Jaw Drop #5 – CRISPR/Cas9

With all the recent and less recent talks about genetic engineering, I think it’s easy to get lost into the topic. Modifying a genome, being bacterial or human, is definetly not a new tactic. We’ve been doing that for decades, what’s new is having found a very strong tool.

CRISPRS/Cas9 mechanism is being increasing in popularity in every scientific journals and in every laboratory. The enthusiasm is definetly not for nothing. This new technique is very powerful and it’s been pretty successful, so there’s no reason in thinking that in the future it could not become even stronger.

With all this arguing about different applications and several variants of CRISPR as a genomic modifying tactic, I think we don’t have to forget where this amazing process comes from. I actually think that knowing from where it was discovered is much more interesting than the plenty applications that we will be able to find for it. In the end, this device was given to us by nature, we were just lucky enough to find it.

A semplicistic view of what CRISPR and CAS system can do.

To simply explain how the system works I will say this. CRISPR is an acronym for an array of interesting pieces of DNA. It stands for “Clustered regularly interspaced short palyndromic repeats”, a bunch of difficult words that just reflect the organization of the array. In practise what happens is these pieces of DNA are transcribed and processed into crRNAs (i.e. CRISPR RNAs). crRNAs are mounted on CAS proteins that can use them as a template probe to find and eliminate complementary RNA or DNA.

I think it’s pretty easy to see how this can be very powerful in the context of genetic engineering. We can basically target any sequence we want to degrade or, with variation, modify or insert, just by building a correct CRISPR array.

What I consider fascinating is that this process was discovered and is happening everyday inside simple organisms such as bacteria! Yes, we found and stole this amazing machinery from bacteria, and now we can engineer genomes like never before.

But now the question is why do bacteria have such a peculiar system of degradating DNA or RNA? Well guess what? We, humans, are not the only ones who have to defend themselves against natural enemies. Bacteria have to fight their lives every moment against viruses, especially bacteriophages. The beauty of all this, is exactly that CRISPR/Cas9 is nothing less than a defence system for bacteria to neutralize viral DNA or RNA from messing up the cell! Impressive right?

But wait? If CAS proteins need a template to eliminate the target DNA/RNA where do they get them from? Well this is even Jaw Dropping! Bacteria actively integrate parts of viral nucleic acids into their own genomes into the CRISPR arrays so that they have templates available next time they will encounter the same virus!!!

Thought bacteria were simple guys and that we’re the coolest? You better rethink your priorities, evolution can teach us still a lot. And in the meantime, let me tell you a story..


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