Internal guide RNA interactions interfere with Cas9-mediated cleavage.

Area of Science:

• Molecular Biology
• Gene Editing Technologies
• Biochemistry

Background:

• The CRISPR/Cas system relies on guide RNAs (gRNAs) to direct Cas9 enzyme for sequence-specific DNA cleavage.
• The precise mechanisms governing gRNA efficiency and Cas9 activity remain incompletely understood.
• Low CRISPR/Cas editing efficiency can stem from issues in forming functional Cas9-gRNA complexes or target recognition in vivo.

Purpose of the Study:

• To investigate the factors limiting gRNA activity in CRISPR/Cas systems.
• To differentiate between in vitro and in vivo influences on Cas9-gRNA complex function.
• To elucidate the roles of genomic context and gRNA secondary structures in modulating Cas9 activity.

Main Methods:

• Comparative analysis of mutagenesis rates in zebrafish embryos and in vitro DNA cleavage assays.
• Utilizing near-identical gRNA sequences with varying in vitro cleavage efficiencies.
• Investigating the impact of genomic factors, such as CTCF, on CRISPR-mediated mutagenesis.

Main Results:

• Genomic factors, exemplified by CTCF, were identified as inhibitors of in vivo mutagenesis.
• Internal secondary structures within gRNAs were shown to reduce in vitro DNA cleavage efficiency.
• gRNAs with internal structures, despite forming non-cleavage-competent complexes, can sequester Cas9, hindering active gRNAs.

Conclusions:

• Both the genomic environment and internal gRNA structures significantly impede Cas9-mediated DNA cleavage.
• These findings reveal previously uncharacterized mechanisms affecting Cas9-gRNA complex formation and function.
• Understanding these inhibitory factors is crucial for optimizing CRISPR/Cas gene editing applications.