The Golgi ribbon structure facilitates anterograde transport of large cargoes.
Bottom Line: Yet the purpose of this remarkable structure has been an enigma.In addition, insect cells that naturally harbor dispersed Golgi stacks have limited capacity to transport artificial oversized cargoes.These results imply that the ribbon structure is an essential requirement for transport of large cargoes in mammalian cells, and we suggest that this is because it enables the dilated rims of cisternae (containing the aggregates) to move across the stack as they transfer among adjacent stacks within the ribbon structure.
Affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520 firstname.lastname@example.org email@example.com.Show MeSH
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Mentions: Our previous results (Volchuk et al., 2000; Lavieu et al., 2013; Pellett et al., 2013) and the current results suggest that cargoes follow distinct secretory tracks within the Golgi according to their size. To explain these results (Figure 6), we propose that large cargoes freshly arrived at the cis-Golgi are first concentrated at the enlarged rim of the cis-Golgi cisternae, where they are physically sequestered from other classical small cargoes. This separation, which remains to be further demonstrated, could simply result from the fact that large aggregates are too big to be accommodated within the narrow confines of the flattened central portions of the stacked cisternae. Fission of the enlarged rims may occasionally occur and would result in a more robust sequestration of the large cargo from the rest of the cisternae (Volchuk et al., 2000). This may be the purpose of the so-called mega-vesicles, which have been reported to contain 20% of the soluble aggregates (Volchuk et al., 2000), but in theory, the enlarged rims may remain physically connected to the cisternae in many cases. Making the assumption that the Golgi ribbon is going through continuous fission–fusion cycles, we propose that single stacks emanating from the ribbon and containing large cargoes within their cis-Golgi cisterna will fuse laterally with one another to form a new ribbon. When the fusion is homotypic (the cis cisterna of one stack fusing with the cis cisterna of an adjacent stack), no net anterograde movement occurs, though such an event many not be entirely unproductive because it could allow additional time for efficient posttranslational modification. However, when the lateral fusion is heterotypic (the cis cisterna of a stack containing the cargo fusing with the medial cisterna of the adjacent stack), this would allow for forward movement of the cargo into the next compartment and so on across the stack.
Affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520 firstname.lastname@example.org email@example.com.