CRISPR and the genome


CRISPR technology is a recent genome-editing tool that acts as molecular scissors capable of specifically cutting any sequence of DNA from the genome and allowing the insertion of changes in it.
Its origin is in a microorganism that inhabits the marshes of Santa Pola (Alicante), in whose genome the biologist Francis Mojica, in 1992 found the bases that would give rise to the CRISPR technique. This genetic editing tool, the most powerful ever discovered, is applicable to fields such as Agriculture, Livestock, Biotechnology and Medicine.
There are regions of the genome of these microorganisms that were repeated many times and he called these sequences with the acronym CRISPR (from the English, ‘clustered regularly interspaced short palindromic repeats’). Years later he discovered that these composed an adaptive immune system: thanks to them, these prokaryotes could survive in an environment as hostile to life as the salt flats are.
The 1970s marked the beginning of the Age of Genetic Engineering, in which important milestones, such as the production of insulin from Escherichia coli or the use of transgenic mice in the study of human diseases, changed the course of Medicine. However, the methods used were still imprecise and difficult to apply on a large scale, resulting in complicated and costly experiments.
Since 2012, through the research of Charpentier and Doudna, researchers have focused on overcoming these limitations in order to develop a genomic editing mechanism capable of generating numerous changes in the genome of a cell in a coordinated and precise manner.
Currently, the strategies used in laboratories to manipulate, in a specific and direct way, sequences of the genome of living organisms are disparate. Current tools include zinc finger nucleases (ZFN), transcription activator nucleases (TALEN) and the revolutionary nucleases of inverse repeated palindromic sequences (CRISPR-Cas).
The first two are complicated and expensive, on the contrary, CRISPR-Cas offers scientists the possibility of changing a DNA sequence in an easier, faster and more precise way at different specific points of the genome within a living organism.
The CRISPR-Cas system is a defense mechanism for some bacteria to eliminate invasive viruses or plasmids. The system is a Cas9 protein with nuclease activity, which cuts the DNA, and an RNA, known as guide RNA, which takes it to the DNA sequence to be edited.

-The process:

Genomic editing with CRISPR-Cas9 includes two steps. In a first stage, the RNA guide, complementary to the region of DNA to be modified and synthesized previously, is associated with the enzyme Cas9. In addition, thanks to the rules of nucleotide complementarity, the RNA hybrid with the sequence of interest present in the genome, directing the Cas9 endonuclease to cut the DNA in the specific region.
In the second stage, the natural repair mechanisms of fragmented DNA are activated. In some cases, this repair results in the appearance of insertion or deletion mutations which, if located within a gene, can lead to the loss of production of the protein it encodes. Thus, one possible application is to disable genes.
If the cell is provided with a DNA molecule to serve as a mould during repair, to which a change has been added, the cell will copy it and the change will be incorporated into the DNA. This other application, the introduction of specific changes in specific positions supposes one of the most promising aspects of the technique, since it would allow to correct errors in the genes responsible for causing diseases.
In addition, the system can also be used to regulate gene expression, or even to introduce epigenetic modifications, inactivating the nuclease activity of Cas9 and incorporating modules that interact with elements regulating gene expression or capable of carrying out changes in methylation or histone modifications.


The development of CRISPR-Cas technology has ushered in a new era of genetic engineering in which the genome of any cell can be edited, corrected and altered in an easy, fast, inexpensive and highly accurate manner.
The genomic edition may seem futuristic, but the edition of genes in humans is getting closer and closer. A breakthrough that could rid humanity of genetic diseases that today have no cure. For example, a new genome-editing tool called CRISPR has already been used in China to create transgenic monkeys.
Genome editing using CRISPR is based on the creation of breakpoints at specific sites in the genome that the cell restores with its own DNA repair machinery.
Through this approach, point mutations can be generated directly or concrete changes can be introduced if a DNA fragment is provided that acts as a mold for the cell. Once the genome has been modified, the changes are permanently fixed in the cells.
Egg, sperm, and any of the cells they originate are part of the pathway by which genes are perpetuated in the next generation. It is the sequence that starts from the reproductive cells, which after being fertilized carry all the information to the future living being.
This inheritance comes from the union of the two parents and is concentrated in a single cell, therefore the technique must be applied at the time of fertilization, so it has already been achieved, cure some genetic disease such as hypertrophic cardiomyopathy, the main cause of sudden death in young adult sportsman and is caused by the mutation of a gene from one of the parents.


The protein p53, also known as genome guardian, is one of the proteins responsible for monitoring and maintaining the integrity of the genome. This protein, which acts as a tumor suppressor, detects DNA damage and determines whether it can be repaired or whether the damaged cell should be removed.
When DNA damage can be repaired, p53 activates the cell’s repair mechanisms. However, if the damage is irreparable, the protein prevents cell division and initiates the cascade of signals that will lead to its programmed death (apoptosis). Thus, by preventing defective cells from dividing, the action of p53 can prevent the formation of tumors.
Recently it has been observed that treating cells with CRISPR produced a selection in favour of those cells that did not have a functional p53 signalling pathway and could therefore continue their cell cycle. Precisely those cells in which there is an increased risk of tumour formation.
Apart from the ethical dilemmas that the DNA may have to be modified in order to obtain an «upon request» one, what has been pointed out above must be taken into account, however it is a probabity, and it is very possible that it is the path to follow in order to cure certain secondary hypogonadisms, which have their origin in polymorphisms (which is a variation in the sequence of a given place of DNA in chromosomes) or DNA deletions (which is the loss of a fragment of DNA from a chromosome).


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