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J. Cell Biol.,
Volume 145, Number 2, April 19, 1999 305-315
* Department of Anatomy, The University of Wisconsin Medical School, Madison, Wisconsin 53706; and Several lines of evidence suggest that microtubules are nucleated at the neuronal centrosome, and
then released for transport into axons and dendrites.
Here we sought to determine whether the microtubule-severing protein known as katanin mediates microtubule release from the neuronal centrosome. Immunomicroscopic analyses on cultured sympathetic
neurons show that katanin is present at the centrosome,
but is also widely distributed throughout the neuron.
Microinjection of an antibody that inactivates katanin results in a dramatic accumulation of microtubules at
the centrosome, indicating that katanin is indeed required for microtubule release from the centrosome.
However, the antibody also causes an inhibition of
axon outgrowth that is more immediate than expected
on this basis alone. It may be that katanin severs microtubules throughout the cell body to keep them sufficiently short to be efficiently transported into developing processes. Consistent with this idea, there were
significantly fewer free ends of microtubules in the cell
bodies of neurons that had been injected with the katanin antibody compared with controls. These results indicate that microtubule-severing by katanin is essential
for releasing microtubules from the neuronal centrosome, and also for regulating the length of the microtubules after their release.
Section of Molecular
and Cellular Biology, University of California-Davis, Davis, California 95616
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