Traffic through the golgi apparatus as studied by radioautography

Abstract

The ability to radiolabel biological molecules, in conjunction with radioautographic or cell fractionation techniques, has brought about a revolution in our knowledge of dynamic cellular processes. This has been particularly true since the 1940's, when isotopes such as 35S and 14C became available, since these isotopes could be incorporated into a great variety of biologically important compounds. The first dynamic evidence for Golgi apparatus involvement in biosynthesis came from light microscope radioautographic studies by Jennings and Florey in the 1950's, in which label was localized to the supranuclear Golgi region of goblet cells soon after injection of 35S-sulfate. When the low energy isotope tritium became available, and when radioautography could be extended to the electron microscope level, a great improvement in spatial resolution was achieved. Studies using 3H-amino acids revealed that proteins were synthesized in the rough endoplasmic reticulum, migrated to the Golgi apparatus, and thence to secretion granules, lysosomes, or the plasma membrane. The work of Neutra and Leblond in the 1960's using 3H-glucose provided dramatic evidence that the Golgi apparatus was involved in glycosylation. Work with 3H-mannose (a core sugar in N-linked side chains), showed that this sugar was incorporated into glycoproteins in the rough endoplasmic reticulum, providing the first radioautographic evidence that glycosylation of proteins did not occur solely in the Golgi apparatus. Studies with the tritiated precursors of fucose, galactose, and sialic acid, on the other hand, showed that these terminal sugars are mainly added in the Golgi apparatus. With its limited spatial resolution, radioautography cannot discriminate between label in adjacent Golgi saccules. Nonetheless, in some cell types, radioautographic evidence (along with cytochemical and cell fractionation data) has indicated that the Golgi is subcompartmentalized in terms of glycosylation, with galactose and sialic acid being added to glycoproteins only within the trans-Golgi compartment. In the last ten years, radioautographic tracing of radioiodinated plasma membrane molecules has indicated a substantial recycling of such molecules to the Golgi apparatus.

Topology of Glycosylation — a Histochemist's View

“…1-2; Hauri and Schweizer, 1992). This appears to be mainly a salvage compartment, from where luminal and membrane ER 2 Topology of N-Glycosylation I 1 17 firmed by radioautography: the insertion of galactose and sialic acid could be localized to the trans Golgi region (for review see Bennett and Wild, 1991). Furthermore, lectinocytochemical patterns mainly confirm the results mentioned above.…”

“…Novel techniques at the electronmicroscopic level (e.g. Bernhard and Avrameas, 1971;Newman et al, 1983;Roth, 1983; Slot and Geuze, 1983;Ellinger and Pavelka, 1985;Pavelka and Ellinger, 1989a; Bennett and Wild, 1991) provided approaches for the precise subcellular localization of various glycoconjugates and of an array of enzymes of the glycosylation machinery, although we are still some way from a complete description. Indeed, electron microscopic immuno-and lectinocytochemistry as well as radioautography are continually enhancing our level of understanding of the, at first, puzzling and complicated series of steps during the biosynthesis of N-and 0-linked glycans; subcompartments of the main glycosylation organelles could be defined.…”

Protein kinase C epsilon is localized to the Golgi via its zinc-finger domain and modulates Golgi function.

“…Previous studies have established that the Golgi network is the exclusive site for sulfation reactions (21)(22)(23). In contrast to the differential effects noted on GAG secretion, the level of total (cellular and secreted) GAG sulfation was markedly inhibited in cells overproducing either fragment s3 or holoPKCs (Fig.…”