The Dendritic Ergic: Microtubule and Actin Cytoskeletons Mediate Stop-and-Go Movement of Mobile Carriers Between Stable Structures

The ER-to-Golgi intermediate compartment (ERGIC) is a membranous organelle that mediates protein transport between the endoplasmic reticulum (ER) and Golgi apparatus. In neurons, clusters of these vesiculotubular structures are situated in throughout the cell in proximity to the ER, passing cargo to the cis-Golgi cisternae located mainly in the perinuclear region. Although ERGIC markers have been identified in neurons, the distribution and dynamics of neuronal ERGIC structures have not been characterized. Here, we argue that long-distance ERGIC transport occurs via an intermittent mechanism in neurons, with mobile elements moving between stationary structures. Using immunofluorescence microscopy, we detected discrete, irregular ERGIC structures in neural soma and dendrites. Slow live-cell imaging (2 frames/minute; 15 minutes) indicated that 8% of dendritic ERGIC structures were stable, remaining in place over long periods. On the other hand, fast live-cell imaging (2 frames/second; 180 seconds) captured mobile ERGIC structures advancing very short distances along dendrites. Importantly, these distances were consistent with the lengths between the stationary ERGIC structures. Kymography revealed ERGIC elements that moved intermittently, emerging from and fusing with stationary ERGIC structures. Surprisingly, this movement was apparently dependent not only on the integrity of the microtubule cytoskeleton, as has been previously reported, but on the actin cytoskeleton as well. Our results indicate that the dendritic ERGIC has a dual nature, with both stationary and mobile structures. The neural ERGIC network transports proteins via a stop-and-go movement that is mediated by the microtubule and actin cytoskeletons.