Fig. 3. Both cutaneous and proprioceptive afferents directly invade the dorsal mantle layer in the absence of netrin 1. (A,C,E,F) Wild-type mice. (B,D,G,H) Netrin 1 mutant mice. DRG axons in the lateral views of whole-mount E12.5 spinal cord preparations (A,B) and on transverse sections of the E13.5 spinal cord (C,D) labeled by DiI, and immunohistochemically labeled with anti-TrkA (E,G) or TrkC (F,H) antibodies at E12.5. (A,B) In both animals, DRG axons bifurcate at DREZ (arrow in insets) and extend longitudinally more than three segments (arrowheads). An epifluorescent picture is merged onto a differential interference contrast (DIC) picture. Insets indicate the site of DiI injection in the DRG. Asterisks indicate DRG. (C,D) In E13.5 wild-type animals, the dorsal funiculus has been formed in the marginal zone, which is composed of DiI-labeled fibers (arrowheads in C). However, in netrin 1 mutant mice, most DRG axons directly invade the dorsal mantle layer forming the ectopic dorsal funiculus (arrowheads in D). (E-H) In wild-type mice, TrkA-(E) and TrkC-positive (F) fibers project to the marginal zone, and their projection into the dorsal mantle layer is not observed. In netrin 1 mutants, TrkA-positive axon bundles stay near the DREZ (G), and many TrkA- and TrkC-positive (H) fibers aberrantly project into the dorsal mantle layer. White broken lines indicate the boundary between the marginal zone and the dorsal mantle layer. Sections were counterstained with Hoechst 33342 (blue). Scale bar: 250 µm in A,B; 200 µm in C,D; 100 µm in E-H.