Mutational Chain Reaction Can Spread Throughout Insect Populations
A report recently published in Science describes a system by which one can introduce mutations into insect genomes and have those mutations quickly spread to all of the mutant’s progeny, and to all of their progeny’s progeny, and so on.The new system does not follow the standard rules of chromosome and gene transmission. An insect carrying one copy of a mutation is normally expected to transmit that mutation to only one half of its progeny. But that’s not the case with the mutations created by Valentino Gantz and Ethan Bier, the authors of the report. An insect carrying one of their mutations will transmit the mutation to ALL of its progeny.
Gantz and Bier inserted two genes into the “yellow gene” of a fruit fly (Drosophila), creating mutants with a yellow cuticle. One of the genes Gantz and Bier inserted encodes for a protein that can cut DNA (an endonuclease), and the second gene tells the endonuclease specifically where to cut. In this case they told the endonuclease to cut the normal copy of the yellow gene.
Fruit flies are diploids, meaning they have two chromosomes. Gantz and Bier essentially inserted the mutation-causing yellow gene into one chromosome, and simply cut the other chromosome in the exact same place. Normally, when a chromosome is cut in this fashion, the cell will attempt to repair the broken chromosome by copying the corresponding section of the unbroken chromosome. However, in this case the “unbroken” chromosome is the one that contains the newly-inserted yellow gene. The cell is fooled into “repairing” its cut chromosome by copying the genetically-altered chromosome. Now it has two identical chromosomes for the new yellow gene, and the yellow-cuticle trait has become homozygous instead of heterozygous.
Whenever a normal copy of the yellow gene finds itself in the presence of the mutated form of the gene, it will become similarly mutated. The authors call this a “mutational chain reaction.” It is also formally known as a homing endonuclease, and they are known to exist in nature.
Homing endonucleases can quickly spread through populations under certain conditions, which could have incredible implications for controlling or even eradicating insect pests. By targeting the appropriate gene, one could set in motion a “mutational chain reaction” that could result in the population’s demise. One could cause a population to self-destruct.
This technology could be applied to any insect species that is amenable to genetic modification, and that includes an ever-growing number of species. Mutation-spreading technologies like this are certain to raise some concerns, and conversations about those concerns are ongoing.
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David O’Brochta is the director of the Insect Genetic Technology Research Coordination Network (IGTRCN) and is a professor in the Department of Entomology and the Institute for Bioscience and Biotechnology Research at the University of Maryland, College Park. He has an active research laboratory focused on insect genetics and molecular genetics with interests in the development of insect genetic technologies and their application to the study of the physiological genetics of mosquitoes, with particular interest in their disease-vector capabilities. Professor O’Brochta teaches at the undergraduate and graduate levels, is the Head of the Institute for Bioscience and Biotechnology Research’s Insect Transformation Facility, and he is the editor of the Royal Entomological Society’s journal Insect Molecular Biology.