Fig. 6. Axon growth defects in mice deficient for Isl1 or Brn3b. (A-F) Optic pathways at the ventral diencephalons after unilateral DiI labeling. In Isl1 nulls and Brn3b nulls, the majority of RGC axons fails to reach the midline at E13.5 (A-C). At E15.5, although the chiasms are formed in the null mice (D-F), the optic nerves are noticeably thinner and axons are de-fasciculated in the optic tract (arrowheads). ON, optic nerve; Ipsi-OT, ipsilateral optic tract; Contra-OT, contralateral optic tract. Scale bars: 100 µm.