The CRISPR revolution has begun and shows no signs of slowing down. CRISPR-Cas nuclease-based genome editing strategies hold great promise for the treatment of genetic disorders. However, a major drawback of these approaches is the generation of potentially harmful double-strand breaks (DSBs). Base editing (BE) is a CRISPR-Cas9-based genome editing technology that allows the introduction of point mutations in the DNA without generating DSBs. Two major classes of base editors have been developed: cytidine base editors or CBEs allowing C>T conversions and adenine base editors or ABEs allowing A>G conversions. On the other hand, the prime editing (PE) system contains a prime editing extended guide RNA (pegRNA)-guided reverse transcriptase instead of a deaminase. The development of PE was a breakthrough as it requires no PAM sequence adjacent to the target site and it can accomplish not only all 12 types of point mutations, but also insertions (of up to 44 bp) and deletions (of up to 80 bp), or even combination of substitutions, insertions, and deletions.
The BEs and PEs are high-precision genome editing tools that can be programmed to alter the desired context of the genome in living cells, without requiring DNA donors. The BE and PE systems have remarkable potential as therapeutic tools to correct disease-causing mutations in the human genome. Over 25% of human pathogenic SNPs can be corrected by targeting the four transition mutations, and in principle, prime-editing could correct up to 89% of known genetic variants associated with human disease. The scope of BE & PE tools has been extensively broadened, allowing higher efficiency, specificity, accessibility to previously inaccessible genetic loci, and multiplexing, while maintaining a low rate of Insertions and Deletions (InDels). The BE and PE toolboxes are promising therapeutic strategies for genetic diseases caused by point mutations and might be more effective than approaches based on the homology-directed repair.
1. Describe CRISPR-Cas Base Editing and Prime Editing systems.
2. Explain the main differences between BE & PE Systems.
3. Discuss applications of BE and PE systems.