Figure 7.

Summary of the Boc gain- and loss-of-function phenotypes at the chiasm. A, In wild-type conditions, axons expressing Boc (red) originate from the VT retina and avoid Shh at the optic chiasm. B, In Boc mutant mice, VT axons do not express Boc and fail to detect Shh at the midline. Instead of being repelled by Shh, they cross the chiasm and project contralaterally (represented by the dashed line). C, Ectopic expression of Boc in presumptive contralateral RGCs prevents their axons from crossing the optic chiasm. Two types of defects were observed: the conversion of contralateral projections into ipsilateral projections and the misrouting of axons to the contralateral optic nerve (represented by the dashed lines). V, Ventral; D, dorsal; N, nasal; T, temporal; on, optic nerve; oc, optic chiasm; ot, optic tract.