Optimizing in vitro Transcribed CRISPR-Cas9 Single-Guide RNA Libraries for Improved Uniformity and Affordability

Area of Science:

• Molecular Biology
• Genomics
• Biotechnology

Background:

• CRISPR-Cas9 technology relies on single-guide RNA (sgRNA) for targeted gene editing.
• Current sgRNA synthesis methods can be costly and suffer from representation biases.
• Optimizing sgRNA library production is crucial for advancing CRISPR-based applications.

Purpose of the Study:

• To develop a scalable and cost-effective sgRNA synthesis workflow.
• To identify and mitigate biases in sgRNA spacer representation during synthesis.
• To improve the uniformity and affordability of sgRNA libraries for CRISPR screens.

Main Methods:

• Utilized large pools of microarray-derived oligos for sgRNA spacers.
• Employed Golden Gate Assembly for dsDNA template construction.
• Performed *in vitro* transcription using T7 RNA polymerase.
• Analyzed spacer representation bias using RNA-seq.
• Tested guanine tetramer addition, emulsion compartmentalization, and reaction optimization for bias reduction.

Main Results:

• Achieved over 70% cost reduction in sgRNA synthesis.
• Identified guanine-rich sequences near the T7 promoter as a major source of bias.
• Guanine tetramer addition reduced bias by 19% but increased high-molecular-weight RNA.
• Emulsion compartmentalization and reaction optimization also reduced bias.
• Demonstrated improved uniformity in large-scale sgRNA libraries.

Conclusions:

• The developed workflow significantly enhances the affordability and scalability of sgRNA library production.
• Strategies for mitigating spacer representation bias are effective, with implications for guide RNA design.
• These advancements will benefit CRISPR-Cas9 screens and other nuclease systems.