Different Effects of sgRNA Length on CRISPR-mediated Gene Knockout Efficiency

Area of Science:

• Molecular Biology
• Gene Editing Technologies
• Cellular Engineering

Background:

• CRISPR-Cas9 technology offers precise genome editing but is limited by off-target effects.
• Truncated 17-nucleotide (nt) single-guide RNAs (sgRNAs) have shown promise in reducing off-target cleavage in certain cell lines.
• The comparative efficacy of 17nt sgRNAs versus full-length 20nt sgRNAs in stem cells remains uncharacterized.

Purpose of the Study:

• To evaluate the on-target gene knockout (KO) efficiency of 17nt and 20nt sgRNAs in human mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs).
• To assess the off-target cleavage profiles associated with both 17nt and 20nt sgRNAs in stem cell contexts.
• To determine the optimal sgRNA length for balancing editing potency and specificity in stem cell genome editing.

Main Methods:

• Utilized a GFP reporter system to quantify gene knockout efficiencies.
• Expressed both 17nt and 20nt sgRNAs via lentiviral vectors in 293T cells, iPSCs, and MSCs.
• Analyzed off-target mutations by sequencing across varying mismatch tolerances.

Main Results:

• Both 17nt and 20nt sgRNAs achieved ~95% KO in 293T cells, but significantly lower efficiencies (60-75%) in iPSCs and MSCs.
• 17nt sgRNAs exhibited 10-20% lower KO efficiency compared to 20nt sgRNAs in iPSCs and MSCs.
• Off-target mutations were observed with 1-2nt mismatches for 17nt sgRNAs and up to 5nt mismatches for 20nt sgRNAs, with occasional unique off-target events for 17nt sgRNAs.

Conclusions:

• Genome editing in stem cells necessitates a balance between on-target potency and off-target effects.
• Full-length 20nt sgRNAs demonstrate superior gene knockout efficiency in iPSCs and MSCs compared to truncated 17nt sgRNAs.
• For applications prioritizing editing efficacy in stem cells, 20nt sgRNAs are the preferred choice.