A Golgi portrait: new perspectives on old problems

Abstract

This classical descriptive approach, updated with contemporary fixation and imaging methods, provides provocative views of Golgi structure. Use of fast-frozen, freeze-substituted tissue and tomographic reconstructions from 250-nm serial sections viewed by dual-axis high-voltage EM permitted Landinsky et al.1xGolgi structure in three dimensions: functional insights from the normal rat kidney. Landinsky, M.S., Mastronarde, D.N., McIntosh, J.R., Howell, K.E., and Staehelin, L.A. J. Cell Biol. 1999; 144: 1135–1149Crossref | PubMed | Scopus (390)See all References1 to model a portion of the Golgi complex of a cultured rat kidney cell in three dimensions at a resolution of ∼7 nm. Their reconstruction raises questions about certain theories of Golgi function and brings to the forefront aspects that have been neglected or overlooked.Tubules connect regions of equivalent cisternae, project past one or more cisternae in cis and trans directions but are not observed between adjacent cisternae. A tubule-based mechanism for anterograde transport between neighbouring cisternae is thus not supported. Extensive reticular structures are not seen in the cis cisternae, thus calling into question the concept of a cis-Golgi network. Similarly, the trans side lacks a ramified tubular reticulum of a trans-Golgi network (TGN) – considered a major locus for sorting and export. Rather, the trans-most cisternae, C5 to C7, reveal striking morphological differences. For example, C7 displays only clathrin-coated buds, whereas C5 and C6 contain only non-clathrin-coated buds.The authors surmise that cargo targeted to the plasma membrane might sort to a different cisterna compared with cargo marked for transport to endosomes and lysosomes. Other structures highlighted in this reconstruction include an extensive trans endoplasmic reticulum (ER) in close contact with cisternae C6 and C7 (possibly offering a path, as the authors suggest, for nonvesicular lipid transfer between the ER and the trans Golgi) and a structurally distinct ER–Golgi intermediate compartment (ERGIC) of branched tubules and flattened sacs located between the ER and the cis Golgi.