Migration of Glycoprotein From the Golgi Apparatus to the Surface of Various Cell Types as Shown by Radioautography After Labeled Fucose Injection Into Rats

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

Functional polarity of the rat hepatocyte surface membrane. Isolation and characterization of plasma-membrane subfractions from the blood-sinusoidal, bile-Canalicular and contiguous surfaces of the hepatocyte

“…3) (Bergeron et al, 1973b). Sugar transferases function mainly, if not exclusively, in the Golgi apparatus (Neutra & LeBlond, 1966;Fleischer & Fleischer, 1970;Bergeron et al, 1973a;Bennet et al, 1974). It was therefore surprising to find that although the microsomal-light (M-L) subfraction contained high specific activities of plasma-membrane marker enzymes, relatively high activities of galactosyl-and sialyl-transferases were also present, contrasting with the very low activities in the other subfractions (Fig.…”

“…To ascertain the extent of this contamination by Golgi membranes, the plasmamembrane subfractions were assayed for galactosyland sialyl-transferase activities, enzymes shown to be localized in Golgi membranes (Fleischer & Fleischer, 1970;Schachter et al, 1970;Bergeron et al, 1973a;Bennet et al, 1974). A similar distribution of the two enzyme activities in the subfractions was observed (Figs.…”

Biogenesis of microsomal membrane glycoproteins in rat liver. III. Release of glycoproteins from the Golgi fraction and their transfer to microsomal membranes.

“…Our findings indicate that lipoglycoprotein units may be involved in such transfers. The autoradiographic and histochemical observations of Bennett et al (10) suggested the transfer of small morphological units from the Golgi system to the plasma membrane; and Hirano et al (34) postulated the involvement of a membrane unit in transferring oligosaccharide chains to the plasma membrane. On the basis of experiments with liver and pancreas cells, Palade (35) concluded that in spite of extensive membrane fusions in biological systems there is no evidence for the mixing of lipid and protein components.…”

“…It has been suggested that acid hydrolases (6) and ~-glucuronidase (7,8), established glycoprotein enzymes, are synthesized in the ER and Golgi system before transfer to the lysosomes. Using histochemical and autoradiographic techniques, Leblond and co-workers (9,10) demonstrated that sugar-containing proteins from the Golgi region are not only secreted but are also used for intracellular construction of the lysosomes, dense bodies, basement and plasma membranes.…”

Biosynthesis of microvillar proteins

“…Vesicles containing newly synthesized glycoproteins have been demonstrated in the apical part of the enterocytes (Bennet et al, 1974;Bernadac et al, 1984). These vesicles may fuse with the plasma membrane forming the pits, and lateral diffusion of the microvillar membrane enzymes then distributes the enzymes, as there is probably no restriction by interaction with the cytoskeleton.…”