What is CRISPR

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What is CRISPR?

Funny you should ask about CRISPR. It is the most talked about latest technology to hit the media. In fact the two ladies; Jennifer Doudna and Emmanuelle Charpentier are slated for a potential Nobel Prize in Chemistry. So that brings us to the question, what’s the buzz about?

Bacteria and viruses happen to have survived on this planet much longer than humans. Those two microbial species have developed a relationship with each other. Since no one wants to be vanquished by another, the bacteria have developed a strategy to prevent the viruses from using its cellular interior from being used as a factory for producing more viruses and then discarding it to the “trash cabinet.” You see, viruses that infect bacteria are called bacteriophages and in so doing, they insert their DNA into the bacteria to circumvent the bacterial machinery so they can produce more of their own progeny. Kind of like your in-laws visiting your home, staying in it and multiplying like rabbits and eventually by proxy taking over the ownership.  Bacteria for obvious reasons don’t like that. It is akin to the Hepatitis virus infecting the human liver cell and using it for its own propagation to the detriment of the host cell, causing inflammation of the liver as a whole and sometime death of the infected individual; Infect a cell, multiply within (CCCs) and then infect more cells and the parade goes on until the immune system kicks in and the fight leads to the hepatic inflammatory damage.

The bacteriophage (virus) has attached itself to the bacterium surface and injected its DNA within it. The Bacterium also happens to have its own piece of coded DNA in place and within it is this nifty fragment called the CRISPR (clustered regularly interspaced short palindromic repeats). These repeats are so called “Spacers” (25-30 nucleotides) and sandwiched within these repeated palindromic segments of nucleic acids are cleaved portions of the infecting virus’s selected DNA fragment. There are many such repeats and bottled in between two CRISPRs is a unique fragment of the many viral DNA fragments that have paid a visit to the bacterial household. Multiple fragments from the same virus or one or two from many different viruses reside here. One can look at it as a “Guest House” All guests visiting the Great House must live in there. Each guest has a bodyguard on duty, where, if they are noted to have mischief in their DNA will be handled swiftly by the bodyguards and delivered to the police (in this case Cas9 protein) without harming the owners of the great house beyond. As I was saying, the CRISPR holds these fragments in check and when a similar virus happens to stroll along that has previously caused mischief by injecting its DNA to cause harm, the CRISPR goes into full throttle with the help of Cas-9 Protein, slashing and dismembering the deadly DNA.

Mechanistically the CRISPR segment creates a messenger RNA that merges with the single strand of the DNA of the double-stranded virus (called guide RNA or gRNA), which is then rapidly segmented further by being cleaved containing multiple smaller strands each containing a viral DNA fragment and the CRISPR spacer called the crRNA. These fragments attach to the transactivated RNA or tracrRNA, which helps bind to the Cas9 protein to start the cutting process of the invading viral DNA.

The Cas9 protein cleaves (cuts) away all the crRNA that are attached to the viral DNA in exactly the spots where they are attached thus fragmenting the viral DNA and rendering it useless from further replication! Imagine the simple ingenuity of the Bacterium. But here is the kicker, the viruses don’t sit back and take this kind of bullying within the CRISPR Guest House either. They perform Single Nucleotide Polymorphisms (SNP) or colloquially, single point mutations and try to hoodwink the bacterium from recognizing the DNA strand. That single SNP is enough to throw the whole game asunder. And it does. But the slow-poke bacterium compared to the Ferrari driven viruses adapt albeit slowly and incorporate the new segment within and the battle for survival proceeds anew. When the bacterium divides the latest CRISPR information also goes with it to the daughter cells to help protect them. And the species lives!

How does this help us?

The answer is simpler than you think. If we can use the nuclease enzyme to cut out a bad portion or multiple bad portions of the human DNA and insert the healthy version into the stem cell, Voila, we have a healthy being! But before you go drinking and smoking hoping for the CRISPR to save your DNA mutations, consider this, we are a long way away from using this technology in humans. Although the unintended consequences in tinkering with a single gene insertion for a single gene = single disease paradigm might be low but inserting mRNAs that enhance or suppress gene functions and placing them as lords over the genome might have serious pitfalls. You might cure the cancer and kill the patient with some other evil. Happens!  As you are aware that “the hip bone is connected to the leg bone…”and so on, a change here might make a big change there. If you are into the butterfly effect the analogy fits well here. Reminds me also of the Lorentz strange attractor, but we will leave that for another day.

We certainly can keep this wonderful technology in the laboratory and mess around till we have more data to configure the monster of Lamarckian twists that lurk within this technology. Many hundreds if not thousands of experiments are needed to evaluate the hypothesis in a controlled environment and after validation, with trepidation move ever so slowly in the human sphere. But those in love with the “Disruption” fall madly in love and leave caution to the wind. And the wind can be destructive. So careful out there, girls and boys!

In cancer for instance, one might snip away a mutated oncogene or have a RNAi sitting adjacent to and enhancing a tumor suppressor gene to shut down the cancer process. The possibilities are endless. Similarly Infectious Diseases could be rendered moot by vaccinating individuals at risk with a CRISPR Cas9 system to destroy the invading bacteria via a nasal spray someday.

Speaking of vaccinations, this is nature’s way of vaccinating against an invader. Plug in the coordinates and destroy the target. Mission Possible!

The mechanism and the understanding are not as daunting as one might think, but using them without safeguards is akin to future genetic disasters. Just sayin!

We have infectious diseases, cancers, chronic illnesses, hereditary genetic misfortunes to consider in alleviating the burdens on humans but we have time and some hard work ahead.

 

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