Unraveling the Golgi ribbon

Abstract

The Golgi apparatus lies at the heart of the secretory pathway where it receives, modifies and sorts protein cargo to the proper intracellular or extracellular location. Although this secretory function is highly conserved throughout the eukaryotic kingdom, the structure of the Golgi complex is arranged very differently among species. In particular, Golgi membranes in vertebrate cells are integrated into a single compact entity termed the Golgi ribbon that is normally localized in the perinuclear area and in close vicinity to the centrosomes. This organization poses a challenge for cell division when the single Golgi ribbon needs to be partitioned into the two daughter cells. To ensure faithful inheritance in the progeny, the Golgi ribbon is divided in three consecutive steps in mitosis, namely disassembly, partitioning and reassembly. However, the structure of the Golgi ribbon is only present in higher animals and Golgi disassembly during mitosis is not ubiquitous in all organisms. Therefore, there must be unique reasons to build up the Golgi in this particular conformation and to preserve it over generations. In this review, we first highlight the diversity of the Golgi architecture in different organisms and revisit the concept of the Golgi ribbon. Following on, we discuss why the ribbon is needed and how it forms in vertebrate cells. Lastly, we conclude with likely purposes of mitotic ribbon disassembly and further propose mechanisms by which it regulates mitosis.

Figure 1. Golgi organization in vertebrate cells

A) A typical interphase Golgi ribbon is composed of interconnected stacks and is localized in the perinuclear region in close vicinity to the centrosome. B) The Golgi ribbon can be positioned in a cellular location different from the perinuclear area. During cytokinesis, a small Golgi ribbon is situated next to the midbody and flanks the intracellular bridge between the two daughter cells. C) In late G2 phase, Golgi stacks lose mutual connectivity but remain clustered in the perinuclear region around the centrosomes. D) Unlinked Golgi stacks are scattered throughout the cytoplasm. E) Golgi matrix proteins, in particular the golgin and GRASP families, are sufficient to assemble and maintain a higher-ordered ribbon structure in the perinuclear region, regardless of the presence of Golgi enzymes or the organization of Golgi membranes.