Genetic Engineering/CRISPR

Author: Patrick Lin

Editors: Simran Gohel and Katelyn Ma

Artist: Tiffany Chen

Gene editing is a technology that allows humans to make changes in an organism’s DNA. This gives humans the ability to add, remove, or alter genetic material in the genome of an organism. The most well-known tool used for gene editing is Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-Associated Protein 9, or for short, CRISPR-Cas9. This has been brought up recently and has been one of the biggest scientific breakthroughs of the century. CRISPR-CAS9 technology has many potential applications but its ability to make gene editing faster, cheaper, and easier raises ethical concerns.

CRISPR is a distinctive feature of the genomes of most bacteria and archaea (single-celled microorganisms). After an attack from a virus, bacteria would integrate new spacers derived from parts of the virus genome into the CRISPR region. This allows the bacteria to “remember” the virus so if the same virus attacks again, a part of the CRISPR region is copied, and processed into RNA segments called CRISPR RNA or crRNA. crRNA and trans-activating crRNA or tracrRNA form a complex and binds with the protein Cas9 to “cut” the complementary virus DNA. To make sure the Cas9 does not cut the bacterial genome, the protein only cuts the target DNA sequence if there is a PAM (protospacer adjacent motif sequence) next to it. This process using CRISPR and Cas9 gives bacteria adaptive immunity against viruses that can be borrowed and modified by humans for genetic engineering.

Humans can create the CRISPR-Cas9 system into a tool that can remove, add, or replace any gene of their choosing. Cas9 proteins act like scissors that are directed by crRNA. Simply changing the nucleotide sequence of the crRNA will allow the crRNA and Cas9 to cut a target gene of a cell. Once the gene is removed from the genome, the cell will naturally repair the broken genome by inserting and removing nucleotides to repair the cut in the genome. This can lead to mutations that may silence or make an unwanted gene useless. The desired gene can also be supplied as a template for the cell to replace an unwanted gene for a desired one.

CRISPR-Cas9 has gained a lot of attention and popularity due to its speed, efficiency, accuracy, and cost. With this technology, large scale genetic engineering projects can be done at a fraction of the time and cost compared to other tools. The original functions of CRISPR are useful for industrial processes that employ cultures of bacteria to manufacture certain goods.

These include food, drugs, vaccines, and fuels. CRISPR can be used to make the cultures more resistant to an attack from specific viruses. Beyond the natural use for CRISPR in bacterial defenses, the technology can be used to modify traits of certain plants to increase crop yield, improve drought resistance, and make the plant more nutritious. CRISPR can also be used to control or eradicate certain diseases through human and animal cells. Disease vectors can be eliminated through the use of gene drives, genetic systems that increase the chances of a particular trait to be passed down. Gene drives can control diseases such as by enhancing sterility within mosquitoes that are vectors for the disease so that non-vectors have a higher chance of passing their traits. Editing human genes can get rid of diseases such as cystic fibrosis, sickle cell, and Huntington's.

Though CRISPR-Cas9 can be beneficial to the world, the numerous potential applications of CRISPR raises concerns about the ethics and unintended consequences of gene editing. The biggest concern about gene editing can be considered safe.

CRISPR is easier to use and more accurate than other methods, but it is not perfect. There is always a risk of off-target edits and mosaicism (the presence of two or more populations of cells with different genotypes in one individual). Another ethical concern is that the human patients affected by gene editing would be embryos and therefore cannot consent to such operations. Knowledge of human genes is very limited so there is a possibility of unintended consequences for future generations of genetically engineered humans. Research to improve gene editing for humans is also limited due to moral objections to the use of human embryos in research.

CRISPR-CAS9 is a relatively new technology that has been used by humans for less than 20 years. Like any new technology, it takes time and research to perfect. Its potential has garnered a lot of excitement. However, caution must be advised when dealing with tools that can alter life and the future itself.

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Citation

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2020, ghr.nlm.nih.gov/primer/genomicresearch/genomeediting.

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