Fig. 4.

Chiasm neuron development in DCC- or netrin-1–deficient mouse embryos. a, b, E12 hypothalamic whole-mount preparations showing CD44 immunostaining of the inverted V-shaped array of chiasm neurons (arrowheads) in heterozygous (HET;a) and netrin-1 mutant (MUT;b) littermates. These inverted V-shaped patterns are similar to that present in wild-type embryos (Sretavan et al., 1994).c, d, CD44 immunostaining of E12.5 coronal sections in wild type (c) and netrin-1 mutant littermates (d) showing CD44-positive neuron cell bodies ventromedially (asterisks) and their axons (arrowheads) that project dorsolaterally. e, f, DiI-labeled RGC axons and CD44-labeled chiasm neurons in midsagittal sections of E14 wild type (e) and DCC mutant (f) littermates. In both, the RGC axons appear as red bundles, whereas the labeled CD44 neurons appear as a lightbrowncurve-shapedgroup(blackarrows). In e andf, sections through the posterior (singleasterisks) and anterior (doubleasterisks) pituitary are visible on theright. Verydarkblackcells are blood cells. In wild-type animals, the distance between the posterior edge of the CD44 neurons and the anterior edge of the pituitary was somewhat variable. A similar degree of variability was seen in the mutants. g, h,Tracings showing the relationship between the posterior portion of the RGC axon bundles and the CD44 neuron array in midline sagittal sections of several wild-type (g) and DCC-deficient (h) embryos. RGC axons in DCC mutants were found in approximately the same position and did not appear closer to CD44 neurons compared with wild type. Scale bars:a–f, 200 μm.