Figure 10

Neuropilin 2 (Npn2) appears to be minimally required for the contralateral pathfinding of GABAergic spinal commissural axons. (A-C’), Anti-GAD65 immunohistochemistry was used to assess the development of GABAergic commissural neurons and their pre- and post-crossing axonal segments in transverse sections derived from Npn2^−/− mouse embryos and wild type littermates. A rather modest thinning of the ventral funiculus (VF) was observed in Npn2^−/−(B, B’, C, C’ ), as compared to WT (A, A’) littermate control spinal cords. Consistent with labeled post-crossing axons destined for the VF following mis-guided trajectories in the absence of Npn2, we identified aberrant GAD65-positive fibers (arrowheads) outside of the spinal cord at the edges of the ventral commissure (VC) or immediately ventral to the VF. (D), A schematic diagram indicating the positions of GABAergic neurons and the ventral (VF) and lateral (LF) funiculi used for quantification in E. (E), Quantification of the normalized fluorescence intensity with a given domain revealed fewer number of axons in the VF, but no significant differences in the width of the ventral commissure (VC) or LF. The ratio of the normalized intensity/area was calculated by averaging the normalized fluorescent intensity (intensity of the specific region/total intensity of the section) over the normalized area (area of the specific region/entire area of the spinal cord). Student’s t-test, *P <0.01; n =4 to 5 embryos per genotype, ten 25 μm thick sections per embryos were analyzed. Scale bars in C, 40 μm for A-C; in C’, 80 μm for A’-C’.