Retinogenesis requires a tightly controlled balance of retinal progenitor cell (RPC) proliferation and differentiation. Deregulation of this mechanism often results in profound neuro-developmental disorders or cancer. Our long term goal is to elucidate the transcriptional mechanisms coupling RPC cell cycle regulation to neuronal differentiation. In this proposal, experiments will define the role of the transcriptional regulato Ronin (Thap11) in retinogenesis. Ronin was identified recently as a novel embryonic stem cell (ESC) pluripotency factor, influencing ESC proliferation and growth. Ronin is also expressed throughout the developing brain and retina, but its role in these tissues is unknown. In preliminary studies, we have found that Ronin mutant retinae phenocopy the Cyclin D1 null mice thereby implicating Ronin as a regulator of the cell cycle G1 to S-phase transition. However, analysis of preliminary Ronin retinal ChIP-seq data showed enrichment for mitochondrial genes rather than cell cycle machinery. Recently, mitochondria have emerged as critical regulators of the G1 to S-phase transition in both flies and rodents by promoting Cyclin E activity and entry into S-phase. Therefore, we hypothesize that Ronin influences the RPC cell cycle by directly regulating genes required for proper mitochondrial function and promotion of S-phase entry. To test this hypothesis, we have assembled a team with diverse expertise, to facilitate a synergistic, multi- disciplinary approach using genetic loss- and gain-of-function experiments, metabolic profiling, live retinal microscopy and genomics. Upon completion of this proposal, we expect that we will have identified a new transcriptional mechanism that couples mitochondrial function to cell cycle progression in RPCs. This deeper understanding of the transcriptional regulation of multipotent, proliferative RPCs will ultimately inform efficacious strategies for retinal cell replacement therapies as well as novel cancer drug targets functioning at the interface of mitochondrial bioenergetics and the cell cycle.
