RT Journal Article
SR Electronic
T1 Synapse-Forming Axons and Recombinant Agrin Induce Microprocess Formation on Myotubes
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 9678
OP 9689
DO 10.1523/JNEUROSCI.21-24-09678.2001
VO 21
IS 24
A1 Chang-Sub Uhm
A1 Birgit Neuhuber
A1 Brian Lowe
A1 Virginia Crocker
A1 Mathew P. Daniels
YR 2001
UL http://www.jneurosci.org/content/21/24/9678.abstract
AB We examined cell-surface behavior at nerve–muscle contacts during synaptogenesis in cocultures of rat ventral spinal cord (VSC) neurons and myotubes. Developing synapses in 1-d-old cocultures were identified by the presence of axon-induced acetylcholine receptor (AChR) aggregation. Identified regions were then examined by transmission and scanning electron microscopy. The myotube surface near contacts with axons that induced AChR aggregation typically displayed ruffles, microvilli, and filopodia (microprocesses), indicating motility of the myotube surface. At some of these contact sites microprocesses were wrapped around the axon, resulting in the partial or total “submersion” of the axon within the myotube contours. Sites of myotube contact with somata and dendrites of the same neurons showed much less evidence of motility and surface interaction than sites of contact with axons. Moreover, the distance between opposed membranes of axons and myotubes was smaller than between dendrites or somata and myotubes, suggesting stronger adhesion of axons. These results suggest polarized expression of molecules involved in the induction of microprocess formation and adhesion in developing VSC neurons. We therefore tested the ability of agrin, which is preferentially secreted by axons, to induce microprocess formation in myotubes. Addition of recombinant C-terminal agrin to culture medium resulted in formation of microprocesses within 3 hr. Myotubes transfected with full-length rat agrin constructs displayed numerous filopodia, as revealed by fluorescence microscopy. The results suggest that the induction of muscle cell surface motility may be linked to the signaling processes that trigger the initial formation of the neuromuscular junction.