Fig. 2. Phenotypes of mildly affected Ndst1 mutant E13.5 embryos. (A,C) Wild-type littermate controls. (B,D) Mutant embryos show lack of eyes and reduced frontonasal process (B) and (D) lack of eye lens. (E,G) Wild-type littermate controls. (F,H) Mutant embryos with mild defects in external features show severe defects in the frontonasal process and forebrain (E16.5, horizontal sections). Lack of olfactory tracts (ot), olfactory bulbs (ob), the eye lens (el) and the hippocampal commissure (hc, arrowhead) is evident. The cortex (cx) is reduced in size and stratification and the cleavage along transverse, sagittal and horizontal axes is defective. Scale bar: 1 mm. (I,J) Coronal sections of a E18.5 wild-type (I) and Ndst1^–/– (J) brain show the lack of the anterior commissure (ac) in the mutant embryo (arrowhead). Axons disperse instead of crossing the midline. Scale bar: 500 µm.