Fig. 4

Loss of Islr2 leads to axon routing errors at the optic chiasm and tract in mice. E16.5 Islr2 mutant mice display expanded chiasms along the antero-posterior axis (brackets in b and c, compared to a). In addition, a greater number of axons enter the opposite optic nerve with retinopetal directionality (arrows in b and c). Although no clear increase in the number of ipsilaterally-projecting fibers relative to the contralateral projection can be observed, other defects were identified along the postcrossing route of RGC axons. Defasciculation effects in the optic tract were observed both at ventral (b' and c')and dorsal locations (b'' and c'', where many axons stray from their normal course (arrowheads). Arrowheads in b' and c' indicate axons departing rostrally from the chiasm, a common phenotype observed in situations when guidance through the chiasm is impaired. I: ipsilateral. C: contralateral. ON: optic nerve. OC: optic chiasm. OT: optic tract. Scale bars: 500 μm (a-c), 200 μm (a'-c' and a''-c'').