The Nobel Prize in Chemistry 2020 – CRISPR/Cas9 genetic scissors

The Nobel Prize in Chemistry 2020 was awarded to Emmanuelle Charpentier and Jennifer Doudna for discovering the CRISPR/Cas9 genetic scissors. Only five other women have won this prize before; Frances H. Arnold, Ada E. Yonath, Dorothy Crowfoot Hodgkin, Irène Joliot-Curie and Marie Curie.

While Charpentier was studying a bacterium called Streptococcus pyogenes, she found a molecule called tracrRNA in the bacteria’s immune system, called a CRISPR/Cas system. The CRISPR/Cas system is a class of immune systems found in prokaryotes that provide sequence-specific adaptive immunity. They use short repeated sequences separated by spacers with unique sequences, adding new spacers means new viruses can be recognised. The non-repeated sequences in CRISPR can match the genetic code of various viruses and target DNA or RNA to protect against viruses. At the same time, Doudna was studying the structure and function of the RNA-based surveillance system in bacteria. They met in 2011, and Charpentier and Doudna discovered they could create a gene editing system.


They designed a CRISPR/Cas9 system that could cut viral DNA and be programmed with an engineered guide RNA to cut any DNA at a sequence-specific site. Tracr-RNA and CRISPR-RNA are fused to form guide RNA which can identify a virus’ DNA, and Cas9 acts as a scissor and cuts off the DNA molecule. They take a gene and alter the code in CRISPR part of the scissors to match the code in the place they need to cut, this cuts the DNA molecules in exactly the right places.

There are many uses for these genetic scissors, research groups have shown that they can be used to modify the genome in cells in mice and humans. Before the scissors, changing the genes in cells took a long time and was very difficult to accomplish, whereas now it can be a lot quicker and easier. Using the genetic scissors, cuts can be made in whichever genome we need and because of this it is very common in research for understanding how different genes function. These scissors are also common in plant breeding as delicate and detailed changes can be used to alter the genome. This means that highly resistant crops can be made that can survive in extreme conditions. In medicine trials are taking place using the CRISPR/Cas9 system for treatments in cancer and inherited diseases. Clinical trials are taking place to see if the CRISPR/Cas9 system can treat diseases such as sickle cell anaemia. Animal experiments have suggested that it could be used in the treatment of diseases such as muscular dystrophy, and Huntington’s disease.

Bibliography:

J Clin Invest. 2021;131(1):e145214. https://doi.org/10.1172/JCI145214.

The Nobel Prize in Chemistry 2020. NobelPrize.org. Nobel Media AB 2021. Mon. 8 Feb 2021. <https://www.nobelprize.org/prizes/chemistry/2020/summary/&gt;

Ran, F., Hsu, P., Wright, J. et al. Genome engineering using the CRISPR-Cas9 system. Nat Protoc 8, 2281–2308 (2013). https://doi.org/10.1038/nprot.2013.143

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