CRISPR/Cas9: The revolution of the genome edition
The genetic code is the footprint of an organism encoded in a stable molecule: deoxyribonucleic acid. With the CRISPR/Cas9 method, editing the genetic information has become much more easy. This wonderful methodology will be very useful for basic scientists, as well as for translational researchers.
- 1) Introduction
- 2) The dream of treating genetic diseases
- 3) Applications of this new tool
- 4) Which diseases can be treated with CRISPR?
- 5) Off-target modifications
- 6) Conclusions
The CRISPR-Cas9 technique has revolutionized the genetic edition. These molecular scissors, one of the discoveries of the year according to Science in 2015 and Princesa de Asturias’s award the same year. This method allows to the researchers to modify the genetic information introducing controlled mutations in the DNA. This methodology has many applications ranging from the fight against diseases to improve transgenic cultivations. A group of researchers around Dr. Emmanuelle Charpentier and Dr. Jennifer Doudna were in charge of the development of this technique. All of them discovered a new tool for editing genes (Jinek et al., 2012). The system consists of two components: a nucleotide strand called Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), which encodes an RNA guide that is able to recognize a region of DNA and furthermore an associated protein called CRISPR (Cas) that treats as an endonuclease and use the RNA guide to specifically cut the DNA into a specific region. This innovative method for editing genes is simple and highly accurate.
After the publication of this revolutionary work performed by Charpentier and Doudna in Science journal, hundreds of scientists began using this new method in their research. As a consequence, the number of papers published containing the words CRISPR / Cas9 in Pubmed database rapidly increased from 100 papers published in 2012 to 3,000 citations in 2017.
2) The dream of treating genetic diseases
Since it was first described, there are numerous findings achieved thanks to this system of cut and paste. One of the advances is a new version of the tool that, instead of editing DNA in human cells, does it on RNA (Cox et al., 2017). This method can alter the genetic expression without making changes in the genome, which is a great potential for both research and treatment of diseases. This new finding has several advantages. From one side, it is able to correct mutations in different time windows, even during key development periods; and on the other, it would alleviate the ethical concerns associated with DNA editing.
On the other hand, scientists from the Broad Institute – belonging to the Massachusetts Institute of Technology (MIT) – characterized subfamilies of the Cas protein and discovered a version capable of cutting RNA, the Cas13. The team, led by Feng Zhang, was the first to use CRISPR for mammalian genome editing and the one who won the battle for the technique patent.
3) Applications of this new tool
This new technique can be used in almost any situation where you want to modify the DNA sequence. It is being very useful in basic research to generate disease models that previously could hardly be studied, as well as to study new targets and drugs. CRISPR allows a modified gene to be inherited with a probability of almost 100%, which can modify entire populations in just a few generations. One of the projects with the greatest impact is to alter malaria-transmitting mosquitoes, either by infertilizing them or by causing them to act against the parasite. Although they have not yet started, these experiments would mean breaking natural selection.
4) Which diseases can be treated with CRISPR?
Today, most studies that are being carried out are focused on monogenic diseases. As of today, no therapy has been approved. The diseases in which more work is manifested in accessible tissues. Some of the expected clinical trials are aimed at Fanconi anemia, or Duchenne muscular dystrophy. However, course treatments are being carried out in China and include cancer patients without other treatment options.
5) Off-target modifications
Genetic editing through CRISPR also involves some associated problems. The generation of different mutant alleles is not uncommon. Recently, it has been shown that unwanted alleles can be generated in similar sequences. This has generated a stir in the scientific community due to unexpected mutations after a mouse model generation using CRISPR technology. However, it was later revealed that these results were the product of errors in the experimental design and subsequent interpretation of results.
Today, CRISPR has become a powerful laboratory tool. Due to its relatively low price and its relative easy of use it has been adopted by thousands of laboratories around the world. However, it has not yet become a technique that transforms medical practice. Basically because in research two years is almost nothing for what is done in laboratories to be transferred to the clinic, agriculture or industry. But do not doubt that this moment will come, before we almost realize it.