CRISPR – Gene Editing is Upon Us

Imagine being able to cure any genetic disease, or prevent bacteria from resisting antibiotics. Also, imagine having the power to alter mosquitoes so that they cant transmit malaria. Finally, imagine if we could prevent cancer or successfully transplant animal organs into human beings without the fear of rejection. Sounds like something from the future? Well, the future is near, and the molecular machinery to achieve these goals are in constant development. These are attainable goals made possible by a family of DNA sequences called CRISPRs.

What on Earth is CRISPR?

CRISPR (pronounced “crisper”) is the acronym for ‘Clustered Regularly Interspaced Short Repeats’. It is a group of DNA sequences found in bacteria that act as a defence system against viruses that could infect a bacterium. CRISPRs are a genetic code, broken up by ‘spacers’ of sequences from viruses that attack a bacterium. If the bacteria encounter the virus again, CRISPR acts like a memory bank, making it easier to defend the cell.

The Discovery of CRISPR

The discovery occurred independently in the 1980s and 1990s by researchers in Japan, the Netherlands, and Spain. In 2001, Francisco Mojica and Ruud Jansen proposed the acronym for CRISPR. They wanted to reduce the confusion caused by the use of different acronyms by different research groups. Mojica hypothesized that CRISPRs were a form of bacterial acquired immunity. In 2007, a team led by Philippe Horvath experimentally verified this. Not too long later, scientists through ingenuity successfully manipulated and used the CRISPR technology in their labs. In 2013, the Zhang lab became the first to publish a method of engineering CRISPRs for use in mouse and humane genome editing.

An artist’s illustration of the CRISPR system in action. [source]

How Does CRISPR Work?

Essentially, naturally-occurring CRISPR gives a cell ‘seek-and-destroy’ capability. In bacteria, CRISPR works by transcribing spacer sequences that identify the target virus DNA. Particularly, one of the enzymes produced by the cell (e.g., Cas9) then binds to the target DNA and cuts it, turning off the target gene and disabling the virus.

In the laboratory, the enzyme Cas9 cuts DNA, while CRISPR tells it where to snip. Rather than using viral signatures, researchers customize CRISPR spacers to seek genes of interest. Scientists have modified Cas9 and other proteins, such as Cpf1, so that they can either cut or activate a gene. Turning a gene on and off makes it easier for scientists to study the function of a gene. Cutting a DNA sequence makes it easy to replace it with a different sequence.

The Wonderful Uses of CRISPR

Researchers use CRISPR to make cell and animal models to identify genes that cause diseases. Besides, they can develop gene therapies and engineer organisms to have desirable traits. Nevertheless, the latter function is highly controversial as it includes ethical issues.

The applicability of CRISPR is enormous. Myriad research efforts include (but not limited to):

  • Applying CRISPR to prevent and treat diseases such as HIV, cancer, Alzheimer’s and Lyme disease. Theoretically, with this method, we can treat any diseases containing genetic components.
  • Developing new drugs to treat blindness and heart disease. CRISPR/Cas9 can potentially remove a mutation that causes retinitis pigmentosa.
  • Extending the shelf life of perishable foods, as well as increasing the resistance of crops to pests and diseases. Besides, increasing their nutritional value and yield is also possible. Recently, a Rutgers University team used the technique to make grapes resistant to downy mildew.
  • Transplanting pig organs (xenotransplantation) into humans without rejection.
  • Making mosquitoes resistant to the parasite that specifically causes Malaria.
Genetically modified mosquitoes without Malaria. [source]

In a nutshell, CRISPR and other genome-editing techniques are currently highly controversial. Several groups raised issues regarding the ethicality of the technology. However, the US FDA proposed guidelines to cover the use of these technologies in 2017. In addition, other governments are also working on regulations to balance benefits and risks. All in all, it is safe to say that gene editing will be on its way in our daily life real soon.

Written by Mitchell Lim

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