Dual Modes of Endoplasmic Reticulum-to-Golgi Transport in Dendrites Revealed by Live-Cell Imaging

Abstract

Organelles of the neuronal secretory pathway are critical for the addition of membrane that accompanies neuronal development, as well as for the proper localization of plasma membrane proteins necessary for polarity, synaptic transmission, and plasticity. Here, we demonstrate that two organizations of the secretory pathway exist in neurons: one requiring processing of membrane and lipids in the Golgi complex of the cell body and one in which endoplasmic reticulum (ER)-to-Golgi trafficking is localized to dendrites. Using timelapse imaging of green fluorescent protein-tagged cargo proteins and compartment markers, we show that organelles of the secretory pathway, including ER, ER exit sites, and Golgi, are present and engage in trafficking in neuronal dendrites. We find that ER-to-Golgi trafficking involves highly mobile vesicular carriers that traffic in both the anterograde and retrograde directions throughout the dendritic arbor. Dendritic Golgi outposts, which appear developmentally during the phase of process outgrowth, are involved in the trafficking of both integral membrane proteins and the secreted neuronal growth factor BDNF. This distributed dendritic Golgi represents an organization of the secretory pathway unique among mammalian cells.

Protein Kinase D Controls the Integrity of Golgi Apparatus and the Maintenance of Dendritic Arborization in Hippocampal Neurons

“…The importance of the Golgi structure necessary for the high turnover of dendritic membrane surface is reflected by the presence of so-called dendritic outposts in the main dendrites (Sytnyk et al, 2002;Horton and Ehlers, 2003). In our hippocampal cultures, Golgi-targeted PKD reporter revealed high endogenous PKD activity at the neuronal Golgi complex.…”

“…A thread-like and reticular structure of the Golgi apparatus has been already described in many neuronal types (Takamine et al, 2000;Fujita and Okamoto, 2005;Horton et al, 2005). Central neuronal Golgi complex is localized in the soma and often extends into the principal dendrites, but Golgi elements were also found as discontinuous structures in the distal dendrites, often near synaptic contacts or in dendritic spines (Gardiol et al, 1999;Pierce et al, 2001;Sytnyk et al, 2002;Horton and Ehlers, 2003). The dispersed localization of the Golgi apparatus indicates unique spatial regulation of the neuronal secretory pathway compared with other mammalian cells.…”

“…The dispersed localization of the Golgi apparatus indicates unique spatial regulation of the neuronal secretory pathway compared with other mammalian cells. Recent investigations on hippocampal pyramidal cells indicated that Golgi outposts located in the dendritic shafts (Sytnyk et al, 2002;Horton and Ehlers, 2003) and the perinuclear Golgi apparatus oriented toward the longest dendrite (Horton et al, 2005) can provide the necessary membrane supply for intensive dendritic growth. In axonal outgrowth and extension, an increasing amount of data suggests that membrane supply and targeting of proteins are regulated in a different way compared with dendritic elongation (Silverman et al, 2001; This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E08 -09 -0957) on February 11, 2009.…”

Microtubule nucleation and organization in dendrites

“…23,50 To identify structures associated with microtubule nucleation within dendrites, Ori-McKenney and colleagues used Drosophila sensory neurons as a model and showed microtubule nucleation at Golgi fragments situated within dendrites, 35 called Golgi outposts. 51 Endosomes and mitochondria, other common membrane-rich organelles in dendrites, were not found to be sites of nucleation. 35 Notably, while g-tubulin is used in both dendrites and axons to seed microtubules, 34 Golgi outposts have only been detected in the dendrites.…”

Generation of noncentrosomal microtubule arrays

“…The MT arrays within these processes are necessary to maintain the processes and may indirectly contribute to synaptic activity. They are believed to provide structural support for each process as well as tracks for the delivery of membrane vesicles (Horton and Ehlers, 2003;Overly et al, 1996;Signor and Scholey, 2000).…”