CRISPR is Overrated
How CRISPR isn’t as good as you think.
In 1987, Yoshizumi Ishino described a new acquired immune system inside of bacteria and archaea that consisted of clustered DNA repeats. In 2012, Jennifer Doudna would later go on to engineer this mechanism as a means of genomic editing. She and her colleagues have won the Nobel Prize in Chemistry just last year in October 2020.
What makes CRISPR-Cas9 so unique and different from other techniques or tools for genomic editing is its sheer simplicity and versatility. With the use of guide RNAs that help to determine and find the locations that CRISPR should be traveling to, the process of using CRISPR is relatively fast and efficient. CRISPR can be used in many ways to manipulate gene expression that don’t include direct excision of a locus. By changing the complex of CRISPR, it can be used as a powerful epigenetic tool that can regulate the methylation and demethylation of the promoter of genes as well.
The original discovery of this CRISPR mechanism and its utilization in genomics is noteworthy in itself. But the modifications and various iterations that have been emerging since its public debut in 2012 are nothing short of field-defining. The star power of this complex has definitely been noticed by many, including sparking a patent war between the Broad Insititute of MIT and Harvard and UC Berkeley which both have valid claims over the rights to the enzyme.
But despite all the hype and expectation surrounding the future applications of this enzyme, there are still serious flaws that would impede its progression into becoming a medicinal tool.
Mistakes, Mistakes, Mistakes
One of the most significant issues with CRISPR-Cas9 is its efficiency. Although it is fairly efficient relative to the other conventional techniques used for manipulating gene expression and gene editing, it is not even close to being a perfect gene-editing tool. With further experimentation being done on the limits of CRISPR, already researchers have identified that CRISPR frequently creates significant unwanted changes to the genome around the specific location where CRISPR is targeting. This included DNA rearrangements and large deletions of thousands of nucleotides which would potentially cause detrimental effects. This was shown by Kathy Niakan, a developmental biologist at the Francis Crick Institute. Her lab used CRISPR-Cas9 to create mutations in the POU5F1 — a gene involved with embryonic development. During this study, they found that 22% of the 18 genome-edited embryos contained these unintentional changes in the DNA sequences surrounding the POU5F1 gene.
A group led by Dieter Egli at Columbia University also studied embryos. The team was targeting a gene EYS which had a mutation that caused blindness. The experiment showed that not only did approximately half of the embryos had lost segments of the chromosome it was located on, this included the entire chromosome at times.
An Uncontrollable Variable
CRISPR-Cas9 relies on the DNA repair system in the cell. The mechanism of the CRISPR complex works by creating an intentional Double-Strand Break in the DNA which means it cuts both strands of the DNA which allows for that specific piece of the DNA to be removed. This gap is then quickly discovered by the built-in DNA repair system in cells which quickly stitch the DNA back together and eliminate the gap. But again, this mechanism is also imperfect. Though most times DNA repair goes smoothly, small changes can be made during the repair process which can add nucleotides to the original sequence or leave some off as well. Broken DNA is always a gamble. The more times DNA is broken, the higher likelihood that it will be changed and essential parts of the DNA or the chromosome will be lost. This is a variable that is entirely out of the control of researchers. The DNA repair mechanism is inherent to cells and the efficiency and reaction to double-strand breaks vary between cell types.
Unrealistic Expectation
The media, the uninformed public, and loads of science fiction material have created an environment where we have been searching for the next scientific breakthrough that will make our fantasies a reality. In this case, it is genetic editing.
Ironically, Dana Caroll, arguably the founder of genome editing, had discovered zinc finger nucleases as a genomic editing tool during the same time as CRISPR was discovered but receive little of the national spotlight with CRISPR. Zinc Finger Nucleases are also able to induce double-strand breaks and edit the genome in a more complex fashion than CRISPR.
Those that are not too informed or have little scientific background really do not understand the actual mechanism of CRISPR and look beyond to the Hollywood scenarios that have been concocted by the media for attention. Yes, there have been experiments with human embryos and some very questionable uses of CRISPR on humans. But these are extremely rare cases that can’t really be replicated through peer-reviewed and regulated research. Based on the error-prone nature of CRISPR-Cas9 in previous experiments and the relative infancy of the field of genome-editing in the context of CRISPR, it is very unlikely CRISPR will have anything to do with directly modifying genes in humans, children, or any animals outside of those used for research. I’m sorry to disappoint, but superhumans are a little farther away than we expected.
CRISPR is certainly an impressive achievement and all credit is given to the researchers that have pioneered this field. It may not have the incredible power the public has perceived it to have, but it will certainly benefit researchers significantly. As a research tool, it has a lot of potential. Its ability to manipulate gene expression through direct editing and epigenetic means makes it a very powerful tool. It will help to create more precise and accurate experiments, create new techniques to be used in the field, and give a deeper understanding of genetics as a whole. Overall, CRISPR is definitely something to still be excited about.
