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The Journal of Neuroscience, December 15, 2001, 21(24):9572-9584
Schwann Cells Express Active Agrin and Enhance Aggregation of
Acetylcholine Receptors on Muscle Fibers
Jie-Fei
Yang,
Guan
Cao,
Samir
Koirala,
Linga V.
Reddy, and
Chien-Ping
Ko
Section of Neurobiology, Department of Biological Sciences,
University of Southern California, Los Angeles, California 90089-2520
To explore novel roles of glial cells in synaptic function and
formation, we examined the expression of agrin in frog Schwann cells
and tested their role in the aggregation of acetylcholine receptors
(AChRs). Using reverse transcription-PCR, we found that Schwann
cells along nerve fibers in tadpoles expressed only the inactive agrin
isoform B0 but began to also express active agrin isoforms B11 and B19
at approximately metamorphosis. During nerve regeneration in the adult,
the expression of these active agrin isoforms in Schwann cells was
upregulated, including the appearance of the most potent isoform, B8.
This upregulation was induced by regenerating axons but not by nerve
injury per se. In muscle cultures, the presence of adult Schwann cells
enhanced the number and the total area of AChR aggregates 2.2- and
4.5-fold, respectively, and this enhancement was eliminated by heparin
treatment. Furthermore, adult Schwann cells in culture expressed active
agrin isoforms and produced agrin protein. Using a novel technique to
selectively ablate perisynaptic Schwann cells (PSCs) at the
neuromuscular junction, we found that PSCs also expressed active agrin
isoforms B11 and B19, and these active isoforms were upregulated,
including the appearance of B8, during reinnervation. Observation
in vivo showed that extrajunctional AChR aggregates were
associated with PSC sprouts after nerve injury and subsequent
reinnervation. These results suggest that, contrary to the prevailing
view that only neurons express active agrin, glial cells also express
active agrin and play a role in the aggregation of AChRs both in
vitro and in vivo.
Key words:
acetylcholine receptors; agrin; complement; frog; glia; muscle; neuromuscular junction; nerve regeneration; Schwann cells
Copyright © 2001 Society for Neuroscience 0270-6474/01/21249572-13$05.00/0
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