The latest tool for cutting DNA is the Crispr Cas9 system, it can snip DNA at a specifically targeted location. Since its indiction to the scientific world Crispr has already changed the world of gene editing. The technique was first discovered in a bacterial immune system and since then has been adapted into an effective tool for genomic research. There are two separate components that make up the Crispr system, first of which is a DNA cutting protein called Cas9 and a Guide RNA molecule. The two components when bound together make a Complex that can cut and identify located sections of DNA. The first step is the binding of the Cas9 and a common sequence in the genome known as a PAM. Once this has occurred the Guide RNA divides and unwinds the double helix. The RNA then matches and binds a articular sequence in the DNA, following this Cas9 can cut the DNA, creating a double strand break. The cell will the try to repair this break however will be unable to, through doing this the Cas9 inadvertently disable the gene. This makes Crispr the ideal tool for knocking out septic genes.
The Future for Gene Editing
Crispr has always been best at as the snipping tool of the gene editing world, but when it comes down to replacing a faulty gene with a healthy one, things get more complicated. In addition to programming a piece of guide RNA to tell Crispr where to cut, there must be a way to provide a copy of the new DNA as the cell’s repair machinery installs it correctly. Andrew Anzalone, a MD-PhD student at Columbia University, wondered if there was a way to merge those two pieces, to create one molecule that both told Crispr where to make its changes and what edits to make.
A few months later, his idea found a home in the lab of David Liu, a Broad Institute chemist who had recently advanced an array of more surgical Crispr systems known as base editors. Anzalone joined Liu’s lab in 2018 and after much trial and error, they wound up with something even more powerful then what was previously thought. The system which was eventually credited to the name ‘prime editing’ can make virtually any alteration additions, deletions or swapping without severing the DNA double helix. It was put best by Liu in saying “If Crispr-Cas9 is like scissors and base editors are like pencils, then you can think of prime editors to be like word processors,”.
Anzalone’s and Liu’s prime editor is actually two enzymes that have been fused together. Thi single molecule acts like a scalpel combined with something called a reverse transcriptase which is able to convert RNA into DNA. This RNA guide is also altered, it finds the DNA in need of fixing and also carries a copy of the edit required to be made. Once the DNA target has been located it makes a minor snip and the reverse transcriptase starts adding the corrected sequence of DNA letter by letter. This then result is two operate flaps of DNA, the original and the edited strand. The cell’s DNA then begins repair machinery swoops in to cut away at the original, permanently installing the desired edit.
This technique is revolutionary as it allows for far more flexibility when editing DNA. “We believe this arises from the fact that prime editing requires three different pairing steps however if any of those three events fail then prime editing can’t proceed.” But Liu says they still need to test that theory further.
Previous Techniques Before CRISPR
Research for ways of editing genomes began as early as the 1960s. It began in test tubes, researchers at UCSF and Stanford bombarded DNA with various combinations of molecular widgets, all borrowed from bacteria. Some of these widgets would slice apart DNA bases and would then connect them back together.
In 1972, after much trial and error over the years, much of which took place in the UCSF laboratory, the researchers eventually landed on a recipe for cutting and pasting DNA. A breakthrough within gene editing, for the first time it was possible to mix and match genes to create hybrid sequences. It made it possible to take a virus such as HIV, delta the genes and then slice in a game from a human cell. It created a gateway for so many possibilities.
For the first time in 1989, gene therapy progressed, however was plagued by unexpected setbacks with the most notable being the death of a patient in 1999. These early setbacks had been largely worked out, and the return of gene therapy had been rejuvenated, and was finally being tested in hundreds of clinical trials across the U.S. including the very famous case of severe combined immunodeficiency syndrome (sometimes called “bubble boy disease”).
But technology still has its drawbacks, gene therapy adds a new gene at an unpredictable spot in a cell’s genome, the gene’s fate isn’t a sure thing as gene don’t work in isolation. They lie amid various DNA segments called regulatory DNA. Consequently, a therapy gene might land near regulatory DNA that silences it, rendering it useless or worse, it might disrupt a healthy gene or turn on a gene that causes cancer. These dangers were recognised however to get around them always was not an easy task.
In the early 2000s, scientists went searching for tools that could be used to better control the DNA slicing mechanism. They found this by cobbling together parts of natural proteins, this resulted in findings that could synthesise artificial proteins able to target mutations at desired locations in a genome. One of the most adequate creations was a zinc-finger nuclease (ZFN). This method quickly found its was into clinical trials.
However engineering proteins was no outbreak within the community, as it could take months or even years to adapt a ZFN to target just one diseased mutation within the DNA. The process was simply too time-consuming to be a cure for deadly diseases to cure those that had been effected in many ways. For nearly a decade, researchers struggled to find a better way until finally a new breakthrough occurred and Crispr had found its way into the gene editing world.
2019-10-24-1571897903