Summary: (Video) The original CRISPR-Cas9 system has revolutionized gene editing, but cutting DNA isn’t all it can do. From turning gene expression on and off to tagging particular sequences with a fluorescent dye, this animation explores some of the exciting upgrades to CRISPR. Scroll down for video.
Techniques to modify DNA in the genome have existed for several decades, and the original CRISPR-Cas9, called CRISPR 1.0, brought an era of faster, cheaper, and more efficient gene editing tools. A short video from the journal Nature shows you how scientists have revolutionized the original CRISPR-Cas9 system, significantly expanding its toolbox, creating a more powerful set of tools. Genetic engineers have discovered how to make CRISPR perform new tricks such as improved gene editing, turning genes on and off, and making genes glow for research.
What are Gene Editing and CRISPR-Cas9?
Gene editing is a group of technologies that give genetic engineers the ability to change an organism’s genetic code, allowing genetic material to be added, removed, or altered at specific locations in the genome. Scientists have developed several approaches to gene editing, the most famous of which is known as CRISPR-Cas9. The letters in CRISPR stand for ‘clustered regularly interspaced short palindromic repeats,’ and Cas9 stands for ‘CRISPR-associated protein 9’. The CRISPR-Cas9 system has generated much excitement because it is faster, cheaper, more accurate than other earlier gene editing methods.
Scientists adapted CRISPR-Cas9 from a naturally occurring gene editing system in bacteria. As a way of defending themselves, the bacteria capture segments of DNA from invading viruses and use them to create DNA snippets known as CRISPR arrays. The CRISPR arrays allow the bacteria to remember particular viruses or closely related ones. If the virus attacks again, the bacteria defend themselves by producing RNA segments from the CRISPR arrays to target the viruses’ DNA. The bacteria then use Cas9 or a similar enzyme to slice the DNA apart, disabling the virus. Putting the two together yields the CRISPR-Cas9 system.
Genetic engineers use the natural CRISPR-Cas9 system when editing genes in the lab. Gene editors create a small piece of RNA with a short guide sequence that binds to a specific target sequence of DNA in a genome. The RNA also binds to the Cas9 enzyme. Just as bacteria do, the modified RNA is used to recognize the DNA sequence, after which, the Cas9 enzyme cuts the DNA at the targeted location. Although gene editors mostly use Cas9, they sometimes use other enzymes, such as Cpf1. Once the DNA is cut, gene editors use the cell’s own DNA repair machinery to add or delete pieces of genetic material or to make changes to the DNA by replacing an existing segment with a customized DNA sequence.
Video on CRISPR Upgrades
This short animation provided by the journal Nature shows you some of the exciting upgrades to the gene editing technology. A transcript follows the video and is divided into topical sections. In case you have problems, here is the direct link: https://youtu.be/4YKFw2KZA5o
Transcript: CRISPR: Gene Editing and Beyond
“The CRISPR-Cas9 system is a tool for cutting DNA at a specifically targeted location. The technique has already revolutionized gene editing but scientists are always looking for new possibilities, so what else can CRISPR do?”
How CRISPR-Cas9 Works
“Since being discovered in a bacterial immune system, CRISPR-Cas9 has been adapted into a powerful tool for genomic research. There are two components to the system: a DNA-cutting protein called Cas9 and an RNA molecule known as the guide RNA. Bound together, they form a complex that can identify and cut specific sections of DNA. First, Cas9 has to locate and bind to a common sequence in the genome called a PAM. Once the PAM is bound, the guide RNA unwinds part of the double helix. The RNA strand is designed to match and bind a particular sequence in the DNA. Once it’s found the correct sequence, Cas9 can cut the DNA – its two nuclease domains each make a nick leading to a double-strand break. Although the cell will try to repair this break, the fixing process is error-prone and often inadvertently introduces mutations that disable the gene. This makes CRISPR a great tool for knocking out specific genes.“
Using CRISPR-Cas9 for Gene Editing
“But making double-strand breaks isn’t all CRISPR can do. Some researchers are deactivating one or both of Cas9’s cutting domains and fusing new enzymes onto the protein. Cas9 can then be used to transport those enzymes to a specific DNA sequence. In one example, Cas9 is fused to an enzyme, a deaminase, which mutates specific DNA bases – eventually replacing cytidine with thymidine. This kind of precise gene editing means you could turn a disease-causing mutation into a healthy version of the gene or introduce a stop codon at a specific place.”
CRISPR-Cas9 for Gene Transcription and Gene Silencing
“But it’s not all about gene editing. Several labs have been working on ways to use CRISPR to promote gene transcription. They do this by deactivating Cas9 completely so it can no longer cut DNA. Instead, transcriptional activators are added to the Cas9 by either fusing them directly or via a string of peptides. Alternatively, the activators can be recruited to the guide RNA instead. These activators recruit the cell’s transcription machinery, bringing RNA polymerase and other factors to the target and increasing transcription of that gene. The same principle applies to gene silencing. A KRAB domain fused to the Cas9 inactivates transcription by recruiting more factors that physically block the gene.”
Using CRISPR-Cas9 to Study the Genome
“A more outside-the-box idea for using CRISPR is to attach fluorescent proteins to the complex so you can see where particular DNA sequences are found in the cell. This could be useful for things like visualizing the 3D architecture of the genome, or to paint an entire chromosome and follow its position in the nucleus.”
Closing Arguments of the CRISPR Video
“CRISPR has already changed the face of research but these new ideas show that what’s been achieved so far could just be the tip of the iceberg when it comes to CRISPR’s potential. Whatever comes next, it seems the CRISPR revolution is far from over.“
Note: This video was first published on October 31, 2017, and was produced by Nature Video with support from Dharmacon. Transcript from the video – Nature Video is entirely responsible for the content of their video.
Articles on Gene Therapy and Gene Editing
- Watch a clip on gene editing in this report on the Future of Medicine (video).
- Learn how a novel Gene Therapy for Blindness May Soon Be Reality.
- Discover how old human cells became rejuvenated with the anti-aging compound resveratrol.
- Learn about a man who is self-experimenting with gene therapy to rejuvenate his body.
- Microsoft’s Bill Gates to Genetically Engineer Laser Lit Mosquitos
- MIT researchers discover how to do Revolutionary CRISPR Gene Editing with Nanoparticles.
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Nature Video. “CRISPR: Gene Editing and Beyond.” Nature Video (via youtube). October 31, 2017. Link. [The cover photo is a screenshot taken from the video.]
Genetics Home Reference. “What are genome editing and CRISPR-Cas9?” National Library of Medicine. Web. Retrieved Nov. 15, 2017. Link.
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