DESCRIPTION (provided by applicant): Optic nerve degenerations as seen in glaucoma, ischemic and traumatic optic neuropathies, are a leading cause of blindness in the U.S. and worldwide, and are very common in the veteran popuation. They are characterized by loss of retinal ganglion cells (RGCs), which are not replaced by endogenous mechanisms, and thus vision loss is generally irreversible. Cell transplantation therapies provide new hope to protect or even to replace degenerated RGCs and restore visual function. However, little is known about the basic molecular mechanisms governing the differentiation of RGCs in normal retinal development, or from other stem cell sources. Here we propose to elucidate how RGCs are specified from retinal progenitor cells (RPCs) during normal retinal development, and apply that knowledge to the study of human induced pluripotent stem cells (hiPSCs). We recently uncovered a new pathway regulating RGC differentiation mediated through a class of SoxC transcription factors (TFs) that is necessary and sufficient to specify RGC fate. Furthermore, we discovered that growth and differentiation factor-15 (GDF15), a transforming growth factor-beta (TGF-β superfamily ligand, promotes RGC differentiation through up-regulation of Sox4 expression. In contrast, GDF11, another TGF-β superfamily member, inhibits RGC differentiation through down-regulation of another TF, Math5. However, it is not known how these two closely related TGF-βsignaling ligands regulate RGC differentiation in opposing ways, nor whether this pathway through Sox4 can be manipulated to enhance approaches to cell therapies. We hypothesize that this novel pathway regulates RGC specification in vivo, and propose to determine, (1) how GDF11 and GDF15 temporal and spatial expression function in RGC differentiation during retinal development; (2) how the differential activation and function of SMAD signaling proteins downstream of GDF11 and GDF15; (3) how SUMOylation and TF cross-talk work in regulating RGC specification; and finally (4) how these pathways promote differentiation of RGC-like cells from hiPSCs, and promote these cells' integration into the retina after cell transplantation in vivo. Through these aims we hope to broaden our basic understanding of the molecular regulation of retinal and RGC development, and take steps towards the application of this understanding to generating cell replacement therapies for glaucoma and other optic neuropathies.