Figure 5

Entire domains of cargo may become post-Golgi transport carriers and fuse intact with the plasma membrane A. Entire cargo domains can exit the Golgi. Transiently expressed VSVG3-YFP cargo was accumulated in the ER and pulsed into the secretory pathway of PtK₂ cells as in Figure 1B. Time at 32°C and the frame number of the corresponding movie (Additional Fileset 5) are indicated. Cargo in Golgi elements(1) forms a domain (2), which remains stable for over 12 minutes (3,4), apparently exchanging material with an adjacent cargo domain (4). A tubule extends from the domain (5) and then the entire domain extends and translocates along the same path as the tubule (6), exiting the vicinity of the originating Golgi element. The extended domain coalesces (7) and repeatedly sheds post-Golgi carriers (8), remaining in the vicinity of a small, separate Golgi element(9). Bar: 5 μm. B. Transport carriers the size of cargo domains can fuse directly with the plasma membrane. Cells were transfected with VSVG3-GFP and subjected to the temperature protocol in Figure 1B. Time at 32°C and the frame number of the corresponding movie are indicated (Additional Fileset 5). A large TC (arrow) hovers briefly near the plasma membrane (PM), makes contact, and fuses (Frame 84). Fusion is indicated by a transient increase in the fluorescence of a microspike waving from the edge of the cell (1), and distortion of the globular shape of the TC to the shape of the PM (2). After fusion, fluorescence from the TC spreads laterally within the PM (3), and is incorporated into waving microspikes (4). Bar: 5 μm.