Radioautographic visualization of3H-fucose incorporation into glycoprotein by osteoblasts and its deposition into bone matrix

Abstract

Summary. The elaboration of bone matrix glycoprotein by osteoblasts of alveolar bone was investigated by radioautography after the intravenous injection of 3H-fucose into young rats. At selected times after injection, animals were sacrificed by intracardiac perfusion and demineralized specimens were prepared for light and electron microscope radioautography.At 5 and 10 min after injection, when the blood fucose level was high, silver grains were restricted to the spheroidal and cylindrical saccules of the Golgi apparatus. At 20 min membrane-limited secretory granules were also labeled. By 35 min, the blood fucose level had dropped and silver grains were detected over the apical cortical cytoplasm, in association with secretory granules located therein. Some grains were present over osteoblast processes and the adjacent prebone matrix. By 4 h most of the silver grains had left the cell. At that time they were observed over prebone, adjacent to osteoblast processes, as well as over the prebone-bone junction where a distinct band of label was noted. In demineralized preparations an electron-dense granular material was present at the prebone-bone junction in association with collagen fibrils.These findings provide evidence that osteoblasts in alveolar bone synthesize fucose-containing glycoprotein and indicate that the addition of 3H-fucose occurs in the Golgi apparatus. The glycoprotein passes to the apical cortical cytoplasm by way of membrane-limited secretory granules, is exteriorized, and accumulates at the site where prebone transforms into bone (the prebone-bone junction). Since this is also the site of the calcification front, the deposition of labeled glycoprotein may be related to the deposition of bone mineral.Send offprint requests to M. Weinstock at the above address,

Molecular and cellular biology of alveolar bone

“…creted in tandem via the same pathway or whether a separate population of secretory granules and a separate exocytotic pathway exist specifically for these proteins. Here, it should be emphasized that the often misquoted early radioautographic studies by Weinstock et al (251,252,255) on bone and teeth demonstrated phosphoprotein and/or glycoprotein deposition into prebone (osteoid) and predentin, fol-lowed by its subsequent accumulation at the mineralization front in these tissues. Thus, as shown for collagen, the release of noncollagenous proteins appears to occur primarily at the base of osteoblast (and odontoblast) cell processes and from the cell body itself.…”

Traffic through the golgi apparatus as studied by radioautography

“…x 10,000, exclusively in the Golgi apparatus of intestinal columnar and goblet cells ( Fig. 4) (Bennett and Leblond, 1970;Michaels and Leblond, 1976), hepatocytes (Bennett and , and the great majority of other cell types (Bennett, 1978;Bennett and Haddad, 1986;Brasileiro et al, 1982;Garant, 1985, 1986;Ginsel et al, 1979;Haddad et al, 1971Haddad et al, , 1977Haddad andBennett, 1987, 1988;Hand, 1979;Lima and Haddad, 1981;Rougier, 1976;Weinstock et al, 1972;Weinstock, 1979). In some exceptional cell types, a significant uptake of 'H-fucose label at the level of the rough endoplasmic reticulum was also noted (Pelletier and Puviani, 1973;Pelletier, 1974;Samuel and Flickinger, 1986).…”

Radioautographic analysis of 3H‐fucose utilization by fibroblasts of the periodontal ligament

“…In contrast, little is known about the synthesis and secretion of non-collagenous glycoproteins from POL fibroblasts. Tritiated fucose has been used in radioautographic studies of the secretion of non-collagenous matrix components from odontoblasts and osteoblasts (Weinstock, Weinstock & Leblond, 1972, Weinstock 1979. In odontoblasts and osteoblasts, 3H-fucose was rapidly incorporated into spheroidal saccules of the Golgi apparatus at 5 to 10 minutes after injection.…”