The Journal of Neuroscience, October 15, 2001, 21(20):8119-8128
Deposition of the NG2 Proteoglycan at Nodes of Ranvier in the
Peripheral Nervous System
Sandra
Martin,
Angela K.
Levine,
Zhi Jiang
Chen,
Yvonne
Ughrin, and
Joel M.
Levine
Department of Neurobiology and Behavior, State University of New
York at Stony Brook, Stony Brook, New York 11794
The node of Ranvier is a complex macromolecular assembly of ion
channels and other proteins that is specialized for the rapid propagation of the action potential. A full understanding of the processes responsible for the assembly and maintenance of the node
requires first the identification and characterization of the proteins
found there. Here we show that NG2, a structurally unique
chondroitin sulfate proteoglycan, is a molecular component of the node
of Ranvier in the peripheral nervous system. In adult sciatic nerve,
NG2 is (1) associated with thin, elongated fibroblast-like cells, (2)
on some but not all basal laminae, and (3) at nodes of Ranvier. At the
nodes, NG2 is restricted to the nodal gap and is absent from the
paranodal or juxtaparanodal region. In dissociated cell cultures of
adult sciatic nerve, perineurial fibroblasts but not Schwann cells
express NG2 on their surfaces. Approximately 45% of the total NG2 in
peripheral nerves is in a soluble, rather than particulate, subcellular
compartment. NG2 is also present in membrane fractions that also
contain high levels of voltage-dependent sodium channels, caspr, and
neuron-glia related cell adhesion molecule. These medium-density
membranes likely correspond to the nodal and paranodal region of the
axon-Schwann cell unit. These results suggest a model in which
perineurial fibroblasts secrete or shed NG2, which subsequently
associates with nodes of Ranvier. The growth-inhibitory and
anti-adhesive properties of NG2 may limit the lateral extension of
myelinating Schwann cells as nodes mature. NG2 may also participate in
the barrier functions of the perineurial linings of the nerve.
Key words:
node of Ranvier; perineurium; nerve-blood barrier; chondroitin sulfate proteoglycan; NG2; extracellular matrix
Copyright © 2001 Society for Neuroscience 0270-6474/01/21208119-10$05.00/0
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