PROJECT SUMMARY The development of a functional central nervous system is dependent upon the proper specification of distinct cell fates by multipotent progenitor cells. While the role of protein-coding genes in this process is well studied, there is a pressing need to understand how non-coding elements, such as microRNAs (miRNAs) and enhancers, contribute to cell fate decisions as a growing number of studies implicate non-coding genomic elements in disease. The long term goal of this project is to elucidate how the microRNA, miR9-2 regulates the timing of cell fate specification during retinal development. miR9-2, along with its distal enhancer, has been linked to retinal disease and associated phenotypes, and disruption of miR9-2, through deletion of its enhancer, can delay the emergence of late-born cell classes. Therefore, the hypothesis of this proposal is that miR9-2, in coordination with its enhancer, regulates specific target transcripts in progenitor cells to control the timing of neurogenesis during retinal development. Here, using in vivo mouse models, single-cell sequencing, and machine-learning directed enhancer bashing approaches, this proposal will dissect the functional role of miR9-2 and its enhancer to understand the regulatory role they play in proper specification of retinal cell classes. The proposed research is significant, because it will provide a comprehensive understanding of the enhancer-miR9-2 regulatory unit and the gene networks, cell classes, and retinal structures under its control. This will further provide an opportunity to model the mechanisms of action by which non-coding elements influence the development and diseases of the central nervous system and may lead to gene targets and pathways with therapeutic potential.