Figure 4.

An RGC axon defect in Nmnat2^gtE/gtE optic nerve. A, Low-magnification wide-field images of NF-L and βIII-Tubulin (TUJ1) immunostaining of horizontal cryosections of the heads of wild-type, Nmnat2^gtE/gtE, and Nmnat2^gtE/gtE;Wld^S/+ E18.5 embryos at the level of the optic nerve (ON), optic chiasma (OX), and optic tract (OT). Maximal length of NF-L and βIII-Tubulin-labeled RGC axons in the Nmnat2^gtE/gtE ON (as revealed by staining of adjacent serial sections for >150 μm in each direction) is indicated by an asterisk. The RGC axon defect appears to be largely corrected in Nmnat2^gtE/gtE;Wld^S/+ embryos. B, Confocal slices of the boxed regions in A highlight abnormal swellings containing accumulations of NF-L at the distal ends of the truncated RGC axons in Nmnat2^gtE/gtE embryos. Arrows point to swellings in higher-magnification images (zoom) of the boxed regions in the panels above. C, NF-L immunostaining and DAPI counterstaining of horizontal sections through the retinas of wild-type and Nmnat2^gtE/gtE E18.5 embryos revealed a normal optic fiber layer (OFL) and no evidence of significant pyknosis in the ganglion cell layer (GCL) in the mutant. Images are representative of n = 3 embryos of each genotype. Nmnat2^+/gtE embryos (n = 3) were indistinguishable from wild-types (data not shown).