Fig. 7

Retinotectal projections in mutants with anterior/posterior pathfinding errors. Ventral focal plane. (A) Wild-type projections. (B) In bashful mutants, axons project anteriorly into the forebrain, where they grow along the edge of the telencephalon (arrow) and occasionally make a complete circuit of the forebrain. (C) In some cases axons project to the ipsilateral tectal lobe in bashful. In these fish, RGC axons project both anteriorly (arrow) and turn (arrowhead) toward the ipsilateral tectal lobe (not seen in this focal plane). The DiI label was photoconverted to make the labeled RGC axons visible using DIC optics. (D-F) In astray mutants, axons grow aberrantly to one of three general destinations. After crossing the midline, axons either grow anteriorly into the anterior telencephalon (D, arrow), fan out toward the contralateral eye (E, arrow) and/or return to the ipsilateral side of the brain (E, arrowhead), or grow ventrally under the tectum to the hindbrain (F, arrow) (reverse dye fill). A majority of axons find their correct target region in the tectum in F. In these cases, axons fail to turn dorsally after crossing the midline and remain at the same dorsal/ventral level as the optic nerve. A, anterior; P, posterior. Scale bars, 100 µm.