Highlights • Stable, high-coverage delivery of a genome-scale sgRNA library to the mouse liver • Screen for hepatocyte fitness uncovers significant hits in single mice • Screen reveals genes uniquely required for hepatocyte fitness in a living organism • Approach is accessible and adaptable to diverse phenotypes and CRISPR applications Summary A complete understanding of the genetic determinants underlying mammalian physiology and disease is limited by the capacity for high-throughput genetic...