What is CRISPR?

By Saumya Sharma


CRISPR’s innovation and development have created an awe inspiring microscoping wonder.


Anyone who has been following the news in the past decade has heard the term “CRISPR”, but what is it?


To understand CRISPR we have to start by understanding what the letters mean. CRISPR is an acronym that stands for Clustered Regularly Interspaced Short Palindromic Repeats. Let's break that down. CRISPR is actually the term for a section of DNA that is commonly found in bacteria. Bacteria use this when they infect people which leads to increased immunity after infection. This section of DNA allows us to find similar segments of DNA and destroy them.


Researchers in 1987 were able to isolate this DNA segment and use proteins to create what we now know as CRISPR. The formal term for this is actually Cas9. Cas9 is similar to a microscopic organic system that uses the CRISPR DNA segment within it to find a complementary DNA segment in its surroundings and alter them. Instead of destroying the DNA it finds, like CRISPR naturally wants to, Cas9 is able to edit the bases in the DNA segment without completely destroying it. This is vital to the success of CRISPR because it allows us to go into DNA segments that are mutilated or compromised and reconstruct them. Cas9 goes into the DNA and identifies a segment that is complementary to the segment within it. From here, Cas9 slices a straight cut into the DNA double helix to create an opening to remove and change the DNA base coding currently present.


Cas9 has a few downsides compared to its more modern counterparts. For one, Cas9’s straight cut into the DNA causes issues when the DNA re-fuses together. This is also an issue of speed due to this being the first approved design. Slower editing in hand with a small scope of target DNA makes Cas9 less ideal relative to newer versions. Cas9 was a more primitive design that only allowed for a very small amount of identifier sequences, targeted DNA segments to look for, to be stored. On top of this, the DNA re-fusing issues made it so that target DNA segments could only be edited once.


In 2015, after years of research on Cas9, researchers patented Cas12a - as the name suggests, Cas12a is based off of Cas9 and is a newer model. With the new research and technology, there are advantages. Cas12a allows the cut into the DNA when a complementary segment has been identified to be “staggered”. A staggered cut in DNA creates cuts that are not perfectly parallel to each other on the ladder of the DNA. This approach to cutting gives Cas12a more locations and flexibility in gene editing, and creates less potential damage to the greater DNA structure. All these things are necessary when wanting to preserve the cells. Cas12a also has the ability to store multiple gene identification segments into its stores. This allows it to target multiple sections of DNA. The stagger cut also allowed for the DNA to re-fuse back together cleaner and that allows Cas12a to go back over the same sequence and edit it again.


The latest Cas derivation was released in 2016. Cas13 is once again based off of the same model as the previous two, but it only edits RNA. RNA is similar in composition to DNA but is single stranded and uses a different base in place of the DNA equivalent. RNA is used in protein synthesis in the body, and Cas13 works here. By editing segments of RNA, Cas13 is able to enact changes on the proteins in cells. Due to the very protein-centric approach of Cas13, it is not as widely used as Cas12a.


CRISPR has many applications in illness and diseases such as metabolic diseases and genetic errors, and with the breakneck speed at which it is developing and being researched, it is sure to be a mainstay in genetic exploration. Looking ahead, the sky's the limit for this microscopic wonder of biotechnological innovation.


Sources

  1. CRISPR history and development for Genome Engineering. Addgene. (n.d.). Retrieved March 25, 2022, from https://www.addgene.org/crispr/history/

  2. CRISPR systems: What’s the difference? - cell. (n.d.). Retrieved March 25, 2022, from https://www.cell.com/pb-assets/products/research-arc/infographics/CrisprVizInfo_vol1a.pdf