Biology Reference
In-Depth Information
Fig. 18.4 Schematic
illustration of
pharmacological strategy for
revealing the progression of
microtubules outward from
the neuronal centrosome.
Nocodazole was the first drug
used to depolymerize pre-
existing microtubules. Next,
after a brief recovery period,
vinblastine was used as an
anti-microtubule drug to
suppress further assembly of
microtubules. Microtubules
redistributed over time.
Adapted from Ahmad and
Baas (
1995
)
centrosome, low levels of a second anti-microtubule drug (vinblastine) were added
to the cultures to suppress further microtubule assembly while not substantially
depolymerizing existing microtubules. Thus, we reasoned that any alterations in the
microtubule array that occur after the addition of the second drug must be the result
of microtubule movements from one location in the cell to another. Consistent with
this expectation, microtubule levels remained roughly the same after the addition of
vinblastine, as did the lengths of individual microtubules over time. Within minutes,
unattached microtubules began to appear in the cytoplasm, and by 10 min many of
these had reached the periphery of the cell body. By 1 h, few or no microtubules
were attached to the centrosome and most of the microtubules were concentrated at
the cell periphery. In the case of the neurons that were able to grow axons under these
conditions, microtubules appeared progressively further down the axons with
increasing time (see Fig.
18.4
). These results suggested that microtubules derived
from the centrosome are transported outward from the centrosome toward cell
periphery and then into and down the length of the axon.
Due to the geometry of the neuron, the density of the microtubule array, and the
pool of free tubulin in neurons, we have not been able to directly visualize
