Humankind has been steadily gaining greater control of our environment for more than 100 millennia. The last couple of centuries, however, have provided by far the greatest increase in our ability to control Mother Nature, and the trend has accelerated even more in the last few decades with the development of techniques for editing genes.
Related to this, genetic researchers have made great strides over the last year or two in developing so-called “gene drive systems”, which introduce a gene of choice throughout a population. Although no gene drives have been undertaken in the wild to date, in laboratory tests these human-introduced genetic changes have converted almost an entire population of insects to carry the new version of a gene.
According to Harvard biologists who have been researching gene drives, they “could potentially prevent the spread of disease, support agriculture by reversing pesticide and herbicide resistance in insects and weeds, and control damaging invasive species.”
More on gene drives
Researchers say that gene drive systems could potentially destroy or modify insect pests, and even reverse genetic resistance to pesticides that may have developed in some species over time. Gene drives could also be very useful in controlling populations of dangerous invasive species such as rats or cockroaches.
However, geneticists point out that gene drives suffer from two significant technical limitations. First, gene drives will work only in sexually reproducing species, and second, the target organism needs to reproduce relatively quickly relative to humans so that the change caused by the gene drive happens on a time scale relevant to living humans.
Of interest, a gene drive that would effectively make a population extinct is known as a crash drive. Researchers are currently developing a crash drive for mosquitoes based in a gene engineered into the Y chromosome that destroys the X chromosome in the sperm, thus ensuring that all mosquito progeny are male. This means that unless the gene drive is altered through mutation (natural selection), the number of females would decrease each generation and the population would eventually collapse.
A research team headed up by Andrea Crisanti and Tony Nolan at Imperial College London reported recently in Nature Biotechnology that they had created mosquitoes with gene drives that disrupt three genes for female fertility, each of which acts at a different stage of egg formation. As the female mosquitoes are infertile only when a copy is inherited from both parents, the gene drives would be completely disseminated through a population before taking their toll. These gene drivers could “suppress mosquito populations to levels that do not support malaria transmission,” according to Crisanti, Nolan and colleagues.
The genetically edited mosquitoes are not yet ready for release. The scientists point out that natural selection will strongly favor wild mosquitoes that acquire resistance to the gene drives, so they need to take steps to prevent resistance from developing. They suggest one possible solution would be to target two or three sites in the same fertility gene, this making natural selection work much harder to evolve a resistance to the gene drive system.