Expression of a Dominant Negative FGF Receptor in Developing GNRH1 Neurons Disrupts Axon Outgrowth and Targeting to the Median Eminence

• Published in: Biology of reproduction 2006-03, Vol.74 (3), p.463-472
• Main Authors: GILL, John C, TSAI, Pei-San
• Format: Article
• Language: English
• Subjects: Animals; Axons - physiology; Biological and medical sciences; Cells, Cultured; Coculture Techniques; Female; Fibroblast Growth Factor 2 - metabolism; Fibroblast Growth Factor 2 - pharmacology; Fundamental and applied biological sciences. Psychology; Gonadotropin-Releasing Hormone - metabolism; Green Fluorescent Proteins - genetics; Hormones and neuropeptides. Regulation; Hypothalamus. Hypophysis. Epiphysis. Urophysis; Male; Median Eminence - cytology; Median Eminence - embryology; Median Eminence - physiology; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Transgenic; Microspheres; Neural Pathways - physiology; Neurons - physiology; Neurons - ultrastructure; Pregnancy; Protein Precursors - metabolism; Receptor, Fibroblast Growth Factor, Type 1 - genetics; Receptor, Fibroblast Growth Factor, Type 1 - metabolism; Signal Transduction - physiology; Stilbamidines; Vertebrates: endocrinology
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod.105.046904

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. Abstract GNRH1 axonal connections to the median eminence are necessary for reproduction and are formed during development by both trophic and directional cues mediated by FGF receptors