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Updated: Apr 28, 2026
Enhanced Genome Editing with Cas9 Ribonucleoprotein in Diverse Cells and Organisms
Published on: May 25, 2018
Efficient mutagenesis by Cas9 protein-mediated oligonucleotide insertion and large-scale assessment of single-guide
James A Gagnon1, Eivind Valen1, Summer B Thyme1
1Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, United States of America.
Abstract:
The CRISPR/Cas9 system has been implemented in a variety of model organisms to mediate site-directed mutagenesis. A wide range of mutation rates has been reported, but at a limited number of genomic target sites. To uncover the rules that govern effective Cas9-mediated mutagenesis in zebrafish, we targeted over a hundred genomic loci for mutagenesis using a streamlined and cloning-free method. We generated mutations in 85% of target genes with mutation rates varying across several orders of magnitude, and identified sequence composition rules that influence mutagenesis. We increased rates of mutagenesis by implementing several novel approaches. The activities of poor or unsuccessful single-guide RNAs (sgRNAs) initiating with a 5' adenine were improved by rescuing 5' end homogeneity of the sgRNA. In some cases, direct injection of Cas9 protein/sgRNA complex further increased mutagenic activity. We also observed that low diversity of mutant alleles led to repeated failure to obtain frame-shift mutations. This limitation was overcome by knock-in of a stop codon cassette that ensured coding frame truncation. Our improved methods and detailed protocols make Cas9-mediated mutagenesis an attractive approach for labs of all sizes.
Insights
Researchers optimized CRISPR/Cas9 gene editing in zebrafish by identifying key sequence rules and novel methods. This significantly improved mutagenesis efficiency across many genomic targets, making gene editing more accessible.
Area of Science:
- Molecular Biology
- Genetics
- Developmental Biology
Background:
- The CRISPR/Cas9 system is a powerful tool for site-directed mutagenesis across model organisms.
- Previous studies reported variable mutation rates at limited genomic sites, highlighting a need for optimization.
Purpose of the Study:
- To elucidate the rules governing effective CRISPR/Cas9-mediated mutagenesis in zebrafish.
- To develop and implement improved, high-throughput methods for zebrafish mutagenesis.
Main Methods:
- Targeted mutagenesis of over a hundred genomic loci in zebrafish using a streamlined, cloning-free CRISPR/Cas9 system.
- Systematic analysis of sequence composition influencing mutation rates.
- Implementation of novel strategies including sgRNA 5' end rescue, direct Cas9 protein/sgRNA complex injection, and knock-in of stop codon cassettes.
Main Results:
- Achieved mutation in 85% of targeted genes with rates spanning several orders of magnitude.
- Identified sequence composition rules critical for successful mutagenesis.
- Enhanced mutation rates through optimized sgRNA design, direct complex delivery, and stop codon cassette knock-in to ensure frameshift mutations.
Conclusions:
- Established sequence-based guidelines for effective CRISPR/Cas9 mutagenesis in zebrafish.
- Developed robust and accessible protocols that increase the efficiency and reliability of gene editing in zebrafish.
- The refined methods empower researchers of all scales to utilize CRISPR/Cas9 for genetic studies in zebrafish.
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