Journal of Neuroscience, Vol 15, 5466-5475, Copyright © 1995 by Society for Neuroscience
Presynaptic differentiation induced in cultured neurons by local application of basic fibroblast growth factor
Z Dai and HB Peng
Department of Cell Biology and Anatomy, University of North Carolina at Chapel Hill 27599, USA.
Recent studies have suggested a role for molecules residing at the muscle
surface in signaling presynaptic development at the neuromuscular junction
(NMJ). Since heparan sulfate-proteoglycan is a major component of the
extracellular matrix of skeletal muscle, factors that are bound to this
proteoglycan, such as basic fibroblast growth factor (bFGF), are in a
strategic position for neuronal signaling. To test this idea, we applied
bFGF to cultured Xenopus spinal cord neurons and monitored the change in
intracellular Ca2+ level with fura-2 ratio imaging. In one-third of the
neurons, local application of bFGF elicited a 30-140% increase in
intracellular Ca2+ level. Ca(2+)-free medium or suramin abolished this
change. Latex beads coated with bFGF induced clustering of synaptic
vesicles at the bead-neurite contacts as evidenced by anti-synaptotagmin
antibody labeling and electron microscopy. This response was also blocked
by Ca(2+)-free medium and by suramin. Uncoated beads or beads coated with
PDGF were ineffective. This induction was also inhibited by a tyrosine
kinase inhibitor, tyrphostin RG-50864, suggesting the role of receptor
tyrosine kinase activation in this process. In addition, bFGF-coated beads
also induced the localization of depolarization-dependent Ca2+ influx to
the bead- neurite contacts. In contrast, depolarization caused a
distributed Ca2+ elevation in untreated neurites. These results suggest
that local presentation of bFGF can mimic the muscle target in signaling
the development of both a cytoplasmic and a membranous specialization for
excitation-secretion coupling observed at the NMJ.
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