The ‘Cutting’ Edge Technology of CRISPR-Cas9

Illustrated by Neha Adari

This year, the Nobel Prize in Chemistry went to two women, Emmanuelle Charpentier and Jennifer Doudna, for the first time in the history of the award. The importance of two women receiving such a prestigious award in a field that has been historically dominated by men is evident, but what likely remains obscure to many people is what they received the prize for: CRISPR-Cas9 technology. 

CRISPR is an acronym that stands for “Clusters of Regularly Interspaced Short Palindromic Repeats” [4]. This is one of many natural defense mechanisms utilized by bacteriophages to protect against viral infections via matching sequences in the viral genome. When a virus infects the bacteria, the bacteria transcribes a single guide RNA (sgRNA) from the CRISPR locus in the bacterial genome. This sgRNA guides a nuclease, a protein with DNA-cleaving capabilities, to a target sequence in the viral DNA, which the nuclease then cleaves [4] . Since the viral genome has been cut, it can no longer infect the bacteria, and the bacteria is protected.

CRISPR has implications as a potential gene editing tool through its ability to target specific DNA sequences via sequence complementation [1]. For example, if a DNA sequence is C-C-C, its complementary sequence is G-G-G. An sgRNA containing a G-G-G sequence would target the C-C-C sequence on the DNA, bind to it and recruit a Cas nuclease to cleave the DNA at that sequence. In 2012, Charpentier and Doudna demonstrated that gRNAs could be constructed via molecular cloning to guide a Cas nuclease to any DNA sequence [1]. This means that scientists can now target specific DNA sequences through engineered gRNAs and recruit the Cas9 complex to cleave the complementary sequence. 

CRISPR revolutionized the field of biomedical research as “it greatly reduces the time and expense of developing animal models with specific genomic changes” [4]. It has been used in humans as a treatment for sickle cell disease and is in clinical trials for treating human diseases caused by known DNA mutations, such as cystic fibrosis and certain inherited forms of blindness [4]. 

Additionally, CRISPR is also being considered as a weapon in the fight against COVID-19. Researchers at University of California Berkeley have developed a diagnostic test for SARS-CoV-2 that delivers results within five minutes. Jennifer Doudna and her team reported that with a “single guide RNA, they could detect as few as 100,000 viruses per microliter of solution,” demonstrating a high degree of sensitivity [3]. Additionally, their test, which does not rely on viral genome amplification, can reveal “not just whether a sample was positive, but also how much virus a patient had” [3]. Data so far suggests that “amongst the [patients] hospitalized with COVID-19… a higher prevalence of detectable SARS-CoV-2 plasma viral load is associated with worse respiratory disease severity” [2]. CRISPR-Cas technology is challenging the world of science and pushing it forward day by day, and so, it seems only fitting that the people who spearheaded its discovery were two women who made Nobel Prize history. 

Edited by: Caelan Miller
Illustrated by: Neha Adari

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