PubMed Health⌕ Search

Biomedical subjects

C H Yoon

Publications and source records attributed to C H Yoon.

At least 37 records · Page 2Linked to original sources
PubMed1996

Topographically specific effects of ELF-1 on retinal axon guidance in vitro and retinal axon mapping in vivo.

Topographic maps, which maintain the spatial order of neurons in the order of their axonal connections, are found throughout the nervous system. In the visual retinotectal projection, ELF-1, a ligand in the tectum, and its receptors in the retina show complementary gradients in expression and binding, indicating they may be positional labels for map development. Here we show that ELF-1 acts as a repellent axon guidance factor in vitro. In vivo, when the tectal ELF-1 pattern is modified by retroviral overexpression, retinal axons avoid ectopic ELF-1 patches and map to abnormally anterior positions. All these effects were seen on axons from temporal but not nasal retina, indicating that ELF-1 could determine nasal versus temporal retinotectal specificity, and providing a direct demonstration of a cell recognition molecule with topographically specific effects on neural map development.

Animals↗
PubMed1995

Similarity of sli-1, a regulator of vulval development in C. elegans, to the mammalian proto-oncogene c-cbl.

Vulval induction during Caenorhabditis elegans development is mediated by LET-23, a homolog of the mammalian epidermal growth factor receptor tyrosine kinase. The sli-1 gene is a negative regulator of LET-23 and is shown here to encode a protein similar to c-Cbl, a mammalian proto-oncoprotein. SLI-1 and c-Cbl share approximately 55 percent amino acid identity over a stretch of 390 residues, which includes a C3HC4 zinc-binding motif known as the RING finger, and multiple consensus binding sites for Src homology 3 (SH3) domains. SLI-1 and c-Cbl may define a new class of proteins that modify receptor tyrosine kinase-mediated signal transduction.

Amino Acid Sequence↗
PubMed1991

Immunohistochemical and biochemical identification of pepsinogen isozymes in the hamster lungs: induction by polychlorinated biphenyls.

Pepsinogens are acid protease enzymes of pepsin usually found in gastric mucosa. In the present study, we demonstrated the presence of pepsinogen isozymes in male Syrian golden hamster lung tissues by a combined immunohistochemical and biochemical approach. Immunohistochemically, using rat pepsinogen 1 antibody, pepsinogen positive cells were observed mainly in the epithelia of the terminal bronchioles. They demonstrated morphological features of Clara cells. The pepsinogen isozyme pattern of lung tissue determined by polyacrylamide gel electrophoresis was similar to that of stomach mucosa. Treatment of hamsters with polychlorinated biphenyls at a dose of 500 mg/kg body weight ip caused a 2.8-fold increase in pepsinogen content (p less than 0.01) as well as increase in numbers of pepsinogen positive cells in the lung.

Animals↗
PubMed1977

Development of Purkinje cell somatic spines in the weaver mouse.

The cerebellar cortices of weaver mice and their normal littermates ranging in age from six to thirteen days after birth were examined with the electron microscope. The initial development of spines, both somatic and dendritic, are the same in both the weaver and its normal littermates despite the extreme paucity of parallel fibers in the former.

Animals↗
PubMed1977

Fine structure of the cerebellum of "staggerer-reeler", a double mutant of mice affected by staggerer and reeler conditions. I. The premature disappearance of the external granular layer and ensuing cerebellar disorganization.

It was reasoned that cerebella of mice carrying both staggerer and reeler conditions, called double mutant, might accentuate some of the anomalies observed in single mutants, thus revealing further details otherwise undetectable. As expected, the cerebellar hypoplasia, the paucity of fissures, granule cells and interneurons of the molecular layer, and the external granular layer hypoplasia, common in both staggerer and reeler, were much more pronounced in double mutant. However, the most striking feature of the double mutant cerebellum was the premature disappearance of the external granular layer. The external granular layer is smaller both in staggerer and reeler as compared to the normal but it persists beyond the normal time (around day 15). In double mutant, however, the external granular layer disappeared by day 7 or 8, reducing the density of granule cells even further. This observation was interpreted as indicating that both the staggerer and reeler genes effect the premature disappearance of the external granular layer. Most of the gross cerebellar anomalies in double mutant such as cerebellar hypoplasia, paucity of fissures and Purkinje and Golgi epithelial cell disalignment could be explained as the result of this premature disappearance of the external granular layer. On the other hand, anomalies of Purkinje cells and Bergmann fibers, which are also present both in staggerer and reeler, did not follow the same additive change.

Animals↗
PubMed1977

Fine structure of the cerebellum of "staggerer-reeler", a double mutant of mice affected by staggerer and reeler conditions. II. Purkinje cell anomalies.

Purkinje cells in double mutant were very similar to those in staggerer both at days 7 and 15, and could not be distinguished from staggerer Purkinje cells by morphological criteria. They were small and immature looking, and their nuclei were invariably eccentric in position both at days 7 and 15. The typical funnel stage was not observed at any time. Somatic spines and their synapses were extermely rare at day 7 when they are abundant in the normal, but they were present at day 15 with typical synapses with climbing fibers. Dendritic spines were also present at day 15 although extremely infrequent, and they showed synapses both with parallel and climbing fibers. More often, however, parallel and climbing fibers were found in synapsis with the smooth surgace of these dentrites. These observations were in close agreement with those of staggerer Purkinje cells. The persistence of staggerer Purkinje cell soma anomalies in double mutant was interpreted as indicating that these anomalies are specific effects of the staggerer gene, being relatively free from environmental influences.

Animals↗
PubMed1977

Fine structure of the cerebellum of "staggerer-reeler", a double mutant of mice affected by staggerer and reeler conditions. III. bergmann fiber anomalies.

Bergmann fibers and the distribution of Golgi epithelial cells were significantly altered in staggerer, reeler and double mutant (affected by both staggerer and reeler conditions). However, the Bergmann fiber anomalies in double mutant were not identical to those of either staggerer or reeler. A comparison of these anomalies with the anomalies described in weaver revealed that the developmental patterns of Bergmann fibers are distinct in all four cerebellar mutants just as are the cytoarchitectural anomalies of these cerebella. The results of the present electronmicroscopic examinations of Bergmann fibers in staggerer and reeler were in good agreement with the findings made with the immunofluorescence technique. There was, however, one important discrepancy between these two sets of observations. Immunofluorescent astrocytic fibers were nearly absent in 21 and 26 day old staggerers while Bergmann fibers were structurally present in nearly normal numbers both at days 21 and 31. A possible reason for this discrepancy was discussed.

Age Factors↗
PubMed1977

Further characterization of rennin action on kappa-casein using carboxymethylcellulose: effects of various additives on the enzymatic hydrolysis of kappa-casein.

The effects of various additives on the reaction of rennin with kappa-casein were investigated by using carboxymethylcellulose. Both urea and sodium 1-anilino-8-naphthalenesulfonate effectively inhibited rennin action at concentrations larger than 2 M and 2 mM, respectively. These reagents, however, activated the enzyme action at the lower concentrations. Both alpha S-and beta-caseins had some ranges of concentrations in which the rennin reaction was activated. Calcium chloride had an inhibitory effect on the rennin action. Neither mercaptoethanol nor KCl had any appreciable effect on the enzymatic hydrolysis of kappa-casein. These results are analyzed in terms of the association and dissociation of kappa-casein due to the presence of these additives in the reaction solutions.

Adsorption↗
PubMed1975

Interaction of cerebellar mutant genes. II. Mice doubly affected by 'reeler' and 'weaver' conditions.

An an extension of a study of the mode of ineraction of mutant genes that affect motor activities and cerebellar cytoarchitectonics, mice doubly affected by both the 'reeler' and 'weaver' conditions were produced. The cerebellum of the double mutant showed both reeler and weaver characteristics. Anomalies present in both mutants were greatly accentuated in the double mutant. In addition to the paucity of fissures and general cerebellar disorganization observed in reeler and the extreme scarcity of granule cells seen in weaver, double mutants showed an additional decrease in the cerebellar size and the molecular layer, and a further loss of external granule cells. These observations were interpreted as indicating that the effects of the reeler and weaver genes upon altering the cytoarchitectonics of the cerebellum were additive.

Animals↗
PubMed1975

Total retinal degeneration in apparent anophthalmos of the Syrian hamster.

Anophthalmia in the Syrian hamster was found to result from an extensive degeneration of retinal tissue and tissues derived from the retina. Eyes of affected animals were normal at the twelfth day of gestation (the average gestation period in the Syrian hamster is 16 days). However, the retina of these eyes showed rapid and extensive degeneration during the first two weeks after birth. In adults, the sclera-choroid complex was the only prominent structure of the original eye, with an occasional remnant of deteriorated lens.

Animals↗