Exocytosis in action

Geri Kreitzer, Enrique Rodriguez-Boulan (Cornell University, New York, NY), and colleagues have provided the first visualization of targeted exocytosis in polarized epithelial cells.Exocytic events can be seen by specialized microscopy techniques that selectively illuminate the bottom of cells. But to see exocytosis on the lateral side of a polarized cell, the researchers had to comb through many confocal images looking for events in which fluorescence intensity diminished due to emptying rather than movement of a vesicle or tubule. One clue was the spread of fluorescence visible only after release of an exocytic cargo.

“Technologically this is not so difficult,” says Kreitzer. “But the analysis was very labor intensive.” The reward was a direct readout of fusion events. Basolateral cargoes were located in the most apical two thirds of the cytoplasm and fused with the corresponding region...