Identification of genes involved in photoreceptor recognition and synapse formation

PROJECT SUMMARY/ABSTRACT Vision loss caused by the death of photoreceptors is a leading cause of irreversible blindness worldwide, yet therapeutic options remain limited. For this reason, the NEI's Retinal Disease Program has identified the development of strategies for the treatment of retinal degenerations as a core program goal. Recently, several laboratories have derived photoreceptors from stem cells, making cell-replacement therapies particularly promising. Additionally, important advances have been made into manipulations that could stimulate retinal regeneration from the retinal Müller glia. The critical barrier for the success of such therapies is the integration of derived photoreceptors into existing retinal circuits to reestablish their function. Yet, we still lack a complete understanding on the mechanisms that underlie the normal wiring of photoreceptors into retinal circuits, especially for cone photoreceptors. Cone photoreceptors of different subtypes are wired into specific retinal circuits, so that functional differences (like spectral sensitivity) may be exploited to extract specific information (like color) from the visual scene. Our main hypothesis for this proposal is that each cone subtype expresses specific genes that allow recognition by its postsynaptic partners (bipolar and horizontal cells), and our main goal is to identify these genes. To accomplish this, we will first generate a complete transcriptomic profiling of the four different cone subtypes in zebrafish, and identify genes that are differentially expressed (aim #1). Based on this differential expression, we will perform a reverse-genetic screen, where we will assess the functional, structural and ultrastructural integrity of the cone synapses (aim #2). This will allow us to identify genes that control the control the formation of synapses between cones and other retinal cells, and that promote the integration of cones into retinal circuits. We believe that this new knowledge could have direct applications in the improvement of cell-replacement or regenerative therapies for retinal degenerations. Moreover, wiring specificity is a key feature of neural circuits in general. This proposal benefits from the experimental accessibility of the retina and our deep knowledge of retinal cell types and circuits, but our approach has the potential to impact the study of other neuronal degenerative diseases.