One-Step Generation of Mice Carrying Reporter and Conditional Alleles by CRISPR/Cas-Mediated Genome Engineering

Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA.
Cell (Impact Factor: 32.24). 08/2013; 154(6). DOI: 10.1016/j.cell.2013.08.022
Source: PubMed


The type II bacterial CRISPR/Cas system is a novel genome-engineering technology with the ease of multiplexed gene targeting. Here, we created reporter and conditional mutant mice by coinjection of zygotes with Cas9 mRNA and different guide RNAs (sgRNAs) as well as DNA vectors of different sizes. Using this one-step procedure we generated mice carrying a tag or a fluorescent reporter construct in the Nanog, the Sox2, and the Oct4 gene as well as Mecp2 conditional mutant mice. In addition, using sgRNAs targeting two separate sites in the Mecp2 gene, we produced mice harboring the predicted deletions of about 700 bps. Finally, we analyzed potential off-targets of five sgRNAs in gene-modified mice and ESC lines and identified off-target mutations in only rare instances.

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Available from: Haoyi Wang, Dec 28, 2014
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    • "To date, CRISPR-mediated gene knockout through NHEJ induced insertion-deletion (Indels) mutations has been employed efficiently, with a frequency of 20%-60% in mouse embryonic stem cells (ESCs) and zygotes (Wang et al., 2013; Yang et al., 2013). However insertion of point mutation or gene at precise position by HDR remains inefficient (Mali et al., 2013b; Wang et al., 2013; Yang et al., 2013).Indel mutations induced by NHEJ at the cleaved site may lead to frame shift mutation and deletion, ultimately resulting in the malfunction of the gene (Bibikova et al., 2002). As HDR mediated gene editing is more precise, the specificity of genome editing could be increased by maximizing the chances of repairing by HDR. "
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    ABSTRACT: CRISPR/Cas, a microbial adaptive immune system, has recently been reshaped as a versatile genome editing approach, endowing genome engineering with high efficiency and robustness. The DNA endonuclease Cas, a component of CRISPR system, is directed to specific target within genomes by guide RNA (gRNA) and performs gene editing function. However, the system is still in its infancy and facing enormous challenges such as off-target mutation. Lots of attempts have been made to overcome such off-targeting and proven to be effective. In this review we focused on recent progress of increasing the CRISPR specificity realized by rational design of gRNA and modification of Cas9 endonuclease. Meanwhile the methods to screen off-target mutation and their effects are also discussed. Comprehensive consideration and rational design to reduce off-target mutation and selection of effective screening assay will greatly facilitate to achieve successful CRISPR/Cas system mediated gene editing.
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    • "The expression level of the tagged protein is also adjustable to the endogenous level by inserting the tag into the endogenous gene locus by homologous recombination (Yang et al. 2013). Therefore, the changes in the protein localization can be tracked over time in single cells and also during development and differentiation in model systems. "
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    • "Similar to cultured human cells, most of the DSBs generated by Cas9 in 3PN zygotes were also repaired through NHEJ (Fig. 2A). ssDNA-mediated editing occurred only in 4 embryos (14.3%), and the edited embryos were mosaic, similar to findings in other model systems (Shen et al., 2013; Yang et al., 2013; Yen et al., 2014). Endogenous homologous sequences were also used as HDR templates, with an estimated editing efficiency of 25% (Fig. 2A "
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    ABSTRACT: Genome editing tools such as the clustered regularly interspaced short palindromic repeat (CRISPR)-associated system (Cas) have been widely used to modify genes in model systems including animal zygotes and human cells, and hold tremendous promise for both basic research and clinical applications. To date, a serious knowledge gap remains in our understanding of DNA repair mechanisms in human early embryos, and in the efficiency and potential off-target effects of using technologies such as CRISPR/Cas9 in human pre-implantation embryos. In this report, we used tripronuclear (3PN) zygotes to further investigate CRISPR/Cas9-mediated gene editing in human cells. We found that CRISPR/Cas9 could effectively cleave the endogenous β-globin gene (HBB). However, the efficiency of homologous recombination directed repair (HDR) of HBB was low and the edited embryos were mosaic. Off-target cleavage was also apparent in these 3PN zygotes as revealed by the T7E1 assay and whole-exome sequencing. Furthermore, the endogenous delta-globin gene (HBD), which is homologous to HBB, competed with exogenous donor oligos to act as the repair template, leading to untoward mutations. Our data also indicated that repair of the HBB locus in these embryos occurred preferentially through the non-crossover HDR pathway. Taken together, our work highlights the pressing need to further improve the fidelity and specificity of the CRISPR/Cas9 platform, a prerequisite for any clinical applications of CRSIPR/Cas9-mediated editing.
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