A brief introduction to Prime Editing
Thomas Nurmi
Prime Editing
Prime editing is a genome replacing technique that allows us to edit genomes in our bodies. Prime editing can be used to modify genes and in consequence limit biological defects and build immunity to illness. This may sound very complex, which it is, however, I am going to explain how it works, what it is used for and why it is such a big deal. I will do so in various ways so that anyone, from beginner to advanced, can appreciate this topic.
Beginner
To start off, the base of prime editing is the manipulation of genomes. Put simply, a genome is an organism’s complete set of DNA (Deoxyribonucleic acid). Our bodies are made up of DNA, a series of letters that make us who we are. The letters are A (adenine), C (cytosine), G (guanine), and T (thymine). Prime editing replaces certain parts in our DNA using search and replace methods. Prime editing allows us to find certain parts in our DNA and gives us the ability to add, subtract or change letters. To do this, scientists and doctors use a combination of a guide RNA (Ribonucleic acid), used to locate the target, Cas9 enzyme, used to cut one strand of DNA, and a reverse transcriptase, which are used to read RNA, create a template and then create DNA that is complementary to the strand of RNA. These components work together to track down, cut, copy and replace DNA, as seen below.
Intermediate
As we learned in the first section, there are 3 main components in prime editing, a guide RNA, Cas9 enzyme and a reverse transcriptase, however this process is much more complex than it seems. Once all three components are established, the prime editing guide (PegRNA),Cas9 enzyme (Enzymes are natural protein catalysts) and reverse transcriptase come together forming a complex. Next the PegRNA leads the complex to the desired gene, the Cas9 enzyme cuts the DNA in a process known as “nicking”. PegRNA has 2 main parts, the complementary sequence (Attaches to the nicked DNA) and the RNA sequence (Creates the new DNA).
Then the reverse transcriptase finds the RNA sequence on the PegRNA (Green)and writes the opposite nucleotide (Purple). This sequence is then placed in the gap where the DNA was nicked.
After this step, one strand of the DNA is edited and the other is not. To fix this, the PegRNA guides the Enzyme to nick the other strand. The first edited strand is used as a guide for the second strand and once a complementary strand is created, both sides of the DNA have been altered.
Advanced
By this point, you should have a pretty good overview of prime editing and how it is used. Now for the fine details, precise process and potential use cases. Doctors David Liu and Andrew Anzalone, members of the Liu group at MIT and Harvard, performed over 175 prime edits on both human and mouse cells to demonstrate prime editing as a proof of concept.To prove prime editing works, they first created sickle cell anemia (A lack in red blood cells, which is inherited) and Tay-Sachs disease (An absence of a fat breaking down enzyme, which is also inherited) and then fixed these mutations. They later stated that prime editing can “Correct about 89% of known pathogenic human genetic variants.” Prior to prime editing, dual strand breaks occurred. This is where morals often conflicted and when cell mutations would occur. This seems to have been fixed with the new single strand changing technology.
DNA has 2 ends, each has a corresponding number. One end is three prime (3') and the other is five prime (5') referring to the number of carbon atoms in the deoxyribose sugar molecule . PegRNA has both a primer binding site (PBS) and reverse transciptase (RT), during the prime editing process, the PBS allows the 3' side of the nicked DNA to hybridize to the PegRNA and the template is created by the RT.
How prime editing is different from CRISPR
Prime editing and CRISPR are very similar however have one very large difference, CRISPR cuts both strands of DNA while prime editing cuts only one. This is a huge change due to the fact that cutting both strands destroys the entire integrity of the DNA and cause tumor growths. CRISPR is also inaccurate and can be unreliable. CRISPR is a very new technology and has revolutionized gene editing, even though there is a lot wrong with the technology, as seen above, prime editing would not have been possible without it.
Future uses for prime editing
Prime editing is important due to its many potential use cases, including birth defects, building immunity against diseases and helping limit the spread of inherited illnesses among various others. Prime editing will not only help in our futures with human alterations, but there are many advantages when it comes to agriculture, including increasing the growth speed and size, creating more product and providing protection against pests.
Summary
Prime editing is an extremely new, innovative and powerful way to edit genes. It has many uses and has greatly improved upon prior technologies. Even though there are some moral and ethical flaws in this process, the future opportunities are limitless. If we use this technology correctly, the world will be changed forever.
Citations:
https://commons.wikimedia.org/w/index.php?curid=87521295
