ addition treatments, while KCI addition treatments reduced NR activity. However, no direct relationship with nitrate was observed. Growth characteristics such leaf length and leaf width were not significantly influenced by chloride addition.