Fig. 1. The optic chiasm is perturbed in Foxd1 deficient embryos. (A) Anterograde DiI labeling in E12.5, E14.5 and E17.5 Foxd1^+/+ (a,c,e) and Foxd1^lacZ/lacZ (b,d,f) embryos reveals that the characteristic X-shape of the optic chiasm becomes elongated and splayed, and that the ipsi- to contralateral ratio of retinal axons increases. Contra, contralateral projection; ipsi, ipsilateral projection; ON, optic nerve; asterisk, midline. (B) P0 embryos lacking Foxd1 (Foxd1^lacZ/lacZ, b-e) display four aberrant phenotypes; compare with Foxd1^+/+ embryos (a,f). (b) Most retinal axons are arrested at the midline and end in `nodules'. (c) Retinal axons reach the midline in a more caudal position than in Foxd1^+/+ littermates and project contra- or ipsilaterally. Axons are arrested as the optic nerves converge (asterisk), adding to the increased breadth of the chiasmatic crossing point; some axons are routed into the optic tracts and grow in an aberrant ipsi-versus contralateral ratio. (d) The position of the crossing site is shifted caudally and the RGC project ipsi- or contralaterally with a greatly increased uncrossed component. (e) Retinal axons take four different routes (arrows) after leaving the optic chiasm, forming two optic tracts on each side rather than one. (f,g) Diagrams summarizing the chiasm phenotypes in Foxd1^+/+ and Foxd1^lacZ/lacZ mice. Scale bars: 200 µm.