Presynaptic differentiation induced in cultured neurons by local application of basic fibroblast growth factor.
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.[1]References
- Presynaptic differentiation induced in cultured neurons by local application of basic fibroblast growth factor. Dai, Z., Peng, H.B. J. Neurosci. (1995) [Pubmed]
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