What is CRISPR-Cas9? Below is a short answer, then a longer answer and then a list of some possible uses of this technology and finally a short introduction to the ethical issues.
Short Answer: It’s a breakthrough gene editing technology which allows scientists to remove and replace genes and/or turn off gene expression. It’s going to have huge effect on treatment of disease, production of food, biofuels, and many others.
Need a bit of a refresher on genes and the like? This IFOD on mapping the genome has some background/refresher: Mapping the Genome
Longer Answer: CRISPR stands for “Clustered Regularly Interspaced Palindromic Repeats.” In the early 1990s scientists discovered that bacteria had palindromic repeats of base pairs in their DNA (CRISPRs) and that between these repeats were copies of foreign viral DNA. This was a crazy discovery – mind blowing that bacteria had strains of viral DNA within their DNA! How? Why?
In the 2000s researchers figured out answers: (a) the viral DNA provided a map to the bacteria for recognizing and destroying viral attackers and (b) the CRISPR sequences signaled the presence of the viral DNA. How did the bacteria get viral DNA inter-spaced by CRISPR sequences in its own DNA? After a bacteria successfully clears a viral infection or otherwise encounters a virus, it would cut and store fragments of the virus’s DNA as a way to retain a genetic memory in order to recognize the virus as a foreign attacker and to assist in defense against the virus. Cas9 is the enzyme that acts like a tiny pair of scissors that cuts the DNA.
Jennifer Doudna, a biologist at University of California at Berkeley and a CRISPR researcher was making dinner for her daughter and was struck with the thought that this amazing defense mechanism that bacteria were employing to fight viral infections could be used as a tool to affirmatively edit genes of anything! Wow. Her lab, in collaboration with another lab in Sweden, led by Dr. Emmanuelle Charpentier, proved that this was possible.
Dr. Doudna and Dr. Charpentier published a paper in 2012 explaining CRISPR -Cas9 and since then gene editing with CRISPR has taken off. It has become ubiquitous in biology labs all over the world.
Here’s a simple explanation published by the National Academy of Sciences explaining how CRISPR-Cas9 works: “The trick is simple: the Cas9 enzyme cuts DNA at a specific sequence, determined by an accompanying bit of RNA called a guide RNA. Then, the cell’s own DNA repair machinery typically takes over in one of two different modes. In the first mode, it simply glues the two pieces back together, but imperfectly, so the leftover scar interrupts and disables the targeted gene. Or, in a second kind of repair, the cell can copy a nearby piece of DNA to fill in the missing sequence. By providing their own DNA template, scientists can induce the cell to fill in any desired sequence, from a small mutation to a whole new gene.”
What is so remarkable about CRISPR-Cas9 as opposed to previous gene editing is that it is (a) cheap, (b) precise and (c) quick. While the technology is improving and needs to be perfected, CRISPR-Cas9 gives scientists the ability to turn off or remove and replace specific genes quickly and cheaply. Here’s a quote by a scientist at the University of Wisconsin: “It really opens up the genome of virtually every organism that’s been sequenced to be edited and engineered.”
It is hard to explain the potential benefits (and drawbacks) of this technology in a mere IFOD. Here’s a very small sample of probable/potential applications:
- It will allow the turning off and on of specific genes to discover what the genes do and how they interact with other genes.
- Turning off genes that are responsible for genetic-based diseases will prevent the disease and may possibly provide a treatment for those with the disease. Think Huntington’s Disease and ALS and the like.
- Experiments are currently being performed using CRISPR to improve the efficacy of immunotherapy cancer treatments. The use of CRISPR technology to fight cancer is very exciting and promising.
- CRISPR treatment trials are being conducted in China on humans using CRISPR to fight the HPV virus that causes cervical cancer.
- Fighting bacteria that are antibiotic resistant (or even replacing the use of antibiotics). Similarly, fighting viruses, which of course are not killed by antibiotics.
- Altering parasites, such as mosquitoes, so that they no longer carry infectious diseases, such as malaria. Wow. Or scientists could get rid of mosquitoes altogether (think about whether that’s a good idea).
- Modifying plant crops so they are more drought resistant, need less (or no) pesticides and are more nutritious. This is a huge area.
There are obvioius ethical issues with CRISPR gene editing technology. Turning off genes that cause horrible diseases such as Huntington’s seems to be a good thing. How about modifying mosquitoes so that they cannot carry malaria? How about making mosquitoes extinct using CRISPR? How about making positive changes to the human genome? Make your embryo smarter, or taller, or less likely to develop Alzheimer’s?
Jennifer Doudna, the discoverer of this technology, now spends much of her time focused on discussions of ethics of CRISPR and how to ensure that it will be used for good and not evil. It does feel like the ability to play God is a slippery slope.
Still interested? Here are two great podcasts about CRISPR technology, one from radiolab and the other from freakonomics: