| The optic vesicle is the embryonic precursor of the optic cup. The optic vesicle starts in the neural tube as a bulge that grows laterally and subsequently makes contact with the overlying surface ectoderm. Patterning of the bipotential tissue of the optic vesicle into neural retina and pigmented epithelium depends on its interaction with surrounding tissues. The role of the surface ectoderm in patterning the optic vesicle was examined. When the surface ectoderm was ablated, the tissue of the optic vesicle displayed an intermediate phenotype; both pigmented and pseudo-columnar. When fibroblast growth factor 1 (FGF1), a known component of the surface ectoderm, was replaced to the developing optic vesicle, the neural retina and pigmented epithelium domains differentiated such the neural retina domain was always closest to the source of FGF. The entire optic vesicle could be induced to form neural retina by the application of multiple sources of FGF1. These results support a model whereby the proximal and distal portions of the optic vesicle are both competent to form neural retina; however, contact with an FGF source, normally provided by the surface ectoderm, may reinforce the neural retinal fate within the distal portion of the optic vesicle. The proximal portion, although originally competent, does not receive an FGF signal. Without reinforcement, the proximal domain slowly loses its potential and differentiates as pigmented epithelium. |
