Expression patterns of Sema 3A, 3F, and netrin-1 in the ON and associated structures. Coronal cryosections across E18.5 retina (A, C, G) and optic nerve (B, D–F) were hybridized with digoxigenin-labeledSema 3A (A, B), netrin-1(C–F), and Sema 3F(G) antisense riboprobes. A, B,All along the nerve, perineural mesenchymal cells express Sema 3A transcripts (A, arrow). C, D,In contrast, the netrin-1 transcripts are detected within the ON, in the optic papilla (p inC) and in the temporal quadrant of the nerve (t in D). E,Double-labeling with antisense netrin-1 riboprobe (blue) and anti-GFAP Ab (brown) shows that netrin-1 mRNAs are expressed by astrocytes (arrows). Inset in E shows a higher magnification of a double-labelednetrin-1⁺/GFAP⁺cell. F, In the chiasmal segment of the ON, double labeling with netrin-1 riboprobe (blue) and anti-NG2 mAb (brown, arrows) shows an exclusion of the two markers at the cellular level. In the papilla, however, NG2⁺cells also express netrin-1 mRNA (F, inset).G,Sema 3F mRNAs are detected in the retina, including the photoreceptor layer and the retinal ganglion cell layer (G, inset, arrow). No signal forSema 3F was detected along the ON. H, A schematic representation of the distribution pattern of cells expressing Sema 3A (blue),netrin-1 (orange), and Sema 3F (purple). n, Nasal;t, temporal. Scale bar: A–C, D, G, 60 μm; G, inset, 30 μm; E,F, 17 μm; E, F, insets, 9 μm.