Commissural axon phenotypes in Nestin–Cre;Ext1flox/flox embryos. A–D, Transverse sections of E11.5 Nestin–Cre;Ext1flox/flox (B, D) and wild-type littermate (A, C) embryos were stained with anti-TAG-1 antibody. drez, Dorsal root entry zone; vc, ventral commissure. Note that, in wild-type mice, TAG-1+ commissural axons extend in a highly fasciculated manner and form a thick ventral commissure, whereas in Nestin–Cre;Ext1flox/flox mice, commissural axons show defasciculation (arrowheads in B), and the size and staining intensity of the ventral commissure are reduced. Scale bar, 100 μm.