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All about CRISPR, the revolutionary gene editing technique

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Science has allowed human beings to exploit their curiosity to find a solution to the problems they face. The definitive creation for which some would call playing God has name and countless applications: CRISPR-Cas9.

Laidea was undertaken by researchers Jennifer Doudna and Emmanuelle Charpentier, who demonstrated with this article the potential that it would have to edit the genome of our cells. In a nutshell, the CRISPR tool-Cas9 it is a molecular scissors and at the same time a glue, It allows cutting at will in the genome, and replacing the extracted fragment with one that we have previously selected. The result will be a correction in the genome that will result in a change in expression, thus managing to cure a disease, change a characteristic of the individual, enhance some cellular process or even create an individual from scratch to our liking.

From the first day I was interested in this tool, as well as how it arose, what basis has led it to be used, its applications, and of course, its ethical consequences. So today I bring you everything you should know about the revolutionary CRISPR tool-Cas9.

What is CRISPR-Cas9 and where does it come from?

CRISPR stands forClustered Regularly Interspaced Short Palindromic Repeats,and Cas9 It is one of the proteins in the nuclease family that is associated with CRISPR, but without a doubt the most curious thing about this genetic editing tool is its origin.

Living beings have different mechanisms to fight against threats that endanger their functioning. What in humans we would know how immune system, It is also present in lower organisms such as bacteria, obviously with different natures and functions but keeping the same idea: fighting threats.

Once at this point, we find a curious mechanism that bacteria have to deal with viruses. The process goes like this:

  1. The virus infects the bacteria, and tries to take over the cellular machinery to carry out its task.
  2. When the cell recognizes exogenous genetic matter, in this case the virus, it transcribes a large RNA molecule made up of palindromic and spacer sequences (we will talk about them shortly)
  3. A complex is formed with said molecule called crRNA that guides the nuclease, in this case Cas9 to the target molecule, which can be the DNA / RNA of the virus, causing its degradation.
  4. But the system does not stay here, it can extract part of the invader’s genome and enter it into a set of known sequences such as CRISPR.
  5. With that information on their part, the cell will be able to efficiently combat the next invasion of a similar virus.

How if health card In this case, the bacteria manages to acquire immunity against a virus in question. Before talking about how this mechanism has been adapted to genetic editing, I am going to tell you a bit about other genetic editing tools that have been used (and continue to be used) so far in order to discuss the success of CRISPR-Cas9.

Genetic editing tools, to what extent can we modify living beings?

Breaking with the classic idea of ​​leaving everything to chance, science has wanted to go one step further by modifying our identity card, DNA, at our will. Of course, there are obstacles when it comes to changing the DNA of an individual without having a risk or a consequence that does not ensure the success of the technique.

There are countless approaches to changing a concerned DNA fragment, each with its own pros and cons. Today in Omicrono Ciencia we are going to mention some of them, until we reach our beloved CRISPR-Cas9:

  • Plasmids and restriction enzymes: The plasmids are small circular fragments whose function shares similarity with a Compact disc. We use known enzymes such as restriction enzymes, which will cut through specific sites of the plasmid so that we will control the cut, thus being able to introduce our fragment of interest, thus having a unit that will allow us to carry this information to the study organism. Although it is a relatively simple and inexpensive technique, it has certain limitations, since in most organisms it does not transfer horizontally and it has a low success rate, as we will find many empty, poorly recirculated or unable to enter the cell. Good for working with bacteria or plants, bad for higher organisms.
  • Specific recombinases:Another of the great advances in biotechnology and synthetic biology was site specific recombinases. These molecules cut, glue, or invert certain pieces of DNA, making genetic editing easier. However, there are problems with non-specific recombinations taking place outside the target, and therefore improvements for this technique continue to be studied.
  • Interference RNA: it is based on a very simple principle: our organism considers all double-stranded RNA invasive. If we want to cancel or reduce the expression of a certain protein with damaging potential for the organism, we study its RNA and introduce its reverse copy, so that a double-chain complex is generated by complementation and our organism degrades it.
  • Nucleases with zinc fingers: The most interesting thing about this technique was the secrecy in which this technique was maintained before any useful information was published for its use. It is a very versatile technique, as we use the properties of zinc fingers to recognize specific DNA sequences throughout the genome. Once the sequence is recognized, the nuclease will cut the double strand of DNA close to the target, so that by homologous recombination DNA from a wild strand can be introduced. In this way we can correct mutations that cause diseases with high efficiency. In this study you can see a little more about their applications, being used in different model organisms to reverse genetic information.

There are many more genetic editing techniques, chemists that employ bacteriphages, classical transgenesis, or even using artificial chromosomes.

From the bacterial immunity mechanism to the technique that will change humanity

There are 3 subtypes of systems with multiple variants, which come to coexist in different organisms. However, type II will be used in genomic editing Since it only needs a Cas9 protein to work, it has an RNA tracer that forms a duplex with the crRNA and gives stability, a PAM sequence and of course, a target only for DNA.

The CRISPR locus integrates sequences that will not be selected at random, as they will depend on the presence of a PAM motif, adjacent to the spacer. Protruding ends are formed and the spacer is integrated. To work with CRISPR-Cas9, we will need a single strand of DNA that is homologous and flanks the junction site of our guide strand, and of course the Cas9 genes.

The countless applications of CRISPR-Cas9

Currently there is a great consensus to use this technique with head and great care. Since it is a technique with few off-target effects, the results border on total success, so it can be said that it has a fairly close field setting.

In this study they show how CRISPR-Cas9 could help establish a stable model for studying brain tumors. Another study that manages to end a genetic disease in mice, and even a study that shows how it manages to treat immunodeficiency.

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