Redefining the entrance and exit of the Golgi apparatus

The Golgi apparatus has a cis-to-trans polarity. The regions on both sides, the cis-Golgi network (CGN) and the trans-Golgi network (TGN), play important roles in controlling the entry and exit of cargo proteins. Regarding CGN, questions have persisted about whether it is commonly present in a variety of eukaryotes. I would summarize recent studies supporting the idea that CGN is a widely conserved compartment in animal, plant, and yeast cells. To clarify confusing terminology, I propose to use the term CGN consistently here. Morphologically, the structure of the Golgi and CGN as well as their spatial relationship with the endoplasmic reticulum exit sites (ERES) vary greatly among species but careful comparison reveals common fundamental characteristics of CGN. While CGN and TGN are sorting compartments regulating cargo traffic on the two faces of the Golgi, they are often mobile and can function independently of the main body Golgi.