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Not every genetic problem needs the text rewritten. Sometimes a gene simply needs to be louder or quieter. Disabled CRISPR proteins can be used as programmable volume controls — parked on a gene to block it, or carrying an amplifier to boost it — without changing the DNA at all.
CRISPRi uses dCas9-KRAB to repress transcription reversibly; CRISPRa uses dCas9 fused to activator domains to increase it. Epigenetic editors write or erase DNA methylation and histone marks for potentially durable, heritable changes in expression without sequence alteration. These approaches avoid every double-strand-break hazard, at the cost of durability that must be demonstrated rather than assumed.
When adjusting beats rewriting
Sources
- National Human Genome Research Institute
Talking Glossary of Genomic Terms ↗
Check your understanding — Intermediate
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1. What is the main practical difference between ex vivo and in vivo editing?
Why: Being able to inspect and select the edited cells before returning them is the central advantage of ex vivo — and the reason the first approvals took that route.
2. Why did liver diseases reach in vivo trials first?
Why: Delivery, not editing chemistry, decides which organ is reachable. LNPs go to the liver by default, so liver targets were available first.
3. What is the main limitation of AAV viral vectors?
Why: The cargo limit is why smaller enzymes like SaCas9 matter, and prior immunity is why a second dose is often not an option.
4. Can you change how active a gene is without changing its DNA letters?
Why: A deactivated Cas9 can carry an activator or repressor and leave the sequence intact. The effect lasts only while the tool is present.