2015 is gone and it is time to look back and take stock of all what we have achieved throughout the year and make new promises for the coming year. 2015 was a year of many changes all over the world and overall it has also been a great year in the field of science and technology. Here, there is a short list of some of the most important scientific discoveries made in 2015:
A vast majority of the scientific community has named CRISPR-Cas9 as the most important scientific discovery of 2015. CRISPR-Cas9 stands for Clustered Regularly Interspaced Short Palindromic Repeats and is known as the immune system of bacteria and Achaea.
The vertebrate immune system is a complex network of specialized molecules, cells, tissues and organs that are responsible for defending the body against foreign substances. Other animals, such as insects, molluscs or crustaceans also have immune system, although it is much simpler. But how can unicellular organisms like bacteria have an immune system?
Viruses can infect bacteria, these viruses are known as bacteriophage. In a simple way, the infection cycle starts when the virus binds to the surface of the bacteria in a specific place and injects its nucleic acid into the cell. Once inside, the viral DNA takes control of the cellular machinery to facilitate the replication of the viral genetic material and the synthesis of viral proteins. Finally, the new virions are released into the environment so they can infect the adjacent cells.
In order to protect themselves from foreign DNA, bacteria have their own defense mechanisms, the restriction-modification systems. The system consists of two enzymes, methylases that add a methyl group (CH3-) to DNA at a specific site, and restriction enzymes that recognize a specific nucleotide sequence and cut the DNA near or at that particular place (restriction site). Bacteria have the ability to methylate their DNA, which allows them to distinguish between foreign DNA and their own DNA. The restriction enzymes cannot cut the methylated DNA, so the foreign DNA would be recognized because it is not methylated.
Within the bacterial genome there are some regions where the nucleotide sequences are palindromes, that is to say, sequences that read the same backward and forward (“A man, a plan, a canal- Panama!”). In the bacterial genome, the alternation between palindromic DNA repeats and spacers sequences (short segments of foreign genetic material) is present in a particular region of the genome known as CRISPR locus. CRISPR regions are associated to genes that encode particular nucleases; Cas (CRISPR-associated sequences), which are proteins specialized for cutting DNA. When a virus attacks bacteria and injects its DNA, the presence of viral DNA provokes the activation of the CRISPR system. The CRISPR sequences are transcribed into RNA to target and cleave a specific site of the viral DNA at two strands. The CRISPR-Cas complex allows to the Cas enzymes to cut the foreign DNA, so the ARN works as a guide to the Cas enzyme, which acts as a scissor, it cuts and inactivates the viral DNA.
Emmanuelle Charpentier and Jennifer Doudna are worldwide known for demonstrating that it was possible to create “guide” RNA that can target any DNA region of any specie and cut it by using a particular enzyme, Cas9. What is more, it also allows the introduction of specific sequences, so the genome can be edited.
The CRISPR-Cas9 technology marks the beginning of a new era in genetic engineering in which you can edit, correct and alter the genome of any cell in an easy, quick, cheap and accurate way. In the future it will serve to cure diseases whose genetic cause is known but they are currently incurable. For example, the MIT (Massachusetts Institute of Technology) announced in March 2014 they had reversed an adult mouse liver disorder (type I tyrosinemia) using this genetic technology.
The ethical controversies of using the CRISPR system are related to the process of modifying the human germ line. In an article published in April 2015, Chinese scientists described the use of CRISPR system to edit the genome of human embryos that would create a heritable modification, which would affect future generations. Although the embryos were nonviable it initiated an ethical debate about the use of this editing tool.
Although this technique still requires many improvements for its effective application, there is no doubt that CRISPR-Cas9 has much to offer and surely we will hear a lot more about it in the future. As John Travis, editor of Science News said: “For better of worse, we all now live in CRISPR’s world”.