CRISPR/Cas9 is a revolutionary gene editing technique that can modify any region of the genome of any species with high precision and accuracy…and it does so without harming other genes.
CRISPR/Cas9 might be popular in the media now, but it has been around for a while. Though it has existed as a gene editing technique for about four years, scientists have been investigating CRISPR in bacteria for much longer—since the 1980s. In fact, the first report on CRISPR was published in 1987, when Japanese scientists discovered CRISPR in the DNA of bacteria.
To break its discovery down a bit, in their attempts to study a particular protein-encoding gene inE.Coli, researchers noticed a pattern of short, repeating, palindromic DNA sequences separated by short, non-repeating, “spacer” DNA sequences.
Over the next five years, researchers realized that these repeats were present in many bacteria and other single-celled organisms. In 2012, scientists coined the term “CRISPR,” short for “clustered regularly interspaced short palindromic repeats,” to describe the pattern.
For another decade, scientists hammered out the details of CRISPR. They figured out that the repeating DNA patterns, along with a family of “Cas” (CRISPR-associated) proteins and specialized RNA molecules, play an important role in bacterial immune systems.
And this system—the entire complex of DNA repeats, Cas proteins, and RNA molecules—was named the CRISPR/Cas system.
HOW DOES IT WORK?
If you’re familiar with the copy/paste function on your computer, then you understand CRISPR…at least at a very basic level.
When bacteria encounter an invading source of DNA, such as from a virus, they can copy and incorporate segments of the foreign DNA into their genome as “spacers” between the short DNA repeats in CRISPR.
These spacers enhance the bacteria’s immune response by providing a template for RNA molecules to quickly identify and target the same DNA sequence in the event of future viral infections. If the RNA molecules recognize an incoming sequence of foreign DNA, they guide the CRISPR complex to that sequence. There, the bacteria’s Cas proteins, which are specialized for cutting DNA, splice and disable the invading gene. The cell attempts to repair the DNA, but that creates a mutation that disables its function permanently.
In the fall of 2012, a team of researchers led by UC Berkeley scientists Jennifer Doudna and Emmanuelle Charpentier announced that they had hijacked the bacteria’s CRISPR/Cas immune system to create a new gene-editing tool. Their CRISPR/Cas9 system involved a Cas protein called Cas9 and hybrid RNA that could be programmed to identify, cut, and even replace any gene sequence.
If the goal is to insert a new gene, a short fragment of DNA or the desired gene with a specific function is inserted to fill the gap and replace the original gene. The new gene is now ready to produce the desired protein in the cell or in a test tube. But that’s not all we can do.
The four main things we can do with CRISPR/Cas9 include:
- Delete a Gene: Undesirable genes can be deleted from the genome, allowing researchers to study the functions specific to the genes and learn about what happens to the cell when these genes are not in the genome
- Add a New Gene: Desirable genes can be added into the genome, allowing researchers to study their functions within the cells. These genes can also add new functions to the cell.
- Activate Dead Genes: Genes that are essential for various functions, but no longer function, can be reactivated using CRISPR-Cas9 system.
- Control Gene Activity Level: Genes are more active than normal can be controlled to produce just the right amount of proteins, which will help maintain balance within the cell under desired conditions.
WHY IS CRISPR-CAS9 SO IMPORTANT?
CRISPR has been used to combat HIV, fight blindness, to edit single letters of DNA, and even as a recording device. In addition, CRISPR can be applied to the following fields:
Human Health: The CRISPR-Cas9 system can revolutionize gene therapy and make it possible to treat a large number of diseases that would be impossible to treat without this technique. This could include diabetes, cancer, cystic fibrosis, and sickle-cell anemia (scientists are already working in these various areas).
New Materials: Manipulating biological circuits using CRISPR-Cas9 will facilitate the generation of synthetic materials that could be useful in various applications, such as oral drug delivery and the production of biosensors.
Drug Development: Engineering cells to optimize a high yield generation of drug precursors in bacterial factories could significantly reduce the cost and accessibility of useful therapeutics
Research Applications: The CRISPR-Cas9 system could allow the creation of new animal and cellular models, which will help us learn more about diseases and test new drugs and vaccines on these models.
Agriculture: CRISPR gene editing tools can edit crops without harming other genes, which will help confer resistance to infections and harsh environments, improving global food security.
Bioenergy: Sustainable and cost-effective biofuels are attractive sources for renewable energy, which could be achieved by creating efficient metabolic pathways for ethanol production in algae or corn.
Although the use of CRISPR/Cas9 carries enormous possibilities to further advance the human health and well-being, the benefits of CRISPR/Cas9 are followed by equally huge risks from potential misuse, but also unforeseen consequences. Could we someday engineer the perfect baby?
Researchers in the United States are already addressing the necessity for regulation of human germline editing. At the end of 2015, the National Institutes of Health still refuses to fund research proposals for CRISPR/Cas germline editing therapies. Nevertheless, it has to be emphasized that this policy does not automatically cover projects that are funded privately.
It’s impossible to know where the next CRISPR innovation or discovery will take us. What we do know, however, is that advancements will be swift.
