Fig. 5

Topographic organization of retinal axon fibers along the developing Xenopus retinotectal path. a Schematic representation of the developing tadpole visual system and of experimental design. b Coronal section of a stage 46 tadpole eye shows localization of a lissamine-tagged control MO (red) after electroporation into the ventral half of the retina and fluorescein-tagged control MO into the dorsal half (green). c, d High magnification confocal images show the trajectories of lissamine-tagged RGCs axon fibers and fluorescein-tagged control MO labeled axon fibers as they exit the eye c and along the optic nerve, chiasm, and optic tract d. Note the topography of RGCs in the eye and their spatial arrangement along the optic nerve and chiasm, where axon fibers from ventral RGCs labeled by the lissamine tag travel along the ventral side of the optic nerve and chiasm while axons of RGCs labeled fluorescein-tagged control MO travel along the dorsal side of the optic nerve. d, e, f Lissamine MO-labeled axon fibers that were originally positioned on the ventral side of the optic nerve are positioned more dorsally after crossing the optic chiasm. In contrast, fluorescein MO-labeled axon fibers that originate in the dorsal portion of the retina shift more ventrally. In the stitched tiled image in d, the ventral tissue border of the brain is demarcated by the dashed line. g At the optic tectum, the lissamine-labeled RGC axon fibers localize to the dorsal branch while the fluorescein-tagged control MO-labeled axon fibers localize ventrally. Small double arrows in the magnified image point to fluorescent debris picked by glial cells. Scale bars: 100 μm for b; 50 μm for c, d, and g; 20 μm for e; 25 μm for f