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J. Cell Biol.,
Volume 142, Number 6, September 21, 1998 1571-1581
Howard Hughes Medical Institute and Departments of Cell Biology and Biochemistry, Duke University Medical Center,
Durham, North Carolina 27710
AnkyrinG (
/) neurons fail to concentrate
voltage-sensitive sodium channels and neurofascin at
their axon proximal segments, suggesting that ankyrinG
is a key component of a structural pathway involved in
assembly of specialized membrane domains at axon
proximal segments and possibly nodes of Ranvier
(Zhou, D., S. Lambert, D.L. Malen, S. Carpenter, L. Boland, and V. Bennett, manuscript submitted for publication). This paper addresses the mechanism for restriction of 270-kD ankyrinG to axon proximal segments by evaluation of localization of GFP-tagged
ankyrinG constructs transfected into cultured dorsal
root ganglion neurons, as well as measurements of fluorescence recovery after photobleaching of neurofascin- GFP-tagged ankyrinG complexes in nonneuronal cells.
A conclusion is that multiple ankyrinG-specific domains, in addition to the conserved membrane-binding
domain, contribute to restriction of ankyrinG to the axonal plasma membrane in dorsal root ganglion neurons.
The ankyrinG-specific spectrin-binding and tail domains are capable of binding directly to sites on the
plasma membrane of neuronal cell bodies and axon
proximal segments, and presumably have yet to be
identified docking sites. The serine-rich domain, which
is present only in 480- and 270-kD ankyrinG polypeptides, contributes to restriction of ankyrinG to axon
proximal segments as well as limiting lateral diffusion
of ankyrinG-neurofascin complexes. The membrane-binding, spectrin-binding, and tail domains of ankyrinG
also contribute to limiting the lateral mobility of ankyrinG-neurofascin complexes. AnkyrinG thus functions
as an integrated mechanism involving cooperation
among multiple domains heretofore regarded as modular units. This complex behavior explains ability of
ankyrinB and ankyrinG to sort to distinct sites in neurons and the fact that these ankyrins do not compensate
for each other in ankyrin gene knockouts in mice.
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