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.
Dai
Z
Z
Department of Cell Biology and Anatomy, University of North Carolina at Chapel Hill 27599, USA.
Peng
H B
HB
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004625:Embryo, Nonmammalian / Q000166:cytology; D005314:Embryonic and Fetal Development; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology*; D008863:Microspheres; D009474:Neurons / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D017729:Presynaptic Terminals / Q000502:physiology*; D013116:Spinal Cord / Q000196:embryology; D013572:Synaptic Vesicles / Q000502:physiology; D014981:Xenopus
D016222:Fibroblast Growth Factor 2; D002118:Calcium