Expression of sema3Aa. A: Schematic diagram of a transverse section of the optic pathway. A RGC resides in the RGC layer (1) and sends out an axon that exits the retina at the optic nerve head (2), crosses the midline at the optic chiasm (3), extends along the pial surface of the diencephalon (4), and enters the main target, the optic tectum (5). B: Transverse section of a 72-hpf brain with an HRP-labelled RGC optic projection (brown). The eyes and skin have been removed. The optic chiasm, pathway, and tectum are labelled 3, 4, and 5, respectively. C and E are lateral views of whole-mount embryos and D and F are stage-matched transverse sections. C, D: sema3Aa transcripts appear in the pretectum/dorsal thalamus and the posterior tectum at 30 hpf. Bilateral nuclei in the dorsal posterior tuberculum also show expression. From 30-72 hpf, sema3Aa transcripts are seen in the telencephalon (asterisk), the hindbrain, and the ventral mesenchymal tissue. E, F: At 50 hpf, signal is maintained in the dorsal posterior tuberculum (F) and the posterior tectum (E). G, H: At 72 hpf, in transverse sections the outer region of the inner nuclear layer begins to express sema3Aa. The boxed area in G is shown at a higher magnification in H. hb, hindbrain; INL, inner nuclear layer; ONL, outer nuclear layer; ptec, posterior tectum; pt/DT, pretectum/dorsal thalamus; PTd, dorsal posterior tuberculum; RGC, retinal ganglion cell layer; vm, ventral mesenchyme. Scale bars = 50μm (B,D,F,G), 10 μm (H).
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