Published online August 20, 2007
doi:10.1083/jcb.200705119
The Journal of Cell Biology, Vol. 178, No. 5, 875-886
The Rockefeller University Press, 0021-9525 $30.00
© 2007 Hedstrom et al.
Neurofascin assembles a specialized extracellular matrix at the axon initial segment
Kristian L. Hedstrom1,
Xiaorong Xu2,
Yasuhiro Ogawa1,
Renato Frischknecht3,
Constanze I. Seidenbecher3,
Peter Shrager2, and
Matthew N. Rasband1
1 Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06032
2 Department of Neurobiology and Anatomy, University of Rochester Medical Center, Rochester, NY 14642
3 Department of Neurochemistry and Molecular Biology, Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany
Correspondence to Matthew N. Rasband: rasband{at}bcm.edu
Action potential initiation and propagation requires clustered Na+ (voltage-gated Na+ [Nav]) channels at axon initial segments (AIS) and nodes of Ranvier. In addition to ion channels, these domains are characterized by cell adhesion molecules (CAMs; neurofascin-186 [NF-186] and neuron glia–related CAM [NrCAM]), cytoskeletal proteins (ankyrinG and ßIV spectrin), and the extracellular chondroitin-sulfate proteoglycan brevican. Schwann cells initiate peripheral nervous system node formation by clustering NF-186, which then recruits ankyrinG and Nav channels. However, AIS assembly of this protein complex does not require glial contact. To determine the AIS assembly mechanism, we silenced expression of AIS proteins by RNA interference. AnkyrinG knockdown prevented AIS localization of all other AIS proteins. Loss of NF-186, NrCAM, Nav channels, or ßIV spectrin did not affect other neuronal AIS proteins. However, loss of NF-186 blocked assembly of the brevican-based AIS extracellular matrix, and NF-186 overexpression caused somatodendritic brevican clustering. Thus, NF-186 assembles and links the specialized brevican-containing AIS extracellular matrix to the intracellular cytoskeleton.
M.N. Rasband's present address is Department of Neuroscience, Baylor College of Medicine, Houston, TX 77030.
Abbreviations used in this paper: AIS, axon initial segment; ankG, ankyrinG; CAM, cell adhesion molecule; CNS, central nervous system; DIV, days in vitro; DRG, dorsal root ganglion; E, embryonic day; MAP2, microtubule-associated protein 2; Nav, voltage-gated Na+; NF, neurofascin; NrCAM, neuron glia–related CAM; PNS, peripheral nervous system; shRNA, short hairpin RNA.

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