The Journal of Neuroscience, March 15, 2000, 20(6):2112-2120
Axonal Transport of Microtubule-Associated Protein 1B (MAP1B) in
the Sciatic Nerve of Adult Rat: Distinct Transport Rates of Different
Isoforms
Dongling
Ma1,
B.
Timothy
Himes1,
Thomas B.
Shea2, and
Itzhak
Fischer1
1 Department of Neurobiology and Anatomy, MCP
Hahnemann University, Philadelphia, Pennsylvania 19129, and
2 University of Massachusetts, Lowell, Massachusetts
Cytoskeletal proteins are axonally transported with slow components
a and b (SCa and SCb). In peripheral nerves, the transport velocity of
SCa, which includes neurofilaments and tubulin, is 1-2 mm/d, whereas
SCb, which includes actin, tubulin, and numerous soluble proteins,
moves as a heterogeneous wave at 2-4 mm/d. We have shown that two
isoforms of microtubule-associated protein 1B (MAP1B), which can be
separated on SDS polyacrylamide gels on the basis of differences in
their phosphorylation states (band I and band II), were transported at
two different rates. All of band I MAP1B moved as a coherent wave at a
velocity of 7-9 mm/d, distinct from slow axonal transport components
SCa and SCb. Several other proteins were detected within the component
that moved at the velocity of 7-9 mm/d, including the leading wave of
tubulin and actin. The properties of this component define a distinct fraction of the slow axonal transport that we suggest to term slow
component c (SCc). The relatively fast transport of the phosphorylated MAP1B isoform at 7-9 mm/d may account for the high concentration of
phosphorylated MAP1B in the distal end of growing axons. In contrast to
band I MAP1B, the transport profile of band II was complex and
contained components moving with SCa and SCb and a leading edge at SCc.
Thus, MAP1B isoforms in different phosphorylation states move with
distinct components of slow axonal transport, possibly because of
differences in their abilities to associate with other proteins.
Key words:
slow axonal transport; cytoskeleton; protein
phosphorylation; sciatic nerve; dorsal root ganglion neurons; tubulin; neurofilaments
Copyright © 2000 Society for Neuroscience 0270-6474/00/2062112-09$05.00/0