There is a rapidly growing body of evidence that Muller glia are a source of retinal progenitors to mediate neural regeneration. Many studies have demonstrated that Muller glia can become proliferating progenitor cells in the retinas of different vertebrate species. Nearly all reports have studied Muller glia-derived progenitors in acutely damaged retinas. However, little is known about the mechanisms that stimulate neurogenesis from Muller glia-derived progenitors in undamaged retinas or retinas undergoing slow, progressive degeneration. Furthermore, the regeneration of retinal neurons in warm-blooded vertebrates is limited compared to that seen in cold-blooded vertebrates. Therefore, the identification of the secreted factors and signaling pathways that permit and/or stimulate neural regeneration from Muller glia-derived progenitors is crucially important to developing new therapies to treat degenerative diseases of the human retina. We have obtained preliminary data indicating that signaling through the glucocorticoid receptor (GCR), p38 MAPK and signals derived from other types of retinal glia significantly impact the neurogenic potential of Muller glia. We will investigate the coordinated activity of different types of retinal glia including the Muller glia, microglia and the recently described Non-astrocytic Inner Retinal Glia-like (NIRG) cells. We have identified the NIRG cells as a distinct type of glial cell that is present in retina of birds, canines and primates. We believe that the NIRG cells influence the ability of Muller glia to become retinal progenitors. We expect that the completion of the experiments described in this proposal will provide significant new information regarding different signaling pathways, secreted factors, and how the microglia and NIRG cells influence the formation of Muller glia-derived retinal progenitors. Identification and understanding of the mechanisms that enhance the neurogenic potential of Muller glia is required to develop new therapies for sight-threatening diseases, such as glaucoma and macular degeneration that involve the loss of retinal neurons.