Genome-Scale CRISPRa Screen Identifies Novel Factors for Cellular Reprogramming

Primed epiblast stem cells (EpiSCs) can be reverted to a pluripotent embryonic stem cell (ESC)-like state by expression of single reprogramming factor. We used CRISPR activation to perform a genome-scale, reprogramming screen in EpiSCs and identified 142 candidate genes. Our screen validated a total of 50 genes, previously not known to contribute to reprogramming, of which we chose Saill for further investigation. We show that Saill augments reprogramming of mouse EpiSCs and embryonic fibroblasts and that these induced pluripotent stem cells are indeed fully pluripotent including formation of chimeric mice. We also demonstrate that Saill synergizes with Nanog in reprogramming and that overexpression in ESCs delays their conversion back to EpiSCs. Lastly, using RNA sequencing, we identify and validate Klf5 and Fam189a2 as new downstream targets of Saill and Nanog. In summary, our work demonstrates the power of using CRISPR technology in understanding molecular mechanisms that mediate complex cellular processes such as reprogramming.