Fig. 7. Wnt2b/wg expression and function during peripheral eye development in vertebrates and invertebrates. (Left) In vertebrates, Wnt2b (blue) is expressed in, and functions in, the RPE and peripheral tip of the OC, where the ciliary body and iris are derived, but not in the retina (yellow; top). At later embryonic stages (below), Wnt2b is maintained in both pigmented and non-pigmented layers of the iris. Wnt2b/ß-catenin signaling is sufficient and necessary for the development of peripheral eye tissues, ciliary body and iris epithelia (green). (Right) In Drosophila, wg (blue) is expressed in the lateral margins, both anterior and posterior, of the eye imaginal disc of the third instar larvae, but not in the retina (yellow; top). In the adult eye (below), wg is restricted to the head capsule immediately adjacent to the pigmented rim (PR), and functions to pattern peripheral tissues, such as head capsule cuticle, pigment rim and dorsal rim ommatidia (green) in a dosage-dependent manner. wg/armadillo signaling in Drosophila is sufficient and necessary for the development of these tissues. The scheme showing a cross section of the adult fly eye is adapted from Tomlinson (Tomlinson, 2003). A, antenna disc; HC, head capsule cuticle; L, lens; PR, pigment rim; MF, morphogenetic furrow; RPE, retinal pigmented epithelium.