About two years later, Kevin Esvelt, a geneticist then at Harvard University, put gene drives and Crispr together. Instead of poking a big fat glass needle loaded up with synthetic DNA into every organism that you want to change, you do it once, with a gene drive that encodes not only the gene you want (or the deactivation of the gene you don’t want) but also instructions to do that same manipulation with the Crispr technique in another genome. So when your altered organism mates, its chromosome gets to work, engineering the chromosome inherited from the mate too. This guarantees that the offspring has the desired change, plus the instructions to make the desired change.
When the offspring reaches maturity and mates, the process repeats. In a perfect “global” gene drive, 100 percent of offspring have the gene drive carrying the desired trait.
The possibility was a tantalizing one for conservation. You could start thinking way bigger than Floreana: the Galapagos island of Santa Cruz, with its 12,000 people. Or, hell, Australia—Campbell’s home country, a massive island with dozens of species endangered largely because of introduced cats and foxes. You could fix every island in the world.
The idea of using gene drives to save species began to hum. Campbell helped organize people from Island Conservation and researchers in the United States, Australia, and New Zealand, as well as the United States Department of Agriculture, to research the approach. The group formalized as the Genetic Biocontrol of Invasive Rodents program, or GBIRd. In June 2016, Paul Thomas, a mouse geneticist from the University of Adelaide, Australia, visited Gould in North Carolina and got fired up. Thomas felt that his lab could be the place to figure out how to make a synthetic gene drive work in rodents. If he could succeed in lab mice, he could succeed with the wild mice and rats that eat the eggs and young of rare species on islands. Thomas joined GBIRd.
Note that he uses the term “local” gene drive. One of his responses to his freak-out was to come up with ways of containing synthetic gene drives to a set number of generations. He calls one approach a “daisy chain,” which would add a sequence of genetic drivers that must be in place to propel the desired gene change. The first driver in the chain is inherited normally, so when it dies out, the gene drive does too. Tweaking the number of drivers in the chain could theoretically allow you to match the size of the population of creatures you want to get rid of on an island.
This daisy-chain method is still being tested in the lab, and Esvelt feels that, barring attempts to tackle global health crises like malaria, no one should try a gene drive in the wild until there is a proven local drive. This past November, Esvelt cowrote an essay in PLOS Biology in which he responded to New Zealand’s interest in using gene drives to eliminate introduced predators like rats, stoats, and Australian possums. He called the basic version of a gene drive unsuitable for conservation purposes and warned against its cavalier deployment. “Do we want a world in which countries and organizations routinely and unilaterally alter shared ecosystems regardless of the consequences to others?” he wrote.
Esvelt has the same concerns about GBIRd’s early and enthusiastic interest in exploring gene drive technology. GBIRd recently said that its members intend to pursue a “precision drive” approach, in which the drive would work only on animals with a specific genetic sequence—kind of like the fail-safe system Thomas is currently using in the lab, but relying on naturally occurring genes rather than introduced bacterial ones. Researchers would have to locate a DNA sequence found only on the target island and nowhere else, a prospect Esvelt thinks is unlikely. “There is a high chance it won’t work out and they are building up hope,” he says. On larger islands, there would be too many genes coming and going from other places for a perfect sequence.
Originally published by WIRED
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