Structure-optimized sgRNA selection with PlatinumCRISPr for efficient Cas9 generation of knockouts

Area of Science:

• Molecular Biology
• Genetics
• Bioinformatics

Background:

• CRISPR-Cas9 gene editing relies on single guide RNA (sgRNA) for DNA cleavage, but efficiency is often below 50% with random sgRNA sequences.
• Maximizing Cas9 nuclease activity is crucial for generating gene deletions and replacements through homologous recombination.

Purpose of the Study:

• To identify intrinsic molecular parameters influencing sgRNA activity for maximal Cas9 nuclease efficiency.
• To develop a computational tool for selecting highly efficient sgRNAs for CRISPR-Cas9 genome editing.
• To investigate mechanisms of CRISPR-Cas9 mediated gene deletion and potential unintended consequences.

Main Methods:

• In vitro assays were used to assess sgRNA activity based on folding and Cas9 structural information.
• Analysis of over 10 datasets identified major constraints in sgRNA design, including secondary structure, seed region, GC context, and motifs.
• A web-based tool, PlatinumCRISPR, was developed to evaluate base-pairing and sequence composition for optimal sgRNA design.

Main Results:

• Defective sgRNA secondary structure, sequence context, and detrimental motifs significantly limit Cas9 activity.
• PlatinumCRISPR aids in selecting efficient sgRNAs, demonstrated by successful gene deletions in Drosophila Ythdc1 and Ythdf.
• Small deletions generated by CRISPR-Cas9 can lead to ectopic reinsertion of DNA fragments, which can be removed by recombination.

Conclusions:

• Optimizing sgRNA design through parameters like secondary structure and sequence context is critical for efficient CRISPR-Cas9 genome editing.
• PlatinumCRISPR provides a valuable resource for selecting high-activity sgRNAs, advancing gene editing applications.
• Understanding unintended consequences, such as ectopic DNA reinsertion, is essential for the safe and effective use of CRISPR-Cas9 technology.