Many growth factors are expressed in the retina, but their functions are not well understood. The objectives of the proposed research are to define the functions of two growth factors, basic fibroblast growth factor (bFGF) and transforming growth factor alpha (TGF-alpha), by modifying their expression and the expression of their receptors during development. Effects of these modifications on proliferation, survival, and cell type choice will be studied using a combination of retinal culture preparations and gene transfer in vivo as well as in vitro. Gene transfer will be performed using a novel type of replication-incompetent retroviral vector that has been designed to reliably co-express multiple genes in individual cells. The goal of these experiments is to provide the basis for methods of optimizing the generation of specific populations of retinal cells and enhancing the survival of existing retina cells; therefore, this information will be applicable to the treatment and prevention of degenerative retinal diseases.