Fig. 4. Axon growth and guidance defects in the developing Fz3^-/- and Celsr3^-/- central nervous system. (A) Anti-neurofilament staining of horizontal sections through E15 WT and Fz3^-/- mouse brains shows a complete absence of thalamocortical and corticothalamic fiber bundles in an otherwise normal-appearing Fz3^-/- forebrain; the normal location of these fibers is indicated by an arrowhead. (B) DiI tracing of commissural axons in E11 WT and Celsr3^-/- mouse spinal cords shows a failure of rostral turning by Celsr^-/- axons after midline crossing. The spinal cord has been opened at the dorsal midline and flattened (an `open book' preparation). DiI was placed in commissural cell bodies beyond the left edge of each image. The vertical white line indicates the midline. A, Anterior/rostral; P, posterior/caudal. Panel A is reproduced with permission from Wang et al. (Wang et al., 2002) and panel B is courtesy of Drs Libing Zhou and Andre Goffinet.