Journal of Neuroscience, Vol 9, 760-768, Copyright © 1989 by Society for Neuroscience
Stable and dynamic forms of cytoskeletal proteins in slow axonal transport
T Tashiro and Y Komiya
Department of Biochemistry, Tokyo University Faculty of Medicine, Japan.
Dynamic organization of the axonal cytoskeleton was investigated by
analyzing slow axonal transport of tubulin and other major cytoskeletal
proteins in the motor axons of rat sciatic nerve 1-4 weeks after injection
of L-35S-methionine into the anterior horn area of L3-L5 lumbar spinal
cord. A large proportion (50-65%) of tubulin transported in the axon was
found to be insoluble when extracted with 1% Triton at 4 degrees C. This
cold-insoluble tubulin was also resistant to other
microtubule-destabilizing agents such as Ca2+, colchicine, and nocodazole,
suggesting that it corresponded to the stably polymerized tubulin specific
to the axon. From the cold-soluble fraction, microtubules containing a
distinct set of associated proteins were recovered by the taxol-dependent
procedure. Transport pattern of cold- soluble and -insoluble tubulin in
this system showed a time-dependent broadening of the tubulin wave
resulting in the appearance of a new faster wave enriched in cold-soluble
tubulin. The slower and the faster waves of tubulin were defined as group V
or slow component a (SCa) and group IV or slow component b (SCb),
respectively, with respect to the 2 subcomponents of slow transport
originally described in the optic system. However, compositions of groups
IV and V in sciatic motor axons differed significantly from those of the
optic system. Actin also exhibited a clear dual wave pattern of transport
that coincided well with that of tubulin, indicating that both actin and
tubulin were the major components of both groups IV and V.(ABSTRACT
TRUNCATED AT 250 WORDS)