CRISPR-Cas9: What You Need to Know

3 Mins read

 CRISPR-Cas9 is one of the biggest discoveries of the 21st century.

Gene editing is when targeted changes are made like deletions and insertions, right in an organism’s genome. Over the past decade, the CRISPR-Cas-9 system has become a very popular method of genome editing, due to it is fast, cheap, precise and relatively easy to use. CRISPR is the rapid and the easiest of the gene-editing tools.

What is CRISPR-Cas9?

CRISPR is a natural process that’s long functioned as a bacterial immune system. Originally found defending single-celled bacteria and archaea against invading viruses, naturally occurring CRISPR uses two main components. The first is CRISPR, short for ”clustered regularly interspaced short palindromic repeats”. The second is Cas, or CRISPR associated proteins, which chop up DNA like molecular scissors.

Jennifer Doudna and Emmanuelle Charpentier at the University of California published a scientific paper showing what happened when the CRISPR-Cas9 system was taken out of bacteria and introduced in eukaryotic cells.

It is important to note that CRISPR is by far not the first system that allows us to edit DNA. However, CRISPR brings advantages over other techniques; it is much easier and faster to use.

How does CRISPR Work?

The way CRISPR works are that researchers create a piece of RNA with a guide sequence which is complementary to a targeted bit of DNA in the host’s genome. In other words, if DNA has a sequence that reads 5′-AATTGC-3′ then the RNA guide sequence is exactly the opposite and reads 3′-UUAACG-5′. The Cas9 protein then attaches to the RNA and the whole thing binds to the target DNA sequence in the host genome. The Cas9-RNA complex then makes a double-strand cut in the genomic DNA, and an alternative piece of DNA can be spliced in the right at that spot.

CRISPR-Cas9 technology works in a variety of cell types and organisms, and it’s been used to study diseases, and generate tissues from stem cells, like heart muscle tissue and neuronal tissue. At the moment, it is also possible to treat a whole, multicellular organism with genome editing. For instance, a mouse with liver disease due to a genetic defect was treated with as CRISPR-Cas9-mediated genetic change, and it improved the mouse’s symptoms.

One important point knıow abouıt this mouse example, however, is that the change was made to somatic cells, rather than germline cells, meaning these genetic modifications are not passed to the next generations. That said, CRISPR-Cas9 technology is able to alter the DNA germline cells, and if that’s done, then the engineered changes can be transmitted across generations.

CRISPR-Cas9 technology is also significantly impacting the development of crops, foods, and industrial fermentation processes. For instance, CRISPR technology could be used to produce crops with better yields or resist drought.

Is Editing DNA with CRISPR-Cas9 Technology Ethical?

CRISPR could create plants that yield larger fruit, mosquitoes that cannot transmit malaria, or even reprogram drug-resistant cancer cells. It is also a powerful tool for studying the genome, allowing scientist to watch what happens when genes are turned off or changed within an organism. However, CRISPR is not perfect yet.

Those are the big questions right now. There are concerns about the power and technical limitations of CRISPR technology. It doesn’t always make just the intended changes, and since it is difficult to predict long term implications of a CRISPR edit, this technology raises big ethical questions. The world’s first gene-edited babies, ‘CRISPR babies’, carry a mutation intended to protect them against HIV infection. Scientific debate and media speculation has swirled around the potential impacts of modifying their gene for CCR5. Also, in 2018 June, drawing on population analysis of variants of the gene CCR5 published in Nature Medicine, headlines blared that the girls might have shortened lives.


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