Points of View on the Tools for Genome/Gene Editing

Area of Science:

• Molecular Biology
• Genetics
• Biotechnology

Background:

• Genome editing technologies rely on sequence-specific DNA-binding proteins.
• Cas9-sgRNA systems utilize RNA-guided DNA recognition, differing from protein-based recognition in other nucleases like ZFN, TALEN, and Homing Endonucleases.
• The simplicity of designing single-guide RNA (sgRNA) for target sites has made Cas9-sgRNA the predominant genome editing tool.

Purpose of the Study:

• To explore the unique characteristics of the Cas9-sgRNA system for genome editing applications.
• To highlight the versatility of Cas9-sgRNA in enabling engineered enzyme activities and precise DNA modifications.
• To discuss strategies for enhancing biosafety in in vivo applications of Cas9-sgRNA.

Main Methods:

• Investigated the RNA-guided DNA recognition mechanism of Cas9, independent of its nuclease domains (HNH and RuvC).
• Utilized Cas9 nuclease-null mutants (Cas9(D10A), Cas9(H840A)) to achieve specific types of DNA strand breakage or no breakage.
• Explored the introduction of engineered enzyme activities by fusing effector domains to Cas9.
• Examined transient expression methods, including riboprotein delivery, virus-like particles, and extracellular vesicles, for in vivo applications.

Main Results:

• Cas9-sgRNA's RNA-guided DNA recognition is independent of its HNH and RuvC nuclease activities.
• Engineered Cas9 variants can mediate double-strand breaks, single-strand breaks, or no breakage at the target site.
• Various engineered enzyme activities, including DNA/histone modifications and deaminations, can be directed to target loci.
• Transient expression and delivery systems (ribonucleoproteins, VLPs, EVs) mitigate off-targeting risks and improve in vivo biosafety.

Conclusions:

• The Cas9-sgRNA system provides a flexible and powerful platform for precise genome editing and functional genomics.
• Engineered Cas9 variants and effector domains enable a wide range of targeted genetic and epigenetic modifications.
• Advanced delivery strategies are crucial for safe and effective in vivo genome editing therapies.