CRISPR turned a bacterial defence against viruses into programmable genetic scissors
Bacteria fight viruses by storing snippets of their DNA and using an enzyme to slice matching invaders. Scientists borrowed that trick. Pair the enzyme Cas9 with a custom guide RNA, deliver it into a cell, and it cuts the genome exactly where you choose, letting genes be switched off, repaired or added inside living organisms.
Editing DNA in complex cells has been possible since the 1980s, but early methods were clumsy. In the 2000s, zinc finger nucleases arrived, and in 2010 so-called TALENs made targeting easier. Both, however, need a new custom protein designed for every DNA target, a slow and difficult job. CRISPR only needs a new strand of guide RNA, which is cheap and easy to make, and several guides can be sent in at once to hit multiple sites.
The pieces came together over a few years. In 2005 Alexander Bolotin in France found a CRISPR region containing a gene for the large protein Cas9. The following year Eugene Koonin, working at a US government biology database centre, proposed how the system works as bacterial immunity, and in 2007 researchers at the food company Danisco showed experimentally that bacteria absorb new viral DNA into the array to repel future attacks. In 2012 teams led by Jennifer Doudna and Emmanuelle Charpentier showed Cas9 could be programmed with RNA to cut chosen DNA, work that won them the 2020 Nobel Prize in Chemistry.
Once the cut is made, the cell's own repair machinery takes over. Messy repairs tend to disable a gene, while supplying a matching template lets researchers write in a precise change. The approach is being used to develop medicines, crops and pest controls, and holds promise against inherited disorders and cancers. In 2023 the first CRISPR-based drug, Casgevy, was approved.
Editing embryos is another matter. The 2019 births of babies from edited embryos, in the affair surrounding the Chinese scientist He Jiankui, provoked outrage, and many bioethicists worry that heritable changes could open the door to eugenics.
Source: CRISPR gene editing
