||The RPE is a polarized pigmented epithelial monolayer that is critical for vision and development of the neural retina. Considering its diverse and required roles, it is surprising how little is known about how it develops. Two transcription factors Mitf and Otx2 have been identified. Both are required for RPE development by activating many RPE terminal differentiation genes. The loss of either factor is catastrophic and induces RPE cells to dedifferentiate and to instead express retina-specific genes in a process termed RPE-to-retina transdifferentiation. Therefore, it is imperative that Mitf and Otx2 expression levels be maintained during development. A few other intrinsic and extrinsic factors have been identified that regulate RPE fate, but only one gene family (Pax genes) has been demonstrated to directly regulate Mitf. In Chapter 2,1 present results demonstrating a previously unknown role for Wnt/B-catenin signaling in the murine RPE. The pathway is active during development, and is required for RPE differentiation by directly regulating both Mitf and Otx2. Conditional inactivation of B-catenin results in many defects including RPE-to-retina transdifferentiation, adhesion defects, and coloboma with optic nerve defects. In Chapter 3,1 show evidence (in collaboration with Shinichi Nagakawa), that the role of Wnt/B-catenin in mouse and chicken is conserved. I also show that Otx2 and ficatenin, when co-transfected into the chicken retina, ectopically induces Mitf expression. This finding is key, since neither factor is sufficient alone to do so. 1 also confirm findings and provide novel evidence that both Otx2 and Mitf-D are able to autoregulate their enhancers to further enhance their expression levels during development In the final chapter, I will emphasize the importance of maintaining RPE fate during development. Maintaining Mitf and Otx2 expression levels is imperative. Consequently, my findings demonstrating that Wnt/B-catenin signaling regulates both are significant. Mitf expression can also be enhanced through integrated Otx2 and Wnt/Bcatenin signaling to enhance Mitf expression even higher (and both can autoregulate). I also provide a model of RPE development incorporating some of the known factors, and describe future directions to further elucidate the role of Wnt/B-catenin signaling in RPE formation.