CRISPR/Cas9: The Versatile DNA Manipulator

When we hear bacteria, our first reaction is usually to grab the hand sanitizer.  So it is surprising to learn that a protein found in some bacteria has become one of the most widely used ways to manipulate DNA.  This protein, CRISPR, is used by bacteria to cut up viral DNA before it can be used to make more viruses.  Scientists have manipulated the protein to have even more functions, as summarized in Schaeffer’s and Nakata’s article.

To understand the versatility and potential CRISPR possess, one must first have an understanding of how our genetics are stored in DNA, and how our DNA results in who we are.  DNA is a like a zipped up zipper, with each tooth having its own identity, marked as a letter.  The four possible letters are A, T, C, and G.  This code can be converted into another molecule, RNA, which is only 1 side of the zipper.  This RNA is used as a template by the cell to make proteins, which are responsible for almost every function of the cell.  This means that by manipulating the DNA of the organism, we can manipulate how it functions.

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CRISPR, with the help of Cas9 that helps speed-up the CRISPR’s performance, is capable of making breaks in the DNA, like cutting in between two zipper teeth.  It does this by using RNA as a guide, so scientists can isolate the RNA for a specific protein, then find the specific piece of DNA that corresponds to that protein called a gene.  The code can be determined for that gene, so it can be compared to other sources of the same gene.  This can give insight into why a person may have a condition, or have the potential to give insight into evolution.  Since CRISPR is capable of making these cuts, it could be used to remove DNA, or new DNA could be introduced.  This means we would potentially manipulate proteins produced, and thus fix some genetic problems.  Since an organism is composed of millions of cells, this would have to occur early in development, which adds another barrier to potentially great advances.

There are also other limitations to CRISPR, but methods are being developed to limit these.  One problem is CRISPR cutting in places that are not desired.  To help fix this, a modified Cas9 has been developed that results in 50-1000 fold less unwanted cuts as opposed to the old system.  This means that the desired DNA manipulation is much more likely to occur without problems.  While we are not able to completely manipulate a human yet, we have determined the whole code of human DNA, called a genome, so we are well on our way to being able to detect and treat diseases or problems that affect us.

           CRISPR and Cas9 have even been manipulated for use beyond DNA alteration.  A “reprogramed” CRISPR/Cas9 system has been developed that recognizes RNA instead of DNA, allowing for the detection, analysis, and alteration of RNA. In addition, Cas9 itself has even been manipulated.  As I mentioned before, RNA is derived from DNA, but RNA production is a more complex process.  Imagine part of the teeth of the zipper are a specific code, called a promoter, where the zipper can attach, but not to both teeth sides at one.  Then the zipper moves down the teeth, making another set of teeth that is free from the template set it is making it from.  This is the RNA, and the zipper is a protein called RNA polymerase.  Often times the RNA polymerase needs help binding to the promoter, so other proteins bind there first which makes it easier for the RNA polymerase to bind, like using a set of tools to attach the zipper.  This explanation is given as manipulated Cas9 have been used to act like these tools, engaging the creation of certain RNA that scientists can manipulate.  They have also been able to bind manipulated Cas9 to promotor regions that cause little to no RNA to be produced.  This means we have the ability to potentially alter a persons expressed traits by turning off and on certain genes.  The benefit to this is it could be used much more easily than attempting to alter the DNA itself.

           The potential applications of CRISPR and Cas9 seem limitless, but one must remember that functionality in certain situations does not mean universality.  While we will likely reach a level where we will be able to alter genomes to create traits that we desire, it raises many issues beyond the realm of science.  One begins to question if it is fair that we could potentially create intelligent, athletic, and/or disease free humans for a certain cost.  There is also the threat of low genetic diversity, as if these methods are made to produce better crops there is the potential a new disease could wipe them all out as they are basically the same organism genetically.  Given the advances in the field, the coming years will be full of discoveries, and it will be interesting to see how these concerns turn out.

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