The use of gene drive technology to control wild populations of insect pests could be foiled by development of genetic resistance, according to a study in Science Advances published Friday.
Genetic variability and the tendency of many insects to inbreed could encourage resistance, the study found. This would be worsened if the genetically engineered trait caused a decrease in fitness.
Meanwhile, a gene drive approach developed by UC San Diego and UC Irvine scientists that might circumvent resistance has received a $2 million shot in the arm from the Bill & Melinda Gates Foundation.
The Science Advances study was conducted in flour beetles. It can be found at j.mp/genedrivefb. Michael J. Wade was the senior author. Douglas W. Drury was first author. Both are of Indiana University.
The British biotech Oxitec has developed genetically engineered male mosquitoes that pass along a trait that causes all their offspring to die.
Oxitec’s mosquitoes have been tested in field trials Panama and Brazil. A trial in Florida is planned to fight the Zika virus. Meanwhile, another trial has been launched using male mosquitoes infected with a sterility-causing bacterium.
However, Oxitec’s approach requires continued releases of new genetically modified mosquitoes. Gene drive could in theory introduce a trait that stays lodged in the population, or at least doesn’t have to be replenished as often.
The gene drive variant would self-propagate, performing a copy-and paste into any unmodified genes present in embryos. So one gene variant inherited from one parent could spread the change to the corresponding gene from the other parent.
UC San Diego researchers Ethan Bier and Valentino Gantz were the first to demonstrate gene drives in insects, using CRISPR/Cas9 technology. They did this first in fruit flies, and then, in a study led by Gantz and UC Irvine’s Anthony James, in mosquitoes.
Their approach is make mosquitoes resistant to malaria parasites. So while the mosquitoes would still bite, they wouldn’t transmit malaria.The researchers have said they expect this approach would minimize resistance.
In October, UC San Diego said it will receive $70 million from one of India’s top philanthropists to develop the Bier/Gantz/James gene drive technology for use in India, where malaria is endemic in some regions. Half of the money is to be spent in transferring the technology to Indian scientists.
In early May, UC Irvine said that James will lead a program to make new malaria-resistant strains of the Anopheles gambiae mosquito.
“Our goal is to see if prototype strains developed in partnership with UC San Diego geneticists Valentino Gantz and Ethan Bier can be refined into something appropriate for disrupting malaria transmission in Africa,” James said in a UC Irvine press release.
The big question is whether the malaria-resisting trait will in some other way make the mosquitoes less efficient at reproducing in the wild.
While the gene drives work well in laboratory populations, it’s not clear whether the natural environment will produce the same results. Nature presents more genetically diverse populations, where differing genes may compete with each other, the Science Advances study said.
Bier and Gantz have said that making mosquitoes immune to malaria parasites should inhibit the development of resistance, since only the parasites would be hurt. But this won’t be known until they have been tested in a natural environment.