Megavesicles Implicated in the Rapid Transport of Intracisternal Aggregates across the Golgi Stack

Engineered protein aggregates ranging up to 400 nm in diameter were selectively deposited within the cis-most cisternae of the Golgi stack following a 15°C block. These aggregates are much larger than the standard volume of Golgi vesicles, yet they are transported across the stack within 10 min after warming the cells to 20°C. Serial sectioning reveals that during the peak of anterograde transport, about 20% of the aggregates were enclosed in topologically free “megavesicles” which appear to pinch off from the rims of the cisternae. These megavesicles can explain the rapid transport of aggregates without cisternal progression on this time scale.