title: Death receptor-based enrichment of Cas9-expressing cells.
abstract: BACKGROUND
  The CRISPR/Cas9 genome editing system has greatly facilitated and expanded our capacity to engineer mammalian genomes, including targeted gene knock-outs. However, the phenotyping of the knock-out effect requires a high DNA editing efficiency.
  
  
  RESULTS
  Here, we report a user-friendly strategy based on the extrinsic apoptosis pathway that allows enrichment of a polyclonal gene-edited cell population, by selecting Cas9-transfected cells that co-express dominant-negative mutants of death receptors. The extrinsic apoptosis pathway can be triggered in many mammalian cell types, and ligands are easy to produce, do not require purification and kill much faster than the state-of-the-art selection drug puromycin. Stringent assessment of our advanced selection strategy via Sanger sequencing, T7 endonuclease I (T7E1) assay and direct phenotyping confirmed a strong and rapid enrichment of Cas9-expressing cell populations, in some cases reaching up to 100 % within one hour. Notably, the efficiency of target DNA cleavage in these enriched cells reached high levels that exceeded the reliable range of the T7E1 assay, a conclusion that can be generalized for editing efficiencies above 30 %. Moreover, our data emphasize that the insertion and deletion pattern induced by a specific gRNA is reproducible across different cell lines.
  
  
  CONCLUSIONS
  The workflow and the findings reported here should streamline a wide array of future low- or high-throughput gene knock-out screens, and should largely improve data interpretation from CRISPR experiments.
authors.affiliation: Department for Bioinformatics and Functional Genomics at the Institute of Pharmacy and Molecular Biotechnology and BioQuant BQ0020, University of Heidelberg, and Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. c.liesche@gmail.com.
authors.forename: C
authors.initials: C
authors.lastname: Liesche
authors.affiliation: Department for Bioinformatics and Functional Genomics at the Institute of Pharmacy and Molecular Biotechnology and BioQuant BQ0020, University of Heidelberg, and Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. venkatraman.lakshmi@gmail.com.
authors.forename: L
authors.initials: L
authors.lastname: Venkatraman
authors.affiliation: Department for Bioinformatics and Functional Genomics at the Institute of Pharmacy and Molecular Biotechnology and BioQuant BQ0020, University of Heidelberg, and Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. s.aschenbrenner@dkfz.de.
authors.forename: S
authors.initials: S
authors.lastname: Aschenbrenner
authors.affiliation: Department of Infectious Diseases/Virology, Cluster of Excellence CellNetworks, Heidelberg University Hospital, BioQuant BQ0030, Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. stefanie.grosse@bioquant.uni-heidelberg.de.
authors.forename: S
authors.initials: S
authors.lastname: Grosse
authors.affiliation: Department of Infectious Diseases/Virology, Cluster of Excellence CellNetworks, Heidelberg University Hospital, BioQuant BQ0030, Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. dirk.grimm@bioquant.uni-heidelberg.de.
authors.forename: D
authors.initials: D
authors.lastname: Grimm
authors.affiliation: Department for Bioinformatics and Functional Genomics at the Institute of Pharmacy and Molecular Biotechnology and BioQuant BQ0020, University of Heidelberg, and Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. r.eils@dkfz.de.
authors.forename: R
authors.initials: R
authors.lastname: Eils
authors.affiliation: Department for Bioinformatics and Functional Genomics at the Institute of Pharmacy and Molecular Biotechnology and BioQuant BQ0020, University of Heidelberg, and Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 267, 69120, Heidelberg, Germany. jbeaudouin@gmail.com.
authors.forename: J
authors.initials: J
authors.lastname: Beaudouin
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D064113:CRISPR-Cas Systems / Q000235:genetics*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D016678:Genome / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D054643:INDEL Mutation / Q000235:genetics; D010641:Phenotype; D011691:Puromycin; D053218:Receptors, Death Domain / Q000235:genetics* / Q000378:metabolism*
chemical_list: D053218:Receptors, Death Domain; D011691:Puromycin