Is Gene Editing In Its Prime?
We may be on track to recondition and repair disease-causing mutations. Yes…you heard that right. Through gene editing’s most nascent form: prime editing, we are offered the most specialized and selective way of genome engineering to overturn mutations.
The Fundamentals
Let’s go over the basics. What is gene editing? Gene editing is the engineering of genomes so that DNA can be modified. Through this, DNA can be replaced, deleted, or inserted.
Prime editing is a type of gene editing complex that writes new DNA for a targeted site. It works by inserting or deleting the four base letters that make up the double helix: adenine (A), thymine (T), cytosine (C), and guanine (G). To put it simply, these four genetic bases are foundational to all things living.
Prime Editing in Action
The principal goal of prime editing is to change any letter of the four bases (A, C, G, T) using insertions and deletions. The prime editing complex uses a molecule called a fusion protein. A fusion protein is two genetically different genes joined together to code for one fusion protein. Inside this fusion protein is the Cas9 endonuclease protein. The Cas9 protein is the key to successful gene editing as it locates and cuts the targeted DNA. The Cas9 protein is attached to a reverse transcriptase enzyme also known as RNA-directed DNA polymerase. This enzyme is composed of retroviruses: RNA viruses inserting themselves into DNA to change that cell’s genomes. Working alongside the reverse transcriptase enzyme is a specific type of RNA called pegRNA. pegRNA is engineered to locate the area necessitating gene edits whilst containing its contents. The complexity of this RNA prime editor is ample as it contains two sectors. A segment that sticks to the DNA and the other that codes the RNA.
Ok, …you’re probably very confused and that's totally okay! Keep reading to understand the cohesiveness of the functions and everything will get a lot less daunting….
Once Cas9 has located the targeted site, it splits one of the strands in the double helix. The reverse transcriptase then stimulates the pegRNA to begin the transfer of genetic material. The pegRNA joins to the nicked DNA whilst the RNA component encodes for the gene edit. The coded material inside pegRNA is relocated to the strand by the reverse transcriptase reading the code. The reverse transcriptase then connects the specified letters to the DNA strand. Through the cell's own natural algorithm an endonuclease protein rids the old section of DNA and seals the new edit. To complete the gene edit, the prime editing complex prompts the other DNA strand to be matched with the new genetic material. This is done by a prime editor RNA (just like the pegRNA) as it removes the unmatched DNA strand.
Wow, that was a lot! To simplify, remember that the Cas9 locates, the pegRNA contains the gene edit, and the reverse transcriptase adds the edits.
Why the Hype?
Scientists around the world have become fascinated by the entrancing idea of prime editing. It has broken the ceiling for what was thought possible by opening the idea of creating immunity for mutation-diseases.
The wonder of prime editing is its success in cells that are inoperative to cell division. Certain systems and cell types like the neurological system do not undergo cell division/mitosis allowing any damage challenging to revert and permanent. This made mutation-induced neurological diseases seemingly impossible to cure. Providentially, Parkinson’s and Huntington's are both neurologically-based mutations diseases that can use prime editing complexes. Through identifying the inheritance pattern scientists can pinpoint which genes are affected and require editing. For example with Parkinson's' disease the LRRK, SNCA, PARK7, PINK1, PRKN are the potential genes that are mutated. With Huntington's the HTT genes are mutated to contain multiple repeats of CAG (those are bases..remember?). The idea of a cure for these diseases is revolutionizing modern medicine to ease the suffering of thousands.
Researchers across the globe without demur employed prime editing as cures in laboratories have been developed for Tay-Sachs and Sickle Cell disease. This is to be tested inside human bodies in the future, sparking excitement for the endless possibilities in cultivating cures.
Prime Editing vs CRISPR
The inchoate prime editing has an older more experienced sibling called CRISPR. Whilst their purpose of successfully editing genomes is aligned, their methodology is disconnected.
CRISPR short for “clustered regularly interspaced short palindromic repeats” and can be seen as a method for producing more irregular and unreliable results. CRISPR uses a scientifically engineered piece of RNA that is bound to the Cas9 protein. The RNA piece recognizes the targeted DNA and the Cas9 is ready to cut.
Sounds pretty similar? This is where CRISPR differentiates itself. CRISPR now requires both strands of the double helix to be cut by Cas9 instead of just one. Once cut, the DNA is inserted or removed through solely the cells’ natural repair mechanisms. This means scientists have a curtailed level of control leading to more unexpected gene additions and removals.
With CRISPR there is a singular pairing step crucial to the outcome. This is when the target DNA is paired with the RNA. Contrastingly, prime editing has three steps. Prime editing’s first step is unchanged with CRISPR’s but following this, a section of the guide RNA must join to the target site. Next, the new DNA must be bound to the original. A failure in any of these pairing steps stifles the result, however, this lengthy process allows for more accurate editing.
Prime editing provides us with a future full of executing mutation reversals. If used to its potential, diseases can be eradicated and patient suffering can be minimized and alleviated. Let's sit back, hang tight, and enjoy the ride because gene editing is about to get a lot more prime!
