Characterizing photoreceptor precursor cells for retinal transplantation

PROJECT SUMMARY Retinal degenerative diseases result in the progressive loss of rod and cone photoreceptor cells. Because the mammalian retina cannot regenerate, photoreceptor cell death leads to irreversible vision loss. It is thus critical to improve our understanding of photoreceptor development and to investigate avenues of photoreceptor regeneration to restore vision. Cell-based therapies involving the transplantation of healthy donor cells have led to functional improvements in vision and represent a promising treatment approach to replace retinal cells. However, these efforts have yielded low rates of donor cell integration, suggesting that the identity of an optimal cell type for photoreceptor replacement is unknown. To address this knowledge gap, we performed unbiased single cell transcriptomics of the neonatal retina to understand the fundamental heterogeneity of developing photoreceptor precursor cells. We identified several novel subpopulations of cone-rod homeobox (Crx)+ cells with transcriptionally and spatially distinct expression profiles consistent with early (Dll1+), intermediate (Dll3+/Neurod4+), and late (Prom1+) photoreceptor precursor cells. Our central hypothesis is that these Crx+ subpopulations represent photoreceptor precursor cells with an increasing degree of lineage commitment to photoreceptor differentiation, and that isolation of a transcriptionally distinct subset of cells will improve the efficiency of integration upon subretinal transplantation in a mouse model of retinal degeneration. To test this hypothesis, we will perform lineage tracing of each subpopulation using inducible Cre recombination during normal development (Aim 1), and determine which subpopulation can most efficiently integrate upon subretinal transplantation into a mouse model of retinal disease (Aim 2). Together, these studies will help define the complex hierarchy of photoreceptor development and identify an optimal cell source for photoreceptor replacement that is critical to advancing the field of retinal regeneration in human blinding diseases.