Golgi Units as Modules in the Ribbon

Using super-resolution microscopies, SCLIM and STORM, and CRISPR/Cas9 knockin technology, we show that the Golgi complex is assembled by a number of small "Golgi units" that are 1-3 μm in diameter. Each Golgi unit can be considered a functional and morphological module because it contains all sets of glycosylation enzymes that occupy small domains named "zones." Golgi units change shape dynamically. They attach, detach, fuse, and separate from each other. The zones of glycosylation enzymes rapidly move near the rim of the unit. However, the behaviors of N- and O-linked glycosylation enzyme zones differ from those of glycosaminoglycan (GAG)-synthesizing enzyme zones in localization and dynamics. Since depletion of giantin dissociates the Golgi units, it is responsible for their attachment. Giantin depletion also prevents the movement of GAG-synthesizing enzymes between units, leading to incomplete GAG synthesis. Here, we present the model of the Golgi and its glycosylation enzymes that can explain a number of characteristics of the glycosylation processes.