The proposed experiments involve several approaches to the understanding of the generation of asymmetry in the formation and continued growth of the vertebrate retina. Using the teleost fish Haplochromis burtoni, a screen designed to reveal the molecular basis of asymmetry at the ciliary margin will be undertaken. This screen will identify genes expressed early in the developmental programs of a retinal or iris cell. Experiments designed to test the level of committment of two proliferative populations of cells in the retina will determine the relative contributions of restrictions in cellular committment vs. signals from the environment. Using a retinotopic slice preparation, cells of the ciliary marginal zone and the rod progenitor population in the outer nuclear layer will be subject to heterotopic and heterochronic transplantations. In this way, we will determine the degree of cell autonomy in the asymmetric decisions made by multipotent retinal progenitors. To examine retinal asymmetry on a larger scale, H. burtoni is well suited because of its differential growth along the nasotemporal axis. The nasal region expands while the temporal pole undergoes relatively little growth in order to preserve the region of high cellular density in the temporal retina. The mechanisms underlying this asymmetric growth are not yet understood. Experiments designed to test the causal role of rod proliferation in this differential retinal expansion will determine whether optical stimuli, cell-cell contact, or a diffusible factor is most important in the shaping of the eye. Thus we may determine whether the addition of rods by the rod progenitors is actively affecting nasal retinal expansion or rather responding to changes in rod density. Overall, the proposed experiments are intended to further our understanding of the cellular and molecular decisions involved in the continued development and growth of the functioning vertebrate eye.
