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J. Cell Biol.,
Volume 144, Number 3, February 8, 1999 447-458
Neuroscience Program, Department of Biological Sciences, Ohio University, Athens, Ohio 45701
We have investigated the axonal transport of
neurofilament protein in cultured neurons by constricting single axons with fine glass fibers. We observed a
rapid accumulation of anterogradely and retrogradely
transported membranous organelles on both sides of
the constrictions and a more gradual accumulation of
neurofilament protein proximal to the constrictions.
Neurofilament protein accumulation was dependent on
the presence of metabolic substrates and was blocked
by iodoacetate, which is an inhibitor of glycolysis.
These data indicate that neurofilament protein moves
anterogradely in these axons by a mechanism that is directly or indirectly dependent on nucleoside triphosphates. The average transport rate was estimated to be
at least 130 µm/h (3.1 mm/d), and ~90% of the accumulated neurofilament protein remained in the axon
after detergent extraction, suggesting that it was
present in a polymerized form. Electron microscopy
demonstrated that there were an abnormally large
number of neurofilament polymers proximal to the
constrictions. These data suggest that the neurofilament proteins were transported either as assembled
polymers or in a nonpolymeric form that assembled locally at the site of accumulation. This study represents
the first demonstration of the axonal transport of neurofilament protein in cultured neurons.
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