Easi-CRISPR: a robust method for one-step generation of mice carrying conditional and insertion alleles using long ssDNA donors and CRISPR ribonucleoproteins

Genetic engineering as a tool for the generation of mouse models to understand disease phenotypes and gene function

The usage of mouse models has been vital for biomedical research over the last decades, yet the generation of these models has been extremely difficult and labor-intensive. The identification and generation of nucleases able to introduce site-specific DNA double-strand breaks, particularly the CRIPSR/Cas system, is a major breakthrough for this field as the endogenous DNA repair machinery can be hijacked to specifically introduce genome modifications at these sites. This allows for the time-efficient and cost-efficient generation of mouse models by delivery of designer nucleases together with donor DNA into fertilized oocytes.

Disruptive non-disruptive applications of CRISPR/Cas9

The bacterial type II Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR Associated (Cas) systems, and in particular Streptococcus pyogenes CRISPR-Cas9, have been broadly applied to edit the genome of bacterial and eukaryotic cells. Cas9, which is an RNA-guided programmable nuclease, is a powerful tool for disrupting protein-coding genes. Cas9 cleaves target sites to generate a double-strand break (DSB) that is repaired via an error-prone repair process, leading to insertion/deletion mutations and gene knockouts. However, Cas9 can also be used to modulate genome function without gene disruption, enabling base editing, transcriptional and epigenetic reprogramming, genome imaging, cellular barcoding, genetic recording, and genetic computation.

Simplified CRISPR tools for efficient genome editing and streamlined protocols for their delivery into mammalian cells and mouse zygotes

Genome editing using the CRISPR/Cas9 system requires the presence of guide RNAs bound to the Cas9 endonuclease as a ribonucleoprotein (RNP) complex in cells, which cleaves the host cell genome at sites specified by the guide RNAs. New genetic material may be introduced during repair of the double-stranded break via homology dependent repair (HDR) if suitable DNA templates are delivered with the CRISPR components. Early methods used plasmid or viral vectors to make these components in the host cell, however newer approaches using recombinant Cas9 protein with synthetic guide RNAs introduced directly as an RNP complex into cells shows faster onset of action with fewer off-target effects. This approach also enables use of chemically modified synthetic guide RNAs that have improved nuclease stability and reduces the risk of triggering an innate immune response in the host cell. This article provides detailed methods for genome editing using the RNP approach with synthetic guide RNAs using lipofection or electroporation in mammalian cells or using microinjection in murine zygotes, with or without addition of a single-stranded HDR template DNA.