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CRISPR-Cas9 and the manipulation of the DNA – MediNick

By CoperNick

 Alice Gaggero

 

January 13, 2020

Since the discovery of the DNA, humans started to search for technology for making and manipulating it. The reason is that there is plenty of applications for this kind of technology.

The major goal is the introduction of site-specific modification that could affect only the interested part and not other ones, reducing the risk of complications. In the last decades a new technology has been developed by scientists: CRISPR-Cas9. 

Figure 1  CRISPR Cascade protein (cyan) bound to CRISPR RNA (green) and phage DNA (red)

 


What is it CRISPR-Cas9?

CRISPR-Cas9 is a method to edit the genomes of living organism. It is based on the antiviral defense system of some bacteria.

In particular, the CRISPR is DNA segments created by the bacteria capturing snippets of the DNA of invading viruses. In this way, the bacteria can “remember” the viruses and recognize them or the ones closely related to them. 

Figure 2   Diagram of the CRISPR prokaryotic antiviral defense mechanism

 

 

If the viruses attack again, the bacteria produce a RNA segment from the CRISPR arrays to target the viruses, and the enzyme Cas9 cuts the DNA apart and so disables the viruses.

The version used by the scientists is really similar to the natural one, and then it is used with other technologies to modify the DNA. Researchers create a small piece of RNA with a guide sequence that binds to a specific target on the DNA. The RNA binds also to the Cas9 enzyme. In nature, the RNA recognizes the DNA sequence, and the Cas9 cuts it. After this process, researchers use the cell’s own DNA repair machinery to add or delete pieces of genetic material or make changes replacing existing segments of the DNA with customized ones.

 


Figure 3  CRISPR-Cas9

 

 

For now, the CRISPR-Cas9 is used for research on other animal cells and plants, but not on a living human.

The history of this technology starts back in the 1987 when the CRISPR was first described by Japanese researchers with a series of experiments on the Escherichia coli, but its role was not clear at the time.

Only in 2005, when scientists observed that many CRISPR derive from DNA sequences of viruses, the hypothesis was made that the CRISPR was involved in the defense system of the bacteria.

Thereon, the secrets of CRISPR-Cas9 have been discovered, and in January 2013 the CRISPR-Cas9 was used for the first time on human cells.

 

Why is this technology so important?

Because it is an extremely precise technology: the only part of the DNA interested in the cutting is the one affected and of interest for the scientists, so it reduces the risk of complications in the cells. Another reason is that compared to other technologies, it is cheaper and easier to use, allowing more experiments to be done.

The fields in which CRIPR-Cas9 could be applied are many and varied.

First of all, obviously, in Biology for the study of different pathologies; but also in Medicine for new treatments against cancer or genetics pathologies. Other applications could be in Agriculture, where the technology could change the pace and course of agricultural research. It could also facilitate the creation of engineered animal models for pharmacological studies and the recreation of human diseases in laboratory, which would allow their better comprehension. Research on CRISPR-Cas9 is still ongoing and there are many issues yet to be solved, like whether it is safe to use this kind of technology on human beings. Another problem are the ethical concerns surrounding this practice: using CRISPR-Cas9 it could be possible to edit somatic cells, like eggs and sperm cells, and while some editing would not affect future generations, others might be passed from one generation to other, and it is an open question whether it is permissible to enhance normal human traits (height, for example). For these reasons, the experiments are conducted on animal or human cells in vitro for now. Germline and embryo genome editing are illegal in many countries today, however, in the future, they could possibly be the response to some genetics disease, without cure to these days.  

 

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