Movement of endoplasmic reticulum in the living axon is distinct from other membranous vesicles in its rate, form, and sensitivity to microtubule inhibitors.
The endoplasmic reticulum (ER) is the major membranous component present throughout the axon. Although other membranous structures such as synaptic vesicles are known to move via fast axonal transport, the dynamics of ER in the axon still remains unknown. To study the dynamics of ER in the axon, we have directly visualized the movement of two ER-specific membrane proteins, the sarcoplasmic/endoplasmic reticulum calcium-ATPase and the inositol 1,4,5-trisphosphate receptor, both of which were tagged with green fluorescence protein (GFP) and expressed in cultured chick dorsal root ganglion neurons. In contrast to GFP-tagged synaptophysin that moved as vesicles at 1 microm/sec predominantly in the anterograde direction in the typical style of fast axonal transport, the two ER proteins did not move in a discrete vesicular form. Their movement determined by the fluorescence recovery after photobleaching technique was bi-directional, 10-fold slower (approximately 0.1 microm/sec), and temperature-sensitive. The rate of movement of ER was also sensitive to low doses of vinblastine and nocodazole that did not affect the rate of synaptophysin-GFP, further suggesting that it is also distinct from the well-documented movement of membranous vesicles in its relation with microtubules.
Aihara
Y
Y
Department of Neurology, Gunma University School of Medicine, 3-39-22 Showa-machi, Maebashi-shi, Gunma-371-8511, Japan. yaihara@med.gunma-u-ac.jp
Inoue
T
T
Tashiro
T
T
Okamoto
K
K
Komiya
Y
Y
Mikoshiba
K
K
D000818:Animals; D001370:Axonal Transport; D001369:Axons / Q000648:ultrastructure*; D019470:Biolistics; D015415:Biomarkers; D015220:Calcium Channels / Q000032:analysis / Q000235:genetics; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000235:genetics; D002478:Cells, Cultured; D002642:Chick Embryo; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*; D005727:Ganglia, Spinal / Q000166:cytology; D049452:Green Fluorescent Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000187:drug effects*; D009038:Motion; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics; D009475:Neurons, Afferent / Q000187:drug effects* / Q000648:ultrastructure; D015739:Nocodazole / Q000494:pharmacology*; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000032:analysis / Q000235:genetics; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D016708:Synaptophysin / Q000378:metabolism; D013696:Temperature; D014162:Transfection; D014747:Vinblastine / Q000494:pharmacology*
D015415:Biomarkers; D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008164:Luminescent Proteins; D009419:Nerve Tissue Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D016708:Synaptophysin; D049452:Green Fluorescent Proteins; D014747:Vinblastine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D015739:Nocodazole