Improved Cas9 activity by specific modifications of the tracrRNA

Area of Science:

• Molecular Biology
• Gene Editing Technologies
• Biotechnology

Background:

• CRISPR/Cas9 is a powerful gene editing tool utilizing Streptococcus pyogenes Cas9 (SpCas9) and guide RNA to create gene-disrupting insertions and deletions (indels).
• Ribonucleoprotein complex (RNP) delivery of SpCas9 is recognized as a safe and effective method, with efficacy dependent on robust indel generation.

Purpose of the Study:

• To investigate the impact of novel sequence modifications in the tracrRNA component of CRISPR/Cas9 on gene editing efficiency.
• To evaluate the efficacy of modified dual-guide RNA (dgRNA) systems with sequence-altered tracrRNAs in various cellular and genetic contexts.

Main Methods:

• Engineered tracrRNA sequences were designed and incorporated into dual-guide RNA (dgRNA) constructs.
• The modified dgRNAs were complexed with Cas9 to form RNPs for delivery.
• Assessed gene editing outcomes, including reporter gene knockdown, indel formation, and surface receptor expression changes (CCR5), across multiple target loci (HIV LTR, CCR5, HBB, BCL11A).

Main Results:

• Sequence modifications in tracrRNA significantly enhanced Cas9 RNP activity, leading to improved indel formation and gene knockdown at tested targets.
• Modified tracrRNAs boosted Cas9-mediated CCR5 surface receptor reduction in cell lines and primary CD4+ T-cells, correlating with increased indel rates.
• Enhanced editing efficiency was observed at additional targets within the HBB locus and the BCL11A GATA site.

Conclusions:

• Novel, facile sequence modifications to tracrRNA can substantially improve the activity of Cas9 RNPs.
• These findings suggest a potential strategy for developing enhanced tracrRNAs to optimize CRISPR/Cas9 RNP-based gene editing for research and clinical applications.