INHIBITION OF FGF RECEPTOR ACTIVITY IN RETINAL GANGLION-CELL AXONS CAUSES ERRORS IN TARGET RECOGNITION

Native fibroblast growth factor receptor (FGFR) function was inhibited in developing Xenopus retinal ganglion cells (RGCs) by in vivo transf ection of a dominant negative FGFR. Axons expressing the dominant nega tive protein advanced at 60% of the normal speed, but nevertheless nav igated appropriately in the embryonic optic pathway. When they neared the optic tectum, however, many axons made erroneous turns, causing th em to bypass rather than enter their target. By contrast, RGC axons ex pressing nonfunctional FGFR mutants entered the tectum correctly. Thes e findings demonstrate a role for FGFR signaling in the extension and targeting of RGC axons and suggest that receptor tyrosine kinase/growt h factor interactions play a critical function in establishing initial connectivity in the vertebrate visual system.