title: Fibroblast growth factor receptor signaling in Xenopus retinal axon extension.
abstract: Fibroblast growth factor receptors (FGFRs) and N-cadherin both regulate axon extension in developing Xenopus retinal ganglion cells (RGCs). Cultured cerebellar neurons have been shown to require FGFR activity for N-cadherin-stimulated neurite outgrowth, raising the possibility that N-cadherin is a FGFR ligand. To investigate this possibility in the developing visual system, retinal neurons were transfected with a dominant-negative FGFR (XFD) and plated on purified N-cadherin substrates. XFD-expressing neurons extended markedly shorter processes than control GFP-expressing neurons, implicating a role for FGFRs in N-cadherin-stimulated neurite outgrowth. To examine whether N-cadherin and FGFRs share the same pathway or use distinct second messenger pathways, specific inhibitors of implicated signaling molecules were added to neurons stimulated by N-cadherin, basic fibroblast growth factor (bFGF), or brain-derived nerve factor (BDNF) (which stimulates RGC outgrowth by a FGFR-independent mechanism). Diacylglycerol (DAG) lipase and Ca2+/calmodulin kinase II inhibitors both significantly reduced outgrowth stimulated by N-cadherin or bFGF but not by BDNF. Furthermore, we show that inhibiting DAG lipase activity in RGC axons extending in vivo toward the optic tectum reversibly slows axon extension without collapsing their growth cones. Thus, a common second-messenger signaling pathway mediating both N-cadherin- and bFGF-stimulated neurite extension is consistent with a model in which N-cadherin directly modulates the FGFR or a model whereby both FGFR and N-cadherin regulate the same second-messenger system.
authors.affiliation: Biology Department, University of California, San Diego, La Jolla 92093-0366, USA.
authors.forename: B
authors.initials: B
authors.lastname: Lom
authors.forename: V
authors.initials: V
authors.lastname: Höpker
authors.forename: S
authors.initials: S
authors.lastname: McFarlane
authors.forename: J L
authors.initials: JL
authors.lastname: Bixby
authors.forename: C E
authors.initials: CE
authors.lastname: Holt
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000502:physiology*; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology; D015820:Cadherins / Q000378:metabolism / Q000494:pharmacology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D003512:Cyclohexanones / Q000494:pharmacology; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D020439:Growth Cones / Q000502:physiology*; D007527:Isoenzymes / Q000502:physiology; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors / Q000502:physiology; D016501:Neurites / Q000502:physiology; D051966:Phospholipase C gamma; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics / Q000502:physiology*; D012160:Retina / Q000166:cytology*; D015290:Second Messenger Systems; D014162:Transfection; D010738:Type C Phospholipases / Q000502:physiology; D014982:Xenopus laevis / Q000196:embryology
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D015820:Cadherins; D003512:Cyclohexanones; D007527:Isoenzymes; D017468:Receptors, Fibroblast Growth Factor; D016222:Fibroblast Growth Factor 2; C063302:KN 62; C036535:1,6-bis(cyclohexyloximinocarbonyl)hexane; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D008071:Lipoprotein Lipase; D010738:Type C Phospholipases; D051966:Phospholipase C gamma