Genetic screens have been the lifeblood of forward genetics. They have enabled widespread discoveries of gene function, leading to meaningful advances in medicine, biotechnology, and agriculture. Nevertheless, technologies for performing these screens have been limited by scale, specificity, and targeting range of tools for investigating and perturbing the genome. | Gersbach and Barrangou Genome Biology 2018 19 42 https s13059-018-1425-1 RESEARCH HIGHLIGHT Open Access Pulling the genome in opposite directions to dissect gene networks Charles A. Gersbach1 2 and Rodolphe Barrangou3 based screens capitalized on high-throughput synthesis Abstract of DNA oligonucleotides encoding gRNA targeting Orthogonal CRISPR-Cas systems have been integrated sequences that could be readily packaged into a lentiviral into combinatorial screens to decipher complex genetic vector 2 . The resulting pools of lentiviral vectors can relationships in two recent studies. be quantifiably dosed and delivered to a population of cells such that each cell receives a single gRNA. Conse- quently if that pool of cells also expresses the RNA- Introduction guided endonuclease Cas9 each cell receives a unique Genetic screens have been the lifeblood of forward gen- genetic perturbation specifically determined by the etics. They have enabled widespread discoveries of gene gRNA targeting sequence. That population of cells can function leading to meaningful advances in medicine then be selected for the gain or loss of specific pheno- biotechnology and agriculture. Nevertheless technolo- typic properties and the unique gRNA sequences within gies for performing these screens have been limited by those selected cells can be identified by next-generation scale specificity and targeting range of tools for investi- sequencing. By mapping those gRNAs back to their gen- gating and perturbing the genome 1 . Recently clus- omic target sites it is possible to determine genes or tered regularly interspaced short palindromic repeats genomic regions that are involved in and responsible for CRISPR -based screens with libraries of guide RNAs modulating the selected cellular phenotype. gRNAs have revolutionized the power of genetic The early CRISPR screens focused on gene knockouts screens by overcoming many of these limitations with using gRNAs targeted to the coding
