RT Journal Article
SR Electronic
T1 Neurofilaments Are Transported Rapidly But Intermittently in Axons: Implications for Slow Axonal Transport
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 6849
OP 6861
DO 10.1523/JNEUROSCI.20-18-06849.2000
VO 20
IS 18
A1 Subhojit Roy
A1 Pilar Coffee
A1 George Smith
A1 Ronald K. H. Liem
A1 Scott T. Brady
A1 Mark M. Black
YR 2000
UL http://www.jneurosci.org/content/20/18/6849.abstract
AB Slow axonal transport conveys cytoskeletal proteins from cell body to axon tip. This transport provides the axon with the architectural elements that are required to generate and maintain its elongate shape and also generates forces within the axon that are necessary for axon growth and navigation. The mechanisms of cytoskeletal transport in axons are unknown. One hypothesis states that cytoskeletal proteins are transported within the axon as polymers. We tested this hypothesis by visualizing individual cytoskeletal polymers in living axons and determining whether they undergo vectorial movement. We focused on neurofilaments in axons of cultured sympathetic neurons because individual neurofilaments in these axons can be visualized by optical microscopy. Cultured sympathetic neurons were infected with recombinant adenovirus containing a construct encoding a fusion protein combining green fluorescent protein (GFP) with the heavy neurofilament protein subunit (NFH). The chimeric GFP–NFH coassembled with endogenous neurofilaments. Time lapse imaging revealed that individual GFP–NFH-labeled neurofilaments undergo vigorous vectorial transport in the axon in both anterograde and retrograde directions but with a strong anterograde bias. NF transport in both directions exhibited a broad spectrum of rates with averages of ≈0.6–0.7 μm/sec. However, movement was intermittent, with individual neurofilaments pausing during their transit within the axon. Some NFs either moved or paused for the most of the time they were observed, whereas others were intermediate in behavior. On average, neurofilaments spend at most 20% of the time moving and rest of the time paused. These results establish that the slow axonal transport machinery conveys neurofilaments.