Gene Editing Technologies
Gene editing is the process of editing genes that is utilised to either study the genome or fix a genetically inherited disease. Around the world, many scientists are working to advance genetic editing technologies so that they could be applied in the real world setting since almost 60% of humans have certain health conditions as a result of their genes. Now with many scientists working on this area of science, many genetic editing techniques have been invented like TALEN editing, CRISPR Cas9 and Prime Editing.
TALEN editing is an older gene editing method and it stands for transcription activator-like effector nucleases. This method utilises the TAL protein which is a customisable protein where each of its amino acids recognizes a specific letter in the DNA sequence of A’s, C’s, G’s and T’s. This ability of the TAL protein (also known as a TAL effector) to recognize and even bind to certain DNA sequences dependent on the composition of itself allows scientists to create different TAL proteins that recognize different genetic sequences. Now having this TAL protein doesn’t fully enable gene editing since by recognizing certain genes doesn’t mean you are actually modifying the sequence. Thus, scientists use the TAL protein in combination with endonucleases which are enzymes that are able to cut DNA strands in a double order fashion. In this way, the genetic sequence that the TAL protein recognizes is cut out, allowing for either the cell to put in a new genetic sequence in its place or giving scientists an opportunity to put a specifically edited piece of DNA in that location. In general, the TALEN editing method is able to cut and paste genes allowing for the editing of the genomic sequence.
Although the TALEN editing method sounds pretty straightforward and accurate, it is known to be pretty inaccurate, making it unusable in the real world. Now with this problem of inaccuracy, scientists were still on the lookout for a new gene editing technology that can allow for the precise editing of the genome. This is when the editing method of CRISPR Cas9 was discovered. CRISPR Cas9 is one of the newer gene editing technologies which stands for clustered regularly interspaced short palindromic repeats and crispr associated protein 9. Within the CRISPR system it works by using a “short” guide RNA that is able to bind to a specific location on the DNA as well as an attached Cas9 enzyme. Both these components locate specific sequences of DNA and cut the DNA in the designated location using the Cas9 which acts like a piece of scissors. By cutting the sequence of DNA, the genetic edit will occur either through the body’s own DNA repair system or a modified DNA segment from the lab will be placed in the specific location causing a precise genetic edit.
Now the way of editing the genome using CRISPR Cas9 is pretty efficient, however there is still a lot more room to improve. Thus, a new method known as Prime editing has also been invented and it is basically an add-on to the method employed by CRISPR Cas9. Prime editing utilises four main components which include the Cas-9 enzyme, the reverse transcriptase enzyme, theRNA template and the pegRNA. When the method is being employed, the pegRNA leads the whole complex(including the Cas-9 enzyme, the reverse transcriptase enzyme, the RNA template and the pegRNA) to the target DNA strand. When the target DNA strand is reached, the Cas-9enzyme nicks the DNA and then to support the DNA the pegRNA attaches to both strands of the DNA. Next, the reverse transcriptase enzyme uses the RNA template to create a modified DNA sequence. This sequence is then placed where the previous DNA was nicked. This allows for the genetic edit of one strand, but the other strand is still remaining so in order to edit the other strand, the Cas9 enzyme also nicks the certain part of the other strand. Then the system relies on the body’s DNA repair system to create the complementary DNA to the edited sequence that is already part of the genome. In the end this process of editing leaves both strands of DNA precisely edited.
Amazing Infographic showing how the prime editing process works: https://www.the-scientist.com/news-opinion/new-prime-editing-method-makes-only-single-stranded-dna-cuts-66608
Now with these various techniques of editing the human genome, the future of genetically editing humans for curing diseases is likely to come soon. Additionally, many scientists are looking to develop more techniques for making the genetic editing process efficient and also possible in large organisms with trillions of cells, each of them having their own set of chromosomes (learn more about the human genome: https://karanchahal.medium.com/what-are-genes-82c4e64dc42b ). Overall this is a brief overview of the genetic editing technologies we use today and also how genetic editing technology has progressed over the years.
