No abstract

A single intravenous injection of L-[ 3H]fucose, a specific glycoprotein precursor, was given to young 35-45 g rats which were sacrificed at times varying between 2 min and 30 h later. Radioautography of over 50 cell types, including renewing and nonrenewing cells, was carried out for light and electron microscope study .At early time intervals (2-10 min after injection), light microscope radioautography showed a reaction over nearly all cells investigated in the form of a discrete clump of silver grains over the Golgi region . This reaction varied in intensity and duration from cell type to cell type . Electron microscope radioautographs of duodenal villus columnar cells and kidney proximal and distal tubule cells at early time intervals revealed that the silver grains were restricted to Golgi saccules . These observations are interpreted to mean that glycoproteins undergoing synthesis incorporate fucose in the saccules of the Golgi apparatus . Since fucose occurs as a terminal residue in the carbohydrate side chains of glycoproteins, the Golgi saccules would be the site of completion of synthesis of these side chains.At later time intervals, light and electron microscope radioautography demonstrated a decrease in the reaction intensity of the Golgi region, while reactions appeared over other parts of the cells : lysosomes, secretory material, and plasma membrane . The intensity of the reactions observed over the plasma membrane varied considerably in various cell types ; furthermore the reactions were restricted to the apical surface in some types, but extended to the whole surface in others .Since the plasma membrane is covered by a "cell coat" composed of the carbohydraterich portions of membrane glycoproteins, it is concluded that newly formed glycoproteins, after acquiring fucose in the Golgi apparatus, migrate to the cell surface to contribute to the cell coat . This contribution implies turnover of cell coat glycoproteins, at least in nonrenewing cell types, such as those of kidney tubules . In the young cells of renewing populations, e .g . those of gastro-intestinal epithelia, the new glycoproteins seem to contribute to the growth as well as the turnover of the cell coat . The differences in reactivity among different cell types and cell surfaces imply considerable differences in the turnover rates of the cell coats .2 5 8

The incorporation of fucose-3 H in rat thyroid follicles was studied by radioautography in the light and electron microscopes to determine the site of fucose incorporation into the carbohydrate side chains of thyroglobulin, and to follow the migration of thyroglobulin once it had been labeled with fucose 3H . Radioautographs were examined quantitatively in vivo at several times after injection of fucose 3H into rats, and in vitro following pulselabeling of thyroid lobes in medium containing fucose 3H . At 3-5 min following fucose3H administration in vivo, 85% of the silver grains were localized over the Golgi apparatus of thyroid follicular cells . By 20 min, silver grains appeared over apical vesicles, and by 1 hr over the colloid . At 4 hr, nearly all of the silver grains had migrated out of the cells into the colloid . Analysis of the changes in concentration of label with time showed that radioactivity over the Golgi apparatus increased for about 20 min and then decreased, while that over apical vesicles increased to reach a maximum at 35 min . Later, the concentration of label over the apical vesicles decreased, while that over the colloid increased . Similar results were obtained in vitro . It is concluded that fucose, which is located at the end of some of the carbohydrate side chains, is incorporated into thyroglobulin within the Golgi apparatus of thyroid follicular cells, thereby indicating that some of these side chains are completed there . Furthermore, the kinetic analysis demonstrates that apical vesicles are the secretion granules which transport thyroglobulin from the Golgi apparatus to the apex of the cell and release it into the colloid .

It takes >14 days for a daughter cell to migrate from the basal stratum to the outermost layer of the epithelium. Labeled daughter cells were detected < or = 90 days in several layers of the corneal epithelium. Therefore it takes >2 weeks for the complete renewal of the epithelium. Our data suggest that the proliferative capability of the centrally located basal cells is enough to guarantee the renewal of the corneal epithelium under physiologic conditions.

OBJECTIVE: Smile esthetics has become a major concern among patients and orthodontists. Therefore, the aim of this study was: (1) To highlight differences in perception of smile esthetics by clinicians, orthodontists and laypeople; (2) To assess factors such as lip thickness, smile height, color gradation, tooth size and crowding, and which are associated with smile unpleasantness. METHODS: To this end, edited photographs emphasizing the lower third of the face of 41 subjects were assessed by three groups (orthodontists, laypeople and clinicians) who graded the smiles from 1 to 9, highlighting the markers that evince smile unpleasantness. Kruskall-Wallis test supplemented by Bonferroni test was used to assess differences among groups. Additionally, the prevailing factors in smile unpleasantness were also described. RESULTS: There was no significant difference (P = 0.67) among groups rates. However, the groups highlighted different characteristics associated with smile unpleasantness. Orthodontists emphasized little gingival display, whereas laypeople emphasized disproportionate teeth and clinicians emphasized yellow teeth. CONCLUSION: Orthodontists, laypeople and clinicians similarly assess smile esthetics; however, noticing different characteristics. Thus, the orthodontist must be careful not to impose his own perception of smile esthetics.