title: CRISPR/Cas9-Mediated Insertion of loxP Sites in the Mouse Dock7 Gene Provides an Effective Alternative to Use of Targeted Embryonic Stem Cells.
abstract: Targeted gene mutation in the mouse is a primary strategy to understand gene function and relation to phenotype. The Knockout Mouse Project (KOMP) had an initial goal to develop a public resource of mouse embryonic stem (ES) cell clones that carry null mutations in all genes. Indeed, many useful novel mouse models have been generated from publically accessible targeted mouse ES cell lines. However, there are limitations, including incorrect targeting or cassette structure, and difficulties with germline transmission of the allele from chimeric mice. In our experience, using a small sample of targeted ES cell clones, we were successful ∼50% of the time in generating germline transmission of a correctly targeted allele. With the advent of CRISPR/Cas9 as a mouse genome modification tool, we assessed the efficiency of creating a conditional targeted allele in one gene, dedicator of cytokinesis 7 (Dock7), for which we were unsuccessful in generating a null allele using a KOMP targeted ES cell clone. The strategy was to insert loxP sites to flank either exons 3 and 4, or exons 3 through 7. By coinjecting Cas9 mRNA, validated sgRNAs, and oligonucleotide donors into fertilized eggs from C57BL/6J mice, we obtained a variety of alleles, including mice homozygous for the null alleles mediated by nonhomologous end joining, alleles with one of the two desired loxP sites, and correctly targeted alleles with both loxP sites. We also found frequent mutations in the inserted loxP sequence, which is partly attributable to the heterogeneity in the original oligonucleotide preparation.
authors.affiliation: Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine 04074.
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Bishop
authors.affiliation: Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine 04074.
authors.forename: Anne
authors.initials: A
authors.lastname: Harrington
authors.affiliation: Horizon Discovery, St. Louis, Missouri 63146.
authors.forename: Evguenia
authors.initials: E
authors.lastname: Kouranova
authors.affiliation: Horizon Discovery, St. Louis, Missouri 63146.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Weinstein
authors.affiliation: Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine 04074.
authors.forename: Clifford J
authors.initials: CJ
authors.lastname: Rosen
authors.affiliation: Horizon Discovery, St. Louis, Missouri 63146.
authors.forename: Xiaoxia
authors.initials: X
authors.lastname: Cui
authors.affiliation: Center for Molecular Medicine, Maine Medical Center Research Institute, Scarborough, Maine 04074 liawl@mmc.org.
authors.forename: Lucy
authors.initials: L
authors.lastname: Liaw
mesh_terms: D000483:Alleles; D000818:Animals; D001483:Base Sequence; D064113:CRISPR-Cas Systems; D064112:Clustered Regularly Interspaced Short Palindromic Repeats; D059766:DNA End-Joining Repair; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism; D004720:Endonucleases / Q000235:genetics* / Q000378:metabolism; D005091:Exons; D005260:Female; D020690:GTPase-Activating Proteins; D000072669:Gene Editing; D018390:Gene Targeting / Q000379:methods*; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008845:Microinjections; D016254:Mutagenesis, Insertional; D000094704:RNA, Guide, CRISPR-Cas Systems / Q000235:genetics* / Q000378:metabolism; D015053:Zygote / Q000166:cytology / Q000378:metabolism
chemical_list: C539620:Dock7 protein, mouse; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D000094704:RNA, Guide, CRISPR-Cas Systems; D004720:Endonucleases
keywords: CRISPR/Cas9; Dock7; KOMP ES cells