TY - JOUR
T1 - Fewer active motors per vesicle may explain slowed vesicle transport in chick motoneurons after three days in vitro
AU - Macosko, Jed C.
AU - Newbern, Jason M.
AU - Rockford, Jean
AU - Chisena, Ernest N.
AU - Brown, Charlotte M.
AU - Holzwarth, George M.
AU - Milligan, Carol E.
N1 - Funding Information:
We thank Anna Taylor for her help with preparing chick motoneurons and Keith Bonin for his helpful discussions. We gratefully acknowledge Todd Fallesen for his input at various stages. This work was supported by a start-up grant by Wake Forest University to JCM and by an NIH grant (NS036081) to CEM.
PY - 2008/5/23
Y1 - 2008/5/23
N2 - Vesicle transport in cultured chick motoneurons was studied over a period of 3 days using motion-enhanced differential interference contrast (MEDIC) microscopy, an improved version of video-enhanced DIC. After 3 days in vitro (DIV), the average vesicle velocity was about 30% less than after 1 DIV. In observations at 1, 2 and 3 DIV, larger vesicles moved more slowly than small vesicles, and retrograde vesicles were larger than anterograde vesicles. The number of retrograde vesicles increased relative to anterograde vesicles after 3 DIV, but this fact alone could not explain the decrease in velocity, since the slowing of vesicle transport in maturing motoneurons was observed independently for both anterograde and retrograde vesicles. In order to better understand the slowing trend, the distance vs. time trajectories of individual vesicles were examined at a frame rate of 8.3/s. Qualitatively, these trajectories consisted of short (1-2 s) segments of constant velocity, and the changes in velocity between segments were abrupt (< 0.2 s). The trajectories were therefore fit to a series of connected straight lines. Surprisingly, the slopes of theses lines, i.e. the vesicle velocities, were often found to be multiples of ~ 0.6 μm/s. The velocity histogram showed multiple peaks, which, when fit with Gaussians using a least squares minimization, yielded an average spacing of 0.57 μm/s (taken as the slope of a fit to peak position vs. peak number, R2 = 0.994). We propose that the abrupt velocity changes occur when 1 or 2 motors suddenly begin or cease actively participating in vesicle transport. Under this hypothesis, the decrease in average vesicle velocity observed for maturing motoneurons is due to a decrease in the average number of active motors per vesicle.
AB - Vesicle transport in cultured chick motoneurons was studied over a period of 3 days using motion-enhanced differential interference contrast (MEDIC) microscopy, an improved version of video-enhanced DIC. After 3 days in vitro (DIV), the average vesicle velocity was about 30% less than after 1 DIV. In observations at 1, 2 and 3 DIV, larger vesicles moved more slowly than small vesicles, and retrograde vesicles were larger than anterograde vesicles. The number of retrograde vesicles increased relative to anterograde vesicles after 3 DIV, but this fact alone could not explain the decrease in velocity, since the slowing of vesicle transport in maturing motoneurons was observed independently for both anterograde and retrograde vesicles. In order to better understand the slowing trend, the distance vs. time trajectories of individual vesicles were examined at a frame rate of 8.3/s. Qualitatively, these trajectories consisted of short (1-2 s) segments of constant velocity, and the changes in velocity between segments were abrupt (< 0.2 s). The trajectories were therefore fit to a series of connected straight lines. Surprisingly, the slopes of theses lines, i.e. the vesicle velocities, were often found to be multiples of ~ 0.6 μm/s. The velocity histogram showed multiple peaks, which, when fit with Gaussians using a least squares minimization, yielded an average spacing of 0.57 μm/s (taken as the slope of a fit to peak position vs. peak number, R2 = 0.994). We propose that the abrupt velocity changes occur when 1 or 2 motors suddenly begin or cease actively participating in vesicle transport. Under this hypothesis, the decrease in average vesicle velocity observed for maturing motoneurons is due to a decrease in the average number of active motors per vesicle.
KW - Anterograde neuron traffic
KW - Cooperative fast axonal transport
KW - In vitro neuronal aging
KW - Processive molecular motors
KW - Retrograde vesicle velocity
KW - Video-enhanced differential interference contrast microscopy (VE-DIC)
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U2 - 10.1016/j.brainres.2008.03.014
DO - 10.1016/j.brainres.2008.03.014
M3 - Article
C2 - 18433736
AN - SCOPUS:43049173712
SN - 0006-8993
VL - 1211
SP - 6
EP - 12
JO - Brain Research
JF - Brain Research
ER -