Bringing gene editing into it’s prime: Prime Editing Technology
Our DNA is essentially our core. DNA, short for deoxyribonucleic acid, is the molecule that contains our genetic code and tells cells what proteins to make. For years, we have thought that our genes are set in stone. For people who suffer from genetic disorders, inadequate treatment methods have made it very difficult for them to lead healthy and normal lives. Only in recent years have we begun to dive deep into our genes and gene-editing technology and see how we can actually alter the basic building blocks of life.
CRISPR gene-editing technology has ushered in a new era of genetic research over the past several years. This technology changed the way that scientists approach gene editing, however; it is not foolproof and is known to create extra cuts in the wrong sections of DNA, interrupting cell function. This is where Prime editing comes in; a versatile and precise genome editing method that can rewrite DNA by only cutting a single strand, allowing researches to edit more types of genetic mutations than existing genome-editing methods.
In this article I will discuss:
- The Prime Editing Basics: the components and how it works.
- CRISPR vs Prime Editing Technology: How Prime editing builds off of CRISPR technology.
- The Future!: How Prime editing can be used to treat genetic disorders and bring genome editing technology to the clinic.
The Prime Editing Basics
Prime editing is a gene-editing method that can perform targeted small insertions, deletions, and base swapping in an exceptionally precise way. It expands the limited scope of current base editing technologies from only 4 possible combination swaps to 12 possible combination swaps. In short, prime editing is a compact solution with improvements from CRISPR technology that greatly impact the final result.
But how does it actually work?
In agreement with CRISPR, prime editing requires a Cas endonuclease (Cas9) and a single guide RNA (sgRNA).
Hold up, what the heck is a Cas endonuclease or a single guide RNA?
Cas endonuclease or Cas9 is a protein that plays a vital role in the immunological defence of certain bacteria against DNA viruses and plasmids. A single guide RNA is a version of the naturally occurring two-peice guide RNA complex turned into a single sequence. The single-guide RNA is used to direct the Cas9 protein to bind and nick a certain section of DNA for genome editing.
In order to edit sequences without generating a double-stranded break, both of these components are slightly modified. Prime editing uses Cas9 nickase fused to an engineered reverse transcriptase, that nicks the DNA rather than generating double-stranded breaks. This fusion is referred to as the prime editor.
In Prime editing, the guide RNA or pegRNA used to control genome editing within the cell is substantially larger than the standard single-guide RNA used in CRISPR genome editing. The Prime editing pegRNA leads this Cas9 protein to the desired spot in the genome and a reverse transcriptase initiates the addition of a new sequence or base into the genome.
There are essentially 5 steps in prime editing.
- The prime editor and pegRNA complex binds together to target the desired DNA section.
- The Cas9 nickase separates one strand of DNA.
- The reverse transcription of RNA inputs the desired sequence into the target DNA.
- This edited strand is incorporated and the original DNA is separated by the cellular endonuclease.
- Finally, the unedited strand is repaired to match the newly edited sequence.
Prime Editing vs. CRISPR
Now that we understand a bit more about how Prime editing actually works, how is it different and better than CRISPR genome editing technology?
The most significant difference between prime editing and CRISPR technology is that prime editing enables targeted editing without generating targeted double-stranded DNA breaks. Previous studies have shown that when CRISPR-Cas9 technology targeted these same mutations it causes off-target DNA changes in 16 predictable locations. Prime editing only altered three of these loci. And one can only imagine the effects of unintended DNA alteration.
What makes Prime Editing so much more precise than CRISPR technology is that it requires three separate steps in which the DNA must match up with parts of the Prime Editing system, whereas CRISPR only requires one. These three separate steps provide more opportunities for the prime editing technology to reject off-target sequences. Prime Editing is basically like picking out all of the raisins in a chocolate chip cookie, replacing them with actual delicious chocolate chips without letting a single crumb of the cookie fall on the floor.
What does the future hold?
The reason why Prime editing technology is so important is that it makes genome editing more precise which allows researchers to better target genes that cause devastating disorders such as Tay-Sachs disease and sickle cell anemia. David Liu, American chemist and biologist, and his team are already using prime editing to alter mutations causing Tay-Sachs disease and sickle cell anemia back to healthy DNA sequences with 35–55% efficiency. New research also shows how prime editing can be used to correct not only single nucleotide mutations but also perform longer nucleotide corrections.
Even though prime editing offers incredible promise to reverse genetic diseases that have seemed to be irreversible for so long, it is still too early to move this technology to the clinic. Researchers are still looking to determine just how many cell types prime editing can be used in and what the long term effects are if there even are any.
The way I see it is that Prime editing takes us one step further into the world of genome editing. It is a refined version of the CRISPR technology that allows us to make more discoveries in terms of curing genetic disorders. Although we still have a long way to go, Prime editing takes us further down the path to fully understanding how to alter our genetics.
Some key takeaways:
- Prime Editing performs genome editing with increased efficiency and precision.
- CRISPR technology, although groundbreaking simply isn’t as advantageous as Prime Editing technology.
- The advancement of prime editing technology highlights the huge leaps and bounds being made in the gene-editing field and shows how it can be used to treat previously irreversible genetic disorders.
If you would like to talk more about genome editing technologies and the world of genetic engineering, reach out to me on LinkedIn here! https://www.linkedin.com/in/francesca-bizzarri-1622471b2/
Some sites that helped me understand how Prime editing works are listed here!
