Fig. 6. Expression of APP, NgCAM, contactin 4 and contactin 3 in the developing visual system. RNA in situ hybridization in sagittal sections of E11.5 chick heads. (A-E) Retina. Each antisense probe detected RNA expression in the RGC layer (arrow). Pigmented epithelium (dark brown line) bounds the retina opposite the RGC layer. (F-J) Each antisense probe detected RNA expression in multiple layers of the tectum. Top, anterior extreme; bottom, posterior extreme; open arrowheads, stratum opticum as identified by GAP43 immunolabeling. (K-Z) Co-staining using RNA in situ hybridization (K-R) or immunohistochemistry (S-Z) for APP (green), DAPI nuclear stain (blue) and immunohistochemistry for GAP43 (red). Solid arrow, RGC layer; open arrow, retinal optic fiber layer; solid arrowhead, pigmented epithelium; open arrowheads, tectal stratum opticum as identified by GAP43 immunolabeling. Scale bars: 500 µm in A-J; 100 µm in K-V; 200 µm in W-Z.