Fig. 4. Function of the Xena/XVASP proteins is not required for axon pathfinding in the optic tract. (A-E) Lateral views of stage 39 whole-mount brains illustrating the axons of control GAP-GFP-expressing (A,B) and FP4-Mito-RFP+GAP-GFP-expressing (C-E) RGC neurons. The solid line approximates the location of the rostral border of the tectum. (A,B) Control axons labeled with GAP-GFP grew in the medial and dorsal optic tracts (MOT and DOT, respectively), turned caudally in the mid-diencephalon (Di) and penetrated into the tectum (Tect), where they arborized. (C) Axons of neurons expressing FP4-Mito navigated correctly. However, only very few retinal axons with impaired function of the Xena/XVASP proteins were detected in the optic tract or in the tectum. (D,E) We confirmed that the GAP-GFP axons in D expressed the Mito construct by detecting the presence of FP4-Mito-RFP on the mitochondria (E; arrows). CH, optic chiasm; Di; mid-diencephalon; DOT/MOT/VOT, dorsal/medial/ventral optic tract, respectively; Tect, tectum; Tel, telencephalon. Scale bar: 84 µm in A; 42 µm in A for B,C; 30 µm in A for D-E.