Figure 4. The early optic cup lip expresses mature fate markers. A-F: Transverse sections through eyes of 31 somite (A-C) and 38 somite (D-G) embryos labeled with Collagen IX (A, B, D) or NaK-ATPase (C, E, F). A: A low magnification of the section shown in B. B, D: Collagen IX (red) is present in the inner layer of the anterior optic cup. The arrows mark the posterior limit of Collagen IX expression. C, E, F: NaK-ATPase is present in the pigmented epithelium and the OCL. F: Expression of NaK-ATPase extends into the anterior of the non-pigmented, inner layer in a 38 somite embryo (arrow). G: Sox2 expression is present in the inner layer of the optic cup. Arrow marks the anterior limit of Sox2 expression. H: Transverse section through the ventral optic cup of a HH23 embryo. Hu is expressed at the posterior neural retina (bracket). The posterior limit of Collagen expression in the anterior eye is indicated (arrow). Scale Bars: 100 µm. HH; Hamburger Hamilton Stage, Coll IX; Collagen IX, NaK; NaK-ATPase.