CRISPR gene editing is an innovative genetic engineering technology that can be used to modify the genomes of living organisms, which consist of deoxyribonucleic acid (DNA).
DEOXYRIBONUCLEIC ACID — is a molecule which carries genetic instructions for the development, functioning, growth, and reproduction of all known organisms.
However, CRISPR has one major drawback — it has off-target effects on other strands of DNA that were not meant to be modified. Prime editing technology tackles this issue, and this is why it is considered one of the best gene editing technologies developed by scientists thus far.
In this article, I will answer:
- What is “Prime Editing”?
- Why is prime editing important?
- How is prime editing different from CRISPR and other gene editing technologies?
- What might the future hold for prime editing?
What Is “Prime Editing”?
A new method of genome editing, called “Prime Editing”, cuts a single strand of DNA that is modified — or rewritten — to add, remove, or replace base pairs.
A NUCLEOTIDE — is one of the building blocks of DNA and ribonucleic acid (RNA), made up of a nucleobase — adenine, thymine, guanine, or cytosine — as well as a molecule of sugar and a molecule of phosphoric acid.
BASE PAIRS — are one of the essential structures in each nucleotide of the DNA double helix, and cause the folded structure of both DNA and RNA. It is a pair of nucleobases that are bonded to each other through hydrogen bonds. Adenine bonds to thymine (A-T) and cytosine bonds to guanine (C-G).
Many professionals who study gene editing have characterized prime editing as “innovative and novel”, but recognize the technique is still more of a prototype and needs to be further developed to be used in significant applications. One of these professionals is Emma Haapaniemi, a group leader at the Centre for Molecular Medicine Norway.
Why Is Prime Editing Important?
“There’s no denying that there’s some off-target effect [with CRISPR] but the fear of the off-target effects is more than the reality”, says Nicholas Katsanis, a genetics medicine researcher at the Children’s Hospital of Chicago.
However, he is excited by prime editing and proud of some aspects of the technology, such as its potential ability to modify a greater range of DNA sequences than other gene editing methods like CRISPR. This idea has also been supported by researchers in Nature.
Has Prime Editing Technology Been Tested? What Do the Tests Show?
Prime editing technology has been tested in human and mouse cells. Teams of scientists have also used prime editing technology to target genes that cause Tay-Sachs disease and sickle cell anemia. The genetic mutations were modified to healthy DNA sequences with 35–55% efficiency, a number which scientists believe CRISPR would also achieve.
How Is Prime Editing Different From CRISPR and Other Gene Editing Technologies?
1. CRISPR
A groundbreaking discovery made through several years of genetic research, CRISPR proposed the ability for scientists to modify human and animal genes. Throughout the past few years, this technology has proven valuable to several research teams, as it has helped develop animal models of genetic diseases. However, CRISPR has not been able to reach clinics and be used to cure diseases in actual human and animal patients. This is due to ethical issues, the execution of the process, and precision. Precision, specifically, regards the potential for off-target effects — this technology can alter unintended strands/parts of DNA.
2. Base Editing Technology
Many recognize the common issue of CRISPR systems — they can produce extra cuts in the wrong parts of DNA, which, in turn, can cause underlying effects on cell function. Scientists proposed an alternative technology — base editing — which did not rely on DNA breaks and was thought to be more accurate than CRISPR. Base editing technology uses an enzyme which trades one DNA nuclease for another.
ENZYMES — are proteins which act as biological catalysts. Catalysts accelerate chemical reactions.
NUCLEASES — are enzymes which cut the chains of nucleotides in nucleic acids into smaller units.
However, base editing technology is only able to make four of the twelve different base pair changes, and recent research has suggested this technology is not as precise as scientists expected it would be.
3. Prime Editing Technology — How Does It Work?
Building on their knowledge of base editing and CRISPR, scientists began researching ways to cut one strand of DNA, leaving the other strand intact. Prime editing uses the same Cas9 nuclease used in the CRISPR system, however, it is combined with two new reagents. One of these reagents is called pegRNA, a guide RNA which leads the Cas9 to the targeted spot on the genome. The second reagent is a reverse transcriptase which starts the addition of a new sequence or base into the genome.
A REVERSE TRANSCRIPTASE — is an enzyme used to create complementary DNA from an RNA template, a process known as reverse transcription.
When the cut strand has been modified with new genetic information added to it, the prime editor nicks the unedited strand, which tells the cell to rebuild it to complement the edited strand.
Upon development, prime editing was tested in a lab, in four different types of human cell and mouse neurons.
The results were outstanding.
To gather sufficient test data to compare prime editing technology’s accuracy with that of CRISPR, the team used the technology to treat four different genetic mutations. The tests show while treating these four genetic mutations, CRISPR caused off-target DNA changes in 16 predictable locations. However, prime editing only affected three of these locations, proving its precision is superior to that of CRISPR.
In terms of the process, prime editing is more complex than CRISPR editing. Prime editing requires three different steps which match DNA with parts of the prime editing system. This may be the reason for its improved accuracy. On the other hand, CRISPR has one step where the guide RNA pairs with the target DNA. This is also one of the three steps in prime editing — the other two steps are:
- A part of the guide RNA called the primer must also bind to the target site.
- The edited DNA must bond to the original site.
If any of these three DNA pairing events are not successful, prime editing cannot occur. Scientists believe each of these three steps independently provides the opportunity to avoid off-target effects.
What Might the Future Hold for Prime Editing?
Access to Prime Editing Technology
Prime Medicine, a company co-founded by David Liu — a scientist who led the development of prime editing technology — has been licensed the technology by the Broad Institute, which previously developed base editing technology.
The technology was licensed under the institute’s “inclusive innovation” model, which allows Prime Medicine to use the technology to aim at certain targets, but also allows other companies to apply to use the technology to edit other genes. Liu’s team has also made the technology available on the Addgene database for research purposes. Liu hopes thousands of researchers use prime editing technology in the coming years.
“It’s really important that the community tests and, if needed, optimizes prime editing in as many different types of cells and organisms as possible.”
Improvements in Disease Diagnosis, Treatment, and Prevention
Prime editing, in theory, has the ability to modify more than 90% of all genetic diseases. Think about being able to prevent cancer and other genetic diseases, like breast cancer, from ever occurring by editing out the genes which develop them.
Engineers and scientists are constantly seeking ways to make practical use of the fundamental sciences they have worked with in labs to benefit humanity.
Prime editing can help generate fetal-like cells which are needed to help patients recover and heal, and the technology can also help develop new vaccines against deadly diseases. Prime editing will also provide researchers and scientists lower-cost alternatives and access to cells like those of Alzheimer’s disease, before death.
Combining Prime Editing and Artificial Intelligence to Develop Effective Autonomous Systems
Artificial intelligence and deep learning have been developed around the idea of human neural networks.
DEEP LEARNING — is a broad family of machine learning methods based on artificial neural networks with representation learning.
NEURAL NETWORKS — are networks or circuits of neurons in human and animal brains. Artificial neural networks are computing systems inspired by biological neural networks, however, they are composed of artificial neurons or nodes.
Therefore, genome editing can influence the development of new computer algorithms used for self-diagnosis and repair, which will be crucial in the upcoming world of autonomous systems.
Key Takeaways
- Prime editing is an innovative search-and-replace genome editing technology which writes new genetic information into a targeted DNA site of a living organism.
- Prime editing technology is important because it can be used to correct genetic mutations in cells crucial to the body. It is a significant step closer to the dream of being able to make any DNA change at any site in the human genome. Scientists hope prime editing will allow them to fix genetic mutations which CRISPR cannot.
- The process of prime editing is more complex than CRISPR editing. Prime editing uses the same Cas9 nuclease used in the CRISPR system, however, it is combined with two new reagents. Prime editing cannot occur if one of its three steps fail, and this makes it more precise with fewer off-target effects than CRISPR.
- With prime editing technology becoming more refined and available, its usefulness will continue to increase in the future. As time goes on, prime editing technology will be used for easier diagnosis, treatment, and prevention of diseases which currently are not [easily] curable. Furthermore, gene editing and artificial intelligence may be used hand-in-hand to develop autonomous medical systems that improve the overall efficiency and precision of prime editing!
Thank you for taking the time to read this article! Have any questions or comments? Feel free to leave a comment or reach out to me through LinkedIn.
