Maybe you’ve already heard of CRISPR. Appearing in many science publications in 2015, it promises to revolutionize biology and help cure a wide array of diseases, including hemophilia and Alzheimer’s. So what is it, exactly?
CRISPR stands for Clustered Regularly-Interspaced Short Palindromic Repeats. Try saying that 10 times out loud. In the 1980s, scientists discovered that genomes in a wide variety of bacteria contain identical DNA sequences with short, different DNA codes between the repeats. These patterns showed up everywhere and the researchers named them CRISPR. It took a few years before scientists realized that these sequences make part of the bacteria’s natural defense system. The bits of DNA are actually snippets of dangerous viruses that have previously attacked the bacteria, and CRISPR stores these snippets so that next time the viruses invade, the bacteria will be ready. Think of the CRISPR system as a collection of mug shots of previous enemies. The microbe can create an RNA copy of the virus mugshots, and send it to Cas enzymes. The enzymes drift around the cell, and if they spot DNA that matches their RNA code, they’ll recognize it as a viral sequence and chop it off to prevent it from replicating.
Jennifer Doudna, a researcher at UC Berkeley, saw an opportunity to use this defensive system as offense. If scientists could put a sequence of genes corresponding to a disease into the CRISPR system, they could potentially program enzymes to snip out precisely an unwanted sequence of genes. This is huge, because although gene-editing tools existed prior, they were expensive, slow and imprecise; researchers could devote $5000 and six months to a gene-editing portion of their research and have them go to waste because the wrong DNA sequence was cut. CRISPR technology brings the price down to $75, and the enzymes are precise about cutting.
There are tremendous applications for this technology. Hemophilia, a medical condition characterized by a severely impaired ability to form blood clots, affects 1 in 5,000 males. Usually, it’s caused by one bad gene. A Korean team has recently used CRISPR technology to cure hemophilia in mice, and if this process can be replicated on humans it could improve the quality of life for many. This example also shows potential ethical problems with this technology. How much gene editing is too much? In early 2015, Chinese scientists used CRISPR on embryos to edit a gene responsible for β-thalassaemia, a potentially fatal blood disorder. This raised alarms from the scientific and ethicist community, because editing an embryo’s genes would also affect the embryo’s descendants, and potentially alter the course of human evolution. Furthermore, the embryo had no say in whether or not it wanted its genes edited.
The technology is still in its infancy. The edited embryos were non-viable, meaning they will never be able to become children, and the editing was only successful for a small fraction of them. However, this fact isn’t stopping people from dreaming: could we edit an elephant into a woolly mammoth or, even better, a chicken into a dinosaur? In a few more decades, perhaps we’ll find out.
February 4, 2016
Author: Sherry Yuan
Editor: T.L. Bloomfield