title: An analysis of possible off target effects following CAS9/CRISPR targeted deletions of neuropeptide gene enhancers from the mouse genome.
abstract: We have successfully used comparative genomics to identify putative regulatory elements within the human genome that contribute to the tissue specific expression of neuropeptides such as galanin and receptors such as CB1. However, a previous inability to rapidly delete these elements from the mouse genome has prevented optimal assessment of their function in-vivo. This has been solved using CAS9/CRISPR genome editing technology which uses a bacterial endonuclease called CAS9 that, in combination with specifically designed guide RNA (gRNA) molecules, cuts specific regions of the mouse genome. However, reports of "off target" effects, whereby the CAS9 endonuclease is able to cut sites other than those targeted, limits the appeal of this technology. We used cytoplasmic microinjection of gRNA and CAS9 mRNA into 1-cell mouse embryos to rapidly generate enhancer knockout mouse lines. The current study describes our analysis of the genomes of these enhancer knockout lines to detect possible off-target effects. Bioinformatic analysis was used to identify the most likely putative off-target sites and to design PCR primers that would amplify these sequences from genomic DNA of founder enhancer deletion mouse lines. Amplified DNA was then sequenced and blasted against the mouse genome sequence to detect off-target effects. Using this approach we were unable to detect any evidence of off-target effects in the genomes of three founder lines using any of the four gRNAs used in the analysis. This study suggests that the problem of off-target effects in transgenic mice have been exaggerated and that CAS9/CRISPR represents a highly effective and accurate method of deleting putative neuropeptide gene enhancer sequences from the mouse genome.
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK.
authors.forename: Elizabeth Anne
authors.initials: EA
authors.lastname: Hay
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK.
authors.forename: Abdulla Razak
authors.initials: AR
authors.lastname: Khalaf
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK.
authors.forename: Pietro
authors.initials: P
authors.lastname: Marini
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Brown
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK.
authors.forename: Karyn
authors.initials: K
authors.lastname: Heath
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK.
authors.forename: Darrin
authors.initials: D
authors.lastname: Sheppard
authors.affiliation: School of Medicine, Medical Science and Nutrition, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, Scotland, UK. Electronic address: mbi167@abdn.ac.uk.
authors.forename: Alasdair
authors.initials: A
authors.lastname: MacKenzie
mesh_terms: D000818:Animals; D001483:Base Sequence / Q000235:genetics; D064113:CRISPR-Cas Systems / Q000235:genetics*; D019295:Computational Biology / Q000379:methods; D004247:DNA / Q000235:genetics; D004720:Endonucleases / Q000235:genetics; D017353:Gene Deletion; D015870:Gene Expression / Q000235:genetics*; D016678:Genome; D051379:Mice; D009479:Neuropeptides / Q000235:genetics*; D000094704:RNA, Guide, CRISPR-Cas Systems / Q000235:genetics*
chemical_list: D009479:Neuropeptides; D000094704:RNA, Guide, CRISPR-Cas Systems; D004247:DNA; D004720:Endonucleases
keywords: 1-cell mouse embryo; CAS9 mRNA; CAS9/CRISPR; CRISPR design tool; Cytoplasmic microinjection; Neuropeptide, enhancer; Off-target effects; PCR; Sanger sequencing; Transgenic mouse; UCSC browser BLAT; gRNA