Spatiotemporal dissection of the trans-Golgi network

The trans -Golgi network (TGN) acts as a sorting hub for membrane traffic. It receives newly synthesized and recycled proteins, sorts and delivers them to specific targets such as the plasma membrane, endosomes, and lysosomes/vacuoles. Accumulating evidence suggests that the TGN is generated from the trans -most cisterna of the Golgi apparatus by maturation, but the detailed transition processes remain obscure. Here we examine spatiotemporal assembly dynamics of various Golgi/TGN-resident proteins in budding yeast by high-speed and high-resolution spinning-disk confocal microscopy. The Golgi-TGN transition gradually proceeds via at least three successive stages: “Golgi stage” mediating glycosylation, “early TGN stage” receiving retrograde traffic, and “late TGN stage” producing transport carriers. During the stage transition periods, earlier and later markers are often compartmentalized within a cisterna. Furthermore, at “late TGN” stage, various types of coat/adaptor proteins exhibit distinct assembly patterns. Altogether, our findings characterize the identity of the TGN as a membrane compartment that is structurally and functionally distinguishable from the Golgi apparatus.