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© The Rockefeller University Press, 0021-9525/1998//1571 $5.00
The Journal of Cell Biology, Volume 142, Number 6, , 1998 1571-1581

Regular Articles

Restriction of 480/270-kD Ankyrin G to Axon Proximal Segments Requires Multiple Ankyrin G-specific Domains



Xu Zhang and Vann Bennett

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.

Key Words: ankyrin • axon initial segment • cell polarity • membrane dynamics • spectrin

Abbreviations used in this paper: CAM, cell adhesion molecule; DRG, dorsal root ganglion; FRAP, fluorescence recovery after photobleaching; GFP, green fluorescent protein; HA, hemagglutinin.

L. Davis (Duke University, HHMI, Durham, NC) is gratefully acknowledged for contributions to culture of DRG neurons. H. Wilson (Duke University) is thanked for advice on transfection with the Helios Gene Gun.

This research was supported in part by a grant from the National Institutes of Health (DK 29808).

Address all correspondence to V. Bennett, Howard Hughes Medical Institute and Departments of Cell Biology and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710. Tel.: (919) 684-3538. Fax: (919) 684-3590. E-mail: benne012{at}mc.duke.edu


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