A “navigator” for genetic engineering

Gene snipping was possible even before the Crispr/Cas9 gene scissors. But it made everything easier

By Sascha Karberg
This Nobel Prize came as no surprise to anyone who knows anything about the subject. For years, the scientific community worldwide has been waiting for Stockholm to honor one of the most important discoveries and developments in the field of molecular biology: the gene scissors with the cumbersome name “Crispr/Cas9. Hardly anyone doubted that the choice would fall on the French microbiologist Emmanuelle Charpentier, who has been researching and living in Berlin since 2015, and her U.S. colleague Jennifer Doudna from the University of California Berkeley.
The fact that it has now become exclusively these two is probably a very wise decision by the Nobel Committee. As with so many scientific breakthroughs, there were a number of other options (see below), but the choice would have been difficult.
The two researchers had already received so many research prizes together in recent years, and had constantly had to deal with media requests and public appearances, that at times they no longer had time to work at all. When, for example, Charpentier took time for her first in-depth interview with the Tagesspiegel in 2016 after several postponements, she preferred to speak in a café outside the gates of the Charité campus – as if she felt a little uncomfortable toward her coworkers for spending time with the press “again” like this, rather than pushing her research in the “Max Planck Research Unit for the Science of Pathogens,” which was founded especially for her. “I didn’t become a scientist to talk to the media,” she said apologetically at the time, not angrily. That’s because the always cheerful, friendly and charming 51-year-old also wants to use the attention to explain how elementarily important basic research is, even on seemingly “off-the-beaten-path” topics, for new therapies and innovations.
After all, what is now considered the method of choice for modifying genetic material, what has already cured the first female patients of life-shortening blood diseases such as sickle cell anemia and beta thalassemia, and what makes it possible to breed more pest- and drought-resistant plants, began in 2011 – and long before that – with research into bacteria such as Streptococcus pyogenes, which is completely unrelated to practical applications.
These and many other microbes evolved a defense system against viruses billions of years ago. Charpentier and many other microbiologists had been trying to figure out how it worked for quite some time. Apparently, bacteria that had survived a virus attack managed to pass on information to their offspring that enabled them to become resistant to a new attack by these viruses. The bacteria “remembered” the respective virus type by incorporating characteristic pieces of genetic material from the pests into their own genome, between “regular arrangements of small, symmetrical repeats”, the “clustered regularly interspaced small palindromic repeats”, or Crispr for short. A kind of library for viral genetic material, where the Crispr sections in a sense represent the shelf, the ordering system. As soon as microbes armed in this way were attacked again by these viruses, they made use of their viral memory and “cut up” the foreign viral genome with a special enzyme, the “Cas9” gene scissors. But how does this enzyme distinguish between viral and bacterial genetic material? How does it find the spot where it should cut?
In 2011, Charpentier says, she had a “gut feeling” about what that might be. A hunch that comes without very much prior lab work. Before the Max Planck Society brought Charpentier to Berlin, she had to move eleven times in the previous thirteen years, including stops at the Pasteur Institute in Paris, New York’s Rockefeller University, Vienna’s Medical University, Sweden’s Umeå University and the Helmholtz Center for Infection Research in Braunschweig. Always chasing research budgets – often far too tight – the Paris-born scientist recounts. In the midst of her move from Vienna to Umeå, she had discovered a special molecule in bacteria – “tracrRNA.” For some time, her lab had been studying such RNA fragments consisting of DNA’s sister molecule. Charpentier’s stomach said: this tracrRNA could be crucial for the bacterial immune system.And indeed: without tracrRNA, the virus defense no longer worked. She had discovered the crucial missing piece to the gene scissors. Charpentier immediately realized that it could be used to build a universal tool that could also cut the genetic material of plants, animals and humans at any desired point in the genome – and only there. She had discovered a kind of “navigator” for the genome.
It is true that genetic researchers had already been able to modify proteins in such a way that they could recognize any genetic sequence among billions of genetic building blocks and then selectively cut and modify it. But these “zinc fingers,” “meganucleases” or “talen” have to be redesigned for each DNA sequence. Too time-consuming and expensive, and slow. In the Crispr gene scissors, on the other hand, the genetic-cutting enzyme Cas9 always remains the same, only the navi has to be adapted: a piece of RNA that can be produced quickly and cheaply, consisting of Charpentier’s tracrRNA, among other things. A simple, modular system.
But a lot of research is needed before that can happen, and Charpentier is just moving again. So at a conference, she tells Jennifer Doudna about her discovery, an RNA specialist. She is interested, and after a few reminder emails from Charpentier, the two women collaborate. They publish the result together in the journal Science on Aug. 17, 2012 – in a sense, the birthday of the Crispr technique.
“It’s never just one person who makes such an important scientific breakthrough possible,” says Simone Spuler of the Max Delbrück Center for Molecular Medicine in Berlin-Buch. “But it’s really to their credit that they brought this important tool into the world and also pointed out its clinical importance from the beginning. Spuler, like virtually every molecular biology lab in the world now, began working with the gene scissors quickly after the “Science” publication. Spuler takes muscle stem cells from patients, repairs the causal gene mutation with the gene scissors, and injects them back. Although a cure cannot yet be expected, Spuler hopes to prevent further paralysis – for example, of the hands of one of her patients, who fears she will never again be able to play her beloved flute.
That the gene scissors also have healing potential first became apparent at the end of last year. Crispr Therapeutics, a company co-founded by Charpentier, announced that two patients were able to overcome their sickle cell anemia and beta thalassemia, genetic blood diseases, thanks to gene scissors therapy. The final results of the study are still pending. But even if there are still problems, side effects and need for optimization – the discovery of the Crispr/Cas9 gene scissors is less than ten years old. Hundreds of laboratories around the world are working on optimizing the tool. Or to modify it in such a way that it acquires new properties. For example, taking away the gene scissors’ ability to cut and turning them into “packagers” of cancer-promoting genes instead.
So after barely ten years of gene scissors research, there is still much to discover and develop. And maybe now, finally, when the hoopla over the Nobel Prize is over, Emmanuelle Charpentier will get the time she so misses in the lab to do it.
Max et moi. Emmanuelle Charpentier on the day of the announcement with the bust of the institute’s namesake, Max Planck. F.: K. Nietfeld/dpa