CRISPR-Cas9 | How it works

CRISPR stands for clustered regularly interspaced short palindromic repeats. Quite a mouthful to say, isn’t it? Frankly, the acronym is a lot nicer.

The concept of CRISPR was first published by Francisco Mojica in 1993. ¹

In 2005, a Danish food producer also found CRISPR in the bacteria they used to produce cheese and yoghurt.¹ CRISPR is just a natural mechanism that the bacteria use to defend itself from any intruding virus. So, in a sense, we’ve been eating CRISPR products for a while now.

Scientists have now taken this natural mechanism and transformed it into a fancy ‘new’ technology: CRISPR-Cas9. But how is this natural process used in CRISPR-Cas9 in the lab? Read on to learn how CRISPR and Cas9 turned into CRISPR-Cas9.

The different roles of CRISPR and Cas9

Yes, there is a difference between CRISPR and Cas9: CRISPR allows bacteria to ‘record’ viruses they are exposed to. They basically keep a diary of all the viruses that have attack them by including a part of the intruding DNA in their own, passing their diary onto the next generation of bacteria.

Cas9 is an enzyme that destroys the intruding DNA, once the virus has invaded the bacteria. It is paired together with RNA, which acts as a sort of ‘map’, guiding Cas9 to the right spot. Cas9 is able to recognize the virus DNA, because RNA copies a short sequence of the attacking virus’ DNA, which draws Cas9’s attention to the right place.^3,4

Cas9 then acts as ‘scissors’, cutting out the virus DNA at that exact point ^4,5, rendering the virus useless. ^2,3

The process: CRISPR + Cas9 = CRISPR-Cas9

When recreated in the lab, scientists and researchers can create this RNA ‘map’ themselves, which targets a specific part of the DNA where they want to make a genetic change. Once the DNA is cut, they can knock-out undesirable DNA sequences and can insert DNA with a desirable trait.

Together, CRISPR-Cas9 can be used to: ⁴

• Delete a part of the DNA
• Repress or activate certain genes
• Purify DNA
• Copy DNA
• Edit DNA

For all these uses, CRISPR-Cas9 works in the same way. But, the way the DNA strand is put back together is different. If left completely alone, the strand might fuse back together randomly, resulting in a strange mutation. Obviously, that’s counterintuitive for the aim of using CRISPR-Cas9. So, scientists typically add a DNA strand produced in the lab and use that strand to glue the two ends back together. This becomes the desired strand of DNA  that can help crops ‘evolve’ ^4,6 ((maybe to be more resistant to some processes, like ‘browning’ in mushrooms⁷)

CRISPR-Cas9 is a recent development of the last few years and its implications have not yet reached their full potential. It’s definitely much more precise than other methods, like GMO. Let us know in the comments what you think of it!

If you want to read more about CRISPR-Cas9 and its safety, click here.