title: Expression of a dominant negative FGF receptor in developing GNRH1 neurons disrupts axon outgrowth and targeting to the median eminence.
abstract: During development, neurons that synthesize and release gonadotropin-releasing hormone (GNRH1) extend their axons to the median eminence (ME) to establish neurosecretory contacts necessary for hormone secretion. Signals that coordinate this process are not known, but could involve the activation of fibroblast growth factor receptors (FGFRs) expressed on developing GNRH1 neurons. Using both whole-animal and cell culture approaches, this study examines the direct role of FGFR signaling in the extension and guidance of GNRH1 axons to the ME. In vivo retrograde labeling with fluorogold (FG) first showed a significant reduction in the projections of GNRH1 axons to the circumventricular organs (including the ME) in transgenic mice expressing a dominant negative FGF receptor (dnFGFR) in GNRH1 neurons. Using a primary GNRH1 neuronal culture system, we examined if compromised axon extension and directional growth led to the reduced axon targeting efficiency seen in vivo. Primary cultures of GNRH1 neurons were established from Embryonic Day 15.5 embryos, an age when GNRH1 neurons are actively targeting the ME. Cultured GNRH1 neurons expressing dnFGFR (dnFGFR neurons) exhibited attenuated activation of signaling pathways and reduced neurite outgrowth in response to FGF2. Further, dnFGFR neurons failed to preferentially target neurites toward cocultured ME explant and FGF2-coated beads, suggesting a defect in axon pathfinding. Together, these findings describe a direct role of FGFR signaling in the elongation and guidance of GNRH1 axons to the ME.
authors.affiliation: Department of Integrative Physiology and the Center for Neuroscience, University of Colorado, Boulder, Colorado 80309-0354, USA. John.Gill@colorado.edu
authors.forename: John C
authors.initials: JC
authors.lastname: Gill
authors.forename: Pei-San
authors.initials: PS
authors.lastname: Tsai
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D005260:Female; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics; D008297:Male; D008473:Median Eminence / Q000166:cytology / Q000196:embryology / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D008863:Microspheres; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure; D011247:Pregnancy; D011498:Protein Precursors / Q000378:metabolism*; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000235:genetics* / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013266:Stilbamidines
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D011498:Protein Precursors; D013266:Stilbamidines; C050866:progonadoliberin I; D016222:Fibroblast Growth Factor 2; D049452:Green Fluorescent Proteins; D007987:Gonadotropin-Releasing Hormone; C496349:Fgfr1 protein, mouse; D051496:Receptor, Fibroblast Growth Factor, Type 1