Double-strand break toxicity is chromatin context independent

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• Cells activate DNA damage response pathways, including cell cycle arrest, upon encountering double-strand breaks (DSBs).
• Previous research indicated that a single DSB from CRISPR/Cas9 can impede cell cycle progression and reduce viability.
• Cellular responses to DSBs can vary independently of the lesion number, suggesting differential toxicity.

Purpose of the Study:

• To systematically investigate whether the genomic location of a single DSB influences its toxicity.
• To determine if specific chromatin features impact the toxicity of CRISPR/Cas9-induced DSBs.
• To identify the key determinants of toxicity for single DSBs generated by CRISPR/Cas9.

Main Methods:

• A CRISPR/Cas9 screen was conducted, targeting 6237 unique sites across the human genome to assess DSB toxicity.
• A data-driven framework was developed to design CRISPR/Cas9 single-guide RNA (sgRNA) pools targeting defined chromatin features.
• Chromatin context was characterized using ChromHMM states, Lamin-B1 DAM-iD, DNAseI hypersensitivity, and RNA-sequencing data.

Main Results:

• The toxicity of DSBs was found to be remarkably consistent across different ChromHMM chromatin states.
• No significant correlation was observed between chromatin features and the toxicity of a single DSB.
• CRISPR/Cas9 cutting efficiency and off-target cleavage events were identified as the principal determinants of sgRNA toxicity.

Conclusions:

• Chromatin features exert minimal to no influence on the toxicity of a single CRISPR/Cas9-induced DSB.
• The efficiency of CRISPR/Cas9 cutting and the occurrence of off-target effects are the critical factors determining DSB toxicity.
• Future studies on DSB toxicity should prioritize sgRNA design for optimal cutting efficiency and minimal off-target activity.