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The Journal of Neuroscience, January 1, 2003, 23(1):175-186
Multiple Regions of the NG2 Proteoglycan Inhibit Neurite
Growth and Induce Growth Cone Collapse
Yvonne M.
Ughrin*,
Zhi Jiang
Chen*, and
Joel M.
Levine
Department of Neurobiology and Behavior, State University of New
York at Stony Brook, Stony Brook, New York 11794
The NG2 chondroitin sulfate proteoglycan, an integral membrane
proteoglycan, inhibits axon growth from cerebellar granule neurons and
dorsal root ganglia (DRG) neurons in vitro. The
extracellular domain of the NG2 core protein contains three subdomains:
an N-terminal globular domain (domain 1), a central extended domain
that has the sites for glycosaminoglycan (GAG) attachment (domain 2),
and a juxtamembrane domain (domain 3). Here, we used domain-specific fusion proteins and antibodies to map the inhibitory activity within
the NG2 core protein. Fusion proteins encoding domain 1 (D1-Fc) or
domain 3 (D3-Fc) of NG2 inhibited axon growth from cerebellar granule
neurons when the proteins were substrate-bound. These proteins also
induced growth cone collapse from newborn DRG neurons when added to the
culture medium. Domain 2 only inhibited axon growth when the GAG chains
were present. Neutralizing antibodies directed against domain 1 or 3 blocked completely the inhibition from substrates coated with D1-Fc or
D3-Fc. When the entire extracellular domain of NG2 was used as a
substrate, however, both neutralizing antibodies were needed to reverse
completely the inhibition. When NG2 was expressed on the surface of
HEK293 cells, the neutralizing anti-D1 antibody was sufficient to block
the inhibition, whereas the anti-D3 antibody had no effect. These
results suggest that domains 1 and 3 of NG2 can inhibit neurite growth
independently. These inhibitory domains may be differentially exposed
depending on whether NG2 is presented as an integral membrane protein
or as a secreted protein associated with the extracellular matrix.
Key words:
regeneration; glial scars; chondroitin sulfate
proteoglycan; spinal cord injury; NG2; growth cone collapse
*
Y.M.U. and Z.J.C. contributed equally to this work.
Copyright © 2003 Society for Neuroscience 0270-6474/03/231175-12$05.00/0
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