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Biomedical subjects

B W Youn

Publications and source records attributed to B W Youn.

11 recordsLinked to original sources
PubMed2001

Mechanisms of organoselenium compounds in chemoprevention: effects on transcription factor-DNA binding.

Data obtained on the effects of selenium compounds on regulatory transcription factor-DNA binding by other laboratories are briefly reviewed, and some of our own results in this area are also presented. We assessed the in vitro and in vivo effects of the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate (p-XSC) on the binding activities of the transcription factors nuclear factor-kappa B (NF-kappa B), activator protein-1 (AP-1), Sp1, and Sp3 using the HCT-116 (human colorectal adenocarcinoma) cell line as a model system. Using nuclear extracts, electrophoretic mobility shift assays were carried out to determine the extent of binding of the transcription factors to their respective consensus recognition sites on radiolabeled oligonucleotides. p-XSC and sodium selenite reduced the consensus site binding activity of NF-kappa B in a concentration-dependent manner when nuclear extracts from cells stimulated with tumor necrosis factor-alpha were incubated with either compound ("in vitro"). However, only p-XSC inhibited NF-kappa B consensus recognition site binding when the cells were pretreated with either compound and were then stimulated with tumor necrosis factor-alpha ("in vivo"). In contrast, the consensus site binding activity of AP-1 was inhibited only with sodium selenite, but not with p-XSC in vitro or in vivo. p-XSC or sodium selenite reduced the consensus site binding of transcription factors Sp1 and Sp3 in concentration- and time-dependent manners when nuclear extracts from cells treated with either compound in vivo were assayed by electrophoretic mobility shift assay. 1,4-Phenylenebis(methylene)thiocyanate, the sulfur analog of p-XSC, which is inactive in chemoprevention, had no effect on the oligonucleotide binding of Sp1 and Sp3. Our observations could provide further clues as to the mechanisms involved in the chemoprevention of cancer by p-XSC.

Animals↗
PubMed1989

Purification and characterization of pre-S-containing hepatitis B surface antigens produced in recombinant mammalian cell culture.

Heterogeneous, pre-S-rich HBsAg particles were expressed in recombinant mammalian cell culture and purified to near homogeneity. The purification process comprises: concentration of cell culture medium, protein precipitation by poly(ethylene glycol), gel filtration column chromatography, isopycnic ultracentrifugation by KBr and sucrose density gradient ultracentrifugation. The resulting HBsAg product was greater than 98% pure, and contained much of pre-S1 and pre-S2 components. Scanning densitometry analysis of the silver-stained HBsAg product showed approximately 70-80% S protein, approximately 10-20% pre-S2 protein, and approximately 5-15% pre-S1 protein. It was estimated that the amount of HBV-specific DNA present the final product was less than 7 pg mg-1 HBsAg. Further biochemical analysis has demonstrated that the HBsAg particles are very heterogeneous in charge and density. Charge heterogeneity was quite random among the particles, but density heterogeneity could be related to the different amounts of pre-S2 component in the particles.

Cells, Cultured↗
PubMed1989

Expression of hepatitis B virus surface antigen containing the pre-S region in mammalian cell culture system.

The surface antigen of hepatitis B virus (HBV) has been expressed in a mouse cell line using metallothionein-bovine papilloma virus vectors. Four different recombinant plasmids were used and it was found that the expression level varies significantly from one plasmid to another. Removing the HBV polyadenylation signal from the plasmid drastically reduced the expression level. Providing even a heterologous polyadenylation signal improved the expression level from the reduced one by at least tenfold. The steady-state level of cytoplasmic HBV-specific RNA was much higher when the polyadenylation signal was present. One of the constructs gave a very high expression level and has been characterized further. It was possible to detect any plasmid in the episomal form in the producing clones and all the HBV DNA was found to be integrated in the mouse chromosome at more than one site. The copy number of the plasmid varied greatly between different clones and in the best one it is approximately 150 copies per haploid genome. Cells can be grown continuously in the presence of cadmium chloride without splitting for more than two months and the excreted surface antigen can be harvested during this period. Western blot analysis showed that the antigen contains the pre-S region.

Animals↗
PubMed1983

Neural tube (canal) morphogenesis in notochordless amphibian (Xenopus laevis) embryos.

Neural tube (canal) morphogenesis was examined in embryos which exhibited notochord defects. Embryos which displayed a range of notochord defects were produced by either ultraviolet irradiation or cold shock treatments. Both treatments produced similar results. The neural canal appeared normal in morphology and internal ciliation in many of the embryos which contained severe notochord defects.

Animals↗
PubMed1981

Tissue interactions during axial structure pattern formation in amphibia.

Tissue interactions have traditionally been assigned important roles in establishing the pattern of amphibian axial structure morphogenesis. Those interactions have been postulated to generate the patterns of neural fold morphogenesis, neural tube formation, and somite development. A review of axial structure development together with a brief discussion of the classical viewpoint, is presented. A re-examination of axis formation has recently been carried out with the SEM. Embryos which displayed major defects in notochord development, ranging from diminished length to complete obliteration, were produced by irradiating fertile eggs prior to first cleavage. A comparative SEM analysis of normal and "notochord defective" embryos revealed that, contrary to previous reports, the notochord is apparently a dispensable component of the developing axial structure system. Lastly, TEM examination of the notochord defective embryos allowed some insight into the ultrastructural alterations which occur in the notochord and neural tube cells of irradiated embryos. Additional information about the structure of the notochord, and the cellular mechanics of somitogenesis emerged from those studies.

Animals↗
PubMed1981

Somitogenesis in the amphibian Xenopus laevis: scanning electron microscopic analysis of intrasomitic cellular arrangements during somite rotation.

The intrasomitic changes in cell arrangement which accompany somite rotation during somitogenesis in Xenopus laevis were analysed with the scanning electron microscope (SEM). Longitudinal, horizontal fractures of whole embryos were examined at various dorsoventral levels of stage-22 to -24 embryos. Observations of the gross morphological features of somitogenesis, and the cellular changes which accompany somite segmentation and somite rotation were made. Several of these observations lead to modifications of previous models for the cellular basis of somitogenesis in Xenopus. Individual cellular rearrangements, rather than simultaneous block rotation of a whole somite, appear to be responsible for the 90 degrees rotation of myotomal cells within a single somite. Cellular arrangements in fused somites were also examined. Some ultraviolet-irradiated embryos displayed a complete lack of a notochord. The somites in those embryos were fused across the midline beneath the neural tube. The dorsal and ventral arms of the somites are not fused. Normal rotation occurs only in the dorsal and ventral arms while, in the majority of cases, cells in the fused region fail to rotate normally. In some cases, individual cells in the fused region undergo partial rearrangement. Those observations support the notion that individual cellular rearrangements account for the rotation of the whole somite.

Animals↗
PubMed1981

Comparative analysis of amphibian somite morphogenesis: cell rearrangement patterns during rosette formation and myoblast fusion.

Detailed SEM observations of the changes in cellular morphology, arrangements, and contacts that occur during the process of somite formation were made in two species of urodele amphibians, Ambystoma mexicanum and Pleurodeles waltlii, and one species of anuran amphibian, Rana sphenocephala. After fixation, embryos were fractured transversely, horizontally, and parasagittally, and the intrasomitic cellular arrangement pattern was examined with the SEM. It was found that Ambystoma and Pleurodeles embryos followed exactly the same development sequence in rosette formation and myoblast fusion. Rana somites did not, however, appear to form rosettes. Those myotomal cells underwent fusion immediately after a few segmentations occurred. Patterns of cellular rearrangement were also described during urodele rosette formation at the time of somite segmentation and during myoblast fusion. Extensive changes in cell shape and orientation appeared to occur during those processes. When cells changed their orientation, they often exhibited a triangular configuration. Probable roles of these triangular-shaped cells in rosette formation and myoblast fusion are discussed. During the initial period of myoblast or myotomal cell fusion, cells first send out specialized cell processes and then establish their cell-cell contacts. The establishment of such contacts eventually leads to tight membrane appositions and fusion. Since myoblast fusion appeared to occur between two cells which were tandemly arranged in a rosette, the origin of multi-nuclearity in the fused cells is discussed. Finally, comparative analyses of the pattern of somite formation and subsequent muscle development were made between different species of amphibians. The possibility is discussed that patterns of somitogenesis may provide useful indicators for determining how different families of amphibians evolved.

Ambystoma mexicanum↗
PubMed1980

An atlas of notochord and somite morphogenesis in several anuran and urodelean amphibians.

A scanning electron microscopic, comparative survey of notochord and somite formation including some details of change in cell morphology and arrangement, was made of selected stages of two species of anuran amphibians (Xenopus laevis and Rana pipiens) and two species of urodeles (Ambystoma mexicanum and Pleurodeles waltlii). The ectoderm or neural plate was removed from fixed embryos and the dorsal aspect of the developing notochord and somite mesoderm was photographed. Micrographs of comparable stages of all species were arranged together to form an atlas of notochord and somite formation. Similar morphogenetic events occur in the same sequence in the four species. Notochordal cells become distinguishable from paraxial mesodermal cells by shape, closeness of packing, and arrangement. Notochordal elongation is accompanied by a decrease in cross-sectional area and by cell rearrangement. Somitic mesoderm becomes distinguished from lateral mesoderm by a change in cell shape and orientation, followed by segmentation of somites. The schedule of somite formation was compared and related to the staging series for each species. The urodeles differ from the anurans in that the notochordal region in the early neurula stages in triangular, with the broadest part in the posterior region of the embryo. In anurans it is uniform in width. This difference may reflect differences in gastrulation and in the mechanism of elongation of the posterior part of the embryo in the neurula.

Ambystoma mexicanum↗