Figure 6

Neuropilin 2 (Npn2) is not required for the pathfinding of post-crossing dI4 axons. (A, B) Confocal micrographs of the post-crossing commissural axon-containing region in open-book preparations derived from the spinal cords of Npn2−/+ and Npn2−/− E11.5 mouse embryos in a Neurog2-tauGFP reporter background. (A) In the Npn2 heterozygous preparation, Neurog2-tauGFP-labeled dI4 axons project diagonally away from the FP, analogous to the contralateral pathfinding behavior of their dI1 counterparts (see Figure 3). (B) In the open-book preparation derived from a Npn2 null littermate, post-crossing dI2 axons project diagonally away from the FP as they do in heterozygous and wild type (data not shown) embryos. (C) The average number of axon bundles crossing the ventral midline at the FP was normalized to the GFP-intensity of each section to generate a ratio of axon bundles/GFP-intensity. A Student’s T-test showed no statistically significant difference between the numbers of axons in the Npn2 homozygous or heterozygous preparations. The data are derived from 4–5 embryos per genotype. Scale bar in A, 25 μm for A-B.