Genome-scale CRISPR screening in a single mouse liver

A complete understanding of the genetic determinants underlying mammalian physiology and disease is limited by the availability of tools for high-throughput genetic dissection in the living organism. Genome-wide screening using CRISPR-Cas9 has emerged as a powerful method for uncovering the genetic regulation of cellular processes, but the need to stably deliver single guide RNAs to millions of cells has largely restricted its implementation to ex vivo systems. There thus remains a pressing need for accessible high-throughput functional genomics in a living organism. Here, we establish genome-wide enrichment and depletion screening in the liver of a single mouse and use this approach to uncover the complete regulation of cellular fitness in a living organism. We uncover regulation of cell fitness not previously identified in cell culture screens, underscoring the power of bringing high-throughput functional genomics into the organism. The approach we developed is accessible, robust, scalable, and adaptable to diverse phenotypes and CRISPR applications. We have hereby established a foundation for high-throughput functional genomics in a living mammal, enabling unprecedented insight into physiology and disease.