Genetic Screens in Human Cells Using the CRISPR-Cas9 System

Improving Whole-Genome Screens Improved methods are needed for the knockout of individual genes in genome-scale functional screens. Wang et al. (p. 80 , published online 12 December) and Shalem et al. (p. 84 , published online 12 December) used the bacterial CRISPR/Cas9 system to power-screen protocols that avoid several of the pitfalls associated with small interfering RNA (siRNA) screens. Genome editing by these methods completely disrupts target genes, thus avoiding weak signals that can occur when transcript abundance is partially decreased by siRNA. Furthermore, gene targeting by the CRISPR system is more precise and appears to produce substantially fewer off-target effects than existing methods.